Discovery of Urinary Biomarkers

Abstract

A myriad of proteins and peptides can be identified in normal human urine. These are derived from a variety of sources including glomerular filtration of blood plasma, cell sloughing, apoptosis, proteolytic cleavage of cell surface glycosylphosphatidylinositol-linked proteins, and secretion of exosomes by epithelial cells. Mass spectrometry-based approaches to urinary protein and peptide profiling can, in principle, reveal changes in excretion rates of specific proteins/peptides that can have predictive value in the clinical arena, e.g. in the early diagnosis of disease, in classification of disease with regard to likely therapeutic responses, in assessment of prognosis, and in monitoring response to therapy. These approaches have potential value, not only in diseases of the kidney and urinary tract but also in systemic diseases that are associated with circulating small protein and peptide markers that can pass the glomerular filter. Most large scale biomarker discovery studies reported thus far have used one of two approaches to identify proteins and peptides whose excretion in urine changes in specific disease states: 1) two-dimensional electrophoresis with mass spectrometric and/or immunochemical identification of proteins and 2) top-down mass spectrometric methods (SELDI-TOF-MS and capillary electrophoresis-MS). These studies have been chiefly in the areas of nephrology, urology, and oncology. We review these applications, focusing on two areas of progress, viz.

Variation in protein levels obtained from human blood cells and biofluids for platelet, peripheral blood mononuclear cell, plasma, urine and saliva proteomics

“…Urinary proteins originate from different sites, e.g. from plasma via glomerular filtration, from renal tubular epithelial cells, from shedding of whole cells or membrane fragments along the tubulus and bladder or from exosome secretion [30,34]. According to recent recommendations for urinary proteomics [33], we collected second morning urine samples and added sodium azide instantly to minimise contamination of proteins from bacteria [3], which can change the urinary proteome profile [33].…”

A qualitative proteome investigation of the sediment portion of human urine: Implications in the biomarker discovery process

“…Furthermore, Zhou et al [9] determined that the sediment phase of urine accounts for approximately 50% of the total protein content by mass and is primarily comprised of uromodulin. Thus, as a simple prefractionation technique, removal of the sediment phase can be considered beneficial for the analysis of low-abundant protein components in urine supernatants [12]. However, Zhou et al clearly demonstrated (through SDS-PAGE images) that several other proteins contribute to the sediment phase of urine; a comprehensive study to identify these proteins has yet to be conducted.…”

Urine screening by Seldi-Tof, followed by biomarker identification, in a Brazilian cohort of patients with Renal Cell Carcinoma (RCC)

“…High molecular weight proteins (albumin, for example) are able to pass through the glomerular filtrate. Small proteins, or peptides (< 10 kDa) are easily filtered by the glomerulus and constitute an important source of information, even if the peptide is the result of proteolysis of larger proteins circulating in plasma (1)(2)(3). Urine is especially attractive for biomarker discovery in urological diseases since any change in concentration of proteins in plasma will reflect in the urine.…”