Epigallocatechin Gallate Suppresses Inflammatory Responses by Inhibiting Toll-like Receptor 4 Signaling and Alleviates Insulin Resistance in the Livers of High-fat-diet Rats

EGCG is a major pharmacological compound in green tea. Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. Inflammation and insulin resistance are involved in the development of the disease. In this study, we investigated the beneficial effect of EGCG on the liver tissue of NAFLD rats induced by a high-fat diet and its underlying mechanism. Thirty Sprague-Dawley rats received a normal diet, a HFD and a HFD+EGCG. The expression levels of inflammatory signaling pathway genes (e.g., TLR4, TRAF6, IKK beta, NF-kappa B, TNF-alpha) and insulin signaling transduction pathway genes (e.g., PI3K, AKT, IRS-1, IRS-2) were detected in the liver. We observed that EGCG decreased the triglyceride (TG) concentration in rat livers and suppressed TLR4, TRAF6, IKK beta, p-IKK beta, p-NF-kappa B, and TNF-alpha levels compared with those in the HFD group, whereas PI3K, AKT, IRS-1, and IRS-2 indicators were improved. EGCG improves obesity-associated subacute hepatic inflammation states, probably through the TLR4 signaling pathway. Furthermore, EGCG also alleviated hepatic insulin resistance. These data indicate that EGCG improves NAFLD from two ways: inhibition of inflammation and improvement of insulin resistance in liver tissues.