Advanced glycation end products-cytokine-nitric oxide sequence pathway in the development of diabetic nephropathy: aminoguanidine ameliorates the overexpression of tumour necrosis factor-alpha and inducible nitric oxide synthase in diabetic rat glomeruli

Aims/hypothesis. Advanced glycation end products are believed to contribute to diabetic microvascular complications by inducing glomerular damage but their role has not been fully clarified. In this study, we explain their ce ntral role in the induction of inducible nitric oxide synthase and producti on of nitric oxide (NO) in streptozotocin-induced diabetic rat glomeruli. Methods. Localization of carboxymethyllysine, which is one of the chemical components of advanced glycation end products, glomerular expression of ind ucible nitric oxide synthase and urinary excretion and glomerular productio n of NO2-/NO3- were examined at 0, 26, 51, and 52 weeks after the induction of diabetes. Therapeutic effects of aminoguanidine were also examined. Results. Carboxymethyllysine was detected in the mesangial area in glomerul i and it progressively accumulated during 52 weeks of observation. Immunohi stochemistry and hybridization studies in situ showed that the number of in ducible nitric oxide synthase-positive cells was notably increased in diabe tic rat glomeruli at 52 weeks. Further, this augmented expression parallele d intraglomerular expression of TNF-alpha and NO2-/NO3- in diabetic rat glo meruli. Treatment with aminoguanidine reduced the expression of TNF-alpha, inducible nitric oxide synthase and intraglomerular NO2-/NO3- production. I t also ameliorated proteinuria in diabetic rats. Conclusion/interpretation. This study showed that carboxymethyllysine possi bly enhances the expression of inducible nitric oxide synthase by stimulati ng the expression of TNF-alpha in diabetic rat glomeruli. The carboxymethyl lysine-cytokine-NO sequence pathway could be one of the major mechanisms in the development of diabetic nephropathy.