Titanium dioxide nanoparticles: a review of current toxicological data

Nanotechnology-Based Approach to Combat Pandemic COVID 19: A Review

The emergence of a novel Corona virus (COVID 19) originated on December 19 from China. The city of Wuhan, the capital city of Hubei province, China, is responsible for an outbreak of respiratory illness known as COVID 19 and it has been rapidly spread across the world claiming millions of lives. The sudden outbreak of novel Coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 or 2019-nCoV), is a big concern for their speedy mitigation using the predictable treatment and creating its approach around the world. Researchers and doctors are in search of rapid diagnosis kit, drugs, and viral-resistant personal protective equipment (PPE) to clinical diagnosis, medication, and prevent the spread of COVID 19. A rational approach with adaptability and broad viewpoint to challenge the growing pain could be overcome by the application of appropriate technology. The nanotechnology-based approach can significantly serve the purpose of the current pandemic situation of COVID 19. But same time implementation of innovative and creative nanotech approach, there is a decisive need for the full knowledge of SARS-CoV-2 pathogenesis. Moreover, to defeat COVID 19, particularly nanotech-based system with their viral inhibitory properties to increase the effective nanotech approach is essential. In this scenario, this review aims to summarize the past, present, and future of nanotech-based systems that can be used to treat COVID 19, highlighting Nano-based compounds. Lastly, the potential application of the different category of Inorganic Nanomaterials/Inorganic organic conjugate /hybrid system and their practical applicability as suitable means for inspiring against COVID 19 has also been discussed.

Highlights Regarding the Use of Metallic Nanoparticles against Pathogens Considered a Priority by the World Health Organization

The indiscriminate use of antibiotics has facilitated the growing resistance of bacteria, and this has become a serious public health problem worldwide. Several microorganisms are still resistant to multiple antibiotics and are particularly dangerous in the hospital and nursing home environment, and to patients whose care requires devices, such as ventilators and intravenous catheters. A list of twelve pathogenic genera, which especially included bacteria that were not affected by different antibiotics, was released by the World Health Organization (WHO) in 2017, and the research and development of new antibiotics against these genera has been considered a priority. The nanotechnology is a tool that offers an effective platform for altering the physicalchemical properties of different materials, thereby enabling the development of several biomedical applications. Owing to their large surface area and high reactivity, metallic particles on the nanometric scale have remarkable physical, chemical, and biological properties. Nanoparticles with sizes between 1 and 100 nm have several applications, mainly as new antimicrobial agents for the control of microorganisms. In the present review, more than 200 reports of various metallic nanoparticles, especially those containing copper, gold, platinum, silver, titanium, and zinc were analyzed with regard to their anti-bacterial activity. However, of these 200 studies, only 42 reported about trials conducted against the resistant bacteria considered a priority by the WHO. All studies are in the initial stage, and none are in the clinical phase of research.

Nanoparticles from the Cosmetics and Medical Industries in Legal and Environmental Aspects

This paper presents the application and role of nanomaterials, with particular emphasis on the cosmetics and medical industries. Methods of obtaining materials at the nanoscale and their characteristic structure, which determines their attractiveness and risk, especially in recent years, have been described. The subject of the work was to indicate the hazards and risks that are associated with the properties of nanomaterials; dimension, and high chemical and physical activity, thus making ways to capture and monitor them difficult. Legal and environmental aspects were taken into account, and the involvement of the European Commission in this subject and the activities carried out in a few European countries as well as in Japan, the USA and Canada were analyzed.

Coenzyme Q10 protects isolated human blood cells from TiO2 nanoparticles induced oxidative/antioxidative imbalance, hemolysis, cytotoxicity, DNA damage and mitochondrial impairment

TiO₂ NPs have been investigated for their toxic potential and studies have reported their toxicity is due to generation of oxidative stress. In the present study, we investigated the toxicity of TiO₂ NPs and explored the potential of well-known antioxidant coenzyme Q10 (CoQ10) in counteracting the NP-induced toxicity in isolated human blood cells. When the isolated blood cells were treated with varying concentrations of TiO₂ NPs (25-100 μg/ml), only 50 μg/ml dose induced statistically significant hemolysis in erythrocytes and cytotoxicity in lymphocytes (p < 0.05). None of the concentrations induced any significant increase in platelet aggregation. To investigate the protective effect of CoQ10, we incubated the isolated blood cells with 50 μg/ml of TiO₂ NPs in the presence and absence of 25 μM of CoQ10 for 3 h. Hemolysis, oxidative stress, LDH leakage and ATPase enzyme activity were studied in erythrocytes; cytotoxic and DNA damaging potential of NPs were determined in lymphocytes, along with mitochondrial membrane potential (MMP) and ADP/ATP ratio. Hemolysis, generation of oxidative stress, LDH leakage and reduced ATPase activity were observed in the erythrocytes treated with NPs alone (50 μg/ml), the results were statistically significant at p < 0.05. Oxidative stress was evident by increased levels of malonaldehyde, indicating lipid peroxidation and generation of reactive oxygen species including hydrogen peroxide, together with statistically significant decrease in the activities of catalase and superoxide dismutase and reduced glutathione levels. In the lymphocytes treated with NPs alone (50 μg/ml), cytotoxicity in MTT assay and DNA damage in comet assay were observed; in addition, mitochondrial membrane potential collapsed and ADP/ATP ratio increased indicating mitochondrial function impairment. However, in the presence of CoQ10, hemolysis, oxidative stress and LDH leakage in the erythrocytes and lymphocyte cytotoxicity and DNA damage were drastically reduced, enzyme activities, MMP and ADP/ATP ratio were restored towards normal levels. TiO₂ NPs induce cytotoxicity, damage DNA in lymphocytes, and induce oxidative/anti-oxidative imbalance in erythrocytes. Antioxidant CoQ10 protects erythrocytes and lymphocytes from toxicity induced by TiO₂ NPs.

Long-Term Exposure to Nanosized TiO2 Triggers Stress Responses and Cell Death Pathways in Pulmonary Epithelial Cells

There is little in vitro data available on long-term effects of TiO₂ exposure. Such data are important for improving the understanding of underlying mechanisms of adverse health effects of TiO₂. Here, we exposed pulmonary epithelial cells to two doses (0.96 and 1.92 µg/cm²) of TiO₂ for 13 weeks and effects on cell cycle and cell death mechanisms, i.e., apoptosis and autophagy were determined after 4, 8 and 13 weeks of exposure. Changes in telomere length, cellular protein levels and lipid classes were also analyzed at 13 weeks of exposure. We observed that the TiO₂ exposure increased the fraction of cells in G1-phase and reduced the fraction of cells in G2-phase, which was accompanied by an increase in the fraction of late apoptotic/necrotic cells. This corresponded with an induced expression of key apoptotic proteins i.e., BAD and BAX, and an accumulation of several lipid classes involved in cellular stress and apoptosis. These findings were further supported by quantitative proteome profiling data showing an increase in proteins involved in cell stress and genomic maintenance pathways following TiO₂ exposure. Altogether, we suggest that cell stress response and cell death pathways may be important molecular events in long-term health effects of TiO₂.

