Polyethylene particle-induced bone resorption in alpha-calcitonin gene-related peptide-deficient mice

Increased UHMWPE Particle-Induced Osteolysis in Fetuin-A-Deficient Mice

Particle-induced osteolysis is a major cause of aseptic prosthetic loosening. Implant wear particles stimulate tissue macrophages inducing an aseptic inflammatory reaction, which ultimately results in bone loss. Fetuin-A is a key regulator of calcified matrix metabolism and an acute phase protein. We studied the influence of fetuin-A on particle-induced osteolysis in an established mouse model using fetuin-A-deficient mice. Ten fetuin-A-deficient (Ahsg−/−) mice and ten wild-type animals (Ahsg+/+) were assigned to test group receiving ultra-high molecular weight polyethylene (UHMWPE) particle implantation or to control group (sham surgery). After 14 days, bone metabolism parameters RANKL, osteoprotegerin (OPG), osteocalcin (OC), alkaline phosphatase (ALP), calcium, phosphate, and desoxypyridinoline (DPD) were examined. Bone volume was determined by microcomputed tomography (μCT); osteolytic regions and osteoclasts were histomorphometrically analyzed. After particle treatment, bone resorption was significantly increased in Ahsg−/− mice compared with corresponding Ahsg+/+ wild-type mice (p = 0.007). Eroded surface areas in Ahsg−/− mice were significantly increased (p = 0.002) compared with Ahsg+/+ mice, as well as the number of osteoclasts compared with control (p = 0.039). Fetuin-A deficiency revealed increased OPG (p = 0.002), and decreased levels of DPD (p = 0.038), OC (p = 0.036), ALP (p < 0.001), and Ca (p = 0.001) compared with wild-type animals. Under osteolytic conditions in Ahsg−/− mice, OPG was increased (p = 0.013), ALP (p = 0.015) and DPD (p = 0.012) were decreased compared with the Ahsg+/+ group. Osteolytic conditions lead to greater bone loss in fetuin-A-deficient mice compared with wild-type mice. Reduced fetuin-A serum levels may be a risk factor for particle-induced osteolysis while the protective effect of fetuin-A might be a future pathway for prophylaxis and treatment.

Chronic Pain in Musculoskeletal Diseases: Do You Know Your Enemy?

Musculoskeletal pain is a condition that characterises several diseases and represents a constantly growing issue with enormous socio-economic burdens, highlighting the importance of developing treatment algorithms appropriate to the patient’s needs and effective management strategies. Indeed, the algic condition must be assessed and treated independently of the underlying pathological process since it has an extremely negative impact on the emotional and psychic aspects of the individual, leading to isolation and depression. A full understanding of the pathophysiological mechanisms involved in nociceptive stimulation and central sensitization is an important step in improving approaches to musculoskeletal pain. In this context, the bidirectional relationship between immune cells and neurons involved in nociception could represent a key point in the understanding of these mechanisms. Therefore, we provide an updated overview of the magnitude of the musculoskeletal pain problem, in terms of prevalence and costs, and summarise the role of the most important molecular players involved in the development and maintenance of pain. Finally, based on the pathophysiological mechanisms, we propose a model, called the “musculoskeletal pain cycle”, which could be a useful tool to counteract resignation to the algic condition and provide a starting point for developing a treatment algorithm for the patient with musculoskeletal pain.

Prednisone prevents particle induced bone loss in the calvaria mouse model

INTRODUCTION

Glucocorticoids are essential in the treatment of many chronic inflammatory and malignant diseases but are known to have detrimental effects on bone. This study aimed to investigate the effects of prednisone on osteoclast functioning in vivo in the calvaria particle-induced bone loss mouse model.

METHODS

12-week-old male C57BL6/J mice received subcutaneously implanted prednisone (2.5 mg/d, 60 day release (n = 14)) or placebo pellets (n = 10). Osteolysis of the calvaria bone was induced two weeks later by application of ultra-high-molecular-weight polyethylene- (UHMWPE) particles to the dome (vs sham operation). The extent of osteolysis was determined histologically and by micro-computer tomography.

RESULTS

Prednisone significantly inhibited particle-induced osteolysis in the skull. No significant difference in osteoclast numbers was seen in mice with prednisone vs placebo treatment. Prednisone treatment alone without particle application did not reduce bone mineral density or deterioration in bone microarchitecture parameters.

CONCLUSIONS

The calvaria particle-induced bone loss mouse model can be adapted to investigate osteoclast activity in vivo and the effect of prednisone on osteoclasts. In this preventive experimental design, the application of short-term low-dose prednisone has osteoprotective effects without measurable systemic side effects on bone parameters.

