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Food Chem Toxicol. 2010 Nov;48(11):3042-50. doi: 10.1016/j.fct.2010.07.042. Epub 2010 Aug 4.

Mammary gland differentiation by early life exposure to enantiomers of the soy isoflavone metabolite equol.

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Division of Pathology and Laboratory Medicine, Cincinnati Children's Hospital Medical Center and the Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA.


The role of soy in reducing breast cancer risk has been suggested to be associated with early exposure to isoflavones, which alter mammary gland morphology. The objective of the study was to determine the effect of dietary exposure to the enantiomers of a key soy isoflavone metabolite, equol, on mammary gland development and later chemoprotection using the DMBA-induced animal model of breast cancer. Animals were exposed to S-(-)equol or R-(+)equol (250 mg/kg diet) during the neonatal (0-21 days) or prepubertal (21-35 days) periods only. Histological evaluation of the mammary glands showed that both enantiomers fed neonatally via the dam led to significant precocial mammary gland differentiation. By day 50, early S-(-)equol or R-(+)equol exposure resulted in a decrease in immature terminal end structures and an increase in mature lobules, suggesting an early 'imprinting' effect. Despite these morphological changes to the mammary gland, neonatal and prepubertal exposure to equol had no long-term chemoprevention against mammary tumors induced by DMBA, although for R-(+)equol there was a trend to delaying tumor formation. In summary, early exposure to equol was not chemopreventive, but neither did it increase tumor formation in response to DMBA, suggesting exposure in early life does not influence breast cancer risk.

[Indexed for MEDLINE]

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