In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

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.

Background —The mechanism of the hemodynamic effect of insulin in the skeletal muscle circulation has not been fully elucidated. The purpose of this study was to assess whether the hemodynamic response to insulin involves the concurrent release of endothelin (ET-1) and nitric oxide (NO), 2 substances with opposing vasoactive properties. Methods and Results —Bioactivity of ET-1 and NO was assessed without insulin and during insulin infusion in the forearm circulation of healthy subjects by use of blockers of ET-1 receptors and by NO synthesis inhibition. In the absence of hyperinsulinemia, ET-1 receptor blockade did not result in any significant change in forearm blood flow from baseline ( P =0.29). Intra-arterial insulin administration did not significantly modify forearm blood flow ( P =0.88). However, in the presence of hyperinsulinemia, ET-1 receptor antagonism was associated with a significant vasodilator response ( P <0.001). In the presence of ET-1 receptor blockade, the vasoconstrictor response to NO inhibition by N ^G -monomethyl- l -arginine was significantly higher after insulin infusion than in the absence of hyperinsulinemia ( P =0.006). Conclusions —These findings suggest that in the skeletal muscle circulation, insulin stimulates both ET-1 and NO activity. An imbalance between the release of these 2 substances may be involved in the pathophysiology of hypertension and atherosclerosis in insulin-resistant states associated with endothelial dysfunction.

Background— Endothelial dysfunction may contribute to the risk of premature atherosclerosis in patients with diabetes. Endothelin (ET-1) may be involved in this process by activating smooth muscle cell mitogenesis and leukocyte adhesion. We sought to assess the activity of endogenous ET-1 in a group of patients with type II diabetes mellitus with the use of antagonists of ET-1 receptors. Methods and Results— Forearm blood flow (FBF) responses (strain gauge plethysmography) to intraarterial infusion of a selective blocker of ET _A receptors (BQ-123) and, on a different occasion, to ET-1, were measured in 15 patients with diabetes and 12 healthy controls. In addition, 5 patients with diabetes received coinfusion of BQ-123 and BQ-788 (a selective blocker of ET _B receptors). In normal subjects, BQ-123 did not significantly modify FBF from baseline ( P =0.16). In contrast, BQ-123 administration resulted in a significant vasodilator response in patients with diabetes ( P <0.001). Infusion of exogenous ET-1 resulted in lower vasoconstrictor responses in patients with diabetes than in controls ( P =0.001), whereas the vasoconstrictor response to norepinephrine was similar in the 2 groups ( P =0.78). In patients with diabetes, the vasodilator response to selective ET _A blockade was not significantly modified by nonselective blockade of ET-1 receptors obtained by coinfusion of BQ-123 and BQ-788. Conclusions— The activity of endogenous ET-1 on ET _A receptors is enhanced in the resistance vessels of patients with diabetes, whereas their sensitivity to exogenous ET-1 is blunted. This abnormality may participate in the pathophysiology of vascular complications associated with diabetes.