Mass spectrometric analysis of glucose-modified ribonuclease

The role of mass spectrometry in the study of non-enzymatic protein glycation in diabetes: an update

Recent studies on non-enzymatic protein glycation are reviewed, and results are critically discussed. Advanced glycation end products (AGE) levels in the body reflect a balance between their formation and catabolism. AGE proteolysis leads to the formation of low-molecular-weight AGE (AGE peptides) that are normally excreted in urine. In the case of diabetic disease and/or renal failure, AGE peptides accumulate in plasma. Because of their high reactivity, these compounds have been thought to play a role in the progression of chronic complications. The structural identification of these compounds is particularly important, and a strategy has been designed for their possible definition. A series of experiments has been devoted to the study of the enzymatic degradation products of in vitro glycated human serum albumin (HSA). This approach, based on different MS methods (LC/ESI/MS, LC/ESI/FTMS, MALDI), led to the detection of the glycated peptides generated by digestion of HSA. A further study was devoted to the possible identification of the peptides identified in the glycated HSA digestion products in the plasma of diabetic and nephropatic subjects. No glycated HSA digestion products were found in plasma samples of the subjects under investigation even if clear differences were found among the LC runs from populations of healthy, diabetic, and nephropatic subjects. Parallel investigations were devoted to the evaluation of glyoxal and methylglyoxal-dicarbonyl compounds that originate at the intermediate stage of the Maillard reaction. This evaluation was performed in diabetic patients, before and after the achievement of good metabolic control, and in nephropatic patients subjected to peritoneal dialysis (PD). In the latter case, results indicated that these dicarbonyl compounds, already present in the dialysis fluids, show a decrease in plasma and in dialysis fluids; those data suggested their reaction at peritoneal membrane level.

Analysis of glycated insulin by MALDI-TOF mass spectrometry

Non-enzymatic glycation of protein is mediated via an interaction between the aldehyde group of a reducing sugar and available alpha- or epsilon-amino moieties of the protein. The above event can alter the biological activity of the protein and therefore, it is of particular interest to monitor the glycation of proteins having important functional roles in metabolism. In the present study, matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) has been used to determine the non-enzymatic glycation of bovine insulin. The degree of insulin glycation was increased in both concentration- and time-dependent manner in relation to exposure to glucose, and the event was more pronounced for monoglycation reaction than that noticed for the diglycation of the hormone. Enzymatic digestion of insulin preparations with endoproteinase Glu C has revealed that each of the B 1-13 and B 22-30 peptide fragments of glycated insulin contains a site of binding of a single glucose molecule. Finally, attempt has been made in order to increase the sensitivity of the glycation assay through efficient enrichment of the glycated insulin on magnetic beads containing immobilized 3-aminophenylboronic acid (APBA) on their surface.