Fisetin Attenuates Human Macrophage Polarization and Pro-Inflammatory Responses via NLRP3 and NF-κB/MAPK Suppression

Natural compounds with anti-inflammatory properties are increasingly explored as therapeutic agents due to their lower risk of side effects compared with conventional drugs. Fisetin, a dietary bioflavonol abundant in fruits and vegetables, exhibits anti-inflammatory activity in several cell types, including murine macrophages. However, its effects on human macrophages remain unclear. In this study, human pro-inflammatory M1 macrophages were generated from THP-1 monocytes using PMA, LPS, and IFN-γ. The effects of fisetin on cytokine and chemokine secretion, reactive oxygen species (ROS) production, apoptosis, and phagocytic activity were evaluated. In addition, the NF-κB, MAPK, and NLRP3 inflammasome pathways were analyzed. This study shows that fisetin pre-treatment significantly suppressed LPS/IFN-γ-induced secretion of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β, IL-8) and chemokines (MCP-1, CCL5, CXCL9, CXCL10). It also reduced ROS generation, NLRP3 inflammasome activation, and phagocytic activity. Mechanistically, fisetin inhibited NF-κB activation as well as JNK/MAPK and p38/MAPK signaling, indicating that its anti-inflammatory actions are mediated through multiple pathways. Importantly, fisetin did not affect the viability or proliferation of THP-1-derived macrophages, suggesting that reduced cytokine release was primarily due to attenuation of macrophage polarization rather than cytotoxicity. Fisetin attenuates inflammatory responses in human M1 macrophages through suppression of NF-κB, MAPK, and NLRP3 inflammasome signaling. By limiting cytokine release, ROS production, and phagocytic activity without impairing cell survival, fisetin emerges as a promising natural candidate for managing chronic inflammatory disorders, including atherosclerosis, neurodegenerative diseases, and inflammatory bowel disease.