Intestinal bacterial hydrolysis is required for the appearance of compound K in rat plasma after oral administration of ginsenoside Rb1 from Panax ginseng

Ginsenoside Rb-1 from Panax ginseng root is transformed into compound K via ginsenosides Rd and F-2 by intestinal bacterial flora. Among 31 defined intestinal strains from man, only Eubacterium sp. A-44 transformed ginsenoside Rb-1 into compound K via ginsenoside Rd. The ginsenoside Rb-1-hydrolysing enzyme isolated from Eubacterium sp. A-44 was identical to ii previously purified geniposide-hydrolysing beta-D-glucosidase. When ginsenoside Rb-1 (200 mg kg(-1)) was administered orally to germ-free rats, neither compound K nor any other metabolite was detected in the plasma, intestinal tract or cumulative faeces 7 or 15 h after administration. Most of the ginsenoside Rb-1 administered was recovered from the intestinal tract, especially the caeca, and cumulative faeces indicating poor absorption of ginsenoside Rb-1. When ginsenoside Rb-1 was administered orally to gnotobiote rats mono-associated with Eubacterium sp. A-44, a significant amount of compound K was detected in the plasma and considerable amounts were found in the caecal contents and cumulative faeces 7 and 15 h after administration. A small amount of ginsenoside Rb-1 was detected in the caecal contents only 7 h after administration. These results indicate that orally administered ginsenoside Rbl is poorly absorbed from the gut but that its metabolite compound K, produced by ginsenoside Rbl-hydrolysing bacteria such as Eubacterium sp. A-44 in the lower part of intestine, is absorbed.