Taurine conjugates as metabolites of arylacetic acids in the ferret

Metabolism of clofibric acid in zebrafish embryos (Danio rerio) as determined by liquid chromatography-high resolution-mass spectrometry

The zebrafish embryo (ZFE) is increasingly used in ecotoxicology research but detailed knowledge of its metabolic potential is still limited. This study focuses on the xenobiotic metabolism of ZFE at different life-stages using the pharmaceutical compound clofibric acid as study compound. Liquid chromatography with quadrupole-time-of-flight mass spectrometry (LC-QToF-MS) is used to detect and to identify the transformation products (TPs). In screening experiments, a total of 18 TPs was detected and structure proposals were elaborated for 17 TPs, formed by phase I and phase II metabolism. Biotransformation of clofibric acid by the ZFE involves conjugation with sulfate or glucuronic acid, and, reported here for the first time, with carnitine, taurine, and aminomethanesulfonic acid. Further yet unknown cyclization products were identified using non-target screening that may represent a new detoxification pathway. Sulfate containing TPs occurred already after 3h of exposure (7hpf), and from 48h of exposure (52hpf) onwards, all TPs were detected. The detection of these TPs indicates the activity of phase I and phase II enzymes already at early life-stages. Additionally, the excretion of one TP into the exposure medium was observed. The results of this study outline the high metabolic potential of the ZFE with respect to the transformation of xenobiotics. Similarities but also differences to other test systems were observed. Biotransformation of test chemicals in toxicity testing with ZFE may therefore need further consideration.

Novel metabolites and roles for α-tocopherol in humans and mice discovered by mass spectrometry-based metabolomics

BACKGROUND

Contradictory results from clinical trials that examined the role of vitamin E in chronic disease could be a consequence of interindividual variation, caused by factors such as xenobiotic use. Cometabolism of vitamin E with other pharmaceutical products could affect the bioavailability of the drug. Thus, it is necessary to understand fully the metabolic routes and biological endpoints of vitamin E.

OBJECTIVE

The objective was to uncover novel metabolites and roles of vitamin E in humans and mouse models.

DESIGN

Human volunteers (n = 10) were fed almonds for 7 d and then an α-tocopherol dietary supplement for 14 d. Urine and serum samples were collected before and after dosing. C57BL/6 mice (n = 10) were also fed α-tocopherol-deficient and -enriched diets for 14 d. Urine, serum, and feces were collected before and after dosing, and liver samples were collected after euthanization. Ultraperformance liquid chromatography electrospray ionization time-of-flight mass spectrometry and multivariate data analysis tools were used to analyze the samples.

RESULTS

Three novel urinary metabolites of α-tocopherol were discovered in humans and mice: α-carboxyethylhydroxychroman (α-CEHC) glycine, α-CEHC glycine glucuronide, and α-CEHC taurine. Another urinary metabolite, α-CEHC glutamine, was discovered in mice after α-CEHC gavage. Increases in liver fatty acids and decreases in serum and liver cholesterol were observed in mice fed the α-tocopherol-enriched diet.

CONCLUSION

Novel metabolites and metabolic pathways of vitamin E were identified by mass spectrometry-based metabolomics and will aid in understanding the disposition and roles of vitamin E in vivo.

