Pyrazole and 4-methylpyrazole are potent inhibitors of alcohol dehydrogenase, and have been used to block the metabolism of ethanol and for treatment of methanol or ethylene glycol poisoning. Pyrazole, but not 4-methylpyrazole, has been shown to be hepatotoxic. The reasons for these differences are not known. 4-Hydroxypyrazole and 4-hydroxymethylpyrazole are major metabolites found in the urine after in vivo administration of pyrazole or 4-methylpyrazole. The enzyme system(s) responsible for the metabolism of these compounds are not known. Preliminary results show that microsomes from rats treated with pyrazole or 4-methylpyrazole display several properties which are very similar to properties found with microsomes from chronic ethanol-fed rats, suggesting the possibility that pyrazole and 4-methylpyrazole may induce a cytochrome P-450 isozyme which is similar to the ethanol-inducible cytochrome P-450. The overall objective of this application is to study the interaction of pyrazole and 4-methylpyrazole with microsomes and to compare the properties of microsomes from pyrazole- and 4-methylpyrazole-treated rats to those found with microsomes from ethanol-treated rats. Properties to be studied include substrate and alcohol metabolism and specificity, kinetic experimens, substrate binding spectra, content of microsomal enzymes, effect of inhibitors, generation of oxygen radicals and promotion of lipid peroxidation. The metabolism of pyrazole and 4-methylpyrazole by microsomes from control and induced rats will be determined and the metabolites characterized. Attempts to purify the pyrazole- and 4-methylpyrazole-inducible cytochrome P-450 and reconstitution experiments with purified enzymes will be carried out. Some experiments on metabolic consequences of pyrazole and 4-methylpyrazole treatment, and the effects of their metabolites, on hepatocyte function will be performed to evaluate why pyrazole, but not 4-methylpyrazole, is hepatotoxic. It is hoped that these studies will provide important information on the metabolism and on biochemical and pharmacological properties of these important compounds, which are widely used in the alcohol field.
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