Effects on osteoclast and osteoblast activities in cultured mouse calvarial bones by synovial fluids from patients with a loose joint prosthesis and from osteoarthritis patients

Investigation of osteoclast cathepsin K activity in osteoclastogenesis and bone loss using a set of chemical reagents

Cathepsin K (CatK) is a lysosomal cysteine protease whose highest expression is found in osteoclasts, which are the cells responsible for bone resorption. Investigations of the functions and physiological relevance of CatK have often relied on antibody-related techniques, which makes studying its activity patterns a challenging task. Hence, we developed a set of chemical tools for the investigation of CatK activity. We show that our probe is a valuable tool for monitoring the proteolytic activation of CatK during osteoclast formation. Moreover, we demonstrate that our inhibitor of CatK impedes osteoclastogenesis and bone resorption and that CatK is stored in its active form in osteoclasts within their lysosomal compartment and mainly in the ruffled borders of osteoclasts. Given that our probe recognizes active CatK within living cells without exhibiting any observed cytotoxicity in the several models tested, we expect that it would be well suited to theranostic applications in CatK-related diseases.

Medical optimization of osteoporosis for adult spinal deformity surgery: a state-of-the-art evidence-based review of current pharmacotherapy

PURPOSE

Osteoporosis is a common, but challenging phenomenon to overcome in adult spinal deformity (ASD) surgery. Several pharmacological agents are at the surgeon's disposal to optimize the osteoporotic patient prior to undergoing extensive reconstruction. Familiarity with these medications will allow the surgeon to make informed decisions on selecting the most appropriate adjuncts for each individual patient.

METHODS

A comprehensive literature review was conducted in PubMed from September 2021 to April 2022. Studies were selected that contained combinations of various terms including osteoporosis, specific medications, spine surgery, fusion, cage subsidence, screw loosening, pull-out, junctional kyphosis/failure.

RESULTS

Bisphosphonates, denosumab, selective estrogen receptor modulators, teriparatide, abaloparatide and romosozumab are all pharmacological agents currently available for adjunctive use. While these medications have been shown to have beneficial effects on improving bone mineral density in the osteoporotic patient, varying evidence is available on their specific effects in the context of extensive spine surgery. There is still a lack of human studies with use of the newer agents.

CONCLUSION

Bisphosphonates are first-line agents due to their low cost and robust evidence behind their utility. However, in the absence of contraindications, optimizing bone quality with anabolic medications should be strongly considered in preparation for spinal deformity surgeries due to their beneficial and favorable effects on fusion and hardware compared to the anti-resorptive medications.

Role of OSCAR Signaling in Osteoclastogenesis and Bone Disease

Formation of mature bone-resorbing cells through osteoclastogenesis is required for the continuous remodeling and repair of bone tissue. In aging and disease this process may become aberrant, resulting in excessive bone degradation and fragility fractures. Interaction of receptor-activator of nuclear factor-κB (RANK) with its ligand RANKL activates the main signaling pathway for osteoclastogenesis. However, compelling evidence indicates that this pathway may not be sufficient for the production of mature osteoclast cells and that co-stimulatory signals may be required for both the expression of osteoclast-specific genes and the activation of osteoclasts. Osteoclast-associated receptor (OSCAR), a regulator of osteoclast differentiation, provides one such co-stimulatory pathway. This review summarizes our present knowledge of osteoclastogenesis signaling and the role of OSCAR in the normal production of bone-resorbing cells and in bone disease. Understanding the signaling mechanism through this receptor and how it contributes to the production of mature osteoclasts may offer a more specific and targeted approach for pharmacological intervention against pathological bone resorption.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

The role of RANKL/RANK/OPG system in the canine model of hip periprosthetic infection osteolysis

Purpose

We aimed to investigate whether the RANKL/RANK/OPG system is associated with the incidence of periprosthetic osteolysis with septic loosening, and to investigate the differences of RANKL/RANK/OPG system expression in synovial fluid surrounding the normal and septic loosening hip prosthesis in canine models.

