Cytoprotective effects of taurine in isolated rat hepatocytes

This study examined the protection of isolated rat hepatocytes against carbon tetrachloride, hydrazine and 1,4-naphthoquinone (1,4-NQ) toxicity. Hepatocytes were incubated with various concentrations of toxicant in the presence and absence of taurine (0-15 mm). The presence of taurine significantly decreased the cytotoxicity of each compound as measured by trypan blue uptake and lactate dehydrogenase leakage. The protection was related to the concentration of taurine, with a significant effect at 10 mm for all three compounds. When ATP was measured, however, taurine failed to protect against the depletion caused by hydrazine, whereas depletion due to 1,4-NQ was significantly ameliorated. The results suggest that taurine may protect cells from cytotoxicity as reflected by membrane damage but biochemical events underlying the toxicity, such as ATP depletion, may not be affected. Taurine may be a useful tool for the investigation of mechanisms of cytotoxicity.

An integrated functional genomic study of acute phenobarbital exposure in the rat

Background

Non-genotoxic carcinogens are notoriously difficult to identify as they do not damage DNA directly and have diverse modes of action, necessitating long term in vivo studies. The early effects of the classic rodent non-genotoxic hepatocarcinogen phenobarbital have been investigated in the Fisher rat using a combination of metabolomics and transcriptomics, to investige early stage mechanistic changes that are predictive of longer term pathology.

Results

Liver and blood plasma were profiled across 14 days, and multivariate statistics used to identify perturbed pathways. Both metabolomics and transcriptomics detected changes in the liver which were dose dependent, even after one day of exposure. Integration of the two datasets associated perturbations with specific pathways. Hepatic glycogen was decreased due to a decrease in synthesis, and plasma triglycerides were decreased due to an increase in fatty acid uptake by the liver. Hepatic succinate was increased and this was associated with increased heme biosynthesis. Glutathione synthesis was also increased, presumably in response to oxidative stress. Liquid Chromatography Mass Spectrometry demonstrated a remodeling of lipid species, possibly resulting from proliferation of the smooth endoplasmic reticulum.

Conclusions

The data fusion of metabolomic and transcriptomic changes proved to be a highly sensitive approach for monitoring early stage changes in altered hepatic metabolism, oxidative stress and cytochrome P450 induction simultaneously. This approach is particularly useful in interpreting changes in metabolites such as succinate which are hubs of metabolism.

Phenylacetylglycine, a putative biomarker of phospholipidosis: Its origins and relevance to phospholipid accumulation using amiodarone treated rats as a model

Amiodarone was given to male Sprague-Dawley rats at a dose of 150 mg kg(-1) day(-1) for 7 consecutive days to induce phospholipidosis in the lungs of treated rats. Amiodarone was given alone or concurrently with phenobarbitone. Animals given amiodarone had raised total phospholipid in serum, lung and lymphocytes, and elevated lyso(bis)phosphatidic acid (LBPA) in all tissues. Urinary and plasma phenylacetylglycine (PAG) and hepatic portal:aortal phenylacetate (PA) ratio were increased, whereas hepatic phenylalanine hydroxylase (PAH) activity and plasma phenylalanine:tyrosine ratio were not affected. Phenobarbitone treatment increased hepatic total P450 content and induced 7-pentoxyresorufin O-dealkylatian (PROD) activity, as expected, but had no effect on any other biochemical parameter. Plasma amiodarone concentration was reduced in rats co-administered both drugs and phospholipid accumulation in target tissues was attenuated compared with rats treated with amiodarone alone. However, phenobarbitone co-administration failed to alter the magnitude of response with regards to urinary PAG excretion and plasma concentration of its precursors after amiodarone treatment. Increased intestinal absorption of PAG precursors probably resulted in the raised urinary PAG after amiodarone treatment. Urinary PAG correlated weakly with serum, lymphocyte and lung phospholipids. However, urinary PAG excretion was similar in rats dosed solely with amiodarone or in combination with phenobarbitone, despite the fact that the degree of phospholipid accumulation was far less in rats given the combined treatment. Nevertheless, urinary PAG was raised only in animals exhibiting abnormal phospholipid accumulation in target tissues and may thus be useful as a surrogate biomarker for phospholipidosis.

Integrated metabonomic analysis of bromobenzene-induced hepatotoxicity: novel induction of 5-oxoprolinosis

We present here a definitive metabonomic analysis in order to detect novel biomarker and metabolite information, implicating specific putative protein targets in the toxicological mechanism of bromobenzene-induced centrilobular hepatic necrosis. Male Han-Wistar rats were dosed with bromobenzene (1.5 g/kg, n = 25) and blood plasma, urine and liver samples were collected for NMR and magic angle spinning (MAS) NMR spectroscopy at various time-points postdose, with histopathology and clinical pathology performed in parallel. Liver samples were analyzed by 600 MHz 1H MAS NMR techniques and the resultant spectra were correlated to sequential 1H NMR measurements in urine and blood plasma using pattern recognition methods. 1D 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by bromobenzene toxicity. In addition to a holistic view of the effect of hepatic toxicity on the metabolome, a number of putative protein targets of bromobenzene and its metabolites were identified including those enzymes of the glutathione cycle, exemplified by the presence of a novel biomarker, 5-oxoproline, in liver tissue, blood plasma, and urine. As such, this work establishes the importance of metabonomics technology in resolving the mechanistic complexity of drug toxicity as well as the benefits of frontloading this approach in drug safety evaluation and biomarker discovery.

Metabonomic deconvolution of embedded toxicity: application to thioacetamide hepato- and nephrotoxicity

We present here the potential of an integrated metabonomic strategy to deconvolute the biofluid metabolic signatures in experimental animals following multiple organ toxicities, using the well-known hepato- and nephrotoxin, thioacetamide. Male Han-Wistar rats were dosed with thioacetamide (150 mg/kg, n = 25), and urine, plasma, liver, and kidney samples were collected postdose for conventional NMR and magic angle spinning (MAS) NMR spectroscopy. These data were correlated with histopathology and plasma clinical chemistry collected at all time points. 1H MAS NMR data from liver and kidney were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. One-dimensional 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by thioacetamide toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra, and hence the combinations of endogenous metabolites marking the main phase of the toxic episode, were identified. The thioacetamide-induced biochemical manifestations included a renal and hepatic lipidosis accompanied by hypolipidaemia; increased urinary excretion of taurine and creatine concomitant with elevated creatine in liver, kidney, and plasma; a shift in energy metabolism characterized by depleted liver glucose and glycogen; reduced urinary excretion of tricarboxylic acid cycle intermediates and raised plasma ketone bodies; increased levels of tissue and plasma amino acids leading to amino aciduria verifying necrosis-enhanced protein degradation and renal dysfunction; and elevated hepatic and urinary bile acids indicating secondary damage to the biliary system. This integrated metabonomic approach has been able to identify the tissue of origin for biomarkers present in the metabolic profiles of biofluids, following the onset and progression of a multiorgan pathology, and as such highlights its potential in the evaluation of embedded toxicity in novel drug candidates.

