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PubMed1995

Interaction of alpha-lipoic acid enantiomers and homologues with the enzyme components of the mammalian pyruvate dehydrogenase complex.

Lipoic acid (alpha-lipoic acid, thioctic acid) is applied as a therapeutic agent in various diseases accompanied by polyneuropathia such as diabetes mellitus. The stereoselectivity and specificity of lipoic acid for the pyruvate dehydrogenase complex and its component enzymes from different sources has been studied. The dihydrolipoamide dehydrogenase component from pig heart has a clear preference for R-lipoic acid, a substrate which reacts 24 times faster than the S-enantiomer. Selectivity is more at the stage of the catalytic reaction than of binding. The Michaelis constants of both enantiomers are comparable (Km = 3.7 and 5.5 mM for R- and S-lipoic acid, respectively) and the S-enantiomer inhibits the R-lipoic acid dependent reaction with an inhibition constant similar to its Michaelis constant. When three lipoic acid homologues were tested, RS-1,2-dithiolane-3-caproic acid was one carbon atom longer than lipoic acid, while RS-bisnorlipoic acid and RS-tetranorlipoic acid were two and four carbon atoms shorter, respectively. All are poor substrates but bind to and inhibit the enzyme with an affinity similar to that of S-lipoic acid. No essential differences with respect to its reaction with lipoic acid enantiomers and homologues exist between free and complex-bound dihydrolipoamide dehydrogenase. Dihydrolipoamide dehydrogenase from human renal carcinoma has a higher Michaelis constant for R-lipoic acid (Km = 18 mM) and does not accept the S-enantiomer as a substrate. Both enantiomers of lipoic acid are inhibitors of the overall reaction of the bovine pyruvate dehydrogenase complex, but stimulate the respective enzyme complexes from rat as well as from Escherichia coli. The S-enantiomer is the stronger inhibitor, the R-enantiomer the better activator. The two enantiomers have no influence on the partial reaction of the bovine pyruvate dehydrogenase component, but do inhibit this enzyme component from rat kidney. The implications of these results are discussed.

Animals↗
PubMed1996

alpha-Lipoic acid dependent regeneration of ascorbic acid from dehydroascorbic acid in rat liver mitochondria.

Rat liver mitochondria were examined for their ability to reduce dehydroascorbic acid to ascorbic acid in an alpha-lipoic acid dependent or independent manner. The alpha-lipoic acid dependent reduction was stimulated by factors that increased the NADH dependent reduction of alpha-lipoic acid to dihydrolipoic acid in coupled reactions. Optimal conditions for dehydroascorbic acid reduction to ascorbic acid were achieved in the presence of pyruvate, alpha-lipoic acid, and ATP. Electron transport inhibitors, rotenone and antimycin A, further enhanced the dehydroascorbic acid reduction. The reactions were strongly inhibited by 1 mM iodoacetamide or sodium arsenite. Mitoplasts were qualitatively similar to intact mitochondria in dehydroascorbate reduction activity. Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase reduced dehydroascorbic acid to ascorbic acid in an alpha-lipoic acid, coenzyme A, and pyruvate or alpha-ketoglutarate dependent fashion. Dehydroascorbic acid was also catalytically reduced to ascorbic acid by purified lipoamide dehydrogenase in an alpha-lipoic acid (K0.5 = 1.4 +/- 0.8 mM) and lipoamide (K0.5 = 0.9 +/- 0.3 mM) dependent manner.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1998

Alpha-lipoic acid in liver metabolism and disease.

