Lipid Peroxidation in Membranes: The Peroxyl Radical Does Not

Letter pubs.acs.org/JPCL

Lipid Peroxidation in Membranes: The Peroxyl Radical Does Not “Float” Julian Garrec,†,‡ Antonio Monari,†,‡ Xavier Assfeld,†,‡ Lluis M. Mir,¶,§,∥ and Mounir Tarek*,†,‡ †

Théorie-Modélisation-Simulation, SRSMC, CNRS, Vandoeuvre-lès-Nancy F-54506, France Théorie-Modélisation-Simulation, SRSMC, Université de Lorraine, Vandoeuvre-lès-Nancy F-54506, France ¶ Laboratoire de Vectorologie et Thérapeutiques Anticancéreuses, Université Paris-Sud, UMR 8203, Orsay F-91405, France § Laboratoire de Vectorologie et Thérapeutiques Anticancéreuses, CNRS, UMR 8203, Orsay F-91405, France ∥ Laboratoire de Vectorologie et Thérapeutiques Anticancéreuses, Gustave Roussy, UMR 8203, Villjuif F-94805, France ‡

S Supporting Information *

ABSTRACT: Lipid peroxidation is a fundamental phenomenon in biology and medicine involved in a wide range of diseases. Some key microscopic aspects of this reaction in cell membranes are still poorly studied. In particular, it is commonly accepted that the propagation of the radical reaction in lipid bilayers is hampered by the rapid diffusion of peroxyl intermediates toward the water interface, that is, out of the reaction region. We investigated the validity of this “floating peroxyl radical” hypothesis by means of molecular modeling. Combining quantum calculations of model systems and atomistic simulations of lipid bilayers containing lipid oxidation products, we show that the peroxyl radical does not “float” at the surface of the membrane. Instead, it remains located quite deep inside the bilayer. In light of our findings, several critical aspects of biological membranes’ peroxidation, such as their protection mechanisms, need to be revisited. Our data moreover help in the design of more efficient antioxidants, localized within reach of the reaction propagating radical. SECTION: Biomaterials, Surfactants, and Membranes ipid peroxidation is an active field of research1−4 because of its implication in regular redox signaling pathways5,6 as well as in oxidative stress, with critical consequences on aging and a number of diseases6,7 including diabetes,8 cancer,9,10 and neurodegenerative disorders.11−13 This class of reactions can affect mono- or polyunsaturated fatty acids, fatty acid esters, phospholipids, and sterols.3 It is characterized by the formation of hydroperoxide derivatives (HPds) as primary products (Figure 1), which can undergo subsequent reorganization and decomposition, leading to a variety of mutagenic and carcinogenic products such as 4-hydroxy-2-nonenal (4HNE)14,15 and malondialdehyde (MDA).16−18 As far as cell membranes are concerned, a high concentration of oxidized compounds in a lipid bilayer affects drastically its biophysical properties, in particular, permeability.19−22 Many experimental and theoretical studies have aimed at unraveling the underlying reaction mechanism in solution, micelles, and liposomes.1−3 It is now well-established that lipid peroxidation proceeds through a chain mechanism initiated by the homolytic cleavage of a weak allylic or bis-allylic C−H bond, forming an aliphatic radical (Figure 1A). The reaction then propagates through the very fast uptake of molecular oxygen, forming a peroxyl radical intermediate (Pl•), followed by a rate-limiting H atom transfer from a second lipid molecule to the Pl•, yielding a HPd and a new aliphatic radical (Figure

L

© 2014 American Chemical Society

Figure 1. Peroxidation mechanism for lipid chains containing a single bis-allylic site (e.g., linoleic acid, linoleate ester, or DLPC). (A) Example of initiation from the sn1 chain of DLPC. A radical initiator I• (such as HO• in vivo3,6) abstracts the bis-allylic H atom at position 11, resulting in the formation of a pentadienyl radical. (B) Simplified mechanism of propagation under thermodynamic control. The mechanism involves four conjugated diene Pl• intermediates leading to the corresponding HPds.

