Kinetics of polymethylmethacrylate particle-induced inhibition of osteoprogenitor differentiation and proliferation

Effect of Alumina Particles on the Osteogenic Ability of Osteoblasts

Biomaterials are used as implants for bone and dental disabilities. However, wear particles from the implants cause osteolysis following total joint arthroplasty (TJA). Ceramic implants are considered safe and elicit a minimal response to cause periprosthetic osteolysis. However, few reports have highlighted the adverse effect of ceramic particles such as alumina (Al2O3) on various cell types. Hence, we aimed to investigate the effect of Al2O3 particles on osteoprogenitors. A comparative treatment of Al2O3, Ti, and UHMWPE particles to osteoprogenitors at a similar concentration of 200 μg/mL showed that only Al2O3 particles were able to suppress the early and late differentiation markers of osteoprogenitors, including collagen synthesis, alkaline phosphatase (ALP) activity and mRNA expression of Runx2, OSX, Col1α, and OCN. Al2O3 particles even induced inflammation and activated the NFkB signaling pathway in osteoprogenitors. Moreover, bone-forming signals such as the WNT/β-catenin signaling pathway were inhibited by the Al2O3 particles. Al2O3 particles were found to induce the mRNA expression of WNT/β-catenin signaling antagonists such as DKK2, WIF, and sFRP1 several times in osteoprogenitors. Taken together, this study highlights a mechanistic view of the effect of Al2O3 particles on osteoprogenitors and suggests therapeutic targets such as NFĸB and WNT signaling pathways for ceramic particle-induced osteolysis.

NF-κB/let-7f-5p/IL-10 pathway involves in wear particle-induced osteolysis by inducing M1 macrophage polarization

NF-κB signaling pathway shows significant influence on wear particle-induced osteolysis, and this study aims to explore the underlying mechanism and the role of let-7f-5p in this process. A mouse calvarial osteolysis model was constructed with PMMA particles, and the bone marrow-derived macrophages (BMMs) were isolated from the osteolysis area. The expression of miRNA and protein was determined by qRT-PCR and western blot, respectively. The level of cytokines was evaluated with ELISA. Recombinant plasmids were transfected into cells for the endogenous expression of related genes. Dual-luciferase reporter assay was performed to determine the interaction between let-7f-5p and IL-10 in macrophage RAW264.7 cells. M1 macrophage polarization and expression of let-7f-5p were promoted in BMMs of osteolysis mouse model, compared with that in sham group. The expression of let-7f-5p was increased in the process of M1 macrophage polarization that induced by PMMA. Let-7f-5p was involved in M1 polarization in macrophages that treated with PMMA. IL-10 was negatively regulated by let-7f-5p. NF-κB regulated the expression of IL-10 through let-7f-5p. NF-κB participated in the PMMA-induced M1 macrophage polarization through let-7f-5p. Let-7f-5p contributed to PMMA-induced osteolysis by promoting M1 polarization of macrophages. The NF-κB/let-7f-5p/IL-10 pathway induces M1 macrophage polarization, and thus contributing to wear particle-induced osteolysis.

Cobalt and titanium nanoparticles influence on mesenchymal stem cell elasticity and turgidity

Bone cells are damaged by wear particles originating from total joint replacement implants. We investigated Mesenchymal stem cells (MSCs) nanomechanical properties when exposed to cobalt and titanium nanoparticles (resembling wear debris) of different sizes for up to 3days using AFM nanoindentation; along with flow-cytometry and MTT assay. The results demonstrated that cells exposed to increasing concentrations of nanoparticles had a lower value of elasticity and spring constant without significant effect on cell metabolic activity and viability but some morphological alteration (bleeping). Cobalt induced greater effects than titanium and this is consistent with the general knowledge of cyto-compatibility of the later. This work demonstrates for the first time that metal nanoparticles do not only influence MSCs enzymes activity but also cell structure; however, they do not result in full membrane damage. Furthermore, the mechanical changes are concentration and particles composition dependent but little influenced by the particle size.

