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

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Abstract
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.