In vitro evidence of dysregulation of blood-brain barrier function after acute and repeated/long-term exposure to TiO(2) nanoparticles

Neurotoxicity of Titanium Dioxide Nanoparticles: A Comprehensive Review

The increasing use of titanium dioxide nanoparticles (TiO2 NPs) across various fields has led to a growing concern regarding their environmental contamination and inevitable human exposure. Consequently, significant research efforts have been directed toward understanding the effects of TiO2 NPs on both humans and the environment. Notably, TiO2 NPs exposure has been associated with multiple impairments of the nervous system. This review aims to provide an overview of the documented neurotoxic effects of TiO2 NPs in different species and in vitro models. Following exposure, TiO2 NPs can reach the brain, although the specific mechanism and quantity of particles that cross the blood-brain barrier (BBB) remain unclear. Exposure to TiO2 NPs has been shown to induce oxidative stress, promote neuroinflammation, disrupt brain biochemistry, and ultimately impair neuronal function and structure. Subsequent neuronal damage may contribute to various behavioral disorders and play a significant role in the onset and progression of neurodevelopmental or neurodegenerative diseases. Moreover, the neurotoxic potential of TiO2 NPs can be influenced by various factors, including exposure characteristics and the physicochemical properties of the TiO2 NPs. However, a systematic comparison of the neurotoxic effects of TiO2 NPs with different characteristics under various exposure conditions is still lacking. Additionally, our understanding of the underlying neurotoxic mechanisms exerted by TiO2 NPs remains incomplete and fragmented. Given these knowledge gaps, it is imperative to further investigate the neurotoxic hazards and risks associated with exposure to TiO2 NPs.

Determinants and mechanisms of inorganic nanoparticle translocation across mammalian biological barriers

Biological barriers protect delicate internal tissues from exposures to and interactions with hazardous materials. Primary anatomical barriers prevent external agents from reaching systemic circulation and include the pulmonary, gastrointestinal, and dermal barriers. Secondary barriers include the blood-brain, blood-testis, and placental barriers. The tissues protected by secondary barriers are particularly sensitive to agents in systemic circulation. Neurons of the brain cannot regenerate and therefore must have limited interaction with cytotoxic agents. In the testis, the delicate process of spermatogenesis requires a specific milieu distinct from the blood. The placenta protects the developing fetus from compounds in the maternal circulation that would impair limb or organ development. Many biological barriers are semi-permeable, allowing only materials or chemicals, with a specific set of properties, that easily pass through or between cells. Nanoparticles (particles less than 100 nm) have recently drawn specific concern due to the possibility of biological barrier translocation and contact with distal tissues. Current evidence suggests that nanoparticles translocate across both primary and secondary barriers. It is known that the physicochemical properties of nanoparticles can affect biological interactions, and it has been shown that nanoparticles can breach primary and some secondary barriers. However, the mechanism by which nanoparticles cross biological barriers has yet to be determined. Therefore, the purpose of this review is to summarize how different nanoparticle physicochemical properties interact with biological barriers and barrier products to govern translocation.

The effect modification of extreme temperatures on mental and behavior disorders by environmental factors and individual-level characteristics in Canada

OBJECTIVE

Ambient extreme temperatures have been associated with mental and behavior disorders (MBDs). However, few studies have assesed whether vulnerability factors such as ambient air pollution, pre-existing mental health conditions and residential environmental factors increase susceptibility. This study aims to evaluate the associations between short-term variations in outdoor ambient extreme temperatures and MBD-related emergency department (ED) visits and how these associations are modified by vulnerability factors.

METHODS

We conducted a case-crossover study of 9,958,759 MBD ED visits in Alberta and Ontario, Canada made between March 1st, 2004 and December 31st, 2020. Daily average temperature was assigned to individual cases with ED visits for MBD using gridded data at a 1 km × 1 km spatial resolution. Conditional logistic regression was used to estimate associations between extreme temperatures (i.e., risk of ED visit at the 2.5th percentile temperature for cold and 97.5th percentile temperature for heat for each health region compared to the minimal temperature risk) and MBD ED visits. Age, sex, pre-existing mental health conditions, ambient air pollution (i.e. PM_2.5, NO₂ and O₃) and residential environmental factors (neighborhood deprivation, residential green space exposure and urbanization) were evaluated as potential effect modifiers.

RESULTS

Cumulative exposure to extreme heat over 0-5 days (odds ratio [OR] = 1.145; 95% CI: 1.121-1.171) was associated with ED visits for any MBD. However, cumulative exposure to extreme cold was associated with lower risk of ED visits for any MBD (OR = 0.981; 95% CI: 0.976-0.987). We also found heat to be associated with ED visits for specific MBDs such as substance use disorders, dementia, neurotic disorders, schizophrenia and personality behavior disorder. Individuals with pre-existing mental health conditions, those exposed to higher daily concentrations of NO₂ and O₃ and those residing in neighborhoods with greater material and social deprivation were at higher risk of heat-related MBD ED visits. Increasing tree canopy coverage appeared to mitigate risks of the effect of heat on MBD ED visits.

CONCLUSIONS

Findings provide evidence that the impacts of heat on MBD ED visits may vary across different vulnerability factors.

The role of the efflux transporter, P-glycoprotein, at the blood-brain barrier in drug discovery

The blood-brain barrier (BBB) expresses a high abundance of transporters, particularly P-glycoprotein (P-gp), that regulate endogenous and exogenous molecule uptake and removal of waste. This review discusses key drug metabolism and pharmacokinetic considerations for the efflux transporter P-gp at the BBB in drug discovery and development. We highlight the differences in P-gp expression and protein levels across species but the limited observations of species-specific substrates. Given the impact of age and disease on BBB biology, we summarise the modulation of P-gp for several neurological disorders and ageing and exemplify several disease-specific hurdles or opportunities for drug exposure in the brain. Furthermore, the review includes observations of CNS-related drug-drug interactions due to the inhibition or induction of P-gp at the BBB in animal studies and humans and the need for continued evaluation especially for compounds with a narrow therapeutic window. This review focusses primarily on small molecules but also considers the impact of new chemical entities, particularly beyond Ro5 molecules and their potential to be recognised as P-gp substrates as well as advanced drug delivery systems which offer an alternative approach to achieve and sustain central nervous system exposure.

How Nanoparticles Open the Paracellular Route of Biological Barriers: Mechanisms, Applications, and Prospects

Biological barriers are essential physiological protective systems and obstacles to drug delivery. Nanoparticles (NPs) can access the paracellular route of biological barriers, either causing adverse health impacts on humans or producing therapeutic opportunities. This Review introduces the structural and functional influences of NPs on the key components that govern the paracellular route, mainly tight junctions, adherens junctions, and cytoskeletons. Furthermore, we evaluate their interaction mechanisms and address the influencing factors that determine the ability of NPs to open the paracellular route, which provides a better knowledge of how NPs can open the paracellular route in a safer and more controllable way. Finally, we summarize limitations in the research models and methodologies of the existing research in the field and provide future research direction. This Review demonstrates the in-depth causes for the reversible opening or destruction of the integrity of barriers generated by NPs; more importantly, it contributes insights into the design of NP-based medications to boost paracellular drug delivery efficiency.

Titanium dioxide and carbon black nanoparticles disrupt neuronal homeostasis via excessive activation of cellular prion protein signaling

Background

Epidemiological emerging evidence shows that human exposure to some nanosized materials present in the environment would contribute to the onset and/or progression of Alzheimer’s disease (AD). The cellular and molecular mechanisms whereby nanoparticles would exert some adverse effects towards neurons and take part in AD pathology are nevertheless unknown.

