The role of osteoclast differentiation in aseptic loosening

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Nano sized gallium oxide surface features for enhanced antimicrobial and osteo-integrative responses

Gallium oxide has known beneficial osteo-integrative properties. This may have importance for improving the osteointegration of orthopedic implants. At high concentrations gallium is cytotoxic. Therefore, integration of gallium into implant devices must be carefully controlled to limit its concentration and release. A strategy based on surface doping of gallium although challenging seems an appropriate approach to limit dose amounts to minimize cytotoxicity and maximize osteointegration benefits. In this work we develop a novel form of patterned surface doping via a block copolymer-based surface chemistry that enables very low gallium content but enhanced osteointegration as proven by comprehensive bioassays. Polystyrene-b-poly 4vinyl pyridine (PS-b-P4VP) BCP (block copolymer) films were produced on surfaces. Selective infiltration of the BCP pattern with a gallium salt precursor solution and subsequent UV-ozone treatment produced a surface pattern of gallium oxide nanodots as evidenced by atomic force and scanning electron microscopy. A comprehensive study of the bioactivity was carried out, including antimicrobial and sterility testing, gallium ion release kinetics and the interaction with human marrow mesenchymal stomal cells and mononuclear cells. Comparing the data from osteogenesis media assay tests with osteoclastogenesis tests demonstrated the potential for the gallium oxide nanodot doping to improve osteointegration properties of a surface.

Desferrioxamine alleviates UHMWPE particle-induced osteoclastic osteolysis by inhibiting caspase-1-dependent pyroptosis in osteocytes

BACKGROUND

Cell death and inflammation are the two important triggers of wear particle-induced osteolysis. Particles, including cobalt-chromium-molybdenum and tricalcium phosphate, have been reported to induce pyroptosis in macrophages and osteocytes. Although macrophage pyroptosis facilitates osteoclastic bone resorption and osteolysis, whether osteocyte pyroptosis is involved in osteoclastic osteolysis still needs further investigation. Desferrioxamine (DFO), an FDA-approved medication and a powerful iron chelator, has been proven to reduce ultrahigh-molecular-weight polyethylene (UHMWPE) particle-induced osteolysis. However, whether DFO can ameliorate UHMWPE particle-induced osteolysis by decreasing pyroptosis in osteocytes is unknown.

RESULTS

A mouse calvarial osteolysis model and the mouse osteocyte cell line MLO-Y4 was used, and we found that pyroptosis in osteocytes was significantly induced by UHMWPE particles. Furthermore, our findings uncovered a role of caspase-1-dependent pyroptosis in osteocytes in facilitating osteoclastic osteolysis induced by UHMWPE particles. In addition, we found that DFO could alleviate UHMWPE particle-induced pyroptosis in osteocytes in vivo and in vitro.

CONCLUSIONS

We uncovered a role of caspase-1-dependent pyroptosis in osteocytes in facilitating osteoclastic osteolysis induced by UHMWPE particles. Furthermore, we found that DFO alleviated UHMWPE particle-induced osteoclastic osteolysis partly by inhibiting pyroptosis in osteocytes. Schematic of DFO reducing UHMWPE particle-induced osteolysis by inhibiting osteocytic pyroptosis. Wear particles, such as polymers, generated from prosthetic implant materials activate canonical inflammasomes and promote the cleavage and activation of caspase-1. This is followed by caspase-1-dependent IL-β maturation and GSDMD cleavage. The N-terminal fragment of GSDMD binds to phospholipids on the cell membrane and forms holes in the membrane, resulting in the release of mature IL-β and inflammatory intracellular contents. This further facilitates osteoclastic differentiation of BMMs, resulting in excessive bone resorption and ultimately leading to prosthetic osteolysis. DFO reduces UHMWPE particle-induced osteolysis by inhibiting osteocytic pyroptosis.

Niobium carbide (MXene) reduces UHMWPE particle-induced osteolysis

Joint replacement surgery is one of the orthopedic surgeries with high successful rates; however, wear debris generated from prostheses can ultimately lead to periprosthetic osteolysis and failure of the implant. The implant-derived particulate debris such as ultrahigh molecular weight polyethylene (UHMWPE) can initiate the local immune response and recruit monocytic cells to phagocytose particles for generating reactive oxygen species (ROS). ROS induces osteoclastogenesis and macrophages to secrete cytokines which ultimately promote the development of osteolysis. In this work, we develop the few-layered Nb2C (FNC) as an antioxidant which possesses the feature of decreasing the production of cytokines and inhibiting osteoclastogenesis by its ROS adsorption. Moreover, local injection of FNC attenuates the UHMWPE-induced osteolysis in a mouse calvarial model. In sum, our results suggest that FNC can be used for treating osteolytic bone disease caused by excessive osteoclastogenesis.

Staphylococcus aureus and Acinetobacter sp. inhibit osseointegration of orthopaedic implants

Bacterial infections routinely cause inflammation and thereby impair osseointegration of orthopaedic implants. Acinetobacter spp., which causes osteomyelitis following trauma, on or off the battlefield, was however reported to cause neither osteomyelitis nor osteolysis in rodents. We therefore compared the effects of Acinetobacter strain M2 to those of Staphylococcus aureus in a murine implant infection model. Sterile implants and implants with adherent bacteria were inserted in the femur of mice. Bacterial burden, levels of pro-inflammatory cytokines, and osseointegration were measured. All infections were localized to the implant site. Infection with either S. aureus or Acinetobacter strain M2 increased the levels of pro-inflammatory cytokines and the chemokine CCL2 in the surrounding femurs, inhibited bone formation around the implant, and caused loss of the surrounding cortical bone leading to decreases in both histomorphometric and biomechanical measures of osseointegration. Genetic deletion of TLR2 and TLR4 from the mice partially reduced the effects of Acinetobacter strain M2 on osseointegration but did not alter the effects of S. aureus. This is the first report that Acinetobacter spp. impair osseointegration of orthopaedic implants in mice and the murine model developed for this study will be useful for future efforts to clarify the mechanism of implant failure due to Acinetobacter spp. and to assess novel diagnostic tools or therapeutic agents.

Virtual screening identified natural Keap1-Nrf2 PPI inhibitor alleviates inflammatory osteoporosis through Nrf2-mir214-Traf3 axis

Overactive osteoclastogenesis is involved in the inflammatory bone loss and could be target for therapy. Here, we applied transcription factor enrichment analysis using public inflammatory osteolysis datasets and identified Nrf2 as the potential therapeutic target. Additionally, in-silico screening was performed to dig out Nrf2-Keap1 PPI inhibitor and Forsythoside-β was found to be the best-performing PHG compound. We firstly tested the effect of Forsythoside-β in inflammatory osteoporosis models and found it was able to attenuate the bone loss by inhibiting osteoclastogenesis and activating Nrf2-signaling in vivo. Forsythoside-β was capable to suppress the differentiation of osteoclast in time and dose-dependent manners in vitro. Further, Forsythoside-β could inhibit the production of reactive oxygen species and induce Nrf2 nuclear-translocation by interrupting Nrf2-Keap1 PPI. Recently, Nrf2 was identified as the epigenetic regulator modulating levels of miRNA in various diseases. We discovered that Forsythoside-β could suppress the expression of mir-214-3p, one of most variable miRNAs during osteoclastogenesis. To clarify the undermining mechanism, by utilizing chip-seq dataset, we found that Nrf2 could bind to promoter of mir-214-3p and further regulate this miRNA. Collectively, Forsythoside-β was able to prevent bone loss through Nrf2-mir-214-3p-Traf3 axis, which could be a promising candidate for treating inflammatory bone loss in the future.

miR-9-5p promotes wear-particle-induced osteoclastogenesis through activation of the SIRT1/NF-κB pathway

To explore the potential function of miR-9-5p in wear-particle-induced osteoclastogenesis, we examined the expression of SIRT1 and miR-9-5p in particle-induced osteolysis (PIO) mice calvariae and polyethylene (PE)-induced RAW 264.7 cells and found that SIRT1 expression was downregulated while miR-9-5p expression was upregulated in both models. We then verified that miR-9-5p targets SIRT1. miR-9-5p was found to promote PE-induced osteoclast formation from RAW 264.7 cells by tartrate-resistant acid phosphatase staining and detection of osteoclast markers, and miR-9-5p activation of the SIRT1/NF-kB signaling pathway was found in cells by detecting the expression of SIRT1/NF-kB pathway-related proteins and rescue assays. In conclusion, we found that miR-9-5p activated the SIRT1/NF-κB pathway to promote wear-particle-induced osteoclastogenesis. miR-9-5p may be a useful therapeutic target for PIO remission and treatment.

