Macrophages at the skeletal tissue-device interface of loosened prosthetic devices express bone-related genes and their products

Evaluation of silver bio-functionality in a multicellular in vitro model: towards reduced animal usage in implant-associated infection research

Background

Despite the extensive use of silver ions or nanoparticles in research related to preventing implant-associated infections (IAI), their use in clinical practice has been debated. This is because the strong antibacterial properties of silver are counterbalanced by adverse effects on host cells. One of the reasons for this may be the lack of comprehensive in vitro models that are capable of analyzing host-bacteria and host-host interactions.

Methods and results

In this study, we tested silver efficacy through multicellular in vitro models involving macrophages (immune system), mesenchymal stem cells (MSCs, bone cells), and S. aureus (pathogen). Our model showed to be capable of identifying each element of culture as well as tracking the intracellular survival of bacteria. Furthermore, the model enabled to find a therapeutic window for silver ions (AgNO₃) and silver nanoparticles (AgNPs) where the viability of host cells was not compromised, and the antibacterial properties of silver were maintained. While AgNO₃ between 0.00017 and 0.017 µg/mL retained antibacterial properties, host cell viability was not affected. The multicellular model, however, demonstrated that those concentrations had no effect on the survival of S. aureus, inside or outside host cells. Similarly, treatment with 20 nm AgNPs did not influence the phagocytic and killing capacity of macrophages or prevent S. aureus from invading MSCs. Moreover, exposure to 100 nm AgNPs elicited an inflammatory response by host cells as detected by the increased production of TNF-α and IL-6. This was visible only when macrophages and MSCs were cultured together.

Conclusions

Multicellular in vitro models such as the one used here that simulate complex in vivo scenarios can be used to screen other therapeutic compounds or antibacterial biomaterials without the need to use animals.

Peri-prosthetic tissue cells show osteogenic capacity to differentiate into the osteoblastic lineage

During the process of aseptic loosening of prostheses, particulate wear debris induces a continuous inflammatory-like response resulting in the formation of a layer of fibrous peri-prosthetic tissue at the bone-prosthesis interface. The current treatment for loosening is revision surgery which is associated with a high-morbidity rate, especially in old patients. Therefore, less invasive alternatives are necessary. One approach could be to re-establish osseointegration of the prosthesis by inducing osteoblast differentiation in the peri-prosthetic tissue. Therefore, the aim of this study was to investigate the capacity of peri-prosthetic tissue cells to differentiate into the osteoblast lineage. Cells isolated from peri-prosthetic tissue samples (n = 22)-obtained during revision surgeries-were cultured under normal and several osteogenic culture conditions. Osteogenic differentiation was assessed by measurement of Alkaline Phosphatse (ALP), mineralization of the matrix and expression of several osteogenic genes. Cells cultured in osteogenic medium showed a significant increase in ALP staining (p = 0.024), mineralization of the matrix (p < 0.001) and ALP gene expression (p = 0.014) compared to normal culture medium. Addition of bone morphogenetic proteins (BMPs), a specific GSK3β inhibitor (GIN) or a combination of BMP and GIN to osteogenic medium could not increase ALP staining, mineralization, and ALP gene expression. In one donor, addition of GIN was required to induce mineralization of the matrix. Overall, we observed a high-inter-donor variability in response to osteogenic stimuli. In conclusion, peri-prosthetic tissue cells, cultured under osteogenic conditions, can produce alkaline phosphatase and mineralized matrix, and therefore show characteristics of differentiation into the osteoblastic lineage. © 2016 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1732-1742, 2017.