Development of a multivariate statistical model to predict peroxisome proliferation in the rat, based on urinary 1H-NMR spectral patterns

A previous report of this work (Ringeissen et al. 2003) described the use of nuclear magnetic resonance (NMR) spectroscopy coupled with multivariate statistical data analysis (MVDA) to identify novel biomarkers of peroxisome proliferation (PP) in Wistar Han rats. Two potential biomarkers of peroxisome proliferation in the rat were described, N-methylnicotinamide (NMN) and N-methyl-4-pyridone-3-carboxamide (4PY). The inference from these results was that the tryptophan-nicotinamide adenine dinucleotide (NAD(+)) pathway was altered in correlation with peroxisome proliferation, a hypothesis subsequently confirmed by TaqMan analysis of the relevant genes encoding two key enzymes in the pathway, aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) and quinolinate phosphoribosyltransferase (EC 2.4.2.19). The objective of the present study was to investigate these data further and identify other metabolites in the NMR spectrum correlating equally with PP. MVDA Partial Least Squares (PLS) models were constructed that provided a better prediction of PP in Wistar Han rats than levels of 4PY and NMN alone. The resulting Wistar Han rat predictive models were then used to predict PP in a test group of Sprague Dawley rats following administration of fenofibrate. The models predicted the presence or absence of PP (above on arbitrary threshold of >2-fold mean control) in all Sprague Dawley rats in the test group.

Sexual dimorphism in urinary metabolite profiles of Han Wistar rats revealed by nuclear-magnetic-resonance-based metabonomics

Gender-dependent metabolic variation in Han Wistar rats (n=25 male and n=25 female) was investigated using (1)H nuclear magnetic resonance (NMR) spectroscopy of urine coupled with chemometric methods. Statistically discriminatory regions of the spectra for male and female rats were identified and biomarker characterization was achieved by the further application of solid-phase extraction chromatography with NMR detection and high-performance liquid chromatography mass spectrometry. A novel discriminating molecule was identified as the sulfate conjugate of m-hydroxyphenylpropionic acid, which was excreted in higher concentrations by male rats. Other gender-related metabolite differences in the urine profiles included higher levels of trimethylamine-N-oxide, N,N'-dimethylglycine, m-hydroxyphenylpropionic acid, N-acetylglycoprotein, and cholate in samples from female animals. These studies emphasize the utility of multicomponent metabolic profiling for investigating physiological and genetic variation in experimental animals that may be of relevance to their use as models of toxicity and disease.

Effects of feeding and body weight loss on the 1H-NMR-based urine metabolic profiles of male Wistar Han rats: implications for biomarker discovery

For almost two decades, 1H-NMR spectroscopy has been used as an 'open' system to study the temporal changes in the biochemical composition of biofluids, including urine, in response to adverse toxic events. Many of these in vivo studies have reported changes in individual metabolites and patterns of metabolites that correlated with toxicological changes. However, many of the proposed novel biomarkers are common to a number of different types of toxicity. These may therefore reflect non-specific effects of toxicity, such as weight loss, rather than a specific pathology. A study was carried out to investigate the non-specific effects on urinary metabolite profiles by administering four hepatotoxic compounds, as a single dose, to rats at two dose levels: hydrazine hydrate (0.06 or 0.08 g kg (1)), 1,2-dimethylhydrazine (0.1 or 0.3 g kg (-1)), alpha-napthylisothiocyanate (0.1 or 0.15 g kg(-1)) and carbon tetrachloride (1.58 or 3.16 g kg(-1)). The study included weight-matched control animals along with those that were dosed, which were then 'pair-fed' with the treated animals so they achieved a similar weight loss. The urinary metabolite profiles were investigated over time using 1H-NMR spectroscopy and compared with the pathology from the same animals. The temporal changes were analysed statistically using multivariate statistical data analysis including principal component analysis, partial least squares, parallel factor analysis and Fisher's criteria. A number of metabolites associated with energy metabolism or which are partially dietary in origin, such as creatine, creatinine, tricarboxylic acid (TCA) cycle intermediates, phenylacetylglycine, fumarate, glucose, taurine, fatty acids and N-methylnicotinamide, showed altered levels in the urine of treated and pair-fed animals. Many of these changes correlated well with weight loss. Interestingly, there was no increase in ketone bodies (acetate and beta-hydroxybutyrate), which might be expected if energy metabolism was switched from glycolysis to fatty acid beta-oxidation. In some instances, the metabolites that changed were considered to be non-specific markers of toxicity, but were also identified as markers of a specific type of toxicity. For example, taurine was raised significantly in carbon tetrachloride-treated animals but reduced in the pair-fed group. However, raised urinary bile acid levels were only seen after alpha-napthylisothiocyanate treatment. The methodology, statistical analysis used and the data generated will help improve the identification of specific markers or patterns of urinary markers of specific toxic effects.

