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

Influence of metallic particles and TNF on the transcriptional regulation of NLRP3 inflammasome-associated genes in human osteoblasts

Introduction

The release of mature interleukin (IL-) 1β from osteoblasts in response to danger signals is tightly regulated by the nucleotide-binding oligomerization domain leucine-rich repeat and pyrin-containing protein 3 (NLRP3) inflammasome. These danger signals include wear products resulting from aseptic loosening of joint arthroplasty. However, inflammasome activation requires two different signals: a nuclear factor-kappa B (NF-κB)-activating priming signal and an actual inflammasome-activating signal. Since human osteoblasts react to wear particles via Toll-like receptors (TLR), particles may represent an inflammasome activator that can induce both signals.

Methods

Temporal gene expression profiles of TLRs and associated intracellular signaling pathways were determined to investigate the period when human osteoblasts take up metallic wear particles after initial contact and initiate a molecular response. For this purpose, human osteoblasts were treated with metallic particles derived from cobalt-chromium alloy (CoCr), lipopolysaccharides (LPS), and tumor necrosis factor-alpha (TNF) alone or in combination for incubation times ranging from one hour to three days. Shortly after adding the particles, their uptake was observed by the change in cell morphology and spectral data.

Results

Exposure of osteoblasts to particles alone increased NLRP3 inflammasome-associated genes. The response was not significantly enhanced when cells were treated with CoCr + LPS or CoCr + TNF, whereas inflammation markers were induced. Despite an increase in genes related to the NLRP3 inflammasome, the release of IL-1β was unaffected after contact with CoCr particles.

Discussion

Although CoCr particles affect the expression of NLRP3 inflammasome-associated genes, a single stimulus was not sufficient to prime and activate the inflammasome. TNF was able to prime the NLRP3 inflammasome of human osteoblasts.

Emerging factors affecting peri-implant bone metabolism

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

CoNiCrMo Particles, but Not TiAlV Particles, Activate the NLRP3 Inflammasome in Periprosthetic Cells

Aseptic loosening is the main reason for arthroplasty failure. The wear particles generated at the tribological bearings are thought to induce an inflammatory tissue response, leading to bone loss and the subsequent loosening of the implant. Different wear particles have been shown to activate the inflammasome, thereby contributing to an inflammatory milieu in the direct vicinity of the implant. The aim of this study was to investigate whether the NLRP3 inflammasome is activated by different metal particles in vitro and in vivo. Three different cell lines representing periprosthetic cell subsets (MM6, MG63 and Jurkat) were incubated with different amounts of TiAlV or CoNiCrMo particles. The activation of the NLRP3 inflammasome was determined through the detection of the caspase 1 cleavage product p20 in a Western blot. The formation of the inflammasome was also investigated in vivo using immunohistological staining for ASC in primary synovial tissues as well as tissues containing TiAlV and CoCrMo particles and in vitro after the stimulation of the cells. The results show that the CoCrMo particles induced ASC more markedly, as a readout for inflammasome formation in vivo, compared to TiAlV particular wear. The CoNiCrMo particles also induced ASC-speck formation in all the tested cell lines, which was not induced by the TiAlV particles. The Western blot shows that NRLP3 inflammasome activation, measured through caspase 1 cleavage, was increased only by the CoNiCrMo particles in the MG63 cells. We conclude from our data that the activation of the inflammasome is mainly driven by CoNiCrMo particles and less by TiAlV particles, indicating that different inflammatory pathways are activated by the different alloys.

Macrophages and Bone Remodeling

Bone remodeling in the adult skeleton facilitates the removal and replacement of damaged and old bone to maintain bone quality. Tight coordination of bone resorption and bone formation during remodeling crucially maintains skeletal mass. Increasing evidence suggests that many cell types beyond osteoclasts and osteoblasts support bone remodeling, including macrophages and other myeloid lineage cells. Herein, we discuss the origin and functions for macrophages in the bone microenvironment, tissue resident macrophages, osteomacs, as well as newly identified osteomorphs that result from osteoclast fission. We also touch on the role of macrophages during inflammatory bone resorption. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

STAT3/Mitophagy Axis Coordinates Macrophage NLRP3 Inflammasome Activation and Inflammatory Bone Loss

