Diet supplemented with UA or EGCG confer protection against DNA damage in colonocytes

Abstract

Diet is an important factor in colorectal cancer. High fat diets are considered a risk factor for the development of colon cancer as they increase the content of bile acids in the colon. Bile acids have shown to induce the formation of reactive oxygen and nitrogen species, and these, in turn, induce DNA damage. On the other hand, diets rich in fruits and vegetables have shown preventive effects on colon cancer. A recent study from our lab showed chemopreventive effects of natural compounds in vitro by protection against oxidative DNA damage and stimulation of DNA repair. In this study, we evaluated the effects of in vivo consumption of two natural compounds, (ursolic acid (UA) and epigallocatechin gallate (EGCG)), and a bile acid, deoxycholic acid (DCA ), on DNA damage in colonocytes and lymphocytes isolated from Fischer 344 rats. These compounds were provided in the diet and administered daily for two weeks. Endogenous DNA damage (strand breaks, oxidized and alkylated bases) was evaluated using the Comet assay. Also, H2O2 and MMS were used, ex vivo, to investigate the potential of our natural compounds to protect against oxidative and alkylating damage, respectively. This study demonstrated that endogenous DNA damage in colonocytes was slightly higher than in lymphocytes. UA and EGCG decreased the levels of endogenous DNA damage in colonocytes, while in lymphocytes, only UA had preventive effects. There was a significant increase of DNA damage with H2O2 treatment when compared with endogenous DNA damage in colonocytes, while treatment with MMS showed a tendency to increase DNA damage but was not significant. UA protected against both types of induced DNA damage, while EGCG only protected against H2O2-induced damage. According to the literature, DCA induces DNA damage in vitro, however after two weeks of in vivo DCA treatment, increase of endogenous DNA damage in colonocytes or lymphocytes was not observed in this study. UA and EGCG protected colonocytes and lymphocytes against DNA damage. These results suggest that UA can protect DNA from both endogenous and induced DNA damage in both cell types. EGCG was found to protect only against endogenous and H2O2-induced DNA damage in colonocytes. Further studies are undergoing to verify the potential of these compounds on induction of DNA repair systems, specifically base excision repair, mismatch repair, and direct repair by O6-methylguanine DNA methyltransferase.