Effect of cobalt ions on the interaction between macrophages and titanium

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.

Inflammasomes NLRP3 and AIM2 in peri-implantitis: A cross-sectional study

BACKGROUND

Inflammasome components NLRP3 and AIM2 contribute to inflammation development by the activation of caspase-1 and IL-1β. They have not been yet evaluated in samples from patients with active peri-implantitis. Thus, the aim of the present study is to analyze the expression of inflammasomes NLRP3 and AIM2 and subsequent caspase 1 and IL-1β assessing the microenvironment of leukocyte subsets in samples from patients with active peri-implantitis.

METHODS

Biopsies were collected from 33 implants in 21 patients being treated for peri-implantitis. Biopsies from gingival tissues from 15 patients with healthy periodontium were also collected for control. These tissues were evaluated through conventional histological stainings. Then, immunohistochemical detection was performed to analyze NLRP3, AIM2, caspase-1, and IL-1β and markers of different leukocyte subsets. PCR for inflammasomes and related genes was also done.

RESULTS

This manuscript reveals a high immunohistochemical and mRNA expression of NLRP3 and AIM2 inflammasomes, caspase-1, and IL-1β in biopsies collected from human peri-implantitis. The expression of the tested markers was significantly correlated with the increase in inflammatory infiltrate, probing depth, presence of biofilm, and bleeding on probing. In these peri-implantitis lesions, the area of biopsy tissue occupied by inflammatory infiltrate was intense while the area occupied by collagen was significantly lower. In comparison with periodontal healthy tissues, the inflammatory infiltrate was statistically significantly higher in the peri-implantitis biopsies and was mainly composed of plasma cells, followed by T and B lymphocytes.

CONCLUSION

In human peri-implantitis, chronic inflammation can be explained in part by the action of IL-1β/caspase 1 induced through NLRP3 and AIM2 inflammasome activation.

Metal ions: the unfading stars of bone regeneration-from bone metabolism regulation to biomaterial applications

In recent years, bone regeneration has emerged as a remarkable field that offers promising guidance for treating bone-related diseases, such as bone defects, bone infections, and osteosarcoma. Among various bone regeneration approaches, the metal ion-based strategy has surfaced as a prospective candidate approach owing to the extensive regulatory role of metal ions in bone metabolism and the diversity of corresponding delivery strategies. Various metal ions can promote bone regeneration through three primary strategies: balancing the effects of osteoblasts and osteoclasts, regulating the immune microenvironment, and promoting bone angiogenesis. In the meantime, the complex molecular mechanisms behind these strategies are being consistently explored. Moreover, the accelerated development of biomaterials broadens the prospect of metal ions applied to bone regeneration. This review highlights the potential of metal ions for bone regeneration and their underlying mechanisms. We propose that future investigations focus on refining the clinical utilization of metal ions using both mechanistic inquiry and materials engineering to bolster the clinical effectiveness of metal ion-based approaches for bone regeneration.

Effects of NLRP3 on implants placement

Bone stability is precisely controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. When the balance is broken, the integrity of the bone structure will be destroyed. Inflammasomes are important protein complexes in response to pathogen-related molecular models or injury-related molecular models, which can promote the activation and secretion of proinflammatory cytokines and activate a local inflammatory response. NOD-like receptor thermal protein domain associated protein (NLRP) 3 inflammasome can promote bone resorption through the activation of the proinflammatory cytokines interleukin (IL)-1β, IL-18 and the induction of caspase-1-mediated pyroptosis. Inhibiting the production of NLRP3 inflammasome may be beneficial to improve comfort and bone stability. The presence of metal particles and microorganisms around implants can activate NLRP3 and promote bone absorption. NLRP3 inflammasome plays an important role in the maintenance of bone stability around implants, however, most studies focus on orthopedic implants and periodontitis. This article reviews the effects of NLRP3 inflammasome on bone formation, resorption and pain induced by implants, and the possibility of NLRP3 as a target for preventing peri-implantitis is discussed.

Balancing the antibacterial and osteogenic effects of double-layer TiO2 nanotubes loaded with silver nanoparticles for the osseointegration of implants

