Factors regulating osteoclast formation in human tissues adjacent to peri-implant bone loss: expression of receptor activator NFkappaB, RANK ligand and osteoprotegerin

Gallium and silver-doped titanium surfaces provide enhanced osteogenesis, reduce bone resorption and prevent bacterial infection in co-culture

Bacterial infection remains a significant problem associated with orthopaedic surgeries leading to surgical site infection (SSI). This unmet medical need can become an even greater complication when surgery is due to malignant bone tumor. In the present study, we evaluated in vitro titanium (Ti) implants subjected to gallium (Ga) and silver (Ag)-doped thermochemical treatment as strategy to prevent SSI and improve osteointegration in bone defects caused by diseases such as osteoporosis, bone tumor, or bone metastasis. Firstly, as Ga has been reported to be an osteoinductive and anti-resorptive agent, its performance in the mixture was proved by studying human mesenchymal stem cells (hMSC) and pre-osteoclasts (RAW264.7) behaviour. Then, the antibacterial potential provided by Ag was assessed by resembling "The Race for the Surface" between hMSC and Pseudomonas aeruginosa in two co-culture methods. Moreover, the presence of quorum sensing molecules in the co-culture was evaluated. The results highlighted the suitability of the mixture to induce osteodifferentiation and reduce osteoclastogenesis in vitro. Furthermore, the GaAg surface promoted strong survival rate and retained osteoinduction potential of hMSCs even after bacterial inoculation. Therefore, GaAg-modified titanium may be an ideal candidate to repair bone defects caused by excessive bone resorption, in addition to preventing SSI. STATEMENT OF SIGNIFICANCE: This article provides important insights into titanium for fractures caused by osteoporosis or bone metastases with high incidence in surgical site infection (SSI) because in this situation bacterial infection can become a major disaster. In order to solve this unmet medical need, we propose a titanium implant modified with gallium and silver to improve osteointegration, reduce bone resorption and avoid bacterial infection. For that aim, we study osteoblast and osteoclast behavior with the main novelty focused on the antibacterial evaluation. In this work, we recreate "the race for the surface" in long-term experiments and study bacterial virulence factors (quorum sensing). Therefore, we believe that our article could be of great interest, providing a great impact on future orthopedic applications.

Biosynthesized Silver Nanoparticles Inhibit Osteoclastogenesis by Suppressing NF-κB Signaling Pathways

Osteoclasts overactivity plays a critical role in the progress of inflammatory bone loss. In addition, ROS can facilitate the formation and function of osteoclasts. Silver nanoparticles (Ag NPs) with ROS scavenging activity are potential candidates for inflammatory bone loss. In this regard, the biosynthetic Ag NPs with low toxicity and high stability by using Flos Sophorae Immaturus extract as the reducing and capping agents are reported. The inflammatory bone loss model is established by injecting LPS. Quantitative reverse transcription-polymerase chain reaction and Western Blot are utilized to determine the expression level of target biomarkers related to osteoclast formation. Ag NPs can significantly reduce the number of TRAP-positive (TRAP+ ) cells. In addition, Ag NPs down-regulate the expression of biomarkers relevant to osteoclast formation. Interestingly, Ag NPs can effectively suppress osteoclast formation via down-regulating ROS-mediated phosphorylation of NF-κB pathways. The in vivo study shows that Ag NPs can ameliorate bone density and decrease osteoclast number. Due to these benefits, the constructed Ag NPs can delay the progression of inflammatory bone loss. These findings suggest that Ag NPs are a potential therapeutic agent in the treatment of inflammatory bone loss.

Inhibitory effects of Formononetin on CoCrMo particle-induced osteoclast activation and bone loss through downregulating NF-κB and MAPK signaling

Wear particle-induced osteoclast over-activation is a major contributor to periprosthetic osteolysis and aseptic loosening, which can cause pathological bone loss and destruction. Hence, inhibiting excessive osteoclast-resorbing activity is an important strategy for preventing periprosthetic osteolysis. Formononetin (FMN) has been shown to have protective effects against osteoporosis, but no previous study has evaluated the effects of FMN on wear particle-induced osteolysis. In this study, we found that FMN alleviated CoCrMo alloy particles (CoPs)-induced bone loss in vivo and inhibited the formation and bone-resorptive function of osteoclasts in vitro. Moreover, we revealed that FMN exerted inhibitory effects on the expression of osteoclast-specific genes via the classical NF-κB and MAPK signaling pathways in vitro. Collectively, FMN is a potential therapeutic agent for the prevention and treatment of periprosthetic osteolysis and other osteolytic bone diseases.

Human umbilical cord mesenchymal stem cells induction in peri-implantitis Rattus norvegicus accelerates and enhances osteogenesis activity and implant osseointegration

Peri-implantitis additional treatment generally aims to repair damaged tissue through a regenerative approach. Human umbilical cord mesenchymal stem cells (hUCMSCs) produce a high osteogenic effect and are capable of modulating the immune system by suppressing inflammatory response, modulating bone resorption, and inducing endogenous osteogenesis.

AIM

This study was intended to discover the effect of hUCMSCs on an implant osseointegration process in peri-implantitis rat subjects as assessed by several markers including interleukin-10 (IL-10), transforming growth factor-β (TGF-β), receptor activator of nuclear factor kappa- β ligand (RANKL), bone morphogenic protein (BMP-2), osterix (Osx), and osteoprotegerin (OPG).

MATERIAL AND METHODS

The research design implemented during this study represented a true experimental design incorporating the use of Rattus norvegicus (Wistar strain) as subjects.

RESULTS

Data analysed by means of a Brown Forsythe test indicated differences between the increase in BMP-2 expression (p < 0.000) and Osx expression (p < 0.001) and between RANKL expression (p < 0.001, Tukey HSD) and OPG expression (p < 0.000, Games Howell).

CONCLUSION

According to the findings of this research, hUCMSCs induction is successful in accelerating and enhancing osteogenic activity and implant osseointegration in peri-implantitis rat subjects.

Norcantharidin ameliorates estrogen deficient-mediated bone loss by attenuating the activation of extracellular signal-regulated kinase/ROS/NLRP3 inflammasome signaling

Osteoporosis, characterized by reduced bone mass, aberrant bone architecture, and elevated bone fragility, is driven by a disruption of bone homeostasis between bone resorption and bone formation. However, up to now, no drugs are perfect for osteoporosis treatment due to different defects. In this study, we demonstrated that norcantharidin (NCTD) could inhibit osteoclast formation and bone resorption by attenuating the ERK, ROS and NLRP3 inflammasomes pathways in vitro. Moreover, our in vivo study further confirms its preventive effects on estrogen-deficiency bone loss by inhibiting osteoclast formation and functions. Therefore, we could conclude that NCTD might be a potential candidates for the prevention and treatment of osteoporosis.

Targeting regulation of stem cell exosomes: Exploring novel strategies for aseptic loosening of joint prosthesis

Periprosthetic osteolysis is a major long-term complication of total joint replacement. A series of biological reactions caused by the interaction of wear particles at the prosthesis bone interface and surrounding bone tissue cells after artificial joint replacement are vital reasons for aseptic loosening. Disorder of bone metabolism and aseptic inflammation induced by wear particles are involved in the occurrence and development of aseptic loosening of the prosthesis. Promoting osteogenesis and angiogenesis and mediating osteoclasts and inflammation may be beneficial in preventing the aseptic loosening of the prosthesis. Current research about the prevention and treatment of aseptic loosening of the prosthesis focuses on drug, gene, and stem cell therapy and has not yet achieved satisfactory clinical efficacy or has not been used in clinical practice. Exosomes are a kind of typical extracellular vehicle. In recent years, stem cell exosomes (Exos) have been widely used to regulate bone metabolism, block inflammation, and have broad application prospects in tissue repair and cell therapy.

