Effect of Titanium and Zirconium Oxide Microparticles on Pro-Inflammatory Response in Human Macrophages under Induced Sterile Inflammation: An In Vitro Study

3-methyl-1H-indol-1-yl dimethylcarbamodithioate attenuates periodontitis through targeting MAPK signaling pathway-regulated mitochondrial function

Periodontitis, the second most common oral disease, is primarily initiated by inflammatory responses and osteoclast differentiation, in which the MAPK signaling pathway and mitochondrial function play important roles. 3-methyl-1H-indol-1-yl dimethylcarbamodithioate (3o), a hybrid of indole and dithiocarbamate, was first synthesized by our group. It has shown anti-inflammatory activity against lipopolysaccharide-induced acute lung injury. However, it is not known if 3o can exert effects in periodontitis. In vitro study: LPS-induced macrophage inflammation initiation and a receptor activator of nuclear factor κB ligand-stimulated osteoclast differentiation model were established. Cell viability, inflammatory cytokines, osteoclast differentiation, the MAPK signaling pathway, and mitochondrial function before and after treatment with 3o were investigated. In vivo study: Alveolar bone resorption, inflammatory cytokine expression, osteoclast differentiation, and the underlying mechanisms were assessed in mice with periodontitis. Inflammatory cytokine expression and osteoclast differentiation appeared downregulated after 3o treatment. 3o inhibited the MAPK signaling pathway and restored mitochondrial function, including mitochondrial reactive oxygen species, mitochondrial membrane potential, and ATP production. Meanwhile, 3o reduced inflammation activation and bone resorption in mice with periodontitis, reflected by the decreased expression of inflammatory cytokines and osteoclasts, implying that 3o inhibited the MAPK signaling pathway and the mitochondrial oxidative DNA damage marker 8-OHdG. These results highlight the protective role of 3o in periodontitis in mice and reveal an important strategy for preventing periodontitis.

Titanium corrosion products from dental implants and their effect on cells and cytokine release: A review

INTRODUCTION

Titanium is considered to be an inert material owing to the ability of the material to form a passive titanium oxide layer. However, once the titanium oxide layer is lost, it can lead to exposure of the underlying titanium substructure and can undergo corrosion.

SUMMARY

The article explores the role of titanium ions and particles from dental implants on cells, cytokine release, and on the systemic redistribution of these particles as well as theories proposed to elucidate the effects of these particles on peri-implant inflammation based on evidence from in-vitro, human, and animal studies. Titanium particles and ions have a pro-inflammatory and cytotoxic effect on cells and promote the release of pro-inflammatory mediators like cytokines. Three theories to explain etiopathogenesis have been proposed, one based on microbial dysbiosis, the second based on titanium particles and ions and the third based on a synergistic effect between microbiome and titanium particles on the host.

CONCLUSION

There is clear evidence from in-vitro and limited human and animal studies that titanium particles released from dental implants have a detrimental effect on cells directly and through the release of pro-inflammatory cytokines. Future clinical and translational studies are required to clarify the role of titanium particles and ions in peri-implant inflammation and the etiopathogenesis of peri-implantitis.

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.

Immune dysregulation and macrophage polarization in peri-implantitis

The term "peri-implantitis" (peri-implantitis) refers to an inflammatory lesion of the mucosa surrounding an endosseous implant and a progressive loss of the peri-implant bone that supports the implant. Recently, it has been suggested that the increased sensitivity of implants to infection and the quick elimination of supporting tissue after infection may be caused by a dysregulated peri-implant mucosal immune response. Macrophages are polarized in response to environmental signals and play multiple roles in peri-implantitis. In peri-implantitis lesion samples, recent investigations have discovered a considerable increase in M1 type macrophages, with M1 type macrophages contributing to the pro-inflammatory response brought on by bacteria, whereas M2 type macrophages contribute to inflammation remission and tissue repair. In an effort to better understand the pathogenesis of peri-implantitis and suggest potential immunomodulatory treatments for peri-implantitis in the direction of macrophage polarization patterns, this review summarizes the research findings related to macrophage polarization in peri-implantitis and compares them with periodontitis.

Severely Damaged Freeze-Injured Skeletal Muscle Reveals Functional Impairment, Inadequate Repair, and Opportunity for Human Stem Cell Application

BACKGROUND

The regeneration of severe traumatic muscle injuries is an unsolved medical need that is relevant for civilian and military medicine. In this work, we produced a critically sized nonhealing muscle defect in a mouse model to investigate muscle degeneration/healing phases.

MATERIALS AND METHODS

We caused a freeze injury (FI) in the biceps femoris of C57BL/6N mice. From day 1 to day 25 post-injury, we conducted histological/morphometric examinations, an analysis of the expression of genes involved in inflammation/regeneration, and an in vivo functional evaluation.

