Effects of titanium dioxide nanoparticles in human gastric epithelial cells in vitro

In Vitro Genotoxicity Evaluation of PAHs in Mixtures Using Experimental Design

Settled dusts are sinks for environmental pollutants, including Polycyclic Aromatic Hydrocarbons (PAHs) that are ubiquitous, persistent, and carcinogenic. To assess their toxicity in mixtures, Toxic Equivalent Factors (TEFs) are routinely used and based on the hypothesis of additive effects, although PAH interactions may occur and remain an open issue. This study investigated genotoxic binary interaction effects for six PAHs in mixtures using two in vitro assays and estimated Genotoxic Equivalent Factors (GEFs) to roughly predict the genotoxicity of PAH in mixtures. The Design of the Experiment approach was used with the micronucleus assay for cytostasis and micronuclei frequency and the alkaline comet assay for DNA damage. GEFs were determined for each PAH independently and in a mixture. For the cytostasis endpoint, no PAHs interaction was noted. BbF and BaP had a synergistic effect on DNA damage. All the PAH interacted between them regarding chromosomal damage. Although the calculated GEFs were similar to the TEFs, the latter may underestimate the genotoxic potential of a PAH mixture. GEFs calculated for PAH alone were lower than GEFs for PAHs in mixtures; thus, mixtures induce greater DNA/chromosomal damage than expected. This research helps to advance the challenging issue of contaminant mixtures' effects on human health.

Ameliorative effect of biosynthesized titanium dioxide nanoparticles using garlic extract on the body weight and developmental toxicity of liver in albino rats compared with chemically synthesized nanoparticles

The application of metallic nanoparticles poses risks to human and animal health. Titanium dioxide nanoparticles (TiO₂NPs) are the most commonly synthesized metallic oxides in the world. Exposure to TiO₂NPs can cause toxicity in the target organisms. This study aimed to evaluate the effects of green and chemical TiO₂NPs on maternal and embryo-fetal livers. Green TiO₂NPs using garlic extract (GTiO₂NPs) and chemical TiO₂NPs (CHTiO₂NPs) were synthesized and characterized by x-ray powder diffraction and high-resolution transmission electron microscopy. The cytotoxicity of both chemical and green TiO₂NPs was determined against HepG₂ cell lines. Fifty pregnant female Albino rats were equally and randomly divided into five groups. Group 1 was kept as a control. Groups 2 and 3 were orally treated with 100 and 300 mg/kg body weight of CHTiO₂NPs, respectively. Groups 4 and 5 were orally treated with 100 and 300 mg/kg of GTiO₂NPs, respectively, from day 6 to 19 of gestation. All dams were euthanized on gestation day 20. All live fetuses were weighed and euthanized. Blood and tissue samples were collected for biochemical, histopathological, and Bax-immunohistochemical expression analyses. Our results indicated that garlic could be used as a reducing agent for the synthesis of TiO₂NPs, and the produced NPs have no toxic effect against HepG₂ cells compared with CHTiO₂NPs. The maternal and fetal bodyweights were greatly reduced among the chemically TiO₂NPs induced animals. The mean serum level of AST and ALT activities and the total protein level significantly increased when TiO₂NPs were administered at high doses. Histologically, the CHTiO₂NPs-treated groups revealed vacuolated and necrotized hepatocytes with congested and dilated blood vessels in the fetal and maternal livers. The immunohistochemistry revealed distinct positive staining of Bax expressed in the hepatocytes. Nevertheless, the biosynthesis of TiO₂NPs using garlic extract had a minimal effect on the normal architecture of the liver. It could be concluded that the bioactivity of TiO₂NPs can be modified by green synthesis using garlic extract. Compared to the CHTiO₂NPs, the exposure to GTiO₂NPs showed reduced liver damage in maternal and embryo-fetal rats.

Adverse Outcome Pathways Associated with the Ingestion of Titanium Dioxide Nanoparticles-A Systematic Review

Titanium dioxide nanoparticles (TiO₂-NPs) are widely used, and humans are exposed through food (E171), cosmetics (e.g., toothpaste), and pharmaceuticals. The oral and gastrointestinal (GIT) tract are the first contact sites, but it may be systemically distributed. However, a robust adverse outcome pathway (AOP) has not been developed upon GIT exposure to TiO₂-NPs. The aim of this review was to provide an integrative analysis of the published data on cellular and molecular mechanisms triggered after the ingestion of TiO₂-NPs, proposing plausible AOPs that may drive policy decisions. A systematic review according to Prisma Methodology was performed in three databases of peer-reviewed literature: Pubmed, Scopus, and Web of Science. A total of 787 records were identified, screened in title/abstract, being 185 used for data extraction. The main endpoints identified were oxidative stress, cytotoxicity/apoptosis/cell death, inflammation, cellular and systemic uptake, genotoxicity, and carcinogenicity. From the results, AOPs were proposed where colorectal cancer, liver injury, reproductive toxicity, cardiac and kidney damage, as well as hematological effects stand out as possible adverse outcomes. The recent transgenerational studies also point to concerns with regard to population effects. Overall, the findings further support a limitation of the use of TiO₂-NPs in food, announced by the European Food Safety Authority (EFSA).