Results

Here, we provide the prime evidence that titanium dioxide (TiO₂) and carbon black (CB) nanoparticles (NPs) bind the cellular form of the prion protein (PrP^C), a plasma membrane protein well known for its implication in prion diseases and prion-like diseases, such as AD. The interaction between TiO₂- or CB-NPs and PrP^C at the surface of neuronal cells grown in culture corrupts PrP^C signaling function. This triggers PrP^C-dependent activation of NADPH oxidase and subsequent production of reactive oxygen species (ROS) that alters redox equilibrium. Through PrP^C interaction, NPs also promote the activation of 3-phosphoinositide-dependent kinase 1 (PDK1), which in turn provokes the internalization of the neuroprotective TACE α-secretase. This diverts TACE cleavage activity away from (i) TNFα receptors (TNFR), whose accumulation at the plasma membrane augments the vulnerability of NP-exposed neuronal cells to TNFα -associated inflammation, and (ii) the amyloid precursor protein APP, leading to overproduction of neurotoxic amyloid Aβ40/42 peptides. The silencing of PrP^C or the pharmacological inhibition of PDK1 protects neuronal cells from TiO₂- and CB-NPs effects regarding ROS production, TNFα hypersensitivity, and Aβ rise. Finally, we show that dysregulation of the PrP^C-PDK1-TACE pathway likely occurs in the brain of mice injected with TiO₂-NPs by the intra-cerebro-ventricular route as we monitor a rise of TNFR at the cell surface of several groups of neurons located in distinct brain areas.

Conclusion

Our in vitro and in vivo study thus posits for the first time normal cellular prion protein PrP^C as being a neuronal receptor of TiO₂- and CB-NPs and identifies PrP^C-coupled signaling pathways by which those nanoparticles alter redox equilibrium, augment the intrinsic sensitivity of neurons to neuroinflammation, and provoke a rise of Aβ peptides. By identifying signaling cascades dysregulated by TiO₂- and CB-NPs in neurons, our data shed light on how human exposure to some NPs might be related to AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00490-x.

Associations of short-term exposure to air pollution and increased ambient temperature with psychiatric hospital admissions in older adults in the USA: a case-crossover study

BACKGROUND

Little is known about the associations between ambient environmental exposures and the risk of acute episodes of psychiatric disorders. We aimed to estimate the link between short-term exposure to atmospheric pollutants, temperature, and acute psychiatric hospital admissions in adults aged 65 years and older in the USA.

METHODS

For this study, we included all people (aged ≥65 years) enrolled in the Medicare programme in the USA who had an emergency or urgent hospital admission for a psychiatric disorder recorded between Jan 31, 2000, and Dec 31, 2016. We applied a case-crossover design to study the associations between short-term exposure to air pollution (fine particulate matter [PM_2·5], ozone, and nitrogen dioxide [NO₂]), ambient temperature, and the risk of acute hospital admissions for depression, schizophrenia, and bipolar disorder in this population. The percentage change in the risk of hospital admission and annual absolute risk differences were estimated.

FINDINGS

For each 5°C increase in short-term exposure to cold season temperature, the relative risk of acute hospital admission increased by 3·66% (95% CI 3·06-4·26) for depression, by 3·03% (2·04-4·02) for schizophrenia, and by 3·52% (2·38-4·68) for bipolar disorder in the US Medicare population. Increased short-term exposure to PM_2·5 and NO₂ was also associated with a significant increase in the risk of acute hospital admissions for psychiatric disorders. Each 5 μg/m³ increase in PM_2·5 was associated with an increase in hospital admission rates of 0·62% (95% CI 0·23-1·02) for depression, 0·77% (0·11-1·44) for schizophrenia, and 1·19% (0·49-1·90) for bipolar disorder; each 5 parts per billion (ppb) increase in NO₂, meanwhile, was linked to an increase in hospital admission rates of 0·35% (95% CI 0·03-0·66) for depression and 0·64% (0·20-1·08) for schizophrenia. No such associations were found with warm season temperature.

INTERPRETATION

In the US Medicare population, short-term exposure to elevated concentrations of PM_2·5 and NO₂ and cold season ambient temperature were significantly associated with an increased risk of hospital admissions for psychiatric disorders. Considering the increasing burden of psychiatric disorders in the US population, these findings suggest that intervening on air pollution and ambient temperature levels through stricter environmental regulations or climate mitigation could help ease the psychiatric health-care burden.

FUNDING

US National Institute of Environmental Health Sciences, US Environmental Protection Agency, and US National Institute on Aging.

Retinal cytotoxicity of silica and titanium dioxide nanoparticles

The retina plays a key role in human vision. It is composed of cells that are essential for vision signal generation. Thus far, conventional medications have been ineffective for treating retinal diseases because of the intrinsic blood-retinal barrier. Nanoparticles (NPs) are promising effective platforms for ocular drug delivery. However, nanotoxicity in the retinal tissue has not received much attention. This study used R28 cells (a retinal precursor cell line that originated from rats) to investigate the safety of two commonly used types of NPs: silica nanoparticles (SiO2NPs, 100 nm) and titanium dioxide nanoparticles (TiO2NPs, 100 nm). Cellular viability and reactive oxygen species generation were measured after 24, 48, and 72 h of exposure to each NP. Cellular autophagy and the mTOR pathways were evaluated. The retinal toxicity of the NPs was investigated in vivo in rat models. Both types of NPs were found to induce significant dose-dependent toxicity on the R28 cells. A significant elevation of reactive oxygen species generation was also observed. Increased autophagy and decreased mTOR phosphorylation were observed after SiO2NPs and TiO2NPs exposure. The diffuse apoptosis of the retinal cellular layers was detected after intravitreal injection.

TGF-β1/SMADs signaling involved in alleviating inflammation induced by nanoparticulate titanium dioxide in BV2 cells

There are increasing safety concerns accompanying the widespread use of nanoparticulate titanium dioxide (nano-TiO₂). It has been demonstrated that nano-TiO₂ can cross the blood-brain barrier and enter the brain, causing damage to the nervous system, consisting mainly of neuroinflammation and neuronal apoptosis. Several studies have linked the TGF-β1/SMADs signaling to the development of inflammatory response in various organs. However, no studies have connected the induction of microglial inflammation by nano-TiO₂ to this signaling. Therefore, this study aimed to investigate the role of TGF-β1/SMADs signaling in microglia inflammatory response induced by nano-TiO₂. The results showed that nano-TiO₂ increased the secretions of pro-inflammatory cytokines (IL-1α, IL-6, and TNF-α) and decreased the expressions of TGF-β1 and SMAD1/2/3 proteins in BV2 cells. When TGF-β1/SMADs signaling was inhibited, the inflammatory effect induced by nano-TiO₂ increased, suggesting a suppressive effect of this signaling on the inflammation. In addition, exogenous TGF-β1 upregulated the expressions of TGF-β1 and SMADs1/2/3 proteins as well as decreased the secretions of pro-inflammatory cytokines (IL-1α, IL-6, and TNF-α) compared to BV2 cells treated with only nano-TiO₂. Our results suggest that nano-TiO₂ may inhibit the TGF-β1/SMADs signaling by suppressing the intracellular secretion of active TGF-β1, leading to microglial activation and the induction or exacerbation of inflammatory responses.