RESULTS

We found that FI activates cytosolic DNA sensing and inflammatory responses. Persistent macrophage infiltration, the prolonged expression of eMHC, the presence of centrally nucleated myofibers, and the presence of PAX7+ satellite cells at late time points and with chronic physical impairment indicated inadequate repair. By looking at stem-cell-based therapeutic protocols of muscle repair, we investigated the crosstalk between M1-biased macrophages and human amniotic mesenchymal stem cells (hAMSCs) in vitro. We demonstrated their reciprocal paracrine effects where hAMSCs induced a shift of M1 macrophages into an anti-inflammatory phenotype, and M1 macrophages promoted an increase in the expression of hAMSC immunomodulatory factors.

CONCLUSIONS

Our findings support the rationale for the future use of our injury model to exploit the full potential of in vivo hAMSC transplantation following severe traumatic injuries.

Scanning Electron Microscopy and EDX Spectroscopy of Commercial Swabs Used for COVID-19 Lateral Flow Testing

The chemical composition of COVID test swabs has not been examined beyond the manufacturer's datasheets. The unprecedented demand for swabs to conduct rapid lateral flow tests and nucleic acid amplification tests led to mass production, including 3D printing platforms. Manufacturing impurities could be present in the swabs and, if so, could pose a risk to human health. We used scanning electron microscopy and energy dispersive X-ray (EDX) spectroscopy to examine the ultrastructure of seven assorted brands of COVID test swabs and to identify and quantify their chemical elements. We detected eight unexpected elements, including transition metals, such as titanium and zirconium, the metalloid silicon, as well as post-transition metals aluminium and gallium, and the non-metal elements sulphur and fluorine. Some of the elements were detected as trace amounts, but for others, the amount was close to reported toxicological thresholds for inhalation routes. Experimental studies have shown that the detrimental effects of unexpected chemical elements include moderate to severe inflammatory states in the exposed epithelium as well as proliferative changes. Given the massive testing still being used in the context of the COVID pandemic, we urge caution in continuing to recommend repeated and frequent testing, particularly of healthy, non-symptomatic, individuals.

In vitro evaluation of different protective techniques to reduce titanium particle contamination during implantoplasty

OBJECTIVES

Our aim is to study titanium remains in a bone model during standardized implantoplasty under different isolation and protective modalities.

MATERIAL AND METHODS

Forty implants were placed in artificial spongy bone blocks mimicking a horizontal bone loss and implant neck protrusion of 5 mm. Samples were randomly divided into four groups (n = 10), which were treated as follows: rubber dam (A), a dental adhesive paste (B), bone wax (C), and an unprotected positive control (D). Implantoplasty was performed using carbide and diamond burs under strict water cooling and standardized suction. After removal of the respective isolation materials, the bone blocks were thoroughly rinsed with tap water for 3 min and titanium chips were collected using a filter integrated in the model. The filter paper was removed and dissolved in 37% hydrochloric acid for 2 h at 120 °C and the titanium remnants were quantified using atomic absorption spectrometry.

RESULTS

None of the test groups were able to completely prevent titanium particle contamination. Rubber dam (691 ± 249 µg) and bone wax (516 ± 157 µg) were found to be significantly more protective than the positive control (2313 ± 747 µg) (p < 0.001) with respect to the amount of titanium particles that remained in the bone model after implantoplasty. The adhesive paste group (1863.5 ± 538 µg) was not significantly different from the positive control (p = 0.19).

CONCLUSIONS

Despite some limitations of the present study, titanium particles resulting from a standardized implantoplasty can be assumed to be significantly reduced when the tissues/bone were protected with rubber dam and bone wax, or a combination, depending on individual accessibility.

CLINICAL RELEVANCE

Tissue protective measures to reduce or avoid particle contamination during implantoplasty is possible and should be considered and further clinically assessed to avoid iatrogenic inflammatory reactions.

Do Titanium Dioxide Particles Stimulate Macrophages to Release Proinflammatory Cytokines and Increase the Risk for Peri-implantitis?

PURPOSE

Titanium dioxide (TiO₂) particles detached from titanium dental implants by tribocorrosion can be phagocytosed by macrophages, releasing various proinflammatory cytokines at the implant sites that may trigger peri-implantitis. The study objective was to measure the association between peri-implantitis and the presence of non-allergy-related proinflammatory cytokines associated with TiO₂ particles.

METHODS

The investigators implemented a retrospective cross-sectional study and enrolled a sample of 60 subjects from a dental practice. Subjects were excluded if the plaque index was grade 3 (Silness and Löe). The predictor variable was a positive or negative TiO₂ stimulation test, an in vitro macrophage proinflammatory response test. The outcome variable was peri-implantitis status defined as present or absent. Three groups were considered: control group with 20 patients without dental implants (group 1), 2 groups of patients with titanium dental implants, one without peri-implantitis (group 2), and the other with peri-implantitis (group 3) (n = 20 each). For patients with implants, depth of the gingival pockets of the implants were measured, and existing bleeding and suppuration were determined to assess peri-implantitis. Radiographs were taken if one or more factors applied to confirm the diagnosis of peri-implantitis. Further covariates were age, sex, duration of implant wear, and number of implants which were analyzed descriptively. Inferential analyses were undertaken using χ² test, Kruskal-Wallis-, Wilcoxon-two-sample tests, and logistic regressions.

