A weight of evidence review of the genotoxicity of titanium dioxide (TiO2)

Genotoxicity assessment of food-grade titanium dioxide

Food-grade titanium dioxide (E171 in Europe), which contains nanoscale particles (NPs), has been approved and used as a white pigment in various common foods. Concerns are growing over the use of E171 as a safe food additive. The purpose of the present research is to evaluate the genotoxicity of E171 using in vivo and in vitro testing systems. In vitro studies, Chinese hamster lung (V79) fibroblast cells were exposed to E171 at doses of 25, 50, 100, and 200 μg/mL. No gene mutations were observed after 24 h of treatment at any concentration using the hypoxanthine guanine phosphoribosyltransferase (Hprt) gene mutation assay. In vivo study, the healthy Kunming mice and SD rats were exposed to E171 through intragastric administration at doses of 250, 500 and 1000 mg/kg body weight every day for 15 days. Genotoxic potential of E171 was evaluated by micronucleus (MN) and comet assays in accordance with the OECD guideline. However, the results showed that E171 did not increase the frequency of bone marrow micronuclei or induce DNA strand breaks in rat liver cells at the doses used in this experiments. Under the conditions described in this report, E171 was concluded to be negative in these in vivo and in vitro genotoxicity tests. These findings suggest that E171 is not genotoxic, offering valuable data for risk assessment.

Investigating the impact of the dispersion protocol on the physico-chemical identity and toxicity of nanomaterials: a review of the literature with focus on TiO2 particles

Particles often require dispersion in aqueous media to allow assessment of their hazard profile. The approach used to disperse particles is not consistent in the published literature, with approaches including stirring, vortexing, shaking or sonication, and the use of biological or chemical stabilisers. Such variations in the dispersion protocol can influence the physico-chemical (PC) identity and toxicity of particles. To better understand the protocol variations and their impacts on human health, this work identified and critically reviewed publications with a specific focus on titanium dioxide (TiO2), which was dominated by nanomaterials (NMs). This review included consideration of both in vitro and in vivo studies, as well as other NMs to help address knowledge gaps and identify any lessons that can be learnt and applied to TiO2. Overall, the evidence gathered showed that variations in the dispersion protocol, specifically the method and parameters of sonication (e.g. power and duration), as well as the dispersion medium choice (and inclusion of biological and chemical stabilisers), were impactful on NM agglomerate size. There is no consensus as to whether a reduction or increase in NM agglomeration enhances or reduces NM toxicity with the outcome of the study dependent on the experimental design (e.g. PC properties of the NM being tested, test model used, time point, and concentrations/doses assessed). Whilst standard protocols for NM dispersion have been generated, they have not been widely adopted and there is unlikely to be one protocol that can be applied to all NMs and test models. Instead, more guidance is needed to inform the considerations that should guide preparation of NM suspensions for hazard testing. These include a recommendation that pilot studies are performed to identify the most suitable dispersion protocol before embarking on a toxicology study. Improved knowledge of the impact of dispersion protocols on PC identity and toxicity of TiO2 will assist in the interpretation of existing toxicology data and feed into the design of future studies which assess TiO2 toxicity.

EFSA prohibits titanium dioxide in food- should pharmaceuticals be next?

Titanium dioxide (TiO2) is a natural, inorganic compound widely used across various industries due to its multiple properties. Recently, the European Food Safety Authority (EFSA) raised safety concerns regarding the use of TiO2 in foods, specifically its potential for genotoxicity, accumulation in the body, and associated health risks when used as a food additive. As a result, its use in food has been banned in the food industry in the European Union (EU) since 2022. Furthermore, the safety of TiO2 is currently being evaluated as a pharmaceutical excipient, and its use is likely to be banned in EU by 2025. The food industry is significantly impacted by the ban, and a subsequent pharmaceutical ban can lead to issues such as the lack of a single replacement for its multiple applications, product redevelopment/revalidation and regulatory submissions. Other regulatory authorities from other countries conducted independent reviews and concluded that there is insufficient evidence to justify a ban on TiO2 in foods, thereby allowing its continued use. Various substitutes, both natural and synthetic, are being explored, however none can fully replicate all the properties provided by TiO2 alone. In this review, we discuss the safety concerns associated with TiO2, which have led to its ban on food products, as well as the challenges that may arise if a similar ban is imposed on its use in pharmaceuticals.

