Toxicity and health effects of ultrafine particles: Towards an understanding of the relative impacts of different transport modes.

Exposure to particulate matter (PM) has been associated with a wide range of adverse health effects, but it is still unclear how particles from various transport modes differ in terms of toxicity and associations with different human health outcomes. This literature review aims to summarize toxicological and epidemiological studies of the effect of ultrafine particles (UFPs), also called nanoparticles (NPs, <100 nm), from different transport modes with a focus on vehicle exhaust (particularly comparing diesel and biodiesel) and non-exhaust as well as particles from shipping (harbor), aviation (airport) and rail (mainly subway/underground). The review includes both particles collected in laboratory tests and the field (intense traffic environments or collected close to harbor, airport, and in subway). In addition, epidemiological studies on UFPs are reviewed with special attention to studies aimed at distinguishing the effects of different transport modes. Results from toxicological studies indicate that both fossil and biodiesel NPs show toxic effects. Several in vivo studies show that inhalation of NPs collected in traffic environments not only impacts the lung, but also triggers cardiovascular effects as well as negative impacts on the brain, although few studies compared NPs from different sources. Few studies were found on aviation (airport) NPs, but the available results suggest similar toxic effects as traffic-related particles. There is still little data related to the toxic effects linked to several sources (shipping, road and tire wear, subway NPs), but in vitro results highlighted the role of metals in the toxicity of subway and brake wear particles. Finally, the epidemiological studies emphasized the current limited knowledge of the health impacts of source-specific UFPs related to different transport modes. This review discusses the necessity of future research for a better understanding of the relative potencies of NPs from different transport modes and their use in health risk assessment.

ZnO nanoparticles-associated mitochondrial stress-induced apoptosis and G2/M arrest in HaCaT cells: a mechanistic approach.

Zinc oxide nanoparticles (ZnO NPs) with their wide range of consumer applications in day-to-day life received great attention to evaluate their effects in humans. This study has been attempted to elucidate the DNA damage response mechanism in a dermal model exposed to ZnO NPs through Ataxia Telangiectasia Mutated (ATM)-mediated ChK1-dependent G2/M arrest. Further, viability parameters and mechanism involved in the cell death with special reference to the consequences arising due to DNA damage were explored. Our study showed that ZnO NPs at concentrations 5 and 10 µg/ml induced significant cytotoxic effect in skin cell line. Moreover, the results confirmed generation of reactive oxygen species (ROS) induces the cell death by genotoxic insult, leading to mitochondrial membrane depolarisation and cell cycle arrest. Subsequently, ZnO NPs treatment created DNA damage as confirmed via Comet assay (increase in olive tail moment), micronucleus assay (increase in micronucleus formation), double-strand breaks (increase in ATM and Ataxia Telangiectasia and Rad3 related (ATR) expression), DNA fragmentation and cell cycle (G2/M arrest) studies. Finally, marker proteins analysis concluded the mechanistic approach by demonstrating the key marker expressions HMOX1 and HSP60 (for oxidative stress), cytochrome c, APAF1, BAX, Caspase 9, Caspase 3 and decrease in BCL2 (for activating apoptotic pathway), pATM, ATR and γH2AX (for double-strand breaks), DNA-PK (involved in DNA repair) and decrease in cell cycle regulators. In together, our data revealed the mechanism of ROS generation that triggers apoptosis and DNA damage in HaCaT cell lines exposed to ZnO NPs.

Health hazards of particles in additive manufacturing: a cross-disciplinary study on reactivity, toxicity and occupational exposure to two nickel-based alloys.

The increasing use of additive manufacturing (AM) techniques (e.g., 3D-printing) offers many advantages but at the same time presents some challenges. One concern is the possible exposure and health risk related to metal containing particles of different sizes. Using the nickel-based alloys Hastelloy X (HX) and Inconel 939 (IN939) as a case, the aim of this cross-disciplinary study was to increase the understanding on possible health hazards and exposure. This was done by performing in-depth characterization of virgin, reused and condensate powders, testing in vitro toxicity (cytotoxicity, genotoxicity, oxidative stress), and measuring occupational airborne exposure. The results showed limited metal release from both HX and IN939, and slightly different surface composition of reused compared to virgin powders. No or small effects on the cultured lung cells were observed when tested up to 100 µg/mL. Particle background levels in the printing facilities were generally low, but high transient peaks were observed in relation to sieving. Furthermore, during post processing with grinding, high levels of nanoparticles (> 100,000 particles/cm3) were noted. Urine metal levels in AM operators did not exceed biomonitoring action limits. Future studies should focus on understanding the toxicity of the nanoparticles formed during printing and post-processing.

