Lupeol reduces M1 macrophage polarization to attenuate immunologic dissonance and fatty acid deposition in rats with diet-induced metabolic syndrome

BACKGROUND: This study aimed to investigate whether lupeol could inhibit the inflammatory mediators associated with the regulation of macrophage phenotypes and functions in rats with diet-induced metabolic syndrome (MS). METHODS: Forty specific-pathogen-free Sprague Dawley rats were fed a high-fat diet (HFD) for 10 weeks to establish an MS model. Lupeol was prepared and administered to the rats intraperitoneally at 20, 50, or 100 mg/kg (the lupeol 20 mg/kg, lupeol 50 mg/kg, and lupeol 100 mg/kg groups respectively). After 28 days of continuous intraperitoneal administration, rats were anesthesia and euthanasia. The obesity index, blood glucose and lipid metabolism indexes of rats in each group were measured. The levels of insulin and inflammatory factors in each group were detected by enzyme-linked immunosorbent assay (ELISA) kits. The pathological changes of liver tissue in rats were observed by hematoxylin and eosin (HE) and oil red O staining. The polarization levels of M1 and M2 macrophages in peripheral blood mononuclear cells (PBMCs) were analyzed by flow cytometry. The transcription levels of M1 and M2 macrophages markers were detected by qRT-PCR. The expressions of inducible nitric oxide synthase (iNOS) and arginase-1 (Arg-1) proteins in heart tissues of rats in each group were analyzed by Western blotting. RESULTS: Lupeol significantly recovered fasting blood glucose and serum insulin levels, and reduced the production of proinflammatory cytokines, including interleukin (IL)-6, tumor necrosis factor alpha (TNF-α), and monocyte chemoattractant protein-1 (MCP-1), in the liver. It also elevated the expression of anti-inflammatory cytokines, including IL-4 and IL-10, in the MS model. Further, after treatment with lupeol, the levels of total cholesterol, triacylglycerol and low-density lipoprotein (LDL) were decreased, and high-density lipoprotein (HDL) were increased. Importantly, in the MS model group, lupeol remarkably inhibited M1 macrophages polarization (F4/80(+)iNOS(+)) while elevating M2 macrophages polarization (F4/80(+)CD206(+)) remarkably. At the same time, the levels of M1 markers, including inducible nitric oxide synthase, IL-1β, IL-6, and TNF-α, were markedly inhibited, while those of M2 markers, such as arginase-1, IL-10, CD206, and TGF-β, were markedly elevated in the MS model rats. CONCLUSIONS: Lupeol might promote M2 polarization of macrophages to relieve damage caused by MS.