Palmatine, an isoquinoline alkaloid from Phellodendron amurense Rupr., ameliorated gouty inflammation by inhibiting pyroptosis via NLRP3 inflammasome

Ethnopharmacological relevance: Palmatine (Pal), derived from Daemonorops margaritae (Hance) Becc and Phellodendron amurense Rupr. is a natural isoquinoline alkaloid widely used in clearing heat and drying dampness, purging the pathogenic fire and removing symptoms, detoxifying toxins and healing sores.

Aim of the study: Gout is a common metabolic inflammatory disease caused by the deposition of MSU crystals (MSU) in joints and non-articulation structures. Given the multiple toxic side effects of clinical anti-gout medications, there is a need to find a safe and effective alternative. We investigated the therapeutic effects of Pal on MSU crystal-induced acute gouty inflammation, targeting the NLRP3 inflammasome mediated pyroptosis.

Materials and methods: In vitro, mouse peritoneal macrophages (MPM) and rat articular chondrocytes were stimulated with LPS plus MSU in the presence or absence of Palmatine. In vivo, arthritis models include the acute gouty arthritis model by injecting MSU crystals in the paws of mice and the air pouch acute gout model by injecting MSU crystals into the mouse subcutaneous tissue of the back. Expression of NLRP3 inflammasome activation and NETosis formation was determined by Western blot, ELISA kit, immunohistochemistry, and immunofluorescence. In addition, the anti-cartilage damage of Palmatine on MSU-induced arthritis mice were also evaluated.

Results: Pal dose-dependently decreased levels of NLRP3 inflammasome activation related proteins NLRP3, ASC, caspase-1, IL-1β, HMGB1 and Cathepsin B. The NETosis protein levels of caspase-11, histone3, PR3 and PAD4 were remarkably reduced by Pal. Pal effectively blocked the activation of NLRP3 inflammasome, attenuated the caspase-11 mediated noncanonical NLRP3 inflammasome activation and intervened the formation of NETs, thereby inhibiting the pyroptosis. In vivo, Pal attenuated MSU-induced inflammation in gouty arthritis and protect the articular cartilage through inhibiting the pyroptosis of proteins NLRP3, ASC, caspase-1, IL-1β, HMGB1 and Cathepsin B, reducing levels of NETosis relevant proteins caspase-11, histone3, PR3 and PAD4 and up-regulating expression of protein MMP-3.

Conclusion: Palmatine ameliorated gouty inflammation by inhibiting pyroptosis via NLRP3 inflammasome.