Quantitative assessment of the kinetics of growth factors release from platelet gel

The time course of the release of growth factors from platelet (PLT) gels has not been thoroughly studied and should be elucidated for a better standardization of the clinical use of these products. Release of PLT-derived growth factor-AB (PDGF-AB), transforming growth factor-beta 1 (TGF-beta 1), epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and insulin-like growth factor-1 (IGF-1) was determined 5, 60, 120, and 300 minutes after PLT gel formation. Control experiments where PLT gel was removed and, afterward, exogenous thrombin was added, were also performed. Protein profiles of the PLT concentrates and of the releasates were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Mean PDGF-AB, TGF-beta 1, EGF, and VEGF concentration increased to 76, 114, 3.7, and 0.8 ng per mL, respectively, in the presence of the PLT gel, but remained at approximately 28, 30, 0.28, and 0.34 ng per mL, respectively, when the PLT gel was removed after formation. IGF-1 content remained unchanged (approx. 80 ng/mL). SDS-PAGE analysis showed that several PLT proteins disappear during PLT gel formation and that the protein patterns of the releasates were undistinguishable at the different time points. There is a gradual and fast release of PDGF-AB, TGF-beta 1, EGF, and VEGF from PLT gel for at least 60 to 300 minutes after gel formation, whereas the IGF releasate concentration remains unchanged. This study may provide useful information to improve clinical applications of PLT gels and to design improved blood-derived biomaterials with controlled release of growth factors.