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 the accelerated aging of proteins in diabetes. To identify reactive carbohydrate intermediates formed in the Maillard reaction under physiological conditions, we studied the decomposition of the model Amadori compound, N alpha-formyl-N epsilon-fructoselysine (fFL) and of Amadori compounds on glycated collagen at pH 7.4 and 37 degrees C. Because of effects of buffer and oxidative conditions on the decomposition of Amadori 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 anaerobic conditions. The half-life of fFL was significantly shorter in phosphate, compared to Hepes buffer, and under aerobic, compared to anaerobic, conditions. The decomposition of both fFL and Amadori adducts on glycated collagen was accelerated by increasing the phosphate concentration and/or pH. Glucose and mannose were identified as major products formed by reversal of the Amadori rearrangement, along with tetroses, pentoses, and 3-deoxyglucosone, formed by reverse aldol, rearrangement, and hydrolysis reactions. The tetrose and pentose products included both aldose and ketose sugars. These same products were also formed in similar yields on decomposition of Amadori adducts on glycated collagen in vitro. The spontaneous decomposition of Amadori compounds to more reactive sugars in vivo, including tetroses, pentoses, and 3-deoxyglucosone, provides a mechanism for generating reactive intermediates under physiological conditions and for propagating damage to protein as a result of glycation of proteins by glucose in vivo.