Establishing structure-property-hazard relationships for multi-walled carbon nanotubes: the role of aggregation, surface charge, and oxidative stress on embryonic zebrafish mortality

Comparison of the developmental effects of lactase or bisphenol A antibody immobilized polycaprolactone/silk fibroin nanofibers on zebrafish embryos

This study aimed to detect the biocompatibility of bioactivated polycaprolactone/silk fibroin-based nanofibers in vivo using zebrafish embryos. Anti-Bisphenol A (BPA) antibody or lactase enzyme was immobilized on electrospun nanofibers, for making the nanofiber bioactive. Lactase immobilized nanofiber was developed to hydrolyze lactose and produce milk with reduced lactose. Anti-BPA antibody immobilized nanofiber was developed to remove bisphenol A from liquids. To test the biocompatibility of the bioactive nanofibers, the zebrafish embryos were divided into 4 groups; control, raw nanofiber, lactase immobilized nanofiber, and anti-BPAantibody immobilized nanofiber groups. In nanofiber-based exposure groups; nanofibers were incubated separately in the embryonic development medium. Subsequently, the embryos were kept in these development mediums for 72 h post-fertilization (72 hpf) and their developmental analyzes were performed. At the end of 72 hpf, zebrafish embryos were homogenized. Lipid peroxidation and nitrite oxide levels, and superoxide dismutase and glutathione-S-transferase activities were determined to monitor the disturbance of oxidant-antioxidant balance in zebrafish embryos. Exposure to bioactive nanofibers slightly disrupted the oxidant-antioxidant balance, but this change did not affect the mortality and hatching times of the embryos. In conclusion, zebrafish embryos have been effectively used in biocompatibility testing for bioactive nanofibers suggesting that these materials are biocompatible.

Effect of boramidic acid modified carbon nanotubes on neurological, morphological and physiological responses of zebrafish (Danio rerio) embryos and larvae

This study aimed to determine the potential toxicological effects of carbon nanotubes (CNTs), their modifications with ethylenediamine (ED) and boric acid (BA) on aquatic organisms. Specifically, the research focused on the morphological, physiological, and histopathological-immuno-histochemical responses in zebrafish (Danio rerio) embryos and larvae, via applying different concentrations of CNTs, CNT-ED, and CNT-ED-BA (Control, 5, 10, and 20 mg/L). The results indicated that 20 mg/L CNT nanoparticles were toxic to zebrafish larvae, with mortality rates increasing with CNT and CNT-ED concentrations, reaching 36.7 % at the highest CNT concentration. The highest dose caused considerable degeneration, necrosis, DNA damage, and apoptosis, as evidenced by histopathological and immunohistochemical tests. In contrast, despite their high concentration, CNT-ED-BA nanoparticles exhibited low toxicity. Behavioral studies revealed that CNT and CNT-ED nanoparticles had a more significant impact on sensory-motor functions compared to CNT-ED-BA nanoparticles. These findings suggest that modifying the nanosurface with boric acid, resulting in boramidic acid, can reduce the toxicity induced by CNT and CNT-ED.

Assessments of carbon nanotubes toxicities in zebrafish larvae using multiple physiological and molecular endpoints

In recent years, carbon nanotubes (CNTs) have become one of the most promising materials for the technology industry. However, due to the extensive usage of these materials, they may be released into the environment, and cause toxicities to the organism. Here, their acute toxicities in zebrafish embryos and larvae were evaluated by using various assessments that may provide us with a novel perspective on their effects on aquatic animals. Before conducting the toxicity assessments, the CNTs were characterized as multiwall carbon nanotubes (MWCNTs) functionalized with hydroxyl and carboxyl groups, which improved their solubility and dispersibility. Based on the results, abnormalities in zebrafish behaviors were observed in the exposed groups, indicated by a reduction in tail coiling frequency and alterations in the locomotion as the response toward photo and vibration stimuli that might be due to the disruption in the neuromodulatory system and the formation of reactive oxygen species (ROS) by MWCNTs. Next, based on the respiratory rate assay, exposed larvae consumed more oxygen, which may be due to the injuries in the larval gill by the MWCNTs. Finally, even though no irregularity was observed in the exposed larval cardiac rhythm, abnormalities were shown in their cardiac physiology and blood flow with significant downregulation in several cardiac development-related gene expressions. To sum up, although the following studies are necessary to understand the exact mechanism of their toxicity, the current study demonstrated the environmental implications of MWCNTs in particularly low concentrations and short-term exposure, especially to aquatic organisms.