Enalapril inhibits inflammatory osteolysis induced by wear debris in a mouse model

Objective

Aseptic loosening, the most frequent complication after total joint replacement, is probably caused by an inflammatory response to the shedding of wear debris from the implant. The only effective treatment is surgical revision. Using a mouse model, we investigated whether enalapril inhibits wear debris-induced inflammatory osteolysis.

Methods

Titanium (Ti) alloy particles were introduced, and calvarial bone from syngeneic mice was implanted into air pouches established in BALB/c mice. Histological and molecular analyses were performed with inflammatory tissue samples obtained from mice treated with and without enalapril.

Results

Enalapril inhibited tissue inflammation and inflammatory osteolysis induced by Ti particles, reducing pouch membrane thickness and decreasing inflammatory cell infiltration. In addition, enalapril inhibited the expression of the inflammatory cytokines vascular endothelial growth factor and tumor necrosis factor-α.

Conclusions

Our study provides evidence that enalapril inhibits Ti particle-induced inflammatory osteolysis, and it may be a potentially useful treatment for aseptic loosening.

Lysosomal disruption by orthopedic wear particles induces activation of the NLRP3 inflammasome and macrophage cell death by distinct mechanisms

Wear particles from orthopedic implants cause aseptic loosening, the leading cause of implant revisions. The particles are phagocytosed by macrophages leading to activation of the nod-like receptor protein 3 (NLRP3) inflammasome and release of interleukin-1β (IL-1β) which then contributes to osteoclast differentiation and implant loosening. The mechanism of inflammasome activation by orthopedic particles is undetermined but other particles cause the cytosolic accumulation of the lysosomal cathepsin-family proteases which can activate the NLRP3 inflammasome. Here, we demonstrate that lysosome membrane disruption causes cathepsin release into the cytoplasm that drives both inflammasome activation and cell death but that these processes occur independently. Using wild-type and genetically-manipulated immortalized murine bone marrow derived macrophages and pharmacologic inhibitors, we found that NLRP3 and gasdermin D are required for particle-induced IL-1β release but not for particle-induced cell death. In contrast, phagocytosis and lysosomal cathepsin release are critical for both IL-1β release and cell death. Collectively, our findings identify the pan-cathepsin inhibitor Ca-074Me and the NLRP3 inflammasome inhibitor MCC950 as therapeutic interventions worth exploring in aseptic loosening of orthopedic implants. We also found that particle-induced activation of the NLRP3 inflammasome in pre-primed macrophages and cell death are not dependent on pathogen-associated molecular patterns adherent to the wear particles despite such pathogen-associated molecular patterns being critical for all other previously studied wear particle responses, including priming of the NLRP3 inflammasome.

DAPT inhibits titanium particle-induced osteolysis by suppressing the RANKL/Notch2 signaling pathway

Artificial prosthesis is wildly used in clinical medicine for degenerative disease such as osteoclast-related diseases. However, the material wear particles released from the surface of prostheses cause prosthetic loosening as a result of aseptic osteolysis in long-term use. Therefore, it is important to find an agent that inhibits the formation and function of osteoclast for therapeutic use. Notch signaling pathway plays a lot of roles in cell proliferation, differentiation, and apoptosis. However, the role of Notch signaling pathway in osteoclastogenesis remains unclear. The aim of this study is to assess the effects of γ-secretase inhibitor DAPT on osteoclastogenesis via Notch signaling pathway in vitro and titanium particle-induced osteolysis in vivo. In animal experiments, the inhibitory effect of DAPT on titanium particle-induced osteolysis in a mouse calvaria model was demonstrated. Interestingly, few resorption pits were observed following administration of DAPT and almost no osteoclasts formed at high concentration of DAPT. in vitro experiments revealed the mechanism of the effects of DAPT on osteoclastogenesis. DAPT inhibited the formation and function of osteoclast by blocking RANKL-induced Notch2-NF-κB complex signaling pathway. In conclusion, these results indicated that DAPT could prevent and cure titanium particle-induced prosthetic loosening and other osteoclast-related diseases.

[Establishment of artificial joint aseptic loosening mouse model by cobalt-chromium particles stimulation]

Objective

To explore the feasibility of establishment of a artificial joint aseptic loosening mouse model by cobalt-chromium particles stimulation.

Methods

Twenty-four 8-week-old male severe combined immunodeficient (SCID) mice were divided into experimental group ( n=12) and control group ( n=12). The titanium nail was inserted into the tibial medullary cavity of mouse in the two groups to simulate artificial joint prosthesis replacement. And the cobalt-chromium particles were injected into the tibial medullary cavity of mouse in experimental group. The survival of the mouse was observed after operation; the position of the titanium nail and the bone mineral density of proximal femur were observed by X-ray film, CT, and Micro-CT bone scanning; and the degree of dissolution of the bone tissue around the tibia was detected by biomechanical test and histological staining.

Results

Two mice in experimental group died, and the rest of the mice survived until the experiment was completed. Postoperative imaging examination showed that there was no obvious displacement of titanium nails in control group, and there were new callus around the titanium nails. In experimental group, there was obvious osteolysis around the titanium nails. The bone mineral density of the proximal tibia was 91.25%±0.67%, and the maximum shear force at the tibial nail-bone interface was (5.93±0.85) N in experimental group, which were significantly lower than those in control group [102.07%±1.87% and (16.76±3.09) N] ( t=5.462, P=0.041; t=3.760, P=0.046). Histological observation showed that a large number of inflammatory cells could be seen around the titanium nails in experimental group, while there was no inflammatory cells, and obvious bone tissue formation was observed in control group.

Conclusion

The artificial joint aseptic loosening mouse model can be successfully established by cobalt-chromium particles stimulation.

Blood Metal Ion Release After Primary Total Knee Arthroplasty: A Prospective Study

Objectives

To investigate the course of in vivo blood metal ion levels in patients undergoing primary total knee arthroplasty (TKA) and to investigate potential risk factors associated with metal ion release in these patients.

Methods

Twenty‐five patients with indication for TKA were included in this prospective study. Whole blood metal ion analysis was performed pre‐operatively and at 1 week, 6 weeks, 3 months, 6 months, and 12 months postoperatively. Clinical scores were obtained using the American Knee Society Score (AKSS) and the Oxford Knee Score (OKS) at each follow‐up and patientsʼ activity levels were assessed by measuring the mean annual walking cycles at 12 months follow‐up. Anteroposterior and lateral radiographs of the operated knee were evaluated postoperatively and at 12‐month follow‐up with regard to implant position and radiological signs of implant loosening. Correlation analysis using multivariate linear regression was performed to investigate the influence of different variables (age, gender, functional scores, number of walking cycles, and body mass index [BMI]) on blood cobalt ion concentrations.

Results

Mean metal ion levels of cobalt, chromium, molybdenum, and titanium were 0.28 μg/L (SD, 0.14), 0.43 μg/L (SD, 0.49), 0.62 μg/L (SD, 0.45), and 1.96 μg/L (SD, 0.98), respectively at 12‐month follow‐up. Mean cobalt ion levels significantly increased 1‐year after surgery compared to preoperative measurements. There was no statistically significant increase of mean metal ion levels of chromium, titanium, and molybdenum at 1‐year follow‐up. Overall, metal ion levels were low and no patient demonstrated cobalt ion levels above 1 μg/L. Postoperative radiographs demonstrated well‐aligned TKAs in all patients and no signs of osteolysis or implant loosening were detected at 1‐year follow‐up. Both the AKSS and OKS significantly improved during the course of the study up to the final follow‐up. Multivariate regression analysis did not show a statistically significant correlation between the tested variables and blood cobalt ion concentrations.

