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ARS Home » Southeast Area » Little Rock, Arkansas » Microbiome and Metabolism Research Unit » Research » Publications at this Location » Publication #195542
Title: DISTRIBUTION AND MOLECULAR FORMS OF SOY ISOFLAVONES IN ORGANS/TISSUES OF RATS AND PIGS

Author
item GU, LIWEI - ACNC/UAMS
item HOUSE, SUZANNE - ACNC
item Prior, Ronald
item BADGER, THOMAS - ACNC/UAMS

Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: 2/2/2026
Publication Date: 3/27/2006
Citation: Gu, L., House, S., Prior, R.L., Badger, T.M. 2006. Distribution and molecular forms of soy isoflavones in organs/tissues of rats and pigs [abstract]. The FASEB Journal. 20(4):A598.

Interpretive Summary: Isoflavones are bioactive components from soy and they may be beneficial for health. After absorption in the intestine, isoflavones exist in different concentrations and several molecular forms in various tissues. Different isoflavones and their different molecular forms have different activities. Tissues having concentrated bioactive isoflavones are expected to be the target tissue where isoflavones exert health effects. Our study was done in pigs and rats to understand the content of different isoflavones in various tissues. We found total isoflavone contents varied markedly in different organs of rats. The lowest contents were found in the brain, spleen, and fat; and the highest in intestines and colon. Approximately 22-45% of total isoflavones were free and the reminder was found in less active conjugates. The organs of rats and pigs differed in contents of isoflavones as well as proportion of free forms and conjugates. Daidzein is one of isoflavones in soy, and it can be metabolized into equol. Equol is considered to be the most bioactive among isoflavones. All rat organs contained equol, whereas pig tissues contained very low levels of equol. Our study delineated isoflavone profiles in tissues and identified new target tissues of isoflavones, which will help to understand their mechanisms of action in humans.

Technical Abstract: In order to assess the potential risks and benefits of soy isoflavones and mechanisms by which health effects occur, it is essential to have a complete understanding of their concentrations and molecular forms in target tissues. Sprague-Dawley rats (n=6) and piglets (n=3) were fed soy protein isolates. Thirteen or twenty organs/tissues were collected from rats or pigs for isoflavone analysis. Rats were perfused and pig tissues were rinsed with 0.09% saline to remove residue blood. A new extraction method enabled us to measure genistein, daidzein, O-DMA, and equol, including aglycone and conjugated forms. Total isoflavone contents varied markedly in different organs of rats (genistein or daidzein, 0.01-14 nmol/g; equol, 0.06-47 nmol/g). The lowest contents were found in brain, spleen, and fat; and the highest in intestines and colon. Approximately 22-45% of total isoflavones were free aglycones, with 21-66% being glucuronides and reminders (14%-42%) being sulfates in rat organs. Total isoflavone contents in pig organs/tissues ranged from 0 to 5.3 nmol/g and 0.4 to 14 nmol/g for genistein and daidzein, respectively (lowest in lung, highest in intestines). The organs of rats and pigs differed in contents of isoflavones as well as proportion of aglycones and conjugates. All rat organs contained equol as the major metabolite of daidzein, whereas pig tissues contained very low level of equol (0-0.2 nmol/g). This study delineated isoflavone profiles in tissues and identified new target tissues of isoflavones, which may help to understand their mechanisms of action in vivo.