Engineered nanomaterials induce alterations in biological barriers: focus on paracellular permeability

Engineered nanoparticles (ENPs) are widely used in medical diagnosis and treatment, as food additives and as energy materials. ENPs may exert adverse or beneficial effects on the human body, which may be linked to interactions with biological barriers. In this review, the authors summarize the influences of four typical metal/metal oxide nanomaterials (Ag, TiO₂, Au, ZnO nanoparticles) on the paracellular permeability of biological barriers. Disruptions on tight junctions, adhesion junctions, gap junctions and desmosomes via complex signaling pathways, such as the MAPK, PKC and ROCK signaling pathways, affect paracellular permeability. Reactive oxygen species and cytokines underlie the mechanism of ENP-triggered alterations in paracellular permeability. This review provides the information necessary for the cautious application of nanoparticles in medicine and life sciences in the future.

Acute titanium dioxide nanoparticles exposure impaired spatial cognitive performance through neurotoxic and oxidative mechanisms in Wistar rats

CONTEXT

Titanium dioxide nanoparticles (TiO2-NPs) are used in many commercial products. However, their effects on human and animal organism remained to be clarified.

OBJECTIVE

The present study aimed to investigate the effects of TiO2-NPs on the behavioural performance, monoamine neurotransmitters and oxidative stress in the rat brain.

MATERIAL AND METHODS

Rats were injected intravenously with a single dose of TiO2-NPs (20 mg/kg body weight) and were subjected to cognitive and emotional tests using Morris water maze and elevated plus maze.

RESULTS

Cognitive capacity as well as the emotional reactivity were significantly disrupted, in TiO2-NPs-administered rats compared to control group. These behavioural effects were correlated with changes in brain neurotransmitter contents reflected by a significant increase in dopamine and a decrease in serotonin levels. TiO2-NPs also induced oxidative stress in the brain manifested by increased levels of H2O2 and malondialdehyde, associated with antioxidant enzymes activities disturbance, in particular, superoxide dismutase and catalase activities. Moreover, TiO2-NPs administration caused histological damages in the brain tissue with abundant lymphocytic clusters, capillary dilations, vascular congestion and oedema.

CONCLUSIONS

Acute intravenous injection of TiO2-NPs impaired behaviour performances through brain biochemical and structural changes and precautions should be taken to their usage in food additive and medical applications.

Potential neurotoxicity of titanium implants: Prospective, in-vivo and in-vitro study

Titanium dioxide (TiO₂) is a frequently used biomaterial, particularly in orthopedic and dental implants, and it is considered an inert and benign compound. This has resulted in toxicological scrutiny for TiO₂ in the past decade, with numerus studies showing potential pathologic downstream effects. Herein we describe case report of a 77-year-old male with subacute CNS dysfunction, secondary to breakdown of a titanium-based carotid stent and leading to blood levels 1000 times higher (3 ppm) than the reported normal. We prospectively collected tissues adjacent to orthopedic implants and found a positive correlation between titanium concentration and time of implant in the body (r = 0.67, p < 0.02). Rats bearing titanium implants or intravascularly treated with TiO₂ nanoparticles (TiNP) exhibited memory impairments. A human blood-brain barrier (BBB) in-vitro model exposed to TiNP showed paracellular leakiness, which was corroborated in-vivo with the decrease of key BBB transcripts in isolated blood vessels from hippocampi harvested from TiNP-treated mice. Titanium particles rapidly internalized into brain-like endothelial cells via caveolae-mediated endocytosis and macropinocytosis and induced pro-inflammatory reaction with increased expression of pro-inflammatory genes and proteins. Immune reaction was mediated partially by IL-1R and IL-6. In summary, we show that high levels of titanium accumulate in humans adjacent to orthopedic implants, and our in-vivo and in-vitro studies suggest it may be neurotoxic.

Ultrasound-activated nano-TiO2 loaded with temozolomide paves the way for resection of chemoresistant glioblastoma multiforme

Background

Glioblastoma multiforme (GBM) is one of the most daunting issues to modern therapeutics, with a higher mortality rate post-diagnosis. Temozolomide (TMZ) is the only available treatment; however, the frequent resistance leaves the oncologists at a dead end. Therefore, new approaches to circumvent the GBM are highly desired. We have employed TiO2 nanosticks loaded with TMZ as nanomedicine for TMZ-resistant GBM resection in this contribution.

Results

The ultrasonication triple-action effect could greatly facilitate tumor ablation by enhancing the TiO2 nanosticks traversing across BBB, releasing the TMZ payload from TiO2 nanosticks and reactive oxygen species (ROS) generation from TiO2 nanosticks within the GBM milieu. The tumor ablation was confirmed by MTT and Annexin(v)-PI assays, apoptotic proteins expression via western blot and ROS level detection in vitro, whereas tumor volume, weight, survival rate, and relative photon flux in the xenograft and orthoptic TMZ-resistant GBM murine models as in vivo.

Conclusion

We found this nanomedicine-based ultrasound modality highly efficient in GBM treatment and is of future clinical application value due to the employment of already FDA-approved techniques and nanomedicine.

Tailoring of P-glycoprotein for effective transportation of actives across blood-brain-barrier

P-Glycoprotein serves as a gatekeeper in the blood-brain-barrier wherein, it shows a vital part in the elimination of xenobiotics, drugs, foreign molecules etc. and guards the central nervous system from infections and external toxic molecules by functioning as an efflux transporter. It plays an essential role in various brain-related conditions like Parkinsonism, Alzheimer's disease, depression, cancer, etc. and terminates the entry of therapeutic agents across blood-brain-barrier which remains a significant challenge serving as major hindrance in pharmacotherapy of disease. The physiological structure and topology of P-glycoprotein and its relation with blood-brain-barrier and central nervous system gives an idea for targeting nanocarriers across the barrier into brain. This review article provides an overview of current understanding of the nanoformulations-based P-gp trafficking strategies like nanocarriers, stem cell therapy, drugs, substrates, polymeric materials, chemical compounds as well as naturally occurring active constituents for improving drug transport in brain across blood-brain-barrier and contributing in effective nanotherapeutic development for treatment of CNS disorders.

Methods used for the measurement of blood-brain barrier integrity

The blood-brain barrier (BBB) comprises the interface between blood, brain and cerebrospinal fluid. Its primary function, which is mainly carried out by tight junctions, is to stabilize the tightly controlled microenvironment of the brain. To study the development and maintenance of the BBB, as well as various roles their intrinsic mechanisms that play in neurological disorders, suitable measurements are required to demonstrate integrity and functional changes at the interfaces between the blood and brain tissue. Markers and plasma proteins with different molecular weight (MW) are used to measure the permeability of BBB. In addition, the expression changes of tight-junction proteins form the basic structure of BBB, and imaging modalities are available to study the disruption of BBB. In the present review, above mentioned methods are depicted in details, together with the pros and cons as well as the differences between these methods, which maybe benefit research studies focused on the detection of BBB breakdown.

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.

Proposing Urothelial and Muscle In Vitro Cell Models as a Novel Approach for Assessment of Long-Term Toxicity of Nanoparticles

Many studies evaluated the short-term in vitro toxicity of nanoparticles (NPs); however, long-term effects are still not adequately understood. Here, we investigated the potential toxic effects of biomedical (polyacrylic acid and polyethylenimine coated magnetic NPs) and two industrial (SiO₂ and TiO₂) NPs following different short-term and long-term exposure protocols on two physiologically different in vitro models that are able to differentiate: L6 rat skeletal muscle cell line and biomimetic normal porcine urothelial (NPU) cells. We show that L6 cells are more sensitive to NP exposure then NPU cells. Transmission electron microscopy revealed an uptake of NPs into L6 cells but not NPU cells. In L6 cells, we obtained a dose-dependent reduction in cell viability and increased reactive oxygen species (ROS) formation after 24 h. Following continuous exposure, more stable TiO₂ and polyacrylic acid (PAA) NPs increased levels of nuclear factor Nrf2 mRNA, suggesting an oxidative damage-associated response. Furthermore, internalized magnetic PAA and TiO₂ NPs hindered the differentiation of L6 cells. We propose the use of L6 skeletal muscle cells and NPU cells as a novel approach for assessment of the potential long-term toxicity of relevant NPs that are found in the blood and/or can be secreted into the urine.

