Effect of a new bioactive fibrous glassy scaffold on bone repair

Researchers have investigated several therapeutic approaches to treat non-union fractures. Among these, bioactive glasses and glass ceramics have been widely used as grafts. This class of biomaterial has the ability to integrate with living bone. Nevertheless, bioglass and bioactive materials have been used mainly as powder and blocks, compromising the filling of irregular bone defects. Considering this matter, our research group has developed a new bioactive glass composition that can originate malleable fibers, which can offer a more suitable material to be used as bone graft substitutes. Thus, the aim of this study was to assess the morphological structure (via scanning electron microscope) of these fibers upon incubation in phosphate buffered saline (PBS) after 1, 7 and 14 days and, also, evaluate the in vivo tissue response to the new biomaterial using implantation in rat tibial defects. The histopathological, immunohistochemistry and biomechanical analyzes after 15, 30 and 60 days of implantation were performed to investigate the effects of the material on bone repair. The PBS incubation indicated that the fibers of the glassy scaffold degraded over time. The histological analysis revealed a progressive degradation of the material with increasing implantation time and also its substitution by granulation tissue and woven bone. Histomorphometry showed a higher amount of newly formed bone area in the control group (CG) compared to the biomaterial group (BG) 15 days post-surgery. After 30 and 60 days, CG and BG showed a similar amount of newly formed bone. The novel biomaterial enhanced the expression of RUNX-2 and RANK-L, and also improved the mechanical properties of the tibial callus at day 15 after surgery. These results indicated a promising use of the new biomaterial for bone engineering. However, further long-term studies should be carried out to provide additional information concerning the material degradation in the later stages and the bone regeneration induced by the fibrous material.

Effects of Nonsteroidal Anti-inflammatory Drugs on Osseointegration: A Review

The purpose of this study was to review the effects of nonsteroidal anti-inflammatory drugs on osseointegration and determine whether they cause failures in dental implants and whether patients who use them chronically can receive dental implants safely. A bibliographic electronic search was performed using the Cochrane Library, PubMed, and Medline databases, selecting articles published between January 1982 and December 2012. The search included the following keywords, either alone or combined: “nonsteroidal anti-inflammatory drugs,” “dental implants,” “bone healing,” and “osteoprogenitor cells.” The inclusion criteria were the following: randomized, double-blind, placebo-controlled clinical studies, in vivo animal model studies of osseointegration, and in vitro studies of the effects of these agents on osteoprogenitor cells. The literature search revealed 360 references. A total of 31 articles met the inclusion criteria, including 2 clinical trials, 20 animal studies, and 9 osteoprogenitor cell studies. The clinical trials revealed that cyclooxygenase-1 (COX-1) inhibitors did not impair osseointegration. The animal studies showed that any drug that is capable of inhibiting COX-2 may impair the osseointegration process. The in vitro studies showed that COX-2 inhibitors are the most potent depressors of osseointegration at the cellular level. Caution must be taken when selecting COX-2 nonsteroidal anti-inflammatory drugs during the postoperative period.

Beneficial effects of tripterygium glycosides tablet on biomarkers in patients with ankylosing spondylitis

The aim of the current study was to explore the effects and possible mechanisms of tripterygium glycosides tablet (TGT) in the treatment of active ankylosing spondylitis (AS). Thirty-six patients with active AS were given a 20 mg TGT treatment three times per day for 12 weeks, and 21 unrelated healthy controls were recruited as the control group. Efficacy measures included the Bath AS disease activity index (BASDAI), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) prior and subsequent to TGT treatment. Serum dickkopf homolog 1 (DKK1) and interleukin-17 (IL-17) levels before and after TGT treatment were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and ELISA assay. The levels of several serum biomarkers were determined by ELISA, including receptor activator of nuclear factor κ-B ligand (RANKL), osteoprotegerin (OPG), bone alkaline phosphatase (BAP), bone morphogenetic protein-2 (BMP-2), matrix metalloproteinase-3 (MMP-3), cross-linked telopeptide of type II collagen (CTX-II), vascular endothelial growth factor (VEGF), and prostaglandin E2 (PGE2). After 12 weeks of TGT treatment, the BASDAI score of the patients was significantly reduced (P<0.05), their levels of ESR and CRP were significantly reduced to a normal level (P<0.05, P<0.05), RT-PCR and ELISA showed a significant increase in the level of DKK1 expression (P<0.05) and a significant decreased IL-17 expression (P<0.05), there was a significant increase in the expression of OPG, BAP and BMP-2 (P<0.01, P<0.01, P<0.01) and a significant reduction in the expression levels of RANKL, CTX-II. MMP-3, PGE2, and VEGF (P<0.01, P<0.01, P<0.01, P<0.05, P<0.01) compared with those of the controls. TGT is effective at improving the signs and symptoms of patients with AS through the regulation of serum biomarkers, and the mechanisms may be associated with the anti-inflammatory effect, inhibition of new bone formation and potential bone-protective effects.

Mouse models of bone healing: fracture, marrow ablation, and distraction osteogenesis

Three commonly used murine surgical models of bone healing [closed fracture with intramedullary fixation, distraction osteogenesis (DO), and marrow ablation by reaming] are presented. Detailed surgical protocols for each model are outlined. The nature of the regenerative processes and the types of research questions that may be addressed with these models are briefly outlined. The relative strengths and weaknesses of these models are compared to a number of other surgical models that are used to address similar research questions.

COX2 inhibition reduces aortic valve calcification in vivo

OBJECTIVE

Calcific aortic valve disease (CAVD) is a significant cause of morbidity and mortality, which affects ≈1% of the US population and is characterized by calcific nodule formation and stenosis of the valve. Klotho-deficient mice were used to study the molecular mechanisms of CAVD as they develop robust aortic valve (AoV) calcification. Through microarray analysis of AoV tissues from klotho-deficient and wild-type mice, increased expression of the gene encoding cyclooxygenase 2 (COX2; Ptgs2) was found. COX2 activity contributes to bone differentiation and homeostasis, thus the contribution of COX2 activity to AoV calcification was assessed.

APPROACH AND RESULTS

In klotho-deficient mice, COX2 expression is increased throughout regions of valve calcification and is induced in the valvular interstitial cells before calcification formation. Similarly, COX2 expression is increased in human diseased AoVs. Treatment of cultured porcine aortic valvular interstitial cells with osteogenic media induces bone marker gene expression and calcification in vitro, which is blocked by inhibition of COX2 activity. In vivo, genetic loss of function of COX2 cyclooxygenase activity partially rescues AoV calcification in klotho-deficient mice. Moreover, pharmacological inhibition of COX2 activity in klotho-deficient mice via celecoxib-containing diet reduces AoV calcification and blocks osteogenic gene expression.

CONCLUSIONS

COX2 expression is upregulated in CAVD, and its activity contributes to osteogenic gene induction and valve calcification in vitro and in vivo.

