Accumulation of 1-methyl-tetrahydro-beta-carboline-3-carboxylic acid in blood and organs of rat. A possible causative substance of eosinophilia-myalgia syndrome associated with ingestion of L-tryptophan

Toxicology and safety study of L-tryptophan and its impurities for use in broiler feed

L-tryptophan has been utilized as a feed additive in animal nutrition to improve growth performance, as well as a dietary supplement to alleviate various emotional symptoms in humans. Despite its benefits, concerns regarding its safety arose following the outbreak of eosinophilia-myalgia syndrome (EMS) among individuals who consumed L-tryptophan. The causative material of EMS was determined to be not L-tryptophan itself, but rather L-tryptophan impurities resulting from a specific manufacturing process. To investigate the effect of L-tryptophan and its impurities on humans who consume meat products derived from animals that were fed L-tryptophan and its impurities, an animal study involving broiler chickens was conducted. The animals in test groups were fed diet containing 0.065%-0.073% of L-tryptophan for 27 days. This study aimed to observe the occurrence of toxicological or EMS-related symptoms and analyze the residues of L-tryptophan impurities in meat products. The results indicated that there was no evidence of adverse effects associated with the test substance in the investigated parameters. Furthermore, most of the consumed EMS-causing L-tryptophan impurities did not remain in the meat of broiler chickens. Thus, this study demonstrated the safety of L-tryptophan and some of its impurities as a feed additive.

Safety concerns regarding impurities in L-Tryptophan associated with eosinophilia myalgia syndrome

L-tryptophan is one of the essential amino acids in humans and across the animal kingdom. It has been widely used as a feed additive for domestic animals and is also administered through dietary supplements in humans. Safety concerns have been raised however since a disease known as eosinophilia-myalgia syndrome (EMS) was reported to be related to L-tryptophan supplements. EMS is a rare condition characterized by inflammation in various organ systems including the muscles, skin, and lungs. Through several studies, it has been speculated that the six components generated during the process of L-tryptophan synthesis are related to the induction of EMS. In this review, we discuss the history of EMS and its controversial correlation with L-tryptophan use reported in several studies. Many in vitro and in vivo studies have been conducted to assess the putative correlation between impurities in L-tryptophan preparations and EMS, but no clear and convincing conclusions have been drawn so far.

Simultaneous determination of L-tryptophan impurities in meat products

L-tryptophan has been used as a feed additive for swine and poultry and as a nutrient supplement for humans. However, some impurities in L-tryptophan have been reported as causative components of eosinophilia-myalgia syndrome. Therefore, from a safety perspective, it is important to analyze meat samples for these impurities. This study aims to develop an analytical method for the simultaneous detection of L-tryptophan impurities in meat products using LC-MS/MS. Among the various impurities, detection methods for (S)-2-amino-3-(5-hydroxy-1H-indol-3-yl)propanoic acid (5-hydroxytryptophan) (HTP), 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA), 3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo-[2,3-b]-indole-2-carboxylic acid (PIC), and 1,1'-ethylidenebistryptophan (EBT) and 2-(3-indoylmethyl)-L-tryptophan (IMT) were developed. The developed method allowed simultaneous determination of these four impurities in 5 min. No interferences from the matrix were observed, and the method showed good sensitivity to each analyte. The method detection limit and limit of quantification in meat matrices were below 11.2 and 35.7 μg/kg, respectively.

Bioactive β-Carbolines in Food: A Review

Harman and norharman, two neuroactive β-carbolines, are present in several plants and in thermally processed foods. They exhibited a wide spectrum of biological and pharmacological effects, including antioxidant, neuroprotective, and anti-inflammatory effects. In this article, we review the progress of recent research on the presence of these compounds in food, as well as their various biological and neuroactive properties. Our findings strongly suggest that some foods, especially coffee, can act as a rich source of β-carbolines, which may possibly be associated with a reduced risk for serious neurodegenerative diseases, such as Parkinson's and Alzheimer's.

Nitrogen-Containing Constituents of Black Cohosh: Chemistry, Structure Elucidation, and Biological Activities

The roots/rhizomes of black cohosh (Actaea racemosa L. syn. Cimicifuga racemosa [L]. Nutt., Ranunculaceae) have been used traditionally by Native Americans to treat colds, rheumatism, and a variety of conditions related to women's health. In recent years black cohosh preparations have become popular dietary supplements among women seeking alternative treatments for menopausal complaints. The popularity of the plant has led to extensive phytochemical and biological investigations, including several clinical trials. Most of the phytochemical and biological research has focused on two abundant classes of compounds: the triterpene glycosides and phenolic acids. A third group of phytoconstituents that has received far less attention consists of the alkaloids and related compounds that contain nitrogen. This chapter summarizes the current state of knowledge of the chemistry and biological activities associated with this group of constituents and provides some perspective on their significance for future research on this interesting plant.

