DNA damage and oxidative stress induced by CeO2 nanoparticles in human dermal fibroblasts: Evidence of a clastogenic effect as a mechanism of genotoxicity

Oxime-functionalized anti-insecticide fabric reduces insecticide exposure through dermal and nasal routes, and prevents insecticide-induced neuromuscular-dysfunction and mortality

Farmers from South Asian countries spray insecticides without protective gear, which leads to insecticide exposure through dermal and nasal routes. Acetylcholinesterase plays a crucial role in controlling neuromuscular function. Organophosphate and carbamate insecticides inhibit acetylcholinesterase, which leads to severe neuronal/cognitive dysfunction, breathing disorders, loss of endurance, and death. To address this issue, an Oxime-fabric is developed by covalently attaching silyl-pralidoxime to the cellulose of the fabric. The Oxime-fabric, when stitched as a bodysuit and facemask, efficiently deactivates insecticides (organophosphates and carbamates) upon contact, preventing exposure. The Oxime-fabric prevents insecticide-induced neuronal damage, neuro-muscular dysfunction, and loss of endurance. Furthermore, we observe a 100% survival rate in rats when repeatedly exposed to organophosphate-insecticide through the Oxime-fabric, while no survival is seen when organophosphate-insecticide applied directly or through normal fabric. The Oxime-fabric is washable and reusable for at least 50 cycles, providing an affordable solution to prevent insecticide-induced toxicity and lethality among farmers.

Cellular Alterations Due to Direct and Indirect Interaction of Nanomaterials with Nucleic Acids

Deoxyribonucleic acid (DNA) represents the main reservoir of genetic information in the cells, which is why it is protected in the nucleus. Entry into the nucleus is, in general, difficult, as the nuclear membrane is a selective barrier to molecules longer than 40 kDa. However, in some cases, the size of certain nanoparticles (NPs) allows their internalization into the nucleus, thus causing a direct effect on the DNA structure. NPs can also induce indirect effects on DNA through reactive oxygen species (ROS) generation. In this context, nanomaterials are emerging as a disruptive tool for the development of novel therapies in a broad range of biomedical fields; although their effect on cell viability is commonly studied, further interactions with DNA or indirect alterations triggered by the internalization of these materials are not always clarified, since the small size of these materials makes them perfectly suitable for interaction with subcellular structures, such as the nucleus. In this context, and using as a reference the predicted interactions presented in a computational model, we describe and discuss the observed direct and indirect effects of the implicated nanomaterials on DNA.

Human and environmental impacts of nanoparticles: a scoping review of the current literature

Use of nanoparticles have established benefits in a wide range of applications, however, the effects of exposure to nanoparticles on health and the environmental risks associated with the production and use of nanoparticles are less well-established. The present study addresses this gap in knowledge by examining, through a scoping review of the current literature, the effects of nanoparticles on human health and the environment. We searched relevant databases including Medline, Web of Science, ScienceDirect, Scopus, CINAHL, Embase, and SAGE journals, as well as Google, Google Scholar, and grey literature from June 2021 to July 2021. After removing duplicate articles, the title and abstracts of 1495 articles were first screened followed by the full-texts of 249 studies, and this resulted in the inclusion of 117 studies in the presented review.In this contribution we conclude that while nanoparticles offer distinct benefits in a range of applications, they pose significant threats to humans and the environment. Using several biological models and biomarkers, the included studies revealed the toxic effects of nanoparticles (mainly zinc oxide, silicon dioxide, titanium dioxide, silver, and carbon nanotubes) to include cell death, production of oxidative stress, DNA damage, apoptosis, and induction of inflammatory responses. Most of the included studies (65.81%) investigated inorganic-based nanoparticles. In terms of biomarkers, most studies (76.9%) used immortalised cell lines, whiles 18.8% used primary cells as the biomarker for assessing human health effect of nanoparticles. Biomarkers that were used for assessing environmental impact of nanoparticles included soil samples and soybean seeds, zebrafish larvae, fish, and Daphnia magna neonates.From the studies included in this work the United States recorded the highest number of publications (n = 30, 25.64%), followed by China, India, and Saudi Arabia recording the same number of publications (n = 8 each), with 95.75% of the studies published from the year 2009. The majority of the included studies (93.16%) assessed impact of nanoparticles on human health, and 95.7% used experimental study design. This shows a clear gap exists in examining the impact of nanoparticles on the environment.

Comparative toxicological evaluations of novel forms nano-pesticides in liver and lung of albino rats

Copper oxide Nanoparticles (CuONPs) are used in different agricultural applications. Large amounts of CuONPs cause organ dysfunction in animals. Our study aim to compare between the toxic effects of CuONanSphere (CuONSp) and CuONanoFlower (CuONF) as new nano-pesticides, determine a less toxic form when used in agricultural applications. To characterize CuONSp and CuONF, we used X-ray diffraction (XRD), Field emission scanning electron microscopy (SEM), and High resolution transmission electron microscopy (HRTEM) and Zeta-sizer device.18 adult male albino rats were divided into three groups (n = 6), (I) control group, (II) and (III) groups were given orally 50 mg/kg/day of CuONSp and CuONF 30 days respectively. CuONSp induced oxidant-antioxidant abnormalities, including an increase in malondialdhyde (MDA) and a decrease in glutathione (GSH) in comparison to CuONF-treated one. CuONSp induced an increase in liver enzymes activities compared to CuONF. Tumour necrosis factor-alfa (TNF-α) detected an increased in liver and lung compared to CuONF. However, histological examinations revealed changes in CuONSp group than CuONF group. Changes in immune-expressions of TNF-α, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kβ) and tumour suppressor gene (p53) were also more identified in CuONSp group than CuONF group. Ultrastructural studies of liver and lung tissues marked alternations were observed in CuONSp group than CuONF group. In conclusion, CuONSp induced biological alternation in liver and lung more than CuONF. So, CuONF is less toxic compared to CuONSp when used as nano-pesticide in agricultural applications.

