Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

Dr. Nadine Brown (Children’s Hospital, Cincinnati, USA) determined the effect of equol enantiomers on mammary gland development and cancer prevention in the animal model of DMBA-induced breast cancer (Brown et al. 2010). Mammary gland development and differentiation in the rat is driven by estrogen, and high estrogen-environment such as early pregnancy has chemopreventive effects on breast cancer formation (Russo et al. 1990). Soy preparations and especially the isoflavones have been controversially discussed regarding their potential effect as chemopreventive agents, especially with regard to the time point of exposure, which indicated a better protection with early exposure (Lamartiniere 2002). Based on this hypothesis Brown tested S-equol in early phases of life.

Rats were exposed to 250 mg/kg of S- or R-equol during the neonatal (0-21 days) or the prepubertal (21-35 days) periods. Histological evaluation of the mammary glands showed that both enantiomers led to significant precocial mammary gland differentiation. Despite these morphological changes at the mammary gland, exposure to equol was found weakly chemopreventive for both, S- and R-equol when supplemented in the neonatal period. When supplementation took place in the prepubertal period, R-equol was found chemopreventive, but S-equol was not. It did, however, also not contribute to tumour growth stimulation in response to DMBA. The effect of R-equol corresponded to a 40 % reduction in tumour burden.

References

Brown NM, Lindley SL and Setchell K (2010). Equol enantiomers mimic genistein in impacting mammary gland development but not in breast cancer prevention. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.

Lamartiniere CA (2002). Timing of exposure and mammary cancer risk. J Mammary Gland Biol Neoplasia 7(1):67-76.

Russo J, Gusterson BA, Rogers AE, Russo IH, Wellings SR and van Zwieten MJ (1990). Comparative study of human and rat mammary tumorigenesis. Lab Invest 62(3):244-278.