Evidence That Hydrogen Sulfide Is a Genotoxic Agent

Abstract

Hydrogen sulfide (H 2 S) 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 H 2 S in the gut or feces of patients suffering from ulcerative colitis and colorectal cancer. However, a mechanistic model that explains the connection between H 2 S 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 Mmol/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 Mmol/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 Na 2 S 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, H 2 S may lead to genomic instability or the cumulative mutations found in adenomatous polyps leading to colorectal cancer.

Hydrogen Sulfide Induces Direct Radical-Associated DNA Damage

“…We previously showed for the first time that sulfide was genotoxic in mammalian cells using a modified SCGE assay where DNA repair was inhibited with hydroxyurea and 1-h-Darabinofuranosylcytosine (23). The present data not only confirm these findings but further show that sulfide is directly genotoxic, independent of cellular metabolism, and strongly suggests that this genotoxicity is mediated by free radicals.…”

“…We showed that Na 2 S was genotoxic in CHO and human intestinal HT-29 cells, but little is known about the nature of this toxicity (23). In a recent study, Baskar et al (35) supported our previous findings that H 2 S was genotoxic.…”

“…However, surprisingly little is known about H 2 S-induced DNA damage and its possible role as a mutagen or carcinogen, or its involvement in chromosomal instability. We previously showed that sulfide at concentrations similar to those found in the human and mouse intestine caused genomic DNA damage in Chinese hamster ovary (CHO) and human HT-29 colonic epithelial cells (23). Intriguingly, genotoxicity was only observed when DNA repair was inhibited with hydroxyurea and 1-h-D-arabinofuranosylcytosine.…”

Taurocholic acid metabolism by gut microbes and colon cancer

“…and the tumor surface in a subset of CRC 118,119 Indeed, the Gaskins' lab demonstrated that sulfide is genotoxic at doses found in the colon providing a reasonable explanation for these observations. [120][121][122][123] The rationale for this hypothesis is also supplemented by our long-term study of mammalian cell responses to the effects of exogenous sulfide. In a series of prior publications, we demonstrated that sulfide induces proliferative and inflammatory pathways in non-transformed intestinal crypt epithelial cells 120,121 and provided unequivocal evidence that sulfide is genotoxic at concentrations less than those measured previously in human colon leading to cellcycle arrest; and DNA damage, which is produced by oxidative stress.…”

“…In a series of prior publications, we demonstrated that sulfide induces proliferative and inflammatory pathways in non-transformed intestinal crypt epithelial cells 120,121 and provided unequivocal evidence that sulfide is genotoxic at concentrations less than those measured previously in human colon leading to cellcycle arrest; and DNA damage, which is produced by oxidative stress. [120][121][122][123] More recently, the genotoxic properties of sulfide have been demonstrated in nontransformed human intestinal epithelial cells with further evidence that sulfide modulates the expression of genes involved in cell-cycle progression, triggering both inflammatory and DNA repair responses. 121 Together with these data, our own published work showing that sulfide is directly genotoxic at high concentrations suggests that H 2 S could be a significant bacterial metabolite that initiates colon cancer.…”