Murine Osteolysis Model Research Articles

Protein phosphatase 2A as a new target for downregulating osteoclastogenesis and alleviating titanium particle-induced bone resorption

Receptor activator of nuclear factor-кB ligand (RANKL)-induced osteoclastogenesis is believed to play a critical role in osteolytic diseases including peri-prosthetic osteolysis (PPO), the primary reason for implant failure and revision surgery. In this study, we observed that protein phosphatase 2A (PP2A), a major serine-threonine phosphatase, was highly expressed in human periprosthetic interface membranes with aseptic loosening and in a murine osteolysis model induced by titanium particle irritation. PP2A inhibition effectively alleviated titanium particle-induced bone destruction at osteolytic sites. In addition, PP2A downregulation significantly decreased osteoclast numbers and RANKL expression, compared with in animals treated with only titanium. Mechanistically, a PP2A selective inhibitor or PP2A siRNA suppressed osteoclastogenesis and alleviated osteoclastic resorption by inhibiting the RANKL-induced nuclear factor-кB and c-Jun N-terminal kinase signaling pathways. Downstream NFATc1 and c-Fos expression were also substantially suppressed by PP2A inhibition or knockdown. Our findings support the importance of PP2A during osteoclastogenesis, identifying PP2A as a novel target for treating particle-induced or other osteoclast-mediated bone resorption diseases. Statement of significanceExcessive osteoclast activation disrupts bone homeostasis and leads to osteoclast-mediated bone resorption diseases, such as peri-prosthetic osteolysis, regarded as the primary reason for implant failure and revision surgery. Here, we firstly demonstrated protein phosphatase 2A (PP2A), a major serine-threonine phosphatase, was highly expressed in human periprosthetic interface membranes with aseptic loosening and murine osteolysis model. Moreover, PP2A inhibition effectively alleviated titanium particle-induced bone destruction and decreased osteoclast numbers. Meanwhile, a PP2A selective inhibitor or PP2A siRNA suppressed osteoclastogenesis and alleviated osteoclastic resorption by inhibiting the nuclear factor-кB and c-Jun N-terminal kinase signaling pathways. Thus, PP2A is involved in osteoclastogenesis and could be a promising target for regulating bone homeostasis and osteolytic responses.

Titanium particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3\u03b2/\u03b2-catenin signal pathway

Wear debris-induced osteogenic inhibition and bone destruction are critical in the initiation of peri-prosthetic osteolysis. However, the molecular mechanism underlying this phenomenon is poorly understood. In this study, we analyzed the involvement of the GSK-3β/β-catenin signal pathway, which is important for bone formation in this pathological condition. We established a titanium (Ti) particle-stressed murine MC3T3-E1 cell culture system and calvariae osteolysis model to test the hypothesis that Ti particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3β/β-catenin signal pathway. Our findings showed that Ti particles reduced osteogenic differentiation induced by osteogenesis-related gene expression, alkaline phosphatase activity and matrix mineralization, as well as pSer9-GSK-3β expression and β-catenin signal activity. Downregulation of GSK-3β activity attenuated Ti particle-induced osteogenic inhibition, whereas the β-catenin inhibitor reversed this protective effect. Moreover, the GSK-3β/β-catenin signal pathway mediated the upregulation of RANKL and downregulation of OPG in Ti particle-stressed MC3T3-E1 cells. In addition, our in vivo results showed that Ti particles induced bone loss via regulating GSK-3β and β-catenin signals. Based on these results, we concluded that the GSK-3β/β-catenin signal pathway mediates the adverse effects of Ti particles on osteoblast differentiation and bone destruction, and can be used as a potential therapeutic target for the treatment of peri-prosthetic osteolysis.

Surgical Modification of the Murine Calvaria Osteolysis Model.