Changes in Metabolism and Mitochondrial Bioenergetics during Polyethylene-Induced Osteoclastogenesis

Changes in mitochondrial bioenergetics are believed to take place during osteoclastogenesis. This study aims to assess changes in mitochondrial bioenergetics and reactive oxygen species (ROS) levels during polyethylene (PE)-induced osteoclastogenesis in vitro. For this purpose, RAW264.7 cells were cultured for nine days and allowed to differentiate into osteoclasts in the presence of PE and RANKL. The total TRAP-positive cells, resorption activity, expression of osteoclast marker genes, ROS level, mitochondrial bioenergetics, glycolysis, and substrate utilization were measured. The effect of tocotrienols-rich fraction (TRF) treatment (50 ng/mL) on those parameters during PE-induced osteoclastogenesis was also studied. During PE-induced osteoclastogenesis, as depicted by an increase in TRAP-positive cells and gene expression of osteoclast-related markers, higher proton leak, higher extracellular acidification rate (ECAR), as well as higher levels of ROS and NADPH oxidases (NOXs) were observed in the differentiated cells. The oxidation level of some substrates in the differentiated group was higher than in other groups. TRF treatment significantly reduced the number of TRAP-positive osteoclasts, bone resorption activity, and ROS levels, as well as modulating the gene expression of antioxidant-related genes and mitochondrial function. In conclusion, changes in mitochondrial bioenergetics and substrate utilization were observed during PE-induced osteoclastogenesis, while TRF treatment modulated these changes.

Proton Pump Inhibitors and the Risk of Early Aseptic Loosening in Hip and Knee Arthroplasty

Introduction

The use of proton pump inhibitors (PPIs) has been associated with a higher risk of osteoporotic fractures and non-unions rates. However, the relation between the use of PPIs and the development of aseptic loosening in arthroplasty procedures has not been studied. The objective of this study is to analyze the relation between the use of PPIs, and the risk of early aseptic loosening in total knee arthroplasty (TKA) and total hip arthroplasty (THA).

Materials and methods

A nested case-control study was conducted on patients who were subjected THA or TKA in our center between 2010 and 2014. Cases were patients subjected to revision surgery due to early aseptic loosening during the study period. Cases were matched with controls who did not require any type of revision surgery by type of joint replacement (THA/TKA), gender, age (+/- 2 years), and follow-up time (±6 months). Odds Ratios were adjusted to potential confounders.

Results

The crude and adjusted ORs (95% CI) of undergoing revision surgery for aseptic loosening following primary total knee arthroplasty or total hip arthroplasty, were 6.25 (2.04-19.23) and 6.10 (1.71-21.73), respectively, for any use PPIs compared with non-users. Crude and adjusted ORs, were 11.6 (2.93-45.88) and 17.1 (2.41-121.66), respectively, for patients with a Proportion of Days Covered (PDC) for PPIs <.5 (Table 2). In addition, the crude and adjusted ORs of undergoing revision surgery, were 5.05 (1.59-16.02) and 5.01 (1.36-18.44), respectively, for patients with a PDC for PPIs ≥.5.

Discussion

These results suggest that PPIs should be used with caution in patients with TKA and THA, and that the use of these drugs should not be prolonged unless there was a justifiable indication.

Conclusions

The use of PPIs and was associated with a higher risk of early aseptic loosening in patients subjected to THA and TKA.

Tricalcium phosphate particles promote pyroptotic death of calvaria osteocytes through the ROS/NLRP3/Caspase-1 signaling axis in amouse osteolysis model

Wear particles-induced inflammatory osteolysis, a major factor of aseptic loosening affects the long-term survival of orthopedic prostheses. Increasing observations have demonstrated that osteocytes, making up over 95% of all the bone cells, is involved in wear particle-induced periprosthetic osteolysis, but its mechanism remains unclear. In the present study, we embedded micro-sized tricalcium phosphate (TCP) particles (30 mg) under the periosteum around the middle suture of the mouse calvaria to establish a calvarial osteolysis model and investigated the biological effects of the particles on calvaria osteocytes in vivo. Results showed that TCP particles induced pyroptosis and activated the NLRP3 inflammasome in calvaria osteocytes, which was confirmed by obvious increases in empty lacunae, protein expressions of speck-like protein containing CARD (ASC), NOD-like receptor protein 3 (NLRP3), cleaved caspase-1 (Casp-1 p20) and cleaved gasdermin D (GSDMD-N), and resulted in elevated ratios of Casp-1 p20/Casp-1 and interleukin (IL)-1β/pro-IL-1β. Simultaneously, TCP particles enhanced serum levels of lactate dehydrogenase (LDH) and IL-1β. Furthermore, the pyroptotic effect was reversed by the Casp-1 inhibitor VX765 or the NLRP3 inhibitor MCC950. In addition, TCP particles increased the levels of intracellular reactive oxygen species (ROS) and malonaldehyde (MDA), whereas decreased the antioxidant enzyme nuclear factor E2-related factor 2 (Nrf2) level, leading to oxidative stress in calvaria osteocytes; the ROS scavenger N-acetylcysteine (NAC) attenuated these effects of pyroptotic death and the NLPR3 activation triggered by TCP particles. Collectively, our data suggested that TCP particles promote pyroptotic death of calvaria osteocytes through the ROS/NLRP3/Caspase-1 signaling axis, contributing to osteoclastogenesis and periprosthetic osteolysis.

Dental and Orthopaedic Implant Loosening: Overlap in Gene Expression Regulation

Objectives

Endoprosthetic loosening still plays a major role in orthopaedic and dental surgery and includes various cellular immune processes within peri-implant tissues. Although the dental and orthopaedic processes vary in certain parts, the clinical question arises whether there are common immune regulators of implant loosening. Analyzing the key gene expressions common to both processes reveals the mechanisms of osteoclastogenesis within periprosthetic tissues of orthopaedic and dental origin.

Methods

Donor peripheral blood mononuclear cells (PBMCs) and intraoperatively obtained periprosthetic fibroblast-like cells (PPFs) were (co-)cultured with [± macrophage-colony stimulating factor (MCSF) and Receptor Activator of NF-κB ligand (RANKL)] in transwell and monolayer culture systems and examined for osteoclastogenic regulations [MCSF, RANKL, osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα)] as well as the ability of bone resorption. Sequencing analysis compared dental and orthopaedic (co-)cultures.

Results

Monolayer co-cultures of both origins expressed high levels of OPG, resulting in inhibition of osteolysis shown by resorption assay on dentin. The high OPG-expression, low RANKL/OPG ratios and a resulting inhibition of osteolysis were displayed by dental and orthopaedic PPFs in monolayer even in the presence of MCSF and RANKL, acting as osteoprotective and immunoregulatory cells. The osteoprotective function was only observed in monolayer cultures of dental and orthopaedic periprosthetic cells and downregulated in the transwell system. In transwell co-cultures of PBMCs/PPFs profound changes of gene expression, with a significant decrease of OPG (20-fold dental versus 100 fold orthopaedic), were identified. Within transwell cultures, which offer more in vivo like conditions, RANKL/OPG ratios displayed similar high levels to the original periprosthetic tissue. For dental and orthopaedic implant loosening, overlapping findings in principal component and heatmap analysis were identified.

Conclusions

Thus, periprosthetic osteoclastogenesis may be a correlating immune process in orthopaedic and dental implant failure leading to comparable reactions with regard to osteoclast formation. The transwell cultures system may provide an in vivo like model for the exploration of orthopaedic and dental implant loosening.

Additive Effect of Parathyroid Hormone and Zoledronate Acid on Prevention Particle Wears-Induced Implant Loosening by Promoting Periprosthetic Bone Architecture and Strength in an Ovariectomized Rat Model

Implant-generated particle wears are considered as the major cause for the induction of implant loosening, which is more susceptible to patients with osteoporosis. Monotherapy with parathyroid hormone (PTH) or zoledronate acid (ZOL) has been proven efficient for preventing early-stage periprosthetic osteolysis, while the combination therapy with PTH and ZOL has exerted beneficial effects on the treatment of posterior lumbar vertebral fusion and disuse osteopenia. However, PTH and ZOL still have not been licensed for the treatment of implant loosening to date clinically. In this study, we have explored the effect of single or combined administration with PTH and ZOL on implant loosening in a rat model of osteoporosis. After 12 weeks of ovariectomized surgery, a femoral particle-induced periprosthetic osteolysis model was established. Vehicle, PTH (5 days per week), ZOL (100 mg/kg per week), or combination therapy was utilized for another 6 weeks before sacrifice, followed by micro-CT, histology, mechanical testing, and bone turnover examination. PTH monotherapy or combined PTH with ZOL exerted a protective effect on maintaining implant stability by elevating periprosthetic bone mass and inhibiting pseudomembrane formation. Moreover, an additive effect was observed when combining PTH with ZOL, resulting in better fixation strength, higher periprosthetic bone mass, and less pseudomembrane than PTH monotherapy. Taken together, our results suggested that a combination therapy of PTH and ZOL might be a promising approach for the intervention of early-stage implant loosening in patients with osteoporosis.