R-alpha-Lipoic acid is found naturally occurring as a prosthetic group in alpha-keto acid dehydrogenase complexes of the mitochondria, and as such plays a fundamental role in metabolism. Although this has been known for decades, only recently has free supplemented alpha-lipoic acid been found to affect cellular metabolic processes in vitro, as it has the ability to alter the redox status of cells and interact with thiols and other antioxidants. Therefore, it appears that this compound has important therapeutic potential in conditions where oxidative stress is involved. Early case studies with alpha-lipoic acid were performed with little knowledge of the action of alpha-lipoic acid at a cellular level, but with the rationale that because the naturally occurring protein bound form of alpha-lipoic acid has a pivotal role in metabolism, that supplementation may have some beneficial effect. Such studies sought to evaluate the effect of supplemented alpha-lipoic acid, using low doses, on lipid or carbohydrate metabolism, but little or no effect was observed. A common response in these trials was an increase in glucose uptake, but increased plasma levels of pyruvate and lactate were also observed, suggesting that an inhibitory effect on the pyruvate dehydrogenase complex was occurring. During the same period, alpha-lipoic acid was also used as a therapeutic agent in a number of conditions relating to liver disease, including alcohol-induced damage, mushroom poisoning, metal intoxification, and CCl4 poisoning. Alpha-Lipoic acid supplementation was successful in the treatment for these conditions in many cases. Experimental studies and clinical trials in the last 5 years using high doses of alpha-lipoic acid (600 mg in humans) have provided new and consistent evidence for the therapeutic role of antioxidant alpha-lipoic acid in the treatment of insulin resistance and diabetic polyneuropathy. This new insight should encourage clinicians to use alpha-lipoic acid in diseases affecting liver in which oxidative stress is involved.

Animals↗
PubMed2002

Interactions of lipoic acid radical cations with vitamins C and E analogue and hydroxycinnamic acid derivatives.

As a powerful natural antioxidant, lipoic acid exerts significant antioxidant activities in vivo and in vitro by deactivation of reactive oxygen and nitrogen species. In this study we present a novel synergistic interaction of lipoic acid with other endogenous or exogenous antioxidants. Antioxidants vitamins C and E analogue (Trolox C) and hydroxycinnamic acid derivatives were found to recycle lipoic acid by donating electrons to lipoic acid radical cations, thereby increasing the antioxidant capacity of lipoic acid in vivo and in vitro. The rate constant of the electron transfer is in the order 10(9)dm(3)mol(-1)s(-1), close to the diffusion-controlled limit, and transfer quantum yield is above 95%.

Ascorbic Acid↗
PubMed2000

Inhibition of L-homocysteic acid and buthionine sulphoximine-mediated neurotoxicity in rat embryonic neuronal cultures with alpha-lipoic acid enantiomers.

In the present report, we have set out to investigate the potential capacity of both the oxidised and reduced forms of RS-alpha-lipoic acid, and its separate R-(+) and S-(-)enantiomers, to prevent cell death induced with L-homocysteic acid (L-HCA) and buthionine sulphoximine (BSO) in rat primary cortical and hippocampal neurons. L-HCA induced a concentration-dependent neurotoxic effect, estimated by cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction, in primary neurons, but was significantly more toxic for hippocampal (EC(50)=197 microM) compared with cortical neurons (EC(50)=1016 microM) whereas D-HCA demonstrated only moderate (<20%) toxicity. On the other hand, cortical and hippocampal cultures were equally susceptible (341 and 326 microM, respectively) to the neurotoxic action of BSO. Antioxidants including butylated hydroxyanisole, propyl gallate and vitamin E protected cells against the neurotoxic effect of L-HCA and BSO. However, N-acetyl-cysteine and tert-butylphenyl nitrone, although capable of abrogating L-HCA-mediated cell death showed no protective effect against BSO-mediated toxicity. RS-alpha-lipoic acid, RS-alpha-dihydrolipoic acid and the enantiomers R-alpha-lipoic acid and S-alpha-lipoic acid protected cells against L-HCA-mediated toxicity with EC(50) values between 3.1-8.3 microM in primary hippocampal neurons and 2.6-16.8 microM for cortical neurons. However, RS-alpha-lipoic acid, RS-alpha-dihydrolipoic acid, and S-alpha-lipoic acid failed to protect cells against the degeneration induced by prolonged exposure to BSO, whereas the natural form, R-alpha-lipoic, was partially active under the same conditions. The present results indicate a unique sensitivity of hippocampal neurons to the effect of L-HCA-mediated toxicity, and suggest that RS-alpha-lipoic acid, and in particular the R-alpha-enantiomeric form is capable of preventing oxidative stress-mediated neuronal cell death in primary cell culture.

Animals↗
PubMed1998

D,L-S-methyllipoic acid methyl ester, a kinetically viable model for S-protonated lipoic acid as the oxidizing agent in reductive acyl transfers catalyzed by the 2-oxoacid dehydrogenase multienzyme complexes.

