Albuminuria is not associated with elevated urinary vesicle concentration but can confound nanoparticle tracking analysis

• Published in: Nephrology (Carlton, Vic.) Vic.), 2017-11, Vol.22 (11), p.854-863
• Main Authors: McNicholas, Kym, Li, Jordan YZ, Michael, Michael Z, Gleadle, Jonathan M
• Format: Article
• Language: English
• Subjects: Albumin; albuminuria; Albuminuria - urine; Biomarkers; Cell signaling; Electron microscopy; Exosomes; extracellular vesicles; Extracellular Vesicles - physiology; glomerular disease; Humans; Immunoblotting; Immunoglobulin G; Kidney transplantation; nanoparticle tracking analysis; Nanoparticles; Particle Size; Protein purification; Transmission electron microscopy; Ultracentrifugation; Urine; Vesicles
• ISSN: 1320-5358; 1440-1797
• DOI: 10.1111/nep.12867

Aim Extracellular vesicles, such as exosomes, are present in urine with reports of roles in intercellular signalling and diagnostic utility. However, the extent to which the concentration and characteristics of urinary vesicles are altered in albuminuric renal disease has not been well characterized. In this study, we examined the number and characteristics of extracellular vesicles in albuminuric urine. Methods Vesicles were isolated from the urine of 32 patients with varying levels of albuminuria using ultracentrifugation and density gradient purification and were examined using nanoparticle tracking analysis, immunoblotting and transmission electron microscopy. The size profile of particles in these urine preparations was compared with albumin‐containing solutions. Results Overall, there were no substantial differences in the number, or characteristics, of vesicles released into proteinuric urine. Analysis of albumin‐containing solutions showed particles of exosome‐like size, suggesting that such particles can mimic exosomes in standard nanoparticle tracking analysis. Albumin and IgG depletion of proteinuric urine resulted in a substantial reduction in the concentration of particles detected by nanoparticle tracking analysis. Conclusion There was no increase in urinary vesicle concentration in patients with albuminuria. Furthermore, these results demonstrate the need for cautious interpretation of nanoparticle tracking analysis of vesicle concentration in biological fluids containing protein and for sophisticated preparative methods in vesicle purification from urine. Summary at a Glance Examination of the number and characteristics of urinary vesicles showed no significant differences between albuminuric and normal urine.