Polymorph- and size-dependent uptake and toxicity of TiO₂ nanoparticles in living lung epithelial cells

Cellular and In Vivo Response to Industrial, Food Grade, and Photocatalytic TiO2 Nanoparticles

We encounter titanium dioxide nanoparticles (TiO2 NPs) throughout our daily lives in the form of food coloring, cosmetics, and industrial materials. They are used on a massive industrial scale, with over 1 million metric tons in the global market. For the workers who process these materials, inhalation is a major concern. The goal of our current research is to provide a direct comparison of the three major types of TiO2 NPs (P25, E171, R101) in terms of surface characterization, cellular response, and in vivo response following introduction into the lungs of mice. In both cellular and in vivo experiments, we observe a pro-inflammatory response to the P25 TiO2 NPs that is not observed in the E171 or R101 TiO2 NPs at mass-matched concentrations. Cellular experiments measured a cytokine, TNF-α, as a marker of a pro-inflammatory response. In vivo experiments in mice measured the number of immune cells and four pro-inflammatory cytokines (IL-6, MIP-2, IP-10, and MCP-1) present in bronchoalveolar lavage fluid. A detailed physical and chemical characterization of the TiO2 NPs shows that the P25 TiO2 NPs are distinguished by smaller primary particles suggesting that samples matched by mass contain a larger number of P25 TiO2 NPs. Cellular dose-response measurements with the P25, E171, and R101 TiO2 NPs support this hypothesis showing increased TNF-α release by macrophages as a function of TiO2 NP dose. Overall, this direct comparison of the three major types of TiO2 NPs shows that the number of particles in a dose, which is dependent on the particle diameter, is a key parameter in TiO2 NP-induced inflammation.

Magnetic Nanoparticles: A Comprehensive Review from Synthesis to Biomedical Frontiers

Nanotechnology has opened new doors of exploration, particularly in materials science and healthcare. Magnetic nanoparticles (MNP), the tiny magnets, because of their various properties, have the potential to bring about radical changes in the field of medicine. The distinctive surface chemistry, nontoxicity, biocompatibility, and, in particular, the inducible magnetic moment of magnetic materials has attracted a great deal of interest in morphological structures from a variety of scientific domains. This review presents a concise overview of MNPs and their crucial properties and synthesis routes. It also aims to highlight the continuous synthesis methods available for MNP production. In recent years, the use of computational methods for understanding the behavior of nanoparticles has been on the rise. Thus, we also discuss the numerical models developed to understand how magnetic nanoparticles can be used in magnetic hyperthermia and targeting the Circle of Wilis. With the increasing use of MNPs in biomedical applications, it becomes necessary to understand the mechanisms of toxicity, which are elucidated in this review. The review focuses on the biomedical applications of MNPs in drug delivery, theranostics, and MRI contrasting agents. We anticipate that this article will broaden the perspective on magnetic nanoparticles and help to understand their functionality and applicability better.

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

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

Influence of silver doping on pro-inflammatory and pro-fibrogenic effects of nano-titanium dioxide in murine lung

Silver is usually loaded on nano-titanium dioxide (TiO2 ) through photodeposition method to enhance visible-light catalytic functions for environment purification. However, little is known about how the toxicity changes after silver doping and how the physicochemical properties of loaded components affect nanocomposite toxicity. In this study, Ag-TiO2 with different sizes and contents of silver particles were obtained by controlling photodeposition time (PDT) and silver addition amount. Pro-inflammatory and pro-fibrogenic responses of these photocatalysts were evaluated in male C57BL/6J murine lung. As a result, silver was well assembled on TiO2 , promoting visible-light catalytic activity. Notably, the size of silver particles increased with PDT. Meanwhile, toxicity results showed that pure TiO2 (P25) mainly caused neutrophil infiltration, while 2 wt/wt% silver-loaded TiO2 recruited more types of inflammatory cells in the lung. Both of them caused the increase of proinflammatory cytokines while decreasing the anti-inflammatory cytokine in bronchoalveolar lavage fluid. However, 2 wt/wt% silver doping also accelerated the lung pro-fibrogenic response of photocatalysts in the subacute phase from evidence of collagen deposition and hydroxyproline concentrations. Mechanistically, the overactivation of TGFBR2 receptors in TGF-β/smads pathways by silver-loaded TiO2 rather than pure TiO2 may be the reason why silver-loaded TiO2 can promote pro-fibrogenic effect response. Intriguingly, the increased toxicity caused by silver doping can be rescued by increasing the size of the loaded silver or decreasing the silver amount. These results may be important for the new understanding of the toxicity of TiO2 -based photocatalysts.

Engineered Nanomaterials for Immunomodulation: A Review

The immune system usually provides a defense against invading pathogenic microorganisms and any other particulate contaminants. Nonetheless, it has been recently reported that nanomaterials can evade the immune system and modulate immunological responses due to their unique physicochemical characteristics. Consequently, nanomaterial-based activation of immune components, i.e., neutrophils, macrophages, and other effector cells, may induce inflammation and alter the immune response. Here, it is essential to distinguish the acute and chronic modulations triggered by nanomaterials to determine the possible risks to human health. Nanomaterials size, shape, composition, surface charge, and deformability are factors controlling their uptake by immune cells and the resulting immune responses. The exterior corona of molecules adsorbed over nanomaterials surfaces also influences their immunological effects. Here, we review current nanoengineering trends for targeted immunomodulation with an emphasis on the design, safety, and potential toxicity of nanomaterials. First, we describe the characteristics of engineered nanomaterials that trigger immune responses. Then, the biocompatibility and immunotoxicity of nanoengineered particles are debated, because these factors influence applications. Finally, future nanomaterial developments in terms of surface modifications, synergistic approaches, and biomimetics are discussed.

