1.3-N-Demethylation of caffeine (1,3,7-trimethylxanthine) is mediated by human cytochrome P450 1A2, whereas 7-N-demethylation and C-8-hydroxylation are reportedly catalyzed by monkey P450 2C9 and rat P450 1A2, respectively.2.Roles of marmoset P450 enzymes in caffeine oxidation were investigated using nine marmoset liver microsomes and 14 recombinantly expressed marmoset P450 enzymes.3.Predominant caffeine 7-N-demethylation and C-8-hydroxylation activities in marmoset liver microsomes were moderately (r=0.78, p<0.05) and highly (r=0.82, p<0.01) correlated with midazolam 1-hydroxylation activities, respectively, while the former was not strongly affected by ketoconazole or -naphthoflavone.4.Caffeine C-8-hydroxylation in liver microsomes was inhibited by ketoconazole and activated by -naphthoflavone, suggesting main involvements of P450 3As.5.Recombinant marmoset P450 3As had high V-max/K-m values for C-8-hydroxylation, comparable to K-m values for marmoset liver microsomes. Marmoset P450 1As efficiently mediated caffeine 3-N-demethylation and C-8-hydroxylation with apparently lower K-m values than those of liver microsomes.6.These results collectively suggest highly active marmoset P450 3A enzymes toward caffeine 8-hydorxylaiton and involvement of multiple P450 isoforms including P450 1A in caffeine 7-N- and 3-N-demethylations in marmoset livers. Marmoset P450s have slightly different properties to human or monkey P450s regarding caffeine metabolic pathways.
