Hydrogen sulfide (H(2)S) is an essential physiological product in brain. We investigated the expression of cystathionine-beta-synthase (CBS) and cystathionine-gamma-lyase (CGL), the two H(2)S synthesizing enzymes, in human cell lines and in human brain. Only astrocytes were strongly immunostained for CBS. Cultured astrocytes synthesized H(2)S at the rate of 15.06 micromol/g protein/h, which was 7.57 fold higher than microglial cells, 10.27 fold higher than SH-SY5Y cells and 11.32 fold higher than NT-2 cells. The H(2)S synthesis in all these cell types was inhibited by the CBS inhibitor hydroxylamine, but not by the CGL inhibitor propargylglycine (PAG). Synthesis of H(2)S by HUVEC cells was inhibited by PAG but not by hydroxylamine indicating that these vascular cells utilize CGL but not CBS. Inflammatory activation of microglia and astrocytes caused induction of NFkappaB, release of the inflammatory mediators TNFalpha, IL-6 and nitrite ions, down-regulation of CBS, and down-regulation of H(2)S synthesis. There was no effect of such treatment on HUVEC cells. The effects were partially reversed by pretreatment of cells with the H(2)S releasing agent NaSH. These data indicate that H(2)S is an endogenous antiinflammatory and neuroprotective agent under the synthetic control of CBS. H(2)S releasing drugs may have therapeutic potential in neurodegenerative disorders of aging such as Alzheimer disease and Parkinson disease.