Enhancement of Antimicrobial Effect of Endodontic Sealers Using Nanoparticles: A Systematic Review

INTRODUCTION

The elimination of biofilms during root canal therapy continues to pose a challenge due to complex anatomies and uninstrumented portions of the root canal system. The incorporation of nanoparticles in endodontic sealers is an area of interest for potentially enhancing antimicrobial activity and improving treatment outcomes. This systematic review evaluated the antimicrobial effects of various nanoparticles in endodontic sealers.

METHODS

Comprehensive literature review was conducted using the electronic Embase, Web of Science, and PubMed databases followed by citation searching for articles eligible per the inclusion criteria.

RESULTS

A total of 1845 citations were screened, of which 13 articles met the inclusion criteria and were included in this review. All included articles were in vitro studies with low-to-moderate quality assessment scores. The incorporation of select nanoparticles was associated with significant enhancement of antibacterial effects in planktonic and/or biofilm forms, whereas other nanoparticles were not.

CONCLUSIONS

The incorporation of certain types and concentrations of nanoparticles into endodontic sealers displayed antimicrobial effects in vitro. The need for well-designed clinical studies translating in vitro findings into clinical practice is warranted. The incorporation of nanoparticles may enhance the antimicrobial properties of endodontic sealers and may improve treatment outcomes.

Metal-Based Nanoparticles in Food Packaging and Coating Technologies: A Review

Food security has continued to be a topic of interest in our world due to the increasing demand for food. Many technologies have been adopted to enhance food supply and narrow the demand gap. Thus, the attempt to use nanotechnology to improve food security and increase supply has emerged due to the severe shortcomings of conventional technologies, which have made them insufficient to cater to the continuous demand for food products. Hence, nanoparticles have been identified to play a major role in areas involving food production, protection, and shelf-life extensions. Specifically, metal-based nanoparticles have been singled out to play an important role in manufacturing materials with outstanding properties, which can help increase the shelf-life of different food materials. The physicochemical and biological properties of metal-based nanoparticles, such as the large surface area and antimicrobial properties, have made them suitable and adequately useful, not just as a regular packaging material but as a functional material upon incorporation into biopolymer matrices. These, amongst many other reasons, have led to their wide synthesis and applications, even though their methods of preparation and risk evaluation remain a topic of concern. This review, therefore, briefly explores the available synthetic methods, physicochemical properties, roles, and biological properties of metal-based nanoparticles for food packaging. Furthermore, the associated limitations, alongside quality and safety considerations, of these materials were summarily explored. Although this area of research continues to garner attention, this review showed that metal-based nanoparticles possess great potential to be a leading material for food packaging if the problem of migration and toxicity can be effectively modulated.

The Cytotoxicity of Tungsten Ions Derived from Nanoparticles Correlates with Pulmonary Toxicity

Tungsten carbide nanoparticles (nano-WC) are prevalent in composite materials, and are attributed to their physical and chemical properties. Due to their small size, nano-WC particles can readily infiltrate biological organisms via the respiratory tract, thereby posing potential health hazards. Despite this, the studies addressing the cytotoxicity of nano-WC remain notably limited. To this purpose, the BEAS-2B and U937 cells were cultured in the presence of nano-WC. The significant cytotoxicity of nano-WC suspension was evaluated using a cellular LDH assay. To investigate the cytotoxic impact of tungsten ions (W⁶⁺) on cells, the ion chelator (EDTA-2Na) was used to adsorb W⁶⁺ from nano-WC suspension. Subsequent to this treatment, the modified nano-WC suspension was subjected to flow cytometry analysis to evaluate the rates of cellular apoptosis. According to the results, a decrease in W⁶⁺ could mitigate the cellular damage and enhance cell viability, which indicated that W⁶⁺ indeed exerted a significant cytotoxic influence on the cells. Overall, the present study provides valuable insight into the toxicological mechanisms underlying the exposure of lung cells to nano-WC, thereby reducing the environmental toxicant risk to human health.

Biocompatibility and Biological Effects of Surface-Modified Conjugated Polymer Nanoparticles

Semiconductiong polymer nanoparticles (Pdots) have a wide range of applications in biomedical fields including biomolecular probes, tumor imaging, and therapy. However, there are few systematic studies on the biological effects and biocompatibility of Pdots in vitro and in vivo. The physicochemical properties of Pdots, such as surface modification, are very important in biomedical applications. Focusing on the central issue of the biological effects of Pdots, we systematically investigated the biological effects and biocompatibility of Pdots with different surface modifications and revealed the interactions between Pdots and organisms at the cellular and animal levels. The surfaces of Pdots were modified with different functional groups, including thiol, carboxyl, and amino groups, named Pdots@SH, Pdots@COOH, and Pdots@NH₂, respectively. Extracellular studies showed that the modification of sulfhydryl, carboxyl, and amino groups had no significant effect on the physicochemical properties of Pdots, except that the amino modification affected the stability of Pdots to a certain extent. At the cellular level, Pdots@NH₂ reduced cellular uptake capacity and increased cytotoxicity due to their instability in solution. At the in vivo level, the body circulation and metabolic clearance of Pdots@SH and Pdots@COOH were superior to those of Pdots@NH₂. The four kinds of Pdots had no obvious effect on the blood indexes of mice and histopathological lesions in the main tissues and organs. This study provides important data for the biological effects and safety assessment of Pdots with different surface modifications, which pave the way for their potential biomedical applications.