The effect of denosumab on pedicle screw fixation: a prospective 2-year longitudinal study using finite element analysis

BACKGROUND

Pedicle screw loosening is a major complication following spinal fixation associated with osteoporosis in elderly. However, denosumab is a promising treatment in patients with osteoporosis. The effect of denosumab on pedicle screw fixation is unknown. Therefore, we investigated whether denosumab treatment improves pedicle screw fixation in elderly patients with osteoporosis.

METHODS

This was a 2-year prospective open-label study. From February 2015 to January 2016, we included 21 patients with postmenopausal osteoporosis who received initial denosumab treatment. At baseline, 12 months, and 24 months, we measured volumetric bone mineral density (BMD) using quantitative computed tomography (QCT) and performed CT-based finite element analysis (FEA). Finite element models of L4 vertebrae were created to analyze the bone strength and screw fixation.

RESULTS

BMD increased with denosumab treatment. FEA revealed that both pullout strength of pedicle screws and compression force of the vertebra increased significantly at 12 and 24 months following denosumab treatment. Notably, pullout strength showed a stronger correlation with three-dimensional volumetric BMD around pedicle screw placement assessed by QCT (r = 0.83, at 24 months) than with two-dimensional areal BMD assessed by dual energy X-ray absorptiometry (r = 0.35, at 24 months).

CONCLUSION

To our knowledge, this is the first study to reveal that denosumab treatment achieved strong pedicle screw fixation with an increase in BMD around the screw assessed by QCT and FEA; therefore, denosumab could be useful for osteoporosis treatment during spinal surgery in elderly patients with osteoporosis.

Is Inflammation a Friend or Foe for Orthodontic Treatment?: Inflammation in Orthodontically Induced Inflammatory Root Resorption and Accelerating Tooth Movement

The aim of this paper is to provide a review on the role of inflammation in orthodontically induced inflammatory root resorption (OIIRR) and accelerating orthodontic tooth movement (AOTM) in orthodontic treatment. Orthodontic tooth movement (OTM) is stimulated by remodeling of the periodontal ligament (PDL) and alveolar bone. These remodeling activities and tooth displacement are involved in the occurrence of an inflammatory process in the periodontium, in response to orthodontic forces. Inflammatory mediators such as prostaglandins (PGs), interleukins (Ils; IL-1, -6, -17), the tumor necrosis factor (TNF)-α superfamily, and receptor activator of nuclear factor (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) are increased in the PDL during OTM. OIIRR is one of the accidental symptoms, and inflammatory mediators have been detected in resorbed roots, PDL, and alveolar bone exposed to heavy orthodontic force. Therefore, these inflammatory mediators are involved with the occurrence of OIIRR during orthodontic tooth movement. On the contrary, regional accelerating phenomenon (RAP) occurs after fractures and surgery such as osteotomies or bone grafting, and bone healing is accelerated by increasing osteoclasts and osteoblasts. Recently, tooth movement after surgical procedures such as corticotomy, corticision, piezocision, and micro-osteoperforation might be accelerated by RAP, which increases the bone metabolism. Therefore, inflammation may be involved in accelerated OTM (AOTM). The knowledge of inflammation during orthodontic treatment could be used in preventing OIIRR and AOTM.

Naringin increases osteoprotegerin expression in fibroblasts from periprosthetic membrane by the Wnt/β-catenin signaling pathway

Background

The osteoclast bone resorption is critical in aseptic loosening after joint replacement. The balance between activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) is considered to play a central role in osteoclast maturation. Fibroblasts from the periprosthetic membrane express RANKL and promote osteoclast formation. Studies have demonstrated that naringin inhibited osteoclastogenesis and wear particle-induced osteolysis. In this study, the naringin-induced OPG/RANKL effects and its underlying mechanism were studied in fibroblasts from periprosthetic membrane.

Methods

Fibroblasts were isolated from the periprosthetic membrane during hip arthroplasty for revision due to aseptic loosening. Fibroblasts were cultured and treated with or without naringin and DKK-1 (the classical inhibitor of Wnt/β-catenin signaling pathway). OPG and RANKL mRNA and protein levels, gene expression of β-catenin, and cyclin D1, which participate in the Wnt signaling pathway, were examined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

Results

The mRNA and protein levels of OPG were enhanced by naringin in a dose-dependent manner compared to that of the non-treated control. In contrast, naringin did not affect the expression of RANKL. Importantly, DKK-1 attenuated OPG expression in fibroblasts under naringin treatment. Moreover, naringin stimulated the gene expression of β-catenin and cyclin D1 in fibroblasts, and the effect could be inhibited by DKK-1.

Conclusion

The results indicated that naringin enhanced OPG expression through Wnt/β-catenin signaling pathway in fibroblasts from periprosthetic membrane, which may be useful to inhibit periprosthetic osteolysis during aseptic loosening after total joint arthroplasty.

Literature review of the causes of pain following total knee replacement surgery: prosthesis, inflammation and arthrofibrosis

Adverse knee pain occurs in 10–34% of all total knee replacements (TKR), and 20% of TKR patients experience more pain post-operatively than pre-operatively. Knee pain is amongst the top five reasons for knee replacement revision in the United Kingdom. The number of TKRs is predicted to continue increasing due to the ageing population.

A narrative literature review was performed on the different causes of pain following TKR. A database search on Scopus, PubMed, and Google Scholar was conducted to look for articles related to TKR, pain, and cause. Articles were selected based on relevance, publication date, quality of research and validation. Relevant sections were added to the review.

One hundred and fourteen articles were identified and potential causes of TKR pain included: arthrofibrosis, aseptic loosening, avascular necrosis, central sensitization, component malpositioning, infection, instability, nerve damage, overstuffing, patellar maltracking, polyethylene wear, psychological factors and unresurfaced patella.

It is important to tailor our approach to address the individual causes of pain. Certain controllable risk factors can be managed pre-operatively to minimize post-operative pain. Risk factors help to predict adverse pain outcomes and identify specific causes.

There are multiple causes of pain following TKR. Some factors will require further extensive studies, and as pain is a commonly attributed reason for TKR revision, its underlying aetiologies should be explored. Understanding these factors helps to develop effective methods for diagnosis, prevention and management of TKR pain, which help to improve patient outcomes.

Cite this article: EFORT Open Rev 2020;5:534-543. DOI: 10.1302/2058-5241.5.200031

Receptor Activator of Nuclear Factor kappa-B Ligand is Not Regulated During Chronic Osteomyelitis in Pigs

Bone loss is a major complication of osteomyelitis and from numerous in-vitro studies, it has been concluded that the bone lysis is caused by elevated expression of the receptor activator of nuclear factor κB ligand (RANKL), leading to increased osteoclast activity. However, we failed to find any relationship between bone loss and osseous RANKL expression in a porcine model of acute and chronic implant-associated osteomyelitis (IAO) due to Staphylococcus aureus or in chronic osteomyelitis lesions in slaughter pigs. Surprisingly, we found that the expression of RANKL was reduced during chronic bone infections. This is in line with the few studies conducted on human samples. A significant bone loss was observed in IAO lesions and in lesions from slaughter pigs, but with no indication of osteoclast involvement using histochemistry, immunohistochemistry for RANKL, receptor activator of nuclear factor kappa-B, osteoprotegerin and cathepsin K, and high-throughput quantitative real-time polymerase chain reaction on bone tissue from osteomyelitic lesions. A strong inflammatory response was seen in the infected animals and, therefore, we propose proteolytic enzymes induced by inflammation to be a major component of the bone loss. Furthermore, we found a significant upregulation of the IL26 gene in infected animals, which can inhibit RANKL-induced osteoclastogenesis, but has no homologue in mice. This finding emphasises that neither murine models nor in-vitro studies can mirror human disease development completely. The present study emphasises that the interactions between microorganisms, the immune system and bone cells in osteomyelitis are too complex to be accurately represented by an in-vitro model.

