High Doses of Bone Morphogenetic Protein 2 Induce Structurally Abnormal Bone and Inflammation In Vivo

Abstract

The major Food and Drug Association-approved osteoinductive factors in wide clinical use are bone morphogenetic proteins (BMPs). Although BMPs can promote robust bone formation, they also induce adverse clinical effects, including cyst-like bone formation and significant soft tissue swelling. In this study, we evaluated multiple BMP2 doses in a rat femoral segmental defect model and in a minimally traumatic rat femoral onlay model to determine its dose-dependent effects. Results of our femoral segmental defect model established a low BMP2 concentration range (5 and 10 μg/mL, total dose 0.375 and 0.75 μg in 75 μg total volume) unable to induce defect fusion, a mid-range BMP2 concentration range able to fuse the defect without adverse effects (30 μg/mL, total dose 2.25 μg in 75 μg total volume), and a high BMP2 concentration range (150, 300, and 600 μg/mL, total dose 11.25, 22.5, and 45 μg in 75 μg total volume) able to fuse the defect, but with formation of cyst-like bony shells filled with histologically confirmed adipose tissue. In addition, compared to control, 4 mg/mL BMP2 also induced significant tissue inflammatory infiltrates and exudates in the femoral onlay model that was accompanied by increased numbers of osteoclast-like cells at 3, 7, and 14 days. Overall, we consistently reproduced BMP2 side effects of cyst-like bone and soft tissue swelling using high BMP2 concentration approaching the typical human 1500 μg/mL.

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

“…Scaffold-based BMP delivery, especially on an absorbable collagen sponge (eg, ACS-rhBMP-2), has become popular as a clinical therapeutic alternative, at least in the United States, on the basis of promising animal and clinical results [20,24,35,37,38,46]. However, evidence of large doses of rhBMP-2 leading to instances of heterotopic ossification, excessive inflammation, or poor bone structure has led to concerns regarding its clinical use, where an exact dose-response relationship has not been determined [6,37,38,47]. It is thought that research that demonstrates efficacy with use of lower doses and/or a more sustained delivery of rhBMP-2 could thus lead to increased use of rhBMP-2 in place of autografts.…”

“…The widespread use of recombinant human BMP-2 (rhBMP-2) highlights its capability to augment large segmental bone defect repair, especially in the context of animal studies, with BMP-2 supplementation showing improved healing compared with allograft and ceramic fillers [25,46]. Concerns about BMP-2 side effects, optimal delivery scaffolds, and BMP-2 release kinetics notwithstanding, rhBMP-2 delivered in an absorbable collagen sponge (ACS-rhBMP-2) has become a popular clinical alternative to bone grafting in the United States while tunable delivery systems with tailored BMP release kinetics are sought [28,47].…”

Novel Wnt Regulator NEL-Like Molecule-1 Antagonizes Adipogenesis and Augments Osteogenesis Induced by Bone Morphogenetic Protein 2

“…12,36 Briefly, 85/15 D,L-PLGA (inherent viscosity, 0.61 dL/g; Absorbable Polymers, Pelham, AL)/chloroform solutions were mixed with 200 to 300 mmediameter sucrose to obtain 94% porosity and were compressed in a polytetrafluoroethylene mold to form scaffolds measuring 6 mm in length and 4 mm in diameter. After freeze-drying overnight, scaffolds were immersed in three changes of distilled deionized water (ddH 2 O) to dissolve the sucrose.…”

“…Before implantation, scaffolds were impregnated with recombinant human BMP2 and/or recombinant human NELL-1. Doses of each growth factor (Table 1) were chosen based on the ability of BMP2 to consistently induce adipocytic bone cysts 12 and NELL-1 to significantly improve bone regeneration in an FSD model in our previous studies. 37 Each growth factor was diluted to the appropriate concentration in phosphate-buffered saline (PBS), added dropwise uniformly to the scaffolds for 20 minutes, and lyophilized in a freeze-drier overnight at À20 C. Implants for PBS controls were generated in the same way, except that no growth factors were added.…”

“…9 Recently, we demonstrated that osteoinductive effects of NELL-1 are partially mediated through binding to the intracellular molecule apoptosis related protein 3 and integrin-b 1 . 10 In translational models of bone repair, exogenous NELL-1 induces potent osseous healing of critical-sized rat calvarial defects, 11 repair of rat femoral segmental defects (FSDs), 12 as well as successful spinal fusion in rats 13,14 and sheep. 15 Based on these results demonstrating reproducible preclinical osteoinductivity in multiple small and large animal models, NELL-1 is being developed for therapeutic use in spinal fusion in humans.…”