Effects of alendronate on bone formation and osteoclastic resorption after implantation of beta-tricalcium phosphate

Bisphosphonate-Functionalized Scaffolds for Enhanced Bone Regeneration

The local sustained release of bioactive substances are attracting increasing attention in bone tissue engineering, which is beneficial to bone tissue formation and helps to improve the bone ingrowth ability of a scaffold. Bisphosphonates (BPs), as a representative kind of osteoclast inhibitors, are proven to possess excellent osteogenic induction capability. Accordingly, various physical and chemical strategies are developed to functionalize bone tissue scaffolds with BPs to achieve controlled release profiles. Compared with traditional treatment modalities, local release of BPs from these composite scaffolds will contribute to continuous bone integration without the risk of many complications. This review explores the molecular mechanisms of BPs on bone metabolism and analyzes the appropriate concentrations of BPs that promote bone regeneration. The advanced BP loading strategies, implant modification technologies, and BP-loaded composite scaffolds based on different matrices are summarized. Finally, the latest advances and the future development of BP-modified scaffolds for enhanced bone regeneration are discussed. This article provides leading-edge design strategies of the BP-functionalized bone engineering scaffolds for improved bone repairability.

Effects of local application of alendronate on early healing of extraction socket in dogs

OBJECTIVE

The aim of the present study was to assess the effects of alendronate (ALN) on bone remodeling following tooth extraction in a dog model.

MATERIAL AND METHODS

For the study, fifteen male Beagles dogs of approximately 12 months of age were used. Mesial roots of four mandibular premolars were endodontically treated, and the distal roots were removed. ALN concentrations of 0.5, 1, and 2 mg/mL were topically applied for 15 min, while a sterile saline was used as a negative control. After the healing period of 1, 2, and 8 weeks, the samples were analyzed by micro-CT and histology.

RESULTS

Treatment with ALN increased vertical distance between the lingual and the buccal crestal bones. While the ALN-treated sockets had preserved more lingual bone areas, control sockets showed better preservation of the buccal bone areas. ALN treatment resulted in more osteoid formation within the extraction sockets compared with the control. Higher bone volume was found in ALN groups than in the control at 2-week and 8-week healing periods, reaching the significant difference only for the extraction sockets pooled for the ALN treatment.

CONCLUSIONS

Although ALN treatment could not prevent buccal bone resorption following tooth extraction in dogs, it proved beneficial for the preservation of the lingual bone and formation of new bone within the socket. There was no clear relation between the ALN dosages and the alterations within the extraction sockets.

CLINICAL RELEVANCE

ALN affects bone remodeling of the extraction socket. The optimal concentration remains to be determined in future studies.

Immune Modulation by Transplanted Calcium Phosphate Biomaterials and Human Mesenchymal Stromal Cells in Bone Regeneration

A wide variety of biomaterials have been developed as both stabilizing structures for the injured bone and inducers of bone neoformation. They differ in chemical composition, shape, porosity, and mechanical properties. The most extensively employed and studied subset of bioceramics are calcium phosphate materials (CaPs). These materials, when transplanted alongside mesenchymal stem cells (MSCs), lead to ectopic (intramuscular and subcutaneous) and orthotopic bone formation in preclinical studies, and effective fracture healing in clinical trials. Human MSC transplantation in pre-clinical and clinical trials reveals very low engraftment in spite of successful clinical outcomes and their therapeutic actions are thought to be primarily through paracrine mechanisms. The beneficial role of transplanted MSC could rely on their strong immunomodulatory effect since, even without long-term engraftment, they have the ability to alter both the innate and adaptive immune response which is critical to facilitate new bone formation. This study presents the current knowledge of the immune response to the implantation of CaP biomaterials alone or in combination with MSC. In particular the central role of monocyte-derived cells, both macrophages and osteoclasts, in MSC-CaP mediated bone formation is emphasized. Biomaterial properties, such as macroporosity and surface microstructure, dictate the host response, and the ultimate bone healing cascade. Understanding intercellular communications throughout the inflammation, its resolution and the bone regeneration phase, is crucial to improve the current therapeutic strategies or develop new approaches.