Carboxymethyl chitosan reduces inflammation and promotes osteogenesis in a rabbit knee replacement model

BACKGROUND

The major causes of failure after total knee arthroplasty (TKA) include prosthesis loosening and infection. This study aimed to investigate the role of carboxymethyl chitosan (CMC) in knee arthroplasty.

METHODS

A total of 20 New Zealand white rabbits that were divided into two groups (10 in the control group and 10 in the chitosan group) were included in the study. They underwent TKA surgery, and all were implanted with titanium rod prostheses; the prosthesis in the chitosan group was coated with CMC. After 12 weeks, all rabbits were euthanized, and the following analyses of some specific surface membrane tissues around the prosthesis were performed: X-ray analysis; micro-computed tomography scan; haematoxylin and eosin, Van Gieson, and Von Kossa staining; reverse transcription polymerase chain reaction; and Western Blotting.

RESULTS

The result of CCK8 test showed CMC can promote cell proliferation and increase cell viability. Radiological result showed better amount of bone deposits and more bone formation in the chitosan group. HE staining result showed CMC reduces inflammation around the prosthesis. The VG and Von Kossa staining results showed CMC can promote bone deposition around prosthesis. And according to the results of PCR and WB, the OCN content was higher in the chitosan group, while the MMPs content was lower. The chitosan group has an increased OPG/RANKL ratio than the control group.

CONCLUSION

CMC can effectively inhibit the inflammatory response around the prosthesis and osteoclast activation and promote osteogenesis by interfering with the osteoprotegerin/receptor activator of nuclear factor kappa-Β ligand/receptor activator of nuclear factor kappa-Β signalling pathway.

No pain, no gain? The effects of pain-promoting neuropeptides and neurotrophins on fracture healing

Neuropeptides and neurotrophins are key regulators of peripheral nociceptive nerves and contribute to the induction, sensitization, and maintenance of pain. It is now known that these peptides also regulate non-neuronal tissues, including bone. Here, we review the effects of numerous neuropeptides and neurotrophins on fracture healing. The neuropeptides calcitonin-gene related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating peptide (PACAP) have varying effects on osteoclastic and osteoblastic activity. Ultimately, CGRP and SP both accelerate fracture healing, while VIP and PACAP seem to negatively impact healing. Unlike the aforementioned neuropeptides, the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have more uniform effects. Both factors upregulate osteoblastic activity, osteoclastic activity, and, in vivo, stimulate osteogenesis to promote fracture healing. Future research will need to clarify the exact mechanism by which the neuropeptides and neurotrophins influence fracture healing. Specifically, understanding the optimal expression patterns for these proteins in the fracture healing process may lead to therapies that can maximize their bone-healing capabilities and minimize their pain-promoting effects. Finally, further examination of protein-sequestering antibodies and/or small molecule agonists and antagonists may lead to new therapies that can decrease the rate of delayed union/nonunion outcomes and fracture-associated pain.

MiR-152 influences osteoporosis through regulation of osteoblast differentiation by targeting RICTOR

Context: Evidence suggests that microRNA (miRNA) regulate gene expression and bone tissue homoeostasis of osteoporosis. MiR-152 has found to be abnormally expressed in osteoporosis, but its role in osteoblast differentiation has not been elucidated. Objective: To understand the potential mechanism of miR-152 in osteoblast differentiation via regulation of RICTOR. Materials and methods: The expression of miR-152 and RICTOR were tested in ovariectomized rat models of osteoporosis. Primary osteoblasts and MC3T -E1 cells were assigned into four groups, namely Control, miR-152 inhibitor, miR-control and miR-152 inhibitor + siRICTOR groups. qRT PCR and Western blot were performed to detect the expressions of miR-152 and RICTOR, respectively. MTT assay was used to evaluate cell viability, and ALP activity determination and mineralization analyses were also conducted. Results: In ovariectomy-induced osteoporotic rats, miR-152 (3.06 ± 0.35) in femoral tissues increased significantly, while RICTOR (0.31 ± 0.04) decreased. Compared with Control group, miR-152 inhibitor group presented appreciable reduction of miR-152 in primary osteoblasts and MC3T3-E1 cells, as well as remarkable increases in RICTOR, p-Akt(s473)/Akt ratio, and osteogenesis-related genes, with enhanced cell viability, ALP activity and mineralization. In comparison with cells in the miR-152 inhibitor group, those in the miR-152 inhibitor + siRICTOR group had no observable difference in miR-152, but were dramatically up-regulated in RICTOR, as well as the corresponding opposite tendencies of other factors. Conclusion: Inhibiting miR-152 promoted osteoblasts differentiation and alleviated osteoporosis by up-regulating RICTOR. Therefore, miR-152 may be an essential mediator of osteoblast differentiation and a new therapeutic strategy for osteoporosis.

