Tea has gained considerable attention as a cancer chemopreventive agent because of the growth inhibitory effect in cell cultures, anticarcinogenic effects in animal models and effect on risk reduction of cancer and heart disease in prospective human cohort studies. The polyphenol content in green tea and theaflavins and thearubigins in black tea have been suggested as responsible agents for the anticarcinogenic activity. A comparison of the polyphenol content of green and black tea prepared from tea bags from different manufacturers showed that due to the different content of tea leaves in the bag, some black tea preparations have similar catechin content compared to green tea preparations. It also has been shown that the antioxidant capacity as determined by the ORAC assay shows great variations among different tea preparations with black tea showing the highest ORAC value. There are only a limited number of studies investigating the bioavailability of green and black tea. Therefore we propose to study the bioavailability of tea polyphenols and their effect on the serum antioxidative capacity from green tea compared to black tea and a green tea extract dietary supplement in men with prostate cancer before the time of prostatectomy. The serum will be also used to study the in vitro growth inhibiting effect in androgen-dependent LNCaP and androgen-independent PC-3 cell lines. Prostate cancer was selected as an excellent model to study the chemoprevention effect of tea catechins because prostate carcinoma are slow growing and often remain subclinical for an extended period of time. Therefore chemoprevention is particularly suited as a primary or adjuvant therapy for maintaining prostate cancer in a dormant state. An important consideration of the effectiveness of dietary supplements in disease prevention is the concentration issue. Catechin concentrations used in in vitro studies are frequently higher than plasma concentrations reached after tea consumption. There are no studies showing tissue concentrations of catechins in humans. Therefore we are proposing to measure prostate tissue concentration of catechins and theaflavins at the time of prostatectomy after 5 days of consumption of either green tea, black tea or a green tea extract dietary supplement. In addition prostate tissues will be analyzed for the enzyme activity of ornithine decarboxylase (ODC), an androgen-responsive, rate-controlling enzyme in the polyamine biosynthesis. Urine will be analyzed for polyphenols to check compliance. The proposed studies will demonstrate if the consumption of 5 cups of green tea, black tea or green tea extract dietary supplement is sufficient to increase the concentration of catechin in prostate tissue to a level which can affect cellular processes contributing to carcinogenesis. Tea, serum, tissue and urine polyphenol concentrations will be analyzed using an HPLC method developed in our laboratory. The serum antioxidant capacity will be determined using the oxygen radical absorbance capacity assay recently established in our laboratory. ODC enzyme activity will be determined measuring the release of 14C CO2 from 14C ornithine. These studies will provide information important in designing studies to critically test the role of dietary supplementation in prostate cancer.
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| Henning, Susanne M; Aronson, William; Niu, Yantao et al. (2006) Tea polyphenols and theaflavins are present in prostate tissue of humans and mice after green and black tea consumption. J Nutr 136:1839-43 |
| Henning, Susanne M; Niu, Yantao; Liu, Yong et al. (2005) Bioavailability and antioxidant effect of epigallocatechin gallate administered in purified form versus as green tea extract in healthy individuals. J Nutr Biochem 16:610-6 |
| Henning, Susanne M; Niu, Yantao; Lee, Nicolas H et al. (2004) Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement. Am J Clin Nutr 80:1558-64 |