Porous bioactive scaffolds: characterization and biological performance in a model of tibial bone defect in rats

The aim of this study was to evaluate the effects of highly porous Biosilicate(®) scaffolds on bone healing in a tibial bone defect model in rats by means of histological evaluation (histopathological and immunohistochemistry analysis) of the bone callus and the systemic inflammatory response (immunoenzymatic assay). Eighty Wistar rats (12 weeks-old, weighing±300 g) were randomly divided into 2 groups (n=10 per experimental group, per time point): control group and Biosilicate® group (BG). Each group was euthanized 3, 7, 14 and 21 days post-surgery. Histological findings revealed a similar inflammatory response in both experimental groups, 3 and 7 days post-surgery. During the experimental periods (3-21 days post-surgery), it was observed that the biomaterial degradation, mainly in the periphery region, provided the development of the newly formed bone into the scaffolds. Immunohistochemistry analysis demonstrated that the Biosilicate® scaffolds stimulated cyclooxygenase-2, vascular endothelial growth factor and runt-related transcription factor 2 expression. Furthermore, in the immunoenzymatic assay, BG presented no difference in the level of tumor necrosis factor alpha in all experimental periods. Still, BG showed a higher level of interleukin 4 after 14 days post-implantation and a lower level of interleukin 10 in 21 days post-surgery. Our results demonstrated that Biosilicate® scaffolds can contribute for bone formation through a suitable architecture and by stimulating the synthesis of markers related to the bone repair.

Cytotoxicity evaluation of biodegradable Zn-3Mg alloy toward normal human osteoblast cells

The recent proposal of using Zn-based alloys for biodegradable implants was not supported with sufficient toxicity data. This work, for the first time, presents a thorough cytotoxicity evaluation of Zn-3Mg alloy for biodegradable bone implants. Normal human osteoblast cells were exposed to the alloy's extract and three main cell-material interaction parameters: cell health, functionality and inflammatory response, were evaluated. Results showed that at the concentration of 0.75mg/ml alloy extract, cell viability was reduced by ~50% through an induction of apoptosis at day 1; however, cells were able to recover at days 3 and 7. Cytoskeletal changes were observed but without any significant DNA damage. The downregulation of alkaline phosphatase protein levels did not significantly affect the mineralization process of the cells. Significant differences of cyclooxygenase-2 and prostaglandin E2 inflammatory biomarkers were noticed, but not interleukin 1-beta, indicating that the cells underwent a healing process after exposure to the alloy. Detailed analysis on the cell-material interaction is further discussed in this paper.

Uncovering the periosteum for skeletal regeneration: the stem cell that lies beneath

The cartilage- and bone-forming properties of the periosteum have long since been recognized. As one of the major sources of skeletal progenitor cells, the periosteum plays a crucial role not only in bone development and growth, but also during bone fracture healing. Aided by the continuous expansion of tools and techniques, we are now starting to acquire more insight into the specific role and regulation of periosteal cells. From a therapeutic point of view, the periosteum has attracted much attention as a cell source for bone tissue engineering purposes. This interest derives not only from the physiological role of the periosteum during bone repair, but is also supported by the unique properties and marked bone-forming potential of expanded periosteum-derived cells. We provide an overview of the current knowledge of periosteal cell biology, focusing on the cellular composition and molecular regulation of this remarkable tissue, as well as the application of periosteum-derived cells in regenerative medicine approaches. This article is part of a Special Issue entitled "Stem Cells and Bone".

Inhibition of beta-catenin signaling by Pb leads to incomplete fracture healing

There is strong evidence in the clinical literature to suggest that elevated lead (Pb) exposure impairs fracture healing. Since Pb has been demonstrated to inhibit bone formation, and Wnt signaling is an important anabolic pathway in chondrocyte maturation and endochondral ossification, we investigated the impact of Wnt therapy on Pb-exposed mice undergoing bone repair in a mouse tibial fracture model. We established that tibial fracture calluses from Pb-treated mice were smaller and contained less mineralized tissue than vehicle controls. This resulted in the persistence of immature cartilage in the callus and decreased β-catenin levels. Reduction of β-catenin protein was concurrent with systemic elevation of LRP5/6 antagonists DKK1 and sclerostin in Pb-exposed mice throughout fracture healing. β-catenin stimulation by the GSK3 inhibitor BIO reversed these molecular changes and restored the amount of mineralized callus. Overall, Pb is identified as a potent inhibitor of endochondral ossification in vivo with correlated effects on bone healing with noted deficits in β-catenin signaling, suggesting the Wnt/β-catenin as a pivotal pathway in the influence of Pb on fracture repair.

Identification and characterization of the novel Col10a1 regulatory mechanism during chondrocyte hypertrophic differentiation

The majority of human skeleton develops through the endochondral pathway, in which cartilage-forming chondrocytes proliferate and enlarge into hypertrophic chondrocytes that eventually undergo apoptosis and are replaced by bone. Although at a terminal differentiation stage, hypertrophic chondrocytes have been implicated as the principal engine of bone growth. Abnormal chondrocyte hypertrophy has been seen in many skeletal dysplasia and osteoarthritis. Meanwhile, as a specific marker of hypertrophic chondrocytes, the type X collagen gene (COL10A1) is also critical for endochondral bone formation, as mutation and altered COL10A1 expression are often accompanied by abnormal chondrocyte hypertrophy in many skeletal diseases. However, how the type X collagen gene is regulated during chondrocyte hypertrophy has not been fully elucidated. We have recently demonstrated that Runx2 interaction with a 150-bp mouse Col10a1 cis-enhancer is required but not sufficient for its hypertrophic chondrocyte-specific reporter expression in transgenic mice, suggesting requirement of additional Col10a1 regulators. In this study, we report in silico sequence analysis of this 150-bp enhancer and identification of its multiple binding factors, including AP1, MEF2, NFAT, Runx1 and TBX5. Using this enhancer as bait, we performed yeast one-hybrid assay and identified multiple candidate Col10a1-interacting genes, including cyclooxygenase 1 (Cox-1) and Cox-2. We have also performed mass spectrometry analysis and detected EF1-alpha, Fus, GdF7 and Runx3 as components of the specific complex formed by the cis-enhancer and nuclear extracts from hypertrophic MCT (mouse chondrocytes immortalized with large T antigen) cells that express Col10a1 abundantly. Notably, some of the candidate genes are differentially expressed in hypertrophic MCT cells and have been associated with chondrocyte hypertrophy and Runx2, an indispensible Col10a1 regulator. Intriguingly, we detected high-level Cox-2 expression in hypertrophic MCT cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays confirmed the interaction between Cox-2 and Col10a1 cis-enhancer, supporting its role as a candidate Col10a1 regulator. Together, our data support a Cox-2-containing, Runx2-centered Col10a1 regulatory mechanism, during chondrocyte hypertrophic differentiation.