The murine calvaria model has been adopted for evaluation of osteolysis and inflammation induced by polyethylene (PE) or metal wear debris. However, this model suffers from several complications. The purpose of our study is to introduce a surgical modification with lower complication rates, thus providing more accurate results. Forty C57/BL6 mice were divided into two groups, both receiving polyethylene particles. Surgical modifications were performed in group 1, and group 2 underwent traditional surgeries. The incidence of fluid leakage was recorded on the operative day. Curst formation, wound dehiscence, and bone exposure were recorded on day 7. Histological osteolysis was demonstrated by HE staining of tissue slices. Micro-CT was used for quantifying evaluation of osteolysis in two groups. Intraoperative fluid leakage was significantly reduced in group 1. Postoperative crust formation, wound dehiscence, and bone exposure were also significantly decreased in group 1. HE staining results revealed obvious osteolysis in group 1 and more obvious osteolysis in group 2. Bone volume fraction (BVF) was (0.32 ± 0.03) in group 1 compared to group 2 (0.24 ± 0.05). Bone mineral density (BMD) was (1.11 ± 0.03) in group 1 compared to group 2 (1.01 ± 0.02). Surgical modifications provide a reliable way for establishment of the murine calvaria osteolysis model.

Protective effect of p38 MAPK inhibitor on wear debris-induced inflammatory osteolysis through downregulating RANK/RANKL in a mouse model.

Aseptic loosening associated with wear particle-induced inflammation is a major cause of joint implant failure. Recent studies have demonstrated the therapeutic effects of p38 mitogen-activated protein kinase (MAPK)-based therapies on chronic inflammatory diseases. The purpose of this study was to investigate whether SB203580, a p38 MAPK inhibitor, inhibits wear debris-induced inflammatory osteolysis in mice through downregulation of receptor activator of nuclear factor kβ (RANK)/RANK ligand (RANKL). We used a murine osteolysis model to study the effect of SB203580 on RANKL/RANK signaling and titanium particle-induced osteolysis in vivo. Pouch membranes with intact bone implants were analyzed using histological analysis and transmission electron microscopy, and the levels of RANK and RANKL protein and mRNA were evaluated by immunohistological staining and real-time reverse transcriptase-polymerase chain reaction. SB203580 had less of an effect on RANK and RANKL expression under wear debris-induced conditions. The number of TRAP-positive cells was remarkably reduced in Ti-particle-induced pouch tissues. These effects were confirmed through the transmission electron microscopy results. These results suggest that p38 MAPK-based therapies are beneficial in preventing aseptic loosening associated with total joint replacement by modulating RANK-RANKL signaling.

Strontium ranelate inhibits titanium-particle-induced osteolysis by restraining inflammatory osteoclastogenesis in vivo

Wear-particle-induced osteolysis is considered to be the main reason for revision after arthroplasty. Although the exact mechanism remains unclear, inflammatory osteoclastogenesis plays an important role in this process. Strontium ranelate (SR) was found to have a therapeutic effect on osteoporosis in postmenopausal women. Based on prior studies, the present authors hypothesized that SR prevents wear-particle-induced osteolysis through restraining inflammatory osteoclastogenesis. The present study used 80 male C57BL/J6 mice to test this hypothesis in a murine osteolysis model. All experimental animals were randomly divided into four groups: a control group; a SR group; a titanium group; and a titanium+SR group. Once titanium particles had been implanted in mice, the mice were administered SR (900mgkg−1day−1) by gavage for 14days. After 14days, the calvaria were collected for micro-computed tomography (μCT), histological and molecular analysis. The results of μCT and histomorphometric analysis demonstrated that SR markedly inhibited bone resorption and the generation of tartrate-resistant acid-phosphatase-positive cells in vivo, compared with titanium-stimulated calvaria. Reverse transcription polymerase chain reaction and ELISAs showed that SR stimulated the mRNA and protein expression of osteoprotegerin, and inhibited gene and protein expression of receptor activators of nuclear factor-kappa B ligand in titanium-particle-charged calvaria. In addition, SR obviously reduced the secretion of tumor necrosis factor-α and interleukin-1β in the calvaria of the titanium group. It was concluded that SR inhibits titanium-induced osteolysis by restraining inflammatory osteoclastogenesis, and that it could be developed as a new drug to prevent and treat aseptic loosening.