1B). An important aspect of this reaction is that the Pl• intermediate is a pretty stable entity with a half-life of ∼1 s.7 Received: March 11, 2014 Accepted: April 22, 2014 Published: April 22, 2014 1653

dx.doi.org/10.1021/jz500502q | J. Phys. Chem. Lett. 2014, 5, 1653−1658

The Journal of Physical Chemistry Letters

Letter

Table 1. Relative Partition Coefficients of Pl• and HPd Groupsa QC method

• b ΔΔGoil→w sol (Pl )

b ΔΔGoil→w sol (HPd)

• b ΔΔΔGoil→w sol (HPd → Pl )

log(Poil/w(Pl•)/Poil/w(HPd))

M05-2X/6-31G* M05-2X/6-31+G** M05-2X/cc-pVTZ B3LYP/6-31G* MP2/6-31+G** MP2/cc-pVTZ MP2/cc-pVQZ CCSD(T)/6-31+G** CCSD(T)/cc-pVTZ CCSD(T)/cc-pVQZ

−1.9 −2.3 −1.9 −1.7 −1.8 −1.3 −1.4 −1.5 −1.0 −1.2

−4.7 −5.0 −4.2 −3.9 −4.6 −3.7 −3.7 −4.3 −3.6 −3.7

2.8 2.7 2.4 2.2 2.8 2.4 2.4 2.9 2.6 2.5

2.1 2.0 1.7 1.6 2.1 1.8 1.7 2.1 1.9 1.8

a

The solvent was described using a polarizable continuum, as implemented in the SMD method of Truhlar and coworkers, which has been shown to provide accurate calculation of partition coefficients for a variety of organic compounds.38 bValues are given in kcal/mol.

(MD) simulations of phospholipids bilayers containing HPd derivatives19,21,22 have shown that oxidized tails conserve a great mobility. Although HPd groups do interact transiently with the carbonyl and phosphate groups through hydrogen bonds, they are not locked in the vicinity of the interface but explore also inner parts of the bilayer; their distribution along the membrane normal spreads over a large distance of ∼1/4 of the total membrane thickness.19 To what extent does the situation differ for polar Pl• derivatives that are the species actually responsible for the chain reaction propagation? In the present Letter, we address this issue by means of molecular modeling, with the aim of assessing the validity of the FPH. To do so, we use two computational approaches of increasing complexity. The first one is based on quantum chemistry (QC) calculations of the “oil”/water partition coefficient of Pl• and HPd groups. As we shall see below, this approach provides an estimation of the relative affinity of the Pl• moiety for the innermost region of the lipid bilayer, with respect to that of a HPd group. We have used a simplified model in which oxidized moieties were described as peroxyl- or hydroperoximethane (CH3OO• or CH3OOH) and their environment was represented by a polarizable continuum model mimicking either bulk water or an oil phase. The partition coefficient of a given species A, Poil/w(A), is related to the solvation free energies of the species in the two 36 solvents, ΔGwsol(A) and ΔGoil sol(A), by the relation

This mechanism is general and follows the same kinetic laws in solution and within phospholipid bilayers.23−25 However, experiments based on linoleic acid, linoleate esters, and their phospholipid counterpart, dilinoleoylphosphatidylcholine (DLPC), have shown that the reaction kinetics is slower in membranes than that in solution.24 It was speculated that “polar peroxyl radicals would diffuse rapidly away from the nonpolar bilayer phase where they are formed towards the more polar aqueous surface”. According to this so-called “floating peroxyl radical” hypothesis (FPH),24,26 Pl• groups would stay in (or close to) the water/lipid interface, far from the inner region of the bilayer where H atom donors are located, hence preventing the propagation reaction from occurring. The FPH is widely accepted, as evidenced by the variety of reviews and articles invoking it.3,27−33 It has important implications on our understanding of several key aspects of lipid peroxidation in biological membranes. First, the FPH is tightly connected to the sensitivity of the bilayer to oxidative stress. If true, the “floating character” of Pl• groups could be viewed as a crucial property that is advantageously exploited by membranes in a self-protection mechanism. Second, the FPH shapes our representation of the mechanism of action of membrane-bound antioxidants. While their ability to capture reactive oxygen species (ROS) that are the radical initiators of the reaction is not discarded, it is often assumed that the membrane-bound antioxidants act rather as Pl• scavengers.34 αTocopherol (aToc), for instance, one of the most biologically relevant antioxidants, is thought to be efficient because the “floating” Pl• encounters its chromanol group at the water/lipid interface where it resides.27,28,31,32 Obviously, this view of the Pl•-trapping mechanism has also critical consequences on the strategies undertaken to design syntetic antioxidants because, in principle, one tries to develop compounds that, once in the membrane, will have their chemically active groups located at the most probable position of the Pl• moieties. However, to the best of our knowledge, the actual location of Pl• groups within the membrane hydrophobic core has never been investigated directly at the atomistic scale. Without more microscopic insight, it is hard to judge whether a Pl• moiety attached to a hydrophobic lipid tail has such a high affinity with the polar phase that it can stay locked at the interface. It is worth stressing that the FPH was proposed in a period where we did not have the detailed microscopic and dynamic view of lipid bilayers that we have today.35 In particular, one should consider the intrinsic fluid-like character of the lipid tails that typically exhibit motions of large amplitude, exploring various depths of the membrane interior. Recent molecular dynamics

log P oil/w(A) =

w oil oil → w ΔGsol (A) − ΔGsol (A) ΔΔGsol (A) = 2.3RT 2.3RT

(1)