Investigation of localized delivery of diclofenac sodium from poly(D,L-lactic acid-co-glycolic acid)/poly(ethylene glycol) scaffolds using an in vitro osteoblast inflammation model

Nonunion fractures and large bone defects are significant targets for osteochondral tissue engineering strategies. A major hurdle in the use of these therapies is the foreign body response of the host. Herein, we report the development of a bone tissue engineering scaffold with the ability to release anti-inflammatory drugs, in the hope of evading this response. Porous, sintered scaffolds composed of poly(D,L-lactic acid-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) were prepared with and without the anti-inflammatory drug diclofenac sodium. Analysis of drug release over time demonstrated a profile suitable for the treatment of acute inflammation with ∼80% of drug released over the first 4 days and a subsequent release of around 0.2% per day. Effect of drug release was monitored using an in vitro osteoblast inflammation model, comprised of mouse primary calvarial osteoblasts stimulated with proinflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). Levels of inflammation were monitored by cell viability and cellular production of nitric oxide (NO) and prostaglandin E2 (PGE2). The osteoblast inflammation model revealed that proinflammatory cytokine addition to the medium reduced cell viability to 33%, but the release of diclofenac sodium from scaffolds inhibited this effect with a final cell viability of ∼70%. However, releasing diclofenac sodium at high concentrations had a toxic effect on the cells. Proinflammatory cytokine addition led to increased NO and PGE2 production; diclofenac-sodium-releasing scaffolds inhibited NO release by ∼64% and PGE2 production by ∼52%, when the scaffold was loaded with the optimal concentration of drug. These observations demonstrate the potential use of PLGA/PEG scaffolds for localized delivery of anti-inflammatory drugs in bone tissue engineering applications.

Microarray Analysis of Gene Expression Reveals that Cyclo-oxygenase-2 Gene Therapy Up-regulates Hematopoiesis and Down-regulates Inflammation During Endochondral Bone Fracture Healing

BACKGROUND

Cyclo-oxygenase-2 (Cox-2) is an inflammatory mediator that is necessary for the tissue repair, including bone fracture healing. Although the application of Cox-2 gene therapy to a murine closed femoral fracture has accelerated bony union, but the beneficial effect was not observed until the endochondral stage of bone repair that is well after the inflammatory stage normally subsides.

METHODS

To identify the molecular pathways through which Cox-2 regulates fracture healing, we examined gene expression profile in fracture tissues in response to Cox-2 gene therapy during the endochondral bone repair phase. Cox-2 gene therapy was applied to the closed murine femur fracture model. Microarray analysis was performed at 10 days post-fracture to examine global gene expression profile in the fracture tissues during the endochondral bone repair phase. The entire repertoire of significantly expressed genes was examined by gene set enrichment analysis, and the most up-regulated individual genes were evaluated further.

RESULTS

The genes that normally promote inflammation were under-represented in the microarray analysis, and the expression of several inflammatory chemokines was significantly down-regulated. There was an up-regulation of two key transcription factor genes that regulate hematopoiesis and erythropoiesis. More surprisingly, there was no significant up-regulation in the genes that are normally involved in angiogenesis or bone formation. However, the expression of two tissue remodeling genes was up-regulated.

CONCLUSIONS

The down-regulation of the inflammatory genes in response to Cox-2 gene therapy was unexpected, given the pro-inflammatory role of prostaglandins. Cox-2 gene therapy could promote bony union through hematopoietic precursor proliferation during endochondral bone repair and thereby enhances subsequently fracture callus remodeling that leads to bony union of the fracture gap.

The spatiotemporal role of COX-2 in osteogenic and chondrogenic differentiation of periosteum-derived mesenchymal progenitors in fracture repair

Periosteum provides a major source of mesenchymal progenitor cells for bone fracture repair. Combining cell-specific targeted Cox-2 gene deletion approaches with in vitro analyses of the differentiation of periosteum-derived mesenchymal progenitor cells (PDMPCs), here we demonstrate a spatial and temporal role for Cox-2 function in the modulation of osteogenic and chondrogenic differentiation of periosteal progenitors in fracture repair. Prx1Cre-targeted Cox-2 gene deletion in mesenchyme resulted in marked reduction of intramembraneous and endochondral bone repair, leading to accumulation of poorly differentiated mesenchyme and immature cartilage in periosteal callus. In contrast, Col2Cre-targeted Cox-2 gene deletion in cartilage resulted in a deficiency primarily in cartilage conversion into bone. Further cell culture analyses using Cox-2 deficient PDMPCs demonstrated reduced osteogenic differentiation in monolayer cultures, blocked chondrocyte differentiation and hypertrophy in high density micromass cultures. Gene expression microarray analyses demonstrated downregulation of a key set of genes associated with bone/cartilage formation and remodeling, namely Sox9, Runx2, Osx, MMP9, VDR and RANKL. Pathway analyses demonstrated dysregulation of the HIF-1, PI3K-AKT and Wnt pathways in Cox-2 deficient cells. Collectively, our data highlight a crucial role for Cox-2 from cells of mesenchymal lineages in modulating key pathways that control periosteal progenitor cell growth, differentiation, and angiogenesis in fracture repair.

β-adrenergic receptor signaling regulates Ptgs2 by driving circadian gene expression in osteoblasts

The sympathetic nervous system modulates bone remodeling and mediates the expression of core clock genes in part through the β-adrenergic receptor (β-AR) in osteoblasts. In this study, we show that in MC3T3-E1 osteoblastic cells that isoproterenol (Iso), a non-selective β-AR agonist, upregulated the transcriptional factor Nfil3, and induced rhythmic mRNA expression of prostaglandin-endoperoxide synthase 2 (Ptgs2, also known as Cox2). The rhythmic effects of Iso on Ptgs2 expression were mediated by interplay between the Per2 and Bmal1 clock genes in osteoblasts. In addition, Ptgs2 was significantly decreased in bone after continuous Iso treatment. Overexpression of Nfil3 decreased Ptgs2 expression in MC3T3-E1 cells. Knockdown of Nfil3 upregulated the expression of Ptgs2 in MC3TC-E1 cells, indicating that Nfil3 negatively regulated Ptgs2 in osteoblasts. Furthermore, Iso acutely induced the expression Nfil3 and increased the binding of Nfil3 to the Ptgs2 promoter in MC3T3-E1 cells. These results suggest that Iso-mediated induction of Nfil3 in osteoblasts regulates the expression of Ptgs2 by driving the expression of circadian clock genes. These findings provide new evidence for a physiological role of circadian clockwork in bone metabolism.

Cellular and molecular bases of skeletal regeneration: what can we learn from genetic mouse models?

Although bone repairs through a very efficient regenerative process in 90% of the patients, many factors can cause delayed or impaired healing. To date, there are no reliable biological parameters to predict or diagnose bone repair defects. Orthopedic surgeons mostly base their diagnoses on radiographic analyses. With the recent progress in our understanding of the bone repair process, new methods may be envisioned. Animal models have allowed us to define the key steps of bone regeneration and the biological and mechanical factors that may influence bone healing in positive or negative ways. Most importantly, small animal models such as mice have provided powerful tools to apprehend the genetic bases of normal and impaired bone healing. The current review presents a state of the art of the genetically modified mouse models that have advanced our understanding of the cellular and molecular components of bone regeneration and repair. The review illustrates the use of these models to define the role of inflammation, skeletal cell lineages, signaling pathways, the extracellular matrix, osteoclasts and angiogenesis. These genetic mouse models promise to change the field of orthopedic surgery to help establish genetic predispositions for delayed repair, develop models of non-union that mimic the human conditions and elaborate new therapeutic approaches to enhance bone regeneration.

