Elevation of individual serum bile acids on exposure to trichloroethylene or alpha-naphthylisothiocyanate

Evaluation of serum bile acid profiles as biomarkers of liver injury in rodents

Bile acids (BAs) have been studied as potential biomarkers of drug-induced liver injury. However, the relationship between levels of individual BAs and specific forms of liver injury remains to be fully understood. Thus, we set out to evaluate cholic acid (CA), glycocholic acid (GCA), and taurocholic acid (TCA) as potential biomarkers of liver injury in rodent toxicity studies. We have developed a sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) assay applicable to rat and mouse serum and evaluated levels of the individual BAs in comparison with the classical biomarkers of hepatotoxicity (alanine aminotransferase [ALT], aspartate aminotransferase [AST], glutamate dehydrogenase (GLDH), alkaline phosphatase, total bilirubin, gamma-glutamyl transferase, and total BAs) and histopathology findings in animals treated with model toxicants. The pattern of changes in the individual BAs varied with different forms of liver injury. Animals with histopathologic signs of hepatocellular necrosis showed increases in all 3 BAs tested, as well as increases in ALT, AST, GLDH, and total BAs. Animals with histopathologic signs of bile duct hyperplasia (BDH) displayed increases in only conjugated BAs (GCA and TCA), a pattern not observed with the other toxicants. Because BDH is detectable only via histopathology, our results indicate the potential diagnostic value of examining individual BAs levels in serum as biomarkers capable of differentiating specific forms of liver injury in rodent toxicity studies.

Serum bile acids as a sensitive biological marker for evaluating hepatic effects of organic solvents

Serum bile acids (SBAs) are suggested as a potentially sensitive and specific indicator of liver function which, accordingly, could provide an early indication of hepatobiliary dysfunction. This offers advantages over more traditional parameters of liver integrity/function. Recent studies have shown that occupational exposure to low levels of halogenated aliphatic or non-halogenated aromatic solvents is associated with significant increases in SBA levels. As this has often been evident in the absence of any effect on conventional parameters of hepatobiliary integrity/function, elevated SBA levels may well be regarded as a sensitive biological marker of exposure/effect of these compounds. In addition, it may be considered that they provide an early indicator of solvent-induced changes in hepatobiliary function. Extensive studies with experimental animals have also provided supporting evidence for these observations in solvent-exposed individuals. Investigations of the mechanisms at cellular and subcellular levels by which these increases occur have suggested that these effects are likely to be the result of selective, dose-related and reversible inhibition of bile acid uptake at the sinusoidal domain of the hepatocyte plasma membrane. Increased concentrations of SBA under low levels of exposure to different solvents have been demonstrated to be a short-lived and reversible effect which is not accompanied by any other evidence of liver damage. Therefore, it could be assumed that it is unlikely that there would be pathological sequelae to these effects, although the longer term ramifications of such effects have not been thoroughly investigated. Nevertheless, the available evidence indicates that investigation of SBA in solvent-exposed workers could provide useful indications of exposure and effect.

Identification of urinary biomarkers useful for distinguishing a difference in mechanism of toxicity in rat model of cholestasis

This (1)H nuclear magnetic resonance metabonomics study was aimed to determine urinary biomarkers of cholestasis resulting from inhibition of biliary secretion of bile or obstruction of bile flow. To inhibit biliary secretion of bile, cyclosporine A was administered to male Sprague-Dawley rats. Obstruction of bile flow was induced by administration of 4,4'-methylene dianiline, alpha-naphthylisothiocyanate or bile duct ligation. Clinical pathological and histopathological examinations were performed to confirm cholestatic injury and (1)H nuclear magnetic resonance spectral data for urine samples were analysed to determine similarities and differences in profiles of metabolites using the Spotfire. In cyclosporine A-treated groups, serum total bilirubin and bile acid were significantly increased but no remarkable hepatic histopathological-changes were observed. In 4,4'-methylene dianiline-, alpha-naphthylisothiocyanate- and bile duct ligation-treated groups, serum alkaline phosphatase, gamma-glutamyltranspeptidase and total bilirubin levels increased significantly, and hepatic histopathological-changes were observed. On urinary (1)H nuclear magnetic resonance spectral analysis, area intensities derived from 0.66 to 1.90 ppm were decreased by cyclosporine A, whereas they were increased by other treatments. These metabolites were identified using the NMR suite as bile acids, branched-chain amino acids, n-butyrate, propionate, methyl malonate and valerate. These metabolites were further investigated by K-means clustering analysis. The cluster of these metabolites is considered to be altered by cholestasis. We conclude that bile acids, valine and methyl malonate have a possibility to be urinary cholestatic biomarkers, which distinguish a difference in mechanism of toxicity. (1)H nuclear magnetic resonance metabonomics thus appears to be useful for determining the mechanisms of toxicity and can be front-loaded in drug safety evaluation and biomarker discovery.

