Role of Human Intestinal Prevotella oris in Hydrolyzing Ginseng Saponins

Abstract

The potential of intestinal bacteria to hydrolyze ginsenoside Rb₁ to 20-O-β-D-glucopyranosyl-20(S)-protopanaxadiol (I) was found in 79% of the fecal specimens from 58 human subjects whose age ranged from 1 to 64 years. Following a ginsenoside-Rb₁ -hydrolyzing activity assay, Prevotella oris strains were then isolated as a major bacterial species possessing the potential. All the intestinal isolates converted ginsenosides Rb₁ and Rd to I, ginsenoside Rb₂ to 20-O-[α-L-arabinopyranosyl-(1→6)-β-D-glucopyranosyl]-20(S)-protopanaxadiol (II), and ginsenoside Rc to 20-O-[α-L-arabinofuranosyl(1→6)-β-D-glucopyranosyl]-20(S)-protopanaxadiol (III) like fecal microflora, but did not attack ginsenosides Re or Rg₁ (protopanaxatriol-type). The isolates were susceptible to colimycin (MIC, 3.13 µg/ml) and then the treatment of specific pathogen free mice with colimycin (20 mg/kg/day) decreased intestinal bacterial Rb₁-hydrolyzing potential from 22.1 ± 1.2% to 4.7 ± 2.7%, while the decreased potential was restored to 30.7 ± 3.7% by the inoculation with P. oris isolates. These results suggest that the metabolism of pro-topanaxadiol saponins to metabolites I-III in the intestines seems most partly due to intestinal P. oris. In addition, the fact that neither intact ginsenoside Rb₁ nor its middle metabolic derivatives but only the final metabolite I was detected at 1.0-7.3 µg/ml in blood after oral administration of mice with ginsenoside Rb₁ (125 mg/kg) allows us to speculate that metabolites I-III are the most likely forms of protopanaxadiol saponins absorbed from the intestines.

key words

Panax ginseng - Araliaceae - ginsenosides - metabolites - intestinal bacteria - Prevotella oris