Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2005
Publication Date: 3/4/2005
Citation: Gu, L., Prior, R.L., Fang, N., Ronis, M.J., Clarkson, T.B., Badger, T.M. 2005. Interspecies differences of isoflavone metabolic phenotypes in female rats, pigs, monkeys and humans. The FASEB Journal. 19(4):A446.
Interpretive Summary: Soy protein isolate (SPI) is the only protein used in soy infant formula. SPI is composed of protein and phytochemicals bound to it, and the protein itself and these phytochemicals can independently affect health. It turns out that the protein and the phytochemicals can be metabolized, and these metabolites can alter body function. Therefore, it is important to understand the molecular forms of these proteins and phytochemicals. We found in this study the monkeys do not have the same metabolites as humans after consuming SPI. Monkeys appear to have convert daidzein to equol at a much higher rate than do humans and since equol is more potent than daidzein, the health effects in monkeys may be quite different than humans.
Technical Abstract: Isoflavone (ISF) metabolic phenotypes have been related to physiological effects in humans. ISF metabolism was studied in animals typically used as models to study health effects in humans. Female rats (n=9), pigs (n=4), monkeys (n=15), and humans (n=6) were fed diets containing soy protein isolate. Total ISF aglycones and metabolites (DHD, DHG, O-DMA, equol) were measured in urine and serum using LC/MS after enzymatic deconjugation. Approximately 79% and 52% (molar ration) of ISF metabolites in rat and monkey serum was equol; whereas less than 10% was detected in the serum of pigs and humans. On the other hand, diadzein and genistein contributed to 82% of metabolites in pigs and 91% of metabolites in humans. Monkeys excreted ISF mostly as unconjugated aglycones (91%). Rats excreted 44% of metabolites as aglycones and a similar proportion as glucuronides. Pigs and humans excreted ISFs in the form of glucuronides (>85%) with less than 10% being aglycone. ISFs in human serum were predominantly glucuronides (73%) with 26% as sulfates and the remainder being aglycones; whereas 64% of ISFs in monkey serum were sulfates and 34% being glucuronides. It appears that pigs have an overall metabolic profile closer to humans than rats or monkeys.