Bone morphogenetic protein-induced heterotopic bone in osteopetrosis

Bisphosphonate-Conjugated Photo-Crosslinking Polyanionic Hyaluronic Acid Microbeads for Controlled BMP2 Delivery and Enhanced Bone Formation Efficacy

In this study, we designed bisphosphonate-conjugated polyanionic hyaluronic acid (HA) microbeads (MBs) for the controlled delivery of bone morphogenetic protein 2 (BMP2). MBs were prepared via the photo-crosslinking of bisphosphonate (alendronate)-conjugated methacrylated HA (Alen-MHA). The polyanionic Alen-MHA MBs actively absorbed cationic BMP2 up to 91.0% of the loading efficacy and displayed a sustained release of BMP2 for 10 days. BMP2/Alen-MHA MBs induced osteogenic-related genes in cellular experiments and showed the highly increased bone formation efficacy in thigh muscle injection and rat spinal fusion animal models. Thus, BMP2/Alen-MHA MBs provide a promising opportunity to improve the delivery efficiency of BMP2.

Basic research: Issues with animal experimentations

In vivo studies using the animals are helpful in developing the treatment strategies as they are important link between the successful in vitro testing and safe human use. Various research projects in the field of fixation of fractures, development of newer biomaterials, chemotherapeutic drugs, use of stem cells in nonunion of fractures and cartilage defects etc., have hugely depended on animal experimentation. The employment of animals in experiments is both scientific and ethical issue. There must be reasonable reasons to show that it will significantly advance the present knowledge and lead to improvement in care. The regulatory bodies exist for humane use and care of animals used for experiments e.g., International Council for Laboratory Animal Science, Council for International Organizations of Medical Sciences, International Union of Biological Sciences, International Committee on Laboratory Animals. In India, Indian National Science Academy, Indian Council of Medical Research, National Centre for Laboratory Animal Sciences promote high standards of laboratory animal quality, care and health. The Committee for the Purpose of Control and Supervision on Experiments on Animals guidelines are well defined and is a must read document for any one interested to carry out research with animal facilities.

Management of subtrochanteric femur fractures with internal fixation and recombinant human bone morphogenetic protein-7 in a patient with osteopetrosis: a case report

Introduction

Osteopetrosis is a group of conditions characterized by defects in the osteoclastic function of the bone resulting in defective bone resorption. Clinically, the condition is characterized by a dense, sclerotic, deformed bone which, despite an increased density observable by radiography, often results in an increased propensity to fracture and delayed union.

Case Presentation

We report the case of a 27-year-old Asian man presenting with bilateral subtrochanteric femur fractures. He had a displaced right subtrochanteric femur fracture after a low-energy fall, which was treated surgically. The second fracture that our patient endured was diagnosed as a stress fracture ten weeks later when he complained of pain in the contralateral left thigh. By that time, the right-sided fracture exhibited no radiographic evidence of healing, and when the left-sided stress fracture was being treated surgically, bone grafting with recombinant human bone morphogenetic protein-7 was also performed on the right side.

Conclusion

While there are no data supporting the use of bone morphogenic proteins in the management of delayed healing in patients with osteopetrosis, no other reliable osteoinductive grafting options are available to treat this condition. Both fractures in our patient healed, but based on the serial radiographic assessment it is uncertain to what degree the recombinant human bone morphogenetic protein-7 may have contributed to the successful outcome. It may have also contributed to the formation of heterotopic bone around the fracture site. Further investigation of the effectiveness and indications of bone morphogenic protein use for the management of delayed fracture healing in patients with osteopetrosis is warranted.

Enhancement of crude bone morphogenetic protein-induced new bone formation and normalization of endochondral ossification by bisphosphonate treatment in osteoprotegerin-deficient mice

Osteoprotegerin (OPG) is a novel secreted member of the tumor necrosis factor receptor family which plays a crucial role in negative regulation of osteoclastic bone resorption. We investigated both the quantity and quality of heterotopic new bone induced by crude bone morphogenetic protein (BMP) as a means of examining bone metabolism by bisphosphonate administration in OPG-/- mice. Four weeks after implantation of crude BMP, the volume of heterotopic new bone in OPG-/- mice without alendronate was significantly less than in wild-type (WT) mice. Alendronate treatment of OPG-/- mice resulted in enhancement of the volume of heterotopic new bone. Histological findings revealed that WT mice showed normal bone formation with persistent cartilage that was interspersed with islands of bone. In contrast, the cartilage was replaced by trabecular bone and bone marrow adipocytes in OPG-/- mice without alendronate. However, some cartilage was still present in OPG-/- mice with alendronate compared to those without alendronate. All bone formation-related parameters and bone resorption-related parameters were significantly lower in OPG-/- mice with alendronate than in those without alendronate. These findings suggest that in stimulated osteoclastogenesis without OPG, osteoinductive activity induced by crude BMP is inhibited and endochondral ossification induced by crude BMP is accelerated. On the other hand, alendronate treatment of OPG-/- mice caused osteoinductive activity induced by crude BMP to increase and endochondral ossification induced by crude BMP to be decelerated. In conclusion, inhibition of stimulated osteoclastogenesis results in the enhancement of new bone formation and normalization of endochondral ossification.

Treatment with recombinant human macrophage colony-stimulating factor resorbs blood clot and restores osteoclastogenesis in heterotopic bone induced by partially purified native bone morphogenetic protein in osteopetrotic (op/op) mice

Native bone morphogenetic protein and associated noncollagenous proteins induced the formation of heterotopic bone in the hindquarter muscles of osteopetrotic (op/op) mice and those of their phenotypically normal littermates (+/?). In op/op mice, the heterotopic bone consisted of a disorganized, densely packed mixture of irregular calcified cartilage, osteoid, chondro-osteoid, and fibrous tissue. Injections of recombinant human macrophage colony-stimulating factor initiated bone resorption that began in the peripheral vascularized regions of the metaphyses and continued in central areas of uncalficified avascular chondro-osteoid. On vascularized surfaces, osteoclasts were stained with tartrate-resistant acid phosphatase. In op/op mice treated with macrophage colony-stimulating factor, the osteoclasts were small, with only two or three nuclei, and they did not exhibit tartrate-resistant acid phosphatase staining. In untreated op/op mice, surgical blood clots persisted in the heterotopic sites as late as 3 weeks after the operation, whereas in treated op/op mice, the blood clots were absorbed almost as rapidly as in normal mice. Histologically, recombinant human macrophage colony-stimulating factor restored normal macrophage functions: absorption and organization of blood clot, osteoclastogenesis, synthesis of tartrate-resistant acid phosphatase, bone remodeling, islands of myelopoiesis, and construction of an ossicle complete with a cortex and a medulla filled with functioning hematopoietic bone marrow.