Adipocytes account for more than 90% of human breast volume and secrete adipocytokines, which play a role in breast cancer development. Among the adipocytokines is leptin, which is secreted mainly by adipocytes and plays a key role in breast cancer development. Leptin expression is up-regulated in both obese and breast cancer patients, and promotes breast cancer cell growth. Exposure to environmental estrogens has also been found to be directly related to the development of breast cancer. Zeranol (Z) is a non-steroidal anabolic growth promoter with estrogenic activity that is widely used in the US beef industry due to its commercial benefits. Gossypol is a natural compound extracted from cottonseed that inhibits breast cancer growth, and is potentially a chemopreventive food component. This study focused on Z and bio-active Z-containing sera (ZS) collected from Z-implanted beef, and evaluated their adverse health risk to humans. We hypothesized that Z increases the risk of breast cancer in obese women. A cell proliferation assay, ELISA analysis, RT-PCR and Western blotting were performed to investigate the interaction of leptin, Z and (-)-gossypol in primary cultured normal human breast pre-adipocytes. The results indicated that Z and ZS stimulated the growth of pre-adipocytes isolated from normal human breast tissues by up-regulating cyclin D1 expression, while (-)-gossypol reversed this effect.

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