Metabolism Clinical and Experimental VOL 48, NO 12 DECEMBER 1999 The Susceptibility of Red Blood Cells to Autoxidation in Type 2 Diabetic Patient With Angiopathy Dildar Konuko~llu, TLilay Akqay, Yddlz Din£:er, and HLisrev Hatemi We examined the in vitro susceptibility of red blood cell (RBC) lipids to oxidation in type 2 diabetic patients with or without angiopathy. Lipid peroxidation was assessed by quantifying thiobarbituric acid (TBA) reactivity as malondialdehyde (MDA). We also examined the RBC antioxidant status by determining glutathione (GSH) levels. Before in vitro oxidation, RBC MDA levels were significantly higher in both diabetic groups than in the controls (P < .001), and a significant difference was found between the two diabetic groups (P < .05). After in vitro treatment of RBCs with hydrogen peroxide, the degree of lipid peroxidative damage was significantly higher in diabetic patients with angiopathy versus diabetics without angiopathy (P < .001). Diabetic patients have low RBC GSH levels compared with controls, and after in vitro oxidation, the levels were significantly decreased in diabetics (P < .001). There was not a significant correlation between RBC MDA levels and glycated hemoglobin (GHb), plasma cholesterol, and triglyceride. The correlation between RBC MDA and GSH was weak (P < .001). We suggest that the results of this study might help to clarify therole of oxidative mechanisms as an in vitro model of degenerative damage in type 2 diabetic angiopathic complications. Copyright© 1999by W.B. Saunders Company A THEROSCLEROSIS is a multifactorial disease, and sev- eral risk factors contribute to its development. These factors are abnormal plasma lipoprotein levels, thrombosis, hypertension, obesity, and smoking. Although some of the factors seem to cluster to a greater extent in diabetics than in nondiabetic patients, on their own, they do not completely explain the increased incidence of atherosclerosis in diabetes.1 Numerous investigators have searched for other factors that may explain the development of early and severe forms of atherosclerosis in diabetes mellitus. One factor commonly considered is the increased level of lipid peroxides in diabetes. 2 Lipid peroxidation, the oxidative alteration of polyunsaturated fatty acids, is an important mechanism in cellular damage in a number of pathological conditions. 3 Therefore, oxidative injury of endothelial cell membranes may be an important mecha- nism. 4 Deleterious effects of free radicals, the unstable, highly reactive chemical species with an unpaired electron in their structure, have also been implicated in the pathogenesis of atherosclerosis. 5 Some studies have demonstrated a direct cytotoxic effect of free radicals on the vascular endothelium. 2,4,6 Another factor contributing to the complications is hemorrheo- logic disturbances, which may play an important role in the impairment of diabetic microvascular flow and diabetic compli- cations. 7,8 It has been shown that red blood cells (RBCs) from diabetic patients exhibit reduced membrane deformability, increased viscosity, and abnormal adherence to endothelial cells. 9 Normal RBCs are resistant to oxidative damage through their antioxidant enzyme systems. However,both enhanced free-radical generation and decreased antioxidants may increase the lipid peroxidation of RBCs in diabetic patients.l° Malondialdehyde (MDA), an index of lipid peroxidation, 11 may be present in RBC membranes of diabetic patients during conditions of increased oxidative stress. ~2 RBC glutathione (GSH) is a physiological constituent of the intracellular antioxi- dant defense system and is present in all mammalian cells. GSH protects the cell against free radicals, hydrogen peroxide, and organic peroxides. 13 GSH peroxidase (EC 1.11.1.9) eliminates organic peroxides in the presence of GSH. During the reaction, GSH is oxidized to GSH disulfide (GSSH). GSSH is then reduced to GSH by NADPH. NADPH is regenerated from NAD by the pentose phosphate shunt. Therefore, depressed GSH levels have been associated with enhanced lipid peroxidation as a result of decreased scavenging of free radicals. ~4 The aim of the present study is to examine the in vitro RBC lipid susceptibility to oxidation and RBC GSH levels in patients with or without angiopathy. From the Departments of Biochemistry and Internal Medicine, Cerrahpaya Medical Faculty, Istanbul University, Istanbul, Turkey. Submitted March 24, 1997; accepted June 15, 1999. Address reprint requests to Dildar Konukoglu, MD, Fatih Sitesi B-4 Blok Daire 5 Silivrikapt, Fatih, Istanbul, Turkey. Copyright © 1999 by W.B. Saunders Company 0026-0495/99/4812-0006510.00/0 Metabolism, Vol 48, No 12 (December), 1999: pp 1481-1484 1481