Neurotoxicity of Titanium Dioxide Nanoparticles: A Comprehensive Review

The systemic and local interactions related to titanium implant corrosion and hypersensitivity reactions: a narrative review of the literature

Both commercially pure titanium and titanium alloys are established biomaterials for implantation in bone and are widely used today in dentistry. Titanium particulates have been shown in some patient clusters to induce cellular immune mediators responsible for type I and IV hypersensitivity reactions, causing amplified corrosion, osteolysis, and increased odds of implant failure. Systemically, titanium particles were found to affect varying organ tissues and cause potentially harmful effects. In vivo and vitro studies have shown that titanium dental implant corrosion can be induced by factors relating to bio-tribocorrosion. In this literature review, the consequences of titanium implant corrosion and particulate dissemination are discussed and later juxtaposed against a promising novel implant material, zirconia. Zirconia offers characteristics similar to titanium along with additional advantages such as being non-corrosive and having a lower propensity for inducing immune responses. From the mounting evidence discussed in this article, metal allergy testing would be advantageous for choosing an appropriate implant material to minimize potential adverse effects on cellular functions of local and diffuse tissues. Objective: This literature review aims to elucidate and describe mechanisms in which titanium implants may become corroded and induce cellular aberrations both locally and systemically in vivo. Implications of this study provide supportive evidence regarding the selection of appropriate biomaterials for implant patients susceptible to mounting a hypersensitivity reaction to titanium.

The implications of the EU ban on titanium dioxide: A comprehensive review of safety concerns and alternatives

Titanium dioxide, a naturally occurring compound, has been extensively utilized across various industries such as food, pharmaceuticals, and cosmetics. In the food sector, it was commonly employed as a color and opacity enhancer under the designation E171. However, due to safety concerns, the EU has prohibited its use as a food additive, effective August 2022, following a six-month transition period. The decision was based on scientific research highlighting risks associated with inhaling titanium dioxide nanoparticles and its potential genotoxic effects. This review also summarizes the implications of this ban on the pharmaceutical industry, where titanium dioxide is utilized in drug manufacturing. While the safety of titanium dioxide in tablets remains inconclusive, the EU's regulatory action has prompted a closer examination of alternative options. While alternatives exist, they may not provide the same benefits as TiO2, particularly in pharmaceuticals. Further research is needed to determine the safety and effectiveness of TiO2 and its alternatives in these applications.

Metal implants in children

Background

Metal implants are increasingly used in children for trauma and deformity correction. This review outlines the current knowledge on the types of metals used and explores reasons for removal and the potential for long-term health issues of metal implants.

Methods

The literature pertaining to these aspects was studied and summarised in this review.

Results

Types of metals used have evolved as well as the development of children-specific implants. Improvements in deformity correction are measurable with likely improved outcomes and reduced health costs. Indications for metal implant removal following successful treatment remain ill-defined; however, the risks of removal are known with a minimum 6% complication rate. Health costs could be reduced by around 6% by judicious decisions to leave metal in place. Implant removal should only be encouraged in the presence of infection, mechanical failure or symptoms that are truly attributable to the implant. In the domain of spinal implants, there is evidence of significant metal ion release, most notably titanium which remains elevated to many times baseline levels beyond 2 years. The detection of titanium at low levels requires special techniques. The long-term health effects on patients and/or their offspring are not well defined, although well described in animal models.

Conclusion

The risks of metal removal are significant. Clinicians need to be aware of potential health risks in the use of metal implants and the potential for covert toxicity effects in children especially with their long life ahead. There is a need for greater awareness of metal alloy composition and implant design to minimise risks.

Level of evidence

Level V.

Effects of Titanium Dioxide Nanoparticles on Chick Embryo: Immunomodulatory, Hepatic and Biochemical Alterations

BACKGROUND

The utilization of titanium dioxide nanoparticles (TiO2 NPs) has significantly increased across various industries.

OBJECTIVES

This study rigorously explored the impact of TiO2 NPs exposure on chicken embryos, focusing particularly on alterations in the immune system, liver functionality and key biochemical markers.

METHODS

The study involved three groups of 30 eggs each, subjected to increasing doses of TiO2 NPs: Group C (control), Group T1 (150 µg/mL) and Group T2 (300 µg/mL). After 48 h of incubation, the eggs in Groups T1 and T2 each received an injection of 0.3 mL of the TiO2 NPs solution. In contrast, the eggs in the control group (Group C) were injected with 0.3 mL of saline solution. Histopathological changes were analysed using haematoxylin and eosin (H&E) staining, whereas amniotic fluid's biochemical properties were examined photometrically. The study also assessed the expression of immune genes (AvBD9, IL6 and IL8L2) through quantitative PCR. The evaluations included growth metrics, amniotic fluid biochemistry and histological analysis of the liver, caecal tonsil and bursa of Fabricius.

RESULTS

The results revealed subcutaneous haemorrhage, significant reductions in total body weight and marked changes in biochemical markers, including urea, creatinine, alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), in the amniotic fluid of the groups treated with TiO2 NPs, compared to the control. Histological examinations indicated noticeable alterations in the liver, caecal tonsil and bursa of Fabricius following TiO2 NP exposure. These alterations were characterized by disruptions in cellular structures and variations in lymphocyte counts. Furthermore, a notable decrease in the expression of immunity genes, namely, AvBD9, IL8L2 and IL6, was observed in the TiO2 NP-treated groups compared to the control.

CONCLUSION

The findings underscore the need for risk assessments of TiO2 NPs exposure due to its impact on development and immunity. Future research should explore its impact on neurodevelopment and degeneration.