Methods

Twelve healthy adult mongrel canines were divided into two groups: experimental and control. Femoral head and stem replacements were conducted on the right side in both groups. The experimental group received the bacteria fluid intra-articular injection and the other group received the same amount of saline in the same day. The synovial fluid samples were gathered at the 1st, 2nd, 4th, 8th, 12th, 16th and 19th week after the bacteria fluid intra-articular injection for enzyme-linked immunosorbent assay (ELISA), the expression of the RANKL/RANK/OPG system.

Results

Surgery on all animals was successful. Two dogs were excluded from the analysis of the result because of a surgery infection or death. The ELISA of the synovial fluid revealed that the ratio of RANKL/OPG showed a significant upward trend (p≤0.05) with time in the test group but the ratio of RANKL/OPG in the control group changed slowly over time (p>0.05). The ratio of RANKL/OPG value between the test and control group showed a significant upward trend, but had no statistical difference (p>0.05) over time.

Conclusions

It could be concluded that the RANKL/RANK/OPG system is correlated with the incidence of periprosthetic osteolysis with septic loosening. Consequently, imbalance RANKL/RANK/OPG system was related to periprosthetic osteolysis with septic loosening.

Contribution of human osteoblasts and macrophages to bone matrix degradation and proinflammatory cytokine release after exposure to abrasive endoprosthetic wear particles

One of the major reasons for failure after total joint arthroplasty is aseptic loosening of the implant. At articulating surfaces, defined as the interface between implant and surrounding bone cement, wear particles can be generated and released into the periprosthetic tissue, resulting in inflammation and osteolysis. The aim of the present study was to evaluate the extent to which osteoblasts and macrophages are responsible for the osteolytic and inflammatory reactions following contact with generated wear particles from Ti-6Al-7Nb and Co-28Cr-6Mo hip stems. To this end, human osteoblasts and THP-1 monocytic cells were incubated with the experimentally generated wear particles as well as reference particles (0.01 and 0.1 mg/ml) for 48 h under standard culture conditions. To evaluate the impact of these particles on the two cell types, the release of different bone matrix degrading matrix metalloproteinases (MMPs), tissue inhibitors of MMPs (TIMPs), and relevant cytokines were determined by multiplex enzyme-linked immunosorbent assays. Following incubation with wear particles, human osteoblasts showed a significant upregulation of MMP1 and MMP8, whereas macrophages reacted with enhanced MMP3, MMP8 and MMP10 production. Moreover, the synthesis of TIMPs 1 and 2 was inhibited. The osteoblasts and macrophages also responded with modified expression of the inflammatory mediators interleukin (IL)-6, IL-8, monocyte chemoattractant protein-1 and vascular endothelial growth factor. These results demonstrate that the release of wear particles affects the release of proinflammatory cytokines and has a negative impact on bone matrix formation during the first 48 h of particle exposure. Human osteoblasts are directly involved in the proinflammatory cascade of bone matrix degradation. The simultaneous activation and recruitment of monocytes/macrophages boosted osteolytic processes in the periprosthetic tissue. By the downregulation of TIMP production and the concomitant upregulation of MMPs as a response to particle exposure, bone formation around implants may be suppressed, resulting in implant failure.

Metastasis-associated protein 1 (MTA1) signaling in rheumatoid synovium: Regulation of inflammatory response and cytokine-mediated production of prostaglandin E2 (PGE2)

Abnormal perpetual inflammatory response and sequential cytokine-induced prostaglandin E2 (PGE2) play important roles in the pathogenesis of rheumatoid arthritis (RA). The underlying regulatory mechanism, however, remain largely unknown. Here, we discovered that expression level of Metastasis associated protein 1 (MTA1), an important chromatin modifier that plays a critical role in transcriptional regulation by modifying DNA accessibility for cofactors, was upregulated in human rheumatoid synovial tissues. Furthermore, a knockdown of MTA1 by siRNA in the human fibroblast-like synovial cell line MH7A was found to impair the 4-hydroxynonenal (4-HNE)-induced transcriptional expression levels of certain proinflammatory cytokines including IL-1β, TNF-α and IL-6. Moreover, endogenous MTA1 was required for the cytokines-induced PGE2 synthesis by rheumatoid synoviocytes. Collectively, the coordinated existence of MTA1 inside distinct cascade loops points to its indispensable role in the modulation of the integrated cytokine network along the pathogenesis of RA. Further exploration of the functional details of this master transcriptional regulator should be an attractive strategy to identify novel therapeutic target for RA and warrants execution.

