Toxicology International (Formerly Indian Journal of Toxicology)

Prasad S. Dalvi , Ramesh R. Dalvi , Leonard H. Billups

Abstract

Objectives: In this study, we investigated whether cytochrome P450s (CYPs) induced by a typical chlorinated hydrocarbon insecticide chlordane (CLD) potentiate hepatic toxicity of carbon disulfide (CS2). Materials and Methods: Male Sprague‑Dawley rats were treated with CLD (25 mg/kg, intraperitoneally (i.p.)) daily for 4 days, and 24 h after the final injection the rats were treated with CS2 (380 mg/kg, i.p.) in corn oil; while controls received the vehicle alone. The rats were then sacrificed at 3, 6, and 24 h following the CS2 treatment. Results: It was found that at 3 h post‑treatment, total hepatic glutathione (GSH) decreased modestly, but lipid peroxidation increased markedly, while all CLD‑inducible CYPs (1A1, 2B1, 2E1, and 3A2) were inhibited by CS2 variably but significantly. On the other hand, samples taken at 24 h following the CS2 treatment showed a significant increase in relative liver weights, hepatic GSH and lipid peroxidation, microsomal reactive oxygen species (ROS), and serum alanine transaminase (ALT) level. Activity of the CYPs was also increased, but remained significantly depressed, especially that of CYP2B1. Livers removed at 3 and 6 h after CS2 treatment showed subtle to distinct apoptotic changes, while a severe lesion of hydropic degeneration of the centrilobular cells with apoptosis was microscopically distinguishable in samples taken at 24 h. Conclusions: These results suggest that the metabolism of CS2 by CLD‑induced CYPs and the generation of lipid peroxides may have in concert contributed to the distinct hepatocellular damage.

Keywords

Carbon disulfide, cytochrome P450s, chlordane, glutathione, lipid peroxidation, oxidative stress, reactive oxygen species

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Ramesh R. Dalvi ¹, Prasad S. Dalvi ², Leonard H. Billups ³

Affiliations
1 Departments of Biomedical Sciences, College of Veterinary Medicine, Nursing and Allied Health, Tuskegee University, Tuskegee, AL 36088, US
2 Department of Physiology, University of Toronto, Toronto, ON M4Y1R6, CA
3 Departments of Pathobiology, College of Veterinary Medicine, Nursing and Allied Health, Tuskegee University, Tuskegee, AL 36088, US

Abstract

The objective of this study was to examine differential metabolism of CS₂ by various hepatic cytochrome P450 (CYP) isoenzymes including CYP1A1, CYP2B1, CYP2E1 and CYP3A2 induced by their selective inducers and to determine if there is a correlation between its metabolic activation and hepatotoxicity. Because 3-methylcholanthrene (3-MC), phenobarbital (PB), isoniazid (INH), and pregnenolone-16α-carbonitrile (PCN) are typical selective inducers of CYP1A1, CYP2B1, CYP2E1, and CYP3A2, respectively, they were chosen in this study to pretreat male Sprague-Dawley rats for induction of the CYP isoforms. Twenty-four h following the final dose of 3 daily doses of the inducers, rats were treated ip with a single dose of 380 mg/kg of CS₂. Half of the rats in each group were sacrificed at 3 h after CS₂ treatment to identify inhibited isoenzymes since CS₂ is metabolized by them in a suicide substrate manner. The remaining animals in the group were sacrificed at 24 h following CS₂ treatment to determine hepatic damage using serum ALT activity and liver histopathology as the indices of toxicity. At 3 h after treatment, activities of all CYPs (1A1, 2B1, 2E1 and 3A2) were inhibited by CS₂ significantly and differentially. However, the inhibition of CYP1A1 and CYP3A2 was reversed at 24 h post-treatment with no serious liver damage. On the other hand, the inhibition of CYP2B1 and CYP2E1 was irreversible and accompanied by severe liver damage especially in phenobarbital-pretreated rats. The results of this study suggest that induced CYP2B1 and to a lesser extent CYP2E1 are responsible for the bioactivation of CS₂ and the observed liver damage.

Keywords

Carbon disulfide; cytochrome P450 (CYP); CYP isoenzymes; CYP inducers, hepatotoxicity

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