Synthesis of cubosomes containing cerium oxide nanoparticles from Lactobacillus acidophilus loaded with glatiramer acetate and carboxymethylcellulose coating

Cerium oxide nanoparticles (nano-series) are used as catalysts in industrial applications due to their free radical scavenging properties. Given that free radicals play an essential role in the pathology of many neurological diseases, we investigated the use of nanocrystals as a potential therapeutic agent for oxidative damage. This project synthesized nano-series from a new and environmentally friendly bio-pathway. Investigation of cerium nitrate in culture medium containing inoculated Lactobacillus acidophilus strain before incubation produces nano-series. Loaded with glatiramer acetate (GA) was formed by coating carboxymethylcellulose (CMC) and CeO₂. FE-SEM analysis showed nano-series in the 9-11 nm range, spherical shape, and uniform particle size distribution. Cubic nanoparticles containing anti-multiple sclerosis (anti-Ms) treatment called GA were used. Glycerol monostearate (GMS) was used as a fat base, and evening primrose extract was used as an anti-inflammatory in cubosomes. Design-Expert® software was used to study the effects of different formulation factors on the properties of GA-loaded cubic dispersions. Thirty GA-labeled cubic dispersions were prepared with GA-labeled carboxymethylcellulose and evaluated in vitro. The results showed an average nano-series size of 89.02 and a zeta potential of -49.9. Cubosomes containing GA-CMC/CeO₂ showed a stable release profile for 180 min. The results showed that cubosomes containing GA-CMC/CeO₂ could be a promising drug carrier with normal release behavior.

CeO2 nanoparticles improve prooxidant/antioxidant balance, life quality and survival of old male rats

Due to its unique redox chemistry, nanoceria is considered as potent free radical scavenger and antioxidant. However, their protective capacity in aging organisms remains controversial. To detect the anti-aging effects associated with the redox activity of 2 and 10 nm nano-CeO2, different test systems were used, including in vitro analysis, in situ assay of mitochondria function and in vivo studies of suitable nano-CeO₂ on aging of male Wistar rats from 22 months-old to the end of life. The 2 nm nanoparticles exhibited not only antioxidant (^·OH scavenging; chemiluminescence assay; decomposition of H₂O₂, phosphatidylcholine autooxidation) but also prooxidant properties (reduced glutathione and reduced nicotinamide adenine dinucleotide phosphate oxidation) as well as affected mitochondria whereas in most test systems 10 nm nano-CeO₂ showed less activity or was inert. Prolonged use of the more redox active 2 nm nano-CeO₂ (0.25-0.3 mg/kg/day) in vivo with drinking water resulted in improvement in physiological parameters and normalization of the prooxidant/antioxidant balance in liver and blood of aging animals. Survival analysis using Kaplan-Meier curve and Gehan tests with Yates' correction showed that by the time the prooxidant-antioxidant balance was assessed (32 months), survival rates exceeded the control values most considerably. The apparent median survival for the control rats was 900 days, and for the experimental rats-960 days. In general, the data obtained indicate the ability of extra-small 2 nm nano-CeO2 to improve quality of life and increase the survival rate of an aging organism.

Nanoparticle-based toxicity in perishable vegetable crops: Molecular insights, impact on human health and mitigation strategies for sustainable cultivation

With the advancement of nanotechnology, the use of nanoparticles (NPs) and nanomaterials (NMs) in agriculture including perishable vegetable crops cultivation has been increased significantly. NPs/NMs positively affect plant growth and development, seed germination, plant stress management, and postharvest handling of fruits and vegetables. However, these NPs sometimes cause toxicity in plants by oxidative stress and excess reactive oxygen species production that affect cellular biomolecules resulting in imbalanced biological and metabolic processes in plants. Therefore, information about the mechanism underlying interactions of NPs with plants is important for the understanding of various physiological and biochemical responses of plants, evaluating phytotoxicity, and developing mitigation strategies for vegetable crops cultivation. To address this, recent morpho-physiological, biochemical and molecular insights of nanotoxicity in the vegetable crops have been discussed in this review. Further, factors affecting the nanotoxicity in vegetables and mitigation strategies for sustainable cultivation have been reviewed. Moreover, the bioaccumulation and biomagnification of NPs and associated phytotoxicity can cause serious effects on human health which has also been summarized. The review also highlights the use of advanced omics approaches and interdisciplinary tools for understanding the nanotoxicity and their possible use for mitigating phytotoxicity.

Kinetic Characterization of Cerium and Gallium Ions as Inhibitors of Cysteine Cathepsins L, K, and S

Heavy metal ions can disrupt biological functions via multiple molecular mechanisms, including inhibition of enzymes. We investigate the interactions of human papain-like cysteine endopeptidases cathepsins L, K, and S with gallium and cerium ions, which are associated with medical applications. We compare these results with zinc and lead, which are known to inhibit thiol enzymes. We show that Ga³⁺, Ce³⁺, and Ce⁴⁺ ions inhibit all tested peptidases with inhibition constants in the low micromolar range (between 0.5 µM and 10 µM) which is comparable to Zn²⁺ ions, whereas inhibition constants of Pb²⁺ ions are one order of magnitude higher (30 µM to 150 µM). All tested ions are linear specific inhibitors of cathepsin L, but cathepsins K and S are inhibited by Ga³⁺, Ce³⁺, and Ce⁴⁺ ions via hyperbolic inhibition mechanisms. This indicates a mode of interaction different from that of Zn²⁺ and Pb²⁺ ions, which act as linear specific inhibitors of all peptidases. All ions also inhibit the degradation of insoluble elastin, which is a common target of these peptidases in various inflammatory diseases. Our results suggest that these ions and their compounds have the potential to be used as cysteine cathepsin inhibitors in vitro and possibly in vivo.

Cerium dioxide, a Jekyll and Hyde nanomaterial, can increase basal and decrease elevated inflammation and oxidative stress

It was hypothesized that the catalyst nanoceria can increase inflammation/oxidative stress from the basal and reduce it from the elevated state. Macrophages clear nanoceria. To test the hypothesis, M0 (non-polarized), M1- (classically activated, pro-inflammatory), and M2-like (alternatively activated, regulatory phenotype) RAW 264.7 macrophages were nanoceria exposed. Inflammatory responses were quantified by IL-1β level, arginase activity, and RT-qPCR and metabolic changes and oxidative stress by the mito and glycolysis stress tests (MST and GST). Morphology was determined by light microscopy, macrophage phenotype marker expression, and a novel three-dimensional immunohistochemical method. Nanoceria blocked IL-1β and arginase effects, increased M0 cell OCR and GST toward the M2 phenotype and altered multiple M1- and M2-like cell endpoints toward the M0 level. M1-like cells had greater volume and less circularity/roundness. M2-like cells had greater volume than M0 macrophages. The results are overall consistent with the hypothesis.