Tryptophan-NAD+ pathway metabolites as putative biomarkers and predictors of peroxisome proliferation

The present study was designed to provide further information about the relevance of raised urinary levels of N-methylnicotinamide (NMN), and/or its metabolites N-methyl-4-pyridone-3-carboxamide (4PY) and N-methyl-2-pyridone-3-carboxamide (2PY), to peroxisome proliferation by dosing rats with known peroxisome proliferator-activated receptor alpha (PPARalpha) ligands [fenofibrate, diethylhexylphthalate (DEHP) and long-chain fatty acids (LCFA)] and other compounds believed to modulate lipid metabolism via PPARalpha-independent mechanisms (simvastatin, hydrazine and chlorpromazine). Urinary NMN was correlated with standard markers of peroxisome proliferation and serum lipid parameters with the aim of establishing whether urinary NMN could be used as a biomarker for peroxisome proliferation in the rat. Data from this study were also used to validate a previously constructed multivariate statistical model of peroxisome proliferation (PP) in the rat. The predictive model, based on 1H nuclear magnetic resonance (NMR) spectroscopy of urine, uses spectral patterns of NMN, 4PY and other endogenous metabolites to predict hepatocellular peroxisome count. Each treatment induced pharmacological (serum lipid) effects characteristic of their class, but only fenofibrate, DEHP and simvastatin increased peroxisome number and raised urinary NMN, 2PY and 4PY, with simvastatin having only a transient effect on the latter. These compounds also reduced mRNA expression for aminocarboxymuconate-semialdehyde decarboxylase (ACMSDase, EC 4.1.1.45), the enzyme believed to be involved in modulating the flux of tryptophan through this pathway, with decreasing order of potency, fenofibrate (-10.39-fold) >DEHP (-3.09-fold) >simvastatin (-1.84-fold). Of the other treatments, only LCFA influenced mRNA expression of ACMSDase (-3.62-fold reduction) and quinolinate phosphoribosyltransferase (QAPRTase, EC 2.4.2.19) (-2.42-fold) without any change in urinary NMN excretion. Although there were no correlations between urinary NMN concentration and serum lipid parameters, NMN did correlate with peroxisome count (r2=0.63) and acyl-CoA oxidase activity (r2=0.61). These correlations were biased by the large response to fenofibrate compared to the other treatments; nevertheless the data do indicate a relationship between the tryptophan-NAD+ pathway and PPARalpha-dependent pathways, making this metabolite a potentially useful biomarker to detect PP. In order to strengthen the observed link between the metabolites associated with the tryptophan-NAD+ pathway and more accurately predict PP, other urinary metabolites were included in a predictive statistical model. This statistical model was found to predict the observed PP in 26/27 instances using a pre-determined threshold of 2-fold mean control peroxisome count. The model also predicted a time-dependent increase in peroxisome count for the fenofibrate group, which is important when considering the use of such modelling to predict the onset and progression of PP prior to its observation in samples taken at autopsy.

Potential urinary and plasma biomarkers of peroxisome proliferation in the rat: identification of N-methylnicotinamide and N-methyl-4-pyridone-3-carboxamide by 1H nuclear magnetic resonance and high performance liquid chromatography

This study identified two potential novel biomarkers of peroxisome proliferation in the rat. Three peroxisome proliferator-activated receptor (PPAR) ligands, chosen for their high selectivity towards the PPARalpha, -delta and -gamma subtypes, were given to rats twice daily for 7 days at doses known to cause a pharmacological effect or peroxisome proliferation. Fenofibrate was used as a positive control. Daily treatment with the PPARalpha and -delta agonists produced peroxisome proliferation and liver hypertrophy. 1H nuclear magnetic resonance spectroscopy and multivariate statistical data analysis of urinary spectra from animals given the PPARalpha and -delta agonists identified two new potential biomarkers of peroxisome proliferation--N-methylnicotinamide (NMN) and N-methyl-4-pyridone-3-carboxamide (4PY)--both endproducts of the tryptophan-nicotinamide adenine dinucleotide (NAD+) pathway. After 7 days, excretion of NMN and 4PY increased 24- and three-fold, respectively, following high doses of fenofibrate. The correlation between total NMN excretion over 7 days and the peroxisome count was r=0.87 (r2=0.76). Plasma NMN, measured using a sensitive high performance liquid chromatography method, was increased up to 61-fold after 7 days' treatment with high doses of fenofibrate. Hepatic gene expression of aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) was downregulated following treatment with the PPARalpha and -delta agonists. The decrease was up to 11-fold compared with controls in the groups treated with high doses of fenofibrate. This supports the link between increased NMN and 4PY excretion and regulation of the tryptophan-NAD+ pathway in the liver. In conclusion, NMN, and possibly other metabolites in the pathway, are potential non-invasive surrogate biomarkers of peroxisome proliferation in the rat.

Characterisation of a potential biomarker of phospholipidosis from amiodarone-treated rats

A novel and relatively simple analytical method for the separation, characterisation and semi-quantitation of phospholipids (PLs) from extracts of complex biological samples has been developed. This methodology allows PL extracts from cells and tissues to be analysed by liquid chromatography (LC) coupled to electrospray ionisation mass spectrometry (ESI-MS). Complex mixtures of PLs were separated on a high-performance liquid chromatography (HPLC) system using 0.5% ammonium hydroxide in methanol/water/hexane/formate mixture with UV detection at 205 nm. Identification and structural characterisation of molecular species were carried out utilising ESI-MS and MS/MS in the negative ion mode. The abnormal accumulation of PLs (phospholipidosis) was induced in male Sprague-Dawley rats by administration of the cationic amphiphilic drug (CAD), amiodarone. Analysis of the PL profile of liver and lung tissues, lymphocytes and serum from treated rats was carried out using this analytical procedure (LC-ESI/MS/MS). Differences in PL profiles between treated and untreated animals were highlighted by principal component analysis (PCA). This led to the selection of a potential metabolic marker of phospholipidosis (PLD) identified as a lyso-bis-phosphatidic acid (LBPA) derivative, also known as bis(monoglycero)phosphate (BMP). This PL was absent in control animals but was present in quantifiable amounts in all samples from amiodarone-treated rats.

Optimisation of collection, storage and preparation of rat plasma for 1H NMR spectroscopic analysis in toxicology studies to determine inherent variation in biochemical profiles

Biofluid 1H NMR spectroscopy has been assessed as a tool for toxicological investigations for almost two decades, with most studies focussing on urinary changes. This study has examined variations in the 1H NMR spectroscopy spectra of plasma collected from control rats at different times of the day. The collection, preparation and storage of samples were optimised and potential sources of variation in samples taken for toxicology studies identified. Plasma samples were collected into heparinised containers and analysed following a standard dilution with D(2)O. The value of deproteinising plasma with acetonitrile to look at low molecular weight metabolites has also been assessed. Variations in lactate and citrate levels in whole blood plasma were found and are consistent with the observation that lactate is one of the most variable metabolites in human plasma. Lipids levels also varied, in particular higher levels of lipids were found in spectra from male rats compared to female rats, and in samples collected in the morning following the feeding period. No significant changes were identified in samples which were snap-frozen and stored for up to 9 months at -80 degrees C. More changes were observed after storage at 4 degrees C or room temperature, including an increase in glycerol and choline levels, which may have resulted from lipid hydrolysis.

