BACKGROUND/OBJECTIVES: The aim of this study was to characterize the effects of Maresin 1 (MaR1) in obesity-related liver steatosis and the mechanisms involved. METHODS: MaR1 effects on fatty liver disease were tested in ob/ob (2-10 mu g kg(-1) i.p., 20 days) and in diet-induced obese (DIO) mice (2 mu g kg(-1), i.p., or 50 mu g kg(-1), oral gavage for 10 days), as well as in cultured hepatocytes. RESULTS: In ob/ob mice, MaR1 reduced liver triglycerides (TG) content, fatty acid synthase (FAS) and stearoyl-CoA desaturase-1 protein expression, while increased acetyl-CoA carboxylase (ACC) phosphorylation and LC3II protein expression, in parallel with a drop in p62 levels. Similar effects on hepatic TG, ACC phosphorylation, p62 and LC3II were observed in DIO mice after MaR1 i.p. injection. Interestingly, oral gavage of MaR1 also decreased serum transaminases, reduced liver weight and TG content. MaR1-treated mice exhibited reduced hepatic lipogenic enzymes content (FAS) or activation (by phosphorylation of ACC), accompanied by upregulation of carnitine palmitoyltransferase (Cpt1a), acyl-coenzyme A oxidase (Acox1) and autophagy-related proteins 5 and 7 (Atg5-7) gene expression, along with increased number of autophagic vacuoles and reduced p62 protein levels. MaR1 also induced AMP-activated protein kinase (AMPK) phosphorylation in DIO mice and in primary hepatocytes, and AMPK inhibition completely blocked MaR1 effects on Cpt1a, Acox1, Atg5 and Atg7 expression. CONCLUSIONS: MaR1 ameliorates liver steatosis by decreasing lipogenic enzymes, while inducing fatty acid oxidation genes and autophagy, which could be related to AMPK activation. Thus, MaR1 may be a new therapeutic candidate for reducing fatty liver in obesity.