Recent trends in the application of nanoparticles in cancer therapy: The involvement of oxidative stress

In the biomedical area, the interdisciplinary field of nanotechnology has the potential to bring numerous unique applications, including better tactics for cancer detection, diagnosis, and therapy. Nanoparticles (NPs) have been the topic of many research and material applications throughout the last decade. Unlike small-molecule medications, NPs are defined by distinct physicochemical characteristics, such as a large surface-to-volume ratio, which allows them to permeate live cells with relative ease. The versatility of NPs as both therapeutics and diagnostics makes them ideal for a broad spectrum of illnesses, from infectious diseases to cancer. A significant amount of data has been participated in the current scientific publications, emphasizing the concept that NPs often produce reactive oxygen species (ROS) to a larger degree than micro-sized particles. It is important to note that oxidative stress governs a wide range of cell signaling cascades, many of which are responsible for cancer cell cytotoxicity. Here, we aimed to provide insight into the signaling pathways triggered by oxidative stress in cancer cells in response to several types of nanomaterials, such as metallic and polymeric NPs and quantum dots. We discuss recent advances in developing integrated anticancer medicines based on NPs targeted to destroy malignant cells by increasing their ROS setpoint.

In Vitro Hepatotoxic and Neurotoxic Effects of Titanium and Cerium Dioxide Nanoparticles, Arsenic and Mercury Co-Exposure

Considering the increasing emergence of new contaminants, such as nanomaterials, mixing with legacy contaminants, including metal(loid)s, it becomes imperative to understand the toxic profile resulting from these interactions. This work aimed at assessing and comparing the individual and combined hepatotoxic and neurotoxic potential of titanium dioxide nanoparticles (TiO₂NPs 0.75–75 mg/L), cerium oxide nanoparticles (CeO₂NPs 0.075–10 μg/L), arsenic (As 0.01–2.5 mg/L), and mercury (Hg 0.5–100 mg/L) on human hepatoma (HepG2) and neuroblastoma (SH-SY5Y) cells. Viability was assessed through WST-1 (24 h) and clonogenic (7 days) assays and it was affected in a dose-, time- and cell-dependent manner. Higher concentrations caused greater toxicity, while prolonged exposure caused inhibition of cell proliferation, even at low concentrations, for both cell lines. Cell cycle progression, explored by flow cytometry 24 h post-exposure, revealed that TiO₂NPs, As and Hg but not CeO₂NPs, changed the profiles of SH-SY5Y and HepG2 cells in a dose-dependent manner, and that the cell cycle was, overall, more affected by exposure to mixtures. Exposure to binary mixtures revealed either potentiation or antagonistic effects depending on the composition, cell type and time of exposure. These findings prove that joint toxicity of contaminants cannot be disregarded and must be further explored.

In vitro genotoxicity assessment and comparison of cerium (IV) oxide micro- and nanoparticles

Cerium (IV) oxide (CeO₂), which is used as a biomaterial, has wide application in areas such as the biomedical, glass polishing, electronic, automotive, and pharmacology industries. Comparing with the literature, in this study, the genotoxic effects of cerium (IV) oxide microparticles (COMPs) and cerium (IV) oxide nanoparticles (CONPs) were investigated for the first time in human peripheral blood cultures at concentrations of 0.78, 1.56, 3.125, 6.25, 12.5, 25, and 50 ppm for 72 h under in vitro conditions. Particle sizes of COMPs and CONPs were determined using scanning electron microscopic analysis. Micronucleus and chromosome aberration tests were used to determine the genotoxicity of COMPs and CONPs. The average particle sizes of COMPs and CONPs were approximately 148.25 and 25.30 nm, respectively. It was determined that CeO₂ particles in both micro and nano sizes were toxic at all concentrations compared to the negative control group (distilled water). Importantly, COMPs and CONPs were genotoxic even at the lowest concentration (0.78 ppm). Comparing particle sizes, the data indicated that COMPs were more toxic than CONPs. The results suggest that genotoxicity of COMPs and CONPs may be a function of applied concentrations and particle sizes.

In Vitro Co-Exposure to CeO2 Nanomaterials from Diesel Engine Exhaust and Benzo(a)Pyrene Induces Additive DNA Damage in Sperm and Cumulus Cells but Not in Oocytes

Benzo(a)pyrene (BaP) is a recognized reprotoxic compound and the most widely investigated polycyclic aromatic hydrocarbon in ambient air; it is widespread by the incomplete combustion of fossil fuels along with cerium dioxide nanomaterials (CeO₂ NMs), which are used in nano-based diesel additives to decrease the emission of toxic compounds and to increase fuel economy. The toxicity of CeO₂ NMs on reproductive organs and cells has also been shown. However, the effect of the combined interactions of BaP and CeO₂ NMs on reproduction has not been investigated. Herein, human and rat gametes were exposed in vitro to combusted CeO₂ NMs or BaP or CeO₂ NMs and BaP in combination. CeO₂ NMs were burned at 850 °C prior to mimicking their release after combustion in a diesel engine. We demonstrated significantly higher amounts of DNA damage after exposure to combusted CeO₂ NMs (1 µg·L^-1) or BaP (1.13 µmol·L^-1) in all cell types considered compared to unexposed cells. Co-exposure to the CeO₂ NMs-BaP mixture induced additive DNA damage in sperm and cumulus cells, whereas no additive effect was observed in rat oocytes. This result could be related to the structural protection of the oocyte by cumulus cells and to the oocyte's efficient system to repair DNA damage compared to that of cumulus and sperm cells.

Cerium Oxide Nanoparticles (Nanoceria): Hopes in Soft Tissue Engineering

Several biocompatible materials have been applied for managing soft tissue lesions; cerium oxide nanoparticles (CNPs, or nanoceria) are among the most promising candidates due to their outstanding properties, including antioxidant, anti-inflammatory, antibacterial, and angiogenic activities. Much attention should be paid to the physical properties of nanoceria, since most of its biological characteristics are directly determined by some of these relevant parameters, including the particle size and shape. Nanoceria, either in bare or functionalized forms, showed the excellent capability of accelerating the healing process of both acute and chronic wounds. The skin, heart, nervous system, and ophthalmic tissues are the main targets of nanoceria-based therapies, and the other soft tissues may also be evaluated in upcoming experimental studies. For the repair and regeneration of soft tissue damage and defects, nanoceria-incorporated film, hydrogel, and nanofibrous scaffolds have been proven to be highly suitable replacements with satisfactory outcomes. Still, some concerns have remained regarding the long-term effects of nanoceria administration for human tissues and organs, such as its clearance from the vital organs. Moreover, looking at the future, it seems necessary to design and develop three-dimensional (3D) printed scaffolds containing nanoceria for possible use in the concepts of personalized medicine.

