Isopanepoxydone inhibits oxidative damage in murine alveolar macrophages via NRF2 and NLRP3 inflammasome

Background: Respiratory diseases due to particulate matter are a serious health issue. We sought to investigate the efficacy of isopanepoxydone (ISO) isolated from the Panus rudis as a therapeutic against particulate matter-induced respiratory complications. Materials and Methods: ISO was isolated from a culture broth of Panus rudis using solvent partition, silica gel, and column chromatography, and high-performance liquid chromatography. Its chemical structure was determined spectroscopically. Murine alveolar macrophages (MH-S) were treated with ISO to investigate the inhibition of nitric oxide (NO) while cytotoxicity was investigated via a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The expression of pro-inflammatory mediators, cytokines, and protein expression levels in the oxidative protective and inflammasome pathway were also investigated. Reactive oxygen species in MH-S cells were investigated using 2′,7′-dichlorofluorescein diacetate while immunofluorescence was performed to investigate the expression of activated apoptosis-associated speck-like proteins (ASC) containing a caspase recruitment domain in MH-S cells. Results: ISO effectively inhibited CFA-induced NO production with no cytotoxicity on MH-S cells and pro-inflammatory mediators and cytokines were also inhibited (except tumor necrosis factor α and interleukin-6). ISO enhanced the protein expression of nuclear factor erythroid 2–related factor 2, while suppressing proteins in the inflammasome pathway, but did not suppress the expression of nuclear factor-kappa B. ISO also reduced detectable ROS other than preventing the activation of ASC. Conclusion: Pathways of action of ISO in MH-S cells that prevent oxidative damage and suppress the expression of proteins in the inflammasome pathway were investigated. ISO may be developed as a treatment for respiratory inflammation.