Dietary soy and green tea in the prevention of prostate cancer Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5138jh090

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  • Prostate cancer risk is significantly lower in Asian countries compared to the US, which has prompted interest in the chemo-preventative action of dietary components such as soy and green tea commonly found in Asian diets, such as soy and green tea. Studies have suggested that soy isoflavones and green tea catechins exert anticarcinogenic effects; however, the effects of dietary soy and green tea on prostate cancer development in vivo are understudied. We proposed that soy and green tea, containing a mixture of bioactive components, would be more potent chemopreventative agents than individual supplements. Using an in vitro system, we observed that soy extract induced significantly more apoptosis and Bax expression than the individual soy isoflavones genistein or daidzein. Similarly, green tea induced more apoptosis than epigallocatechin gallate (EGCG), by decreasing inhibitors of apoptosis proteins, XIAP, cIAP-1 and cIAP-2. Notably, soy extract and green tea did not induce cell cycle arrest or apoptosis in non-cancerous benign prostate hyperplasia (BPH-1) cells, suggesting that the effects of whole foods were tumor-cell specific. Chronic inflammation and nuclear factor-kappa B (NFkB) have been implicated in prostate cancer development, suggesting that factors that inhibit NFkB may serve as effective chemo-preventative agents. We therefore examined the effects of dietary soy, green tea, and the combination of soy and green tea in vivo on inflammation, NFkB activation and cancer development using a hormone-induced prostate cancer model. The combination of both soy and green tea decreased prostate inflammatory infiltration and cytokine (TNFa, IL-6 and IL-1b) levels, increased Bax expression, and decreased prostate hyperplasia. Interestingly, these effects were not apparent in soy alone or tea alone treated animals. The combination of soy and green tea also suppressed NFkB p50 activity via induction of IkBa. Together these results suggest that the combination of soy and green tea may inhibit hormone-induced proinflammatory NFkB signals that contribute to prostate cancer development. These studies suggest that food products that bear a combination of active compounds may be more efficacious as chemo-preventative agents than individual compounds, and combination of different dietary compounds may offer additional beneficial effects. This “whole food” based approach is significant for the development of dietary recommendations for prostate cancer prevention.
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