Purpose of the study: Bone morphogenetic proteins (BMPs) are osteoinducing proteins which play a primordial role in bone repair. To obtain optimal mineralization in vivo, high doses of heparin binding growth factor must be used. Studies have demonstrated that functionalized dextranes (FD) present affinity for heparin binding growth factor. We studied the capacity of dextrane derivatives to interact with BMP-2 and potentialize its biological activity in vitro.

Material and methods: Different soluble FD were obtained by random substitution of carbosymethyl (CM), benzylamide (B) and sulfate (Su) groups on native dextrane chains. Gel electrophoresis was used to study the affinity of the anionic FDs for BMP-2. The effect of polymers on osteoinduction activity of BMP-2 was evaluated by histochemistry. ALP (an early marker) synthesized by mypoblasts C2C12 were dosed seven days after injection in presence of BMP-2 associated or not with polymers. IN addition, expression of osteocalcin (late marker) was quantified by RT-PCR.

Results: Electrophoresis demonstrated that DMCB and DMCBSu interacted with BMP-2. These interactions appeared to increase with B level but decreased with Su level. We worked with FD1, a DMCB with a high affinity for BMP-2. The ALP activity was clearly potentialized when BMP-2 was associated with heparin and even better with FD1. Expression of osteocalcin was also amplified with the FD1-BMP-2 association. The influence on the biological activity of BMP-2 of FD, presenting different degrees of substitution, was also tested. Only FDs containing a high concentration of B expressed affinity for BMP-2, potentializing the biological activity of the protein.

Discussion: Dextanes functionalized with a high rate of benzylamide substitution interact with BMP-2 while sulfate substitution limits such interaction. Only FDS which interact with BMP-2 can potentialize the protein’s biological activity in vitro. Two hypotheses can be put forward: i) FD presents BMP-2 to its receptor cell, ii) FD protects BMP-2 from proteolytic degradation or capture by antagonists. The capacity of FD1 to potentialize the biological activity of BMP-2 could be a way of reducing the quantity of growth factor needed for optimal bone repair.