Dimethyl fumarate ameliorates autoimmune hepatitis in mice by blocking NLRP3 inflammasome activation.

Dimethyl fumarate (DMF) is a fumaric acid derivative clinically approved for the treatment of some inflammatory diseases, but the underlying mechanism for its therapeutic effects remains incompletely understood. NLR family pyrin domain containing 3 (NLRP3) inflammasome activation has critical roles in innate immune responses to various infections and sterile inflammations. In this study, we aimed to explore whether DMF affects auto-immune hepatitis (AIH) in mice induced by concanavalin A (Con A) by modulating NLRP3 inflammasome activation. The results showed that DMF suppressed the activation of NLRP3 inflammasome activation in lipopolysaccharide-primed murine bone marrow-derived macrophages upon ATP or nigericin treatment, as evidenced by reduced cleavage of pro-caspase-1, release of mature interleukin-1ß (IL-1ß) and generation of gasdermin D N-terminal fragment (GSDMD-NT). DMF also greatly reduced ASC speck formation upon the stimulation of nigericin or ATP, indicating its inhibitory effect on NLRP3 inflammasome assembly. Consistent with reduced generation of GSDMD-NT, ATP or nigericin-induced pyroptosis was markedly suppressed by DMF. Moreover, DMF treatment alleviated mitochondrial damage induced by ATP or nigericin. Interestingly, all these effects were reversed by the protein kinase A (PKA) pathway inhibitors (H89 and MDL-12330A). Mechanistically, DMF enhanced PKA signaling and thus increased NLRP3 phosphorylation at PKA-specific sites to attenuate its activation. Importantly, DMF decreased serum levels of inflammatory cytokines and ameliorated liver injury in Con A-induced AIH of mice, concomitant with reduced the generation of caspase-1p10 and GSDMD-NT and alleviating mitochondrial aggregation in the liver. Collectively, DMF displayed anti-inflammatory effects by inhibiting NLRP3 inflammasome activation likely through regulating PKA signaling, highlighting its potential application in treating AIH.

Gout-associated monosodium urate crystal-induced necrosis is independent of NLRP3 activity but can be suppressed by combined inhibitors for multiple signaling pathways.

Monosodium urate (MSU) crystals, the etiological agent of gout, are formed in joints and periarticular tissues due to long-lasting hyperuricemia. Although MSU crystal-triggered NLRP3 inflammasome activation and interleukin 1ß (IL-1ß) release are known to have key roles in gouty arthritis, recent studies revealed that MSU crystal-induced necrosis also plays a critical role in this process. However, it remains unknown what forms of necrosis have been induced and whether combined cell death inhibitors can block such necrosis. Here, we showed that MSU crystal-induced necrosis in murine macrophages was not dependent on NLRP3 inflammasome activation, as neither genetic deletion nor pharmacological blockade of the NLRP3 pathway inhibited the necrosis. Although many cell death pathways (such as ferroptosis and pyroptosis) inhibitors or reactive oxygen species inhibitors did not have any suppressive effects, necroptosis pathway inhibitors GSK'872 (RIPK3 inhibitor), and GW806742X (MLKL inhibitor) dose-dependently inhibited MSU crystal-induced necrosis. Moreover, a triple combination of GSK'872, GW806742X, and IDN-6556 (pan-caspase inhibitor) displayed enhanced inhibition of the necrosis, which was further fortified by the addition of MCC950 (NLRP3 inhibitor), suggesting that multiple cell death pathways might have been triggered by MSU crystals. Baicalin, a previously identified inhibitor of NLRP3, inhibited MSU crystal-induced inflammasome activation and suppressed the necrosis in macrophages. Besides, baicalin gavage significantly ameliorated MSU crystal-induced peritonitis in mice. Altogether, our data indicate that MSU crystals induce NLRP3-independent necrosis, which can be inhibited by combined inhibitors for multiple signaling pathways, highlighting a new avenue for the treatment of gouty arthritis.