Suitability of Nanoparticles to Face Benzo(a)pyrene-Induced Genetic and Chromosomal Damage in M. galloprovincialis. An In Vitro Approach

Benzo(a)pyrene (B(a)P) is a well-known genotoxic agent, the removal of which from environmental matrices is mandatory, necessitating the application of cleaning strategies that are harmless to human and environmental health. The potential application of nanoparticles (NPs) in the remediation of polluted environments is of increasing interest. Here, specifically designed NPs were selected as being non-genotoxic and able to interact with B(a)P, in order to address the genetic and chromosomal damage it produces. A newly formulated pure anatase nano-titanium (nano-TiO2), a commercial mixture of rutile and anatase, and carbon black-derived hydrophilic NPs (HNP) were applied. Once it had been ascertained that the NPs selected for the work did not induce genotoxicity, marine mussel gill biopsies were exposed in vitro to B(a)P (2 μg/mL), alone and in combination with the selected NPs (50 µg/mL nano-TiO2, 10 µg/mL HNP). DNA primary reversible damage was evaluated by means of the Comet assay. Chromosomal persistent damage was assessed on the basis of micronuclei frequency and nuclear abnormalities by means of the Micronucleus-Cytome assay. Transmission Electron Microscopy (TEM) was performed to investigate the mechanism of action exerted by NPs. Pure Anatase n-TiO2 was found to be the most suitable for our purpose, as it is cyto- and genotoxicity free and able to reduce the genetic and chromosomal damage associated with exposure to B(a)P.

Metabolomics screening of serum biomarkers for occupational exposure of titanium dioxide nanoparticles

Although nanotoxicology studies have shown that respiratory exposure of titanium dioxide nanoparticles (TiO₂ NPs) could induce adverse health effects, limited biomarkers associated with occupational exposure of TiO₂ NPs were reported. The purpose of this study is to screen serum biomarkers among workers occupationally exposed to TiO₂ NPs using metabolomics. Compared with the control group, a total of 296 serum metabolites were differentially expressed in the TiO₂ NPs-exposed group, of which the relative expression of 265 metabolites increased, and the remaining 31 decreased. Three machine learning methods including random forest (RF), support vector machines (SVM), and boruta screened eight potential biomarkers and simultaneously selected a metabolite, Liquoric acid. Through multiple linear regression analysis to adjust the influence of confounding factors such as gender, age, BMI, smoking and drinking, occupational exposure to TiO₂ NPs was significantly related to the relative expression of the eight potential biomarkers. Meanwhile, the receiver operating characteristic curves (ROCs) of these potential biomarkers had good sensitivity and specificity. These potential biomarkers were related to lipid peroxidation, and had biological basis for occupational exposure to TiO₂ NPs. Therefore, it was demonstrated that the serum metabolites represented by Liquoric acid were good biomarkers of occupational exposure to TiO₂ NPs.

Adsorption of proteins on TiO2 particles influences their aggregation and cell penetration

TiO₂ nanoparticles known as E171 are one controversial food additive due to its potential toxicity. In this work, the main hypothesis is that the proteins adsorbed on the TiO₂ nanoparticles prevent their aggregation and favor the cell penetration. To do so, the TiO₂ nanoparticles were coated with gelatin and β-lactoglobulin to reach interfacial concentrations about 0.25 mg/mg and 0.32 mg/mg, respectively. The measurement of NP size showed that the protein coating improve the colloidal stability of TiO₂ nanoparticles. The FTIR analysis suggests that the β-lactoglobulin structure is modified after adsorption. The penetration of TiO₂ penetration inside human intestinal epithelial cells was shown and quantify by using confocal Raman microscopy. The promoting role of the protein coating on the cell penetration was demonstrated for both the gelatin and β-lactoglobulin. Finally, the results allow establishing a correlation between the ability of proteins to prevent NP aggregation and the cell penetration.

Correlating Quantitative Measurements of Radical Production by Photocatalytic TiO2 with Daphnia magna Toxicity

Increased use of titanium dioxide (TiO₂ ) nanoparticles (NPs) in domestic and industrial applications has increased the risk for adverse environmental outcomes based on an elevated likelihood of organism exposure. Anatase TiO₂ NP exposure to ultraviolet A (UV-A) radiation in aquatic environments generates radical oxygen species (ROS), which may ultimately be responsible for increased organism toxicity. We have identified and measured the 2 most relevant ROS species, hydroxyl and superoxide radicals, and described that ROS can be modeled using the highly reactive hydroxyl radical to provide an upper bound for toxicity. The TiO₂ NPs were co-exposed to increasing natural organic matter (NOM) amounts (measured as concentration of dissolved organic carbon [DOC]) and simulated-sunlight UV-A intensities. Radical production rate was determined using fluorescence spectroscopy and was positively correlated with increases in TiO₂ concentration and UV-A intensity, and negatively correlated with increased DOC concentration. Daphnia magna toxicity was also found to decrease with NOM addition, which is attributed to the decreased radical production rate with increased DOC concentrations. We demonstrate that the rate of ROS production from simulated-sunlight-irradiated TiO₂ NPs can be quantified using relatively simple fluorescent techniques. We show that toxicity to TiO₂ NP varies greatly with conditions, and that concentration alone is a poor predictor of toxicity. Describing toxicity/hydroxyl radical measurement may be a more accurate way to describe overall risk. We provide a framework for a simple model to describe toxicity/hydroxyl radical. These conclusions demonstrate the importance of considering exposure conditions as a means of risk management during TiO₂ NP toxicity testing, waste management, and regulatory decisions. Environ Toxicol Chem 2021;40:1322-1334. © 2021 SETAC.

Nono-titanium dioxide exposure during the adolescent period induces neurotoxicities in rats: Ameliorative potential of bergamot essential oil

INTRODUCTION

In adolescence, the brain is still maturing, and disorders in maturation may affect the normal development of the brain. Exposure to titanium dioxide nanoparticles (TiO₂ NPs) has various potential negative effects on the central nervous system. Bergamot essential oil (BEO) has been found to be effective for neuroprotection.

METHODS

The rats were injected intraperitoneally with TiO₂ NPs (20 mg/kg) and/or BEO (200 mg/kg). The endogenous antioxidant state and inflammatory parameters were estimated using ELISA kits, and then the memory ability and anxiety-like behavior in rats were assessed.

RESULTS

TiO₂ NPs exposure during the adolescent period induced anxiety-like behavior, cognitive impairment, neuroinflammation and oxidative damage in hippocampus, and BEO treatment could significantly ameliorate the neurotoxicities induced by TiO₂ NPs exposure.

CONCLUSION

Our results suggest that the negative effects of TiO₂ NPs exposure during the adolescent period on anxiety-like behavior and cognitive function may be related to oxidative stress and neuroinflammation induced by TiO₂ NPs exposure. In addition, BEO may ameliorate the neurotoxicities induced by TiO2 NPs exposure in adolescent rats through the antioxidant and anti-inflammatory activity of BEO.

Non-toxic doses of modified titanium dioxide nanoparticles (m-TiO2NPs) in albino CFW mice

Modified titanium dioxide (m-TiO₂NPs) is a novel photocatalytic nanomaterial. Its level of toxicity was evaluated to be used in photodynamic treatment for cervical cancer. In the toxicity studies (Irwin test, acute and repeated doses (10 days)), female albino Swiss Webster (CFW) mice, 28 days old were used; the m-TiO₂NPs was administered in single 300, 600 and 5,000 mg/kg of body weight (b.w) doses injected in the peritoneal zone. No adverse events or mortality were produced. Daily intraperitoneal doses of 300 and 600 mg/kg b.w every 24 h for 10 days did not produce adverse effects or mortality. There were no abnormal clinical signs or behavioral changes (neurological or physiological) in any of the mice. All organs exhibited normal architecture, and histological studies determined that m-TiO₂NPs does not produce changes in the cells or tissues. Based on the test results, it is concluded that the m-TiO₂NPs has not a toxic effect in doses equal to or less than 5,000 mg/kg b.w.

