Making urinary extracellular vesicles a clinically tractable source of biomarkers for inherited tubulopathies using a small volume precipitation method: proof of concept

Abstract

Biomarkers of inherited tubulopathies would be useful for clarifying diagnoses in patients where genetic screening is not readily available or where disease-attributable mutations are not found. Urinary extracellular vesicles (uEVs) obtained by ultracentrifugation can be used as a source of biomarkers for inherited tubulopathies such as Gitelman Syndrome (GS), however, ultracentrifugation requires costly equipment and is thus not usually accessible. In contrast, precipitation methods can extract uEVs using standard laboratory centrifuges, thus making uEVs extracted by this method clinically tractable as a source of biomarkers for GS and other inherited tubulopathies. Here we optimise a precipitation method for extracting urinary extracellular vesicles (uEVs) and provide proof of concept that these uEVs are a source of biomarkers using GS an exemplar tubulopathy. For method optimisation, uEVs were precipitated from fresh and frozen (for up to 6 years), small volume (1–2 mL) urine samples from healthy volunteers and GS patients. Nanoparticle tracking analysis was used to calculate the concentration of uEVs. Thiazide sensitive sodium-chloride cotransporter (NCC) content was determined by densitometry of Western blots. NCC content of uEVs was lower in GS patients (n = 11) than healthy volunteers (n = 12; P = 0.001). Three of four patients clinically suspected for GS, in whom only a single SLC12A3 mutation was identified, had lower uEV NCC content than all healthy volunteers tested. In the clinical setting, sufficient uEVs can be extracted from frozen, small volume urine samples using precipitation methods to distinguish patients with GS from healthy volunteers, and thus this source of uEVs could be utilised as an additional diagnostic test for GS and similar disorders.