Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2005
Publication Date: 3/14/2005
Citation: Gu, L., Prior, R.L., Fang, N., Ronis, M.J., Badger, T.M. 2005. Organ and subcellular distribution of genistein and diadzein in rats. The FASEB Journal. 19(4):A447.
Interpretive Summary: There are many health effects attributed to consumption of soy foods. Some of these effects are thought to be due to isoflavones bound to the protein. Until now, the subcellular distribution within cells was not known. We found in this study the isoflavones and their metabolites are highest in the cytosol, the fluid that contains the cellular organelles, such as the nucleus. This is important information, because it now allows further detailed studies to learn how the cells alter the molecular forms of the isoflavones and will help us determine the biologically active molecules that are responsible for the health effects of soy foods.
Technical Abstract: Many of the health effects of soyfoods are attributed to isoflavones (ISFs). Little is known about the molecular forms and the relative concentrations of soy ISFs in target organs. Acid hydrolysis or enzymatic hydrolysis (glucuronidase and sulfatase) was used to study ISF content in heart, brain, epididymis, fat, lung, testis, liver, pituitary gland, prostate gland, mammary glands, uterus, and kidney from rats fed an AIN-93G diet containing soy protein isolate. Heart had the lowest ISF content (undetectable) and the kidney had the highest (1.8 plus/minus 0.6 nmol/g genistein; 3.1 plus/minus 1.1 nmole/g diadzein). Acid hydrolysis released more (20-60%) aglycone in tissues than enzymatic digestion; both hydrolysis methods gave similar levels of ISFs in serum. Total ISF content within the liver as conjugated aglycone was 35% and the remainder was conjugated mainly as glucuronide, with some mixed glucuronide and sulfate conjugates. Subcellular distribution of total ISFs was 55-60% cytosolic, and 13-16% in each of the nuclear, mitochondria, and microsomal fractions. Soy ISFs: 1) distribute in a wide variety of tissues; 2) exist mainly as glucuronides and aglycones, at least in liver, and 3) the concentrations of the free aglycones, which are thought to be the bioactive molecules, are in the 200-250 pmol/g range, far below that required for in vitro effects of genistein and diadzein.