SRM/MRM targeted proteomics as a tool for biomarker validation and absolute quantification in human urine

Urine has always been one of the most suitable body fluids for clinical applications. Absolute quantification of disease protein biomarkers in body fluids such as urine is a key step in the biomarker development pipeline. Nevertheless, identification of groups of proteins in complex biological samples is challenging. Traditional affinity-based methodologies such as ELISA are used to verify the presence of biomarkers in clinical samples. More recently, targeted mass spectrometry-based strategies have been developed for biomarker validation, offering an alternative. The great advantage of targeted mass spectrometry-based methodologies is that they allow accurate and specific simultaneous quantification of several biomarkers (multiplexing). Peptides are used as protein surrogates, measured using triple quadrupole instruments in selected reaction monitoring/multiple reaction monitoring mode. In this review, the workflow of selected reaction monitoring/multiple reaction monitoring for disease biomarker validation in urine is presented and assay performance in the latest studies is described.