Signal transducer and activator of transcription 3 (STAT3), a cytokine-responsive transcription factor, is known to play a role in immunity and bone remodeling. However, whether and how STAT3 impacts macrophage NLR family pyrin domain containing 3 (NLRP3) inflammasome activation associated with inflammatory bone loss remains unknown. Here, STAT3 signaling is hyperactivated in macrophages in the context of both non-sterile and sterile inflammatory osteolysis, and this was highly correlated with the cleaved interleukin-1β (IL-1β) expression pattern. Strikingly, pharmacological inhibition of STAT3 markedly blocks macrophage NLRP3 inflammasome activation in vitro, thereby relieving inflammatory macrophage-amplified osteoclast formation and bone-resorptive activity. Mechanistically, STAT3 inhibition in macrophages triggers PTEN-induced kinase 1 (PINK1)-dependent mitophagy that eliminates dysfunctional mitochondria, reverses mitochondrial membrane potential collapse, and inhibits mitochondrial reactive oxygen species release, thus inactivating the NLRP3 inflammasome. In vivo, STAT3 inhibition effectively protects mice from both infection-induced periapical lesions and aseptic titanium particle-mediated calvarial bone erosion with potent induction of PINK1 and downregulation of inflammasome activation, macrophage infiltration, and osteoclast formation. This study reveals the regulatory role of the STAT3/mitophagy axis at the osteo-immune interface and highlights a potential therapeutic intervention to prevent inflammatory bone loss. © 2022 American Society for Bone and Mineral Research (ASBMR).

The Experimental Exploration of TCM Theory "Treating the Same Disease with Different Approaches" on an Ulcerative Colitis Model

There is a relationship between lung injury and ulcerative colitis. Currently, traditional Chinese medicine (Huangqi Jiegeng (HQJGD) and Huangqi Huanglian decoctions (HQHLD)) is commonly used for UC-related lung injury; however, the mechanisms of these drugs remain unclear. In this study, UC models were established with the mucous membrane of colon allergize combined with TNBS-alcohol enteroclysis for 4 weeks. The pathological changes in the lung, intestine, liver, and kidney were observed; cytokines, chemokines, and adhesion molecules in lung tissue were detected in order to explore the immunological mechanism of UC-related lung injury and the intervention mechanism of traditional Chinese medicine in treating the lung and intestine in the immune-TNBS-ethanol rat model. Histology examinations demonstrated evident pathological changes in the lungs and intestines of the model groups. Furthermore, all groups treated with TCMs demonstrated reduced expressions of toll-like receptor 4, nuclear factor kappa-B, and macrophage migration inhibitory factor. Additionally, radioimmunoassay and immunohistochemistry showed tumor necrosis factor-α, interleukin-6, and 8 expression downregulation. The results showed that HQJGD and HQHLD could alleviate pulmonary inflammation in UC-related lung injury by obviously improving the pathology and fibrosis of the lung, inhibiting the positive feedback loop of MIF/NF-κB, and reducing lymphocyte homing to bronchial mucosa. This model revealed the immune mechanism of UC-related lung injury and the intervention mechanism of the Chinese medicine, which provided the rationale for treating ulcerative colitis clinically, so as to demonstrate the theory of “the lung and the large intestine being interior-exteriorly related” and “treating the same disease with different approaches.”

Involvement of NF-κB/NLRP3 axis in the progression of aseptic loosening of total joint arthroplasties: a review of molecular mechanisms

Particulate wear debris can trigger pro-inflammatory bone resorption and result in aseptic loosening. This complication remains major postoperative discomforts and complications for patients who underwent total joint arthroplasty. Recent studies have indicated that wear debris-induced aseptic loosening is associated with the overproduction of pro-inflammatory cytokines. The activation of osteoclasts as a result of inflammatory responses is associated with osteolysis. Moreover, stimulation of inflammatory signaling pathways such as the NF-κB/NLRP3 axis results in the production of pro-inflammatory cytokines. In this review, we first summarized the potential inflammatory mechanisms of wear particle-induced peri-implant osteolysis. Then, the therapeutic approaches, e.g., biological inhibitors, herbal products, and stem cells or their derivatives, with the ability to suppress the inflammatory responses, mainly NF-κB/NLRP3 signaling pathways, were discussed. Based on the results, activation of macrophages following inflammatory stimuli, overproduction of pro-inflammatory cytokines, and subsequent differentiation of osteoclasts in the presence of wear particles lead to bone resorption. The activation of NF-κB/NLRP3 signaling pathways within the macrophages stimulates the production of pro-inflammatory cytokines, e.g., IL-1β, IL-6, and TNF-α. According to in vitro and in vivo studies, novel therapeutics significantly promoted osteogenesis, suppressed osteoclastogenesis, and diminished particle-mediated bone resorption. Conclusively, these findings offer that suppressing pro-inflammatory cytokines by regulating both NF-κB and NLRP3 inflammasome represents a novel approach to attenuate wear-particle-related osteolytic diseases.