Neurotoxicology of Nanomaterials

The remarkable advances coming about through nanotechnology promise to revolutionize many aspects of modern life; however, these advances come with a responsibility for due diligence to ensure that they are not accompanied by adverse consequences for human health or the environment. Many novel nanomaterials (having at least one dimension <100 nm) could be highly mobile if released into the environment and are also very reactive, which has raised concerns for potential adverse impacts including, among others, the potential for neurotoxicity. Several lines of evidence led to concerns for neurotoxicity, but perhaps none more than observations that inhaled nanoparticles impinging on the mucosal surface of the nasal epithelium could be internalized into olfactory receptor neurons and transported by axoplasmic transport into the olfactory bulbs without crossing the blood-brain barrier. From the olfactory bulb, there is concern that nanomaterials may be transported deeper into the brain and affect other brain structures. Of course, people will not be exposed to only engineered nanomaterials, but rather such exposures will occur in a complex mixture of environmental materials, some of which are incidentally generated particles of a similar inhalable size range to engineered nanomaterials. To date, most experimental studies of potential neurotoxicity of nanomaterials have not considered the potential exposure sources and pathways that could lead to exposure, and most studies of nanomaterial exposure have not considered potential neurotoxicity. Here, we present a review of potential sources of exposures to nanoparticles, along with a review of the literature on potential neurotoxicity of nanomaterials. We employ the linked concepts of an aggregate exposure pathway (AEP) and an adverse outcome pathway (AOP) to organize and present the material. The AEP includes a sequence of key events progressing from material sources, release to environmental media, external exposure, internal exposure, and distribution to the target site. The AOP begins with toxicant at the target site causing a molecular initiating event and, like the AEP, progress sequentially to actions at the level of the cell, organ, individual, and population. Reports of nanomaterial actions are described at every key event along the AEP and AOP, except for changes in exposed populations that have not yet been observed. At this last stage, however, there is ample evidence of population level effects from exposure to ambient air particles that may act similarly to engineered nanomaterials. The data give an overall impression that current exposure levels may be considerably lower than those reported experimentally to be neurotoxic. This impression, however, is tempered by the absence of long-term exposure studies with realistic routes and levels of exposure to address concerns for chronic accumulation of materials or damage. Further, missing across the board are "key event relationships", which are quantitative expressions linking the key events of either the AEP or the AOP, making it impossible to quantitatively project the likelihood of adverse neurotoxic effects from exposure to nanomaterials or to estimate margins of exposure for such relationships.

Unravelling the Potential Cytotoxic Effects of Metal Oxide Nanoparticles and Metal(Loid) Mixtures on A549 Human Cell Line

Humans are typically exposed to environmental contaminants' mixtures that result in different toxicity than exposure to the individual counterparts. Yet, the toxicology of chemical mixtures has been overlooked. This work aims at assessing and comparing viability and cell cycle of A549 cells after exposure to single and binary mixtures of: titanium dioxide nanoparticles (TiO2NP) 0.75-75 mg/L; cerium oxide nanoparticles (CeO2NP) 0.0.75-10 μg/L; arsenic (As) 0.75-2.5 mg/L; and mercury (Hg) 5-100 mg/L. Viability was assessed through water-soluble tetrazolium (WST-1) and thiazolyl blue tetrazolium bromide (MTT) (24 h exposure) and clonogenic (seven-day exposure) assays. Cell cycle alterations were explored by flow cytometry. Viability was affected in a dose- and time-dependent manner. Prolonged exposure caused inhibition of cell proliferation even at low concentrations. Cell-cycle progression was affected by TiO2NP 75 mg/L, and As 0.75 and 2.5 μg/L, increasing the cell proportion at G0/G1 phase. Combined exposure of TiO2NP or CeO2NP mitigated As adverse effects, increasing the cell surviving factor, but cell cycle alterations were still observed. Only CeO2NP co-exposure reduced Hg toxicity, translated in a decrease of cells in Sub-G1. Toxicity was diminished for both NPs co-exposure compared to its toxicity alone, but a marked toxicity for the highest concentrations was observed for longer exposures. These findings prove that joint toxicity of contaminants must not be disregarded.

Effects of Titanium Dioxide Nanoparticles Exposure on Human Health-a Review

Recently, an increased interest in nanotechnology applications can be observed in various fields (medicine, materials science, pharmacy, environmental protection, agriculture etc.). Due to an increasing scope of applications, the exposure of humans to nanoparticles (NPs) is inevitable. A number of studies revealed that after inhalation or oral exposure, NPs accumulate in, among other places, the lungs, alimentary tract, liver, heart, spleen, kidneys and cardiac muscle. In addition, they disturb glucose and lipid homeostasis in mice and rats. In a wide group of nanoparticles currently used on an industrial scale, titanium dioxide nanoparticles-TiO₂ NPs-are particularly popular. Due to their white colour, TiO₂ NPs are commonly used as a food additive (E 171). The possible risk to health after consuming food containing nanoparticles has been poorly explored but it is supposed that the toxicity of nanoparticles depends on their size, morphology, rate of migration and amount consumed. Scientific databases inform that TiO₂ NPs can induce inflammation due to oxidative stress. They can also have a genotoxic effect leading to, among others, apoptosis or chromosomal instability. This paper gives a review of previous studies concerning the effects of exposure to TiO₂ NPs on a living organism (human, animal). This information is necessary in order to demonstrate potential toxicity of inorganic nanoparticles on human health.

Long-Term Particulate Matter Exposure and Onset of Depression in Middle-Aged Men and Women

BACKGROUND

Long-term exposure to particulate matter (PM) air pollution is associated with all-cause mortality and adverse cognitive outcomes, but the association with developing depression remains inconsistent.

OBJECTIVE

Our goal was to evaluate the prospective association between PM air pollution and developing depression assessed using the Center for Epidemiological Studies Depression (CES-D) scale.

METHODS

Subjects were drawn from a prospective cohort study of 123,045 men and women free of depressive symptoms at baseline who attended regular screening exams in Seoul and Suwon, South Korea, from 2011 to 2015. Exposure to PM with an aerodynamic diameter of [Formula: see text] ([Formula: see text] and [Formula: see text], respectively) was estimated using a land-use regression model based on each subject's residential postal code. Incident depression was defined as a CES-D score [Formula: see text] during follow-up. As a sensitivity analyses, we defined incident depression using self-reports of doctor's diagnoses or use of antidepressant medications during follow-up.

RESULTS

The mean baseline 12-month concentrations of [Formula: see text] and [Formula: see text] were 50.6 (4.5) and [Formula: see text], respectively. The hazard ratios (HRs) and 95% confidence intervals (CIs) for developing depression associated with a [Formula: see text] increase in 12- and 60-month [Formula: see text] exposure were 1.11 (95% CI: 1.06, 1.16) and 1.06 (95% CI: 1.01, 1.11), respectively. The corresponding HRs for 12-month [Formula: see text] exposure was 0.96 (95% CI: 0.64, 1.43). Similar results were obtained when incident depression was identified using self-reports of doctor's diagnoses or the use of antidepressant medications.

CONCLUSION

In this large cohort study, we found a positive association between long-term exposure to outdoor [Formula: see text] air pollution and the developing depression. We did not find an association for outdoor [Formula: see text] air pollution; however, we had a much shorter follow-up for subjects' exposure to [Formula: see text]. https://doi.org/10.1289/EHP4094.

