FORMATION OF REACTIVE INTERMEDIATES FROM AMADORI COMPOUNDS UNDER PHYSIOLOGICAL CONDITIONS

The Maillard or browning reaction between reducing sugars and proteins contributes to the chemical aging of tissue proteins in vivo and to t he accelerated aging of proteins in diabetes. To identify reactive car bohydrate intermediates formed in the Maillard reaction under physiolo gical conditions, we studied the decomposition of the model Amadori co mpound, N-alpha-formyl-N-epsilon-fructoselysine (fFL) and of Amadori c ompounds on glycated collagen at pH 7.4 and 37 degrees C. Because of e ffects of buffer and oxidative conditions on the decomposition of Amad ori compounds, the kinetics and products of decomposition were studied in varying phosphate concentrations and in N-2-hydroxyethylpiperazine -N'-2-ethanesulfonic acid (Hepes) buffer under both aerobic and anaero bic conditions. The half-life of fFL was significantly shorter in phos phate, compared to Hepes buffer, and under aerobic, compared to anaero bic, conditions. The decomposition of both fFL and Amadori adducts on glycated collagen was accelerated by increasing the phosphate concentr ation and/or pH. Glucose and mannose were identified as major products formed by reversal of the Amadori rearrangement, along with tetroses, pentoses, and 5-deoxyglucosone, formed by reverse aldol, rearrangemen t, and hydrolysis reactions. The tetrose and pentose products included both aldose and ketose sugars. These same products were also formed i n similar yields on decomposition of Amadori adducts on glycated colla gen in vitro. The spontaneous decomposition of Amadori compounds to mo re reactive sugars in vivo, including tetroses, pentoses, and 3-deoxyg lucosone, provides a mechanism for generating reactive intermediates u nder physiological conditions and for propagating damage to protein as a result of glycation of proteins by glucose in vivo. (C) 1995 Academ ic Press, Inc.