Soy Isoflavones Modulate Azoxymethane-Induced Rat Colon Carcinogenesis Exposed Pre- and Postnatally and Inhibit Growth of DLD-1 Human Colon Adenocarcinoma Cells by Increasing the Expression of Estrogen Receptor-beta

Author: Raju J, Bielecki A, Caldwell D, Lok E, Taylor M, Kapal K, Curran I, Cooke GM, Bird RP, Mehta R
Publication: J Nutr. 2009 Mar;139(3):474-81

Epidemiological studies indicate a protective effect of soy consumption against the development of cancer, including breast and prostate cancer. In Asian countries, were people traditionally eat a lot of soy foods, cancer rates relatively low. This study conducted by the University of Windsor, Onataria, investigated the lifetime protective effect of soy isoflavones in a rat model of colon cancer. It will be difficult to extrapolate the obtained results to humans because the lifetime of the rats in the experiment was only 2 years, but the results looked very promising. The lifetime exposure of the rats already starter when the rats were still in the embryonic stage by feeding soy isoflavones to the mother rats with. Also during lactation the young rats were exposed to soy isoflavones through the milk.

Rats were divided in three groups: control, low isoflavones dose (40 mg/kg) and high dose (1000 mg/kg). Colon cancer was induced in Sprague-Dwaley rats by injecting them with azoxymethane, a genotoxic colonic carcinogen is routinely used to induce colon tumours in rodents. After 26 weeks later, the rats were killed and investigated for colon aberrant crypt foci (clusters of abnormal tube-like glands in the lining of the colon) and tumors. The scientists found that the exposure to soy isoflavones had no influence on the number or multiplicity of the colon aberrant crypt foci but that the low-dose isoflavones resulted in a decreased tumor burden and size. Only 95% of the rats of the high-dose isoflavones group developed colon tumors as opposed to 100% of the control group and low-dose isoflavones group. Soy isoflavones also increased the expression of estrogen receptor-beta. On the other hand, no adverse or toxic effects of soy isoflavones were detected.

An in-vitro test showed that soy isoflavones stopped the growth of cultured human colon adenocarcinoma cells and also increased estrogen receptor-beta expression, indicating that this receptor plays a role in the anti-cancer effect of soy isoflavones.

The study concluded that that pre- and postnatal exposure to dietary soy isoflavones suppresses the growth of colon tumors in rats.