The neurotoxicity induced by engineered nanomaterials

Engineered nanomaterials (ENMs) have been widely used in various fields due to their novel physicochemical properties. However, the use of ENMs has led to an increased exposure in humans, and the safety of ENMs has attracted much attention. It is universally acknowledged that ENMs could enter the human body via different routes, eg, inhalation, skin contact, and intravenous injection. Studies have proven that ENMs can cross or bypass the blood-brain barrier and then access the central nervous system and cause neurotoxicity. Until now, diverse in vivo and in vitro models have been developed to evaluate the neurotoxicity of ENMs, and oxidative stress, inflammation, DNA damage, and cell death have been identified as being involved. However, due to various physicochemical properties of ENMs and diverse study models in existing studies, it remains challenging to establish the structure-activity relationship of nanomaterials in neurotoxicity. In this paper, we aimed to review current studies on ENM-induced neurotoxicity, with an emphasis on the molecular and cellular mechanisms involved. We hope to provide a rational material design strategy for ENMs when they are applied in biomedical or other engineering applications.

Physical, morphological and chemical modification of Al-based nanofillers in by-products of incinerated nanocomposites and related biological outcome

The number of products containing nanomaterials is increasing this last ten years. Information and literature about the end-of-life of nanocomposites often remains partial and does not address the overall fate and transformations of nanoparticles that may affect biological responses. This paper underlines that the physico-chemical features of nanoparticles can be modified by the incineration process and the available toxicological data on pristine nanofillers might not be relevant to assess the modified nanoparticles included in soot. Combustion tests have been performed at lab-scale using a cone calorimeter modified to collect fumes (particulate matter and gas phase) and have been characterized using various techniques. Nanocomposites selected were poly(ethylene vinyl acetate) containing Al-based nanoparticles, i.e. boehmites or alumina. Evaluations of in vitro cytotoxicity responses on pristine nanofillers, soot and residual ash, show that safe boehmite nanoparticles, become toxic due to a chemical modification after incineration process.

Triphenyl Phosphate (TPHP)-Induced Neurotoxicity in Adult Male Chinese Rare Minnows ( Gobiocypris rarus)

The neurotoxicity of triphenyl phosphate (TPHP) in exposed humans and laboratory animals is under debate. The rapid crossing of the blood-brain barrier (BBB) and high distribution of TPHP in fish brains have raised widespread concerns about potential neurotoxicity. Adult male Chinese rare minnows ( Gobiocypris rarus) were used as a model and exposed to 0, 20, or 100 μg/L TPHP for 28 days. We evaluated the BBB permeability, neuroinflammatory response, cell proliferation and apoptosis, synaptic plasticity and synapse loss in fish brains via the learning/memory performance of fish following 28 days of TPHP exposure. TPHP significantly increased the BBB permeability, activated the neuroinflammatory response, and decreased the tight junction-related mRNA levels of claudin-5α and occludin in the fish brain. In addition, cell proliferation was inhibited by treatment with 100 μg/L TPHP, but no significant apoptosis was observed in the brain. Fish exposed to 100 μg/L TPHP exhibited significantly decreased dendritic arborization in pyramidal neurons in the cerebellum (Ce), and the maze test indicated impaired learning/memory performance. Taken together, these findings provide scientific evidence that TPHP is neurotoxic to fish and further suggest that TPHP may not be a safe alternative for aquatic organisms.

Titanium dioxide nanoparticles induce mouse hippocampal neuron apoptosis via oxidative stress- and calcium imbalance-mediated endoplasmic reticulum stress

The purpose of this study was to explore the potential neurotoxicity and the underlying mechanism of titanium dioxide nanoparticles (TiO₂-NPs) to mouse hippocampal neuron HT22 cells. We found that TiO₂-NPs had concentration-dependent and time-dependent cytotoxicities to HT22 cells by the MTT assay. Propidium iodide (PI) staining with FACScan flow cytometry proved that TiO₂-NPs dose-dependently increased the apoptosis rate in HT22 cells, and the apoptotic features were observed by Hochest 33258 and AO/EB staining. The levels of calcium (Ca²⁺) and reactive oxygen species (ROS) were significantly increased in TiO₂-NPs-treated cells. Further studies by western blot and real-time QPCR proved that the protein and mRNA levels of GRP78, IRE-1α, ATF6, CHOP and caspase-12 were up-regulated after TiO₂-NPs treatment, which indicates that TiO₂-NPs-induced cytotoxicity is related to endoplasmic reticulum stress (ERS). Apoptosis-related protein cleaved caspase-3 and pro-apoptotic protein Bax expression levels were up-regulated, and the anti-apoptotic protein Bcl-2 expression level was down-regulated in TiO₂-NPs-treated cells. The antioxidant N-acetyl-L-cysteine (NAC) can significantly reduce TiO₂-NPs-induced ERS characterized by the down-regulation of GRP78 and cleaved caspase-12 levels, which indicates that oxidative stress is participated in TiO₂-NPs-induced ERS. Our study suggests that TiO₂-NPs-induced apoptosis in HT22 cells is through oxidative stress- and calcium imbalance-mediated ERS.

Penetration, distribution and brain toxicity of titanium nanoparticles in rodents' body: a review

Titanium dioxide (TiO2) has been vastly used commercially, especially as white pigment in paints, colorants, plastics, coatings, cosmetics. Certain industrial uses TiO2 in diameter <100 nm. There are three common exposure routes for TiO2: (i) inhalation exposure, (ii) exposure via gastrointestinal tract, (iii) dermal exposure. Inhalation and gastrointestinal exposure appear to be the most probable ways of exposure, although nanoparticle (NP) penetration is limited. However, the penetration rate may increase substantially when the tissue is impaired. When TiO2 NPs migrate into the circulatory system, they can be distributed into all tissues including brain. In brain, TiO2 lead to oxidative stress mediated by the microglia phagocytic cells which respond to TiO2 NPs by the production and release of superoxide radicals that convert to multiple reactive oxygen species (ROS). The ROS production may also cause the damage of blood-brain barrier which then becomes more permeable for NPs. Moreover, several studies have showed neuron degradation and the impairment of spatial recognition memory and learning abilities in laboratory rodent exposed to TiO2 NPs.

Endothelial barrier dysfunction induced by nanoparticle exposure through actin remodeling via caveolae/raft-regulated calcium signalling

The rapid development of modern nanotechnology has resulted in nanomaterial being use in nearly all applications of life, raising the potential risk of nanomaterial exposure alongside the need to design safe and effective materials. Previous work has demonstrated a specific effect of gold nanoparticles (GNPs) of approximately 20 nm on endothelial barrier function in vitro. To expand our understanding of this size-specific effect, titanium dioxide, silicon dioxide, and polystyrene nanoparticles (NPs) in this similar size range were studied. All tested nanoparticles were found to have minimal effects on cell viability, but exhibited a significant detrimental effect on endothelial barrier function. Nanoparticles in the size range of 20 to 30 nm were internalized by endothelial cells through caveolae/raft-mediated endocytosis, causing intracellular calcium elevation by approximately 30% at 2 hours after administration, and triggering myosin light chain kinase (MLCK)-regulated actomyosin contraction. These effects culminated in an increase in endothelial monolayer permeability across all particle types within the 20-30 nm range. This nanoparticle exposure-induced endothelial barrier dysfunction may provide valuable information for designing safer nanomaterials or potential applications of this nanoparticle exposure-induced permeability effect in biomedicine.