The improvement of Ag nanoparticles (AgNPs), in particular, loaded titania nanotubes, includes not only the antibacterial effect but also balancing the side effects from the antibacterial effect and osteogenesis properties, which can lead to an increased success rate of implants. Herein, based on the various needs of the graft to inhibit bacteria at different stages in vivo, we used a special osteogenic honeycomb-like "large tube over small tube" double-layered nanotube structure and created ultra-small-sized silver nanoparticles uniformly loaded on the surface and the interior of double-layer nanotubes by an optimized sputter coating method to ensure the time-dependent controllable release of antibacterial Ag ions from grafts and achieve the balance of the antibacterial effect and osteogenesis properties. The release of Ag⁺ from DNT-Ag8 was determined by inductively coupled plasma spectrometry. The release rate of Ag was slow; it was 30% on the first day and plateaued by the 19th day. Porphyromonas gingivalis adhesion and live bacteria were less abundant on the surface of DNT-Ag8, reaching an antibacterial efficiency of 55.6% in vitro. DNT-Ag8 shows a significantly higher antibacterial effect in a rat model infected with Staphylococcus aureus. An in vitro study demonstrated that DNT-Ag8 had no adverse effects on the adhesion, viability, proliferation, ALP staining, or activity assays of rat BMSCs. In contrast, it increased the expression of osteogenic genes. In vivo, DNT-Ag8 promoted bone-implant osseointegration in a beagle mandibular tooth loss model. This study demonstrated that the uniform loading of small-diameter silver nanoparticles using a honeycomb bilayer nanotube template structure is a promising method for modifying titanium surfaces to improve both bacteriostasis and osseointegration.

Topography-mediated immunomodulation in osseointegration; Ally or Enemy

Osteoimmunology is at full display during endosseous implant osseointegration. Bone formation, maintenance and resorption at the implant surface is a result of bidirectional and dynamic reciprocal communication between the bone and immune cells that extends beyond the well-defined osteoblast-osteoclast signaling. Implant surface topography informs adherent progenitor and immune cell function and their cross-talk to modulate the process of bone accrual. Integrating titanium surface engineering with the principles of immunology is utilized to harness the power of immune system to improve osseointegration in healthy and diseased microenvironments. This review summarizes current information regarding immune cell-titanium implant surface interactions and places these events in the context of surface-mediated immunomodulation and bone regeneration. A mechanistic approach is directed in demonstrating the central role of osteoimmunology in the process of osseointegration and exploring how regulation of immune cell function at the implant-bone interface may be used in future control of clinical therapies. The process of peri-implant bone loss is also informed by immunomodulation at the implant surface. How surface topography is exploited to prevent osteoclastogenesis is considered herein with respect to peri-implant inflammation, osteoclastic precursor-surface interactions, and the upstream/downstream effects of surface topography on immune and progenitor cell function.

Ti Ions Induce IL-1β Release by Activation of the NLRP3 Inflammasome in a Human Macrophage Cell Line

The aim of the present study was to investigate whether titanium (Ti)-induced release of interleukin (IL)-1β acts through the assembly of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome. In addition, we examined whether particulate Ti or TiO₂ activates the same intracellular pathways with the assembly of the NLRP3 inflammasome as Ti ions. Ti ions are known to induce IL-1β maturation and release by the formation of metal-protein aggregates. Wild-type THP-1 (wt.) cells and NLRP3^- and ASC^- (apoptosis-associated speck-like protein containing caspase recruitment domain (CARD)) knockdown cells were used in the experimental analyses. Macro- and nanoparticles (NPs) of both Ti and TiO₂ were used as test agents. IL-1β release as a biomarker for inflammasome activation and cell viability was also analyzed. Periodate-oxidized adenosine triphosphate (oATP) was used to attenuate downstream signaling in NLRP3 inflammasome activation. Cellular uptake of Ti was examined using transmission electron microscopy. Cells exposed to the Ti-ion solution showed a dose-dependent increase in the release of IL-1β; conversely, exposure to particulate Ti did not result in increased IL-1β release. Cell viability was not affected by particulate Ti. Knockdown cells exposed to Ti showed a statistically significant reduction in the release of IL-1β compared with wt. cells (p < 0.001). Cellular uptake was detected in all Ti mixtures, and aggregates with various structures were observed. Ti ion-induced release of bioactive IL-1β in THP-1 cells involves the assembly of the NLRP3 inflammasome.

The Effect of Neutrophil-Derived Products on the Function of Leukocytes Obtained after Titanium Implantation in the Ovine Model

Simple Summary

Titanium is one of the most commonly used biomaterials for implantation as a part of the orthopedic procedures. However, this biomaterial can cause an excessive inflammatory response, even leading to rejection of the implant. Therefore, the aim of our study was to assess the overall organism response after insertion of Ti implant and the activity of neutrophils and monocyte-derived macrophages (MDM), to evaluate the possible negative effect of this biomaterial on the host cells. Our study revealed that insertion of the Ti implant did not evoke systemic inflammatory response or activation of leukocytes. Additionally, we evaluated the activity of neutrophils and MDM after stimulation with autologous neutrophil products, namely, antimicrobial neutrophil extract and neutrophil degranulation product as two potential regulators of inflammatory response. Antimicrobial neutrophil extract appeared to be a factor causing the decrease of secretory neutrophil response and polarization of MDM towards pro-resolving phenotype, whereas the neutrophil degranulation product acted as pro-inflammatory.