Model Complexity as Determining Factor for In Vitro Nanosafety Studies: Effects of Silver and Titanium Dioxide Nanomaterials in Intestinal Models

With the rising interest in the effects of orally ingested engineered nanomaterials (ENMs), much effort is undertaken to develop and advance intestinal in vitro models. The cytotoxic, proinflammatory, and DNA damaging properties of polyvinylpyrrolidone-capped silver (Ag-PVP) and titanium dioxide (TiO₂ , P25) ENM in four in vitro models of increasing complexity-from proliferating Caco-2 and HT29-MTX-E12 monocultures to long-term transwell triple cultures including THP-1 macrophages to reproduce the human intestine in healthy versus inflamed-like state-are studied. Results are compared against in vivo effects of the same ENM through intestinal tissue analysis from 28-day oral exposure studies in mice. Adverse responses are only observed in monocultures and suggest toxic potential for both ENM, typically showing stronger effects for Ag-PVP than for TiO₂ . By contrast, no adverse effects are observed in either the transwell cultures or the analyzed murine tissues. The data provide further support that monoculture models represent a cost and time efficient tool for early-phase hazard assessment. However, the observed similarities in morphology and ENM effects in murine intestinal tissue and the in vitro triple culture model suggest that advanced multifacetted research questions concerning oral ENM exposure are more adequately addressed by the more complex and time intensive models.

Non-Animal Strategies for Toxicity Assessment of Nanoscale Materials: Role of Adverse Outcome Pathways in the Selection of Endpoints

Faster, cheaper, sensitive, and mechanisms-based animal alternatives are needed to address the safety assessment needs of the growing number of nanomaterials (NM) and their sophisticated property variants. Specifically, strategies that help identify and prioritize alternative schemes involving individual test models, toxicity endpoints, and assays for the assessment of adverse outcomes, as well as strategies that enable validation and refinement of these schemes for the regulatory acceptance are needed. In this review, two strategies 1) the current nanotoxicology literature review and 2) the adverse outcome pathways (AOPs) framework, a systematic process that allows the assembly of available mechanistic information concerning a toxicological response in a simple modular format, are presented. The review highlights 1) the most frequently assessed and reported ad hoc in vivo and in vitro toxicity measurements in the literature, 2) various AOPs of relevance to inhalation toxicity of NM that are presently under development, and 3) their applicability in identifying key events of toxicity for targeted in vitro assay development. Finally, using an existing AOP for lung fibrosis, the specific combinations of cell types, exposure and test systems, and assays that are experimentally supported and thus, can be used for assessing NM-induced lung fibrosis, are proposed.

Evaluation of the neurotoxic effects of engineered nanomaterials in C57BL/6J mice in 28-day oral exposure studies

In recent years, concerns have emerged about the potential neurotoxic effects of engineered nanomaterials (NMs). Titanium dioxide and silver are among the most widely used types of metallic NMs. We have investigated the effects of these NMs on behaviour and neuropathology in male and female C57BL/6J mice following 28-day oral exposure with or without a 14-day post-exposure recovery. The mice were fed ad libitum with food pellets dosed with 10 mg/g TiO₂, 2 mg/g polyvinylpyrrolidone-coated Ag or control pellets. Behaviour was evaluated by X-maze, open field, string suspension and rotarod tests. Histological alterations were analysed by immunohistochemistry and brain tissue homogenates were investigated for markers of oxidative stress, inflammation and blood-brain barrier disruption. Effects of the NMs on tyrosine and serine/threonine protein kinase activity in mouse brains were investigated by measuring kinase activity on peptide microarrays. Markers of inflammation, oxidative stress and blood-brain barrier integrity were not significantly affected in the male and female mice following exposure to Ag or TiO₂. Both types of NMs also revealed no consistent significant treatment-related effects on anxiety and cognition. However, in the Ag NM exposed mice altered motor performance effects were observed by the rotarod test that differed between sexes. At 1-week post-exposure, a diminished performance in this test was observed exclusively in the female animals. Cortex tissues of female mice also showed a pronounced increase in tyrosine kinase activity following 28 days oral exposure to Ag NM. A subsequent Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) based toxicokinetic study in female mice revealed a rapid and persistent accumulation of Ag in various internal organs including liver, kidney, spleen and the brain up to 4 weeks post-exposure. In conclusion, our study demonstrated that subacute exposure to foodborne TiO₂ and Ag NMs does not cause substantial neuropathological changes in mice. However, the toxicokinetic and specific toxicodynamic findings indicate that long-term exposures to Ag NM can cause neurotoxicity, possibly in a sex-dependent manner.

Nanoparticles induced embryo-fetal toxicity

Applications of nanomaterials cause a general concern on their toxicity when they intentionally (such as in medicine) or unintentionally (environment exposure) enter into the human body. As a special subpopulation, pregnant women are more susceptible to nanoparticle (NP)-induced toxicity. More importantly, prenatal exposures may affect the entire life of the fetus. Through blood circulation, NPs may cross placental barriers and enter into fetus. A cascade of events, such as damage in placental barriers, generation of oxidative stress, inflammation, and altered gene expression, may induce delayed or abnormal fetal development. The physicochemical properties of NPs, exposure time, and other factors directly affect nanotoxicity in pregnant populations. Even though results from animal studies cannot directly extrapolate to humans, compelling evidence has already shown that, for pregnant women, caution must be taken when dealing with nanomedicines or NP pollutants.

Antibiotic tetracycline enhanced the toxic potential of photo catalytically active P25 titanium dioxide nanoparticles towards freshwater algae Scenedesmus obliquus

Titanium dioxide nanoparticles (TiO₂ NPs) often co-exist with the other co-contaminants like antibiotics. The antibiotics can potentially modify the toxic effects of the co-contaminants like the NPs in the environment. Hence, the present study aims to understand the toxic potential of a binary mixture of tetracycline (TC) and TiO₂ NPs to a model freshwater alga - Scenedesmus obliquus. Since, TiO₂ NPs are known to be photo-catalytically active, non-irradiated (NI-TiO₂ NPs), UVA pre-irradiated (UVA-TiO₂ NPs), and UVB pre-irradiated (UVB-TiO₂ NPs) TiO₂ NPs was mixed separately with TC and their toxicity evaluated. It was observed that the cell viability for the three experimental groups decreased significantly (p < 0.001) with respect to the individual NPs-treated algae. Abbott's model suggested that the interaction between TC and Ni-TiO₂ NPs was additive for all the concentrations of NI-TiO₂ NPs tested. However, in the case of both the UV pre-irradiated NPs, the interaction was additive for the lower concentration (1.56 μM) and synergistic for both the higher concentrations (3.13, and 6.26 μM). At the concentrations tested the cell membrane damage and intracellular uptake of NPs increased significantly (p < 0.05) for the mixture in comparison with the individual NPs treated algae. This study suggested that even a non-lethal concentration of TC (EC₁₀ = 0.135 μM) increased the toxic potential of the TiO₂ NPs significantly and when this antibiotic was used in combination with the UV pre-irradiated NPs, toxicity even increased to a higher level.