Early Diagnosis of Orthopedic Implant Failure Using Macromolecular Imaging Agents

To develop and evaluate diagnostic tools for early detection of wear particle-induced orthopaedic implant loosening. N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer was tagged with a near infrared dye and used to detect the inflammation induced by polymethylmethacrylate (PMMA) particles in a murine peri-implant osteolysis model. It was established by inserting an implant into the distal femur and challenging with routine PMMA particles infusion. The osteolysis was evaluated by micro-CT and histological analysis at different time points. Significant peri-implant osteolysis was found 3-month post PMMA particle challenge by micro-CT and histological analysis. At 1-month post challenge, when there was no significant peri-implant bone loss, the HPMA copolymer-near infrared dye conjugate was found to specifically target the femur with PMMA particles deposition, but not the contralateral control femur with phosphate buffered saline (PBS) infusion. The results from this study demonstrate the feasibility of utilizing the macromolecular diagnostic agent to detect particle-induced peri-implant inflammation prior to the development of detectable osteolysis. Recognition of this early pathological event would provide the window of opportunity for prevention of peri-implant osteolysis and subsequent orthopaedic implant failure.

Development of Polymeric Nanocarrier System for Early Detection and Targeted Therapeutic Treatment of Peri-Implant Osteolysis

Extensive research has implicated inflammation as a necessary and causative factor in the development of peri-implant osteolysis, suggesting that such an inflammatory response is the sentinel event for the process. The potential to impact the clinical course of this condition is hampered by the lack of an effective medical therapy, as well as a limited ability for early detection prior to radiographically evident osteolysis. Advances in nanotechnology have allowed for the production of engineered water-soluble nanocarriers, which exploit changes in the microvascular architecture for selective distribution to inflamed tissues. Evaluation of the uptake of the nanocarriers in sites of inflammation has elucidated a novel mechanism of cellular uptake and retention of these particles. The current review discusses the development of a novel, biocompatible, water-soluble nanocarrier utilizing copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA), conjugated to imaging and therapeutic agents for the detection and targeted treatment of inflammatory conditions. We performed Medline searches for the terms "periprosthetic osteolysis," "murine osteolysis model," "HPMA osteolysis," and "HPMA inflammation." These searches identified 631, 306, 1, and 6 articles, respectively. These were then manually searched for articles relevant to the development of mouse models for inflammatory osteolysis and the use of HPMA copolymer technology in mouse models of inflammation. Promising results in a small animal model of osteolysis have demonstrated the capability for detection prior to the development of bone loss, and have highlighted the utility of nanocarriers for selective drug delivery to the affected tissues. Challenges to the clinical translation of HPMA nanocarriers in peri-implant osteolysis remain, and the future research directions necessary for human clinical application are reviewed.

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.

Inhibition of p38 Mitogen-Activated Protein Kinase Down-regulates the Inflammatory Osteolysis Response to Titanium Particles in a Murine Osteolysis Model

The p38 mitogen-activated protein kinase (p38 MAPK) pathway is involved in the osteoclast differentiation. The aim of the study was to investigate whether SB203580, a p38 MAPK inhibitor, inhibits wear-debris-induced inflammatory osteolysis in mice. Forty-five mice were implanted with calvaria bone from syngeneic littermates; then, titanium (Ti) particles were injected into established air pouches to provoke inflammatory osteolysis. At 14days after bone/Ti implantation, pouch membranes with intact bone implants underwent histological and molecular analysis. SB203580 had less effect on MMP-9 and TNF-α expression under wear-debris-induced conditions. SB203580, by inhibiting the expression of p38 MAPK and phospho-p38 MAPK, inhibited Ti particle wear-debris-induced inflammatory osteolysis. It also remarkably decreased the number of tartrate-resistant acid phosphatase positive cells in Ti-particle-induced pouch tissues. Results suggest that p38 MAPK may be critical in a murine osteolysis model. SB203580 may notably inhibit wear-debris-induced inflammatory osteolysis by down-regulating expression of MMP-9 and TNF-α via the p38 MAPK pathway.