From literature to predictive modeling: Insights and machine learning applications from in vitro comet assays related to the genotoxicity of titanium dioxide nanomaterials

The genotoxicity of titanium dioxide nanomaterials (TiO2 NMs) remains a debated topic in the scientific community. In this study, we applied the read-across concept based on machine learning (ML) algorithms to predict the genotoxic potential of TiO₂ NMs. Key objectives included: (i) compiling a systematic dataset capturing DNA damage percentage from in vitro comet assays, (ii) creating a homogenized dataset integrating physicochemical properties, exposure conditions, and experimental details, (iii) training ML models for prediction, (iv) evaluating model performance, and (v) identifying the features that contribute the most to predictive accuracy. The dataset was divided into three parts: the Entire dataset (all features), the Physicochemical dataset, and the Experimental design dataset. Extra Trees Regressor and XGB Regressor demonstrated high predictive accuracy, achieving R2 values of 0.906 and 0.788 for the P-chem and Experimental dataset, respectively. Exposure concentration, cold lysis conditions, and electrophoresis parameters emerged as key predictors of DNA damage, alongside contributions from NM properties. These findings highlight the intricate interplay between NM properties and experimental conditions in genotoxicity assessments. By providing a FAIR dataset, this study facilitates future research, allowing for the integration of additional variables and quality criteria to enhance the modeling approach. This work reinforces the value of nano-informatics in nanosafety and serves as a footing for advancing data-driven hazard assessment methodologies, positioning ML-enabled read-across strategies as a valuable tool for regulatory nanosafety framework.

Evaluating the color stability of titanium dioxide-free film coats under environmental and light stress

Titanium dioxide (TiO2) is an opacifier/colorant in tablet film coatings and capsule shells. Recently, questions about its safety have raised concerns that it may be banned from medicinal products in the European Union (EU); however, little information exists on alternatives to enable the pharmaceutical industry to pivot. This study evaluated the color stability of film coats containing alternate opacifiers, calcium carbonate (CaCO3), and rice starch. Placebo tablets were coated with film coating systems containing different polymers (hydroxypropyl methylcellulose (HPMC) or polyvinyl alcohol (PVA)), opacifiers (CaCO3, rice starch, or TiO2) and pigments (FD&C Blue No. 2, iron oxides, or non-pigmented); the coated tablets were exposed to environmental stress (temperature/humidity) and light stress and color changes were quantified spectrophotometrically. The HPMC-formulated coats containing CaCO3 or rice starch showed comparable stability to TiO2. The PVA-based coats containing FD&C Blue No. 2 or iron oxide colorants exhibited color changes when exposed to elevated temperature/humidity, which was more pronounced with CaCO3 than with TiO2. No meaningful color changes were observed under white or UV light stress for any coat. This study demonstrated PVA coating systems pose a stability risk, whereas these alternate opacifiers presented an overall low color stability risk, offering potential TiO2 alternatives.

Do We Need Titanium Dioxide (TiO2) Nanoparticles in Face Masks?

The use of face masks has proven to be an effective preventive measure during the COVID-19 pandemic. However, concerns have emerged regarding the safety of metal (nano)particles incorporated into face masks for antimicrobial purposes. Specifically, this review examines the risks associated with TiO2 nanoparticles (NPs), which are classified as a possible human carcinogen. The inhalation of TiO2 NPs can cause multiple adverse effects, including oxidative stress, pulmonary inflammation, histopathological changes, and (secondary) genotoxicity. Different aspects are discussed, such as the composition and filtration efficiency of face masks, the antimicrobial mode of action and effectiveness of various metals, and the hazards of TiO2 NPs to human health, including exposure limits. A conservative risk assessment was conducted using different worst-case scenarios of potential (sub)chronic TiO2 exposure, derived from published leaching experiments. Most face masks are considered safe, especially for occasional or single use. However, the nanosafety of a minority of face masks on the European market may be inadequate for prolonged and intensive use. Important uncertainties remain, including the risks of combined exposure to TiO2 NPs and silver biocides, and the lack of direct exposure measurements. Considering the potential safety issues and the limited added protective value of TiO2 NPs, it is recommended to ban all applications of TiO2 in face masks based on the precautionary principle.

Comparative analysis of the protective effects of fluoride compounds on dental erosion in mouse model

BACKGROUND

Dental erosion development is affected by various factors such as types and amounts of acids, drinking habits and lifestyle choices. To prevent the onset and progression, identification of early erosive lesions as well as increased knowledge of the preventive treatment possibilities is of the importance. The aim of this study is to compare the protective effects of various fluoride compounds against dental erosion utilizing an established mouse model.

METHODS

Three groups of ten young CD-1 mice were provided cola drink ad libitum during six weeks. Fluoride solutions containing metal components, TiF₄ (0.5 mol/l, pH 1.2, 9500 ppm F) and SnF₂ (0.5 mol/l, pH 2.6, 9500 ppm F), and a non-metal fluoride, NaF (0.5 mol/l, pH 8, 9500 ppm F) were applied to the molars under sedation twice a week. Additionally, one positive (acidic drink) and one negative (distilled water) control group were included. Mandibular molars were thereafter dissected and analyzed using scanning electron microscopy (SEM). The first molars were transversely ground, observed by SEM, and tooth height and dental hard tissue loss were measured. Further, pulp structure was described.

RESULTS

The application of metal fluorides, TiF₄ and SnF₂, resulted in the formation of a protective coating layer on the molars. The overall protective effects of fluoride compounds on the development of dental erosion were evident in increasing succession from NaF, TiF₄ to SnF₂. Molars applied NaF showed a 6% reduction in tooth tissue loss compared to the untreated positive control molars. TiF₄ and SnF₂ treated molars continued to display decreased tooth tissue loss by 37% and 67%, respectively.