Sol-Gel Synthesis, Physico-Chemical and Biological Characterization of Cerium Oxide/Polyallylamine Nanoparticles

Cerium oxide nanoparticles (CeO2-NPs) have great applications in different industries, including nanomedicine. However, some studies report CeO2-NPs-related toxicity issues that limit their usage and efficiency. In this study, the sol-gel method was applied to the synthesis of CeO2-NPs using poly(allylamine) (PAA) as a capping and/or stabilizing agent. The different molecular weights of PAA (15,000, 17,000, and 65,000 g/mol) were used to investigate the physico-chemical and biological properties of the NPs. In order to understand their performance as an anticancer agent, three cell lines (MCF7, HeLa, and erythrocyte) were analyzed by MTT assay and RBC hemolysis assay. The results showed that the CeO2-NPs had anticancer effects on the viability of MCF7 cells with half-maximal inhibitory concentration (IC50) values of 17.44 ± 7.32, 6.17 ± 1.68, and 0.12 ± 0.03 μg/mL for PAA15000, PAA17000, PAA65000, respectively. As for HeLa cells, IC50 values reduced considerably to 8.09 ± 1.55, 2.11 ± 0.33, and 0.20 ± 0.01 μg/mL, in order. A decrease in the viability of cancer cells was associated with the 50% hemolytic concentration (HC50) of 0.022 ± 0.001 mg/mL for PAA15000, 3.74 ± 0.58 mg/mL for PAA17000, and 7.35 ± 1.32 mg/mL for PAA65000. Ultraviolet-Visible (UV-vis) spectroscopy indicated that an increase in the PAA molecular weight led to a blue shift in the bandgap and high amounts of Ce3+ on the surface of the nanoceria. Thus, PAA65000 could be considered as a biocompatible nanoengineered biomaterial for potential applications in cancer nanomedicine.

Treatment of Human Lens Epithelium with High Levels of Nanoceria Leads to Reactive Oxygen Species Mediated Apoptosis

Nanoceria (cerium oxide nanoparticles) have been shown to protect human lens epithelial cells (HLECs) from oxidative stress when used at low concentrations. However, there is a lack of understanding about the mechanism of the cytotoxic and genotoxic effects of nanoceria when used at higher concentrations. Here, we investigated the impact of 24-hour exposure to nanoceria in HLECs. Nanoceria's effects on basal reactive oxygen species (ROS), mitochondrial morphology, membrane potential, ATP, genotoxicity, caspase activation and apoptotic hallmarks were investigated. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) studies on isolated mitochondria revealed significant uptake and localization of nanoceria in the mitochondria. At high nanoceria concentrations (400 µg mL-1), intracellular levels of ROS were increased and the HLECs exhibited classical hallmarks of apoptosis. These findings concur with the cells maintaining normal ATP levels necessary to execute the apoptotic process. These results highlight the need for nanoceria dose-effect studies on a range of cells and tissues to identify therapeutic concentrations in vitro or in vivo.

Combined Raman and AFM detection of changes in HeLa cervical cancer cells induced by CeO2 nanoparticles – molecular and morphological perspectives

Raman and AFM analyses represent a tool for the evaluation of cytotoxic and anti-proliferative effects in cells induced by CeO₂ nanoparticles.

Micronuclei Detection by Flow Cytometry as a High-Throughput Approach for the Genotoxicity Testing of Nanomaterials

Thousands of nanomaterials (NMs)-containing products are currently under development or incorporated in the consumer market, despite our very limited understanding of their genotoxic potential. Taking into account that the toxicity and genotoxicity of NMs strongly depend on their physicochemical characteristics, many variables must be considered in the safety evaluation of each given NM. In this scenario, the challenge is to establish high-throughput methodologies able to generate rapid and robust genotoxicity data that can be used to critically assess and/or predict the biological effects associated with those NMs being under development or already present in the market. In this study, we have evaluated the advantages of using a flow cytometry-based approach testing micronucleus (MNs) induction (FCMN assay). In the frame of the EU NANoREG project, we have tested six different NMs—namely NM100 and NM101 (TiO₂NPs), NM110 (ZnONPs), NM212 (CeO₂NPs), NM300K (AgNPs) and NM401 (multi-walled carbon nanotubes (MWCNTs)). The obtained results confirm the ability of AgNPs and MWCNTs to induce MN in the human bronchial epithelial BEAS-2B cell line, whereas the other tested NMs retrieved non-significant increases in the MN frequency. Based on the alignment of the results with the data reported in the literature and the performance of the FCMN assay, we strongly recommend this assay as a reference method to systematically evaluate the potential genotoxicity of NMs.

Cerium Oxide Nanoparticles Absorption through Intact and Damaged Human Skin

Cerium oxide (CeO2) nanoparticles (NPs) are used in polishing products and absorbents, as promoters in wound healing, and as organopesticide decontaminants. While systemic bioaccumulation and organ toxicity has been described after inhalation, data on CeO2 NPs' transdermal permeation are lacking. Our study was an in vitro investigation of the permeation of 17-nm CeO2 NPs dispersed in synthetic sweat (1 g L-1) using excised human skin on Franz cells. Experiments were performed using intact and needle-abraded skin, separately. The average amount of Ce into intact and damaged skin samples was 3.64 ± 0.15 and 7.07 ± 0.78 µg cm-2, respectively (mean ± SD, p = 0.04). Ce concentration in the receiving solution was 2.0 ± 0.4 and 3.3 ± 0.7 ng cm-2 after 24 h (p = 0.008). The Ce content was higher in dermal layers of damaged skin compared to intact skin (2.93 ± 0.71 µg cm-2 and 0.39 ± 0.16 µg cm-2, respectively; p = 0.004). Our data showed a very low dermal absorption and transdermal permeation of cerium, providing a first indication of Ce skin uptake due to contact with CeO2.

Redox interactions and genotoxicity of metal-based nanoparticles: A comprehensive review

Nanotechnology is a growing science that may provide several new applications for medicine, food preservation, diagnostic technologies, and sanitation. Despite its beneficial applications, there are several questions related to the safety of nanomaterials for human use. The development of nanotechnology is associated with some concerns because of the increased risk of carcinogenesis following exposure to nanomaterials. The increased levels of reactive oxygen species (ROS) that are due to exposure to nanoparticles (NPs) are primarily responsible for the genotoxicity of metal NPs. Not all, but most metal NPs are able to directly produce free radicals through the release of metal ions and through interactions with water molecules. Furthermore, the increased production of free radicals and the cell death caused by metal NPs can stimulate reduction/oxidation (redox) reactions, leading to the continuous endogenous production of ROS in a positive feedback loop. The overexpression of inflammatory mediators, such as NF-kB and STATs, the mitochondrial malfunction and the increased intracellular calcium levels mediate the chronic oxidative stress that occurs after exposure to metal NPs. In this paper, we review the genotoxicity of different types of metal NPs and the redox mechanisms that amplify the toxicity of these NPs.

