Updated in 10/7/2010 9:36:48 PM      Viewed: 64 times      (Journal Article)
Toxicology in Vitro 14 (4): 321-327 (2000)

Cytochrome P450-mediated metabolism and cytotoxicity of aflatoxin B1 in bovine hepatocytes

ABSTRACT
Aflatoxin B 1 (AFB 1 ) biotransformation comprises cytochrome P450 -mediated reactions resulting in hydroxylated and demethylated metabolites as well as AFB 1 epoxides. As the latter are highly nucleophilic, the species-specific rate of epoxidation and the ability for rapid conjugation to glutathione by glutathione S -transferase determines the individual susceptibility to AFB 1 . Here we show the time- and dose-dependent rate of AFB 1 -metabolism in bovine hepatocytes . Aflatoxin M 1 (AFM 1 ) is the most prominent metabolite formed within the first 2–8 hr of incubation, whereas AFB 1 -dhd is detectable in medium mainly after a prolonged incubation period. The delayed formation of AFB 1 -dhd corresponds to the cytotoxicity demonstrated by the MTT assay. α-Naphthoflavone and ketoconazole , inhibitors of CYP1A and CYP3A , respectively in humans , were used to evaluate the contribution of specific P450 isoenzymes in bovine biotransformation of AFB 1 . Initial experiments confirmed that α-naphthoflavone and ketoconazole inhibited ethoxyresorufin O -deethylation and testosterone 6β-hydroxylation also in bovine hepatocytes . Both inhibitors reduced AFM 1 and AFB 1 -dhd formation concentration dependently, suggesting that both enzyme groups contribute to the formation of these metabolites. However, the formation of AFM 1 was less inhibited by both compounds than the formation of AFB 1 -dhd.