Are clinical findings of systemic titanium dispersion following implantation explained by available in vitro evidence? An evidence-based analysis

In vivo assessment of TiO2 based wear nanoparticles in periprosthetic tissues

A multimodal approach combining inductively coupled plasma mass spectrometry (ICP-MS), single-particle ICP-MS (spICP-MS), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) and Raman spectroscopy enabled a deeper insight into the balance between total titanium (Ti), the soluble titanium fraction and titanium dioxide based particle fraction levels in periprosthetic tissues collected from patients undergoing revision surgery. Hydrofluoric acid usage in the sample digestion allowed for complete digestion of TiO2 particles, thus enabling accurate estimation of total Ti levels. The TiO2 fraction represents 38-94% of the titanium load in the six samples where particles were detected, and the fraction is present mainly in samples from patients with aseptically loosened total hip arthroplasty. Further attention was given to this fraction determining the elemental composition, particle count, particle size and modification of TiO2. The spICP-MS analysis confirmed the presence of the TiO2-derived (nano)particles (NPs) with a 39- to 187-nm median size and particle count up to 2.3 × 1011 particles per gram of tissue. On top of that, the SEM-EDS confirmed the presence of the TiO2 nanoparticles with 230-nm median size and an anatase crystal phase was determined by Raman spectroscopy. This study presents a novel multimodal approach for TiO2 particle determination and characterization in tissue samples and is the first in vivo study of this character.

Antibiofilm peptides enhance the corrosion resistance of titanium in the presence of Streptococcus mutans

Titanium alloys have gained popularity in implant dentistry for the restoration of missing teeth and related hard tissues because of their biocompatibility and enhanced strength. However, titanium corrosion and infection caused by microbial biofilms remains a significant clinical challenge leading to implant failure. This study aimed to evaluate the effectiveness of antibiofilm peptides 1018 and DJK-5 on the corrosion resistance of titanium in the presence of Streptococcus mutans. Commercially pure titanium disks were prepared and used to form biofilms. The disks were randomly assigned to different treatment groups (exposed to S. mutans supplied with sucrose) including a positive control with untreated biofilms, peptides 1018 or DJK-5 at concentrations of 5 μg/mL or 10 μg/mL, and a negative control with no S. mutans. Dynamic biofilm growth and pH variation of all disks were measured after one or two treatment periods of 48 h. After incubation, the dead bacterial proportion, surface morphology, and electrochemical behaviors of the disks were determined. The results showed that peptides 1018 and DJK-5 exhibited significantly higher dead bacterial proportions than the positive control group in a concentration dependent manner (p < 0.01), as well as far less defects in microstructure. DJK-5 at 10 μg/mL killed 84.82% of biofilms and inhibited biofilm growth, preventing acidification due to S. mutans and maintaining a neutral pH. Potential polarization and electrochemical impedance spectroscopy data revealed that both peptides significantly reduced the corrosion and passive currents on titanium compared to titanium surfaces with untreated biofilms, and increased the resistance of the passive film (p < 0.05), with 10 μg/mL of DJK-5 achieving the greatest effect. These findings demonstrated that antibiofilm peptides are effective in promoting corrosion resistance of titanium against S. mutans, suggesting a promising strategy to enhance the stability of dental implants by endowing them with antibiofilm and anticorrosion properties.

CypD-mediated mitochondrial dysfunction contributes to titanium ion-induced MC3T3-E1 cell injury

Titanium (Ti) ion can stimulate osteoblast apoptosis and therefore have a high potential to play a negative role in the aseptic loosening of implants. Mitochondrial abnormalities are closely related to osteoblast dysfunction. However, the mitochondrial molecular mechanism of Ti ion induced osteoblastic cell apoptosis is still unclear. This study investigated in vitro mitochondrial oxidative stress (mtROS) mediated mitochondrial dysfunction involved in Ti ion-induced apoptosis of murine MC3T3-E1 osteoblastic cells. In addition to reducing mitochondrial membrane potential (MMP) and decreasing adenosine triglyceride production, exposure to Ti ions increased mitochondrial oxidative stress. Moreover, mitochondrial abnormalities significantly contributed to Ti ion induction of osteoblastic cellular apoptosis. A mitochondria-specific antioxidant, mitoquinone (MitoQ), alleviated Ti ion-induced mitochondrial dysfunction and apoptosis in osteoblastic cells, indicating that Ti ion mainly induces mitochondrial oxidative stress to produce a cytotoxic effect on osteoblasts. Here we show that the primary regulator of mitochondrial permeability transition pore (mPTP), cyclophilin D (CypD), is involved in mitochondrial dysfunction and osteoblast cell apoptosis induced by Ti ion. Overexpression of CypD exacerbates osteoblast apoptosis and impairs osteogenic function. Moreover, detrimental effects of CypD were rescued by cyclosporin A (CsA), an inhibitor of CypD, which shows its protective effect on mitochondrial and osteogenic osteoblast functions. Based on new insights into the mitochondrial mechanisms underlying Ti ion-induced apoptosis of osteoblastic cells, the findings of this study lay the foundation for the clinical use of CypD inhibitors to prevent or treat implant failure.

