Effects of protein dose and delivery system on BMP-mediated bone regeneration

Abstract

Delivery of recombinant proteins is a proven therapeutic strategy to promote endogenous repair mechanisms and tissue regeneration. Bone morphogenetic protein-2 (rhBMP-2) has been used to promote spinal fusion and repair of challenging bone defects; however, the current clinically-used carrier, absorbable collagen sponge, requires high doses and has been associated with adverse complications. We evaluated the hypothesis that the relationship between protein dose and regenerative efficacy depends on delivery system. First, we determined the dose-response relationship for rhBMP-2 delivered to 8-mm rat bone defects in a hybrid nanofiber mesh/alginate delivery system at six doses ranging from 0 to 5 μg. Next, we directly compared the hybrid delivery system to the collagen sponge at 0.1 and 1.0 μg. Finally, we compared the in vivo protein release properties of the two delivery methods. In the hybrid delivery system, bone volume, connectivity and mechanical properties increased in a dose-dependent manner to rhBMP-2. Consistent bridging of the defect was observed for doses of 1.0 μg and greater. Compared to collagen sponge delivery at the same 1.0 μg dose, the hybrid system yielded greater connectivity by week 4 and 2.5-fold greater bone volume by week 12. These differences may be explained by the significantly greater protein retention in the hybrid system compared to collagen sponge. This study demonstrates a clear dose-dependent effect of rhBMP-2 delivered using a hybrid nanofiber mesh/alginate delivery system. Furthermore, the effective dose was found to vary with delivery system, demonstrating the importance of biomaterial carrier properties in the delivery of recombinant proteins.

Hydrogel-based Delivery of rhBMP-2 Improves Healing of Large Bone Defects Compared With Autograft

“…Bilateral critically sized segmental defects (8 mm length) [8,34] were created in the middiaphysis of femora of 13-week-old female Sasco Sprague-Dawley rats (Charles River, Wilmington, MA, USA) after stabilization of each femur with a fixation plate (Fig. 1A).…”

“…All materials were aseptically prepared in a laminar flow hood, and the hydrogels were stored sterile overnight at 4°C. During surgery, 150 lL of alginate hydrogel, kept on ice between uses, was injected into the defect space through the perforations in the NFM tube as previously established [8,27,34].…”

“…The central 121 image slices corresponding to approximately the central 4.6 mm of the defect length were analyzed for differences. BV and BD across the two treatment groups and time points were calculated for statistical comparisons (n = 14 per group) as described previously [8,27,34]. To accurately quantify the amount of new bone formation in the presence of mature autograft material, the respective 2-week BVs were used as a baseline to subtract from the subsequent volumes for each sample.…”

“…We have previously observed higher mineral content and biomechanical properties in critically sized femoral segmental defects treated with a perforated nanofiber mesh enclosing RGD-alginate and rhBMP-2 (NMA-rhBMP-2) hybrid delivery system at equivalent doses and with advantageous rhBMP-2 release kinetics as compared with ACS-rhBMP-2 [8,9,27,28]. However, its performance relative to autograft, the gold standard, is unknown.…”

The Interaction of BMP2‐Induced Defect Healing in Rat and Fixator Stiffness Modulates Matrix Alignment and Contraction

“…Although BMP2 treatment in these dosages typically leads to successful healing, a series of preclinical and clinical studies have employed lower dosages to induce the bone self‐healing cascade 9, 10. Similarly, a reduced BMP2 dosage is quite efficient to induce successful healing of rat critical‐sized bone defects 4, 11…”