Mechanism-based inhibition of CYP3A4 by constituents of Zingiber aromaticum

Sixteen compounds isolated from Zingiber aromaticum and showing concentration-dependent inhibition with IC50 values less than 100 μM, were analyzed for their possibility of time-, concentration-, and NADPH-dependent inhibition of CYP3A4 and four were analyzed for CYP2D6. All seven kaempferol glycosides and two kaempferol derivatives (4, 5, 8—14) appear to be the mechanism-based inhibitors of CYP3A4 enzyme in which the inhibition is irreversible and driven by the catalytic process. The other compounds showed no NADPH-dependent inhibition or reversible inhibition, and thus do not appear to be mechanism-based inhibitors. KI values for compounds 4, 5, 8—14 were in the range of 2.21—27.01 μM, whereas the kinact values were 0.23—0.65 min−1. Kaempferol-3-O-(2,3,4-tri-O-acetyl-α-L-rhamnopyranoside) (5) was found to be the most potent CYP3A4 inactivator with KI and kinact values of 2.21 μM and 0.45 min−1, respectively.