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Gastrointestinal dysfunction is common in diabetes, and several studies indicate that loss of neuronal nitrergic inhibition may play an important role in its pathogenesis. However, the mechanisms responsible for this effect remain largely unknown. We have previously shown that advanced glycation end-products (AGEs) formed by non-enzymatic glycation dependent processes, can inhibit the expression of intestinal neuronal nitric oxide synthase (nNOS) in vitro acting via their receptor, receptor for AGEs. We now hypothesized that this effect may also be important in experimental diabetes in vivo. We aimed to evaluate the role of AGEs on duodenal nNOS expression and the effects of aminoguanidine (a drug that prevents AGE formation) and ALT-711 (AGE cross-link breaker) in experimental diabetes. Streptozotocin induced diabetic rats were randomized to no treatment, treatment with aminoguanidine (1 g L−1 daily through drinking water) at the induction of diabetes, or treatment with ALT-711 (3 mg kg−1 intraperitoneally), beginning at week 6. A fourth group was used as healthy controls. We performed real time polymerase chain reaction, Western blotting and immunohistochemistry to detect nNOS expression. AGE levels were analysed using sandwich ELISA. Diabetes enhanced accumulation of AGEs in serum, an effect that was prevented by treatment with aminoguanidine and ALT-711. Further, diabetic rats showed a significant reduction in duodenal nNOS expression by mRNA, protein and immunocytochemistry, an effect that was prevented by aminoguanidine. ALT-711 had similar effects on nNOS protein and immunohistochemistry (but not on mRNA levels). The generation of AGEs in diabetes results in loss of intestinal nNOS expression and may be responsible for enteric dysfunction in this condition. This study suggests that treatment directed against AGEs may be useful for the treatment of gastrointestinal complications of diabetes. [ABSTRACT FROM AUTHOR]

Diabetes mellitus results in a loss of neuronal nitric oxide synthase (nNOS) expression in the myenteric plexus but the underlying mechanisms remain unknown. We hypothesized that this may be mediated by advanced glycation end-products (AGEs), a class of modified protein adducts formed by non-enzymatic glycation that interact with the receptor for AGE (RAGE) and which are important in the pathogenesis of other diabetic complications. Whole mount preparations of longitudinal muscles with adherent myenteric plexus (LM-MPs) from the duodenum of adult male rats were exposed to glycated bovines serum albumin (AGE-BSA) or BSA for 24 h. Western blotting, immunohistochemistry and real-time reverse transcriptase polymerase chain reaction (RT-PCR) for mRNA showed a significant reduction in nNOS expression in LM-MPs after exposure to AGE-BSA. NO release, as measured by the Griess reaction, was also significantly reduced by AGE-BSA. A neutralizing antibody against RAGE attenuated the reduction of nNOS protein caused by AGE-BSA. Immunohistochemistry revealed co-localization of RAGE expression with Hu, a marker for neuronal cells but not for S-100, a glial marker. Advanced glycation end-products reduce nNOS expression in the rat myenteric neurones acting via the receptor RAGE. Our results suggest novel pathways for disruption of the nitrergic phenotype in diabetes. [ABSTRACT FROM AUTHOR]