Hence, the difference in partition coefficient between Pl• and HPd groups reads oil → w oil → w ⎛ P oil/w(Pl•) ⎞ (Pl•) − ΔΔGsol (HPd) ΔΔGsol ⎟= log⎜ oil/w 2.3RT (HPd) ⎠ ⎝P

=

oil → w (HPd → Pl•) ΔΔΔGsol 2.3RT

(2)

To evaluate the different terms of eq 2, we have used a range of QC methods, including representative density functional theory (DFT) and post-Hartree−Fock approaches. All calculations were made with the Gaussian 09 package37 (see the Suppporting Information for details). Our results are summarized in Table 1. 1654



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• Overall, the values of ΔΔΔGoil→w sol (HPd → Pl ) or, alteroil→w • oil→w (Pl )/P (HPd) are fairly innatively speaking, log P dependent from the chosen QC method. The 1−2 order of magnitude ratio that we have found between Poil/w(Pl•) and Poil/w(HPd) indicates that Pl• have an intrinsic higher affinity with the membrane interior and a lower affinity with water than HPd. From this first estimation, we expect that the distribution of Pl• radicals along the direction perpendicular to the membrane is shifted toward the center of the membrane with respect to the distribution of HPd groups. This is obviously not in agreement with the generally accepted FPH. The above reasoning is based on the relative affinity of a given species for two very distinct homogeneous phases (water and oil) treated as dielectric continuums. It does not consider the large interfacial region that exists in membrane bilayers. In addition, we have so far focused on Pl• and HPd groups alone. Within oxidized lipids, these moieties are attached to long lipophilic tails that will always counterbalance their affinity with the polar phase. To further address this issue, we have used a second computational approach based on classical MD simulations of a hydrated phosphatidylcholine (DLPC) bilayer containing a few oxidized lipids (Figure 2).

altered.23 This setup enables an extensive configuration sampling without inducing strong structural modification of the bilayer. To test the effect of the Z,E versus E,E diene configuration and the positioning of the oxidized group along the sn1 hydrophobic tail, we considered the Z,E-13-Ox, E,E-13Ox, and E,E-9-Ox (Ox = HPd or Pl•) isomers (see Figure 1B for the definition). In total, we have performed using the GROMACS simulation package39 six independent 300 ns long simulations. Details about the computational setup are reported in the Supporting Information. In all of our simulations, both Pl• and HPd oxidized moieties exhibit large displacements, exploring different depths inside the bilayer (Figures S1 and S2, Supporting Information). This is consistent with previous simulations of HPd derivatives performed by others.19,21,22 We have computed the distribution of Pl•, HPd, phosphate, and carbonyl groups and water molecules along the membrane normal (Figure 3). The

Figure 3. Comparison of Pl• and HPd localization along the membrane normal. The position z of a given chemical group (either Pl•, HPd, carbonyl, or phosphate) is given relative to the center of the membrane (z = 0). Distributions were computed from simulations of Z,E-13-Pl• and Z,E-13-HPd isomers (see Figure S3 (Supporting Information) for other isomers). The distributions of Pl• and HPd groups were scaled by a factor of 32 for the sake of clarity.

decrease of water concentration from its bulk value at z > 30 Å to 0 at z ≈ 10 Å indicates the interfacial region. As anticipated by our continuum model calculations, Pl• groups stay, on average, deeper in the membrane than HPd groups. For Z,E-13 isomers, the maximum of the Pl• distribution is shifted by about 11 Å with respect to that of HPd. The shift is almost the same as that for E,E-13 isomers (Figure S3A, Supporting Information) but is smaller for E,E-9 isomers (∼6.5 Å, Figure S3B, Supporting Information). This correlates with the fact that the C9 atom is closer to the polar phase than the C13 atom. As already found by others,19,21,22 HPds form transient Hbonds with water and H-bond acceptors of phospholipids, namely, carbonyl and phosphate groups (Table 2). In fact, HPd moieties have a higher probability of presence in the region of lipid carbonyl groups, just below phosphate groups (see Figure 2B for a representative snapshot). This finding is consistent with the fact that HPd moieties form 2−4 times more H-bonds with carbonyls than with phosphates (Table 2). These specific short-range interactions tend to favor the location of HPd groups in the vicinity of polar heads, although this is counterbalanced by the intrinsic hydrophobic character of the