Removal of flocculated TiO2 nanoparticles by settling or dissolved air flotation

Engineered nanoparticles of TiO₂ (TiO₂-NPs) are used in the industry for a great number of applications. After their usage, the particles end up in aquatic environments, contaminating supply waters and watercourses. Bench-scale studies report removal of TiO₂-NPs (450 nm, the mean volumetric diameter) by flocculation followed by settling or by dissolved air flotation (4 bar saturation pressure and 30% recycling ratio). Floc formation was conducted after heterocoagulation with iron hydroxide (30-40 mg L^-1Fe³⁺⁾ and gelatinized corn starch (10-20 mgL^-1) as flocculant, at pH 7. Particle size distribution and zeta potential, removal efficiencies as a function of time and microphotography of flocs were analyzed. Mechanisms involve ferric hydroxide precipitation, heterocoagulation with the nanoparticles and flocculation of the loaded carrier precipitates with gelatinized starch. Best results showed removals between 95-100% of TiO₂-NPs, either by settling or flotation after 5 min. Clear treated waters with low turbidity < 3 nephelometric turbidity units (NTU) and TiO₂-NPs concentrations <1 mg L^-1 were obtained. A practical advantage in DAF was the higher solids content (1.9% w/w) of the sludge, when compared to settling (0.7% w/w). This would facilitate the sludge dewatering and disposal, but DAF has the disadvantage of the poor efficiency at high concentration of the nanoparticles of titanium oxide (>100 mg L^-1). Conversely, the removal by settling of the flocs increased at high dosages. It is believed that both processes are sustainable in terms of reagents and the removal efficiencies of TiO₂ nanoparticles from water.

Exploring urine biomarkers of early health effects for occupational exposure to titanium dioxide nanoparticles using metabolomics

Many experimental studies have demonstrated that titanium dioxide nanoparticles (TiO2 NPs) could induce adverse health effects in vivo and in vitro. But epidemiological evidence and biomarkers related to early health effects are still lacking. This study aimed to explore biomarkers in the urine samples of workers occupationally exposed to a relatively low concentration of TiO2 NPs. A cross-sectional study was conducted in Jinan, China, involving 132 employees of a TiO2 NP manufacturing plant, among which the exposed group and control group were 1 : 1 matched by confounding factors such as gender, age, BMI, smoking and drinking. Untargeted metabolomics was performed in urine samples using high performance liquid chromatography-mass spectrometry (HPLC-MS) technology. The differential metabolites between the TiO2 NP exposed group and the control group were analyzed and then screened for potential biomarkers using bioinformatics methods. Metabolomics found a total of 1760 differentially expressed metabolites in the TiO2 NP exposed group, of which 60 differential metabolites were simultaneously confirmed by one-dimensional and multi-dimensional statistical analysis. Among these 60 differential metabolites, the relative expression of 27 metabolites increased, and the remaining 33 decreased. Pathway enrichment analysis further found that the metabolic pathway of long chain acyl-coa dehydrogenase deficiency (Lcad) was significantly enriched. Ten differential metabolites were selected as potential biomarkers of occupational exposure to TiO2 NPs using machine learning methods, including dibenzyl ether, quassimarin, tryptophan, etc. The receiver operating characteristic curves (ROCs) of these potential biomarkers showed good sensitivity and specificity. These potential biomarkers also had biological basis for occupational exposure to TiO2 NPs. Therefore, urine metabolites represented by dibenzyl ether are considered as good biomarkers of early health effects for occupational exposure to TiO2 NPs.

Estimates of lung burden risk associated with long-term exposure to TiO2 nanoparticles as a UV-filter in sprays

Titanium dioxide (TiO2) nanoparticles (NPs) are employed as an ultraviolet filter in sunscreen products because of their high ultraviolet absorptivity. However, sunscreen sprays may pose health risks due to the toxicity of inhaled TiO2 NPs. Therefore, we estimated the potential human health risk posed by inhaled TiO2 NPs emitted from sunscreen sprays. The physiology-based lung model was employed to predict the lung TiO2 NPs burden caused by long-term exposure. A Hill-based dose-response model described the relationship between lung inflammation and TiO2 NP accumulation. The Weibull threshold model was used to estimate the threshold amount of accumulation inducing 0.5% of the maximum increase in neutrophils. The potential health risk was assessed using a hazard quotient-based probabilistic risk model. All data obtained to date indicate that application of sunscreen sprays poses no significant health risk. However, using data simulations based on the threshold criterion, we discovered that in terms of practical strategies for preventing the risks posed by inhaled TiO2 NPs emitted from spray products, the suggested daily use amount and pressing number are 40 g (95% confidence interval: 11-146 g) and 66 (18-245), respectively. In this study, we successfully translated the potential health risk of long-term exposure to NP-containing sunscreen sprays and recommendations for daily application into mechanistic insights.

Combined Toxicity of Metal Nanoparticles: Comparison of Individual and Mixture Particles Effect

Toxicity of metal nanoparticles (NPs) are closely associated with increasing intracellular reactive oxygen species (ROS) and the levels of pro-inflammatory mediators. However, NP interactions and surface complexation reactions alter the original toxicity of individual NPs. To date, toxicity studies on NPs have mostly been focused on individual NPs instead of the combination of several species. It is expected that the amount of industrial and highway-acquired NPs released into the environment will further increase in the near future. This raises the possibility that various types of NPs could be found in the same medium, thereby, the adverse effects of each NP either could be potentiated, inhibited or remain unaffected by the presence of the other NPs. After uptake of NPs into the human body from various routes, protein kinases pathways mediate their toxicities. In this context, family of mitogen-activated protein kinases (MAPKs) is mostly efficient. Despite each NP activates almost the same metabolic pathways, the toxicity induced by a single type of NP is different than the case of co-exposure to the combined NPs. The scantiness of toxicological data on NPs combinations displays difficulties to determine, if there is any risk associated with exposure to combined nanomaterials. Currently, in addition to mathematical analysis (Response surface methodology; RSM), the quantitative-structure-activity relationship (QSAR) is used to estimate the toxicity of various metal oxide NPs based on their physicochemical properties and levels applied. In this chapter, it is discussed whether the coexistence of multiple metal NPs alter the original toxicity of individual NP. Additionally, in the part of "Toxicity of diesel emission/exhaust particles (DEP)", the known individual toxicity of metal NPs within the DEP is compared with the data regarding toxicity of total DEP mixture.

Research progress on the carcinogenicity of metal nanomaterials

With the rapid development of nanotechnology, new nanomaterials with enormous potentials continue to emerge, especially metal nanomaterials. Metal nanomaterials possess the characteristics of metals and nanomaterials, so they are widely used in many fields. But at the same time, whether the use or release of metal nan4omaterials into the environment is toxic to human beings and animals has now attained widespread attention at home and abroad. Currently, it is an indisputable fact that cancer ranks among the top causes of death among residents worldwide. The properties of causing DNA damage and mutations possessed by these metal nanomaterials make them unpredictable influences in the body, subsequently leading to genotoxicity and carcinogenicity. Due to the increasing evidence of their roles in carcinogenicity, this article reviews the toxicological and carcinogenic effects of metal nanomaterials, including nano-metal elements (nickel nanoparticles, silver nanoparticles, and cobalt nanoparticles) and nano-metal oxides (titanium dioxide nanoparticles, silica nanoparticles, zinc oxide nanoparticles, and alumina nanoparticles). This article provides a reference for the researchers and policymakers to use metal nanomaterials rationally in modern industries and biomedicine.

