Science
Lithium's effect on depression clarified Research at UCLA on lithium's
though lithium must be administered continuously, it needs about two role in membrane transport weeks to take hold. At the same time, the therapeutic dose—which varies of choline indicates that greatly from patient to patient—is very close to the toxic dose. ion reduces the turnover of The red blood cell test could show physicians ahead of time whether a choline in the brain given patient is going to respond well to lithium—and afterward, whether to continue taking it. "Manic-depressive illness may have She also has shown that lithium 20 different causes," says Barbara slows down the transport of choline Ehrlich of the University of Califorboth into and out of the brain. A colnia's medical school in Los Angeles. league at UCLA, Richard S. Jope, has "And lithium makes a thousand confirmed that this phenomenon althings change in the body. So which lows choline and its daughter acetylof these things causes the differcholine to build up inside the nerve ence?" cells. "This fits in perfectly with the Ehrlich isn't the only one who Davis-Janowsky theory of affective wonders. It's been 30 years since the disorders," Ehrlich explains. Australian physician John Cade dis- Ehrlich uses atomic absorption spectro- John M. Davis of the Illinois State covered that lithium salts could con- photometer for blood lithium tests Psychiatric Institute, and David Jatrol the violent mood swings of his nowsky of the University of Califormanic-depressive patients. Lithium problem is to figure out which effects nia, San Diego, first proposed their carbonate now has become the drug are important. theory in 1972 after they found that of choice for a large fraction of Ehrlich's own work as graduate the drug physostigmine, which was manic-depressives. Yet scientists still student of UCLA physiologist Jared known to raise the brain's acetylchodon't know exactly what lithium is M. Diamond represents a significant line levels, could cause a patient to doing. step in that direction. Diamond has lapse from the manic phase into the During the past six or seven years, been impressed. "She's received dis- depressive phase. however, they've started to find out. tinction and renown very rapidly for Considering other data on the illFor instance, they think that manic- a graduate student," he says. ness, they hypothesize that during depressive illness almost certainly is During Ehrlich's first year of re- mania there is a decreased availability a hereditary disease that produces search, for example, she perfected an of acetylcholine in the brain and an some kind of biochemical defect. And analytical technique using flameless increased availability of the neurolithium probably interacts with the atomic absorption spectroscopy that transmitter dopamine. Depression is transport system in cellular mem- improved the detection limits on just the reverse. branes, the same system that controls lithium in the blood by a factor of "Our own hypothesis is that lithithe body's natural levels of sodium, 10,000. um boosts the level of acetylcholine," potassium, calcium, and magnesium "This has enabled us to look at says Ehrlich. "So this fits in with the ions. fluxes of lithium in and out of cells at clinical findings that lithium works on In addition, most signs point to the therapeutic concentrations," she says. acute mania, but does not have conclusion that the manic-de- "Without it you have the choice of marked effects on acute depression. pressive's wild swings from euphoria either working with very high levels of "Also, it takes about two weeks for to despair are simply the outward lithium or using a lot of blood. Most litjiium to have therapeutic effects," symptoms of a breakdown in the people have used a lot of lithium be- she says, "and we find with red cells brain's chemical communication cause it's hard to get patients to give that it takes two weeks to reach system. The neurotransmitters, such up a pint of blood each time." maximum choline levels in the cell." as dopamine and acetylcholine, Davis tells C&EN that the 1972 Then, while investigating the efsomehow surge out of control, and fects of lithium on the membrane paper sparked the first real interest in lithium somehow brings them back transport of choline (a precursor tq acetylcholine in connection with into line. the neurotransmitter acetylcholine), manic-depressive illness. Previous But the problem is not to show that she and her colleagues discovered theories had held that the disease was lithium has some particular effect in that the choline content of red blood caused by an imbalance of dopamine the body. The tiny ion is such a good cells rises markedly during lithium alone. mimic of the body's natural electro- therapy, and, in fact, is a good mea"But most physiological systems, lytes—particularly sodium and po- sure of the effectiveness of that such as hunger, thirst, or pleasure tassium—that its impact is observ- therapy. centers of the brain, are controlled by able everywhere from the brain to the This finding could prove important a balance of the neurotransmitters," kidneys. As Ehrlich points out, the in clinical practice, Ehrlich says. Al- he says, "rarely by an unopposed 16
C&EN May 7, 1979
