Alexey Shemyakin

Endothelin-1 Reduces Glucose Uptake in Human Skeletal Muscle In Vivo and In Vitro

OBJECTIVE Endothelin (ET)-1 is a vasoconstrictor and proinflammatory peptide that may interfere with glucose uptake. Our objective was to investigate whether exogenous ET-1 affects glucose uptake in the forearm of individuals with insulin resistance and in cultured human skeletal muscle cells. RESEARCH DESIGN AND METHODS Nine male subjects (aged 61 ± 3 years) with insulin resistance (M value <5.5 mg/kg/min or a homeostasis model assessment of insulin resistance index >2.5) participated in a protocol using saline infusion followed by ET-1 infusion (20 pmol/min) for 2 h into the brachial artery. Forearm blood flow (FBF), endothelium-dependent vasodilatation, and endothelium-independent vasodilatation were assessed. Molecular signaling and glucose uptake were determined in cultured skeletal muscle cells. RESULTS ET-1 decreased forearm glucose uptake (FGU) by 39% (P < 0.05) after the 2-h infusion. ET-1 reduced basal FBF by 36% after the 2-h infusion (P < 0.05) and impaired both endothelium-dependent vasodilatation (P < 0.01) and endothelium-independent vasodilatation (P < 0.05). ETA and ETB receptor expression was detected on cultured skeletal muscle cells. One-hour ET-1 incubation increased glucose uptake in cells from healthy control subjects but not from type 2 diabetic patients. Incubation with ET-1 for 24 h reduced glucose uptake in cells from healthy subjects. ET-1 decreased insulin-stimulated Akt phosphorylation and increased phosphorylation of insulin receptor substrate-1 serine 636. CONCLUSIONS ET-1 not only induces vascular dysfunction but also acutely impairs FGU in individuals with insulin resistance and in skeletal muscle cells from type 2 diabetic subjects. These findings suggest that ET-1 may contribute to the development of insulin resistance in skeletal muscle in humans.

Effect of arginase inhibition on ischemia-reperfusion injury in patients with coronary artery disease with and without diabetes mellitus.

Background Arginase competes with nitric oxide synthase for their common substrate L-arginine. Up-regulation of arginase in coronary artery disease (CAD) and diabetes mellitus may reduce nitric oxide bioavailability contributing to endothelial dysfunction and ischemia-reperfusion injury. Arginase inhibition reduces infarct size in animal models. Therefore the aim of the current study was to investigate if arginase inhibition protects from endothelial dysfunction induced by ischemia-reperfusion in patients with CAD with or without type 2 diabetes (Clinical trial registration number: NCT02009527). Methods Male patients with CAD (n = 12) or CAD + type 2 diabetes (n = 12), were included in this cross-over study with blinded evaluation. Endothelium-dependent vasodilatation was assessed by flow-mediated dilatation (FMD) of the radial artery before and after 20 min ischemia-reperfusion during intra-arterial infusion of the arginase inhibitor (Nω-hydroxy-nor-L-arginine, 0.1 mg/min) or saline. Results The forearm ischemia-reperfusion was well tolerated. Endothelium-independent vasodilatation was assessed by sublingual nitroglycerin. Ischemia-reperfusion decreased FMD in patients with CAD from 12.7±5.2% to 7.9±4.0% during saline administration (P<0.05). Nω-hydroxy-nor-L-arginine administration prevented the decrease in FMD in the CAD group (10.3±4.3% at baseline vs. 11.5±3.6% at reperfusion). Ischemia-reperfusion did not significantly reduce FMD in patients with CAD + type 2 diabetes. However, FMD at reperfusion was higher following nor-NOHA than following saline administration in both groups (P<0.01). Endothelium-independent vasodilatation did not differ between the occasions. Conclusions Inhibition of arginase protects against endothelial dysfunction caused by ischemia-reperfusion in patients with CAD. Arginase inhibition may thereby be a promising therapeutic strategy in the treatment of ischemia-reperfusion injury.

Amino acid metabolism reflecting arginase activity is increased in patients with type 2 diabetes and associated with endothelial dysfunction

Background: Endothelial dysfunction contributes to the development of vascular complication in diabetes. Arginase has emerged as a key mechanism behind endothelial dysfunction by its reciprocal regulation of nitric oxide production by substrate competition. We hypothesized that increased arginase activity in patients with type 2 diabetes shifts the metabolism of l-arginine from nitric oxide synthase to arginase resulting in an increase in the plasma ratio of ornithine/citrulline, and that this ratio is associated with endothelial dysfunction. Methods: Forearm endothelium-dependent vasodilatation and endothelium-independent vasodilatation were determined in 15 patients with type 2 diabetes and 10 healthy controls and related to amino acids reflecting arginase and nitric oxide synthase activity. Results: Compared to healthy controls, patients with diabetes had impaired endothelium-dependent vasodilatation and endothelium-independent vasodilatation. The ratios of ornithine/citrulline and proline/citrulline were 60% and 95% higher, respectively, in patients with diabetes than in controls (p < 0.001). The plasma ornithine/arginine ratio was 36% higher in patients with diabetes, indicating increased arginase activity. These ratios were inversely correlated to endothelium-dependent vasodilatation and endothelium-independent vasodilatation. Conclusion: Patients with diabetes and macrovascular complications have increased amino acid ratios reflecting a shift in arginine metabolism due to arginase activation. These changes are inversely related to endothelial function supporting that arginase activity contributes to endothelial dysfunction.

Increased arginase levels contribute to impaired perfusion after cardiopulmonary resuscitation

The postcardiac arrest syndrome occurs after global hypoxia leading to microcirculatory impairment. Nitric oxide (NO) is a key molecule regulating microvascular function. The enzyme arginase has been suggested to modulate microvascular function by regulating NO metabolism. Therefore, we investigated whether arginase increases following global hypoxia and resuscitation and tested whether arginase inhibition influences altered microcirculation in resuscitated patients.