Does 5-hydroxytryptophan cause acute and chronic toxic perturbations in rats?

In 1989, an epidemic of eosinophilia-myalgia syndrome (EMS) occurred in the United States that was attributed to contaminated l-tryptophan (LT). Features of tryptophan-induced EMS included debilitating myalgia and marked peripheral eosinophilia. Although the contaminant(s) was found only in the product produced by a single manufacturer (Showa Denko), all LT was withdrawn from the market and replaced by 5 hydroxytryptophan (5HTP). The belief was that the latter should not contain the implicated contaminant(s), because it was manufactured by a process entirely different from the banished LT. Nevertheless, in 1994 a case diagnosed as EMS appeared. Although the exact causative factor(s) in LT and the possible 5-HTP-induced EMS are uncertain, many reported finding "Peak E" in contaminated LT and the presence of "Peak X" in the 5-HTP of the 1994 case. The latter finding led some to assume that Peak X was a potential pathological agent in 5-HTP that might cause future cases of EMS. To determine whether 5-HTP could cause EMS, we followed 120 male Sprague-Dawley rats, 7 to 8 weeks of age (body weight 200-250 g), for 1 year. They were divided into three groups of 40. One group acted as control, drinking only water; a second group received a low dose of 5-HTP in their drinking water (87.5 mg/dL); and the last group drank a high dose of 5-HTP, 875 mg/dL. No significant differences in the body weights of these three groups of animals were observed over the year. After 2 months, systolic blood pressures (SBP) in the 5-HTP groups were significantly lower for the duration of the study. At the end of 12 months, SBP of the control group averaged 140 mm Hg, the low-dose 5-HTP group averaged 133 mm Hg, and the high-dose group averaged 125 mm Hg. Even though enough 5-HTP was given to cause a physiological response, no significant differences were found in the hematological values, including eosinophil count. Also, no significant differences were found in hepatic and renal values. In the histological studies, no treatment-related changes were noted in the hearts, livers, pancreases, leg striated muscles, and small intestines. In particular, there was no evidence of eosinophilic infiltration and fascial/perimysial inflammation. Accordingly, no significant evidence of EMS was seen in rats receiving high-dose 5-HTP for 1 year.

1-Methyl-1,2,3,4-tetrahydrocarbolin-2-ium-3-carboxylate

The title compound, C₁₃H₁₄N₂O₂, is a natural product isolated from Cicer arietinum L. (chickpea). The benzene ring and pyrrole rings display planar conformations and the piperidine ring has a half-chair conformation. Inter­molecular C—H⋯π inter­actions between a methyl H atom and the pyrrole ring of an adjacent mol­ecule are present in the crystal structure.

Comparison of the Protective Effect of Indole beta-carbolines and R-(-)-deprenyl Against Nitrogen Species-Induced Cell Death in Experimental Culture Model of Parkinson's Disease

Background

The membrane permeability transition of mitochondria has been suggested to be involved in toxic and oxidative forms of cell injury. Mitochondrial dysfunction is considered to play a critical role in neurodegeneration in Parkinson's disease. Despite the suggestion that indole β-carbolines may be neurotoxic, these compounds provide a protective effect against cytotoxicity of other neurotoxins. In addition, the effect of indole β-carbolines on change in the mitochondrial membrane permeability due to reactive nitrogen species (RNS), which may lead to cell death, has not been clarified.

Methods

Differentiated PC12 cells were used as the experimental culture model for the investigation of neuronal cell injury, which occurs in Parkinson's disease. The effect of indole β-carbolines (harmalol and harmine) on differentiated PC12 cells against toxicity of S-nitroso-N-acetyl-DL-penicillamine (SNAP) was determined by measuring the effect on the change in transmembrane potential, cytochrome c release, formation of ROS, GSH contents, caspase-3 activity and cell viability, and was compared to that of R-(-)-deprenyl.

