The effects of heparin binding proteins in platelet releasate on bone formation

Platelet releasates (PR) from platelet-rich plasma (PRP) preparations are often used as an adjuvant for tissue repair. However, many in vitro and in vivo published studies have shown inconsistent results since outcomes depended on the methods of PRP preparation, the dosage of PRP and wound repair models used. Among the 300 proteins released by platelets, a number of them have the ability to bind to heparin, a sulfated glycosaminoglycan well known for its anticoagulant activity. In this study, we focused on the heparin binding proteins in PR by testing PR with the heparin-heparin binding protein complexes, PR with slow releasing heparin binding proteins from agarose-bound heparin, and PR with the heparin binding proteins removed. The bone-forming effect of each of these PR as an adjuvant to demineralized bone matrix (DBM) was tested. When heparin was added to the PR preparation, DBM bone-forming potential was completely lost. However, when heparin was added as agarose-bound heparin and co-implanted with DBM, both alkaline phosphatase activity and areas of new bone formation increased. The study revealed that stripping off heparin binding proteins from PR did not affect ectopic DBM bone formation, whereas the controlled release of such proteins favors osteoinduction.