Pre-analytical influences on the population heterogeneity of human extracellular vesicles sourced for nanomedicine uses

Separation of U87 glioblastoma cell-derived small and medium extracellular vesicles using elasto-inertial flow focusing (a spiral channel)

Nanoscale and microscale cell-derived extracellular vesicle types and subtypes are of significant interest to researchers in biology and medicine. Extracellular vesicles (EVs) have diagnostic and therapeutic potential in terms of biomarker and nanomedicine applications. To enable such applications, EVs must be isolated from biological fluids or separated from other EV types. Developing methods to fractionate EVs is of great importance to EV researchers. Our goal was to begin to develop a device that would separate medium EVs (mEVs, traditionally termed microvesicles or shedding vesicles) and small EVs (sEVs, traditionally termed exosomes) by elasto-inertial effect. We sought to develop a miniaturized technology that works similar to and provides the benefits of differential ultracentrifugation but is more suitable for EV-based microfluidic applications. The aim of this study was to determine whether we could use elasto-inertial focusing to re-isolate and recover U87 mEVs and sEVs from a mixture of mEVs and sEVs isolated initially by one round of differential ultracentrifugation. The studied spiral channel device can continuously process 5 ml of sample fluid per hour. Using the channel, sEVs and mEVs were recovered and re-isolated from a mixture of U87 glioma cell-derived mEVs and sEVs pre-isolated by one round of differential ultracentrifugation. Following two passes through the spiral channel, approximately 55% of sEVs were recovered with 6% contamination by mEVs (the recovered sEVs contained 6% of the total mEVs). In contrast, recovery of U87 mEVs and sEVs re-isolated using a typical second centrifugation wash step was only 8% and 53%, respectively. The spiral channel also performed similar to differential ultracentrifugation in reisolating sEVs while significantly improving mEV reisolation from a mixture of U87 sEVs and mEVs. Ultimately this technology can also be coupled to other microfluidic EV isolation methods in series and/or parallel to improve isolation and minimize loss of EV subtypes.

Development and Testing of a Continuous Flow-Electrical-Split-Flow Lateral Transport Thin Separation System (Fl-El-SPLITT)

In this work, a new high-volume, continuous particle separation device that separates based upon size and charge is described. Two continuous flow-electrical-split-flow lateral transport thin (Fl-El-SPLITT) device architectures (a platinum electrode on a porous membrane and a porous graphite electrode under a membrane) were developed and shown to improve particle separations over a purely electrical-SPLITT device. The graphite FL-El-SPLITT device architecture achieved the best separation of approximately 60% of small (28 nm) vs large (1000 nm) polystyrene particles. Fl-El-SPLITT (platinum) achieved a 75% separation on a single pass using these same particles. Fl-El-SPLITT (platinum) achieved a moderate 26% continuous separation of U87 glioma cell-derived small extracellular vesicles (EVs) from medium EVs. Control parameter testing showed that El-SPLITT continuously directed particle motility within a channel to exit a selected port based upon the applied voltage using either direct current or alternating current. The transition from one port to the other was dependent upon the voltage applied. Both large and small polystyrene particles transitioned together rather than separating at each of the applied voltages. These data present the first ever validation of El-SPLITT in continuous versus batch format. The Fl-El-SPLITT device architecture, monitoring, and electrical and fluid interfacing systems are described in detail for the first time. Capabilities afforded to the system by the flow addition include enhanced particle separation as well as the ability to filter out small particles or desalinate fluids. High-throughput continuous separations based upon electrophoretic mobility will be streamlined by this new technique that combines electrical and flow fields into a single device.

Detection of Inflammation-Related Melanoma Small Extracellular Vesicle (sEV) mRNA Content Using Primary Melanocyte sEVs as a Reference

Melanoma-derived small extracellular vesicles (sEVs) participate in tumor pathogenesis. Tumor pathogenesis is highly dependent on inflammatory processes. Given the potential for melanoma sEVs to carry tumor biomarkers, we explored the hypothesis that they may contain inflammation-related mRNA content. Biophysical characterization showed that human primary melanocyte-derived sEVs trended toward being smaller and having less negative (more neutral) zeta potential than human melanoma sEVs (A-375, SKMEL-28, and C-32). Using primary melanocyte sEVs as the control population, RT-qPCR array results demonstrated similarities and differences in gene expression between melanoma sEV types. Upregulation of pro-angiogenic chemokine ligand CXCL1, CXCL2, and CXCL8 mRNAs in A-375 and SKMEL-28 melanoma sEVs was the most consistent finding. This paralleled increased production of CXCL1, CXCL2, and CXCL8 proteins by A-375 and SKMEL-28 sEV source cells. Overall, the use of primary melanocyte sEVs as a control sEV reference population facilitated the detection of inflammation-related melanoma sEV mRNA content.