Platelet Activation by Collagen Provides Sustained Release of Anabolic Cytokines

Background: Platelet-rich plasma (PRP) has been increasingly used in sports medicine applications. Platelets are thought to release growth factors important in wound healing, including transforming growth factor (TGF-beta 1), platelet-derived growth factor (PDGF-AB), and vascular endothelial growth factor (VEGF). However, little is known about the effect of platelet activator choice on growth factor release kinetics. Hypothesis: The choice of platelet activator would affect the timing and level of growth factor release from PRP. Study Design: Controlled laboratory study. Methods: Platelet-rich plasma aliquots were activated with either thrombin or collagen. A control group of whole blood aliquots was clotted with thrombin. Supernatant containing the released growth factors was collected daily for 1 week. Levels of TGF-beta 1, PDGF-AB, and VEGF were measured using enzyme-linked immunosorbent assay (ELISA). Results: The use of thrombin as an activator resulted in immediate release of TGF-beta 1 and PDGF-AB, while the collagen-activated PRP clots released similar amounts each day for 5 days. The use of collagen as an activator resulted in an 80% greater cumulative release of TGF-beta 1 from the PRP aliquots over 7 days (P < .001). Concentrating platelets to 3 times the systemic blood level resulted in a 3-fold higher release of TGF-beta 1, 2.5-fold greater release of PDGF, and 5-fold greater release of VEGF (all P < .0001) when compared with whole blood control clots, but no significant differences in the timing of release were noted. Conclusion: These experiments demonstrated that the choice of platelet activator can significantly influence the release kinetics of cytokines from PRP, with thrombin resulting in an immediate release and collagen having a more sustained release pattern. Clinical Relevance: The level and rate of growth factor release depends on the selected platelet activator, a factor that should be considered when selecting a PRP system for a given application.