Carbon nanotubes and nanofibers seen as emerging threat to fish: Historical review and trends

Since the discovery of the third allotropic carbon form, carbon-based one-dimensional nanomaterials (1D-CNMs) became an attractive and new technology with different applications that range from electronics to biomedical and environmental technologies. Despite their broad application, data on environmental risks remain limited. Fish are widely used in ecotoxicological studies and biomonitoring programs. Thus, the aim of the current study was to summarize and critically analyze the literature focused on investigating the bioaccumulation and ecotoxicological impacts of 1D-CNMs (carbon nanotubes and nanofibers) on different fish species. In total, 93 articles were summarized and analyzed by taking into consideration the following aspects: bioaccumulation, trophic transfer, genotoxicity, mutagenicity, organ-specific toxicity, oxidative stress, neurotoxicity and behavioral changes. Results have evidenced that the analyzed studies were mainly carried out with multi-walled carbon nanotubes, which were followed by single-walled nanotubes and nanofibers. Zebrafish (Danio rerio) was the main fish species used as model system. CNMs' ecotoxicity in fish depends on their physicochemical features, functionalization, experimental design (e.g. exposure time, concentration, exposure type), as well as on fish species and developmental stage. CNMs' action mechanism and toxicity in fish are associated with oxidative stress, genotoxicity, hepatotoxicity and cardiotoxicity. Overall, fish are a suitable model system to assess the ecotoxicity of, and the environmental risk posed by, CNMs.

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Ecotoxicological evaluation of functional carbon nanodots using zebrafish (Danio rerio) model at different developmental stages

Considering functional carbon nanodots (FCNs) are potential to be applied in many areas, their risk and toxicity to organisms are imperative to be evaluated. Thus, this study conducted acute toxicity test of zebrafish (Danio rerio) at embryonic and adult stage to estimate the toxicity of FCNs. Results show that the toxic effects of FCNs and nitrogen doped FCNs (N-FCNs) at their 10% lethal concentration (LC₁₀) values on zebrafish are expressed in developmental retardation, cardiovascular toxicity, renal damage and hepatotoxicity. There are interactive relationships between these effects, but the main reason should be ascribed to the undesirable oxidative damage induced by high doses of materials, as well as the biodistribution of FCNs and N-FCNs in vivo. Even so, FCNs and N-FCNs can promote the antioxidant activity in zebrafish tissues to cope with the oxidative stress. FCNs and N-FCNs are not easy to cross the physical barriers in zebrafish embryos or larvae, and can be excreted from intestine by adult fish, which proves their biosecurity to zebrafish. In addition, because of the differences in physicochemical properties, especially nano-size and surface chemical property, FCNs show higher biosecurity to zebrafish than N-FCNs. The effects of FCNs and N-FCNs on hatching rates, mortality rates and developmental malformations are dose-dependent and time-dependent. The LC₅₀ values of FCNs and N-FCNs on zebrafish embryo at 96 hpf are 1610 mg/L and 649 mg/L, respectively. According to the Acute Toxicity Rating Scale of the Fish and Wildlife Service, the toxicity grades of FCNs and N-FCNs are both defined as "practically nontoxic", and FCNs are "Relatively Harmless" to embryos because their LC₅₀ values are above 1000 mg/L. Our results prove the biosecurity of FCNs-based materials for future practical application.

