Roles of advanced glycation end-products in the progression of diabetic nephropathy

Available data indicate that the development of diabetic nephropathy is linked to hyperglycaemia. Glucose reacts nonenzymatically with proteins to form Schiff base and Amadori products. Further incubation of these early products leads to the formation of advanced glycation end-products (AGEs). AGEs seem to play a central role in the progression of diabetic nephropathy. Immunohistochemically, AGEs were also detected in an expanded mesangial matrix, especially in nodular lesions from patients with diabetic nephropathy. AGEs staining was noted in the Bowman's capsule, periglomerular fibrosis in sclerosing glomeruli. In our ultrastructural study of mesangial matrix from patients with diabetic nephropathy by high-resolution scanning electron microscopy after cellular removal, the meshwork structure was evident at higher magnification. In nodular lesions, the loose meshwork structure appeared to be composed of various sized strands, ranging from 6 to 24 nm (mean ± SD: 11.4 ± 3.8 nm). The pore sizes were variable, ranging from 4 to 70 nm (mean ± SD: 23.6 ± 12.3 nm), and were statistically larger than those of normal controls. As the AGEs are localized most notably in nodular lesions, advanced glycations play a role in the progression of diabetic nephropathy through impairment of the assembly of matrix proteins in vivo. Because type V and type VI collagens are the major components of nodular lesions, increases in these interstitial and fibril or microfibril collagens may contribute to the formation of wider strands in the mesangial matrix of a nodular lesion. As no metalloprotease that is specific for type VI collagen has been identified thus far, AGEs formation might occur preferentially in type VI collagen-rich nodular lesions, which are sites of slow turnover.