Association of multiple metals with lipid markers against different exposure profiles: A population-based cross-sectional study in China

We sought to evaluate whether essential and toxic metals are cross-sectionally related to blood lipid levels using data among adults from Shimen (n = 564) and Huayuan (n = 637), two counties with different exposure profiles in Hunan province of China. Traditional and grouped weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) were performed to assess association between exposure to a mixture of 22 metals measured in urine or plasma, and lipid markers. Most of the exposure levels of metals were significantly higher in Shimen area than those in Huayuan area (all P-values < 0.001). Traditional WQS regression analyses revealed that the WQS index were both significantly associated with lipid markers in two areas, except for the HDL-C. Grouped WQS revealed that essential metals group showed significantly positive associations with lipid markers except for HDL-C in Huayuan area, while toxic metals group showed significantly negative associations except for HDL-C and LDL-C in Huayuan area. There were no significant joint effects, but potential non-linear relationships between metals mixture and TC or LDL-C levels were observed in BKMR analyses. Although consistent significantly associations of zinc and titanium with TG levels were found in both areas, the metals closely related to other lipid markers were varied by sites. Additionally, the BKMR analyses revealed an inverse U shaped association of iron with LDL-C levels and interaction effects of zinc and cadmium on LDL-C in Huayuan area. The relationship between metal exposure and blood lipid were not identical against different exposure profiles.

Composable Microfluidic Plates (cPlate): A Simple and Scalable Fluid Manipulation System for Multiplexed Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assay (ELISA) is the gold standard method for protein biomarkers. However, scaling up ELISA for multiplexed biomarker analysis is not a trivial task due to the lengthy procedures for fluid manipulation and high reagent/sample consumption. Herein, we present a highly scalable multiplexed ELISA that achieves a similar level of performance to commercial single-target ELISA kits as well as shorter assay time, less consumption, and simpler procedures. This ELISA is enabled by a novel microscale fluid manipulation method, composable microfluidic plates (cPlate), which are comprised of miniaturized 96-well plates and their corresponding channel plates. By assembling and disassembling the plates, all of the fluid manipulations for 96 independent ELISA reactions can be achieved simultaneously without any external fluid manipulation equipment. Simultaneous quantification of four protein biomarkers in serum samples is demonstrated with the cPlate system, achieving high sensitivity and specificity (∼ pg/mL), short assay time (∼1 h), low consumption (∼5 μL/well), high scalability, and ease of use. This platform is further applied to probe the levels of three protein biomarkers related to vascular dysfunction under pulmonary nanoparticle exposure in rat's plasma. Because of the low cost, portability, and instrument-free nature of the cPlate system, it will have great potential for multiplexed point-of-care testing in resource-limited regions.

Nanocomposites containing titanium dioxide for environmental remediation

Titania is considered to be one of the most versatile material in its nanoform. Scientific community looks towards it to address various pressing global problems. One such problem is aquatic pollution arising from organic chemicals such as dyes, pesticides, antibiotics etc. due to industrial, domestic and agricultural activities. Titania proves to be very effective to address this problem owing to its superior photocatalytic properties. In this review, we will review the recent advances in titania-based nanocomposites. The recent advances discussed in this review include synthesis of titania, modification of titania, exploration of various supports such as silica, carbon, graphene etc., that is documented to enhance its environmental remediation properties.

A review on in vivo and in vitro nanotoxicological studies in plants: A headlight for future targets

Owing to the unique properties and useful applications in numerous fields, nanomaterials (NMs) received a great attention. The mass production of NMs has raised major concern for the environment. Recently, some altered growth patterns in plants have been reported due to the plant-NMs interactions. However, for NMs safe applications in agriculture and medicine, a comprehensive understanding of bio-nano interactions is crucial. The main goal of this review article is to summarize the results of the toxicological studies that have shown the in vitro and in vivo interactions of NMs with plants. The toxicity mechanisms are briefly discussed in plants as the defense mechanism works to overcome the stress caused by NMs implications. Indeed, the impact of NMs on plants varies significantly with many factors including physicochemical properties of NMs, culture media, and plant species. To investigate the impacts, dose metrics is an important analysis for assaying toxicity and is discussed in the present article to broadly open up different aspects of nanotoxicological investigations. To access reliable quantification and measurement in laboratories, standardized methodologies are crucial for precise dose delivery of NMs to plants during exposure. Altogether, the information is significant to researchers to describe restrictions and future perspectives.

Plasma titanium level is positively associated with metabolic syndrome: A survey in China's heavy metal polluted regions

OBJECTIVE

Several heavy metals have been reported to be associated with metabolic syndrome(MetS) in general population, while effects of multiple metals exposure on MetS in residents living in heavy metal polluted regions have not been investigated. We aimed to assess the association of 23 metal levels and MetS among population living in China's heavy metal polluted regions.

METHODS

From August 2016 to July 2017, a total of 2109 eligible participants were consecutively enrolled in our study in Hunan province, China. The levels of plasma and urine metals were measured by inductively coupled plasma mass spectrometer (ICP-MS). MetS was defined by the criteria of the International Diabetes Federation. Multivariable regression models were applied to analysis the potential relationship.

RESULTS

In the overall population, crude model showed positive relationship of plasma titanium (Ti) with MetS and negative association of urine vanadium, iron, and selenium with MetS. After adjusted for potential confounders, only plasma Ti was positive associated with MetS (adjusted OR for Q4 versus Q1: 1.46; 95% CI: 1.06-1.99), and this positive correlation was explained by abdominal obesity (OR = 1.84, 95% CI: 1.41-2.39) and high triglycerides (OR = 2.23, 95% CI: 1.68-2.96). Further linear regression analysis revealed significant association of plasma Ti levels with waist circumference (β = 0.0056, 95% CI: 0.0004-0.0109, P = 0.036) and triglycerides (β = 0.0012, 95% CI: 0.0006-0.0019, P < 0.001), respectively.

CONCLUSION

High plasma Ti level was associated with increased risk of MetS via increasing waist circumference and triglycerides in people under high metal exposure.

Unraveling the publication trends in inhalable nano-systems

Nano-systems (size range: 1 ~ 1000 nm) have been widely investigated as pulmonary drug delivery carriers, and the safety of inhaled nano-systems has aroused general interests. In this work, bibliometric analysis was performed to describe the current situation of related literature, figure out the revolutionary trends, and eventually forecast the possible future directions. The relevant articles and reviews from 2001 to 2020 were retrieved from the Web of Science Core Collection. The documents were processed by Clarivate Analytic associated with Web of Science database, Statistical Analysis Toolkit for Informetric, bibliometric online platform and VOSviewer, and the data were visualized. The bibliometric overview of the literature was described, citation analysis was performed, and research hotspots were showcased. The bibliometric analysis of 3362 documents of interest indicated that most of the relevant source titles were in the fields of toxicology, pharmacy, and materials science. The three research hotspots were the biological process of inhalable nano-systems in vivo, the manufacture of inhalable nano-systems, and the impact of nano-systems on human health in the environment. Toxicity and safety have always been the keywords. The USA was the major contributing country, and international collaboration and co-authorship were common phenomena. The general situation and development trend of literature of inhalable nano-systems were summarized. It was anticipated that bibliometrics analysis could provide new ideas for the future research of inhalable nano-systems.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11051-021-05384-1.

