No major difference in inhibitory susceptibility between CYP2C9.1 and CYP2C9.3

Objective. CYP2C9 is a polymorphic enzyme, and CYP2C9*3 is associated with decreased metabolic activity. In addition to the impaired metabolism, we investigated whether the CYP2C9*3 exhibited altered inhibitory susceptibility compared with CYP2C9*1. Method. In the present study, CYP2C9.1 and CYP2C9.3 were expressed in yeast. Using typical CYP2C9 substrates (diclofenac, tolbutamide and S-warfarin) and a potent CYP2C9 inhibitor (nicardipine), the K-i values for nicardipine on the three metabolisms in CYP2C9*1 and CYP2C9*3 were determined. Result. The ratios of K-i (CYP2C9*3) /K-i (CYP2C9*1) on tolbutamide, diclofenac and S-warfarin metabolisms were 1.2, 3.1 and 0.8, respectively. Conclusion. In conclusion, there are no significant differences in the inhibitory susceptibility between the two CYP2C9 enzymes.