Aortic Oxidative Stress, Inflammation and DNA Damage Following Pulmonary Exposure to Cerium Oxide Nanoparticles in a Rat Model of Vascular Injury

Pulmonary exposure to cerium oxide nanoparticles (CeO₂ NPs) can occur either at the workplace, or due to their release in the environment. Inhaled CeO₂ NPs are known to cross the alveolar–capillary barrier and reach various parts of the body, including the vasculature. The anticancer drug cisplatin (CP) causes vascular damage. However, the effects CeO₂ NPs on vascular homeostasis in a rat model of CP-induced vascular injury remain unclear. Here, we assessed the impact and underlying mechanism of pulmonary exposure to CeO₂ NPs on aorta in rats given a single intraperitoneal injection of cisplatin (CP, 6 mg/kg) to induce vascular damage. Six days later, the rats were intratracheally instilled with either CeO₂ NPs (1 mg/kg) or saline (control), and various variables were studied 24 h thereafter in the aortic tissue. The concentration of reduced glutathione and the activity of catalase were significantly increased in the CP + CeO₂ NPs group compared with both the CP + saline and the CeO₂ NPs groups. The activity of superoxide dismutase was significantly decreased in the CP + CeO₂ NPs group compared with both the CP + saline and CeO₂ NPs groups. The expression of nuclear factor erythroid-derived 2-like 2 (Nrf2) by the nuclei of smooth muscles and endocardial cells assessed by immunohistochemistry was significantly augmented in CeO₂ NPs versus saline, in CP + saline versus saline, and in CP + CeO₂ NPs versus CeO₂ NPs. Moreover, the concentrations of total nitric oxide, lipid peroxidation and 8-hydroxy-2-deoxyguanosine were significantly elevated in the CP + CeO₂ NPs group compared with both the CP + saline and the CeO₂ NPs groups. Similarly, compared with both the CP + saline and CeO₂ NPs groups, the combination of CP and CeO₂ NPs significantly elevated the concentrations of interleukin-6 and tumour necrosis factor-α. Additionally, aortic DNA damage assessed by Comet assay was significantly increased in CeO₂ NPs compared with saline, and in CP + saline versus saline, and all these effects were significantly aggravated by the combination of CP and CeO₂ NPs. We conclude that pulmonary exposure to CeO₂ NPs aggravates vascular toxicity in animal model of vascular injury through mechanisms involving oxidative stress, Nrf2 expression, inflammation and DNA damage.

Engineering highly effective antimicrobial selenium nanoparticles through control of particle size

The overuse of antibiotics has induced the rapid development of antibiotic resistance in bacteria. As a result, antibiotic efficacy has become limited, and infection with multidrug-resistant bacteria is considered to be one of the largest global human health threats. Consequently, new, effective and safe antimicrobial agents need to be developed urgently. One promising candidate to address this requirement is selenium nanoparticles (Se NPs), which are made from the essential dietary trace element Se and have antimicrobial activity against Gram-positive bacteria. The size of nanomaterials can strongly affect their biophysical properties and functions; however, the effects of the size of Se NPs on their antibacterial efficacy has not been systematically investigated. Therefore, in this work, spherical Se NPs ranging from 43 to 205 nm in diameter were fabricated, and their mammalian cytotoxicity and antibacterial activity as a function of their size were systematically studied. The antibacterial activity of the Se NPs was shown to be strongly size dependent, with 81 nm Se NPs showing the maximal growth inhibition and killing effect of methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MSSA and MRSA). The Se NPs were shown to have multi-modal mechanisms of action that depended on their size, including depleting internal ATP, inducing ROS production, and disrupting membrane potential. All the Se NPs were non-toxic towards mammalian cells up to 25 μg mL-1. Furthermore, the MIC value for the 81 nm particles produced in this research is 16 ± 7 μg mL-1, significantly lower than previously reported MIC values for Se NPs. This data illustrates that Se NP size is a facile yet critical and previously underappreciated parameter that can be tailored for maximal antimicrobial efficacy. We have identified that using Se NPs with a size of 81 nm and concentration of 10 μg mL-1 shows promise as a safe and efficient way to kill S. aureus without damaging mammalian cells.

Skin toxicity of topically applied nanoparticles

Nowadays, nanoproducts have found numerous applications, allowing them to enter the human body in different ways. Skin is a major body organ that acts as the first-line barrier between the internal organs and external environment. Although the inhalation and ingestion of nanoparticles is more dangerous compared with skin exposure, there are noteworthy information gaps in skin exposure to nanoparticles that need much attention. Despite the few reviews in the literature on the cytotoxic effects of nanoparticles, no research has reviewed the clinical side effects of nanoparticles following topical admonition, including skin inflammation, skin cancer and genetic toxicity.

Prevention of pesticide-induced neuronal dysfunction and mortality with nucleophilic poly-Oxime topical gel

Organophosphate-based pesticides inhibit acetylcholinesterase (AChE), which plays a pivotal role in neuromuscular function. While spraying in the field, farmworkers get exposed to pesticides through the dermal route. Internalized pesticide inhibits AChE, which leads to neurotoxicity, cardiotoxicity, cognitive dysfunction, loss of endurance, and death in severe cases. Here, we present a nucleophilic pyridine-2-aldoxime-functionalized chitosan-based topical gel (poly-Oxime gel) that rapidly deactivates organophosphates, methyl parathion (MPT), on the skin of rats, which leads to reduced AChE inhibition in the blood and tissues. Testing the robustness of poly-Oxime gel, we report reduction in AChE inhibition following repeated dermal administration of MPT in the presence of poly-Oxime gel. Furthermore, poly-Oxime gel prevented MPT-induced neuromuscular dysfunction, loss of endurance, and locomotor coordination. We observe a 100% survival in rats following topical MPT administration in the presence of poly-Oxime gel. This prophylactic gel may therefore help farmworkers by limiting pesticide-induced toxicity and mortality.

