| Diabetes mellitus is a pervasive disease, affecting 18 million people in the United States alone (2002 estimate). Diabetes is broadly classified by the underlying cause and the ability to produce insulin: insulin-dependent diabetes mellitus is an autoimmune disease (IDDM) while non-insulin dependent diabetes mellitus (NIDDM) has both genetic and environmental underlying factors. Even though the disease etiology differs significantly between IDDM and NIDDM and within NIDDM alone, the result is an inability to efficiently regulate glucose uptake into cells, leading to chronic plasma hyperglycemia. Ultimately however, it is the secondary complications, not hyperglycemia, that are responsible for the morbidity and mortality of the disease. One of the underlying mechanisms of diabetic complications is oxidative stress, which arises from the production of free radicals from a variety of sources. The relative importance of each source varies with cell or tissue type. Red blood cells were used in this study to determine the mechanisms of glucose-induced oxidative stress because of their relative simplicity and involvement in microvascular health.; Human red blood cells were treated in vitro with hyperglycemic concentrations of glucose and the effects on cellular redox status measured. The goal of this work was to determine the mechanisms of glucose-induced oxidative stress by measuring the effect on oxidant-producing enzymes, antioxidant enzymes, and metabolites. There is a decrease in glutathione peroxidase and glucose-6-phosphate dehydrogenase activities and in cellular ATP and oxidized glutathione content. In addition, aldose reductase activity is stimulated. These changes may affect the ability of erythrocytes to prevent free radical-mediated cellular damage. Indeed, hyperglycemia stimulates oxidation of erythrocyte plasma membrane phospholipids, as measured by malondialdehyde formation. Hyperglycemia stimulates the hemoglobin-mediated monooxygenase activity during both acute and chronic exposure, though through different mechanisms. Acute hyperglycemia stimulates activity via production of NADPH, while chronic hyperglycemia induces the nonenzymatic glycation of the N-terminus. This activity may be the source of free radicals under hyperglycemic conditions. Together, these data provide a model for hyperglycemia-induced oxidative stress in human erythrocytes. |
