Chemopreventive effect of dietary flavonoid morin on chemically induced rat tongue carcinogenesis

The modifying effects of dietary exposure of the flavonoid morin on 4-nitro quinoline 1-oxide (4-NQO)-induced tongue tumorigenesis, the activities of p hase II detoxifying enzymes glutathione S-transferase (GST) and quinone red uctase (QR) in liver and tongue, and cell proliferation activity in tongue were investigated in male F344 rats. At 7 weeks of age, all animals except those treated with morin alone and control group were given 4-NQO (20 ppm) in drinking water for 8 weeks to induce oval neoplasms. Starting 7 days bef ore 4-NQO exposure, experimental groups were fed experimental diets contain ing morin (100 and 500 ppm) far 110 weeks ("initiation feeding"). Starting 1 week after the cessation of exposure to 4-NQO, other experimental groups given 4-NQO and a basal diet were given experimental diets for 22 weeks ("p ost-initiation feeding"). At week 32 week, "initiation feeding" of morin ca used a significant reduction in the incidence of tongue carcinoma (by 44-10 0%). "Post-initiation feeding" with morin also significantly decreased the frequency of tongue carcinoma (by 44%). Morin feeding elevated liver GST an d QR activities and GST activity in the anterior portion of tongue. Feeding with morin significantly lowered QR activity of the posterior part of the tongue. Dietary exposure to morin significantly decreased the proliferating cell nuclear antigen-positive index in the posterior portion. Also, morin feeding lowered tongue polyamine levels, especially in the "post-initiation feeding" group. Our results indicate that morin acts as a chemopreventive agent against tongue carcinogenesis induced by 4-NQO through modification o f detoxifying enzyme activities and/or cell proliferation activities. (C) 1 999 Wiley-Liss, Inc.