Recent advances in the field of transition metal dichalcogenides for biomedical applications

Nanosheets of transition metal dichalcogenide (TMDs), the graphene-like two-dimensional (2D) materials, exhibit a unique combination of properties and have attracted enormous research interest for a wide range of applications including catalysis, functional electronics, solid lubrication, photovoltaics, energy materials and most recently in biomedical applications. Their potential for use in biosensors, drug delivery, multimodal imaging, antimicrobial agents and tissue engineering is being actively studied. However, the commercial translation of exfoliated TMDs has been limited due to the low aqueous solubility, non-uniformity, lack of control over the layer thickness, and the long-term colloidal stability of the exfoliated material. There is wide interest in the synthesis and exfoliation of TMDs resulting in the reporting of increasing numbers of new methods and their biomedical applications. The unique physicochemical characteristics of the TMD nanosheets have been exploited to tether them with biological payload to achieve selective localized delivery in vivo. The large surface-to-volume ratio, good cytocompatibility, ease of surface modification, tunable bandgap, strong spin-orbit coupling, and high optical and thermal conversion efficiency of TMD nanosheets make them favorable over traditional nanomaterials for biomedical research. Moreover, the presence of abundant active edge sites on the 2D TMDs makes them suitable for catalytic activities, while the large surface area and the interspace between layers are particularly conducive to ion or small molecule intercalation, making them useful for energy storage applications with rapid redox reaction capabilities. One of the major limitations of the exfoliated TMDs has been their limited colloidal stability in aqueous media. In this review, we summarize the recent advances in the exfoliation and synthesis of single-layered TMDs, their biomedical efficacy in terms of cytotoxicity, combinatorial therapy and diagnostic imaging, as well as antimicrobial activity. We highlight the current challenges in the field and propose strategies for the future.

Very low concentration of cerium dioxide nanoparticles induce DNA damage, but no loss of vitality, in human spermatozoa

Cerium dioxide nanoparticles (CeO₂NP) are widely used for industrial purposes, as in diesel, paint, wood stain and as potential therapeutic applications. The Organization for Economic Cooperation and Development included CeO₂NP in the priority list of nanomaterials requiring urgent evaluation. As metal nanoparticles can cross the blood-testis barrier, CeO₂NP could interact with spermatozoa. The genotoxicity of CeO₂NP was demonstrated in vitro on human cell lines and mouse gametes. However, the effects of CeO₂NP on human spermatozoa DNA remain unknown. We showed significant DNA damage induced in vitro by CeO₂NP on human spermatozoa using Comet assay. The genotoxicity was inversely proportional to the concentration (0.01 to 10 mg·L^-1). TEM showed no internalization of CeO₂NP into the spermatozoa. This study shows for the first time that in vitro exposure to very low concentrations of cerium dioxide nanoparticles can induce significant DNA damage in human spermatozoa. These results add new and important insights regarding the reproductive toxicity of priority nanomaterials, which require urgent evaluation.

In vitro evaluation of the genotoxicity of CeO2 nanoparticles in human peripheral blood lymphocytes using cytokinesis-block micronucleus test, comet assay, and gamma H2AX

Engineered nanoparticles (ENPs) are used in a wide range of applications because of their unique properties. Cerium dioxide nanoparticles (CeO₂ NPs) are one of the important ENPs, and they can cause negative health effects, such as genotoxicity, in humans and other living organisms. The aim of this work was to analyze the genotoxic effects of short-term (3-24 h) CeO₂ NPs exposure to cultured human blood lymphocytes. Three genotoxicity systems "cytokinesis-block micronucleus test, comet assay, and gamma H2AX test" were used to show the genotoxic potential of CeO₂ NPs (particle size <25 nm, concentrations: 6, 12, and 18 µg/mL). Hydrogen peroxide was selected as the positive-control genotoxic agent. Our results indicate that CeO₂ NPs have genotoxic potential on human peripheral blood lymphocytes cells even at 3-24 h exposure under in vitro conditions.

Decreased Uptake and Enhanced Mitochondrial Protection Underlie Reduced Toxicity of Nanoceria in Human Monocyte-Derived Macrophages

Cerium dioxide nanoparticles (nanoceria), currently used as catalysts including additives to diesel fuel, also present potential as a novel therapeutic agent for disorders involving oxidative stress. However, little is known about the effects of nanoceria on primary human cells involved in the innate immune response. Here, we evaluate nanoceria effects on monocyte derived macrophages (MDMs) from healthy human subjects. Peripheral blood monocytes were isolated from healthy human volunteers. MDMs were obtained by maturing monocytes over a five-day period. MDMs were exposed to well-characterized nanoceria suspensions (0, 5, 10, 20 μg/mL) for 24 or 48 hours. We evaluated particle uptake, ultrastructural changes, cytotoxicity, and mitochondrial damage in MDMs through transmission electron microscopy (TEM), confocal imaging, flow cytometry, spectrometry, western blots, and immunofluorescence techniques. The role that intracellular concentration of nanoceria plays in the toxicity of MDMs was evaluated by 3D image analysis and compared to monocytes as a nanoceria sensitive cell model. Nanoceria failed to induce cytotoxicity in MDMs at the tested doses. Nanoceria-exposed MDMs showed no mitochondrial damage and displayed significant accumulation of anti-apoptotic proteins (Mcl-1 and Bcl-2) during the maturation process. TEM and confocal analyses revealed efficient uptake of nanoceria by MDMs, however 3D image analyses revealed lower nanoceria accumulation per unit cell volume in MDMs compared to monocytes. Taken together, our results suggest that mitochondrial protection and reduced volume-corrected intracellular nanoparticle concentration account for the lower sensitivity of human MDMs to nanoceria.

Intranasal Delivery of Copper Oxide Nanoparticles Induces Pulmonary Toxicity and Fibrosis in C57BL/6 mice

Copper oxide nanoparticles (CuO NPs) are widely used as catalysts or semiconductors in material fields. Recent studies have suggested that CuO NPs have adverse genotoxicity and cytotoxicity effects on various cells. However, little is known about the toxicity of CuO NPs following exposure to murine lungs. The purpose of this fundamental research was to investigate whether CuO NPs could induce epithelial cell injury, pulmonary inflammation, and eventually fibrosis in C57BL/6 mice. Our studies showed that CuO NPs aggravated pulmonary inflammation in a dose-dependent manner. CuO NPs induced apoptosis of epithelial cells as indicated by TUNEL staining, flow cytometry and western blot analysis, which was partially caused by increased reactive oxygen species (ROS). In addition, CuO NPs exposure promoted collagen accumulation and expression of the progressive fibrosis marker α-SMA in the lung tissues, indicating that CuO NP inhalation could induce pulmonary fibrosis in C57BL/6 mice. All data provide novel evidence that there is an urgent need to prevent the adverse effects of CuO NPs in the human respiratory system.