Results

Specific inhibitors of caspases (z-LEHD.fmk, z-DQMD.fmk) and antioxidants (N-acetylcysteine, dithiothreitol, melatonin, carboxy-PTIO and uric acid) depressed cell death in PC12 cells due to SNAP. β-Carbolines and R-(-)-deprenyl attenuated the SNAP-induced cell death and GSH depletion concentration dependently with a maximal inhibitory effect at 25-50 µM. The compounds inhibited the nuclear damage, decrease in mitochondrial transmembrane potential, cytochrome c release and formation of reactive oxygen species caused by SNAP in PC12 cells. β-Carbolines and R-(-)-deprenyl attenuated the H₂O₂-induced cell death and depletion of GSH.

Conclusions

The results suggest that indole β-carbolines attenuate the SNAP-induced viability loss in PC12 cells by inhibition of change in the mitochondrial membrane permeability, which may be caused by free radicals. Indole β-carbolines appear to exert a protective effect against the nitrogen species-mediated neuronal cell injury in Parkinson's disease comparable to R-(-)-deprenyl.

Safety of 5-hydroxy-L-tryptophan

5-Hydroxy-L-tryptophan (5-HTP) is the immediate precursor in the biosynthesis of 5-hydroxy-tryptamine (5-HT; serotonin) from the essential amino acid L-tryptophan (L-Trp). The use of L-Trp as a dietary supplement was discontinued in 1989 due to an outbreak of eosinophilia-myalgia syndrome (EMS) that was traced to a contaminated synthetic L-Trp from a single manufacturer. 5-HTP has since become a popular dietary supplement in lieu of the removal of L-Trp from the market. Because of its chemical and biochemical relationship to L-Trp, 5-HTP has been under vigilance by consumers, industry, academia and government for its safety. However, no definitive cases of toxicity have emerged despite the worldwide usage of 5-HTP for last 20 years, with the possible exception of one unresolved case of a Canadian woman. Extensive analyses of several sources of 5-HTP have shown no toxic contaminants similar to those associated with L-Trp, nor the presence of any other significant impurities. A minor chromatographic peak (peak X) reported in some 5-HTP samples lacks credibility due to chromatographic artifacts and infinitesimal concentrations, and has raised undue speculations concerning its chemistry and toxicity.

Identification and occurrence of tryptamine- and tryptophan-derived tetrahydro-beta-carbolines in commercial sausages

The identification and occurrence of tetrahydro-beta-carbolines were studied in different kinds of commercial sausages including cooked, fresh, dry-fermented, and ripened sausages, such as salamis and Spanish chorizo, salchichon, fuet, and morcilla, both smoked and unsmoked. Four compounds were identified in several sausages by high-performance liquid chromatography-mass spectrometry (HPLC-MS): 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1), 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid diastereoisomers (2a,b), 1,2,3,4-tetrahydro-beta-carboline (3), and 1-methyl-1,2,3,4-tetrahydro-beta-carboline (4). The latter two (3 and 4) are now reported for the first time in meat products. The presence and occurrence of tetrahydro-beta-carbolines were highly variable depending on each particular sample of sausage, and it did not follow a single specific pattern. The concentration range taken as a sum of the four carbolines varied from undetectable levels to 33 microg/g, with the highest content found in ripened, dry-fermented, and smoked sausages (salami, chorizo, and morcilla) and the lowest in cooked sausages (Frankfurt). Formation of tetrahydro-beta-carbolines might occur during elaboration and the ripening process from a chemical condensation between tryptophan or tryptamine and aldehydes (formaldehyde and acetaldehyde). Smoked samples had higher concentrations of formaldehyde-derived 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1) and 1,2,3,4-tetrahydro-beta-carboline (tryptoline) (3) than those unsmoked. Also, 1 and 3 were more concentrated in the outer part of the sausage, likely to be in contact with smoke. It is concluded that some dry-fermented and/or smoked sausages may be significant dietary sources of tetrahydro-beta-carbolines.

Tetrahydro-beta-carboline alkaloids occur in fruits and fruit juices. Activity as antioxidants and radical scavengers

Tetrahydro-beta-carbolines are biologically active alkaloids that occur and accumulate in mammalian tissues, fluids, and brain, but their ultimate origin or biological role is still uncertain. Four tetrahydro-beta-carboline alkaloids: 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline, are found as naturally occurring substances in some fruit and fruit juices. These compounds occur in the microg/g level in those products, and a characteristic and distinct profile appears to exist depending on the type of fruit and juice involved. Thus, 1-methyl-1,2,3,4-tetrahydro-beta-carboline may appear in tomato, tomato juice, and kiwi; 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline in bananas, pineapple, tomato, and their corresponding juices; and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in oranges and grapefruits, although it also occurred in most juices. Fruit-occurring tetrahydro-beta-carboline alkaloids acted as antioxidants and free radical scavengers in the ABTS assay when compared with ascorbic acid and Trolox. This suggests that tetrahydro-beta-carboline alkaloids might act as antioxidants when absorbed and accumulated in the body, contributing to the antioxidant effect of fruit products containing these compounds.

