Impaired Bone Healing Research Articles

Characterization of Macrophage Subtypes during the Acute Inflammatory Phase of Fracture Healing

Abstract Inflammation has been associated with immunological dysfunctions and chronic inflammatory diseases but is important for normal repair processes like bone healing. Macrophages (mØ) are important for bone growth, maintenance, and regeneration. MØ are distinct from other bone cells and play an important role in the inflammatory stage of bone healing. Previous data has shown that ablation of mØs during the inflammatory stage can severely impair bone healing and exacerbate bone loss in osteoporotic models. However, little research has focused on characterizing the mØ subtypes found during the inflammatory stage. We hypothesized that different mØ subtypes are activated during inflammation and release factors to regulate bone repair. Therefore, bone marrow was collected from mice femurs at days 0, 1, 2, 4, and 7 after fracture and mØ were isolated using established methods. MØ subtypes were identified using anti-F4/80, anti-CD80, and anti-CD86 antibodies via flow cytometry and cytokine expression was quantified using Luminex. When compared to unfractured controls, a 40–50% increase in MHC class II+/CD80+ double positive mØs and MHC class II+/CD86+ double positive mØs were found on day 2 post-fracture, which remained elevated through day 4 or 7, respectively. No differences were found in mØ populations between femurs in naïve (unfractured) mice. mØs of the fractured limbs expressed higher levels of cytokines overtime. Our results suggest that different subtypes of mØs are present during the inflammatory stage and may support diverse functions such as effertocytosis, chemotaxis, and tissue anabolism or catabolism, which provides insight into their contribution in normal or uncontrolled inflammatory related processes and conditions.

Signal crosstalk between cytokine RANKL and AhR signaling in osteoclasts controls bone homeostasis

Abstract The nuclear receptor aryl hydrocarbon receptor (AhR) plays a crucial role in receptor activator of nuclear factor (NF)-kB ligand (RANKL)-mediated osteoclastogenesis. A considerable amount of evidence reveals that AhR is also a key modulator of skeletal remodeling. However, the mechanism underlying the regulation of AhR expression in osteoclasts and the signaling pathway through which AhR controls osteoclastogenesis remain unclear. We found that the expression of AhR in bone marrow-derived osteoclasts was upregulated by RANKL at an earlier stage than the expression of signature osteoclast genes such as NFATc1, c-Src, integrin avb3, and cathepsin K. In response to RANKL, bone marrow macrophages isolated from AhR−/− mice exhibited impaired phosphorylation of Akt and mitogen-activated protein kinase as well as NF-kB, while their response to the macrophage colony-stimulating factor remained unchanged. Osteoclast differentiation mediated by the AhR signaling pathway was also regulated in a RANKL/c-Fos-dependent manner. Further, ligand activation of AhR by the smoke toxin benzo [a] pyrene (BaP) accelerated osteoclast differentiation in a receptor-dependent manner, and AhR-dependent regulation of mitochondrial biogenesis in osteoclasts was observed. Moreover, AhR−/− mice exhibited impaired bone healing with delayed endochondral ossification. Taken together, the present results suggest the new role that the RANKL-AhR-c-Fos signaling axis plays a critical role in osteoclastogenesis, thereby identifying the potential of AhR in treating pathological, inflammatory, or metabolic disorders of the bone.

Genetic polymorphisms of NOS2 and predisposition to fracture non-union: A case control study based on Han Chinese population.

