Potential Metabolic Bioactivation Pathways Involving Cyclic Tertiary

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Chem. Res. Toxicol. 1997, 10, 924-940

Invited Review Potential Metabolic Bioactivation Pathways Involving Cyclic Tertiary Amines and Azaarenes Neal Castagnoli, Jr.,*,† John M. Rimoldi,‡ Jeff Bloomquist,§ and Kay P. Castagnoli† Departments of Chemistry and Entomology, Virginia Tech, Blacksburg, Virginia 24061-0212, and Department of Medicinal Chemistry and National Center for the Development of Natural Products, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, Mississippi 38677D Received June 4, 1997

Enzyme-Catalyzed Ring r-Carbon Oxidation of Cyclic Tertiary Amines This review focuses on the biotransformation of cyclic tertiary amines and selected azaarenes to potentially toxic metabolites. Special emphasis will be placed on 6-membered azacycles due to the ongoing interest in the neurotoxicity of pyridinium and structurally related azaarenium systems. Two enzyme systems, members of the cytochrome P450 family of hemoproteins (1) and the mitochondrial membrane-bound flavoproteins, monoamine oxidases A and B (MAO-A and MAO-B)1 (2, 3), are of special relevance, and the metabolic pathways proposed to account for their catalytic activity will be considered. The two-electron oxidations catalyzed by these enzymes convert the amine substrate (1) to the corresponding iminium oxidation product (2). A catalytic pathway proposed for these transformations (Scheme 1) proceeds by an initial single-electron transfer (SET) step from the lone pair of the amine substrate 1 followed by deprotonation of the resulting aminyl radical cation 2 to form the carbon radical 3. In the MAO-catalyzed reaction (4, 5), this one-electron oxidation is coupled to the oneelectron reduction of oxidized flavin adenine dinucleotide (FAD) to give the flavin semiquinone FADH•, while in the P450-catalyzed reaction (6-8), it is coupled to the reduction of the activated porphyrin iron oxo species (FedO) to give FeOH. The subsequent one-electron oxidation of 3 yields, in the MAO pathway, the fully reduced flavin FADH2 and the iminium product 5. In the case of P450, radical recombination produces the R-carbinolamine 4 which will be in equilibrium with the iminium product 5. Subsequent hydrolysis of 5 yields the aldehyde 6 and secondary amine 7. An alternative pathway involves a direct hydrogen atom transfer (HAT) step (1 f 3) that does not pass through a radical cation intermediate. * Address correspondence to this author. Phone: (540) 231-8202. Fax: (540) 231-8890. E-mail: [email protected]. † Department of Chemistry, Virginia Tech. ‡ University of Mississippi. § Department of Entomology, Virginia Tech. 1Abbreviations: 7-NI, 7-nitroindazole (32); FAD, flavin adenine dinucleotide (14); FADH2, reduced flavin adenine dinucleotide (16); HAT, hydrogen atom transfer; HP, haloperidol (72); HPP+, pyridinium derivative (75) of haloperidol; HPTP, tetrahydropyridine derivative (73) of haloperidol; MAO, monoamine oxidase; MPDP+, 1-methyl-4-phenyl2,3-dihydropyridinium species (24); MPP+, 1-methyl-4-phenylpyridinium species (25); MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (23); nNOS, neuronal nitric oxide synthase; PAs, pyrrolizidine alkaloids (102); RHP, reduced haloperidol (78); RHPP+, reduced haloperidol pyridinium metabolite (79); SET, single-electron transfer.

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Experimental evidence supporting the SET pathway is derived in part from the mechanism-based inactivator properties of cyclopropylamines (9) and cyclobutylamines (10). For example, the cytochrome P450-catalyzed (6) and MAO-B-catalyzed (11) oxidations of N-benzylcyclopropylamine (8) are reported to form the cyclopropylaminyl radical cation intermediate 9 which, via the primary carbon-centered radical 10, inactivates the enzymes by covalent modification of the active site (Scheme 2). Evidence against the SET pathway in the MAOcatalyzed reaction includes the inability to detect radical cation intermediates by rapid-scan stopped flow and magnetic field techniques (12). Energy calculations also indicate a higher value for ∆Gelectron transfer vs ∆Gq for the rate-limiting reduction of MAO by amine substrates under anaerobic conditions (13). Furthermore, the substrate properties, as opposed to the expected inactivator properties, of certain 4-substituted 1-cyclopropyl-1,2,3,6tetrahydropyridinyl derivatives suggest that aminyl radical cations may not be obligatory intermediates in the MAO-catalyzed oxidation of cyclic tertiary allylamines (14-17). Arguments also have been advanced which challenge the SET pathway for the P450-catalyzed oxidations of amines (18). For example, almost identical deuterium isotope effect profiles for the oxidative Ndemethylation of para-substituted N,N-dimethylaniline derivatives have been observed with a chemical model of the HAT pathway and the corresponding enzymecatalyzed reaction (19). No such correlation was found when comparing the enzyme-catalyzed reaction and a chemical model of the SET pathway. Additional arguments against the SET pathway have been based on the stereochemical course and isotope effects observed in the P450-catalyzed oxidation of (S)-nicotine (20). Unpublished results from the authors’ laboratory show that 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (11), a good time- and concentration-dependent inactivator of MAO-A and MAO-B (21), is an excellent substrate for rat and human liver microsomal enzymes. Two principal metabolites are the dihydropyridinium (12) and Ndecyclopropyl (13) species (Scheme 3). No evidence of inactivation was observed suggesting that the oxidation may not proceed via a cyclopropylaminyl radical cation. In view of these results some investigators have considered HAT as an alternative catalytic pathway for these transformations (12-20). A polar mechanism also has been proposed to account for the MAO-catalyzed oxidations of primary and second© 1997 American Chemical Society

Invited Review

Chem. Res. Toxicol., Vol. 10, No. 9, 1997 925

Scheme 1. Proposed Pathways for the MAO- and Cytochrome P450-Catalyzed Oxidations of Tertiary Amines

Scheme 2. Proposed Pathway for the Mechanism-Based Inactivation of MAO and Cytochrome P450 by Benzylcyclopropylamine

Scheme 3. Cytochrome P450-Catalyzed Oxidation of 1-Cyclopropyl-4-phenyl-1,2,3,6tetrahydropyridine (11)

bond cleavage. Cyclic tertiary amines (17) also undergo oxidative N-dealkylation (Scheme 5) via exocyclic iminium intermediates (18) to yield aldehydes (6) and cyclic secondary amines (19). The corresponding oxidation of a ring R-carbon atom, however, generates cyclic iminium intermediates (20) that will be in equilibrium with the corresponding amino aldehydes (21). These intermediary metabolites often are oxidized further to the corresponding lactams (22) in a reaction that is catalyzed by aldehyde oxidase (25), a molybdenum-containing liver cytosolic enzyme (26) that, in addition to carboxy aldehydes (27), catalyzes the oxidation of a variety of azaarene (28), azaarenium (29), and cyclic iminium (30) species to the corresponding lactams. As will be discussed below, in the absence of aldehyde oxidase, R-carbon oxidations of some cyclic tertiary amines can lead to chemically reactive and toxic metabolites.

Studies on the Parkinsonian-Inducing Neurotoxin MPTP

ary amines (22). According to this pathway (Scheme 4), the amine substrate 1 forms an adduct (15) with FAD (14). Subsequent cleavage of 15 yields the iminium metabolite 5 and FADH2 (16). Results from model chemical studies with various reported inactivators of MAO have provided additional support for this mechanism (23, 24). Many MAO- and P450-mediated biotransformations of amines may be classified as N-dealkylation reactions since the substrates undergo oxidative carbon-nitrogen

Potential bioactivation pathways for cyclic tertiary amines are of particular interest because of the parkinsonian-inducing properties of the nigrostriatal neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [MPTP (23); Scheme 6] (31, 32). Hepatic cytochrome P450s catalyze both the oxidative N-demethylation (33-36) and ring R-carbon oxidation of MPTP (37), the latter reaction leading to the 1-methyl-4-phenyl-2,3-dihydropyridinium species, MPDP+ (24). Compound 24 is an excellent substrate for liver aldehyde oxidase which catalyzes its conversion to the lactam 26 (38). The possibility that the neurodegenerative properties of MPTP were mediated by toxic metabolites led to brain tissue homogenate studies (39, 40) that established MPTP’s unexpected and excellent (Vmax/Km ) 1400 min-1 mM-1 at 37 °C) (41) MAO-B substrate properties. MAO-B catalyzes regiospecifically (42) the C-6 (allylic) R-carbon oxidation of MPTP (Scheme 6). Unlike liver homogenates, however, brain homogenates do not convert 24 to 26, presumably because of the absence of aldehyde oxidase activity (26).

Scheme 4. Proposed Polar Pathway for the MAO-Catalyzed Oxidation of Primary and Secondary Amines

926 Chem. Res. Toxicol., Vol. 10, No. 9, 1997 Scheme 5. Alternative Oxidative Biotransformation Pathways for Cyclic Tertiary Amines

Scheme 6. Oxidative Metabolism of the Parkinsonian-Inducing Agent MPTP (23)

Scheme 7. Alternative Fates for the Dihydropyridinium Metabolite (24) of MPTP

Compound 24 is chemically unstable. It undergoes a bimolecular disproportionation-type reaction in which the free base (27) derived from 24 functions as a hydride donor while 24 serves as a hydride acceptor (Scheme 7) (43). The net result is the formation of stoichiometric amounts of MPTP and the pyridinium compound MPP+ (25). A second reaction sequence involves an initial Diels-Alder cycloaddition between 24 and 27 followed by ring cleavage, elimination of methylamine, and reduction of the resulting eniminium product by a second mole of 27 to yield the partially reduced isoquinoline system 28 and MPP+ as shown in Scheme 7 (44). The extent to which these or similar reactions occur in vivo is not known. The principal fate of 24 in brain homogenates is its further oxidation to MPP+ as shown in Scheme 6 (45). This reaction may involve MAO-B catalysis (46), although nonenzymatic oxidation of MPDP+ is likely to be the principal pathway responsible for this oxidation (38). The neurotoxicological significance of the MAO-B-catalyzed conversion of MPTP to MPP+ was dramatically docu-

Castagnoli, Jr., et al.

mented by experiments in which the MAO inactivator pargyline (29) was shown to protect monkeys against MPTP’s neurotoxicity (47). Similar experiments in a mouse model using the selective inhibitor (R)-deprenyl (30) established that the bioactivation reaction is MAOB, and not MAO-A, mediated (48, 49).

Extensive metabolic, biochemical, and toxicological investigations (2, 3, 50-52) have established that the neurodegenerative properties of MPTP are mediated by the MAO-B-generated pyridinium metabolite MPP+ (25). The selective toxicity of MPTP is remarkable since the target nigrostriatal neurons do not catalyze the bioactivation reaction (53) presumably because they lack MAO-B activity (54-56). This dilemma appears to have been resolved by the demonstration that MPP+ is concentrated in the dopaminergic nigrostriatal nerve terminals via the dopamine transporter (57, 58). On the other hand, the selective toxicity of MPP+ on nigrostriatal dopaminergic pathways is not reflected in differences in striatal vs mesolimbic transporters (59) or vesicular transporters in the sensitive C57BL/6 mouse compared to the insensitive CD1 mouse (60). It is thought that MPTP is metabolized in MAO-B rich glial cells (61, 62) following which the toxic pyridinium metabolite is selectively sequestered by the striatal dopaminergic neurons via the transporter. Once localized intraneuronally, MPP+ is concentrated further within the inner mitochondrial membrane (63), by forces derived from the mitochondrial membrane potential (64), where it selectively inhibits complex I of the electron transport chain (65-69), a property which is shared by several MPP+ analogs (70, 71). The inhibition of mitochondrial respiration by MPP+ (72, 73) and related compounds (74) is enhanced by the lipophilic anion tetraphenylborate which is known to facilitate the passive transport of cations through biological membranes. The depletion of ATP following inhibition of complex I has been considered to be the principal cause of cell death (75). It should be pointed out that not all of the available evidence is consistent with the sequence of events summarized above (76, 77). For example, it has been difficult to demonstrate that treatment with MPTP actually leads to compromised mitochondrial respiration (78, 79). Furthermore, rats are not susceptible to the neurotoxicity of MPTP even though high concentrations of striatal MPP+ are reached (53, 80). The detailed molecular events leading to the selective loss of nigrostriatal neurons following exposure to MPTP are still under debate. Recent interest has focused on the possibility that compromised mitochondrial energy production pathways and other factors leading to the formation of chemically reactive free radicals, such as superoxide radical anion (O2•-), the one-electron reduction product of dioxygen (O2), may be responsible for the neurological lesion caused by MPTP (81-88). A particularly attractive hypothesis has emerged which is based on the properties of neuronal nitric oxide (nitrogen monoxide, NO), a free radical derived from L-arginine in a reaction catalyzed by neuronal nitric oxide synthase (nNOS) (90-94). NO reacts with O2•- to form the lipid-

Invited Review

peroxidizing agent peroxynitrite (ONOO-) (95, 96). Thus, chemically induced degenerative processes may involve oxidative stress mediated by ONOO-. NO has been implicated in the neurodegeneration caused by methamphetamine (97-99) and excitotoxins such as NMDA, malonate, and 3-nitropropionic acid (100). Since MPTP, via MPP+, increases lipid peroxidation by inhibiting complex I of the mitochondrial respiratory chain (101), the participation of NO, via ONOO-, in the MPTP-induced degeneration of nigrostriatal neurons has been investigated with the aid of the selective nNOS inhibitors S-methylthiocitrulline (31) (102) and 7-nitroindazole (7-NI, 32) (103). One report claims that inhibition

of NOS reduced the MPP+-induced formation of hydroxyl radicals in the striatum without interfering with inhibition of complex I activity (104). In related studies, mice (105, 106) and baboons (107) were treated with 7-NI prior to MPTP administration and then maintained on 7-NI for various periods of time prior to sacrifice. Both the mice and baboons were protected from the neurotoxic effects of MPTP. The conclusion that the inhibition of nNOS is the only factor mediating 7-NI’s neuroprotection may not be correct, however, since pretreatment of C57BL/6 mice with 7-NI receiving a neurotoxic dose of MPTP was found to decrease the neostriatal levels of MPP+ by up to 47% (108). This effect of 7-NI is likely to be a consequence of its competitive inhibition of MAO-B [Ki ) 4 µM using mitochondrial membrane preparations from C57 mice and MPTP as the substrate (Km ) 40 µM)]. Studies with nNOS inhibitors that do not alter striatal levels of MPP+ should help to resolve this important issue. The neurotoxic properties of MPP+ appear to be shared by a variety of related azaarenium derivatives (109-111) as evidenced from results of studies involving direct intracerebral injections (112, 113) and intracerebral microdialysis techniques (114-116) as well as cytotoxicity studies using neuronal (117-119), primary mouse astrocyte (120, 121), PC12 (122), and primary rat liver (123) cell cultures. On the other hand, relatively few of the corresponding precursors to these azaarenium derivatives display MPTP-type neurotoxicity in vivo. With few exceptions (14-17), only 1-methyl-1,2,3,6-tetrahydropyridinyl derivatives bearing selected substituents at C-4 are reported to be good substrates for MAO-A and/or MAO-B (124-128). These relatively strict structural requirements for MAO-A and MAO-B substrates have been represented in several molecular models of the active sites of MAO-A and MAO-B (129-131). Even tetrahydropyridines that display good MAO-A and/or MAO-B substrate properties, however, may not be MPTPtype neurotoxins. In these cases, the intermediate dihydropyridinium metabolites often do not undergo further oxidation to the pyridinium species (132, 133). Of particular interest are the 1-methyl- and 1-cyclopropyl4-(aryloxy)-1,2,3,6-tetrahydropyridinyl derivatives 33 which undergo MAO-catalyzed oxidation to dihydropyridinium metabolites 34 that spontaneously hydrolyze to

Chem. Res. Toxicol., Vol. 10, No. 9, 1997 927 Scheme 8. MAO-Catalyzed r-Carbon Oxidation of 4-(Aryloxy)tetrahydropyridines 33

yield the corresponding arenols 35 and 2,3-dihydro-4pyridones 36 (Scheme 8) (15, 134). The hydrolytic instability of these dihydropyridinium metabolites has been exploited to construct potential nitrogen-containing prodrugs which are linked at C-4 to the tetrahydropyridinyl carrier. For example the tetrahydropyridinyl phosphoroamidate 37 is metabolized to the dihydropyridinium intermediate 38 which, upon hydrolysis, releases the cytotoxic phosphoramide mustard 39. A second example is the tetrahydropyridinyl carbamate prodrug 40 which is converted to the dihydropyridinium metabolite 41 in an MAO-A selective reaction. Hydrolysis of 41 results in the carbamic acid 42 that decarboxylates to yield the potent MAO-B selective mechanism-based inactivator (R)-nordeprenyl (43) (Scheme 9) (136). These developments point to potential opportunities to design proneuroprotectants utilizing insights that have been gained in studies which have focused on the mechanism of action of proneurotoxicants.