Conclusion

A statistically significant increase of mean cobalt ion concentration at 1‐year follow‐up was found in this cohort of patients with well‐functioning TKA, although overall blood metal ion levels were relatively low. Despite low systemic metal ion concentrations seen in this cohort, the local effects of increased metal ion concentrations in the periprosthetic environment on the long‐term outcome of TKA should be further investigated.

Effects of staphylococcal infection and aseptic inflammation on bone mass and biomechanical properties in a rabbit model

Background/objective

Orthopaedic implants are important devices aimed at relieving pain and improving mobility. Staphylococcal infection and aseptic loosening are two common events associated with inflammatory osteolysis that lead to implant failures. Bone mass and biomechanical properties are important indicators that could influence patient outcomes after revision surgery. However, the dynamics of bacterial infections and their influence on bone mass and biomechanical properties remain unclear. Hence, in this study, we developed rabbit aseptic inflammation and staphylococcal infection models to determine the effects of coagulase-positive and coagulase-negative bacterial infection, as well as aseptic inflammation, on the mass and biomechanical properties of the bone.

Methods

Sixty New Zealand white rabbits were randomly assigned to 6 groups, and each group had 10 rabbits. The medullary cavities in rabbits of each group were injected with phosphate-buffered saline (100 ​μL), titanium (Ti)-wear particles (300 μg/100 ​μL), a low concentration of Staphylococcus epidermidis (10⁵/100 ​μL), a high concentration of S. epidermidis (10⁸/100 ​μL), a low concentration of Staphylococcus aureus (10⁵/100 ​μL), and a high concentration of S. aureus (10⁸/100 ​μL), respectively. At four and eight weeks after surgery, the rabbits were sacrificed, and the tibias on the surgical side were analysed via histopathology, microcomputed tomography, and nanoindentation testing.

Results

Histopathological analysis demonstrated that inflammatory responses and bacterial loads caused by high concentrations of staphylococcal infections, particularly coagulase-positive staphylococci, are more detrimental than low concentrations of bacterial infection and Ti-wear particles. Meanwhile, microcomputed tomography and nanoindentation testing showed that high concentrations of S. aureus caused the highest loss in bone mass and most biomechanical function impairment in rabbits experiencing aseptic inflammation and staphylococcal infections.

Conclusions

Inflammatory osteolysis caused by a high concentration of coagulase-positive staphylococci is significantly associated with low bone mass and impaired biomechanical properties.

The translational potential of this article

It is necessary to obtain an overall assessment of the bone mass and biomechanical properties before revision surgery, especially when S. aureus infection is involved. In addition, a better understanding of these two parameters might help develop a reasonable treatment regimen and reduce the risk of adverse events after revision surgery.

Phillyrin Attenuates Osteoclast Formation and Function and Prevents LPS-Induced Osteolysis in Mice

As the sole cell type responsible for bone resorption, osteoclasts play a pivotal role in a variety of lytic bone diseases. Suppression of osteoclast formation and activation has been proposed as an effective protective therapy for new bone. In this study, we reported for the first time that phillyrin (Phil), an active ingredient extracted from forsythia, significantly inhibited RANKL-induced osteoclastogenesis and bone resorption in vitro and protected against lipopolysaccharide-induced osteolysis in vivo. Further molecular investigations demonstrated that Phil effectively blocked RANKL-induced activations of c-Jun N-terminal kinase and extracellular signal-regulated kinase, which suppressed the expression of c-Fos and nuclear factor of activated T-cells cytoplasmic 1. Taken together, these data suggested that Phil might be a potential antiosteoclastogenesis agent for treating osteoclast-related bone lytic diseases.

Puerarin Exerts Protective Effects on Wear Particle-Induced Inflammatory Osteolysis

Wear particle-stimulated inflammatory bone destruction and the consequent aseptic loosening remain major postoperative problems for artificial joints. Studies have indicated that puerarin promotes osteogenesis and alleviates lipopolysaccharide-induced osteoclastogenesis in vitro. However, the underlying molecular mechanism by which puerarin interacts with receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclast formation in vitro and wear particle-stimulated osteolysis in vivo has not been reported. In this work, the protective effects exerted by puerarin on titanium particle-stimulated bone destruction in vivo and on RANKL-induced osteoclast activation in osteoclastic precursor cells in vitro were investigated. As expected, puerarin significantly inhibited wear particle-mediated bone resorption and proinflammatory cytokine productions in a calvarial resorption model. Additionally, puerarin inhibited RANKL-induced osteoclast activation, bone resorption ability, and F-actin ring formation in vitro as puerarin concentration increased. Furthermore, mechanistic investigation indicated that reduced RANKL-stimulated MEK/ERK/NFATc1 signaling cascades might regulate the protective effect of puerarin. Conclusively, these results indicate that puerarin, a type of polyphenol, might serve as a protective agent to prevent osteoclast-related osteolytic diseases.

Wear Particle-induced Priming of the NLRP3 Inflammasome Depends on Adherent Pathogen-associated Molecular Patterns and Their Cognate Toll-like Receptors: An In Vitro Study

BACKGROUND

Orthopaedic wear particles activate the NLRP3 inflammasome to produce active interleukin 1β (IL1β). However, the NLRP3 inflammasome must be primed before it can be activated, and it is unknown whether wear particles induce priming. Toll-like receptors (TLRs) are thought to mediate particle bioactivity. It remains controversial whether pathogen-associated molecular patterns (PAMPs) and/or alarmins are responsible for TLR activation by wear particles.

QUESTIONS/PURPOSES

(1) Does priming of the NLRP3 inflammasome by wear particles depend on adherent PAMPs? (2) Does priming of the NLRP3 inflammasome by wear particles depend on TLRs and TIRAP/Mal? (3) Does priming of the NLRP3 inflammasome by wear particles depend on cognate TLRs? (4) Does activation of the NLRP3 inflammasome by wear particles depend on adherent PAMPs?

METHODS

Immortalized murine macrophages were stimulated by as-received titanium particles with adherent bacterial debris, endotoxin-free titanium particles, or titanium particles with adherent ultrapure lipopolysaccharide. To study priming, NLRP3 and IL1β mRNA and IL1β protein levels were assessed in wild-type, TLR4, TLR2, and TIRAP/Mal macrophages. To study activation, IL1β protein secretion was assessed in wild-type macrophages preprimed with ultrapure lipopolysaccharide.

RESULTS

Compared with titanium particles with adherent bacterial debris, endotoxin-free titanium particles induced 86% less NLRP3 mRNA (0.05 ± 0.03 versus 0.35 ± 0.01 NLRP3/GAPDH, p < 0.001) and 91% less IL1β mRNA (0.02 ± 0.01 versus 0.22 ± 0.03 IL1β/GAPDH, p < 0.001). ProIL1β protein level was robustly increased in wild-type macrophages stimulated by particles with adherent PAMPs but was not detectably produced in macrophages stimulated by endotoxin-free particles. Adherence of ultrapure lipopolysaccharide to endotoxin-free particles reconstituted stimulation of NLRP3 and IL1β mRNA. Particles with adherent bacterial debris induced 79% less NLRP3 mRNA (0.09 ± 0.004 versus 0.43 ± 0.13 NLRP3/GAPDH, p < 0.001) and 40% less IL1β mRNA (0.09 ± 0.04 versus 0.15 ± 0.03 IL1β/GAPDH, p = 0.005) in TLR4 macrophages than in wild-type. Similarly, those particles induced 49% less NLRP3 mRNA (0.22 ± 0.10 versus 0.43 ± 0.13 NLRP3/GAPDH, p = 0.004) and 47% less IL1β mRNA (0.08 ± 0.02 versus 0.15 ± 0.03 IL1β/GAPDH, p = 0.012) in TIRAP/Mal macrophages than in wild-type. Particles with adherent ultrapure lipopolysaccharide induced 96% less NLRP3 mRNA (0.012 ± 0.001 versus 0.27 ± 0.05 NLRP3/GAPDH, p = 0.003) and 91% less IL1β mRNA (0.03 ± 0.01 versus 0.34 ± 0.07 IL1β/GAPDH, p < 0.001) expression in TLR4 macrophages than in wild-type. In contrast, those particles did not induce less NLRP3 and IL1β mRNA in TLR2 macrophages. IL1β protein secretion was equivalently induced by particles with adherent bacterial debris or by endotoxin-free particles in a time-dependent manner in wild-type macrophages. For example, particles with adherent bacterial debris induced 99% ± 2% of maximal IL1β secretion after 12 hours, whereas endotoxin-free particles induced 92% ± 11% (p > 0.5).