CONCLUSIONS

The metal fluorides offer superior protection against dental erosion compared to the traditional fluoride compound. The results particularly emphasize the protective effect of SnF₂, which was most effective in preserving enamel structure and minimizing dentin exposure. This suggests that SnF₂ could be an effective option for preventing dental erosions.

The role of resveratrol in delivering antioxidant, anti-inflammatory, and anti-apoptotic defense against nephrotoxicity generated by titanium dioxide

Titanium dioxide is a prevalent food ingredient for human ingestion. We investigated the nephrotoxic effects of titanium dioxide in Wistar albino rats subjected to oral exposure for 14 days. The rats were categorized into four groups (n = 8): (1) control (saline solution), (2) exposure to titanium dioxide (30 mg/kg), (3) exposure to resveratrol (100 mg/kg), and (4) exposure to both titanium dioxide and resveratrol. The investigations revealed that the administration of titanium dioxide resulted in considerable histological abnormalities and a significant prevalence of apoptotic cells marked by caspase-3 in the titanium dioxide group, with a markedly elevated quantity and strong staining of cells reacting with 4-HN across the tissue in the kidney. Blood serum assessments revealed that BUN and creatinine levels were elevated in the titanium group relative to the other three groups, with a reduction in these levels observed in the group receiving both titanium and resveratrol (P < 0.05). The assessment of oxidative stress markers in kidney tissue revealed that GSH-Px and SOD activity considerably decreased in the titanium dioxide group relative to the other experimental groups. In contrast, MDA levels increased markedly (P < 0.05). The activities of GSH-Px and SOD were significantly elevated in the group receiving both titanium dioxide and resveratrol compared to the titanium dioxide-only group (P < 0.05). The analysis of inflammation markers TNF-α and IL-6 revealed a substantial rise in their levels in the titanium dioxide group compared to the other groups (P < 0.05).

Bioactivity Assessment of Functionalized TiO2 Powder with Dihydroquercetin

Biological activities, including cell viability, oxidative stress, genotoxicity/antigenotoxicity, and antimicrobial activity, were evaluated for a visible-light-responsive TiO2-based ICT complex with dihydroquercetin (DHQ) and compared with pristine TiO2, its inorganic component. Pristine TiO2 did not induce cytotoxicity in MRC-5 or HeLa cells within the tested concentration range (1-20 mg/mL), while TiO2/DHQ displayed a significant reduction in cell viability in both cell lines at higher concentrations (≥10 mg/mL). The analysis of reactive oxygen species (ROS) production revealed that TiO2/DHQ significantly reduced ROS levels in both cell types (MRC-5 and HeLa), with HeLa cells showing a more substantial reduction at lower concentrations. Genotoxicity assessment using the comet assay demonstrated that TiO2 induced DNA damage in MRC-5 cells, while TiO2/DHQ did not, indicating that DHQ mitigates the genotoxic potential of TiO2. Furthermore, TiO2/DHQ exhibited antigenotoxic effects by reducing H2O2-induced DNA damage in MRC-5 cells, supporting its protective role against oxidative stress. Preliminary antimicrobial tests revealed that TiO2/DHQ exhibits antimicrobial activity against E. coli under visible-light excitation, while TiO2 does not. These findings suggest that the TiO2-based ICT complex with DHQ with enhanced antioxidant properties can potentially serve as a safe, non-toxic biocide agent.

Synthesis of spherical and rods-like titanium oxide nanoparticles (TiO2 NPs) and evaluation of their cytotoxicity towards colon cells in vitro

Titanium oxide nanoparticles (TiO2 NPs) are currently used as ingredients in medicines and sunscreens. Unfortunately, recent information about TiO2 NPs indicates their undesirable biological effect on colon cells. Therefore, the aim of this work was to synthesize and evaluate the physicochemical characterization of spherical (TiO2 NSs) and rods-like (TiO2 NRs) NPs, followed by assessment their cytotoxicity. For this purpose, both normal colon epithelial cells (CRL-1790) and cancerous colon cells (SW480) were used. Scanning transmission electron microscopy (STEM) showed that TiO2 NSs with a diameter of ≈10 nm and TiO2 NRs with the size of the longer axis ≈25 nm and shorter axis ≈3 nm were obtained. Based on the selected area electron diffraction (SAED) patterns, it was found that crystalline phases were obtained for both TiO2 NPs. The UV-Vis spectra showed no contamination of TiO2 NPs. Zeta potential values were 9.7 mV and 3.1 mV for NSs and NRs, respectively. Cytotoxicity of TiO2 NPs was assessed using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium) test for various concentration of NPs. The cytotoxic effect for both TiO2 NPs was visible for concentration of 75 μg/ml (for CRL-1790) and 50 μg/ml (for SW480) and higher, and it did not depend on the shape. Moreover, both types of TiO2 NPs (in higher concentration) induce the generation of reactive oxygen species (ROS) in cells cultured with these NPs. Holotomographic microscopy studies showed increased cellular uptake of TiO2 NPs by SW480. The obtained results for the synthesized TiO2 NPs are a promising prospect for their use in biomedical application.

