Abstract

Hydrogen sulfide (H₂S) is a gaseous mediator synthesized in mammalian tissues by three main enzymes—cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), and 3-mercaptopyruvate-sulfurtransferase—and its levels increase under inflammatory conditions or sepsis. Since H₂S and H₂S-releasing molecules afford inhibitory properties in leukocyte trafficking, we tested whether endogenous annexin A1 (AnxA1), a glucocorticoid-regulated inhibitor of inflammation acting through formylated-peptide receptor 2 (ALX), could display intermediary functions in the anti-inflammatory profile of H₂S. We first investigated whether endogenous AnxA1 could modulate H₂S biosynthesis. To this end, a marked increase in CBS and/or CSE gene products was quantified by quantitative real-time polymerase chain reaction in aortas, kidneys, and spleens collected from AnxA1^−/− mice, as compared with wild-type animals. When lipopolysaccharide-stimulated bone marrow–derived macrophages were studied, H₂S-donor sodium hydrosulfide (NaHS) counteracted the increased expression of inducible nitric oxide synthase and cyclooxygenase 2 mRNA evoked by the endotoxin, yet it was inactive in macrophages harvested from AnxA1^−/− mice. Next we studied the effect of in vivo administration of NaHS in a model of interleukin-1β (IL-1β)–induced mesenteric inflammation. AnxA1^+/+ mice treated with NaHS (100 μmol/kg) displayed inhibition of IL-1β–induced leukocyte adhesion/emigration in the inflamed microcirculation, not observed in AnxA1^−/− animals. These results were translated by testing human neutrophils, where NaHS (10–100 μM) prompted an intense mobilization (>50%) of AnxA1 from cytosol to cell surface, an event associated with inhibition of cell/endothelium interaction under flow. Taken together, these data strongly indicate the existence of a positive interlink between AnxA1 and H₂S pathway, with nonredundant functions in the control of experimental inflammation.