Comparing approaches to normalize, quantify, and characterize urinary extracellular vesicles

Charles J. Blijdorp, Omar A.Z. Tutakhel, Thomas A. Hartjes, Thierry P.P. van den Bosch, Martijn H. van Heugten, Juan Pablo Rigalli, Rob Willemsen, Usha M. Musterd-Bhaggoe, Eric R. Barros, Roger Carles-Fontana, Cristian A. Carvajal, Onno J. Arntz, Fons A.J. van de Loo, Guido Jenster, Marian C. Clahsen-Van Groningen, Cathy A. Cuevas, David Severs, Robert A. Fenton, Martin E. van Royen, Joost G.J. HoenderopRené J.M. Bindels, Ewout J. Hoorn*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

16 Citations (Scopus)

Abstract

Background Urinary extracellular vesicles (uEVs) are a promising source for biomarker discovery, but optimal approaches for normalization, quantification, and characterization in spot urines are unclear. 

Methods Urine samples were analyzed in a water-loading study, from healthy subjects and patients with kidney disease. Urine particles were quantified in whole urine using nanoparticle tracking analysis (NTA), time-resolved fluorescence immunoassay (TR-FIA), and EVQuant, a novel method quantifying particles via gel immobilization. 

Results Urine particle and creatinine concentrations were highly correlated in the water-loading study (R2 0.96) and in random spot urines from healthy subjects (R2 0.47-0.95) and patients (R2 0.41-0.81). Water loading reduced aquaporin-2 but increased Tamm-Horsfall protein (THP) and particle detection by NTA. This finding was attributed to hypotonicity increasing uEV size (more EVs reach the NTA size detection limit) and reducing THP polymerization. Adding THP to urine also significantly increased particle count by NTA. In both fluorescence NTA and EVQuant, adding 0.01% SDS maintained uEV integrity and increased aquaporin-2 detection. Comparison of intracellular- and extracellular-epitope antibodies suggested the presence of reverse topology uEVs. The exosome markers CD9 and CD63 colocalized and immunoprecipitated selectively with distal nephron markers. 

Conclusions uEV concentration is highly correlated with urine creatinine, potentially replacing the need for uEV quantification to normalize spot urines. Additional findings relevant for future uEV studies in whole urine include the interference of THP with NTA, excretion of larger uEVs in dilute urine, the ability to use detergent to increase intracellular-epitope recognition in uEVs, and CD9 or CD63 capture of nephron segment-specific EVs.

Original languageEnglish
Pages (from-to)1210-1226
Number of pages17
JournalJournal of the American Society of Nephrology
Volume32
Issue number5
DOIs
Publication statusPublished - May 2021

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