A review of research on the impact of E171/TiO2 NPs on the digestive tract

Nanotechnology utilises particles of between 1 and 100 nm in size. In recent years, it has enjoyed widespread application in a variety of areas. However, this has also raised increasing concerns regarding the effects that the use of nanoparticles may have on human health. The nanoparticles of titanium dioxide (TiO₂ NPs) are among the most promising nanomaterials and have already found wide use in cosmetics, medicine and, the food industry. A nano-sized (diameter < 100 nm) fraction of TiO₂ is present, at a certain percentage, in the E171 ( in the EU) pigment commonly used as an additive in food, whose presence raises particular concerns in terms of its potential negative health impact. The consumption of E171 food additive is increasingly associated with disorders of the intestinal barrier, including intestinal dysbiosis. It may disrupt the normal functions of the gastrointestinal tract (GIT) including: enzymatic digestion of primary nutrients (lipids, proteins, or carbohydrates). The aim of this review is to provide a comprehensive and reliable overview of studies conducted in recent years in terms of the substance's potentially negative impact on human and animal alimentary systems.

Functionalized Titanium Nanoparticles Induce Oxidative Stress and Cell Death in Human Skin Cells

Purpose

Methods

Results

Conclusion

Advances in genotoxicity of titanium dioxide nanoparticles in vivo and in vitro

Titanium dioxide nanoparticles (TiO₂ NPs) are currently one of the most widely used nanomaterials. Due to an increasing scope of applications, the exposure of humans to TiO₂ NP is inevitable, such as entering the body through the mouth with food additives or drugs, invading the damaged skin with cosmetics, and entering the body through the respiratory tract during the process of production and handling. Compared with TiO₂ coarse particles, TiO₂ NPs have stronger conductivity, reaction activity, photocatalysis, and permeability, which may lead to greater toxicity to organisms. Given that TiO₂ was classified as a category 2B carcinogen (possibly carcinogenic to humans), the genotoxicity of TiO₂ NPs has become the focus of attention. There have been a series of previous studies investigating the potential genotoxicity of TiO₂ NPs, but the existing research results are still controversial and difficult to conclude. More than half of studies have shown that TiO₂ NPs can cause genotoxicity, suggesting that TiO₂ NPs are likely to be genotoxic to humans. And the genotoxicity of TiO₂ NPs is closely related to the exposure concentration, mode and time, and experimental cells/animals as well as its physicochemical properties (crystal type, size, and shape). This review summarized the latest research progress of related genotoxic effects through in vivo studies and in vitro cell tests, hoping to provide ideas for the evaluation of TiO₂ NPs genotoxicity.

Patch test-relevant concentrations of metal salts cause localized cytotoxicity, including apoptosis, in skin ex vivo

Background

Metal alloys containing contact sensitizers (nickel, palladium, titanium) are extensively used in medical devices, in particular dentistry and orthopaedic surgery. The skin patch test is used to test for metal allergy.

Objective

To determine whether metal salts, when applied to freshly excised skin at patch test–relevant concentrations and using a method which mimics skin patch testing, cause in changes in the epidermis and dermis.

Methods

Tissue histology, apoptosis, metabolic activity, and inflammatory cytokine release were determined for two nickel salts, two palladium salts, and four titanium salts.

Results

Patch test–relevant concentrations of all metal salts caused localized cytotoxicity. This was observed as epidermis separation at the basement membrane zone, formation of vacuoles, apoptotic nuclei, decreased metabolic activity, and (pro)inflammatory cytokine release. Nickel(II) sulfate hexahydrate, nickel(II) chloride hexahydrate, titanium(IV) bis(ammonium lactato)dihydroxide, and calcium titanate were highly cytotoxic. Palladium(II) chloride, sodium tetrachloropalladate(II), titanium(IV) isopropoxide, and titanium(IV) dioxide showed mild cytotoxicity.

Conclusion

The patch test in itself may be damaging to the skin of the patient being tested. These results need further verification with biopsies obtained during clinical patch testing. The future challenge is to remain above the elicitation threshold at noncytotoxic metal concentrations.

Molecular mechanism of mice gastric oxidative damage induced by nanoparticulate titanium dioxide

Background

Nanoparticulate titanium dioxide (Nano-TiO₂) has been widely used in food industry, and it has been demonstrated to have adverse effects on mice and human stomach, but its mechanism is rarely concerned. The aim of this study is to determine the effects of nano-TiO₂ on the stomach and confirm the role of oxidative stress and apoptosis in the mice gastric damage caused by nano-TiO₂, as well as its molecular mechanisms.

Methods

Mice were continuously exposed to nano-TiO₂ with 1.25, 2.5 and 5 mg/kg bw by intragastric administration for 9 months in the present study. The ultrastructure, levels of reactive oxygen species (ROS) and peroxides, activities of antioxidant enzymes and mitochondria-related enzymes, ATP contents as well as apoptosis-related factors expression in mice stomach were examined.

Results

Oxidative stress, apoptosis and nano-TiO₂ aggregation were found in gastric mucosal smooth muscle cells after nano-TiO₂ exposure. Nano-TiO₂ exposure also resulted in the over-production of ROS and peroxides, decrease of ATP production and activities of antioxidant enzymes and mitochondria-related ATPases, upregulation of apoptosis-related factors including γH2AX, Cyt c, caspase 3, and p-JNK expression, and down-regulation of Bcl-2 expression in mice stomach.

Conclusions

The gastric toxicity of mice induced by chronic exposure to low dose nano-TiO₂ may be associated with oxidative stress and mitochondria-mediated apoptosis in mice.

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.