Smart Nanocarrier-Based Cancer Therapeutics

Considerable advances in the field of cancer have been made; however, these have not been translated into similar clinical progress which results in the high prevalence and increased cancer-related mortality rate worldwide. Available treatments have several challenges such as off-target side effects, non-specific long-term potential biodisruption, drug resistance, and overall inadequate response rates and high probability of recurrence. The limitations associated with independent cancer diagnosis and therapy can be minimized by an emerging interdisciplinary research field of nanotheranostics which include successful integration of diagnosis and therapy on a single agent using nanoparticles. This may offer a powerful tool in developing innovative strategies to enable "personalized medicine" for diagnosis and treatment of cancer. Nanoparticles have been proven to be powerful imaging tools or potent agents for cancer diagnosis, treatment, and prevention. The nanotheranostic provides minimally invasive in vivo visualization of drug biodistribution and accumulation at the target site with real-time monitoring of therapeutic outcome. This chapter intends to cover several important aspects and the advances in the field of nanoparticles-mediated cancer therapeutics including nanocarrier development, drug/gene delivery, intrinsically active nanoparticles, tumor microenvironment, and nanotoxicity. The chapter represents an overview of challenges associated with cancer treatment, rational for nanotechnology in cancer therapeutics, novel concepts of multifunctional nanomaterials for cancer therapy along with their classification and their clinical prospective in different cancers. A special focus is on the nanotechnology: regulatory perspective for drug development in cancer therapeutics. Obstacles hindering further development of nanomaterials-mediated cancer therapy are also discussed. In general, the objective of this chapter is to improve our perceptive in the design and development of nanotechnology for cancer therapeutics.

Toxicity of metal-based nanoparticles: Challenges in the nano era

With the rapid progress of nanotechnology, various nanoparticles (NPs) have been applicated in our daily life. In the field of nanotechnology, metal-based NPs are an important component of engineered NPs, including metal and metal oxide NPs, with a variety of biomedical applications. However, the unique physicochemical properties of metal-based NPs confer not only promising biological effects but also pose unexpected toxic threats to human body at the same time. For safer application of metal-based NPs in humans, we should have a comprehensive understanding of NP toxicity. In this review, we summarize our current knowledge about metal-based NPs, including the physicochemical properties affecting their toxicity, mechanisms of their toxicity, their toxicological assessment, the potential strategies to mitigate their toxicity and current status of regulatory movement on their toxicity. Hopefully, in the near future, through the convergence of related disciplines, the development of nanotoxicity research will be significantly promoted, thereby making the application of metal-based NPs in humans much safer.

Lack of mutagenicity of TiO2 nanoparticles in vitro despite cellular and nuclear uptake

The potential genotoxicity of titanium dioxide (TiO₂) nanoparticles (NPs) is a conflictive topic because both positive and negative findings have been reported. To add clarity, we have carried out a study with two cell lines (V79-4 and A549) to evaluate the effects of TiO₂ NPs (NM-101), with a diameter ranging from 15 to 60 nm, at concentrations 1-75 μg/cm². Using two different dispersion procedures, cell uptake was determined by Transmission Electron Microscopy (TEM). Mutagenicity was evaluated using the Hprt gene mutation test, while genotoxicity was determined with the comet assay, detecting both DNA breaks and oxidized DNA bases (with formamidopyrimidine glycosylase - Fpg). Cell internalization, as determined by TEM, shows TiO₂ NM-101 in cytoplasmic vesicles, as well as close to and inside the nucleus. Such internalization did not depend on the state of agglomeration, nor the dispersion used. In spite of such internalization, no cytotoxicity was detected in V79-4 cells (relative growth activity and plating efficiency assays) or in A549 cells (AlamarBlue assay) after exposure lasting for 24 h. However, a significant decrease in the relative growth activity was detected at longer exposure times (48 and 72 h) and at the highest concentration 75 µg/cm². When the modified enzyme-linked alkaline comet assay was performed on A549 cells, although no significant induction of DNA damage was detected, a positive concentration-effects relationship was observed (Spearman's correlation = 0.9, p 0.0001). Furthermore, no significant increase of DNA oxidized purine bases was observed. When the frequency of Hprt gene mutants was determined in V79-4 cells, no increase was observed in the exposed cells, relative to the unexposed cultures. Our general conclusion is that, under our experimental conditions, TiO₂ NM-101 exposure does not exert mutagenic effects despite the evidence of NP uptake by V79-4 cells.

Synthesis and Characterization of Titanium Oxide Nanoparticles with a Novel Biogenic Process for Dental Application

The prevalence of dental caries has been largely consonant over time despite the enhancement in dental technologies. This study aims to produce novel GIC restorative material by incorporating TiO₂ nanoparticles synthesized by Bacillus subtilis for the treatment of dental caries. The TiO₂ nanoparticles were prepared by inoculating a fresh culture of Bacillus subtilis into a nutrient broth for 24 h, which was then characterized by XRD, DRS, FTIR, AFM, SEM, TEM and EDX. These TiO₂ nanoparticles were incorporated in GIC restorative material at different concentrations (0–10% TiO₂ -GIC) and were tested for their mechanical properties in a universal testing machine. The XRD analysis revealed synthesis of anatase and rutile-phased TiO₂ nanoparticles with a particle size of 70.17 nm that was further confirmed by SEM and TEM analysis. The EDX spectrum indicated prominent peaks of titanium and oxygen with no impurities in the prepared material. Treatment with 5% TiO₂ -GIC proved to be most effective for the treatment of dental caries with no observable cytotoxic effect. An increase in the compressive strength of TiO₂ nanoparticle-reinforced GIC was observed as the concentration of the TiO₂ nanoparticles was increased up to 5%; subsequently, the compressive strength was lowered. An increase in the flexural strength was observed in GIC containing 0%, 3% and 5% TiO₂ nanoparticles sequentially. Based on the results, it can be concluded that Bacillus subtilis-derived TiO₂ nanoparticles have excellent potential for developing next generation of restorative materials for dental issues.

Toxicity of Nanoparticles in Biomedical Application: Nanotoxicology

Nanoparticles are of great importance in development and research because of their application in industries and biomedicine. The development of nanoparticles requires proper knowledge of their fabrication, interaction, release, distribution, target, compatibility, and functions. This review presents a comprehensive update on nanoparticles' toxic effects, the factors underlying their toxicity, and the mechanisms by which toxicity is induced. Recent studies have found that nanoparticles may cause serious health effects when exposed to the body through ingestion, inhalation, and skin contact without caution. The extent to which toxicity is induced depends on some properties, including the nature and size of the nanoparticle, the surface area, shape, aspect ratio, surface coating, crystallinity, dissolution, and agglomeration. In all, the general mechanisms by which it causes toxicity lie on its capability to initiate the formation of reactive species, cytotoxicity, genotoxicity, and neurotoxicity, among others.

