Localization of glycated proteins in the glomeruli of patients with diabetic nephropathy

Glycation of proteins is regarded as one of the major causes of the development and progression of diabetic nephropathy. Based on the numerous reports on experimental models and on our own newly developed techniques, we planned to localize Amadori products and advanced glycation end-products (AGEs), as well as the mRNA expression of cytokines, enzymes and their inhibitors, which are responsible for the expansion of the mesangial areas of the glomeruli. Ten patients with diabetic nephropathy were examined. Patients with immunoglobulin (Ig) A nephropathy and normal portions of the surgically removed kidneys served as controls. Amadori products and AGEs in biopsy specimens were stained by specific monoclonal antibodies, and mRNA expression of the above substances was detected by in situ hybridization. There was a parallel progression in the degree of staining with anti-Amadori product antibody or anti-AGE antibody with the severity of tissue damage in patients with diabetic nephropathy. Patients with IgA nephropathy and normal renal tissues did not show any positive staining with these antibodies. The expression of transforming growth factor beta 1, stromelysin and tissue inhibitor of matrix proteinase 1 in the glomeruli was decreased in diabetic patients with advanced tissue damage, but they were progressively expressed in the advanced stage of IgA nephropathy. It is concluded that Amadori products and of AGEs were formed in parallel in diabetic kidneys. The decrease in the expression of the cytokine and enzymes might be due to altered protein formation associated with glycation.