Denosumab for treating periprosthetic osteolysis; study protocol for a randomized, double-blind, placebo-controlled trial

Background

Wear-induced osteolysis is the main factor in reducing the longevity of total hip arthroplasty (THA). The transmembrane Receptor Activator of Nuclear Factor κ B (RANK) and its corresponding ligand RANKL is an important regulator of osteoclast activity and bone resorption and is associated with osteolysis around implant. Inhibiting RANKL with denosumab is effective in vivo in preventing osteoporosis-related fractures. In vitro, osteoclasts can be blocked in animal models of osteolysis. We hypothesize that denosumab is effective in reducing wear-induced osteolysis around uncemented acetabular implants in THA.

Methods/design

A randomized, double-blind, placebo-controlled trial will be conducted. We will include 110 patients, 40–85 years of age, with a known osteolytic lesion around an uncemented acetabular component ≥7 years after the primary operation. The patients will be randomized in a 1:1 ratio to subcutaneous injections of 60 mg denosumab or placebo for a total of 6 doses with start on day one and every 6 months with last treatment at 30 months. The primary endpoint will be the change in volume of the osteolytic lesion at 3 years measured with three-dimensional computed tomography (3D-CT). Secondary endpoints include functional outcome scores, change in bone mineral density of the lumbar spine, serological markers of bone turnover and adverse events.

Discussion

In vitro results of both bisphosphonates and RANKL inhibitors have been promising, showing reduced osteolysis with treatment. This is, to our knowledge, the first clinical trial testing the efficacy of denosumab in reducing wear-induced osteolysis. The study is an academic, phase II trial from an independent center and is designed to demonstrate efficacy in reducing volume of osteolytic lesions around a total hip arthroplasty.

Trial registration

ClinicalTrials.gov (NCT02299817) 2014-11-20

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).

The biological response to a failed extra-articular polyester ligament used for AC Joint reconstruction at the shoulder girdle: a retrieval analysis of five cases

The LockDown device (previously called Surgilig) is a braided polyester mesh which is mostly used to reconstruct the dislocated acromioclavicular joint. More than 11,000 have been implanted worldwide. Little is known about the tissue reaction to the device nor to its wear products when implanted in an extra-articular site in humans. This is of importance as an adverse immunological reaction could result in osteolysis or damage to the local tissues, thereby affecting the longevity of the implant. We analysed the histology of five LockDown implants retrieved from five patients over the last seven years by one of the senior authors. Routine analysis was carried out in all five cases and immunohistochemistry in one. The LockDown device acts as a scaffold for connective tissue which forms an investing fibrous pseudoligament. The immunological response at the histological level seems favourable with a limited histiocytic and giant cell response to micron-sized wear particles. The connective tissue envelope around the implant is less organised than a native ligament.

The coupling of bone and cartilage turnover in osteoarthritis: opportunities for bone antiresorptives and anabolics as potential treatments?

Osteoarthritis (OA) is the most common form of arthritic disease, and a major cause of disability and impaired quality of life in the elderly. OA is a complex disease of the entire joint, affecting bone, cartilage and synovium that thereby presents multiple targets for treatment. This manuscript will summarise emerging observations from cell biology, preclinical and preliminary clinical trials that elucidate interactions between the bone and cartilage components in particular. Bone and cartilage health are tightly associated. Ample evidence has been found for bone changes during progression of OA including, but not limited to, increased turnover in the subchondral bone, undermineralisation of the trabecular structure, osteophyte formation, bone marrow lesions and sclerosis of the subchondral plate. Meanwhile, a range of investigations has shown positive effects on cartilage health when bone resorption is suppressed, or deterioration of the cartilage when resorption is increased. Known bone therapies, namely oestrogens, selective oestrogen receptor modifiers (SERMs), bisphosphonates, strontium ranelate, calcitonin and parathyroid hormone, might prove useful for treating two critical tissue components of the OA joint, the bone and the cartilage. An optimal treatment for OA likely targets at least these two tissue components. The patient subgroups for whom these therapies are most appropriate have yet to be fully defined but would likely include, at a minimum, those with high bone turnover.

