Platelet-rich plasma-derived fibrin clot formation stimulates collagen synthesis in periodontal ligament and osteoblastic cells in vitro

Background: Platelet-rich plasma (PRP) contains several growth factors, including platelet-derived growth factor (PDGF) and transforming growth factor-β (TGF-β), at high levels. We have demonstrated the PRP functions like TGF-β to modulate cell proliferation in a cell-type specific manner. In addition, PRP forms gel-like materials in several, but not all, cell cultures tested. This study was designed to investigate PRP's action on extracellular matrix production in periodontal ligament (PDL) and osteoblastic MG63 cell cultures. Methods: PRP was prepared from the plasma obtained from autologous blood of healthy volunteers and stored at -20°C until used. Cells treated with PRP (0.5% to 2%) were immunocytochemically stained for type I collagen and fibrin and the viscosity of the culture media was visually evaluated. Fibrinogen in PRP was detected by immunodot-blotting while endogenous thrombin expression in cells was detected by a modified enzyme-linked immunosorbent assay. Results: Gel-like material rapidly (<30 minutes) formed in cultures of either PDL or osteoblastic MG63 cell cultures after addition of PRP (≥0.5%). PRP changed cell shape and up-regulated type I collagen at 24 hours. Fibrinogen was detected in the PRP preparations and insoluble fibrin networks were found in the newly formed gel-like material. PRP's action on collagen synthesis was mimicked by purified fibrinogen and blocked by thrombin inhibitor. Thrombin was expressed both in PDL and MG63 cells. Conclusions: These findings demonstrated that the gel-like material formed in cell cultures of either PDL or MG63 cells is fibrin clot that is capable of up-regulating collagen synthesis in the extracellular matrix. Our data suggest the possibility that fibrinogen, converted to fibrin, in combination with growth factors present in PRP might effectively promote wound healing at sites of injury in periodontal tissue.