Investigating the relationship between occupational exposure to nanomaterials and symptoms of nanotechnology companies' employees

PURPOSE

The increasing use of nanomaterials in academic and industrial environments has raised concerns about the potential effects of these materials on human and the environment. Researches have shown that occupational exposure to nanomaterials can affect employees' health. Many companies are active in the field of nanotechnology in Iran. Therefore, this study was designed and conducted to investigate the relationship between the symptoms of these companies' employees and exposure to nanomaterials.

METHODS

The study was conducted among employees of 52 nanotechnology companies in Tehran. For this study, the employees of these companies were categorized in two groups: "exposed" and "non-exposed" to nanomaterials. Data collection tools included the NanoTool method form and a nonspecific symptom questionnaire designed and validated by a team of 19 experts in various fields. Finally, data were analyzed using SPSS.22 software.

RESULTS

The results showed that the frequency of cutaneous (such as roughness, itching and redness), respiratory (such as cough, sneezing, and burning throat) and ocular (such as burning, itching and redness) symptoms were higher among the exposed workers to nanomaterials. Examination of the correlation between these symptoms in the two studied groups showed that symptoms with high frequency have a significant relationship with exposure to nanomaterials.

CONCLUSIONS

Given the high prevalence of some symptoms among the employees of the studied companies and their association with exposure to nanomaterials, it seems necessary to take control measures to reduce the exposure of employees to nanomaterials and consequently reduce the Investigated symptoms.

TiO2 genotoxicity: An update of the results published over the last six years

TiO₂ particles are broadly used in daily products, including cosmetics for their UV-absorbing property, food for their white colouring property, water and air purification systems, self-cleaning surfaces and photoconversion electrical devices for their photocatalytic properties. The toxicity of TiO₂ nano- and microparticles has been studied for decades, and part of this investigation has been dedicated to the identification of their potential impact on DNA, i.e., their genotoxicity. This review summarizes data retrieved from their genotoxicity testing during the past 6 years, encompassing both in vitro and in vivo studies, mostly performed on lung and intestinal models. It shows that TiO₂ particles, both nano- and micro-sized, produce genotoxic damage to a variety of cell types, even at low, realistic doses.

Titanium Dioxide Nanoparticles in Food and Personal Care Products-What Do We Know about Their Safety?

Titanium dioxide (TiO2) is a material of diverse applications commonly used as a food additive or cosmetic ingredient. Its prevalence in products of everyday use, especially in nanosize, raises concerns about safety. Current findings on the safety of titanium dioxide nanoparticles (TiO2 NPs) used as a food additive or a sunscreen compound are reviewed and systematized in this publication. Although some studies state that TiO2 NPs are not harmful to humans through ingestion or via dermal exposure, there is a considerable number of data that demonstrated their toxic effects in animal models. The final agreement on the safety of this nanomaterial has not yet been reached among researchers. There is also a lack of official, standardized guidelines for thorough characterization of TiO2 NPs in food and cosmetic products, provided by international authorities. Recent advances in the application of 'green-synthesized' TiO2 NPs, as well as comparative studies of the properties of 'biogenic' and 'traditional' nanoparticles, are presented. To conclude, perspectives and directions for further studies on the toxicity of TiO2 NPs are proposed.

Reactive Oxygen Species-Related Nanoparticle Toxicity in the Biomedical Field

The unique physicochemical characteristics of nanoparticles have recently gained increasing attention in a diverse set of applications, particularly in the biomedical field. However, concerns about the potential toxicological effects of nanoparticles remain, as they have a higher tendency to generate excessive amounts of reactive oxygen species (ROS). Due to the strong oxidation potential, the excess ROS induced by nanoparticles can result in the damage of biomolecules and organelle structures and lead to protein oxidative carbonylation, lipid peroxidation, DNA/RNA breakage, and membrane structure destruction, which further cause necrosis, apoptosis, or even mutagenesis. This review aims to give a summary of the mechanisms and responsible for ROS generation by nanoparticles at the cellular level and provide insights into the mechanics of ROS-mediated biotoxicity. We summarize the literature on nanoparticle toxicity and suggest strategies to optimize nanoparticles for biomedical applications.

TiO2 nanoparticles enhance the chemotherapeutic effects of 5-fluorouracil in human AGS gastric cancer cells via autophagy blockade

AIMS

Nanoparticles (NPs)-based drugs have been recently introduced to improve the efficacy of current therapeutic strategies for the treatment of cancer; however, the molecular mechanisms by which a NP interacts with cellular systems still need to be delineated. Here, we utilize the autophagic potential of TiO2 NPs for improving chemotherapeutic effects of 5-fluorouracil (5-FU) in human AGS gastric cells.

MATERIALS AND METHODS

Cell growth and viability were determined by trypan blue exclusion test and MTT assay, respectively. Vesicular organelles formation was evaluated by acridine orange staining of cells. Cell cycle and apoptosis were monitored by flow cytometry. Reactive oxygen species (ROS) level were measured by DCHF-DA staining. Autophagy was examined by q-PCR and western blotting. Molecular docking was used for studying NP interaction with autophagic proteins.

KEY FINDINGS

TiO2 NPs increase ROS production, impair lysosomal function and subsequently block autophagy flux in AGS cells. In addition, the autophagy blockade induced by non-toxic concentrations of TiO2 NPs (1 μg/ml) can promote cytotoxic and apoptotic effects of 5-FU in AGS cells.

SIGNIFICANCE

These results confirm the beneficial effects of TiO2 NPs in combination with chemotherapy in in vitro model of gastric cancer, which may pave the way to develop a possible solution to circumvent chemoresistance in cancer.

