Increased collagen degradation around loosened total hip replacement implants

Roles of inflammatory cell infiltrate in periprosthetic osteolysis

Classically, particle-induced periprosthetic osteolysis at the implant-bone interface has explained the aseptic loosening of joint replacement. This response is preceded by triggering both the innate and acquired immune response with subsequent activation of osteoclasts, the bone-resorbing cells. Although particle-induced periprosthetic osteolysis has been considered a foreign body chronic inflammation mediated by myelomonocytic-derived cells, current reports describe wide heterogeneous inflammatory cells infiltrating the periprosthetic tissues. This review aims to discuss the role of those non-myelomonocytic cells in periprosthetic tissues exposed to wear particles by showing original data. Specifically, we discuss the role of T cells (CD3+, CD4+, and CD8+) and B cells (CD20+) coexisting with CD68+/TRAP- multinucleated giant cells associated with both polyethylene and metallic particles infiltrating retrieved periprosthetic membranes. This review contributes valuable insight to support the complex cell and molecular mechanisms behind the aseptic loosening theories of orthopedic implants.

Nano wear particles and the periprosthetic microenvironment in aseptic loosening induced osteolysis following joint arthroplasty

Joint arthroplasty is an option for end-stage septic arthritis due to joint infection after effective control of infection. However, complications such as osteolysis and aseptic loosening can arise afterwards due to wear and tear caused by high joint activity after surgery, necessitating joint revision. Some studies on tissue pathology after prosthesis implantation have identified various cell populations involved in the process. However, these studies have often overlooked the complexity of the altered periprosthetic microenvironment, especially the role of nano wear particles in the etiology of osteolysis and aseptic loosening. To address this gap, we propose the concept of the "prosthetic microenvironment". In this perspective, we first summarize the histological changes in the periprosthetic tissue from prosthetic implantation to aseptic loosening, then analyze the cellular components in the periprosthetic microenvironment post prosthetic implantation. We further elucidate the interactions among cells within periprosthetic tissues, and display the impact of wear particles on the disturbed periprosthetic microenvironments. Moreover, we explore the origins of disease states arising from imbalances in the homeostasis of the periprosthetic microenvironment. The aim of this review is to summarize the role of relevant factors in the microenvironment of the periprosthetic tissues, in an attempt to contribute to the development of innovative treatments to manage this common complication of joint replacement surgery.

Using Cu as a Spacer to Fabricate and Control the Porosity of Titanium Zirconium Based Bulk Metallic Glass Foams for Orthopedic Implant Applications

In this study, a porous titanium zirconium (TiZr)-based bulk metallic foam was successfully fabricated using the Cu spacer by employing the hot press method. TiZr-based bulk metallic foams with porosities ranging from 0% to 50% were fabricated and analyzed. The results indicate that thermal conductivity increased with the addition of Cu spacer; the increased thermal conductivity reduced the holding time in the hot press method. Moreover, the compressive strength decreased from 1261 to 76 MPa when the porosity of the TiZr-based bulk metallic foam increased to 50%, and the compressive strength was predictable. In addition, the foam demonstrated favorable biocompatibility in cell viability, cell migration capacity, and calcium deposition tests. Moreover, the pore size of the porous TiZr-based bulk metallic foam was around 120 µm. In conclusion, TiZr-based bulk metallic foam has favorable biocompatibility, mechanical property controllability, and porous structure for bone ingrowth and subsequent enhanced osteointegration. This porous TiZr-based bulk metallic foam has great potential as an orthopedic implant to enhance bone healing and decrease healing time.

Dental and Orthopaedic Implant Loosening: Overlap in Gene Expression Regulation

Objectives

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

Methods

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

Results

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

Conclusions

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

Macrophage Polarization and the Osteoimmunology of Periprosthetic Osteolysis

PURPOSE OF REVIEW

Joint replacement has revolutionized the treatment of end-stage arthritis. We highlight the key role of macrophages in the innate immune system in helping to ensure that the prosthesis-host interface remains biologically robust.