In vitro models of molecular and nano-particle transport across the blood-brain barrier

The blood-brain barrier (BBB) is the tightest endothelial barrier in humans. Characterized by the presence of tight endothelial junctions and adherens junctions, the primary function of the BBB is to maintain brain homeostasis through the control of solute transit across the barrier. The specific features of this barrier make for unique modes of transport of solutes, nanoparticles, and cells across the BBB. Understanding the different routes of traffic adopted by each of these is therefore critical in the development of targeted therapies. In an attempt to move towards controlled experimental assays, multiple groups are now opting for the use of microfluidic systems. A comprehensive understanding of bio-transport processes across the BBB in microfluidic devices is therefore necessary to develop targeted and efficient therapies for a host of diseases ranging from neurological disorders to the spread of metastases in the brain.

The inflammatory response to silver and titanium dioxide nanoparticles in the central nervous system

Despite the increasing number of neurotoxicological studies on metal-containing nanoparticles (NPs), the NP-induced neuroinflammation has not yet been well understood. This review provides a comprehensive understanding of inflammatory responses to two typical metal-containing NPs, namely silver NPs (Ag-NPs) and titanium dioxide NPs (TiO₂-NPs). Ag-NPs and TiO₂-NPs could translocate into the CNS through damaged blood-brain barrier, nerve afferent signaling and eye-to-brain ways, and even cell uptake. NPs could stimulate the activation of glial cells to release proinflammatory cytokines and generate reactive oxygen species and nitric oxide production, resulting in the neuroinflammation. The potential mechanisms of Ag-NPs and TiO₂-NPs causing inflammation are complex, including several immune response relevant signaling pathways. Some parameters governing their ability to cause neuroinflammation are presented as well.

Size- and shape-dependent effects of titanium dioxide nanoparticles on the permeabilization of the blood-brain barrier

Titanium dioxide nanoparticles (TiO₂-NPs) have been found to translocate into the brain by penetrating the blood-brain barrier (BBB), but it remains largely unknown how their physicochemical characteristics may impact BBB permeabilization. By testing TiO₂ particles of different shapes and various sizes, we found that: (1) small, spherical TiO₂-NPs permeabilized a BBB-like human brain microvasculature endothelial cell monolayer better than rod-like or large particles; (2) TiO₂-NPs stimulated F-actin stress fiber formation, and induced paracellular gaps and ROCK II activation. The TiO₂-NP-mediated BBB permeabilization was associated with intracellular uptake and cytoskeletal re-organization; and (3) in rats, spherical, small TiO₂-NPs significantly increased the BBB permeability and entered the brain. The TiO₂-NPs were accumulated in the brain, but no obvious pathological anomaly was observed in the cerebral cortex and hippocampus. Our study investigated the neurotoxicity of TiO₂-NPs, thereby providing scientific evaluation for the potential biomedical applications of TiO₂-NPs.

Blood brain barrier permeable gold nanocluster for targeted brain imaging and therapy: an in vitro and in vivo study

Blood brain barrier (BBB) is a dynamic interface, comprising polarized endothelial cells, that separates the brain from the circulatory system. The highly protective nature of this tight junction impairs diagnosis and treatment of brain disorders. In this study, we designed a sub atomic size, near infrared emitting, dual function glutathione gold cluster with high fluorescence yield to facilitate permeability of BBB, for imaging applications and drug delivery. The gold cluster was then modified with Levodopa (l-dopa), to utilize the large amino acid transporter 1 (LAT1) pathways to enhance brain entry. Uptake and permeability of the nanoprobes were demonstrated using an established model of BBB, comprising brain endothelial cells (bEnd.3). The uptake and the clearance of l-dopa modified cluster was faster than the glutathione cluster. l-Dopa modified cluster supports the slow and sustained delivery of a model drug, pilocarpine, to the brain. Results of in vivo imaging and drug release in normal mice hold promise for considering the probe for early diagnosis of brain diseases, when the barrier is not disrupted, and for subsequent drug treatment.

Brain Inflammation, Blood Brain Barrier dysfunction and Neuronal Synaptophysin Decrease after Inhalation Exposure to Titanium Dioxide Nano-aerosol in Aging Rats

Notwithstanding potential neurotoxicity of inhaled titanium dioxide nanoparticles (TiO₂ NPs), the toxicokinetics and consequences on blood-brain barrier (BBB) function remain poorly characterized. To improve risk assessment, we need to evaluate the impact on BBB under realistic environmental conditions and take into account vulnerability status such as age. 12-13 week and 19-month-old male rats were exposed by inhalation to 10 mg/m³ of TiO₂ nano-aerosol (6 hrs/day, 5 day/week, for 4 weeks). We showed an age-dependent modulation of BBB integrity parameters suggesting increased BBB permeability in aging rats. This alteration was associated with a significant increase of cytokines/chemokines in the brain, including interleukin-1β, interferon-γ, and fractalkine as well as a decreased expression of synaptophysin, a neuronal activity marker. These observations, in absence of detectable titanium in the brain suggest that CNS-related effects are mediated by systemic-pathway. Moreover, observations in terms of BBB permeability and brain inflammation underline age susceptibility. Even if TiO₂ NPs were not evidenced in the brain, we observed an association between the exposure to TiO₂ NPs and the dysregulation of BBB physiology associated with neuroinflammation and decreased expression of neuronal activity marker, which was further exacerbated in the brain of aged animal's.

Neurotoxic effect of active ingredients in sunscreen products, a contemporary review

Sunscreen application is the main strategy used to prevent the maladies inflicted by ultraviolet (UV) radiation. Despite the continuously increasing frequency of sunscreen use worldwide, the prevalence of certain sun exposure-related pathologies, mainly malignant melanoma, is also on the rise. In the past century, a variety of protective agents against UV exposure have been developed. Physical filters scatter and reflect UV rays and chemical filters absorb those rays. Alongside the evidence for increasing levels of these agents in the environment, which leads to indirect exposure of wildlife and humans, recent studies suggest a toxicological nature for some of these agents. Reviews on the role of these agents in developmental and endocrine impairments (both pathology and related mechanisms) are based on both animal and human studies, yet information regarding the potential neurotoxicity of these agents is scant. In this review, data regarding the neurotoxicity of several organic filters: octyl methoxycinnamate, benzophenone-3 and −4, 4-methylbenzylidene camphor, 3-benzylidene camphor and octocrylene, and two allowed inorganic filters: zinc oxide and titanium dioxide, is presented and discussed. Taken together, this review advocates revisiting the current safety and regulation of specific sunscreens and investing in alternative UV protection technologies.

Gold Nanoparticles Induced Endothelial Leakiness Depends on Particle Size and Endothelial Cell Origin

The endothelium presents a formidable barrier for cancer nanomedicine, as the intravenously introduced nanomedicine needs to leave the blood vessel at the tumor site. Endothelial permeability and retention effect (EPR) is not dependable since it is derived from tumors. Certain nanoparticles with specific characteristics are able to induce micrometer sized gaps between endothelial cells. This effect is called "nanoparticle induced endothelial leakiness" (NanoEL). NanoEL therefore allows the nanotechnology to control access to the tumor even in the absence of any EPR effect. Morever, NanoEL can be applicable to noncancer issues, thereby expanding its usefulness in other subfields of nanomedicine. In this paper, we have shown that Gold (Au) nanoparticles within the range of 10-30 nm are good NanoEL inducing particles. As not all endothelial cells have the same permeability, we found that human mammary endothelial cells and human skin endothelial cells are sensitive to Au induced NanoEL, while human umbilical vein endothelial cells are insensitive, reflective of their innate nature of endothelial permeability. The size window and endothelial cell type sensitivity then helps the nanotechnologists to design future nanoparticles that either exploit NanoEL as a nanotechnology driven strategy to access immature tumors, which do not induce the EPR effect, or avoid NanoEL as a nanotoxic side effect.