Suitability of the In Vitro Cytokinesis-Block Micronucleus Test for Genotoxicity Assessment of TiO2 Nanoparticles on SH-SY5Y Cells

Standard toxicity tests might not be fully adequate for evaluating nanomaterials since their unique features are also responsible for unexpected interactions. The in vitro cytokinesis-block micronucleus (CBMN) test is recommended for genotoxicity testing, but cytochalasin-B (Cyt-B) may interfere with nanoparticles (NP), leading to inaccurate results. Our objective was to determine whether Cyt-B could interfere with MN induction by TiO₂ NP in human SH-SY5Y cells, as assessed by CBMN test. Cells were treated for 6 or 24 h, according to three treatment options: co-treatment with Cyt-B, post-treatment, and delayed co-treatment. Influence of Cyt-B on TiO₂ NP cellular uptake and MN induction as evaluated by flow cytometry (FCMN) were also assessed. TiO₂ NP were significantly internalized by cells, both in the absence and presence of Cyt-B, indicating that this chemical does not interfere with NP uptake. Dose-dependent increases in MN rates were observed in CBMN test after co-treatment. However, FCMN assay only showed a positive response when Cyt-B was added simultaneously with TiO₂ NP, suggesting that Cyt-B might alter CBMN assay results. No differences were observed in the comparisons between the treatment options assessed, suggesting they are not adequate alternatives to avoid Cyt-B interference in the specific conditions tested.

Characterization of toxicological effects of complex nano-sized metal particles using in vitro human cell and whole blood model systems

Metal oxide fumes form at high temperatures, for instance, during welding or firing ammunition. Inhalation exposure to high levels of airborne metal oxide particles can cause metal fume fever, cardiovascular effects, and lung damage in humans, but the associated underlying pathological mechanisms are still not fully understood. Using human alveolar epithelial cells, vascular endothelial cells, and whole blood model systems, we aimed to elucidate the short-term effects of well-characterized metal particles emitted while firing pistol ammunition. Human lung epithelial cells exposed to gunshot smoke particles (0.1-50 μg/ml) produced reactive oxygen species (ROS) and pro-inflammatory cytokines (interleukin 8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF)) that activate and recruit immune cells. Particles comprising high copper (Cu) and zinc (Zn) content activated human endothelial cells via a non-ROS-mediated mechanism that triggered immune activation (IL-8, GM-CSF), leukocyte adhesion to the endothelium (soluble intercellular adhesion molecule 1 (sICAM-1)), and secretion of regulators of the acute-phase protein synthesis (interleukin 6 (IL-6)). In human whole blood, metal oxides in gunshot smoke demonstrated intrinsic properties that activated platelets (release of soluble cluster of differentiation 40 ligand (sCD40L), platelet-derived growth factor B-chain homodimer(PDGF-BB), and vascular endothelial growth factor A (VEGF-A)) and blood coagulation and induced concomitant release of pro-inflammatory cytokines from blood leukocytes that further orchestrate thrombogenesis. The model systems applied provide useful tools for health risk assessment of particle exposures, but more studies are needed to further elucidate the mechanisms of metal fume fever and to evaluate the potential risk of long-term cardiovascular diseases.

Cytotoxicity and DNA damage evaluation of TiO2 and ZnO nanoparticles. Uptake in lung cells in culture

The cytotoxicity and DNA damage of titanium dioxide and zinc oxide nanoparticles (TiO₂ and ZnO NPs) have been studied in a human lung carcinoma cell line (A549) after 24 h exposure. TiO₂ and ZnO NPs had mean diameters of 12.9 ± 2.8 and 24.1 ± 8.0 nm, respectively. ZnO NPs reduced cell viability from 250 μg/mL, increasing reactive oxygen species (ROS) and decreased GSH/GSSG ratio. The comet assay detected DNA damage from 50 μg/mL. TiO₂ NPs induced cytotoxicity and DNA damage from 50 to 100 μg/mL, respectively, along with a decrease of the GSH/GSSG ratio. Both particles were found inside the cells, within membrane-bound vesicles. The internalization mechanism is promoted partially by caveolae-mediated endocytosis and, in the case of TiO₂ NPs, also by macropinocytosis.

siRNA delivery to macrophages using aspherical, nanostructured microparticles as delivery system for pulmonary administration

The delivery of oligonucleotides such as siRNA to the lung is a major challenge, as this group of drugs has difficulties to overcome biological barriers due to its polyanionic character and the associated hydrophilic properties, resulting in inefficient delivery. Especially in diseases such as asthma, chronic obstructive pulmonary disease and cystic fibrosis, where increased proinflammation is present, a targeted RNA therapy is desirable due to the high potency of these oligonucleotides. To address these problems and to ensure efficient uptake of siRNA in macrophages, a microparticulate, cylindrical delivery system was developed. In the first step, this particle system was tested for its aerodynamic characteristics to evaluate the aerodynamic properties to optimize lung deposition. The mass median aerodynamic diameter of 2.52 ± 0.23 µm, indicates that the desired target should be reached. The inhibition of TNF-α release, as one of the main mediators of proinflammatory reactions, was investigated. We could show that our carrier system can be loaded with siRNA against TNF-α. Gel electrophoreses allowed to demonstrate that the load can be incorporated and released without being degraded. The delivery system was found to transport a mass fraction of 0.371% [%w/w] as determined by inductively coupled plasma mass spectroscopy. When investigating the release kinetics, the results showed that several days are necessary to release a major amount of the siRNA indicating a sustained release. The cylindrical microparticles with an aspect ratio of 3.3 (ratio of length divided by width) were then tested in vitro successfully reducing TNF-α release from human macrophages significantly by more than 30%. The developed formulation presents a possible oligonucleotide delivery system allowing due to its internal structure to load and protect siRNA.

