Aseptic loosening caused by peri-implant osteolysis (PIO) is a common complication after joint replacement, and there is still no better treatment than revision surgery. The wear particle-induced inflammation response, especially subsequent osteoclastic bone resorption, is responsible for PIO. As the importance of wear particles in inducing autophagy in cells around the prosthesis in PIO has been discovered, this might be a central process underlying aseptic loosening. However, the role of autophagy induced by wear particles in osteoclastogenesis during PIO remains unclear. In this study, we investigated the role of autophagy in osteoclastogenesis and verified it in a mouse calvarial osteolysis model. We found that osteoclasts were increased in the interface membranes of patients with aseptic loosening. In vitro, knocking down the Atg5 gene or using autophagy inhibitors (3-MA, LY294002) to inhibit autophagy was found to repress osteoclastogenesis and decrease expression of the osteoclast-related genes TRAP, cathepsin K, and matrix metalloprotein 9 (MMP-9) with or without titanium (Ti) particles. In vivo, 3-MA and LY294002 repressed Ti particle-stimulated osteolysis and osteoclastogenesis and reduced expression of the pro-inflammatory factors TNF-α, IL-1β, and IL-6. Our results suggest that 3-MA and LY294002 might be the potential medicines to prevent and treat PIO and aseptic loosening.

Aseptic prosthesis loosening (APL) is one of the most prevalent complications associated with arthroplasty. The main cause is the periprosthetic osteolysis induced by wear particles. However, the specific mechanisms of crosstalk between immune cells and osteoclasts/osteoblasts during osteolysis are unclear. In this study, we report the role and mechanism of macrophage-derived exosomes in wear particle-induced osteolysis. The results of exosomes up-taken experiments revealed that osteoblast and mature osteoclasts capture macrophage-derived exosomes (M-Exo). Next-generation sequencing and RT-qPCR on M-Exo revealed that exosomal microRNA miR-3470b was downregulated in wear particle-induced osteolysis. The results of analysis on Luciferase reporter assays/fluorescence in situ hybridization (FISH)/immunofluorescence (IF)/immunohistochemistry (IHC) and co-culture experiments demonstrated that wear particles induced osteoclast differentiation by increasing the expression of NFatc1 via M-Exo miR-3470b targeting TAB3/ NF-κB signaling. We also illustrate that engineered exosomes enriching miR-3470b facilitated to suppressed the osteolysis; the microenvironment enriching with miR-3470b could suppress wear particle-induced osteolysis via inhibition of TAB3/ NF-κB in vivo. In summary, our findings indicate that macrophage-derived exosomes transfer to osteoclasts to induce osteolysis in wear particle-induced APL. Engineering exosomes enriching with miR-3470b might be a novel strategy for the targeting treatment of bone resorption-related diseases.

Staphylococcus aureus (S. aureus) is a leading cause of Periprosthetic joint infection (PJI), a severe complication after joint arthroplasty. Immunosuppression is a major factor contributing to the infection chronicity of S. aureus PJI, posing significant treatment challenges. This study investigates the relationship between the immunosuppressive biofilm milieu and S. aureus PJI outcomes in both discovery and validation cohorts. This scRNA‐seq analysis of synovium from PJI patients reveals an expansion and heightened activity of monocyte‐related myeloid‐derived suppressor cells (M‐MDSCs) and regulatory T cells (Treg). Importantly, CXCL16 is significantly upregulated in M‐MDSCs, with its corresponding CXCR6 receptor also elevated on Treg. M‐MDSCs recruit Treg and enhance its activity via CXCL16‐CXCR6 interactions, while Treg secretes TGF‐β, inducing M‐MDSCs proliferation and immunosuppressive activity. Interfering with this cross‐talk in vivo using Treg‐specific CXCR6 knockout PJI mouse model reduces M‐MDSCs/Treg‐mediated immunosuppression and alleviates bacterial burden. Immunohistochemistry and recurrence analysis show that PJI patients with CXCR6^high synovium have poor prognosis. This findings highlight the critical role of CXCR6 in Treg in orchestrating an immunosuppressive microenvironment and biofilm persistence during PJI, offering potential targets for therapeutic intervention.

Background/Aims: Prosthesis loosening is closely associated with chronic inflammatory cytokine secretion by macrophages, which are activated by wear particles or inflammatory stimulants such as lipopolysaccharide (LPS). Reactive oxygen species (ROS) are critical regulators of inflammation, but their enzymatic sources in response to wear particles and their effects on peri-implant LPS-tolerance remain unclear. Methods: Three ROS-related enzymes—nicotinamide adenine dinucleotide phosphate oxidase (NOX)-1 and -2 and catalase—were investigated in interface membrane tissues and in titanium (Ti) particle-stimulated macrophages in vitro. The generation of ROS and downstream inflammatory effects were measured with or without pre-incubation with apocynin, an NOX inhibitor. Results: Pre-exposure to Ti particles attenuated NF-κB activation in LPS-stimulated macrophages, indicating that wear particles suppress immune response, which may lead to chronic inflammation. NOX-1 and -2 were highly expressed in aseptically loosened interface membranes and in macrophages stimulated with Ti particles; the particles induced a moderate amount of ROS generation, NF-κB activation, and TNF-a secretion in macrophages, and these effects were suppressed by apocynin. Conclusion: Wear particles induce ROS generation through the NOX signaling pathway, resulting in persistent inflammation and delayed loosening. Thus, the suppression of NOX activity may be a useful strategy for preventing prosthesis loosening.

This study aims to evaluate the efficacy of baicalein, a flavonoid derived from Scutellaria baicalensis, against Staphylococcus aureus (S. aureus), focusing on its inhibitory and eradicative effects on biofilms, as well as its cellular cytotoxicity. The goal is to provide preliminary evidence for its potential application in the management of periprosthetic joint infection (PJI). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of baicalein against the standard strain of S. aureus ATCC 29213, a clinical strain of methicillin-sensitive S. aureus 115 (MSSA 115), and a clinical strain of methicillin-resistant S. aureus 49 (MRSA 49) were determined using broth microdilution and colony counting methods. Bactericidal kinetics over a 24-h period were evaluated using a time-kill assay. Biofilm inhibition and eradication were assessed on 96-well and titanium alloy plates, while the cellular cytotoxicity of baicalein was examined using the cell counting kit-8 (CCK-8) assay on human primary synovial fibroblasts and chondrocytes. The MIC of baicalein was 32 μg/mL for the ATCC 29213, and 64 μg/mL for both MSSA115 and MRSA49. Meanwhile, the MBC for all three strains was 128 μg/mL. Baicalein exhibited a time-dependent bactericidal activity, with maximum efficacy at 24 h. Biofilm inhibition was evident at concentrations equal to or exceeding the MIC, as confirmed by biofilm biomass and metabolic activity assays, along with scanning electron and confocal laser microscope. However, baicalein was unable to completely eradicate preformed biofilms. Baicalein demonstrated significant cytotoxic effects on both synovial fibroblasts and chondrocytes after exposure for 16 and 24 h. Baicalein shows significant bactericidal effects and effectively inhibits S. aureus biofilm formation. These findings suggest its potential as a promising local antibacterial agent for postoperative continuous intra-articular lavage in the treatment of S. aureus-related early postoperative or acute hematogenous PJIs.