system. So we thought that manicdepressive illness might be an unsettled transmitter balance." Other investigators have since replicated their findings and extended them, he adds. For example, both Parkinson's disease and tardive dyskinesia, a disorder characterized by abnormal movements of the tongue and mouth, appear to be related to similar imbalances. On the other hand, if lithium's inability to lift a patient out of the depressive phase is in accord with the Davis-Janowsky theory, its long-term effectiveness in preventing depression is harder to explain. "Lithium's prophylactic effect on depression is unexplained by any of the present theories," Davis admits. "These theories aren't proved." Still, he says, Ehrlich's findings on lithium fit in with his own theory very well. In reaching these findings, Ehrlich first studied the transport of choline across what is known as the bloodbrain barrier. "The capillaries in the brain are different from those in other parts of the body," she explains. "They have 'tight junctions.' That is, in capillaries elsewhere there is free diffusion of fluid between the cells of the capillary walls. But in the brain there has to be a special mechanism for transport through the cells." By injecting rats with radioactive choline, Ehrlich showed that lithium inhibits the rate of .choline transfer into the brain about 20%. The inhibition seems quite specific, she says. The rate for both tyrosine and tryptophan, precursors for different neurotransmitters, are totally unaffected by lithium. Working next with frogs, Ehrlich looked at the movements of choline across a part of the blood-brain barrier known as the choroid plexus, a membrane inside the brain that regulates the ionic composition of the cerebral-spinal fluid. In this case lithium caused no change, she says. But this isn't too surprising, she adds, pointing out that choline is not normally transported across this membrane. For example, she has measured choline levels in the cérébro-spinal fluid of human patients being treated with lithium and found the levels unchanged. Again working with frogs, Ehrlich next looked at choline's normal route of exit from the brain, the arachnoid membrane. There again, lithium lowered the rate of choline transport about 20%. "Taking these three things together," she says, "we can infer that lithium reduces the turnover of choline in the brain." Mitch Waldrop, C&EN West Coast
Stable isotope labeling of sugars simplified A new way to label sugar molecules produced, according to Barker. The with stable atomic isotopes in prac- steps for introducing stable isotope tically any position has been devel- labels also have been adapted for oped by biochemists at Michigan certain sugars having phosphate State University, East Lansing. Their groups, which are important in many contribution, part of a national pro- metabolic reactions. gram to exploit stable atomic isoThe yields of the modified Kiliani topes, will help spread the use of procedure are reasonably high, giving methods, such as nuclear magnetic about 80 to 90% overall carbon-13 resonance spectroscopy and mass enrichment in a particular position spectrometry, into broader biomedi- from the starting cyanide, Barker cal applications. notes. By loading up these sugars with So far, the Michigan group, in- so much of a particular isotope, mecluding biochemistry department tabolism studies by NMR spectroschairman Robert Barker, graduate copy become more feasible. student Anthony Serianni, and their The development of the sugarcolleagues, has worked mainly with labeling procedure by Barker and his the stable isotope carbon-13 in la- colleagues stems, in part, from a beling a large variety of sugars. But long-standing collaboration with Nick the method also works with deuteri- A. Matwiyoff, who is a division leader um and oxygen-18 meaning that of the Stable Isotopes Resource of the sugar molecules can be outfitted with Los Alamos National Laboratory in isotopes in any position. New Mexico. The Los Alamos group The method for introducing the has supplied the Michigan scientists isotopes is a takeoff on the almost with simple compounds. In turn, the century-old Kiliani reaction that ex- Michigan group shares its labeled tends sugar molecules one carbon at sugar products with the Los Alamos a time by adding molecules of cyanide team. to them. But the Michigan scientists The Los Alamos program is the have refined and changed the condi- largest of its kind in the world, Mattions of that reaction sequence con- wiyoff says. For example, the facility siderably, making it far more efficient now is set up to produce about 20 kg and useful for a large variety of of carbon-13 enriched carbon monsugars. oxide per year. And it can convert When a molecule of cyanide is that material into about 100 grams added to the first carbon of a recipi- per day of the more useful cyanide ent sugar, the resulting molecule is intermediate. Initially, the enrichreduced directly with hydrogen over ment involves a cryogenic distillation a palladium and barium sulfate cat- of carbon monoxide, during which the alyst. Hence, intermediate lactones carbon-13-containing compound is and acids are avoided, in contrast to separated from other isotopes along the classic Kiliani reaction. Also, a 700-foot column. molecular deuterium may be substiTen years ago, the best enrichtuted for hydrogen during the re- ments of carbon-13 were in the 90% duction, and oxygen-18-labeled water range. The Los Alamos facility procan be introduced into the original duces compounds that are enriched to sugar (by an exchange reaction) be- the 99% level or better—and at a far fore cyanide is added. cheaper price than a decade ago. The Though the procedure has been price has been driven down from designed for batches consisting of about $1000 to $4000 per gram to about 25 millimoles of material, siz- about $60, according to Matwiyoff. able amounts of certain sugars have Besides carbon-13, both oxygen-17 been made. For example, 10 grams of and oxygen-18 are produced at the glucose and 5 grams of ribose, each Los Alamos facility, although in lower labeled in the first carbon, have been quantities and at somewhat lower
Shortcut for labeling sugars devised 13(
H~C=^0 I R Exchange reaction
Afdose sugar
K13CN
*
p N H?O, m
\ .%M3QrO H~C~18OH I ί Pd/BaS0 4 H-C~ 1 8 OH R R Cyanohydrin Enlarged, labeled aldose
May 7, 1979 C&EN
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