IN-VITRO KINETIC-STUDIES OF FORMATION OF ANTIGENIC ADVANCED GLYCATIONEND-PRODUCTS (AGES) - NOVEL INHIBITION OF POST-AMADORI GLYCATION PATHWAYS

Nonenzymatic protein glycation (Maillard reaction) leads to heterogene ous, toxic, and antigenic advanced glycation end products (''AGEs'') a nd reactive precursors that have been implicated in the pathogenesis o f diabetes, Alzheimer's disease, and normal aging, In vitro inhibition studies of AGE formation in the presence of high sugar concentrations are difficult to interpret, since AGE-forming intermediates may oxida tively arise from free sugar or from Schiff base condensation products with protein amino groups, rather than from just their classical Amad ori rearrangement products. We recently succeeded in isolating an Amad ori intermediate in the reaction of ribonuclease A (RNase) with ribose (Khalifah, R. G., Todd, P., Booth, A. A., Yang, S. X., Mott, J. D., a nd Hudson, B. G. (1996) Biochemistry 35, 4645-4654) for rapid studies of post-Amadori AGE formation in absence of free sugar or reversibly f ormed Schiff base precursors to Amadori products. This provides a new strategy for a better understanding of the mechanism of AGE inhibition by established inhibitors, such as aminoguanidine, and for searching for novel inhibitors specifically acting on post-Amadori pathways of A GE formation, Aminoguanidine shows little inhibition of post-Amadori A GE formation in RNase and bovine serum albumin, in contrast to its app arently effective inhibition of initial (although not late) stages of glycation in the presence of high concentrations of sugar, Of several derivatives of vitamins B-1 and B-6 recently studied for possible AGE inhibition in the presence of glucose (Booth, A. A., Khalifah, R. G., and Hudson, B. G. (1996) Biochem. Biophys. Res. Commun. 220, 113-119), pyridoxamine and, to a lesser extent, thiamine pyrophosphate proved t o be novel and effective post-Amadori inhibitors that decrease the fin al levels of AGEs formed, Our mechanism-based approach to the study of AGE inhibition appears promising for the design and discovery of nove l post-Amadori AGE inhibitors of therapeutic potential that may comple ment others, such as aminoguanidine, known to either prevent initial s ugar attachment or to scavenge highly reactive dicarbonyl intermediate s.