A unified in silico model based on perturbation theory for assessing the genotoxicity of metal oxide nanoparticles

Nanomaterials (NMs) are an ever-increasing field of interest, due to their wide range of applications in science and technology. However, despite providing solutions to many societal problems and challenges, NMs are associated with adverse effects with potential severe damages towards biological species and their ecosystems. Particularly, it has been confirmed that NMs may induce serious genotoxic effects on various biological targets. Given the difficulties of experimental assays for estimating the genotoxicity of many NMs on diverse biological targets, development of alternative methodologies is crucial to establish their level of safety. In silico modelling approaches, such as Quantitative Structure-Toxicity Relationships (QSTR), are now considered a promising solution for such purpose. In this work, a perturbation theory machine learning (PTML) based QSTR approach is proposed for predicting the genotoxicity of metal oxide NMs under various experimental assay conditions. The application of such perturbation approach to 6084 NM-NM pair cases, set up from 78 unique NMs, afforded a final PTML-QSTR model with an accuracy better than 96% for both training and test sets. This model was then used to predict the genotoxicity of some NMs not included in the modelling dataset. The results for this independent data set were in excellent agreement with the experimental ones. Overall, that thus suggests that the derived PTML-QSTR model is a reliable in silico tool to rapidly and cost-efficiently assess the genotoxicity of metal oxide NMs. Finally, and most importantly, the model provides important insights regarding the mechanism of the genotoxicity triggered by these NMs.

Assessing the risk of main activities of nanotechnology companies by the NanoTool method

Purpose. Nanotechnology can be considered one of the greatest developments over the past few decades. Despite many applications of nanomaterials in various fields, there are concerns about their effects on humans and the environment. Therefore, this study was conducted to assess the risk level of activities involving nanomaterials in nanotechnology companies in Tehran, Iran. Materials and methods. After identifying the main activities of 18 nanotechnology companies, these activities were assessed using the NanoTool method, which is a method for assessing risks of activities involving nanomaterials. Data were analyzed using SPSS version 22. Results. The results showed that in six activities (33.30%) the risk level was 4 (RL4), in eight activities (44.40%) the risk level was 3 (RL3) and four activities (22.30%) had risk level 2 (RL2). Also, it was found that 78.88% of the controls used by these companies were not enough to reduce the risks of nanomaterials and need to be upgraded. Conclusions. The high level of risk in the activities involving nanomaterials shows that there are serious problems regarding the safety of nanomaterials in the nanotechnology companies in Tehran, Iran.

Nanotechnologies in Food Science: Applications, Recent Trends, and Future Perspectives

Nanotechnology is a key advanced technology enabling contribution, development, and sustainable impact on food, medicine, and agriculture sectors. Nanomaterials have potential to lead qualitative and quantitative production of healthier, safer, and high-quality functional foods which are perishable or semi-perishable in nature. Nanotechnologies are superior than conventional food processing technologies with increased shelf life of food products, preventing contamination, and production of enhanced food quality. This comprehensive review on nanotechnologies for functional food development describes the current trends and future perspectives of advanced nanomaterials in food sector considering processing, packaging, security, and storage. Applications of nanotechnologies enhance the food bioavailability, taste, texture, and consistency, achieved through modification of particle size, possible cluster formation, and surface charge of food nanomaterials. In addition, the nanodelivery-mediated nutraceuticals, synergistic action of nanomaterials in food protection, and the application of nanosensors in smart food packaging for monitoring the quality of the stored foods and the common methods employed for assessing the impact of nanomaterials in biological systems are also discussed.

Genotoxicity Assessment of Nanomaterials: Recommendations on Best Practices, Assays, and Methods

Nanomaterials (NMs) present unique challenges in safety evaluation. An international working group, the Genetic Toxicology Technical Committee of the International Life Sciences Institute's Health and Environmental Sciences Institute, has addressed issues related to the genotoxicity assessment of NMs. A critical review of published data has been followed by recommendations on methods alterations and best practices for the standard genotoxicity assays: bacterial reverse mutation (Ames); in vitro mammalian assays for mutations, chromosomal aberrations, micronucleus induction, or DNA strand breaks (comet); and in vivo assays for genetic damage (micronucleus, comet and transgenic mutation assays). The analysis found a great diversity of tests and systems used for in vitro assays; many did not meet criteria for a valid test, and/or did not use validated cells and methods in the Organization for Economic Co-operation and Development Test Guidelines, and so these results could not be interpreted. In vivo assays were less common but better performed. It was not possible to develop conclusions on test system agreement, NM activity, or mechanism of action. However, the limited responses observed for most NMs were consistent with indirect genotoxic effects, rather than direct interaction of NMs with DNA. We propose a revised genotoxicity test battery for NMs that includes in vitro mammalian cell mutagenicity and clastogenicity assessments; in vivo assessments would be added only if warranted by information on specific organ exposure or sequestration of NMs. The bacterial assays are generally uninformative for NMs due to limited particle uptake and possible lack of mechanistic relevance, and are thus omitted in our recommended test battery for NM assessment. Recommendations include NM characterization in the test medium, verification of uptake into target cells, and limited assay-specific methods alterations to avoid interference with uptake or endpoint analysis. These recommendations are summarized in a Roadmap guideline for testing.