Polyethylene particles stimulate expression of ITAM-related molecules in peri-implant tissues and when stimulating osteoclastogenesis in vitro

Wear particle-induced orthopaedic prosthesis loosening is associated with elevated osteoclast activity. The immunoreceptor tyrosine-based activation motif (ITAM)-related molecules OSCAR, FcRγ, TREM2 and DAP12 are important for osteoclast formation. The aim of this study was to determine if these molecules are involved in peri-implant loosening by investigating their expression in peri-implant tissues obtained at revision of joint replacement components containing polyethylene (PE) wear particles, and in osteoclasts formed in vitro in the presence of PE particles. The results showed that there was a marked and statistically significant increase in protein levels of the ITAM-related molecules in the revision tissues. The levels of OSCAR, FcRγ, TREM2 and DAP12 mRNA in the revision tissues were also increased. In vitro PE particles stimulated osteoclast resorption in the presence of 50 ng ml(-1) receptor activator NFκB (RANKL) and significantly elevated the expression of OSCAR, FcRγ, TREM2 and DAP12 during osteoclast formation. These findings suggest that the ITAM signalling molecules and their co-receptors have a role in pathogenic bone loss associated with implant PE wear.

The role of Th17 lymphocytes in the autoimmune and chronic inflammatory diseases

The emerging role of interleukin-17 as a hallmark proinflammatory cytokine of the adaptive immune system produced by a new T helper cell subset termed "Th17" has received considerable attention. In this review we will focus on recent information regarding IL-17 and its relevance in autoimmune and chronic inflammatory diseases.

The role of osteoclast-associated receptor in osteoimmunology

The term osteoimmunology is coined for molecular and cellular cross talk between the skeletal and immune system. Immunomodulatory signals have long been implicated as key regulators of bone metabolism. Recently, osteoclast-associated receptor (OSCAR), an IgG-like receptor, has been identified as an important osteoimmunological mediator. OSCAR expression in bone is highly conserved across different species, and the molecule is an important costimulatory receptor for osteoclast differentiation through activation of NFATc1. In humans, OSCAR is expressed by macrophages, monocytes, and monocyte-derived dendritic cells and modulates the response of the innate and adaptive immune systems by promoting cell activation and maturation, Ag presentation, and proinflammatory circuits. Human studies indicate that OSCAR may contribute to the pathogenesis and severity of osteoporosis and rheumatoid arthritis. In this paper, we review the structure-function relationship, expression pattern, and physiological role of OSCAR in osteoimmunology and summarize its potential implications for human diseases.

IL-17 as a future therapeutic target for rheumatoid arthritis

The discovery of interleukin (IL)-17 and its major cell source, the type 17 T-helper (TH17) lymphocyte, has been a major step in the understanding of erosive arthritis. This Review summarizes current knowledge of the role of IL-17 in this context derived from both animal models and studies in patients with rheumatoid arthritis. Evidence shows that IL-17 is present at sites of inflammatory arthritis and that, in synergistic interactions, it amplifies the inflammation induced by other cytokines, primarily tumor necrosis factor. In several animal models of arthritis, inhibition of IL-17 limits inflammation and joint erosion. Initial observations from phase I trials show that signs and symptoms of RA are significantly suppressed following treatment with anti-IL-17 antibodies, without notable adverse effects. The emergence of IL-17 blockade as a future therapy in rheumatoid arthritis is highlighted, along with the potential goals and limitations of this therapeutic approach.

IL-17 and Th17 cells in human inflammatory diseases

IL-17 was discovered in 1995/96 as a T cell derived cytokine with effects on inflammation and neutrophil activation. In 2006, the precise cell source of IL-17 was identified in the mouse, and these cells were named Th17 cells. They play a role in various human diseases associated with inflammation and destruction such as rheumatoid arthritis, psoriasis, Crohn's disease, multiple sclerosis, where IL-17 can be seen as a therapeutic target.

