Delayed Bone Repair Research Articles

Aging alters the effect of adiponectin receptor signaling on bone marrow-derived mesenchymal stem cells.

Adiponectin receptor signaling represents a promising therapeutic target for age-related conditions such as osteoporosis and diabetes. However, the literature presents conflicting evidence regarding the role of adiponectin signaling in bone homeostasis and fracture repair across different health states, ages, and disease conditions. These inconsistencies may arise from the complex endocrine and paracrine feedback mechanisms regulating adiponectin, as well as the variability in adiponectin isoforms and receptor expressions. In this study, we observed differential expression of adiponectin receptors in the bone marrow (BM) of aged mice, characterized by elevated levels of adiponectin receptor 2 and reduced levels of receptor 1, as corroborated by both single-cell sequencing and invivo staining. Additionally, circulating levels of adiponectin and its local expression were significantly higher in aged mice compared to younger counterparts. Treatment with adiponectin receptor agonist, AdipoRon, enhanced bone regeneration and repair in young mice by promoting osteogenesis and reducing osteoclastogenesis. Conversely, in aged mice, AdipoRon treatment led to cellular senescence, delayed bone repair, and inhibited osteogenic activity. Notably, the adiponectin receptor 1-Wnt and adiponectin receptor 2-MAPK and mTOR signaling pathways were differentially activated in AdipoRon-treated BM mesenchymal stem cells from young and aged mice. Additionally, the NF-κB, and AKT pathways were consistently downregulated in BM macrophages of both age groups following AdipoRon administration. In conclusion, aging significantly modulates the impact of adiponectin receptor signaling on BM mesenchymal stem cells. This modulation is potentially attributable to changes in receptor transcription and distribution, as well as differential activation of downstream signaling pathways.

Periostin+ myeloid cells improved long bone regeneration in a mechanosensitive manner

Myeloid cells are pivotal in the inflammatory and remodeling phases of fracture repair. Here, we investigate the effect of periostin expressed by myeloid cells on bone regeneration in a monocortical tibial defect (MTD) model. In this study, we show that periostin is expressed by periosteal myeloid cells, primarily the M2 macrophages during bone regeneration. Knockout of periostin in myeloid cells reduces cortical bone thickness, disrupts trabecular bone connectivity, impairs repair impairment, and hinders M2 macrophage polarization. Mechanical stimulation is a regulator of periostin in macrophages. By activating transforming growth factor-β (TGF-β), it increases periostin expression in macrophages and induces M2 polarization. This mechanosensitive effect also reverses the delayed bone repair induced by periostin deficiency in myeloid cells by strengthening the angiogenesis-osteogenesis coupling. In addition, transplantation of mechanically conditioned macrophages into the periosteum over a bone defect results in substantially enhanced repair, confirming the critical role of macrophage-secreted periostin in bone repair. In summary, our findings suggest that mechanical stimulation regulates periostin expression and promotes M2 macrophage polarization, highlighting the potential of mechanically conditioned macrophages as a therapeutic strategy for enhancing bone repair.

Tmem119 deficiency delays bone repair in mice

Tmem119 was identified as a bone anabolic factor in osteoblasts, however the roles of Tmem119 on bone repair have remained unknown. Therefore, we herein investigated the roles of Tmem119 on bone repair by examining the bone repair process after a femoral bone defect using Tmem119-deficient mice. In Tmem119-deficient mice, bone repair after a femoral bone defect was significantly delayed 10 and 14 days after bone injury in female and male mice with 3-dimensional micro-computed tomography analyses, respectively. The number of alkaline phosphatase-positive cells at the damaged sites was significantly decreased 7 days after bone injury in Tmem119-deficient mice, although the number of Osterix-positive cells was not significantly different 4 days after bone injury. The number of tartrate-resistant acid phosphatase-positive multinucleated cells as well as the number and luminal area of CD31-positive vessels at the damaged sites were not significantly different between Tmem119-deficient and wild-type mice. The present study first showed that Tmem119 deficiency delayed bone repair partly through a decrease in the osteoblastic bone formation of differentiated osteoblasts.

Effects of boric acid on alveolar sockets filling after dental extraction in rats.

