engleski

Favored and disfavored pathways of the Maillard reaction in vitro and in vivo

N6-1, 4-dideoxy-5, 6-dioxoglucosone-lysine (DDGL) is a protein-bound dicarbonyl compound derived from the Amadori product (AP) and a precursor of the lysine-arginine crosslink glucosepane - a dominant protein crosslink produced by the Maillard reaction in vivo. A major unanswered question is whether AP can also be a precursor of lysine-lysine crosslink and if so can the crosslink be formed solely from AP or is AP enolisation to DDGL required. To clarify this question we looked for the major products in model incubation systems composed of ε-amino caproic acid and glucose or Nε-(1-deoxy-D-fructos-1-yl)-aminocaproic acid (AP) in phosphate buffer, pH 7.4 in the presence of DTPA and as such we isolated a new imidazolium crosslink - GLUCOLD and the previously described crossline. Based on the crossline structure it was suggested that it can be a product of the reaction between the AP and DDGL. We confirmed the proposed mechanism by showing that crossline generation is catalyzed by phosphate ions which catalyzed not only the AP formation, but also the DDGL generation measured as its OPD derivative. In addition, crossline formation was slowed down in the presence of guanidinobutyric acid which competes for the same precursor (DDGL) for glucosepane formation. Retention of glucose moiety from C3-C6 in the GLUCOLD structure indicates GLUCOLD formation directly from the AP, however for the complete imidazolium ring closure additional carbonyl compound is needed and because of that its yields are increased in aprotic media and by addition of glyoxal or glycolaldehyde into the reaction mixture. An LC-MS/MS method for crossline and GLUCOLD quantification in biological samples was also developed. Although these crosslinks were the major products isolated from the in vitro model reaction systems they did not significantly participate in the total AGE pool in vivo. Glucosepane, on the other hand, represents the major lysine-arginine product in vitro as well as in vivo. Different reaction mechanisms for GLUCOLD and crossline formation demonstrate more complex pathways in lysine-lysine crosslink generation, while arginine reacts predominantly with dicarbonyl compounds and as a dicarbonyl trapping agent enhances 5, 6-dioxoglucosone formation and concomitantly enriches amounts of the glucosepane.

dicarbonyl compounds; Amadori product; crosslink; Maillard reaction; imidazolium; LC-MS/MS; glucosepane

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