Mesenchymal stem cells in the aseptic loosening of total joint replacements

Peri-prosthetic osteolysis remains as the main long-term complication of total joint replacement surgery. Research over four decades has established implant wear as the main culprit for chronic inflammation in the peri-implant tissues and macrophages as the key cells mediating the host reaction to implant-derived wear particles. Wear debris activated macrophages secrete inflammatory mediators that stimulate bone resorbing osteoclasts; thus bone loss in the peri-implant tissues is increased. However, the balance of bone turnover is not only dictated by osteoclast-mediated bone resorption but also by the formation of new bone by osteoblasts; under physiological conditions these two processes are tightly coupled. Increasing interest has been placed on the effects of wear debris on the cells of the bone-forming lineage. These cells are derived primarily from multipotent mesenchymal stem cells (MSCs) residing in bone marrow and the walls of the microvasculature. Accumulating evidence indicates that wear debris significantly impairs MSC-to-osteoblast differentiation and subsequent bone formation. In this review, we summarize the current understanding of the effects of biomaterial implant wear debris on MSCs. Emerging treatment options to improve initial implant integration and treat developing osteolytic lesions by utilizing or targeting MSCs are also discussed. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1195-1207, 2017.

Biological responses of human mesenchymal stem cells to titanium wear debris particles

Wear debris-induced osteolysis is a major cause of orthopedic implant aseptic loosening, and various cell types, including macrophages, monocytes, osteoblasts, and osteoclasts, are involved. We recently showed that mesenchymal stem/osteoprogenitor cells (MSCs) are another target, and that endocytosis of titanium (Ti) particles causes reduced MSC proliferation and osteogenic differentiation. Here we investigated the mechanistic aspects of the endocytosis-mediated responses of MSCs to Ti particulates. Dose-dependent effects were observed on cell viability, with doses >300 Ti particles/cell resulting in drastic cell death. To maintain cell viability and analyze particle-induced effects, doses <300 particles/cell were used. Increased production of interleukin-8 (IL-8), but not IL-6, was observed in treated MSCs, while levels of TGF-β, IL-1β, and TNF-α were undetectable in treated or control cells, suggesting MSCs as a likely major producer of IL-8 in the periprosthetic zone. Disruptions in cytoskeletal and adherens junction organization were also observed in Ti particles-treated MSCs. However, neither IL-8 and IL-6 treatment nor conditioned medium from Ti particle-treated MSCs failed to affect MSC osteogenic differentiation. Among other Ti particle-induced cytokines, only GM-CSF appeared to mimic the effects of reduced cell viability and osteogenesis. Taken together, these results strongly suggest that MSCs play both responder and initiator roles in mediating the osteolytic effects of the presence of wear debris particles in periprosthetic zones.

Improvement of intertrochanteric bone quality in osteoporotic female rats after injection of polylactic acid-polyglycolic acid copolymer/collagen type I microspheres combined with bone mesenchymal stem cells

PURPOSE

Osteoporosis mainly involves cancellous bone, and the spine and hip, with their relatively high cancellous bone to cortical bone ratio, are severely affected. Studies of bone mesenchymal stem cells (BMSCs) from osteoporotic patients and animal models have revealed that osteoporosis is often associated with reduction of BMSCs' proliferation and osteogenic differentiation. Our aim was to test whether polylactic acid-polyglycolic acid copolymer(PLGA)/collagen type I(CoI) microspheres combined with BMSCs could be used as injectable scaffolds to improve bone quality in osteoporotic female rats.

METHODS

PLGA microspheres were coated with CoI. BMSCs of the third passage and were cultured with PLGA/CoI microspheres for seven days. Forty three-month-old female non-pregnant SD rats were ovariectomized to establish osteoporotic animal models. Three months after being ovariectomized, the osteoporotic rats were randomly divided into five groups: SHAM group, PBS group, cell group, microsphere (MS) group, and cell+MS group. Varying materials were injected into the intertrochanters of each group's rats. Twenty rats were sacrificed at one month and three months post-op, respectively. The femora were harvested in order to measure the intertrochanteric bone mineral density (BMD) with DEXA and trabecular thickness (Tb.Th), percentage of trabecular area (%Tb.Ar), bone volume fraction (BV/TV) and trabecular spacing (Tb.Sp) with Micro CT. One-way ANOVA and Kruskal-Wallis tests were used.

RESULTS

BMSCs seeded on PLGA/CoI microspheres had a nice adhesion and proliferation. At one month post-op, the BMD (0.33 ± 0.01 g/cm(2)), Tb.Th (459.65 ± 28.31 μm), %Tb.Ar (9.61 ± 0.29 %) and Tb.Sp (2645.81 ± 94.91 μm) of the cell+ MS group were better than those of the SHAM group and the cell group. At three months post-op, the BMD (0.32 ± 0.01 g/cm(2)), Tb.Th (372.81 ± 38.45 μm), %Tb.Ar (6.65 ± 0.25 %), BV/TV (6.62 ± 0.25 %) and Tb.Sp (1559.03 ± 57.06 μm) of the cell + MS group were also better than those of the SHAM group and the cell group.