No Association of CALCA Polymorphisms and Aseptic Loosening after Primary Total Hip Arthroplasty

Studies of aseptic loosening showed an influence of calcitonin and α-CGRP, both encoded from the calcitonin/α-CGRP (CALCA) gene by alternative splicing. The aim of this study was to detect a possible association of the CALCA polymorphisms P1(rs1553005), P2(rs35815751), P3(rs5240), and P4(rs2956) with the time to aseptic loosening after THA. 320 patients suffering from aseptic loosening after primary total hip arthroplasty were genotyped for CALCA-P1 polymorphism and 161 patients for CALCA-P2 and CALCA-P3 polymorphisms and 160 patients for CALCA-P4 polymorphism. CALCA genotypes were determined by polymerase chain reaction and restriction-fragment length polymorphism. The genotype distribution of CALCA-P1 was CC 10%, CT 43%, and 46% TT. CALCA-P2 showed a distribution of 90.7%II, 8.7% ID, and 0.6% DD. The CALCA-P3 genotype distribution was 97.5% TT and 2.5% TC. The CALCA-P4 genotype distribution was 48.1% AA, 40% AT, and 11.9% TT. Significant differences between the CALCA genotypes were not found concerning age at implantation and replantation, BMI, gender, and cementation technique. No associations of the time for aseptic loosening were found. In conclusion, we did not find a significant association of CALCA polymorphisms and the time to aseptic loosening after primary THA in a Western European group.

Micrometer-Sized Titanium Particles Induce Aseptic Loosening in Rabbit Knee

Wear debris induced aseptic loosening is the leading cause of total knee arthroplasty (TKA) failure. The complex mechanism of aseptic loosening has been a major issue for introducing effective prevention and treatment methods, so a simplified yet efficient rabbit model was established to address this concern with the use of micrometer-sized titanium particles. 20 New Zealand white rabbits were selected and divided into two groups (control = 10, study = 10). A TKA surgery was then performed for each of them, with implantation of a titanium rod prosthesis which was coated evenly with micrometer-sized titanium in the study group and nothing in the control group, into right femoral medullary cavity. After 12 weeks, all the animals were euthanized and X-ray analyses, H&E staining, Goldner Masson trichrome staining, Von Kossa staining, PCR, and Western blotting of some specific mRNAs and proteins in the interface membrane tissues around the prosthesis were carried out. The implantation of a titanium rod prosthesis coated with 20 μm titanium particles into the femoral medullary cavity of rabbits caused continuous titanium particle stimulation around the prosthesis, effectively inducing osteolysis and aseptic loosening. Titanium particle-induced macrophages produce multiple inflammatory factors able to activate osteoclast differentiation through the OPG/RANKL/RANK signaling pathway, resulting in osteolysis while suppressing the function of osteoblasts and reducing bone ingrowth around the prosthesis. This model simulated the implantation and loosening process of an artificial prosthesis, which is an ideal etiological model to study the aseptic prosthetic loosening.

Impact of vitamin E-blended UHMWPE wear particles on the osseous microenvironment in polyethylene particle-induced osteolysis

Aseptic loosening mediated by wear particle-induced osteolysis (PIO) remains the major cause of implant loosening in endoprosthetic surgery. The development of new vitamin E (α-tocopherol)-blended ultra-high molecular weight polyethylene (VE-UHMWPE) with increased oxidation resistance and improved mechanical properties has raised hopes. Furthermore, regenerative approaches may be opened, as vitamin E supplementation has shown neuroprotective characteristics mediated via calcitonin gene-related peptide (CGRP), which is known to affect bone remodeling in PIO. Therefore, the present study aimed to further clarify the impact of VE-UHMWPE wear particles on the osseous microenvironment and to identify the potential modulatory pathways involved. Using an established murine calvaria model, mice were subjected to sham operation (SHAM group), or treated with UHMWPE or VE-UHMWPE particles for different experimental durations (7, 14 and 28 days; n=6/group). Morphometric analysis by micro-computed tomography detected significant (p<0.01) and comparable signs of PIO in all particle-treated groups, whereas markers of inflammation [tumor necrosis factor (TNF)-α/tartrate resistant acid phosphatase (TRAP) staining] and bone remodeling [Dickkopf-related protein 1 (DKK-1)/osteoprotegerin (OPG)] were most affected in the early stages following surgery. Taking the present data into account, VE-UHMWPE appears to have a promising biocompatibility and increased ageing resistance. According to the α-CGRP serum levels and immunohistochemistry, the impact of vitamin E on neuropeptidergic signaling and its chance for regenerative approaches requires further investigation.