Titanium dioxide nanoparticles - physicochemical characterization and cytotoxic risk

Titanium dioxide (TiO2) nanoparticles (NPs) are incorporated into numerous consumer products yet data as to potential adverse health effects remains inconclusive. In this paper we physically characterize 16 nanoforms of TiO2 from different manufacturers of different size, crystalline structure and surface chemistry. Physical measurements of the particles were performed and compared with those provided by manufacturers revealing several discrepancies. We then examined the biological effects of these particles in cell culture in 3 commonly used cell lines for testing materials. We were unable to validate that anatase particles are more cytotoxic than rutile particles as has been reported, and generally found that the particles produced few effects and no significant production of reactive oxygen species under the conditions used. While some particles do exhibit a dose dependent cytotoxicity that increases over time in some cell lines, the effects were not consistent between cell lines and do not appear to be linked to crystalline structure or any of the specific physical characteristics that were measured including, size, charge and surface composition, nor a correlation with the production of reactive oxygen species.

Updated assessment of the genotoxic potential of titanium dioxide based on reviews of in vitro comet, mode of action and cellular uptake studies, and recent publications

In 2021 the European Food Safety Authority (EFSA) concluded that "A concern for genotoxicity of TiO2 particles that may be present in E 171 could therefore not be ruled out.". A detailed review of the genotoxicity of titanium dioxide (TiO2) was subsequently published by Kirkland et al. (2022) using a comprehensive weight of evidence (WoE) approach in which test systems and endpoints were allocated different levels of relevance. At that time only 34 publications met the reliability and quality criteria for being most relevant in the evaluation of genotoxicity, and based on these it was concluded that the existing evidence did not support a direct DNA damaging mechanism for TiO2. Recently a number of regulatory opinions have been published, in which papers were cited that described in vitro DNA damage (mainly comet), mode of action, and cellular uptake studies that were not discussed in Kirkland et al. (2022). Furthermore, a number of additional papers have been published recently or have been identified from the regulatory opinions as a result of using extended search criteria. A total of 70 publications not previously reviewed in Kirkland et al. (2022) have been reviewed here, and again show that the published data on the genotoxicity of TiO2 are inconsistent, often of poor quality, and in some cases difficult to interpret. The cellular uptake studies show some evidence of cytoplasmic uptake, particularly in cells treated in vitro, but there is no convincing evidence of nuclear uptake. In terms of genotoxicity, the conclusions of Kirkland et al. (2022) that existing evidence does not support a direct DNA damaging mechanism for titanium dioxide (including nano forms), and that the main mechanism leading to TiO2 genotoxicity is most likely indirect damage to DNA through generation of reactive oxygen species (ROS), are still valid.

Nano titanium dioxide induces HaCaT cell pyroptosis via regulating the NLRP3/caspase-1/GSDMD pathway

Nano-titanium dioxide (Nano-TiO2) is extensively utilized across various industries and has the capacity to penetrate human tissues through multiple biological barriers. The HaCaT cell line, as one of human immortalized keratinocytes, is usually used as a model for studying skin drug toxicology. The objective was to assess the toxic effects of nano-TiO2 on HaCaT cells and to trigger pyroptosis. We used MTT method to evaluate the effects of three nano-TiO2 particle sizes (15 nm, 30 nm and 80 nm) on cell viability at different concentrations. Subsequently, we used LDH, Hoechst 33342 and propidium iodide (PI) double staining, scanning electron microscopy (SEM), Western blotting (WB) and real-time quantitative polymerase chain reaction (RT-qPCR) to evaluate the effects of different particle sizes on cells at the same concentration. Our findings indicated that HaCaT cell viability diminished with increasing nano-TiO2 concentrations. Moreover, nano-TiO2 increased LDH level in cellular supernatant. Fluorescence double staining, SEM, WB and RT-qPCR showed that nano-TiO2 induced cell membrane damage by activating pyroptosis pathway of NLRP3/caspase-1/GSDMD. These results suggest that nano-TiO2 toxicity in HaCaT cells is influenced by both dose and particle size, and is associated with the induction of pyroptosis. Frequent and large exposures to nano- TiO2 in daily life may cause serious health hazards.

