Effect of Glycemic Control on Cardiovascular Dysfunction and Oxidative Stress in Type 2 Diabetes

Research Abstract

The present study was conducted firstly, to evaluate whether an intensive glycemic control may improve both endothelial dysfunction (i.e. ADMA levels) and oxidative stress in type 2 diabetic patients with or without hypertension. Secondary, to assess the role of blood pressure regulation using ACE inhibitors on modulating endothelial dysfunction and oxidative stress in hypertensive diabetic patients. The current study was conducted in the Out-patient Clinic of Beni- Sueif University Hospital and comprising 90 subjects; 72 patients with type 2 diabetes along with 18 healthy control volunteers. Inclusion criteria for patients enrolled in the study included the following: age between 40-70 years; receiving stable antidiabetic therapy (sulfonylurea, metformin and/or insulin) for at least 6-8 months and no history of ketoacidosis. In hypertensive diabetic patients submitted to the study, the antihypertensive treatment was ACE inhibitors for at least 6-8 months. Exclusion criteria included the following: clinically significant hepatic, neurological, endocrinologic or other major systemic diseases, such as malignancy; elevated plasma transaminases activities over twice the upper normal limit; elevated plasma creatinine concentration (> 1.7 mg/dl); acute major cardiovascular events in the previous 6 months; acute illnesses; current evidence of acute or chronic inflammatory diseases and hormone replacement therapy for women subjected to the study. Exclusion criteria also included anemia, hyperbilirubinemia, treatment with glucocorticoids, antineoplastic agents, psychoactive agents, bronchodilators, statins or vitamin supplements. The patients enrolled in the present study were classified into the following groups according to presence or absence of hypertension and glycemic control where the patients were subdivided into good glycemic control (HbA1C ≤ 7.0 %) and poor glycemic control (HbA1C > 7.0 %) along with normal subjects: / 2317953 / ػ ث شٌٙ ١ذ/ شحجصز أح ذّ حؾجصٞ – د ٟٕ عٛ ٠ف س ف : 2317958 س: 2319397 2317950 Web site: www.pharm.bsu.edu.eg Mail: pharm@bsu.edu.eg Group (1) (control group): included eighteen healthy individuals. Group (2): included eighteen normotensive good controlled diabetic patients. Group (3): included eighteen normotensive poorly controlled diabetic patients. Group (4): included eighteen hypertensive good controlled diabetics treated with ACE inhibitors. Group (5): included eighteen hypertensive poorly controlled diabetics treated with ACE inhibitors. Five milliliters of venous blood samples were withdrawn after 12- 14 hours overnight fast from each subject enrolled in the study. Each blood sample was collected into tubes containing EDTA and divided into 2 aliquots. The first aliquot was of 1.5 ml whole blood used for estimation of GSH, HbA1C and blood hemoglobin. The second aliquot was of 3.5 ml blood centrifuged at 2000 x g for 10 minutes to obtain plasma for estimation of plasma glucose, plasma total bilirubin, plasma creatinine, lipid profile and plasma MDA levels, AST and ALT activities. The remaining plasma was stored at –20ºC for subsequent estimation of plasma ADMA levels. The present study showed a significant increase in FPG levels and HbA1C levels in normotensive and hypertensive diabetics compared with normal control. In addition, there was a significant increase in FPG levels and HbA1C levels in normotensive and hypertensive poorly controlled diabetics compared with normotensive and hypertensive good controlled diabetics, respectively. The increased HbA1C levels may be attributed to the intracellular hyperglycemia which increases non-enzymatic attachment of glucose molecules to primary amino groups of hemoglobin protein, forming a stable Amadori products such as the HbA1C adduct in normotensive and hypertensive poorly controlled diabetics. The decreased FPG and HbA1C levels in normotensive and hypertensive good controlled diabetics is mainly due to intensive glycemic control via hypoglycemic drugs. ACE inhibitors may partly influence glycemic control in hypertensive diabetics through vasodilatation which may promote an access of glucose and insulin into skeletal muscle tissue, the main target organ for insulin action. Fasting plasma glucose levels were correlated with HbA1C levels in all diabetic groups in the current study. / 2317953 / ػ ث شٌٙ ١ذ/ شحجصز أح ذّ حؾجصٞ – د ٟٕ عٛ ٠ف س ف : 2317958 س: 2319397 2317950 Web site: www.pharm.bsu.edu.eg Mail: pharm@bsu.edu.eg The present study showed a significant