ABSTRACT
Prostate carcinoma is the second leading cause of death as a result of cancer in men in the Western world.1 Evidence shows that androgens can be risk factors for prostate cancer development.2 Androgen action in many organs, such as prostate and skin, is dependent on the conversion of testosterone (T) by a NADPH-dependent 5α-reduc-
12.1 Introduction ................................................................................................. 211 12.2 Aromatase and 5α-Reductase in Estradiol Biosynthesis ............................ 212 12.3 Inhibition of Aromatase by Tea Polyphenols .............................................. 213 12.4 Inhibition of 5α-Reductase by Finasteride and Dutasteride ....................... 214 12.5 Chemoprevention of Prostate Cancer with Finasteride .............................. 214 12.6 Inhibition of 5α-Reductase by Tea Polyphenols ......................................... 215 12.7 Inhibitory Effects of Tea Polyphenols and 5GG on the Expression of
Androgen Receptor Protein ........................................................................ 215 12.8 Inhibitory Effects of TF3 and 5GG on the Expression of Androgen
Regulated Gene (PSA) ................................................................................ 216 12.9 Inhibitory Effects of Tea Polyphenols and 5GG on Cell Proliferation
of LNCaP Prostate Cancer Cells ................................................................. 216 12.10 The Mechanism of Prostate Cancer Chemoprevention by Tea
and Tea Polyphenols .................................................................................... 216 Acknowledgments and Notes ................................................................................. 217 References .............................................................................................................. 218
tase to 5α-dihydrotestosterone (DHT), which then binds to androgen receptor (AR) to exert its biological function.3 Inhibition of 5α-reductase would limit the availability of DHT; therefore, 5α-reductase inhibitors would be useful in selective treatment of DHT-dependent diseases, such as benign prostate hyperplasia, prostate cancer, hirsutism, male pattern alopecia, and acne, without affecting testosterone-dependent testicular function, sexual behavior, and muscle growth.3,4
There are at least two different isoenzymes (type 1 and type 2) of 5α-reductase in mammalian organs. Their differential localization in cells5 suggests that they may play selective roles in the development and growth of androgen-sensitive organs or tumors. Most 5α-reductase inhibitors are steroids, such as nasteride and dutasteride, or compounds with steroid-like structures. In this chapter, it is demonstrated that major constituents of black tea polyphenol theaavins and of green tea polyphenol catechins inhibit the enzyme 5α-reductase.4,6 The presence of 5α-reductase inhibitors in tea beverage may implicate to known geographic differences in the incidence of prostate cancer in certain populations that preferentially consume these beverages.7