RECENT FINDINGS

Osteoimmunology is of great interest to researchers investigating the fundamental biological and material aspects of joint replacement. Constant communication between cells of the monocyte/macrophage/osteoclast lineage and the mesenchymal stem cell-osteoblast lineage determines whether a durable prosthesis-implant interface is obtained, or whether implant loosening occurs. Tissue and circulating monocytes/macrophages provide local surveillance of stimuli such as the presence of byproducts of wear and can quickly polarize to pro- and anti-inflammatory phenotypes to re-establish tissue homeostasis. When these mechanisms fail, periprosthetic osteolysis results in progressive bone loss and painful failure of mechanical fixation. Immune modulation of the periprosthetic microenvironment is a potential intervention to facilitate long-term durability of prosthetic interfaces.

Design and Synthesis of Water-Soluble and Potent MMP-13 Inhibitors with Activity in Human Osteosarcoma Cells

Osteoarthritis is a degenerative disease, often resulting in chronic joint pain and commonly affecting elderly people. Current treatments with anti-inflammatory drugs are palliative, making the discovery of new treatments necessary. The inhibition of matrix metalloproteinase MMP-13 is a validated strategy to prevent the progression of this common joint disorder. We recently described polybrominated benzotriazole derivatives with nanomolar inhibitory activity and a promising selectivity profile against this collagenase. In this work, we have extended the study in order to explore the influence of bromine atoms and the nature of the S1′ heterocyclic interacting moiety on the solubility/selectivity balance of this type of compound. Drug target interactions have been assessed through a combination of molecular modeling studies and NMR experiments. Compound 9a has been identified as a water-soluble and highly potent inhibitor with activity in MG-63 human osteosarcoma cells.

Fibroblast-like cells change gene expression of bone remodelling markers in transwell cultures

Introduction

Periprosthetic fibroblast-like cells (PPFs) play an important role in aseptic loosening of arthroplasties. Various studies have examined PPF behavior in monolayer culture systems. However, the periprosthetic tissue is a three-dimensional (3D) mesh, which allows the cells to interact in a multidirectional way. The expression of bone remodeling markers of fibroblast-like cells in a multilayer environment changes significantly versus monolayer cultures without the addition of particles or cytokine stimulation. Gene expression of bone remodeling markers was therefore compared in fibroblast-like cells from different origins and dermal fibroblasts under transwell culture conditions versus monolayer cultures.

Methods

PPFs from periprosthetic tissues (n = 12), osteoarthritic (OA) synovial fibroblast-like cells (SFs) (n = 6), and dermal fibroblasts (DFs) were cultured in monolayer (density 5.5 × 10³/cm²) or multilayer cultures (density 8.5 × 10⁵/cm²) for 10 or 21 days. Cultures were examined via histology, TRAP staining, immunohistochemistry (anti-S100a4), and quantitative real-time PCR.

Results

Fibroblast-like cells (PPFs/SFs) and dermal fibroblasts significantly increased the expression of RANKL and significantly decreased the expression of ALP, COL1A1, and OPG in multilayer cultures. PPFs and SFs in multilayer cultures further showed a higher expression of cathepsin K, MMP-13, and TNF-α. In multilayer PPF cultures, the mRNA level of TRAP was also found to be significantly increased.

Conclusion

The multilayer cultures are able to induce significant expression changes in fibroblast-like cells depending on the nature of cellular origin without the addition of any further stimulus. This system might be a useful tool to get more in vivo like results regarding fibroblast-like cell cultures.

The Effects of Biomaterial Implant Wear Debris on Osteoblasts

Aseptic loosening subsequent to periprosthetic osteolysis is the leading cause for the revision of arthroplasty failure. The biological response of macrophages to wear debris has been well established, however, the equilibrium of bone remodeling is not only dictated by osteoclastic bone resorption but also by osteoblast-mediated bone formation. Increasing evidence shows that wear debris significantly impair osteoblastic physiology and subsequent bone formation. In the present review, we update the current state of knowledge regarding the effect of biomaterial implant wear debris on osteoblasts. The interaction of osteoblasts with osteoclasts and macrophages under wear debris challenge, and potential treatment options targeting osteoblasts are also presented.

Diagnosis and management of implant debris-associated inflammation

Introduction: Total joint replacement is one of the most common, safe, and efficacious operations in all of surgery. However, one major long-standing and unresolved issue is the adverse biological reaction to byproducts of wear from the bearing surfaces and modular articulations. These inflammatory reactions are mediated by the innate and adaptive immune systems.Areas covered: We review the etiology and pathophysiology of implant debris-associated inflammation, the clinical presentation and detailed work-up of these cases, and the principles and outcomes of non-operative and operative management. Furthermore, we suggest future strategies for prevention and novel treatments of implant-related adverse biological reactions.Expert opinion: The generation of byproducts from joint replacements is inevitable, due to repetitive loading of the implants. A clear understanding of the relevant biological principles, clinical presentations, investigative measures and treatments for implant-associated inflammatory reactions and periprosthetic osteolysis will help identify and treat patients with this issue earlier and more effectively. Although progressive implant-associated osteolysis is currently a condition that is treated surgically, with further research, it is hoped that non-operative biological interventions could prolong the lifetime of joint replacements that are otherwise functional and still salvageable.