Tetrahydroisoquinolines and Tetrahydro-β-carboline The MPTP-induced parkinsonian syndrome and limited evidence of a definitive genetic link to Parkinson’s disease (137-140) have generated considerable interest in the possibility that xenobiotic agents may contribute to the etiology of this disease (141-143). Although to date no environmental chemicals with MPTP-type activity have been identified, considerable attention has been given to certain endogenous compounds which show some potential as parkinsonian-inducing agents. Studies conducted over 20 years ago established that amines bearing electron rich arene moieties, including dopamine and serotonin, may react with aldehydes and ketones to form reactive iminium intermediates that undergo PictetSpengler-type intramolecular condensation reactions to generate various tetrahydroisoquinolines and tetrahydroβ-carbolines (144, 145). Interest in these compounds eventually subsided since little convincing evidence could be provided to document that these compounds had any significant biological activity (146). The MPTP saga, however, has led some investigators to view these compounds, which share some structural features with MPTP, as potential neurotoxins that might contribute to the neurodegenerative processes leading to idiopathic Parkinson’s disease. A variety of chemical, biochemical, pharmacological, and toxicological studies have been performed on several tetrahydroisoquinolines (147-165). Evidence has been presented to document the presence of compounds 4450 in cerebral spinal fluid of patients suffering from Parkinson’s disease (166-171). Recent reports state that the R-enantiomer of N-methylsalsolinol (48), when injected into the striatum of rats, causes a parkinsonian-

928 Chem. Res. Toxicol., Vol. 10, No. 9, 1997


Scheme 9. MAO-Catalyzed Bioactivation of Tetrahydropyridinyl Derivatives 37 and 40 To Form Phosphoramide Mustard (39) and (R)-Nordeprenyl (43)

like syndrome that may be mediated by events similar to those described for MPTP (172, 173). A brain Nmethyltransferase is reported to catalyze the conversion of tetrahydroisoquinoline (44), a substance found in various foods (174), to the corresponding tertiary Nmethyl derivative 45 (175-177). Furthermore, 45 appears to be a substrate for both MAO-A and MAO-B (178). The resulting isoquinolinium metabolite 51 selectively destroys tyrosine hydroxylase immunoreactive (dopamine-containing) cells in tissue culture (179). Compound 51 also is reported to be a more potent inhibitor of mitochondrial respiration (complex I) than MPP+ (180). Finally, chronic treatment of monkeys with tetrahydroisoquinoline or 1-methyltetrahydroiosquinoline (49) leads to a parkinsonian syndrome (181). Contrary to expectations, however, 51 did not release [3H]dopamine from preloaded synaptosomes (182).

Similar types of experiments with the tricyclic tetrahydro-β-carboline system have generated comparable results (183-192). Of particular interest is the possibility that the highly neurotoxic (193-196) 2,9-dimethyl-βcarbolinium species 52 may be present in human brain tissue (197, 198) and may be formed from the corresponding β-carboline 53 by the action of an S-adenosi-

nylmethionine-dependent transmethylase (199, 200). An earlier report showing that the structurally related 2-methyl-1,2,3,4-tetrahydro-β-carboline (54) is a substrate, albeit a poor one, for MAO-B (201, 202) contributes to the speculation that some endogenous amines may possess MPTP-like properties. It is important to remember that, since idiopathic Parkinson’s disease evolves over the course of a lifetime, compounds with even modest toxic potential may contribute to the neurodegenerative processes that lead to loss of the nigrostriatal neurons. Neutral azaarenes that partition into the brain also are of potential toxicological interest since in situ Nmethylation would result in the formation of quaternary products with potential MPP+-type mitochondrial toxicity. In vivo N-methylation of an azaarene was first reported about 100 years ago following His’ detection of the N-methylpyridinium species 56 in the urine of dogs treated with pyridine (55) (203). This metabolite subsequently has been observed in vivo in several animal species (204-208). The N-methylation of pyridine is catalyzed by cytosolic enzymes expressed in liver, lung, and kidney (209). In all cases, S-methyladenosinylmethionine is the methyl donor. It is likely that mammalian tissues express several N-methyltransferases that catalyze the methylation of a variety of azaarenes (210). Crooks et al. have characterized two amine N-methyltransferases present in rabbit liver cytosolic fractions (211). Of special toxicological interest is the bis-N-methylation of 4,4′-bipyridine (57) to form the known lung toxin paraquat (58) (212). Guinea pig homogenates prepared from liver, lung, spleen, and brain catalyze the N-methylation of the unnatural R-isomer 59 (to give 60) but not the naturally occurring S-isomer 61 of the tobacco alkaloid nicotine (213). Although enzyme activity was detected in brain homogenates of the guinea pig, later attempts to detect pyridinium metabolites in the brain of rats administered (S)-nicotine failed (214). The enantioselectivity of this biotransformation must be species selective since the in vivo metabolism of (S)-nicotine and (S)-cotinine (63) in dog and human results in the formation of the (S)-Nmethylpyridinium metabolites 62 and 64 (215). Finally, nicotinamide N-methyltransferase (NNMT; EC 2.1.1.1),

Invited Review

which catalyzes the conversion of nicotinamide (65) to its N-methylpyridinium metabolite 66, has been studied extensively (216-218). The extent to which these types of enzymes may form N-methylated azaarenium metabolites with MPP+-type mitochondrial toxicity in the central nervous system remains to be determined.


dihydropyridinium products 70. In the brain, which lacks aldehyde oxidase activity, these intermediates may spontaneously oxidize to the pyridinium products 71. Various members of the cytochrome P450 family of enzymes and coenzymes are known to be present in rodent (225-241) and human (242-247) brain. Consequently, it may be reasonable to speculate that appropriately functionalized piperidinyl derivatives may be converted to the corresponding pyridinium metabolites in the central nervous system. A compound of interest in this context is haloperidol (HP, 72; Scheme 11), a potent neuroleptic agent that, like other members of this pharmacological class, causes severe extrapyramidal side effects (248, 249) including parkinsonism and a condition known as tardive dyskinesia (late appearing dyskinesia) that, in many cases, is irreversible (250, 251). This 4-piperidinol derivative resembles MPTP in that it bears an aryl group at C-4 of the azacycle. Furthermore, simple dehydration of HP, a reaction which is reported to occur in microsomal incubations (252), gives the corresponding 1,2,3,6-tetrahydropyridine derivative HPTP (73), an even closer analog of MPTP.

Piperidinols and Related Compounds A variety of cyclic tertiary amines undergo cytochrome P450-catalyzed oxidative metabolism to form chemically reactive iminium metabolites (219-223). In addition to MPTP, structures of particular interest are piperidinyl derivatives bearing a potential leaving group (Y) at C-4. Such compounds (67, Scheme 10) are at the same oxidation state as MPTP. Consequently, ring R-carbon oxidation of 67 will generate iminium products 68, which, as the corresponding enamine free bases 69, will undergo spontaneous elimination (224) to form the unstable

HP and HPTP are not substrates for MAO-B, but the conversion of HPTP to the pyridinium product HPP+ (75), presumably via the dihydropyridinium intermediate 74, is catalyzed by MAO-A (253). An alternative metabolic pathway that may lead to 75 involves initial conversion of HP to the corresponding cyclic iminium species 76 which, via the free base amino enol 77, would be expected to undergo rapid conversion to the dihydropyridinium intermediate 74. Subsequent autoxidation of 74, a reaction which has been well characterized (254), will yield 75 (Scheme 11). The proposed reaction sequence 72 f 76 is an example of the ring R-carbon oxidation pathway for cyclic tertiary amines (17 f 20) outlined in Scheme 4. Oxidative N-dealkylation (pathway 17 f 18 f 6 + 19, Scheme 4) is a major metabolic pathway for HP (255, 256), and therefore ring R-carbon oxidation (vs

Scheme 10. Proposed Bioactivation Pathway of Functionalized Piperidinyl Derivatives

Scheme 11. Proposed Metabolic Pathways Leading to Pyridinium Metabolites HPP+ (75) and RHPP+ (79) of HP/HPTP (72/73) and RHP (78), Respectively


oxidation of the exocyclic methylene carbon) might be expected to be a competing pathway. With the aid of HPLC fluorescence (257) and mass spectral techniques, the pyridinium metabolite 75 has been unambiguously characterized in the urine of rodents (258) and baboons (259) treated with either HP or HPTP and in the urine of humans treated with HP (260). The related pyridinium analog 79, in which the butyrophenone carbonyl group of 75 is reduced to the corresponding carbinol, also has been detected in rodent (261), baboon (259), and human (262) urine samples. This “reduced haloperidol pyridinium metabolite” (RHPP+) is likely to be derived from “reduced haloperidol” [RHP (78)], a major circulating metabolite of HP (263). Both pyridinium metabolites have been identified in the brains of rodents (258) and humans (264, 265). Metabolic studies with rodent (266) and human liver (267) and brain (268) microsomal preparations have demonstrated the NADPHdependent oxidation of both HP and HPTP to HPP+. Members of the P4503A subfamily of cytochrome P450s, enzymes which are effective in catalyzing the R-carbon oxidation of amine substrates (269) and which may be present in rat brain mitochondria (270), are likely to be the major catalysts in this reaction (266, 267). Evidence to support a neuroleptic-induced pathological brain lesion in humans (271) and animals (272-276) is limited. On the other hand, there is reasonable evidence to suspect that, if formed in the brain, HPP+, and possibly RHPP+, could cause neuronal injury. HPP+ is toxic to dopaminergic and serotonergic mesencephalic cells present in cultures derived from rat embryos (277) and to cultured dopaminergic neuroblastoma cells (278). It inhibits the uptake of radiolabeled dopamine by brain preparations (277, 279). Like MPP+, this pyridinium metabolite of HP is a potent inhibitor of complex I of the mitochondrial respiratory chain (280). Compromised mitochondrial energy production is a potentially important link between Parkinson’s disease (281-289), neuroleptic-induced extrapyramidal disorders (290-293), and MPTP-induced parkinsonism. Future studies in this area could prove to be fruitful both in terms of understanding neurodegenerative processes and drug-induced motor disorders and in terms of developing therapeutic agents to treat these conditions. Two other tetrahydropyridines of interest are the 4-(4fluorophenoxy)-1,2,3,6-tetrahydropyridinyl derivative 78


and the 1,2,5,6-tetrahydro-3-pyridinecarboxylic acid derivative 79. Extensive toxicity studies in the monkey established that 78 causes neuronal degeneration of several brain loci including the nigrostriatal system (294). Neurotoxic complications also were observed with 79, a candidate drug which was under development as an anticonvulsant agent (295). Individuals receiving a single 25 mg dose of 79 developed a parkinsonian syndrome and symptoms reminiscent of behavior observed in manic and schizophrenic patients. Some of the drug-induced CNS disorders were in evidence for several weeks after the initial exposure. The major urinary metabolite of 79 is the corresponding pyridinium product 80 (296). The detailed pathways underlying the neurodegenerative properties of 78 and the behavioral effects of 79 remain to be established.

Piperidines The cytochrome P450-catalyzed oxidation of piperidinyl derivatives may lead to reactive intermediates that result in enzyme inactivation (297). A piperidinyl derivative of considerable biological interest is the powerful psychotomimetic drug phencyclidine (81). This compound can lead to long lasting behavioral disorders (298) and pathological changes in cerebrocortical neurons (299). Studies on the metabolism of phencyclidine have revealed a complex metabolic profile involving hydroxylation on both the cyclohexyl and piperidinyl rings (300-302). Several of these hydroxylated metabolites also have been observed in rat brain microsomal preparations (303).

Scheme 12. Cytochrome P450-Mediated r-Carbon Oxidation of Phencyclidine (82) to Reactive Intermediates That Inactivate the Enzyme

Invited Review Scheme 13. Metabolic Bioactivation Pathway for 1-Methylaziridines


incubation mixtures of 82 with brain and liver homogenates is the C-formyl derivative 87 that may be generated by tetrahydrofolic acid-mediated formylation of the enamine 83 (313).

