Pharmacokinetic interaction of diosmetin and silibinin with other drugs: Inhibition of CYP2C9-mediated biotransformation and displacement from serum albumin.

Diosmin and silibinin (SIL) are polyphenolic compounds which are the active components of several drugs and dietary supplements. After the oral administration of diosmin (flavonoid glycoside), only its aglycone diosmetin (DIO) reaches the systemic circulation. Both DIO and SIL form complexes with serum albumin and are able to inhibit several cytochrome P450 enzymes. Therefore, it is reasonable to hypothesize that these polyphenols may displace some drugs from serum albumin and inhibit their biotransformation, potentially leading to the disruption of drug therapy. In this study, the inhibitory action of DIO and SIL on CYP2C9-catalyzed metabolism of diclofenac to 4'-hydroxydiclofenac was examined, using warfarin as a positive control. Furthermore, interaction of DIO and SIL with human and bovine serum albumins as well as the displacement of warfarin from albumin by DIO and SIL were tested, employing steady-state fluorescence spectroscopy, fluorescence anisotropy, ultrafiltration, and molecular modeling. It is demonstrated that DIO and SIL are potent inhibitors of CYP2C9 enzyme and are able to displace the Site I ligand warfarin from human serum albumin. Because DIO and SIL may interfere with the pharmacokinetics of several drugs through both ways, we need to consider the potentially hazardous consequences of the consumption of diosmin or SIL together with other drugs.