Potential of short chain fatty acids to modulate the induction of DNA damage and changes in the intracellular calcium concentration by oxidative stress in isolated rat distal colon cells

Abstract

Short chain fatty acids (SCFA) are considered to be beneficial fermentation products in the gut by exerting trophic effects in non-transformed colon cells and by slowing proliferation and enhancing differentiation in colonic tumour cells. We have studied the further effects of SCFA on cellular events of early carcinogenesis, genotoxicity and cytotoxicity in rat distal colon cells. Cytotoxicity was assessed by measuring trypan blue exclusion and by determining the H2O2-induced changes in intracellular calcium concentration ([Ca2+]i) using a fluorospectrophotometer and the calcium-sensitive fluorescent dye Fura-2. The microgel electrophoresis technique (COMET assay) was used to assess oxidative DNA damage. Individual SCFA and physiological SCFA mixtures were investigated for their potential to prevent DNA and cell damage induced by H2O2. For this, freshly isolated colon cells were treated with H2O2 (100-500 microM) and 6.25 mM SCFA. We have found 100-500 microM H2O2 to cause a fast initial increase in [Ca2+]i, whereafter the levels gradually further increased. Addition of SCFA did not affect [Ca2+]i nor did it reduce the H2O2-induced increase in [Ca2+]i. Butyrate and acetate were able to reduce the induction of DNA damage by 100, 200 and 500 microM H2O2, respectively. In contrast, i-butyrate and propionate were ineffective. The degree of reduction of DNA damage for the two protective SCFA was similar. Physiological mixtures containing acetate, propionate and butyrate in ratios of 41:21:38 or 75:15:10 that are expected to arise in the colon after fermentation of resistant starches and pectin, respectively, did not show significant antigenotoxic effects. The major difference between butyrate and acetate, on one hand, and i-butyrate and propionate, on the other hand, is that the former compounds are utilized best as energy sources by the colon cells. Therefore, our results on antigenotoxicity coupled with the findings on [Ca2+]i homeostasis indicate that molecular effects on the energy system render these non-transformed, freshly isolated colon cells to be less susceptible to H2O2.