|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 2005 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 2004 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 2003 : ¥700,000 (Direct Cost : ¥700,000)
The structures of soybean isoflavones are similar to that of estrogen and have received attention as beneficial compounds for preventing hormone-dependent cancer and life-related diseases. However, few studies regarding the effects of other food factors on isoflavone bioavailability have been reported. Daidzein that is a major isoflavone found in soybean is metabolized to equol by intestinal microflora, and the metabolite exhibits a stronger estrogenic activity than daidzein. Recent studies suggest that the clinical effectiveness of isoflavones might be due to their ability to produce equol in the intestine. Fructooligosaccharides (FOS), a mixture of indigestible and fermentable sugars, stimulate the growth of bifidobacteria in the intestine. Thus, it is postulated that dietary FOS may affect the bioavailability of isoflavone glycosides and stimulate transformation of daidzein to equol.
In 2003, since it is postulated that equol production may increase at 12h after feeding isoflavone co
njugates, 12 h-starvated rats were used. The rats were fed a diet with isoflavone conjugates (I) or a diet with I and FOS (IF) for two weeks before the starvation. However, there was no significant difference on equol production from daidzein between the I and IF groups. No significant difference was also observed on the production by 12 h-starvation.
In 2004, the kinetics of equol and O-desmethylangolensin(O-DMA), another metabolite of daidzein, in rats fed a FOS supplemented diet or a control diet were examined in blood collected from central vein, and by measuring urinary excretion at 24-48h and 48-72h after a single intragastric administration of isoflavone conjugates. In the FOS fed group, equol concentration was significantly higher in the FOS-fed group than in the control group at 48h and 72h. Thus, FOS enhanced equol production from daidzein, but opposite result was observed for O-DMA. Furthermore, to determine a direct effect of equol on bone loss, eight-week-old female ovariectomized (OVX) mice were used. As the results, equol inhibited bone loss apparently without estrogenic activity in the reproductive organs of OVX mice.
In 2005, to determine changes in intestinal microbiota produced by the administration of FOS and isoflavones, terminal restriction fragment length polymorphism (T-RFLP) analysis of amplified 16S rRNA genes was used. Sequence analysis indicated that despite isoflavone administration, FOS-fed rats were colonized mainly by members of Bifidobacterium and Lactobacillus. The results of real-time PCR indicated that Lactobacillus was classified as L. murinus or L. animalis. Bifidobacterium is one of species, which can produce equol, indirectly. However, identifying equol-producing bacteria was complicated. Other factors, which may enhance equol production, are also existed such as hydrogen gas and short chain fatty acids. FOS increase hydrogen gas, propionate, and butyrate in vivo, but in an in vitro study, FOS inhibited equol production. Further studies should be conducted to clarify this discrepancy between the results of the in vivo and in vitro studies. Less