Figure 2. Representative snapshots from the MD simulations of oxidized DLPC bilayers. Both panels show a zoom on a selected oxidized lipid (whose carbon atoms are represented in yellow) bearing either a Pl• (A) or a HPd (B) group. Hydrophobic tails of other lipids and nonpolar hydrogens are not represented for the sake of clarity. N and P atoms of phosphatidylcholines are shown in blue and tan, respectively. Carbonyl oxygens of lipids other than the selected lipid are depicted in pink. Interfacial water molecules are represented by a transparent envelop. We refer the reader to Figure S5 (Supporting Information) for more explicit representations of the system.

Our choice for DLPC was motivated by the fact that the FPH was originally formulated based on experiments comparing this phospholipid and its molecular counterpart in solution, namely, linoleic acid (or linoleate ester).24 It is also worth mentioning that much of the research effort in the field of lipid peroxidation has focused on lipids containing one single bis-allylic site per tail.1−3,24 The number of oxidized/nonoxidized lipids that we considered was 4/128 in each leaflet, which is well below the threshold of 10%, above which the structural integrity of the membrane is known to be seriously 1655



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Table 2. Average Number of H-Bondsa oxidized lipid

carbonyl groups

phosphate groups

water

Z,E-13-HPd E,E-13-HPd E,E-9-HPd Z,E-13-Pl• E,E-13-Pl• E,E-9- Pl•

2.4 ± 0.9 1.9 ± 0.9 2.5 ± 0.9

0.8 ± 0.6 1.0 ± 0.6 0.6 ± 0.6

5.6 ± 1.6 7.6 ± 1.6 6.2 ± 1.6 b b b

effect for the Pl• groups. This absence of a “floating” effect does not support the FPH. Finally, our MD simulations provide a unique way to evaluate the probability of molecular encounters between the Pl• group and its reactive partners. In a DLPC bilayer, the rate-limiting H atom transfer occurs from the C11−H11 group of a nearby phospholipid tail to the Pl• group. Figure 4 clearly shows that,

H-bonds are between Pl• or HPd groups and phospholipid head groups (carbonyl or phosphate) or water. Statistical errors were estimated using a block-averaging strategy. bH-bonds formed only occasionally. a

lipid tail to which it is attached. Note that HPds do not constantly “float” at the bilayer subsurface but also transiently dive deeper in the membrane. Quite interestingly, the main qualitative picture emerging, that is, the strong “floating” propensity of (HPd) products and their ability to hydrogen bond with the solvent beneath the lipid head groups, appears to be insensitive to salt and HPd concentrations, as recently shown in an extensive MD simulations study.22 The chemical nature of a Pl• group (absence of polar hydrogens) makes it a H-bond acceptor, not a donor like a HPd. As a consequence, the above-mentioned mechanism of stabilization of the oxidized group in the carbonyl region is impossible for a Pl•; it remains most of the time in the innermost part of the bilayer, quite far from any polar head group, as illustrated in the snapshot of Figure 2A (see also the distribution of Pl• in Figure 3 and the corresponding time series in Figure S2, Supporting Information). In fact, our simulations indicate that the presence of a Pl• moiety on a hydrophobic tail, whatever the C9 or C13 site to which it is attached, does not affect significantly the distribution of the position of the tail inside the bilayer. To further quantify this, we define a hydrophobic tail displacement, + , using the z position of the carbon that can bear an oxidized group (C13 or C9; see Figure 1) + = ⟨zC9/13(Ox)⟩ − ⟨zC9/13(DLPC)⟩

Figure 4. Co-localizations of the reactants of the H atom transfer step. The yellow distribution corresponds to H11 atoms, while the three other curves represent the distribution of Pl• groups for all of the isomers that we have considered in this study (scaled by a factor of 64 for the sake of clarity).