After extraction, dental alveolus filling aims to reduce bone loss and maintain the alveolus volume during patient rehabilitation. Boric acid (BA) is a boron-derived compound with osteogenic properties and an interesting candidate for alveoli filling. This study aims to investigate the osteogenic capacity of the local application of BA in dental socket preservation. Thirty-two male Wistar rats were submitted to upper right incisor extraction and randomly divided into four groups (n = 8): control group (no intervention), BA (8 mg/kg) socket filling, bone graft (Cerabone®, Botiss, Germany), and BA + bone graft socket filling. Animals were euthanized 28 days after dental extraction. MicroCT and histological analysis were performed to evaluate the newly formed bone on the dental alveolus. MicroCT analysis demonstrated that bone volume fraction (BV/TV), bone surface (BS), bone surface/bone volume ratio (BS/BV), bone surface density (BS/TV), trabecular thickness (Tb.Th), total bone porosity (Po-tot), and total volume of pore space (Po.V(tot)) from BA and BA + bone graft rats were significantly different from the control group. Histological evaluation displayed a delayed bone repair in BA rats, with the presence of connective tissue and inflammatory infiltrate. However, the BA + bone graft group demonstrated histological aspects like the bone graft animals, with less organized osteoblasts, suggesting inferior bone repair. Osteogenic capacity did not depend on the BA local application after 28 days of dental extraction. The presence of inflammation in the BA group can represent toxicity induced by the substance dosage used.

Extracellular vesicles secreted from mouse muscle cells improve delayed bone repair in diabetic mice.

Humoral factors that are secreted from skeletal muscles can regulate bone metabolism and contribute to muscle-bone relationships. Although extracellular vesicles (EVs) play important roles in physiological and pathophysiological processes, the roles of EVs that are secreted from skeletal muscles in bone repair have remained unclear. In the present study, we investigated the effects of the local administration of muscle cell-derived EVs on bone repair in control and streptozotocin-treated diabetic female mice. Muscle cell-derived EVs (Myo-EVs) were isolated from the conditioned medium from mouse muscle C2C12 cells by ultracentrifugation, after which Myo-EVs and gelatin hydrogel sheets were transplanted on femoral bone defect sites. The local administration of Myo-EVs significantly improved delayed bone repair that was induced by the diabetic state in mice 9 days after surgery. Moreover, this administration significantly enhanced the ratio of bone volume to tissue volume at the damaged sites 9 days after surgery in the control mice. Moreover, the local administration of Myo-EVs significantly blunted the number of Osterix-positive cells that were suppressed by the diabetic state at the damage sites after bone injury in mice. Additionally, Myo-EVs significantly blunted the mRNA levels of Osterix and alkaline phosphatase (ALP), and ALP activity was suppressed by advanced glycation end product 3 in ST2 cells that were treated with bone morphogenetic protein-2. In conclusion, we have shown for the first time that the local administration of Myo-EVs improves delayed bone repair that is induced by the diabetic state through an enhancement of osteoblastic differentiation in female mice.

Irisin improves delayed bone repair in diabetic female mice.

Irisin is a proteolytic product of fibronectin type II domain-containing 5, which is related to the improvement in glucose metabolism. Numerous studies have suggested that irisin is a crucial myokine linking muscle to bone in physiological and pathophysiological states. We examined the effects of local irisin administration with gelatin hydrogel sheets and intraperitoneal injection of irisin on the delayed femoral bone repair caused by streptozotocin (STZ)-induced diabetes in female mice. We analyzed the femurs of mice using quantitative computed tomography and histological analyses and then measured the mRNA levels in the damaged mouse tissues. Local irisin administration significantly blunted the delayed bone repair induced by STZ 10days after a femoral bone defect was generated. Local irisin administration significantly blunted the number of Osterix-positive cells that were suppressed by STZ at the damaged site 4days after a femoral bone defect was generated, although it did not affect the mRNA levels of chondrogenic and adipogenic genes 4days after bone injury in the presence or absence of diabetes. On the other hand, intraperitoneal injection of irisin did not affect delayed bone repair induced by STZ 10days after bone injury. Irisin significantly blunted the decrease in Osterix mRNA levels induced by advanced glycation end products or high-glucose conditions in ST2 cells in the presence of bone morphogenetic protein-2. We first showed that local irisin administration with gelatin hydrogel sheets improves the delayed bone repair induced by diabetic state partially by enhancing osteoblastic differentiation.

