Insulin resistance and nonalcoholic steatohepatitis (NASH), characterized by hepatic steatosis combined with inflammation, are major sequelae of obesity. Currently, lifestyle modification (i.e., weight loss) is the first-line therapy for NASH. However, weight loss resolves steatosis but not inflammation. In this study, we tested the ability of resolvin D1 (RvD1), an anti-inflammatory and proresolving molecule, to promote the resolution initiated by calorie restriction in obese mice with NASH. Calorie restriction reduced adipose and liver weight (-56 and -13%, respectively; P<0.001), serum leptin and resistin levels, hepatic steatosis, and insulin resistance. In addition to these, mice receiving RvD1 during the dietary intervention showed increased adiponectin expression at both the mRNA and protein levels and reduced liver macrophage infiltration (-15%, P<0.01). Moreover, RvD1 skewed macrophages from an M1- to an M2-like anti-inflammatory phenotype, induced a specific hepatic miRNA signature (i.e., miR-219-5p and miR-199a-5p), and reduced inflammatory adipokine mRNA and protein expression and macrophage innate immune response. In precision-cut liver slices (PCLSs), which override the influence of circulating factors, RvD1 attenuated hypoxia-induced mRNA and protein expression of COX-2, IL-1β, IL-6, and CCR7. Of note, RvD1 anti-inflammatory actions were absent in macrophage-depleted PCLSs. In summary, RvD1 acts as a facilitator of the hepatic resolution process by reducing the inflammatory component of obesity-induced NASH.
Keywords: NAFLD; anti-inflammatory mediators; inflammation; macrophages; weight loss.