Inhibition of titanium-particle-induced inflammatory osteolysis after local administration of dopamine and suppression of osteoclastogenesis via D2-like receptor signaling pathway

Chronic inflammation and extensive osteoclast formation play critical roles in wear-debris-induced peri-implant osteolysis. We investigated the potential impact of dopamine on titanium-particle-induced inflammatory osteolysis in vivo and in vitro. Twenty-eight C57BL/6J mice were randomly assigned to four groups: sham control (PBS treatment), titanium (titanium/PBS treatment), low- (titanium/2 μg kg(-1) day(-1) dopamine) and high-dopamine (titanium/10 μg kg(-1) day(-1) dopamine). After 2 weeks, mouse calvariae were collected for micro-computed tomography (micro-CT) and histomorphometry analysis. Bone-marrow-derived macrophages (BMMs) were isolated to assess osteoclast differentiation. Dopamine significantly reduced titanium-particle-induced osteolysis compared with the titanium group as confirmed by micro-CT and histomorphometric data. Osteoclast numbers were 34.9% and 59.7% (both p < 0.01) lower in the low- and high-dopamine-treatment groups, respectively, than in the titanium group. Additionally, low RANKL, tumor necrosis factor-α, interleukin-1β and interleukin-6 immunochemistry staining were noted in dopamine-treatment groups. Dopamine markedly inhibited osteoclast formation, osteoclastogenesis-related gene expression and pro-inflammatory cytokine expression in BMMs in a dose-dependent manner. Moreover, the resorption area was decreased with 10(-9) M and 10(-8) M dopamine to 40.0% and 14.5% (both p < 0.01), respectively. Furthermore, the inhibitory effect of dopamine was reversed by the D2-like-receptor antagonist haloperidol but not by the D1-like-receptor antagonist SCH23390. These results suggest that dopamine therapy could be developed into an effective and safe method for osteolysis-related disease caused by chronic inflammation and excessive osteoclast formation.

Intermittent Administration of Parathyroid Hormone [1-34] Prevents Particle-Induced Periprosthetic Osteolysis in a Rat Model

We examined whether intermittent administration of parathyroid hormone [1-34] (PTH[1-34]; 60 μg/kg/day) can prevent the negative effects of titanium (Ti) particles on implant fixation and periprosthetic osteolysis in a rat model. Eighteen adult male rats (12 weeks old, bones still growing) received intramedullary Ti implants in their bilateral femurs; 6 rats from the blank group received vehicle injections, and 12 rats from the control group and PTH treatment group received Ti particle injections at the time of operation and intra-articular injections 2 and 4 weeks postoperatively. Six of the rats that received Ti particles from the PTH group also received PTH[1-34] treatment. Six weeks postoperatively, all specimens were collected for assessment by X-ray, micro-CT, biomechanical, scanning electron microscopy (SEM), and dynamic histomorphometry. A lower BMD, BV/TV, Tb.N, maximal fixation strength, and mineral apposition rate were observed in the control group compared to the blank group, demonstrating that a periprosthetic osteolysis model had been successfully established. Administration of PTH[1-34] significantly increased the bone mineral density of the distal femur, BV/TV, Tb.N, Tb.Th, Tb.Sp, Con.D, SMI, and maximal fixation strength in the PTH group compared to that in the control group. SEM revealed higher bone-implant contact, thicker lamellar bone, and larger trabecular bone area in the PTH group than in the control group. A higher mineral apposition rate was observed in the PTH group compared to both the blank and control groups. These findings imply that intermittent administration of PTH[1-34] prevents periprosthetic osteolysis by promoting bone formation. The effects of PTH[1-34] were evaluated at a suprapharmacological dosage to the human equivalent in rats; therefore, additional studies are required to demonstrate its therapeutic potential in periprosthetic osteolysis.

The role of calcitonin receptor signalling in polyethylene particle-induced osteolysis