Potential Bioactivation Pathways Involving Other Azacyclic Systems

Phencyclidine undergoes R-carbon oxidation to form the chemically reactive iminium intermediate 82 (Scheme 12) (304), a pathway which is associated with both covalent binding to macromolecules (305) and inactivation of the enzyme responsible for its formation (306309). Recent studies employing P4502B1 reconstituted in a system containing NADPH-cytochrome P450 reductase have established that the reactive species leading to enzyme inactivation escapes from the active site. Therefore phencyclidine should not be classified as a mechanism-based inactivator (310). The structure(s) of the metabolite(s) mediating the inactivation is (are) not known at present. Studies with synthetic 82 suggest that this iminium intermediate itself is not directly involved since enzyme inactivation with 82 is NADPH dependent (307, 308, 311). Incubations of 82 with rat liver microsomes in the presence of an NADPH-generating system have led to the characterization of the amino enone 86 (312). The pathway to 86 may proceed via allylic oxidation of the enamine 83 followed by further oxidation of the resulting allylic alcohol 84. A candidate for the enzyme-inactivating species, therefore, is the dihydropyridinium derivative 85, a good Michael acceptor, that would be in equilibrium with 84. A second novel phencyclidine metabolite which has been identified in

1-Methylaziridines (89). The unstable N-oxides (90) formed metabolically from 1-methylaziridines (89) spontaneously fragment to yield the highly toxic nitrosomethane (CH3NO) and an olefin (90) as shown in Scheme 13. The subject has been reviewed (314). The Noxidation reaction has been observed in isolated hepatocytes (315) and microsomes (316) obtained from rat liver. A good correlation has been found between the fragmentation reactivity of a series of 1-methylaziridine N-oxides and cytotoxicity (317). Nitrosomethane was shown to be the ultimate species responsible for the cytotoxic effects. This toxicity appears to be directly linked to inhibition of mitochondrial respiration (318). Aziridines lacking the 1-methyl substituent do not undergo fragmentation reactions and are not cytotoxic. (S)-Nicotine (61). Tritium-labeled (S)-nicotine (61) is converted by NADPH-supplemented rabbit liver microsomes to reactive intermediates that form covalent adducts with biomacromolecules (319). The bioactivation pathway is likely to proceed via the iminium intermediate 91 since covalent binding is inhibited by cyanide ion, which traps 91 as the corresponding R-cyanoamine 92, and by the addition of the liver cytosolic fraction containing aldehyde oxidase, which catalyzes the conversion of 91 to the corresponding lactam (S)-cotinine (64). MAO-B has been shown to catalyze the oxidation of the iminium intermediate to the corresponding pyrrolyl derivative β-nicotyrine (94), presumably via the enamine free base 93 (320). The catalytic role of MAO-B in this reaction was confirmed by showing that the reaction was inhibited by low concentrations of (R)-deprenyl (30). These find-

Scheme 14. Proposed Metabolic Pathway for Conversion of (S)-Nicotine to Pyrrolinones 98 and Hydroxypyrrolinone 99



Scheme 15. Metabolic Bioactivation Pathway of the Pyrrolizidine Alkaloids

ings may be relevant to the recent report that brain MAO-B activity in smokers is almost 40% lower than those in a control group of nonsmokers and former smokers (321). The potential metabolic conversion of (S)-nicotine to β-nicotyrine led to metabolic studies on this electron rich pyrrolyl compound that established its conversion by rabbit liver microsomes to an equilibrium mixture of ∆3and ∆4-pyrrolinones 98 (322). These chemically unstable pyrrolinones underwent autoxidation to the hydroxypyrrolinone 99. The reaction pathway proposed to account for these products is shown in Scheme 14. Although no direct evidence exists for the sequence 94 f 95 f 96 f 97 f 98, incubation of 97, generated in situ from the corresponding synthetic acetoxy derivative 100, results in the formation of a carbon-centered radical, most likely 101, that can be trapped with nitrone radical-trapping agents (323). The formation of these chemically reactive intermediates represents a potential bioactivation pathway for (S)-nicotine that may contribute to the complex pattern of toxic effects associated with chronic exposure to tobacco products. Pyrrolizidine Alkaloids. The pyrrolizidine alkaloids (102, PAs) constitute a large class of natural products (324), many of which are carcinogenic (324, 326), genotoxic (327), neurotoxic (328), and hepatotoxic (329). Three major metabolic pathways have been established for PAs: ester hydrolysis, N-oxidation, and R-carbon oxidation. It is the conversion of PAs to the pyrrolyl metabolites 105 via the P450-mediated (330) R-carbon oxidation pathway (Scheme 15) that is associated with the toxicity of this class of compounds (331-333). The two possible R-carbon oxidation products, 103 (via oxidation at C-3) and 104 (via oxidation at C-8), generate the same pyrrolyl metabolites. These primary metabolites are highly reactive and short-lived species. Thus, cleavage of the R1OCO-C bond of 105 gives the electrophilic species 106 which, following reaction with nucleophilic groups present on biomacromolecules, will yield the C-7 adducts 107 (334). Although the initially formed pyrrolyl esters are toxic, compounds which form cross-linked products (109), presumably via intermediates such as 108, belong to the most toxic members of this class of compounds (335).

Summary A major theme explored in this review is the MAOand cytochrome P450-catalyzed R-carbon oxidations of selected cyclic tertiary amines to give iminium metabolites that undergo further chemical modifications to form known or potentially toxic products. The most dramatic illustration of this type of bioactivation process is the conversion of the parkinsonian-inducing neurotoxin MPTP (23) by brain MAO-B to the iminium (dihydropyridinium) metabolite 24 which is oxidized further to the pyridinium species MPP+ (25). The selective destruction of nigrostriatal neurons by MPP+ is dependent on a unique sequence of events (transport into the nerve terminals by the dopamine transporter, localization in the inner mitochondrial membrane by electromotive forces, and inhibition of complex I of the mitochondrial electron transport chain) that, fortunately, are unlikely to be encountered with many substances. A second example of a well-documented metabolic bioactivation sequence involves the highly toxic pyrrolizidine alkaloids (102). These compounds undergo cytochrome P450-catalyzed R-carbon oxidation which converts the 3-pyrrolinyl moiety present in the parent alkaloids into a pyrrolyl-containing metabolite (105). The presence of labile functional groups results in the spontaneous conversion of 105 to reactive electrophilic products (106 and 108) that undergo Michael addition reactions with nucleophiles on biomacromolecules leading to a variety of toxic outcomes. Less clearly defined are the potential contributions to neurodegenerative processes that may be mediated by low-level, long term exposure to less potent toxins. Examples of potential proneurotoxins are the endogenously formed tetrahydroisoquinolines (such as 40-50) and tetrahydro-β-carbolines (such as 54) that may be biotransformed to neurotoxic isoquinolinium (such as 51) and β-carbolinium (such as 52) species in the brain. A similar argument can be made for 4-piperidinols (compounds that are at the same oxidation state as the tetrahydropyridines) which may be metabolized via iminium intermediates to amino enols that spontaneously convert to dihydropyridinium species and hence to pyridinium metabolites (67 f 68 f 69 f 70 f 71, Scheme

Invited Review


10). This type of reaction sequence has been well documented with the parkinsonian-inducing neuroleptic agent haloperidol (72) which is metabolized in humans, baboons, and rodents to the pyridinium species HPP+ (75), a potent inhibitor of mitochondrial respiration. Finally, an appreciation of the R-carbon oxidations of fully reduced azacycles such as (S)-nicotine (61) and phencyclidine (82) to chemically reactive metabolites that form covalent adducts with proteins, including the enzymes that are responsible for their formation, may prove of toxicological importance when attempting to account for the effects of chronic abuse of these potent drugs.

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Acknowledgment. The studies cited in this review originating in the authors’ laboratory were supported by the National Institute of Neurological and Communicative Disorders and Strokes (NS 28792) and by the Harvey W. Peters Center for the Study of Parkinson’s Disease.

References (1) Ortiz de Montellano, P. R., Ed. (1995) Cytochrome P450: Structure, Mechanism, and Biochemistry, 2nd ed., Plenum Press, New York. (2) Singer, T. P., Ramsay, R. R., Sonsalla, P. K., Nicklas, W. J., and Heikkila, R. E. (1993) Biochemical mechanisms underlying MPTP-induced and idiopathic parkinsonism - new vistas. Adv. Neurol. 60, 300-305. (3) Tipton, K. F., and Singer, T. P. (1993) Advances in our understanding of the mechanism of the neurotoxicity of MPTP and related compounds. J. Neurochem. 61, 1191-1206. (4) Silverman, R. B. (1992) Electron Transfer Chemistry of Monoamine Oxidase. In Advances in Electron Transfer Chemistry (Mariano, P. S., Ed.) Vol. 2, pp 177-213, JAI Press, Greenwich, CT. (5) Silverman, R. B. (1995) Radical ideas about monoamine oxidase. Acc. Chem. Res. 28, 335-342. (6) Hanzlik, R. P., and Tullman, R. H. (1982) Suicidal inactivation of cytochrome P-450 by cyclopropylamines: Evidence for cationradical intermediates. J. Am. Chem. Soc. 104, 2048-2050. (7) Guengerich, F. P., and Macdonald, T. L. (1984) Chemical mechanisms of catalysis by cytochromes P-450: a unified view. Acc. Chem. Res. 17, 9-16. (8) Guengerich, F. P., Bell, L. C., and Okazaki, O. (1995) Interpretations of cytochrome P450 mechanisms from kinetic studies. Biochimie 77, 573-580. (9) Silverman, R. B., Cesarone, J. M., and Lu, X. (1993) Stereoselective ring opening of 1-phenylcyclopropylamine catalyzed by monoamine oxidase-B. J. Am. Chem. Soc. 115, 4955-4961. (10) Silverman, R. B., Zhou, J. P., and Eaton, P. E. (1993) Inactivation of monoamine oxidase by (aminomethyl)cubane. First evidence for an R-radical during enzyme catalysis. J. Am. Chem. Soc. 115, 8841-8842. (11) Silverman, R. B., and Hoffman, S. J. (1980) Mechanism of inactivation of mitochondrial monoamine oxidase by N-cyclopropyl-N-arylalkylamines. J. Am. Chem. Soc. 102, 884-886. (12) Miller, R. J., and Edmondson, D. E. (1995) Mechanistic probes of monoamine oxidase B catalysis: Rapid scan stopped flow and magnetic field independence of the reductive half reaction. J. Am. Chem. Soc. 117, 7830-7831. (13) Walker, M. C., and Edmondson, D. E. (1994) Structure-activity relationships in the oxidation of benzylamine analogues by bovine liver mitochondrial monoamine oxidase B. Biochemistry 33, 70887098. (14) Kuttab, S., Kalgutkar, A., and Castagnoli, N., Jr. (1994) Mechanistic studies on the monoamine oxidase-B catalyzed oxidation of 1,4-disubstituted tetrahydropyridines. Chem. Res. Toxicol. 7, 740-744. (15) Rimoldi, J. M., Wang, Y.-X., Nimkar, S. K., Kuttab, S. H., Anderson, A. H., Burch, H., and Castagnoli, N., Jr. (1995) Probing the mechanism of bioactivation of MPTP type analogs by monoamine oxidase B: Structure-activity studies on substituted 4-phenyl-, 4-phenoxy- and 4-thiophenoxy-1-cyclopropyl-1,2,3,6-tetrahydropyridines. Chem. Res. Toxicol. 8, 703-710. (16) Anderson, A. H., Kuttab, S., and Castagnoli, N., Jr. Deuterium isotope effect studies on the MAO-B catalyzed oxidation of 4-benzyl-1-cyclopropyl-1,2,3,6-tetrahydropyridine. Biochemistry 35, 3335-3340. (17) Nimkar, S. K., Anderson, A., Rimoldi, J. M., Stanton, M., Mabic, S., and Castagnoli, N., Jr. (1996) Synthesis and MAO-B catalyzed

(23)

(24)

(25)

(26)

(27)

(28)

(29) (30)

(31) (32)

(33)

(34)

(35)

(36)

(37)

(38)

oxidation of C-4 heteroaromatic substituted MPTP analogs. Chem. Res. Toxicol. 6, 1013-1022. Karki, S. B., and Dinnocenzo, J. (1995) On the mechanism of amine oxidations by P450. Xenobiotica 25, 711-724. Karki, S. B., Dinnocenzo, J. P., and Korzekwa, K. R. (1995) Mechanism of oxidative amine dealkylation of substituted N,Ndimethylanilines by cytochrome P-450. Application of isotope effect profiles. J. Am. Chem. Soc. 117, 3657-3658. Carlson, T. J., Jones, J. P., Peterson, L., Castagnoli, N., Jr., and Trager, W. F. (1995) Stereoselectivity and isotope effects associated with cytochrome P450-catalyzed oxidation of (S)-nicotine. Drug Metab. Dispos. 23, 749-756. Hall, L., Murray, S., Castagnoli, K., and Castagnoli, N., Jr. (1992) Studies on 1,2,3,6-tetrahydropyridine derivatives as potential monoamine oxidase inactivators. Chem. Res. Toxicol. 5, 625-633. Kim, J.-M., Bogdan, M. A., and Mariano, P. S. (1993) Mechanistic analysis of 3-methyllumiflavin-promoted oxidative deamination of benzylamine. A potential model for monoamine oxidase catalysis. J. Am. Chem. Soc. 115, 10591-10595. Kim, J.-M., Hoegy, S. E., and Mariano, P. S. (1995) Flavin chemical models for monoamine oxidase inactivation by cyclopropylamines, R-silylamines, and hydrazines. J. Am. Chem. Soc. 117, 100-105. Wang, Y.-X., and Castagnoli, N., Jr. (1995) Decyclopropylation of 1-cyclopropyl-4-hydroxy-4-(2-methylphenyl)piperidine N-oxide. Tetrahedron Lett. 36, 3981-3983. Turner, N. A., Doyle, W. A., Ventom, A. M., and Bray, R. C. (1995) Properties of rabbit liver adehyde oxidase and the relationship of the enzyme to xanthine oxidase and dehydrogenase. Eur. J. Biochem. 232, 636-657. Moriwaki, Y., Yamamoto, T., Yamaguchi, K., Takahashi, S., and Higashino, K. (1996) Immunohistochemical localization of aldehyde and xanthine oxidase in rat tissues using polyconal antibodies. Histochem. Cell Biol. 105, 71-79. Ruenitz, P. C., and Bai, X. G. (1995) Acidic metabolites of TamoxifensAspects of formation and fate in the female rat. Drug Metab. Dispos. 23, 993-998. Beedham, C., Critchley, D. J. P., and Rance, D. J. (1995) Substrate specificity of human liver aldehyde oxidase toward substituted quinazolines and phthalazines: A comparison with hepatic enzyme from guinea pig, rabbit, and baboon. Arch. Biochem. Biophys. 319, 481-490. Beedham, C. (1985) Molybdenum hydroxylases as drug-metabolizing enzymes. Drug Metab. Rev. 16, 119-156. Baker, J. K., and Little, T. L. (1985) Metabolism of phencyclidine. The role of the carbinolamine intermediate in the formation of lactam and amino acid metabolites of nitrogen heterocycles. J. Med. Chem. 28, 46-50. Langston, J. W. (1996) The etiology of Parkinson’s disease with emphasis on the MPTP story. Neurology 47 (Suppl.), S153-S160. Singer, T. P., Ramsay, R. R., Sonsalla, P. K., Nicklas, W. J., and Heikkila, R. E. (1993) Biochemical mechanism underlying MPTPinduced and idiopathic parkinsonism - new vistas. In Advances in Neurology, Parkinson’s Disease from Basic Research to Treatment (Narabayashi, H., Nagatsu, T., Yanagisawa, N., and Mizuno, Y., Eds.) pp 300-305, Raven Press, New York. Coleman, T., Ellis, S. W., Martin, I. J., Lennard, M. S., and Tucker, G. T. (1996) 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is N-demethylated by cytochromes P450 2D6, 1A2 and 3A4 - Implications for susceptibility to Parkinson’s disease. J. Pharmacol. Exp. Ther. 277, 685-690. Weissman, J., Trevor, A., Adams, J., Baillie, T., and Castagnoli, N., Jr. (1985) Metabolism of the nigrostriatal toxin 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine by liver homogenate fractions. J. Med. Chem. 28, 997-1001. Narimatsu, S., Tachibana, M., Masubuchi, Y., and Suzuki, T. (1996) Cytochrome P4502D and -2C enzymes catalyze the oxidative N-demethylation of the parkinsonism-inducing substance 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in rat liver microsomes. Chem. Res. Toxicol. 9, 93-98. Modi, S., Gilham, D. E., Sutcliffe, M. J., Lian, L. Y., Primrose, W. U., Wolf, C. R., and Roberts, G. C. (1997) 1-Methyl-4-phenyl1,2,3,6-tetrahydropyridine as a substrate of cytochrome P4502D6: Allosteric effects of NADPH-cytochrome P450 reductase. Biochemistry 36, 4461-4470. Ottoboni, S., Carlson, T., Castagnoli, K., Trager, W. F., and Castagnoli, N., Jr. (1990) Studies on the cytochrome P-450 catalyzed ring R-carbon oxidation of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Chem. Res. Toxicol. 3, 423-427. Wu, E., Shinka, T., Caldera-Munoz, P., Yoshizumi, H., Trevor, A., and Castagnoli, N., Jr. (1988) Metabolic studies on the nigrostriatal toxin MPTP and its MAO-B generated dihydropyridinium metabolite MPDP+. Chem. Res. Toxicol. 1, 186-194.

