Chemistry and Biological Effects of Melanoidins and Glyceraldehyde-Derived Pyridinium as Advanced Glycation End Products

: Blue pigments (blue‐M1 and blue‐M2) and red pigments (red‐M1 and red‐M2) were generated in a xylose‐glycine reaction system. Blue‐M2 was identified as an addition compound of di‐xylulose‐glycine to blue‐M1 that involved two pyrrolopyrrole structures. We identified red pigments as isomers of addition compounds of xylulose‐glycine to the condensed compound between pyrrolopyrrole‐2‐carbaldehyde and pyrrole‐2‐carbaldehyde. These pigments have polymerizing activity, suggesting that they are important Maillard reaction intermediates through the formation of melanoidins. Melanoidins induced IFN‐γ and IL‐12 expression in spleen cells exposed to allergen and in macrophages, respectively. These findings suggest that melanoidins have a suppressive effect on allergic reaction as a novel physiological effect. On the other hand, we identified a glyceraldehyde‐derived advanced glycation end product (AGE) formed from glyceraldehyde and N‐acetylarginine as well as glyceraldehyde‐derived pyridinium (GLAP) in physiological conditions. The AGE was identified as 5‐methylimidazoline‐4‐one (MG‐H1), which has been reported to be formed from arginine and methylglyoxal. GLAP, which induced reactive oxygen species (ROS) production in HL‐60 cells, is supposed to be a toxic AGE, while MG‐H1 is a nontoxic AGE.