Vessel-on-a-chip models for studying microvascular physiology, transport, and function in vitro

To understand how the microvasculature grows and remodels, researchers require reproducible systems that emulate the function of living tissue. Innovative contributions toward fulfilling this important need have been made by engineered microvessels assembled in vitro with microfabrication techniques. Microfabricated vessels, commonly referred to as "vessels-on-a-chip," are from a class of cell culture technologies that uniquely integrate microscale flow phenomena, tissue-level biomolecular transport, cell-cell interactions, and proper three-dimensional (3-D) extracellular matrix environments under well-defined culture conditions. Here, we discuss the enabling attributes of microfabricated vessels that make these models more physiological compared with established cell culture techniques and the potential of these models for advancing microvascular research. This review highlights the key features of microvascular transport and physiology, critically discusses the strengths and limitations of different microfabrication strategies for studying the microvasculature, and provides a perspective on current challenges and future opportunities for vessel-on-a-chip models.

Toxicological Consequences of Titanium Dioxide Nanoparticles (TiO2NPs) and Their Jeopardy to Human Population

Titanium dioxide nanoparticles (TiO₂ NPs) are the most produced nanomaterial for food additives, pigments, photocatalysis, and personal care products. These nanomaterials are at the forefront of rapidly developing indispensable nanotechnology. In all these nanomaterials, titanium dioxide (TiO₂) is the most common nanomaterial which is being synthesized for many years. These nanoparticles of TiO₂ are widely used at the commercial level, especially in cosmetic industries. High usage in such a way has increased the toxicological consequences of the human population. Several studies have shown that TiO₂ NPs accumulated after oral exposure or inhalation in the alimentary canal, lungs, heart, liver, spleen, cardiac muscle, and kidneys. Additionally, in mice and rats, they disturb glucose and lipid homeostasis. Moreover, TiO₂ nanoparticles primarily cause adverse reactions by inducing oxidative stress that leads to cell damage, inflammation, genotoxicity, and adverse immune responses. The form and level of destruction are strongly based on the physical and chemical properties of TiO₂ nanoparticles, which administer their reactivity and bioavailability. Studies give indications that TiO₂ NPs cause both DNA strand breaks and chromosomal damages. The effects of genotoxicity do not depend only on particle surface changes, size, and exposure route, but also relies on the duration of exposure. Most of these effects may be because of a very high dose of TiO₂ NPs. Despite increased production and use, epidemiological data for TiO₂ NPs is still missing. This review discusses previous research regarding the impact of TiO₂ NP toxicity on human health and highlights areas that require further understanding in concern of jeopardy to the human population. This review is important to point out areas where extensive research is needed; thus, their possible impact on individual health should be investigated in more details.

Multiple metals exposure and arterial stiffness: A panel study in China

Chronic exposure to metals has been linked to arterial stiffness. However, the effects of exposure to multiple metals on arterial stiffness have rarely been studied. We aimed to investigate the associations of 23 urinary metals with arterial stiffness in a panel study of 127 Chinese adults with 3 repeated visits. Urinary metal measurements were conducted once a day for 4 consecutive days of each visit. Brachial-ankle pulse wave velocity (baPWV) and ankle-brachial index (ABI) were measured in health examinations during each visit. Linear mixed models, least absolute shrinkage and selection operator (LASSO) penalized regression models, and generalized linear models were applied to investigate the associations between multiple metals and arterial stiffness parameters. The odds ratio (OR) for peripheral arterial disease (PAD) was examined using generalized estimating equations. After adjusting for potential covariates and other metals, we found ABI reductions were associated with one unit increase in 4-day average (lag 0-3 day) of ln-transformed urinary titanium (Ti) [β = -0.019 (SE = 0.010), P = 0.045], and cobalt (Co) [β = -0.012 (SE = 0.006), P = 0.048], whereas no significant associations were observed for baPWV at different lag days. Stratified analyses revealed that urinary Ti was inversely related to ABI among never-smokers or in the winter. In addition, the current day or 4-day average of ln-transformed urinary Ti was associated with an increased OR of 1.94 (95% CI: 1.28, 2.92) or 3.30 (95% CI: 1.64, 6.63) for PAD, respectively. Our study showed significant associations of exposure to Ti and Co with arterial stiffness. Particularly, Ti may increase the risk of PAD.

Safe Nanoparticles: Are We There Yet?

The field of nanotechnology has grown over the last two decades and made the transition from the benchtop to applied technologies. Nanoscale-sized particles, or nanoparticles, have emerged as promising tools with broad applications in drug delivery, diagnostics, cosmetics and several other biological and non-biological areas. These advances lead to questions about nanoparticle safety. Despite considerable efforts to understand the toxicity and safety of these nanoparticles, many of these questions are not yet fully answered. Nevertheless, these efforts have identified several approaches to minimize and prevent nanoparticle toxicity to promote safer nanotechnology. This review summarizes our current knowledge on nanoparticles, their toxic effects, their interactions with mammalian cells and finally current approaches to minimizing their toxicity.

Possible Adverse Effects of Food Additive E171 (Titanium Dioxide) Related to Particle Specific Human Toxicity, Including the Immune System

Titanium dioxide (TiO₂) is used as a food additive (E171) and can be found in sauces, icings, and chewing gums, as well as in personal care products such as toothpaste and pharmaceutical tablets. Along with the ubiquitous presence of TiO₂ and recent insights into its potentially hazardous properties, there are concerns about its application in commercially available products. Especially the nano-sized particle fraction (<100 nm) of TiO₂ warrants a more detailed evaluation of potential adverse health effects after ingestion. A workshop organized by the Dutch Office for Risk Assessment and Research (BuRO) identified uncertainties and knowledge gaps regarding the gastrointestinal absorption of TiO₂, its distribution, the potential for accumulation, and induction of adverse health effects such as inflammation, DNA damage, and tumor promotion. This review aims to identify and evaluate recent toxicological studies on food-grade TiO₂ and nano-sized TiO₂ in ex-vivo, in-vitro, and in-vivo experiments along the gastrointestinal route, and to postulate an Adverse Outcome Pathway (AOP) following ingestion. Additionally, this review summarizes recommendations and outcomes of the expert meeting held by the BuRO in 2018, in order to contribute to the hazard identification and risk assessment process of ingested TiO₂.

Nanomedicine: Photo-activated nanostructured titanium dioxide, as a promising anticancer agent

The multivariate condition of cancer disease has been approached in various ways, by the scientific community. Recent studies focus on individualized treatments, minimizing the undesirable consequences of the conventional methods, but the development of an alternative effective therapeutic scheme remains to be held. Nanomedicine could provide a solution, filling this gap, exploiting the unique properties of innovative nanostructured materials. Nanostructured titanium dioxide (TiO₂) has a variety of applications of daily routine and of advanced technology. Due to its biocompatibility, it has also a great number of biomedical applications. It is now clear that photo-excited TiO₂ nanoparticles, induce generation of pairs of electrons and holes which react with water and oxygen to yield reactive oxygen species (ROS) that have been proven to damage cancer cells, triggering controlled cellular processes. The aim of this review is to provide insights into the field of nanomedicine and particularly into the wide context of TiO₂-NP-mediated anticancer effect, shedding light on the achievements of nanotechnology and proposing this nanostructured material as a promising anticancer photosensitizer.