Cellular proliferation and differentiation induced by single-layer molybdenum disulfide and mediation mechanisms of proteins via the Akt-mTOR-p70S6K signaling pathway

Single-layer molybdenum disulfide (SLMoS₂) is a novel kind of 2D nanosheet that has attracted great attention regarding its use in biosensors, drug delivery, tissue engineering, and therapy. However, our results demonstrated that SLMoS₂ accelerated proliferation and promoted myogenic differentiation and epithelial-mesenchymal transition (EMT) in human embryonic lung fibroblasts (HELFs). The abnormal proliferation and differentiation of HELFs contribute to idiopathic pulmonary fibrosis. Specifically, SLMoS₂ significantly stimulated the expression of myofibroblast- and mesenchymal-associated genes and proteins. The Akt-mTOR-p70S6K signaling pathway plays a critical role in the acceleration of proliferation and promotion of myogenic differentiation and EMT in HELFs induced by SLMoS₂. After cell uptake, SLMoS₂ was primarily located in the cytoplasm and the perinuclear region and activated Akt-dependent signaling due to the generation of reactive oxygen species (ROS). Moreover, bovine serum albumin (BSA) binding markedly inhibited the cellular uptake of SLMoS₂ and the production of intracellular ROS due to an increased thickness and reduced adhesion of HELFs. BSA binding also mitigated the SLMoS₂-activated phosphorylation of Akt-dependent signaling pathways. This study is the first to illustrate the induction of cellular proliferation and differentiation by SLMoS₂ and the related mediation by proteins through Akt-mTOR-p70S6K signaling pathway.

CeO2 nanoparticle fate in environmental conditions and toxicity on a freshwater predator species: a microcosm study

We studied the fate and toxicity of two types of CeO₂ NPs (bare or citrate-coated) in environmentally relevant conditions, using large indoor microcosms. Long-term exposure was carried out on a three-leveled freshwater trophic chain, comprising microbial communities as primary producers, chironomid larvae as primary consumers, and amphibian larvae as secondary consumers. Whereas coated NPs preferentially sedimented, bare NPs were mainly found in the water column. However, mass balance indicated low recovery (51.5%) for bare NPs, indicating possible NP loss, against 98.8% of recovery for coated NPs. NPs were rather chemically stable, with less than 4% of dissolution. Chironomid larvae ingested large amounts of NPs and were vectors of contamination for amphibian larvae. Although bioaccumulation in amphibian larvae was important (9.47 and 9.74 mg/kg for bare and coated NPs, respectively), no biomagnification occurred through the trophic chain. Finally, significant genotoxicity was observed in amphibian larvae, bare CeO₂ NPs being more toxic than citrate-coated NPs. ᅟ.

Cerium Chloride Application Promotes Wound Healing and Cell Proliferation in Human Foreskin Fibroblasts

This study investigated the effect of cerium chloride (CeCl₃) on cell migration and gene expression of human foreskin fibroblasts (HFF). HFF were exposed to three different CeCl₃ solutions (1%, 5% and 10%, w/v %) for three different time durations (1, 5 and 10 min). 72 h after exposure to CeCl₃, cell viability was assessed by MTT test. A scratch-wounded assay determined the cell migration and the width of the wound, measured at 24 h. Gene expression patterns for cyclins B1, D1 and E1 were analyzed by RT-PCR (p < 0.05, t-test). The viability proliferation increased at 1- and 5-min exposures for all CeCl₃ concentrations, in contrast to no treatment (p < 0.05 at 24 h). No influence of CeCl₃ was found after 10 min. The scratch assay showed increased cell migration up to 60% at 1 and 5 min after 24 h at 5% and 10%. Cyclin B1, D1 and E1 all showed upregulation, confirming an increase in cell proliferation. This study demonstrates that exposure time and concentration of CeCl₃ may have a positive effect on fibroblast viability and migration. Application of CeCl₃ may be beneficial as a cell-stimulating agent leading to therapeutic tissue fibrosis or more resistant tissue around teeth, when warranted, during different periodontal therapies.

Evaluation of tumorigenic potential of CeO2 and Fe2O3 engineered nanoparticles by a human cell in vitro screening model

With rapid development of novel nanotechnologies that incorporate engineered nanomaterials (ENMs) into manufactured products, long-term, low dose ENM exposures in occupational settings is forecasted to occur with potential adverse outcomes to human health. Few ENM human health risk assessment efforts have evaluated tumorigenic potential of ENMs. Two widely used nano-scaled metal oxides (NMOs), cerium oxide (nCeO₂) and ferric oxide (nFe₂O₃) were screened in the current study using a sub-chronic exposure to human primary small airway epithelial cells (pSAECs). Multi-walled carbon nanotubes (MWCNT), a known ENM tumor promoter, was used as a positive control. Advanced dosimetry modeling was employed to ascertain delivered vs. administered dose in all experimental conditions. Cells were continuously exposed in vitro to deposited doses of 0.18 μg/cm² or 0.06 μg/cm² of each NMO or MWCNT, respectively, over 6 and 10 weeks, while saline- and dispersant-only exposed cells served as passage controls. Cells were evaluated for changes in several cancer hallmarks, as evidence for neoplastic transformation. At 10 weeks, nFe₂O₃- and MWCNT-exposed cells displayed a neoplastic-like transformation phenotype with significant increased proliferation, invasion and soft agar colony formation ability compared to controls. nCeO₂-exposed cells showed increased proliferative capacity only. Isolated nFe₂O₃ and MWCNT clones from soft agar colonies retained their respective neoplastic-like phenotypes. Interestingly, nFe₂O₃-exposed cells, but not MWCNT cells, exhibited immortalization and retention of the neoplastic phenotype after repeated passaging (12 - 30 passages) and after cryofreeze and thawing. High content screening and protein expression analyses in acute exposure ENM studies vs. immortalized nFe₂O₃ cells, and isolated ENM clones, suggested that long-term exposure to the tested ENMs resulted in iron homeostasis disruption, an increased labile ferrous iron pool, and subsequent reactive oxygen species generation, a well-established tumorigenesis promotor. In conclusion, sub-chronic exposure to human pSAECs with a cancer hallmark screening battery identified nFe₂O₃ as possessing neoplastic-like transformation ability, thus suggesting that further tumorigenic assessment is needed.

