Identification of absolute conversion to geraldol from fisetin and pharmacokinetics in mouse

Fisetin (3,3′,4′,7-tetrahydroxyflavone) is a flavonoid found in several fruits, vegetables, nuts, and wine and has anti-oxidant, anti-inflammatory, and anti-angiogenic properties. Geraldol is the 3′-methoxylated metabolite of fisetin (3,4′,7-trihydroxy-3′-methoxyflavone). The concentration of fisetin and geraldol in mouse plasma was determined by LC–MS/MS, following direct protein precipitation. These concentrations were determined after administration of fisetin at doses of 2 mg/kg (i.v.) and 100 and 200 mg/kg (p.o.). The method was validated in terms of linearity, accuracy, precision, matrix effect, and stability. The pharmacokinetics parameters of fisetin and geraldol were successfully determined using a validated method in mice. Results indicated that fisetin was very rapidly methylated to geraldol in vivo. Following administration of fisetin, it was observed that the C_max and AUC values for geraldol were higher than those of fisetin. The absolute bioavailability of fisetin was calculated as 7.8% and 31.7% after oral administration of 100 and 200 mg/kg fisetin, respectively. This method was successfully applied to determine the pharmacokinetic parameters of fisetin and its main metabolite geraldol in mouse plasma. Geraldol was the dominant circulating metabolite after fisetin administration in vivo.