Biofabrication of a co-culture system in an osteoid-like hydrogel matrix

Biofabrication aims to develop functional, biological constructs using automated processes (additive manufacturing, AM) involving different cell types and biomaterials (Groll  et al 2016  Biofabrication 13001 1-6). As bone tissue is based on the crosstalk between osteoblasts and osteoclasts at least, evaluating cell-cell and cell-material interactions is of interest to understand bone remodeling. There is increasing interest in the role of osteoclasts not only considering bone resorption, but also their influence on the proliferation, migration and differentiation of osteoblasts. Osteoid-like, non-mineralized matrix is used here for the 3D cultivation of osteoblast and osteoclast progenitor cells to evaluate interactions in an early stage of bone formation. The AM technology bioplotting was used to tailor a 3D environment with defined properties. These results could be helpful to transfer this approach to the fabrication of bone tissue in regenerative medicine approaches. Gelatin is derived from collagen, which is the main phase of osteoid. Oxidized alginate-gelatin crosslinked hydrogel was used to immobilize osteoblastic (ST2) and osteoclastic (RAW) progenitor cells. Cell viability and number, the expression of different proteins like alkaline phosphatase (ALP), osteopontin (OPN) and tartrate resistant acid phosphatase (TRAP) were investigated. Release of vascular endothelial growth factor (VEGF) by the immobilized cells was analyzed. Microscopy techniques were used to evaluate cell morphology during an incubation period of 21 days. The biofabrication process was compatible with the cells. Cells migrated, proliferated and expressed their specific proteins indicating cell differentiation. The co-culture showed increased OPN concentration, which is a major protein of the osteoid involved in the mineralization process. TRAP activity was increased compared to single culture. ST2 single culture showed higher ALP activity compared to the co-culture. VEGF concentration of the co-culture was strongly increased. The results indicate the importance of using co-cultures to fabricate bone tissue by biofabrication. Especially the influence of the osteoblast/osteoclast crosstalk, in an early stage of bone formation, is shown here, using a 3D hydrogel based cell culture model created by biofabrication.

Intrauterine Bone Marrow Transplantation in Osteogenesis Imperfecta Mice Yields Donor Osteoclasts and Osteomacs but Not Osteoblasts

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The goal of osteogenesis imperfecta (OI) cell therapy is osteoblast replacement

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In utero transplantation (IUT) of bone marrow was conducted in OI mice

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Donor-derived osteoblasts were absent following bone marrow IUT

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Donor-derived hematopoietic cells included osteoclasts and osteal macrophages

Nanoparticle Uptake: The Phagocyte Problem

Phagocytes are key cellular participants determining important aspects of host exposure to nanomaterials, initiating clearance, biodistribution and the tenuous balance between host tolerance and adverse nanotoxicity. Macrophages in particular are believed to be among the first and primary cell types that process nanoparticles, mediating host inflammatory and immunological biological responses. These processes occur ubiquitously throughout tissues where nanomaterials are present, including the host mononuclear phagocytic system (MPS) residents in dedicated host filtration organs (i.e., liver, kidney spleen, and lung). Thus, to understand nanomaterials exposure risks it is critical to understand how nanomaterials are recognized, internalized, trafficked and distributed within diverse types of host macrophages and how possible cell-based reactions resulting from nanomaterial exposures further inflammatory host responses in vivo. This review focuses on describing macrophage-based initiation of downstream hallmark immunological and inflammatory processes resulting from phagocyte exposure to and internalization of nanomaterials.

Macrophages-Key cells in the response to wear debris from joint replacements

The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening, and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of proinflammatory and pro-osteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.

Adenosine A2A receptor activation prevents wear particle-induced osteolysis

Prosthesis loosening, associated with wear particle-induced inflammation and osteoclast-mediated bone destruction, is a common cause for joint implant failure, leading to revision surgery. Adenosine A(2A) receptors (A(2A)Rs) mediate potent anti-inflammatory effects in many tissues and prevent osteoclast differentiation. We tested the hypothesis that an A(2A)R agonist could reduce osteoclast-mediated bone resorption in a murine calvaria model of wear particle-induced bone resorption. C57BL/6 and A(2A)R knockout (A(2A)R KO) mice received ultrahigh-molecular weight polyethylene particles and were treated daily with either saline or the A(2A)R agonist CGS21680. After 2 weeks, micro-computed tomography of calvaria demonstrated that CGS21680 reduced particle-induced bone pitting and porosity in a dose-dependent manner, increasing cortical bone and bone volume compared to control mice. Histological examination demonstrated diminished inflammation after treatment with CGS21680. In A(2A)R KO mice, CGS21680 did not affect osteoclast-mediated bone resorption or inflammation. Levels of bone resorption markers receptor activator of nuclear factor κB (RANK), RANK ligand, cathepsin K, CD163, and osteopontin were reduced after CGS21680 treatment, together with a reduction in osteoclasts. Secretion of interleukin-1β (IL-1β) and tumor necrosis factor-α was significantly decreased, whereas IL-10 was markedly increased in bone by CGS21680. These results in mice suggest that site-specific delivery of an adenosine A(2A)R agonist could enhance implant survival, delaying or eliminating the need for revision arthroplastic surgery.