A non-union, especially atrophic non-unions, is a permanent failure of healing following a fracture and can be difficult to treat. Approximately 5–10% of fractures will result in a non-union during the healing process. non-unions can be classified into two types: atrophic non-union which is often due to impaired bone healing with a potential biological mechanism, and hypertrophic non-union which is due to inadequate fixation after fracture. Genetic variations also play an important role in the fracture healing response. Previous studies based on animal models have indicated that NOS2 might be greatly involved in the bone fracture healing process. In this case-control study, 346 nonunion patients were compared to 883 patients with normal fracture healing to investigate the potential genetic association between NOS2 and the fracture healing process using study subjects of Chinese Han ancestry. Twenty-seven single nucleotide polymorphisms (SNPs) covering NOS2 were genotyped in our study subjects and analyzed. In addition to the single marker-based analysis, we performed a gene-by-environment analysis to examine the potential interactions between genetic polymorphisms and some environmental factors. SNP rs2297514 showed significant association with the fracture healing process after adjusting for age and gender (OR = 1.38, P = 0.0005). Our results indicated that the T allele of rs2297514 significantly increased the risk of a non-union during the fracture healing process by 38% compared to the C allele. Further stratification analyses conducted for this SNP using data from subgroups classified by different sites of fracture indicated that significance could only be observed in the tibial diaphysis subgroup (N = 428, OR = 1.77, P = 0.0007) but not other groups including femur diaphysis, humeral shaft, ulnar shaft, and femur neck. Gene-by-environment interaction analyses of the three environmental factors showed no significant results. In this study, rs2297514 was significantly associated with the non-union status of fracture healing using a large Chinese population-based study sample. Our findings replicated those of a previous preliminary study and offered strong evidence linking NOS2 and fracture healing.

Impaired bone healing at tooth extraction sites in CD24-deficient mice: A pilot study.

AimTo use a micro-computed tomography (micro-CT) to quantify bone healing at maxillary first molar extraction sites, and test the hypothesis that bone healing is impaired in CD24-knockout mice as compared with wild-type C57BL/6J mice.Materials and methodsUnder ketamine-xylazine general anaesthesia, mice had either extraction of the right maxillary first molar tooth or sham operation. Mice were sacrificed 1 (n = 12/group), 2 (n = 6/group) or 4 (n = 6/group) weeks postoperatively. The right maxillae was disected. Micro-CT was used to quantify differences in bone microstructural features at extrction sites, between CD24-knockout mice and wild-type mice.ResultsCD24-Knockout mice displayed impaired bone healing at extraction sites that was manifested as decreased trabecular bone density, and decreased number and thickness of trabeculae.ConclusionsThis pilot study suggests that CD24 plays an important role in extraction socket bone healing and may be used as a novel biomarker of bone quality and potential therapeutic target to improve bone healing and density following alveolar bone injury.

Delivery of cellular factors to regulate bone healing.

Bone tissue has a strong intrinsic regenerative capacity, thanks to a delicate and complex interplay of cellular and molecular processes, which tightly involve the immune system. Pathological settings of anatomical, biomechanical or inflammatory nature may lead to impaired bone healing. Innovative strategies to enhance bone repair, including the delivery of osteoprogenitor cells or of potent cytokines/morphogens, indicate the potential of 'orthobiologics', but are not fully satisfactory. Here, we review different approaches based on the delivery of regenerative cues produced by cells but in cell-free, possibly off-the-shelf configurations. Such strategies exploit the paracrine effect of the secretome of mesenchymal stem/stromal cells, presented in soluble form, shuttled through extracellular vesicles, or embedded within the network of extracellular matrix molecules. In addition to osteoinductive molecules, attention is given to factors targeting the resident immune cells, to reshape inflammatory and immunity processes from scarring to regenerative patterns.

The Impact of Type 2 Diabetes on Bone Fracture Healing.

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease known by the presence of elevated blood glucose levels. Nowadays, it is perceived as a worldwide epidemic, with a very high socioeconomic impact on public health. Many are the complications caused by this chronic disorder, including a negative impact on the cardiovascular system, kidneys, eyes, muscle, blood vessels, and nervous system. Recently, there has been increasing evidence suggesting that T2DM also adversely affects the skeletal system, causing detrimental bone effects such as bone quality deterioration, loss of bone strength, increased fracture risk, and impaired bone healing. Nevertheless, the precise mechanisms by which T2DM causes detrimental effects on bone tissue are still elusive and remain poorly studied. The aim of this review was to synthesize current knowledge on the different factors influencing the impairment of bone fracture healing under T2DM conditions. Here, we discuss new approaches used in recent studies to unveil the mechanisms and fill the existing gaps in the scientific understanding of the relationship between T2DM, bone tissue, and bone fracture healing.