The detection of peptides from the calcitonin (CT) family in the periarticular tissue of loosened implants has raised hopes of opening new regenerative therapies in the process of aseptic loosening, which remains the major cause of early implant failure in endoprosthetic surgery. We have previously shown the roles of α-calcitonin gene-related peptide (α-CGRP) and the CALCA gene which encodes α-CGRP/CT in this process. To uncover the role of direct calcitonin receptor (CTR) mediated signalling, we studied particle-induced osteolysis (PIO) in a murine calvaria model with a global deletion of the CTR (CTR-KO) using μCT analysis and histomorphometry. As expected, CTR-KO mice revealed reduced bone volume compared to wild-type (WT) controls (p<0.05). In CTR-KO mice we found significantly higher RANKL (receptor activator of NF-κB ligand) expression in the particle group than in the control group. The increase in osteoclast numbers by the particles was twice as high as the increase of osteoclasts in the WT mice (400 vs. 200%). Changes in the eroded surface and actual osteolysis due to ultrahigh-molecular-weight polyethylene particles were similar in WTs and CTR-KOs. Taken together, our findings strengthen the relevance of the OPG/RANK/RANKL system in the PIO process. CTR seems to have an effect on osteoclast differentiation in this context. As there were no obvious changes of the amount of PIO in CTR deficiency, regenerative strategies in aseptic loosening of endoprosthetic implants based on peptides arising from the CT family should rather focus on the impact of α-CGRP.

Calcitonin gene-related peptide modulates the production of pro-inflammatory cytokines associated with periprosthetic osteolysis by THP-1 macrophage-like cells

OBJECTIVE

An anti-resorptive impact of the neuropeptide calcitonin gene-related peptide (CGRP) on periprosthetic osteolysis, the leading cause of early prosthesis loosening, has been shown previously. In this study, the impact of CGRP on pro-inflammatory cytokine production associated with periprosthetic osteolysis was analysed using THP-1 macrophage-like cells.

METHODS

Cells were stimulated with ultra-high-molecular-weight polyethylene (UHMWPE) particles (cell-to-particle ratios of 1:100 and 1:500) and lipopolysaccharides (LPS; 1 µg/ml) to establish osteolytic conditions, and simultaneously treated with CGRP (10(-8)M). Receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and tumour necrosis factor (TNF)-α mRNA expression were measured by quantitative RT-PCR. RANK protein was detected by Western blot. Secreted protein levels of TNF-α as well as interleukin (IL)-1β and IL-6 were quantified in cell culture supernatants by ELISA and Bio-Plex cytokine assay, respectively.

RESULTS

Activation of macrophage-like cells failed to enhance the production of RANK but led to a dose- and time-dependent increase of TNF-α mRNA and secreted protein levels of TNF-α, IL-1β and IL-6. Application of CGRP time-dependently suppressed TNF-α mRNA expression induced by low-particle concentrations and LPS, while both particle- and LPS-induced secretion of TNF-α was inhibited. A pronounced inhibitory effect of CGRP on LPS-induced cytokine production at 24 h of incubation was also observed with IL-1β and IL-6.

CONCLUSIONS

CGRP shows a time-dependent inhibitory effect on the secretion of osteolysis-associated pro-inflammatory cytokines, indicating an indirect anti-resorptive influence of the neuropeptide on both aseptic prosthesis loosening and bacterially induced bone resorption which might enhance the life time of total joint replacements.

Effect of CGRP-adenoviral vector transduction on the osteoblastic differentiation of rat adipose-derived stem cells

Calcitonin gene-related peptide (CGRP) promotes osteoblast recruitment and osteogenic activity. However, no evidence suggests that CGRP could affect the differentiation of stem cells toward osteoblasts. In this study, we genetically modified adipose-derived stem cells (ADSCs) by introducing the CGRP gene through adenoviral vector transduction and investigated on cellular proliferation and osteoblast differentiation in vitro and osteogenesis in vivo as well. For the in vitro analyses, rat ADSCs were transducted with adenoviral vectors containing the CGRP gene (Ad-CGRP) and were cultured in complete osteoblastic medium. The morphology, proliferative capacity, and formation of localized regions of mineralization in the cells were evaluated. The expression of alkaline phosphatase (ALP) and special markers of osteoblasts, such as Collagen I, Osteocalcin (BPG) and Osteopontin (OPN), were measured by cytochemistry, MMT, RT-PCR, and Western blot. For the in vivo analyses, the Ad-CGRP-ADSCs/Beta-tricalcium phosphate (β-TCP) constructs were implanted in rat radial bone defects for 12 weeks. Radiography and histomorphology evaluations were carried out on 4 weeks and 12 weeks. Our analyses indicated that heterogeneous spindle-shaped cells and localized regions of mineralization were formed in the CGRP-transduced ADSCs (the transduced group). A higher level of cellular proliferation, a high expression level of ALP on days 7 and 14 (p<0.05), and increased expression levels of Collagen I, BPG and OPN presented in transduced group (p<0.05). The efficiency of new bone formation was dramatically enhanced in vivo in Ad-CGRP-ADSCs/β-TCP group but not in β-TCP group and ADSCs/β-TCP group. Our results reveal that ADSCs transduced with an Ad-CGRP vector have stronger potential to differentiate into osteoblasts in vitro and are able to regenerate a promising new tissue engineering bone in vivo. Our findings suggest that CGRP-transduced ADSCs may serve as seed cells for bone tissue engineering and provide a potential way for treating bone defects.