Primary and Secondary Genotoxicity of Nanoparticles: Establishing a Co-Culture Protocol for Assessing Micronucleus Using Flow Cytometry.

Genotoxicity is an important endpoint to assess for understanding the risks associated with nanoparticles (NPs). Most genotoxicity studies performed on NPs have focused on primary genotoxicity analyzed by comet- or micronuclei (MN) assay using microscopic scoring. Here, we established a protocol for a more efficient version of MN assessment using flow cytometry and, importantly, both primary and secondary (inflammation-driven) genotoxicity was assessed. Human bronchial epithelial cells (HBEC-3kt) were exposed to nickel oxide (NiO) NPs directly or indirectly. The indirect exposure was done to assess secondary genotoxicity, and in this case immune cells (THP-1 derived macrophages) were exposed on inserts and the HBEC were cultured in the lower compartment. The results in monocultures showed that no increased MN formation was observed in the HBEC cells but instead a clear MN induction was noted in THP-1 cells indicating higher sensitivity. No MN formation was either observed when the HBEC were indirectly exposed, but an increase in DNA strand breaks was detected using the comet assay. Taken together, the present study emphasizes the feasibility of assessing primary and secondary genotoxicity and, furthermore, shows a clear MN induction in THP-1 monoculture following NiO NPs exposure.

Toxicity evaluation of particles formed during 3D-printing: Cytotoxic, genotoxic, and inflammatory response in lung and macrophage models.

Additive manufacturing (AM) or "3D-printing" is a ground-breaking technology that enables the production of complex 3D parts. Its rapid growth calls for immediate toxicological investigations of possible human exposures in order to estimate occupational health risks. Several laser-based powder bed fusion AM techniques are available of which many use metal powder in the micrometer range as feedstock. Large energy input from the laser on metal powders generates several by-products, like spatter and condensate particles. Due to often altered physicochemical properties and composition, spatter and condensate particles can result in different toxicological responses compared to the original powder particles. The toxicity of such particles has, however, not yet been investigated. The aim of the present study was to investigate the toxicity of condensate/spatter particles formed and collected upon selective laser melting (SLM) printing of metal alloy powders, including a nickel-chromium-based superalloy (IN939), a nickel-based alloy (Hastelloy X, HX), a high-strength maraging steel (18Ni300), a stainless steel (316L), and a titanium alloy (Ti6Al4V). Toxicological endpoints investigated included cytotoxicity, generation of reactive oxygen species (ROS), genotoxicity (comet and micronucleus formation), and inflammatory response (cytokine/chemokine profiling) following exposure of human bronchial epithelial cells (HBEC) or monocytes/macrophages (THP-1). The results showed no or minor cytotoxicity in the doses tested (10-100 µg/mL). Furthermore, no ROS generation or formation of micronucleus was observed in the HBEC cells. However, an increase in DNA strand breaks (detected by comet assay) was noted in cells exposed to HX, IN939, and Ti6Al4V, whereas no evident release of pro-inflammatory cytokine was observed from macrophages. Particle and surface characterization showed agglomeration in solution and different surface oxide compositions compared to the nominal bulk content. The extent of released nickel was small and related to the nickel content of the surface oxides, which was largely different from the bulk content. This may explain the limited toxicity found despite the high Ni bulk content of several powders. Taken together, this study suggests relatively low acute toxicity of condensates/spatter particles formed during SLM-printing using IN939, HX, 18Ni300, 316L, and Ti6Al4V as original metal powders.

Tuning the ATP-triggered pro-oxidant activity of iron oxide-based nanozyme towards an efficient antibacterial strategy.

An alarming increase in bacterial resistance towards various types of antibiotics makes it imperative to design alternate or combinational therapies to treat stubborn bacterial infections. In this perspective, emerging tools like nanozymes, nanomaterials with biological enzyme like characteristics, are being utilised to control infections caused by bacterial pathogens. Among several nanozymes used for antibacterial applications, Fe3O4 nanoparticles (NP) received great attention due to their effective peroxidase like activity. The pH dependent peroxidase activity of Fe3O4 NP results in generation of OH radical via the unique Fenton chemistry of iron. However, their pH dependent activity is restricted to acidic environment and dramatic loss in antibacterial activity is observed at near neutral pH. Here we describe a novel strategy to overcome the pH lacunae of citrate coated Fe3O4 NP by utilizing adenosine triphosphate disodium salt (ATP) as a synergistic agent to accelerate the OH radical production and restore its antibacterial activity over a wide range of pH. This synergistic combination (30 µg/mL Fe3O4 NP and 2.5 mM ATP) shows a high bactericidal activity against both gram positive (B. subtilis) and gram negative (E. coli) bacterial strains, in presence of H2O2, at neutral pH. The synergistic effect (Fe3O4 NP + ATP) is determined from the viability assessment and membrane damage studies and is further confirmed by comparing the concentration of generated OH radicals. Over all, this study illustrates ATP assisted and OH-mediated bactericidal activity of Fe3O4 nanozyme at near neutral pH.

