Exosomes are vesicles that are released from the kidney into urine. They contain protein and RNA from the glomerulus and all sections of the nephron and represent a reservoir for biomarker discovery. Current methods for the identification and quantification of urinary exosomes are time consuming and only semi-quantitative. Nanoparticle tracking analysis (NTA) counts and sizes particles by measuring their Brownian motion in solution. In this study, we applied NTA to human urine and identified particles with a range of sizes. Using antibodies against the exosomal proteins CD24 and aquaporin 2 (AQP2), conjugated to a fluorophore, we could identify a subpopulation of CD24- and AQP2-positive particles of characteristic exosomal size. Extensive pre-NTA processing of urine was not necessary. However, the intra-assay variability in the measurement of exosome concentration was significantly reduced when an ultracentrifugation step preceded NTA. Without any sample processing, NTA tracked exosomal AQP2 upregulation induced by desmopressin stimulation of kidney collecting duct cells. NTA was also able to track changes in exosomal AQP2 concentration that followed desmopressin treatment of mice and a patient with central diabetes insipidus. When urine was stored at room temperature, 4°C or frozen, nanoparticle concentration was reduced; freezing at −80°C with the addition of protease inhibitors produced the least reduction.We have demonstrated the potential of NTA in the identification of urinary exosomes. Development of this technology could allow rapid quantification of kidney tubular exosome excretion in health and disease and provide a crucial quality control for protein or RNA biomarker discovery studies.
Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCB110
Poster Communications: Quantification of human urinary exosomes by nanoparticle tracking analysis
W. Oosthuyzen1, N. E. Sime1, J. R. Ivy1, E. J. Turtle1, J. M. Street4, J. Pound2, L. E. Bath3, D. J. Webb1, C. D. Gregory2, M. A. Bailey1, J. W. Dear1
1. Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, Edinburgh, City of, United Kingdom. 2. MRC Centre for Inflammation Research, University of Edinburgh, Edinburgh, United Kingdom. 3. Edinburgh Centre for Endocrinology, National Health Services - Lothian, Edinburgh, United Kingdom. 4. Renal Diagnostics and Therapeutics Unit, National Institutes of Health, Bethesda, Maryland, United States.
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Where applicable, experiments conform with Society ethical requirements.