Role of Macrophages and Plasminogen Activator Inhibitor-1 in Delayed Bone Repair Induced by Glucocorticoids in Mice.

Glucocorticoids delay fracture healing and induce osteoporosis. However, the mechanisms by which glucocorticoids delay bone repair have yet to be clarified. Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of plasminogen activators and an adipocytokine that regulates metabolism. We herein investigated the roles of macrophages in glucocorticoid-induced delays in bone repair after femoral bone injury using PAI-1-deficient female mice intraperitoneally administered with dexamethasone (Dex). Dex significantly decreased the number of F4/80-positive macrophages at the damaged site two days after femoral bone injury. It also attenuated bone injury-induced decreases in the number of hematopoietic stem cells in bone marrow in wild-type and PAI-1-deficient mice. PAI-1 deficiency significantly weakened Dex-induced decreases in macrophage number and macrophage colony-stimulating factor (M-CSF) mRNA levels at the damaged site two days after bone injury. It also significantly ameliorated the Dex-induced inhibition of macrophage phagocytosis at the damaged site. In conclusion, we herein demonstrated that Dex decreased the number of macrophages at the damaged site during early bone repair after femoral bone injury partly through PAI-1 and M-CSF in mice.

Role of tissue factor in delayed bone repair induced by diabetic state in mice.

BackgroundTissue factor (TF) is the primary activator of the extrinsic coagulation protease cascade. Although TF plays roles in various pathological states, such as thrombosis, inflammatory diseases, cancer, and atherosclerosis, its involvement in bone metabolism remains unknown.Materials and methodsThe present study examined the roles of TF in delayed bone repair induced by a diabetic state in mice using wild-type (WT) and low TF-expressing (LTF) male mice. A diabetic state was induced by intraperitoneal injections of streptozotocin (STZ).ResultsA prolonged diabetic state significantly reduced total and trabecular bone mineral densities (BMD) as well as cortical bone thickness in WT and LTF mice; these BMD parameters were similar between WT and LTF mice treated with or without STZ. The diabetic state induced in WT mice delayed the repair of the femur following injury. The diabetic state induced in LTF mice was associated with further delays in bone repair. In in vitro experiments, TF significantly decreased receptor activator of nuclear factor-κB ligand-induced osteoclast formation and osteoclastogenic gene expression in RAW264.7 cells. However, it did not affect the gene expression levels of runt-related transcription factor 2 and osterix as well as alkaline phosphatase activity in mouse primary osteoblasts.ConclusionLow TF state was associated with enhanced bone repair delay induced by diabetic state in mice. The TF-induced suppression of bone remodeling may be a contributing factor to the protective effects of TF against delayed bone repair in a diabetic state.

PAI-1 is involved in delayed bone repair induced by glucocorticoids in mice.

Glucocorticoid (GC) treatments induce osteoporosis and chronic GC treatments have been suggested to induce delayed bone repair; however, the mechanisms by which GC induces delayed bone repair remain unclear. We herein investigated the roles of plasminogen activator inhibitor-1 (PAI-1) in GC-induced effects on bone repair after femoral bone injury using female mice with a PAI-1 deficiency and their wild-type counterparts. Dexamethasone (Dex) increased plasma PAI-1 levels as well as PAI-1 mRNA levels in the adipose tissues and muscles of wild-type mice. PAI-1 deficiency significantly blunted Dex-induced delayed bone repair in mice. Moreover, PAI-1 deficiency significantly blunted Runx2 mRNA levels suppressed by Dex as well as Dex-induced osteoblast apoptosis at the damaged site 7days after bone injury in mice. On the other hand, PAI-1 deficiency did not affect adipogenic gene expression enhanced by Dex at the damaged site 7days after bone injury in mice. In conclusion, we herein showed for the first time that PAI-1 is involved in delayed bone repair after bone injury induced by GC in mice. PAI-1 may influence early stage osteoblast differentiation and apoptosis during the osteoblastic restoration phase of the bone repair process.