Protective effects of COX-2 inhibitor on titanium-particle-induced inflammatory osteolysis via the down-regulation of RANK/RANKL

Particle-wear-induced inflammatory osteolysis remains a major problem for the long-term success of total joint arthroplasty. Previous studies have demonstrated that cyclooxygenase-2 (COX-2) is expressed abundantly in the tissue around a failed implant. However, the role of COX-2 in the development of particle-wear-induced osteoclastogenesis remains unclear. The aim of the study was to test the hypothesis that Dynastat, a COX-2 inhibitor, ameliorates particle-wear-induced inflammatory osteoclastogenesis through the down-regulation of the receptor activators of nuclear factor-κB (RANK) and nuclear factor-κB ligand (RANKL) expression in a murine osteolysis model. Titanium (Ti) particles were introduced into established air pouches in BALB/c mice, followed by the implantation of calvaria bone from syngeneic littermates. Dynastat was given to mice intraperitoneally 2days before the introduction of Ti particles and maintained until the mice were sacrificed. Pouch tissues were collected 14days after Ti inoculation for molecular and histological analysis. The results showed that Dynastat has more impact on Ti-particle-induced prostaglandin E2 expression and less on the expression of interleukin-1β and tumor necrosis factor-α. Dynastat inhibited Ti-particle-induced osteoclastogenesis by reducing the gene activation of RANK and RANKL, and diminishing the RANKL expression in Ti-particle-charged pouches. Dynastat markedly reduced the number of tartrate-resistant acid-phosphatase-positive cells in pouch tissues stimulated by Ti particles. In conclusion, this study provides evidence that Dynastat can markedly inhibit Ti-particle-induced osteoclastogenesis by the down-regulation of RANK/RANKL in a murine air pouch model, and is a promising therapeutic candidate for the treatment of inflammatory osteolysis induced by wear particles.

Early Detection and Treatment of Wear Particle-Induced Inflammation and Bone Loss in a Mouse Calvarial Osteolysis Model Using HPMA Copolymer Conjugates

Wear particle-induced inflammation is considered to be the major cause of aseptic implant loosening and clinical failure after total joint replacement. Due to the frequent absence of symptoms, early detection and intervention prior to implant failure presents a significant challenge. To address this issue, a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-based optical imaging contrast agent (P-IRDye) was developed and used for the detection of wear particle-induced inflammation employing a murine calvaria osteolysis model. The particle-induced osteolysis of calvaria was evaluated by H&E, tartrate-resistant acid phosphatase (TRAP) staining and μ-CT after necropsy. One-day post particle implantation, P-IRDye was administrated to the mice via tail vein injection. Live imaging of the animals 6 days after implantation revealed the preferential distribution and sustained retention of the macromolecular contrast agent at the site of particle implantation. Immunohistochemical staining and FACS analyses of the calvaria-associated soft tissue revealed extensive uptake of the HPMA copolymer by F4/80, Ly-6G (Gr1) and CD11c positive cells, which accounts for the retention of the macromolecular probes at the inflammatory sites. To test the potential of the system for therapeutic intervention, an acid-labile HPMA copolymer-dexamethasone conjugate (P-Dex) was prepared and shown to prevent the particle-induced inflammation and bone damage in the calvaria osteolysis model.

Protection against titanium particle induced osteolysis by cannabinoid receptor 2 selective antagonist

Osteolysis and subsequent aseptic loosening are the most common causes of failure of total joint arthroplasty. Osteolysis is initiated by inflammatory response to wear debris, resulting in localized, osteoclastic peri-implant bone loss. However, there were no effective measures for prevention and treatment of periprosthetic osteolysis. The aim of the current study was to determine whether CB2 selective antagonist (AM630) inhibits wear debris-induced osteolysis in a murine osteolysis model. Titanium (Ti) particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. AM630 was given to mice intraperitoneally 2 days before Ti particles introduction and maintained until the sacrifice of the mice. Mice without drug treatment, as well as mice injected with saline alone, were included. Each group contains 10 mice. Pouch tissues were harvested 14 days after bone implantation for histological and molecular analysis. Ti particles stimulation significantly increased CB2 expression. However, less CB2 was observed in AM630 treatment group. AM630 inhibited Ti particle-induced osteolysis associated gene activity of RANK, RANKL and CPK, and diminished RANKL expression in Ti particle stimulated pouches. AM630 markedly reduced the number of TRAP+ cells in pouch tissues. In conclusion, this study provides the evidence that blockage of CB2 with AM630 can markedly reduce Ti particle induced osteolysis in a murine air pouch model. This finding points to the possibility that CB2 selective antagonists like AM630 may have potential value for prevention and treatment of wear particle induced osteolysis.

