Cooperativity ofα-naphthoflavone in cytochrome P450 3A-dependent drug oxidation activities in hepatic and intestinal microsomes from mouse and human

Abstract

1. The effects of several CYP3A substrates (α-naphthoflavone (αNF), terfenadine, midazolam, erythromycin) on nifedipine oxidation and testosterone 6-β-hydroxylation activities were investigated in hepatic and intestinal microsomes from mouse and human. 2. αNF (10 μM) and terfenadine (100 μM) inhibited nifedipine oxidation activities (at substrate concentration of 100 μM) in mouse hepatic microsomes to ∼50%, but not in mouse intestinal microsomes. αNF (30 μM) stimulated nifedipine oxidation activities in mouse and human intestinal microsomes and in human hepatic microsomes to ∼1.3-1.8-fold. Inhibitory potencies (50% inhibition concentration, IC₅₀) of midazolam and erythromycin for nifedipine oxidations were calculated to be ∼90 μM in human intestinal microsomes. In contrast, testosterone (100 μM) stimulated the nifedipine oxidation activities ∼1.5-fold in hepatic and intestinal microsomes from mouse and human. 3. αNF showed different effects on the kinetic parameters including the Hill coefficients of nifedipine oxidation and testosterone 6-β-hydroxylation catalysed by hepatic and intestinal microsomes from mouse and human. Cooperativity in nifedipine oxidation was increased by the addition of αNF to pooled human hepatic microsomes, but little effects of αNF could be observed in individual human intestinal microsomes. 4. These results suggest that CYP3A enzymes in liver and intestine might have different characteristics and that observations from hepatic microsomes should not be directly applicable to intestine metabolism in some cases. Studies of drug-drug interactions of CYP3A substrates are recommended to be performed using intestinal samples.