Identification of a novel blue pigment as a melanoidin intermediate in the D-xylose-glycine reaction system.

Some blue pigments were formed in the D-xylose (1 M)-glycine (0.1 M) reaction system. A novel blue pigment, designated as Blue-M2 (blue Maillard intermediate-2), was identified as 5-[1,4-dicarboxymethyl-5-(2,3-dihydroxypropyl)-1,4-dihydropyrrolo[3,2-b]pyrrole-2-ylmethylene]-1,4-dicarboxymethyl-2-{5-[N-carboxymethyl(2,3,4-trihydroxytetrahydrofuran-2-yl)methylamino]-2-hydroxymethyl-4-(1,2,3-trihydroxypropyl)tetrahydrofuran-3-yl}-4,5-dihydropyrrolo-[3,2-b]pyrrole-1-ium. Blue-M2 is presumed to have been generated by the reaction between Blue-M1, which was identified as the major blue pigment in a previous paper (Hayase et al., Biosci. Biotechnol. Biochem., 63, 1512-1514 (1999)), and di-D-xyluloseglycine. Blue pigments are important Maillard reaction intermediates through the formation of melanoidins.

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-gamma 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.