Carbon nanotubes accelerates the bio-induced vivianite formation

Vivianite widely existed in digested sludge and activated sludge as a potential phosphate resource recovered from wastewater treatment plants (WWTPs). As an important product of extracellular electron transfer (EET) and biological iron reduction, the production of vivianite can be enhanced by conductive materials. Carbon nanotubes (CNTs) with excellent electrical conductivity have been reported to promote electron transfer, which was applied in wastewater treatment to accelerate the degradation of the contaminants. However, the impact of CNTs on vivianite formation was barely reported. In this study, the iron reduction, vivianite recovery, and the biotoxicity of CNTs were investigated in order to determine the influence of CNTs towards the vivianite production. The enhancement of vivianite production after CNTs adding reached up to 17 % by promoting the electron transfer between dissimilative iron-reducing bacteria (DIRB) and Fe(III). However, at the initial stage (0-24 h), Fe(III) reduction efficiency decreased by 81 % after inoculating with sewage sludge, which was attributed to CNTs destroying of the cell membrane (as indicated by SEM, CLSM and AFM analysis). The biotoxicity of CNTs stimulated DIRB to secret extracellular polymeric substances (EPS) and form bio-flocs to resist the physical puncture. After 48 h, the proportion of living DIRB in 1000 mg/L CNTs batch increased to 98 %, which was 79 % higher than 12 h. As a result, the vivianite recovery of raw sewage with 1000 mg/L CNTs increased to 44 ± 1 %, which was 33 % higher than that in the CNT-0.

Reproductive and Developmental Nanotoxicity of Carbon Nanoparticles

The presented review aims to summarize the knowledge regarding the reproductive and developmental toxicity of different types of carbon nanoparticles, such as graphene, graphene oxide, multi- and single-walled nanotubes, fullerenes, and nanodiamonds. Carbon nanoparticles have unique chemical and physical properties that make them an excellent material that can be applied in many fields of human activity, including industry, food processing, the pharmaceutical industry, or medicine. Although it has a high degree of biocompatibility, possible toxic effects on different tissue types must also be taken into account. Carbon nanoparticles are known to be toxic to the respiratory, cardiovascular, nervous, digestive system, etc., and, according to current studies, they also have a negative effect on reproduction and offspring development.

Cytocompatibility of carboxylated multi-wall carbon nanotubes in stem cells from human exfoliated deciduous teeth

Carboxylated multi-wall carbon nanotube (MWCNT-COOH) presents unique properties due to nanoscale dimensions and permits a broad range of applications in different fields, such as bone tissue engineering and regenerative medicine. However, the cytocompatibility of MWCNT-COOH with human stem cells is poorly understood. Thus, studies elucidating how MWCNT-COOH affects human stem cell viability are essential to a safer application of nanotechnologies. Using stem cells from the human exfoliated deciduous teeth model, we have evaluated the effects of MWCNT-COOH on cell viability, oxidative cell stress, and DNA integrity. Results demonstrated that despite the decreased metabolism of mitochondria, MWCNT-COOH had no toxicity against stem cells. Cells maintained viability after MWCNT-COOH exposure. MWCNT-COOH did not alter the superoxide dismutase activity and did not cause genotoxic effects. The present findings are relevant to the potential application of MWCNT-COOH in the tissue engineering and regenerative medicine fields.

Small organic molecules act as a trigger in an "unzippering" mechanism to facilitate carbon nanotube dispersion

In binary dispersing agents system, the contribution and roles of different sized molecules to carbon nanotubes (CNTs) dispersion remain unclear, which hinders the understanding of the environmental behaviour and risks of CNTs. This study compared the dispersion of CNTs by m-nitrobenzoic acid (NBA), trans-cinnamic acid (TCA), tannic acid (TA), and their mixtures. The dispersion efficiency of CNTs significantly reduced with the increased solid-phase concentration (Q_e) of TA due to the adsorption of TA on newly exposed CNTs surfaces. However, the CNTs dispersion efficiency by NBA or TCA was independent of Q_e because the dispersed CNTs surface was completely occupied by NBA or TCA without new exposed sites available for subsequent adsorption. The mixture of NBA or TCA with TA significantly enhanced the dispersion efficiency of CNTs, indicating a synergistic effect of CNTs dispersion. The addition of NBA or TCA decreased the hydrodynamic diameter of CNTs dispersed by TA, which indicated that NBA or TCA facilitated TA wedging into CNTs bundles for more complete separation of CNTs. This study highlighted the triggering effect of small molecules in the "unzippering" mechanism for improving the dispersing efficiency of CNTs by large molecules.