DMY protects the knee joints of rats with collagen-induced arthritis by inhibition of NF-κB signaling and osteoclastic bone resorption

Collagen-induced arthritis (CIA) is a widely used animal model for studying rheumatoid arthritis (RA), which manifests serious joint dysfunction, progressive bone erosion and articular cartilage destruction. Considering that joint damage in RA is caused by systemic inflammation and dihydromyricetin (DMY), the main flavonoid of Ampelopsis Michx, possesses anti-inflammatory properties, in the present study we have investigated the potential capability of DMY to inhibit inflammation-mediated joint damage and explore the underlying mechanisms. A rat model of RA induced by CIA was administered with DMY for 5 weeks. Prior to histological analysis, the knee joints were scanned by microcomputed tomography (μCT) to detect bone damage. Articular cartilage destruction was assessed by Alcian blue and Toluidine blue staining and the pathological alteration of osteoblasts and osteoclasts in joints was evaluated by hematoxylin-eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining, respectively. The effects of DMY on osteoblast differentiation and osteoclast formation in vitro were investigated. Consistent with the in vivo results, DMY had no significant effect on osteoblast differentiation but an inhibitory effect on osteoclast formation. Furthermore, we determined that the mechanism of the DMY-suppressed osteoclast formation was blocking the phosphorylation of I-κB kinase (IKK) so as to hinder the activation of nuclear factor-κB (NF-κB). Collectively, DMY could ameliorate knee joint damage, especially in articular cartilage, which is the weight-bearing region, by inhibiting osteoclast formation through NF-κB signaling.

Tussilagone Inhibits Osteoclastogenesis and Periprosthetic Osteolysis by Suppressing the NF-κB and P38 MAPK Signaling Pathways

Background

Aseptic prosthetic loosening is one of the main factors causing poor prognosis of limb function after joint replacement and requires troublesome revisional surgery. It is featured by wear particle-induced periprosthetic osteolysis mediated by excessive osteoclasts activated in inflammatory cell context. Some natural compounds show antiosteoclast traits with high cost-efficiency and few side effects. Tussilagone (TUS), which is the main functional extract from Tussilago farfara generally used for relieving cough, asthma, and eliminating phlegm in traditional medicine has been proven to appease several RAW264.7-mediated inflammatory diseases via suppressing osteoclast-related signaling cascades. However, whether and how TUS can improve aseptic prosthetic loosening via modulating osteoclast-mediated bone resorption still needs to be answered.

Methods

We established a murine calvarial osteolysis model to detect the preventative effect of TUS on osteolysis in vivo. Micro-CT scanning and histomorphometric analysis were used to determine the variation of bone resorption and osteoclastogenesis. The anti–osteoclast-differentiation and anti–bone-resorption bioactivities of TUS in vitro were investigated using bone slice resorption pit evaluation, and interference caused by cytotoxicity of TUS was excluded according to the CCK-8 assay results. Quantitative polymerase chain reaction (qPCR) analysis was applied to prove the decreased expression of osteoclast-specific genes after TUS treatment. The inhibitory effect of TUS on NF-κB and p38 MAPK signaling pathways was testified by Western blot and NF-κB-linked luciferase reporter gene assay.

Results

TUS better protected bones against osteolysis in murine calvarial osteolysis model with reduced osteoclasts than those in the control group. In vitro studies also showed that TUS exerted antiosteoclastogenesis and anti–bone-resorption effects in both bone marrow macrophages (BMMs) and RAW264.7 cells, as evidenced by the decline of osteoclast-specific genes according to qPCR. Western blotting revealed that TUS treatment inhibited IκBα degradation and p38 phosphorylation.

Conclusions

Collectively, our studies proved for the first time that TUS inhibits osteoclastogenesis by suppressing the NF-κB and p38 MAPK signaling pathways, therefore serving as a potential natural compound to treat periprosthetic osteolysis-induced aseptic prosthetic loosening.

Quercetin inhibits macrophage polarization through the p-38α/β signalling pathway and regulates OPG/RANKL balance in a mouse skull model

Aseptic loosening caused by wear particles is a common complication after total hip arthroplasty. We investigated the effect of the quercetin on wear particle‐mediated macrophage polarization, inflammatory response and osteolysis. In vitro, we verified that Ti particles promoted the differentiation of RAW264.7 cells into M1 macrophages through p‐38α/β signalling pathway by using flow cytometry, immunofluorescence assay and small interfering p‐38α/β RNA. We used enzyme‐linked immunosorbent assays to confirm that the protein expression of M1 macrophages increased in the presence of Ti particles and that these pro‐inflammatory factors further regulated the imbalance of OPG/RANKL and promoted the differentiation of osteoclasts. However, this could be suppressed, and the protein expression of M2 macrophages was increased by the presence of the quercetin. In vivo, we revealed similar results in the mouse skull by μ‐CT, H&E staining, immunohistochemistry and immunofluorescence assay. We obtained samples from patients with osteolytic tissue. Immunofluorescence analysis indicated that most of the macrophages surrounding the wear particles were M1 macrophages and that pro‐inflammatory factors were released. Titanium particle‐mediated M1 macrophage polarization, which caused the release of pro‐inflammatory factors through the p‐38α/β signalling pathway, regulated OPG/RANKL balance. Macrophage polarization is expected to become a new clinical drug therapeutic target.

NFκB (Nuclear Factor κ-Light-Chain Enhancer of Activated B Cells) Activity Regulates Cell-Type-Specific and Context-Specific Susceptibility to Calcification in the Aortic Valve

OBJECTIVE

Although often studied independently, little is known about how aortic valve endothelial cells and valve interstitial cells interact collaborate to maintain tissue homeostasis or drive valve calcific pathogenesis. Inflammatory signaling is a recognized initiator of valve calcification, but the cell-type-specific downstream mechanisms have not been elucidated. In this study, we test how inflammatory signaling via NFκB (nuclear factor κ-light-chain enhancer of activated B cells) activity coordinates unique and shared mechanisms of valve endothelial cells and valve interstitial cells differentiation during calcific progression. Approach and Results: Activated NFκB was present throughout the calcific aortic valve disease (CAVD) process in both endothelial and interstitial cell populations in an established mouse model of hypercholesterolemia-induced CAVD and in human CAVD. NFκB activity induces endothelial to mesenchymal transformation in 3-dimensional cultured aortic valve endothelial cells and subsequent osteogenic calcification of transformed cells. Similarly, 3-dimensional cultured valve interstitial cells calcified via NFκB-mediated osteogenic differentiation. NFκB-mediated endothelial to mesenchymal transformation was directly demonstrated in vivo during CAVD via genetic lineage tracking. Genetic deletion of NFκB in either whole valves or valve endothelium only was sufficient to prevent valve-specific molecular and cellular mechanisms of CAVD in vivo despite the persistence of a CAVD inducing environment.

CONCLUSIONS

Our results identify NFκB signaling as an essential molecular regulator for both valve endothelial and interstitial participation in CAVD pathogenesis. Direct demonstration of valve endothelial cell endothelial to mesenchymal transformation transmigration in vivo during CAVD highlights a new cellular population for further investigation in CAVD morbidity. The efficacy of valve-specific NFκB modulation in inhibiting hypercholesterolemic CAVD suggests potential benefits of multicell type integrated investigation for biological therapeutic development and evaluation for CAVD.

Tocotrienols Regulate Bone Loss through Suppression on Osteoclast Differentiation and Activity: A Systematic Review

Background

There are accumulating studies reporting that vitamin E in general exhibits bone protective effects. This systematic review, however discusses the effects of a group of vitamin E isomers, tocotrienols in preventing bone loss through osteoclast differentiation and activity suppression.

Objective

This review is aimed to discuss the literature reporting the effects of tocotrienols on osteoclasts, the cells specialized for resorbing bone.