Direct subcutaneous injection of polyethylene particles over the murine calvaria results in dramatic osteolysis

PURPOSE

The murine calvarial model has been widely employed for the in vivo study of particle-induced osteolysis, the most frequent cause of aseptic loosening of total joint replacements. Classically, this model uses an open surgical technique in which polyethylene (PE) particles are directly spread over the calvarium for the induction of osteolysis. We evaluated a minimally invasive modification of the calvarial model by using a direct subcutaneous injection of PE particles.

METHODS

Polyethylene (PE) particles were injected subcutaneously over the calvaria of C57BL6J ten-week-old mice ("injection" group) or were implanted after surgical exposure of the calvaria ("open" group) (n = 5/group). For each group, five additional mice received no particles and served as controls. Particle-induced osteolysis was evaluated two weeks after the procedure using high-definition microCT imaging.

RESULTS

Polyethylene particle injection over the calvaria resulted in a 40% ± 1.8% decrease in the bone volume fraction (BVF), compared to controls. Using the "open surgical technique", the BVF decreased by 16% ± 3.8% as compared to controls (p < 0.0001).

CONCLUSIONS

Direct subcutaneous injection of PE particles over the murine calvaria produced more profound resorption of bone. Polyethylene particle implantation by injection is less invasive and reliably induces osteolysis to a greater degree than the open technique. This subcutaneous injection method will prove useful for repetitive injections of particles, and the assessment of potential local or systemic therapies.

MMP-9 inhibition suppresses wear debris-induced inflammatory osteolysis through downregulation of RANK/RANKL in a murine osteolysis model

Wear debris-induced osteolysis in periprosthetic tissue with aseptic loosening is a serious problem after total joint arthroplasty. Matrix metalloproteinase-9 (MMP-9) is expressed in osteoclast cells that surround loosening peri-implant tissue, but the molecular mechanism of MMP-9 action in wear debris-induced osteolysis remains ambiguous. We used a murine osteolysis model to examine the hypothesis that administration of an MMP-9 inhibitor reduces the expression of receptor activator of nuclear factor-κB (RANK) and nuclear factor-κB ligand (RANKL) and, thereby, suppressesdebris-induced inflammatory osteolysis. Experiments were performed in 3 groups of 15 mice: a control, a titanium (Ti) and a Ti plus tetracycline group. To provoke inflammatory osteolysis, calvarial bone was implanted from syngeneic littermates, followed by injection of Ti particles into established air pouches for all groups except the control. Tetracycline was administered daily by intraperitoneal (i.p.) injection, and PBS was administered by i.p. injection to the control and Ti groups. Mice were sacrificed 14 days after bone-Ti implantation. Pouch membranes with the intact bone implants were collected for histological and molecular analysis. Tetracycline had minimum effect on the expression of MMP-9 and tumor necrosis factor-α (TNF-α) but it decreased gene activation and inhibited the expression of RANK and RANKL, thereby inhibiting Ti-particle-induced inflammatory osteolysis. Tetracycline decreased the number of tartrate-resistant acid phosphatase (TRAP)-positive cells in the pouch tissues. Our results in the murine osteolysis model suggest that through the downregulation of RANK/RANKL, tetracycline significantly inhibits debris-induced inflammatory osteolysis. Its use in clinical practice may help prevent complications experienced by patients who have undergone total joint arthroplasty.

Calcitonin substitution in calcitonin deficiency reduces particle-induced osteolysis

Background

Periprosthetic osteolysis is a major cause of aseptic loosening in joint arthroplasty. This study investigates the impact of CT (calcitonin) deficiency and CT substitution under in-vivo circumstances on particle-induced osteolysis in Calca -/- mice.

Methods

We used the murine calvarial osteolysis model based on ultra-high molecular weight polyethylene (UHMWPE) particles in 10 C57BL/6J wild-type (WT) mice and twenty Calca -/- mice. The mice were divided into six groups: WT without UHMWPE particles (Group 1), WT with UHMWPE particles (Group 2), Calca -/- mice without UHMWPE particles (Group 3), Calca -/- mice with UHMWPE particles (Group 4), Calca -/- mice without UHMWPE particles and calcitonin substitution (Group 5), and Calca -/- mice with UHMWPE particle implantation and calcitonin substitution (Group 6). Analytes were extracted from serum and urine. Bone resorption was measured by bone histomorphometry. The number of osteoclasts was determined by counting the tartrate-resistant acid phosphatase (TRACP) + cells.