Dog bites man or man bites dog? The enigma of the amino acid conjugations

The proposition posed is that the value of amino acid conjugation to the organism is not, as in the traditional view, to use amino acids for the detoxication of aromatic acids. Rather, the converse is more likely, to use aromatic acids that originate from the diet and gut microbiota to assist in the regulation of body stores of amino acids, such as glycine, glutamate, and, in certain invertebrates, arginine, that are key neurotransmitters in the central nervous system (CNS). As such, the amino acid conjugations are not so much detoxication reactions, rather they are homeostatic and neuroregulatory processes. Experimental data have been culled in support of this hypothesis from a broad range of scientific and clinical literature. Such data include the low detoxication value of amino acid conjugations and the Janus nature of certain amino acids that are both neurotransmitters and apparent conjugating agents. Amino acid scavenging mechanisms in blood deplete brain amino acids. Amino acids glutamate and glycine when trafficked from brain are metabolized to conjugates of aromatic acids in hepatic mitochondria and then irreversibly excreted into urine. This process is used clinically to deplete excess nitrogen in cases of urea cycle enzymopathies through excretion of glycine or glutamine as their aromatic acid conjugates. Untoward effects of high-dose phenylacetic acid surround CNS toxicity. There appears to be a relationship between extent of glycine scavenging by benzoic acid and psychomotor function. Glycine and glutamine scavenging by conjugation with aromatic acids may have important psychosomatic consequences that link diet to health, wellbeing, and disease.

Design, synthesis, hydrolysis kinetics and phamacodynamic profiles of histidine and alanine conjugates of aceclofenac

The gastrointestinal toxicity associated with aceclofenac can be reduced by condensing its carboxylic acid group with methyl esters of amino acids like histidine and alanine to give amide linkage by the Schotten-Baumann method. Physicochemical characterization of the conjugates was carried out by various analytical and spectral methods. The synthesized conjugates were also subjected to in vitro hydrolysis in simulated gastric fluid (SGF) at pH 1.2, simulated intestinal fluid (SIF) at pH 7.4 and SIF+ 80% human plasma at pH 7.4. The release of free aceclofenac from histidine and alanine conjugated aceclofenac showed negligible hydrolysis in SGF compared to SIF. This indicated that the conjugates do not break in stomach, but release aceclofenac in SIF. Both synthesized conjugates showed excellent pharmacological response and encouraging hydrolysis rate in SIF and SIF + 80% human plasma. Marked reduction of the ulcer index and comparable increase in analgesic and anti-inflammatory activities were obtained in both cases compared to aceclofenac alone. These findings suggest that the conjugates are better in action compared to the parent drug and have fewer gastrointestinal side-effects.

Detailed NMR, including 1,1-ADEQUATE, and anticancer studies of compounds from the echinoderm Colobometra perspinosa

From the dichloromethane/methanol extract of the crinoid Colobometra perspinosa, collected south east of Richards Island (Bedara), Family Islands, Central Great Barrier Reef, Australia, 3-(1'-hydroxypropyl)-1,6,8-trihydroxy-9,10-anthraquinone [one of the two stereoisomers of rhodoptilometrin, (1)], 3-propyl-1,6,8-trihydroxy-9,10-anthraquinone (3), 2-[(phenylacetyl)amino]ethanesulfonic acid (4), and 4-hydroxybutanoic acid (5) were isolated. Comparison of (1)H- and (13)C-NMR data for rhodoptilometrin (1) with those reported in the literature showed significant differences for some resonances associated with rings A and C. In an attempt to provide accurately assigned (1)H- and (13)C-NMR data, as well as to confirm the structure of 1, a thorough NMR investigation of this compound was undertaken. Measurements included: concentration dependent (13)C, 1D selective NOE, HSQC, HMBC and 1,1-ADEQUATE. The NMR data for 4 and 5 are reported here for the first time, as is their occurrence from the marine environment. The in vitro anticancer activity of the original extract was found to be associated with 1, 3 and 5.

Taurine in development and nutrition

Taurine is an amino acid that is widely distributed in the fluids and tissues of man. In mammals, taurine is a major end-product of methionine metabolism. Taurine is found in most mammalian tissues but is only present in trace amounts in many plants. During fetal development of the brain in man and other mammals taurine is present in high concentrations and declines to lower, adult concentrations during neonatal life. However, during this time there is a net accumulation of taurine when the amount per brain rather than per gram of tissue is calculated. In man, taurine is apparently an essential nutrient, unlike in other animals which have a much greater capacity to synthesize this compound. The human infant, is particular, needs a dietary supply of taurine to synthesize the bile salt taurocholate. Thus, taurine appears to be an important component of the developing brain and must be supplied to man in the diet.