NMR and pattern recognition studies on liver extracts and intact livers from rats treated with alpha-naphthylisothiocyanate

The metabolite profiles from livers of toxin-treated rats were investigated using high resolution 1H NMR spectroscopy of aqueous (acetonitrile/water), lipidic (chloroform/methanol) extracts and magic angle spinning (MAS)-NMR spectroscopy of intact tissue. Rats were treated with the model cholestatic hepatotoxin, alpha-naphthylisothiocyanate (ANIT, 150 mg/kg) and NMR spectra of liver were analysed using principal components analysis (PCA) to extract novel toxicity biomarker information. 1H NMR spectra of control aqueous extracts showed signals from a range of organic acids and bases, amino acids, sugars, and glycogen. Chloroform/methanol extracts showed signals from a range of saturated and unsaturated triglycerides, phospholipids and cholesterol. The MAS 1H NMR spectra of livers showed a composite of signals found in both aqueous and lipophilic extracts. Following ANIT treatment, 1H NMR-PCA of aqueous extracts indicated a progressive reduction in glucose and glycogen, together with increases in bile acid, choline, and phosphocholine signals. 1H NMR-PCA of chloroform/methanol extracts showed elevated triglyceride levels. The 1H MAS-NMR-PCA analysis allowed direct detection of all of the ANIT-induced tissue perturbations revealed by 1H NMR of extracts, enabling metabolic characterisation of the lesion, which included steatosis, bile duct obstruction and altered glucose/glycogen metabolism. MAS-NMR spectroscopy requires minimal sample preparation and, unlike 1H NMR spectroscopy of tissue extracts, does not discriminate metabolites based on their solubility in a particular solvent and so this is a particularly useful exploratory tool in biochemical toxicology.

Methionine synthase activity and sulphur amino acid levels in the rat liver tumour cells HTC and Phi-1

Methionine dependence has been reported in tumour cells and suggested as a possible target for chemotherapeutic drugs. The underlying defect has not been extensively researched, nor have levels of sulphur amino acids been examined in these cells. This study compared two rat liver tumour cell lines. One was found to be methionine dependent (HTC) and the other found to be methionine independent (Phi-1). The methionine-dependent cell line (HTC) was discovered to contain markedly less methionine synthase activity, the enzyme activity being less responsive to methionine concentration than in the methionine-independent cells (Phi-1). HTC cells had lower cysteine requirements and contained larger concentrations of reduced glutathione (GSH) and taurine than the Phi-1 cells. Also, in contrast to Phi-1 cells, no glutathione was found in the media of the HTC cells, although large quantities of cysteinylglycine were detected. These results suggested that differences in methionine synthase activity might be partly responsible for methionine dependence and that methionine-dependent cells may have different metabolic requirements for other sulphur amino acids.

NMR and pattern recognition studies on the time-related metabolic effects of alpha-naphthylisothiocyanate on liver, urine, and plasma in the rat: an integrative metabonomic approach

We present here a novel integrative metabonomic approach to probe toxic effects of drugs in experimental animals using alpha-naphthylisothiocyanate (ANIT) as a model hepatotoxicant. Male Han-Wistar rats were dosed with ANIT (150 mg/kg, n = 25), and plasma and liver samples were collected for NMR and magic-angle spinning (MAS) NMR spectroscopy at 3, 7, 24, 31, and 168 h postdosing. Urine was collected continuously for 3 days prior to dosing and up to 168 h postdose. Histopathology and plasma clinical chemistry was also performed at all time points. Liver samples were analyzed either intact by 600 MHz 1H MAS NMR techniques or using high resolution (liquid state) 1H NMR of water-acetonitrile extracts. These data were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. 1D 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by ANIT toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra and hence the combinations of endogenous metabolites marking the main phase of the toxic episode were identified. The ANIT-induced biochemical manifestations included a hepatic lipidosis associated with hyperlipidaemia; hyperglycaemia and glycosuria; increased urinary excretion of taurine and creatine; a shift in energy metabolism characterized by increased plasma ketone bodies with reduced urinary excretion of tricarboxylic acid cycle intermediates and raised hepatic bile acids leading to bile aciduria. The integration of metabolic data derived from several sources gives a holistic approach to the study of time-related toxic effects in the intact system and enables the characterization of key metabolic effects during the development and recovery from a toxic lesion.

Metabonomic investigations into hydrazine toxicity in the rat

The systemic biochemical effects of oral hydrazine administration (dosed at 75, 90, and 120 mg/kg) have been investigated in male Han Wistar rats using metabonomic analysis of (1)H NMR spectra of urine and plasma, conventional clinical chemistry, and liver histopathology. Plasma samples were collected both pre- and 24 h postdose, while urine was collected predose and daily over a 7 day postdose period. (1)H NMR spectra of the biofluids were analyzed visually and via pattern recognition using principal component analysis. The latter showed that there was a dose-dependent biochemical effect of hydrazine treatment on the levels of a range of low molecular weight compounds in urine and plasma, which was correlated with the severity of the hydrazine induced liver lesions. In plasma, increases in the levels of free glycine, alanine, isoleucine, valine, lysine, arginine, tyrosine, citrulline, 3-D-hydroxybutyrate, creatine, histidine, and threonine were observed. Urinary excretion of hippurate, citrate, succinate, 2-oxoglutarate, trimethylamine-N-oxide, fumarate and creatinine were decreased following hydrazine dosing, whereas taurine, creatine, threonine, N-methylnicotinic acid, tyrosine, beta-alanine, citrulline, Nalpha-acetylcitrulline and argininosuccinate excretion was increased. Moreover, the most notable effect was the appearance in urine and plasma of 2-aminoadipate, which has previously been shown to lead to neurological effects in rats. High urinary levels of 2-aminoadipate may explain the hitherto poorly understood neurological effects of hydrazine. Metabonomic analysis of high-resolution (1)H NMR spectra of biofluids has provided a means of monitoring the progression of toxicity and recovery, while also allowing the identification of novel biomarkers of development and regression of the lesion.