Evaluation of a collagen matrix in a mandible defect in rats submitted to the use of bisphosphonates.

Purpose:To assess the effect of a collagen matrix (Mucograft®) on the inflammatory process in a semi-critical experimental defect model in rats treated with bisphosphonates.Methods:Eighteen Wistar rats were randomly divided into three groups: saline (CG), alendronate (ALD) 5mg/kg (AG) or zoledronic acid (ZA) 0.2mg/kg (ZG). ALD was administered orally for 10 weeks and ZA was administered intravascularly on days 0, 7 and 14 and 49. On day 42, a 2mm defect was created and filled with Mucograft® collagen matrix. The contralateral side was filled with a clot (control side). The animals were euthanized 70 days after the beginning of the experiment and the hemimandibles were radiographically and histologically (counting of empty osteocyte lacunae (%), apoptotic (%) and total osteoclasts, neutrophil and mononuclear inflammatory cells) analyzed. The variables were submitted to ANOVA/Bonferroni and t test (parametric data) (p <0.05, GraphPad Prism 5.0).Results:Significant bone repair occurred in the groups treated with Mucograft®. High number of total inflammatory cells and neutrophils cells were showed in AG (p=0.026 and p=0.035) and AZ groups (p=0.005, p=0.034) on the control sides associated with delayed bone repair and the presence of devitalized bone tissue in AG and ZG on the Mucograft® side.Conclusion:Mucograft® collagen matrix attenuated the inflammatory process in a mandible defect in rats submitted to the use of bisphosphonates (AG and ZG).

USE OF PHOTOBIOMODULATION IN THE ALVEOLAR REPAIR OF PATIENTS SUBMITTED TO DENTAL EXTRACTION AFTER RADIOTHERAPY IN THE HEAD AND NECK

Introduction Delayed bone repair postdental extraction in patients who underwent head and neck radiation is a clinical challenge, and an adequate management is necessary to prevent osteoradionecrosis. Objective To evaluate the effect of photobiomodulation (PBM) in the alveolar mucosal healing of patients submitted to simple dental extraction after 3+ months of head and neck radiation therapy. Study Design Forty surgical procedures were performed into 2 groups: G1 dental extraction + PBM and G2 dental extraction + sham-PBM. Both groups received antibiotic therapy and closed surgical alveoli under first intention. The primary outcome was complete mucosal coverage at 14 days, with secondary outcomes being infection, postoperative pain, and analgesic use at 7 days. Results G1 presented a mucosal lining in a shorter time, where 94.7% presented complete mucosal lining (P < .0001) after 14 days, NNT = 1.056 (95% confidence interval [CI] = 0.954-1.181). G1 patients also presented less postoperative pain (P = 0.005) and lower administration of analgesics (P = .005). Conclusions The use of PBM has been shown to promote mucosal lining of the surgical alveolus in less time and with less postoperative pain. Delayed bone repair postdental extraction in patients who underwent head and neck radiation is a clinical challenge, and an adequate management is necessary to prevent osteoradionecrosis. To evaluate the effect of photobiomodulation (PBM) in the alveolar mucosal healing of patients submitted to simple dental extraction after 3+ months of head and neck radiation therapy. Forty surgical procedures were performed into 2 groups: G1 dental extraction + PBM and G2 dental extraction + sham-PBM. Both groups received antibiotic therapy and closed surgical alveoli under first intention. The primary outcome was complete mucosal coverage at 14 days, with secondary outcomes being infection, postoperative pain, and analgesic use at 7 days. G1 presented a mucosal lining in a shorter time, where 94.7% presented complete mucosal lining (P < .0001) after 14 days, NNT = 1.056 (95% confidence interval [CI] = 0.954-1.181). G1 patients also presented less postoperative pain (P = 0.005) and lower administration of analgesics (P = .005). The use of PBM has been shown to promote mucosal lining of the surgical alveolus in less time and with less postoperative pain.