Strategies Developed to Induce, Direct, and Potentiate Bone Healing.

Bone exhibits a great ability for endogenous self-healing. Nevertheless, impaired bone regeneration and healing is on the rise due to population aging, increasing incidence of bone trauma and the clinical need for the development of alternative options to autologous bone grafts. Current strategies, including several biomolecules, cellular therapies, biomaterials, and different permutations of these, are now developed to facilitate the vascularization and the engraftment of the constructs, to recreate ultimately a bone tissue with the same properties and characteristics of the native bone. In this review, we browse the existing strategies that are currently developed, using biomolecules, cells and biomaterials, to induce, direct and potentiate bone healing after injury and further discuss the biological processes associated with this repair.

Forces associated with launch into space do not impact bone fracture healing

Segmental bone defects (SBDs) secondary to trauma invariably result in a prolonged recovery with an extended period of limited weight bearing on the affected limb. Soldiers sustaining blast injuries and civilians sustaining high energy trauma typify such a clinical scenario. These patients frequently sustain composite injuries with SBDs in concert with extensive soft tissue damage. For soft tissue injury resolution and skeletal reconstruction a patient may experience limited weight bearing for upwards of 6 months.Many small animal investigations have evaluated interventions for SBDs. While providing foundational information regarding the treatment of bone defects, these models do not simulate limited weight bearing conditions after injury. For example, mice ambulate immediately following anesthetic recovery, and in most cases are normally ambulating within 1–3 days post-surgery. Thus, investigations that combine disuse with bone healing may better test novel bone healing strategies. To remove weight bearing, we have designed a SBD rodent healing study in microgravity (µG) on the International Space Station (ISS) for the Rodent Research-4 (RR-4) Mission, which launched February 19, 2017 on SpaceX CRS-10 (Commercial Resupply Services). In preparation for this mission, we conducted an end-to-end mission simulation consisting of surgical infliction of SBD followed by launch simulation and hindlimb unloading (HLU) studies. In brief, a 2 mm defect was created in the femur of 10 week-old C57BL6/J male mice (n = 9–10/group). Three days after surgery, 6 groups of mice were treated as follows: 1) Vivarium Control (maintained continuously in standard cages); 2) Launch Negative Control (placed in the same spaceflight-like hardware as the Launch Positive Control group but were not subjected to launch simulation conditions); 3) Launch Positive Control (placed in spaceflight-like hardware and also subjected to vibration followed by centrifugation); 4) Launch Positive Experimental (identical to Launch Positive Control group, but placed in qualified spaceflight hardware); 5) Hindlimb Unloaded (HLU, were subjected to HLU immediately after launch simulation tests to simulate unloading in spaceflight); and 6) HLU Control (single housed in identical HLU cages but not suspended). Mice were euthanized 28 days after launch simulation and bone healing was examined via micro-Computed Tomography (µCT). These studies demonstrated that the mice post-surgery can tolerate launch conditions. Additionally, forces and vibrations associated with launch did not impact bone healing (p = .3). However, HLU resulted in a 52.5% reduction in total callus volume compared to HLU Controls (p = .0003). Taken together, these findings suggest that mice having a femoral SBD surgery tolerated the vibration and hypergravity associated with launch, and that launch simulation itself did not impact bone healing, but that the prolonged lack of weight bearing associated with HLU did impair bone healing. Based on these findings, we proceeded with testing the efficacy of FDA approved and novel SBD therapies using the unique spaceflight environment as a novel unloading model on SpaceX CRS-10.

Effect of zileuton on osteoporotic bone and its healing, expression of bone, and brain genes in rats.