decrease in plasma ADMA levels in normotensive and hypertensive diabetics compared with normal control. The decreased ADMA levels in normotensive and hypertensive poorly controlled diabetic patients is attributed to increased renal excretion that results from increased glomerular filtration rate while decreased ADMA levels in normotensive and hypertensive good controlled diabetics was attributed to increased degradation by DDAH enzyme. ACE inhibitors may also decrease plasma ADMA levels in hypertensive diabetics. Plasma ADMA levels were correlated with both plasma MDA and blood GSH levels in all diabetic groups, supporting the relationship between ADMA and oxidative stress. The present work showed a significant increase in plasma MDA levels in normotensive and hypertensive diabetics compared with normal control. In addition, there was a significant increase in MDA levels in normotensive and hypertensive poorly controlled diabetics compared with normotensive and hypertensive good controlled diabetics, respectively. In diabetes, there is an increased production of free radicals, which in turn promotes lipid peroxidation with the formation of MDA the end product of lipid peroxidation. The decreased MDA levels in normotensive and hypertensive good controlled diabetics may be a consequence of intensive glycemic control reflected by low HbA1C levels and also due to antioxidant properties of hypoglycemic drugs used in treatment of diabetes. The antioxidant effect of ACE inhibitors may also contribute to decreased MDA levels in hypertensive diabetics. Significant correlation was found between plasma MDA and GSH levels in all diabetic groups in the present investigation. The current work found a significant decrease in blood GSH levels in normotensive and hypertensive diabetics compared with normal control. In addition, there was a significant decrease in GSH levels in normotensive and hypertensive poorly controlled diabetics compared with normotensive and hypertensive good controlled diabetics, respectively. The decreased GSH level in diabetics may be caused by increased sorbitol synthesis which leads to NADPH depletion, and limits reduction of GSSG to GSH catalyzed by glutathione reductase. Also, decreased activity of enzymes involved in pentose phosphate pathway which generates NADPH in diabetics, so reduction of GSSG is limited and finally, GSSG can pass through erythrocyte membrane due to oxidative stress-induced membrane damage. In addition to effect of intensive glycemic / 2317953 / ػ ث شٌٙ ١ذ/ شحجصز أح ذّ حؾجصٞ – د ٟٕ عٛ ٠ف س ف : 2317958 س: 2319397 2317950 Web site: www.pharm.bsu.edu.eg Mail: pharm@bsu.edu.eg control, the effect of hypoglycemic drugs on improving antioxidant status may contribute to increased GSH levels in normotensive and hypertensive good controlled diabetics compared with those normotensive and hypertensive poorly controlled diabetics. In hypertensive diabetics, the treatment with ACE inhibitors which possess antioxidant properties may also contribute to enhancement of GHS levels. A negative correlation between blood GSH and HbA1C levels in all diabetic groups was found. No significant difference was observed in all measured parameters in the present study when comparing normotensive with hypertensive diabetics which may be attributed to the use of ACE inhibitors in treatment of hypertensive diabetics, so their parameter levels become similar to those in normotensive diabetics. From the present study we can conclude firstly, that there is a relevant relationship between glycemic control, oxidative stress and endothelial dysfunction. Secondary, that diabetes-associated conditions such as hypertension may result in an increased cellular production of reactive oxygen species which impairs endothelial function. Finally and more importantly, besides the role of antidiabetic drugs and ACE inhibitors in modulating glycemic control and regulating hypertension respectively, they have great antioxidant activities which affect endothelial function and oxidative status in diabetic patients. Further studies are needed to investigate the effect of different hypoglycemic drugs on DDAH activity as a mechanism that lowers ADMA levels in diabetic patients and to investigate the antioxidant properties of these drugs which may be of benefit in delaying diabetic complications. Also, to investigate the role of blood pressure-lowering effect of antihypertensive drugs in modulation of oxidative stress and endothelial dysfunction.

Research Keywords

Effect of Glycemic Control on Cardiovascular Dysfunction and Oxidative Stress in Type 2 Diabetes