Enzymes and cytokines disease in total hip arthroplasty: promoters of immune loosening

Introducción. Una de las causas más importantes de falla de la prótesis de cadera lo constituye el fenómeno de aflojamiento, el cual se relaciona con la liberación de enzimas mediada por citocinas y produce la lisis del hueso que soporta el implante.Objetivo. Describir los mecanismos de interacción biológica de las moléculas promotoras del aflojamiento de la prótesis total de cadera que con mayor frecuencia están presentes en el proceso.Materiales y métodos. Se realizó una búsqueda de artículos originales y casos clínicos en las bases de datos PubMed y Scopus, sin límite de fecha de publicación, utilizando los términos MeSH “hip prosthesis loosening”, “aseptic loosening”, “cytokines” y “hip arthroplasty failure”. La extracción de datos se hizo mediante la lectura de 250 estudios, de los cuales se seleccionaron 66 para fines de redacción.Resultados. Los autores describen las moléculas más representativas implicadas en el aflojamiento de la prótesis de cadera, además se presentan las interacciones entre ellas.Conclusiones. Enzimas y citocinas han sido ampliamente estudiadas por cuatro décadas, aunque sus mecanismos de interacción son poco conocidos. Los autores proponen un mecanismo de interacción, proceso que podría denominarse “enfermedad de las enzimas y citocinas” o “aflojamiento inmunológico”.

Factors regulating bone remodeling processes in aseptic implant loosening

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

Genetic susceptibility to total hip arthroplasty failure: a case-control study on the influence of MMP 1 gene polymorphism

Background

Genetic factors plays an important role in early failure of total hip arthroplasty (THA) etiology and MMP-1 gene polymorphism rs5854 may be involved. The present study was conducted to reveal the possible association between MMP-1 rs5854 C/T polymorphism and the risk of early failure of THA (aseptic loosening).

Methods

The rs5854 single nucleotide polymorphism (SNP) in MMP-1 gene was genotyped in 63 subjects who were diagnosed as aseptic loosening after total hip arthroplasty within 10 years and in 81 age and gender matched controls.

Results

The genotype frequencies of the MMP-1 rs5854 C/T polymorphism were 57.1% (CC), 28.6% (CT), and 14.3% (TT) in patients with failure of THA, and 79.0% (CC), 17.3% (CT), and 3.7% (TT) in the controls (P = 0.0099). Rs5854 polymorphism was found to be significantly associated with increased risk of aseptic loosening.

Conclusion

The results showed the rs5854 SNP was associated with increased risk of the early aseptic loosening susceptibility.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_177

Contributions of human tissue analysis to understanding the mechanisms of loosening and osteolysis in total hip replacement

Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. "Control" samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.

The potential role of increasing the release of mouse β- defensin-14 in the treatment of osteomyelitis in mice: a primary study

Mammalian β-defensins are small cationic peptides that have been implicated in mediating innate immune defenses against microbial infection. Mouse β-defensin-14 (MBD-14), based on structural and functional similarities, appears to be an ortholog of human β-defensin-3 (HBD-3). Previous studies identified signaling pathway p38 mitogen-activated protein kinase (MAPK) that contributed to the expression of MBD-14 in mouse osteoblasts upon contacted with methicillin-resistance Staphylococcus aureus (MRSA) supernatant, which provided a theoretical basis as a promising therapeutic target in the treatment of intramedullary infection with MRSA in vivo. In this study, the medullary cavities of tibiae were contaminated with MRSA 10(3) colony forming units and different doses of p38 MAPK agonists anisomycin were followed as group III or IV in 30 mice. Fifteen animals that received phosphate- buffered saline served as group II and 15 mice were not contaminated with MRSA and received phosphate-buffered saline served as controls (group I). Follow-up was 7 days. In day 1, day 4 and day 7 postoperatively, infection was evaluated by blood routine, microbiological and histological analyses after sacrifice. All animals of group II developed microbiological and histological signs of infection. Histological signs of infection, white blood counts and cultures of group III and IV showed significantly reduced bacterial growth compared to cultures of group II. Simultaneously, different doses of anisomycin significantly induced the expression of osteoblast-associated genes, including alkaline phosphatase, osteocalcin and collagen type I. In addition, the expression of HBD-3 in human interfacial membranes around infected periprosthetic joint by staphylococcus contaminated was evaluated, and the expression pattern changed with significant induction of HBD-3 in infected periprosthetic joint compared with aseptic loosening under inflammatory conditions. Our primary study indicated that the potential antibacterial role of increased MBD-14 in the osteomyelitis mouse model.

