Possible role of metabolism by the intestinal bacteria in geniposide-induced cytotoxicity was investigated in human hepatoma HepG2 cells. Initially, toxic effects of geniposide and its metabolite genipin were compared. Genipin, a deglycosylated form of geniposide, was cytotoxic at the concentrations that geniposide was not. As metabolic activation systems for geniposide, human intestinal bacterial cultures, fecal preparation (fecalase) and intestinal microbial enzyme mix were employed in the present study. When geniposide was incubated with human intestinal bacteria, either Bifidobacterium longum HY8001 or Bacteroides fragilis, for 24 h, the cultured media caused cytotoxicity in HepG2 cells. Fecalase and intestinal enzyme mix were also effective to metabolically activate geniposide to its cytotoxic metabolite. The present results indicated that genipin, a metabolite of geniposide, might be more toxic than geniposide, and that intestinal bacteria might have a role in biotransformation of geniposide to its toxic metabolite. In addition, among three activation systems tested, intestinal microbial enzyme mix would be convenient to use in detecting toxicants requiring metabolic activation by intestinal bacteria.

No abstract

-Baicalin, a glycoside present in Scutellaria baicalensis Georgi, is metabolized to its aglycone, baicalein, in intestine. In the present study, possible role of metabolism of baicalin by intestinal bacteria to baicalein in baicalin-induced toxicity was investigated in HepG2 cell cultures. As an intestinal bacterial metabolic system for baicalin, human fecal preparation containing intestinal microflora (fecalase) was employed. Initially, when cytotoxic effects of baicalin and baicalein were compared, baicalin was more cytotoxic than baicalein in HepG2 cells. When baicalin was incubated with fecalase, it was metabolized to baicalein. In addition, baicalin-incubated with fecalase reduced cytotoxicity of HepG2 cells in a concentration-dependent manner. Moreover, baicalin-incubated with fecalase significantly caused an increase in Bcl-2 expression together with a decrease in Bax expression and cleaved Caspase-3. Furthermore, anti-apoptotic effect by the incubation of baicalin with fecalase was also confirmed by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling assay. Taken all together, the findings suggested that metabolism of baicalin by human fecalase to baicalein might have protective effects against baicalin-induced toxicity in HepG2 cells.

No abstract

Orally administered herbal glycosides are metabolized to their hydrophobic compounds by intestinal microflora in the intestine of animals and human, not liver enzymes, and absorbed from the intestine to the blood. Of these metabolites, some, such as quercetin and kaempherol, are mutagenic. The fecal bacterial enzyme fraction (fecalase) of human or animals has been used for measuring the mutagenicity of dietary glycosides. However, the fecalase activity between individuals is significantly different and its preparation is laborious and odious. Therefore, we developed a fecal microbial enzyme mix (FM) usable in the Ames test to remediate the fluctuated reaction system activating natural glycosides to mutagens. We selected, cultured, and mixed 4 bacteria highly producing glycosidase activities based on a cell-free extract of feces (fecalase) from 100 healthy Korean volunteers. When the mutagenicities of rutin and methanol extract of the flos of Sophora japonica L. (SFME), of which the major constituent is rutin, towards Salmonella typhimurium strains TA 98, 100, 102, 1,535, and 1,537 were tested using FM and/or S9 mix, these agents were potently mutagenic. These mutagenicities using FM were not significantly different compared with those using Korean fecalase. SFME and rutin were potently mutagenic in the test when these were treated with fecalase or FM in the presence of S9 mix, followed by those treated with S9 mix alone and those with fecalase or FM. Freeze-dried FM was more stable in storage than fecalase. Based on these findings, FM could be usable instead of human fecalase in the Ames test.