AdipoRon promotes diabetic fracture repair through endochondral ossification-based bone repair by enhancing survival and differentiation of chondrocytes

Diabetic bone defects may exhibit impaired endochondral ossification (ECO) leading to delayed bone repair. AdipoRon, a receptor agonist of adiponectin polymers, can ameliorate diabetes and related complications, as well as overcome the disadvantages of the unstable structure of artificial adiponectin polymers. Here, the effects of AdipoRon on the survival and differentiation of chondrocytes in a diabetic environment were explored focusing on related mechanisms in gene and protein levels. In vivo, AdipoRon was applied to diet-induced-obesity (DIO) mice, a model of obesity and type 2 diabetes, with femoral fracture. Sequential histological evaluations and micro-CT were examined for further verification. We found that AdipoRon could ameliorate cell viability, apoptosis, and reactive oxygen species (ROS) production and promote mRNA expression of chondrogenic markers and cartilaginous matrix production of ATDC5 cells in high glucose medium via activating ERK1/2 pathway. Additionally, DIO mice with intragastric AdipoRon administration had more neocartilage and accelerated new bone formation. These data suggest that AdipoRon could stimulate bone regeneration via ECO in diabetes.

Delayed bone repair in diabetes is improved by pyridoxamine

Delayed bone repair in diabetes is improved by pyridoxamine

Role of Macrophages and Plasminogen Activator Inhibitor-1 in Delayed Bone Repair in Diabetic Female Mice.

Delayed fracture healing is a clinical problem in diabetic patients. However, the mechanisms of diabetic delayed bone repair remain unknown. Here, we investigate the role of macrophages in diabetic delayed bone repair after femoral bone injury in streptozotocin (STZ)-treated and plasminogen activator inhibitor-1 (PAI-1)-deficient female mice. STZ treatment significantly decreased the numbers of F4/80-positive cells (macrophages) but not granulocyte-differentiation antigen-1-positive cells (neutrophils) at the damaged site on day 2 after femoral bone injury in mice. It significantly decreased the messenger RNA (mRNA) levels of macrophage colony-stimulating factor, inducible nitric oxide synthase (iNOS), interleukin (IL)-6, and CD206 at the damaged site on day 2 after bone injury. Moreover, STZ treatment attenuated a decrease in the number of hematopoietic stem cells in bone marrow induced by bone injury. On the other hand, PAI-1 deficiency significantly attenuated a decrease in the number of F4/80-positive cells induced by STZ treatment at the damaged site on day 2 after bone injury in mice. PAI-1 deficiency did not affect the mRNA levels of iNOS and IL-6 in F4/80- and CD11b-double-positive cells from the bone marrow of the damaged femurs decreased by diabetes in mice. PAI-1 deficiency significantly attenuated the phagocytosis of macrophages at the damaged site suppressed by diabetes. In conclusion, we demonstrated that type 1 diabetes decreases accumulation and phagocytosis of macrophages at the damaged site during early bone repair after femoral bone injury through PAI-1 in female mice.

Contribution of methylglyoxal to delayed healing of bone injury in diabetes.

Patients with diabetes are vulnerable to delayed bone fracture healing or pseudoarthrosis. Chronic sustained hyperglycemia, reactive intermediate derivatives of glucose metabolism, such as methylglyoxal (MGO), and advanced glycation end‑products (AGEs) are implicated in diabetic complications. In the present study, it was examined whether MGO is able to cause disturbed bone healing in diabetes. Diabetes was induced in male mice by injection of streptozotocin (50mg/kg) for 5days. A bone defect (1.0‑mm diameter) was created in the left distal femur, and bone repair was assessed from an examination of computed tomography scans. ST2 cells were exposed to MGO (0‑400µM) to investigate osteoblastic differentiation, cell viability, and damage. Consequently, blood glucose and hemoglobin A1c levels in diabetic mice were determined to be 493±14.1mg/dl and 8.0±0.05%, respectively. Compared with non‑diabetic control mice, diabetic mice exhibited markedly delayed bone healing, with increased levels of the MGO‑derived AGEs, Nε‑(carboxymethyl)‑lysine and Nδ‑(5‑hydro‑5‑methyl‑4‑imidazolone‑2‑yl)‑ornithine, in the sera and femurs. MGO inhibited the osteoblastic differentiation of ST2 cells in a dose‑dependent manner, and markedly decreased cell proliferation through cytotoxicity. In conclusion, MGO has been demonstrated to cause impaired osteoblastic differentiation and delayed bone repair in diabetes. Therefore, detoxification of MGO may be a potentially useful strategy against bone problems in patients with diabetes.