Food grade titanium dioxide (E171) interferes with monocyte-macrophage cell differentiation and their phagocytic capacity

Food grade titanium dioxide E171 has been used in products such as confectionery, doughs and flours to enhance organoleptic properties. The European Union has warned about adverse effects on humans due to oral consumption. After oral exposure, E171 reaches the bloodstream which raises the concern about effects on blood cells such as monocytes. One of the main functions of these cells is the differentiation of macrophages leading to the phagocytosis of foreign particles. The aim of this study was to evaluate the effect of E171 exposure on the phagocytic capacity and differentiation process of monocytes (THP-1) into macrophages. Physicochemical E171 properties were evaluated, and THP-1 monocytes were exposed to 4, 40 and 200 μg/ml. Cell viability, uptake capacity, cytokine release, the differentiation process, cytoskeletal arrangement and E171 internalization were assayed. Results showed that E171 particles had an amorphous shape with a mean of hydrodynamic size of ∼46 nm in cell culture media. Cell viability decreased until the 9th day of exposure, while the uptake capacity decreased up to 62% in a concentration dependent manner in monocytes. Additionally, the E171 exposure increased the proinflammatory cytokines release and decreased the cell differentiation by a 61% in macrophages. E171 induced changes in cytoskeletal arrangement and some of the E171 particles were located inside the nuclei. We conclude that E171 exposure in THP-1 monocytes induced an inflammatory response, impaired the phagocytic capacity, and interfered with cell differentiation from monocytes to macrophages.

Nano-TiO2 regulates the MAPK (ERK, P38) pathway to promote apoptosis and inhibit proliferation of human colon cells

BACKGROUND

Nano titanium dioxides (TiO2) are widely used in drug development, food additives and packaging materials. Although several studies have demonstrated the poisonousness of TiO2 in vivo and in vitro, the underlying molecular mechanisms have not been fully revealed.

METHODS

Characterization of TiO2 by FTIR, XRD, TEM and DLS. The NCM460 cell line, representing normal colon epithelial cells, was utilized as a model to assess the impact of TiO2 nanoparticles (TiO2-NPs) on cell proliferation and apoptosis. The potential molecular mechanisms underlying its toxic effects were investigated through transcriptome analysis, RT-qPCR, and western blot experiments.

RESULTS

The particle size of the TiO2-NPs used is about 25 nm, which has typical characteristics of anatase. TiO2-NPs at a concentration of 30-60 μg/mL will cause changes in colon cell morphology, decreased proliferation ability, and increased number of apoptotic cells. TiO2-NPs at a concentration of 6 μg/mL did not significantly modify the transcriptome expression profile of colon cells; while 30 μg/mL had a significant effect, leading to up-regulation of gene expression. The differentially expressed genes predominantly modulate the MAPK signaling pathway, TNF signaling pathway, cytokine-cytokine receptor interaction, and other related pathways. Further, western blot analysis revealed that higher concentrations of TiO2-NPs (30-60 μg/mL) could up-regulate the expression of P53, P21 and Bax, while down-regulating the expression of Bcl2 by regulating the MAPK (ERK, P38) signaling pathway. Simultaneously, it also promoted the decreased in Fos protein expression and inhibited the phosphorylation of Jun and Fos.

CONCLUSION

This study demonstrates that TiO2-NPs may exert potential toxic effects on colon cells, and therefore the intake of TiO2-NPs should be strictly regulated in practical applications.

Systematic review of mechanistic evidence for TiO2 nanoparticle-induced lung carcinogenicity

Nano-sized titanium dioxide particles (TiO2 NPs) are a high-production volume nanomaterial widely used in the paints, cosmetics, food and photovoltaics industry. However, the potential carcinogenic effects of TiO2 NPs in the lung are still unclear despite the vast number of in vitro and in vivo studies investigating TiO2 NPs. Here, we systematically reviewed the existing in vitro and in vivo mechanistic evidence of TiO2 NP lung carcinogenicity using the ten key characteristics of carcinogens for identifying and classifying carcinogens. A total of 346 studies qualified for the quality and reliability assessment, of which 206 were considered good quality. Using a weight-of-evidence approach, these studies provided mainly moderate to high confidence for the biological endpoints regarding genotoxicity, oxidative stress and chronic inflammation. A limited number of studies investigated other endpoints important to carcinogenesis, relating to proliferation and transformation, epigenetic alterations and receptor-mediated effects. In summary, TiO2 NPs might possess the ability to induce chronic inflammation and oxidative stress, but it was challenging to compare the findings in the studies due to the wide variety of TiO2 NPs differing in their physicochemical characteristics, formulation, exposure scenarios/test systems, and experimental protocols. Given the limited number of high-quality and high-reliability studies identified within this review, there is a lack of good enough mechanistic evidence for TiO2 NP lung carcinogenicity. Future toxicology/carcinogenicity research must consider including positive controls, endotoxin testing (where necessary), statistical power analysis, and relevant biological endpoints, to improve the study quality and provide reliable data for evaluating TiO2 NP-induced lung carcinogenicity.