Electrical Potentiometry with Intraoral Applications

Dental implants currently in use are mainly made of titanium or titanium alloys. As these metallic elements are immersed in an electrolytic medium, galvanic currents are produced between them or with other metals present in the mouth. These bimetallic currents have three potentially harmful effects on the patient: micro-discharges, corrosion, and finally, the dispersion of metal ions or their oxides, all of which have been extensively demonstrated in vitro. In this original work, a system for measuring the potentials generated in vivo is developed. Specifically, it is an electrogalvanic measurements system coupled with a periodontal probe that allows measurement of the potentials in the peri-implant sulcus. This device was tested and verified in vitro to guarantee its applicability in vivo. As a conclusion, this system is able to detect galvanic currents in vitro and it can be considered capable of being employed in vivo, so to assess the effects they may cause on dental implants.

Effects of titanium dioxide microparticles and nanoparticles on cytoskeletal organization, cell adhesion, migration, and proliferation in human gingival fibroblasts in the presence of lipopolysaccharide

BACKGROUND AND OBJECTIVE

Titanium wear particles may participate in the etiology of peri-implantitis. However, the influence of titanium wear particles on biological behavior of human gingival fibroblasts (HGFs) in the presence of LPS is still not clear. The present study demonstrated the effects of titanium dioxide micro- and nanoparticles (TiO₂  MPs and NPs) on HGF cell viability, cytoskeletal organization, adhesion, migration, and proliferation in vitro, and LPS was used to mimic the in vivo condition.

METHODS

Primary HGFs were treated with TiO₂ MPs (primary particle size <5 μm, 0.1 mg/ml) and NPs (primary particle size <100 nm, 0.1 mg/ml) with or without 1 μg/ml LPS. The effects of TiO₂ MPs and NPs on HGFs cell viability was measured by CCK-8 assay. The proliferation of HGF was detected by Ki67 nuclear staining. The confocal laser scanning microscope (CLSM) was used to detect the internalization of TiO₂ MPs and NPs in HGFs as well as the arrangement of F-actin, vinculin, and vimentin organization. Wound healing assay and transwell assay were performed to measure the migration of HGFs induced by TiO₂ MPs and NPs. Cell adhesion was measured using fibronectin-coated plates. The relative mRNA and protein expression of adhesion relative protein such as focal adhesion kinase (FAK), fibronectin (FN), and type I collagen (COL1) were measured using quantitative RT-PCR and western blot analysis. One-way analysis of variance (ANOVA) and Student's t-test were used to analyze the statistical significance, and p < .05 was considered statistically significant.

RESULTS

TiO₂ NPs significantly inhibited HGF cell viability, proliferation, and migration compared with TiO₂ MPs group and control group. Compared with control group (2.64 ± 0.09), the mean absorbance of the cells in 1 mg/ml TiO₂ MPs group and 0.25 mg/ml TiO₂ NPs group were significantly decreased to 1.93 ± 0.33 (p < .05) and 2.22 ± 0.18 (p < .01), respectively. The cytoskeleton disruption was found in TiO₂ NPs group. The mRNA and protein expression were significantly downregulated by TiO₂ NPs. Furthermore, both TiO₂ NPs and MPs induced more adverse effects on HGFs in the presence of LPS.

CONCLUSION

Our results indicate that TiO₂ NPs but not TiO₂ MPs significantly disrupt the cytoskeletal organization and inhibited cell adhesion, migration, and proliferation of HGFs. However, in the presence of LPS, TiO₂ MPs, and TiO₂ NPs enhance these negative effects in HGFs. Titanium wear particles are probably involved in the initiation and progression of peri-implant diseases.

Titanium Nanoparticles Enhance Production and Suppress Stabilin-1-Mediated Clearance of GDF-15 in Human Primary Macrophages

Macrophages are key innate immune cells that mediate implant acceptance or rejection. Titanium implants degrade over time inside the body, which results in the release of implant wear-off particles. Titanium nanoparticles (TiNPs) favor pro-inflammatory macrophage polarization (M1) and lower tolerogenic activation (M2). GDF-15 regulates immune tolerance and fibrosis and is endocytosed by stabilin-1. How TiNPs affect the healing activities of macrophages and their release of circulating cytokines is an open question in regenerative medicine. In this study for the first time, we identified the transcriptional program induced and suppressed by TiNPs in human pro-inflammatory and healing macrophages. Microarray analysis revealed that TiNPs altered the expression of 5098 genes in M1 (IFN-γ-stimulated) and 4380 genes in M2 (IL-4–stimulated) macrophages. 1980 genes were differentially regulated in both M1 and M2. Affymetrix analysis, confirmed by RT-PCR, demonstrated that TiNPs upregulate expression of GDF-15 and suppress stabilin-1, scavenger receptor of GDF-15. TiNPs also significantly stimulated GDF-15 protein secretion in inflammatory and healing macrophages. Flow cytometry demonstrated, that scavenging activity of stabilin-1 was significantly suppressed by TiNPs. Confocal microscopy analysis showed that TiNPs impair internalization of stabilin-1 ligand acLDL and its transport to the endocytic pathway. Our data demonstrate that TiNPs have a dual effect on the GDF-15/stabilin-1 interaction in macrophage system, by increasing the production of GDF-15 and suppressing stabilin-1-mediated clearance function. In summary, this process can result in a significant increase of GDF-15 in the extracellular space and in circulation leading to unbalanced pro-fibrotic reactions and implant complications.