The Tissue Fibrinolytic System Contributes to the Induction of Macrophage Function and CCL3 during Bone Repair in Mice

Macrophages play crucial roles in repair process of various tissues. However, the details in the role of macrophages during bone repair still remains unknown. Herein, we examined the contribution of the tissue fibrinolytic system to the macrophage functions in bone repair after femoral bone defect by using male mice deficient in plasminogen (Plg –/–), urokinase-type plasminogen activator (uPA –/–) or tissue-type plasminogen activator (tPA –/–) genes and their wild-type littermates. Bone repair of the femur was delayed in uPA –/– mice until day 6, compared with wild-type (uPA +/+) mice. Number of Osterix-positive cells and vessel formation were decreased in uPA –/– mice at the bone injury site on day 4, compared with those in uPA +/+ mice. Number of macrophages and their phagocytosis at the bone injury site were reduced in uPA –/– and Plg –/–, but not in tPA –/– mice on day 4. Although uPA or plasminogen deficiency did not affect the levels of cytokines, including TNF-α, IL-1β, IL-6, IL-4 and IFN-γ mRNA in the damaged femur, the elevation in CCL3 mRNA levels was suppressed in uPA –/– and Plg –/–, but not in tPA –/– mice. Neutralization of CCL3 antagonized macrophage recruitment to the site of bone injury and delayed bone repair in uPA +/+, but not in uPA –/– mice. Our results provide novel evidence that the tissue fibrinolytic system contributes to the induction of macrophage recruitment and CCL3 at the bone injury site, thereby, leading to the enhancement of the repair process.

Pulsed electromagnetic field treatment enhances healing callus biomechanical properties in an animal model of osteoporotic fracture.

Delayed bone healing has been noted in osteoporosis patients and in the ovariectomized (OVX) rat model of estrogen-depletion osteopenia. Pulsed electromagnetic field (PEMF) devices are clinically approved as an adjunct to cervical fusion surgery in patients at high risk for non-fusion and for the treatment of fracture non-unions. These bone growth stimulating devices also accelerate the healing of fresh fracture repair in skeletally mature normal rats but have not been tested for efficacy to accelerate and/or enhance the delayed bone repair process in OVX rats. The current study tested the hypothesis that daily PEMF treatments would improve the fracture healing response in skeletally mature OVX rats. By 6 weeks of healing, PEMF treatments resulted in improved hard callus elastic modulus across fibula fractures normalizing the healing process in OVX rats with respect to this mechanical property. Radiographic evidence showed an improved hard callus bridging across fibula fractures in OVX rats treated with PEMF as compared to sham treatments. These findings provide a scientific rationale for investigating whether PEMF might improve bone-healing responses in at-risk osteoporotic patients.

Plasminogen Activator Inhibitor-1 Is Involved in Impaired Bone Repair Associated with Diabetes in Female Mice

Previous studies suggest that fracture healing is impaired in diabetes; however, the underlying mechanism remains unclear. Here, we investigated the roles of plasminogen activator inhibitor-1 (PAI-1) in the impaired bone repair process by using streptozotocin (STZ)-induced diabetic female wild-type (PAI-1 +/+) and PAI-1-deficient (PAI-1 −/−) mice. Bone repair and the number of alkaline phosphatase (ALP)-positive cells at the site of a femoral bone damage were comparable in PAI-1 +/+ and PAI-1 −/− mice without STZ treatment. Although the bone repair process was delayed by STZ treatment in PAI-1 +/+ mice, this delayed bone repair was blunted in PAI-1 −/− mice. The reduction in the number of ALP-positive cells at the site of bone damage induced by STZ treatment was attenuated in PAI-1 −/− mice compared to PAI-1 +/+ mice. On the other hand, PAI-1 deficiency increased the levels of ALP and type I collagen mRNA in female mice with or without STZ treatment, and the levels of Osterix and osteocalcin mRNA, suppressed by diabetic state in PAI-1 +/+ mice, were partially protected in PAI-1 −/− mice. PAI-1 deficiency did not affect formation of the cartilage matrix and the levels of types II and X collagen and aggrecan mRNA suppressed by STZ treatment, although PAI-1 deficiency increased the expression of chondrogenic markers in mice without STZ treatment. The present study indicates that PAI-1 is involved in the impaired bone repair process induced by the diabetic state in part through a decrease in the number of ALP-positive cells.