Estrogen deficiency and aging are associated with osteoporosis, impaired bone healing, and lower cognitive performance. Close functional and physical connections occur between bone and the central nervous system. An anti-inflammatory drug, zileuton (which is an inhibitor of arachidonate 5-lipoxygenase), is known to have a positive effect on bone tissue repair and brain ischemia. We studied the effect of zileuton on osteopenic bone and its healing and on the genes considered to be crucial for the cross talks between bone and brain. Three-month-old Sprague-Dawley rats were ovariectomized or left untreated. After 8 wk, bilateral metaphyseal tibia osteotomy with plate osteosynthesis was performed in all rats. Ovariectomized rats were fed with food containing zileuton (1, 10, or 100 mg/kg body wt) for 5 wk. In tibiae, bone volume, callus and cortical volume, and gene expression of osteocalcin and alkaline phosphatase were enhanced by zileuton (10 or 100 mg); biomechanical properties and bone density were not changed. In femur, zileuton enlarged cortical volume distal and trabecular volume proximal, decreasing their density. The expression level of brain Sema3a, known to regulate bone mass positively, was downregulated after ovariectomy. In contrast, bone Sema4d, a negative regulator of bone mass, was upregulated in the tibia callus after ovariectomy, whereas zileuton treatment (10 or 100 mg) resulted in reverse effects. Here, we describe for the first time the expression of Rbbp4 mRNA and its increase in tibia after ovariectomy. Zileuton caused downregulation of Rbbp4 in the hippocampus and had an effect on bone healing, changed the expression of genes involved in cross talk between bones and brain, and may be a potent drug for further examination in estrogen deficiency-related dysfunction(s). NEW & NOTEWORTHY Zileuton, a 5-lipoxygenase inhibitor, increased bone volume, callus and cortical volume in osteotomized tibia, and trabecular and cortical volume in femur. Although the expression of Sema3a (positively regulating bone mass) in brain was downregulated and Sema4d (negatively regulating bone mass) was upregulated in tibia callus after ovariectomy, zileuton could counteract these effects. Rbbp4 (involved in age-related memory loss) was increased in tibia callus after ovariectomy.

The Validity of Nano-chitosan/ Nano-Hydroxyapatite as a Promoter of Bone Healing in Ovariectomized Rats

Background: Nano-hydroxyapatite (nHA) is a biomaterial successfully used in bone tissue engineering. As well, Nano-chitosan (nCTS) is one of the natural polymers used in tissue engineering research. The unique properties of nCTS/nHA composite materials have attracted research interest especially in bioapplications. Estrogen deficiency is responsible for osteoporosis which is a metabolic bone disease characterized by delayed bone healing.Aim of study: to investigate the putative effect of nCTS/nHA combination on the healing of bony defects in experimental postmenopausal hypoestrogenic rat model.Materials and Methods: Forty eight, 6 month old, virgin female rats were randomly allocated into four equal groups; ovariectomy (OVX), Sham, OVX- nCTS/nHA treated, and Sham- nCTS/nHA treated groups. Sixty days following OVX or Sham surgery, a critical-sized defect on the right side of mandible was created in all groups then filled with nCTS/nHA hydrogel only in the third and fourth groups. Two and four weeks following bony defect surgery, six animals per group were euthanized and bone samples were processed for light microscopic (LM) examination, X-ray elemental microanalysis and scanning electron microscopic (SEM) examination.Results: LM and SEM examinations of OVX group revealed delayed bone healing during both experimental periods in comparison with other groups. Interestingly, application of nCTS/nHA revealed improvement in bone healing process. X-ray elemental microanalysis of OVX group depicted marked significant decrease in calcium level below those of other groups. However, using nCTS/nHA revealed significant increase in calcium level suggesting its augmenting role in bone mineralization.Conclusion: Estrogen deficiency impaired bone healing process. However, the synergistic effect of nCTS / nHA has the ability to improve the impaired bone healing in rats with OVX-induced osteoporosis.Key words: Nano-hydroxyapatite, Nano-chitosan, Ovariectomy, Estrogen deficiency, Bone healingAbbreviations: nHA: Nano-hydroxyapatite; nCTS: Nano-chitosan; OVX: ovariectomy; LM: light microscope; SEM; scanning electron microscope.

