EVs analysis in the COVID-19 era: insights on serum inactivation protocols towards downstream isolation and analysis

Since the outbreak of COVID-19 crisis, the handling of biological samples from known or suspected SARS-CoV-2 positive individuals demanded the use of inactivation protocols aimed at ensuring laboratory operators safety. While not standardized, these practices can be roughly divided in two categories, namely heat inactivation and solvent-detergent treatments. As such, these routine procedures should also apply to samples intended for Extracellular Vesicles (EVs) analysis. Assessing the impact of virus inactivating pre-treatments is therefore of pivotal importance, given the well-known variability introduced by different pre-analytical steps on downstream EVs isolation and analysis. Common guidelines on inactivation protocols tailored to best address EVs-specific requirements will be likely needed among the EVs community, yet deep investigations in this direction havent been reported so far. In the attempt of sparking interest on this highly relevant topic, we here provide preliminary insights on SARS-CoV-2 inactivation practices to be adopted prior serum EVs analysis by comparing solvent/detergent treatment vs. heat inactivation. Our analysis entailed the evaluation of EVs recovery and purity along with biochemical, biophysical and biomolecular profiling by means of Nanoparticle Tracking Analysis, Western Blotting, Atomic Force Microscopy, Transmission Electron Microscopy, miRNA content (digital droplet PCR) and tetraspanin assessment by antibody microarrays. Our data suggest an increase in ultracentrifugation (UC) recovery following heat-treatment, however accompanied by a marked enrichment in EVs-associated contaminants. On the contrary, solvent/detergent treatment is promising for small EVs (< 150nm range), yet a depletion of larger vesicular entities was detected. This work represents a first step towards the identification of optimal bio-samples inactivation protocols targeted to EVs analysis.