contrary to what the FPH suggests, there is no significant spatial separation between the reactants, independently of the Pl• isomer that is considered. The slower propagation kinetics observed in membranes compared to the same reaction in homogeneous solution24 should be related to other factors. It has been suggested that an additional factor that might slow down the propagation in membranes is the inherent slow diffusion of reactants in these media.3 This fact is corroborated by the ratio between the diffusion coefficients of a given hydrophobic chain, for example, heptane in benzene (1.8 × 10−5 cm2/s)40 and the lateral diffusion of an oxidized lipid chain in a bilayer (0.2−0.7 × 10−7 cm2/s depending on the salt and oxidized lipid concentration),22 although it is nontrivial to relate quantitatively the diffusion coefficient ratio to the difference in the values of the effective kinetic constants that are measured experimentally. An alternative reaction partner of the Pl• can be an antioxidant located in the bilayer, for example, aToc. Despite several decades of research, the detailed mechanism of action of this class of antioxidants is not fully understood.29,41,42 Experiments conducted in solution have shown that aToc can hinder the peroxidation chain reaction by giving a hydroxyl hydrogen atom to the Pl• intermediate43 (thus forming a relatively stable tocopheroxyl radical). However, the same reaction in a phospholipid bilayer is ∼1000 times slower.43 It is also well-established that the chromanol group of aToc bearing the sacrificial H atom is located at the membrane interface.44,45 Our findings support a scenario that is consistent with these experimental results; once peroxidation is initiated inside a membrane, the radical chain reaction propagates in the apolar phase, and the chromanol group of aToc is not optimally located to interrupt it, resulting in slower kinetics compared to the reaction in solution. Such a scheme implies that the main role of aToc in vivo is rather to capture the initial ROS coming either from the cytosol or the extracellular medium. To conclude, our two computational models provide a consistent picture in which Pl• intermediates do not “float” at the polar surface of the phospholipid bilayer, as was originally suggested. A hydrophobic tail to which a Pl• group is attached

(3)

where zC9/13(Ox) and zC9/13(DLPC) are the positions of the C9 (or C13) atom of the oxidized tail and nonoxidized lipid tails, respectively, and ⟨...⟩ denotes an average value. The distributions of these two parameters are shown in Figure S4 (Supporting Information). Following this definition, a positive value of + indicates that the carbon atom bearing the oxidized group is displaced toward bulk water. Table 3 summarizes the Table 3. Values of the Hydrophobic Tail Displacement, + (see text for definition), in All of Our Simulations Z,E-13-Ox E,E-13-Ox E,E-9-Ox a

Ox = Pl•

Ox = HPd

0a −1a 0a

8a 7a 5a

Values are given in Å.

displacements that we have obtained with the isomers that we have considered. Note however that the corresponding distributions have a finite width of ∼10 Å (see Figure S4, Supporting Information). While HPd groups have a clear tendency to drag the lipid tail in the direction of the polar phase, as already found by others,19,21,22 we do not find such an 1656