CONCLUSIONS

This cell culture study showed that adherent PAMPs are required for priming of the NLRP3 inflammasome by wear particles and this process is dependent on their cognate TLRs and TIRAP/Mal. In contrast, activation of the NLRP3 inflammasome by titanium particles is not dependent on adherent PAMPs. Animal and implant retrieval studies are needed to determine whether wear particles have similar effects on the NLRP3 inflammasome in vivo.

CLINICAL RELEVANCE

Our findings, together with recent findings that aseptic loosening associates with polymorphisms in the TIRAP/Mal locus, support that adherent PAMPs may contribute to aseptic loosening in patients undergoing arthroplasty.

Targeting Anion Exchange of Osteoclast, a New Strategy for Preventing Wear Particles Induced- Osteolysis

Joint replacement is essential for the treatment of serious joint disease. However, prosthetic failure remains an important clinical issue, with periprosthesis osteolysis (PO), caused by osteoclastic bone resorption induced by wear particles, being the leading cause of failure. Nuclear factor of activated T cells c1 (NFATc1) appears to play an important role in wear particle-induced osteoclastogenesis, with bicarbonate/chloride exchanger, solute carrier family 4, anion exchanger, member 2, (SLC4A2) being upregulated during osteoclastogenesis in an NFATc1-dependent manner. Anion exchange mediated by SLC4A2 in osteoclasts could affect the bone resorption activity by regulating pHi. This study investigated the role and mechanism of SLC4A2 in wear particle-induced osteoclast differentiation and function in vitro. The use of 4, 4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), an anion exchange inhibitor, suppressed wear particle-induced PO in vivo. Furthermore, controlled release of DIDS from chitosan microspheres can strengthen the PO therapy effect. Therefore, anion exchange mediated by osteoclastic SLC4A2 may be a potential therapeutic target for the treatment of aseptic loosening of artificial joints.

Stevioside Prevents Wear Particle-Induced Osteolysis by Inhibiting Osteoclastogenesis and Inflammatory Response via the Suppression of TAK1 Activation

Aseptic loosening and periprosthetic osteolysis are the leading causes of total joint arthroplasty failure, which occurs as a result of chronic inflammatory response and enhanced osteoclast activity. Here we showed that stevioside, a natural compound isolated from Stevia rebaudiana, exhibited preventative effects on titanium particle-induced osteolysis in a mouse calvarial model. Further histological assessment and real-time PCR analysis indicated that stevioside prevented titanium particle-induced osteolysis by inhibiting osteoclast formation and inflammatory cytokine expression in vivo. In vitro, we found that stevioside could suppress RANKL-induced osteoclastogenesis and titanium particle-induced inflammatory response in a dose-dependent manner. Mechanistically, stevioside achieved these effects by disrupting the phosphorylation of TAK1 and subsequent activation of NF-κB/MAPKs signaling pathways. Collectively, our data suggest that stevioside effectively suppresses osteoclastogenesis and inflammatory response both in vitro and in vivo, and it might be a potential therapy for particle-induced osteolysis and other osteolytic diseases.

Inhibitory activity of linarin on osteoclastogenesis through receptor activator of nuclear factor κB ligand-induced NF-κB pathway

Linarin, a natural flavonoid glycoside widely found in plants, has been reported to possess anti-inflammation, neuroprotection and osteogenic properties. However, its impact on osteoclast remains unclear. In the present study, the effects of linarin on osteoclastogenesis and its underlying molecular mechanisms of action were investigated. Using the culture systems of osteoclasts derived from bone marrow macrophages (BMMs), we found that linarin dose-dependently inhibited osteoclasts formation and bone resorptive activity. The Cell Counting Kit-8 test displayed that the viability of cells was not influenced by linarin at doses up to 10 μg/mL. In addition, linarin downregulated osteoclast-related genes expression, including nuclear factor of activated T cells cytoplasmic 1 (NFATc1), tartrate resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR) and c-Fos, as shown by quantitative real time polymerase chain reaction (RT-qPCR). Western blot analysis further showed that linarin inhibited receptor activator of nuclear factor κB ligand (RANKL)-induced nuclear factor kappa B (NF-κB) p65 and NFATc1 activity. The present findings show that linarin exerted a potent inhibitory effect on osteoclastogenesis through RANKL-induced NF-κB signaling pathway. In conclusion, the results suggest that linarin has anti-osteoclastic effects and may serve as potential modulatory agents for the prevention and treatment of bone loss-associated diseases.

Lithium chloride inhibits titanium particle-induced osteoclastogenesis by inhibiting the NF-κB pathway

Osteoclast over-activation and inflammation responses promote peri-implant osteolysis (PIO), which is the leading cause of aseptic artificial joint loosening. We examined the effect of lithium chloride (LiCl) on wear debris-induced osteoclastogenesis and inflammation. Fifty-Six C57BL/6J male mice were randomly distributed into four groups: sham control (sham, treated with phosphate buffered saline [PBS]), vehicle (treated with titanium/PBS), low-LiCl (L-LiCl, titanium: 50 mg/kg LiCl) and high-LiCl (H-LiCl, titanium: 200 mg/kg LiCl). After 14 days, mouse calvaria were harvested for micro-computed tomography and histomorphological and molecular analyses. Bone marrow-derived macrophages (BMMs) were extracted to examine osteoclast differentiation, and the RAW264.7 cell line was used to investigate osteoclastogenesis mechanisms. LiCl reduced the number of osteoclasts, debris-induced osteolysis, and the expression of inflammatory factors, thereby preventing bone loss in vivo. In vitro, LiCl inhibited osteoclastogenesis and osteoclastic bone resorption by inhibiting the RANKL-induced NF-κB signaling pathway. LiCl's activation of the canonical Wnt/β-catenin signaling pathway was not associated with LiCl's inhibition of osteoclastogenesis. These results suggest that LiCl may be an effective agent for treatment of osteolytic diseases caused by chronic inflammation and over-activation of osteoclasts.

Direct influence of titanium and zirconia particles on the morphology and functionality of mature human osteoclasts

Within the last ten years of biomedical implants, the focus is increasingly on bioceramics, specifically on zirconia (ZrO₂ ). Hence, we analyzed the impact of ZrO₂ particles in comparison to titanium particles on mature human osteoclasts (OCs) as little is known about the direct effect of wear particles on mature OCs and their role in the osteolytic process during aseptic endoprosthesis loosening. Changes in cell morphology and functionality of OCs incubated with particles in different concentrations were investigated in vitro. OCs tend to be enlarged after three days of cultivation with both types of particles, especially with high concentrations of ZrO₂ , suggesting increased cell fusion. Further, we identified significantly increased expression of OC specific and bone matrix related genes: VNR, RANK, TRAP, and CTSK pointing on a direct stimulatory particle effect on the functionality of mature OCs. In completion, we quantified the bone resorption activity of particle treated mature OCs but could not detect a significant difference in bone resorption compared to OCs cultivated without particles. However, we could identify significantly higher gene expression of MMP-1 in particle treated OCs compared to untreated control OCs after three days of incubation. We also detected an impaired production of the tissue inhibitor of metalloproteinase, especially for OCs treated with high ZrO₂ concentrations. In conclusion, our in vitro data show that abrasion particles could have a direct influence on mature OCs and therefore could promote increased OC-mediated bone resorption during aseptic loosening of total joint replacements. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2608-2615, 2017.