Cerium Oxide Nanoparticles in Lung Acutely Induce Oxidative Stress, Inflammation, and DNA Damage in Various Organs of Mice

CeO₂ nanoparticles (CeO₂ NPs) which are used as a diesel fuel additive are emitted in the particulate phase in the exhaust, posing a health concern. However, limited information exists regarding the in vivo acute toxicity of CeO₂ NPs on multiple organs. Presently, we investigated the acute (24 h) effects of intratracheally instilled CeO₂ NPs in mice (0.5 mg/kg) on oxidative stress, inflammation, and DNA damage in major organs including lung, heart, liver, kidneys, spleen, and brain. Lipid peroxidation measured by malondialdehyde production was increased in the lungs only, and reactive oxygen species were increased in the lung, heart, kidney, and brain. Superoxide dismutase activity was decreased in the lung, liver, and kidney, whereas glutathione increased in lung but it decreased in the kidney. Total nitric oxide was increased in the lung and spleen but it decreased in the heart. Tumour necrosis factor-α increased in all organs studied. Interleukin- (IL-) 6 increased in the lung, heart, liver, kidney, and spleen. IL-1β augmented in the lung, heart, kidney, and spleen. Moreover, CeO₂ NPs induced DNA damage, assessed by COMET assay, in all organs studied. Collectively, these findings indicate that pulmonary exposure to CeO₂ NPs causes oxidative stress, inflammation, and DNA damage in multiple organs.

Threshold Dose of Three Types of Quantum Dots (QDs) Induces Oxidative Stress Triggers DNA Damage and Apoptosis in Mouse Fibroblast L929 Cells

Although it has been reported that fluorescent quantum dots (QDs) have obvious acute toxic effects in vitro, their toxic effects at low doses or threshold doses are still unknown. Therefore, we evaluated the biological histocompatibility and in vitro toxicity of three types of QDs at threshold doses. Also, we compared the toxic effects of QDs with different raw chemical compositions and sizes. The results showed that low concentrations of QDs (≤7 μg/mL) had no obvious effect on cell viability and cell membrane damage, oxidative damage, cell apoptosis or DNA damage. However, QD exposure led to a significant cytotoxicity at higher doses (≥14 μg/mL) and induced abnormal cellular morphology. In addition, when comparing the three types of QDs, 2.2 nm CdTe QDs exposure showed a significantly increased proportion of apoptotic cells and significant DNA damage, suggesting that size and composition contribute to the toxic effects of QDs. Based on these discussions, it was concluded that the concentration (7 μg/mL) may serve as a threshold level for these three types of QDs only in L929 fibroblasts, whereas high concentrations (above 14 μg/mL) may be toxic, resulting in inhibition of proliferation, induction of apoptosis and DNA damage in L929 fibroblasts.

Sleep Deprivation-Induced Blood-Brain Barrier Breakdown and Brain Dysfunction are Exacerbated by Size-Related Exposure to Ag and Cu Nanoparticles. Neuroprotective Effects of a 5-HT3 Receptor Antagonist Ondansetron

Military personnel are often subjected to sleep deprivation (SD) during combat operations. Since SD is a severe stress and alters neurochemical metabolism in the brain, a possibility exists that acute or long-term SD will influence blood-brain barrier (BBB) function and brain pathology. This hypothesis was examined in young adult rats (age 12 to 14 weeks) using an inverted flowerpot model. Rats were placed over an inverted flowerpot platform (6.5 cm diameter) in a water pool where the water levels are just 3 cm below the surface. In this model, animals can go to sleep for brief periods but cannot achieve deep sleep as they would fall into water and thus experience sleep interruption. These animals showed leakage of Evans blue in the cerebellum, hippocampus, caudate nucleus, parietal, temporal, occipital, cingulate cerebral cortices, and brain stem. The ventricular walls of the lateral and fourth ventricles were also stained blue, indicating disruption of the BBB and the blood-cerebrospinal fluid barrier (BCSFB). Breakdown of the BBB or the BCSFB fluid barrier was progressive in nature from 12 to 48 h but no apparent differences in BBB leakage were seen between 48 and 72 h of SD. Interestingly, rats treated with metal nanoparticles, e.g., Cu or Ag, showed profound exacerbation of BBB disruption by 1.5- to 4-fold, depending on the duration of SD. Measurement of plasma and brain serotonin showed a close correlation between BBB disruption and the amine level. Repeated treatment with the serotonin 5-HT3 receptor antagonist ondansetron (1 mg/kg, s.c.) 4 and 8 h after SD markedly reduced BBB disruption and brain pathology after 12 to 24 h SD but not following 48 or 72 h after SD. However, TiO2-nanowired ondansetron (1 mg/kg, s.c) in an identical manner induced neuroprotection in rats following 48 or 72 h SD. However, plasma and serotonin levels were not affected by ondansetron treatment. Taken together, our observations are the first to show that (i) SD could induce BBB disruption and brain pathology, (ii) nanoparticles exacerbate SD-induced brain damage, and (iii) serotonin 5-HT3 receptor antagonist ondansetron is neuroprotective in SD that is further potentiated byTiO2-nanowired delivery, not reported earlier.

Anti-cancer effects of cerium oxide nanoparticles and its intracellular redox activity

Data on medical applications of cerium oxide nanoparticles CeO2 (CONP) are promising, yet information regarding their action in cells is incomplete and there are conflicting reports about in vitro toxicity. Herein, we have studied cytotoxic effect of CONP in several cancer and normal cell lines and their potential to change intracellular redox status. The IC50 was achieved only in two of eight tested cell lines, melanoma 518A2 and colorectal adenocarcinoma HT-29. Self-propagating room temperature method was applied to produce CONP with an average crystalline size of 4 nm. The results confirmed presence of Ce(3+) and O(2-) vacancies. The induction of cell death by CONP and the production of reactive oxygen species (ROS) were analyzed by flow-cytometry. Free radicals related antioxidant capacity of the cells was studied by the reduction of stable free radical TEMPONE using electron spin resonance spectroscopy. CONP showed low or moderate cytotoxicity in cancer cell lines: adenocarcinoma DLD1 and multi-drug resistant DLD1-TxR, non-small cell lung carcinoma NCI-H460 and multi-drug resistant NCI-H460/R, while normal cell lines (keratinocytes HaCaT, lung fetal fibroblasts MRC-5) were insensitive. The most sensitive were 518A2 melanoma and HT-29 colorectal adenocarcinoma cell lines, with the IC50 values being between 100 and 200 μM. Decreased rate of TEMPONE reduction and increased production of certain ROS species (peroxynitrite and hydrogen peroxide anion) indicates that free radical metabolism, thus redox status was changed, and antioxidant capacity damaged in the CONP treated 518A2 and HT-29 cells. In conclusion, changes in intracellular redox status induced by CONP are partly attributed to the prooxidant activity of the nanoparticles. Further, ROS induced cell damages might eventually lead to the cell death. However, low inhibitory potential of CONP in the other human cell lines tested indicates that CONP may be safe for human usage in industry and medicine.