Recent advances and future prospects of iron oxide nanoparticles in biomedicine and diagnostics.

Superparamagnetic iron oxide nanoparticles (SPIONs) are considered as chemically inert materials and, therefore, being extensively applied in the areas of imaging, targeting, drug delivery and biosensors. Their unique properties such as low toxicity, biocompatibility, potent magnetic and catalytic behavior and superior role in multifunctional modalities have epitomized them as an appropriate candidate for biomedical applications. Recent developments in the area of materials science have enabled the facile synthesis of Iron oxide nanoparticles (IONPs) offering easy tuning of surface properties and surface functionalization with desired biomolecules. Such developments have enabled IONPs to be easily accommodated in nanocomposite platform or devices. Additionally, the tag of biocompatible material has realized their potential in myriad applications of nanomedicines including imaging modalities, sensing, and therapeutics. Further, IONPs enzyme mimetic activity pronounced their role as nanozymes in detecting biomolecules like glucose, and cholesterol etc. Hence, based on their versatile applications in biomedicine, the present review article focusses on the current trends, developments and future prospects of IONPs in MRI, hyperthermia, photothermal therapy, biomolecules detection, chemotherapy, antimicrobial activity and also their role as the multifunctional agent in diagnosis and nanomedicines.

ATP-mediated intrinsic peroxidase-like activity of Fe3O4-based nanozyme: One step detection of blood glucose at physiological pH.

Fe3O4 nanoparticles (Fe3O4 NPs), demonstrating peroxidase-like activity has garnered attention in the detection of several biomolecules, therefore, emerged as an excellent nano-biosensing agent. The intrinsic peroxidase-like activity of Fe3O4 NPs at acidic pH is the fundamental action driving the oxidation of substrates like TMB, resulting in a colorimetric product formation used in the detection of biomolecules. Hence, the detection sensitivity essentially depends on the ability of oxidation by Fe3O4 NPs in presence of H2O2. However, the limited sensitivity and pH condition constraint have been identified as the major drawbacks in the detection of biomolecules at physiological pH. Herein, we report overwhelming of the fundamental limitation of acidic pH and tuning the peroxidase-like activity of Fe3O4 NPs at physiological pH by using ATP. In presence of ATP, Fe3O4 NPs exhibited enhanced peroxidase-like activity over a wide range of pH and temperatures. Mechanistically, it was found that the ability of ATP to participate in single electron transfer reaction, through complexation with Fe3O4 NPs, results in the generation of hydroxyl radicals which are responsible for enhanced peroxidase activity at physiological pH. We utilized this ATP-mediated enhanced peroxidase-like activity of Fe3O4 NPs for single step detection of glucose with a colorimetric detection limit of 50µM. Further, we extended this single step detection method to monitor glucose level in human blood serum and detected in a time span of <5min at pH 7.4.

Toxicity evaluation of carbon nanotubes in normal human bronchial epithelial cells.

Carbon nanotubes (CNTs) are well known for their exceptional thermal, mechanical and electrical properties. For many CNT applications it is of the foremost importance to know their health hazards related to their exposure. Normal human bronchial epithelial cells (BEAS-2B) has been used for assessment the cytotoxicity of SWCNT (Diameter--1.2-1.5 nm) and DWCNT (Diameter--1.3-5 nm). Clear interference of CNTs with conventional in vitro cytotoxicity assays (MTT, NRU and LDH) dye was found which was confirmed by acellular system. However morphological changes and flow cytometry showed the characteristics of cytotoxicity. Thus our study showed that there is a need of appropriate method for the assessment of cytotoxicity of CNT.

Toxicity of graphene in normal human lung cells (BEAS-2B).

Graphite nanomaterials such as thermally exfoliated graphite oxide (GO) are versatile in many applications. However, little is known about its effects on biological systems. In this study we characrerized the GO using dynamic light scattering (DLS) along with the toxicological aspects related to cytotoxicity and apoptosis in normal human lung cells (BEAS-2B). A significant concentration and time dependent decrease in cell viability was observed at different concentrations (10-100 microg/ml) by the MTT assay after 24 and 48 h of exposure and significant increase of early and late apoptotic cells was observed as compared to control cells. Our study demonstrates that GO induces cytotoxicity and apoptosis in human lung cells.