Particulate matter from indoor environments of classroom induced higher cytotoxicity and leakiness in human microvascular endothelial cells in comparison with those collected from corridor

We investigated the physicochemical properties (size, shape, elemental composition, and endotoxin) of size resolved particulate matter (PM) collected from the indoor and corridor environments of classrooms. A comparative hazard profiling of these PM was conducted using human microvascular endothelial cells (HMVEC). Oxidative stress-dependent cytotoxicity responses were assessed using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and high content screening (HCS), and disruption of monolayer cell integrity was assessed using fluorescence microscopy and transwell assay. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) analysis showed differences in the morphology and elemental composition of PM of different sizes and origins. While the total mass of PM collected from indoor environment was lower in comparison with those collected from the corridor, the endotoxin content was substantially higher in indoor PM (e.g., ninefold higher endotoxin level in indoor PM_8.1-20 ). The ability to induce oxidative stress-mediated cytotoxicity and leakiness in cell monolayer were higher for indoor PM compared to those collected from the corridor. In conclusion, this comparative analysis suggested that indoor PM is relatively more hazardous to the endothelial system possibly because of higher endotoxin content.

The Effect of Different Types of Nanoparticles on FUS and TDP-43 Solubility and Subcellular Localization

Increased environmental pollution has been suggested as one of the possible causes for increased incidence of neurodegenerative and developmental disorders. Through the environmental pollution, everyday consumer products and nanomedical applications, we are also exposed to various nanoparticles (NPs). Specific types of NPs have been shown to be able to cause neural damage in vivo through processes such as disruption of the blood-brain barrier, induction of neuroinflammation, increase in oxidative stress and protein aggregation. In this study, we analysed the influence of PEI-coated magnetic NPs designed for biotechnological applications and industrial SiO₂, TiO₂ N and TiO₂ P25 NPs on intracellular localization and solubility of fused in farcoma (FUS) and TAR-DNA binding protein 43 (TDP-43) that are important pathological hallmarks of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). SH-SY5Y neuroblastoma cells and B16 mouse melanoma cells were exposed to NPs for 24 h and analysed using confocal microscopy and Western blot. Exposure to 50 μg/ml TiO₂ N and 4 μg/ml PEI NPs in SH-SY5Y cells caused cell toxicity-induced changes in expression in different biochemical/cellular fractions for both FUS and TDP-43 proteins. TiO₂ N induced a drop in nuclear levels of TDP-43 and increase in cytoplasmic levels of FUS, while PEI NPs increased nuclear levels of FUS. Furthermore, TiO₂ N and PEI induced a reduction of FUS and TDP-43 quantity in the less soluble urea fraction. No formation of stress granules was observed. These results demonstrate that TiO₂ N and PEI NPs can affect the behaviour of FUS and TDP-43 proteins; however, the changes were relatively minor compared to pathological changes even for the high NP concentrations (50 μg/ml) used in this study.

Hazardous Effects of Titanium Dioxide Nanoparticles in Ecosystem

Although nanoparticles (NPs) have made incredible progress in the field of nanotechnology and biomedical research and their applications are demanded throughout industrial world particularly over the past decades, little is known about the fate of nanoparticles in ecosystem. Concerning the biosafety of nanotechnology, nanotoxicity is going to be the second most priority of nanotechnology that needs to be properly addressed. This review covers the chemical as well as the biological concerns about nanoparticles particularly titanium dioxide (TiO₂) NPs and emphasizes the toxicological profile of TiO₂ at the molecular level in both in vitro and in vivo systems. In addition, the challenges and future prospects of nanotoxicology are discussed that may provide better understanding and new insights into ongoing and future research in this field.

Influence of silver and titanium dioxide nanoparticles on in vitro blood-brain barrier permeability

An in vitro blood-brain barrier (BBB) model being composed of co-culture with endothelial (bEnd.3) and astrocyte-like (ALT) cells was established to evaluate the toxicity and permeability of Ag nanoparticles (AgNPs; 8nm) and TiO₂ nanoparticles (TiO₂NPs; 6nm and 35nm) in normal and inflammatory central nervous system. Lipopolysaccharide (LPS) was pre-treated to simulate the inflammatory responses. Both AgNPs and Ag ions can decrease transendothelial electrical resistance (TEER) value, and cause discontinuous tight junction proteins (claudin-5 and zonula occludens-1) of BBB. However, only the Ag ions induced inflammatory cytokines to release, and had less cell-to-cell permeability than AgNPs, which indicated that the toxicity of AgNPs was distinct from Ag ions. LPS itself disrupted BBB, while co-treatment with AgNPs and LPS dramatically enhanced the disruption and permeability coefficient. On the other hand, TiO₂NPs exposure increased BBB penetration by size, and disrupted tight junction proteins without size dependence, and many of TiO₂NPs accumulated in the endothelial cells were observed. This study provided the new insight of toxic potency of AgNPs and TiO₂NPs in BBB.

Knowledge gaps between nanotoxicological research and nanomaterial safety

With the wide research and application of nanomaterials in various fields, the safety of nanomaterials attracts much attention. An increasing number of reports in the literature have shown the adverse effects of nanomaterials, representing the quick development of nanotoxicology. However, many studies in nanotoxicology have not reflected the real nanomaterial safety, and the knowledge gaps between nanotoxicological research and nanomaterial safety remain large. Considering the remarkable influence of biological or environmental matrices (e.g., biological corona) on nanotoxicity, the situation of performing nanotoxicological experiments should be relevant to the environment and humans. Given the possibility of long-term and low-concentration exposure of nanomaterials, the reversibility of and adaptation to nanotoxicity, and the transgenerational effects should not be ignored. Different from common pollutants, the specific analysis methodology for nanotoxicology need development and exploration furthermore. High-throughput assay integrating with omics was highlighted in the present review to globally investigate nanotoxicity. In addition, the biological responses beyond individual levels, special mechanisms and control of nanotoxicity deserve more attention. The progress of nanotoxicology has been reviewed by previous articles. This review focuses on the blind spots in nanotoxicological research and provides insight into what we should do in future work to support the healthy development of nanotechnology and the evaluation of real nanomaterial safety.

In vitro screening of nanomedicines through the blood brain barrier: A critical review

The blood-brain barrier accounts for the high attrition rate of the treatments of most brain disorders, which therefore remain one of the greatest health-care challenges of the twenty first century. Against this background of hindrance to brain delivery, nanomedicine takes advantage of the assembly at the nanoscale of available biomaterials to provide a delivery platform with potential to raising brain levels of either imaging or therapeutic agents. Nevertheless, to prevent later failure due to ineffective drug levels at the target site, researchers have been endeavoring to develop a battery of in vitro screening procedures that can predict earlier in the drug discovery process the ability of these cutting-edge drug delivery platforms to cross the blood-brain barrier for biomedical purposes. This review provides an in-depth analysis of the currently available in vitro blood-brain barrier models (both cell-based and non-cell-based) with the focus on their suitability for understanding the biological brain distribution of forthcoming nanomedicines. The relationship between experimental factors and underlying physiological assumptions that would ultimately lead to a more predictive capacity of their in vivo performance, and those methods already assayed for the evaluation of the brain distribution of nanomedicines are comprehensively discussed.

