Development of a LC–MS/MS method to investigate the interference of pharmacokinetics of the main constituents inSaxifraga stolonifera: Involvement of drug metabolism enzymes
A specific and sensitive LC–MS/MS method was established for the simultaneous determination of bergenin, protocatechuic acid and gallic acid, the main active constituents of Saxifraga stolonifera (L.) Meerb. herb, in rat plasma. After fully validated, the method was applied to the comparative pharmacokinetic studies of the three compounds orally administered alone and in combination in the S. stolonifera extract, respectively. The results showed that the pharmacokinetic parameters, including Cmax, Tmax, AUC, CLz/F, MRT0-∞, were significantly different for both bergenin and protocatechuic acid in the extract as compared to the corresponding compounds administered alone. However, the pharmacokinetic behavior of gallic acid in the extract did not differ from that administered alone. Further studies found that quercetin, coexisting in the herb extract, significantly decreased the glucuronidation of bergenin through inhibiting the activities of UGT1A1 and UGT1A3, and reduced the metabolism of protocatechuic acid by inhibiting the activity of catechol-O-methyltransferase. Quercetin and other flavonoids occurring in the S. stolonifera extract might increase the absorption and improve the bioavailability of bergenin and protocatechuic acid by slowing down the liver metabolism. The findings provide a good guidance for the development and clinical application of S. stolonifera.