D,L-S(6,8)-Methyllipoic acid methyl ester triflate salt (D,L-S-methyllipoic acid methyl ester) was synthesized as a model for S-protonated lipoic acid, suggested to be the active form of lipoic acid in the reductive acylation catalyzed by the E1 and E2 enzymes of the 2-oxoacid dehydrogenase multienzyme complexes by a previous model [Chiu, C. C., Chung, A., Barletta, G., and Jordan, F. (1996) J. Am. Chem. Soc. 118, 11026-11029]. While in that earlier study lipoic acid could only trap only the enamine/C2 alpha-carbanion intermediate in an intramolecular model, and with the assistance of mercury compound to shift the equilibrium to the products, D,L-S-methyllipoic acid methyl ester could trap the enamine derived from 2-alpha-methoxybenzyl-3,4,5-trimethylthiazolium salt in an intermolecular reaction in the absence of a mercury compound, and with a rate constant of 6.6 x 10(4) M-1 S-1. A tetrahedral adduct at the C2 alpha-position formed between the enamine and D,L-S-methyllipoic acid methyl ester was isolated and characterized. The reaction likely takes place by two-electron nucleophilic attack, since no evidence was found for C2 alpha-linked homodimers, expected from a free-radical mechanism. The results suggest that, in the reductive acyl transfer, there is nucleophilic attack by the enamine at one of the sulfur atoms of the lipoic acid [probably at S8, according to Frey, P. A., Flournoy, D. S., Gruys, K., and Yang, Y. S. (1989) Ann. N.Y. Acad. Sci. 373, 21-35], while there is concomitant electrophilic catalysis by a proton juxtaposed at S6 via a general acid catalyst located on the E1 enzyme. Oxidation of the enamine derived from C2 alpha-hydroxybenzyl-3,4,5-trimethylthiazolium salt by D,L-S-methyllipoic acid methyl ester was also deduced on the basis of the formation of 2-benzoylthiazolium ion as a major product; however, the tetrahedral intermediate could not be detected. Oxidation of the enamine by D,L-S-methyllipoic acid methyl ester can take place with either an ether or an alcohol at the C2 alpha position of the enamine.

Acylation↗
PubMed1980

Electrochemical detection and counting of Escherichia coli in the presence of a reducible coenzyme, lipoic acid.

Reduction of lipoic acid by bacteria coupled to oxygen consumption during glucose absorption can be followed potentiometrically with a pair of gold and reference electrodes in a minimal culture medium. The variations in potential as a function of time have the shape of a wave. A theoretical expression was derived relating the size of the original inoculum to the time preceding the appearance of the wave. The validity of that relation was experimentally verified with Escherichia coli, and the time needed for a drop of 100 mV was determined. Detection of small inocula, e.g., down to a range of 10 viable E. coli per liter, is possible in about 11 h by yeast extract stimulation. The method, technically simple and adequately sensitive, suggests the possibility of automated detectors of bacterial contaminations.

Bacteriological Techniques↗
PubMedDate not supplied

[Possibilities of correcting some metabolic disorders in experimental endotoxic shock by treatment with a combination of alpha-lipoic acid and epsilon aminocaproic acid].

Alpha-Lipoic acid associated with xi-aminocaproic acid proves to have a protector effect in the posttreatment of endotoxinic shock in rabbits, produced by the administration of E. coli O111, in doses of 1.5 mg/kg body weight. This effect was observed when administered early in the stage of energy privation, and was manifested by a longer survival, diminution of lactacidemia and protection of labile phosphate reserves.

Aminocaproates↗
PubMed1994

Mutants of Escherichia coli K-12 that are resistant to a selenium analog of lipoic acid identify unknown genes in lipoate metabolism.

