Potentiation of carbon tetrachloride-induced hepatotoxicity by 1,3-butanediol

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

Induction of rat hepatic mixed-function oxidases by acetone and other physiological ketones: their role in diabetes-induced changes in cytochrome P450 proteins

1. To evaluate the role of ketone bodies in diabetes-induced changes in hepatic cytochrome P450 composition, rats were treated with acetone, 3-hydroxybutyrate or 1,3-butanediol. 2. Treatment with acetone enhanced the rat hepatic O-dealkylations of ethoxyresorufin and methoxyresorufin, and the hydroxylation of p-nitrophenol, but had no effect on lauric acid hydroxylation and ethylmorphine N-demethylation. Neither 3-hydroxybutyrate nor 1,3-butanediol modulated the metabolism of the above substrates. 3. Immunoblot analysis of hepatic microsomal proteins revealed that treatment with acetone increased the apoprotein levels of P4501A2, P4502B1/2 and P4502E1. 4. It is concluded that acetone is responsible, at least partly, for the diabetes-induced increase in hepatic microsomal P4501A2, P4502B1/2 and P4502E1 proteins but does not mediate the increases in the P4503A1 and P4504A1 proteins. On the basis of work from our own and other laboratories a mechanism for the diabetes-induced changes in hepatic cytochrome P450 proteins is proposed.

Dichloroacetic acid and trichloroacetic acid increase chloroform toxicity

Dichloro- and trichloroacetic acids (DCA and TCA) and chloroform are formed during chlorination disinfection of drinking water. The effects of DCA and TCA treatment on CHCl3 toxicity were assessed in these studies. Male and female rats were gavaged with DCA or TCA (0.92 and 2.45 mmol/kg administered 3 times over 24 h). Three hours after the last dose CHCl3 was injected ip (0.75 mg/kg). Male rats experienced some weight loss (15%) and slight increases of ALT and BUN, but there were no effects of either DCA or TCA on any of these responses. In females, CHCl3 increased plasma ALT and this response was greater (up to threefold) in the DCA group, compared to saline controls. Similarly, BUN was increased by CHCl3 and this was more severe (up to threefold) in both the DCA and TCA pretreated groups. These results show that CHCl3 toxicity is increased by DCA and TCA, and this effect is gender-specific, occurring only in females. DCA increases both liver and kidney toxicity, whereas TCA affects only kidney toxicity.

Effect of 1,3-butanediol on rat liver microsomal NDMA demethylation and other monooxygenase activities

The administration of 1,3-butanediol (BD) previously has been shown to elevate blood concentrations of ketone bodies, to potentiate carbon tetrachloride hepatotoxicity, and to increase the hepatic microsomal content of cytochrome P450 and the activity of aniline hydroxylase. In the present study, oral treatment (10 g/kg) with racemic BD and each of its enantiomers (R-BD and S-BD) induced NDMA demethylase activity by approx. 1.5-fold in rat hepatic microsomes obtained 12 h later, suggesting an induction of P450IIE1, the acetone/ethanol-inducible form of P450. The results agreed with an immunochemically determined increase in the levels of this isozyme. No change in P450 content, NADPH-cytochrome-c reductase, or in pentoxyresorufin dealkylase activity were detected. Blood levels of acetone were determined during a 10-h period after BD administration and showed a higher initial rate of increase by R-BD, possibly due to steroselective metabolic oxidative metabolism. However, no difference in the induction of NDMA demethylase activity by the enantiomers could be detected. Induction of P450IIE1 probably contributes to the previously described potentiation of haloalkane-induced hepatotoxicity by BD administration.

1,3-Butanediol-induced increases in ketone bodies and potentiation of CCl4 hepatotoxicity

Evidence previously reported suggest that 1,3-butanediol (BD) enhances the hepatotoxic effect of a single small dose of carbon tetrachloride (CCl4) in a dose-related manner. The present study provides additional information concerning the quantitative relationship between the severity of the ketotic state produced by BD and the magnitude of the potentiation observed and emphasizes the use of ketone bodies (KB) to predict the potential hazard of the BD-CCl4 interaction. Liver damage was modulated in male Sprague-Dawley rats by varying the concentration of the BD solutions ingested prior to a CCl4 challenge (0.1 ml/kg, i.p.). These data were compared to ketone bodies in plasma, hepatic tissue and urine. BD produced a dose-dependent metabolic ketosis observable at dosages between 1.1 and 9.9 g/kg per day given for 7 days. Plasma and liver data correlated well together. Concomitantly, potentiation of the CCl4-induced liver injury was also dose-related for the same dosage range; the minimum effective dosage of BD for potentiation was estimated as 1.1 g/kg per day. The linear correlations between hepatic or plasma KB values and the indices of hepatic dysfunction (ALT, OCT) were highly significant. Using a semiquantitative method, a correlation was also found for the urinary KB data. These results suggest that plasma KB concentrations might be useful for predicting possible potentiation of the hepatonecrotic effect of CCl4 by BD.

Taurolithocholate-induced intrahepatic cholestasis: potentiation by methyl isobutyl ketone and methyl n-butyl ketone in rats

Haloalkane-induced hepatonecrogenesis can be potentiated by the prior administration of methyl isobutyl ketone (MIBK) and methyl n-butyl ketone (MBK). We investigated the possibility that these ketones could potentiate the cholestasis induced by taurolithocholate (TLC) in rats. Daily ketone pretreatment for 3 or 7 days resulted in an enhancement of the diminution in bile flow observed after TLC challenge. When the ketones were administered without TLC challenge, cholestasis was not observed; in fact, slight increases in bile flow did occur. The data suggest that MIBK may be more effective than MBK as a potentiator. Preliminary experiments with 2,5-hexanedione (HD), a metabolite of MBK and a potent potentiator of haloalkane hepatonecrosis, were included in the study. HD appeared to be a less potent potentiator of TLC-induced cholestasis. Although some ketones can potentiate cholestatic as well as hepatonecrogenic reactions, different mechanisms of action appear to be involved in these two phenomena.