Antisense oligonucleotide targeting TNF‐α can suppress co‐cr‐mo particle‐induced osteolysis

The most common cause of implant failure in joint replacement is aseptic loosening due to particle-induced osteolysis. TNF-alpha has been shown to be one of the key factors in the process of osteoclastogenesis. Anti-TNF agents are useful in the treatment of joint inflammation related to osteolysis. This study investigated the effect of a single subcutaneous dose of an antisense oligonucleotide (ASO) on particle-induced osteolysis. We utilized the murine calvaria osteolysis model in C57BL/J6 mice. Bone resorption was measured by the toluidine blue staining. Osteoclasts were detected by tartrate resistant acid phosphatase (TRAP) staining assay and were quantified by a TRAP quantification kit. Results show that bone resorption is 0.347 +/- 0.09 mm(2) in mice with particle implantation, and decreased to 0.123 +/- 0.05 mm(2) and 0.052 +/- 0.02 mm(2) after ASO treatment with low and high doses, respectively. The number of osteoclasts in animal calvaria treated with ASO is reduced compared with that of untreated animals, and the quantification results indicate that about 90% of osteoclastogenesis is suppressed by the ASO. In addition, the osteoclastogenesis can be reestablished by the addition of TNF-alpha. In conclusion, we demonstrate that the antisense oligonucleotide targeting to TNF-alpha can suppress osteolysis induced by metal particles in a murine calvaria model. This new finding may be of value in the search for novel therapeutic methods for implant loosening.

Macrophage depletion diminishes implant‐wear‐induced inflammatory osteolysis in a mouse model

The purpose of this study was to determine whether macrophage depletion using clodronate liposomes diminishes wear-debris-induced inflammatory osteolysis in a murine osteolysis model. Ultra high molecular weight polyethylene (UHMWPE) particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. Macrophages were depleted by the intraperitoneal injection of clodronate liposome (2 mg) 2 days before bone implantation and re-injection every 3 days (1 mg) until the sacrifice of the mice. Mice without clodronate liposome therapy or treated with empty liposome as well as mice injected with saline alone were included in this study as controls. Pouch tissues were collected 14 days after bone implantation for molecular and histology analysis. Our findings indicated that (1) macrophage depletion in clodronate-liposome-treated mice was achieved, as illustrated by F4/80 immunostaining in both pouch and spleen tissues; (2) clodronate-liposome treatment significantly reduced UHMWPE-induced tissue inflammation, with diminished pouch membrane thickness, reduced inflammatory cellular infiltration, and lowered interleukin 1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) expression; (3) clodronate-liposome treatment markedly reduced the number of TRAP(+) cells in pouch tissues and protected against bone collagen depletion. In conclusion, this study demonstrates that macrophage depletion using clodronate-liposome reduces UHMWPE particle-induced inflammatory osteolysis. This observation supports the hypothesis that macrophages contribute to the severity of UHMWPE particles induced inflammatory osteolysis, and suggest that macrophage depletion represents a viable therapeutic approach to the prevention and treatment of patients with aseptic loosening.

Implant wear induces inflammation, but not osteoclastic bone resorption, in RANK–/– mice