The effect of taurine depletion by beta-alanine treatment on the susceptibility to ethanol-induced hepatic dysfunction in rats

Alcohol was administered chronically to female Sprague-Dawley rats in a nutritionally adequate totally liquid diet for 28 days. This resulted in significant hepatic steatosis and lipid peroxidation. Beta-alanine, when co-administered with alcohol, seemed to increase hepatic steatosis, as assessed histologically, but decreased triglyceride levels as measured biochemically. In addition, beta-alanine and especially alcohol co-administered with beta-alanine, significantly increased homocysteine and cysteine excretion into urine throughout the 28-day period of ethanol administration. Serum homocysteine levels were significantly higher in alcohol- and alcohol plus beta-alanine-treated animals compared to pair-fed control animals. Alcohol did not affect the urinary excretion of taurine, except after 21 days, when levels were reduced. Levels of liver taurine were markedly depleted in animals receiving alcohol and particularly alcohol plus beta-alanine, compared to pair-fed controls. Liver and serum taurine levels were also markedly depleted in animals receiving beta-alanine and alcohol plus beta-alanine, compared to non-beta-alanine-treated animals. There was evidence of slight cholestasis in animals treated with alcohol and more so with alcohol plus beta-alanine, as indicated by raised serum alkaline phosphatase and bile acids. These in vivo findings demonstrate for the first time that animals treated with beta-alanine may be more susceptible to ethanol-induced hepatic dysfunction, possibly as a result of taurine depletion.

Reversal of ethanol-induced hepatic steatosis and lipid peroxidation by taurine: a study in rats

Alcohol (ethanol) was administered chronically to female Sprague-Dawley rats in a nutritionally adequate, totally liquid diet for 28 days. This resulted in significant hepatic steatosis and lipid peroxidation. When taurine was administered for 2 days following alcohol withdrawal it was found to reduce alcohol-induced lipid peroxidation and completely reversed hepatic steatosis. The reversal of hepatic steatosis was demonstrated both biochemically and histologically. Two days following alcohol withdrawal, the apparent activity of the alcohol-inducible form of cytochrome P450 (CYP2E1) was unchanged although total cytochrome P450 content was increased. In addition, alcohol significantly inhibited hepatic methionine synthase activity and increased homocysteine excretion in urine. Although alcohol did not affect the urinary excretion of taurine (a non-invasive marker of liver damage), levels of serum and hepatic taurine were markedly raised in animals given taurine following their treatment with alcohol, compared to animals given taurine alone. There was evidence of slight bile duct injury in animals treated with alcohol and with alcohol followed by taurine, as indicated by raised serum alkaline phosphatase (ALP) and cholesterol. Aspartate aminotransferase (AST) was also slightly raised. The effects of taurine on reversing hepatic steatosis may be due to the enhanced secretion of hepatic triglycerides. It is suggested that increased bile flow as a result of taurine treatment may have contributed to the removal of lipid peroxides. These in-vivo findings demonstrate for the first time that hepatic steatosis and lipid peroxidation, occurring as a result of chronic alcohol consumption, can be reversed by administration of taurine to rats for 2 days.

Effect of hydrazine upon vitamin B12-dependent methionine synthase activity and the sulphur amino acid pathway in isolated rat hepatocytes

The effect of the industrial chemical, hydrazine (4-12 mM), on methionine synthase (EC 2.1.1.13) activity and levels of the sulphur amino acids homocysteine, cysteine, and taurine as well as GSH were investigated in vitro in isolated rat hepatocyte suspensions and monolayers in order to explain some of the adverse in vivo effects of hydrazine. None of the concentrations of hydrazine were overtly cytotoxic in hepatocyte suspensions (measured as lactate dehydrogenase [LDH] leakage) after 3 hr. However, after 24 hr in culture cells treated with 12 mM, hydrazine showed a significant increase in LDH leakage. Methionine synthase activity was reduced by hydrazine (8 and 12 mM) in suspensions (by 45 and 55%, after 3 hr) and monolayers (12 mM; 65-80% after 24 hr). This was not due to nitric oxide production and the inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine, failed to protect against the hydrazine-induced loss of ATP and GSH and the reduction in urea synthesis at 24 hr. Homocysteine export was increased by 6 mM hydrazine, and total taurine content of treated cells was increased by 12 mM hydrazine. Thus, hydrazine was found to have several important and possibly deleterious effects on some parts of the sulphur amino acid pathway.

The effects of the beta 2-agonist drug clenbuterol on taurine levels in heart and other tissues in the rat

The administration of a single subcutaneous dose of clenbuterol to rats altered the level of taurine in certain tissues. Taurine levels in cardiac tissue were significantly decreased 3 h after the administration of 250 micrograms/kg of clenbuterol and remained significantly depressed at 12 h post-dose only returning to control values by 24 h. The level of taurine in the liver increased 3 h after clenbuterol administration but was lower than the control value at 24 h post dose. Lung taurine levels were significantly lower than the control value at 12 hr post dose and remained depressed until 24 h post dose. Clenbuterol caused a significant increase in taurine levels in serum and muscle at 3 and 6 hr postdosing respectively but not at other time points. Serum creatine kinase (CK), activity was slightly but significantly raised at the 12 and 24 h time point. The effects of clenbuterol on tissue taurine content were not dose-dependent over the range studied (63-500 micrograms/kg). However taurine levels in the lung were significantly reduced at all doses and in the heart were significantly lower in the treated groups at all except the lowest dose, 12 h post dosing. Liver taurine levels were significantly increased at the highest dose of 500 micrograms/kg. The reduction of taurine concentrations in the heart, caused by clenbuterol, is of concern as taurine has been shown to have protective properties in many tissues especially the heart.

Is there a correlation between taurine levels and xenobiotic-induced perturbations in protein synthesis?: a study with tetracycline in rats

Changes in urinary levels of taurine have been reported in rats following treatment with various xenobiotics including those which alter protein synthesis and/or are hepatotoxic. This paper reports on the time course of the urinary elevation of taurine following treatment of rats with tetracycline (50, 150 and 200 mg.kg-1). Maximum taurine excretion occurred 8-12 h following dosing. Serum albumin and total protein were significantly lower after 24 h (200 mg.kg-1). The increase in urinary taurine was dose-related and reflected in the raised serum levels of taurine 24 h after dosing. Serum and urinary protein and [3H]-leucine incorporation into acid precipitable protein in liver and muscle were reduced by tetracycline (100, 150 and 200 mg.kg-1) 10 h after dosing. The reduction in protein synthesis was correlated with increased urinary and serum levels of taurine at 10 h. The use of taurine as a non-invasive marker of protein synthesis is discussed.