Performance and Sustainability Tradeoffs of Oxidized Carbon Nanotubes as a Cathodic Material in Lithium-Oxygen Batteries

Climate change mitigation efforts will require a portfolio of solutions, including improvements to energy storage technologies in electric vehicles and renewable energy sources, such as the high-energy-density lithium-oxygen battery (LOB). However, if LOB technology will contribute to addressing climate change, improvements to LOB performance must not come at the cost of disproportionate increases in global warming potential (GWP) or cumulative energy demand (CED) over their lifecycle. Here, oxygen-functionalized multi-walled carbon nanotube (O-MWCNT) cathodes were produced and assessed for their initial discharge capacities and cyclability. Contrary to previous findings, the discharge capacity of O-MWCNT cathodes increased with the ratio of carbonyl/carboxyl moieties, outperforming pristine MWCNTs. However, increased oxygen concentrations decreased LOB cyclability, while high-temperature annealing increased both discharge capacity and cyclability. Improved performance resulting from MWCNT post-processing came at the cost of increased GWP and CED, which in some cases was disproportionately higher than the level of improved performance. Based on the findings presented here, there is a need to simultaneously advance research in improving LOB performance while minimizing or mitigating the environmental impacts of LOB production.

Similar toxicity mechanisms between graphene oxide and oxidized multi-walled carbon nanotubes in Microcystis aeruginosa

In photosynthetic microorganisms, the toxicity of carbon nanomaterials (CNMs) is typically characterized by a decrease in growth, viability, photosynthesis, as well as the induction of oxidative stress. However, it is currently unclear how the shape of the carbon structure in CNMs, such as in the 1-dimensional carbon nanotubes (CNTs) compared to the two-dimensional graphene oxide (GO), affects the way they interact with cells. In this study, the effects of GO and oxidized multi-walled CNTs were compared in the cyanobacterium Microcystis aeruginosa to determine the similarities or differences in how the two CNMs interact with and induce toxicity to cyanobacteria. Using change in Chlorophyll a concentrations, the effective concentrations inducing 50% inhibition (EC₅₀) at 96 h are found to be 11.1 μg/mL and 7.38 μg/mL for GO and CNTs, respectively. The EC₅₀ of the two CNMs were not found to be statistically different. Changes in fluorescein diacetate and 2',7'-dichlorodihydrofluorescein diacetate fluorescence, measured at the EC₅₀ concentrations, suggest a decrease in esterase enzyme activity but no oxidative stress. Scanning and transmission electron microscopy imaging did not show extensive membrane damage in cells exposed to GO or CNTs. Altogether, the decrease in metabolic activity and photosynthetic activity without oxidative stress or membrane damage support the hypothesis that both GO and CNTs induced indirect toxicity through physical mechanisms associated with light shading and cell aggregation. This indirect toxicity explains why the intrinsic differences in shape, size, and surface properties between CNTs and GO did not result in differences in how they induce toxicity to cyanobacteria.

Developmental Toxicity of Few-Layered Black Phosphorus toward Zebrafish

Black phosphorus (BP) has extensive applications in various fields. The release of BP into aquatic ecosystems and the potential toxic effects on aquatic organisms are becoming major concerns. Here, we investigated the developmental toxicity of few-layered BP toward the zebrafish. We found that BP could adsorb on the surface of the chorion and could subsequently penetrate within the embryo. After exposure of embryos to 10 mg/L BP, developmental malformations appeared at 96 hpf, especially heart deformities such as pericardial edema and bradycardia, accompanied by severe circulatory system failure. Using transgenic zebrafish larvae, we further characterized cardiovascular defects with cardiac enlargement and impaired cardiac vessels as indicators of damage to the cardiovascular system upon BP exposure. We performed transcriptomic analysis on zebrafish embryos treated with a lower concentration of 2 mg/L. The results showed disruption in genes associated with muscle development, oxygen involved processes, focal adhesion, and VEGF and MAPK signaling pathways. These alterations also indicated that BP carries a risk of developmental perturbation at lower concentrations. This study provides new insights into the effects of BP on aquatic organisms.

