Osseous regeneration in the rat calvarium using novel delivery systems for recombinant human bone morphogenetic protein‐2 (rhBMP‐)

Abstract

In the current investigation, we report osseous regeneration in critical-size rat calvarial defects using recombinant human bone morphogenetic protein-2 (rhBMP-2) and novel delivery systems based on biomaterials. The novel systems combine rhBMP-2 with dry powder microparticles of poly(D,L-lactide-co-glycolide) (PLGA). The mixture of rhBMP-2 with PLGA microparticles is added to an aqueous solution of biopolymer to yield a semisolid paste. The biopolymers tested include autologous blood clot, hydroxypropyl methylcellulose, and sodium alginate cross-linked with calcium ion. Insoluble collageneous bone matrix was also studied as a control. Test articles were made at 0-, 10-, and 30-micrograms doses of rhBMP-2 and imiplanted in 8-mm-diameter rat calvarial defects (which will not heal if left untreated). The animals were examined 21 days after implantation by radiography, radiomorphometry, histology, and histomorphometry. All tested materials containing rhBMP-2 restored radiopacity and normal contouring to the calvarial defects. Samples without added rhBMP-2 yielded only soft tissue within the defects. Histology showed restoration of inner and outer bone tables plus marrow constituents. The PLGA microparticles were significantly resorbed at the 21-day time point. Although small differences between delivery systems were evident at 0- and 10-micrograms rhBMP-2 doses, all test articles performed essentially equivalently at the 30-micrograms dose. Thus, novel delivery systems for rhBMP-2 offer the promise of combining the intrinsic bioactivity of the osteoinductive protein with pharmaceutically acceptable biomaterials.

Ex vivo gene therapy with stromal cells transduced with a retroviral vector containing the BMP4 gene completely heals critical size calvarial defect in rats

“…Moreover, it is relatively easy to insert test substances such as ex vivo viral transduced cells into the defect and hold them tightly in place with skin sutures. 23 In this study, we showed that implantation of a gelatin matrix impregnated with MLV-based BMP4 vector transduced stromal cells completely healed a large cranial critical size bone defect within 4 weeks in the rat. Therefore, this study provides strong evidence that retroviralbased gene therapy with a growth promoting gene has the potential for repairing large skeletal defects.…”

Repair of Ulnar Segmental Defect by Recombinant Human Bone Morphogenetic Protein-2 in Dogs.

“…In addition, partially purified BMPs may be contaminated with several osteoinductive factors other than BMPs or with other unknown factors. rhBMPs are free of other growth factors and can be produced in unlimited quantity, and species-specificity of BMP-2 is thought to present less of a problem in clinical use [2,5,9,22,25,28]. Heckman and Boyan [7] reported that canine BMPs combined with bovine DBM carrier were also ineffective, suggesting that purity of the carrier is also an important factor for osteoinduction.…”

“…Although various bone graft techniques have been established [18][19][20], there are disadvantages to each such as additional surgical invasion and limited bone source in autograft, immunomediated rejection and transmission of infectious agents in allograft or xenografts, and technical difficulty in vascularized grafts. Recently, therefore much interest has been focused on the application of bone morphogenetic protein (BMP) as a bone graft substitute in reconstructive orthopedic surgery [4,5,9,11,15,22].…”

Synthetic biodegradable polymers as drug delivery systems for bone morphogenetic proteins

“…BMP have been tested with a variety of biodegradable polymers including PLA , PGA, and PLAGA, and other polymers such as polyethylene glycol, poly--caprolactone, and polyphosphazetes [40][41][42][43][44][45][46]. However, none has proven equal to collagen [47,48].…”