Hepatic and Renal Toxicity Induced by TiO2 Nanoparticles in Rats: A Morphological and Metabonomic Study

Titanium dioxide (TiO₂) nanoparticles (NPs) are produced abundantly and are frequently used as a white pigment in the manufacture of paints, foods, paper, and toothpaste. Despite the wide ranges of uses, there is a lack of information on the impact of NPs on animal and human health. In the present study, rats were exposed to different doses of TiO₂ nanoparticles and sacrificed, respectively, 4 days, 1 month, and 2 months after treatment. Dosage of TiO₂ in tissues was performed by ICP-AES and revealed an important accumulation of TiO₂ in the liver. The nanoparticles induced morphological and physiological alterations in liver and kidney. In the liver, these alterations mainly affect the hepatocytes located around the centrilobular veins. These cells were the site of an oxidative stress evidenced by immunocytochemical detection of 4-hydroxynonenal (4-HNE). Kupffer cells are also the site of an important oxidative stress following the massive internalization of TiO₂ nanoparticles. Enzymatic markers of liver and kidney functions (such as AST and uric acid) are also disrupted only in animals exposed to highest doses. The metabonomic approach allowed us to detect modifications in urine samples already detectable after 4 days in animals treated at the lowest dose. This metabonomic pattern testifies an oxidative stress as well as renal and hepatic alterations.

Bio-Effects of TiO2 Nanoparticles on Human Colorectal Cancer and Umbilical Vein Endothelial Cell Lines

Background: Due to the possible biomedical potential of nanoparticles, titanium dioxide nanoparticles (TiO2 NPs) have received great attention in cancer research. Although selectivity of cytotoxicity with TiO2 NPs in various cells is clinically significant comparisons of cancer and non-cancer cells have been limited. Therefore, we here studied exposure to TiO2 NPs in colorectal cancer cells (CRCs) and human umbilical vein endothelial cells (HUVECs). Methods: After characterization of TiO2 NPs, culture and treatment of cells (HCT116, HT29 and HUVEC), viability was assessed by MTT assay and in terms of morphological features. Acridine orange (AO) and propidium iodide (PI) assays were carried out to estimate the incidence of apoptosis. The RT-PCR method was also employed to evaluate the expression of P53, Bax, Bcl-2 and Caspase 3. Results: Exposure to increasing concentrations of TiO2 NPs enhanced overall cell survival of HCT116 cells and reduced the Bcl-2 and Caspase 3 expression while the ratio of Bax/Bcl-2 was down-regulated. TiO2 NPs at 400 and 50 μg/ml concentrations suppressed cell proliferation and induced apoptosis of HT29 cells and also up-regulated P53 and Bax at the mRNA level, enhanced the Bax/Bcl-2 ratio and eventually up-regulated Caspase 3 mRNA. Although, inhibition of cell proliferation in HUVECs was seen at 200 and 400 μg/ml TiO2 NPs, it was not marked. Conclusion: TiO2 NPs have selective bio-effects on exposed cells with dose- and cell-dependent influence on viability. Cell proliferation in HCT116 as a metastatic colorectal cancer cell line appeared to be stimulated via multiple signaling pathways, with promotion of apoptosis in less metastatic cells at 50 and 400 μg/ml concentrations. This was associated with elevated P53, Bax and Caspase 3 mRNA and reduced Bcl-2 expression. However, TiO2 NPs did not exert any apparent significant effects on HUVECs as hyperproliferative angiogenic cells.

Potentially harmful elements in house dust from Estarreja, Portugal: characterization and genotoxicity of the bioaccessible fraction

Due to their behavioral characteristics, young children are vulnerable to the ingestion of indoor dust, often contaminated with chemicals that are potentially harmful. Exposure to potentially harmful elements (PHEs) is currently exacerbated by their widespread use in several industrial, agricultural, domestic and technological applications. PHEs cause adverse health effects on immune and nervous systems and can lead to cancer development via genotoxic mechanisms. The present study is an integrated approach that aims at assessing the genotoxicity of bioaccessible PHEs following ingestion of contaminated house dust. A multidisciplinary methodology associating chemical characterization of five house dust samples, extraction of the bioaccessible PHEs in gastric extracts by the unified BARGE method, determination of the bioaccessible fraction and in vitro genotoxicity of gastric extracts in adenocarcinoma gastric human (AGS) cells was developed. The five gastric extracts induced dose-dependent genotoxicity in AGS cells. Copper (bioaccessible concentration up to 111 mg/kg) was probably the prevalent PHE inducing primary DNA damage (up to 5.1-fold increase in tail DNA at 0.53 g/l of gastric extract). Lead (bioaccessible concentration up to 245 mg/kg) was the most prevalent PHE inducing chromosome-damaging effects (r = 0.55; p < 0.001 for micronucleated cells induction). The association of principal component analysis and Spearman's correlations was decisive to understand the chromosome-damaging properties of the bioaccessible PHEs in AGS cells. This methodology could be used on a larger-scale study to provide useful information for science-based decision-making in regulatory policies, and a better estimation of human exposure and associated health risks.