Toluene-induced elevation of serum bile acids: relationship to bile acid transport

Raised concentrations of serum bile acids (SBA) following occupational exposure to a number of halogenated aliphatic hydrocarbon solvents and after in vivo exposure of experimental animals to these substances have been reported in several studies in recent years. However, the widely used nonchlorinated aromatic hydrocarbon solvent, toluene, has not been critically examined for its effect on serum bile acids. Accordingly, the effect of in vivo treatment with toluene on SBA and its direct in vitro effects on the transport of bile acids by isolated rat hepatocytes were investigated in this study. In vivo treatment with toluene (2.3 mmol/kg body weight, ip, on each of 3 consecutive days) resulted in a significant rise in the serum concentrations of total and some individual bile acids while other parameters of hepatobiliary function were unaltered. Administration of a higher dose of solvent (9.2 mmol/kg body weight, i.p.) resulted in a further increase in total SBA levels together with a significant rise in serum activities of some liver enzymes. In vitro application of noncytotoxic doses of toluene in the vapor phase to hepatocytes isolated from untreated rats resulted in a significant inhibition of the initial rate-(V0)-of uptake of cholic acid (CA). Similarly, accumulation of CA and taurocholic acid (TC) over an extended incubation time by hepatocytes exposed to toluene was significantly inhibited. Kinetic analysis revealed a noncompetitive inhibition of CA uptake as suggested by a decline in Vmax and an unaltered K(m). In contrast, the initial rate of efflux of these substates and their continuous efflux from preloaded cells were unaffected by exposure to toluene. Thus, toluene exposure inhibited the transport and accumulation of bile acids by hepatocytes in a manner largely similar to that of halogenated solvents, and this inhibition could explain the raised SBA concentrations following in vivo exposure to this solvent. These findings are consistent with and provide mechanistic data to support previous studies where increased SBA levels (in the absence of any evidence of liver injury as measured by liver enzyme tests) were reported in workers following occupational exposure to this solvent. Additionally, in full agreement with our previous investigations in which SBA levels were found to be a sensitive biological marker of exposure to halogenated aliphatic hydrocarbon solvents, the data support a similar role for SBA on exposure to toluene as well.

In vitro interference with hepatocellular uptake of bile acids by xylene

Occupational exposure to a mixture of two widely used aromatic hydrocarbon solvents, xylene and toluene, has been associated with a significant rise in the concentrations of serum bile acids (SBA). We have recently shown that toluene interferes with the transport of bile acids by hepatocytes and this could explain elevated SBA after occupational exposure or following in vivo administration of this compound to experimental animals. However, it is not known if xylene, like its monomethylated homologue, toluene, could interfere with the processes of bile acid transport by hepatocytes. Therefore, the present studies were undertaken to examine this possibility. Direct addition of a non-cytotoxic dose (2.5 microliters/2.8 x 10(6) cells) of xylene (in vapour phase) to hepatocytes isolated from untreated rats significantly inhibited the initial rates (determined from slope of the lines in the linear range (20-80 s)) of uptake (V0) of 10 microM cholic acid (CA) and-taurocholic acid (TC) by 37 and 48%, respectively (P < 0.05). Similarly, accumulation of these substrates by hepatocytes over an extended incubation time up to 30 min was significantly inhibited to the same extent by xylene exposure. This inhibitory effect was found to be reversible when sufficient time was allowed for the cells to recover. In contrast, the initial rates (V0) of efflux (determined from slope of the lines in the linear range (1-5 min)) of these bile acids (25 microM) and their continuous efflux (up to 30 min) from preloaded cells incubated with a similar dose of xylene were not (except for the 1 min time point) significantly different from those of controls. In conclusion, xylene interferes with the transport of bile acids by hepatocytes in a manner largely similar to that of its monomethylated homologue, toluene. These findings extend our previous observations on aliphatic and aromatic hydrocarbon solvents and provide mechanistic data at a cellular level to support a causal role for xylene (as well as toluene) in raised SBA levels of exposed individuals.

