Immunocytochemical detection of advanced glycated end products in rat renal tissue as a function of age and diabetes

Background. High blood glucose levels play major roles in the pathogenesis of renal diabetic complications through non-enzymatic glycation. For long-lived molecules this leads to formation of advanced glycation end products (AGE), and the renal extracellular matrix appears to be one of the targets for such processes. Using immunocytochemistry, we studied the appearance and deposition of AGE products in renal tissues from normal and diabetic rats at different ages, to evaluate the effects of aging and hyperglycemia. Methods. The streptozotocin-injected rat represented our model of hyperglycaemic condition. The immunogold techniques were applied at the light and electron microscope levels using specific monoclonal and polyclonal antibodies against AGE adducts. The results were analyzed by morphometry. Results. In normoglycemic animals, significant increases in labeling were detected in tubular basement membranes and mesangial matrix at 12 to 15 months of age. In contrast, in diabetic animals, significant increases in labeling were found for all extracellular matrices as soon as after two months of hyperglycemia. Labelings were also detected in cellular compartments, particularly in nuclei that showed increases in diabetic condition. The labeling was particularly intense in proximal convoluted tubules and their endosomal compartment, due to the reabsorption of urinary AGE products. Conclusion. The presence of AGE products in the renal extracellular matrix of old normoglycemic animals and their rapid appearance in hyperglycemia, indicate that AGE products may participate in the pathogenesis of renal complications. Furthermore, the non-enzymatic glycation is not restricted to extracellular matrices but also affects cellular proteins.