Involvement of human CYP3A4 in the formation of hepatotoxic metabolites of clivorine / 中国药理学与毒理学杂志

ABSTRACT

AIM　This study was conducted to identify the human CYP isoforms responsible for the biotransformation of clivorine in human liver microsomes and the mechanism of metabolism-induced hepatotoxicity of clivorine. METHODS　Human liver microsomes were used to investigate the metabolism of clivorine in vitro. Selective CYP-450 inhibitors and cDNA expressed human CYPs were used to study their effects on the formation of hepatotoxic metabolites and the metabolism of clivorine and the principal CYP-450 isoform involved in the formation of hepatotoxic metabolite. RESULTS　Four metabolites, namely dehydroretronecine(DHR), 7-glutathionyl-dehydroretronecine(7-GSH-DHR), 7,9-diglutathionyl-dehydroretronecine(7,9-diGSH-DHR) and clivoric acid were found in the microsomal incubations. Chemical inhibition studies indicated that the metabolism of clivorine and the formation of pyrrolic metabolites as well as the bound pyrroles were strongly inhibited by CYP3A inhibitor ketoconazole(Ket). Whereas α-naphthoflavone(Nap), sulfaphenazole(Sulp), quinidine(Qui), diethyldithiocarbamate(DDC) have no significant effects on the metabolism of clivorine and the formation of pyrrolic metabolites in human liver microsomes. The results of metabolism of clivorine by cDNA expressed human CYPs showed that only CYP3A4 was found to be capable of catalyzing the metabolism of clivorine, while CYP1A2, CYP2C9, CYP2D6 and CYP2E1 did not play significant roles in the metabolism of clivorine and the formation of pyrrolic metabolites. CONCLUSION　The resultsdemonstrated that the pyrrolic metabolites were the major in vitro metabolites of clivorine and CYP3A4 was the major CYP isoform involved in clivorine metabolism and the formation of hepatotoxic pyrrolic metabolites in human liver microsomes. CYP3A4 plays a key role in the clivorine induced hepatotoxicity.