Taurine: protective properties against ethanol-induced hepatic steatosis and lipid peroxidation during chronic ethanol consumption in rats

Alcohol was administered chronically to female Sprague Dawley rats in a nutritionally adequate totally liquid diet for 28 days. This resulted in hepatic steatosis and lipid peroxidation. Taurine, when co-administered with alcohol, reduced the hepatic steatosis and completely prevented lipid peroxidation. The protective properties of taurine in preventing fatty liver were also demonstrated histologically. Although alcohol was found not to affect the urinary excretion of taurine (a non-invasive marker of liver damage), levels of serum and liver taurine were markedly raised in animals receiving alcohol + taurine compared to animals given taurine alone. The ethanol-inducible form of cytochrome P-450 (CYP2E1) was significantly induced by alcohol; the activity was significantly lower than controls and barely detectable in animals fed the liquid alcohol diet containing taurine. In addition, alcohol significantly increased homocysteine excretion into urine throughout the 28 day period of ethanol administration; however, taurine did not prevent this increase. There was evidence of slight cholestasis in animals treated with alcohol and alcohol + taurine, as indicated by raised serum bile acids and alkaline phosphatase (ALP). The protective effects of taurine were attributed to the potential of bile acids, especially taurine conjugated bile acids (taurocholic acid) to inhibit the activity of some microsomal enzymes (CYP2E1). These in vivo findings demonstrate for the first time that hepatic steatosis and lipid peroxidation, occurring as a result of chronic alcohol consumption, can be ameliorated by administration of taurine to rats.

Ethionine toxicity in vitro: the correlation of data from rat hepatocyte suspensions and monolayers with in vivo observations

The hepato-steatogenic compound ethionine has been used to investigate the correlations between in vivo and in vitro toxicity data. The aim was to find a suitable model of toxicity in hepatocyte suspensions or monolayers in vitro, which could predict the known toxicity of ethionine in vivo and which could be implemented in screening compounds of unknown toxicity. Thus a variety of markers of cytotoxicity, metabolic competence and liver-specific functions were investigated in rat hepatocyte suspensions and monolayers and compared with in vivo data in the rat. The following markers were measured in the appropriate system: (1) Neutral red uptake; 3-(4,5 dimethyl)thiazol-2-yl,-2,5-diphenyl tetrazolium bromide (MTT) reduction; lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) leakage (cytotoxicity). (2) ATP levels, protein synthesis and glutathione (GSH) levels (metabolic competence). (3) Urea and triglyceride synthesis and beta-oxidation (liver specific functions). Ethionine (0-30 mM) did not affect the markers of direct cytotoxicity, except neutral red uptake, which was reduced by 18 and 30 mM ethionine after 20 h in culture. ATP and GSH depletion occurred in hepatocyte suspensions at the highest concentrations of ethionine (20 and 30 mM) after 1 h. In monolayers, GSH levels were reduced after 4 h, but not 20 h. Urea synthesis was increased in hepatocyte suspensions from 1 to 3 h by 10-30 mM ethionine and reduced after 20 h in cultured hepatocytes (18-30 mM). Protein synthesis was reduced and beta-oxidation was increased in ethionine-treated hepatocyte suspensions. Unfortunately, there was no measurable effect on triglyceride accumulation within cells (the major biochemical change in vivo) in either system. Ethionine treated hepatocytes in suspension showed the same rate of triglyceride synthesis and transportation out of cells as control cells. Thus, hepatocyte suspensions were able to mimic the early biochemical effects of ethionine in vivo (ATP and GSH depletion, inhibition of protein synthesis) and some effects on urea synthesis, but monolayer cultures appeared to be less sensitive to the toxicity of ethionine. However, neither in vitro system was able to model the effects of ethionine on the accumulation of triglycerides in vivo.

Triglyceride disposition in isolated hepatocytes after treatment with hydrazine

Treatment of animals with hydrazine causes the accumulation of triglycerides in the liver but the mechanism remains unclear. Therefore, the effect of hydrazine on hepatic triglyceride synthesis and subsequent transport was studied in a hepatocyte model, in vitro in order to isolate liver cells from extrahepatic influences. Hepatocytes were isolated and either incubated in suspension with [14C]palmitate in the presence of hydrazine (2-12 mM) or pre-incubated with [14C]palmitate, washed free of the fatty acid and then incubated with hydrazine (2-12 mM). Hydrazine resulted in a significant reduction in the incorporation of [14C]palmitate into triglycerides and reduction in the transportation of triglycerides out of cells. When [14C]palmitate was in the incubation medium, ATP levels were reduced by lower concentrations of hydrazine than have previously been reported. None of the concentrations of hydrazine used affected cell membrane integrity (viability) as measured by LDH leakage. The 14CO2 produced by the beta-oxidation of [14C]palmitate was also measured in short term incubations (30 min) carried out in sealed vessels. There was a dose dependent increase in 14CO2 produced by very low concentrations of hydrazine (0.01-0.1 mM) after which the effect was maximal and concentrations above 8 mM hydrazine decreased 14CO2 production. The data suggest that the inhibition of transportation of triglycerides out of cells by hydrazine may have a more important role in the accumulation of triglycerides in the liver than has been previously recognised. However, the model was not able to mimic the accumulation of triglycerides in hepatocytes seen in vivo.