Results

Bone resorption was significantly increased in Calca -/- mice compared with their corresponding WT. The eroded surface in Calca -/- mice with particle implantation was reduced by 20.6% after CT substitution. Osteoclast numbers were significantly increased in Calca -/- mice after particle implantation. Serum OPG (osteoprotegerin) increased significantly after CT substitution.

Conclusions

As anticipated, Calca -/- mice show extensive osteolysis compared with wild-type mice, and CT substitution reduces particle-induced osteolysis.

Effects of alpha-calcitonin gene-related peptide on osteoprotegerin and receptor activator of nuclear factor-κB ligand expression in MG-63 osteoblast-like cells exposed to polyethylene particles

BACKGROUND

Recent studies demonstrated an impact of the nervous system on particle-induced osteolysis, the major cause of aseptic loosening of joint replacements.

METHODS

In this study of MG-63 osteoblast-like cells we analyzed the influence of ultra-high molecular weight polyethylene (UHMWPE) particles and the neurotransmitter alpha-calcitonin gene-related peptide (CGRP) on the osteoprotegerin/receptor activator of nuclear factor-κB ligand/receptor activator of nuclear factorκB (OPG/RANKL/RANK) system. MG-63 cells were stimulated by different UHMWPE particle concentrations (1:100, 1:500) and different doses of alpha-CGRP (10-7 M, 10-9 M, 10-11 M). RANKL and OPG mRNA expression and protein levels were measured by RT-PCR and Western blot.

RESULTS

Increasing particle concentrations caused an up-regulation of RANKL after 72 hours. Alpha-CGRP showed a dose-independent depressive effect on particle-induced expression of RANKL mRNA in both cell-particle ratios. RANKL gene transcripts were significantly (P < 0.05) decreased by alpha-CGRP treatment after 48 and 72 hours. OPG mRNA was significantly down-regulated in a cell-particle ratio of 1:500 after 72 hours. Alpha-CGRP concentrations of 10-7 M lead to an up-regulation of OPG protein.

CONCLUSION

In conclusion, a possible osteoprotective influence of the neurotransmitter alpha-CGRP on particle stimulated osteoblast-like cells could be shown. Alpha-CGRP might be important for bone metabolism under conditions of particle-induced osteolysis.

Alpha-calcitonin gene-related peptide can reverse the catabolic influence of UHMWPE particles on RANKL expression in primary human osteoblasts

Background and purpose: A linkage between the neurotransmitter alpha-calcitonin gene-related peptide (alpha-CGRP) and particle-induced osteolysis has been shown previously. The suggested osteoprotective influence of alpha-CGRP on the catabolic effects of ultra-high molecular weight polyethylene (UHMWPE) particles is analyzed in this study in primary human osteoblasts. Methods: Primary human osteoblasts were stimulated by UHMWPE particles (cell/particle ratios 1:100 and 1:500) and different doses of alpha-CGRP (10^-7 M, 10^-9 M, 10^-11 M). Receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) mRNA expression and protein levels were measured by RT-PCR and Western blot. Results: Particle stimulation leads to a significant dose-dependent increase of RANKL mRNA in both cell-particle ratios and a significant down-regulation of OPG mRNA in cell-particle concentrations of 1:500. A significant depression of alkaline phosphatase was found due to particle stimulation. Alpha-CGRP in all tested concentrations showed a significant depressive effect on the expression of RANKL mRNA in primary human osteoblasts under particle stimulation. Comparable reactions of RANKL protein levels due to particles and alpha-CGRP were found by Western blot analysis. In cell-particle ratios of 1:100 after 24 hours the osteoprotective influence of alpha-CGRP reversed the catabolic effects of particles on the RANKL expression. Interpretation: The in-vivo use of alpha-CGRP, which leads to down-regulated RANKL in-vitro, might inhibit the catabolic effect of particles in conditions of particle induced osteolysis.

Biochemical markers of particle induced osteolysis in C57BL/6 mice

BACKGROUND

Micro-structural changes associated with ultra high molecular weight polyethylene particle (UHMWPE) induced osteolysis, the most frequent cause of aseptic loosening, have been intensively investigated in the mammalian calvarian model by histomorphometry and micro-computed tomography. However, little is known regarding the serological changes that occur during this process.

METHODS

Serological parameters for bone metabolism [calcium, phosphate, osteocalcin (OCN), deoxypyridinoline (DPD)/creatinine, alkaline phosphatase, osteoprotegerin and receptor activator of nuclear factor-κB] were analyzed in this animal model for particle induced osteolysis. Ten C57BL/6 mice were divided at random into sham operated and UHM-WPE implanted groups. Blood and urine samples were collected prior to and at 14 days after surgery.