The Crosstalk between Osteoclasts and Osteoblasts Is Dependent upon the Composition and Structure of Biphasic Calcium Phosphates

Biphasic calcium phosphates (BCPs), consisting of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), exhibit good biocompatibility and osteoconductivity, maintaining a balance between resorption of the biomaterial and formation of new bone. We tested whether the chemical composition and/or the microstructure of BCPs affect osteoclasts (OCs) differentiation and/or their ability to crosstalk with osteoblasts (OBs). To this aim, OCs were cultured on BCPs with HA content of 5, 20 or 60% and their differentiation and activity were assessed. We found that OC differentiation is partially impaired by increased HA content, but not by the presence of micropores within BCP scaffolds, as indicated by TRAP staining and gene profile expression. We then investigated whether the biomaterial-induced changes in OC differentiation also affect their ability to crosstalk with OBs and regulate OB function. We found that BCPs with low percentage of HA favored the expression of positive coupling factors, including sphingosine-kinase 1 (SPHK1) and collagen triple helix repeat containing 1 (Cthrc1). In turn, the increase of these secreted coupling factors promotes OB differentiation and function. All together our studies suggest that the chemical composition of biomaterials affects not only the differentiation and activity of OCs but also their potential to locally regulate bone formation.

An Injectable Complex of β-tricalcium Phosphate Granules, Hyaluronate, and rhFGF-2 on Repair of Long-bone Fractures with Large Fragments

We evaluated the effects of an injectable complex of β-tricalcium phosphate (β-TCP) granules, hyaluronate, and recombinant human fibroblast growth factor-2 (rhFGF-2) on repair of unstable intertrochanteric fractures in elderly patients. Twenty-five patients (range, 76-91 years) having 31.A2 fractures (AO classification) were treated with injection of the complex followed by intramedullary nails. Bone regeneration and β-TCP resorption, unions of intertrochanteric fractures and displaced lesser trochanters to the shaft, and varus deformity of the femoral neck were assessed by X-ray and CT scans. Fracture union occurred in all cases and union of the displaced lesser trochanter to the shaft was obtained in 24 cases by 12 weeks. It is of interest that β-TCP granules were completely resorbed and marked new bone formation around the lesser trochanter was observed in all cases compared to cases not treated with the complex. Based on the results of intertrochanteric fractures, we applied this technique to two patients with subtrochanteric or humeral fractures in elderly patients, and obtained bone union. This complex is a paste-like material that is easy to handle, and it may be of considerable use in treatment of both unstable intertrochanteric fractures and other cortical bone defects with minimal surgical invasion.

Osteoconductive action of alendronate after implantation of beta tricalcium phosphate in rat adjuvant-induced arthritis

The aim of the study was to determine the effect of alendronate on resorption of β-tricalcium phosphate (β-TCP) and bone formation in rats with adjuvant-induced arthritis (AIA). After preparation of a model of AIA in rats (day 0), alendronate or vehicle was injected intraperitoneally once daily five times in a week. Cylindrical β-TCP was implanted into the rat femoral condyle on day 7. Rats were killed on days 12, 15, and 21, and specimens and serum samples were collected. Specimens were analyzed by tartrate-resistant acid phosphate (TRAP) staining, immunohistochemistry of the ED1 protein, and in situ hybridization with digoxigenin-labeled α1 chain of type I procollagen (COL1A1). Mineralized bone sections were analyzed by Villanueva bone stain. The serum osteocalcin level was measured using an enzyme-linked immunosorbent assay kit. Alendronate decreased the number of TRAP-positive cells attached to β-TCP, the numbers of ED1-positive multinucleated giant cells, and resorption of β-TCP. In AIA rats treated with alendronate, COL1A1 mRNA-positive cells adhered to β-TCP were round or cuboid whereas the cells in untreated AIA rats were fibroblast-like cells. Alendronate increased calcification of newly formed bone whereas it did not restore the bone formation suppressed with inflammation. These results suggest that alendronate has the potential to conduct mature bone after implantation of β-TCP in AIA. Alendronate may help to reduce insufficiency of newly formed bone after implantation of β-TCP in diseases characterized by increased bone resorption such as rheumatoid arthritis.

Use of an Injectable Complex of β-Tricalcium Phosphate Granules, Hyaluronate, and Fibroblast Growth Factor-2 on Repair of Unstable Intertrochanteric Fractures

We evaluated effects of an injectable complex of β-tricalcium phosphate (β-TCP) granules, hyaluronate, and recombinant human fibroblast growth factor-2 (rhFGF-2) on repair of unstable intertrochanteric fractures in elderly patients. Twenty-five patients (range, 76-91 years) having 31.A2 fractures (AO classification) were treated with injection of the complex followed by intramedullary nails. Bone regeneration and β-TCP resorption, unions of intertrochanteric fractures and displaced lesser trochanters to the shaft, and varus deformity of the femoral neck were assessed by X-ray and CT scans. Fracture union occurred in all cases and union of the displaced lesser trochanter to the shaft was obtained in 24 cases by 12 weeks. It is of interest that β-TCP granules were completely replaced by bone and marked new bone formation around the lesser trochanter was observed in all cases compared to cases not treated with the complex. This complex is a paste-like material that is easy to handle, and it may be of considerable use in treatment of both unstable intertrochanteric fractures and other cortical bone defects with minimal surgical invasion.