Evidence That Hydrogen Sulfide Is a Genotoxic Agent

Abstract

Hydrogen sulfide (H₂S) produced by commensal sulfate-reducing bacteria, which are often members of normal colonic microbiota, represents an environmental insult to the intestinal epithelium potentially contributing to chronic intestinal disorders that are dependent on gene-environment interactions. For example, epidemiologic studies reveal either persistent sulfate-reducing bacteria colonization or H₂S in the gut or feces of patients suffering from ulcerative colitis and colorectal cancer. However, a mechanistic model that explains the connection between H₂S and ulcerative colitis or colorectal cancer development has not been completely formulated. In this study, we examined the chronic cytotoxicity of sulfide using a microplate assay and genotoxicity using the single-cell gel electrophoresis (SCGE; comet assay) in Chinese hamster ovary (CHO) and HT29-Cl.16E cells. Sulfide showed chronic cytotoxicity in CHO cells with a %C1/2 of 368.57 μmol/L. Sulfide was not genotoxic in the standard SCGE assay. However, in a modified SCGE assay in which DNA repair was inhibited, a marked genotoxic effect was observed. A sulfide concentration as low as 250 μmol/L (similar to that found in human colon) caused significant genomic DNA damage. The HT29-Cl.16E colonocyte cell line also exhibited increased genomic DNA damage as a function of Na₂S concentration when DNA repair was inhibited, although these cells were less sensitive to sulfide than CHO cells. These data indicate that given a predisposing genetic background that compromises DNA repair, H₂S may lead to genomic instability or the cumulative mutations found in adenomatous polyps leading to colorectal cancer. (Mol Cancer Res 2006;4(1):9–14)