Absorption and plasma disposition of genistin differ from those of genistein in healthy women.

The chemical forms in which isoflavones appear in food or supplements seem to play an important role in their absorption efficiency. However, the influence of the chemical form of isoflavones on their plasma disposition has never been reported, although the metabolites of isoflavones circulating in the blood may have biological activity themselves. The purpose of the study was to investigate the pharmacokinetic profiles of genistein (GEN) and its phase II metabolites in the plasma and urine of healthy young women after multiple doses of pure aglycone and glucoside forms of GEN. Genistein-7-glucuronide (G-7-G), 4'-glucuronide (G-4'-G), 7-sulfate (G-7-S), 4'-sulfate (G-4'-S), 4',7-diglucuronide (G-4',7-diG), and 7-glucuronide-4'-sulfate (G-7-G-4'-S) besides unconjugated GEN were observed in human plasma after ingestion of GEN and its glucoside. Among these metabolites, G-4',7-diG and G-7-G-4'-S were the major ones, comprising both about 30% of the total amount of GEN in plasma. Compared with the aglycone, the amount of total GEN in vivo and those of G-4',7-diG and G-7-G-4'-S were increased after the glucoside intake. No difference was observed in urinary excretion between the aglycone and the glucoside. Overall, the absorption and plasma disposition of GEN were affected by the glucoside form.