Inhibition of aromatase activity by green tea extract catechins and their endocrinological effects of oral administration in rats

We orally administered polyphenone-60 (P-60), green tea extract catechins, in the diet (0, 1.25 and 5%) to male rats for 2, 4 and 8 weeks initiated at 5 weeks old. It was found that a 5% dose to male rats for 2–8 weeks induced goiters and decreased weights of the body, testis and prostate gland. Endocrinologically, elevating plasma thyroid stimulating hormone (TSH), luteinizing hormone (LH) and testosterone levels and decreasing tri-iodothyronine (T3) and thyroxine (T4) levels were induced by this treatment. We also found that P-60 as a whole and some of its constituents exhibited inhibitory effects on human placental aromatase activity by in vitro assay. The concentration of P-60 that required producing 50% inhibition of the aromatase activity (IC50 value) was 28 μg/ml. The IC50 values of (−)-catechin gallate (Cg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg) and (−)-gallocatechin gallate (GCg) were 5.5×10−6, 1.0×10−4, 6.0×10−5 and 1.5×10−5 m, respectively. (−)- Epicatechin gallate (ECg) at 1.0×10−4 m produced 20% inhibition. (−)-Epicatechin (EC) and (+)-catechin (CT) exhibited no effects on aromatase activity. The endocrinological changes observed in vivo were in conformity with antithyroid effects and aromatase inhibition effects of P-60 and its constituents.