Insulin resistance is characteristic of obesity, type 2 diabetes, and components of the cardiometabolic syndrome, including hypertension and dyslipidemia, that collectively contribute to a substantial risk for cardiovascular disease. Metabolic actions of insulin in classic insulin target tissues (eg, skeletal muscle, fat, and liver), as well as actions in nonclassic targets (eg, cardiovascular tissue), help to explain why insulin resistance and metabolic dysregulation are central in the pathogenesis of the cardiometabolic syndrome and cardiovascular disease. Glucose and lipid metabolism are largely dependent on mitochondria to generate energy in cells. Thereby, when nutrient oxidation is inefficient, the ratio of ATP production/oxygen consumption is low, leading to an increased production of superoxide anions. Reactive oxygen species formation may have maladaptive consequences that increase the rate of mutagenesis and stimulate proinflammatory processes. In addition to reactive oxygen species formation, genetic factors, aging, and reduced mitochondrial biogenesis all contribute to mitochondrial dysfunction. These factors also contribute to insulin resistance in classic and nonclassic insulin target tissues. Insulin resistance emanating from mitochondrial dysfunction may contribute to metabolic and cardiovascular abnormalities and subsequent increases in cardiovascular disease. Furthermore, interventions that improve mitochondrial function also improve insulin resistance. Collectively, these observations suggest that mitochondrial dysfunction may be a central cause of insulin resistance and associated complications. In this review, we discuss mechanisms of mitochondrial dysfunction related to the pathophysiology of insulin resistance in classic insulin-responsive tissue, as well as cardiovascular tissue.

Green tea is rich in polyphenol flavonoids including catechins. Epigallocatechin 3-gallate (EGCG) is the most abundant and potent green tea catechin. EGCG has been extensively studied for its beneficial health effects as a nutriceutical agent. Based upon its chemical structure, EGCG is often classified as an antioxidant. However, treatment of cells with EGCG results in production of hydrogen peroxide and hydroxyl radicals in the presence of Fe (III). Thus, EGCG functions as a pro-oxidant in some cellular contexts. Recent investigations have revealed many other direct actions of EGCG that are independent from anti-oxidative mechanisms. In this review, we discuss these novel molecular mechanisms of action for EGCG. In particular, EGCG directly interacts with proteins and phospholipids in the plasma membrane and regulates signal transduction pathways, transcription factors, DNA methylation, mitochondrial function, and autophagy to exert many of its beneficial biological actions.

Context: Hesperidin, a citrus flavonoid, and its metabolite hesperetin may have vascular actions relevant to their health benefits. Molecular and physiological mechanisms of hesperetin actions are unknown. Objective: We tested whether hesperetin stimulates production of nitric oxide (NO) from vascular endothelium and evaluated endothelial function in subjects with metabolic syndrome on oral hesperidin therapy. Design, Setting, and Interventions: Cellular mechanisms of action of hesperetin were evaluated in bovine aortic endothelial cells (BAEC) in primary culture. A randomized, placebo-controlled, double-blind, crossover trial examined whether oral hesperidin administration (500 mg once daily for 3 wk) improves endothelial function in individuals with metabolic syndrome (n = 24). Main Outcome Measure: We measured the difference in brachial artery flow-mediated dilation between placebo and hesperidin treatment periods. Results: Treatment of BAEC with hesperetin acutely stimulated phosphorylation of Src, Akt, AMP kinase, and endothelial NO synthase to produce NO; this required generation of H₂O₂. Increased adhesion of monocytes to BAEC and expression of vascular cell adhesion molecule-1 in response to TNF-α treatment was reduced by pretreatment with hesperetin. In the clinical study, when compared with placebo, hesperidin treatment increased flow-mediated dilation (10.26 ± 1.19 vs. 7.78 ± 0.76%; P = 0.02) and reduced concentrations of circulating inflammatory biomarkers (high-sensitivity C-reactive protein, serum amyloid A protein, soluble E-selectin). Conclusions: Novel mechanisms for hesperetin action in endothelial cells inform effects of oral hesperidin treatment to improve endothelial dysfunction and reduce circulating markers of inflammation in our exploratory clinical trial. Hesperetin has vasculoprotective actions that may explain beneficial cardiovascular effects of citrus consumption.

Epigallocatechin gallate (EGCG) is a major polyphenol in green tea that has beneficial effects in the prevention of cardiovascular disease. Autophagy is a cellular process that protects cells from stressful conditions. To determine whether the beneficial effect of EGCG is mediated by a mechanism involving autophagy, the roles of the EGCG-stimulated autophagy in the context of ectopic lipid accumulation were investigated. Treatment with EGCG increased formation of LC3-II and autophagosomes in primary bovine aortic endothelial cells (BAEC). Activation of calmodulin-dependent protein kinase kinase β was required for EGCG-induced LC3-II formation, as evidenced by the fact that EGCG-induced LC3-II formation was significantly impaired by knockdown of calmodulin-dependent protein kinase kinase β. This effect is most likely due to cytosolic Ca²⁺ load. To determine whether EGCG affects palmitate-induced lipid accumulation, the effects of EGCG on autophagic flux and co-localization of lipid droplets and autophagolysosomes were examined. EGCG normalized the palmitate-induced impairment of autophagic flux. Accumulation of lipid droplets by palmitate was markedly reduced by EGCG. Blocking autophagosomal degradation opposed the effect of EGCG in ectopic lipid accumulation, suggesting the action of EGCG is through autophagosomal degradation. The mechanism for this could be due to the increased co-localization of lipid droplets and autophagolysosomes. Co-localization of lipid droplets with LC3 and lysosome was dramatically increased when the cells were treated with EGCG and palmitate compared with the cells treated with palmitate alone. Collectively, these findings suggest that EGCG regulates ectopic lipid accumulation through a facilitated autophagic flux and further imply that EGCG may be a potential therapeutic reagent to prevent cardiovascular complications.