Effect of lycopene on TiO2 nanoforms induced oxidative stress and neuroinflammation in SH-SY5Y cells: an in vitro study

Due to its antioxidant action, the carotenoid lycopene has been demonstrated to have a protective effect in several disease models; however, its effect on the nanoform of titanium oxide (nano-TiO2)-induced neurotoxicity has not yet been determined. The purpose of this study was to evaluate how lycopene affects neuronal damage brought on by nano-TiO2 and the mechanisms involved. SH-SY5Y cells were treated with different concentrations of nano-TiO2 for 48 hours, the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test was used after that to evaluate cell viability. IC50 of nano-TiO2 was determined and the results revealed that IC50 is equal 40 µM/mL, lycopene (10 µM) was applied to SH-SY5Y human neuroblastoma cells an hour before exposure to 40 µM nano-TiO2. Reactive oxygen species, lipid peroxidation, nitric oxide, glutathione, superoxide dismutase, and catalase, tumor necrosis factor-alpha, interleukin 1 beta, nuclear factor kappa B, and apoptotic markers (Bcl2, Bax, and caspase-3), were measured to determine the anti-oxidant effect of lycopene. In SH-SY5Y neuroblastoma cells, pretreatment with 10 µM lycopene significantly reduced the toxicity brought on by exposure to nano-TiO2, according to MTT assay findings and lactate dehydrogenase (LDH) cytotoxicity assessment. In cells exposed to nano-TiO2, lycopene pretreatment significantly boosted the activity of antioxidative enzymes and reduced oxidative stress. Furthermore, when SH-SY5Y cells were subjected to nano-TiO2, lycopene pretreatment stopped neuroinflammation and apoptosis. The findings of this study suggest that lycopene may be an effective neuroprotective against oxidative stress and neuroinflammation and may be used to stop neuronal death or injury in a variety of neurological illnesses.

Exposure to Titanium Dioxide Nanoparticles Leads to Specific Disorders of Spermatid Elongation via Multiple Metabolic Pathways in Drosophila Testes

Titanium dioxide nanoparticles (TiO2 NPs) have been extensively utilized in various applications. However, the regulatory mechanism behind the reproductive toxicity induced by TiO2 NP exposure remains largely elusive. In this study, we employed a Drosophila model to assess potential testicular injuries during spermatogenesis and conducted bulk RNA-Seq analysis to elucidate the underlying mechanisms. Our results reveal that while prolonged exposure to lower concentrations of TiO2 NPs (0.45 mg/mL) for 30 days did not manifest reproductive toxicity, exposure at concentrations of 0.9 and 1.8 mg/mL significantly impaired spermatid elongation in Drosophila testes. Notably, bulk RNA-seq analysis revealed that TiO2 NP exposure affected multiple metabolic pathways including carbohydrate metabolism and cytochrome P450. Importantly, the intervention of glutathione (GSH) significantly protected against reproductive toxicity induced by TiO2 NP exposure, as it restored the number of Orb-positive spermatid clusters in Drosophila testes. Our study provides novel insights into the specific detrimental effects of TiO2 NP exposure on spermatid elongation through multiple metabolic alterations in Drosophila testes and highlights the protective role of GSH in countering this toxicity.

Aggravated visual toxicity in zebrafish larvae upon co-exposure to titanium dioxide nanoparticles and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate

The bioavailability and toxicity of organic pollutants in aquatic organisms can be largely affected by the co-existed nanoparticles. However, the impacts of such combined exposure on the visual system remain largely unknown. Here, we systematically investigated the visual toxicity in zebrafish larvae after single or joint exposure to titanium dioxide nanoparticles (n-TiO2) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) at environmentally relevant levels. Molecular dynamics simulations revealed the enhanced transmembrane capability of the complex than the individual, which accounted for the increased bioavailability of both TBPH and n-TiO2 when combined exposure to zebrafish. Transcriptome analysis showed that co-exposure to n-TiO2 and TBPH interfered with molecular pathways related to eye lens structure and sensory perception of zebrafish. Particularly, n-TiO2 or TBPH significantly suppressed the expression of βB1-crystallin and rhodopsin in zebrafish retina and lens, which was further enhanced after co-exposure. Moreover, we detected disorganized retinal histology, stunted lens development and significant visual behavioral changes of zebrafish under co-exposure condition. The overall results suggest that combined exposure to water borne n-TiO2 and TBPH increased their bioavailability, resulted in severer damage to optic nerve development and ultimately abnormal visual behavior patterns, highlighting the higher potential health risks of co-exposure to aquatic vertebrates.

Use of Biomaterials in 3D Printing as a Solution to Microbial Infections in Arthroplasty and Osseous Reconstruction

The incidence of microbial infections in orthopedic prosthetic surgeries is a perennial problem that increases morbidity and mortality, representing one of the major complications of such medical interventions. The emergence of novel technologies, especially 3D printing, represents a promising avenue of development for reducing the risk of such eventualities. There are already a host of biomaterials, suitable for 3D printing, that are being tested for antimicrobial properties when they are coated with bioactive compounds, such as antibiotics, or combined with hydrogels with antimicrobial and antioxidant properties, such as chitosan and metal nanoparticles, among others. The materials discussed in the context of this paper comprise beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), hydroxyapatite, lithium disilicate glass, polyetheretherketone (PEEK), poly(propylene fumarate) (PPF), poly(trimethylene carbonate) (PTMC), and zirconia. While the recent research results are promising, further development is required to address the increasing antibiotic resistance exhibited by several common pathogens, the potential for fungal infections, and the potential toxicity of some metal nanoparticles. Other solutions, like the incorporation of phytochemicals, should also be explored. Incorporating artificial intelligence (AI) in the development of certain orthopedic implants and the potential use of AI against bacterial infections might represent viable solutions to these problems. Finally, there are some legal considerations associated with the use of biomaterials and the widespread use of 3D printing, which must be taken into account.