Impact of the Physicochemical Features of TiO2 Nanoparticles on Their In Vitro Toxicity

The concern about titanium dioxide nanoparticles (TiO₂-NPs) toxicity and their possible harmful effects on human health has increased. Their biological impact is related to some key physicochemical properties, that is, particle size, charge, crystallinity, shape, and agglomeration state. However, the understanding of the influence of such features on TiO₂-NP toxicity remains quite limited. In this study, cytotoxicity, proinflammatory response, and oxidative stress caused by five types of TiO₂-NPs with different physicochemical properties were investigated on A549 cells used either as monoculture or in co-culture with macrophages differentiated from the human monocytic THP-1 cells. We tailored bulk and surface TiO₂ physicochemical properties and differentiated NPs for size/specific surface area, shape, agglomeration state, and surface functionalization/charge (aminopropyltriethoxysilane). An impact on the cytotoxicity and to a lesser extent on the proinflammatory responses depending on cell type was observed, namely, smaller, large-agglomerated TiO₂-NPs were shown to be less toxic than P25, whereas rod-shaped TiO₂-NPs were found to be more toxic. Besides, the positively charged particle was slightly more toxic than the negatively charged one. Contrarily, TiO₂-NPs, whatever their physicochemical properties, did not induce significant ROS production in both cell systems compared to nontreated control groups. These results may contribute to a better understanding of TiO₂-NPs toxicity in relation with their physicochemical features.

Characterization of the in Vitro Osteogenic Response to Submicron TiO2 Particles of Varying Structure and Crystallinity

Titanium oxide (TiO2) nano-/microparticles have been widely used in orthopedic and dental sciences because of their excellent mechanical properties, chemical stability, and ability to promote the osseointegration of implants. However, how the structure and crystallinity of TiO2 particles may affect their osteogenic activity remains elusive. Herein, we evaluated the osteogenic response to submicron amorphous, anatase, and rutile TiO2 particles with controlled size and morphology. First, the ability of TiO2 particles to precipitate apatite was assessed in an acellular medium by using a simulated body fluid (SBF). Three days after the addition to SBF, anatase and rutile TiO2 particles induced the precipitation of aggregates of nanoparticles with a platelike morphology, typical for biomimetic apatite. Conversely, amorphous TiO2 particles induced the precipitation of particles with poor Ca/P atomic ratio only after 14 days of exposure to SBF. Next, the osteogenic response to TiO2 particles was assessed in vitro by incubating MC3T3-E1 preosteoblasts with the particles. The viability and mineralization efficiency of osteoblastic cells were maintained in the presence of all the tested TiO2 particles despite the differences in the induction of apatite precipitation in SBF by TiO2 particles with different structures. Analysis of the particles' surface charge and of the proteins adsorbed onto the particles from the culture media suggested that all the tested TiO2 particles acquired a similar biological identity in the culture media. We posited that this phenomenon attenuated potential differences in osteoblast response to amorphous, anatase, and rutile particles. Our study provides an important insight into the complex relationship between the physicochemical properties and function of TiO2 particles and sheds light on their safe use in medicine.

Green Synthesis of Ag-MnO2 Nanoparticles using Chelidonium majus and Vinca minor Extracts and Their In Vitro Cytotoxicity

Medicinal plants are often used as reducing agents to prepare metal nanoparticles through green-synthesis due to natural compounds and their potential as chemotherapeutic drugs. Thus, three types of eco-friendly Ag-MnO₂ nanoparticles (Ag-MnO₂NPs) were synthesized using C. majus (CmNPs), V. minor (VmNPs), and a 1:1 mixture of the two extracts (MNPs). These NPs were characterized using S/TEM, EDX, XRD, and FTIR methods, and their biological activity was assessed in vitro on normal keratinocytes (HaCaT) and skin melanoma cells (A375). All synthesized NPs had manganese oxide in the middle, and silver oxide and plant extract on the exterior. The NPs had different forms (polygonal, oval, and spherical), uniformly distributed, with crystalline structures and different sizes (9.3 nm for MNPs; 10 nm for VmNPs, and 32.4 nm for CmNPs). The best results were obtained with VmNPs, which reduced the viability of A375 cells up 38.8% and had a moderate cytotoxic effect on HaCaT (46.4%) at concentrations above 500 µg/mL. At the same concentrations, CmNPs had a rather proliferative effect, whereas MNPs negatively affected both cell lines. For the first time, this paper proved the synergistic action of the combined C. majus and V. minor extracts to form small and uniformly distributed Ag-MnO₂NPs with high potential for selective treatments.

Aging-independent and size-dependent genotoxic response induced by titanium dioxide nanoparticles in mammalian cells

Titanium dioxide nanoparticles (TiO₂ NPs) are subjected to various transformation processes (chemical, physical and biological processes) in the environment, potentially affecting their bioavailability and toxic properties. However, the size variation of TiO₂ NPs during aging process and subsequent effects in mammalian cells are largely unknown. The aim of this study was to illustrate the adverse effects of TiO₂ NPs in different sizes (5, 15 and <100 nm) during aging process on human-hamster hybrid (A_L) cells. There was an aging-time dependent enhancement of average hydrodynamic size in TiO₂ NPs stock suspensions. The cytotoxicity of fresh TiO₂ NPs increased in a size-dependent manner; in contrast, their genotoxicity decreased with the increasing sizes of NPs. No significant toxicity difference was observed in cells exposed to either fresh or 60 day-aged TiO₂ NPs. Both Fresh and aged TiO₂ NPs efficiently induced mitochondrial dysfunction and activated Caspase-3/7 in a size-dependent manner. Using mitochondrial-DNA deficient (ρ⁰) A_L cells, we further discovered that mitochondrial dysfunction made significant contribution to the size-dependent toxicity induced by TiO₂ NPs during the aging process. Taken together, our data indicated that TiO₂ NPs could significantly induced the cytotoxicity and genotoxicity in an aging time-independent and size-dependent manner, which were triggered by mitochondrial dysfunction. Our study suggested the necessity to include size as an additional parameter for the cautious monitoring of TiO₂ NPs disposal before entering the environment.