RESULTS

The sample was composed of 35 female and 25 male patients with a mean age of 54.2 years (standard deviation = 14.76). The overall TiO₂ stimulation test positivity frequency was 28.3% and were 30.0%, 5.0%, and 50.0% in the control, implants without peri-implantitis, and implants with peri-implantitis groups. No statistically significant differences could be seen in the frequencies of the TiO₂ stimulation test results between control group and combined groups 2 and 3 (P-value = .84). The risk for positive TiO₂ patients with a titanium implant of developing peri-implantitis was statistically significant and higher compared to negative TiO₂ patients (odds ratio, 19.0 with 95% confidence interval [2.12,170.38]; P-value< .01).

CONCLUSIONS

The data in this study showed a statistically significant relationship between a positive TiO₂ stimulation test and peri-implantitis. Further studies with larger numbers of subjects are recommended to confirm this result.

NLRP3 inflammasome activation in response to metals

Implant surgery is followed by a series of inflammatory reactions that directly affect its postoperative results. The inflammasome plays a vital role in the inflammatory response by inducing pyroptosis and producing interleukin-1β, which plays a critical role in inflammation and tissue damage. Therefore, it is essential to study the activation of the inflammasome in the bone healing process after implant surgery. As metals are the primary implant materials, metal-induced local inflammatory reactions have received significant attention, and there has been more and more research on the activation of the NLRP3 (NOD-like receptor protein-3) inflammasome caused by these metals. In this review, we consolidate the basic knowledge on the NLRP3 inflammasome structures, the present knowledge on the mechanisms of NLRP3 inflammasome activation, and the studies of metal-induced NLRP3 inflammasome activation.

Bioactive Surface of Zirconia Implant Prepared by Nano-Hydroxyapatite and Type I Collagen

Zirconia, with its excellent mechanical strength and esthetics, has a growing potential for applications in dentistry and orthopedics. However, in order for zirconia to have a high affinity with bone tissue, the bioactivity of the surface must be further increased. In order to increase the bioactivity of zirconia, research was conducted to make a porous support or to fill the porous structure with nano-hydroxyapatite (nHA). In this case, there is a risk that physically filled nHA could be released depending on the living environment. In this study, nHA and type I collagen were introduced to the zirconia surface by chemical covalent bonding to increase bioactivity and ensure safety in the body. The chemical reaction of the surface was confirmed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. In addition, the biological activity was evaluated by examining the cytotoxicity and bone formation ability of the modified zirconia using osteoblasts. As a result, it was found that the bioactivity of the zirconia surface was greatly improved by immobilizing nHA and type I collagen.

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 Characterization of Titanium Particles Released from Bone-Level Titanium Dental Implants: Effect of the Size of Particles on the Ion Release and Cytotoxicity Behaviour

Many studies are being carried out on the particles released during the implantoplasty process in the machining of dental implants to remove bacterial biofilms. However, there are no studies on the release of particles produced by the insertion of bone-level dental implants due to the high compressive frictional loads between the rough titanium implant and the bone tissue. This paper aims to characterize the released particles and determine the release of titanium ions into the physiological environment and their cytocompatibility. For this purpose, 90 dental implants with a neck diameter of 4 mm and a torque of 22 Ncm were placed in 7 fresh cow ribs. The placement was carried out according to the established protocols. The implants had a roughness Ra of 1.92 μm. The arrangement of the particles in the bone tissue was studied by micro-CT, and no particle clusters were observed. The different granulometries of 5, 15, and 30 μm were obtained; the specific surface area was determined by laser diffraction; the topography was determined by scanning electron microcopy; and the particles were chemically analysed by X-ray energy microanalysis. The residual stresses of the particles were obtained by X-ray diffraction using the Bragg-Bentano configuration. The release of titanium ions to the physiological medium was performed using ICP-MS at 1, 3, 7, 14, and 21 days. The cytocompatibility of the particles with HFF-1 fibroblast and SAOS-2 osteoblast cultures was characterized. The results showed that the lowest specific surface area (0.2109 m²/g) corresponds to the particles larger than 30 μm being higher than 0.4969 and 0.4802 m²/g of those that are 5 and 15 μm, respectively, observing in all cases that the particles have irregular morphologies without contamination of the drills used in the surgery. The highest residual stresses were found for the small particles, -395 MPa for the 5 μm particles, and -369 for the 15 μm particles, and the lowest residual stresses were found for the 30 μm particles with values of -267 MPa. In all cases, the residual stresses were compressive. The lowest ion release was for the 30 μm samples, as they have the lowest specific surface area. Cytocompatibility studies showed that the particles are cytocompatible, but it is the smallest ones that are lower and very close to the 70% survival limit in both fibroblasts and osteoblasts.