934 Chem. Res. Toxicol., Vol. 10, No. 9, 1997 (39) Chiba, K., Trevor, A. J., and Castagnoli, N., Jr. (1984) Metabolism of the neurotoxic tertiary amine MPTP by brain monoamine oxidase. Biochem. Biophys. Res. Commun. 120, 1228-1232. (40) Chiba, K., Peterson, L. A., Castagnoli, K. P., Trevor, A. J., and Castagnoli, N., Jr. (1985) Studies on the molecular mechanism of bioactivation of the selective nigrostriatal toxin 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP). Drug Metab. Dispos. 13, 342-347. (41) Wang, Y.-X., and Castagnoli, N., Jr. (1995) Studies on the monoamine oxidase (MAO)-catalyzed oxidation of phenyl-substituted 1-methyl-4-phenoxy-1,2,3,6-tetrahydropyridine derivatives: Factors contributing to MAO-A and MAO-B selectivity. J. Med. Chem. 38, 1904-1910. (42) Ottoboni, S., Caldera, P., Trevor, A., and Castagnoli, N., Jr. (1989) Deuterium isotope effect measurements on the interactions of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine with monoamine oxidase B. J. Biol. Chem. 264, 13684-13688; Additions and Corrections (1990) 265, 8345. (43) Peterson, L. A., Caldera, P., Trevor, A., Chiba, K., and Castagnoli, N., Jr. (1985) Studies on the 1-methyl-4-phenyl-2,3-dihydropyridinium species, 2,3-MPDP+, the monoamine oxidase catalyzed oxidation product of the nigrostriatal toxin 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine. J. Med. Chem. 28, 1432-1436. (44) Leung, L., Ottoboni, S., Oppenheimer, N., and Castagnoli, N., Jr. (1989) Characterization of a product derived from the 1-methyl4-phenyl-2,3-dihydropyridinium ion, a metabolite of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. J. Org. Chem. 54, 1052-1055. (45) Markey, J. P., Johannessen, J. N., Chiueh, C. C., Burns, R. S., and Herkenha, M. A. (1984) Intra-neuronal generation of a pyridinium metabolite may cause drug-induced parkinsonism. Nature 311, 464-467. (46) Salach, J. I., Singer, T. P., Castagnoli, N., Jr., and Trevor, A. (1984) Oxidation of the neurotoxic amine 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine (MPTP) by monoamine oxidases A and B and suicide inactivation of the enzymes by MPTP. Biochem. Biophys. Res. Commun. 125, 831-835. (47) Langston, J. W., Irwin, I., Langston, E. B., and Forno, L. S. (1984) Pargyline prevents MPTP-induced parkinsonism in primates. Science 225, 1480-1482. (48) Heikkila, R. E., Manzino, L., Cabbat, F. S., and Duvoisin, R. C. (1984) Protection against the dopaminergic neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by monoamine oxidase inhibitors. Nature 311, 467-469. (49) Heikkila, R. E., Youngster, S. K., Panek, D. U., Giovanni, A., and Sonsalla, P. K. (1988) Studies with the neurotoxicant 1-methyl4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and several of its analogs. Toxicology 49, 493-501. (50) Jackson-Lewis, V., Jakwec, M., Burke, R. E., and Przedborski, S. (1995) Time course and morphology of dopaminergic neuronal death caused by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Neurodegeneration 4, 257-269. (51) Espino, A., Cutillas, B., Tortosa, A., Ferrer, I., Bartrons, R., and Ambrosio, A. (1995) Chronic effects of single intrastriatal injections of 6-hydroxydopamine or 1-methyl-4-phenylpyridinium studied by microdialysis in freely moving rats. Brain Res. 695, 151-157. (52) Langston, J. W., Irwin, I., Langston, E. B., and Forno, L. S. (1984) 1-Methyl-4-phenylpyridinium ion (MPP+): Identification of a metabolite of MPTP, a toxin selective to the substantia nigra. Neurosci. Lett. 48, 87-92. (53) Nwanze, E., Souverbie, F., Jonsson, G., and Sundstrom, E. (1995) Regional biotransformation of MPTP in the CNS of rodents and its relation to neurotoxicity. Neurotoxicology 16, 469-477. (54) Fingerg, J. P. M., Wang, J., Goldstein, D. S., Kopin, I. J., and Bankiewicz, K. S. (1995) Influence of selective inhibition of monoamine oxidase A or B on striatal metabolism of L-DOPA in hemiparkinsonian rats. J. Neurochem. 65, 1213-1220. (55) Kondoh, Y., Murakami, M., Yin, W. M., Mizusawa, S., Nakamichi, H., and Nagata, K. (1994). Quantitative distribution of rat brain monoamine oxidase A by [C-14]clorgyline autoradiography. Exp. Brain Res. 99, 375-382. (56) Berry, M. D., Juorio, A. V., and Paterson, I. A. (1994) The functional role of monoamine oxidases A and B in the mammalian central nervous system. Prog. Neurobiol. 42, 375-391. (57) Javitch, J. A., D’Amato, R. J., Strittmatter, S. M., and Snyder, S. H. (1985) Parkinsonism-inducing neurotoxin N-methyl-4-phenyl1,2,3,6-tetrahydropyridine: Uptake of the metabolite N-methyl4-phenylpyridine by dopamine neurons explains selective toxicity. Proc. Natl. Acad. Sci. U.S.A. 82, 2173-2177. (58) Dungigan, C. D., and Shamoo, A. E. (1996) Identification of the major transport pathway for the parkinsonism inducing neurotoxin 1-methyl-4-phenylpyridinium. Neuroscience 75, 37-41. (59) Hung, H. D., Tao, P. L., and Lee, E. H. Y. (1995) 1-Methyl-4phenylpyridinium (MPP+) uptake does not explain the differential


(60)

(61)

(62)

(63)

(64)

(65)

(66)

(67)

(68)

(69)

(70)

(71)

(72)

(73)

(74)

(75)

(76)

(77)

(78)

toxicity of MPP+ in the nigrostriatal and mesolimbic dopaminergic pathways. Neurosci. Lett. 196, 93-96. Kilbourn, M., and Frey, K. L. (1996) Striatal concentrations of vesicular monoamine transporters are identical in MPTP sensitive (C57BL/6) and insensitive (CD1) mouse strains. Eur. J. Pharmacol. 307, 227-232. Brooks, W. J., Jarvis, M. F., and Wagner, G. C. (1989) Astrocytes as a primary locus for the conversion of MPTP into MPP+. J. Neural. Transm. 76, 1-12. Dimonte, D. A., Royland, J. E., and Langston, J. W. (1996) Astrocytes as the site for bioactivation of neurotoxins. Neurotoxicology 17, 697-703. Ramsay, R. R., Salach, J. I., and Singer, T. P. (1986) Uptake of the neurotoxin 1-methyl-4-phenylpyridine (MPP+) by mitochondria and its relation to inhibition of the mitochondrial oxidation of NAD+-linked substrates by MPP+. Biochem. Biophys. Res. Commun. 134, 743-748. Sayre, L. M., Singh, M. P., Arora, P. K., Wang, F., McPeak, R. J., and Hoppel, C. L. (1990) Inhibition of mitochondrial respiration by analogues of the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium: structural requirements for accumulation-dependent enhanced inhibitory potency on intact mitochondria. Arch. Biochem. Biophys. 280, 274-283. Nicklas, W. J., Vyas, I., and Heikkila, R. E. (1985) Inhibition of NADH-linked oxidation in brain mitochondria by 1-methyl-4phenylpyridinium, a metabolite of the neurotoxin 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine. Life Sci. 36, 2503-2508. Vyas, I., Heikkila, R. E., and Nicklas, W. J. (1986) Studies on the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine: Inhibition of NAD-linked substrate oxidation by its metabolite, 1-methyl-4-phenylpyridinium. J. Neurochem. 46, 1501-1607. Santiago, M., Granero, L., Machado, A., and Cano, J. (1995) Complex I inhibitor effect on the nigral and striatal release of dopamine in the presence and absence of nomifensine. Eur. J. Pharmacol. 280, 251-256. Singh, M. P., Wang, F., Hoppel, C. L., and Sayre, L. M. (1991) Inhibition of mitochondrial respiration by neutral, monocationic, and dicationic bis-pyridines related to the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium cation (MPP+). Arch. Biochem. Biophys. 286, 138-146. Ramsay, R. R., Salach, J. I., Dadgar, J., and Singer, T. P. (1986) Inhibition of mitochondrial NADPH dehydrogenase by pyridine derivatives and possible relation to experimental and idiopathic parkinsonism. Biochem. Biophys. Res. Commun. 135, 269-275. Youngster, S.-K., Gluck, M. R., Heikkila, R. E., and Nicklas, W. J. (1990) 4′-Alkylated analogs of 1-methyl-4-phenylpyridinium ion are potent inhibitors of mitochondrial respiration. Biochem. Biophys. Res. Commun. 169, 758-764. Gluck, M. R., Youngster, S. K., Ramsay, R. R., Singer, T. P., and Nicklas, W. J. (1994) Studies on the characterization of the inhibitory mechanism of 4′-alkylated 1-methyl-4-phenylpyridinium and phenylpyridine analogues in mitochondria and electron transport particles. J. Neurochem. 63, 655-661. Sayre, L. M., Wang, F. J., and Hoppel, C. L. (1989) Tetraphenylborate potentiates the respiratory inhibition by the dopaminergic neurotoxin MPP+ in both electron transport particles and intact mitochondria. Biochem. Biophys. Res. Commun. 161, 809818. Ramsay, R. R., Melhorn, R. J., and Singer, T. P. (1989) Enhancement by tetraphenylboron of the interaction of the 1-methyl-4phenylpyridinium ion (MPP+) with mitochondria. Biochem. Biophys. Res. Commun. 159, 983-990. Gluck, M. R., Krueger, M. J., Ramsay, R. R., Sablin, S. O., Singer, T. P., and Nicklas, W. J. (1993) Characterization of the inhibitory mechanism of 1-methyl-4-phenylpyridinium and 4-phenylpyridine analogs in inner membrane preparations. J. Biol. Chem. 269, 3167-3174. Dimonte, D., Jewell, S. A., Ekstrom, G., Sandy, M. S., and Smith, M. T. (1986) 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridine (MPP+) cause rapid ATP depletion in isolated hepatocytes. Biochem. Biophys. Res. Commun. 137, 310-315. Takada, M., Campbell, K. J., and Hattori, T. (1991) Regional localization of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) uptake - mismatch between uptake and neurotoxic sites. Neurosci. Lett. 133, 137-140. Aluchi, T., Matsunaga, M., and Nakaya, K. (1992) Distribution of 1-methyl-4-phenylpyridine, which inhibits the respiratory chain, in mitochondria. J. Pharmacobio-Dyn. 15, 5077. Gerlach, M., Gotz, M., Dirr, A., Kupsch, A., Janetzky, B., Oeretl, W., Sautter, J., Schwarz, J., Reichmann, H., and Riederer, P. (1996) Acute MPTP treatment produces no changes in mitochondrial complex activities and indices of oxidative damage in the

Invited Review common marmoset ex vivo one week after exposure to the toxin. Neurochem. Int. 28, 41-49. (79) Davey, G. P., and Clark, J. B. (1996) Threshold effects and control of oxidative phosphorylation in nonsynaptic rat brain mitochondria. J. Neurochem. 66, 1617-1624. (80) Zuddas, A., Fascetti, F., Corsini, G. U., and Piccardi, M. P. (1994) In brown Norway rats, MPP+ is accumulated in the nigrostriatal dopaminergic terminals but it is not neurotoxic: A model of natural resistance to MPTP toxicity. Exp. Neurol. 127, 54-61. (81) Koller, W. C. (1997) Neuroprotective therapy for Parkinson’s disease. Exp. Neurol. 144, 24-29. (82) Ambrosio, S., Espino, A., Cutillas, B., and Bartrons, R. (1996) MPP+ toxicity in rat striatal slices: Relationship between non selective effects and free radical production. Neurochem. Res. 21, 73-78. (83) Sriram, K., Pai, K. S., Boyd, M. R., and Ravindranath, V. (1997) Evidence for generation of oxidative stress in brain by MPTP: In vitro and in vivo studies in mice. Brain Res. 749, 44-52. (84) Fallon, J., Matthews, R. G., Hyman, B. T., and Beal, M. F. (1997) MPP+ produces progressive neuronal degeneration which is mediated by oxidative stress. Exp. Neurol. 144, 193-198. (85) Desole, M. S., Esposito, G., Fresu, L., Bigheli, R., Sircana, S., Delogu, R., Miele, M., and Miele, E. (1996) Further investigation of allopurinol effects on MPTP induced oxidative stress in the striatum and brain stem of the rat. Pharmacol. Biochem. Behav. 54, 377-383. (86) Akaneya, Y., Takahashi, M., and Hatanaka, H. (1995) Involvement of free radicals in MPP+ neurotoxicity against rat dopaminergic neurons in culture. Neurosci. Lett. 193, 53-56. (87) Gotz, M. E., Kunig, G., Riederer, P., and Youdim, M. B. H. (1994) Oxidative stress: Free radical production in neural degeneration. J. Pharmacol. Exp. Ther. 63, 37-122. (88) Kang, D., Miyako, K., Kuribayashi, F., Hasegawa, E., Mitsumoto, A., Nagano, T., and Takeshige, K. (1997) Changes of energy metabolism induced by 1-methyl-4-phenylpyridinium (MPP+) and related compounds in rat pheochromocytoma PC12 cells. Arch. Biochem. Biophys. 337, 75-80. (89) Koppenol, W. H., and Traynham, J. G. (1996) Say NO to nitric oxide: Nomenclature for nitrogen- and oxygen-containing compounds. Methods Enzymol. 268, 3-7. (90) Paakkari, I., and Lindsberg, P. (1995) Nitric oxide in the central nervous system. Ann. Med. 27, 369-377. (91) Gerlach, M., Ehler, D., Blumdegen, D., Lange, K. W., Mayer, B., Reichmann, H., and Riederer, P. (1995) Regional distribution and characterization of nitric oxide synthase activity in the brain of the common marmoset. Neuroreport 6, 1141-1145. (92) Dawson, V. L., and Dawson, T. M. (1996) Nitric oxide neurotoxicity. J. Chem. Neuroanat. 10, 179-190. (93) Dawson, V. L., and Dawson, T. M. (1996) Nitric oxide actions in neurochemistry. Neurochem. Int. 29, 97-110. (94) Dawson, V. L., and Dawson, T. M. (1996) Nitric oxide in neuronal degeneration. Proc. Soc. Exp. Biol. Med. 211, 33-40. (95) Schulz, J. B., Matthews, R. T., and Beal, M. F. (1995) Role of nitric oxide in neurodegenerative diseases. Curr. Opin. Neurol. 8, 480486. (96) Packer, M. A., Porteous, C. M., and Murphy, M. P. (1996) Superoxide production by mitochondria in the presence of nitric oxide forms peroxynitrite. Biochem. Mol. Biol. Int. 40, 527-534. (97) Abekawa, T., Ohmori, T., and Koyama, T. (1996) Effects of nitric oxide synthesis inhibition on methamphetamine induced dopaminergic and serotonergic neurotoxicity in the rat brain. J. Neural Transm. 103, 671-680. (98) Itzhak, Y., and Ali, S. F. (1996) The neuronal nitric oxide synthase inhibitor, 7-nitroindazole, protects against methamphetamine induced neurotoxicity in vivo. J. Neurochem. 67, 1770-1773. (99) Dimonte, D. A., Royland, J. E., Jakowec, M. W., and Langston, J. W. (1996) Role of nitric oxide in methamphetamine neurotoxicity: Protection by 7-nitroindazole, an inhibitor of neuronal nitric oxide synthase. J. Neurochem. 67, 2443-2450. (100) Schulz, J. B., Matthews, R. T., Jenkins, B. G., Ferrante, R. J., Siwek, D., Henshaw, D. R., Cipolloni, P. B., Meccocci, P., Koweall, N. W., Rosen, B. R., and Beal, M. F. (1995) Blockade of neuronal nitric oxide synthase protects against excitotoxicity in vivo. J. Neurosci. 15, 8419-8429. (101) Wu, R. M., Mohanakumar, K. P., Murphy, D. L., and Chiueh, C. C. (1994) Antioxidant mechanism and protection of nigral neurons against MPP+ toxicity by deprenyl (selegiline). Ann. N. Y. Acad. Sci. 738, 214-221. (102) Matthews, R. T., Yang, L. C., and Beal, M. F. (1997) SMethylthiocitrulline, a neuronal nitric oxide synthase inhibitor, protects against malonate and MPTP neurotoxicity. Exp. Neurol. 143, 282-286. (103) Moore, P. K., and Blandward, P. A. (1996) 7-Nitroindazole: An inhibitor of nitric oxide synthase. Methods Enzymol. 268, 393398.