How air pollution alters brain development: the role of neuroinflammation

The present review synthesizes lines of emerging evidence showing how several samples of children populations living in large cities around the world suffer to some degree neural, behavioral and cognitive changes associated with air pollution exposure. The breakdown of natural barriers warding against the entry of toxic particles, including the nasal, gut and lung epithelial barriers, as well as widespread breakdown of the blood-brain barrier facilitatethe passage of airborne pollutants into the body of young urban residents. Extensive neuroinflammation contributes to cell loss within the central nervous system, and likely is a crucial mechanism by which cognitive deficits may arise. Although subtle, neurocognitive effects of air pollution are substantial, apparent across all populations, and potentially clinically relevant as early evidence of evolving neurodegenerative changes. The diffuse nature of the neuroinflammation risk suggests an integrated neuroscientific approach incorporating current clinical, cognitive, neurophysiological, radiological and epidemiologic research. Neuropediatric air pollution research requires extensive multidisciplinary collaborations to accomplish the goal of protecting exposed children through multidimensional interventions having both broad impact and reach. While intervening by improving environmental quality at a global scale is imperative, we also need to devise efficient strategies on how the neurocognitive effects on local pediatric populations should be monitored.

A review on potential neurotoxicity of titanium dioxide nanoparticles

As the rapid development of nanotechnology in the past three decades, titanium dioxide nanoparticles (TiO2 NPs), for their peculiar physicochemical properties, are widely applied in consumer products, food additives, cosmetics, drug carriers, and so on. However, little is known about their potential exposure and neurotoxic effects. Once NPs are unintentionally exposed to human beings, they could be absorbed, and then accumulated in the brain regions by passing through the blood-brain barrier (BBB) or through the nose-to-brain pathway, potentially leading to dysfunctions of central nerve system (CNS). Besides, NPs may affect the brain development of embryo by crossing the placental barrier. A few in vivo and in vitro researches have demonstrated that the morphology and function of neuronal or glial cells could be impaired by TiO2 NPs which might induce cell necrosis. Cellular components, such as mitochondrial, lysosome, and cytoskeleton, could also be influenced as well. The recognition ability, spatial memory, and learning ability of TiO2 NPs-treated rodents were significantly impaired, which meant that accumulation of TiO2 NPs in the brain could lead to neurodegeneration. However, conclusions obtained from those studies were not consistent with each other as researchers may choose different experimental parameters, including administration ways, dosage, size, and crystal structure of TiO2 NPs. Therefore, in order to fully understand the potential risks of TiO2 NPs to brain health, figure out research areas where further studies are required, and improve its bio-safety for applications in the near future, how TiO2 NPs interact with the brain is investigated in this review by summarizing the current researches on neurotoxicity induced by TiO2 NPs.

Titanium dioxide nanoparticles modulate the toxicological response to cadmium in the gills of Mytilus galloprovincialis

We investigated the influence of titanium dioxide nanoparticles (nano-TiO2) on the response to cadmium in the gills of the marine mussel Mytilus galloprovincialis in terms of accumulation and toxicity. Mussels were in vivo exposed to nano-TiO2, CdCl2, alone and in combination. Several cellular biomarkers were investigated in gills: ABC transport proteins and metallothioneins at gene/protein (abcb1, abcc-like and mt-20) and functional level, GST activity, NO production and DNA damage (Comet assay). Accumulation of total Cd and titanium in gills as in whole soft tissue was also investigated. Significant responses to Cd exposure were observed in mussel gills as up-regulation of abcb1 and mt-20 gene transcription, increases in total MT content, P-gp efflux and GST activity, DNA damage and NO production. Nano-TiO2 alone increased P-gp efflux activity and NO production. When combined with Cd, nano-TiO2 reduced the metal-induced effects by significantly lowering abcb1 gene transcription, GST activity, and DNA damage, whereas, additive effects were observed on NO production. A lower concentration of Cd was observed in the gills upon co-exposure, whereas, Ti levels were unaffected. A competitive effect in uptake/accumulation of nano-TiO2 and Cd seems to occur in gills. A confirmation is given by the observed absence of adsorption of Cd onto nano-TiO2 in sea water media.

Environmental influence in the brain, human welfare and mental health

The developing human brain is shaped by environmental exposures--for better or worse. Many exposures relevant to mental health are genuinely social in nature or believed to have social subcomponents, even those related to more complex societal or area-level influences. The nature of how these social experiences are embedded into the environment may be crucial. Here we review select neuroscience evidence on the neural correlates of adverse and protective social exposures in their environmental context, focusing on human neuroimaging data and supporting cellular and molecular studies in laboratory animals. We also propose the inclusion of innovative methods in social neuroscience research that may provide new and ecologically more valid insight into the social-environmental risk architecture of the human brain.

Tissue biodistribution of intravenously administrated titanium dioxide nanoparticles revealed blood-brain barrier clearance and brain inflammation in rat

BACKGROUND

Notwithstanding increasing knowledge of titanium dioxide nanoparticles (TiO2 NPs) passing through biological barriers, their biodistribution to the central nervous system (CNS) and potential effects on blood-brain barrier (BBB) physiology remain poorly characterized.

METHODS

Here, we report time-related responses from single-dose intravenous (IV) administration of 1 mg/kg TiO2 NPs to rats, with particular emphasis on titanium (Ti) quantification in the brain. Ti content in tissues was analyzed using inductively coupled plasma mass spectrometry. Integrity and functionality of the BBB as well as brain inflammation were characterized using a panel of methods including RT-PCR, immuno-histo chemistry and transporter activity evaluation.

RESULTS

Biokinetic analysis revealed Ti biopersistence in liver, lungs and spleen up to one year after TiO2 NPs administration. A significant increase of Ti in the brain was observed at early end points followed by a subsequent decrease. In-depth analysis of Ti in the total brain demonstrated quantitative Ti uptake and clearance by brain microvasculature endothelial cells (BECs) with minimal translocation in the brain parenchyma. The presence of Ti in the BECs did not affect BBB integrity, despite rapid reversible modulation of breast cancer resistance protein activity. Ti biopersistence in organs such as liver was associated with significant increases of tight junction proteins (claudin-5 and occludin), interleukin 1β (IL-1β), chemokine ligand 1 (CXCL1) and γ inducible protein-10 (IP-10/CXCL10) in BECs and also increased levels of IL-1β in brain parenchyma despite lack of evidence of Ti in the brain. These findings mentioned suggest potential effect of Ti present at a distance from the brain possibly via mediators transported by blood. Exposure of an in vitro BBB model to sera from TiO2 NPs-treated animals confirmed the tightness of the BBB and inflammatory responses.

CONCLUSION

Overall, these findings suggest the clearance of TiO2 NPs at the BBB with persistent brain inflammation and underscore the role of Ti biopersistence in organs that can exert indirect effects on the CNS dependent on circulating factors.

Interactions between nanosized materials and the brain

The current rapid development of nanotechnologies and engineered nanomaterials (ENM) will impact the society in a major fashion during the coming decades. This development also causes substantial safety concerns. Among the many promising applications of ENM, products that can be used for diagnosis and treatment of diseases, including conditions that affect the nervous system, are under development. ENM can pass the blood brain barrier (BBB) and accumulate within the brain. It seems that the nano-form rather than the bulk form of the chemicals pass the BBB, and that there is an inverse relationship between particle size and the ability to penetrate the BBB. Although translocation of ENM to the brain is possible during experimental conditions, the health relevance for real-life situations is far from clear. One major reason for this is that studies have been using nanoparticle concentrations that are far higher than the ones that can be expected during realistic exposures. However, very high exposure to the CNS can cause effects on neurotransmission, redox homeostasis and behavior. Available studies have been focusing on possible effects of the first generation of ENM. It will be necessary to study possible health effects also of expected novel sophisticated materials, independent of the outcome of present studies. The prospects for intended or targeted medical applications are promising since it has been shown that ENM can be made to pass the BBB and reach specific regions or cells within the brain.