A novel role for interferon regulatory factor 1 (IRF1) in regulation of bone metabolism

Increased risk of bone fractures is observed in patients with chronic inflammatory conditions, such as inflammatory bowel disease and rheumatoid arthritis. Members of the Interferon Response Factor family of transcriptional regulators, IRF1 and IRF8, have been identified as genetic risk factors for several chronic inflammatory and autoimmune diseases. We have investigated a potential role for the Irf1 gene in bone metabolism. Here, we report that Irf1(-/-) mutant mice show altered bone morphology in association with altered trabecular bone architecture and increased cortical thickness and cellularity. Ex vivo studies on cells derived from bone marrow stimulated with Rank ligand revealed an increase in size and resorptive activity of tartrate-resistant acid-positive cells from Irf1(-/-) mutant mice compared with wild-type control mice. Irf1 deficiency was also associated with decreased proliferation of bone marrow-derived osteoblast precursors ex vivo, concomitant with increased mineralization activity compared with control cells. We show that Irf1 plays a role in bone metabolism and suggest that Irf1 regulates the maturation and activity of osteoclasts and osteoblasts. The altered bone phenotype of Irf1(-/-) mutants is strikingly similar to that of Stat1(-/-) mice, suggesting that the two interacting proteins play a critical enabling role in the common regulation of these two cell lineages.

Can we enhance fracture vascularity: What is the evidence?

Angiogenesis is a vital component of bone healing. The formation of the new blood vessels at the fracture site restores the hypoxia and nutrient deprivation found at the early stages after fracture whilst at a later stage facilitates osteogenesis by the activity of the osteoprogenitor cells. Emerging evidence suggests that there are certain molecules and gene therapies that could promote new blood vessel formation and as a consequence enhance the local bone healing response. This article summarizes the current in vivo evidence on therapeutic approaches aiming at the augmentation of the angiogenic signalling during bone repair.

Role of donor and host cells in muscle-derived stem cell-mediated bone repair: differentiation vs. paracrine effects

Murine muscle-derived stem cells (MDSCs) have been shown capable of regenerating bone in a critical size calvarial defect model when transduced with BMP 2 or 4; however, the contribution of the donor cells and their interactions with the host cells during the bone healing process have not been fully elucidated. To address this question, C57/BL/6J mice were divided into MDSC/BMP4/GFP, MDSC/GFP, and scaffold groups. After transplanting MDSCs into the critical-size calvarial defects created in normal mice, we found that mice transplanted with BMP4GFP-transduced MDSCs healed the bone defect in 4 wk, while the control groups (MDSC-GFP and scaffold) demonstrated no bone healing. The newly formed trabecular bone displayed similar biomechanical properties as the native bone, and the donor cells directly participated in endochondral bone formation via their differentiation into chondrocytes, osteoblasts, and osteocytes via the BMP4-pSMAD5 and COX-2-PGE2 signaling pathways. In contrast to the scaffold group, the MDSC groups attracted more inflammatory cells initially and incurred faster inflammation resolution, enhanced angiogenesis, and suppressed initial immune responses in the host mice. MDSCs were shown to attract macrophages via the secretion of monocyte chemotactic protein 1 and promote endothelial cell proliferation by secreting multiple growth factors. Our findings indicated that BMP4GFP-transduced MDSCs not only regenerated bone by direct differentiation, but also positively influenced the host cells to coordinate and promote bone tissue repair through paracrine effects.

Aging periosteal progenitor cells have reduced regenerative responsiveness to bone injury and to the anabolic actions of PTH 1-34 treatment

A stabilized tibia fracture model was used in young (8-week old) and aged (1-year old) mice to define the relative bone regenerative potential and the relative responsiveness of the periosteal progenitor population with aging and PTH 1-34 (PTH) systemic therapy. Bone regeneration was assessed through gene expressions, radiographic imaging, histology/histomorphometry, and biomechanical testing. Radiographs and microCT showed increased calcified callus tissue and enhanced bone healing in young compared to aged mice. A key mechanism involved reduced proliferation, expansion, and differentiation of periosteal progenitor cell populations in aged mice. The experiments showed that PTH increased calcified callus tissue and torsional strength with a greater response in young mice. Histology and quantitative histomorphometry confirmed that PTH increased callus tissue area due primarily to an increase in bone formation, since minimal changes in cartilage and mesenchyme tissue area occurred. Periosteum examined at 3, 5, and 7 days showed that PTH increased cyclin D1 expression, the total number of cells in the periosteum, and width of the periosteal regenerative tissue. Gene expression showed that aging delayed differentiation of both bone and cartilage tissues during fracture healing. PTH resulted in sustained Col10a1 expression consistent with delayed chondrocyte maturation, but otherwise minimally altered cartilage gene expression. In contrast, PTH 1-34 stimulated expression of Runx2 and Osterix, but resulted in reduced Osteocalcin. β-Catenin staining was present in mesenchymal chondroprogenitors and chondrocytes in early fracture healing, but was most intense in osteoblastic cells at later times. PTH increased active β-catenin staining in the osteoblast populations of both young and aged mice, but had a lesser effect in cartilage. Altogether the findings show that reduced fracture healing in aging involves decreased proliferation and differentiation of stem cells lining the bone surface. While PTH 1-34 enhances the proliferation and expansion of the periosteal stem cell population and accelerates bone formation and fracture healing, the effects are proportionately reduced in aged mice compared to young mice. β-Catenin is induced by PTH in early and late fracture healing and is a potential target of PTH 1-34 effects.

Timing matters: NSAIDs interfere with the late proliferation stage of a repaired rotator cuff tendon healing in rats

INTRODUCTION

Rotator cuff (RC) tear is a common problem that causes pain and can limit shoulder function. Non-steroidal anti-inflammatory drugs (NSAIDs) are often prescribed for musculoskeletal pain, including the pain subsequent to RC repair. NSAIDs have been reported to affect bone metabolism and fracture healing(,) but there is little evidence about their effect on tendon healing. We investigated the effect of meloxicam (non-steroidal anti-inflammatory drug) on the healing of RC tendons when given immediately after surgical repair.

MATERIALS AND METHODS

Thirty-nine rats underwent acute RC tear and repair. Group A (n = 13) received daily intraperitoneal (IP) injections of meloxicam for the first 10 postoperative days. Group B (n = 13) received IP injections of meloxicam starting from postoperative day 11. Group C (n = 13, controls) received daily IP injections of saline for 3 weeks. The animals were killed 3 weeks after surgery and the RC was evaluated by gross inspection, biomechanical testing and histological examination.

RESULTS

Group B displayed a significantly lower mean maximal load at 3 weeks than group C (P = 0.02) and group A (P = 0.05). Stiffness was significantly lower in B group as compared to A group (P = 0.05). Qualitative examination of histology specimens did not disclose any apparent differences with respect to cellularity, vascularity, healing, and collagen orientation.

CONCLUSIONS

We conclude that meloxicam decreases the biomechanical strength of repaired rat RCs when administered between 11 and 20 days after the repair.

BMP-2 induces ATF4 phosphorylation in chondrocytes through a COX-2/PGE2 dependent signaling pathway

OBJECTIVE

Bone morphogenic protein (BMP)-2 is approved for fracture non-union and spine fusion. We aimed to further dissect its downstream signaling events in chondrocytes with the ultimate goal to develop novel therapeutics that can mimic BMP-2 effect but have less complications.

METHODS

BMP-2 effect on cyclooxygenase (COX)-2 expression was examined using Real time quantitative PCR (RT-PCR) and Western blot analysis. Genetic approach was used to identify the signaling pathway mediating the BMP-2 effect. Similarly, the pathway transducing the PGE2 effect on ATF4 was investigated. Immunoprecipitation (IP) was performed to assess the complex formation after PGE2 binding.