Alpha-naphthylisothiocyanate-induced elevation of serum bile acids: lack of causative effect on bile acid transport

In recent years chemicals including chlorinated solvents have been found to interfere with the transport of bile acids (BA) by hepatocytes, which probably accounts for the raised serum bile acids (SBA) after exposure. However, the known cholestatic agent, alpha-naphthylisothiocyanate (ANIT) has never been fully examined for its effect on these processes. Accordingly, the direct effects in vitro and the effects of in vivo treatment on bile acid transport have been investigated in this study. Direct addition of ANIT (5-100 microns) to hepatocytes isolated from untreated rats did not result in any change in uptake or efflux of taurocholic acid (TC), one of the most obviously elevated SBA in ANIT-treated rats. Additionally, accumulation of TC over an extended incubation period was not affected by ANIT. In vivo treatment with ANIT (50 mumol/kg i.p. on each of 3 consecutive days) resulted in a marked elevation of total serum bile acids (TSBA) and a slight increase in the activity of serum alkaline phosphatase (ALP) and a very mild hyperbilirubinemia, while other markers of liver injury were unaltered. In hepatocytes isolated from these rats, Km and Vmax for uptake and V0 for efflux were no different between ANIT and vehicle-treated animals. In conclusion, ANIT showed no effects on transport of BA on in vitro exposure or after treatment in vivo where SBA were clearly elevated. The lack of effects of ANIT on transport of bile acids is consistent with other postulated mechanisms of action. Furthermore, this indicates that the effects noted with solvents are not necessarily replicated by substances known to cause histopathological cholestasis.

Individual serum bile acids in apprentice spray painters in association with solvent exposure

The effects of exposure to solvents on serum bile acids were investigated by comparing a group of apprentice vehicle spray painters (exposed group) with one of apprentice electricians. Apprentice spray painters from the study were subdivided into high- and low-solvent-exposure groups. Concentrations of individual serum bile acids (SBA) were measured and compared with conventional liver function tests (LFTs). Total, free, glycine- and taurine-conjugated SBA were consistently found to be present at higher levels in the spray painters than in the electricians, even at the beginning of the apprenticeship. Total SBA tended to increase in spray painters with increasing years of exposure during the apprenticeship, but this was significant at only one time point. No rises were observed over the sampling period in electricians. The mean values of individual and total SBA concentrations were all found to be higher in the high-exposure group than in the low-exposure group, with some differences reaching statistical significance. None of the routine liver biochemistry parameters was different between spray painters and electricians. gamma-Glutamyl transferase (GGT) was the only enzyme found to be significantly different between the high- and low-exposure groups, but all values were within the normal range. This study suggests that occupational exposure even to low levels of solvent mixtures results in increases in SBA. The increased SBA may be indicative of a subclinical liver dysfunction. Alternatively, they may reflect solvent exposure only, with the raised levels having no pathologic implication or consequence.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

Assessment of hepatobiliary function in vivo and ex vivo in the rat

Many xenobiotics cause hepatobiliary toxicity and cholestasis in the rat. Initial assessment of hepatobiliary damage in rats can be accomplished by measuring serum concentrations of bile acids and bilirubin, serum activities of liver-associated enzymes such as 5'-nucleotidase, alkaline phosphatase, gamma-glutamyltranspeptidase, and plasma clearances of dyes [e.g., bromosulfophthalein (BSP)] excreted primarily through the bile. More detailed evaluation of hepatobiliary disturbances involves cannulation of the bile duct of anesthetized rats and subsequent measurement of rates of bile flow, bile acid excretion, and bile composition. Canalicular bile flow can be estimated from clearances of nonmetabolized sugars (i.e., erythritol) which enter bile via paracellular transport. Tight junction permeability also can be assessed by either biliary excretion of such a marker as horseradish peroxidase or sucrose following portal vein infusion or via retrograde biliary infusion. Subsequent morphologic evaluation of the liver provides information on damage to cells which may contribute to hepatobiliary dysfunction (i.e., bile duct obstruction). Isolated perfused livers offer the ability to measure all of the above mentioned parameters as well as to make a more accurate determination of the effects of xenobiotics on bile acid-dependent and -independent bile flow. A good example of the advantage of combining techniques as well as following complete time courses of changes in hepatobiliary function is provided by using studies of alpha-naphthylisothiocyanate-induced hepatotoxicity.