Rifampin suppresses osteoclastogenesis and titanium particle-induced osteolysis via modulating RANKL signaling pathways

Wear particles liberated from the surface of prostheses are considered to be main reason for osteoclast bone resorption and that extensive osteoclastogenesis leads to peri-implant osteolysis and subsequent prosthetic loosening. The aim of this study was to assess the effect of rifampin on osteoclastogenesis and titanium (Ti) particle-induced osteolysis. The Ti particle-induced osteolysis mouse calvarial model and bone marrow-derived macrophages (BMMs) were used. Rifampin, at dose of 10 or 50 mg/kg/day, was respectively given intraperitoneally for 14 days in vivo. The calvariae were removed and processed for Further histological analysis. In vitro, osteoclasts were generated from mouse BMMs with receptor activator of nuclear factor-κB ligand (RANKL) and the macrophage colony stimulating factor. Rifampin at different concentrations was added to the medium. The cell viability, tartrate-resistant acid phosphatase (TRAP) staining, TRAP activity and resorption on bone slices were analysis. Osteoclast-specific genes and RANKL-induced MAPKs signaling were tested for further study of the mechanism. Rifampin inhibited Ti-induced osteolysis and osteoclastogenesis in vivo. In vitro data indicated that rifampin suppressed osteoclast differentiation and bone resorption in a dose-dependent manner. Moreover, rifampin significantly reduced the expression of osteoclast-specific markers, including TRAP, cathepsin K, V-ATPase d2, V-ATPase a3, c-Fos, and nuclear factor of activated T cells (NFAT) c1. Further investigation revealed that rifampin inhibited osteoclast formation by specifically abrogating RANKL-induced p38 and NF-κB signaling. Rifampin had significant potential for the treatment of particle-induced peri-implant osteolysis and other diseases caused by excessive osteoclast formation and function.

Desferrioxamine reduces ultrahigh-molecular-weight polyethylene-induced osteolysis by restraining inflammatory osteoclastogenesis via heme oxygenase-1

As wear particles-induced osteolysis still remains the leading cause of early implant loosening in endoprosthetic surgery, and promotion of osteoclastogenesis by wear particles has been confirmed to be responsible for osteolysis. Therapeutic agents targeting osteoclasts formation are considered for the treatment of wear particles-induced osteolysis. In the present study, we demonstrated for the first time that desferrioxamine (DFO), a powerful iron chelator, could significantly alleviate osteolysis in an ultrahigh-molecular-weight polyethylene (UHMWPE) particles-induced mice calvaria osteolysis model. Furthermore, DFO attenuated calvaria osteolysis by restraining enhanced inflammatory osteoclastogenesis induced by UHMWPE particles. Consistent with the in vivo results, we found DFO was also able to inhibit osteoclastogenesis in a dose-dependent manner in vitro, as evidenced by reduction of osteoclasts formation and suppression of osteoclast specific genes expression. In addition, DFO dampened osteoclasts differentiation and formation at early stage but not at late stage. Mechanistically, the reduction of osteoclastogenesis by DFO was due to increased heme oxygenase-1 (HO-1) expression, as decreased osteoclasts formation induced by DFO was significantly restored after HO-1 was silenced by siRNA, while HO-1 agonist COPP treatment enhanced DFO-induced osteoclastogenesis inhibition. In addition, blocking of p38 mitogen-activated protein kinase (p38MAPK) signaling pathway promoted DFO-induced HO-1 expression, implicating that p38 signaling pathway was involved in DFO-mediated HO-1 expression. Taken together, our results suggested that DFO inhibited UHMWPE particles-induced osteolysis by restraining inflammatory osteoclastogenesis through upregulation of HO-1 via p38MAPK pathway. Thus, DFO might be used as an innovative and safe therapeutic alternative for treating wear particles-induced aseptic loosening.

Blockade of NF-κB and MAPK pathways by ulinastatin attenuates wear particle-stimulated osteoclast differentiation in vitro and in vivo

Ulinastatin, a urinary trypsin inhibitor (UTI), is widely used to clinically treat lipopolysaccharide (LPS)-related inflammatory disorders recently. Adherent pathogen-associated molecular patterns (PAMPs), of which LPS is the best-studied and classical endotoxin produced by Gram-negative bacteria, act to increase the biological activity of osteopedic wear particles such as polymethyl-methacrylate (PMMA) and titanium particles in cell culture and animal models of implant loosening. The present study was designed to explore the inhibitory effect of UTI on osteoclastogenesis and inflammatory osteolysis in LPS/PMMA-mediated Raw264.7 cells and murine osteolysis models, and investigate the potential mechanism. The in vitro study was divided into the control group, LPS-induced group, PMMA-stimulated group and UTI-pretreated group. UTI (500 or 5000 units/ml) pretreatment was followed by PMMA (0.5 mg/ml) with adherent LPS. The levels of inflammatory mediators including tumour necrosis factor-α (TNF-α), matrixmetallo-proteinases-9 (MMP-9) and interleukin-6 (IL-6), receptor activation of nuclear factor NF-κB (RANK), and cathepsin K were examined and the amounts of phosphorylated I-κB, MEK, JNK and p38 were measured. In vivo study, murine osteolysis models were divided into the control group, PMMA-induced group and UTI-treated group. UTI (500 or 5000 units/kg per day) was injected intraperitoneally followed by PMMA suspension with adherent LPS (2×10⁸ particles/25 μl) in the UTI-treated group. The thickness of interfacial membrane and the number of infiltrated inflammatory cells around the implants were assessed, and bone mineral density (BMD), trabecular number (Tb.N.), trabecular thickness (Tb.Th.), trabecular separation (Tb.Sp.), relative bone volume over total volume (BV/TV) of distal femur around the implants were calculated. Our results showed that UTI pretreatment suppressed the secretion of proinflammatory cytokines including MMP-9, IL-6, TNF-α, RANK and cathepsin K through down-regulating the activity of nuclear factor kappa B (NF-κB) and MAPKs partly in LPS/PMMA-mediated Raw264.7 cells. Finally, UTI treatment decreased the inflammatory osteolysis reaction in PMMA-induced murine osteolysis models. In conclusion, these results confirm the anti-inflammatory potential of UTI in the prevention of particle disease.

Peri-implant tissue response and biodegradation performance of a Mg-1.0Ca-0.5Sr alloy in rat tibia

Biodegradable magnesium (Mg) alloys combine the advantages of traditional metallic implants and biodegradable polymers, having high strength, low density, and a stiffness ideal for bone fracture fixation. A recently developed Mg-Ca-Sr alloy potentially possesses advantageous characteristics over other Mg alloys, such as slower degradation rates and minimal toxicity. In this study, the biocompatibility of this Mg-Ca-Sr alloy was investigated in a rat pin-placement model. Cylindrical pins were inserted in the proximal tibial metaphyses in pre-drilled holes orthogonal to the tibial axis. Implant and bone morphologies were investigated using μCT at 1, 3, and 6 weeks after implant placement. At the same time points, the surrounding tissue was evaluated using H&E, TRAP and Goldner's trichrome staining. Although gas bubbles were observed around the degrading implant at early time points, the bone remained intact with no evidence of microfracture. Principle findings also include new bone formation in the area of the implant, suggesting that the alloy is a promising candidate for biodegradable orthopedic implants.