Nanoparticles of Titanium and Zinc Oxides as Novel Agents in Tumor Treatment: a Review

Cancer has become a global problem. On all continents, a great number of people are diagnosed with this disease. In spite of the progress in medical care, cancer still ends fatal for a great number of the ill, either as a result of a late diagnosis or due to inefficiency of therapies. The majority of the tumors are resistant to drugs. Thus, the search for new, more effective therapy methods continues. Recently, nanotechnology has been attributed with big expectations in respect of the cancer fight. That interdisciplinary field of science creates nanomaterials (NMs) and nanoparticles (NPs) that can be applied, e.g., in nanomedicine. NMs and NPs are perceived as very promising in cancer therapy since they can perform as drug carriers, as well as photo- or sonosensitizers (compounds that generate the formation of reactive oxygen species as a result of either electromagnetic radiation excitation with an adequate wavelength or ultrasound activation, respectively). Consequently, two new treatment modalities, the photodynamic therapy (PDT) and the sonodynamic therapy (SDT) have been created. The attachment of ligands or antibodies to NMs or to NPs improve their selective distribution into the targeted organ or cell; hence, the therapy effectiveness can be improved. An important advantage of the targeted tumor treatment is lowering the cyto- and genotoxicity of active substance towards healthy cells. Therefore, both PDT and SDT constitute a valuable alternative to chemo- or radiotherapy. The vital role in cancer eradication is attributed to two inorganic sensitizers in their nanosized scale: titanium dioxide and zinc oxide.

In vitro uptake and toxicity studies of metal nanoparticles and metal oxide nanoparticles in human HT29 cells

In this paper, we investigated the toxicological behavior of metal nanoparticles (gold, silver) and metal oxide nanoparticles (copper oxide, zinc oxide, titanium dioxide) in vitro in human colorectal adenocarcinoma cells (HT29). We analyzed the cellular uptake by ICP-MS and TEM, the influence on cell viability by MTT assay and trypan blue exclusion test, their effect on DNA damage and/or generation of oxidized bases by alkaline comet assay, and their potential to induce apoptosis by flow cytometry after 24-h nanoparticle treatment with concentrations between 2 and 10 µg/ml. We determined the amount of metal taken up by a single HT29 cell, ranging from 0.02 pg/cell up to 1.39 pg/cell. Cell viability assays showed a significantly decrease for metal oxide nanoparticles using trypan blue exclusion test and for all nanoparticles, except titanium dioxide, using MTT assay. Genotoxic effects after nanoparticle treatment were not observed for the tested concentrations. Apoptosis induction was significantly increased for silver nanoparticles (tested for two sizes) as well as for titanium dioxide and zinc oxide nanoparticles. Our results indicate potential health risks of oral NP uptake by food ingredients or food contamination, making further mechanistic investigations on cellular uptake and toxicity necessary.

Progress of in vivo studies on the systemic toxicities induced by titanium dioxide nanoparticles

Titanium dioxide nanoparticles (TiO2 NPs) are inorganic materials with a diameter of 1-100 nm. In recent years, TiO2 NPs have been used in a wide range of products, including food, toothpaste, cosmetics, medicine, paints and printing materials, due to their unique properties (high stability, anti-corrosion, and efficient photocatalysis). Following exposure via various routes including inhalation, injection, dermal deposition and gastrointestinal tract absorption, NPs can be found in various organs in the body potentially inducing toxic effects. Thus more attention to the safety of TiO2 NPs is necessary. Therefore, the present review aims to provide a comprehensive evaluation of the toxic effects induced by TiO2 NPs in the lung, liver, stomach, intestine, kidney, spleen, brain, hippocampus, heart, blood vessels, ovary and testis of mice and rats in in vivo experiments, and evaluate their potential toxic mechanisms. The findings will provide an important reference for human risk evaluation and management following TiO2 NP exposure.

Moving into advanced nanomaterials. Toxicity of rutile TiO2 nanoparticles immobilized in nanokaolin nanocomposites on HepG2 cell line

Immobilization of nanoparticles on inorganic supports has been recently developed, resulting in the creation of nanocomposites. Concerning titanium dioxide nanoparticles (TiO₂ NPs¹), these have already been developed in conjugation with clays, but so far there are no available toxicological studies on these nanocomposites. The present work intended to evaluate the hepatic toxicity of nanocomposites (C-TiO₂²), constituted by rutile TiO₂ NPs immobilized in nanokaolin (NK³) clay, and its individual components. These nanomaterials were analysed by means of FE-SEM⁴ and DLS⁵ analysis for physicochemical characterization. HepG2 cells were exposed to rutile TiO₂ NPs, NK clay and C-TiO₂ nanocomposite, in the presence and absence of serum for different exposure periods. Possible interferences with the methodological procedures were determined for MTT,⁶ neutral red uptake, alamar blue (AB), LDH,⁷ and comet assays, for all studied nanomaterials. Results showed that MTT, AB and alkaline comet assay were suitable for toxicity analysis of the present materials after slight modifications to the protocol. Significant decreases in cell viability were observed after exposure to all studied nanomaterials. Furthermore, an increase in HepG2 DNA damage was observed after shorter periods of exposure in the absence of serum proteins and longer periods of exposure in their presence. Although the immobilization of nanoparticles in micron-sized supports could, in theory, decrease the toxicity of single nanoparticles, the selection of a suitable support is essential. The present results suggest that NK clay is not the appropriate substrate to decrease TiO₂ NPs toxicity. Therefore, for future studies, it is critical to select a more appropriate substrate for the immobilization of TiO₂ NPs.