Results

Out of the total 22 studies from the literature search, only 11 of them were identified as relevant, which comprised of eight animal studies, two in vitro studies and only one combination of both. The in vivo studies indicated that tocotrienols improve the bone health and reduce bone loss via inhibition of osteoclast formation and resorption activity, which could be through regulation of RANKL and OPG expression as seen from their levels in the sera. This is well supported by data from the in vitro studies demonstrating the suppression of osteoclast formation and resorption activity following treatment with tocotrienol isomers.

Conclusion

Thus, tocotrienols are suggested to be potential antioxidants for prevention and treatment of bone-related diseases characterized by increased bone loss.

Stachydrine prevents LPS-induced bone loss by inhibiting osteoclastogenesis via NF-κB and Akt signalling

Osteoclast overactivation‐induced imbalance in bone remodelling leads to pathological bone destruction, which is a characteristic of many osteolytic diseases such as rheumatoid arthritis, osteoporosis, periprosthetic osteolysis and periodontitis. Natural compounds that suppress osteoclast formation and function have therapeutic potential for treating these diseases. Stachydrine (STA) is a bioactive alkaloid isolated from Leonurus heterophyllus Sweet and possesses antioxidant, anti‐inflammatory, anticancer and cardioprotective properties. However, its effects on osteoclast formation and function have been rarely described. In the present study, we found that STA suppressed receptor activator of nuclear factor‐κB (NF‐κB) ligand (RANKL)‐induced osteoclast formation and bone resorption, and reduced osteoclast‐related gene expression in vitro. Mechanistically, STA inhibited RANKL‐induced activation of NF‐κB and Akt signalling, thus suppressing nuclear factor of activated T cells c1 induction and nuclear translocation. In addition, STA alleviated bone loss and reduced osteoclast number in a murine model of LPS‐induced inflammatory bone loss. STA also inhibited the activities of NF‐κB and NFATc1 in vivo. Together, these results suggest that STA effectively inhibits osteoclastogenesis both in vitro and in vivo and therefore is a potential option for treating osteoclast‐related diseases.

Impact of Periprosthetic Fibroblast-Like Cells on Osteoclastogenesis in Co-Culture with Peripheral Blood Mononuclear Cells Varies Depending on Culture System

Co-culture studies investigating the role of periprosthetic fibroblasts (PPFs) in inflammatory osteoclastogenesis reveal contrary results, partly showing an osteoprotective function of fibroblasts and high OPG expression in monolayer. These data disagree with molecular analyses of original periosteolytic tissues. In order to find a more reliable model, PPFs were co-cultivated with peripheral blood mononuclear cells (PBMCs) in a transwell system and compared to conventional monolayer cultures. The gene expression of key regulators of osteoclastogenesis (macrophage colony-stimulating factor (MCSF), receptor activator of NF-κB ligand (RANK-L), osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα)) as well as the ability of bone resorption were analyzed. In monolayer co-cultures, PPFs executed an osteoprotective function with high OPG-expression, low RANK-L/OPG ratios, and a resulting inhibition of osteolysis even in the presence of MCSF and RANK-L. For transwell co-cultures, profound changes in gene expression, with a more than hundredfold decrease of OPG and a significant upregulation of TNFα were observed. In conclusion, we were able to show that a change of culture conditions towards a transwell system resulted in a considerably more osteoclastogenic gene expression profile, being closer to findings in original periosteolytic tissues. This study therefore presents an interesting approach for a more reliable in vitro model to examine the role of fibroblasts in periprosthetic osteoclastogenesis in the future.

Do electrical current and laser therapies improve bone remodeling during an orthodontic treatment with corticotomy?

OBJECTIVES

Evaluate the bone remodeling during orthodontic movement with corticotomy when submitted to low-intensity electrical stimulation application (microcurrent-MC) and low-level laser therapy (LLLT).

MATERIAL AND METHODS

One hundred and fifty Wistar rats were divided into the following 5 groups: (C) submitted to tooth movement; (Cort) tooth movement/corticotomy; (Cort-L) tooth movement/corticotomy/laser AsGaAl 808 nm (4.96J/50s); (Cort-Mc) tooth movement/corticotomy/microcurrent (10 μA/5 min); (Cort-L-Mc) tooth movement/corticotomy and laser/microcurrent alternated. Inflammation, angiogenesis, and osteogenesis were evaluated in the periodontal ligament (PDL) and alveolar bone on the 7th, 14th, and 21st days of orthodontic movement.

RESULTS

The quantification of inflammatory infiltrate, angiogenesis and expression of TGF-β1, VEGF, and collagen type I were favorably modulated by the application of therapies such as low-level laser therapy (LLLT), MC, or both combined. However, electrical stimulation increased fibroblasts, osteoclasts and RANK numbers, birefringent collagen fiber organization, and BMP-7 and IL-6 expression.

CONCLUSIONS

Low-level laser therapy (LLLT) and MC application both improved the process of bone remodeling during orthodontic treatment with corticotomy. Still, electrical current therapy promoted a more effective tooth displacement but presented expected root resorption similar to all experimental treatments.

CLINICAL RELEVANCE

It is important to know the effects of minimally invasive therapies on cellular and molecular elements involved in the bone remodeling of orthodontic treatment associated with corticotomy surgery, in order to reduce the adverse effects in the use of this technique and to establish a safer clinical routine.

A bone-targeting drug-delivery system based on Semaphorin 3A gene therapy ameliorates bone loss in osteoporotic ovariectomized mice

Osteoporosis is a serious health problem worldwide. Semaphorins (Sema) have been described as key molecules involved in the cross-talk between bone cells (osteoblasts/osteoclasts). In this study, we investigated whether plasmid containing Sema3a could ameliorate bone loss in an ovariectomized (OVX) mouse model via (AspSerSer)₆, a selectively bone-targeting moiety. Plasmid pcDNA3.1(+)-Sema3a-GFP was fabricated and transfected cells with the plasmid demonstrated statistically higher levels of Sema3A in vitro (p < 0.001). Mice were ovariectomized and injected twice weekly with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP for four weeks. The aim of the study was twofold: firstly to design an effective bone-targeting drug-delivery system (AspSerSer)₆. Secondly, the effects of Sem3A gene therapy on bone loss was investigated. Here, the targeting selectivity of pcDNA3.1(+)-Sema3a-GFP via (AspSerSer)₆ to the trabecular bone surface was firstly verified by histological observation of frozen sections and immunofluorescence staining. Then, bone microstructure analysis by Micro-CT indicated significantly less bone loss in mice treated with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP compared to the control group (p < 0.05). Furthermore,H&E staining and Safranin O staining of the decalcified sections demonstrated statistically significantly higher bone area/total area in the mice that were injected with (AspSerSer)₆-(STR-R8)+pcDNA3.1(+)-Sema3a-GFP (p < 0.001, p < 0.01,respectively). TRAP staining and immunohistochemistry staining of COL I demonstrated lower numbers of osteoclasts and significantly increased numbers of osteoblasts in the bone-targeting moiety delivering pcDNA3.1(+)-Sema3a-GFP group, when compared to the control group (p < 0.01, p < 0.001,respectively). Together, our findings have identified that, (AspSerSer)₆, a bone-targeting drug-delivery system based on semaphorin3A gene therapy, ameliorated bone loss in osteoporotic ovariectomized mice, by suppressing osteoclastic bone resorption and simultaneously increasing osteoblastic bone formation. Gene therapy by local site-specific Sema3A overexpression might be a potential new strategy for treating osteoporosis and bone defects.

Comparative Evaluation of Cell Viability Immediately After Osteotomy for Implants With Drills and Piezosurgery: Immunohistochemistry Analysis

OBJECTIVE

To evaluate the effect of reusing drills and piezosurgery tips during implant osteotomy on immediate bone cell viability through immunohistochemical analysis.

MATERIALS AND METHODS

Six male rabbits were divided into 2 groups and then divided into 5 subgroups-correspond to drills and tips used 10, 20, 30, 40, and 50 times, respectively. All animals received 10 osteotomies in each tibia, by use of the classic drilling procedure in one group (G1) and the piezosurgery device in the other group (G2). For immunohistochemical technique were utilized the osteoprotegerin, RANKL, osteocalcin, and caspase 3. Control procedures were performed by omitting the primary antibodies (negative control).