Diseases that may benefit from manipulating the Th17 pathway

The discovery of IL-17 and of the Th17 pathway has been a step in the classification of human diseases. Th17 targeting appears rather straightforward in diseases associated with inflammation and matrix destruction, such as rheumatoid arthritis, psoriasis, and Crohn's disease. In other conditions where IL-17 is expressed and Th17 activated, it is unclear whether this is a primary or secondary event, making the use of Th17 inhibitors less obvious.

Use of routine clinical multimodality imaging in a rabbit model of osteoarthritis--part II: bone mineral density assessment

OBJECTIVE

To assess bone mineral density (BMD) at different depths from the articular surface in vivo and temporally in a rabbit model of osteoarthritis (OA) using clinical computed tomography (CT) equipment.

METHODS

The knee joints of rabbits (N=10 with Anterior cruciate ligament transection (ACLT) and contralateral sham joints, and N=6 unoperated controls) were scanned in a transverse image plane with a single-slice helical CT scanner. BMD was calculated at defined depths from the articular surface to the growth plate in the lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibial plateau (LTP) and medial tibial plateau (MTP). Baseline BMD was measured at 2 weeks before surgery, and then repeated at weeks 2, 4 and 8 post-surgery in all 10 operated rabbits, and again at week 12 in five of the operated rabbits and at weeks -2 and 8 in the six control rabbits.

RESULTS

In the control joints, BMD decreased with increasing distance into the epiphysis and remained stable over time within each depth. A significant reduction in BMD was observed at week 2 post-operatively in three compartments (LFC, MFC and MTP) in the ACLT joints and persisted to week 12. A modest reduction in BMD occurred in the LTP and MTP of the sham joints at week 12 alone.

CONCLUSION

Clinical CT equipment permitted rapid, repeated, in vivo, non-invasive BMD assessment in a rabbit model of OA. A marked BMD reduction was measured with progression of OA until the end point at 12 weeks.

Should subchondral bone turnover be targeted when treating osteoarthritis?

OBJECTIVE

Osteoarthritis (OA) is the most common form of arthritic disease, and it is a major cause of disability and impaired quality of life in the elderly. OA is a complex disease of the entire joint, including bone and cartilage, thereby presenting alternative approaches for treatment. This review summarizes emerging observations from cell biology to preliminary clinical trials, describing interactions between the bone and cartilage components. We speculate whether a treatment for OA would be possible without targeting the bone compartment?

METHODS

Peer-reviewed articles found using pre-defined search criteria and published in the PubMed database until June 2007 are summarized. In addition, abstracts from the OsteoArthritis Research Society International (OARSI) conferences in the time period 2000-2007 were included.

RESULTS

Bone and cartilage health seem to be tightly associated. Ample evidence is found for bone changes during progression of OA, including, but not limited to, increased turnover in the subchondral bone, thinning of the trabecular structure, osteophytes, bone marrow lesions and sclerosis of the subchondral plate. In addition, a range of investigations has described secondary positive effects on cartilage health when bone resorption was suppressed, or deterioration of the cartilage when resorption is increased.

CONCLUSION

An optimal treatment for OA might include targeting both the bone and cartilage compartments. Hence, as several cell systems are to be targeted in a safe manner, limited options seem possible.

Effects of synovial fluid from aseptic prosthesis loosening on collagen production in osteoblasts

Synovial fluid from a loose prosthesis may act as a vehicle for factors that regulate bone turnover. The effect of such synovial fluid on osteoblasts has been studied. Synovial fluid obtained from patients who underwent revision hip arthroplasty because of aseptic prosthesis loosening was studied regarding the effect on protein synthesis, procollagen I mRNA expression, the secretion of procollagen I carboxyterminal propeptide (PICP) and osteocalcin in MG63 osteoblasts. Protein synthesis was increased and procollagen I mRNA expression was decreased by synovial fluid from patients with prosthesis loosening. Synovial fluid stimulated the total PICP in cell medium, but there was no change after correction for cell protein content in the cells. Synovial fluid in patients with prosthesis loosening has a general stimulatory effect on collagen formation and osteoblast proliferation because of a stimulatory effect on cell growth. Aseptic prosthesis loosening may be associated with an increase in bone formation.