Evaluation of individual aging degree by standard-free, label-free LC-MS/MS quantification of formaldehyde-modified peptides

In this study, a standard-free, label-free LC-MS/MS method is proposed to evaluate aging based on the cross-linkage theory. First, an aging-biomarker screening model was set up in vitro with formaldehyde and the most abundant protein in plasma, human serum albumin (HSA), based on the Maillard reaction. The modification level of peptides cleaved from HSA was investigated using a liquid chromatography tandem mass spectrometry (LC-MS/MS) method with an ¹⁸O-labeling technique. One formaldehyde-insensitive peptide and six formaldehyde-sensitive peptides that would be verified for being putative peptide-biomarkers were screened via the in vitro aging model. These six putative biomarkers were then preliminarily verified by plasma samples with the aldehyde-insensitive peptide serving as the internal standard. The verification results indicated that the peptides LDELRDEGK and VFDEFKPLVEEPQNLIK showed a significant quantitative difference among young/mid-aged/elderly groups of people.