Safety of titanium dioxide (E171) as a food additive for humans

Titanium dioxide (TiO2), also known as E171, is commonly used as a white colorant in food, pharmaceuticals, cosmetics, and toothpaste. However, in May 2021, the European Food Safety Authority (EFSA) expert panel, in evaluating the safety of titanium dioxide (E171) as a food additive, concluded that a concern for genotoxicity could not be ruled out. This occurred several years after EFSA had previously considered titanium dioxide to be safe as a food additive. EFSA based this new interpretation on the results of genotoxicity tests of TiO2 nanomaterials. EFSA noted that available data are insufficient to define threshold doses/concentrations of TiO2 particles below which genotoxicity will not occur in tissues containing these particles. Here, it is argued that EFSA made a manifest error regarding the safety of titanium dioxide (E171) particles as a food additive for humans. First, the notion of particle size distribution of TiO2 particles is explained. Second, the changing opinions from the various EFSA evaluations in 2016, 2018, 2019 vs. 2021 are discussed. Third, the low toxicity of TiO2 particles is described in rats exposed by oral gavage and feeding studies in rats and mice. Fourth, the importance of low absorption rates from the gastrointestinal tract vs. circulation in rats and humans but not in mice is identified. Fifth, other international health scientists have weighed in on the EFSA (EFSA J, 2021, 19 (5), 6585) decision and generally disagreed with EFSA's opinion on the safety of E171 TiO2. A common theme voiced by the United Kingdom, Canada, Australia, and New Zealand agencies is that it is inappropriate to compare nanoparticle toxicity studies of dispersed/sonicated nanoparticles with the content of E171 TiO2 in foods because the test materials used in key studies considered by EFSA (EFSA J, 2021, 19 (5), 6585) are not representative of E171 TiO2 particles. Finally, a group of experts recently considered the genotoxicity of TiO2 and could not find support for a direct DNA damaging mechanism of TiO2 (nano and other forms). For these reasons, it is suggested that EFSA made a manifest error on the safety of E171 as a food additive.

The DaNa projects: public communication of (nano)material safety data-from conspiracy theories to study quality

In this perspective, the authors give their view on the developments and experiences on communicating on (nano)materials safety. We would like to share our experiences with the scientific community in order to make them useful for future communication activities. We present the long-term work of the science communication projects DaNa, DaNa2.0 and DaNa4.0, running from 2009 to 2023. Starting in the early 2000s with the beginnings of nanotechnology research, communication on the safety of nanomaterials with the public was still very new and faced the projects with many challenges. Today, science communication is indispensable for the dissemination of scientific findings and a fact-based approach like the DaNa "Knowledge Base Materials" creates a trustworthy dialogue with the public. This long-term project series has made a significant contribution to communication on the safety of nanomaterials, perhaps even the largest among publicly funded project series worldwide.

Genotoxicity evaluation of food additive titanium dioxide using a battery of standard in vivo tests

The increasing use of titanium dioxide (TiO2) nanoparticles (NPs) has raised concern about the safety of food additive TiO2. TiO2 has been considered no longer safe by EFSA due to concerns over genotoxicity, however, there are conflicting opinions upon the safety of TiO2 as a food additive, and the number of in vivo genotoxicity studies conducted on food additive TiO2 was limited. In order to investigate the potential genotoxicity of food additive TiO2, we evaluated the genotoxicity of a commercial food additive TiO2 (average size of 135.54 ± 41.01 nm, range from 60.83 to 230.16 nm, NPs account for 30% by number) using a battery of standard in vivo tests, including mammalian erythrocyte micronucleus test, mammalian bone marrow chromosomal aberration test and in vivo mammalian alkaline comet test. After 15 days of consecutive intragastric administration at doses of 250, 500, and 1000 mg/kgBW, food additive TiO2 neither increased the frequencies of bone marrow micronuclei or chromosomal aberration in mice, nor induced DNA strand breakage in rat liver cells. These results indicate that under the condition of this study, food additive TiO2 does not have genotoxic potential although it contains a fraction of NPs.

The toxicological effects of nano titanium dioxide on target organs and mechanisms of toxicity

Nano-titanium dioxide (TiO2 NPs) is widely used for its extremely high stability, corrosion resistance, and photocatalytic properties and has penetrated into various fields of production and life. Assessing its toxicity to different organs should be a key part of preclinical toxicity assessment of TiO2 NPs, which is relatively incomprehensive yet. Therefore, this review focuses on the toxic effects of TiO2 NPs on various organs in mammals and biological mechanisms from different organs. The commonality of toxic effects on various target organs reflected in tissue structure damage and dysfunction, such as liver damage and dysfunction; pulmonary fibrosis; and renal impairment (including hematuria and nephritis); damage of brain tissue and neurons; alteration of intestinal villi; and weight loss. And effects on the reproductive system are affected by different sexes, including ovarian dysfunction, testicular development damage, and sperm viability reduction. We believe that the toxic mechanisms of TiO2 NPs in target organs have commonalities, such as oxidative stress, inflammatory responses, and organelle damage. However, different target organ toxicities also have their specificities. TiO2 NPs disturb the intestinal flora and cause undesirable changes in feces products. And in spleen are infiltration of neutrophils and lymphadenopathy and eventually immune deficiency. Although the toxic pathways are different, but there may be a close link between the different toxic pathways. In this article, the main manifestations of the toxic effects of titanium dioxide nanoparticles on major mammalian organs are reviewed, in order to provide basic data for their better application from a medical perspective.