Lipoic acid is a disulfide-containing cofactor required for the reactions catalyzed by alpha-ketoacid dehydrogenase enzyme complexes. We report the chemical synthesis and biological properties of lipoic acid analogs in which one or both sulfur atoms were replaced by selenium. Replacement of either the C-6 or the C-8 sulfur atom with selenium results in lipoic acid derivatives with apparently unaltered biological properties. However, simultaneous replacement of both sulfur atoms gave an analog (selenolipoic acid) that inhibited growth of wild-type Escherichia coli when present in minimal glucose medium at 50 ng/ml. This growth inhibition was reversed by the addition of either excess lipoic acid or acetate plus succinate. Labeling experiments with [75Se]selenolipoic acid showed that this compound was efficiently incorporated into the alpha-ketoacid dehydrogenase complexes of growing cells. Spontaneously arising selenolipoic acid-resistant (slr) mutants were isolated. Two of these isolates resistant to high levels of selenolipoic acid were studied in detail. The slr-1 mutation, which was mapped to min 99.6 of the E. coli chromosome, increased the lipoate requirement of lipA strains by 4-fold and appeared to define a gene encoding a lipoate-protein ligase. The slr-7 mutation, which was mapped to min 15.25 of the chromosome, completely suppressed the lipoate requirement of lipA strains and defined a gene of unknown function in the synthesis of lipoic acid.

Chromosome Mapping↗
PubMed1995

Reduction and transport of lipoic acid by human erythrocytes.

Reduction of exogenous lipoic acid to dihydrolipoate is known to occur in several mammalian cells and tissues. Dihydrolipoate is a potent radical scavenger, and may provide significant antioxidant protection. Because lipoic acid appears in the bloodstream after oral administration, we have examined the reduction of exogenous lipoate by human erythrocytes. Normal human erythrocytes reduced lipoate to dihydrolipoate only in the presence of glucose; deoxyglucose did not substitute for glucose, indicating that the reduction of lipoate requires glucose metabolism. Furthermore, the reduction was shown to be NADPH dependent. Erythrocytes isolated from a human subject with a genetic deficiency of glucose-6-phosphate dehydrogenase (and, therefore, deficient in the formation of NADPH) did not reduce lipoate. Dehydroepiandrosterone, a specific inhibitor of glucose-6-phosphate dehydrogenase, inhibited lipoate reduction. Our findings imply that some of the reduction of exogenous lipoic acid is catalysed by glutathione reductase, a flavoprotein dehydrogenase; mitomycin C, an inhibitor of FAD-dependent reductases, inhibited lipoate reduction by erythrocytes, and glutathione reductase purified from human erythrocytes was observed to reduce lipoic acid in a cell-free system. We further explored these findings with erythrocyte ghosts and liposomes. Our results indicate that a transport system exists for alpha-lipoic acid and dihydrolipoate; resealed erythrocyte ghosts, containing trapped lipoamide dehydrogenase and pyridine nucleotides, reduced externally added lipoate. By contrast, liposomes prepared with enzyme and pyridine nucleotides did not catalyze reduction of lipoate. This work indicates that uptake of exogenous lipoate and reduction to dihydrolipoate by normal human erythrocytes may contribute to oxidant protection in the human bloodstream.

Biological Transport↗
PubMed1995

Role of DL alpha-lipoic acid in gentamicin induced nephrotoxicity.

The effect of DL alpha-lipoic acid on the nephrotoxic potential of gentamicin was examined. Intraperitoneal injection of gentamicin (100 mg/kg/day) to rats resulted in decreased activity of the glycolytic enzymes-hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase. The two gluconeogenic enzymes--glucose-6-phosphatase and fructose-1,6-diphosphatase, the transmembrane enzymes namely the Na+, K(+)-ATPase, Ca(2+)-ATPase, Mg(2+)-ATPase and the brushborder enzyme alkaline phosphatase, also showed decreased activities. This decrease in the activities of ATPases and alkaline phosphatase suggests basolateral and brush border membrane damage. Decreased activity of the TCA cycle enzymes isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), suggests a loss in mitochondrial integrity. These biochemical disturbances were effectively counteracted by lipoic acid administration. Lipoic acid administration by gastric intubation at two different concentrations (10 mg and 25 mg/kg/day) brought about an increase in the activity of the glycolytic enzymes, ATPases and the TCA cycle enzymes. The gluconeogenic enzymes however showed a further decrease in their activities at both the concentrations of lipoic acid administered. These observations shed light on the nephroprotective action of lipoic acid against experimental aminoglycoside toxicity and the protection afforded at 25 mg/kg/day of lipoic acid was noted to be higher than that at 10 mg level.

