Abstract
High-fat diet (HFD) and ethanol could synergistically induce liver damage, but the underlying mechanisms remain to be elucidated. M1-polarized macrophages have been demonstrated to be key players in ethanol-induced liver damage. The current study was designed to investigate whether hepatic steatosis could promote ethanol-induced liver injury by promoting liver macrophage M1 polarization. In the in vivo study, 12 weeks of HFD feeding induced a moderate increase in the F4/80 expression and protein levels of p-IKKα/β, p-IκBα, and p-p65, which was suppressed by single binge. In contrast, 8 weeks of HFD and multiple binges (two binges per week during the last 4 weeks) synergistically increased the F4/80 expression, mRNA levels of M1 polarization biomarkers including Ccl2, Tnfa, and Il1b, and protein levels of p65, p-p65, COX2, and Caspase 1. In the in vitro study, a nontoxic free fatty acids (FFAs) mixture (oleic acid/palmitic acid = 2: 1) induced a moderate increase of protein levels of p-p65 and NLRP3 in murine AML12 hepatocytes, which was inhibited by ethanol co-exposure. Ethanol alone induced proinflammatory polarization of murine J774A.1 macrophages evidenced by the enhanced secretion of TNF-α, increased mRNA levels of Ccl2, Tnfa, and Il1b, and upregulated protein levels of p65, p-p65, NLRP3, and Caspase 1, which was augmented by FFAs exposure. Collectively, these results suggest that HFD and multiple binges could synergistically induce liver damage by promoting the proinflammatory activation of macrophages in mice livers.