Biol. Pharm. Bull. 28(10) 1903—1908 (2005)

Araliaceae) is frequently used as a traditional medicine, taken orally, in China, Korea, Japan and other Asian countries. The major components of ginseng, the ginsenosides, are glycosides that contain an aglycone with a dammarane skeleton. These ginsenosides have been reported to show various biological activities, including immunomodulatory effect, anti-inflammatory activity and antitumor effects. To explain these pharmacological actions, it is thought that ginseng saponins must be metabolized by human intestinal bacteria after their oral administration. For example, ginsenoside Rb1, Rb2 and Rc are transformed to 20-O-b-D-glucopyranosyl-20(S)-protopanaxadiol (compound K) by human intestinal bacteria, with ginsenoside Re transformed to protopanaxatriol. Akao et al. reported that compound K was detected in the blood after the oral administration of ginsenoside Rb1 to rats. We also reported that compound K was detected in the urine when ginsenoside Rb1 was orally administered to rats. Tawab et al. reported that ginsenoside F1, compound K and ginsenoside Rh1 were detected in the urine and blood when ginseng extract was orally administered to humans. These results suggest that protopanaxadiol ginsenosides may be metabolized, mainly to compound K, and protopanaxatriol ginsenosides to ginsenoside Rh1 and ginsenoside F1. Thus, these findings are in contrast with the report of Hasegawa et al. who suggested that ginsenoside Re was metabolized mainly to protopanaxatriol by human intestinal microflora. Therefore, to clarify the metabolism of the ginsenoside Re by human intestinal microflora, the ginsenoside Re-metabolizing intestinal bacteria were isolated from human feces, their metabolic activity measured and the estrogenic effect of ginsenoside Re, as well as its main metabolites, investigated.