Hydrogen sulfide inhibits nitric oxide production and nuclear factor-κB via heme oxygenase-1 expression in RAW264.7 macrophages stimulated with lipopolysaccharide

Hydrogen sulfide (H2S), a regulatory gaseous molecule that is endogenously synthesized by cystathionine γ-lyase (CSE) and/or cystathionine β-synthase (CBS) from L-cysteine (L-Cys) metabolism, is a putative vasodilator, and its role in nitric oxide (NO) production is unexplored. Here, we show that at noncytotoxic concentrations, H2S was able to inhibit NO production and inducible NO synthase (iNOS) expression via heme oxygenase (HO-1) expression in RAW264.7 macrophages stimulated with lipopolysaccharide (LPS). Both H2S solution prepared by bubbling pure H2S gas and NaSH, a H2S donor, dose dependently induced HO-1 expression through the activation of the extracellular signal-regulated kinase (ERK). Pretreatment with H2S or NaHS significantly inhibited LPS-induced iNOS expression and NO production. Moreover, NO production in LPS-stimulated macrophages that are expressing CSE mRNA was significantly reduced by the addition of L-Cys, a substrate for H2S, but enhanced by the selective CSE inhibitor β-cyano-L-alanine but not by the CBS inhibitor aminooxyacetic acid. While either blockage of HO activity by the HO inhibitor, tin protoporphyrin IX, or down-regulation of HO-1 expression by HO-1 small interfering RNA (siRNA) reversed the inhibitory effects of H2S on iNOS expression and NO production, HO-1 overexpression produced the same inhibitory effects of H2S. In addition, LPS-induced nuclear factor (NF)-κB activation was diminished in RAW264.7 macrophages preincubated with H2S. Interestingly, the inhibitory effect of H2S on NF-κB activation was reversed by the transient transfection with HO-1 siRNA, but was mimicked by either HO-1 gene transfection or treatment with carbon monoxide (CO), an end product of HO-1. CO treatment also inhibited LPS-induced NO production and iNOS expression via its inactivation of NF-κB. Collectively, our results suggest that H2S can inhibit NO production and NF-κB activation in LPS-stimulated macrophages through a mechanism that involves the action of HO-1/CO.