GOODWIN, C.R.; DENZEL, S.A.; AMAN, S.A.; WOHLGEMUTH, S.E.; JULIAN, D.*: Free radical scavengers decrease toxic effects of hydrogen sulfide in vitro
Hydrogen sulfide (H2S) is well known as a metabolic toxin that poisons mitochondrial cytochrome c oxidase. H2S occurs naturally in a number of marine environments and a variety of invertebrates have specific physiological adaptations that allow them to tolerate this toxin. The most important of these adaptations is generally thought to be the ability to oxidize H2S to other less toxic thiols, especially thiosulfate. However, it has recently been shown that metal-catalyzed H2S oxidation in seawater produces free radicals. If free radicals are also produced by H2S oxidation in animal tissues, then free radical damage could be an important factor in H2S toxicity. To test this, we have exposed C6 rat glioma cells in culture to various concentrations and durations of H2S, both in the absence and in the presence of free radical scavengers. After H2S exposure, we assayed cell survival using the MTT assay and apoptosis using fluorescent nuclear stains. We found that the scavengers N-mercaptoproprionyl-glycine (NMPG) and reduced glutathione (GSH) protected cells in a dose-dependent manner from a 12-hour exposure to 1 mM H2S (evidenced by increased cell survival and decreased apoptosis). Oxidized glutathione (GSSG) and all scavengers tested increased sulfide oxidation, but some scavengers (e.g., SOD and dimethyl thiourea) decreased survival, suggesting that protection is provided both by sulfide oxidation and by scavenging specific free radical species. In animal tissues, we propose that reduction of GSSG to GSH can be linked with H2S oxidation, with GSH scavenging the resulting free radicals, thereby regenerating GSSG.