Cytocompatibility of the selected calcium phosphate based bone cements: comparative study in human cell culture

Calcium phosphate cements (CPC) are valuable bone fillers. Recently they have been also considered as the basis for drug-, growth factors- or cells-delivery systems. Broad possibilities to manipulate CPC composition provide a unique opportunity to obtain materials with a wide range of physicochemical properties. In this study we show that CPC composition significantly influences cell response. Human bone derived cells were exposed to the several well-characterized different cements based on calcium phosphates, magnesium phosphates and calcium sulfate hemihydrate (CSH). Cell viability assays, live/dead staining and real-time observation of cells in contact with the materials (time-laps) were performed. Although all the investigated materials have successfully passed a standard cytocompatibility assay, cell behavior in a direct contact with the materials varied depending on the material and the experimental system. The most recommended were the α-TCP-based materials which proved suitable as a support for cells in a direct contact. The materials which caused a decrease of calcium ions concentration in culture induced the negative cell response, however this effect might be expected efficiently compensated in vivo. All the materials consisting of CSH had negative impact on the cells. The obtained results strongly support running series of cytocompatibility studies for preclinical evaluation of bone cements.

Sheep Hip Arthroplasty Model of Failed Implant Osseointegration

Early secure stability of an implant is important for long-term survival. We examined whether micromotion of implants consistently would induce bone resorption and formation of a fibrous membrane and thereby prevent osseointegration.

One micromotion implant was inserted into one of the medial femoral condyles in ten sheep. The micromotion device consists of an anchor bearing a PMMA implant and a PE plug. During each gait cycle the PE plug will make the PMMA implant axially piston 0.5 mm. After 12 weeks of observation the bone specimens were harvested and a post-mortem control implant was inserted into the contra-lateral medial femoral condyle.

Histomorphometrical evaluation showed that the surface on the implant observed for 12 weeks was covered by fibrous tissue. The control implants were covered by lamellar bone. No difference was found with respect to the volume fraction of lamellar bone in a 1 mm zone around the implants.

This study indicates that implant micromotion is sufficient to induce bone resorption and formation of a fibrous membrane.

Gambogic acid inhibits osteoclast formation and ovariectomy-induced osteoporosis by suppressing the JNK, p38 and Akt signalling pathways

Excessive osteoclast formation and bone resorption are key causes of osteoporosis. Natural compounds can serve as alternative therapeutic agents for the prevention and treatment of osteoporosis, and some natural compounds may have advantages over traditional drugs. In the present paper, we report that the natural compound GBA (gambogic acid), which is bioavailable, effective and less toxic, inhibits osteoclast formation, thereby attenuating osteoclastic bone resorption in vitro. Further in vivo studies demonstrated that GBA prevented ovariectomy-induced bone loss in a dose-dependent manner. Moreover, we demonstrated that GBA suppressed RANKL (receptor activator of nuclear factor κB ligand)-induced JNK (c-Jun N-terminal kinase), p38 and Akt phosphorylation. Taken together, our results demonstrate that GBA inhibits osteoclast formation in vitro and in vivo, suggesting that it is of potential value in the treatment of osteoclast-related diseases.

Biological responses of preosteoblasts to particulate and ion forms of Co-Cr alloy

This study compared the particulate and ion forms of a cobalt-chrome (Co-Cr) alloy on the differentiation/activation of preosteoblasts. Mouse preosteoblasts (MC3T3-E1) were cultured in an osteoblast-induction medium in the presence of particulate and ion forms of a Co-Cr alloy, followed by cell proliferation and cytotoxicity evaluations. The maturation and function of osteoblasts were assessed by alkaline phosphatase (ALP) assay and related gene expressions. Both particulate and ion forms of the metals significantly reduced the proliferation of MC3T3-E1 cells in a dose-dependent manner. Similarly, cells challenged with high concentrations of particles and ions exhibited a marked cytotoxic effect and diminished expression of ALP. Real-time (RT) polymerase chain reaction (PCR) data have suggested that cells with Co-Cr particles dramatically promoted over-expression of monocyte chemo-attractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), whereas Co(2+) ions treatment predominately up-regulated expressions of receptor activator of nuclear factor kappa-B ligand (RANKL), nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), and down-regulated expression of osteoprotegerin (OPG) and Osterix (Osx). Overall, this study provides evidence that both Co-Cr alloy particles and metal ions interfered with the MC3T3-E1 cells for their growth, maturation, and functions. Further, Co-Cr particles exhibited stronger effects on inflammatory mediators, while metal ions showed more influence on inhibition of osteoblast differentiation and promotion of osteoclastogenesis.

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).

Inhibitory effects of ursolic acid on osteoclastogenesis and titanium particle-induced osteolysis are mediated primarily via suppression of NF-κB signaling

Ursolic acid (UA), a pentacyclic triterpenoid found in a variety of plants, has attracted considerable attention because of its important biological and pharmacological activities. However, its effect on osteoclasts and mechanism of action require further investigation. In this study, we evaluated the effects of UA on osteoclastogenesis and osteoclast-mediated osteolysis in vitro and in vivo, and explored its possible mechanism of action. The results indicated that UA could inhibit receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis and the bone resorptive function of osteoclasts in a concentration-dependent manner in vitro. Further, UA effectively inhibited the mRNA and protein expression of NFATc1, primarily via the suppression of nuclear factor-κB (NF-κB) signaling, and partly through the suppression of c-Jun N-terminal kinase (JNK) signaling. Additionally, UA treatment downregulated the expression of NFATc1-regulated osteoclast marker genes. Likewise, UA induced dose-dependent attenuation of titanium (Ti) particle-induced mouse calvarial bone loss, and decreased the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts. In conclusion, these results demonstrate that UA protects against wear particle-induced osteolysis by suppressing osteoclast formation and function. These effects are associated with the inhibition of the NF-κB- and JNK-related signaling pathways.

Do genetic susceptibility, Toll-like receptors, and pathogen-associated molecular patterns modulate the effects of wear?

Overwhelming evidence supports the concept that wear particles are the primary initiator of aseptic loosening of orthopaedic implants. It is likely, however, that other factors modulate the biologic response to wear particles. This review focuses on three potential other factors: genetic susceptibility, Toll-like receptors (TLRs), and bacterial pathogen-associated molecular patterns (PAMPs). WHERE ARE WE NOW?: Considerable evidence is emerging that both genetic susceptibility and TLR activation are important factors that modulate the biologic response to wear particles, but it remains controversial whether bacterial PAMPs also do so. WHERE DO WE NEED TO GO?: Detailed understanding of the roles of these other factors may lead to identification of novel therapeutic targets for patients with aseptic loosening. HOW DO WE GET THERE?: Highest priority should be given to polymorphism replication studies with large numbers of patients and studies to replicate the reported correlation between bacterial biofilms and the severity of aseptic loosening.

The inhibition of RANKL-induced osteoclastogenesis through the suppression of p38 signaling pathway by naringenin and attenuation of titanium-particle-induced osteolysis

The aim of this study was to assess the effect of naringenin on osteoclastogenesis and titanium particle-induced osteolysis. Osteolysis from wear-induced particles and aseptic loosening are the most frequent late complications of total joint arthroplasty leading to revision of the prosthesis. Osteolysis during aseptic loosening is most likely due to increased bone resorption by osteoclasts. Through in vitro studies, we demonstrated that naringenin, a naturally occurring flavanone in grapefruit and tomatoes, exerts potent inhibitory effects on the ligand of the receptor activator of nuclear factor-κB (RANKL)-induced osteoclastogenesis and revealed that the mechanism of action of naringenin, which inhibited osteoclastogenesis by suppression of the p38 signaling pathway. Through in vivo studies, we proved that naringenin attenuated titanium particle-induced osteolysis in a mouse calvarial model. In general, we demonstrated that naringenin inhibited osteoclastogenesis via suppression of p38 signaling in vitro and attenuated titanium particle-induced osteolysis in vivo. This study also suggested that naringenin has significant potential for the treatment of osteolysis-related diseases caused by excessive osteoclast formation and activity.