Perioperative glucocorticosteroid treatment delays early healing of a mandible wound by inhibiting osteogenic differentiation

AimThe purpose of this study is to investigate the effects of dexamethasone on repair of a critical size defect of the mandible in male Sprague-Dawley rats. Materials and methodsFifty rats were divided into 2 groups: saline control and dexamethasone-treated groups. A 1mm×3mm full-thickness bone defect was created at the inferior border of the mandible. Saline or dexamethasone was administered once a day for 5days after postoperative palinesthesia. On days 1, 3, 6, 10 and 17, after cessation of drug administration, 5 samples from each group were analysed. The bone defect healing process was examined and analysed by stereology, radiology, histology and histochemical staining for total collagen, tartrate-resistant acid phosphatase staining for osteoclasts and immunohistochemical staining for the COX-2, RUNX2 and osteocalcin antigens. ResultsThe dexamethasone-treated rats exhibited significantly lower radiopacity properties compared to the control rats. Histological staining revealed that the osteogenic differentiation and maturation of a callus in the defect region was significantly delayed from day 1 to day 10 in the dexamethasone group after cessation of drug administration compared to the control group. Consistent with the histological data, the level of total collagen protein was significantly lower in the dexamethasone group than in the control group. However, there was no significant difference between the 2 groups at day 17. Immunohistochemical analysis of COX-2, RUNX2 and osteocalcin expression showed that, at day 1, COX-2 and RUNX2 expression in the dexamethasone group was significantly lower than in the control group. There was no significant difference in osteocalcin expression between the two groups at each time point. There was no significant difference in the number of osteoclasts between the two groups. ConclusionIn a model of bone healing of a mandible defect, dexamethasone-treated rats exhibited impaired osteogenic differentiation and maturation due to the inhibition of COX-2, osteogenic gene, RUNX2 and collagen protein expression, which resulted in delayed bone repair. Although perioperative short-term therapy did not exhibit long-term effects on wound healing of the maxillofacial bone, the application of glucocorticoids should be cautiously considered in the clinic.

PDGF-Simvastatin Delivery Stimulates Osteogenesis in Heat-induced Osteonecrosis

Heat generated during implant osteotomy might lead to osteonecrosis and delayed bone repair, thus resulting in impaired early osseointegration and fixation of bone-anchoring devices. In this study, we proposed to overcome heat-induced injury to bone by fabricating core-shell polymeric biodegradable microspheres encapsulating a mitogenic factor, platelet-derived growth factor (PDGF), and a differentiation factor, simvastatin, in a simultaneous or sequential release profile. Microspheres encapsulating bovine serum albumin (BSA), PDGF, simvastatin, PDGF-in-core with simvastatin-in-shell, and simvastatin-in-core with PDGF-in-shell were delivered to fill standardized osteotomy sites on edentulous ridges of rat maxillae under irrigated or non-irrigated conditions. In the absence of irrigation, significant reduction of cell viability and increase in inflammation and sequestrum formation without evidence of osteogenesis were observed. Both PDGF and simvastatin deliveries facilitated cell viability and reduced osteonecrosis. Localized osteogenesis was seen under simvastatin treatment, while generalized but primitive osteogenesis was noted in PDGF-treated osteotomy sites. In addition, sequential PDGF-simvastatin delivery further augmented osteogenesis and promoted bone maturation. The results suggested that sequential PDGF-simvastatin delivery was an effective modality to prevent heat-induced complications and facilitate bone apposition after implant osteotomy, potentially favoring the early fixation of bone-anchoring devices and oral implant osseointegration.