The unfavorable role of titanium particles released from dental implants

Titanium is considered to be a metal material with the best biological safety. Studies have proved that the titanium implanted in the bone continuously releases titanium particles (Ti particles), significantly increasing the total titanium content in human body. Generally, Ti particles are released slowly without causing a systemic immune response. However, the continuous increased local concentration may result in damage to the intraepithelial homeostasis, aggravation of inflammatory reaction in the surrounding tissues, bone resorption and implant detachment. They also migrate with blood flow and aggregate in the distal organ. The release of Ti particles is affected by the score of the implant surface structure, microenvironment wear and corrosion, medical operation wear, and so on, but the specific mechanism is not clear. Thus, it difficult to prevent the release completely. This paper reviews the causes of the Ti particles formation, the damage to the surrounding tissue, and its mechanism, in particular, methods for reducing the release and toxicity of the Ti particles.

Titanium Wear of Dental Implants from Placement, under Loading and Maintenance Protocols

The objective of this review was to analyze the process of wear of implants leading to the shedding of titanium particles into the peri-implant hard and soft tissues. Titanium is considered highly biocompatible with low corrosion and toxicity, but recent studies indicate that this understanding may be misleading as the properties of the material change drastically when titanium nanoparticles (NPs) are shed from implant surfaces. These NPs are immunogenic and are associated with a macrophage-mediated inflammatory response by the host. The literature discussed in this review indicates that titanium NPs may be shed from implant surfaces at the time of implant placement, under loading conditions, and during implant maintenance procedures. We also discuss the significance of the micro-gap at the implant-abutment interface and the effect of size of the titanium particles on their toxicology. These findings are significant as the titanium particles can have adverse effects on local soft and hard tissues surrounding implants, implant health and prognosis, and even the health of systemic tissues and organs.

Exploring titanium(IV) chemical proximity to iron(III) to elucidate a function for Ti(IV) in the human body

Despite its natural abundance and widespread use as food, paint additive, and in bone implants, no specific biological function of titanium is known in the human body. High concentrations of Ti(IV) could result in cellular toxicity, however, the absence of Ti toxicity in the blood of patients with titanium bone implants indicates the presence of one or more biological mechanisms to mitigate toxicity. Similar to Fe(III), Ti(IV) in blood binds to the iron transport protein serum transferrin (sTf), which gives credence to the possibility of its cellular uptake mechanism by transferrin-directed endocytosis. However, once inside the cell, how sTf bound Ti(IV) is released into the cytoplasm, utilized, or stored remain largely unknown. To explain the molecular mechanisms involved in Ti use in cells we have drawn parallels with those for Fe(III). Based on its chemical similarities with Fe(III), we compare the biological coordination chemistry of Fe(III) and Ti(IV) and hypothesize that Ti(IV) can bind to similar intracellular biomolecules. The comparable ligand affinity profiles suggest that at high Ti(IV) concentrations, Ti(IV) could compete with Fe(III) to bind to biomolecules and would inhibit Fe bioavailability. At the typical Ti concentrations in the body, Ti might exist as a labile pool of Ti(IV) in cells, similar to Fe. Ti could exhibit different types of properties that would determine its cellular functions. We predict some of these functions to mimic those of Fe in the cell and others to be specific to Ti. Bone and cellular speciation and localization studies hint toward various intracellular targets of Ti like phosphoproteins, DNA, ribonucleotide reductase, and ferritin. However, to decipher the exact mechanisms of how Ti might mediate these roles, development of innovative and more sensitive methods are required to track this difficult to trace metal in vivo.

The role of citrate, lactate and transferrin in determining titanium release from surgical devices into human serum

The presence of ionic titanium in the serum of patients with titanium implants is currently unexplained. This is presumed due to corrosion, and yet the serum titanium concentration measured in patients is far greater than that predicted by its solubility. The binding of titanium ion as Ti(IV) to human transferrin (hTF) in serum indicates that Ti(IV) ions interact with human physiology. This is an intriguing finding since there is currently no known role for titanium ions in human physiology. Thus, understanding the factors that determine in vivo titanium ion release is relevant to further understanding this metal's interactions with human biochemistry. The present study sought to determine the extent of titanium ion release of into human serum in vitro, and the role of citrate, lactate and hTF in this process. It was found that, when surgical devices of commercially pure titanium were placed into human serum, citrate and lactate concentrations were the prime determinants of titanium release. Crystallography revealed Ti(IV) bound to hTF in the presence of citrate alone, signalling that citrate can act as an independent ligand for Ti(IV) binding to hTF. Based on these findings, a two-stage process of titanium ion release into human serum that is dependent upon both citrate and hTF is proposed to explain the ongoing presence of titanium ion in human subjects with implanted titanium devices.