On the Cellular Basis of Hydrogen Sulfide Toxicity

Hydrogen sulfide (H2S) produced by colonic sulfate-reducing bacteria represents an insult to the intestinal epithelium potentially contributing to chronic disorders that are dependent on gene-environment interactions. Clinical and epidemiologic studies reveal either persistent sulfate-reducing bacteria colonization or higher H2S concentrations in the gut or feces of patients suffering from ulcerative colitis and/or colorectal cancer. However, there is not a satisfactory mechanistic model able to explain these circumstantial observations. In these studies, we first 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 HT-29 cl.16E cells. Sulfide showed chronic cytotoxicity in CHO cells with a %C1/2 of 368.57 Mmol/L. Sulfide was genotoxic for both cell lines but this effect was observed only when DNA repair was inhibited. The HT-29 cl.16E colonocyte cell line was less sensitive to sulfide than CHO cells. Furthermore when naked nuclei were directly treated with sulfide, DNA damage was observed at concentrations two orders of magnitude lower than previously observed with intact cells. This damage was effectively quenched by co-treatment with butylhydroxyanisole. Sulfide treatment also increased the number of oxidized bases recognized by formamidopyrimidine [fapy]-DNA glycosylase. These results confirmed the genotoxicity of sulfide and suggested that sulfide-induced genotoxicity is mediated by free radicals. Consequently we sought to define the early (30 min) and late (4 h) response of human non-transformed intestinal epithelial cells (FHs 74 Int) to a genotoxic---but not cytotoxic---concentration of sulfide (500 muM Na2S) using pathway specific quantitative RT-PCR arrays. Significant changes in gene expression were predominantly observed at 4 h, including PTGS2 (Cox-2; 7.9 fold upregulation), and IL-1A (interleukin 1 alpha; 5.2 fold downregulation). Functional pathway analysis indicated that sulfide modulates cell cycle progression and triggers both an inflammatory and DNA repair response. Together, these observations stress the possible role of sulfide as an insult in the intestinal environment that, given a predisposing genetic background, may lead to genomic instability or the cumulative mutations found in adenomatous polyps leading to colorectal cancer.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Animal Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Attene Ramos, Matias Sebastian

Contributors dc:contributor

• Gaskins, H.R.

• Biology, Molecular

Language dc:language

eng

Identifier

(MiAaPQ)AAI3347276

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/83616