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Abstract
Liver microsomal territrem A (TRA) metabolism was studied in 7-wk-old female Wistar rats. Pretreatment with phenobarbital (PB) or dexamethasone (DEX) resulted in a significant increase in 4 g -hydroxymethyl-4 g -demethylterritrem A (MA 1 ) production. SKF 525A (0.025 and 0.05 mM), a general cytochrome P-450 (CYP450) inhibitor, blocked MA 1 formation in liver microsomes from PB-pretreated female rats. Anti-CYP2B antibody had no marked effect on MA 1 formation, although orphenadrine (0.5 mM), which inhibits CYP2B, blocked MA 1 formation in liver microsomes from PB-treated female rats. An immunoinhibition study showed that anti-CYP3A2 antibody reduced MA 1 formation to nondetectable levels in liver microsomes from PB-treated female rats. Furthermore, immunoblotting showed that CYP3A1 protein was expressed in 7-wk-old female rat and only MA 1 was formed from TRA using supersomes from CYP3A1-expressing baculovirus-infected insect cells. Further, Western blot analysis indicated that CYP3A2 protein was expressed in 2-wk-old rats of both sexes and 7-wk-old male rats, and 3 metabolites of TRA, such as MA 1 , MAX, and MA 2 , were formed using supersomes from CYP3A2-expressing baculovirus-infected insect cells. These results suggest that MA 1 formation in liver microsomes of 7-wk-old female Wistar rats is mediated by CYP3A1.