Engineered nanomaterials: From their properties and applications, to their toxicity towards marine bivalves in a changing environment

As a consequence of their unique characteristics, the use of Engineered Nanomaterials (ENMs) is rapidly increasing in industrial, agricultural products, as well as in environmental technology. However, this fast expansion and use make likely their release into the environment with particular concerns for the aquatic ecosystems, which tend to be the ultimate sink for this type of contaminants. Considering the settling behaviour of particulates, benthic organisms are more likely to be exposed to these compounds. In this way, the present review aims to summarise the most recent data available from the literature on ENMs behaviour and fate in aquatic ecosystems, focusing on their ecotoxicological impacts towards marine and estuarine bivalves. The selection of ENMs presented here was based on the OECD's Working Party on Manufactured Nanomaterials (WPMN), which involves the safety testing and risk assessment of ENMs. Physical-chemical characteristics and properties, applications, environmental relevant concentrations and behaviour in aquatic environment, as well as their toxic impacts towards marine bivalves are discussed. Moreover, it is also identified the impacts derived from the simultaneous exposure of marine organisms to ENMs and climate changes as an ecologically relevant scenario.

Evidence for Nanoparticle-Induced Lysosomal Dysfunction in Lung Adenocarcinoma (A549) Cells

Background: Polystyrene nanoparticles (PNP) are taken up by primary rat alveolar epithelial cell monolayers (RAECM) in a time-, dose-, and size-dependent manner without involving endocytosis. Internalized PNP in RAECM activate autophagy, are delivered to lysosomes, and undergo [Ca²⁺]-dependent exocytosis. In this study, we explored nanoparticle (NP) interactions with A549 cells. Methods: After exposure to PNP or ambient pollution particles (PM0.2), live single A549 cells were studied using confocal laser scanning microscopy. PNP uptake and egress were investigated and activation of autophagy was confirmed by immunolabeling with LC3-II and LC3-GFP transduction/colocalization with PNP. Mitochondrial membrane potential, mitophagy, and lysosomal membrane permeability (LMP) were assessed in the presence/absence of apical nanoparticle (NP) exposure. Results: PNP uptake into A549 cells decreased in the presence of cytochalasin D, an inhibitor of macropinocytosis. PNP egress was not affected by increased cytosolic [Ca²⁺]. Autophagy activation was indicated by increased LC3 expression and LC3-GFP colocalization with PNP. Increased LMP was observed following PNP or PM0.2 exposure. Mitochondrial membrane potential was unchanged and mitophagy was not detected after NP exposure. Conclusions: Interactions between NP and A549 cells involve complex cellular processes leading to lysosomal dysfunction, which may provide opportunities for improved nanoparticle-based therapeutic approaches to lung cancer management.

Titanium dioxide nanoparticles induce apoptosis by interfering with EGFR signaling in human breast cancer cells

Titanium dioxide nanoparticles, due to their smaller size and increased surface area comparted to the bulk form, are known to be bioreactive and have unexpected toxicological outcomes. Previous studies have shown that nanoscale titanium dioxide induces reactive oxygen species (ROS)-mediated cytotoxicity and genotoxicity. Although many reports have discussed the ROS-mediated cytotoxic effects of titanium dioxide nanoparticles (TiO2-NPs), their effects on the receptor-ligand association are unknown. In this study, the possibility that TiO2-NPs can interfere with the receptor-ligand binding was assessed by monitoring alterations in the phosphorylation status of proteins downstream of the epidermal growth factor receptor (EGFR) signaling cascade. TiO2-NPs blocked ligand-induced EGFR autophosphorylation, leading to the deactivation of EGFR downstream effectors such as Akt and extracellular signal-regulated kinase signaling, inducing cell death.

Endocytosis, intracellular fate, accumulation, and agglomeration of titanium dioxide (TiO2) nanoparticles in the rainbow trout liver cell line RTL-W1

There is increasing evidence that titanium dioxide (TiO2) nanoparticles (NPs) present in water or diet can be taken up by fish and accumulate in internal organs including the liver. However, their further fate in the organ is unknown. This study provides new insights into the interaction, uptake mechanism, intracellular trafficking, and fate of TiO2 NPs (Aeroxide® P25) in fish liver parenchymal cells (RTL-W1) in vitro using high-resolution transmission electron microscopy (TEM) and single particle inductively coupled plasma mass spectrometry (spICP-MS) as complementary analytical techniques. The results demonstrate that following their uptake via caveolae-mediated endocytosis, TiO2 NPs were trafficked through different intracellular compartments including early endosomes, multivesicular bodies, and late endosomes/endo-lysosomes, and eventually concentrated inside multilamellar vesicles. TEM and spICP-MS results provide evidence that uptake was nano-specific. Only NPs/NP agglomerates of a specific size range (~ 30-100 nm) were endocytosed; larger agglomerates were excluded from uptake and remained located in the extracellular space/exposure medium. NP number and mass inside cells increased linearly with time and was associated with an increase in particle diameter suggesting intracellular agglomeration/aggregation. No alterations in the expression of genes regulated by the redox balance-sensitive transcription factor Nrf-2 including superoxide dismutase, glutamyl cysteine ligase, glutathione synthetase, glutathione peroxidase, and glutathione S-transferase were observed. This shows that, despite the high intracellular NP burden (~ 3.9 × 102 ng Ti/mg protein after 24 h) and NP-interaction with mitochondria, cellular redox homeostasis was not significantly affected. This study contributes to a better mechanistic understanding of in vitro particokinetics as well as the potential fate and effects of TiO2 NPs in fish liver cells.