The Impact of Nanoparticles on Innate Immune Activation by Live Bacteria

The innate immune system evolved to detect and react against potential dangers such as bacteria, viruses, and environmental particles. The advent of modern technology has exposed innate immune cells, such as monocytes, macrophages, and dendritic cells, to a relatively novel type of particulate matter, i.e., engineered nanoparticles. Nanoparticles are not inherently pathogenic, and yet cases have been described in which specific nanoparticle types can either induce innate/inflammatory responses or modulate the activity of activated innate cells. Many of these studies rely upon activation by agonists of toll-like receptors, such as lipopolysaccharide or peptidoglycan, instead of the more realistic stimulation by whole live organisms. In this review we examine and discuss the effects of nanoparticles on innate immune cells activated by live bacteria. We focus in particular on how nanoparticles may interfere with bacterial processes in the context of innate activation, and confine our scope to the effects due to particles themselves, rather than to molecules adsorbed on the particle surface. Finally, we examine the long-lasting consequences of coexposure to nanoparticles and bacteria, in terms of potential microbiome alterations and innate immune memory, and address nanoparticle-based vaccine strategies against bacterial infection.

The toxic influence of silver and titanium dioxide nanoparticles on cultured ovarian granulosa cells

The application of metal nanoparticles in modern society is growing, but there is insufficient data concerning their influence on reproductive processes and comparison of their biological activity. The present experiments aimed to compare the effects of silver and titanium dioxide nanoparticles (AgNPs and TiO2NPs) on ovarian granulosa cell functions. AgNPs and TiO2NPs were added to culture of porcine granulosa cells at doses 0, 0.01, 0.1, 1 or 10 μg/mL. The mRNAs for proliferating cell nuclear antigen (PCNA), cyclin B1, bax and caspase 3 were quantified by RT-PCR; release of progesterone was analyzed by ELISA. It was shown that both AgNPs and TiO2NPs significantly reduced all the measured parameters. ED₅₀ of the inhibitory influence of AgNPs on the main ovarian cell parameters was higher than ED₅₀ of TiO2NPs. The ability of AgNPs and TiO2NPs to suppress ovarian granulosa cell functions should be taken into account by their application.

Preparation and characterization of titanium dioxide nanoparticles and in vitro investigation of their cytotoxicity and antibacterial activity against Staphylococcus aureus and Escherichia coli

Titanium dioxide nanoparticles (TiO₂ NPs) are photo-active metallic nanoparticles becoming promising agents in modern biomedical applications. Herein, a novel process for the synthesis of TiO₂ NPs with high stability was developed by a sol-gel process and to investigate their cytotoxicity and antibacterial activity. Numerous experiments have been performed to confirm the morphologies, compositions, and physicochemical properties of prepared TiO₂ NPs, such as field emission scanning electron microscopy, dynamic light scattering, Zeta potential, Fourier transform infrared spectroscopy and X-ray diffraction. MTT assay was applied to assess the cytotoxicity of the prepared nanoparticles. The results indicate that the synthesized nanoparticles' diameter is about 68 nm and contains the anatase phase, in the range of 2θ from 25 to 80 °C. The hydrodynamic radius of nanoparticles is about 140.4 nm, and the zeta potential of nanoparticles is about -44.6 mV. The MTT results have not shown any toxicity; the antibacterial inhibitory effect of TiO₂ NPs at 200 mg/mL concentrations exhibited superior antibacterial activity at 15.9 ± 0.1, 14.0 ± 0.1 against Staphylococcus aureus and Escherichia coli, respectively. In conclusion, colloidal solutions with high stability were successfully synthesized, contributing to decreased dimensions and increased antibacterial properties.

Markers of oxidative stress after three days of nanoTiO2 sunscreen use in humans: a pilot study

OBJECTIVE

Recent experimental studies point to a high reactivity of nanoparticles and the potential of sunscreens to penetrate the skin. We measured 20 markers of oxidative stress and inflammation to find out whether skin exposure to nanoTiO₂ sunscreen may elevate the level of the markers in exhaled breath condensate (EBC) and urine of exposed subjects, as was suggested by our earlier study.

METHODS

Six volunteers (3 males and 3 females), with a mean age of 48.0 ± 6.7 years, used commercial sunscreen for three days continuously. The first samples were collected before the test. The second samples were collected on day 4, before the sunscreen was washed off, and the third samples on day 11. The following biomarkers were measured: malondialdehyde, 4-hydroxy-trans-hexenal, 4-hydroxy-trans-nonenal, aldehydes C6-C12, 8-isoProstaglandin F2α, o-tyrosine, 3-chlorotyrosine, 3-nitrotyrosine, 8-hydroxy-2-deoxyguanosine, 8-hydroxyguanosine, 5-hydroxymethyl uracil, and leukotrienes B4, C4, D4, and E4, using liquid chromatography-electrospray ionisation-tandem mass spectrometry.

RESULTS

In the urine, 4-hydroxy-trans-hexenal was significantly higher in post-exposure sample 2, and the same trend was seen in all urinary markers. In EBC, no difference was seen between the mean values of 20 post-test markers as compared with pre-test samples.

CONCLUSION

This study suggests potential side effects of the sunscreen - borderline elevation of markers of oxidative stress/inflammation - which may relate to the absorption of the nanoTiO₂, and the non-significant difference may be explained by the small number of subjects. The effect was not seen in EBC, where nanoTiO₂ was not found. A larger study is needed, as according to our previous study, the beneficial effect of the sunscreen to suppress oxidative stress caused by UV radiation may be questioned.

Hepatotoxicity induced by nanomaterials: mechanisms and in vitro models

The unique physicochemical properties of materials at nanoscale have opened a plethora of opportunities for applications in the pharmaceutical and medical field, but also in consumer products from food and cosmetics industries. As a consequence, daily human exposure to nanomaterials through distinct routes is considerable and, therefore, may raise health concerns. Many nanomaterials have been described to accumulate and induce adversity in the liver. Among these, silica and some types of metallic nanoparticles are the most broadly used in consumer products and, therefore, the most studied and reported. The reviewed literature was collected from PubMed.gov during the month of March 2020 using the search words "nanomaterials induced hepatotoxicity", which yielded 181 papers. This present paper reviews the hepatotoxic effects of nanomaterials described in in vitro and in vivo studies, with emphasis on the underlying mechanisms. The induction of oxidative stress and inflammation are the manifestations of toxicity most frequently reported following exposure of cells or animal models to different nanomaterials. Furthermore, the available in vitro models for the evaluation of the hepatotoxic effects of nanomaterials are discussed, highlighting the continuous interest in the development of more advanced and reliable in vitro models for nanotoxicology.

From nano to micrometer size particles - A characterization of airborne cement particles during construction activities

Although, photocatalytic cement contains nanosized TiO₂, a possibly carcinogen, no exposure assessments exist for construction workers. We characterized airborne nanoparticle exposures during construction activities simulated in an exposure chamber. We collected some construction site samples for regular cement in Switzerland and Thailand for comparison. Airborne nanoparticles were characterized using scanning mobility particle sizer (SMPS), portable aerosol spectrometer (PAS), diffusion size classifier (DiSCmini), transmission electron microscopy (TEM), scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray diffraction. Bagged photocatalytic cement had 2.0 wt% (GSD ± 0.55) TiO₂, while TiO₂ in aerosols reached 16.5 wt% (GSD ± 1.72) during bag emptying and 9.7 wt% (GSD ± 1.36) after sweeping. The airborne photocatalytic cement particles were far smaller (approximately 50 nm) compared to regular cement. Cutting blocks made from photocatalytic cement or concrete, resulted in similar amounts of airborne nano TiO₂ (2.0 wt% GSD ± 0.57) particles as in bagged material. Both photocatalytic and regular cement had a geometric mean diameter (GMD) < 3.5 μm. Main exposures for Thai workers were during sweeping and Swiss workers during drilling and polishing cement blocks. Targeted nanoparticle exposure assessments are needed as a significantly greater exposure to nano TiO₂ were observed than what would have been predicted from the material's nano- TiO₂ contents.