Ethanol potentiation of carbon tetrachloride hepatotoxicity: possible role for the in vivo inhibition of aldehyde dehydrogenase

A potentiation of CCl4-induced hepatotoxicity was observed in rats pretreated with ethanol 18 hr prior to CCl4 exposure. Hepatic microsomal aldehyde dehydrogenase (ALDH) was significantly inhibited in animals sacrificed 1 hr following the sequential exposure, however, no more so than in those animals receiving CCl4 alone. The animals receiving ethanol alone had ALDH activity similar to vehicle treated controls. Twenty-four hours following a potentiating dose of ethanol and CCl4 an 81 and 57% decline in NAD+-dependent microsomal and mitochondrial ALDH activity was observed, respectively. Similar results were observed for microsomal and mitochondrial NADP+-dependent ALDH activity. The decline in membrane-bound ALDH was greater in potentiated animals than in those receiving CCl4 alone. A relatively smaller decline in cytosolic ALDH activity was observed in CCl4 treated rats with or without ethanol pre-exposure. The data suggest that inhibition of membrane bound ALDH may be one of the major mechanisms of in vivo potentiation of CCl4-induced hepatotoxicity by ethanol.

Role of biotransformation in the potentiation of halocarbon hepatotoxicity by 2,5-hexanedione

2,5-Hexanedione (2,5-HD) pretreatment potentiated CHCl3-induced hepatotoxicity. 2,5-HD significantly increased hepatic cytochrome P-450, NADPH cytochrome c reductase, aniline hydroxylation, p-nitroanisole O-demethylation, and aminopyrine N-demethylation in both male and female mice. 2,5-HD pretreatment potentiated CHCl3-induced centrilobular necrosis and increased serum alanine amino transferase (ALT) activity by 20 times more than CHCl3 alone. Similarly, 2,5-HD pretreatment potentiated CDCl3-induced hepatotoxicity as well as CCl4-induced hepatotoxicity in male mice, but did not potentiate trichloroethylene-, 1,1,2-trichloroethane-, or perchloroethylene-induced hepatotoxicity. In female mice, 2,5-HD pretreatment potentiated CHCl3- and CDCl3-induced hepatotoxicity as well as trichloroethylene-, 1,1,2-trichloroethane-, and carbon tetrachloride-induced hepatotoxicity, but not perchloroethylene-induced hepatotoxicity. 2,5-HD pretreatment had no preferential effect on either CHCl3- or CDCl3-induced hepatotoxicity in females. However, phenobarbital pretreatment did differentiate CHCl3- and CDCl3-induced hepatotoxicity in females. 2,5-HD-induced potentiation of halocarbon hepatotoxicity is sex dependent.

Functional and biochemical correlates of chlordecone exposure and its enhancement of CCl4 hepatotoxicity

Animals pretreated with chlordecone exhibit a greatly increased hepatotoxic response to CCl4 challenge. Possible mechanisms underlying this interaction were examined. A single p.o. administration of chlordecone (5 mg/kg) was followed by CCl4 (200 microliter/kg) administered i.p. 48 h later. Twenty-four hours later, animals treated with chlordecone mccl4 had decreased hepatic excretory function (20% of controls) and elevated plasma transaminase activities and bilirubin. Hepatic mixed function oxidase activity was assessed as pentobarbital sleeping time and was not affected by chlordecone pretreatment. Irreversible binding of label from 14CCl4 to hepatic protein or lipid was not different in the chlordecone group compared to vehicle controls. Hepatic and renal glutathione concentrations were not affected by chlordecone alone (at 6 h, 1, 2, 3, 5 and 7 days) or by a combination of chlordecone (48 h) and CCl4 (24 h). CCl4-induced lipid peroxidation of liver tissue, measured in vitro or in vivo, was not increased by chlordecone treatment. Thus, while the mechanism for the enhanced toxicity remains to be elucidated, these results suggest that the interaction between chlordecone and CCl4 is a subtle one, not causally involving increased covalent binding of the toxin, increased susceptibility of tissue lipids to peroxidative damage or decreased hepatic GSH.

Potentiation of CCl4 hepatotoxicity in rats by a metabolite of 2-butanone: 2,3-butanediol

The role of ketaone metabolism in 2-butanone-induced potentiaion of carbon tetrachloride (CCl4) hepatotoxicity was studied in rats. The blood concentrations of 2-butanol, 3-hydroxy-2-butanone and 2,3-butanediol detected 4 h after dosing were 3.2 mg/100 ml, 2.4 mg/100 ml and 8.6 mg/100 ml, respectively. Eighteen hours after 2-butanone, the concentration of 2,3-butanediol rose to 25.6 mg/100 ml, while the concentrations of 2-butanol and 3-hydroxy-2-butanone declined to 0.6 mg/100 ml and 1.4 mg/100 ml, respectively. A 16-h pretreatment with either 2-butanone (2.1 ml/kg, p.o.) or 2,3-butanediol (2.12 ml/kg, p.o.) markedly enhanced the hepatotoxic response to CCl4 (0.1 ml/kg, i.p.), as measured by serum glutamic pyruvic transaminase activity and hepatic triglyceride content. In vivo, limited formation of 3-hydroxy-2-butanone occurred after this dose of 2,3-butanediol. These data suggest that the production of 3-hydroxy-2-butanone and 2,3-butanediol via 2-butanone metabolism may participate in the augmented necrogenic effect of CCl4 seen after pretreatment with 2-butanone.