Serum metalloproteinases 2 and 9 as predictors of gait status, pressure ulcer and mortality after hip fracture

Introduction

The aim of this study is to evaluate the serum activity of metalloproteinases (MMPs) -2 and -9 as predictors of pressure ulcer (PU), gait status and mortality 6 months after hip fracture.

Methods

Eighty-seven patients over the age of 65 admitted to the orthopedic unit from January to December 2010 with hip fracture were prospectively evaluated. Upon admission, patient demographic information, including age, gender and concomitant diseases, was recorded. Blood samples were taken for analysis of MMP -2 and -9 activity by gel zymography and for biochemical examination within the first 72 hours of the patient’s admission, after clinical stabilization. The fracture pattern (neck, trochanteric or subtrochanteric), time from admission to surgery, surgery duration and length of hospital stay were also recorded.

Results

Two patients were excluded due to the presence of pathological fractures (related to cancer), and three patients were excluded due to the presence of PU before admission. Eighty-two patients, with a mean age of 80.4 ± 7.3 years, were included in the analysis. Among these patients, 75.6% were female, 59.8% had PU, and 13.4% died 6 months after hip fracture. All patients underwent hip fracture repair. In a univariate analysis, there were no differences in serum MMP activity between hip fracture patients with or without PU. In addition, the multiple logistic regression analysis models, which were adjusted by age, gender, length of hospital stay and C-reactive protein, showed that the pro-MMP-9 complexed with neutrophil gelatinase-associated lipocalin form (130 kDa) was associated with gait status recovery 6 months after hip fracture.

Conclusions

In conclusion, serum pro-MMP-9 is a predictor of gait status recovery 6 months after hip fracture.

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.

Up-regulated expression of MIF by interfacial membrane fibroblasts and macrophages around aseptically loosened implants

BACKGROUND

Local chronic inflammatory reaction plays an important role in the process of aseptic loosening of implants after total joint replacement. In addition, macrophage migration inhibitory factor (MIF) is a key upstream regulator of inflammation, and it is a significant regulator of inflammatory diseases. The purpose of this study is to investigate if the fibroblasts and macrophages in the interfacial membranes overexpress MIF.

MATERIALS AND METHODS

The 15 tissue samples of interfacial membranes were obtained from the tissues around the aseptically loosened femoral implants adjacent to osteolytic lesion in 15 patients. The 15 control synovial samples of hip joints were obtained from 15 patients who underwent primary hip arthroplasty because of the fresh fracture of the femoral neck. The levels of MIF protein and mRNA were evaluated by ELISA assay, immunofluorescence labeling, and real-time RT-PCR. Fibroblasts and macrophages were identified by immunofluorescence labeling.

RESULTS

The levels of MIF protein and mRNA were significantly increased, as well as the numbers of MIF+ fibroblasts and macrophages in the interfacial membranes compared with the control synovium.

CONCLUSION

Not only the macrophages, but also the fibroblasts in interfacial membranes overexpress MIF. MIF may play a significant role in the process of aseptic-loosening implants after total joint replacement.