The impact of photocatalytic Ag/TiO2 and Ag/N-TiO2 nanoparticles on human keratinocytes and epithelial lung cells

The potential human health risks following the exposure to inorganic nanoparticles (NPs) is a very important issue for their application in leather finishing industry. The aim of our study was to investigate the cytotoxic effect of silver (Ag)/titanium dioxide (TiO₂) NPs on human cells. Photocatalytic NPs were prepared by electrochemical deposition of Ag on the surface of TiO₂ and nitrogen (N)-TiO₂ NPs and, subsequently, physico-chemical characterized. Then, a set of experiments have been performed to study the cytotoxicity and cell death mechanisms involved, the changes in cell morphology and the production of ROS induced in human keratinocytes (HaCaT) and human lung epithelial cells (A549) by exposure to NPs. Moreover, the changes in major signaling pathways and the inflammatory response induced by Ag/N-TiO₂ NPs in A549 cells were investigated. The data showed that cell death by late apoptosis/necrosis is induced in cells as function of the dose and the type of NPs and is characterized by morphological changes and cytoskeletal disorganization and an increase in reactive oxygen species (ROS) production. The exposure of A549 cells to Ag/N-TiO₂ NPs determine the activation of ERK1/2 MAP-kinase pathway and the release of pro-inflammatory mediators CXCL1, GM-CSF and MIF, known to be involved in the recruitment of circulating neutrophils and monocytes.

Reactive oxygen species independent genotoxicity of indium tin oxide nanoparticles triggered by intracellular degradation

Indium tin oxide (ITO) is widely used as a transparent conducting electrode in photoelectron devices. Because ITO production has soared, the potential health hazards caused by occupational exposure to this material have attracted much attention. However, little is known about the mechanisms of the toxic action of ITO nanoparticles (NPs). The present study was designed to examine the genotoxic mechanisms of ITO NPs using human lung epithelial A549 cells. We found that exposing A549 cells to ITO NPs triggered the intracellular accumulation of ITO NPs, the generation of reactive oxygen species (ROS), and the induction of DNA damage. Treatment of the cells with N-acetyl-l-cysteine (NAC), an ROS quenching agent, decreased intracellular ROS levels but not DNA damage, indicating that the genotoxic effect of ITO NPs is not mediated by intracellular ROS. Interestingly, treatment with ammonium chloride, a lysosomotropic agent, decreased intracellular solubility of ITO NPs and attenuated DNA damage. Nuclear accumulation of indium ions in ITO-NP-exposed cells was confirmed by inductively coupled plasma-mass spectrometry. Our results indicate that the ITO-NP-mediated genotoxicity is caused by indium ions that are solubilized in the acidic lysosomal condition and accumulated in the nucleus where they damage DNA, without the involvement of ROS.

Uniform TiO2 nanoparticles induce apoptosis in epithelial cell lines in a size-dependent manner

The size of titanium dioxide (TiO₂) nanoparticles is a vital parameter that determines their cytotoxicity. However, most reported studies have employed irregular shapes and sizes of TiO₂ nanoparticles, as it is difficult to produce nanoparticles of suitable sizes for research. We produced good model TiO₂ nanoparticles of uniform shape and size for use in studying their cytotoxicity. In this work, spherical, uniform polyethylene glycol-modified TiO₂ (TiO₂-PEG) nanoparticles of differing sizes (100, 200, and 300 nm) were prepared using the sol-gel method. A size-dependent decrease in cell viability was observed with increasing nanoparticle size. Furthermore, apoptosis was found to be positively associated with nanoparticle size, as evidenced by an increase in caspase-3 activity with increasing nanoparticle size. Larger nanoparticles exhibited higher cellular uptake, suggesting that larger nanoparticles more strongly induce apoptosis. In addition, the cellular uptake of different sizes of nanoparticles was energy dependent, suggesting that there are size-dependent uptake pathways. We found that 100 and 200 nm (but not 300 nm) nanoparticles were taken up via clathrin-mediated endocytosis. These results utilizing uniform nanoparticles suggest that the size-dependent cytotoxicity of nanoparticles involves active cellular uptake, caspase-3 activation, and apoptosis in the epithelial cell line (NCI-H292). These findings will hopefully aid in the future design and safe use of nanoparticles.

Host-sensitized sharp samarium emission from doped titanium dioxide nanoparticles as non-cytotoxic photostable reporters for live-cell imaging

This work introduces APTMS capped Ti(Sm)O₂ nanoparticles as reporters for live-cell imaging with negligible cytotoxicity and resistance to photobleaching.

Detecting Interactions between Nanomaterials and Cell Membranes by Synthetic Nanopores

Engineered nanomaterials have been increasingly utilized in industry for various consumer products, environmental treatments, energy storage, and biomedical applications. Meanwhile, it has been established that certain nanomaterials can be toxic to biological cells from extensive experimental and theoretical studies. Despite that the exact molecular mechanisms of this nanomaterial toxicity are still not well understood, it is ubiquitous that their interactions with cell membranes, through either endocytosis or penetration (and thus potential lysis), act as the first step toward the inflammation or even the death of a cell. To facilitate the study of nanomaterial-membrane interactions, here we demonstrate a nanopore-based single-molecule approach that can be applied to monitor a specific nanomaterial-membrane interaction in real time. Combined with molecular dynamics and experimental approaches, we show how an ionic current can be used to detect membrane damage by a graphene nanosheet and illustrate the underlying molecular mechanism. More generally, we expect that measured transmembrane ionic currents (both DC and AC) can signify many particle-induced membrane modifications, such as hole formation, particle adsorption, and protein insertion.

