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.

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.

A sustained release of lovastatin from biodegradable, elastomeric polyurethane scaffolds for enhanced bone regeneration.

Scaffolds prepared from biodegradable polyurethanes (PUR) have been investigated as a supportive matrix and delivery system for skin, cardiovascular, and bone tissue engineering. In this study, we combined reactive two-component PUR scaffolds with lovastatin (LV), which has been reported to have a bone anabolic effect especially when delivered locally, for effective bone tissue regeneration. To incorporate LV into PUR scaffolds, LV was combined with the hardener component before scaffold synthesis. The PUR scaffolds containing LV (PUR/LV) demonstrated a highly porous structure with interconnected pores, which supported in vitro cell attachment and proliferation and in vivo osteoconductive potential. The PUR/LV scaffolds showed sustained release of biologically active LV, as evidenced by the fact that LV releasates significantly enhanced osteogenic differentiation of osteoblastic cells in vitro. A study of bone formation in vivo using a rat plug defect model showed that the PUR/LV scaffolds were biocompatible. Further, locally delivered LV enhanced new bone formation in the PUR scaffolds at week 4, while there were no obvious effects at week 2. These results suggest that the sustained LV delivery system from PUR scaffolds is a potentially safe and effective device for bone regeneration.