Chem. Res. Toxicol., Vol. 10, No. 9, 1997 935 (104) Smith, T. S., Swerdlow, R. H., Parker, W. D., Jr., and Bennett, J. P., Jr. (1994) Reduction of MPP+-induced hydroxy radical formation and nigrostriatal MPTP toxicity by inhibiting nitric oxide synthase. Neuroreport 5, 2598-2600. (105) Schulz, J. B., Matthews, R. T., Muqit, M. M. K., Browne, S. E., and Beal, M. F. (1995) Inhibition of neuronal nitric oxide synthase by 7-nitroindazole protects against MPTP-induced neurotoxicity in mice. J. Neurochem. 64, 936-939. (106) Przedborski, S., Jackson-Lewis, V., Yokoyama, R., Shibata, T., Dawson, V. L., and Dawson, T. M. (1996) Role of neuronal nitric oxide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)induced dopaminergic neurotoxicity. Proc. Natl. Acad. Sci. U.S.A. 93, 4565-4571. (107) Hantraye, P., Brouillet, E., Ferrante, R., Palfi, S., Dolan, R., Matthews, R. T., and Beal, M. F. (1996) Inhibition of neuronal nitric oxide synthase prevents MPTP-induced parkinsonism in baboons. Nature Med. 2, 1017-1021. (108) Castagnoli, K., Palmer, S., Anderson, A., Bueters, T., and Castagnoli, N., Jr. (1997) The neuronal nitric oxide synthase inhibitor 7-nitroindazole also inhibits the monoamine oxidaseB-catalyzed oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Chem. Res. Toxicol. 10, 364-368. (109) Murphy, M. P., Krueger, M. J., Sablin, S. O., Ramsay, R. R., and Singer, T. P. (1995) Inhibition of Complex I by hydrophobic analogues of N-methyl-4-phenylpyridinium (MPP+) and the use of an ion-selective electrode to measure their accumulation by mitochondria and electron-transport particles. Biochem. J. 306, 359-365. (110) McNaught, K. S. P., Thull, U., Carrupt, P.-A., Altomare, C., Cellamare, S., Carotti, A., Testa, B., Jenner, P., and Marsden, C. D. (1995) Inhibition of complex I by isoquinoline derivatives structurally related to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Biochem. Pharmacol. 50, 1903-1911. (111) Altomare, C., Carrupt, P.-A., El Tayar, N., Testa, B., and Nagatsu, T. (1991) Electronic and conformational effects on the lipophilicity of isomers and analogs of the neurotoxin 1-methyl4-phenylpyridinium (MPP+). Helv. Chim. Acta 74, 290-296. (112) Heikkila, R. E., Nicklas, W. J., and Duvoisin, R. C. (1985) Dopaminergic neurotoxicity after the stereotaxic administration of the 1-methyl-4-phenylpyridinium ion (MPP+) to rats. Neurosci. Lett. 59, 135-140. (113) Sun, C. J., Johannessen, J. N., Gessner, W., Namura, I., Singhaniyom, W., Brossi, A., and Chiueh, C. C. (1988) Neurotoxic damage to the nigrostriatal system in rats following intranigral administration of MPDP+ and MPP+. J. Neural Transm. 74, 7586. (114) Rollema, H., Damsma, G., Horn, A. S., De Vries, J. B., and Westerink, B. H. C. (1986) Brain dialysis in conscious rats reveals an instantaneous massive release of striatal dopamine in response to MPP+. Eur. J. Pharmacol. 126, 345-346. (115) Rollema, H., Johnson, E. A., Booth, R. G., Caldera, P., Lampen, P., Youngster, S. K., Trevor, A., Naiman, N., and Castagnoli, N., Jr. (1990) In vivo intracerebral microdialysis studies in rats of MPP+ analogs and related charged species. J. Med. Chem. 33, 2221-2230. (116) Santiago, M., Machado, A., and Cano, J. (1996) Nigral and striatal comparative study of the neurotoxic action of 1-methyl4-phenylpyridinium ion: Involvement of dopamine uptake system. J. Neurochem. 66, 1182-1190. (117) Saporito, M. S., Heikkila, R. E., Youngster, S. K., Nicklas, W. J., and Geller, H. B. (1992) Dopaminergic neurotoxicity of 1-methyl-4-phenylpyridinium analogs in cultured neurons: Relationship to the dopamine uptake system and inhibition of mitochondrial respiration. J. Pharmacol. Exp. Ther. 260, 14001409. (118) Sanchez-Ramos, J. R., Barrett, J. N., Goldstein, M., Weiner, W. J., and Hefti, F. (1986) 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridinium (MPP+) but not 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) selectively destroys dopaminergic neurons in cultures of dissociated rat mesencephalic neurons. Neurosci. Lett. 72, 215-220. (119) Mytilineou, C., Cohen, G., and Heikkila, R. E. (1985) 1-Methyl4-phenylpyridine (MPP+) is toxic to mesencephalic dopamine neurons in culture. Neurosci. Lett. 57, 19-24. (120) Dimonte, D. A., Wu, E. Y., Irwin, I., Delanney, L. E., and Langston, J. W. (1991) Biotransformation of 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine in primary cultures of mouse astrocytes. J. Pharmacol. Exp. Ther. 258, 594-600. (121) Dimonte, D. A., Wu, E. Y., Delanney, L. E., Irwin, I., and Langston, J. W. (1992) Toxicity of 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine in primary cultures of mouse astrocytes. J. Pharmacol. Exp. Ther. 261, 44-49. (122) Marongui, M. D., Piccardi, M. P., Bernardi, F., Corsini, G. U., and Del Zompo, M. (1988) Evaluation of the toxicity of the dopaminergic neurotoxin MPTP and MPP+ in PC12 pheochro-


(123)

(124)

(125)

(126)

(127)

(128)

(129)

(130)

(131)

(132)

(133)

(134)

(135) (136)

(137) (138)

(139) (140) (141)

(142) (143)

mocytoma cells: Binding and biological studies. Neurosci. Lett. 94, 349-354. Snyder, J. W., Alexander, G. M., Ferraro, T. N., Grothusen, J. R., and Farber, J. L. N. (1993) Methyl-4-phenylpyridinium (MPP+) potentiates the killing of cultured hepatocytes by catecholamines. Chem.-Biol. Interact. 88, 209-223. Mabic, S., and Castagnoli, N., Jr. (1996) Assessment of structural requirements for the monoamine oxidase-B-catalyzed oxidation of 1,4-disubstituted-1,2,3,6-tetrahydropyridine derivatives related to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. J. Med. Chem. 39, 3694-3700. Wang, Y.-X., and Castagnoli, N., Jr. (1995) Studies on the monoamine oxidase (MAO)-catalyzed oxidation of phenylsubstituted 1-methyl-4-phenoxy-1,2,3,6-tetrahydropyridine derivatives: factors contributing to MAO-A and MAO-B selectivity. J. Med. Chem. 38, 1904-1910. Kalgutkar, A. S., Castagnoli, K., Hall, A., and Castagnoli, N., Jr. (1994) Novel 4-(aryloxy)tetrahydropyridine analogs of MPTP as monoamine oxidase A and B substrates. J. Med. Chem. 37, 944-949. Maret, G., El Tayar, N., Carrupt, P.-A., Testa, B., Jenner, P., and Bairds, M. (1990) Toxication of MPTP (1-methyl-4-phenyl1,2,3,6-tetrahydropyridine) and analogs by monoamine oxidase. Biochem. Pharmacol. 40, 783-792. Youngster, S. K., Sonsalla, P. K., Sieber, B.-A., and Heikkila, R. E. (1989) Structure-activity study of the mechanism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. I. Evaluation of the biological activity of MPTP analogs. J. Pharmacol. Exp. Ther. 249, 820-828. Palmer, S. L., Mabic, S., and Castagnoli, N., Jr. (1997) Probing the active sites of monoamine oxidase A and B with 1,4disubstituted tetrahydropyridine substrates and inactivators. J. Med. Chem. 40, 1982-1989. Altomare, C., Carrupt, P.-A., Gaillard, P., El Tayar, N., Testa, B., and Carotti, A. (1992) Quantitative structure-metabolism relationship analyses of MAO-mediated toxication of 1-methyl4-phenyl-1,2,3,6-tetrahydropyridine and analogues. Chem. Res. Toxicol. 5, 366-375. Efange, S. M. N., Michelson, R. H., Tan, A. K., Krueger, M. J., and Singer, T. P. (1993) Molecular size and flexibility as determinants of selectivity in the oxidation of N-methyl-4phenyl-1,2,3,6-tetrahydropyridine analogs by monoamine oxidase A and B. J. Med. Chem. 36, 1278-1283. Naiman, N., Rollema, H., Johnson, E., and Castagnoli, N., Jr. (1990) Studies on 4-benzyl-1-methyl-1,2,3,6-tetrahydropyridine, a nonneurotoxic analogue of the parkinsonian inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Chem. Res. Toxicol. 3, 133-138. Dalvie, D., Zhao, Z., and Castagnoli, N., Jr. (1992) Characterization of an unexpected product from a monoamine oxidase B generated 2,3-dihydropyridinium species. J. Org. Chem. 57, 7321-7324. Zhao, A., Dalvie, D., Naiman, N., Castagnoli, K., and Castagnoli, N., Jr. (1992) Design, synthesis, and biological evaluation of novel 4-substituted 1-methyl-1,2,3,6-tetrahydropyridine analogs of MPTP. J. Med. Chem. 35, 4473-4478. Wang, Y.-X., and Castagnoli, N., Jr. (1997) Potential latent nitrogen mustard derivatives designed to target monoamine oxidase rich cells. Bioorg. Med. Chem., in press. Flaherty, P., Castagnoli, K., Wang, Y.-X., and Castagnoli, N., Jr. (1996) Synthesis and selective monoamine oxidase B-inhibiting properties of 1-methyl-1,2,3,6-tetrahydropyrid-4-yl carbamate derivatives: Potential prodrugs of (R)- and (S)-nordeprenyl. J. Med. Chem. 39, 4756-4761. Muller, U., and Graeber, M. B. (1996) Neurogenetic diseases: Molecular diagnosis and therapeutic approaches. J. Mol. Med. 74, 71-84. Golbe, L. K., Di Iorio, G., Sanges, G., Lazzarini, A. M., La Sala, S., Bonavita, V., and Duvoisin, R. C. (1996) Clinical genetic analysis of Parkinson’s disease in the Contusi kindred. Ann. Neurol. 40, 767-775. Taussig, D., and Plante-Bordeneuve, V. (1997) Atypical familial parkinsonian syndromes. Parkinson diseases or specific entities? Presse Med. 26, 290-296. Schapira, A. H. (1995) Nuclear and mitochondrial genetics in Parkinson’s disease. J. Med. Genet. 32, 411-414. Michel, P. P., Dandapani, B. K., Knusel, B., Sanchez-Ramos, J., and Hefti, F. (1990) Toxic effects of potential environmental neurotoxins related to 1-methyl-4-phenylpyridinium on cultured rat dopaminergic neurons. J. Pharmacol. Exp. Ther. 248, 842850. Langston, J. W. (1990) Do environmental toxins cause Parkinson’s disease? A critical review. Neurology 40, 17-30. Polymeropoulos, M. B., Higgins, J. J., Johnson, W. G., Ide, S. E., Di Iorio, G., Sanges, G., Stenroos, E. S., Pho, L. T., Schaffer,


(144)

(145) (146) (147)

(148)

(149) (150) (151)

(152)

(153)

(154) (155)

(156)

(157) (158)

(159)

(160)

(161) (162)

(163)

(164)

A. A., Lazzarini, A. M., Nussbaum, R. L., and Duvoisin, R. C. (1996) Mapping of a gene for Parkinson’s disease to chromosome 4q21q23. Science 274, 1197-1199. Wyatt, R. J., Erderyli, E., DoAmaral, J. R., Elliott, G. R., Tenson, J., and Barchas, J. D. (1975) Tryptoline formation by a preparation from brain with 5-methyltetrahydrofolic acid and tryptamine. Science 187, 853-855. Mandel, L. R., Rosegay, A., Walker, R. W., and VandenHeuvel, W. J. A. (1974) 5-Methyltetrahydrofolic acid as a mediator in the formation of pyridoindoles. Science 186, 741-743. Halushka, P. V., and Hoffmann, P. C. (1968) Does tetrahydropapaveroline contribute to the cardiovascular actions of dopamine? Biochem. Pharmacol. 17, 1873-1880. Naoi, M., Maruyama, W., Zhang, J. H., Takahashi, T., Deng, Y. L., and Dostert, P. (1995) Enzymatic oxidation of the dopaminergic neurotoxin, (R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, into 1,2(N)-dimethyl-6,7-dihydroxyisoquinolinium ion. Life Sci. 57, 1061-1066. Naoi, M., Maruyama, W., Minami, M., Dostert, P., Parvez, S. H., and Nagatsu, T. (1993) Salsolinols and other 6,7-dihydroxy1,2,3,4-tetrahydroisoquinolines as inhibitors of monoamine oxidase - in vivo and in vitro study. Biogenic Amines 9, 367-379. Liptrot, J., Holdup, D., and Phillipson, O. (1993) 1,2,3,4Tetrahydro-2-methyl-4,6,7-isoquinolinetriol depletes catecholamines in rat brain. J. Neurochem. 61, 202-206. Yoshida, M., Ogawa, M., Suzuki, K., and Nagatsu, T. (1993) Parkinsonism produced by tetrahydroisoquinoline (TIQ) or the analogues. Adv. Neurol. 60, 207-211. Fukuda, T. (1994) 2-Methyl-1,2,3,4-tetrahydroisoquinoline dose dependently reduces the number of tyrosine hydroxylase-immunoreactive cells in the substantia-nigra and locus ceruleus of C57BL/6J mice. Brain Res. 639, 325-328. Takahashi, T., Deng, Y., Maruyama, W., Dostert, P., Kawai, M., and Naoi, M. (1994) Uptake of a neurotoxin-candidate, (R)-1,2dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, into human dopaminergic neuroblastoma SH-SY5Y cells by the dopamine transport system. J. Neural Transm. 98, 107-118. Faraj, B. A., Camp, V. M., and Kutner, M. (1991) Interrelationship between activation of dopaminergic pathways and cerebrospinal fluid concentration of dopamine tetrahydroisoquinoline metabolite salsolinol in humans: Preliminary findings. Alcohol Clin. Exp. Res. 15, 86-89. Ayala, A., Parrado, J., Cano, J., and Machado. A. (1994) Reduction of 1-methyl-1,2,3,4-tetrahydroisoquinoline level in substantia nigra of the aged rat. Brain Res. 638, 334-336. Maruyama, W., Nakahara, D., Dostert, P., Hashiguchi, H., Ohta, S., Hirobe, M., Takahashi, A., Nagatsu, T., and Naoi, M. (1993) Selective release of serotonin by endogenous alkaloids, 1-methyl6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, (R)- and (S)-salsolinol, in the rat striatum: In vivo microdialysis study. Neurosci. Lett. 149, 115-118. Maruyama, W., Takahashi, T., Minami, M., Takahashi, A., Dostert, P., Nagatsu, T., and Naoi, M. (1993) Cytotoxicity of dopamine-derived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines. Adv. Neurol. 60, 224-230. Fa, Z., and Dryhurst, G. (1993) Oxidation chemistry of the endogenous central nervous system alkaloid salsolinol-1-carboxylic acid. J. Med. Chem. 36, 11-20. Dostert, P., Benedetti, M. S., Dellavedova, F., Allievi, C., Lacroix, R., Dordain, G., Vernay, D., and Durif, F. (1993) Dopaminederived tetrahydroisoquinolines and Parkinson’s disease. Adv. Neurol. 60, 218-223. Minami, M., Takahashi, T., Maruyama, W., Takahashi, A., Dostert, P., Nagatsu, T., and Naoi, M. (1992) Inhibition of tyrosine hydroxylase by R and S enantiomers of salsolinol, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline. J. Neurochem. 58, 2097-2101. Willets, J. M., Lambert, D. G., Lunec, J., and Griffiths, H. R. (1995) Studies on the neurotoxicity of 6,7-dihydroxy-1-methyl1,2,3,4-tetrahydroisoquinoline (salsolinol) in SH-SY5Y cells. Eur. J. Pharmacol.- Environ. Toxicol. Pharmacol. 293, 319-326. Moser, A., Scholz, J., Bamberg, H., and Bohem, V. (1996) The effect of N-methyl-norsalsolinol on monoamine oxidase of the rat caudate nucleus in vitro. Neurochem. Int. 28, 109-112. McNaught, K. S. P., Thull, U., Carrupt, P.-A., Altomare, C., Cellamare, X., Carotti, A., Testa, B., Jenner, P., and Marsden, C. D. (1996) Nigral cell loss produced by infusion of isoquinoline derivatives structurally related to 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine. Neurodegeneration 5, 265-274. Takahashi, T., Maruyama, W., Deng, Y., Dostert, P., Nakahara, D., Niwa, T., Ohta, S., and Naoi, M. (1997) Cytotoxicity of endogenous isoquinolines to human dopaminergic neuroblastoma SH SY5Y cells. J. Neural Transm. 104, 59-66. McNaught, K., Thull, U., Carrupt, P.-A., Altomare, C., Cellamare, S., Carotti, A., Testa, B., Jenner, P., and Marsden, C.

