Popular natural glycosides such as glycyrrhizin (GL, licorice), barbaloin (aloe) and baicalin (BG, Scutellaria baicalensis) were studied regarding their metabolic fates and actions in relation to intestinal bacteia by using germ-free and gnotobiote rats. When GL was administered orally, the aglycone, glycyrrhetic acid (GA), was not detected in the plasma or intestinal contents of germ-free rats, but was detected in considerable amounts in the plasma and intestinal contents of conventional and gnotobiote rats, associated with the human intestinal bacterium Eubacterium sp. strain GLH capable of hydrolyzing GL to GA. GL was not detected in the plasma of the three groups of rats after oral administration. GL was effective in the conventional and gnotobiote rats with liver injury caused experimentally by carbon tetrachloride, but not in germfree rats with liver injury. These results indicate that orally administered GL is a prodrug and activated to GA by intestinal bacteria. Barbaloin, a laxative, was ineffective in conventional rats, but showed strong purgative action to gnotobiote rats associated with the human intestinal bacterium Eubacterium sp. strain BAR, which is capable of transforming barbaloin to aloe-emodin anthrone. Barbaloin is also a prodrug and activated to aloe-emodin anthrone by human intestinal bacteria. Animal differences in the laxative effect of barbaloin are due to species differences in intestinal bacteria. When BG was administered orally to conventional rats, BG, but not the aglycone baicalein (B), was found in the plasma. However, when BG was administered to germ-free rats, both BG and B were hardly detected in the plasma. Even after oral administration of B, BG was detected, but not B. These findings suggest that BG is a prodrug hydrolyzed to B by intestinal bacteria, and then conjugated to BG from the absorbed B in the body.
Since long, it has been known that many types of mammalian cancer relates to exogenous causes and thus should be susceptible to intervention and prevention. Among these exogenous sources, microbes and microbial products have turned out to be of key importance. These microbial influence (s) upon tumorigenesis can be investigated either by comparative analysis of the composition of the microbial flora in individuals belonging to high- and low-risk populations, by investigating spontaneous tumor development in germfree (GF), ex-germfree (EX-GF) and conventional (CONV) animals and by investigation of fat and function of carcinogens and procarcinogens in GF, EX-GF and CONV animals. These three major routes of investigations are examplified. In the future, it is reasonable to assume that gnotobiotic and transgenic technology will contribute substantially to a better understanding of the complex interplay between a host and its micrioflora in tumorigenesis.
Adhesion to intestinal surfaces is considered a prerequisite for effective probiotic bacterial strains. In this study, the in vitro adhesion properties of dairy strains Lactobacillus rhamnosus LC-705, Lactococcus lactis ssp. cremoris ARH 74 and Propionibacterium freudenreichii ssp. shermanii JS were investigated using human intestinal Caco-2 cell cultures. Lactobacillus strain GG (ATCC 53103) was used as a positive probiotic control, because the strain is known to adhere to Caco-2 cell cultures. Enterotoxigenic human E. coli (H 10407) and bovine E. coli (B 44) strains were used as positive and negative control, respectively. Bacteria were radioactively labeled, and the adhesion to Caco-2 cell cultures was assessed using liquid scintillation. The tested strains adhered to Caco-2 cell cultures and the adherence was similar to that of Lactobacillus strain GG. The adhesion was significantly higher when compared to the negative E. coli control. Adhesion was concentration dependent and no saturation level was achieved with bacterial concentrations used in this study. The Caco-2 cell cultures were also pretreated with nonlabeled bacteria of one strain prior to adhesion of radiolabeled bacteria. The nonlabeled adhered bacteria influenced the adhesion of radiolabeled bacteria in only one case: the adhesion of P. freudenreichii was significantly reduced by previously adhered L. rhamnosus LC-705. This result may indicate competition for adhesion sites between these strains. The adhesion properties of Lc. lactis and P. freudenreichii to intestinal cells make the strains interesting as potential new probiotic strains.
The effects of the cell wall components of Lactobacillus casei on serum cholesterol and liver cholesterol levels were examined in diet-induced hypercholesterolemic rats. Male Sprague-Dawley rats at five weeks of age were fed a hypercholesterolemic diet that contained cholesterol (0.5 g cholesterol/100 g diet) and sodium cholate (0.125 g sodium cholate/ 100 g diet) for 13 days. The test diet was supplemented with cell wall components from the Lactobacillus casei strain Shirota (LC, 4 g/100 g diet) or its protease-treated preparation (LP, 4 g/100g diet). Hypercholesterolemia was observed in all of the groups fed the hypercholesterolemic diet; however, LP suppressed the elevation of serum total cholesterol level at seven days. Furthermore, both LC and LP significantly lowered the serum total cholesterol level in comparison with the control group, and maintained normal levels of serum HDL-cholesterol at the time of sacrifice. LP also increased fecal sterol excretion, while LC had no effect.