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Comparison of the estrogenic potencies of standardized soy extracts by immature rat uterotrophic bioassay.

de Lima Toccafondo Vieira M, Duarte RF, Campos LM, Nunan Ede A

Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil.

Soy phytoestrogens, isoflavones, are a primary class of plant-based estrogen alternatives being sold over the counter nowadays. Genistein, daidzein and glycitein are the major isoflavones found in soybeans, as aglycones and glycosides. Each isoflavone shows distinctive estrogenic activity and pharmacokinetics. Soy dry extracts, employed as pharmaceutical raw material for manufacturing isoflavone supplements, are standardized to contain 40% of total isoflavones, but the amount of each isoflavone is highly diverse. The influence of these compositional differences on the estrogenic potency of soy extracts was evaluated by uterotrophic bioassay. Five commercial samples of standardized soy dry extract, homogeneously suspended in arachis oil, were administered per os in serial doses (125-4150mg/kg bw/day) to immature female rats for 3 days. Soy extract samples with considerable diversity in isoflavone composition revealed different estrogenic potencies. Our results indicate a need of standardization of the individual isoflavone content in soy extracts.

Published 25 December 2007 in Phytomedicine, 15(1): 31-7.
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