RESULTS

BMP-2 increased COX-2 expression in primary mouse costosternal chondrocytes (PMCSC). The results from the C9 Tet-off system demonstrated that endogenous BMP-2 also upregulated COX-2 expression. Genetic approaches using PMCSC from ALK2(fx/fx), ALK3(fx/fx), ALK6(-/-), and Smad1(fx/fx) mice established that BMP-2 regulated COX-2 through activation of ALK3-Smad1 signaling. PGE-2 EIA showed that BMP-2 increased PGE2 production in PMCSC. ATF4 is a transcription factor that regulates bone formation. While PGE2 did not have significant effect on ATF4 expression, it induced ATF4 phosphorylation. In addition to stimulating COX-2 expression, BMP-2 also induced phosphorylation of ATF4. Using COX-2 deficient chondrocytes, we demonstrated that the BMP-2 effect on ATF4 was COX-2-dependent. Tibial fracture samples from COX-2(-/-) mice showed reduced phospho-ATF4 immunoreactivity compared to wild type (WT) ones. PGE2 mediated ATF4 phosphorylation involved signaling primarily through the EP2 and EP4 receptors and PGE2 induced an EP4-ERK1/2-RSK2 complex formation.

CONCLUSIONS

BMP-2 regulates COX-2 expression through ALK3-Smad1 signaling, and PGE2 induces ATF4 phosphorylation via EP4-ERK1/2-RSK2 axis.

Should non-steroidal anti-inflammatory drugs be used continuously in ankylosing spondylitis?

OBJECTIVE

The 2010 update of ASAS/EULAR recommendations for managing ankylosing spondylitis (AS) specify that continuous non-steroidal anti-inflammatory drug (NSAID) treatment should be preferred in patients with persistently active, symptomatic disease. Here, our objective was to assess whether continuous NSAID therapy improves disease control and influences radiographic progression compared to on-demand therapy. We also assessed the safety profiles of both regimens.

METHODS

We performed a review by searching the PubMed and Embase databases using two MeSH term combinations to compare continuous and on-demand NSAID therapy in terms of disease control, radiographic progression, and safety.

RESULTS

The only study evaluating the impact of continuous NSAID therapy on disease control showed no significant difference with on-demand therapy. In four studies, continuous treatment was associated with slower radiographic progression, as assessed in three studies using the modified Stoke Ankylosing Spondylitis Spinal Score (m-SASSS). Three studies compared the safety of continuous and on-demand celecoxib, two in osteoarthritis and one in AS, and found no significant differences regarding the usual side effects of Cox-2 inhibitors.

CONCLUSIONS

Several studies showed slower radiographic progression with continuous NSAID therapy in AS. No studies demonstrated superiority of continuous NSAID therapy regarding symptom control. Continuous NSAID therapy (at least with Cox-2 inhibitors) does not modify safety compared to on-demand therapy.

Cyclic tensile force up-regulates BMP-2 expression through MAP kinase and COX-2/PGE2 signaling pathways in human periodontal ligament cells

Periodontal ligament cells play important roles in the homeostasis of periodontal tissue by mechanical stress derived from mastication, such as tension, compression, fluid shear, and hydrostatic force. In the present study, we showed that cyclic tensile force increased the gene expression level of bone morphogenetic protein (BMP)-2, a crucial regulator of mineralization, in human periodontal ligament cells using real-time PCR. Signaling inhibitors, PD98059/U0126 (extracellular signal-regulated kinase (ERK) inhibitors) and SB203580/SB202190 (p38 inhibitors), revealed that tensile force-mediated BMP-2 expression was dependent on activation of the ERK1/2 and p38 mitogen-activated protein (MAP) kinase pathways. Cyclic tensile force also induced cyclooxygenase-2 (COX-2) gene expression in a manner dependent on ERK1/2 and p38 MAP kinase pathways, and induced prostaglandin E2 (PGE2) biosynthesis. NS-398, a COX-2 inhibitor, significantly reduced tensile force-mediated BMP-2 expression, indicating that PGE2 synthesized by COX-2 may be involved in the BMP-2 induction. The inhibitory effect of NS-398 was completely restored by the addition of exogenous PGE2. However, stimulation with PGE2 alone in the absence of tensile force had no effect on the BMP-2 induction, indicating that some critical molecule(s) other than COX-2/PGE2 may be required for cyclic tensile force-mediated BMP-2 induction. Collectively, the results indicate that cyclic tensile force activates ERK1/2 and p38 MAP kinase signaling pathways, and induces COX-2 expression, which is responsible for the sequential PGE2 biosynthesis and release, and furthermore, mediates the increase in BMP-2 expression at the transcriptional level.

NSAIDs and fracture healing

PURPOSE OF REVIEW

Published data raise concerns about the use of nonselective NSAIDs and selective cyclo-oxygenase (COX)-2 inhibitors as anti-inflammatory or analgesic drugs in patients after a recent fracture or who are undergoing (uncemented) arthroplasty or osteotomy. However, clinical reports on the effect of COX-2 inhibition on fracture healing in humans have been variable and inconclusive. This review gives an overview of the published data and an advice when to avoid NSAIDs.

RECENT FINDINGS

Prostaglandins play an important role as mediators of inflammation and COX are required for their production. Inflammation is an essential step in the fracture healing process in which prostaglandin production by COX-2 is involved. Data from animal studies suggest that NSAIDs, which inhibit COX-2, can impair fracture healing due to the inhibition of the endochondral ossification pathway. Animal data suggest that the effects of COX-2 inhibitors are dependent on the timing, duration, and dose, and that these effects are reversible.

SUMMARY

These animal data, together with the view of limited scientifically robust clinical evidence in humans, indicate that physicians consider only short-term administration of COX-2 inhibitors or other drugs in the pain management of patients who are in the phase of fracture or other bone defect healing. COX-2-inhibitors should be considered a potential risk factor for fracture healing, and therefore to be avoided in patients at risk for delayed fracture healing.

Immunohistochemical localization of key arachidonic acid metabolism enzymes during fracture healing in mice

This study investigated the localization of critical enzymes involved in arachidonic acid metabolism during the initial and regenerative phases of mouse femur fracture healing. Previous studies found that loss of cyclooxygenase-2 activity impairs fracture healing while loss of 5-lipoxygenase activity accelerates healing. These diametric results show that arachidonic acid metabolism has an essential function during fracture healing. To better understand the function of arachidonic acid metabolism during fracture healing, expression of cyclooxygenase-1 (COX-1), cyclooxygenase -2 (COX-2), 5-lipoxygenase (5-LO), and leukotriene A4 hydrolase (LTA4H) was localized by immunohistochemistry in time-staged fracture callus specimens. All four enzymes were detected in leukocytes present in the bone marrow and attending inflammatory response that accompanied the fracture. In the tissues surrounding the fracture site, the proportion of leukocytes expressing COX-1, COX-2, or LTA4H decreased while those expressing 5-LO remained high at 4 and 7 days after fracture. This may indicate an inflammation resolution function for 5-LO during fracture healing. Only COX-1 was consistently detected in fracture callus osteoblasts during the later stages of healing (day 14 after fracture). In contrast, callus chondrocytes expressed all four enzymes, though 5-LO appeared to be preferentially expressed in newly differentiated chondrocytes. Most interestingly, osteoclasts consistently and strongly expressed COX-2. In addition to bone surfaces and the growth plate, COX-2 expressing osteoclasts were localized at the chondro-osseous junction of the fracture callus. These observations suggest that arachidonic acid mediated signaling from callus chondrocytes or from callus osteoclasts at the chondro-osseous junction regulate fracture healing.

