Grape pomace extract attenuates high fat diet-induced endotoxemia and liver steatosis in mice

Obesity is a prominent global health concern associated with chronic inflammation and metabolic disorders, such as insulin resistance, type 2 diabetes, and non-alcoholic fatty liver disease (NAFLD). Excessive consumption of saturated fats exacerbates these conditions by increasing intestinal barrier permeability and circulating endotoxins. This study aims to investigate, in a murine model of high-fat diet (HFD)-induced obesity, the potential beneficial effects of a grape pomace extract (GPE), rich in phenolic compounds, at mitigating endotoxemia, and liver steatosis. Underlying mechanisms were characterized in an in vitro model of intestinal inflammation and permeabilization, as induced by tumor necrosis factor alpha (TNF alpha) in Caco-2 cell monolayers. Consumption of a HFD (60% calories from fat) for 13 weeks induced obesity, insulin resistance, and liver damage, evidenced by higher levels of plasma alanine aminotransferase (ALT), hepatic triglycerides content, and steatosis. In addition, HFD caused metabolic endotoxemia, hepatic toll-like receptor 4 (TLR4) upregulation and inflammation. GPE supplementation significantly reduced body weight and subcutaneous and visceral adipose tissue weight, and attenuated metabolic dysregulation. Furthermore, GPE decreased circulating LPS levels and mitigated HFD-mediated hepatic TLR4 upregulation, nuclear factor kappa B (NF-kappa B) activation, and downstream expression of proteins involved in oxidative stress and inflammation (NOX4, TNF alpha, and F4/80). In Caco-2 cells, GPE mitigated TNF alpha-induced monolayer permeabilization, decreased tight junction (TJ) protein levels, enhanced cellular oxidant production, activated redox-sensitive signaling, i.e., NF-kappa B and ERK1/2, and increased NOX1 and MLCK mRNA levels, the latter being a key regulator of monolayer permeability. The above findings suggest that GPE may protect against HFD-induced obesity and associated metabolic dysfunction (insulin resistance and NAFLD) by modulating intestinal barrier integrity and related endotoxemia.