Interface membrane fibroblasts around aseptically loosened endoprostheses express MMP-13

The objective of this article was to assess whether matrix metalloproteinase-13 (MMP-13) is produced by cells of the peri-implant interface tissues and to further characterize these cells. Tissue specimens were collected from the bone-prosthesis interface at the time of revision surgery of clinically loosened hip and knee arthroplasties (n = 27). Synovial tissues from osteoarthritic patients and young patients with mild joint deformity were used as controls (n = 6). Tissue samples were fixed in 4% PFA, decalcified with EDTA, and embedded in paraffin. Sections (4 microm) were stained with hematoxylin/eosin and for the osteoclastic marker enzyme tartrate resistant acid phosphatase. Monocytes/macrophages were characterized with a monoclonal antibody against CD68 and mRNAs encoding MMP-13 and alpha(1) collagen I (COL1A1) were detected by in situ hybridization. Cells expressing transcripts encoding MMP-13 were found in 70% of the interface tissues. These cells colocalized with a cell population expressing COL1A1 mRNA, and were fibroblastic in appearance. MMP-13 expressing cells were found in the close vicinity of osteoclasts and multinuclear giant cells. No signals for transcripts encoding MMP-13 were detected in multinuclear giant cells or in osteoclasts. Control tissues were negative for transcripts encoding MMP-13 mRNA. Fibroblasts of the interface from aseptically loosened endoprostheses selectively express MMP-13. By the expression and the release of MMP-13, these fibroblastic cells may contribute to the local degradation of the extracellular matrix and to bone resorption.

MyD88, IRAK1 and TRAF6 knockdown in human chondrocytes inhibits interleukin-1-induced matrix metalloproteinase-13 gene expression and promoter activity by impairing MAP kinase activation

Interleukin-1 (IL-1) is the major prototypic proinflammatory cytokine that stimulates degradation of cartilage in arthritis by inducing prominent collagen II-degrading matrix metalloproteinase-13 (MMP-13). Nothing is known about the involvement of adaptor proteins, MyD88, IRAK1 and TRAF6 in MMP-13 regulation. Here we investigated for the first time the role of these proteins in IL-1-regulated MMP-13 expression in chondrocytes. MyD88 homodimerization inhibitory peptide diminished the expression of MMP-13 gene, promoter activity, phosphorylation of mitogen-activated protein kinases (MAPKs), c-Jun and activating protein 1 (AP-1) activity. Knockdown of MyD88, IRAK1 and TRAF6 by RNA interference (RNAi) drastically down-regulated the expression of IL-1-induced MMP-13 mRNA and protein levels and MMP-13 promoter-driven luciferase activity. Non-specific control siRNA had no effect. Mechanisms of MMP-13 inhibition involved reduced phosphorylation of ERK, p38, JNK and c-Jun as well as AP-1 transcription factor binding activity. The genetic evidence presented here demonstrates that MyD88, IRAK1 and TRAF6 proteins are crucial early mediators for the IL-1-induced MMP-13 regulation through MAPK pathways and AP-1 activity. These proteins could constitute important therapeutic targets for arthritis-associated cartilage loss by MMP-13.

Circulating cathepsin K and cystatin C in patients with cancer related bone disease: clinical and therapeutic implications

The clinical significance of serum cathepsin K and cystatin C was assessed in patients with breast cancer (BCa) or prostate cancer (PCa) with confined disease (M0) or bone metastasis (BM). Cathepsin K and cystatin C circulating levels were determined by ELISAs in 63 cancer patients, in 35 patients with nonmalignant diseases and in 42 healthy blood donors (control group). In BCa patients, cathepsin K serum levels were significantly lower than in sex matched control group (HS; p=0.0008) or in patients with primary osteoporosis (OP; p=0.0009). On the contrary, cystatin C levels were significantly higher in BCa patients than in HS (p=0.0001) or OP (p=0.017). In PCa patients, cathepsin K concentrations did not significantly differ from those measured in sex matched HS or in patients with benign prostatic hyperplasia (BPH). Conversely, cystatin C was more elevated in cancer patients than in controls (p=0.0001) or BPH patients (p=0.0078). Furthermore, in PCa patients, a positive correlation was observed between cystatin C and cathepsin K (r(S)=0.34; p=0.047). No further relationship was highlighted between these molecules and the clinicobiological parameters of BCa or PCa progression including the number of bone lesions. Moreover, ROC curve analysis showed a poor diagnostic performance of cathepsin K and cystatin C in the detection of BM patients. Interestingly, the administration of zoledronic acid (ZA), a bisphosphonate derivative endowed with a potent antiosteoclastic activity, induced in BM patients a marked increase of cathepsin K and cystatin C serum levels compared to baseline values. However, this phenomenon was statistically significant only in the PCa group. In conclusion Cystatin C and cathepsin K may be regarded as possible markers to monitor the therapeutic response to bisphosphonate treatments. Nevertheless, their clinical value as specific gauges of skeletal metastasis remains questionable.