Comparative Urine Protein Phenotyping Using Mass Spectrometric Immunoassay

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Abstract
Reported here, human urine samples were analyzed for β-2-microglobulin (β2m), transthyretin (TTR), cystatin C, urine protein 1 (UP1), retinol binding protein (RBP), albumin, transferrin, and human neutrophil defensin peptides (HNP) using mass spectrometric immunoassay (MSIA). MSIA is a unique analytical technique, which allows for the generation of distinct protein profiles of specific target proteins from each subject, which may be subsequently used in comparative protein expression profiling between all subjects. Comparative profiling allows for the rapid identification of variations within individual protein expression profiles. Although the majority of analyses performed in this study revealed homology between study participants, roughly one-quarter showed variation in the protein profiles. Some of these observed variants included a point mutation in TTR, absence of wild-type RBP, monomeric forms UP1, a novel β2m glycated end product and altered HNP ratios. MSIA has been previously used in the analysis of blood proteins, but this study shows how MSIA easily transitions to the analysis of urine samples. This study displays how qualitative urine protein differentiation is readily achievable with MSIA and is useful in identifying proteomic differences between subjects that might be otherwise overlooked with other analytical techniques due to complexity of the resulting data or insufficient sensitivity. Keywords: proteomics • protein variations • MALDI-TOF • urine • biomarker discovery