RESULTS

Bone formation and resorption responses presented in more intense way during the piezosurgery. The expression of osteocalcin had become quite intense in piezosurgery groups, but with reduced immunostaining from the 30th osteotomy. The caspase 3 showed the viability of the osteoblast from the 20th osteotomy with piezosurgery and remained constant until the 50th.

CONCLUSION

Piezosurgery provides greater osteoblastic cell viability than the system of conventional drilling.

CLINICAL RELEVANCE

This study will provide data so that the authors can recycle the drills and tips for implant placement, thus enabling a better cell viability for osseointegration.

Relationship of Blood Metal Ion Levels and Leukocyte Profiles in Patients With Articular Surface Replacement Metal-on-Metal Hip Replacement

The purpose of this study was to compare blood leukocyte profiles and metal ion concentrations between hip resurfacing arthroplasty (articular surface replacement) patients with and without revision. A total of 25 articular surface replacement patients were recruited (10 with stable implants and 15 undergoing revision). Blood concentrations of chromium (Cr) and cobalt (Co) were measured. Flow cytometry was used to quantify the subpopulations of leukocytes, including CD14⁺ monocytes, CD16⁺ monocytes, CD3⁺ T-lymphocytes, CD19⁺ B-lymphocytes, CD4⁺ helper T-cells, and CD45⁺RA memory vs naïve T-cells. Patients undergoing revision had higher blood Co (mean, 10.85 µg/L) and Cr (mean, 3.19 µg/L) levels than patients with stable implants (mean Co, 3.06 µg/L; mean Cr, 1.07 µg/L) (P<.05). The number of CD4⁺ helper T-cells was higher in patients with stable implants (mean, 842±311 cells/µL) than in patients undergoing revision (mean, 591±208 cells/µL) (P<.05). There was a significant association between total metal ion levels (Co+Cr) and the number of CD14⁺ monocytes (P=.045) and inflammatory CD16⁺ monocytes (P=.046). The authors observed that the increase in blood metal ions was associated with an increase in CD16⁺ monocytes. They believe that continued analysis of blood leukocyte profiles may be helpful in defining differences among failed articular surface replacement, stable articular surface replacement, and failed metal-on-polyethylene implants. [Orthopedics. 2018; 41(3):e424-e431.].

The Effect of RANKL/OPG Balance on Reducing Implant Complications

Despite the phenomenal success of implants particularly in the realms of dentistry and orthopaedics, there are still challenges to overcome. The failure of implants resulting from infection, prosthetic loosening, and non-union continue to be the most notorious examples. The cascade of fracture healing and bone repair, especially with the presence of an implant, is complex because it involves a multifaceted immune response alongside the intricate process of bone formation and remodelling. Bone loss is a serious clinical problem that is frequently accompanied by chronic inflammation, illustrating that there is a convoluted relationship between inflammation and bone erosion. The effects of pro-inflammatory factors play a significant role in initiating and maintaining osteoclastogenesis that results in bone resorption by osteoclasts. This is because there is a disruption of the relative ratio between Receptor Activator of Nuclear Factor κB-Ligand (RANKL) and osteoprotegerin (OPG), which is central to modulating bone repair and remodelling. This review aims to provide a background to the bone remodelling process, the bone repair cascade post-implantation, and the associated complications. Furthermore, current clinical solutions that can influence bone formation via either internal or extrinsic mechanisms will be described. These efficacious treatments for osteolysis via targeting the RANKL/OPG ratio may be crucial to reducing the incidence of related implant failures in the future.

Histological Analysis of Early Osteolysis in Total Ankle Arthroplasty

BACKGROUND

The purpose of this study was to perform a histological comparative analysis of tibiotalar joint samples taken from areas of osteolysis adjacent to total ankle arthroplasties vs control synovial specimens to determine the reaction to and presence of polyethylene (PE) particles.

METHODS

A total of 57 pathology samples were identified in the osteolysis group, while 11 were identified in the control group. For each sample, hematoxylin and eosin, Oil Red O (ORO), and macrophage marker CD163-stained slides were created. Polarized light and ORO stain were used to identify PE particles. The presence of metal particles and giant cell reaction to PE particles were also scored.

RESULTS

Macrophages, PE particles, metallosis, and foreign body giant cell reaction scores were significantly higher in the osteolysis group compared with the control group. In the osteolysis group, ORO staining was positive in 93% (53/57), birefringent material was present in 96.5% (55/57), and macrophage infiltrates were present in 96.5% (55/57). Foreign body giant cell reaction with giant cells surrounding PE particles was present in 49.1% (28/57) of osteolytic specimens. The presence of foreign body giant cell reaction was associated with significantly higher macrophage, ORO, and polarizable material scores. The average time to surgery for osteolysis from the index ankle replacement was 6.0 (range, 0-15) years for the 57 patients in the osteolysis group.

CONCLUSION

This study is the largest ankle arthroplasty histological analysis to show that areas of osteolysis consist of abundant polyethylene wear particles, present both intracellularly and extracellularly. Furthermore, these areas were associated with a CD163⁺ macrophage infiltrate and frequently a foreign body reaction with giant cells engulfing PE particles. It is likely that implant wear particles play a significant role in osteolysis based on the histopathology.

LEVEL OF EVIDENCE

Level III, retrospective comparative series.

Factors regulating bone remodeling processes in aseptic implant loosening

This study was undertaken to screen periprosthetic tissues (PPTs) under specified conditions for a series of molecular components and describe them in bone remodeling processes within aseptic loosening. PPT samples were obtained from patients undergoing revision surgery of endoprostheses (n = 24) and synovial tissues from patients with OA (control) (n = 18), patients with any form of inflammatory arthritides were excluded. Tissue samples were examined via microbiology, histology (H&E, TRAP), immunohistochemistry (CD68/anti-S100a4), quantitative real-time PCR (ALP, COL1A1, cathepsin K, M-CSF, MMP13, OPG, RANK, RANKL, TNF-α, and TRAP) and an endotoxin-assay. PPT samples contained a variety of cellular components and stained positive for TRAP (56%), CD68 (100%), and S100a4 (100%). Wear debris were found in cells staining positive for CD68 and S100a4. In PPTs significantly higher ALP, COL1A1, MMP-13, RANK, RANKL, and TRAP expression were found along with a significantly higher RANKL/OPG ratio and a significantly lower OPG expression. No significant difference was observed for M-CSF, TNF-α, cathepsin K, and endotoxin levels. In conclusion we found osteogenic proteins (ALP, COL1A1), a proteolytic enzyme (MMP-13), markers for osteoclast differentiation (RANK, RANKL), and osteoclast activity (TRAP) to be increased in PPT, whereas OPG expression decreased significantly in comparison to control. We present data about a large series of molecular components in PPT and describe novel and key findings about their expression levels in regards to aseptic implant loosening. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:248-257, 2017.

The Effect of Orthognathic Surgery on Osteoprotegerin as Immunological Caliper of Bone Healing

BACKGROUND:

Osteoprotegerin (OPG) is considered to be the cytokine that plays an important role in the healing process. OPG regulates bone cell biology, osteoblast–osteoclast, bone-immune cross-talk and maintenance of bone mass. It plays an important role in the development, induction, and repair of bone. Orthognathic surgery as multiples segmental osteotomies has been taken as a model surgery to assess the changes in osteoprotegerin levels in the post-operative bone healing period.

AIM:

The aim of the study was to evaluate OPG as immunological caliper of bone healing.

MATERIAL AND METHODS:

OPG was evaluated in nine patients seeking orthognathic surgery. Patients were examined and checked to be medically and immunologically free prior to surgery. Blood samples were collected immediate pre-operative as control group and for six weeks post-operative as study group.

RESULTS:

Data were collected from nine consecutive patients. The results showed higher levels of OPG. it showed significant increase in the immediate post-operative value (p = 0.001) which started to increase gradually during the six weeks (p < 0.001).

