Analysis of glucose metabolism in diabetic rat retinas

• Published in: American journal of physiology: endocrinology and metabolism 2006-06, Vol.290 (6), p.E1057-E1067
• Main Authors: Ola, M. Shamsul, Berkich, Deborah A, Xu, Yuping, King, M. Todd, Gardner, Thomas W, Simpson, Ian, LaNoue, Kathryn F
• Format: Article
• Language: English
• Subjects: Animals; Diabetes Mellitus, Experimental - enzymology; Diabetes Mellitus, Experimental - metabolism; Diabetic Retinopathy - enzymology; Diabetic Retinopathy - metabolism; Glucose - metabolism; Glucose-6-Phosphate - metabolism; Glyceraldehyde-3-Phosphate Dehydrogenases - chemistry; Glycolysis; In Vitro Techniques; Oxidation-Reduction; Phosphoric Monoester Hydrolases - metabolism; Polymers - metabolism; Rats; Rats, Sprague-Dawley; Retina - metabolism; Retina - pathology; Time Factors
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.00323.2005

Departments of 1 Cellular and Molecular Physiology, 4 Neural and Behavioral Sciences, and 3 Ophthalmology, Pennsylvania State College of Medicine, Hershey, Pennsylvania; and 2 Laboratory of Metabolic Control, The National Institute of Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, Maryland Submitted 19 July 2005 ; accepted in final form 13 December 2005 This study was conceived in an effort to understand cause and effect relationships between hyperglycemia and diabetic retinopathy. Numerous studies show that hyperglycemia leads to oxidative stress in the diabetic retinas, but the mechanisms that generate oxidative stress have not been resolved. Increased electron pressure on the mitochondrial electron transfer chain, increased generation of cytosolic NADH, and decreases in cellular NADPH have all been cited as possible sources of reactive oxygen species and nitrous oxide. In the present study, excised retinas from control and diabetic rats were exposed to euglycemic and hyperglycemic conditions. Using a microwave irradiation quenching technique to study retinas of diabetic rats in vivo, glucose, glucose-derived metabolites, and NADH oxidation/reduction status were measured. Studying excised retinas in vitro, glycolytic flux, lactate production, and tricarboxylic acid cycle flux were evaluated. Enzymatically assayed glucose 6-phosphate and fructose 6-phosphate were only slightly elevated by hyperglycemia and/or diabetes, but polyols were increased dramatically. Cytosolic NADH-to-NAD ratios were not elevated by hyperglycemia nor by diabetes in vivo or in vitro. Tricarboxylic acid cycle flux was not increased by the diabetic state nor by hyperglycemia. On the other hand, small increases in glycolytic flux were observed with hyperglycemia, but glycolytic flux was always lower in diabetic compared with control animals. An observed decrease in activity of glyceraldehyde-3-phosphate dehydrogenase may be partially responsible for slow glycolytic flux for retinas of diabetic rats. Therefore, it is concluded that glucose metabolism, downstream of hexokinase, is not elevated by hyperglycemia or diabetes. Metabolites upstream of glucose such as the sorbitol pathway (which decreases NADPH) and polyol synthesis are increased. diabetic retinopathy; hyperglycemia; reactive oxygen species; mitochondria; glycolysis; polyols Address for reprint requests and other correspondence: K. F. LaNoue, Dept. of Cellular and Molecular Physiology, Pennsylvania S