Study of aberrant modifications in peptides as test bench to investigate the immunological response to non-enzymatic glycation

A side effect of diabetes is the formation of glycated proteins and, from them, the production of the advanced early glycation end products that could determine aberrant immune responses at systemic level. We investigated relevant aberrant post-translational modification (PTM) in diabetes based on synthetic peptides modified on lysine side chain residues with the 1-deoxyfructopyranosyl moiety (deoxyFru) as a possible modification related to glycation. The PTM peptides were used as molecular probes for the detection of possible specific autoantibodies developed by diabetic patients. The PDC-E2(167-186) sequence from pyruvate dehydrogenase complex was selected and tested as a candidate peptide for antibody detection. The structure-based designed type I’ β-turn CSF114 peptide was also used as a synthetic scaffold Twenty-seven consecutive type 1 diabetic patients and 29 healthy controls were recruited for the study. In principle, the ‘chemical reverse approach’, based on the use of patient sera to screen the synthetic modified peptides, would lead to the identification of specific probes able to characterize highly specific autoantibodies as disease biomarkers of autoimmune disorders.. Quite surprisingly both peptides modified with the (1-deoxyfructosyl)-lysine did not lead to significant results. Both IgG and IgM differences between the two populations were not significant. These data can be rationalized considering that: i) IgGs in diabetic subjects exhibit a high degree of glycation, leading to a decreased functionality; ii) IgGs in diabetic subjects exhibit a privileged response vs proteins containing advanced glycation products (e.g. methylglyoxal, glyoxal, glucosone, hydroimidazolone, dihydroxyimidazolidine) and only a minor one with respect to (1-deoxyfructosyl)-lysine.