Adenoviral‐mediated transfer of human BMP‐6 gene accelerates healing in a rabbit ulnar osteotomy model

Abstract

This study evaluated healing of rabbit bilateral ulnar osteotomies 6 and 8 weeks after surgery in response to percutaneous injection of transgenic adenoviral (Ad) bone morphogenetic protein-6 (BMP-6) vector or green fluorescent protein vector control (Ad-GFP) administered 7 days after surgery compared to untreated osteotomy controls. The amount, composition and biomechanical properties of the healing bone repair tissue were compared among groups and to historical data for intact rabbit ulnae obtained from similar studies at the same institution. Quantitative computed tomography was used to determine area, density and mineral content of the mineralized callus in the harvested ulnae. Maximum torque, torsional stiffness, and energy absorbed to failure were determined at 1.5"/s. Calcified sections of excised ulnae (5 pm) were stained with Goldner's Trichrome and Von Kossa, and evaluated for callus composition, maturity, cortical continuity, and osteotomy bridging. Radiographic assessment of bone formation indicated greater mineralized callus in the ulnae injected with Ad-hBMP-6 as early as 1 week after treatment (2 weeks after surgery) compared to untreated osteotomy ulnae (p < 0.006) and Ad-GFP treated osteotomy ulnae (p < 0.002). Quantitative computed tomography confirmed greater bone area and bone mineral content at the osteotomy at 6 weeks in Ad-BMP-6 treated osteotomy as compared to untreated osteotomy ulnae (p < 0.001) and Ad-GFP treated osteotomy ulnae 0, < 0.01). Ad-BMP-6 treated osteotomy ulnae were stronger (p < 0.001 and 0.003) and stiffer (p = 0.004 and 0.003) in torsion at 6 weeks than untreated osteotomy ulnae or Ad-GFP treated osteotomy ulnae, respectively. Maximum torque, torsional stiffness, and energy absorbed to failure were greater in Ad-BMP-6 treated osteotomy ulnae compared to their respective untreated contralateral osteotomy ulnae at 8 weeks [p < 0.031. Maximum torque and torsional stiffness in the Ad-BMP-6 treated osteotomy ulnae were not different to intact ulnae values at 6 and 8 weeks. These experiments confirm that BMP-6 can be potently osteoinductive in vivo resulting in acceleration of bone repair.

Delayed administration of adenoviral BMP-2 vector improves the formation of bone in osseous defects

“…1,2 A growing literature describes the responsiveness of bone to transfer of osteogenic cDNAs encoding bone morphogenetic proteins (BMPs) -2, -4, -6, -7 and -9. [3][4][5][6][7][8][9] The properties of those BMPs have many potential clinical applications, such as to accelerate the healing of fractures, improve the repair of non-unions and segmental defects, enhance spinal fusion and provide better fixation for prosthetic implants.…”

“…3,10 The direct, local injection of adenovirus carrying human BMP-2 cDNA (Ad.BMP-2) heals critical-sized segmental defects in rabbits and rats. 10,11 This vector also accelerates the healing of tibial fractures in osteoporotic sheep, 12,13 and Ad.BMP-6 accelerates the healing of tibial fractures in rabbits.…”

“…10,11 This vector also accelerates the healing of tibial fractures in osteoporotic sheep, 12,13 and Ad.BMP-6 accelerates the healing of tibial fractures in rabbits. 3 Despite these promising data, there is a need to ensure a more reliable and robust outcome. For instance, in a recent, detailed study in a rat femoral model, we found that 25% of critical-sized defects failed to heal in response to Ad.BMP-2 and cartilaginous areas persisted in many of the healed bones.…”

“…3,14 Thus, it may be better to wait until a stable hematoma has formed. Along these lines, it may be more efficacious to delay the injection until the periosteum has become activated and osteoprogenitor cells have migrated into the defect.…”

Osteonecrosis of the femoral head: treatment with ancillary growth factors

“…The off-label use of recombinant BMP has led to complications including local edema, resorption of surrounding bone, and ectopic bone formation, as seen in multiple animal models in the setting of ON of the femoral head [23•, 27]. Likewise, studies have shown that cellmediated gene therapy approaches have been found to be more efficient at delivering growth factors [36,37,66]. Although vector-mediated cell-based therapy has shown promise in animal models, the transition to clinical trials is potentially limited in a nonlife-threatening disease such as ON due to the complications previously seen with their use, including death and lymphoproliferative disorders [67][68][69].…”