Bergamottin (BGM) is a major furanocoumarin constituent of grapefruit and is reported to have inhibitory effects on cytochrome P450 enzymes. This study investigated the chemical interactions between BGM and the enzyme CYP2C9 . BGM exhibited time-, concentration-, and NADPH-dependent inhibition of CYP2C9. Co-incubation with diclofenac, a reversible inhibitor of CYP2C9, attenuated the time-dependent enzyme inhibition. Exhaustive dialysis did not restore enzyme activity post-inhibition. Glutathione (GSH) and catalase/superoxide dismutase failed to reverse BGM-induced CYP2C9 inactivation. A GSH trapping study suggested that BGM was metabolized to an epoxide and/or γ-ketoenal that may have been responsible for the enzyme inactivation. In conclusion, BGM can be characterized as a mechanism-based inactivator of CYP2C9 acting via the formation of an epoxide and/or γ-ketoenal.
Grapefruit-mediated fruit–drug interaction has been well discussed in clinical practice. However, the biochemical mechanisms for such interaction are far beyond our understanding. The objectives of the present study aimed at the interaction between bergaptol (BGT) and CYP2C9. BGT, one of the major furanocoumarin constituents in grapefruit, has been reported to inhibit the activity of CYP2C9. And a number of furan-containing compounds are known to act as mechanism-based inactivators of CYP2C9. In this study, BGT was found to induce time-, concentration-, and NADPH-dependent irreversible inhibition of CYP2C9. A GSH conjugate was detected in an incubation mixture containing CYP2C9, BGT, NADPH, and GSH. Further mechanistic investigation revealed that a γ-ketoenal metabolite was responsible for the enzyme inactivation. The obtained data indicate that BGT was a mechanism-based inactivator of CYP2C9. The study would facilitate the understanding of the mechanistic insight into fruit–drug interactions mediated by grapefruits.
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