Protective activity of butyrate on hydrogen peroxide-induced DNA damage in isolated human colonocytes and HT29 tumour cells

Abstract

Epidemiological studies support the involvement of short-chain fatty acids (SCFA) in colon physiology and the protective role of butyrate on colon carcinogenesis. Among the possible mechanisms by which butyrate may exert its anti-carcinogenicity an antioxidant activity has been recently suggested. We investigated the effects of butyrate and mixtures of SCFA (butyrate, propionate and acetate) on DNA damage induced by H(2)O(2) in isolated human colonocytes and in two human colon tumour cell lines (HT29 and HT29 19A). Human colonocytes were isolated from endoscopically obtained samples and the DNA damage was assessed by the comet assay. H(2)O(2) induced DNA damage in normal colonocytes in a dose-dependent manner which was statistically significant at concentrations over 10 microM. At 15 microM H(2)O(2) DNA damage in HT29 and HT29 19A cells was significantly lower than that observed in normal colonocytes (P < 0.01). Pre-incubation of the cells with physiological concentrations of butyrate (6.25 and 12.5 mM) reduced H(2)O(2) (15 microM) induced damage by 33 and 51% in human colonocytes, 45 and 75% in HT29 and 30 and 80% in HT29 19A, respectively. Treatment of cells with a mixture of 25 mM acetate + 10.4 mM propionate + 6.25 mM butyrate did not induce DNA damage, while a mixture of 50 mM acetate + 20.8 mM propionate + 12.5 mM butyrate was weakly genotoxic only towards normal colonocytes. However, both mixtures were able to reduce the H(2)O(2)-induced DNA damage by about 50% in all cell types. The reported protective effect of butyrate might be important in pathogenetic mechanisms mediated by reactive oxygen species, and aids understanding of the apparent protection toward colorectal cancer exerted by dietary fibres, which enhance the butyrate bioavailability in the colonic mucosa.