Quantification of titanium dioxide nanoparticles in human urine by single-particle ICP-MS

The increasing use of titanium dioxide nanoparticles in daily use consumer products such as cosmetics, personal care products, food additives, and even medicine has led to growing concerns regarding human safety. It would be ideal to track exposure to this emerging nanopollutant, for example through bioassays, however, so far nanoparticle assessment in biological matrices such as urine remains challenging. The lack of data is mainly due to the limitations of the current metrology, but also to the low expected concentration in human samples. In this study, a quantification method for titanium dioxide nanoparticles in urine has been developed and validated following the ISO/CEI 17025:2017 guidelines. The detection limit for titanium dioxide nanoparticle mass concentration by single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was 0.05 ng mL^-1. The particle size limit was determined using three different approaches, with the highest calculated limit value approaching 50 nm. Repeatability and reproducibility of 14% and 18% respectively were achieved for particle mass concentration, and 6% for both parameters for particle size determination. Method trueness and recovery were 98% and 84%, respectively.

Are Titania Photocatalysts and Titanium Implants Safe? Review on the Toxicity of Titanium Compounds

Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.

Insights and controversies on sunscreen safety

Although sunlight provides several benefits, ultraviolet (UV) radiation plays an important role in the development of various skin damages such as erythema, photoaging, and photocarcinogenesis. Despite cells having endogenous defense systems, damaged DNA may not be efficiently repaired at chronic exposure. In this sense, it is necessary to use artificial defense strategies such as sunscreen formulations. UV filters should scatter, reflect, or absorb solar UV radiation in order to prevent direct or indirect DNA lesions. However, the safety of UV filters is a matter of concern due to several controversies reported in literature, such as endocrine alterations, allergies, increased oxidative stress, phototoxic events, among others. Despite these controversies, the way in which sunscreens are tested is essential to ensure safety. Sunscreen regulation includes mandatory test for phototoxicity, but photogenotoxicity testing is not recommended as a part of the standard photosafety testing program. Although available photobiological tests are still the first approach to assess photosafety, they are limited. Some existing tests do not always provide reliable results, mainly due to limitations regarding the nature of the assessed phototoxic effect, cell UV sensitivity, and the irradiation protocols. These aspects bring queries regarding the safety of sunscreen wide use and suggest the demand for the development of robust and efficient in vitro screening tests to overcome the existing limitations. In this way, Saccharomyces cerevisiae has stood out as a promising model to fill the gaps in photobiology and to complete the mandatory tests enabling a more extensive and robust photosafety assessment.

Food-Grade TiO2 Particles Generate Intracellular Superoxide and Alter Epigenetic Modifiers in Human Lung Cells

Titanium dioxide (TiO₂) particles are a common ingredient in food, providing the bright white color for many candies, gums, and frostings. While ingestion of these materials has been examined previously, few studies have examined the effect of these particles on lung cells. Inhalation is an important exposure pathway for workers processing these foods and, more recently, home users who purchase these particles directly. We examine the response of lung cells to food-grade TiO₂ particles using a combination of fluorescence microscopy and RT-PCR. These experiments show that TiO₂ particles generate intracellular reactive oxygen species, specifically superoxide, and alter expression of two epigenetic modifiers, histone deacetylase 9 (HDAC9) and HDAC10. We use a protein corona formed from superoxide dismutase (SOD), an enzyme that scavenges superoxide, to probe the relationship between TiO₂ particles and superoxide generation. These experiments show that low, non-cytotoxic, concentrations of food-grade TiO₂ particles lead to cellular responses, including altering two enzymes responsible for epigenetic modifications. This production of superoxide and change in epigenetic modifiers could affect human health following inhalation. We expect this research will motivate future in vivo experiments examining the pulmonary response to food-grade TiO₂ particles.

Titanium Dioxide Nanoparticles Induced HeLa Cell Necrosis under UVA Radiation through the ROS-mPTP Pathway

Titanium dioxide nanoparticles (nano-TiO₂), as a common nanomaterial, are widely used in water purification, paint, skincare and sunscreens. Its safety has always been a concern. Prior studies have shown that ultraviolet A (UVA) can exacerbate the toxicity of nano-TiO₂, including inducing cell apoptosis, changing glycosylation levels, arresting cell cycle, inhibiting tumor cell and bacterial growth. However, whether the combination of UVA and nano-TiO₂ cause cell necrosis and its mechanism are still rarely reported. In this study, we investigated the cytotoxicity and phototoxicity of mixture crystalline nano-TiO₂ (25% rutile and 75% anatase, 21 nm) under UVA irradiation in HeLa cells. Our results showed that the abnormal membrane integrity and the ultrastructure of HeLa cells, together with the decreased viability induced by nano-TiO₂ under UVA irradiation, were due to cell necrosis rather than caspase-dependent apoptosis. Furthermore, nano-TiO₂ and UVA generated the reactive oxygen species (ROS) and caused the mitochondrial permeability transition pore (mPTP) of HeLa cells to abnormally open. Cell viability was significantly increased after adding vitamin C (VC) or cyclosporin A (CsA) individually to inhibit ROS and mPTP. Clearance of ROS could not only impede the opening of mPTP but also reduce the rate of cell necrosis. The results suggest the possible mechanism of HeLa cell necrosis caused by nano-TiO₂ under UVA irradiation through the ROS-mPTP pathway.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

A key moment for TiO2: Prenatal exposure to TiO2 nanoparticles may inhibit the development of offspring

Applications of TiO₂ nanoparticles (NPs) in food, personal care products and industries pose risks on human health, particularly on vulnerable populations including pregnant women and infants. Fetus, deficient in mature defense system, is more susceptible to NPs. Publications on the developmental toxicity of TiO₂ NPs on the maternal-exposed progeny have emerged. This review presents the main exposure routes of TiO₂ NPs during pregnancy, including skin penetration, ingestion and inhalation, followed by transport of TiO₂ NPs to the placenta. Accumulation of TiO₂ NPs in placenta may cause dysfunction in nutrient transfer. TiO₂ NPs can be even transported to the fetus and generate toxicities, such as impairments of nervous and reproductive system, and failure in lung and cardiovascular development. The toxicities rely on the crystalline phase and concentrations, and the main mechanisms include the accumulation of excessive reactive oxygen species, DNA damage, and over-activation of signaling pathways such as MAPK which impairs neurotransmission. Finally, this review remarks on the significance for identifying TiO₂ NPs dosage safe for both mother and fetus, and particular attention should be paid at TiO₂ NPs concentrations safe for mother but toxic to fetus. Importantly, research on the epigenetic trans-generational inheritance of TiO₂ NPs is urgently needed to provide insights for deciding the prospects of TiO₂ NPs applications.