Invited Review

(165)

(166)

(167)

(168)

(169)

(170) (171)

(172)

(173)

(174)

(175)

(176)

(177)

(178)

(179)

(180)

(181)

(182)

(183)

D. (1996) Nigral cell loss produced by infusion of isoquinoline derivatives structurally related to 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine. Biochem. Pharmacol. 52, 29-34. Naoi, M., Maruyama, W., and Dostert, P. (1995) Dopaminederived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines: oxidation and neurotoxicity. Prog. Brain Res. (Netherlands) 106, 227-239. Niwa, T., Takeda, N., and Sasaoka, T. (1991) Detection of tetrahydroisoquinoline in parkinsonian brain as an endogenous amine by use of gas chromatography-mass spectrometry. J. Chromatogr. 491, 397-403. Niwa, T., Takeda, N., and Oshizumi, H. (1991) Presence of 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and 1,2dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, novel endogenous amines in parkinsonian and normal human brains. Biochem. Biophys. Res. Commun. 177, 603-609. Moser, A., and Kompf, D. (1992) Presence of methyl-6,7dihydroxy-1,2,3,4-tetrahydroisoquinolines, derivatives of the neurotoxin isoquinoline, in parkinsonian lumbar CSF. Life Sci. 50, 1885-1891. Kotake, Y., Tasaki, Y., Makino, Y., Ohta, S., and Hirobe, M. (1995) 1-Benzyl-1,2,3,4-tetrahydroisoquinoline as a parkinsonisminducing agent: A novel endogenous amine in mouse brain and parkinsonian CSF. J. Neurochem. 65, 2633-2638. Cashaw, J. L. (1993) Tetrahydropapaveroline in brain regions of rats after acute ethanol administration. Alcohol 10, 133-138. Kajita, M., Niwa, T., Jujisaki, M., Ueki, M., Nimura, K., Sato, M., Egami, K., Naoi, M., Yoshida, M., and Nagatsu, T. (1995) Detection of 1-phenyl-N-methyl-1,2,3,4-tetrahydroisoquinoline and 1-phenyl-1,2,3,4-tetrahydroisoquinoline in human brain by gas chromatography tandem mass spectrometry. J. Chromatogr. B Biomed. Appl. 669, 345-351. Naoi, M., Maruyama, W., Dostert, P., Hashizume, Y., Nakahara, D., Takahashi, T., and Ota, M. (1996) Dopamine-derived endogenous 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-(R)-salsolinol, induced parkinsonism in rat: Biochemical, pathological and behavioral studies. Brain Res. 709, 285-295. Naoi, M., Maruyama, W., Dostert, P., and Hashizume, Y. (1996) Animal model of Parkinson’s disease induced by naturally occuring 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline. Biogenic Amines 12, 135-147. Makino, Y. H., Ohta, S., and Tachikawa, O. (1988) Presence of tetrahydroisoquinoline and 1-methyltetrahydroisoquinoline in foods: compounds related to Parkinson’s disease. Life Sci. 43, 373-378. Naoi, M., Matsuura, S., Takahashi, T., and Nagatsu, T. A. (1988) An N-methyltransferase in human brain catalyzes N-methylation of 1,2,3,4-tetrahydroisoquinoline into N-methyl-1,2,3,4tetrahydroisoquinoline, a precursor of a dopaminergic neurotoxin, N-methylisoquinolinium ion. Biochem. Biophys. Res. Commun. 161, 1213-1219. Niwa, T., Yoshizumi, H., and Tatematsu, A. (1990) Endogenous synthesis of N-methyl-1,2,3,4-tetrahydroisoquinoline, a precursor of N-methylisoquinolinium ion, in the brains of primates with parkinsonism after systemic administration of 1,2,3,4-tetrahydroisoquinoline. J. Chromatogr. 533, 145-151. Naoi, M., Dostert, P., Yoshida, M., and Nagatsu, T. (1993) N-Methylated tetrahydroisoquinolines as dopaminergic neurotoxins. Adv. Neurol. 60, 212-217. Naoi, M., Matsuura, S., and Parvez, H. (1989) Oxidation of N-methyl-1,2,3,4-tetrahydroisoquinoline into the N-methylisoquinolinium ion by monoamine oxidase. J. Neurochem. 52, 653655. Niijima, K., Araki, M., Ogawa, M., Suzuki, K., Mizuno, Y., Nagatsu, I., Kimura, H., Yoshida, M., and Nagatsu, T. (1991) N-Methylisoquinolinium ion (NMIQ+) destroys cultured mesencephalic dopamine neurons. Biogenic Amines 8, 61-67. Suzuki, K., Mizuno, Y., Yamauchi, Y., Nagatsu, T., and Mitsuo, Y. (1992) Selective inhibition of complex-I by N-methylisoquinolinium ion and N-methyl-1,2,3,4-tetrahydroisoquinoline in isolated mitochondria prepared from mouse brain. J. Neurol. Sci. 109, 219-223. Yoshida, M., Niwa, T., and Nagatsu, T. (1990) Parkinsonism in monkeys produced by chronic administration of an endogenous substance of the brain, tetrahydroisoquinoline: The behavioral and biochemical changes. Neurosci. Lett. 119, 109-113. Sayre, L. M., Wang, F., Arora, P. K., Riachi, N. J., Harik, S. I., and Hoppel, C. L. (1991) Dopaminergic neurotoxicity in vivo and inhibition of mitochondrial respiration in vitro by possible endogenous pyridinium-like substances. J. Neurochem. 57, 2106-2115. Kuhn, W., Muller, T., Grosse, H., and Rommelspacher, H. (1996) Elevated levels of harman and norharman in cerebrospinal fluid of parkinsonian patients. J. Neural Transm. 103, 1435-1440.

Chem. Res. Toxicol., Vol. 10, No. 9, 1997 937 (184) Fields, J., Albores, R., Neafsey, E., and Collins, M. (1992) Inhibition of mitochondrial succinate oxidation - similarities and differences between N-methylated β-carbolines and MPP+. Arch. Biochem. Biophys. 294, 539-543. (185) May, T., Pwlik, M., and Rommelspacher, H. 3H-Harman binding experiments. 2. Regional and subcellular distribution of specific 3H-harman binding and monoamine oxidase subtype-A and subtype-B activity in the marmoset and rat. J. Neurochem. 56, 500-508. (186) Cobuzzi, R. J., Neafsey, E. J., and Collins, M. A. (1994) Differential cytotoxicities of N-methyl-beta-carbolinium analogues of MPP+ in PC12 cells - Insights into potential neurotoxicants in Parkinson’s disease. J. Neurochem. 62, 1503-1510. (187) Collins, M. A., Neafsey, E. J., Matsubara, K., Cobuzzi, R., Albores, R., Fields, J., and Rollema, H. (1992) Indole-N-methylation of beta-carbolines - The brain’s bioactivation route to toxins in Parkinson’s disease. Ann. N. Y. Acad. Sci. 648, 263265. (188) Zhang, F., Goyal, R. N., Blank, C. L., and Dryhurst, G. (1992) Oxidation chemistry and biochemistry of the central mammalian alkaloid 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-β-carboline. J. Med. Chem. 35, 82-93. (189) Kuhn, W., Muller, T., Grosse, H., Dierks, T., and Rommelspacher, H. (1995) Plasma levels of the beta-carbolines harman and norharman in Parkinson’s disease. Acta Neurol. Scand. 92, 451-454. (190) Tsuchiya, H., Yamada, K., Ohtani, S., Takagi, N., Todoriki, H., and Hayashi, T. (1995) Determination of tetrahydro-beta-carbolines in rat brain by gas chromatography-negative-ion chemical ionization mass spectrometry without interference from artifactual formation. J. Neurosci. Methods 62, 37-41. (191) Heim, C., and Sontag, K. H. (1997) The halogenated tetrahydrobeta-carboline TALCO: A progressively acting neurotoxin. J. Neural Transm. 50 (Suppl.), 107-111. (192) Collins, M. A., Neafsey, E. J., and Matsubara, K. (1996) Beta-carbolines: Metabolism and neurotoxicity. Biogenic Amines 12, 171-180. (193) Neafsey, E. J., Albores, R., Gearhart, D., Kindel, G., Raikoff, K., Ramayo, F., and Collins, M. A. (1995) Methyl-beta-carbolinium analogs of MPP+ cause nigrostriatal toxicity after substantia nigra injections in rats. Brain Res. 675, 279-288. (194) Collins, M. A., Neafsey, E. J., Matsubara, K., Cobuzzi, R. J., and Rollema, H. (1992) Indole-N-methylated beta carbolinium ions and potential brain bioactivated neurotoxins. Brain Res. 570, 154-160. (195) Matsubara, K., Idzu, T., Kobayashi, Y., Nakahara, D., Maruyama, W., Kobayashi, S., Kimura, K., and Naoi, M. (1995) N-Methyl-4-phenylpyridinium and an endogenously formed analog, N-methylated beta-carbolinium, inhibit striatal tyrosine hydroxylation in freely moving rats. Neurosci. Lett. 199, 199-202. (196) Fields, J. Z., Albores, R., Neafsey, E. J., and Collins, M. A. (1992) Similar inhibition of mitochondrial respiration by 1-methyl-4phenyl-pyridinium (MPP+) and by a unique N-methylated betacarboline analogue, 2,9-dimethyl-norharman (2,9Me2NH). Ann. N. Y. Acad. Sci. 648, 272-274. (197) Matsubara, K., Collins, M. A., Akane, A., Ikebuchi, J., Neafsey, E. J., Kagawa, M., and Shiono, H. (1993) Potential bioactivated neurotoxicants, N-methylated beta-carbolinium ions, are present in human brain. Brain Res. 610, 90-96. (198) Matsubara, K., Kobayashi, S., Kobayashi, Y., Yamashita, K., Koide, H., Hatta, M., Iwamoto, K., Tanaka, O., and Kimura, K. (1995) Beta-Carbolinium cations, endogenous MPP(+) analogs, in the lumbar cerebrospinal fluid of patients with Parkinson’s disease. Neurology 45, 2240-2245. (199) Gearhart, D. A., Neafsey, E. J., and Collins, M. A. (1997) Characterization of brain beta-carboline-2-N-methyltransferase, an enzyme that may play a role in idiopathic Parkinson’s disease. Neurochem. Res. 22, 113-121. (200) Matsubara, K., Neafsey, E. J., and Collins, M. A. (1992) Novel S-adenosylmethionine-dependent indole-N-methylation of betacarbolines in brain particulate fractions. J. Neurochem. 59, 511518. (201) Booth, R. G., Trevor, A., Singer, T. P., and Castagnoli, N., Jr. (1989) Studies on semirigid tricyclic analogs of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. J. Med. Chem. 32, 473-477. (202) Rollema, H., Booth, R. G., and Castagnoli, N., Jr. (1988) In vivo dopaminergic neurotoxicity of the 2-β-methyl-carbolinium ion, a potential endogenous MPP+ analog. Eur. J. Pharmacol. 153, 131-134. (203) His, W. (1887) U ¨ ber das stoffwechselproduct des pyridins. (Concerning the metabolism of pyridine.) Arch. Exp. Pathol. Pharmakol. 22, 253-260. (204) Abderhalden, E., Brahm, C., and Schittenhelm, A. (1909) Vergleichende studien u¨ber den stoffwechsel verschliedener tierarten.