The inactivation of methionine synthase in isolated rat hepatocytes by sodium nitroprusside

Methionine synthase, the enzyme that catalyses the transfer of a methyl group from 5-methyl tetrahydrofolate to homocysteine via the cofactor methylcobalamin, is one of the two established mammalian enzymes that utilise a biologically active vitamin B-12 derivative. Through its substrates, products and downstream metabolites, methionine synthase is directly involved in the sulphur amino acid pathways, polyamine biosynthesis, biological methylations and one-carbon-unit transfers. Rat liver methionine synthase was shown to be inactivated by the nitric oxide donor sodium nitroprusside. The inactivation occurred during the treatment of isolated rat hepatocytes in a time-dependent and dose-dependent manner with an apparent IC50 value of 170 microM. Highly purified rat liver methionine synthase was inactivated in a partially irreversible manner with an apparent IC50 value of 10 microM. The inactivation has been attributed to nitric oxide released by sodium nitroprusside. Since biomolecules possessing transition state metals are targets for nitric oxide, the possibility of a nitric oxide-cobalamin interaction could explain the observed inactivation. Nitric oxide is directly involved in different aspects of liver metabolic functions both under physiological and pathological conditions like sepsis and inflammation. The nitric-oxide-induced inactivation of methionine synthase could offer a rational explanation for the cellular and cytotoxic effects of this highly reactive molecule.

Effect of treatment with beta-agonists on tissue and urinary taurine levels in rats. Mechanism and implications for protection

Administration of clenbuterol to rats in the drinking water over a four day period increased incorporation of [3H]leucine into muscle protein but did not result in an increase in body or muscle weight. However, both urinary and liver taurine were significantly reduced at the highest dose of clenbuterol (2 mg.kg-1.day-1). Salbutamol also reduced urinary levels of taurine in both rats and humans. The reduction in the body pool of taurine caused by beta-agonists may be of concern as taurine has been shown to have protective properties.

Changes in taurine as an indicator of hepatic dysfunction and biochemical perturbations. Studies in vivo and in vitro

We have shown that urinary taurine level may be used as a biomarker of pathological and biochemical lesions. Detection of changes in the urinary concentration of this low molecular weight metabolite indicates biochemical lesions which may also be associated with pathological damage. Hepatotoxic compounds such as CCl4, galactosamine and thioacetamide that cause hepatic necrosis and compounds such as hydrazine and ethionine that cause fatty liver all result in elevated urinary taurine levels in rats. However compounds which do not cause liver damage, such as cycloheximide, also raise urinary taurine levels. All of these substances are known to or are believed to inhibit protein synthesis. Conversely, compounds which increase protein synthesis, such as phenobarbital and clenbuterol, significantly decrease urinary taurine levels. Compounds which interfere with hepatic GSH synthesis will also change urinary taurine levels. Thus, depletion of GSH with diethyl maleate or phorone decreases urinary taurine whereas inhibition of GSH synthesis with compounds such as buthionine sulphoximine increases urinary taurine levels. In isolated hepatocytes in vitro, leakage of taurine occurs in response to cytotoxic compounds such as hydrazine and allyl alcohol. However, total taurine levels were increased by the hepatotoxicant CCl4. Taurine synthesis is decreased by depletion of GSH with allyl alcohol in isolated hepatocytes. Therefore taurine levels are an important potential biomarker for biochemical lesions induced by chemicals both in vivo and in vitro, in particular changes in protein and GSH synthesis.

The biochemical effects of clenbuterol: with particular reference to taurine and muscle damage

Administration of clenbuterol to rats in the drinking water over a 4 day period increased incorporation of [3H]leucine into muscle protein and caused a slight reduction in urinary 3-methylhistidine but did not result in an increase in body or muscle weight. However, both urinary and liver taurine were significantly reduced at the highest dose of clenbuterol (2 mg.kg-1.day-1). Serum creatine kinase, muscle isoenzyme (CK-MM) was raised and single muscle fibre injury was observed in the soleus muscle in animals treated with the middle dose (0.2 mg.kg-1.day-1) and highest dose (2 mg.kg-1.day-1). The reduction in the body pool of taurine caused by clenbuterol is of concern as taurine has been shown to have protective properties.

The in vivo and in vitro protective properties of taurine

1. Taurine is a ubiquitous, free amino acid found in mammalian systems. 2. The biological functions of taurine are unclear. 3. Various in vivo data suggest that taurine has a variety of protective functions and deficiency leads to pathological changes. 4. Depletion in rats of taurine increases susceptibility to liver damage from carbon tetrachloride. 5. Susceptibility to a variety of hepatotoxicants correlates with the estimated hepatic taurine level. 6. In vitro data suggest that taurine can protect cells against toxic damage. 7. Taurine protects isolated hepatocytes against carbon tetrachloride, hydrazine and 1,4-naphthoquinone but not against allyl alcohol, alpha-naphthylisothiocyanate (ANIT) or diaminodiphenyl methane (DAPM) cytotoxicity. 8. The mechanisms of protection are unclear but may include modulation of calcium levels, osmoregulation and membrane stabilization.

Studies on the muscle toxicant 2,3,5,6-tetramethyl p-phenylenediamine: effects on various biomarkers including urinary creatine and taurine

The effect of the specific muscle toxicant, 2,3,5,6-tetramethyl p-phenylenediamine (TMPD), on urinary creatine and taurine, markers of testicular and liver dysfunction, respectively, has been investigated in male Sprague-Dawley rats. Damage to the gastrocnemius and soleus muscles was accompanied by a rise in serum creatine kinase (predominantly the muscle-specific isoenzyme, CK-MM), alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Increases in serum alpha-hydroxybutyrate dehydrogenase (HBDH) and total lactate dehydrogenase (LDH) (mainly isoenzymes, LDH1 and LDH2), occurred but only minor damage to the heart and no rise in CK-MB, (heart muscle isoenzyme) was seen. Damage to stage XIV tubules in the testis was evident histologically after the highest dose. This was accompanied by an increase in LDH-C4 testis-specific isoenzyme and a decrease in serum testosterone. Apart from reduced serum albumin, no other serum parameters indicated liver damage and there was only slight liver steatosis in some animals at the highest dose. Urinary taurine was not significantly raised after any dose of TMPD, but there was a significant increase in urinary creatine after the highest dose. It can be concluded that in the presence of discrete muscle damage, the use of urinary taurine and urinary creatine as markers of liver and testicular dysfunction, respectively, is not confounded. However, a variety of different markers should be used in conjunction to fully delineate the tissue damage due to toxic chemicals.