Shared Inflammatory Pathology of Stroke and COVID-19

Though COVID-19 is primarily characterized by symptoms in the periphery, it can also affect the central nervous system (CNS). This has been established by the association between stroke and COVID-19. However, the molecular mechanisms that cause stroke related to a COVID-19 infection have not been fully explored. More specifically, stroke and COVID-19 exhibit an overlap of molecular mechanisms. These similarities provide a way to better understand COVID-19 related stroke. We propose here that peripheral macrophages upregulate inflammatory proteins such as matrix metalloproteinases (MMPs) in response to SARS-CoV-2 infection. These inflammatory molecules and the SARS-CoV-2 virus have multiple negative effects related to endothelial dysfunction that results in the disruption of the blood-brain barrier (BBB). Finally, we discuss how the endothelial blood-brain barrier injury alters central nervous system function by leading to astrocyte dysfunction and inflammasome activation. Our goal is to elucidate such inflammatory pathways, which could provide insight into therapies to combat the negative neurological effects of COVID-19.

Interleukin-4 repairs wear particle induced osteolysis by modulating macrophage polarization and bone turnover

Periprosthetic osteolysis remains as a major complication of total joint replacement surgery. Modulation of macrophage polarization with interleukin-4 (IL-4) has emerged as an effective means to limit wear particle-induced osteolysis. The aim of this study was to evaluate the efficacy of local IL-4 delivery in treating preexisting particle-induced osteolysis. To this end, recently established 8 week modification of murine continuous femoral intramedullary particle infusion model was utilized. Subcutaneous infusion pumps were used to deliver polyethylene (PE) particles into mouse distal femur for 4 weeks to induce osteolysis. IL-4 was then added to the particle infusion for another 4 weeks. This delayed IL-4 treatment (IL-4 Del) was compared to IL-4 delivered continuously (IL-4 Cont) with PE particles from the beginning and to the infusion of particles alone for 8 weeks. Both IL-4 treatments were highly effective in preventing and repairing preexisting particle-induced bone loss as assessed by μCT. Immunofluorescence indicated a significant reduction in the number of F4/80 + iNOS + M1 macrophages and increase in the number of F4/80 + CD206 + M2 macrophages with both IL-4 treatments. Reduction in the number of tartrate resistant acid phosphatase + osteoclasts and increase in the amount of alkaline phosphatase (ALP) + osteoblasts was also observed with both IL-4 treatments likely explaining the regeneration of bone in these samples. Interesting, slightly more bone formation and ALP + osteoblasts were seen in the IL-4 Del group than in the IL-4 Cont group although these differences were not statistically significant. The study is a proof of principle that osteolytic lesions can be repaired via modulation of macrophage polarization.

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

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

Investigation of Cytotoxicity, Oxidative Stress, and Inflammatory Responses of Tantalum Nanoparticles in THP-1-Derived Macrophages

