L-Arginine-Dependent Nitric Oxide Production in the Blood of Patients with Type 2 Diabetes: A Pilot, Five-Year Prospective Study.

Backgound: Type 2 diabetes mellitus (T2DM) is a major cardiovascular risk factor. Nitric oxide (NO) is one of the many molecules that regulate vascular tone, and red blood cells (RBCs) are known to play an important role in adjusting cardiac function through NO export from RBCs. Our study prospectively investigated the L-arginine (L-arg)-nitric oxide (NO) metabolic pathway in the erythrocytes and plasma of subjects with T2DM. Methods: RBCs and plasma were collected from patients with T2DM (n = 10), at first clinical onset (baseline) and after five years of disease evolution (follow-up). L-arg content was assayed by competitive enzyme-linked immunoassay. Arginase activity and nitrate/nitrite levels were measured using spectrophotometry. Results: When compared to baseline, L-arg content decreased in RBCs and remained similar in the plasma; NO production decreased in RBCs and the plasma; and arginase activity was lower in RBCs and increased in plasma. Conclusions: The L-arg/NO metabolic pathway decreases in the RBCs of patients with T2DM five years after the first clinical onset. The persistent decrease in RBCs' arginase activity fails to compensate for the sustained decrease in RBCs' NO production in the diabetic environment. This pilot study indicates that the NO-RBC pool is depleted during the progression of the disease in the same cohort of T2DM patients.

L-arginine catabolism is driven mainly towards nitric oxide synthesis in the erythrocytes of patients with type 2 diabetes at first clinical onset.

BACKGROUND: We investigated the l-arginine (l-Arg)-nitric oxide (NO) metabolic pathway in the erythrocytes (RBCs) and plasma of subjects with type 2 diabetes at first clinical onset. METHODS: RBCs and plasma were collected from 26 patients with type 2 diabetes at first clinical onset and 19 age-matched non-diabetes subjects as controls. l-Arg content was assayed by capillary electrophoresis. We measured arginase activity and nitrate/nitrite concentrations by spectrophotometry, and glycosylated haemoglobin (HbA1c) by standardized immunoturbidimetry. RESULTS: We found that, when compared with controls, l-Arg content was similar in RBCs while decreased in the plasma of patients with type 2 diabetes. Interestingly, arginase activity was lower in RBCs and increased in plasma of patients with diabetes. NO production was higher in RBCs in patients with type 2 diabetes, while no difference was found in the plasma of our subjects. CONCLUSIONS: l-Arg catabolism is driven mainly towards NO synthesis in RBCs of patients with type 2 diabetes at first clinical onset. The decreased RBC arginase activity could be considered a potential mechanism of increased RBC NO production in early diabetes. Therefore, the RBC pool would represent a potentially compensatory intravascular compartment for endothelial dysfunction in diabetes.

Erythrocyte caspase-3 and antioxidant defense is activated in red blood cells and plasma of type 2 diabetes patients at first clinical onset.

OBJECTIVES: We studied erythrocyte (RBC) caspase-3 activity and oxidative status in plasma and RBCs of 33 patients with type 2 diabetes at first clinical onset and 23 age-matched non-diabetes control subjects. METHODS: Caspase-3 activity was assayed during the life span of RBCs; lipid peroxides and total antioxidant capacity (TEAC) were assessed in plasma and RBCs as indicators of oxidative stress and non-enzymatic antioxidant defense; and superoxide dismutase, catalase, and glutathione peroxidase activity were measured in RBCs as enzymatic antioxidants. RESULTS: We found that, compared to controls, RBCs caspase-3 is activated early in type 2 diabetes (P < 0.05); TEAC and malondialdehyde increased in plasma of patients with early diabetes, even when hypertension and macroangiopathy were present (P < 0.01); and RBCs TEAC, malondialdehyde (P < 0.01), superoxide dismutase, and glutathione peroxidase (P < 0.05) exhibited similar behavior in patients with diabetes and hypertensive patients with diabetes. DISCUSSION: Increased antioxidant defense in plasma and RBCs of early type 2 diabetes patients is a potential mechanism that can overcome oxidative damage induced by reactive oxygen species overproduction, and occurs even in RBCs with a decreased life span. This observation could provide a possible explanation for the controversial effects of antioxidant supplementation in diabetes patients.