Abstract

Titanium (Ti) is currently the most common biomaterial used for orthopedic implants; however, these implants may cause deleterious immune response. To investigate the possible mechanisms involved in excessive inflammation, we assessed the activity of neutrophils and monocyte-derived macrophages (MDMs) during the insertion of the Ti implant in a sheep model. The study was conducted on 12 sheep, 4 of which were control animals and 8 were in the experimental group with inserted Ti implant. Neutrophil secretory response was estimated at two time points T0 before surgery and T1 1 h after implantation and was based on the release of enzymes from neutrophil granules and reactive oxygen and nitrogen species (RONS) generation. MDM function was evaluated 5 months after implantation, on the basis of RONS generation arginase activity and morphological changes. Moreover, the influence of some autologous neutrophil derived products, namely, antimicrobial neutrophil extract (ANE) and neutrophil degranulation products (DGP) on leukocytes was estimated. Our study revealed that Ti implant insertion did not cause any adverse effects up to 5 months after surgical procedure. Stimulation of neutrophil cultures with ANE decreased the enzyme release as well as superoxide generation. Treatment of MDM with ANE diminished superoxide and NO generation and increased arginase activity. On the other hand, MDM stimulated with DGP showed elevated superoxide and NO generation as well as decreased arginase activity. To summarize, ANE exerted an anti-inflammatory and pro-resolving effect on studied leukocytes, whereas DGP acted as pro-inflammatory.

Inflammasomes in Alveolar Bone Loss

Bone remodeling is tightly controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Fine tuning of the osteoclast-osteoblast balance results in strict synchronization of bone resorption and formation, which maintains structural integrity and bone tissue homeostasis; in contrast, dysregulated bone remodeling may cause pathological osteolysis, in which inflammation plays a vital role in promoting bone destruction. The alveolar bone presents high turnover rate, complex associations with the tooth and periodontium, and susceptibility to oral pathogenic insults and mechanical stress, which enhance its complexity in host defense and bone remodeling. Alveolar bone loss is also involved in systemic bone destruction and is affected by medication or systemic pathological factors. Therefore, it is essential to investigate the osteoimmunological mechanisms involved in the dysregulation of alveolar bone remodeling. The inflammasome is a supramolecular protein complex assembled in response to pattern recognition receptors and damage-associated molecular patterns, leading to the maturation and secretion of pro-inflammatory cytokines and activation of inflammatory responses. Pyroptosis downstream of inflammasome activation also facilitates the clearance of intracellular pathogens and irritants. However, inadequate or excessive activity of the inflammasome may allow for persistent infection and infection spreading or uncontrolled destruction of the alveolar bone, as commonly observed in periodontitis, periapical periodontitis, peri-implantitis, orthodontic tooth movement, medication-related osteonecrosis of the jaw, nonsterile or sterile osteomyelitis of the jaw, and osteoporosis. In this review, we present a framework for understanding the role and mechanism of canonical and noncanonical inflammasomes in the pathogenesis and development of etiologically diverse diseases associated with alveolar bone loss. Inappropriate inflammasome activation may drive alveolar osteolysis by regulating cellular players, including osteoclasts, osteoblasts, osteocytes, periodontal ligament cells, macrophages, monocytes, neutrophils, and adaptive immune cells, such as T helper 17 cells, causing increased osteoclast activity, decreased osteoblast activity, and enhanced periodontium inflammation by creating a pro-inflammatory milieu in a context- and cell type-dependent manner. We also discuss promising therapeutic strategies targeting inappropriate inflammasome activity in the treatment of alveolar bone loss. Novel strategies for inhibiting inflammasome signaling may facilitate the development of versatile drugs that carefully balance the beneficial contributions of inflammasomes to host defense.

Application of Natural Neutrophil Products for Stimulation of Monocyte-Derived Macrophages Obtained before and after Osteochondral or Bone Injury

We evaluated the use of some neutrophil products, namely; autologous rabbit antimicrobial neutrophil extract (rANE), heterologous porcine antimicrobial neutrophil extract (pANE), neutrophil degranulation products (DGP) and neutrophil microvesicles (MVs) for stimulation of monocyte-derived macrophages (MDMs) to improve healing. Two animal models were evaluated; the rabbit model for autologous osteochondral transplantation (OT) with application of rabbit ANE, DGP or MVs for MDMs stimulation, and the ovine model of the insertion of a Ti implant with the use of porcine ANE, and ovine DGP or MVs for MDMs stimulation. Macrophage activity was assessed on the basis of free radical generation and arginase activity. We estimated that DGP acted in a pro-inflammatory way both on rabbit and ovine MDMs. On the other hand, MVs acted as anti-inflammatory stimulator on MDMs in both experiments. The response to ANE depended on origin of extract (autologous or heterologous). Macrophages from rabbits before and after OT stimulated with autologous extract generated lower amount of NO and superoxide, especially after transplantation. In the ovine model of Ti implant insertion, heterologous ANE evoked increased macrophage pro-inflammatory activity. Our study revealed that these neutrophil products could regulate activity of macrophages, polarizing them into pro-or anti-inflammatory phenotypes that could enhance bone and osteochondral tissue healing.

