2005 年 27 巻 3 号 p. 177-184
The suppressive effect of (-)-epigallocatechin gallate (EGCG), the major polyphenolic constituent present in green tea, on 7,12-dimethylbenz[a]anthracene (DMBA)-induced chromosome aberrations (CA) in rat bone marrow cells was studied. Rats given EGCG before the DMBA injection displayed a considerably suppressed frequency of DMBA-induced CA in their bone marrow cells. The suppressive effect of EGCG (60 mg/kg body weight) given 24 h before was observed 24, 30, 48 and 72 h after the DMBA injection, but not at the early period (6, 12 and 18 h) after the DMBA treatment. On the other hand, EGCG (60 mg/kg body weight) given 0.5 h before DMBA suppressed DMBA-induced CA at all periods after the DMBA injection. The suppression of EGCG given 24 h or 0.5 h before was observed for all doses of DMBA (25, 50, 75 and 100 mg/kg) investigated. EGCG given at 60 mg/kg body weight 0.5 h before the DMBA injection showed greater suppressive effect than the same dose given 24 h before. The suppressive effect of EGCG given 0.5 h before was dosedependent in the range of 20-60 mg/kg body weight. Methyl methanesulfonate (MMS: direct-acting carcinogen)-induced CA were not suppressed by EGCG.
The administration of dehydroepiandrosterone (DHEA), a typical substrate for hydroxysteroid sulfotransferases, 0.5 h before DMBA injection also significantly suppressed DMBA-induced CA but DHEA given 24 h before did not.
These results suggest that EGCG has two different suppression mechanisms for DMBA-induced CA depending on the administration time. The suppression of DMBA-induced CA by EGCG given 24 h or 0.5 h before may result from the modification of microsomal enzyme system or the inhibition of sulfotransferase activity by EGCG, respectively.