Toxicogenomics analysis of mouse lung responses following exposure to titanium dioxide nanomaterials reveal their disease potential at high doses

Titanium dioxide nanoparticles (TiO₂NPs) induce lung inflammation in experimental animals. In this study, we conducted a comprehensive toxicogenomic analysis of lung responses in mice exposed to six individual TiO₂NPs exhibiting different sizes (8, 20 and 300nm), crystalline structure (anatase, rutile or anatase/rutile) and surface modifications (hydrophobic or hydrophilic) to investigate whether the mechanisms leading to TiO₂NP-induced lung inflammation are property specific. A detailed histopathological analysis was conducted to investigate the long-term disease implications of acute exposure to TiO₂NPs. C57BL/6 mice were exposed to 18, 54, 162 or 486 µg of TiO₂NPs/mouse via single intratracheal instillation. Controls were exposed to dispersion medium only. Bronchoalveolar lavage fluid (BALF) and lung tissue were sampled on 1, 28 and 90 days post-exposure. Although all TiO₂NPs induced lung inflammation as measured by the neutrophil influx in BALF, rutile-type TiO₂NPs induced higher inflammation with the hydrophilic rutile TiO₂NP showing the maximum increase. Accordingly, the rutile TiO₂NPs induced higher number of differentially expressed genes. Histopathological analysis of lung sections on Day 90 post-exposure showed increased collagen staining and fibrosis-like changes following exposure to the rutile TiO₂NPs at the highest dose tested. Among the anatase, the smallest TiO₂NP of 8nm showed the maximum response. The anatase TiO₂NP of 300nm was the least responsive of all. The results suggest that the severity of lung inflammation is property specific; however, the underlying mechanisms (genes and pathways perturbed) leading to inflammation were the same for all particle types. While the particle size clearly influenced the overall acute lung responses, a combination of small size, crystalline structure and hydrophilic surface contributed to the long-term pathological effects observed at the highest dose (486 µg/mouse). Although the dose at which the pathological changes were observed is considered physiologically high, the study highlights the disease potential of certain TiO₂NPs of specific properties.

Trihalomethanes in liver pathology: Mitochondrial dysfunction and oxidative stress in the mouse

Trihalomethanes (THMs) are disinfection byproducts found in chlorinated water, and are associated with several different kinds of cancer in human populations and experimental animal models. Metabolism of THMs proceeds through enzymes such as GSTT1 and CYP2E1 and gives rise to reactive intermediates, which form the basis for their toxic activities. The aim of this study was to assess the mitochondrial dysfunction caused by THMs at low levels, and the resulting hepatic histological and biochemical changes in the mouse. Male ICR mice were administered with two THMs: dibromochloromethane (DBCM) and bromodichloromethane (BDCM); once daily, by gavage, to a total of four administrations. Animals were sacrificed four weeks after DBCM and BDCM administrations. Blood biochemistry was performed for alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bilirubin (TB), albumin (Alb), total protein (TP), creatinine, and urea. Animals exposed to DBCM and BDCM showed elevated ALT and TB levels (p < 0.05) as compared with controls. Histological analysis confirmed the presence of vacuolar degenerescence and a multifocal necrotizing hepatitis in 33% of animals (n = 2). Mitochondrial analysis showed that THMs reduced mitochondrial bioenergetic activity (succinate dehydrogenase (SQR), cytochrome c oxidase (COX), and ATP synthase) and increased oxidative stress (glutathione S-transferase (GST)) in hepatic tissues (p < 0.05). These results add detail to the current understanding of the mechanisms underlying THM-induced toxicity, supporting the role of mitochondrial dysfunction and oxidative stress in liver toxicity caused by DBCM and BDCM. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1009-1016, 2016.

Causes of genome instability: the effect of low dose chemical exposures in modern society

Genome instability is a prerequisite for the development of cancer. It occurs when genome maintenance systems fail to safeguard the genome's integrity, whether as a consequence of inherited defects or induced via exposure to environmental agents (chemicals, biological agents and radiation). Thus, genome instability can be defined as an enhanced tendency for the genome to acquire mutations; ranging from changes to the nucleotide sequence to chromosomal gain, rearrangements or loss. This review raises the hypothesis that in addition to known human carcinogens, exposure to low dose of other chemicals present in our modern society could contribute to carcinogenesis by indirectly affecting genome stability. The selected chemicals with their mechanisms of action proposed to indirectly contribute to genome instability are: heavy metals (DNA repair, epigenetic modification, DNA damage signaling, telomere length), acrylamide (DNA repair, chromosome segregation), bisphenol A (epigenetic modification, DNA damage signaling, mitochondrial function, chromosome segregation), benomyl (chromosome segregation), quinones (epigenetic modification) and nano-sized particles (epigenetic pathways, mitochondrial function, chromosome segregation, telomere length). The purpose of this review is to describe the crucial aspects of genome instability, to outline the ways in which environmental chemicals can affect this cancer hallmark and to identify candidate chemicals for further study. The overall aim is to make scientists aware of the increasing need to unravel the underlying mechanisms via which chemicals at low doses can induce genome instability and thus promote carcinogenesis.

Applications of the comet assay in particle toxicology: air pollution and engineered nanomaterials exposure

Exposure to ambient air particles is associated with elevated levels of DNA strand breaks (SBs) and endonuclease III, formamidopyrimidine DNA glycosylase (FPG) and oxoguanine DNA glycosylase-sensitive sites in cell cultures, animals and humans. In both animals and cell cultures, increases in SB and in oxidatively damaged DNA are seen after exposure to a range of engineered nanomaterials (ENMs), including carbon black, carbon nanotubes, fullerene C60, ZnO, silver and gold. Exposure to TiO2 has generated mixed data with regard to SB and oxidatively damaged DNA in cell cultures. Nanosilica does not seem to be associated with generation of FPG-sensitive sites in cell cultures, while large differences in SB generation between studies have been noted. Single-dose airway exposure to nanosized carbon black and multi-walled carbon nanotubes in animal models seems to be associated with elevated DNA damage levels in lung tissue in comparison to similar exposure to TiO2 and fullerene C60. Oral exposure has been associated with augmented DNA damage levels in cells of internal organs, although the doses have been typically very high. Intraveneous and intraperitoneal injection of ENMs have shown contradictory results dependent on the type of ENM and dose in each set of experiments. In conclusion, the exposure to both combustion-derived particles and ENMs is associated with increased levels of DNA damage in the comet assay. Particle size, composition and crystal structure of ENM are considered important determinants of toxicity, whereas their combined contributions to genotoxicity in the comet assay are yet to be thoroughly investigated.