(205)

(206) (207)

(208) (209)

(210)

(211)

(212)

(213)

(214)

(215) (216) (217) (218)

(219) (220) (221)

(222)

(223)

(224) (225)

(226)

(227)

(Various studies concerning the oxidative metabolism in animals.) Hoppe-Seyler’s Z. Physiol. Chem. 59, 32-34. Totani, G., and Hoshiai, Z. (1910) U ¨ ber das verhalten des pyridins im organismus der ziege und des schweins. (Concerning the fate of pyridine in the goat and the pig.) Hoppe-Seyler’s Z. Physiol. Chem. 68, 83-84. Shaker, M. S., Crooks, P. A., and Damani, L. A. (1982) Highperformance liquid chromatographic analysis of the in vivo metabolites of [14C]pyridine. J. Chromatogr. 237, 489-495. Damani, L. A., Crooks, P. A., Shaker, M. D., Caldwell, J., D’Souza, J., and Smith, R. L. (1982) Species differences in the metabolic C- and N-oxidation and N-methylation of [14C]pyridine in vivo. Xenobiotica 12, 527-534. D’Souza, M. S., Caldwell, J., and Smith, R. L. (1980) Species variations in the N-methylation and quaternization of [14C]pyridine. Xenobiotica 10, 151-154. Damani, L. A., Shaker, M. S., Crooks, P. A., Godin, C. S., and Nwosu, C. (1986) N-Methylation and quaternization of pyridine in vitro by rabbit lung, liver and kidney N-methyltransferases: An S-adenosyl-L-methionine-dependent reaction. Xenobiotica 16, 645-650. Damani, L. A. (1985) Oxidation of tertiary heteroaromatic amines. In Biological Oxidation of Nitrogen in Organic Molecules: Chemistry, Toxicology and Pharmacology (Gorrod, J. W., and Damani, L. A., Eds.) pp 205-218, Ellis Horwood Ltd., Chichester, England. Crooks, P. A., Godin, C. S., Damani, L. A., Ansher, S. S., and Jakoby, W. G. (1988) Formation of quaternary amines by N-methylation of azahetercycles with homogeneous amine Nmethyltransferases. Biochem. Pharmacol. 37, 1673-1677. Godin, C. S., and Crooks, P. A. (1989) N-Methylation as a toxication route for xenobiotics. II In vivo formation of N,N′dimethyl-4,4′-bipyridyl in the guinea pig. Drug Metab. Dispos. 17, 180-185. Cundy, K. C., Godin, C. S., and Crooks, P. A. (1985) Stereospecific in vitro N-methylation of nicotine in guinea pig tissues by an S-adenosylmethionine-dependent N-methyltransferase. Biochem. Pharmacol. 34, 281-284. Crooks, P. A., Li, M., and Duvoisin, L. P. (1995) Determination of nicotine metabolites in rat brain after peripheral radiolabeled nicotine administration: Detection of nornicotine. Drug Metab. Dispos. 23, 1175-1177. McKennis, H., Jr., Turnbell, L. B., and Borman, E. R. (1963) N-Methylation of nicotine and cotinine in vivo. J. Biol. Chem. 238, 719-723. Weinshilboum, R. (1989) Methyltransferase pharmacogenetics. Pharmacol. Ther. 43, 77-90. Weinshilboum, R. (1988) Pharmacogenetics of methylation: Relationship to drug metabolism. Clin. Biochem. 21, 201-210. Rini, J., Szumlanski, C., Guerciolini, R., and Weinshilboum, R. (1990) Human liver nicotinamide N-methyltransferase: Ionpairing radiochemical assay, biochemical properties and individual variation. Clin. Chim. Acta 186, 359-374. Testa, B. (1995) Biochemistry of Redox Reactions, pp 216-224, Academic Press, London. Gorrod, J. W., and Aislaitner, G. (1994) The metabolism of alicyclic amines to reactive iminium ion intermediates. Eur. J. Drug Metab. Pharmacokin. 19, 209-217. Matsumoto, H., Ohta, S., and Hirobe, M. (1991) Application of chemical cytochrome P-450 model systems to studies on drug metabolism. IV. Mechanism of piperidine metabolism pathways via an iminium intermediate. Drug Metab. Dispos. 19, 768-780. Sayre, L. M., Engelhart, D. A., Venkataraman, B., Babu, M. K. M., and McCoy, G. D. (1991) Generation and fate of enamines in the microsomal metabolism of cyclic tertiary amines. Biochem. Biophys. Res. Commun. 179, 1368-1376. Arora, P. K., Riachi, N. J., Harik, S. I., and Sayre, L. M. (1988) Chemical oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its in vivo metabolism in rat brain and liver. Biochem. Biophys. Res. Commun. 152, 1339-1347. Grouts, W. C., Essawi, M., and Portoghese, P. S. (1980) R-Cyanation of tertiary amines. Synth. Commun. 10, 495-502. Norris, P. J., Hardwick, J. P., and Emson, P. C. (1994) Localization of NADPH cytochrome P450 oxidoreductase in rat brain by immunohistochemistry and in situ hybridization and a comparison with the distribution of neuronal NADPH-diaphorase staining. Neuroscience 61, 331-350. Anandatheerthavarada, H. K., Shankar, S. K., and Ravindranath, V. (1990) Rat brain cytochromes P450 - catalytic, immunochemical properties and inducibility of multiple forms. Brain Res. 536, 339-343. Warner, M., Ko¨hler, C., Hansson, T., and Gustafsson, J. A° . (1988) Regional distribution of cytochrome P-450 in the rat brain: Spectral quantitation and contribution of P-450b,e and P-450c,d. J. Neurochem. 50, 1057-1065.

Castagnoli, Jr., et al. (228) Bergh, A. F., and Strobel, H. W. (1992) Reconstitution of the brain mixed function oxidase system: Purification of NADPHcytochrome P450 reductase and partial purification of cytochrome P450 from whole rat brain. J. Neurochem. 59, 575-581. (229) Wyss, A., Gustafsson, J. A° ., and Warner, M. (1995) Cytochromes P450 of the 2D subfamily in rat brain. Mol. Pharmacol. 47, 1148-1155. (230) Stromstedt, M., Warner, M., and Gustafsson, J. A° . (1994) Cytochrome P450s of the 4A subfamily in the brain. J. Neurochem. 63, 671-676. (231) Yoo, M., Ryu, H. M., Shin, S. W., Yun, C. H., Lee, S. C., Ji, Y. M., and You, K. H. (1997) Identification of cytochrome P450 2E1 in rat brain. Biochem. Biophys. Res. Commun. 231, 254-256. (232) Riedl, A. G., Watts, P. M., Edwards, R. J., Boobis, A. R., Jenner, P., and Marsden, C. D. (1996) Selective localisation of P450 enzymes and NADPH-P450 oxidoreductase in rat basal ganglia using anti-peptide antisera. Brain Res. 743, 324-328. (233) Sequeira, D. J., and Strobel, H. W. (1996) In vitro metabolism of imipramine by brain microsomes: effects of inhibitors and exogenous cytochrome P450 reductase. Brain Res. 738, 24-31. (234) Aoyama, Y., Horiuchi, T., and Yoshida, Y. Lanosterol 14demethylase activity expressed in rat brain microsomes. J. Biochem. (Tokyo) 120, 982-989. (235) Bergh, A. F., and Strobel, H. W. (1996) Anatomical distribution of NADPH-cytochrome P450 reductase and cytochrome P4502D forms in rat brain: Effects of xenobiotics and sex steroids. Mol. Cell. Biochem. 162, 31-41. (236) Stromstedt, M., and Waterman, M. R. (1996) Messenger RNAs encoding steroidogenic enzymes are expressed in rodent brain. Res. Mol. Brain Res. 34, 75-88. (237) Tindberg, N., Baldwin, H. A., Cross, A. J., and IngelmanSundberg, M. (1996) Induction of cytochrome P450 2E1 expression in rat and gerbil astrocytes by inflammatory factors and ischemic injury. Mol. Pharmacol. 50, 1065-1072. (238) Tindberg, N., and Ingelman-Sundberg, M. (1996) Expression, catalytic activity, and inducibility of cytochrome P450 2E1 (CYP2E1) in the rat central nervous system. J. Neurochem. 67, 2066-2073. (239) Norris, P. J., Hardwick, J. P., and Emson, P. C. (1996) Regional distribution of cytochrome P450 2D1 in the rat central nervous system. J. Comp. Neurol. 366, 244-258. (240) Igarashi, K., Kasuya, F., Fukui, M., Usuki, E., and Castagnoli, N., Jr. (1995) Studies on the metabolism of haloperidol (HP): the role of CYP3A in the production of the neurotoxic pyridinium metabolite HPP+ found in rat brain following ip administration of HP. Life Sci. 57, 2439-2446. (241) Stapleton, G., Steel, M., Richardson, M., Mason, J. O., Rose, K. A., Morris, R. G., and Lathe, R. (1995) A novel cytochrome P450 expressed primarily in brain. J. Biol. Chem. 270, 29739-29745. (242) Ghersiegea, J. F., Perrin, R., Leiningermuller, B., Grassiot, M. C., Jeandel, C., Gloquet, J., Cuny, G., Siest, G., and Minn, A. (1993) Subcellular localization of cytochrome-P450, and activities of several enzymes responsible for drug metabolism in human brain. Biochem. Pharmacol. 45, 647-658. (243) Bhamre, S., Anandatheerthavarada, H. K., Shankar, S. K., Boyd, M. R., and Ravindranath, V. (1993) Purification of multiple forms of cytochrome-P450 from a human brain and reconstitution of catalytic activities. Arch. Biochem. Biophys. 301, 251-255. (244) Bhamre, S., Anandatheerthavarada, H. K., Shankar, S. K., and Ravindranath, V. (1992) Microsomal cytochrome P450 in human brain regions. Biochem. Pharmacol. 44, 1223-1225. (245) Tyndale, R. F., Sunahara, R., Inaba, T., Kalow, W., Gonzalez, F. J., and Niznik, H. B. (1991) Neuronal cytochrome-P450IID1 (debrisoquine/sparteine-type)-potent inhibition of activity by (-)cocaine and nucleotide sequence identify to human hepatic P450gene CYP2D6. Mol. Pharmacol. 40, 63-68. (246) For reviews of xenobiotic metabolism in the brain, see: Ravindranath, V., and Boyd, M. R. (1995) Xenobiotic metabolism in brain. Drug Metab. Rev. 27, 419-448. Bhagwat, S. V., Boyd, M. R., and Ravindranath, V. (1995) Brain mitochondrial cytochromes P450: Xenobiotic metabolism, presence of multiple forms and their selective inducibility. Arch. Biochem. Biophys. 320, 73-83. Warner, M., Ahlgren, R., Zaphiropoulos, P. G., Hayashi, S., and Gustafsson, J. A° . (1991) Identification and localization of cytochromes P450 expressed in brain. Methods Enzymol. 206, 631-640. (247) Lephart, E. D. (1996) A review of brain aromatase cytochrome P450. Brain Res. Rev. 22, 1-26. (248) Casey, D. E. (1995) Motor and mental aspects of extrapyramidal syndromes. Int. Clin. Psychopharmacol. 3 (Suppl.), 105-114. (249) Levinson, D. F. (1991) Pharmacologic treatment of schizophrenia. Clin. Ther. 13, 326-352. (250) Miller, R., and Chouinard, G. (1993) Loss of striatal cholinergic neurons as a basis for tardive dyskinesia and L-Dopa-induced

Invited Review

(251) (252) (253) (254)

(255) (256)

(257)

(258)

(259)

(260)

(261)

(262)

(263)

(264) (265)

(266)

(267)

(268) (269)

(270)

(271)

dyskinesias, neuroleptic-induced supersensitivity psychosis and refractory schizophrenia. Biol. Psych. 34, 713-738. Gerlach, J., and Casey, D. (1988) Tardive Dyskinesia. Acta Psychiatr. Scand. 77, 369-378. Rang, J., and Gorrod, J. W. E. (1991) Dehydration is the first step in the bioactivation of haloperidol to its pyridinium metabolite. Toxicol. Lett. 59, 117-123. Usuki, E. (1996) Studies on the metabolic bioactivation of haloperidol (HP) and its tetrahydropyridine dehydration product. Ph.D. Thesis, pp 53-60, Virginia Tech, Blacksburg, VA. Subramanyam, B., Woolf, T., and Castagnoli, N., Jr. (1991) Studies on the in vitro conversion of haloperidol to a potentially neurotoxic pyridinium metabolite. Chem. Res. Toxicol. 4, 123128. Forsman, A., Fo¨lsch, G., Larsson, M., and Ohman, R. (1977) On the metabolism of haloperidol in man. Curr. Ther. Res. 21, 606617. Miyazaki, H., Matsunage, Y. U., Nambu, K., Ohe, Y., Yoshida, K., and Hashimoto, M. (1986) Disposition and metabolism of [14C]-haloperidol in rats. Arzheim.-Forsch./Drug Res. 36, 443452. Igarashi, K., and Castagnoli, N., Jr. (1992) Determination of the pyridinium metabolite derived from haloperidol in brain tissue, plasma, and urine by high performance liquid chromatography with fluorescence detection. J. Chromatogr. Biomed. Appl. 579, 277-283. Subramanyam, B., Rollema, H., Woolf, T., and Castagnoli, N., Jr. (1990) Identification of a potentially neurotoxic pyridinium metabolite of haloperidol in rats. Biochem. Biophys. Res. Commun. 166, 238-244. Avent, K. M., Usuki, E., Eyles, D. W., Keeve, R., Van der Schyf, C. J., Castagnoli, N., Jr., and Pond, S. M. (1996) Haloperidol and its tetrahydropyridine derivative (HPTP) are metabolized to potentially neurotoxic pyridinium species in the baboon. Life Sci. 59, 1473-1482. Subramanyam, B., Pond, S., Eyles, D., Whiteford, H., Fouda, H., and Castagnoli, N., Jr. (1991) Identification of a potentially neurotoxic pyridinium metabolite in the urine of schizophrenic patients treated with haloperidol. Biochem. Biophys. Res. Commun. 181, 573-578. Van der Schyf, C. J., Castagnoli, K., Usuki, E., Fouda, H. G., Rimoldi, J. M., and Castagnoli, N., Jr. (1994) Metabolic studies on haloperidol and its tetrahydropyridine analog in C57BL/6 mice. Chem. Res. Toxicol. 7, 281-285. Eyles, D. W., McLenna, H. R., Jones, A., McGrath, J. J., Stedman, T. J., and Pond, S. M. (1994) Quantitative analysis of two pyridinium metabolites of haloperidol in patients with schizophrenia. Clin. Pharmacol. Ther. 56, 512-520. Eyles, D. W., Stedman, T. J., and Pond, S. M. (1994) Nonlinear relationship between circulating concentrations of reduced haloperidol and haloperidol: Evaluation of possible mechanisms. Psychopharmacology 116, 161-166. Eyles, D. W., Avent, K. M., Stedman, T. J., and Pond, S. M. (1997) Two pyridinium metabolites of haloperidol are present in the brain of patients at post-mortem. Life Sci. 60, 529-534. Igarashi, K., Kasuya, F., Fukui, M., Abe, T., and Castagnoli, N., Jr. (1995) Simultaneous determination of haloperidol and its neurotoxic metabolite in plasma and brain tissue from schizophrenic patients treated with haloperidol using HPLC and solidphase extraction. Jpn. J. Forensic Toxicol. 13, 31-38. Igarashi, K., Kasuya, F., Fukui, M., Usuki, E., and Castagnoli, N., Jr. (1995) Studies on the metabolism of haloperidol (HP): The role of CYP3A in the production of the neurotoxic pyridinium metabolite HPP+ found in rat brain following i.p. administration of HP. Life Sci. 57, 2439-2446. Usuki, E., Pearce, R., Parkinson, A., and Castagnoli, N., Jr. (1996) Studies on the conversion of haloperidol and its tetrahydropyridine dehydration product to potentially neurotoxic pyridinium metabolites by human liver microsomes. Chem. Res. Toxicol. 9, 800-806. Eyles, D. W., McGrath, J. J., and Pond, S. M. (1996) Formation of pyridinium species of haloperidol in human liver and brain. Psychopharmacology 125, 214-219. Coutts, R. T., Su, P., and Baker, G. B. (1994) Involvement of CYP2D6, CYP3A4, and other cytochrome P-450 isozymes in N-dealkylation reactions. J. Pharmacol. Toxicol. Methods 31, 177-186. Jayosi, Z., Cooper, K. O., and Thomas, P. E. (1992) Brain cytochrome P450 and testosterone metabolism by rat brain subcellular fractions: Presence of cytochrome P450 3A immunoreactive protein in rat brain mitochondria. Arch. Biochem. Biophys. 298, 265-270. Christensen, E., Moller, J. E., and Faurbye, A. (1970) Neuropathologic investigation of 28 brains from patients with dyskinesias. Acta Psychiatr. Scand. 46, 14-23.

