Hydrogen sulfide (H2S) is an important gasotransmitter that generated in mammalian cells from L-cysteine metabolism. Little is known about its protective role in oxidative stress. In the present study, we investigated whether H2S could affect homocysteine (HCY)-induced cytotoxicity and oxidative stress in vascular smooth muscle cells. Cultured A-10 cells were exposed to HCY treatment in the presence or absence of NaHS (donor of H2S). HCY induced cytotoxicity, increased levels of H2O2, ONOO-, and O-2(center dot-) in a time- and concentration-dependent manner. Low levels of NaHS (30 or 50 mu M) protected A-10 cells from cytotoxicity, decreased the production of H2O2, ONOO-, and O-2(center dot-) in the presence of HCY. Furthermore, NaHS enhanced inhibitory effects of NAC, GSH, DPI, SOD, L-NAME, or vitamin C on oxidized DCF or O-2(center dot-) formation induced by HCY. In conclusion, our findings provide the first evidence that low levels of H2S decrease reactive oxygen species and improve cell viability and by doing so limit cellular damage induced by HCY. (c) 2006 Elsevier Inc. All rights reserved.