Glucose as a factor of importance for regulating arginase activity in red blood cells

Background: Nitric oxide (NO) is an important biological messenger in the cardiovascular system. NO causes vasodilation, inhibits inflammation and platelet activation. The bioavailability of NO is reduced in various cardiovascular diseases including atherosclerosis and diabetes compared to a healthy state. NO is formed by the enzyme nitric oxide synthase (NOS) which can be found throughout the vasculature. The amino acid L-arginine is a substrate in the reaction of NO production. The mechanism of reduced bioavailability of NO is not completely understood but it is thought to be mainly reduced production of NO and increased inactivation of NO. Emerging evidence suggest that the enzyme arginase is a major contributor to this mechanism. Arginase also uses L-arginine as a substrate to produce urea and ornithine. Experimental data demonstrate that arginase activity is increased in rats with type 2 diabetes compared with healthy controls. Glucose has been reported to regulate arignase activity in endothelial cells. Red blood cells (RBCs) contain high levels of arginase which regulates NO but this regulation in RBCs and it‘s function in these cells is unknown. The aim of this study was to test the hypothesis if there is a difference in arginase activity in RBCs between healthy individuals and patients with type 2 diabetes. Another objective was to investigate if high glucose concentration would affect arginase activity in red blood cells. Methods: Red blood cells were extracted from healthy individuals and patients with type 2 diabetes . These cells were incubated for 24 and 48 hours in a buffer solution containing 0 mM, 5.5 mM or 25 mM glucose. Arginase activity was determined by measuring the amount of urea produced using spectrophotometry. Results: Arginase activity at baseline, (i.e. 0 hours) of incubation did not differ between healthy individuals and patients with type 2 diabetes. Arginase activity decreased with time in both groups. Arginase activity reached a steady-state at 24 hours of incubation. There was no significant difference between arginase activity whether they were incubated with 5.5 mM glucose concentration or 25mM glucose concentration. Discussion: According to the results of this study glucose does not effect arginase activity in red blood cells. There is not a significant difference in arginase activity in red blood cells between healthy subjects and patients with type 2 diabetes. Keywords: Nitric oxide (NO), nitric oxide synthase (NOS), arginase, arginase activity, diabetes type 2, glucose, incubation