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

Cytotoxicity evaluation after coexposure to perchloroethylene and selected peroxidant drugs in rat hepatocytes

There is evidence of hepatotoxic effects caused by Perchloroethylene (PCE), presumably due to reactive metabolic intermediates; lipid peroxidation is under study as a potential mechanism of toxicity. We aimed to verify if PCE levels comparable to those reached in the blood of exposed subjects can cause cell damage and lipid peroxidation. The association of PCE with lipid peroxidation inducing drugs (cyclosporine A, valproic acid and amiodarone) was also tested on rat isolated hepatocytes. AST and LDH release, MTT test and lipid peroxidation assay showed that PCE determines dose-dependent effects on rat isolated hepatocytes. The toxic potential resulting from our data would be valproic acid < cyclosporine A < amiodarone. While valproic acid and cyclosporine caused a mild toxicity, the effects of amiodarone were more severe; in particular, the association of PCE with amiodarone showed a clear additive effect. The role of lipid peroxidation in the liver toxicity exerted by the tested compounds was confirmed by our data, and resulted relevant after treatment of cells with amiodarone and PCE. Extrapolating these results to human, we can suggest that a subject professionally exposed to PCE, who chronically assumes a lipid peroxidation inducing drug like amiodarone, may be potentially exposed to a higher risk of liver toxicity.

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.

The joint neurotoxic action of inhaled methyl butyl ketone vapor and dermally applied O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens: potentiating effect

The neurotoxic action of inhaled technical grade methyl butyl ketone and dermally applied (O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) was studied. Three groups of five hens each were treated 5 days/week for 90 days with a dermal dose of 1.0 mg/kg of EPN (85%) on the unprotected back of the neck. These groups were exposed simultaneously to 10, 50, or 100 ppm of technical methyl butyl ketone (MBK; methyl n-butyl ketone:methyl isobutyl ketone, 7:3) in inhalation chambers. A fourth group was treated only with the dose of EPN and a fifth group with only 100 ppm MBK. The control consisted of a group of five hens treated with a dose of 0.1 ml acetone. Treatment was followed by a 30-day observation period. Simultaneous exposure to EPN and MBK greatly enhanced the neurotoxicity produced when compared to the neurotoxicity produced by either chemical when applied alone. Continued exposure to EPN and MBK resulted in earlier onset and more severe signs of neurotoxicity than exposure to either individual compound. The severity and characteristics of histopathologic lesions in hens given the same daily dermal dose of EPN in combination with inhaled MBK depended on the MBK concentration. Histopathologic changes were more severe and prevalent in the 100 ppm MBK:1 mg/kg EPN group than in the others. In this group, Wallerian-type degeneration was seen along with paranodal axonal swellings. The morphology and distribution of these lesions were characteristic of those induced by MBK. In the 50 ppm MBK:1 mg/kg EPN group axonal swelling was evident but not clearly identifiable as paranodal. Hens treated with 10 ppm MBK:1 mg/kg EPN had minimal lesions with low incidence of axonal swellings. These were not as large as those seen in MBK neurotoxicity, but instead resembled the histopathologic lesions caused by EPN. The results indicate that the combined treatment gave a value for neurotoxicity coefficient which was two times the additive neurotoxic effect of each treatment alone. Pretreatment with three daily ip doses of 5 mmol/kg technical grade MBK or methyl n-butyl ketone (MnBK), equally increased chicken hepatic microsomal cytochrome P-450 content. Also, hepatic microsomes from MBK-treated hens metabolized [14C]EPN in vitro to [14C]EPN oxon to a much greater extent than those from control hens. These results suggest that MBK potentiates the neurotoxic effect of EPN, at least in part, by increasing the metabolic activation of EPN to the more neurotoxic metabolite EPN oxon.(ABSTRACT TRUNCATED AT 400 WORDS)

Microsomal cytochrome P-450 "handprints": five fractions from anion-exchange high-pressure liquid chromatography provide a rapid preliminary screen for selectivity in the induction and destruction of rat hepatic cytochrome P-450 subpopulations

Anion-exchange HPLC was used to monitor changes in rat hepatic cytochrome P-450 fractions resulting from animal exposure to several inducing and hepatotoxic agents. The column eluant was divided into five fractions and the cytochrome P-450 content in each was determined. Induction of hepatic cytochrome P-450 following 2,5-hexanedione and SKF 525-A pretreatment of animals showed an induction pattern in the five-fraction "handprint" similar to that produced by phenobarbital. The patterns of induction following beta-naphthoflavone, clofibrate, and isosafrole pretreatments were unique in comparison to each other and also compared to that of phenobarbital. The pattern of cytochrome P-450 loss after allyl alcohol was similar to that seen after cobalt chloride treatment, but differed from that seen following acetaminophen administration. Five-fraction quantitation of the eluant from anion-exchange HPLC of microsomes appears to be a useful technique to screen for and convey the effects of previously uncharacterized inducers and the effects of hepatotoxic agents or heme synthesis inhibitors on rat hepatic cytochrome P-450 subpopulations.