L-tryptophan reacts with naturally occurring and food-occurring phenolic aldehydes to give phenolic tetrahydro-beta-carboline alkaloids: activity as antioxidants and free radical scavengers

The reaction between the essential amino acid l-tryptophan and flavoring or naturally occurring phenyl and phenolic aldehydes was studied, and the alkaloidal reaction products were characterized by NMR and HPLC-MS. Benzaldehyde, vanillin, syringaldehyde, salicylaldehyde, and anisaldehyde condensed with l-tryptophan in aqueous-acidic media affording the corresponding phenolic tetrahydro-beta-carboline-3-carboxylic acid as two diastereoisomers, 1S,3S-cis and 1R,3S-trans. With the exception of benzaldehyde, the rest of the aldehydes needed heating conditions (70 degrees C) to significantly form tetrahydro-beta-carbolines over time with the cyclization highly favored at low pH. This suggests a likely formation of these compounds under conditions that may occur in foods, food processing, or cooking. The new phenolic tetrahydro-beta-carboline alkaloids were assayed, for the first time, for their activity as free radical scavengers and antioxidants and showed good antioxidant properties with Trolox equivalent antioxidant capacity (TEAC) values much higher than those of ascorbic acid and the water soluble vitamin E analogue, Trolox, in the 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) assay.

Identification and occurrence of the novel alkaloid pentahydroxypentyl-tetrahydro-beta-carboline-3-carboxylic acid as a tryptophan glycoconjugate in fruit juices and jams

The novel carbohydrate-derived beta-carboline, 1-pentahydroxypentyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, was identified in fruit- and vegetable-derived products such as juices, jams, and tomato sauces. This compound occurred as two diastereoisomers, a cis isomer (the major compound) and a trans isomer, ranging from undetectable amounts to 6.5 microg/g. Grape, tomato, pineapple, and tropical juices exhibited the highest amount of this alkaloid (up to 3.8 mg/L), whereas apple, banana, and peach juices showed very low or nondetectable levels. This tetrahydro-beta-carboline was also found in jams (up to 0.45 microg/g), and a relative high amount was present in tomato concentrate (6.5 microg/g) and sauce (up to 1.8 microg/g). This beta-carboline occurred in fruit-derived products as a glycoconjugate from a chemical condensation of D-glucose and L-tryptophan that is highly favored at low pH values and high temperature. Production, processing treatments, and storage of fruit juices and jams can then release this beta-carboline. Fruit-derived products and other foods containing this compound might be an exogenous dietary source of this glucose-derived tetrahydro-beta-carboline.

Reaction of tryptophan with carbohydrates: identification and quantitative determination of novel beta-carboline alkaloids in food

The formation of various carbohydrate-derived beta-carbolines was observed when model reactions of tryptophan with glucose were studied by means of HPLC with diode array detection, as well as by means of HPLC-MS. Isolation of these compounds and subsequent characterization by tandem mass spectrometry and NMR spectroscopy led to the identification of diastereomeric 1-(1,3,4,5-tetrahydroxypent-1-yl)-9H-pyrido[3,4-b]indoles (1a/b), 1-(1,4,5-trihydroxypent-1-yl)-9H-pyrido[3,4-b]indoles (2a/b), and E/Z isomers of 1-(1,5-dihydroxypent-3-en-1-yl)-9H-pyrido[3,4-b]indole (3a/b). HPLC-MS was used to prove the presence of these novel beta-carboline alkaloids in various food samples. In addition, quantitative determination of beta-carbolines 1a, 1b, and 2a/b in numerous products was achieved by means of HPLC with fluorometric detection. Concentrations ranged from 12 to 1922 microg/L for 1a and 1b and from 3 to 644 microg/L for 2a/b. The highest concentrations of all carbohydrate-derived beta-carbolines under study were found in ketchup, soy sauce, and fish sauce.