Generation of closed transverse fractures in small animals

The most common procedure that has been developed for use in rats and mice to model fracture healing is described. The nature of the regenerative processes that may be assessed and the types of research questions that may be addressed with this model are briefly outlined. The detailed surgical protocol to generate closed simple transverse fractures is presented, and general considerations when setting up an experiment using this model are described.

The murine femoral bone graft model and a semiautomated histomorphometric analysis tool

Preclinical studies of bone repair remain a high priority because of unresolved clinical problems associated with treating critical segmental defects and complications of fracture healing. Over the last decade, the murine femoral allograft model has gained popularity due to its standardized surgery and potential for examining a vast array of radiographic, biomechanical, and histological outcome measures. Here, we describe these methods and a novel semiautomated histomorphometric approach to quantify the amount of bone, cartilage, and undifferentiated mesenchymal tissue in demineralized paraffin sections of allografted murine femurs using the Visiopharm Image Analysis Software System.

PTH promotes allograft integration in a calvarial bone defect

Allografts may be useful in craniofacial bone repair, although they often fail to integrate with the host bone. We hypothesized that intermittent administration of parathyroid hormone (PTH) would enhance mesenchymal stem cell recruitment and differentiation, resulting in allograft osseointegration in cranial membranous bones. Calvarial bone defects were created in transgenic mice, in which luciferase is expressed under the control of the osteocalcin promoter. The mice were given implants of allografts with or without daily PTH treatment. Bioluminescence imaging (BLI) was performed to monitor host osteprogenitor differentiation at the implantation site. Bone formation was evaluated with the aid of fluorescence imaging (FLI) and microcomputed tomography (μCT) as well as histological analyses. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the expression of key osteogenic and angiogenic genes. Osteoprogenitor differentiation, as detected by BLI, in mice treated with an allograft implant and PTH was over 2-fold higher than those in mice treated with an allograft implant without PTH. FLI also demonstrated that the bone mineralization process in PTH-treated allografts was significantly higher than that in untreated allografts. The μCT scans revealed a significant increase in bone formation in allograft + PTH treated mice comparing to allograft + PBS treated mice. The osteogenic genes osteocalcin (Oc/Bglap) and integrin binding sialoprotein (Ibsp) were upregulated in the allograft + PTH treated animals. In summary, PTH treatment enhances osteoprogenitor differentiation and augments bone formation around structural allografts. The precise mechanism is not clear, but we show that infiltration pattern of mast cells, associated with the formation of fibrotic tissue, in the defect site is significantly affected by the PTH treatment.

BMP9 and COX-2 form an important regulatory loop in BMP9-induced osteogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) can self-renew and differentiate into osteogenic, chondrogenic, adipogenic and myogenic lineages. It's reported that bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic BMPs to initiate the commitment of MSCs to osteoblast lineage. Cyclooxygenase-2 (COX-2) is critical for bone fracture healing and osteogenic differentiation in MSCs. However, the relationship between COX-2 and BMP9 in osteogenesis remains unknown. Herein, we investigate the role of COX-2 in BMP9-induced osteogenesis in MSCs. We demonstrate that COX-2 is up-regulated as a target of BMP9 in MSCs. Both COX-2 inhibitor (NS-398) and COX-2 knockdown siRNAs can effectively decrease alkaline phosphatase (ALP) activities induced by BMP9 in MSCs. NS-398 also down-regulates BMP9-induced expression of osteopontin and osteocalcin, so does the matrix mineralization. The in vivo studies indicate that knockdown of COX-2 attenuates BMP9-induced ectopic bone formation. In perinatal limb culture assay, NS-398 is shown to reduce the hypertropic chondrocyte zone and ossification induced by BMP9. Mechanistically, knockdown of COX-2 significantly inhibits the BMP9 up-regulated expression of Runx2 and Dlx-5 in MSCs, which can be rescued by exogenous expression of COX-2. Furthermore, knockdown of COX-2 apparently reduces BMP9 induced BMPR-Smad reporter activity, the phosphorylation of Smad1/5/8, and the expression of Smad6 and Smad7 in MSCs. NS-398 blocks the expression of BMP9 mediated by BMP9 recombinant adenovirus. Taken together, our findings suggest that COX-2 plays an important role in BMP9 induced osteogenic differentiation in MSCs; BMP9 and COX-2 may form an important regulatory loop to orchestrate the osteogenic differentiation in MSCs.

Basic science of bone healing

Bone healing is a complex process that can be influenced by both host and environmental factors. In this article, we review the biology involved in the regeneration of new bone after fracture, and factors influencing bone healing, including diabetes, smoking, NSAID use, and bisphosphonates.

Periosteum: biology and applications in craniofacial bone regeneration

The bone-regenerative potentials of the periosteum have been explored as early as the 17th century. Over the past few years, however, much has been discovered in terms of the molecular and cellular mechanisms that control the periosteal contribution to bone regeneration. Lineage tracing analyses and knock-in transgenic mice have helped define the relative contributions of the periosteum and endosteum to bone regeneration. Additional studies have shed light on the critical roles that BMP, FGF, Hedgehog, Notch, PDGF, Wnt, and inflammation signaling have or may have in periosteal-mediated bone regeneration, fostering the path to novel approaches in bone-regenerative therapy. Thus, by examining the role that each pathway has in periosteal-mediated bone regeneration, in this review we analyze the status of the current research on the regenerative potential of the periosteum. The provided analysis aims to inform both clinician-scientists who may have interest in the current studies about the biology of the periosteum as well as dental surgeons who may find this review useful to perform periosteal-harnessing bone-regenerative procedures.

Serotonin 2B receptor (5-HT2B R) signals through prostacyclin and PPAR-ß/δ in osteoblasts

Osteoporosis is due to an imbalance between decreased bone formation by osteoblasts and increased resorption by osteoclasts. Deciphering factors controlling bone formation is therefore of utmost importance for the understanding and the treatment of osteoporosis. Our previous in vivo results showed that bone formation is reduced in the absence of the serotonin receptor 5-HT2B, causing impaired osteoblast proliferation, recruitment, and matrix mineralization. In this study, we investigated the signaling pathways responsible for the osteoblast defect in 5-HT2BR(-/-) mice. Notably, we investigated the phospholipase A2 pathway and synthesis of eicosanoids in 5-HT2BR(-/-) compared to wild type (WT) osteoblasts. Compared to control osteoblasts, the lack of 5-HT2B receptors was only associated with a 10-fold over-production of prostacyclin (PGI2). Also, a specific prostacyclin synthase inhibitor (U51605) rescued totally osteoblast aggregation and matrix mineralization in the 5-HT2BR(-/-) osteoblasts without having any effect on WT osteoblasts. Prostacyclin is the endogenous ligand of the nuclear peroxisome proliferator activated receptor ß/δ (PPAR-ß/δ), and its inhibition in 5-HT2BR(-/-) cells rescued totally the alkaline phosphatase and osteopontin mRNA levels, cell-cell adhesion, and matrix mineralization. We conclude that the absence of 5-HT2B receptors leads to the overproduction of prostacyclin, inducing reduced osteoblast differentiation due to PPAR-ß/δ -dependent target regulation and defective cell-cell adhesion and matrix mineralization. This study thus reveals a previously unrecognized cell autonomous osteoblast defect in the absence of 5-HT2BR and highlights a new pathway linking 5-HT2B receptors and nuclear PPAR- ß/δ via prostacyclin.