Chem. Res. Toxicol., Vol. 10, No. 9, 1997 939 (272) Meshul, C. K., and Casey, D. E. (1989) Regional, reversible ultrastructural changes in rat brain with chronic neuroleptic treatment. Brain Res. 489, 338-346. (273) Meshul, C. K., and Tan, S. E. (1994) Haloperidol-induced morphological alterations are associated with changes in calcium/ calmodulin kinase II activity and glutamate immunoreactivity. Synapse 18, 205-217. (274) Meshul, C. K., Buckman, J. F., Allen, C., Riggan, J. P., and Feller, D. J. (1996) Activation of corticostriatal pathway leads to similar morphological changes observed following haloperidol treatment. Synapse 22, 350-361. (275) Meshul, C. K., Stallbaumer, R. K., Taylor, B., and Janowsky, A. (1994) Haloperidol-induced morphological changes in striatum are associated with glutamate synapses. Brain Res. 648, 181195. (276) Roberts, R. C., Gaither, L. A., Gao, X.-M., Kashyap, S. M., and Tamminga, C. A. (1995) Ultrastructural correlates of haloperidolinduced oral dyskinesias in rat striatum. Synapse 20, 234-243. (277) Bloomquist, J., King, E., Wright, A., Mytilineou, C., Kimura, K., Castagnoli, K., and Castagnoli, N., Jr. (1994) 1-Methyl-4phenylpyridinium-like neurotoxicity of a pyridinium metabolite derived from haloperidol: Cell culture and neurotransmitter uptake studies. J. Pharmacol. Exp. Ther. 270, 822-830. (278) Fang, J., Zuo, D., and Yu, P. H. (1995) Comparison of the cytotoxicity of a quaternary pyridinium metabolite of haloperidol (HP+) with the neurotoxin N-methyl-4-phenylpyridinium (MPP+) towards cultured dopaminergic neuroblastoma cells. Psychopharmacology 121, 373-378. (279) Fang, J., and Yu, P. H. (1995) Effect of haloperidol and its metabolites on dopamine and noradrenaline uptake in rat brain slices. Psychopharmacology 121, 379-384. (280) Rollema, H., Skolnik, M., d’Engelbronner, J., Igarashi, K., Usuki, E., and Castagnoli, N., Jr. (1994) MPP+-like neurotoxicity of a pyridinium metabolite derived from haloperidol: In vivo microdialysis and in vitro mitochondrial studies. J. Pharmacol. Exp. Ther. 268, 380-387. (281) Owen, A. D., Schapira, A. H., Jenner, P., and Marsden, C. D. (1996) Oxidative stress and Parkinson’s disease. Ann. N. Y. Acad. Sci. 786, 217-223. (282) Schapira, A. H. (1994) Evidence for mitochondrial dysfunction in Parkinson’s diseasesa critical appraisal. Mov. Disord. 9, 125138. (283) Blake, C. I., Spitz, E., Leehdy, M., Hoffer, B. J., and Boyson, S. J. (1997) Platelet mitochondrial respiratory chain function in Parkinson’s disease. Mov. Disord. 12, 3-8. (284) Schoffner, J. M. (1995) Mitochondrial defects in basal ganglia diseases. Curr. Opin. Neurol. 8, 474-479. (285) Penn, A. M., Roberts, T., Hodder, J., Allen, P. S., Zhu, G., and Martin, W. R. (1995) Generalized mitochondrial dysfunction in Parkinson’s disease detected by magnetic resonance spectroscopy of muscle. Neurology 45, 2097-2099. (286) Bowling, A. C., and Beal, M. F. (1995) Bioenergetic and oxidative stress in neurodegenerative diseases. Life Sci. 56, 1151-1171. (287) Beal, M. F. (1995) Aging, energy, and oxidative stress in neurodegenerative diseases. Ann. Neurol. 38, 357-366. (288) Haas, R. H., Nasirian, F., Nakano, K., Ward, D., Pay, M., Hill, R., and Shults, C. (1995) Low platelet mitochondrial complex I and complex II/III activity in early untreated Parkinson’s disease. Ann. Neurol. 37, 714-722. (289) Bindoff, L. A., Birch-Machin, M. A., Cartlidge, N. E., Parker, W. D., Jr., and Turnbull, D. M. (1991) Respiratory chain abnormalities in skeletal muscle from patients with Parkinson’s disease. J. Neurol. Sci. 104, 203-208. (290) Swerdlow, R. H., Parks, J. K., Miller, S. W., Tuttle, J. B., Trimmer, P. A., Sheehan, J. P., Bennett, J. P., Jr., Davis, R. E., and Parker, W. D., Jr. (1996) Origin and functional consequences of the complex I defect in Parkinson’s disease. Ann. Neurol. 40, 663-671. (291) Veitch, K., and Hue, L. (1993) Flunarizine and cinnarizine inhibit mitochondrial complexes I and II: Possible implication for parkinsonism. Mol. Pharmacol. 45, 158-163. (292) Przedborski, S., Jackson-Lewis, V., and Fahn, S. (1995) Antiparkinsonian therapies and brain mitochondrial complex I activity. Mov. Disord. 10, 312-317. (293) Prince, J. A., Yassin, M. S., and Oreland, L. (1997) Neuroleptic induced mitochondrial enzyme alterations in the rat brain. J. Pharmacol. Exp. Ther. 280, 261-267. (294) Barsoum, N. J., Gough, A. W., Sturgess, J. M., and De La Iglesia, F. W. (1986) Parkinson-like syndrome in nonhuman primates receiving a tetrahydropyridine derivative. Neurotoxicology 7, 119-126. (295) Taylor, C. P., and Sedman, A. J. (1991) Pharmacology of the gamma-aminobutyric acid-uptake inhibitor CI-966 and its metabolites: preclinical and clinical studies. In Transmitter Amino Acid Receptors: Structures, Transduction and Models for


(296)

(297)

(298) (299) (300) (301) (302) (303) (304)

(305)

(306)

(307)

(308)

(309)

(310)

(311)

(312)

(313)

(314) (315)

Drug Development (Barnard, E. A., and Costa, E., Eds.) pp 251271, Thieme Medical Publishers, Inc., New York. Radulovic, L., Woolf, T., Bjorge, S., Taylor, C., Reilyl, M., Bockbrader, H., and Chang, T. (1993) Identification of a pyridinium metabolite in human urine following a single oral dose of 1-[2-{bis[4-(trifluoromethyl)phenyl]methoxy}ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid monohydrochloride, a γ-aminobutyric acid uptake inhibitor. Chem. Res. Toxicol. 6, 341-344. Sayre, L. M., Engelhart, D. A., Nadkarnik, D. V., Babu, M. K., Klein, M. E., and McCoy, G. (1995) Haemoprotein-mediated metabolism of enamines and the possible involvement of oneelectron oxidations. Xenobiotica 25, 769-775. Johnson, K. M., and Jones, S. M. (1990) Neuropharmacology of phencyclidine: Basic mechanisms and therapeutic potential. Annu. Rev. Pharmacol. Toxicol. 30, 707-750. Olney, J. W., Labruyere, J., and Price, M. T. (1989) Pathological changes induced in cerebrocortical neurons by phencyclidine and related drugs. Science 244, 1360-1362. Pohorecki, R., Rayburn, W., Coon, W. W., and Domino, E. F. (1989) Some factors affecting phencyclidine biotransformation by human liver and placenta. Drug Metab. Dispos. 17, 271-274. Domino, E. F. (1986) Biotransformation of phencyclidine. Drug Metab. Rev. 16, 285-320. Laurenzana, E. M., and Owens, S. M. (1997) Metabolism of phencyclidine by human liver microsomes. Drug Metab. Dispos. 25, 557-563. Laurenzana, E. M., and Owens, S. M. (1997) Brain microsomal metabolism of phencyclidine in male and female rats. Brain Res. 756, 256-265. Ward, D., Kalir, A., Trevor, A., Adams, J., Baillie, T., and Castagnoli, N., Jr. (1982) Metabolic formation of iminium species: the metabolism of phencyclidine. J. Med. Chem. 25, 491-492. Ward, D., Trevor, A., Adams, J. D., Baillie, T. A., and Castagnoli, N., Jr. (1982) Metabolism of phencyclidine: The role of iminium ion formation in covalent binding to rabbit microsomal protein. Drug Metab. Dispos. 10, 690-695. Hoag, M. K. P., Trevor, A. J., Asscher, Y., Weissman, J., and Castagnoli, N., Jr. (1984) Metabolism-dependent inactivation of liver microsomal enzymes by phencyclidine. Drug Metab. Dispos. 12, 371-375. Hoag, M. K. P., Trevor, A. J., Kalir, A., and Castagnoli, N., Jr. (1987) Phencyclidine iminium ion: NADPH-dependent metabolism, covalent binding to macromolecules and inactivation of cytochrome(s) P-450. Drug Metab. Dispos. 15, 485-490. Osawa, Y., and Coon, M. J. (1989) Selective mechanism-based inactivation of the major phenobarbital-inducible P-450 cytochrome from rabbit liver by phencyclidine and its oxidation product, the iminium compound. Drug. Metab. Dispos. 17, 7-13. Owens, S. M., Gunnell, M., Laurenzana, E. M., and Valentine, J. L. (1993) Dose- and time-dependent changes in phencyclidine metabolite covalent binding in rats and the possible role of CYP2D1. J. Pharmacol. Exp. Ther. 265, 1261-1266. Sharma, U., Roberts, E. S., Kent, U. M., Owens, S. M., and Hollenberg, P. F. (1997) Metabolic inactivation of cytochrome P4502B1 by phencyclidine: Immunochemical and radiochemical analyses of the protective effects of glutathione. Drug. Metab. Dispos. 25, 243-250. Crowley, J. R., and Hollenberg, P. F. (1995) Mechanism-based inactivation of rat liver cytochrome P4502B1 by phencyclidine and its oxidative product, the iminium ion. Drug Metab. Dispos. 23, 786-793. Hoag, M. K. P., Schmidt-Peetz, M., Lampen, P., Trevor, A., and Castagnoli, N., Jr. (1988) Metabolic studies on phencyclidine: characterization of a phencyclidine iminium ion metabolite. Chem. Res. Toxicol. 1, 128-131. Zhao, Z., Leung, L. Y., Trevor, A., Castagnoli, N., Jr. (1991) C-Formylation in the presence of rat brain mitochondria of the 2,3,4,5-tetrahydropyridine metabolite derived from the psychotomimetic drug phencyclidine. Chem. Res. Toxicol. 4, 426-429. Hata, Y., and Watanabe, M. (1994) Metabolism of aziridines and the mechanism of their cytotoxicity. Drug Metab. Rev. 26, 575604. Hata, Y., Watanabe, M., Tonda, K., and Hirata, M. (1987) Aziridine biotransformation by microsomes and lethality to hepatocytes isolated from rat. Chem.-Biol. Interact. 63, 171184.

Castagnoli, Jr., et al. (316) Hata, Y., Watanabe, M., Matsubara, T., and Touchi, A. (1976) Fragmentation reaction of ylide. 5. A new metabolic reaction of aziridine derivatives. J. Am. Chem. Soc. 98, 6033-6036. (317) Hata, Y., Watanabe, M., Shiratori, O., and Takase, S. (1978) Cytotoxic activity and fragmentation of aziridines in microsomes. Biochem. Biophys. Res. Commun. 80, 911-916. (318) Hinkle, P. C., and Yu, M. L. (1979) The phosphorus/oxygen ratio of mitochondrial oxidative phosphorylation. J. Biol. Chem. 254, 2450-2455. (319) Shigenaga, M. K., Trevor, A. J., and Castagnoli, N., Jr. (1987) Metabolism-dependent covalent binding of (S)-[5-3H]nicotine to liver and lung microsomal macromolecules. Drug Metab. Dispos. 16, 397-402. (320) Shigenaga, M. K. (1990) Studies on the metabolism and bioactivation of (S)-nicotine and beta-nicotyrine. Ph.D. Thesis, University of California, San Francisco, CA. (321) Fowler, J. S., Volkow, N. D., Wang, G. J., Pappas, N., Logan, J., MacGregor, R., Alexoff, D., Shea, C., Schlyer, D., Wolf, A. P., Warner, D., Zezulkova, I., and Cilento, R. (1996) Inhibition of monoamine oxidase B in the brains of smokers. Nature 379, 733-736. (322) Shigenaga, M. K., Kim, B. H., Caldera-Munoz, P., Cairns, T., Jacob, P., III, Trevor, A. J., and Castagnoli, N., Jr. (1989) Liver and lung microsomal metabolism of the tobacco alkaloid β-nicotyrine. Chem. Res. Toxicol. 2, 282-287. (323) Liu, X. (1995) In vitro and in vivo studies on the biotransformation of β-nicotyrine, a minor tobacco alkaloid. Ph.D. Thesis, Virginia Tech, Blacksburg, VA. (324) Mattocks, A. R. (1986) Chemistry and Toxicology of Pyrrolizidine Alkaloids, Academic Press, New York. (325) Kim, H.-K., Stermitz, E. R., Molyneux, R. J., Wilson, D. W., Taylor, D., and Coulombe, R. A., Jr. (1993) Structural influences on pyrrolizidine alkaloid-induced cytopathology. Toxicol. Appl. Pharmacol. 122, 61-69. (326) Chan, P. C., Mahler, J., Bucher, J. R., Travlos, G. S., and Reid, J. B. (1994) Toxicity and carcinogenicity of riddlelliine following 13 weeks of treatment to rats and mice. Toxicon 32, 891-908. (327) Campesato, V. R., Graf, U., Reguly, M. L., and de Andrade, H. H. (1997) Recominagenic activity of intergerrimine, a pyrrolizidine alkaloid from Senecio brasiliaensis, in somatic cells of Drosophila melanogaster. Environ. Mol. Mutagen. 29, 91-97. (328) Huxtable, R. J., Yan, C. C., Wild, S., Maxwell, S., and Cooper, R. (1996) Physicochemical and metabolic basis for the differing neurotoxicity of the pyrrolizidine alkaloids, trichodesmine and monocrotaline. Neurochem. Res. 21, 141-146. (329) Rizk, A. F. M., and Kamel, A. (1991) Toxicity, carcinogenicity, pharmacology, and other biological activities of pyrrolizidine alkaloids. In Naturally Occurring Pyrrolizidine Akaloids (Rizk, A. F. M., Ed.) pp 211-226, CRC Press, Boston, MA. (330) Chung, W. G., Miranda, C. L., and Buhler, D. R. (1995) A cytochrome P450B form is the major bioactivation enzyme for the pyrrolizidine alkaloid senecionine in guinea pig. Xenobiotica 25, 929-939. (331) Segall, H. J., Wilson, D. W., Lame´, M. W., Moein, S., and Qinrwe, X. K. (1991) Metabolism of pyrrolizidine alkaloids. In Handbook of Natural Toxins (Keeler, R. F., and Tu, A. T., Eds.) pp 3-26, Marcel Dekker, New York. (332) Chung, W.-G., and Buhler, D. R. (1995) Major factors for the susceptibility of guinea pig to the pyrrolizidine alkaloid jacobine. Drug Metab. Dispos. 23, 1263-1267. (333) Buhler, D. R., and Kedzierski, B. (1986) Biological reactive intermediates of pyrrolizidine alkaloids. In Biological Reactive Intermediates (Kocsis, J. J., Jollow, D. J., Witmer, C. M., Nelson, J. O., and Snyder, R., Eds.) Vol. 3, pp 611-620, Plenum Publishing Corp., New York. (334) Mattocks, A. R., and Bird, I. P. (1983) Pyrrolic and N-oxide metabolites formed from pyrrolizidine alkaloids by hepatic microsomes in vivo: Relevance to in vivo hepatotoxicity. Chem.Biol. Interact. 43, 209-222. (335) Kim, H. Y., Stermitz, F. R., and Coulombe, R. A., Jr. (1995) Pyrrolizidine alkaloid-induced DNA-protein cross-links. Carcinogenesis 16, 2691-2697.

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