Tantalum (Ta) is gaining attention as a biomaterial in bone tissue engineering. Although the clinical advantage of Ta-based implants for primary and revision total joint replacement (TJA) has been well documented, few studies investigated the effect of wear products of Ta implants on peri-implant cells, and their potential contribution to aseptic implant loosening. This study is aimed at examining the cytotoxicity, oxidative stress, and proinflammatory potential of Ta and TiO₂ nanoparticles (NPs) on macrophages in vitro. NPs were characterized using scanning electron microscopy, dynamic light scattering, and energy-dispersive X-ray. To test the NP-mediated cellular response in macrophages, THP-1-derived macrophages were challenged with both NPs, and cytotoxicity was analyzed using CCK-8 and LDH assays. Flow cytometry was used to investigate particle uptake and their internalization routes. NP-mediated oxidative stress was investigated by measuring the production of reactive oxygen species, and their proinflammatory potential was determined by quantifying the production of TNFα and IL-1β in cell culture supernatants using ELISA. We found that both Ta and TiO₂ NPs were taken up through actin-dependent phagocytosis, although TiO₂ NPs did also show some involvement of macropinocytosis and clathrin-mediated endocytosis. Ta NPs caused no apparent toxicity, while TiO₂ NPs demonstrated significant cytotoxicity at a concentration of over 100μg/mL at 24 h. Ta NPs induced negligible ROS generation and proinflammatory cytokines (TNFα, IL-1β) in macrophages. In contrast, TiO₂ NPs markedly induced these effects in a dose-dependent manner. Our findings indicate that Ta NPs are inert, nontoxic, and noninflammatory. Therefore, Ta could be considered an excellent biomaterial in primary and revision joint arthroplasty implants.

Tumor necrosis factor primes and metal particles activate the NLRP3 inflammasome in human primary macrophages

Aseptic loosening of total joint replacements is driven by a macrophage-mediated inflammatory reaction to implant-derived wear particles. Phagocytosis of implant debris has been suggested to activate the NLRP3 inflammasome leading to secretion of interleukin (IL)-1β. However, factors and molecular mechanisms driving the particle-induced inflammasome activation are yet to be fully elucidated. In this study, we investigated the inflammasome response of human primary macrophages to titanium, chromium, and molybdenum particles in vitro. We observed that particles alone were not sufficient to induce IL-1β secretion, but an additional priming signal-such as bacterial lipopolysaccharide (LPS)-was required to license the inflammasome activation. By using specific inhibitors against the inflammasome signaling pathway, we demonstrate that the particle-induced IL-1β secretion depended upon activation of the NLRP3 inflammasome. We further hypothesized that tumor necrosis factor (TNF) could substitute for LPS as a priming signal, and found that particle stimulation together with preceding TNF treatment resulted in inflammasome-dependent IL-1β production as well. Our results show that the NLRP3 inflammasome mediates wear particle responses in human primary macrophages, and its activation does not necessarily require the presence of bacterial components, but can be induced under aseptic conditions by TNF priming. STATEMENT OF SIGNIFICANCE: This study was conducted to elucidate the molecular mechanisms of metal particle-induced IL-1β secretion in human primary macrophages. Production of this pro-inflammatory mediator from wear particle-activated macrophages has been associated with increased bone loss around total joint replacements-a condition eventually requiring revision surgery. Our results confirm that together with a co-stimulatory priming signal, particles of common implant metals elicit macrophage-mediated IL-1β secretion through activation of the NLRP3 inflammasome pathway. We also present a concept of TNF priming in this context, demonstrating that the particle-related IL-1β secretion can take place in a truly sterile environment. Thus, inhibition of inflammasome signaling appears a means to prevent wear particle-induced inflammation and development of peri‑prosthetic osteolysis.

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.

Periprosthetic Osteolysis: Mechanisms, Prevention and Treatment

Clinical studies, as well as in vitro and in vivo experiments have demonstrated that byproducts from joint replacements induce an inflammatory reaction that can result in periprosthetic osteolysis (PPOL) and aseptic loosening (AL). Particle-stimulated macrophages and other cells release cytokines, chemokines, and other pro-inflammatory substances that perpetuate chronic inflammation, induce osteoclastic bone resorption and suppress bone formation. Differentiation, maturation, activation, and survival of osteoclasts at the bone-implant interface are under the control of the receptor activator of nuclear factor kappa-Β ligand (RANKL)-dependent pathways, and the transcription factors like nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Mechanical factors such as prosthetic micromotion and oscillations in fluid pressures also contribute to PPOL. The treatment for progressive PPOL is only surgical. In order to mitigate ongoing loss of host bone, a number of non-operative approaches have been proposed. However, except for the use of bisphosphonates in selected cases, none are evidence based. To date, the most successful and effective approach to preventing PPOL is usage of wear-resistant bearing couples in combination with advanced implant designs, reducing the load of metallic and polymer particles. These innovations have significantly decreased the revision rate due to AL and PPOL in the last decade.