Abstract
Isoniazid (INH), a widely used drug in the prophylaxis and treatment of tuberculosis, is associated with a 1 to 2% risk of severe and potentially fatal hepatotoxicity. There is evidence that the INH metabolite hydrazine plays an important role in the mechanism of this toxicity. Metabolism of INH leads to the production of hydrazine via both direct and indirect pathways. In both cases, the activity of an INH amidase is required to hydrolyze an amide bond. In the present study, using a model of INH-induced hepatotoxicity in rabbits, pretreatment of rabbits with the amidase inhibitor bis-p-nitrophenyl phosphate 30 min before injection of INH inhibited the formation of INH-derived hydrazine and decreased measures of hepatocellular damage, hepatic triglyceride accumulation, and hypertriglyceridemia. Bis-p-nitrophenyl phosphate also potently inhibited the production of hydrazine from INH in in vitro microsomal incubations (IC50 2 μM). Although hepatic glutathione stores are decreased, they are not depleted in animals with INH-induced hepatotoxicity. Significant effects on hepatic microsomal cytochrome P-450 1A1/2 and cytochrome P-450 2E1 activities suggest that these isozymes may be involved in the mechanism of the toxicity. In conclusion, this study demonstrates the importance of amidase activity in this rabbit model of hepatotoxicity and provides additional evidence in support of the role of hydrazine in the mechanism of INH-induced hepatotoxicity.
Footnotes
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Send reprint requests to: Dr. James M. Wright, M.D., Ph.D., F.R.C.P.(C), Department of Pharmacology and Therapeutics, University of British Columbia, 2176 Health Sciences Mall, Vancouver British Columbia, Canada V6T 1Z3. E-mail: jmwright{at}unixg.ubc.ca.
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↵1 This research project was supported by program project grant GM 32165 from the National Institutes of Health, Bethesda, MD. T.C.S was supported by a University Graduate Fellowship from the University of British Columbia.
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↵2 The abstract from this manuscript has been previously published: Sarich TC, Adams SP, Petricca G and Wright JM (1998) Inhibition of isoniazid-induced hepatotoxicity in rabbits by treatment with bis-p-nitrophenyl phosphate (abstract).Naunyn-Schmiedeberg’s Arch Pharmacol 358(Suppl 2):R438.
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↵3 Current address: Department of Clinical Pharmacology, Clinical R & D, Astra Hässle AB, S-431 83 Mölndal, Sweden.
- Abbreviations:
- ALT
- alanine aminotransferase
- ASAL
- argininosuccinic acid lyase
- BNPP
- bis-p-nitrophenyl phosphate
- CYP
- cytochrome P-450
- EROD
- ethoxyresorufin-O-deethylase
- INH
- isoniazid
- PROD
- pentoxyresorufin-O-dealkylase
- VEH
- vehicle
- Received July 22, 1998.
- Accepted December 20, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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