Electrospun fibers as a scaffolding platform for bone tissue repair

The purpose of the study is to investigate the effects of electrospun fiber diameter and orientation on differentiation and ECM organization of bone marrow stromal cells (BMSCs), in attempt to provide rationale for fabrication of a periosteum mimetic for bone defect repair. Cellular growth, differentiation, and ECM organization were analyzed on PLGA-based random and aligned fibers using fluorescent microscopy, gene analyses, electron scanning microscopy (SEM), and multiphoton laser scanning microscopy (MPLSM). BMSCs on aligned fibers had a reduced number of ALP+ colony at Day 10 as compared to the random fibers of the same size. However, the ALP+ area in the aligned fibers increased to a similar level as the random fibers at Day 21 following stimulation with osteogenic media. Compared with the random fibers, BMSCs on the aligned fibers showed a higher expression of OSX and RUNX2. Analyses of ECM on decellularized spun fibers showed highly organized ECM arranged according to the orientation of the spun fibers, with a broad size distribution of collagen fibers in a range of 40-2.4 μm. Taken together, our data support the use of submicron-sized electrospun fibers for engineering of oriented fibrous tissue mimetic, such as periosteum, for guided bone repair and reconstruction.

Supplementation with fish oil and genistein, individually or in combination, protects bone against the adverse effects of methotrexate chemotherapy in rats

Cancer chemotherapy has been shown to induce long-term skeletal side effects such as osteoporosis and fractures; however, there are no preventative treatments. This study investigated the damaging effects of anti-metabolite methotrexate (MTX) subcutaneous injections (0.75 mg/kg BW) for five days and the potential protective benefits of daily oral gavage of fish oil at 0.5 mL/100 g BW (containing 375 mg of n-3 PUFA/100 g BW), genistein (2 mg/100 g BW), or their combination in young adult rats. MTX treatment alone significantly reduced primary spongiosa height and secondary spongiosa trabecular bone volume. Bone marrow stromal cells from the treated rats showed a significant reduction in osteogenic differentiation but an increase in adipogenesis ex vivo. Consistently, stromal cells had significantly higher mRNA levels of adipogenesis-related proliferator activator activated receptor-γ (PPAR-γ) and fatty acid binding protein (FABP4). MTX significantly increased the numbers of bone-resorbing osteoclasts and marrow osteoclast precursor cell pool while significantly enhancing the mRNA expression of receptor activator for nuclear factor kappa B ligand (RANKL), the RANKL/osteoprotegerin (OPG) ratio, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the bone. Supplementary treatment with fish oil and/or genistein significantly preserved trabecular bone volume and osteogenesis but suppressed MTX-induced adipogenesis and increases in osteoclast numbers and pro-osteoclastogenic cytokine expression. Thus, Fish oil and/or genistein supplementation during MTX treatment enabled not only preservation of osteogenic differentiation, osteoblast number and bone volume, but also prevention of MTX treatment-induced increases in bone marrow adiposity, osteoclastogenic cytokine expression and osteoclast formation, and thus bone loss.

NSAID therapy effects on healing of bone, tendon, and the enthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of skeletal injuries. The ability of NSAIDs to reduce pain and inflammation is well-established. However, the effects of NSAID therapy on healing of skeletal injuries is less defined. NSAIDs inhibit cyclooxygenase activity to reduce synthesis of prostaglandins, which are proinflammatory, lipid-signaling molecules. Inhibition of cyclooxygenase activity can impact many physiological processes. The effects of NSAID therapy on healing of bone, tendon, and the tendon-to-bone junction (enthesis) have been studied in animal and cell culture models, but human studies are few. Use of different NSAIDs with different pharmacological properties, differences in dosing regimens, and differences in study models and outcome measures have complicated comparisons between studies. In this review, we summarize the mechanisms by which bone, tendon, and enthesis healing occurs, and describe the effects of NSAID therapy on each of these processes. Determining the impact of NSAID therapy on healing of skeletal tissues will enable clinicians to appropriately manage the patient's condition and improve healing outcomes.

Delayed fracture healing in tetranectin-deficient mice

Tetranectin is a plasminogen-binding protein that enhances plasminogen activation, which has been suggested to play a role in tissue remodeling. Recently, we showed that tetranectin has a role in the wound-healing process. In this study, we investigated whether tetranectin plays a role in fracture healing. The fracture-healing process was studied using a femoral osteotomy model in tetranectin-null mice, previously generated by the authors. Radiographic imaging, micro-computed tomography (μCT), and histological analysis were used to evaluate osteotomy healing. In wild-type mice, a callus was apparent from 7 days, and most samples showed marked callus formation and rebridging of the cortices at the osteotomy site at 21 days. In contrast, in the tetranectin-null mice there was no callus formation at 7 days and much less callus formation and no bridging of cortices were observed at 21 days. At 35 days, all osteotomy sites showed clear rebridging, and secondary bone formation was achieved in wild-type mice by 42 days. In contrast, no clear rebridging or secondary bone formation was observed at 42 days in the tetranectin-null mice. Analysis using μCT at 21 days after osteotomy revealed that the callus area in tetranectin-null mice was smaller than that in wild-type mice. Histological analysis also showed that soft tissue and callus formation were smaller in the tetranectin-null mice at the early stage of the healing process after drill-hole injury. These results suggested that tetranectin could have a role in the positive regulation at the early stage of the fracture-healing process, which was reflected in the delayed fracture healing in tetranectin-deficient mice.

Preoperative irradiation for the prevention of heterotopic ossification induces local inflammation in humans

Radiation of the hip is an established method to prevent heterotopic ossification (HO) following total hip arthroplasty (THA) but the precise mechanism is unclear. As inflammatory processes are suggested to be involved in the pathogenesis of HO, we hypothesized that the preoperative irradiation impacts local immune components. Therefore, we quantified immune cell populations and cytokines in hematomas resulting from the transection of the femur in two groups of patients receiving THA: patients irradiated preoperatively (THA-X-hematoma: THA-X-H group) in the hip region (7 Gy) in order to prevent HO and patients who were not irradiated (THA-H group) but were postoperatively treated with non-steroidal anti-inflammatory drugs (NSAIDs). Radiation resulted in significantly increased frequencies of T cells, cytotoxic T cells, NKT cells and CD25+CD127- Treg cells, whereas the number of naive CD45RA-expressing cytotoxic T cells was reduced. These results indicate differential immune cell activation, corroborated by our findings of significantly higher concentrations of pro-inflammatory cytokines (e.g., IL-6, IFNγ) and chemokines (e.g., MCP-1, RANTES) in the THA-X-H group as compared to THA-H group. In contrast, the concentration of the angiogenic VEGF was significantly suppressed in the THA-X-H group. We conclude that preoperative irradiation results in significant changes in immune cell composition and cytokine secretion in THA-hematomas, establishing a specific - rather proinflammatory - milieu. This increase of inflammatory activity together with the observed suppression in VEGF secretion may contribute to the prevention of HO.