Inflammation-Induced Osteogenesis in a Rabbit Tibia Model.

Pathologic conditions associated with bone formation can serve as models to identify bone-promoting mediators. The inflammatory response to bacterial infections generally leads to osteolysis and impaired bone healing, but paradoxically, it can also have pro-osteogenic effects. As a potential model to investigate pro-osteogenic stimuli, this study characterizes the bone formation in an established rabbit tibia model of periprosthetic infection. Our hypothesis was that the infection with Staphylococcus aureus (S. aureus) correlates with bone formation as a response to local inflammation. Fluorochromes showed excessive subperiosteal bone formation in infected tibiae, starting the first week and continuing throughout the study period. Despite the observed cortical lysis on micro-CT after 28 days, infection resulted in a twofold higher bone volume in the proximal tibiae compared to uninfected controls. The ipsilateral fibulae, nor the contralateral fibulae or tibiae were affected by infection. Next, we sought to confine the cause of stimulated bone formation to the isolated S. aureus cell wall. In absence of virulent bacterial infection, the S. aureus cell wall extract induced bone in a more favorable way without cortical lysis. This suggests that the sterile inflammatory reaction to bacterial antigens may be harnessed for bone regenerative purposes. Future investigations in this rabbit tibia model can lead to further identification of effective stimuli for clinical application.

Adiponectin improves the osteointegration of titanium implant under diabetic conditions by reversing mitochondrial dysfunction via the AMPK pathway in vivo and in vitro.

The loosening rate of titanium implants in diabetic patients is high. The underlying mechanisms remain elusive and, with the rapid increase of diabetic morbility, efficacious strategies to mitigate this problem have become increasingly important. Our study showed that the mitochondrial impairment and the consequent oxidative stress in osteoblasts at the titanium-bone interface (TBI) play a critical role in the diabetes-induced poor bone repair and implant destabilization, which could become therapeutic targets. Furthermore, adiponectin, a cytokine, promotes the bio-functional recovery of osteoblasts and bone regeneration at the TBI in diabetes. This provides APN as a novel bioactive component used in material-engineering to promote the osteointegration of implants, which could reduce implant failure, especially for diabetic patients.

Evaluation of bone turnover markers and serum minerals variations for predicting fracture healing versus non-union processes in adult sheep as a model for orthopedic research

Bone turnover markers (BTMs) have been considered as an auxiliary method of following the fracture healing process and for early prediction of impaired bone healing. A better understanding of the potential of BTMs in this application could allow for earlier interventions and improved patient care. The aim of this study with a large animal experimental model was to assess the variation of bone formation markers − namely the total alkaline phosphatase (ALP) and its bone-specific isoform (BALP), serum concentration of intact osteocalcin (OC), N-terminal propeptide type III procollagen (PIIINP) and of bone resorption markers – namely tartrate resistant acid phosphatase (TRAP) and deoxypyridinoline crosslink (DPD) during the first stages of a normal fracture healing process and of a segmental critical size defect (CSD), which progresses to a non-union process. Thirty healthy female sheep (Portuguese Churra-da-Terra-Quente breed), approximately 4-years-old, were enrolled in this study. Jugular venous blood samples were collected pre-operatively and at 1, 2, 3, 4, 6, 8, 10 and 12 post-operative weeks. The animals of the CSD group showed significant lower serum levels of BALP, OC and significant higher serum PIIINP levels at early stages of the fracture healing process, compared with animals that progressed in a normal fracture healing process. Serum BALP, OC and PIIINP levels could be useful as non-invasive auxiliary tools with other complementary methods for predicting the outcome of traumatic bone fractures.

