Luteolin attenuates hepatic and adipocyte fibrosis and insulin resistance by targeting toll-like receptors signaling pathway in diet-induced obese mice

The flavonoid luteolin possess a variety of anti-inflammatory properties, but little has known about the detailed mechanisms linked to the anti-metabolic syndrome action of luteolin based on the integration of the transcriptional profile and the phenotype biomarkers. The aim of this study was to investigate the protective role of luteolin on inflammation-mediated metabolic diseases, focusing on its role in modulating toll-like receptor (TLR) signaling pathway triggered up-regulation of pro-inflammatory cytokines. Above all, it provides novel insights into the effect of luteolin on the link among adiposopathy, insulin resistance, hepatic steatosis and fibrosis. C57BL/6J mice were fed a normal, high-fat, and high-fat + 0.005% (w/w) luteolin diet for 16 weeks. In this study, (a) luteolin treatment resulted in an improvement in chronic low-grade inflammation by modulating TLR-signaling pathway resulting in reduced pro-inflammatory cytokines and macrophage accumulation; (b) there is a positive relationship of TLR5, MKK4/7, p38 and JNK-related gene expressions and lipogenesis in luteolin-treated obese mice, which is linked to an attenuation of hepatic lipotoxicity with an increased hepatic anti-oxidant system; (c) luteolin prevented hepatic and adipocyte fibrosis by decreasing ECM accumulation and cathepsin gene expressions; (d) Emr1 and Ccl7 genes, important markers inducing low-grade inflammation, are affected by advancing age as well as body weight, and luteolin treatment normalized those gene expressions; (e) luteolin treatment improved insulin resistance by normalizing pancreatic islet dysfunction, and differentially modulating the plasma GLP-1 and GIP levels. Taken together, luteolin ameliorates the deleterious effects of diet-induced obesity and its comorbidity. Total RNA of adipose tissues was obtained from normal diet, high-fat diet and luteolin added high-fat diet-fed mice and mRNA expression-associated with inflammation was measured.