Optimization of Urinary Small Extracellular Vesicle Isolation Protocols: Implications in Early Diagnosis, Stratification, Treatment and Prognosis of Diseases in the Era of Personalized Medicine

Extracellular vesicles isolation from urine was severely interfered by polymeric Tamm-Harsefall protein due to its ability to entrap exosome. Studies had been reported to optimize the extraction of urine extracellular vesicles by using reducing agents, surfactants, salt precipitation or ultrafiltration, but rarely based on highly specific purification methods. We optimized the density gradient centrifugation method for the isolation of urinary small extracellular vesicles (sEV) and compared seven differential centrifugation protocols to obtain the high-yield and high-purity sEV isolation procedures. Our study showed Tris sucrose gradient centrifugation at 25°C had more concentrated distribution of exosomal marker in the gradient compared to Tris sucrose gradient centrifugation at 4°C and PBS sucrose gradient centrifugation. Dissolving the 16000 g pellet using Tris, Nonidet™ P 40 or Dithiothreitol then pooling the supernatants did not increase the exosomal markers and number of nanoparticles in sEV preparation compared to the control and PBS groups. Differential centrifugation at room temperature without ultrafiltration recovered more exosome-like vesicles, exosomal markers and nanoparticles than that at 4°C or combining ultrafiltration. Differential centrifugation at RT without ultrafiltration and salt precipitation recovered the highest number of nanoparticles than other protocols. However, differential centrifugation at RT combining 100 kd ultrafiltration obtained the highest purity of sEV calculated by Nanoparticle number/Total protein. In conclusion, we had established two urinary sEV isolation procedures that can recovered higher yield of sEV and more pure preparation of sEV. It is not recommended to treating 16000 g pellet with reducing agents or surfactants to increase the yield of sEV.