Effects of the green tea polyphenol epigallocatechin-3-gallate on high-fat diet-induced insulin resistance and endothelial dysfunction

Abstract

Insulin resistance, a hallmark of metabolic disorders, is a risk factor for diabetes and cardiovascular disease. Impairment of insulin responsiveness in vascular endothelium contributes to insulin resistance. The reciprocal relationship between insulin resistance and endothelial dysfunction augments the pathophysiology of metabolism and cardiovascular functions. The most abundant green tea polyphenol, epigallocatechin-3-gallate (EGCG), has been shown to have vasodilator action in vessels by activation of endothelial nitric oxide synthase (eNOS). However, it is not known whether EGCG has a beneficial effect in high-fat diet (HFD)-induced endothelial dysfunction. Male C57BL/6J mice were fed either a normal chow diet (NCD) or HFD with or without EGCG supplement (50 mg·kg(-1)·day(-1)) for 10 wk. Mice fed a HFD with EGCG supplement gained less body weight and showed improved insulin sensitivity. In vehicle-treated HFD mice, endothelial function was impaired in response to insulin but not to acetylcholine, whereas the EGCG-treated HFD group showed improved insulin-stimulated vasodilation. Interestingly, EGCG intake reduced macrophage infiltration into aortic tissues in HFD mice. Treatment with EGCG restored the insulin-stimulated phosphorylation of eNOS, insulin receptor substrate-1 (IRS-1), and protein kinase B (Akt), which was inhibited by palmitate (200 μM, 5 h) in primary bovine aortic endothelial cells. From these results, we conclude that supplementation of EGCG improves glucose tolerance, insulin sensitivity, and endothelial function. The results suggest that EGCG may have beneficial health effects in glucose metabolism and endothelial function through modulating HFD-induced inflammatory response.

Green tea polyphenol epigallocatechin-3-gallate ameliorates insulin resistance in non-alcoholic fatty liver disease mice

“…Recent studies have shown a strong correlation between the consumption of green tea and the prevention of NAFLD. Other studies have shown that EGCG reduced the severity of liver injury by reducing circulating insulin, improving insulin sensitivity and attenuating insulin resistance in type 2 diabetes mellitus (T2DM) or NAFLD mice [12][13][14] . Although EGCG reduces circulating insulin, it is not clear whether IDE is involved.…”

Canola Oil Influence on Azoxymethane-induced Colon Carcinogenesis, Hypertriglyceridemia and Hyperglycemia in Kunming Mice

“…Hyperglycemia may be caused by lipid metabolism dysfunction (Jang et al, 2013, Ezhumalai et al, 2014. The hypertriglyceridemia observed in ACG was not the result of AOM-induced hyperglycemia, because the plasma glucose concentration in COG was similar to the ACG, however plasma triglyceride concentration in the COG was significantly lower than that in ACG.…”

Development of an Experimental Model of Metabolic Syndrome in Sprague Dawley Rat

“…Our study use the combination the streptozotocin and high fat diet (40%) fat to maintain the hyperglycemic state. Previous report suggested that HFD administration induce insulin resistance via PKC activation by high level free fatty acid that consequently interfered IRS activation (Jang, 2013). Moreover, our study used the combination of animal fat and hydrogenated fat to maintain insulin resistance.…”