Characterization of a renal medium chain acyl-CoA synthetase responsible for glycine conjugation in mouse kidney mitochondria

Glycine conjugation of a series of benzoic acid derivatives was investigated in mouse kidney mitochondria. The chlorine and methyl substitutions in the para- and meta-positions of the benzene ring yielded an increase in glycine conjugation. The acids with a methoxy group showed a low degree of glycine conjugation. In addition, the acids with nitro or amino groups were conjugated to a slight extent with glycine. The in vitro conjugation of salicylic acid with glycine occurred not in liver but in kidney. The specificity of the renal medium chain acyl-CoA synthetase catalyzing the first reaction of glycine conjugation was also examined. The enzyme accepted not only medium chain fatty acids but also aromatic and arylacetic acids. The highest activity was shown with hexanoic acid. High activities were observed for benzoic acid derivatives with alkyl and alkoxyl groups in the para- and meta-positions of the benzene ring. An ortho-substituted acid exhibited no activity. In addition, the enzyme was less active with valproic acid, tranexamic acid, indomethacin and ketoprofen. The enzyme was inhibited by diflunisal, 2-hydroxydodecanoic acid and salicylic acid, which did not act as substrates. There was a poor correlation between the activity of the medium chain acyl-CoA synthetase and glycine conjugation of eleven substituted benzoic acids. These findings suggest that the present medium chain acyl-CoA synthetase is involved in glycine conjugation of the substituted acids in mouse kidney mitochondria, but there may be a larger contribution of another isoenzyme.

Molecular specificity of a medium chain acyl-CoA synthetase for substrates and inhibitors: conformational analysis

Amino acid conjugation is an important route of detoxification of xenobiotic and endogenous carboxylic acids. The specificity of the purified medium chain acyl-CoA synthetase catalyzing the first reaction of amino acid conjugation was investigated further for substrates and inhibitors. Molecular modeling techniques were applied to derive the molecular characteristics of substrates and inhibitors for the medium chain acyl-CoA synthetase. The purified enzyme accepted not only straight medium chain fatty acids but also aromatic acids. Of the arylacetic acids, activity was obtained with naphthylacetic acids, whereas introduction of a methyl group at the alpha-position caused loss of activity. High activity was also observed with cyclohexanoic acid. Diflunisal, 2-hydroxydodecanoic acid, and nalidixic acid inhibited the medium chain acyl-CoA synthetase activity for hexanoic acid, with Ki values of 0.8, 4.4, and 12.3 microM, respectively. The inhibitory carboxylic acids were competitive with respect to hexanoic acid. The hydroxyl or ketone (oxo) groups at the beta-position of carboxylic acids were an important determinant for inhibitory activity. All substrates and inhibitors contained a flat hydrophobic region coplanar to the carboxylate group. In addition, the substrates had negative values for charge on the carbon in the beta-position of carboxylic acids.

Metabolic fate and hepatocyte toxicity of reverse amide analogs of conjugated ursodeoxycholate in the rat

Reverse amide analogs of conjugated bile acids were tested for their effects on the viability of cultured primary rat hepatocytes, for their transport and metabolism in the intact rat, and for their susceptibility to hydrolysis by intestinal bacteria. Succinylnorursodeoxycholanylamide (SNUDCN) and its parent C23 amine showed the same general lack of toxicity toward hepatocytes as the normal conjugates of ursodeoxycholic acid, at concentrations up to 500 microM. The 3alpha,7alpha,12alpha-trihydroxy analog and its parent amine were more toxic than the corresponding dihydroxy compounds, although their effects were similar to those observed for the normal conjugates of cholic acid. Following intraduodenal infusion, greater than 80% of administered SNUDCN appeared in the bile of bile fistula rats. Analysis of bile fractions indicated the presence of SNUDCN (81.5 mol% of original amount) and two metabolites, the taurine conjugate of SNUDCN (9.4 mol%) and SNUDCN containing an additional hydroxy group (9.1 mol%). Although SNUDCN underwent an efficient first pass enterohepatic circulation, it displayed a shorter biological half life than taurocholate (T1/2: 8.9 h vs 39.6 h, respectively). The reverse amide analogs were not hydrolyzed by any of a variety of intestinal bacteria known to hydrolyze normal conjugated bile acids. Despite the shorter half-life, the reverse amide analogs may be of potential use in the targeting of therapeutic bile acids to the colon.