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(11) Simonian, N. A.; Coyle, J. T. Oxidative Stress in Neurodegenerative Diseases. Annu. Rev. Pharmacol. Toxicol. 1996, 36, 83− 106. (12) Montine, T. J.; Montine, K. S.; McMahan, W.; Markesbery, W. R.; Quinn, J. F.; Morrow, J. D. F2-Isoprostanes in Alzheimer and Other Neurodegenerative Diseases. Antioxid. Redox Signaling 2005, 7, 269−275. (13) Porter, F. D.; Scherrer, D. E.; Lanier, M. H.; Langmade, S. J.; Molugu, V.; Gale, S. E.; Olzeski, D.; Sidhu, R.; Dietzen, D. J.; Fu, R.; et al. Cholesterol Oxidation Products are Sensitive and Specific BloodBased Biomarkers for Niemann-Pick C1 Disease. Sci. Transl. Med. 2010, 2, 56ra81. (14) Uchida, K. 4-Hydroxy-2-nonenal: a Product and Mediator of Oxidative Stress. Prog. Lipid Res. 2003, 42, 318−343. (15) Schneider, C.; Porter, N. A.; Brash, A. R. Routes to 4Hydroxynonenal: Fundamental Issues in the Mechanisms of Lipid Peroxidation. J. Biol. Chem. 2008, 283, 15539−15543. (16) Esterbauer, H.; Schaur, R. J.; Zollner, H. Chemistry and Biochemistry of 4-Hydroxynonenal, Malonaldehyde and Related Aldehydes. Free Radic. Biol. Med. 1991, 11, 81−128. (17) Marnett, L. J. Lipid Peroxidation-DNA Damage by Malondialdehyde. Mutat. Res. 1999, 424, 83−95. (18) West, J. D.; Marnett, L. J. Endogenous Reactive Intermediates as Modulators of Cell Signaling and Cell Death. Chem. Res. Toxicol. 2006, 19, 173−194. (19) Wong-Ekkabut, J.; Xu, Z.; Triampo, W.; Tang, I.-M.; Tieleman, D. P.; Monticelli, L. Effect of Lipid Peroxidation on the Properties of Lipid Bilayers: A Molecular Dynamics Study. Biophys. J. 2007, 93, 4225−4236. (20) Jurkiewicz, P.; Olżyńska, A.; Cwiklik, L.; Conte, E.; Jungwirth, P.; Megli, F. M.; Hof, M. Biophysics of Lipid Bilayers Containing Oxidatively Modified Phospholipids: Insights from Fluorescence and EPR Experiments and from MD Simulations. Biochim. Biophys. Acta 2012, 1818, 2388−2402. (21) Vernier, P. T.; Levine, Z. A.; Wu, Y.-H.; Joubert, V.; Ziegler, M. J.; Mir, L. M.; Tieleman, D. P. Electroporating Fields Target Oxidatively Damaged Areas in the Cell Membrane. PloS One 2009, 4, e7966. (22) Jarerattanachat, V.; Karttunen, M.; Wong-Ekkabut, J. Molecular Dynamics Study of Oxidized Lipid Bilayers in NaCl Solution. J. Phys. Chem. B 2013, 117, 8490−8501. (23) Barclay, L. R. C.; Baskin, K. A.; Kong, D.; Locke, S. J. Autoxidation of Model Membranes. The Kinetics and Mechanism of Autoxidation of Mixed Phospholipid Bilayers. Can. J. Chem. 1987, 65, 2541−2550. (24) Barclay, L. R. C. 1992 Syntex Award Lecture Model Biomembranes: Quantitative Studies of Peroxidation, Antioxidant Action, Partitioning, and Oxidative Stress. Can. J. Chem. 1993, 71, 1− 16. (25) Xu, L.; Davis, T. a.; Porter, N. A. Rate Constants for Peroxidation of Polyunsaturated Fatty Acids and Sterols in Solution and in Liposomes. J. Am. Chem. Soc. 2009, 131, 13037−13044. (26) Barclay, L.; Ingold, K. Autoxidation of Biological Molecules. 2. Autoxidation of a Model Membrane. Comparison of the Autoxidation of Egg Lecithin Phosphatidylcholine in Water and in Chlorobenzene. J. Am. Chem. Soc. 1981, 103, 6478−6485. (27) Atkinson, J.; Epand, R. F.; Epand, R. M. Tocopherols and Tocotrienols in Membranes: A Critical Review. Free Radic. Biol. Med. 2008, 44, 739−764. (28) Buettner, G. R. The Pecking Order of Free Radicals and Antioxidants: Lipid Peroxidation, α-Tocopherol, and Ascorbate. Arch. Biochem. Biophys. 1993, 300, 535−543. (29) Krumova, K.; Friedland, S.; Cosa, G. How Lipid Unsaturation, Peroxyl Radical Partitioning, and Chromanol Lipophilic Tail Affect the Antioxidant Activity of α-Tocopherol: Direct Visualization via HighThroughput Fluorescence Studies Conducted with Fluorogenic αTocopherol Analogues. J. Am. Chem. Soc. 2012, 134, 10102−10113. (30) Turco Liveri, M. L.; Sciascia, L.; Allegra, M.; Tesoriere, L.; Livrea, M. A. Partition of Indicaxanthin in Membrane Biomimetic

in the course of the reaction behaves in a very similar fashion as a nonoxidized lipid, exploring the innermost region of the membrane up to the neighborhood of phosphatidylcholine heads. Overall, our results propose a new view of the peroxidation reaction occurring in the complex, nonhomogeneous environment of a phospholipid bilayer, providing a better understanding of this class of reactions.

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

Dynamical behavior of the Pl• group, representative time series of the z position of Pl• and HPd groups, additional distributions, and computational details. This material is available free of charge via the Internet at http://pubs.acs.org.

Corresponding Author

*E-mail: [email protected]. Phone: +33 (0)3 83 68 43 74. Fax: +33 (0)3 83 68 43 71. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by ANR (Agence Nationale de la Recherche) (ANR-10- BLAN-096) and ANSES (Agence Nationale de la Sécurité Sanitaire de l’Alimentation de l’Environnement et du Travail) (MARFEM). Research was conducted in the scope of the LEA EBAM. A.M. thanks the CNRS for the funding of the “Chaire d’excellence” program.

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REFERENCES

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