Non-enzymatic glycation of IgG: an in vivo study.

The IgG glycation level of 30 healthy subjects and 60 type 2 diabetic patients with different degrees of metabolic control was evaluated by matrix-assisted laser desorption ionization mass spectrometry, a technique allowing the determination of mass increase of the IgG molecule. When applied to the digested mixture obtained by the action of papain on the plasma protein fraction, the same method established the mass increase of Fab and Fc fragments of IgG; for the former, a higher mass increase was found, possibly explained by its high reactivity to glucose. Experimental results were confirmed by molecular modeling calculations. Results suggest that the immunodeficiency observed in diabetic patients may be due to the inhibition of molecular recognition between antibody and antigen as a result of a change in functionality of the modified Fab fragment of IgG.

Advanced glycation end products: a highly complex set of biologically relevant compounds detected by mass spectrometry.

Structural information on 'AGE-peptides,' a class of substances belonging to advanced glycation end products (AGE) and originating by proteolysis of glycated proteins, was gained through various analytical approaches on the mixture produced by proteinase K digestion of in vitro glycated bovine serum albumin. Both matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS) were employed, and the results were compared with those from conventional spectroscopic methods (UV, fluorescence, gel permeation). The data acquired by the various techniques all depict the digestion mixtures as highly complex, with components exhibiting molecular mass in the range 300-3500 Da. In the analysis of HPLC/ESI-MS data, identification of AGE-peptides was facilitated by 3D mapping. Structural information was gained by means of multiple mass spectrometric experiments.

Matrix-assisted laser desorption/ionization mass spectrometry, enzymatic digestion, and molecular modeling in the study of nonenzymatic glycation of IgG.

The glycation-induced functional change of immunoglobulins is of particular interest. The glycation levels of IgG in 10 healthy subjects and 20 diabetic patients with different degrees of metabolic control were studied by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. It reveals the number of glucose molecules that have condensed on the protein, which range from 1 to 5 for healthy subjects, from 5 to 9 for well controlled diabetic patients, and from 10 to 25 for poorly controlled ones. The identification of the most favored glycation sites has been obtained by MALDI analysis of standard and in vitro glycated IgG and plasma protein fraction of a healthy subject after digestion with papain, releasing Fab and Fc fragments of the molecule. Both experiments, as well as molecular modeling of the whole protein, confirm that the most of glucose molecules have condensed on the Fab fragment of IgG, suggesting that the immune deficiency observed in diabetic patients may be explained at the molecular level by a more effective glycation of the Fab fragment, thus inhibiting the process of molecular recognition between antibody and antigen.

Direct evaluation of glycated and glyco-oxidized globins by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been applied to achieve a qualitative and quantitative evaluation of glycated globins on a wide number of healthy and diabetic subjects. The method allowed us to establish that both alpha- and beta-globins are glycated and that, in addition to simply glycated products, other species are detected. Investigations by different sample treatments and by analysis of the glycated beta-globin fraction obtained by preparative chromatography indicated that these species correspond to glyco-oxidized globins. Consequently MALDI-MS can be validly employed to evaluate not only the glycation level, but also the degree of oxidative stress. The percentages of glycated and glycooxidized species were calculated from the related MALDI spectra by the measurement of the related peak areas, without any other treatment of data. A linear relationship between HbA1c values and the total percentage of glycated and glyco-oxidized globins has been found, and its slope (< 1) has been rationalized by the uncorrected evaluation of glycated globins content in the standard samples employed for HbA1c measurements.

Evaluation of IgG glycation levels by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been employed for the evaluation of the glycation level of IgG from healthy subjects and also from well- and badly-controlled diabetic patients. The measurements have been performed on untreated plasma protein fractions. The data obtained have shown that a clear mass increase, originating from non-enzymatic glycation processes, is observed in the case of diabetic patients: for well-controlled ones it is in the range 512-1565 Da, while it becomes 827-4270 Da for badly-controlled diabetic patients. This approach indicates that MALDI mass spectrometry is a highly specific tool that can be employed in the metabolic control of diabetic patients and in studies relating the IgG glycation level to possible immunological impairment.

A highly specific method for the characterization of glycation and glyco-oxidation products of globins.

A new method, based on matrix-assisted laser desorption/ionization (MALDI) measurements, has been developed for the evaluation of the glycation level of globins, a relevant parameter for diabetes control. It shows high levels of reproducibility and specificity, allowing the different glycated and glyco-oxidized products of both alpha- and beta-globins to be distinguished. Such specificity is reflected in its possible diagnostic use not only for the control of diabetes, but also for the occurrence of 'oxidative stress'. The comparison, for the same samples, of the obtained MALDI data with the related HbA1c values, determined by a high performance liquid chromatographic method, allowed it to be established that HbA1c percentages are not, as usually retained, related to the simply glycated beta-globin, but to the whole pool of glycated and glyco-oxidized alpha- and beta-globins.

The in vivo glyco-oxidation of alpha- and beta-globins investigated by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) has been employed for the determination of molecular weights of alpha- and beta-globins obtained from blood samples of healthy and diabetic subjects. Glycated species, originating from the reaction of glucose with the proteins, are easily evident. The MALDI measurements allowed one to distinguish between simple glycation and glyco-oxidation processes of haemoglobin. In fact, together with the products arising from simple glucose condensation on the two proteins, compounds at different oxidation levels were evident. Due to its high specificity, MALDI must be considered a valuable tool for diagnosis in the diabetes field.