Luteolin alleviates NLRP3 inflammasome activation and directs macrophage polarization in lipopolysaccharide-stimulated RAW264.7 cells

Pure plant extract luteolin has been demonstrated to possess numerous biological effects. However, the specific effect of luteolin on macrophage polarization and NOD-like receptor protein 3 (NLRP3) inflammasome activation has not been documented. In this study, Cultured RAW264.7 cells were treated with or without luteolin in the presence or absence of LPS. Subsequently, cell viability was tested by CCK-8 assay. Total reactive oxygen species (ROS) were measured by flow cytometry. NLRP3, apoptosis-associated speck-like protein containing CARD (ASC), caspase-1, inducible nitric oxide synthase (iNOS) and Arginase (Arg-1) protein expression was detected using western blotting. Enzyme-linked immunosorbent assay (ELISA) kits were used to detect the level of TNF-alpha, IL-18, and Interleukin-1 beta (IL-1 beta). Increased production of ROS and expression of NLRP3, ASC, caspase-1, IL-18 and IL-1 beta proteins were observed in RAW264.7 cells incubated with LPS and were effectively inhibited by 2 mu M luteolin. Furthermore, 2 mu M luteolin pretreatment enhanced the expression of M2 macrophage markers (Arg-1 and IL-10), and decreased the expression of markers associated with M1 macrophage polarization (TNF-alpha, IL-6 and iNOS). These results indicated that low-dose luteolin inhibits NLRP3 inflammasomes activation and promotes macrophage polarization toward an M2 phenotype, which provides new evidence for the anti-inflammation activity of luteolin.