Regulation of Endothelial Cell Permeability by Platelet-Derived Extracellular Vesicles

Background Platelet (Plt) derived-extracellular vesicles (Plt-EVs) have hemostatic properties similar to Plts. In addition to hemostasis, Plts also function to stabilize the vasculature and maintain endothelial cell (EC) barrier integrity. We hypothesized that Plt-EVs would inhibit vascular endothelial cell permeability, similar to fresh Plts. To investigate this hypothesis we utilized in vitro and in vivo models of vascular endothelial compromise and bleeding. Methods In vitro: Plt-EVs were isolated by ultracentrifugation and characterized for Plt markers and particle size distribution. Effects of Plts and Plt-EVs on endothelial barrier function was assessed by trans - endothelial electrical resistance (TEER) measurements and histological analysis of endothelial junction proteins. Hemostatic potential of Plt-EVs and Plts were assessed by multiple electrode Plt aggregometry. In vivo: The effects of Plts and Plt-EVs on vascular permeability and bleeding were assessed in NOD-SCID mice by an established Miles Assay of vascular permeability and a tail snip bleeding assay. Results In vitro: Plt-EVs displayed exosomal size distribution and expressed Plt specific surface markers. Plts and Plt-EVs decreased EC permeability and restored EC junctions after thrombin challenge. Multiplate aggregometry revealed that Plt-EVs enhanced Thrombin Receptor Activating Peptide (TRAP) mediated aggregation of whole blood, whereas Plts enhanced TRAP, Arachidonic Acid (ASPI), Collagen, and Adenosine Diphosphate (ADP) mediated aggregation. In vivo: Plt-EVs are equivalent to Plts in attenuating VEGF-A induced vascular permeability and uncontrolled blood loss in a tail snip hemorrhage model. Conclusion Our study is the first to report that Plt-EVs might provide a feasible product for transfusion in trauma patients to attenuate bleeding, inhibit vascular permeability and mitigate the endotheliopathy of trauma (EOT). Study Type Original Article Level of evidence This is a pre-clinical study so it does not confirm to the level of evidence table for all clinical studies and case reports. Corresponding Author: Shibani Pati, MD, PhD, Associate Professor, Department of Laboratory Medicine, University of California, San Francisco, 513 Parnassus Avenue, HSE 715, San Francisco, CA 94143. (415)502-1634 Authors have contributed equally towards this manuscript (Byron Miyazawa and Alpa Trivedi) Conflicts of Interest: The authors have no conflicts to declare. Funding Source: This study was not supported by any external funding source Presented at 77th Annual Meeting of AAST, 4th World Trauma Congress, 28-09-2018, San Diego, CA © 2019 Lippincott Williams & Wilkins, Inc.

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