Individual serum bile acids as early indicators of carbon tetrachloride- and chloroform-induced liver injury

Individual serum bile acids (SBA) are emerging as potentially useful early indicators of liver injury. This study was undertaken to compare the usefulness of individual SBA with the routinely used assays for detecting the effects of the hepatotoxicants carbon tetrachloride (CCl4) and chloroform (CHCl3). Serum samples were assayed for liver injury by determination of alanine aminotransferase (ALT), aspartate amino-transferase (AST), alkaline phosphatase (ALP), bilirubin and total bile acid (by enzymatic kit). These results were compared with levels of individual SBA measured by high performance liquid chromatography (HPLC). Liver samples from CCl4-treated rats were taken for light and electron microscopic examination. The highest dose for each chemical caused increases in serum ALT and AST but not ALP. Chloroform at the highest dose increased bilirubin. Total SBA levels as assayed by the kit were elevated in response to CCl4 and CHCl3 at doses below which serum enzymes and bilirubin were increased. Some individual SBA were increased at a still lower dose for each of these two chlorinated solvents. At the lowest dose of CCl4 tested no consistent light microscopic or ultrastructural changes were found. At all the higher doses periacinar cells displayed typical accumulation of lipid droplets and degranulation and dilation of rough endoplasmic reticulum. The extent of the ultrastructural changes were dose-dependent. Thus individual SBA assayed by HPLC may be considered as a very sensitive indicator of liver injury induced by the classical hepatotoxicants carbon tetrachloride and chloroform.

Effects of hexachloro-1,3- butadiene and 1,1,2,2- tetrachloroethylene on individual serum bile acids

Rats were exposed to hexachlorobutadiene (HCBD) or tetrachloroethylene (TET) in order to determine which of these chemicals was more likely to be responsible for elevations in individual serum bile acids (SBA) found in workers exposed primarily to these two chemicals. Increases in cholic and taurocholic acids were found on exposure to high doses of HCBD. Elevations of SBA occurred right down to low exposures for TET, however, with cholic, chenodeoxycholic, and glycocholic acids being the most sensitive bile acids. Only at high doses for each chemical was there any indication of liver injury as determined by routinely used parameters such as serum enzymes or bilirubin. The data suggest that TET is likely to play a role in the elevated individual SBA in an exposure situation where both this chemical and HCBD are found.

New perspectives in biomonitoring liver function by means of serum bile acids: experimental and hypothetical biochemical basis

The functional activity of the liver and the variety of its responses to injury makes the choice of appropriate tests of function a difficult task. Because of the highly efficient uptake of bile acids by the normal hepatocyte, the determination of serum bile acid (SBA) concentration has been proposed as a test to detect early changes of liver function not associated with cytotoxicity. Several biomonitoring studies have been carried out on subjects occupationally exposed to hepatotoxic substances, by evaluating SBAs as indicators of early liver dysfunction. Even though these studies are not exactly comparable because of the different protocols adopted, most of them show a significant increase in SBA concentrations among the exposed subjects compared with unexposed controls. Furthermore, higher prevalences of subjects with abnormal SBA concentrations occur in those exposed to mixtures of organic solvents. Increased SBA concentrations among the subjects exposed to various xenobiotics have been explained by assuming a change in function of hepatocytes. As regards the nature of the mechanisms involved in the increase in SBA concentrations, recent experimental observations pointed out that some chlorinated aliphatics were able to inhibit cell membrane ATPases and alter cytosolic calcium homeostasis. The lack of any relation, however, between exposure and SBA concentrations remains an important point to clarify and at present prevents the use of measurement of SBA concentrations as an index of effect.

Effects of trichloroethylene on hepatic and splenic lymphocytotoxic activities in rodents

The effects of trichloroethylene (TRI), a widely used industrial solvent, on various immunological and toxicological parameters have been examined in Sprague-Dawley rats and B6C3F1 mice. Rats were administered TRI in vivo at 0.05, 0.5 and 5.0 mmol/kg per day intraperitoneally (i.p.) for 3 days. Mice were similarly treated with TRI at 10.0 mmol/kg. The highest TRI dose resulted in decreased splenocyte count and relative spleen weights, in rats and mice respectively and inhibition of hepatic natural killer cell (NK), natural cytotoxic cell (NC) and NPK cell (a newly described immune cell killing) activities in both rats and mice. High dose TRI in vitro resulted in minor decreases (less than 10%) in splenocyte viability, inhibition of LPS-stimulated mitogenesis in rat cells and marked inhibitions of NK and NC activities in all groups of effector cells. At the lowest in vitro dose mouse hepatic NK activity was still inhibited. Overall the data show that TRI is able to inhibit the activity of lymphocytotoxic cells which are involved in the immune surveillance of cancerous cells. This inhibition is particularly evident in the liver after in vivo administration and both liver and spleen cells after in vitro exposure. This suggests the possibility that compromised immune function may play a role in the carcinogenic responses in experimental animals on exposure to TRI.