SMEPPI: An indenone derivative that selectively inhibits M1 macrophage activation and enhances phagocytic activity

SMEPPI is a small molecule synthesized as a derivative of KR-62980 that has anti-diabetic and anti-inflammatory activities. Despite the established physiological effects of KR-62980, the effects and benefits of SMEPPI remain largely unexplored. This study investigated the immunomodulatory functions of SMEPPI on macrophages and inflammatory diseases. SMEPPI did not affect the differentiation and maturation of bone marrow-derived monocytes into macrophages, nor did it affect the proliferation of M1 or M2 macrophages. Although SMEPPI did not affect M2 macrophage polarization, it significantly inhibited IL-1β and IL-6 cytokine production in both M1 macrophages and activated RAW264.7 macrophages. Importantly, SMEPPI inhibited the expression and phosphorylation of NF-κB p65 through inhibition of Akt expression, preventing its translocation to the nucleus. It also promoted p65 degradation through the stimulation of the proteasomal degradation pathway by inducing the expression of proteasome-related genes, thereby inhibiting p65 transcriptional activity. SMEPPI also enhanced the expression of various molecules associated with macrophage phagocytosis, including CD68, CD33, and lectins, thereby increasing phagocytic activity. Moreover, SMEPPI mitigated lipopolysaccharides-induced acute lung injury by suppressing IL-1β and IL-6 production in M1 macrophages and reduced mortality related to severe lung injury. These findings indicate that SMEPPI effectively regulates inflammatory diseases by impeding p65-induced cytokine production and enhancement of phagocytosis by M1 macrophages.