Accurate mass measurements by Fourier transform mass spectrometry in the study of advanced glycation end products/peptides

Abstract

The Maillard reaction occurring between sugars and amino groups is important in living systems. When amino groups belonging to protein chains are involved, the Maillard reaction has been invoked as responsible for protein cross-linking and the production of 'toxic' compounds. The reaction leads to the production of a heterogeneous group of substances, usually called advanced glycation end products (AGEs). Classical analytical approaches, such as spectroscopic (ultraviolet, fluorescence) and mass spectrometric (matrix-assisted laser desorption/ionization, liquid chromatography/electrospray ionization mass spectrometry) methods, have shown that the digestion mixture is highly complex. However, there are clear differences between the digestion mixtures of glycated and unglycated human serum albumin (HSA). In the former case, possible glycated peptides belonging to the AGE peptide class may be identified. Tandem mass spectrometric experiments on selected species seemed to be promising as regards structural information, but it was thought of interest to undertake the present investigation, based on liquid chromatography/electrospray ionization Fourier transform mass spectrometry, in order to obtain definitive results on their elemental composition. Using this approach, about 20 glycated peptides were detected and their possible structures were postulated by examining the known sequence of HSA.

Enzymatic digestion and mass spectrometry in the study of advanced glycation end products/peptides

“…The present study is the logical evolution of previous studies devoted to identifying glycated peptides originating from enzymatic digestion of in vitro glycated HSA with proteinase K [11] and trypsin [12]. In principle, it would lead to the structural identification of AGE peptides whose presence, in further researches, will be verified in plasma samples of healthy, diabetic, and end-stage renal failure subjects.…”

“…Their mass value ranges from 1290 to 2208 Da, and some of them were already identified in the previous study performed by LC/FT-MS on glycated HSA [12].…”

“…In vitro glycation of pure, defatted HSA was carried out with glucose, according to a published procedure [12]. Briefly, HSA (Sigma, St Louis, MO) [100 mg/mL (1.5⅐10 Ϫ3 M) in 0.01 M phosphate buffer (Carlo Erba Reagenti, Rodano, Italy), pH 7.4, containing 5 mM toluene (Carlo Erba Reagenti) as a bacteriostatic] was incubated with 0.5 M D-glucose (Sigma, St Louis) at 37°C for 28 days.…”

“…For more specific results, in a further study [12] human serum albumin (HSA) was glycated in vitro and a more specific enzyme was employed for its digestion.…”

Characterization of glycation adducts on human serum albumin by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

“…Further rearrangement and cleavage of this fructosamine can lead to other modifications, known as advanced glycation end products (AGEs). Figure 1 provides a summary of such products, as identified in previous work with HSA and other glycated proteins [6,[9][10][11][12][13][14][15][16][17][18][19][20].…”