Long-chain polyunsaturated fatty acids may mutually benefit both obesity and osteoporosis

The overconsumption of n-6 polyunsaturated fatty acids (PUFA), resulting in a high ratio of n-6 to n-3 PUFA, may contribute to the increased pathogenesis of obesity and osteoporosis by promoting low-grade chronic inflammation (LGCI). As evidence suggests, both obesity and osteoporosis are linked on a cellular and systemic basis. This review will analyze if a relationship exists between LGCI, fat, bone, and n-3 PUFA. During the life cycle, inflammation increases, fat mass accumulates, and bone mass declines, thus suggesting that a connection exists. This review will begin by examining how the current American diet and dietary guidelines may fall short of providing an anti-inflammatory dose of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It will then define LGCI and outline the evidence for a relationship between fat and bone. Inflammation as it pertains to obesity and osteoporosis and how EPA and DHA can alleviate the associated inflammation will be discussed, followed by some preliminary evidence to show how mesenchymal stem cell (MSC) lineage commitment may be altered by inflammation to favor adipogenesis. Our hypothesis is that n-3 PUFA positively influence obesity and osteoporosis by reducing LGCI, ultimately leading to a beneficial shift in MSC lineage commitment. This hypothesis essentially relates the need for more focused research in several areas such as determining age and lifestyle factors that promote the shift in MSC commitment and if current intakes of EPA and DHA are optimal for fat and bone.

The growing role of eicosanoids in tissue regeneration, repair, and wound healing

Tissue repair and regeneration are essential processes in maintaining tissue homeostasis, especially in response to injury or stress. Eicosanoids are ubiquitous mediators of cell proliferation, differentiation, and angiogenesis, all of which are important for tissue growth. Eicosanoids regulate the induction and resolution of inflammation that accompany the tissue response to injury. In this review, we describe how this diverse group of molecules is a key regulator of tissue repair and regeneration in multiple organ systems and biologic contexts.

Intermittent administration of human parathyroid hormone before osteosynthesis stimulates cancellous bone union in ovariectomized rats

It has been reported that intermittent administration of human parathyroid hormone (h-PTH) promotes bone healing after surgery for osteoporotic fractures. If bone healing is promoted by the administration of h-PTH during pre-operative waiting period, we can prevent prolonged bed rest. Therefore, we evaluated the effects of pre-operative h-PTH treatment on cancellous bone union and its mechanism for fracture healing in ovariectomized rats as a model for osteoporosis. Ovariectomized 7-month-old female Sprague-Dawley rats underwent an osteotomy of the proximal tibia as a fracture model, and h-PTH (30 μg/kg body weight) or vehicle was administered as a pre-operative treatment for one week. After the one-week treatment, tibiae were fixed with wire for osteosynthesis, and h-PTH or vehicle was administered for 1 or 3 weeks following wire fixation. In addition to bone histomorphometry, we used alcian blue/hematoxylin stained sections for evaluating cartilage volume and immunostained sections for analyzing the expression of proliferating cell nuclear antigen (PCNA) for cell proliferation and that of Sox9 and Runx2, differentiation markers for cartilage cells and osteoblasts, respectively. Pre-operative treatment with PTH significantly increased bone volume. Pre-operative and pre- to post-operative treatment with PTH for 2 weeks significantly promoted bone union. Pre-operative treatment with PTH significantly increased cartilage volume, and pre- to post-operative treatment with PTH for 2 weeks significantly increased the percentage of cells positive for Runx2 (p < 0.01), but not PCNA or Sox9. Pre-operative administration of h-PTH enhances bone union by promoting cartilage formation and cell differentiation to osteoblasts, but not by promoting cell proliferation.

Cellular and molecular mechanisms of accelerated fracture healing by COX2 gene therapy: studies in a mouse model of multiple fractures

This study sought to determine the cellular and molecular mechanisms of cyclooxygenase-2 (COX2) gene therapy to accelerate fracture repair in a mouse multiple tibial fractures model. The lenti-COX2 (or lenti-gfp control vector) was injected into fractures on day 1 post-fracture. At days 3-7, the COX2 treatment increased Sdf1-, Cxcr4-, Nes-, and Podxl-expressing mesenchymal stem cells (MSCs) within fracture calluses, suggesting an enhanced MSC recruitment or expansion. The COX2-treated mice formed smaller cartilaginous calluses that had less cartilage tissues than control mice. The expression of Sox9 mRNA was 7-fold less in COX2-treated than in control calluses at day 14, implying that COX2 reduces chondrocytic differentiation of MSCs. The therapy also enhanced angiogenesis as reflected by increased immunostaining of CD31, vWF, and α-SMA over controls in the cartilaginous callus at day 14-21. At which time, the COX2 gene therapy promoted bony remodeling of the cartilaginous callus to bridge the fracture gap that was accompanied by 2-fold increase in osteoclasts along the surface of the woven bone and an onset of osteogenesis. Blocking angiogenesis with daily injection of endostatin from day 4 to day 10 into fracture sites blocked the COX2-mediated reduction of callus size that was associated with an increase in hypertrophic chondrocytes and concomitant reduction in osteoclasts. In conclusion, COX2 accelerates fracture healing in part through three biological actions: 1) increased recruitment/expansion of MSCs; 2) decreased cartilaginous callus formation; and 3) increased angiogenesis-dependent cartilage remodeling. These effects were associated with an earlier onset of bony bridging of the fracture gap.

Primary cilia-mediated mechanotransduction in human mesenchymal stem cells

Physical loading is a potent stimulus required to maintain bone homeostasis, partly through the renewal and osteogenic differentiation of mesenchymal stem cells (MSCs). However, the mechanism by which MSCs sense a biophysical force and translate that into a biochemical bone forming response (mechanotransduction) remains poorly understood. The primary cilium is a single sensory cellular extension, which has recently been shown to demonstrate a role in cellular mechanotransduction and MSC lineage commitment. In this study, we present evidence that short periods of mechanical stimulation in the form of oscillatory fluid flow (OFF) is sufficient to enhance osteogenic gene expression and proliferation of human MSCs (hMSCs). Furthermore, we demonstrate that the cilium mediates fluid flow mechanotransduction in hMSCs by maintaining OFF-induced increases in osteogenic gene expression and, surprisingly, to limit OFF-induced increases in proliferation. These data therefore demonstrate a pro-osteogenic mechanosensory role for the primary cilium, establishing a novel mechanotransduction mechanism in hMSCs. Based on these findings, the application of OFF may be a beneficial component of bioreactor-based strategies to form bone-like tissues suitable for regenerative medicine and also highlights the cilium as a potential therapeutic target for efforts to mimic loading with the aim of preventing bone loss during diseases such as osteoporosis. Furthermore, this study demonstrates a role for the cilium in controlling mechanically mediated increases in the proliferation of hMSCs, which parallels proposed models of polycystic kidney disease. Unraveling the mechanisms leading to rapid proliferation of mechanically stimulated MSCs with defective cilia could provide significant insights regarding ciliopathies and cystic diseases. Stem Cells2012;30:2561–2570