In Vitro and In Vivo Models for Evaluating the Oral Toxicity of Nanomedicines

Toxicity studies for conventional oral drug formulations are standardized and well documented, as required by the guidelines of administrative agencies such as the US Food & Drug Administration (FDA), the European Medicines Agency (EMA) or European Medicines Evaluation Agency (EMEA), and the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). Researchers tend to extrapolate these standardized protocols to evaluate nanoformulations (NFs) because standard nanotoxicity protocols are still lacking in nonclinical studies for testing orally delivered NFs. However, such strategies have generated many inconsistent results because they do not account for the specific physicochemical properties of nanomedicines. Due to their tiny size, accumulated surface charge and tension, sizeable surface-area-to-volume ratio, and high chemical/structural complexity, orally delivered NFs may generate severe topical toxicities to the gastrointestinal tract and metabolic organs, including the liver and kidney. Such toxicities involve immune responses that reflect different mechanisms than those triggered by conventional formulations. Herein, we briefly analyze the potential oral toxicity mechanisms of NFs and describe recently reported in vitro and in vivo models that attempt to address the specific oral toxicity of nanomedicines. We also discuss approaches that may be used to develop nontoxic NFs for oral drug delivery.

The Known and Unknown about the Environmental Safety of Nanomaterials in Commerce

The widespread nanomaterial use in commercial products has fed significant concern over environmental health and safety ramifications. Initially, little was known as to how these highly reactive particulates interacted with biological systems. Nanomaterials have introduced complexities not normally considered in traditional safety assessments of chemicals and therefore have generated uncertainty in the reliability of standard tests of safety. Advances in understanding the potential impacts of nanomaterials have occurred since their introduction, particularly for those used in the greatest quantities in commerce. The impact of characteristics such as charge, size, surface functionalization, chemical composition, and certain transformations on the potential effect of nanomaterials in the environment continue to move the field forward. However, generalizations of risk based on any one factor across nanomaterials is not possible. Estimating risk also remains difficult due to the introduction of materials that are new and more complex, minimal information on the specific molecular interactions of nanomaterials and organisms, and the need for more tools for measuring the dynamics of nanomaterial state and fate in complex matrices. Finally, exposure estimates are difficult due to difficulty of environmental monitoring which may be exacerbated by lack of information on nanomaterials in products and new uses in the marketplace.

Sensible graphene oxide differentiates macrophages and Leishmania: a bio-nano interplay in attenuating intracellular parasite

Leishmania is an obligate intracellular protozoan parasite, which resides in human macrophage vacuoles that are referred to as parasitophorus vacuoles. Amphotericin B (AmB) is the first-line drug with 99% cure rates; however, overdose-induced toxic side effects are a major limitation. To improve the efficacy at lower dose and subsequently to avoid toxicity and to further investigate the role of charge dynamics on the efficacy, a graphene oxide (GO)-based composite of AmB was developed with native negatively charged GO and amine-conjugated positively charged AGO. The AGO composite resulted in enhanced uptake as confirmed by confocal and FACS analysis. Thus, AGO caused a strong inhibition of amastigotes, with IC50 values 5-fold lower than free AmB. The parasitophorus vacuoles harbour a hydrolytic and acidic environment, which is favourable for the parasites, as they don't attenuate this condition. AGO-AmB was able to modify the intracellular pH of the Leishmania donovani-infected macrophages, generating unfavourable conditions for the amastigote, and thus improving its efficacy.