Determination of taurine in biological samples and isolated hepatocytes by high-performance liquid chromatography with fluorimetric detection

A high-performance liquid chromatographic method with fluorimetric detection is described for the routine and selective determination of taurine in urine, serum, tissues and isolated hepatocytes. The preparation and use of ion-exchange resins to extract taurine from biological samples is included. Taurine was derivatised with o-phthalaldehyde/2-mercaptoethanol prior to injection onto a C18 column (LiChrospherR 100 RP-18, 5 microns, 125 x 4 mm I.D.). Isocratic elution of the adduct was carried out using NaH2PO4 (0.05 M, pH 5.4) in methanol and water (43:57, v/v). Homoserine was used as an internal standard to facilitate the standardisation and quantitation of samples and analysis was completed in 6 min with homoserine and taurine eluting after 3 and 4 min, respectively. The method will detect 0.5 pmol of taurine on the column. Appropriate dilutions of these biological samples enable these samples to be assayed on an autosampler, using the same standard curve. Concentrations of taurine in human, dog and rat urine, rat liver, serum and isolated hepatocytes are reported.

Taurine protects against the cytotoxicity of hydrazine, 1,4-naphthoquinone and carbon tetrachloride in isolated rat hepatocytes

Exposure of rat hepatocytes to hydrazine, carbon tetrachloride or 1,4-naphthoquinone results in cytotoxicity determined as uptake of Trypan blue and leakage of lactate dehydrogenase (LDH). After exposure of hepatocytes to hydrazine and 1,4-naphthoquinone, ATP was also measured and was found to be depleted. Addition of the beta-amino acid taurine to the hepatocyte incubation buffer partially protects the cells against the cytotoxicity of these three different cytotoxic compounds, as indicated by Trypan blue uptake and LDH leakage. Taurine also reduces the depletion of ATP caused by 1,4-naphthoquinone but not hydrazine. It is suggested that taurine may have a cytoprotective effect in vitro and may be a useful tool for the investigation of mechanisms of cytotoxicity.

Effect of various non-hepatotoxic compounds on urinary and liver taurine levels in rats

Administration of compounds which alter protein synthesis or sulphur amino acid metabolism in rats results in changes in the excretion of urinary taurine. Treatment with diethylmaleate (DEM) or phorone, which will deplete glutathione (GSH), reduces taurine excretion, whereas treatment with buthionine sulphoximine (BSO), which will inhibit glutathione synthesis, increases taurine excretion. Treatment with cycloheximide, an inhibitor of protein synthesis, increases taurine excretion, whereas pretreatment with phenobarbital, which will increase protein synthesis, decreases taurine excretion. Administration of agents which damage organs other than the liver such as the kidney, heart and testes, does not increase urinary taurine.

Investigations into the effects of various hepatotoxic compounds on urinary and liver taurine levels in rats

The effect of various hepatotoxicants on urinary taurine and urinary creatine has been studied in the rat. Several hepatotoxic agents, carbon tetrachloride, thioacetamide, galactosamine and allyl alcohol which all caused hepatic necrosis (sometimes accompanied by steatosis), resulted in a rise in urinary taurine and in some cases creatine, when administered to rats. Ethionine and hydrazine also raised urinary taurine but caused only steatosis and did not raise urinary creatine. Therefore urinary taurine and possibly creatine may be useful markers of liver injury and dysfunction. Liver taurine levels were also affected by some of the hepatotoxicants but in those cases where there was a rise in urinary taurine this could not be accounted for by the loss in liver taurine. It is suggested that the increase in urinary taurine is partly due to changes in protein synthesis and hence in sulphur amino acid metabolism caused by hepatotoxic agents. However, bromobenzene did not increase urinary taurine and alpha-naphthylisothiocyanate and lithocholate caused reduced levels. It is suggested that this lack of increase in urinary taurine may be due to depletion of glutathione or interference with the biliary system.

The correlation between urinary and liver taurine levels and between pre-dose urinary taurine and liver damage

Analysis of data from several studies has shown that urinary taurine levels are highly significantly correlated with liver taurine concentration in control rats. Furthermore, urinary taurine levels measured before dosing with various hepatotoxic agents are significantly correlated with serum AST and ALT values measured after dosing with hepatotoxicants. That is, animals with low urinary taurine values and therefore low liver taurine concentrations tend to show greater hepatic damage. These data suggest that taurine may have a protective function in the liver.

Reduction of liver taurine in rats by beta-alanine treatment increases carbon tetrachloride toxicity

Treatment of rats with beta-alanine increases the urinary taurine levels and markedly reduces the concentration of taurine in the liver. Dosing with carbon tetrachloride (CCl4) during treatment with beta-alanine results in a marked decrease in urinary taurine concomitant with a decrease in food intake. Treatment of animals with beta-alanine increases the hepatotoxicity of single doses of CCl4 as determined histologically and by measurement of serum alanine transaminase (ALT) and aspartate transaminase (AST) levels. Urinary creatine is also raised significantly after the administration of CCl4 in beta-alanine-treated animals. However, the accumulation of triglycerides (TRIG) in the liver caused by dosing with CCl4 was not influenced by beta-alanine treatment. The data suggest that liver taurine levels may be an important factor in determining the degree of CCl4-induced cellular necrosis but not hepatic triglyceride accumulation.

Taurine, a possible urinary marker of liver damage: a study of taurine excretion in carbon tetrachloride-treated rats

Carbon tetrachloride (CCl4) caused a dose-dependent increase in urinary taurine which correlated with both the histological and biochemical assessment of liver damage. The peak elevation in urinary taurine occurred within the first 48 h after dosing but there was still significant taurinuria 72 and 96 h after the intermediate dose (1 ml.kg-1) and highest dose (2 ml.kg-1), respectively. Levels of taurine in serum were also elevated over the 24 h period following a hepatotoxic dose (2 ml.kg-1) of CCl4. In contrast, although initially elevated, levels of taurine in the liver declined over the 24 h period following dosing and were significantly lower 96 h after a hepatotoxic dose of CCl4 (2 ml.kg-1). Male rats showed a different urinary profile for taurine than female rats after dosing with CCl4. A reduction in food intake seemed to lower urinary taurine levels although these changes were not statistically significant. There was a significant correlation between the level of urinary taurine and the level of serum AST for individual animals given a hepatotoxic dose of CCl4 (2 ml.kg-1). The data presented suggest that: i) taurine is produced by the liver in response to a toxic insult and subsequent leakage from damaged cells leads to increased levels in the urine; ii) the urinary taurine level may be a useful non-invasive marker of liver damage.