Abstract

Abstract Objectives Obesity is a global epidemic and complex disease associated with an expansion of white adipose tissue (WAT). Obesity is accompanied by chronic low-grade inflammation, characterized by elevated levels of secreted pro-inflammatory cytokines and M1 macrophage infiltration into WAT. Eicosapentaenoic acid (EPA), a long-chain omega-3 polyunsaturated fatty acid, has been reported to have anti-obesity and anti-inflammatory properties. Moreover, we previously showed that EPA dose-dependently improved glucose intolerance, and inflammation in diet-induced obese mice. The objective of this study is to further determine mechanisms underlying these metabolic protective effects of EPA in epididymal WAT (e-WAT). Methods Male B6 mice were fed a HF diet (45% kcal fat) or a HF diet supplemented with 9, 18, or 36 g/kg of EPA-enriched fish oil (EPA 9, 18 or 36) for 14 weeks. We performed histological assessments in eWAT to determine adipocyte size; and measure macrophage infiltration by immunohistochemistry using galectin-3. RNA was isolated from eWAT for RNA sequencing and gene expression analyses. Data were analyzed using GraphPad Prism software. Results EPA36-fed mice had significantly lower body weight and fat percentage, compared to HF (P < 0.05). In addition, EPA18 and 36 significantly decreased weight of e-WAT (P < 0.05) and increased glucose clearance compared to HF (P < 0.05). Moreover, all EPA doses had smaller adipocytes (P < 0.05). Compared to HF, EPA18 and 36 significantly reduced macrophage infiltration in e-7.43 fold, respectively. Consistent with these changes, EPA18 and 36 reduced the mRNA levels of HF-induced inflammatory markers, including arachidonate 5-lipoxygenase (Alox5) and leukotriene B4 receptor (Ltb4r) compared to HF (P < 0.05). RNA Seq analyses revealed that EPA18 attenuated HF-induced inflammation in part by up-regulating cyclic AMP (cAMP)-dependent protein kinase A (PKA) signaling pathways and down-regulating triggering receptor expressed on myeloid cells 1 (TREM1) signaling. Conclusions EPA dose-dependently ameliorated HF-induced obesity and inflammation by reducing adipocyte size and macrophage infiltration and modulating pro- and anti-inflammatory pathways in e-WAT. These effects were achieved at human equivalent doses, that are currently prescribed for reducing triglycerides. Funding Sources USDA NIFA NIH.