An In Silico study of TiO2 nanoparticles interaction with twenty standard amino acids in aqueous solution

Titanium dioxide (TiO₂) is probably one of the most widely used nanomaterials, and its extensive exposure may result in potentially adverse biological effects. Yet, the underlying mechanisms of interaction involving TiO₂ NPs and macromolecules, e.g., proteins, are still not well understood. Here, we perform all-atom molecular dynamics simulations to investigate the interactions between TiO₂ NPs and the twenty standard amino acids in aqueous solution exploiting a newly developed TiO₂ force field. We found that charged amino acids play a dominant role during the process of binding to the TiO₂ surface, with both basic and acidic residues overwhelmingly preferred over the non-charged counterparts. By calculating the Potential Mean Force, we showed that Arg is prone to direct binding onto the NP surface, while Lys needs to overcome a ~2 kT free energy barrier. On the other hand, acidic residues tend to form “water bridges” between their sidechains and TiO₂ surface, thus displaying an indirect binding. Moreover, the overall preferred positions and configurations of different residues are highly dependent on properties of the first and second solvation water. These molecular insights learned from this work might help with a better understanding of the interactions between biomolecules and nanomaterials.

Differential toxicity of Al2O3 particles on Gram-positive and Gram-negative sediment bacterial isolates from freshwater

The current study was aimed to explore the differential effects on Gram-positive and Gram-negative freshwater sediment bacterial isolates upon exposure to nano-particles and bulk particles of Al2O3 at low concentrations (0.25, 0.5, and 1 mg/L). The Gram-negative Pseudomonas aeruginosa was more susceptible to both the nano-forms and bulk forms than the Gram-positive Bacillus altitudinis. The generation of reactive oxygen species (ROS) and release of lipopolysaccharide due to membrane damage were dependent on the dose of nano-Al2O3. The Fourier transform infrared spectroscopy (FT-IR) studies confirmed the attachment of nano-Al2O3 on bacterial cells, which may lead to subsequent changes in the cell membrane composition and integrity. Internalization of nano-Al2O3 was estimated to be more for P. aeruginosa than for B. altitudinis cells. As a role of defense mechanism, the biofilm formation and production of extracellular polymeric substances (EPSs; polysaccharide and protein) were increased with respect to the concentration of toxicant. Nano-Al2O3 was estimated to cause more DNA damage than the bulk particles in both Gram-positive and Gram-negative bacterial strains.

Microglial cells (BV-2) internalize titanium dioxide (TiO2) nanoparticles: toxicity and cellular responses

Because of their whitening and photocatalytic effects, titanium dioxide nanoparticles (TiO2-NPs) are widely used in daily life. These NPs can be found in paints, plastics, papers, sunscreens, foods, medicines (pills), toothpastes, and cosmetics. However, the biological effect of TiO2-NPs on the human body, especially on the central nervous system, is still unclear. Many studies have demonstrated that the brain is one of the target organs in acute or chronic TiO2-NPs toxicity. The present study aimed to investigate the effect of TiO2-NPs at different concentrations (0.1 to 200 μg/mL) on murine microglial cells (BV-2) to assess their activity on cell growth and viability, as well as their neurotoxicity. Different parameters were measured: cell viability, cell proliferation and DNA content (SubG1 peak), mitochondrial depolarization, overproduction of reactive oxygen species (especially superoxide anions), and ultrastructural changes. Results showed that TiO2-NPs induced some cytotoxic effects with a slight inhibition of cell growth. Thus, at high concentrations, TiO2-NPs were not only able to inhibit cell adhesion but also enhanced cytoplasmic membrane permeability to propidium iodide associated with a loss of mitochondrial transmembrane potential and an overproduction of superoxide anions. No induction of apoptosis based on the presence of a SubG1 peak was detected. The microscopic observations also indicated that small groups of nanosized particles and micron-sized aggregates were engulfed by the BV-2 cells and sequestered as intracytoplasmic aggregates after 24-h exposure to TiO2-NPs. Altogether, our data show that the accumulation TiO2-NPs in microglial BV-2 cells favors mitochondrial dysfunctions and oxidative stress.

Noise Removal with Maintained Spatial Resolution in Raman Images of Cells Exposed to Submicron Polystyrene Particles

The biodistribution of 300 nm polystyrene particles in A549 lung epithelial cells has been studied with confocal Raman spectroscopy. This is a label-free method in which particles and cells can be imaged without using dyes or fluorescent labels. The main drawback with Raman imaging is the comparatively low spatial resolution, which is aggravated in heterogeneous systems such as biological samples, which in addition often require long measurement times because of their weak Raman signal. Long measurement times may however induce laser-induced damage. In this study we use a super-resolution algorithm with Tikhonov regularization, intended to improve the image quality without demanding an increased number of collected pixels. Images of cells exposed to polystyrene particles have been acquired with two different step lengths, i.e., the distance between pixels, and compared to each other and to corresponding images treated with the super-resolution algorithm. It is shown that the resolution after application of super-resolution algorithms is not significantly improved compared to the theoretical limit for optical microscopy. However, to reduce noise and artefacts in the hyperspectral Raman images while maintaining the spatial resolution, we show that it is advantageous to use short mapping step lengths and super-resolution algorithms with appropriate regularization. The proposed methodology should be generally applicable for Raman imaging of biological samples and other photo-sensitive samples.

Statistics, damned statistics and nanoscience - using data science to meet the challenge of nanomaterial complexity

For many years dealing with the complexity of nanoscale materials, the polydispersivity of individual samples, and the persistent imperfection of individual nanostructures has been secondary to our search for novel properties and promising applications. For our science to translate into technology, however, we will inevitably need to deal with the issue of structural diversity and integrate this feature into the next generation of more realistic structure/property predictions. This is challenging in the field of nanoscience where atomic level precision is typically inaccessible (experimentally), but properties can depend on structural variations at the atomic scale. Fortunately there exists a range of reliable statistical methods that are entirely applicable to nanoscale materials; ideal for navigating and analysing enormous amount of information required to accurately describe realistic samples. Combined with advances in automation and information technology the field of data science can assist us in dealing with our big data, characterising our uncertainties, and more rapidly identifying useful structure/property relationships. Taking greater advantage of data-driven methods involves thinking differently about our research, but applied appropriately these methods can accelerate the discovery of nanomaterials that are optimised to make the transition from science to technology.