Signaling of RANK (receptor activator of nuclear factor kappa B) through its ligand RANKL appears critical in osteolysis associated with aseptic loosening (AL). The purpose of this study was to investigate the role of RANK in a murine osteolysis model developed in RANK knockout (RANK(-/-)) mice. Ultra high molecular weight polyethylene (UHMWPE) debris was introduced into established air pouches on RANK(-/-) mice, followed by implantation of calvaria bone from syngeneic littermates. Wild type C57BL/6 (RANK(+/+)) mice injected with either UHMWPE or saline alone were included in this study. Pouch tissues were collected 14 days after UHMWPE inoculation for molecular and histology analysis. Results showed that UHMWPE stimulation induced strong pouch tissue inflammation in RANK(-/-) mice, as manifested by inflammatory cellular infiltration, pouch tissue proliferation, and increased gene expression of IL-1beta, TNFalpha, and RANKL. However, the UHMWPE-induced inflammation in RANK(-/-) mice was not associated with the osteoclastic bone resorption observed in RANK(+/+) mice. In RANK(+/+) mice subjected to UHMWPE stimulation, a large number of TRAP(+) cells were found on the implanted bone surface, where active osteoclastic bone resorption was observed. No TRAP(+) cells were found in UHMWPE-containing pouch tissues of RANK(-/-) mice. Consistent with the lack of osteoclastic activity shown by TRAP staining, no significant UHMWPE particle-induced bone resorption was found in RANK(-/-) mice. A well preserved bone collagen content (Van Gieson staining) and normal plateau surface contour [microcomputed tomography (microCT)] of implanted bone was observed in RANK(-/-) mice subjected to UHMWPE stimulation. In conclusion, this study provides the evidence that UHMWPE particles induce strong inflammatory responses, but not associated with osteoclastic bone resorption in RANK(-/-) mice. This indicates that RANK signaling is essential for UHMWPE particle-induced osteoclastic bone resorption, but does not participate in UHMWPE particle-induced inflammatory response.

Erythromycin inhibits wear debris‐induced inflammatory osteolysis in a murine model

Up to 20% of patients with total joint arthroplasty will develop radiographic evidence of aseptic loosening (AL), which most likely results from an inflammatory response to billions of wear debris shed from the implant. Our previous work has demonstrated that erythromycin (EM), a macrolide antibiotic, inhibits wear debris-induced inflammatory osteoclastogenesis through the reduction of cytokine production and osteoclast differentiation, both of which involve the NF-kappaB pathway. The aim of the current study was to determine whether EM inhibits wear debris-induced inflammatory osteolysis in a murine osteolysis model. Ultrahigh molecular-weight polyethylene (UHMWPE) debris was introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. EM (2 mg/kg/day) was given to mice intraperitoneally 2 days before UHMWPE introduction and maintained until the sacrifice of the mice. Mice with and without EM treatment, as well as control mice injected with saline alone were included in this study. Pouch tissues were collected 14 days after UHMWPE inoculation for molecular and histology analysis. Our findings indicate that: (1) EM reduced UHMWPE-induced tissue inflammation, including the diminished pouch membrane thickness, reduced inflammatory cellular infiltration, and lowered IL-1beta and TNF-alpha expression (mRNA and protein); (2) EM inhibited UHMWPE-induced osteoclastogenesis, with reduced gene activation of RANK, RANKL, and CPK, and diminished RANKL expression in UHMWPE stimulated pouches, and (3) EM markedly reduced the number of TRAP(+) cells in pouch tissues, and protected against bone collagen depletion. In conclusion, this study provides the evidence that EM inhibits the UHMWPE particles-induced inflammatory osteolysis in a murine model, and represents a promising therapeutic candidate for the prevention and treatment of AL.

The decrease of particle-induced osteolysis after a single dose of bisphosphonate

The most common cause of implant failure in joint replacement is aseptic loosening due to particle-induced osteolysis. Bisphosphonates have been shown to be effective against particle-induced osteolysis when administered daily. We investigated the effect of a single subcutaneous dose of a more potent third generation bisphosphonate on particle-induced osteolysis.We utilized the murine calvaria osteolysis model in C57BL/J6 mice. Bone resorption was measured as resorption within the midline suture using Giemsa staining. Twenty-eight mice were used, seven per group. Seven animals were treated with a single dose of zoledronic acid (ZA) directly after surgery and seven animals were treated four days postoperatively. For statistical analysis one-way ANOVA and a Student's t-test were used.Bone resorption was 0.26±0.09mm2 in animals with particle implantation, 0.14±0.05mm2 in animals with particle implantation and ZA treatment directly after surgery (p=0.0047), and 0.15±0.05mm2 in animals with particle implantation and ZA treatment on the fourth postoperative day (p=0.006).In conclusion, particle-induced bone resorption was markedly decreased by a single s.c. dose of a third generation bisphosphonate. This important new finding holds great promise, because single dose treatment of particle-induced osteolysis may reduce side effects compared to repeated application of bisphosphonates.