Small Extracellular Vesicles From Platelet-Rich and Platelet-Poor Plasma Are Primarily From Platelets and Protect Synoviocytes From IL-1β–Induced Inflammation

Background: Small extracellular vesicles (sEVs) circulate throughout the body via blood. They contain various cargoes, including microRNA (miRNA), and have known roles in modulating inflammation and disease. Plasma-based orthobiologics such as platelet-rich plasma (PRP) are commonly used to treat osteoarthritis and synovitis. The role of extracellular vesicle–derived miRNA in PRP therapy is unknown. Purpose: To characterize sEVs from PRP and platelet-poor plasma (PPP) by using known sEV markers, quantify sEV miRNA content, and evaluate sEV bioactivity via an in vitro IL-1β–induced synovitis model. Study Design: Controlled laboratory study. Methods: sEVs were isolated from leukocyte-rich PRP, leukocyte-poor PRP, and PPP by precipitation or tangential flow methods. The size and concentration of sEVs were quantified, and their cellular origin was determined. The total miRNA content of sEVs was analyzed, and the cellular pathways affected by the sEV miRNA cargo were determined. The effect of plasma-derived sEVs on synoviocyte proliferation and response to inflammation was determined in an IL-1β–induced synovitis model. sEVs were also fluorescently stained, and incorporation was visualized through fluorescent imaging. Results: sEVs isolated from plasma were predominantly derived from platelets, with a small subset derived from monocytes and macrophages. miRNA contained within sEVs targeted various cellular pathways, including metabolism, PI3K-AKT, and calcium signaling. IL-1β–treated synoviocytes treated with native PRP, PPP, or their isolated sEVs were protected from the catabolic effects of IL-1β as compared with the same treatments depleted of sEVs. Conclusion: sEVs were present in all tested fluids. Most sEVs were derived from platelets, with a small subset from white blood cells. miRNA within the sEV affected various cell signaling pathways associated with inflammation, and plasma sEVs were crucial in protecting synoviocytes from inflammation. Clinical Relevance: sEVs in PRP are one mechanism of action by which PRP can protect synoviocytes from inflammation.