Impaired osteogenesis of T1DM bone marrow-derived stromal cells and periosteum-derived cells and their differential in-vitro responses to growth factor rescue

BackgroundPoor bone quality, increased fracture risks, and impaired bone healing are orthopedic comorbidities of type 1 diabetes (T1DM). Standard osteogenic growth factor treatments are inadequate in fully rescuing retarded healing of traumatic T1DM long bone injuries where both periosteal and bone marrow niches are disrupted. We test the hypotheses that osteogenesis of bone marrow-derived stromal cells (BMSCs) and periosteum-derived cells (PDCs), two critical skeletal progenitors in long bone healing, are both impaired in T1DM and that they respond differentially to osteogenic bone morphogenetic proteins (BMPs) and/or insulin-like growth factor-1 (IGF-1) rescue.MethodsBMSCs and PDCs were isolated from Biobreeding Diabetes Prone/Worcester rats acquiring T1DM and normal Wistar rats. Proliferation, osteogenesis, and adipogenesis of the diabetic progenitors were compared with normal controls. Responses of diabetic progenitors to osteogenesis rescue by rhBMP-2/7 heterodimer (45 or 300 ng/ml) and/or rhIGF-1 (15 or 100 ng/ml) in normal and high glucose cultures were examined by alizarin red staining and qPCR.ResultsDiabetic BMSCs and PDCs proliferated slower and underwent poorer osteogenesis than nondiabetic controls, and these impairments were exacerbated in high glucose cultures. Osteogenesis of diabetic PDCs was rescued by rhBMP-2/7 or rhBMP-2/7 + rhIGF-1 in both normal and high glucose cultures in a dose-dependent manner. Diabetic BMSCs, however, only responded to 300 ng/nl rhBMP-2/7 with/without 100 ng/ml rhIGF-1 in normal but not high glucose osteogenic culture. IGF-1 alone was insufficient in rescuing the osteogenesis of either diabetic progenitor. Supplementing rhBMP-2/7 in high glucose osteogenic culture significantly enhanced gene expressions of type 1 collagen (Col 1), osteocalcin (OCN), and glucose transporter 1 (GLUT1) while suppressing that of adipogenic marker peroxisome proliferator-activated receptor gamma (PPARγ) in diabetic PDCs. The same treatment in high glucose culture only resulted in a moderate increase in Col 1, but no significant changes in OCN or GLUT1 expressions in diabetic BMSCs.ConclusionsThis study demonstrates more effective osteogenesis rescue of diabetic PDCs than BMSCs by rhBMP-2/7 with/without rhIGF-1 in a hyperglycemia environment, underscoring the necessity to tailor biochemical therapeutics to specific skeletal progenitor niches. Our data also suggest potential benefits of combining growth factor treatment with blood glucose management to optimize orthopedic therapeutic outcomes for T1DM patients.

Can Spatiotemporal Fluoride (18F\u2212) Uptake be Used to Assess Bone Formation in the Tibia? A Longitudinal Study Using PET/CT