Adenosine Triphosphatases↗
PubMed1997

Lipoic acid reduces the activities of biotin-dependent carboxylases in rat liver.

In the past, lipoic acid has been administered to patients and test animals as therapy for diabetic neuropathy and various intoxications. Lipoic acid and the vitamin biotin have structural similarities. We sought to determine whether the chronic administration of lipoic acid affects the activities of biotin-dependent carboxylases. For 28 d, rats received daily intraperitoneal injections of one of the following: 1) a small dose of lipoic acid [4.3 micromol/( kg.d)]; 2) a large dose of lipoic acid [15.6 micromol/(kg.d)]; or 3) a large dose of lipoic acid plus biotin [15.6 and 2.0 micromol/(kg.d), respectively]. Another group received n-hexanoic acid [14.5 micromol/(kg.d)], which has structural similarities to lipoic acid and biotin and thus served as a control for the specificity of lipoic acid. A fifth group received phosphatidylcholine in saline injections and served as the vehicle control. The rat livers were assayed for the activities of acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and beta-methylcrotonyl-CoA carboxylase. Urine was analyzed for lipoic acid; serum was analyzed for indicators of liver damage and metabolic aberrations. The mean activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase were 28-36% lower in the lipoic acid-treated rats compared with vehicle controls (P < 0.05). Rats treated with lipoic acid plus biotin had normal carboxylase activities. Carboxylase activities in livers of n-hexanoic acid-treated rats were normal despite some evidence of liver injury. Propionyl-CoA carboxylase and acetyl-CoA carboxylase were not significantly affected by administration of lipoic acid. This study provides evidence consistent with the hypothesis that chronic administration of lipoic acid lowers the activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase in vivo by competing with biotin.

Acetyl-CoA Carboxylase↗
PubMed1994

Alpha-lipoic acid supplementation prevents symptoms of vitamin E deficiency.

alpha-Lipoic acid, an essential cofactor in mitochondrial dehydrogenases, has recently been shown to be a potent antioxidant in vitro, as well as being capable of regenerating vitamin E in vitro. In this study, using a new animal model for rapid vitamin E deficiency in adult animals and a new technique for tissue extraction of oxidized and reduced alpha-lipoic acid, we examined the antioxidant action of alpha-lipoic acid in vivo. Vitamin E-deficient adult hairless mice displayed obvious symptoms of deficiency within five weeks, but if the diet was supplemented with alpha-lipoic acid the animals were completely protected. At five weeks on a vitamin E-deficient diet animals exhibited similar decreases in tissue vitamin E levels, whether supplemented or unsupplemented with alpha-lipoic acid: vitamin E levels in liver, kidney, heart, and skin decreased 70 to 85%; levels in brain decreased only 25%. These data show that there was no effect of alpha-lipoic acid supplementation on vitamin E tissue concentrations, arguing against a role for alpha-lipoic acid in regenerating vitamin E in vivo.

Animals↗
PubMed1996

Efficient reduction of lipoamide and lipoic acid by mammalian thioredoxin reductase.

Reduction of the antioxidant lipoic acid has been proposed to be catalyzed in vivo by lipoamide dehydrogenase (LipDH) or glutathione reductase (GR). We have found that thioredoxin reductase (TR) from calf thymus, calf liver, human placenta, and rat liver efficiently reduced both lipoic acid and lipoamide with Michaelis-Menten type kinetics in NADPH-dependent reactions. In contrast to LipDH, lipoic acid was reduced almost as efficiently as lipoamide. Under equivalent conditions at 20 degrees C, pH 8.0, mammalian TR reduced lipoic acid by NADPH 15 times more efficiently than the corresponding NADH dependent reduction catalyzed by LipDH (297 min-1 for TR vs. 20.3 min-1 for LipDH). Moreover, TR was 2.5 times faster in reducing lipoic acid with NADPH than in catalyzing the reverse reaction (oxidation of dihydrolipoic acid with NADP+). In contrast, LipDH was only 0.048 times as efficient in the forward reaction as compared to the reverse reaction (using NADH and NAD+). We conclude that all or part of the previously described NADPH-dependent lipoamide dehydrogenase (diaphorase) activities in mammalian systems should be attributed to TR. Our results suggest that in mammalian cells a significant part of the therapeutically important reduction of lipoic acid is catalyzed by thioredoxin reductase.

