Glycation of Protein in Diabetes

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This research program addresses the hypothesis that damage to proteins and other biomolecules by nonenzymatic glycation and Maillard or browning reactions contributes to the pathogenesis of the long-term complications of diabetes. The proposed mechanism involves formation of irreversible advanced glycation and lipoxidation end-products (AGE/ALEs) that affect protein structure and function and alter metabolism in tissues in which complication develop. We have tested the Maillard hypothesis by evaluating the effects of AGE/ALE inhibitors on the chemical modification of proteins and development of complications in animal models of diabetes, including the streptozotocin-diabetic and Zucker obese rat.These studies have raised questions about the effects of AGE/ALE inhibitors on enzymatic crosslinking of proteins, have led to the identification of a new class of AGE/ALEs derived from cysteine, and have yielded insight into the carbonyl trapping activity and mechanism of action of the AGE/ALE inhibitor pyridoxamine (PM). During the continuation period of this grant, our Specific Aims are: 1)to evaluate the effects of diabetes, hyperlipidemia and AGE/ALE inhibitors on the formation of enzymatic, as well as nonenzymatic, chemical modifications and crosslinks in collagen, including studies on the chelating activity of AGE/ALE inhibitors in vivo; 2) to study the formation and biological significance of Cys-AGE/ALEs in diabetes and hyperlipidemia, including basic research on the reaction of protein sulfhydryl groups with glyoxal, methylglyoxal and fumarate, comparison of levels of Cys-AGE/ALEs in intracellular and extracellular proteins, effects of treatment with AGE/ALE- inhibitors, identification of major intracellular proteins modified by Cys-AGE/ALEs, and evaluation of the regulatory significance of Cys-AGE/ALE formation; 3) to continue studies on PM in order to identify reactive intermediates trapped by this compound in vitro and in vivo, to evaluate effects of PM on levels of dicarbonyl intermediates in plasma, and to evaluate the effects of PM on AGE/ALE formation and development of pathology in a non-hyperlipidemic animal model, the diabetes prone BB/Wor rat.Through this work, we hope to gain a better understanding of the role of AGE/ALEs in the pathogenesis of diabetic complication and the mechanism of action of AGE/ALE inhibitors, leading eventually to the development of more effective therapies for treatment of diabetes and its complications.