4. Bioavailability of GCP

GCP, mainly genistein, is well absorbed from the small intestine and is taken up by the liver where genistein aglycone are conjugated with glucuronic acid and then transported into bile where it undergoes enterohepatic circulation. The excreted genistein in the bile was in the form of 7-O-beta-glucuronide. The re-infused genistein 7-O-beta-glucuronide was also well absorbed from the gut, although it occurred in the distal small intestine. Genistein in the form of glucuronide and sulfate conjugates, circulates and is distributed into systemic circulation and then excreted into the urine, mostly as glucuronide and sulfate conjugates.

After GCP administration, changes in serum concentration of genistein were detected as described below:

Method: 8 healthy male and female human subjects (4 of each) were given GCP in a 2g dose via oral administration. Whole peripheral blood was taken and tested at 0, 1, 3, 5, 7 and 24 hours after GCP ingestion. Urine was collected at 0, 2, 4, 6, 8, and 24 hours after GCP ingestion. The concentrations of GCP in serum and in urine were detected by HPLC. Soybean extract (SEB, a material in GCP) was taken as a control.

Results: GCP concentration in serum increased to peak levels 3 hours after GCP ingestion. The levels went down slowly during the next 5 to 7 hours and down to baseline 24 hours later. The results show there was a significantly higher genistein peak in the GCP intake group (apx. 5x higher than the SBE control), indicating that GCP is well absorbed in serum.