title: Metabolism and hepatotoxicity of the naturally occurring benzo[b]pyran precocene I.
abstract: The in vitro metabolism of precocene I by liver microsomes from control and treated rats and the effects of precocene I on the function and histology of the rat liver were examined. The major metabolites (80-90% of total metabolites) from all microsomal preparations were the cis and trans 3,4-diols of precocene I produced with a cis/trans isomer ratio of 1:2. These diols appear to arise mainly by spontaneous hydrolysis of precocene I 3,4-oxide. (+)-(3R,4R)-cis- and (-)-(3R,4S)-trans-precocene I 3,4-diols were the predominant enantiomers of the 3,4-diol formed. The enantiomeric excess of these diols (2-50%) is dependent on the microsomal preparation, with microsomes from control rats exhibiting the highest stereoselectivity and microsomes from phenobarbital-treated rats the least. 6-Hydroxyprecocene I was the next major metabolite and was formed to the extent of 5% (control), 10% and 17% (phenobarbital and 3-methylcholanthrene treatment, respectively) of total metabolites. Treatment of rats with a single i.p. dose of precocene I (300 mg/kg) resulted in extensive hepatic damage as evidenced by a marked increase of plasma glutamic pyruvic transaminase levels and histologic observation in liver sections of severe centrolobular necrosis. Although phenobarbital treatment of rats increased the rate of liver microsomal metabolism of precocene I by approximately 50% (nmol products/nmol cytochrome P-450/min) compared to liver microsomes from control rats, hepatic damage caused by precocene I was not significantly affected. Depletion of glutathione levels in the rats with diethyl maleate prior to precocene I treatment dramatically increased the severity of hepatic insult, whereas treatment of the rats with the mixed function oxidase inhibitor piperonyl butoxide prior to treatment with precocene I blocked hepatic damage. Treatment of rats with cysteamine prior to treatment with precocene I protected the animals against the toxic effects. Neither cis nor trans precocene I 3,4-diol nor 3,4-dihydroprecocene I elicited impaired liver function or cellular damage. The above results are consistent with the view that precocene I 3,4-oxide is the metabolite responsible for the hepatotoxic effects observed when precocene I is injected into rats.
mesh_terms: D000410:Alanine Transaminase / Q000378:metabolism; D000818:Animals; D001578:Benzopyrans / Q000378:metabolism* / Q000633:toxicity; D002851:Chromatography, High Pressure Liquid; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects; D008099:Liver / Q000187:drug effects; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D001578:Benzopyrans; C019539:precocene I; D008748:Methylcholanthrene; D000410:Alanine Transaminase; D010634:Phenobarbital