Examination of the inflammatory response following implantation of titanium plates coated with phospholipids in rats

Implantation of biomaterials like titanium (Ti) causes inflammatory reactions possibly affecting implant functionality. Surface modifications could improve biocompatibility and functionality of implants. Biomembrane-derived phospholipids might be useful as implant coating due to their biomimetic properties. In vitro studies demonstrated beneficial effects for 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphoethanolamin (POPE) as coating regarding interactions with cells and bacteria. Therefore, this in vivo study aimed at examining local inflammatory reactions after implantation of POPE-coated Ti plates. Ti implants with POPE attached non-covalently or covalent via octadecylphosphonic acid (OPA), with OPA alone and uncoated controls were simultaneously implanted intramuscularly in rats for 7, 14 and 56 days. The peri-implant tissue was quantitatively analyzed by immunohistochemistry for total macrophages, tissue macrophages, T cells, antigen-presenting cells and proliferating cells. Overall, both POPE-coated series were comparable to the controls. Furthermore, no differences were found between POPE coating on a covalently linked OPA monolayer and POPE coating dried from solution. Together with earlier in vitro results, this demonstrates the potential of phospholipids for implant surface modification.

Osteopontin deficiency impairs wear debris-induced osteolysis via regulation of cytokine secretion from murine macrophages

OBJECTIVE

To investigate the molecular mechanisms underlying particle-induced osteolysis, we focused on osteopontin (OPN), a cytokine and cell-attachment protein that is associated with macrophage chemoattractant and osteoclast activation.

METHODS

We compared OPN protein levels in human periprosthetic osteolysis tissues with those in osteoarthritis (OA) synovial tissues. To investigate the functions of OPN during particle-induced osteolysis in vivo, titanium particles were implanted onto the calvaria of OPN-deficient mice and their wild-type (WT) littermates. Mice were killed on day 10 and evaluated immunohistologically. The effects of OPN deficiency on the secretion of inflammatory cytokines were examined using cultured bone marrow-derived macrophages (BMMs). BMMs from OPN-deficient and WT mice were cultured with titanium particles for 12 hours, and the concentrations of inflammatory cytokines in the conditioned media were measured by enzyme-linked immunosorbent assay.

RESULTS

Expression of OPN protein was enhanced in human periprosthetic osteolysis tissues as compared with OA synovial tissues. In the particle-induced model of osteolysis of the calvaria, bone resorption was significantly suppressed by OPN deficiency via inhibition of osteoclastogenesis, whereas an inflammatory reaction was observed regardless of the genotype. Results of immunostaining indicated that OPN protein was highly expressed in the membrane and bone surface at the area of bone resorption in WT mice. When BMMs were exposed to titanium particles, the concentration of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1alpha (IL-1alpha), IL-1beta, and IL-6, as well as chemotactic factors, such as monocyte chemoattractant protein 1 and macrophage inflammatory protein 1alpha, in the conditioned medium were significantly reduced by OPN deficiency. Whereas phagocytic activity of BMMs was not attenuated by OPN deficiency, phagocytosis-mediated NF-kappaB activation was impaired in OPN-deficient BMMs. These data indicated that OPN was implicated in the development of particle-induced osteolysis via the orchestration of pro-/antiinflammatory cytokines secreted from macrophages.

CONCLUSION

OPN plays critical roles in wear debris-induced osteolysis, suggesting that OPN is a candidate therapeutic target for periprosthetic osteolysis.

Osteal macrophages: a new twist on coupling during bone dynamics

Osteoimmunological interactions are central to maintaining bone homeostasis and are key mechanisms in bone pathology. Macrophages are highly adaptable cells with pleiotropic actions. They have important roles in development, homeostasis and both innate and adaptive immunity. Macrophages can have broad ranging effects on bone, particularly in pathologic situations, but they are most commonly considered for their in vitro potential as an osteoclast precursor. We have recently shown that, like most tissues, the endosteum and periosteum contain a population of resident tissue macrophages (OsteoMacs) that impact on the bone formation process and are likely to play important roles in the bone niche. This review discusses the wider impact of macrophages in bone homeostasis and disease and proposes novel roles for OsteoMacs in bone modelling and remodelling.