Oskar Kövamees

Arginase Inhibition Improves Endothelial Function in Patients With Coronary Artery Disease and Type 2 Diabetes Mellitus

Background— Endothelial dysfunction plays an important role in the early development of atherosclerosis and vascular complications in type 2 diabetes mellitus. Increased expression and activity of arginase, metabolizing the nitric oxide substrate L-arginine, may result in reduced production of nitric oxide and thereby endothelial dysfunction. We hypothesized that inhibition of arginase activity improves endothelial function in patients with coronary artery disease (CAD) and type 2 diabetes mellitus. Methods and Results— Three groups of subjects were included: 16 patients with CAD, 16 patients with CAD and type 2 diabetes mellitus (CAD+Diabetes), and 16 age-matched healthy control subjects. Forearm endothelium-dependent and endothelium-independent vasodilatation were assessed with venous occlusion plethysmography before and during intra-arterial infusion of the arginase inhibitor N&ohgr;-hydroxy-nor-L-arginine (nor-NOHA; 0.1 mg/min). Nor-NOHA was also coinfused with the nitric oxide synthase inhibitor (NG-monomethyl L-arginine). The expression of arginase was determined in the internal mammary artery of patients undergoing bypass surgery. Nor-NOHA markedly increased endothelium-dependent vasodilatation (up to 2-fold) in patients with CAD+Diabetes and CAD (P<0.001) but not in the control group. NG-monomethyl L-arginine completely inhibited the increase in endothelium-dependent vasodilatation induced by nor-NOHA. Endothelium-independent vasodilatation was slightly improved by nor-NOHA in the CAD+Diabetes group. Arginase I was expressed in vascular smooth muscle cells and endothelial cells, and arginase II was expressed in endothelial cells of patients with and without diabetes mellitus. Conclusions— Arginase inhibition markedly improves endothelial function in patients with CAD and type 2 diabetes mellitus suggesting that increased arginase activity is a key factor in the development of endothelial dysfunction.

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.

Arginase inhibition improves endothelial function in patients with familial hypercholesterolaemia irrespective of their cholesterol levels

Elevated LDL cholesterol is an important risk factor for atherosclerosis. Endothelial dysfunction, an early event in the development of atherosclerosis, is characterized by a reduction in nitric oxide (NO) bioavailability. Arginase has emerged as a key regulator of endothelial function through competition with NO synthase for the common substrate l‐arginine. Arginase in endothelial cells is activated by oxidized LDL. The study aim was to investigate the importance of arginase for endothelial dysfunction in patients with familial hypercholesterolaemia (FH).

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.

High-density lipoprotein-associated sphingosine-1-phosphate activity in heterozygous familial hypercholesterolaemia

Patients with heterozygous familial hypercholesterolaemia (FH) suffer from high plasma cholesterol and an environment of increased oxidative stress. We examined its potential effects on high‐density lipoprotein (HDL)‐associated sphingosine‐1‐phosphate (S1P) content (HDL‐S1P) and HDL‐mediated protection against oxidative stress, both with and without statin treatment.

Erythrocytes From Patients With Type 2 Diabetes Induce Endothelial Dysfunction Via Arginase I.

BACKGROUND Cardiovascular complications are major clinical problems in type 2 diabetes mellitus (T2DM). The authors previously demonstrated a crucial role of red blood cells (RBCs) in control of cardiac function through arginase-dependent regulation of nitric oxide export from RBCs. There is alteration of RBC function, as well as an increase in arginase activity, in T2DM. OBJECTIVES The authors hypothesized that RBCs from patients with T2DM induce endothelial dysfunction by up-regulation of arginase. METHODS RBCs were isolated from patients with T2DM and age-matched healthy subjects and were incubated with rat aortas or human internal mammary arteries from nondiabetic patients for vascular reactivity and biochemical studies. RESULTS Arginase activity and arginase I protein expression were elevated in RBCs from patients with T2DM (T2DM RBCs) through an effect induced by reactive oxygen species (ROS). Co-incubation of arterial segments with T2DM RBCs, but not RBCs from age-matched healthy subjects, significantly impaired endothelial function but not smooth muscle cell function in both healthy rat aortas and human internal mammary arteries. Endothelial dysfunction induced by T2DM RBCs was prevented by inhibition of arginase and ROS both at the RBC and vascular levels. T2DM RBCs induced increased vascular arginase I expression and activity through an ROS-dependent mechanism. CONCLUSIONS This study demonstrates a novel mechanism behind endothelial dysfunction in T2DM that is induced by RBC arginase I and ROS. Targeting arginase I in RBCs may serve as a novel therapeutic tool for the treatment of endothelial dysfunction in T2DM.

Arginase inhibition improves endothelial function in patients with type 2 diabetes mellitus despite intensive glucose-lowering therapy

Arginase is implicated in the pathogenesis behind endothelial dysfunction in type 2 diabetes mellitus (T2DM) by its inhibition of nitric oxide formation. Strict glycaemic control is not sufficient to improve endothelial function or cardiovascular outcomes in patients with T2DM, thus other treatment strategies are needed. We hypothesized that arginase inhibition improves endothelial function beyond glucose‐lowering therapy following glucose optimization in patients with poorly controlled T2DM.

Red Blood Cells in Type 2 Diabetes Impair Cardiac Post-Ischemic Recovery Through an Arginase-Dependent Modulation of Nitric Oxide Synthase and Reactive Oxygen Species

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