Javier Esparza

Inhibition of TGF-β signaling by 1D11 antibody treatment increases bone mass and quality in vivo

Transforming growth factor β (TGF‐β) is an abundant bone matrix protein that influences osteoblast and osteoclast interactions to control bone remodeling. As such, TGF‐β represents an obvious pharmacologic target with the potential to regulate both bone formation and resorption to improve bone volume and strength. To investigate the skeletal effect of TGF‐β inhibition in vivo, we used an antibody (1D11) specifically directed at all three isoforms of TGF‐β. Normal mice were treated with 1D11 or control antibody (4 weeks), and cortical and trabecular bone was assessed by micro–computed tomographic (µCT) scanning. Bone volume and cellular distribution were determined by histomorphometric analysis of vertebrae and long bones. Also, whole‐bone strength was assessed biomechanically by three‐point bend testing, and tissue‐level modulus and composition were analyzed by nanoindentation and Raman microspectroscopy, respectively. TGF‐β blockade by 1D11 increased bone mineral density (BMD), trabecular thickness, and bone volume by up to 54%, accompanied by elevated osteoblast numbers and decreased osteoclasts. Biomechanical properties of bone also were enhanced significantly by 1D11 treatment, with increased bending strength and tissue‐level modulus. In addition, Raman microspectroscopy demonstrated that 1D11‐mediated TGF‐β inhibition in the bone environment led to an 11% increase in the mineral‐to‐collagen ratio of trabecular bone. Together these studies demonstrate that neutralizing TGF‐β with 1D11 increases osteoblast numbers while simultaneously decreasing active osteoclasts in the marrow, resulting in a profound increase in bone volume and quality, similar to that seen in parathyroid hormone (PTH)–treated rodent studies.

Local injection of lovastatin in biodegradable polyurethane scaffolds enhances bone regeneration in a critical‐sized segmental defect in rat femora

Statins, a class of naturally‐occurring compounds that inhibit HMG‐CoA reductase, are known to increase endogenous bone morphogenetic protein‐2 (BMP‐2) expression. Local administration of statins has been shown to stimulate fracture repair in in vivo animal experiments. However, the ability of statins to heal more challenging critical‐sized defects at the mid‐diaphyseal region in long bones has not been investigated. In this study, we examined the potential of injectable lovastatin microparticles combined with biodegradable polyurethane (PUR) scaffolds in preclinical animal models: metaphyseal small plug defects and diaphyseal segmental bone defects in rat femora. Sustained release of lovastatin from the lovastatin microparticles was achieved over 14 days. The released lovastatin was bioactive, as evidenced by its ability to stimulate BMP‐2 gene expression in osteoblastic cells. Micro‐computed tomography (CT) and histological examinations showed that lovastatin microparticles, injected into PUR scaffolds implanted in femoral plug defects, enhanced new bone formation. Furthermore, bi‐weekly multiple injections of lovastatin microparticles into PUR scaffolds implanted in critical‐sized femoral segmental defects resulted in increased new bone formation compared to the vehicle control. In addition, bridging of the defect with newly formed bone was observed in four of nine defects in the lovastatin microparticle treatment group, whereas none of the defects in the vehicle group showed bridging. These observations suggest that local delivery of lovastatin combined with PUR scaffold can be an effective approach for treatment of orthopaedic bone defects and that multiple injections of lovastatin may be useful for large defects. Copyright

Local application of a proteasome inhibitor enhances fracture healing in rats

The ubiquitin/proteasome system plays an important role in regulating the activity of osteoblast precursor cells. Proteasome inhibitors (PSIs) have been shown to stimulate the differentiation of osteoblast precursor cells and to promote bone formation. This raises the possibility that PSIs might be useful for enhancing fracture healing. In this study, we examined the effect of the local administration of PSI on fracture repair in rats. The effects of treatment on the healing of a fractured femur were assessed based on radiographs, micro‐computed tomography (μCT) analysis, biomechanical testing, and histological analysis. PSI enhanced osteogenic differentiation in bone marrow‐ and periosteum‐derived mesenchymal progenitor cells in vitro. Moreover, the local administration of PSI in vivo promoted fracture healing in rats, as demonstrated by an increased fracture callus volume in radiographs at 2 weeks post‐fracture, and improved radiographic scores. By week 4, PSI treatment had enhanced biomechanical strength and mineral density in the callus as assessed using bending tests, and μCT, respectively. Histological sections demonstrated that PSI treatment accelerated endochondral ossification during the early stages of fracture repair. Although further investigations are necessary to assess its clinical use, the local administration of PSIs might be a novel, and effective therapeutic approach for fracture repair.