Comparison of oral bioavailability of genistein and genistin in rats

Genistein (GT) is an isoflavone from Leguminosae and has received much attention as a phytoestrogen. Genistin is a glycoside form of GT (genistein-7-O-β-d-glucopyranoside, GT-glu) is mainly found in soy-derived foods. In this study, we examined the pharmacokinetic properties and bioavailability of GT in rats and compared with those of GT-glu. In order to characterize and compare the pharmacokinetics of GT and GT-glu, these compounds were administered intravenously and orally. The plasma concentration of GT was determined by HPLC after enzymatic hydrolysis. After oral administration of GT with various doses (4, 20, 40 mg/kg), the bioavailability of GT was 38.58, 24.34 and 30.75%, respectively. The Tmax, Cmax and AUC(0–∞) of GT after oral administration of GT (40 mg/kg), were 2 h, 4876.19 ng/ml, 31,269.66 ng h/ml, respectively. When smaller amount of GT was administered, the faster Tmax was observed. Oral administration of GT-glu resulted in longer Tmax, lower Cmax, and greater bioavailability than that of GT. The pharmacokinetic parameters of GT following oral administration of GT-glu (64 mg/kg as GT-glu, 40 mg/kg as GT) were obtained as follows: 8 h (Tmax), 3763.96 ng/ml (Cmax), 51,221.08 ng h/ml (AUC(0–∞)) and 48.66% (absolute bioavailability), respectively. These results indicate that the oral bioavailability of GT-glu is greater than that of GT.