Tetrahydro-beta-carboline-3-carboxylic acid compounds in fish and meat: possible precursors of co-mutagenic beta-carbolines norharman and harman in cooked foods

The presence of tetrahydro-beta-carbolines and beta-carbolines was studied in raw, cooked and smoked fish and meat. 1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) usually was the major beta-carboline found, whereas 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA) appeared in smoked and 'well done' cooked samples. THCA was detected in raw fish (nd-2.52 micrograms/g), cooked fish (nd-6.43 micrograms/g), cooked meats (nd-0.036 microgram/g), smoked fish (0.19-0.67 microgram/g) and smoked meats (0.02-1.1 micrograms/g). Smoked and cooked samples contained higher amounts of THCA and MTCA than raw products. Deep cooking of fish and meat increased both THCA and MTCA, and this was accompanied by the formation of more beta-carbolines, norharman and harman. The tetrahydro-beta-carbolines THCA and MTCA were chemical precursors of the co-mutagens norharman and harman during cooking. These and previous results confirm that foods are an important source of beta-carbolines in humans.

Tetrahydro-beta-carboline-3-carboxylic acids and contaminants of L-tryptophan

Methods for the separation, identification, and quantitative assay of contaminants of L-tryptophan implicated in eosinophilia-myalgia syndrome (EMS) are described. Propylsulfonic acid (PRS), benzenesulfonic acid (SCX), and octyl-derivatized silica (C8) bonded-phase cartridges were used for the separation; LC-MS and GC-MS for identification; and HPLC-UV-fluorescence detection for quantitative analyses of norharman, harman, tetrahydro-beta-carboline-3-carboxylic acid (TCCA), 1-methyltetrahydro-beta-carboline-3-carboxylic acid (MTCA), 1,1'-ethylidenbis(tryptophan) (EBT), and 3-(phenylamino)alanine (PAA). The tissue distribution, excretion, and metabolism of these contaminants of L-tryptophan associated with EMS after acute and chronic dosage regimens are described. Considerable amounts of EBT were observed in the large intestine of rats administered EBT, showing a transfer without decomposition in gastric fluid. In addition, MTCA was detected in the blood and urine as well as the organs of rats treated with EBT, suggesting MTCA as a major metabolite of EBT. PAA accumulated markedly in the brain, among the organs of rats, after both acute and chronic administration of PAA, while MTCA accumulated in the kidneys of rats after chronic dosage of MTCA. Ethanol and/or acetaldehyde-induced formation of MTCA, as well as tryptophan-induced formation of TCCA, occurred endogenously in man and animals.

beta-carbolines that accumulate in human tissues may serve a protective role against oxidative stress

beta-Carbolines are tricyclic nitrogen heterocycles formed in plants and animals as Maillard reaction products between amino acids and reducing sugars or aldehydes. They are being detected increasingly in human tissues, and their physiological roles need to be understood. Two beta-carboline carboxylates have been reported to accumulate in the human eye lens. We report here on the identification of another beta-carboline, namely 1-methyl-1-vinyl -2, 3,4-trihydro-beta-carboline-3-carboxylic acid, in the lenses of some cataract patients from India. Analysis of these three lenticular beta-carbolines using photodynamic and antioxidant assays shows all of them to be inert as sensitizers and effective as antioxidants; they quench singlet oxygen, superoxide and hydroxyl radicals and inhibit the oxidative formation of higher molecular weight aggregates of the test protein, eye lens gamma-crystallin. Such antioxidative ability of beta-carbolines is of particular relevance to the lens, which faces continual photic and oxidative stress. The beta-carboline diacid IV is also seen to display an unexpected ability of inhibiting the thermal coagulation of gamma-crystallin and the dithiothreitol-induced precipitation of insulin. These results offer experimental support to earlier suggestions that one of the roles that the beta-carbolines have is to offer protection against oxidative stress to the human tissues where they accumulate.

1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid and 1,2, 3,4-tetrahydro-beta-carboline-3-carboxylic acid in fruits

1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA), as two diastereoisomers (1S,3S and 1R,3S), occurred in commercial fruits. Citrus fruits exhibited the highest content; other fruits contained very low levels or none at all. The content of MTCA was as follows: orange, 0.35-2.47 microg/g; lemon, 0.15-2.05 microg/g; grapefruit, 1.12-8.37 microg/g; mandarin, 0.57-2.5 microg/g; banana, nd-0.74 microg/g; pear, nd-0.017 microg/g; grape, 0.01-0.22 microg/g, tomato, 0.05-0.25 microg/g; and apple, nd-0.012 microg/g). THCA, if present, usually occurred at <0.05 microg/g. Fruit ripening and softening during storage were accompanied with a significant increase of MTCA, in both pears and bananas. Those and previous results confirm that foods are an important source of tetrahydro-beta-carbolines in humans.

