Objectives: Crystal-induced arthropathies are characterized by deposition of crystals into joints, resulting in articular inflammation and injury. Examples of such crystals are monosodium urate (MSU) involved in gout, and hydroxyapatite crystals (HA) involved in the pathogenesis of osteoarthritis (OA). Both of these crystals induce proinflammatory cytokines production by macrophages such as interleukin-1β (IL-1β) and interleukin-6 (IL-6). Hydrogen sulfide (H2S) is an important signaling molecule which has been recently involved in various pathophysiological processes, such as hypertension, inflammation, neurodegenerative diseases and metabolic disorders. Physiological and pharmacological levels of H2S can be reached, in vitro and in vivo, by H2S donors. This study was aimed at investigating the effect and the mechanism of action of H2S donors on crystal-induced pro-inflammatory responses in murine and human macrophages.
Methods: Immortalized murine bone marrow-derived macrophages (iBMDMs), human leukemia monocytic cell line (THP1) and primary murine bone marrow derived macrophages (BMDM) were primed (lipopolysaccharide or Pam3Cys), stimulated with HA or MSU crystals and treated with H2S donors (NaHS, sodium thiosulfate or GYY4137). H2S effect on crystal induced IL-6 and MCP-1 secretion were assayed by ELISA. H2S modulation of genes involved in inflammation was studied by qRT-PCR. Effects of H2S on inflammasome activation were assessed by immunoblot measuring caspase-1 processing and IL-1b maturation. Finally, H2S effects on crystal-induced reactive oxygen species (ROS) and cell proliferation were assayed by ROS quantification and MTT respectively.
Results: In vitro, H2S prevented HA crystal-induced IL6 and MCP-1 secretion in a dose-dependent manner. Moreover, we found that H2S diminished the activation of NLRP3 by HA and MSU crystals as indicated by reduced processed caspase-1 and cleaved IL-1b in cell supernatants. Finally, H2S decreased HA-induced ROS generation and restored normal cell proliferation.
Conclusions: In murine macrophages and human monocytes, H2S reduces crystal-induced IL-6 and IL-1b secretion, the latter by inhibiting NLRP3 inflammasome activation. Our study suggests that H2S-releasing compounds may be useful as anti-inflammatory drugs in crystal-associated diseases such as gout and OA.