Biliary elimination of oral 2,4-dichlorophenoxyacetic acid and its metabolites in male and female Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters

The role of biliary elimination in the metabolic disposition of 2,4-D was evaluated in male and female Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters. Following cannulation of the bile duct, an intragastric (ig) dose of 2,4-D (200 mg/kg) was administered and bile was collected at 30- or 60-min intervals for up to 6 h. Bile flow rates were constant in rats, increased in mice, and decreased in hamsters throughout the collection periods. Total recovery of radioactivity was greatest in male mice (about 7% of administered dose over 4 h). Female mice and rats of both sexes excreted about 3% over the same interval and male and female hamsters about 1%. About 71-88% of the activity in bile was parent compound. The glycine conjugate of 2,4-D was found in bile from mice, rats, and hamsters and the taurine conjugate in bile from mice. The only sex-dependent difference in the metabolite profile was in mice. Male mice excreted twice as much glycine conjugate as female mice. An additional minor metabolite (4-7%) was present in rat and mouse bile. This was tentatively identified as 2,4-D-glucuronide based on its hydrolysis by beta-glucuronidase. One more very minor metabolite (3%) was detected in rat bile but was not characterized due to its lability. The results of this study indicate that there are species-dependent differences in the biliary elimination of 2,4-D but not sex-dependent differences.

Studies on the metabolism of arylacetic acids. 6. Comparative metabolic conjugation of 1- and 2-naphthylacetic acids in the guinea pig, mouse, hamster and gerbil

The patterns of metabolic conjugation of the isomeric 1- and 2-naphthylacetic acids have been compared in guinea pig, mouse, hamster and gerbil. Equimolar doses of [carboxy-14C]1- and 2-naphthylacetic acids were given to these species by i.p. injection, their urine collected and urinary metabolites examined by t.l.c. before and after treatment with beta-glucuronidase or mild alkali. 2. Urinary excretion of 14C following administration of 14C-1-naphthylacetic acid was 76-93% of dose in 72 h, the bulk being eliminated in 24 h. Urinary metabolites comprised 1-naphthylacetic-glycine and -glucuronide together with the unchanged acid. 3. Following administration of 14C-2-naphthylacetic acid, some 68-94% of the 14C dose was recovered in the urine in 72 h, with the majority in the 0-24 h urine. All four species excreted 2-naphthylacetyl-glucuronide and -glycine: additionally, 2-naphthylacetyl-taurine was excreted by mouse, gerbil and hamster and the glutamine conjugate was also present in hamster urine.

The utilization of exogenous taurine for the conjugation of xenobiotic acids in the ferret

Although the occurrence of the taurine conjugation mechanism for various xenobiotic acids is well established, nothing is known of the source of the taurine used for this conjugation. [14C]Taurine was administered alone and in combination with 2-naphthylacetic acid or clofibric acid (both of which are known to form taurine conjugates) to to ferrets, and the 0--24 h urine collected. Of the dose of [14C]taurine, 26% was recovered in the urine in 24 h and the only 14C-containing material present was unchanged taurine. When either 2-naphthylacetic acid or clofibric acid was co-administered with [14C]taurine, 21 and 17%, respectively, of the 14C dose was recovered in the 0--24 h urine. In both cases, two 14C compounds were present--unchanged taurine (minor) and the taurine conjugate of the acid in question (major). Comparison of these results with those previously obtained with 14C-labelled 2-naphthylacetic and clofibric acids, shows that the taurine used for their conjugation is derived from a pool freely accessible to exogenous taurine. The results are discussed in terms of the availability for metabolic utilization of taurine in the animal body, and of the use of co-administration of [14C]taurine with a xenobiotic acid for the identification of taurine conjugates.