CONCLUSIONS:

Significant higher levels of OPG during the healing period of orthognathic surgery suggest the its use as immunological caliper of bone healing.

Alendronate stimulates osteoprotegerin expression in fibroblasts from periprosthetic membrane

PURPOSE

Aseptic loosening of an implant after total joint arthroplasty is still a major complication that results from periprosthetic osteolysis. Fibroblasts in the interface membrane express receptor activator of nuclear factor kappa B ligand (RANKL) and stimulate osteoclast formation. Studies demonstrate that through the control of osteoclastic bone loss bisphosphonates inhibit wear particle-induced bone resorption around total hip arthroplasty. The majority of bisphosphonates studies have focused on their effects on osteoblasts and osteoclasts. Little attention has been paid to their action on fibroblasts.

METHODS

We isolated fibroblasts from the interface membrane that was obtained when revision hip arthroplasty was performed because of aseptic loosening. Fibroblasts were stimulated with alendronate. RANKL and osteoprotegerin (OPG) assays were performed using enzyme-linked immunosorbent assay kit and real time Reverse Transcription- Polymerase Chain Reaction (RT-PCR).

RESULTS

We found that alendronate stimulated OPG mRNA and protein expression in a time and dose dependent manner. By contrast, alendronate did not affect RANKL expression.

CONCLUSIONS

The results indicate that alendronate modulated OPG production by fibroblasts from periprosthetic membrane, which may prove helpful for the inhibition of bone loss during aseptic loosening following total joint arthroplasty.

Wear products of total hip arthroplasty: The case of polyethylene

Among the bearing surfaces involved in a total hip arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) is the weak link. It is submitted to the friction of a harder bearing, producing wear particles, which, in turn, initiate an inflammatory reaction ultimately leading to osteolysis. This kind of bone deterioration sometimes turns out to an aggressive granuloma and may provoke implant loosening. Wear resistance of UHMWPE depends on its molecular weight and crystallinity. Some steps of the manufacturing process were improved to optimize its tribological properties and to slow down degradation resulting from mechanical (abrasion) and chemical (oxidation) phenomena. Its preparation and conservation must be performed in an inert atmosphere, i.e. without ambient oxygen. Its resistance to abrasion depends on its cross-linking degree. Its cross-linking rate was observed to increase proportionally to the irradiation doses, improving its wear resistance. However, its mechanical properties are impaired and moreover, it becomes oxidation sensitive. It is therefore necessary to submit it to a thermal treatment to eliminate free radicals that were produced during irradiation. More recently impregnation by vitamin E, a powerful anti-oxidant product, was proposed to preserve the polymer from in vivo oxidation while maintaining its mechanical properties. We raised the hypothesis that last-generation UHMWPE could offer the same wear resistance as the most performing bearings (ceramic-on-ceramic). Recent clinical results confirm the tribological performance of highly crosslinked UHMWPE in vivo. However, it remains to be seen whether this excellent wear resistance would persist under eccentric load such as edge loading, and if, in the long run, this kind of bearing proves capable of reducing the risk of osteolysis in young and active patients.

Role of RANKL in the regulation of NFATc1 and c‑Src mRNA expression in osteoclast‑like cells

This study was designed to determine the effects of receptor activator of nuclear factor κB ligand (RANKL) on the mRNA expression of nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1) and c‑Src in rat osteoclast‑like cells. The marrow cells were exposed to macrophage colony-stimulating factor (M‑CSF; 25 ng/ml) and different concentrations of RANKL (0, 50, 75 and 100 ng/ml) for 9 days. The mRNA expression of NFATc1 and c‑Src was determined by polymerase chain reaction. Compared with the M‑CSF (25 ng/ml)+RANKL (0 ng/ml) group, the levels of NFATc1 and c‑Src mRNA expression were significantly increased in the M‑CSF (25 ng/ml)+RANKL (75 and 100 ng/ml) groups (P<0.01, P<0.01, P<0.01 and P<0.01, respectively). Compared with the M‑CSF (25 ng/ml)+RANKL (50 ng/ml) group, the levels of NFATc1 and c‑Src mRNA expression was significantly increased in the M‑CSF (25 ng/ml)+RANKL (75 and 100 ng/ml) groups (P<0.05, P<0.01, P<0.01 and P<0.01, respectively). Compared with M‑CSF (25 ng/ml)+RANKL (75 ng/ml) group, the levels of NFATc1 and c‑Src mRNA expression was significantly increased in the M‑CSF (25 ng/ml)+RANKL (100 ng/ml) group, (P<0.01 and P<0.01, respectively). These data suggest that RANKL could regulate the expression of NFATc1 and c‑Src mRNA in the marrow culture system.

Evidence that osteocyte perilacunar remodelling contributes to polyethylene wear particle induced osteolysis

Periprosthetic osteolysis (PO) leading to aseptic loosening, is the most common cause of failure of total hip replacement (THR) in the mid- to long-term. Polyethylene (PE) particulates from the wear of prosthesis liners are bioactive and are implicated in the initiation and or progression of osteolysis. Evidence exists that cells of the osteoblast/osteocyte lineage are affected by PE particles and contribute to the catabolic response by promoting osteoclastic bone resorption. In this study, we hypothesised that osteocytes contribute directly to PO by removing bone from their perilacunar matrix. Osteocyte responses to ultra-high molecular weight PE (UHMWPE) particles were examined in vitro in human primary osteocyte-like cultures, in vivo in the mouse calvarial osteolysis model, and in the acetabulum of patients undergoing revision total hip replacement (THR) surgery for PO. Osteocytes exposed to UHMWPE particles showed upregulated expression of catabolic markers, MMP-13, carbonic anhydrase 2 (CA2), cathepsin K (CTSK) and tartrate resistant acid phosphatase (TRAP), with no effect on cell viability, as assessed by Caspase 3 activity. Consistent with this catabolic activity causing perilacunar bone loss, histological analysis of calvarial sections from mice exposed to UHMWPE revealed a significant (p<0.001) increase in osteocyte lacunar area (Lac.Ar) compared to sham-operated animals. Furthermore, acetabular biopsies from patients with PO also showed significantly (p<0.001) increased osteocyte lacunar size in trabecular bone adjacent to PE particles, compared with osteocyte lacunar size in bone from primary THR patients. Together, these findings suggest a previously unrecognised action of UHMWPE wear particles on osteocytes, which directly results in a loss of osteocyte perilacunar bone. This action may exacerbate the indirect pro-osteoclastic action of UHMWPE-affected osteocytes, previously shown to contribute to aseptic loosening of orthopaedic implants.

STATEMENT OF SIGNIFICANCE

This study addresses the clinical problem of periprosthetic osteolysis, bone loss in response to polyethylene wear particles derived from materials used in orthopaedic implants. Periprosthetic osteolysis has been thought to be due largely to wear particles stimulating the activity of bone resorbing osteoclasts. However, in this study we demonstrate for the first time that polyethylene particles stimulate another type of bone loss, mediated by the direct activity of bone mineral embedded osteocytes, termed osteocytic osteolysis or osteocyte perilacunar remodelling. This study provides new mechanistic insight into wear-particle mediated bone loss and represents a new paradigm for the way in which bone cells, namely osteocytes, the key controlling cell type in bone, react to biomaterials.

Inhibitory Effects of Lanthanum Chloride on Wear Particle-Induced Osteolysis in a Mouse Calvarial Model

Osteolysis is a bone disorder associated with progressive destruction of bone tissues. However, the effects of lanthanum chloride (LaCl3) on osteolysis remain unknown. Therefore, the aim of this study was to determine the effects of LaCl3 on osteolysis in vivo. In a mouse calvarial model, C57BL/6J mice were injected with wear particles with or without LaCl3. Microcomputed tomography, hematoxylin and eosin staining, and tartrate-resistant acid phosphatase staining were performed for the pathological characterization of calvariae, and eight calvariae per group were prepared for the assay of TNF-α, IL-1β, and RANKL secretion using quantitative enzyme-linked immunosorbent assay (ELISA). In mice treated with high-dose LaCl3, particle-induced osteolysis and inflammatory reaction were reduced compared with that in the vehicle-treated control. Moreover, treatment with high-dose LaCl3 suppressed the wear particle-induced decrease in bone mineral content, bone mineral density, and bone volume fraction. Bone destruction and resorption were higher in the LaCl3-treated group than in the saline-treated group but lower than those in the wear particle group. Finally, our results showed that treatment with a high dose of LaCl3 suppressed osteoclastogenesis. Thus, LaCl3 may represent a novel therapeutic agent for the treatment or prevention of wear particle-induced osteolysis and aseptic loosening.