CONCLUSION

The PLGA/CoI microspheres combined with BMSCs can repair bone defects more quickly. This means that PLGA/CoI microspheres combined with BMSCs can promote trabecular reconstruction and improve bone quality in osteoporotic rats. This scaffold can provide a promising minimally invasive surgical tool for enhancement of bone fracture healing or prevention of fracture occurrence which will in turn minimize complications endemic to patients with osteoporosis.

Polymethylmethacrylate particles impair osteoprogenitor viability and expression of osteogenic transcription factors Runx2, osterix, and Dlx5

Polymethylmethacrylate (PMMA) particles have been shown to inhibit the differentiation of osteoprogenitor cells, but the mechanism of this inhibitory effect has not been investigated. We hypothesize that the inhibitory effects of PMMA particles involve impairment of osteoprogenitor viability and direct inhibition of transcription factors that regulate osteogenesis. We challenged MC3T3-E1 osteoprogenitors with PMMA particles and examined the effects of these materials on osteoprogenitor viability and expression of transcription factors Runx2, osterix, Dlx5, and Msx2. MC3T3-E1 cells treated with PMMA particles over a 72-h period showed a significant reduction in cell viability and proliferation as indicated by a dose- and time-dependent increase in supernatant levels of lactate dehydrogenase, an intracellular enzyme released from dead cells, a dose-dependent decrease in cell number and BrdU uptake, and the presence of large numbers of positively labeled Annexin V-stained cells. The absence of apoptotic cells on TUNEL assay indicated that cell death occurred by necrosis, not apoptosis. MC3T3-E1 cells challenged with PMMA particles during the first 6 days of differentiation in osteogenic medium showed a significant dose-dependent decrease in the RNA expression of Runx2, osterix, and Dlx5 on all days of measurement, while the RNA expression of Msx2, an antagonist of Dlx5-induced osteogenesis, remained relatively unaffected. These results indicate that PMMA particles impair osteoprogenitor viability and inhibit the expression of transcription factors that promote osteoprogenitor differentiation.

The effect of titanium particles on rat bone marrow stem cells in vitro

In arthroplasty prostheses and dental implant, titanium is an excellent biocompatible material for its advanced physical qualities and better biocompatibility. However, it was reported that high ratios of titanium particles can be liberated due to the continual loading or articulation cycles of the implant. Because bone marrow stem cells (BMSCs) located adjacent to the implant are critical contributors to osseous tissue integrity, this study researched the influence of titanium particles on BMSCs' viability, proliferation, and cell skeleton. In addition, the phagocytosis of titanium particles by BMSCs and expression of tumor suppressor protein p53 were also examined. It was found that exposure of BMSCs to titanium particles disrupted their viability and proliferation in vitro, which may due to the phagocytosis of titanium particles by BMSCs. Moreover, cell skeleton was destroyed and the p53 protein level increased as the titanium particles were added. For these results, it was concluded that titanium particles had a cytotoxic effect on BMSCs in vitro and would inhibit the bone formation around the implant.

Ultrahigh molecular weight polyethylene wear debris inhibits osteoprogenitor proliferation and differentiation in vitro

Polyethylene wear debris induces progressive osteolysis by increasing bone degradation and suppressing bone formation. Polyethylene particles inhibit the function of mature osteoblasts, but whether polyethylene particles also interfere with the proliferation and differentiation of osteoprogenitor cells is unknown. In this study, we investigated the effects of ultrahigh molecular weight polyethylene (UHMWPE) particles on the osteogenic activity of primary murine bone marrow osteoprogenitors and MC3T3-E1 preosteoblastic cells in vitro. Submicron-sized UHMWPE particles generated from wear simulator tests were isolated from serum-containing solution by density gradient centrifugation. The particles were coated onto the surface of culture wells at concentrations of 0.038, 0.075, 0.150, 0.300, and 0.600% v/v in a layer of type I collagen matrix. Primary murine bone marrow cells and MC3T3-E1 preosteoblasts were seeded onto the particle-collagen matrix and induced to differentiate in osteogenic medium for 20 days. Exposure of both cell populations to UHMWPE particles resulted in a dose-dependent decrease in mineralization, proliferation, alkaline phosphatase activity, and osteocalcin production when compared with control cells cultured on collagen matrix without particles. Complete suppression of osteogenesis was observed at particle concentrations > or =0.150% v/v. This study demonstrated that UHMWPE particles inhibit the osteogenic activity of osteoprogenitor cells, which may result in reduced periprosthetic bone regeneration and repair.