Titanium-doped PET nanoplastics, from opaque milk bottle degradation, as a model of environmental true-to-life nanoplastics. Hazardous effects on Drosophila

Micro and nanoplastics (MNPLs) are emergent environmental pollutants, resulting from the degradation of plastic waste, requiring urgent information on their potential risks to human health. To determine such risks, reliable true-to-life materials are essential. In this work, we have used titanium-doped PET NPLs [PET(Ti)NPLs], obtained by grinding opaque milk polyethylene terephthalate (PET) bottles, as a true-to-life MNPLs model. These opaque PET bottles, with an average size of 112 nm, contain about 3% Ti in the form of titanium dioxide rod nanoparticles. TEM investigation confirmed the mixed Ti/PET nature of the obtained true-to-life NPLs, and the rod shape of the embedded TiO2NPs. In the in vivo Drosophila model neither PET(Ti)NPLs nor TiO2NPs reduced the survival rates, although their internalization was confirmed in different compartments of the larval body by using confocal and transmission electron microscopies. The presence of Ti in the PET(Ti)NPLs permitted to quantify its presence both in larvae (2.1 ± 2.2 μg/g of Ti) and in the resulting adults (3.4 ± 3.2 μg/g of Ti) after treatment with 500 μg/g food of PET(Ti)NPL, suggesting its potential use to track their fate in more complex organisms such as mammals. PET(Ti)NPLs, as well as TiO2NPs, altered the expression of genes driving different response pathways, inducing significant oxidative stress levels (up to 10 folds), and genotoxicity. This last result on the genotoxic effects is remarkable in the frame of the hot topic discussion on the risk that titanium compounds, used as food additives, may pose to humans.

Lung carcinogenicity by whole body inhalation exposure to Anatase-type Nano-titanium Dioxide in rats

To investigate the carcinogenicity of anatase-type nano-titanium dioxide (aNTiO2), F344/DuCrlCrlj rats were exposed to aNTiO2 aerosol at concentrations of 0, 0.5, 2, and 8 mg/m3. The rats were divided into 2 groups: carcinogenicity study groups were exposed for two years, and satellite study groups were exposed for one year followed by recovery for 1 day, 26 weeks, and 52 weeks after the end of exposure. In the carcinogenicity groups, bronchiolo-alveolar carcinomas were observed in two 8 mg/m3-exposed males, showing an increasing trend by Peto's test. However, this incidence was at the upper limit of JBRC's historical control data. Bronchiolo-alveolar adenomas were observed in 1, 2, 3, and 4 rats of the 0, 0.5, 2, and 8 mg/m3-exposed females and were not statistically significant. However, the incidence in the 8 mg/m3-exposed females exceeded JBRC's historical control data. Therefore, we conclude there is equivocal evidence for the carcinogenicity of aNTiO2 in rats. No lung tumors were observed in the satellite groups. Particle-induced non-neoplastic lesions (alveolar epithelial hyperplasia and focal fibrosis) were observed in exposed males and females in both the carcinogenicity and satellite groups. Increased lung weight and neutrophils of bronchoalveolar lavage fluid were observed in the 8 mg/m3-exposed carcinogenicity groups. The aNTiO2 deposited in the lungs of the satellite group rats was decreased at 26 weeks after the end of exposure compared to 1 day after the end of exposure. At 52 weeks after the end of exposure, the decreased level was the same at 26 weeks after the end of exposure.

Gastrointestinal tract exposure to particles and DNA damage in animals: A review of studies before, during and after the peak of nanotoxicology

Humans ingest particles and fibers on daily basis. Non-digestible carbohydrates are beneficial to health and food additives are considered safe. However, titanium dioxide (E171) has been banned in the European Union because the European Food Safety Authority no longer considers it non-genotoxic. Ingestion of microplastics and nanoplastics are novel exposures; their potential hazardous effects to humans have been under the radar for many years. In this review, we have assessed the association between oral exposure to man-made particles/fibers and genotoxicity in gastrointestinal tract cells and secondary tissues. We identified a total of 137 studies on oral exposure to particles and fibers. This was reduced to 49 papers with sufficient quality and relevance, including exposures to asbestos, diesel exhaust particles, titanium dioxide, silver nanoparticles, zinc oxide, synthetic amorphous silica and certain other nanomaterials. Nineteen studies show positive results, 25 studies show null results, and 5 papers show equivocal results on genotoxicity. Recent studies seem to show null effects, whereas there is a higher proportion of positive genotoxicity results in early studies. Genotoxic effects seem to cluster in studies on diesel exhaust particles and titanium dioxide, whereas studies on silver nanoparticles, zinc oxide and synthetic amorphous silica seem to show mainly null effects. The most widely used genotoxic tests are the alkaline comet assay and micronucleus assay. There are relatively few results on genotoxicity using reliable measurements of oxidatively damaged DNA, DNA double strand breaks (γH2AX assay) and mutations. In general, evidence suggest that oral exposure to particles and fibers is associated with genotoxicity in animals.

