The effects of cell type and culture condition on the procoagulant activity of human mesenchymal stromal cell-derived extracellular vesicles

Background Mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) have great potential as a cell-free therapy in wound healing applications. Because EV populations are not equivalent, rigorous characterization is needed before clinical use. Although there has been much focus on their RNA composition and regenerative capabilities, relatively less is known regarding the effects of MSC cell type (adipose tissue; Ad-MSCs or bone marrow; BM-MSCs) and culture condition (monolayer or spheroid) on MSC-EV performance, including characteristics related to their ability to promote coagulation, which could determine EV safety if administered intravenously. Methods The successful isolation of EVs derived from Ad-MSCs or BM-MSCs cultured in either monolayer or spheroid cultures was confirmed by NanoSight (particle size distribution) and Western blot (surface marker expression). EV surface expression of procoagulant molecules (tissue factor and phosphatidylserine) was evaluated by flow cytometry. EV thrombogenicity was tested using calibrated thrombogram, and clotting parameters were assessed using thromboelastography and a flow-based adhesion model simulating blood flow over a collagen-expressing surface. Results MSC cell type and culture condition did not impact EV size distribution. EVs from all groups expressed phosphatidylserine and tissue factor on their surfaces, were functionally thrombogenic, and tended to increase clotting rates compared to the negative control of serum free media without EVs. On average, EVs did not form significantly larger or stronger clots than the negative control, regardless of cell source or culture condition. Additionally, EVs interfered with platelet adhesion in an in vitro flow based assay. Conclusions: Adipose derived EVs were more thrombogenic and expressed higher amounts of phosphatidylserine. Our findings suggest that, like intact MSCs, source variability amongst EVs is an important factor when considering EVs for potential therapeutic purposes. Level of Evidence Therapeutic/ Care Management Level II Address for reprints: Tiffani Chance MS 3650 Chambers Pass, Bldg 3610, JBSA-Fort Sam Houston, TX 78234-4504 Fax Number: 210-539-6244 Phone number: 210-539-7771 Email: tiffani.c.chance.ctr@mail.mil Conflict of interest statement: The opinions or assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense List of meetings at which the paper was presented: 10th Annual Meeting of Military Health System Research Symposium, August 20-23, 2018 in Kissimmee, FL Disclosures of funding received for this work from any of the following organizations (NIH; Welcome Trust; HHMI): None This paper is respectfully being submitted for consideration into the Military Healthy System Research Symposium (MHSRS) supplement © 2019 Lippincott Williams & Wilkins, Inc.

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