On the Cellular Basis of Hydrogen Sulfide Toxicity
Attene Ramos, Matias Sebastian
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Permalink
https://hdl.handle.net/2142/83616
Description
Title
On the Cellular Basis of Hydrogen Sulfide Toxicity
Author(s)
Attene Ramos, Matias Sebastian
Issue Date
2008
Doctoral Committee Chair(s)
Gaskins, H.R.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
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.
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