Bone Morphogenetic Proteins

The bone morhogenetic proteins (BMPs) are a group of dimeric proteins in the trasforming growth factor- (TGF-) based on amino acid homology. More than 20 BMPs have been identified, several of which have significant osteogenic effects. Since these proteins govern the three key steps in the bone induction cascade (chemotaxis and mitosis of mesenchymal cells, differentiation into cartilage and then replacement by bone) BMPs are true pleiotropic morphogens. The biological action are mediated via specific BMP receptors found on the cell surface. These are serine/threonine kinases that phosphorylate intracellular proteins called Smads. The activated Smads are then traslocated to the nucleus, where they regulate either positive or negative expression of genes involved in bone formation. There are different BMPs sources to use in orthopaedic practice. The available amounts of BMPs, the morbidity associated with harvesting of the graft and the variability in success rate are issues to be considered in autografting. The osteoinductive capacity of allograft (mineralized or demineralized) is highly variable and may be inadequate for any bone-inductive effect in humans. A recombinant production system have several advantages: its reproducibility, high concentrations, consistent purity and activity of BMP, and ability to ensure freedom from adventitious agents. However, selection of the best carrier material is difficult in order to control retention time of BMP and localize its activity. A partial solution is derived by ultraconcentration of autologous platelets that contains multiple growth factors delivered locally in physiological way. The amount of BMPs and a possible antagonism between different growth factors are still topics of discussion.