Polymethylmethacrylate particles inhibit osteoblastic differentiation of MC3T3-E1 osteoprogenitor cells

Orthopedic wear debris has been implicated as a significant inhibitory factor of osteoblast differentiation. Polymethylmethacrylate (PMMA) particles have been previously shown to inhibit the differentiation of osteoprogenitors in heterogeneous murine marrow stromal cell cultures, but the effect of PMMA particles on pure osteoprogenitor populations remains unknown. In this study, we challenged murine MC3T3-E1 osteoprogenitor cells with PMMA particles during their initial differentiation in osteogenic medium. MC3T3-E1 cultures challenged with PMMA particles showed a gradual dose-dependent decrease in mineralization, cell number, and alkaline phosphatase activity at low particle doses (0.038-0.150% v/v) and complete reduction of these outcome parameters at high particle doses (> or =0.300% v/v). MC3T3-E1 cultures challenged with a high particle dose (0.300% v/v) showed no rise in these outcome parameters over time, whereas cultures challenged with a low particle dose (0.075% v/v) showed a normal or reduced rate of increase compared to controls. Osteocalcin production was not significantly affected by particles at all doses tested. MC3T3-E1 cells grown in conditioned medium from particle-treated MC3T3-E1 cultures showed a significant reduction in mineralization only. These results indicate that direct exposure of MC3T3-E1 osteoprogenitors to PMMA particles results in suppression of osteogenic proliferation and differentiation.

Effect of vertebroplasty filler materials on viability and gene expression of human nucleus pulposus cells

Consequences of intradiscal cement leakage--often occurring after vertebral cement augmentation for the treatment of vertebral compression fractures--are still unknown. In this study, we have investigated the influences of vertebroplasty filler materials (polymethylmethacrylate-, calcium phosphate- and calcium sulfate-based bone cement) on isolated nucleus pulposus cells. Cell viability of cultured human nucleus pulposus cells were measured after treatment with vertebroplasty filler materials. Gene expression profile of selected genes was determined with quantitative real-time PCR. The widely used polymethylmethacrylate and calcium phosphate cement significantly decreased cell number in a dose- and time-dependent manner while calcium sulfate cement affected cell viability less. Expression of genes involved in matrix metabolism of nucleus pulposus--aggrecan, collagens, small proteoglycans--as well as important transcription factors have also significantly changed due to treatment (e.g., 2.5-fold decrease in aggrecan expression was determined in cultures due to polymethylmethacrylate treatment). Our results suggest that vertebroplasty filler materials--depending on the type of applied material--can accelerate the degeneration of nucleus pulposus cells resulting in a less flexible disc in case of intradiscal cement leakage. This process may increase the risk of a subsequent new vertebral fracture, the main complication of vertebral augmentation.

What are the local and systemic biologic reactions and mediators to wear debris, and what host factors determine or modulate the biologic response to wear particles?

New clinical and basic science data on the cellular and molecular mechanisms by which wear particles stimulate the host inflammatory response have provided deeper insight into the pathophysiology of periprosthetic bone loss. Interactions among wear particles, macrophages, osteoblasts, bone marrow-derived mesenchymal stem cells, fibroblasts, endothelial cells, and T cells contribute to the production of pro-inflammatory and pro-osteoclastogenic cytokines such as TNF-alpha, RANKL, M-SCF, PGE2, IL-1, IL-6, and IL-8. These cytokines not only promote osteoclastogenesis but interfere with osteogenesis led by osteoprogenitor cells. Recent studies indicate that genetic variations in TNF-alpha, IL-1, and FRZB can result in subtle changes in gene function, giving rise to altered susceptibility or severity for periprosthetic inflammation and bone loss. Continuing research on the biologic effects and mechanisms of action of wear particles will provide a rational basis for the development of novel and effective ways of diagnosis, prevention, and treatment of periprosthetic inflammatory bone loss.