Animals↗
PubMed2003

Plasma kinetics, metabolism, and urinary excretion of alpha-lipoic acid following oral administration in healthy volunteers.

R(+)-alpha-lipoic acid is a natural occurring compound that acts as an essential cofactor for certain dehydrogenase complexes. The redox couple alpha-lipoic acid/dihydrolipoic acid possesses potent antioxidant activity. Exogenous racemic alpha-lipoic acid orally administered for the symptomatic treatment of diabetic polyneuropathy is readily and nearly completely absorbed, with a limited absolute bioavailability of about 30% caused by high hepatic extraction. Although the pharmacokinetics of the parent drug have been well characterized in humans, relatively little is known regarding the excretion of alpha-lipoic acid and the pharmacokinetics of any metabolites in humans. In the present study, plasma concentration-time courses, urinary excreted amounts, and pharmacokinetic parameters of alpha-lipoic acid metabolites were evaluated in 9 healthy volunteers after multiple once-daily oral administration of 600 mg racemic alpha-lipoic acid. The primary metabolic pathways of alpha-lipoic acid in man, S-methylation and beta-oxidation, were quantitatively confirmed by an HPLC-electrochemical assay newly established prior to the beginning of this study. Major circulating metabolites were the S-methylated beta-oxidation products 4,6-bismethylthio-hexanoic acid and 2,4-bismethylthio-butanoic acid, whereas its conjugated forms accounted for the major portion excreted in urine. There was no statistically significant difference in the pharmacokinetic parameters Cmax, AUC, and tmax between day 1 and day 4. Despite the prolonged half-lives of the major metabolites compared to the parent drug, no evidence of accumulation was found. Mean values of 12.4% of the administered dose were recovered in the urine after 24 hours as the sum of alpha-lipoic acid and its metabolites. The results of the present study revealed that urinary excretion of alpha-lipoic acid and five of its main metabolites does not play a significant role in the elimination of alpha-lipoic acid. Therefore, biliary excretion, further electrochemically inactive degradation products, and complete utilization of alpha-lipoic acid as a primary substrate in the endogenous metabolism should be considered.

Administration, Oral↗
PubMed1992

Tissue lipids in experimental calcium oxalate lithiasis and the effect of DL alpha-lipoic acid.

The function of DL alpha-lipoic acid (6,8-thioctic acid) as a prosthetic group in the oxidative decarboxylation of alpha-keto acids, pyruvate and alpha-ketoglutarate in mitochondria is well known. Its role is well extended to certain reactions in lipid biosynthesis. In addition, lipoic acid has been shown to prevent the induced precipitation of calcium oxalate crystals in the renal tissues of laboratory animals. Here, the effect of alpha-lipoic acid was studied, on altered tissue lipid levels manifested during experimental renal lithiasis. Raised tissue cholesterol, triglyceride and low phospholipid levels were some of the striking significant observations made in calculogenic rats. Lipoic acid treatment reduced tissue cholesterol and triglyceride levels significantly and raised phospholipids. The alterations may have a bearing in relation to calcium oxalate stone formation.

Animals↗
PubMed1998

Chromatographic analysis of lipoic acid and related compounds.

The analysis of lipoic acid and related compounds, such as its reduced form dihydrolipoic acid, its amide form lipoamide and other analogues, in biological and food samples is important in biochemistry, nutritional and clinical chemistry. This review summarizes the chromatographic methods for the determination of lipoic acid and related compounds, and their applications to various samples such as bacteria, tissues, drugs and food. Gas chromatographic methods with flame ionization detection and flame photometric detection are commonly used for the quantification of lipoic acid present as its protein-bound form, after acid or base hydrolysis of these samples. High-performance liquid chromatographic methods with ultraviolet, fluorescence and electrochemical detection are mainly used for the determination of free lipoic acid and related compounds, such as dihydrolipoic acid, lipoamide and other analogues. Moreover, gas chromatography-mass spectrometry and capillary electrophoresis methods are also developed.

Animals↗