Detection and Quantitation of β-2-Microglobulin Glycosylated End Products in Human Serum by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

beta-2-Microglobulin (beta 2M) is a major protein component found in the amyloid deposits of dialysis-related amyloidosis (DRA) patients. Evidence has been shown that the advanced glycosylated end-products (AGEs) of beta 2M present in sera were related to DRA. We demonstrated that matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a useful tool to investigate the nature of glycosylation of beta 2M and detection of beta 2M or beta 2M-AGEs in human serum. The high-mass end of beta 2M-AGE distribution was found to extend to the neighborhood of 12,868 Da, corresponding to condensations with seven glucose molecules. We also have shown that both beta 2M and beta 2M-AGEs can be detected at low picomole levels directly in bovine serum. Based on these findings, the sera of DRA patients were studied to determine whether beta 2M-AGEs can be detected by MALDI-MS. In an attempt to investigate the possibility of quantitation with MALDI, human sera samples with different concentrations of beta 2M-AGE were examined. We were able to correlate the concentration of beta 2M-AGE with the number of detected AGE products, pointing to the feasibility of MALDI as a quantitative tool.