Caffeic acid phenethyl ester abrogates bone resorption in a murine calvarial model of polyethylene particle-induced osteolysis

Particle-induced bone loss by osteoclasts is a common cause of aseptic loosening around implants. This study investigates whether caffeic acid phenethyl ester (CAPE), a potent and specific inhibitor of nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1 and nuclear factor kappa B, at a low dose reduces bone resorption in a murine calvarial model of polyethylene (PE) particle-induced osteolysis. The effects of particles and CAPE treatment on gastrointestinal tract (GIT) histopathology were also evaluated. Mice were scanned using in vivo animal micro-computed tomography (μCT) as a baseline measurement. PE particles (2.82 × 10(9) particles/mL) were implanted over the calvariae on day 0. CAPE was administered subcutaneously (1 mg/kg/day) at days 0, 4, 7 and 10. Mice were killed at day 14 and serum was analysed for Type-1 carboxyterminal collagen crosslinks (CTX)-1 and osteoclast-associated receptor (OSCAR) levels. Ex vivo μCT scans were conducted to assess bone volume (BV) change and percentage area of calvarial surface resorbed. Calvarial and GIT tissue was processed for histopathology. By day 14, PE particles significantly induced calvarial bone loss compared with control animals as evidenced by resorption areas adjacent to the implanted PE in three-dimensional μCT images, an increase in percentage of resorbed area (p = 0.0022), reduction in BV (p = 0.0012) and increased Tartrate-resistant acid phosphatase positive cells. Serum CTX-1 (p = 0.0495) and OSCAR levels (p = 0.0006) significantly increased in the PE implant group. CAPE significantly inhibited PE particle-induced calvarial osteolysis, as evidenced by a significant reduction in surface bone resorption (p = 0.0012) and volumetric change (p = 0.0154) compared with PE only, but had no effect on systemic CTX-1. Neither particles nor CAPE had an effect on GIT histopathology.

Parthenolide reduces empty lacunae and osteoclastic bone surface resorption induced by polyethylene particles in a murine calvarial model of peri-implant osteolysis

The study aimed to determine the effects of parthenolide (PAR) on bone volume (BV) and bone surface resorption as assessed by live-animal microcomputed tomography (μCT) and possible osteocyte death as indicated by empty lacunae histologically in polyethylene (PE) particle-induced calvarial osteolysis in mice. Baseline μCT scans were conducted 7 days preimplantation of 2 × 10(8) PE particles/mL over the calvariae (day 0). PAR at 1 mg/kg/day was subcutaneously injected on days 0, 4, 7, and 10. At day 14, BV and surface resorption was analyzed with μCT. Calvarial tissue was processed for histomorphometric osteocyte evaluation. Serum was analyzed for type-1 carboxy-terminal collagen crosslinks (CTX-1) and osteoclast associated receptor (OSCAR) levels by ELISA. PE significantly decreased BV (p = 0.0368), increased surface bone resorption area (p = 0.0022), and increased the percentage of empty lacunae (p = 0.0043). Interestingly, PAR significantly reduced the resorption surface area (p = 0.0022) and the percentage of empty osteocyte lacunae (p = 0.0087) in the PE-calvariae, but it did not affect BV, serum CTX-1 or OSCAR levels. The ability of PAR to inhibit PE-induced surface bone erosion may better reflect the in vivo situation, where bone resorption occurs on the surface at the bone-implant interface and may also be related to the role of osteocytes in this pathology.

Osteoimmunology: Major and Costimulatory Pathway Expression Associated with Chronic Inflammatory Induced Bone Loss

The field of osteoimmunology has emerged in response to the range of evidences demonstrating the close interrelationship between the immune system and bone metabolism. This is pertinent to immune-mediated diseases, such as rheumatoid arthritis and periodontal disease, where there are chronic inflammation and local bone erosion. Periprosthetic osteolysis is another example of chronic inflammation with associated osteolysis. This may also involve immune mediation when occurring in a patient with rheumatoid arthritis (RA). Similarities in the regulation and mechanisms of bone loss are likely to be related to the inflammatory cytokines expressed in these diseases. This review highlights the role of immune-related factors influencing bone loss particularly in diseases of chronic inflammation where there is associated localized bone loss. The importance of the balance of the RANKL-RANK-OPG axis is discussed as well as the more recently appreciated role that receptors and adaptor proteins involved in the immunoreceptor tyrosine-based activation motif (ITAM) signaling pathway play. Although animal models are briefly discussed, the focus of this review is on the expression of ITAM associated molecules in relation to inflammation induced localized bone loss in RA, chronic periodontitis, and periprosthetic osteolysis, with an emphasis on the soluble and membrane bound factor osteoclast-associated receptor (OSCAR).

Anti-RANKL treatment improves screw fixation in cancellous bone in rats

Bisphosphonates improve implant fixation in randomised clinical trials of knee prostheses, hip prostheses and dental implants. However, a limited amount of bone resorption is required for bisphosphonates to exert an effect. Anti-RANKL treatment does not have this limitation, and we therefore tested whether if they might be more effective for improvement of implant fixation. This is of interest, as anti-RANKL treatment with denosumab is now in common clinical use. Male SD rats received a stain-less steel screw in the right proximal tibia and a drill hole in the left (n = 42). They were randomised to subcutaneous injections of either alendronate (20 μg/kg/day), alendronate (200 μg/kg/day), osteoprotegerin with an Fc tag (OPG-Fc; 8 mg/kg, twice weekly), or saline control. After 4 weeks, the fixation of the steel screw was measured by pull-out test. The tibia with the drill hole was evaluated with μCT. OPG-Fc increased the pull-out force compared to saline controls by 153% (p < 0.001). There was no significant difference between OPG-Fc and the alendronate groups. OPG-Fc increased the bone density (BV/TV) in the previous drill hole compared to controls 7-fold (p < 0.001). This increase was higher than with any alendronate dose (p < 0.001). OPG-Fc increased the bone density of the L5 vertebral body, but there was no significant difference between OPG-Fc and alendronate. Our results suggest that screw fixation in cancellous bone can be dramatically improved by an anti-RANKL agent. The effect was comparable to very high bisphosphonate doses. Screw insertion in cancellous bone elicits a metaphyseal fracture healing response, and our findings might be relevant not only for implant fixation, but also for fracture healing in cancellous bone.

Incorporation of raloxifene-impregnated allograft around orthopedic titanium implants impairs early fixation but improves new bone formation

BACKGROUND

The anti-osteoporotic drug raloxifene reduces the risk of vertebral fractures by increasing bone mass density. We investigated whether raloxifene offers any benefits in augmenting early fixation of orthopedic implants in the setting of impaction bone grafting.

METHODS

24 non-weight-bearing grafted gap implants were inserted bilaterally into the tibia of 12 dogs. The 2.5-mm peri-implant gap was filled with either raloxifene-impregnated or untreated bone allograft. Implants were harvested after 28 days. Implant fixation was assessed by mechanical testing and histomorphometric evaluation.

RESULTS

Raloxifene-treated allograft reduced early implant fixation compared to untreated allograft, as measured by inferior maximum shear strength (p < 0.001) and apparent shear stiffness (p = 0.001). We found that the raloxifene group had more newly formed bone in the gap around the implant (p = 0.02), but also less allograft (p = 0.03).

INTERPRETATION

The accelerated allograft resorption in the raloxifene group explained the impaired early fixation, despite its stimulation of new bone formation. Our results with local and possible high-dose treatment are not consistent with current theory regarding the mechanism of how systemic raloxifene administration counteracts the decrease in BMD in postmenopausal women. Instead of being solely anti-resorptive as generally held, our results indicate a possible anabolic side of raloxifene.