Bone Morphogenetic Protein-2 Binds As Multilayers To A Collagen Delivery Matrix:  An Equilibrium Thermodynamic Analysis

Recombinant human bone morphogenetic protein-2 (rhBMP-2) promotes bone growth but must be retained at the delivery site for optimal efficacy in vivo. rhBMP-2 release from a collagen-based matrix has shown favorable pharmacokinetics. The present study assessed binding affinity and binding saturation of rhBMP-2 to a collagen matrix as a function of solution and rhBMP-2 isoform variables. Results indicate that rhBMP-2 binds to the collagen matrix with affinities on the order of 103 to 104 M-1. Maximum binding, ν, was primarily a function of pH for heterogeneous rhBMP-2 and the extended (T266/T266) isoform. However, binding saturation of the <Q283/<Q283 isoform was unaffected by pH. Overall, binding saturation was higher than the calculated saturation of a rhBMP-2 monolayer, suggesting both hydrophobic and ionic interactions in a multilayer formation. The contributions of pH and ionic strength to the linkage free energy of interaction was on the order of 1.3 kcal mol-1 and ∼0.3 kcal mol-1, respectively. This thermodynamic approach can serve to optimize interactions between therapeutic proteins and delivery systems.