RESULTS

Implantation of UHMWPE lead to a significant decrease in bone volume (p=0.027). Both groups (sham/UHMWPE) showed a significant increase in calcium (p=0.004/p=0.027) and phosphate (p=0.001/p=0.001), without correlation to particle implantation. Significantly higher concentrations of DPD/creatinine (p=0.034) and OCN (p=0.022) were found after implantation of UHM-WPE. In addition, parameters could not be correlated to particle induced osteolysis.

CONCLUSIONS

DPD can be regarded as a valuable parameter for detecting UHMWPE induced osteolysis in the calvarian model. Further studies of serum parameters should focus on the clinical relevance in aseptic prosthetic loosening.

BCL2-938C>A and CALCA-1786T>C polymorphisms in aseptic loosened total hip arthroplasty

The search for influencing factors and new pathways in aseptic loosening of arthroplasties is a major focus of recent studies. Analyses of polymorphisms of genes revealed a correlation between a specific allele variant and aseptic loosening. The BCL2 gene encoding Bcl-2 with its BCL2 -938C > A polymorphism is a crucial factor of cell cycle control and cell survival. The CALCA -1786T > C polymorphism belongs to the CALCA gene encoding alpha-Calcitonin Gene Related Peptide (CGRP) and Calcitonin. Both proteins are important in bone metabolism and capable to influence the process of aseptic loosening. To date, no studies are reported for aseptic loosening with these two single nucleotide polymorphisms (SNPs). In a retrospective study we determined the distribution of the BCL2-938C > A and the CALCA-1786T > C polymorphisms in 87 subjects with aseptic loosened hip arthroplasties using RFLP and pyrosequencing analysis. Genotype distribution with prognosis of the hip arthroplasty showed neither an association with clinical characteristics of the patients nor the implantation technique. We were unable to detect any influence of these polymorphisms on time to aseptic loosening.

Alumina ceramic particles, in comparison with titanium particles, hardly affect the expression of RANK-, TNF-alpha-, and OPG-mRNA in the THP-1 human monocytic cell line

Particle-induced osteolysis is the most frequent cause of aseptic loosening after total joint replacement. We performed a study to illuminate the effect of ceramic particles with different diameters and concentrations on the mRNA expression of certain key regulators in particle-induced aseptic osteolysis (RANK, RANKL, OPG, and TNF-alpha) in THP-1 macrophage-like cells. Titanium particles were used as a positive control. RNA was analyzed by quantitative RTPCR. Our results demonstrate that alumina ceramic particles, regardless of particle size, caused only slight upregulations of RANK, TNF-alpha, and OPG mRNA, whose levels were significantly lower in comparison with those of titanium particles (p < 0.05). The continuous increasing tendency to time and particle-dependent mRNA expression of all the parameters stimulated by titanium particles was not found after stimulation with ceramic materials. Even after the concentration of ceramic particles was increased, only a mild upregulation of mRNA expression was found. Furthermore, we observed that the bioinert properties of ceramic particles did not change much in diameters ranging from 0.5 to 1.5 microm. At most of the measuring time points, there was no significant difference between the reactions of the large and small particles in this range. Our results support the theory about the relative bioinert properties of alumina ceramic particles.

Particle-induced osteolysis in three-dimensional micro-computed tomography

Small-animal models are useful for the in vivo study of particle-induced osteolysis, the most frequent cause of aseptic loosening after total joint replacement. Microstructural changes associated with particle-induced osteolysis have been extensively explored using two-dimensional (2D) techniques. However, relatively little is known regarding the 3D dynamic microstructure of particle-induced osteolysis. Therefore, we tested micro-computed tomography (micro-CT) as a novel tool for 3D analysis of wear debris-mediated osteolysis in a small-animal model of particle-induced osteolysis. The murine calvarial model based on polyethylene particles was utilized in 14 C57BL/J6 mice randomly divided into two groups. Group 1 received sham surgery, and group 2 was treated with polyethylene particles. We performed 3D micro-CT analysis and histological assessment. Various bone morphometric parameters were assessed. Regression was used to examine the relation between the results achieved by the two methods. Micro-CT analysis provides a fully automated means to quantify bone destruction in a mouse model of particle-induced osteolysis. This method revealed that the osteolytic lesions in calvaria in the experimental group were affected irregularly compared to the rather even distribution of osteolysis in the control group. This is an observation which would have been missed if histomorphometric analysis only had been performed, leading to false assessment of the actual situation. These irregularities seen by micro-CT analysis provide new insight into individual bone changes which might otherwise be overlooked by histological analysis and can be used as baseline information on which future studies can be designed.