Cobalt-chromium alloys fabricated with four different techniques: Ion release, toxicity of released elements and surface roughness

OBJECTIVE

To investigate the metal ion release, surface roughness and cytoxicity for Co-Cr alloys produced by different manufacturing techniques before and after heat treatment. In addition, to evaluate if the combination of materials affects the ion release.

METHODS

Five Co-Cr alloys were included, based on four manufacturing techniques. Commercially pure titanium, CpTi grade 4 and a titanium alloy were included for comparison. The ion release tests involved both Inductive Coupled Plasma Optical Emission Spectrometry and Inductive Coupled Plasma Mass Spectrometry analyses. The surface analysis was conducted with optical interferometry. Cells were indirectly exposed to the materials and cell viability was evaluated with the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) method.

RESULTS

All alloys showed a decrease of the total ion release when CpTi grade 4 was present. The total ion release decreased over time for all specimens and the highest ion release was observed from the cast and milled Co-Cr alloy in acidic conditions. The cast and laser-melted Co-Cr alloy and the titanium alloy became rougher after heat treatment. All materials were within the limits of cell viability according to standards.

SIGNIFICANCE

The ion release from Co-Cr alloys is influenced by the combination of materials, pH and time. Surface roughness is influenced by heat treatment. Furthermore, both ion release and surface roughness are influenced by the manufacturing technique and the alloy type. The clinical implication needs to be further investigated.

Effect of cobalt ions on the interaction between macrophages and titanium

Inflammation and bone reduction around dental implants are described as peri‐implantitis and can be caused by an inflammatory response against bacterial products and toxins. Titanium (Ti) forms aggregates with serum proteins, which activate and cause release of the cytokine interleukin (IL‐1β) from human macrophages. It was hypothesized that cobalt (Co) ions can interact in the formation of pro‐inflammatory aggregates, formed by titanium. To test this hypothesis, we differentiated THP‐1 cells into macrophages and exposed them to Ti ions alone or in combination with Co ions to investigate if IL‐1β release and cytotoxicity were affected. We also investigated aggregate formation, cell uptake and human biopsies with inductively coupled plasma atomic emission spectroscopy and electron microscopy. Co at a concentration of 100 µM neutralized the IL‐1β release from human macrophages and affected the aggregate formation. The aggregates formed by Ti could be detected in the cytosol of macrophages. In the presence of Co, the Ti‐induced aggregates were located in the cytosol of the cultured macrophages, but outside the lysosomal structures. It is concluded that Co can neutralize the Ti‐induced activation and release of active IL‐1β from human macrophages in vitro. Also, serum proteins are needed for the formation of metal‐protein aggregates in cell medium. Furthermore, the structures of the aggregates as well as the localisation after cellular uptake differ if Co is present in a Ti solution. Phagocytized aggregates with a similar appearance seen in vitro with Ti present, were also visible in a sample from human peri‐implant tissue. © 2018 The Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2518–2530, 2018.

Novel ultrafine-grained β-type Ti-28Nb-2Zr-8Sn alloy for biomedical applications

Titanium alloys are widely accepted as orthopedic or dental implant materials in the medical field. It is important to evaluate the biocompatibility of an implant material prior to use. A new β-type ultrafine-grained Ti-28Nb-2Zr-8Sn (TNZS) alloy with low Young's modulus of 31.6 GPa was fabricated. This study aims to evaluate the biocompatibility of TNZS alloy. In this study, we examined the microstructure, chemical composition and surface wettability of the TNZS alloy. The mouse embryonic osteoblast MC3T3-E1 cells and human umbilical vein endothelial cells (HUVECs) were cultured to study the cytocompatibility of TNZS alloy. Also, we evaluated the proinflammatory response of TNZS alloy in vitro and in vivo. The results show that the TNZS did not cause cytotoxicity, genotoxicity to MC3T3-E1 cells and HUVECs. Whereas, the TNZS alloy could significantly promote the cell proliferation, cell spreading and cell adhesion of MC3T3-E1 cells and HUVECs, as well as facilitate the osteogenic differentiation of MC3T3-E1 cells. Moreover, the TNZS alloy did not induce any remarkable proinflammatory response in vitro and in vivo. Thus, the novel TNZS alloy with an elasticity closer to that of human bone is biologically safe and could be a potential candidate for biomedical implant application. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1628-1639, 2019.