Latham J, G. Dunlop D, Oreffo RO. Bone and metal: an orthopaedic perspective on osseointegration of metals

The area of implant osseointegration is of major importance, given the predicted significant rise in the number of orthopaedic procedures and an increasingly ageing population. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant bulk properties and surface characteristics. Our understanding and ability to modify these mechanisms through alterations in implant design is continuously expanding. The following review considers the main aspects of material and surface alterations in metal implants, and the extent of their subsequent influence on osseointegration. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. The complexity of achieving this outcome through incorporation and balance of contributory factors is highlighted through a clinical case report.

The prevention of titanium-particle-induced osteolysis by OA-14 through the suppression of the p38 signaling pathway and inhibition of osteoclastogenesis

Wear-particle-induced osteolysis leads to prosthesis loosening, which is one of the most common causes of joint-implant failure, a problem that must be fixed using revision surgery. Thus, a potential treatment for prosthetic loosening is focused on inhibiting osteoclastic bone resorption, which prevents wear-particle-induced osteolysis. In this study, we synthesized a compound named OA-14 (N-(3- (dodecylcarbamoyl)phenyl)-1H-indole-2-carboxamide) and examined how OA-14 affects titanium (Ti)-particle-induced osteolysis and osteoclastogenesis. We report that OA-14 treatment protected against Ti-particle-induced osteolysis in a mouse calvarial model. Interestingly, the number of tartrate-resistant acid phosphatase-positive osteoclasts decreased after treatment with OA-14 in vivo, which suggested that OA-14 inhibits osteoclast formation. To test this hypothesis, we conducted in vitro studies, and our results revealed that OA-14 markedly diminished osteoclast differentiation and osteoclast-specific gene expression in a dose- and time-dependent manner. Moreover, OA-14 suppressed osteoclastic bone resorption and F-actin ring formation. Furthermore, we determined that OA-14 inhibited osteoclastogenesis by specifically blocking the p38-Mitf-c-fos-NFATc1 signaling cascade induced by RANKL (ligand of receptor activator of nuclear factor κB). Collectively, our results suggest that the compound OA-14 can be safely used for treating particle-induced peri-implant osteolysis and other diseases caused by excessive osteoclast formation and function.

Geraniin suppresses RANKL-induced osteoclastogenesis in vitro and ameliorates wear particle-induced osteolysis in mouse model

Wear particle-induced osteolysis and subsequent aseptic loosening remains the most common complication that limits the longevity of prostheses. Wear particle-induced osteoclastogenesis is known to be responsible for extensive bone erosion that leads to prosthesis failure. Thus, inhibition of osteoclastic bone resorption may serve as a therapeutic strategy for the treatment of wear particle induced osteolysis. In this study, we demonstrated for the first time that geraniin, an active natural compound derived from Geranium thunbergii, ameliorated particle-induced osteolysis in a Ti particle-induced mouse calvaria model in vivo. We also investigated the mechanism by which geraniin exerts inhibitory effects on osteoclasts. Geraniin inhibited RANKL-induced osteoclastogenesis in a dose-dependent manner, evidenced by reduced osteoclast formation and suppressed osteoclast specific gene expression. Specially, geraniin inhibited actin ring formation and bone resorption in vitro. Further molecular investigation demonstrated geraniin impaired osteoclast differentiation via the inhibition of the RANKL-induced NF-κB and ERK signaling pathways, as well as suppressed the expression of key osteoclast transcriptional factors NFATc1 and c-Fos. Collectively, our data suggested that geraniin exerts inhibitory effects on osteoclast differentiation in vitro and suppresses Ti particle-induced osteolysis in vivo. Geraniin is therefore a potential natural compound for the treatment of wear particle induced osteolysis in prostheses failure.

Hypericin suppresses osteoclast formation and wear particle-induced osteolysis via modulating ERK signalling pathway

Osteoclast-induced bone resorption and wear-particle-induced osteolysis leads to prosthetic loosening, one of the most common causes of joint implant failure, resulting in revision surgery. Thus, inhibition of osteoclastic bone resorption, which further prevents wear particle-induced osteolysis, is a potential treatment strategy for prosthetic loosening. Here, we examined the therapeutic effect of hypericin (HP), which was photosensitive, on osteoclastogenesis and wear particle-induced osteolysis in the absence of visible light. HP inhibited RANKL-induced osteoclast differentiation in bone marrow macrophages (BMMs) and RAW264.7 cell line without any evidence of cytotoxicity. The bone-resorbing activity of mature osteoclasts was significantly inhibited by HP. As HP has been previously reported to inhibit signalling pathway such as ERK and NF-κB in other cells, which is also important in osteoclast differentiation. We thus examined the molecular mechanism and showed that HP significantly inhibited the ERK/mitogen-activated protein kinase (MAPK) signalling pathway without affecting nuclear factor kappaB (NF-κB), c-Jun N-terminal kinase (JNK) and p38 signalling in RANKL-stimulated BMMs. Further in vivo studies revealed HP attenuated osteoclast formation and subsequently prevented wear particle-induced bone erosion. Taken together, the results suggest that HP inhibits RANKL-mediated osteoclastogenesis via affecting ERK signalling in vitro and suppresses wear particle-induced osteolysis in vivo. We therefore conclude that HP may be an innovative and safe alternative treatment for osteoclast-related prosthetic loosening.

Mitigative effect of erythromycin on PMMA challenged preosteoblastic MC3T3-E1 cells

Background. Aseptic loosening (AL) is a major complication of total joint replacement. Recent approaches to limiting AL have focused on inhibiting periprosthetic inflammation and osteoclastogenesis. Questions/Purposes. The purpose of this study was to determine the effects of erythromycin (EM) on polymethylmethacrylate (PMMA) particle-challenged MC3T3 osteoblast precursor cells. Methods. MC3T3 cells were pretreated with EM (0–10 μg/mL) and then stimulated with PMMA (1 mg/mL). Cell viability was evaluated by both a lactate dehydrogenase (LDH) release assay and cell counts. Cell differentiation was determined by activity of alkaline phosphatase (ALP). Gene expression was measured via real-time quantitative RT-PCR. Results. We found that exposure to PMMA particles reduced cellular viability and osteogenetic potential in MC3T3 cell line. EM treatment mitigated the effects of PMMA particles on the proliferation, viability and differentiation of MC3T3 cells. PMMA decreased the gene expression of Runx2, osterix and osteocalcin, which can be partially restored by EM treatment. Furthermore, EM suppressed PMMA- induced increase of NF-κB gene expression. Conclusions. These data demonstrate that EM mitigates the effects of PMMA on MC3T3 cell viability and differentiation, in part through downregulation of NF-κB pathway. EM appeared to represent an anabolic agent on MC3T3 cells challenged with PMMA particles.

Controlled-release of bone morphogenetic protein-2 from a microsphere coating applied to acid-etched Ti6AL4V implants increases biological bone growth in vivo

A central clinical challenge regarding the surgical treatment of bone and joint conditions is the eventual loosening of an orthopedic implant as a result of insufficient bone ingrowth at the bone-implant interface. We investigated the in vivo effectiveness of a coating containing recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded microspheres applied to acid-etched Ti6Al4V cylinders for implantation. Three groups of rabbits (24 per group) were used for implantation: (1) acid-etched Ti6Al4V implants coated with a mixture of rhBMP-2-loaded microspheres (125 ng rhBMP-2/mg microspheres) and α-butyl cyanoacrylate; (2) acid-etched, uncoated implants; and (3) bare, smooth uncoated implants. After implantation, 12 rabbits from each group were used for bone ingrowth determination at 4, 5, 6, 7, 8, and 12 weeks (2 rabbits per time point), while the remainder were used for histological analysis and push-out testing at 12 weeks. Scanning electron microscopy showed significant improvement in bone growth of the rhBMP-2 microspheres/α-butyl cyanoacrylate group compared with the other groups (p<0.01). Histological analysis and push-out testing also demonstrated enhanced bone growth of the rhBMP-2 group over that in the other two groups (p<0.01). The rhBMP-2 group showed the most significant bone growth, suggesting that coating acid-etched implants with a mixture of rhBMP-2-loaded microspheres and α-butyl cyanoacrylate may be an effective method to improve the osseointegration of orthopedic implants.

