Mechanistic Insight of Platelet-Rich Plasma (PRP) in Mesenchymal and Vascular Progenitors

Abstract

Background: Platelet-rich plasma (PRP) is broadly used for disease intervention, pain management and tissue repair without clear elucidation of its mechanisms of action. Clinically, 100% PRP is injected and yields unknown local concentrations when applied in cardiac infarcts, osteoarthritic joints, tendon injuries and numerous other conditions. Methods: Human PRP samples (26 donors) were obtained per conventional clinical methods. Human bone-marrow mesenchymal stem/progenitor cells (MSCs) were assayed for migration, proliferation and differentiation in response to different PRP concentrations. Human umbilical cord vascular endothelial cells (HUVEC) were assayed for endothelial tube formation. Cleaved Caspase 3 and TUNEL were assayed to evaluate apoptosis. Pro-inflammatory cytokines and FasL were assayed by ELISA. Osmotic pressure and pH were measured. All quantitative data were statistically treated. Findings: MSCs treated with 50% PRP detached into Caspase-3 and TUNEL debris, relative to scarce cell death upon exposure to ≤25% PRPs. Upon 50%-PRP treatment, MSCs produced ~180-fold more IL-1β and ~20-fold more FasL, relative to ≤25% PRPs. IL-6 and TNFα surged upon MSC exposure to 50% PRP. Osmotic pressure of 50% PRP was aberrantly high. Medium pH was neutral throughout the tested 7 days. Nonetheless, 1% to 25% PRPs induced dose-dependent MSC migration. Diluted PRPs induced endothelial tube formation directly or by PRP-treated MSC secretome. Diluted PRPs further elicited context-dependent biomineralization. BMP2, PDGF-BB, VEGF and pro-inflammatory cytokines including IL-1β, IL-6, TNFα had significantly lower concentration in bone marrow than in platelets. Interpretation: PRP's clinical use by aggregating growth factors is inevitably coupled with accumulation of excessive pro-inflammatory cytokines and apoptotic ligands. Cell death elicited by ≥50% PRPs suggests that PRP concentration and composition should be tailored for a given clinical indication. Robust biomineralization induced by PRPs may have implications in fracture healing, atherosclerosis and fibrodysplasia dissecans. Certain factors are preferentially stored in platelets, rather than bone marrow, likely owing to evolution and survival. Funding Statement: This work is funded by NIH grants R01AR065023, R01DE025643, R01DE023112, and R01DE026297. Declaration of Interests: We declare no competing interests. Dr. Jeremy Mao has co-founded biotechnology companies but without reference to PRP technologies in the past and presence. Ethics Approval Statement: IRB approval mentioned by authors in acquisition and use of human blood samples.