Role of Aldose Reductase in Diabetic Complications

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The polyol pathway enzyme aldose reductase (AR) has been implicated in several pleiotrophic complicationsof diabetes. In animal models, AR inhibitors (ARI) prevent or delay multiple diabetic complications. However, the clinical efficacy of ARI remains uncertain, and the physiological role of AR is unclear. Our results during the current funding period show that AR-catalyzed reduced products of lipid aldehydes-glutathione conjugates (such as GS-DHN, glutathione dihydroxynonane), formed under hyperglycemia-induced oxidative stress, mediate NF-KB and API activation that increases inflammatory markers. We have shown that nitrosation activates and glutathiolation inactivates AR. Our central hypothesis is that by altering the cellular redox state, and inducing post-translational modifications, prolonged diabetes perturbs the redox poise and stress signaling leading to an increase in cytokine production and inflammation which in turn induces or exacerbates secondary diabetic complications. To test this hypothesis, we will extend the studies to understand the mechanistic relationship between hyperglycemia and inflammation and identify the role of AR in cytokine production and inflammation. Specifically our aim is to continue our investigations to further understand the mechanisms by which AR mediates hyperglycemia-induced activation of PKC and TACE that cause TNF-a secretion leading to smooth muscle cell hyperplasia, vascular endothelial cell apoptosis, inflammation, and insulin resistance. Accordingly,the aims are extension of the current grant. Completion of our aims will verify our hypothesis and identify the mechanisms through which AR could mediate hyperglycemia- induced inflammatory signals that cause secondary diabetic complicationsincluding insulin resistance. Also the results of additional structural studies on AR would help us in developing more specific and targeted inhibitor(s) of AR. Thus the aims of the next five years are to: (1) investigate the mechanisms by which reduced lipid aldehydes-glutathione conjugates (such as GS-DHN) in hyperglycemia activate PKC and NF-KB and trigger inflammation; (2) delineate the role of AR in regulating TNF-a production during hyperglycemia; (3) identify protein kinase(s) activated by AR- catalyzed reduced lipid aldehydes-glutathione conjugates (GS-DHN) that phosphorylate PKC; and (4) develop specific and targeted aldose reductase inhibitors. Based on our recent crystal structure of the AR-NADPH-glutathione analogue ternary complex and biochemical analysis of the glutathione binding site of AR, molecular modeling, site-directed mutations will be performed to further probe glutathione binding site and the nature of the interaction between AR and glutathione conjugates. This will help in developing structure-based AR inhibitors which will prevent the binding of GS-HNE without affecting the binding and reduction of toxic lipid aldehydes such as HNE. This approach is potentially important in minimizing the toxicity of AR inhibitors thereby greatly improvingthe therapeutic application of AR inhibitors.