BackgroundWhen a bone is broken for any reason, it is important for the orthopaedic surgeon to know how bone healing is progressing. There has been resurgence in the use of the fluoride (18F−) ion to evaluate various bone conditions. This has been made possible by availability of positron emission tomography (PET)/CT hybrid scanners together with cyclotrons. Absorbed on the bone surface from blood flow, 18F− attaches to the osteoblasts in cancellous bone and acts as a pharmacokinetic agent, which reflects the local physiologic activity of bone. This is important because it shows bone formation indicating that the bone is healing or no bone formation indicating no healing. As 18F− is extracted from blood in proportion to blood flow and bone formation, it thus enables determination of bone healing progress.Questions/purposesThe primary objective of this study was to determine whether videos showing the spatiotemporal uptake of 18F− via PET bone scans could show problematic bone healing in patients with complex tibia conditions. A secondary objective was to determine if semiquantification of radionuclide uptake was consistent with bone healing.MethodsThis study investigated measurements of tibia bone formation in patients with complex fractures, osteomyelitis, and osteotomies treated with a Taylor Spatial FrameTM (TSF) by comparing clinical healing progress with spatiotemporal fluoride (18F−) uptake and the semiquantitative standardized uptake value (SUV). This procedure included static and dynamic image acquisition. For intrapatient volumes acquired at different times, the CT and PET data were spatially registered to bring the ends of the bones that were supposed to heal into alignment. To qualitatively observe how and where bone formation was occurring, time-sequenced volumes were reconstructed and viewed as a video. To semiquantify the uptake, the mean and maximum SUVs (SUVmean, SUVmax) were calculated for the ends of the bones that were supposed to heal and for normal bone, using a spherical volume of interest drawn on the registered volumes. To make the semiquantitative data comparable for all patients with multiple examinations, the SUVmean and SUVmax difference per day (SUVmeanDPD and SUVmaxDPD) between the first PET/CT scan and each subsequent one was calculated. Indicators of poor healing progress were (1) uneven distribution of the radionuclide uptake between ends of the bones that were supposed to heal as seen in the video or, (2) low absolute magnitude of the SUV difference data. Twenty-four patients treated between October 2013 and April 2015 with a TSF gave informed consent to be examined with 18F− PET/CT bone scans. Twenty-two patients successfully completed treatment, one of whom had only one PET/CT scan.ResultsObservation of 18F− uptake was able to identify three patients whose healing progress was poor, indicated by uneven distribution of radionuclide uptake across the ends of the bones that were supposed to heal. An absolute magnitude of the SUVmaxDPD of 0.18 or greater indicated good bone formation progress. This was verified in 10 patients by the days between the operation to attach and to remove the TSF being less than 250 days, whereas other SUVmaxDPD values were ambiguous, with 11 patients achieving successful completion.ConclusionsObservation of the spatiotemporal uptake of 18F− appears to be a promising method to enable the clinician to assess the progress of bone formation in different parts of the bone. Bone uptake which is uneven across the ends of bone that were supposed to heal or very low bone uptake might indicate impaired bone healing where early intervention may then be needed. However, semiquantification of 18F− uptake (SUVmaxDPD), SUVmeanDPD) was ambiguous in showing consistency with the bone-healing progress.Level of EvidenceLevel III, diagnostic study.

Quickly Manufactured, Drug Eluting, Calcium Phosphate Composite Coating

AbstractCalcium phosphate (CaP) ceramics have been prevalently used as coatings for implants because of their excellent osteoconductive and bioactive properties. Yet, bone regeneration procedures might have complications such as bacterial infection, local inflammation, bone destruction, and impaired bone healing. Here, we present a novel in situ electrodeposition of CaP with chitosan nanoparticles containing antibiotics. The deposition was shown to be fast and efficient. The deposited layer of octacalcium phosphate (OCP) and monotite contained a large amount of gentamicin, which was released gradually over a period of 15 days. These phases may be beneficial for bone growth, as OCP has higher solubility than the stoichiometric hydroxyapatite (HAp) and is commonly considered as a precursor to HAp, while monotite has even faster resorbability. In addition, both the cytotoxicity and biomineralization of the coating were studied, and the coating was proven to be non‐cytotoxic and highly biomimetic.

Impaired Bone Healing Metabolic and Mechanical Causes

Impaired Bone Healing Metabolic and Mechanical Causes

CD31+ Cells From Peripheral Blood Facilitate Bone Regeneration in Biologically Impaired Conditions Through Combined Effects on Immunomodulation and Angiogenesis.

