Abstract:
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.