Metabolism of adiphenine. II. Identification of major excretion metabolites in rats

1. Major metabolites isolated from rat urine after administration of a single dose of [14C]adiphenine or [3H]adiphenine were identified by chromatography and n.m.r. spectrometry, and by comparison with authentic reference compounds chemically synthesized. 2. Adiphenine was extensively metabolized by hydrolysis of the ester bond into diethylaminoethanol, diphenylacetic acid, diphenylacetic acid glucuronide and, in small quantities, the corresponding glycine and glutamine conjugates.

Influence of the gut microflora on the metabolism of 4-nitrobenzoic acid in the marmoset

1. 4-Nitrobenzoic acid was metabolized by the marmoset to amino derivatives to the extent of 18.8% (p.o.) and 11.4% (i.p.) of the dose. 2 Reduction of 4-nitrobenzoic acid was significantly decreased by antibiotic pretreatment; the mean decrease in reduction was 81% for animals doses orally and 73% for intraperitoneally dosed marmosets. 3. 4-Nitrohippuric acid was the major metabolite of 4-nitrobenzoic acid, accounting for 30.6% and 49.6% of p.o. and i.p. doses respectively. 4. Antibiotic pretreatment affected the marmosets' normal capacity to reduce 4-nitrobenzoic acid for many weeks after the initial administration. 5. Maximum radioactivity in the blood, after an oral dose, was reached in 30-40 min; the average half-life for the elimination of 4-nitro[carboxy-14C]benzoic acid and its metabolites was 30.4 +/- 3 min after an intramuscular dose. 6. Radioactivity of 4-nitro[carboxy-14C]benzoic acid representing 3.4% of the dose was excreted in rat bile in 24 h.

Enterohepatic recycling of phenolphthalein, morphine, lysergic acid diethylamide (LSD) and diphenylacetic acid in the rat. Hydrolysis of glucuronic acid conjugates in the gut lumen

1. Biliary elimination in female Wistar albino rats 3 h after i.p. injection of [3H]phenolphthalein, [3H]morphine, 14C-LSD and [14C]diphenylacetic acid was 90%, 45%, 75% and 57% respectively, predominantly as glucuronides. 2. Infusion of 3 h bile from the previous experiments into the duodena of bile-duct-cannulated animals demonstrated enterohepatic circulation, amounting in 24 h to 85%, 41%, 28% and 66% of the infused doses of the conjugates of phenolphthalein, morphine, LSD and diphenylacetic acid respectively. 3. Pretreatment with antibiotics to suppress intestinal microflora decreased this enterohepatic recirculation to 22%, 8.6% and 21% in 24 h for phenolphthalein, morphine and diphenylacetic acid glucuronides respectively. Antibiotic pretreatment did not influence the absorption and re-excretion of infused doses of the free aglycones, thus demonstrating the importance of bacterial beta-glucuronidase hydrolysis of the biliary conjugates. 4. The extent of intestinal absorption of the aglycones after bacterial beta-glucuronidase hydrolysis of the conjugates is related to their lipid-solubility as estimated by octan-1-ol:0.1 M phosphate buffer partition ratios (P-values). 5. The persistence of compounds in the enterohepatic circulation is determined by the faecal and urinary elimination of the circulating compounds. Faecal elimination is governed by the extent of intestinal absorption of the circulating compounds, which is influenced by the efficacy of intestinal hydrolysis of the conjugates and the relative lipophilicity of the aglycones released.