Genotoxicity Evaluation of Titanium Dioxide Nanoparticles In Vivo and In Vitro: A Meta-Analysis

BACKGROUND

Recent studies have raised concerns about genotoxic effects associated with titanium dioxide nanoparticles (TiO2 NPs), which are commonly used. This meta-analysis aims to investigate the potential genotoxicity of TiO2 NPs and explore influencing factors.

METHODS

This study systematically searched Chinese and English literature. The literature underwent quality evaluation, including reliability evaluation using the toxicological data reliability assessment method and relevance evaluation using routine evaluation forms. Meta-analysis and subgroup analyses were performed using R software, with the standardized mean difference (SMD) as the combined effect value.

RESULTS

A total of 26 studies met the inclusion criteria and passed the quality assessment. Meta-analysis results indicated that the SMD for each genotoxic endpoint was greater than 0. This finding implies a significant association between TiO2 NP treatment and DNA damage and chromosome damage both in vivo and in vitro and gene mutation in vitro. Subgroup analysis revealed that short-term exposure to TiO2 NPs increased DNA damage. Rats and cancer cells exhibited heightened susceptibility to DNA damage triggered by TiO2 NPs (p < 0.05).

CONCLUSIONS

TiO2 NPs could induce genotoxicity, including DNA damage, chromosomal damage, and in vitro gene mutations. The mechanism of DNA damage response plays a key role in the genotoxicity induced by TiO2 NPs.

Genotoxicity assessment of titanium dioxide nanoparticles using a standard battery of in vivo assays

As one representative of nanometal oxides, titanium dioxide nanoparticles (TiO2-NPs) have been widely used, particularly in the food industry. The genotoxicity of TiO2-NPs has attracted great attention over the years. This study was undertaken to investigate the chromosome and DNA damage effects of TiO2-NPs (0, 50, 150, and 500 mg/kg BW) using rodent models. After a comprehensive characterization, we conducted a standard battery of in vivo genotoxicity tests, including the chromosomal aberration test (CA), micronucleus (MN) test, and the comet test. The results of all these tests were negative. There were no structural or numerical chromosomal abnormalities in mice bone marrow cells, no increase in the frequency of micronucleated polychromatic erythrocytes in mice bone marrow cells, and no elevation in % tail DNA in rat hepatocytes. This indicated that TiO2-NPs did not cause chromosomal damage or have a direct impact on DNA. These findings suggested that TiO2-NPs did not exhibit genotoxicity and provided valuable data for risk assessment purposes.

Phototoxic or Photoprotective?-Advances and Limitations of Titanium (IV) Oxide in Dermal Formulations-A Review

The widespread role of titanium (IV) oxide (TiO₂) in many industries makes this substance of broad scientific interest. TiO₂ can act as both a photoprotector and photocatalyst, and the potential for its role in both applications increases when present in nanometer-sized crystals. Its sunlight-scattering properties are used extensively in sunscreens. Furthermore, attempts have been made to incorporate TiO₂ into dermal formulations of photolabile drugs. However, the propensity to generate reactive oxygen species (ROS) rendering this material potentially cytotoxic limits its role. Therefore, modifications of TiO₂ nanoparticles (e.g., its polymorphic form, size, shape, and surface modifications) are used in an effort to reduce its photocatalytic effects. This review provides an overview of the potential risks arising from and opportunities presented by the use of TiO₂ in skin care formulations.

Long Non-Coding RNA Expression Profile Alteration Induced by Titanium Dioxide Nanoparticles in HepG2 Cells

The liver is considered the major target organ affected by oral exposure to titanium dioxide nanoparticles (TiO₂ NPs), but the mechanism of hepatotoxicity is not fully understood. This study investigated the effect of TiO₂ NPs on the expression profile of long non-coding RNA (lncRNA) in hepatocytes and tried to understand the potential mechanism of hepatotoxicity through bioinformatics analysis. The human hepatocellular carcinoma cells (HepG2) were treated with TiO₂ NPs at doses of 0-200 μg/mL for 48 h and then RNA sequencing was implemented. The differential lncRNAs between the control and TiO₂ NPs-treated groups were screened, then the lncRNA-mRNA network and enrichment pathways were analyzed via multivariate statistics. As a result, 46,759 lncRNAs were identified and 129 differential lncRNAs were screened out. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the targeted mRNAs of those differential lncRNAs were enriched in the Hedgehog signaling pathway, Vasopressin-regulated water reabsorption, and Glutamatergic synapse. Moreover, two lncRNA-mRNA networks, including lncRNA NONHSAT256380.1-JRK and lncRNA NONHSAT173563.1-SMIM22, were verified by mRNA detection. This study demonstrated that an alteration in the lncRNA expression profile could be induced by TiO₂ NPs and epigenetics may play an important role in the mechanism of hepatotoxicity.