Controlled revascularization and inflammation are key elements regulating endogenous regeneration after (bone) tissue trauma. Peripheral blood-derived cell subsets, such as regulatory T-helper cells and circulating (endothelial) progenitor cells, respectively, can support endogenous tissue healing, whereas effector T cells that are associated with an aged immune system can hinder bone regeneration. CD31 is expressed by diverse leukocytes and is well recognized as a marker of circulating endothelial (precursor) cells; however, CD31 is absent from the surface of differentiated effector T cells. Thus, we hypothesized that by separating the inhibitory fractions from the supportive fractions of circulating cells within the peripheral blood (PB) using the CD31 marker, bone regeneration in biologically compromised conditions, such as those observed in aged patients, could be improved. In support of our hypothesis, we detected an inverse correlation between CD31+ cells and effector T cells in the hematomas of human fracture patients, dependent on the age of the patient. Furthermore, we demonstrated the regenerative capacity of human PB-CD31+ cells in vitro. These findings were translated to a clinically relevant rat model of impaired bone healing. The transplantation of rat PB-CD31+ cells advanced bone tissue restoration in vivo and was associated with an early anti-inflammatory response, the stimulation of (re)vascularization, and reduced fibrosis. Interestingly, the depletion or enrichment of the highly abundant CD31+/14+ monocytes from the mixed CD31+ cell population diminished tissue regeneration at different levels, suggesting combined effects within the PB-CD31+ subsets. In summary, an intraoperative enrichment of PB-CD31+ cells might be a novel option to facilitate endogenous regeneration under biologically impaired situations by supporting immunomodulation and vascularization. © 2016 American Society for Bone and Mineral Research.

The Nuclear Receptor AhR Controls Bone Homeostasis by Regulating Osteoclast Differentiation via the RANK/c-Fos Signaling Axis.

The aryl hydrocarbon receptor (AhR) pathway plays a key role in receptor activator of NF-κB ligand (RANKL)-mediated osteoclastogenesis. However, the mechanism underlying the regulation of AhR expression in osteoclasts and the signaling pathway through which AhR controls osteoclastogenesis remain unclear. We found that the expression of AhR in bone marrow-derived osteoclasts was upregulated by RANKL at an earlier stage than was the expression of signature osteoclast genes such as those encoding cathepsin K and NFAT, cytoplasmic, calcineurin-dependent 1. In response to RANKL, bone marrow macrophages isolated from AhR-/- mice exhibited impaired phosphorylation of Akt and MAPK as well as NF-κB, whereas their response to M-CSF remained unchanged. Osteoclast differentiation mediated by the AhR signaling pathway was also regulated in an RANKL/c-Fos-dependent manner. Furthermore, ligand activation of AhR by the smoke toxin benzo[a]pyrene accelerated osteoclast differentiation in a receptor-dependent manner, and AhR-dependent regulation of mitochondrial biogenesis in osteoclasts was observed. Moreover, AhR-/- mice exhibited impaired bone healing with delayed endochondral ossification. Taken together, the present results suggest that the RANKL/AhR/c-Fos signaling axis plays a critical role in osteoclastogenesis, thereby identifying the potential of AhR in treating pathological, inflammatory, or metabolic disorders of the bone.

Celecoxib inhibits osteoblast maturation by suppressing the expression of Wnt target genes

Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to impair bone healing. We previously reported that in colon cancer cells, celecoxib, a COX-2-selective NSAID, inhibited the canonical Wnt/β-catenin signaling pathway. Since this pathway also plays an important role in osteoblast growth and differentiation, we examined the effect of celecoxib on maturation of osteoblast-like cell line MC3T3-E1. Celecoxib induced degradation of transcription factor 7-like 2, a key transcription factor of the canonical Wnt pathway. Subsequently, we analyzed the effect of celecoxib on two osteoblast differentiation markers; runt-related transcription factor 2 (RUNX2) and alkaline phosphatase (ALP), both of which are the products of the canonical Wnt pathway target genes. Celecoxib inhibited the expression of both RUNX2 and ALP by suppressing their promoter activity. Consistent with these observations, celecoxib also strongly inhibited osteoblast-mediated mineralization. These results suggest that celecoxib inhibits osteoblast maturation by suppressing Wnt target genes, and this could be the mechanism that NSAIDs inhibit bone formation and fracture healing.