Neuropharmacology of progressive myoclonus epilepsy: response to 5-hydroxy-L-tryptophan

Low concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF) of patients with progressive myoclonus epilepsy (PME) suggest hypofunctional serotonergic neurotransmission. To study this hypothesis, we enrolled 6 patients with PME [Unverricht-Lündborg disease (U-L), mitochondrial encephalomyopathy, or Lafora disease] in a controlled, double-blinded, dose-ranging, cross-over add-on pilot clinical trial of 5-hydroxy-L-tryptophan (L-5-HTP) plus carbidopa after 2 other patients had received open-label L-5-HTP for compassionate use. Prestudy CSF 5-HIAA concentrations were low (< 20 ng/ml) in 6 patients regardless of the etiology of PME. One patient with U-L disease showed clinical improvement and a fivefold increase in CSF 5-HIAA, and 1 with Lafora disease showed a twofold increase in CSF 5-HIAA without improvement. A patient with Lafora disease reported enough improvement in myoclonus-evoked convulsions to continue chronic use of the drug. One patient with mitochondrial encephalomyopathy developed status epilepticus during treatment with L-5-HTP. As a group, patients had no statistically significant changes in myoclonus evaluation scale scores, subjective and objective measures of ataxia, seizure frequency, antiepileptic drug (AED) levels, or routine blood tests. These data suggest a serotonergic abnormality regardless of the underlying etiology of PME, but one that seldom responds to acute treatment with L-5-HTP.

Accumulation of 3-(phenylamino)alanine, a constituent in L-tryptophan products implicated in eosinophilia-myalgia syndrome, in blood and organs of the Lewis rats

3-(Phenylamino)alanine (PAA), a newly discovered impurity in case-associated L-tryptophan tablets, has been investigated as a possible contributing factor in the etiology of eosinophilia-myalgia syndrome (EMS). We have studied distribution and elimination of PAA in rats which were administered a single 5 mg/kg dose of PAA by gastric gavage. PAA concentrations in blood, brain, kidney and liver were measured by high-performance liquid chromatography (HPLC) with electrochemical detection. The concentration of PAA in each tissue reached a maximum at 5 h, and then gradually declined. A high level of PAA still remained at 24 h, indicating gradual elimination. The concentration of PAA in brain at 5 h was 2139 ng/g tissue, demonstrating passage through the blood-brain barrier. Consecutive administration of PAA (5 mg/kg) for 4 days resulted in approximately double the concentration in all tissues. Chronic treatment using PAA incorporated into food pellets for 6 weeks resulted in similar accumulations in each tissue, and following 12 days on a PAA free diet, levels of this drug were still detectable in all tissues.

Identification of four metabolites of 3-(phenylamino)alanine, a constituent in L-tryptophan products implicated in eosinophilia-myalgia syndrome, in rats

3-(Phenylamino)alanine (PAA), a contaminant found in L-tryptophan tablets, has been discussed as a possible cause of eosinophilia-myalgia syndrome (EMS). We administered PAA (100 mg/kg) by gastric gavage to Wistar rats to determine its distribution and metabolism. We developed a purification procedure, using Bond Elut SCX cartridges followed by high performance liquid chromatography (HPLC) in order to determine levels of PAA. The level of PAA in blood was 4.22 micrograms/ml at 5 h and urinary excretion was 21.7 micrograms for 5 h and 84.6 micrograms between 5 and 24 h. The amount of PAA in the contents of the large intestine at 5 h was 0.76 microgram, indicating poor transfer of PAA to the large intestine. However, the highest concentration of PAA was 12.3 micrograms/g in the brain, indicating the passage of PAA through the blood-brain barrier. In addition to detecting PAA in the blood and organs, we also detected four metabolites of PAA in urine. We used gas chromatography mass spectrometry to identify PAA in rat liver, as well as N-(hydroxyphenyl)glycine, N-phenylglycine, 3-(pheylamino)lactic acid, and 3-(hydroxyphenylamino)-lactic acid in rat urine. These results suggest that the degradation pathway of PAA is similar to that of phenylalanine.