Genotoxicity of metal oxide nanomaterials: review of recent data and discussion of possible mechanisms

Nanotechnology has rapidly entered into human society, revolutionized many areas, including technology, medicine and cosmetics. This progress is due to the many valuable and unique properties that nanomaterials possess. In turn, these properties might become an issue of concern when considering potentially uncontrolled release to the environment. The rapid development of new nanomaterials thus raises questions about their impact on the environment and human health. This review focuses on the potential of nanomaterials to cause genotoxicity and summarizes recent genotoxicity studies on metal oxide/silica nanomaterials. Though the number of genotoxicity studies on metal oxide/silica nanomaterials is still limited, this endpoint has recently received more attention for nanomaterials, and the number of related publications has increased. An analysis of these peer reviewed publications over nearly two decades shows that the test most employed to evaluate the genotoxicity of these nanomaterials is the comet assay, followed by micronucleus, Ames and chromosome aberration tests. Based on the data studied, we concluded that in the majority of the publications analysed in this review, the metal oxide (or silica) nanoparticles of the same core chemical composition did not show different genotoxicity study calls (i.e. positive or negative) in the same test, although some results are inconsistent and need to be confirmed by additional experiments. Where the results are conflicting, it may be due to the following reasons: (1) variation in size of the nanoparticles; (2) variations in size distribution; (3) various purities of nanomaterials; (4) variation in surface areas for nanomaterials with the same average size; (5) differences in coatings; (6) differences in crystal structures of the same types of nanomaterials; (7) differences in size of aggregates in solution/media; (8) differences in assays; (9) different concentrations of nanomaterials in assay tests. Indeed, due to the observed inconsistencies in the recent literature and the lack of adherence to appropriate, standardized test methods, reliable genotoxicity assessment of nanomaterials is still challenging.

Identification of nanoscale ingredients in commercial food products and their induction of mitochondrially mediated cytotoxic effects on human mesenchymal stem cells

Titanium dioxide (E171) and silicon dioxide (E551) are common additives found in food products, personal-care products, and many other consumer products used in daily life. Recent studies have reported that these food additives (manufactured E171 and E551) contain nanosized particles of less than 100 nm. However, the particle size distribution and morphology of added TiO2 and SiO2 particles are not typically stated on the package label. Furthermore, there is an increasing debate regarding health and safety concerns related to the use of synthetic food additives containing nanosized ingredients in consumer products. In this study, we identified the size and morphology of TiO2 and SiO2 particles in commercially available food products by using transmission electron microscope (TEM). In addition, the in vitro toxicological effects of E171 and E551 on human mesenchymal stem cells (hMSCs), an adult stem cell-based model, were assessed using the MTT assay and a flow cytometry-based JC-1 assay. Our TEM results confirmed the presence of nanoscale ingredients in food products, and the in vitro toxicology results indicated that the nanoscale E171 and E551 ingredients induced dose-dependent cytotoxicity, changes in cellular morphology, and the loss of mitochondrial trans-membrane potential in hMSCs. These preliminary results clearly demonstrated that the nanoscale E171 and E551 particles had adverse effects on hMSCs by inducing oxidative stress-mediated cell death. Accordingly, further studies are needed to identify the specific pathway involved, with an emphasis on differential gene expression in hMSCs.

Genotoxicity of titanium dioxide nanoparticles

Titanium dioxide nanoparticles (TiO₂-NPs, <100 nm) are increasingly being used in pharmaceuticals and cosmetics due to the unique properties derived from their small sizes. However, their large surface-area to mass ratio and high redox potential may negatively impact human health and the environment. TiO₂-NPs can cause inflammation, pulmonary damage, fibrosis, and lung tumors and they are possibly carcinogenic to humans. Because cancer is a disease involving mutation, there are a large number of studies on the genotoxicity of TiO₂-NPs. In this article, we review the results that have been reported in the literature, with a focus on data generated from the standard genotoxicity assays. The data include genotoxicity results from the Ames test, in vitro and in vivo Comet assay, in vitro and in vivo micronucleus assay, sister chromatid exchange assay, mammalian cell hypoxanthine-guanine phosphoribosyl transferase gene assay, the wing somatic mutation and recombination assay, and the mouse phosphatidylinositol glycan, class A gene assay. Inconsistent results have been found in these assays, with both positive and negative responses being reported. The in vitro systems for assessing the genotoxicity of TiO₂-NPs have generated a greater number of positive results than the in vivo systems, and tests for DNA and chromosome damage have produced more positive results than the assays measuring gene mutation. Nearly all tests for measuring the mutagenicity of TiO₂-NPs were negative. The current data indicate that the genotoxicity of TiO₂-NPs is mediated mainly through the generation of oxidative stress in cells.