title: Oxidation of the alcohol dehydrogenase inhibitor pyrazole to 4-hydroxypyrazole by microsomes. Effect of cytochrome P-450 inducing agents.
abstract: Pyrazole and its analogues are widely used to inhibit alcohol dehydrogenase and to block the metabolism of ethanol. Experiments were conducted to demonstrate that pyrazole is oxidized to 4-hydroxypyrazole by isolated rat liver microsomes. A HPLC procedure employing UV and electrochemical detection was developed for the separation and quantitation of 4-hydroxypyrazole. Pyrazole metabolism was NADPH-dependent, sensitive to inhibition by carbon monoxide, and was depressed in the presence of other substrates such as aniline or ethanol. Prior treatment of rats with either pyrazole or 4-methylpyrazole resulted in an increase in pyrazole oxidation to 4-hydroxypyrazole by microsomes. Increases were observed when rates were expressed either per mg of protein or per nmol of P-450. Microsomes from pyrazole- and 4-methylpyrazole-treated rats had Km values for pyrazole of about 0.29 and 0.14 mM, respectively, and Vmax values of about 0.5 and 0.7 nmol of 4-hydroxypyrazole per min per mg of protein, respectively. Chronic consumption of ethanol for 24 days resulted in an increase in pyrazole oxidation (per mg of protein and per nmol of P-450) as compared to pair-fed controls. By contrast, phenobarbital treatment lowered the rate of production of 4-hydroxypyrazole. Treatment with 3-methylcholanthrene resulted in an increase in pyrazole oxidation when rates were expressed per mg of protein, but not per nmol of P-450. These results show that pyrazole is oxidized to 4-hydroxypyrazole by microsomes in a P-450-dependent manner and that this metabolism can be increased by certain inducers, e.g. pyrazole, 4-methylpyrazole, and chronic ethanol treatment.
mesh_terms: D000426:Alcohol Dehydrogenase / Q000037:antagonists & inhibitors*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D000077604:Fomepizole; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D010084:Oxidation-Reduction; D011720:Pyrazoles / Q000378:metabolism* / Q000493:pharmacokinetics* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D011720:Pyrazoles; D009243:NAD; C031280:pyrazole; C014606:4-hydroxypyrazole; D000077604:Fomepizole; D003577:Cytochrome P-450 Enzyme System; D000426:Alcohol Dehydrogenase