Osteoclast Generation and Cytokine Profile at Prosthetic Interfaces: A Study on Tissue of Patients with Aseptic Loosening or Implant-Associated Infections

Aseptic loosening of implants or loosening due to persistent bacterial infection remains a severe complication in orthopaedic surgery. To investigate underlying cellular and molecular mechanisms, particularly with regard to bone loss, tissue samples of patients requiring surgery were examined. By histological methods and by quantitative RT-PCR, respectively, infiltration of leukocytes, expression of osteoclast-typical genes and of proinflammatory cytokines was determined. Samples were taken directly from osteolytic sites and for comparison from adjacent sites, distant sites and from muscle. At osteolytic sites, cathepsin K and the metalloproteinases MMP1 and MMP9 were found, as was expression of inflammation-related cytokines, particularly of interleukin (IL)-1β, CXCL8, S100A9 and a very moderate expression of receptor activator of NfκB ligand (RANKL) and tumour necrosis factor (TNF) a. Of note, expression of these parameters gradually decreased from sites of osteolysis to adjacent tissue, to distant tissue to muscle. In patients with infection and osteolysis, expression of cytokines, notably of CXCL8, was markedly enhanced, especially in adjacent and distant tissues, where expression was 10- to 20-fold higher compared to tissue of aseptic patients. A possible source of CXCL8 could be infiltrated cells, particularly neutrophils, because they were found in infected tissue only. Histological examination of the biopsies revealed an additional CXCL8 source, namely endothelial cells of small blood vessels. In conclusion, aseptic loosening and implant-associated infection are associated with osteoclast generation and a local inflammatory response. The proinflammatory environment could promote the differentiation of precursor cells to osteoclasts, thereby linking inflammation to bone resorption. The higher expression of cytokines, particularly of CXCL8 in tissue of patients with bacterial infection, could explain the accelerated time course of bone resorption as it occurs in infection compared to aseptic loosening.

Therapeutic potentials of naringin on polymethylmethacrylate induced osteoclastogenesis and osteolysis, in vitro and in vivo assessments

Wear debris associated periprosthetic osteolysis represents a major pathological process associated with the aseptic loosening of joint prostheses. Naringin is a major flavonoid identified in grapefruit. Studies have shown that naringin possesses many pharmacological properties including effects on bone metabolism. The current study evaluated the influence of naringin on wear debris induced osteoclastic bone resorption both in vitro and in vivo. The osteoclast precursor cell line RAW 264.7 was cultured and stimulated with polymethylmethacrylate (PMMA) particles followed by treatment with naringin at several doses. Tartrate resistant acid phosphatase (TRAP), calcium release, and gene expression profiles of TRAP, cathepsin K, and receptor activator of nuclear factor-kappa B were sequentially evaluated. PMMA challenged murine air pouch and the load bearing tibia titanium pin-implantation mouse models were used to evaluate the effects of naringin in controlling PMMA induced bone resorption. Histological analyses and biomechanical pullout tests were performed following the animal experimentation. The in vitro data clearly demonstrated the inhibitory effects of naringin in PMMA induced osteoclastogenesis. The naringin dose of 10 μg/mL exhibited the most significant influence on the suppression of TRAP activities. Naringin treatment also markedly decreased calcium release in the stimulated cell culture medium. The short-term air pouch mouse study revealed that local injection of naringin ameliorated the PMMA induced inflammatory tissue response and subsequent bone resorption. The long-term tibia pin-implantation mouse model study suggested that daily oral gavage of naringin at 300 mg/kg dosage for 30 days significantly alleviated the periprosthetic bone resorption. A significant increase of periprosthetic bone volume and regaining of the pin stability were found in naringin treated mice. Overall, this study suggests that naringin may serve as a potential therapeutic agent to treat wear debris associated osteolysis.

Toll-like receptors-2 and 4 are overexpressed in an experimental model of particle-induced osteolysis

Aseptic loosening secondary to particle-associated periprosthetic osteolysis remains a major cause of failure of total joint replacements (TJR) in the mid- and long term. As sentinels of the innate immune system, macrophages are central to the recognition and initiation of the inflammatory cascade, which results in the activation of bone resorbing osteoclasts. Toll-like receptors (TLRs) are involved in the recognition of pathogen-associated molecular patterns and danger-associated molecular patterns. Experimentally, polymethylmethacrylate and polyethylene (PE) particles have been shown to activate macrophages via the TLR pathway. The specific TLRs involved in PE particle-induced osteolysis remain largely unknown. We hypothesized that TLR-2, -4, and -9 mediated responses play a critical role in the development of PE wear particle-induced osteolysis in the murine calvarium model. To test this hypothesis, we first demonstrated that PE particles caused observable osteolysis, visible by microCT and bone histomorphometry when the particles were applied to the calvarium of C57BL/6 mice. The number of TRAP positive osteoclasts was significantly greater in the PE-treated group when compared to the control group without particles. Finally, using immunohistochemistry, TLR-2 and TLR-4 were highly expressed in PE particle-induced osteolytic lesions, whereas TLR-9 was downregulated. TLR-2 and -4 may represent novel therapeutic targets for prevention of wear particle-induced osteolysis and accompanying TJR failure.

Inhibition of the PI3K/AKT pathway reduces tumor necrosis factor-alpha production in the cellular response to wear particles in vitro

Joint replacement is the most effective treatment for end-stage osteoarticular disease. However, macrophage-mediated aseptic loosening of joint prosthesis severely hampers the clinical effects of joint replacement. Until now, the mechanism by which macrophages regulate the secretion of inflammatory cytokines after particle stimulation is not clear. It is well known that the PI3K/AKT pathway participates in multiple cellular processes, including cell growth, survival, and inflammation. However, whether the PI3K/AKT pathway participates in the proinflammatory response of macrophages after particle stimulation and secondary aseptic loosening is still unknown. In this study, ceramic and titanium particles of different sizes were prepared to stimulate macrophages. LY294002, a specific inhibitor of PI3K, was pretreated prior to particle stimulation. The expression of tumor necrosis factor-alpha (TNF-α) and all the subunits of PI3K and AKT were detected by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blot. The result showed that LY294002 could suppress the RNA and protein expression of TNF-α in RAW264.7 cells after stimulation of different particles. The subunits of PI3K (p110β and p85β), followed by activation of phosphor-AKT (Ser473), participated in the regulation of activating macrophages by wear particles, ultimately resulting in the secretion of TNF-α.

Nanoparticles and their potential for application in bone

Biomaterials are commonly applied in regenerative therapy and tissue engineering in bone, and have been substantially refined in recent years. Thereby, research approaches focus more and more on nanoparticles, which have great potential for a variety of applications. Generally, nanoparticles interact distinctively with bone cells and tissue, depending on their composition, size, and shape. Therefore, detailed analyses of nanoparticle effects on cellular functions have been performed to select the most suitable candidates for supporting bone regeneration. This review will highlight potential nanoparticle applications in bone, focusing on cell labeling as well as drug and gene delivery. Labeling, eg, of mesenchymal stem cells, which display exceptional regenerative potential, makes monitoring and evaluation of cell therapy approaches possible. By including bioactive molecules in nanoparticles, locally and temporally controlled support of tissue regeneration is feasible, eg, to directly influence osteoblast differentiation or excessive osteoclast behavior. In addition, the delivery of genetic material with nanoparticulate carriers offers the possibility of overcoming certain disadvantages of standard protein delivery approaches, such as aggregation in the bloodstream during systemic therapy. Moreover, nanoparticles are already clinically applied in cancer treatment. Thus, corresponding efforts could lead to new therapeutic strategies to improve bone regeneration or to treat bone disorders.