Effects of titanium dioxide nanoparticles on lead bioconcentration and toxicity on thyroid endocrine system and neuronal development in zebrafish larvae

Effects of TiO2, SiO2, Ag and CdTe/CdS quantum dots nanoparticles on toxicity of cadmium towards Chlamydomonas reinhardtii

Nanoparticles (NPs) are inevitably released into the aquatic environment for being widely used and may affect the toxicity of other contaminants already present in the environment, such as trace metals. However, the effects of NPs on the ecotoxicity of cadmium (Cd), a common environmental trace metal pollutant, are not well explored. In this study, effects of four widely used NPs TiO₂ (n-TiO₂), SiO₂ (n-SiO₂), Ag (n-Ag) and CdTe/CdS core/shell quantum dots (QD) on the toxicity of Cd to the freshwater algae Chlamydomonas reinhardtii were assessed respectively. Cd reduced the algae biomass, impaired the photosynthetic activities, and led to intracellular oxidative stress of algae. At non-toxic concentrations, both n-TiO₂ (100 mg L^-1) and n-SiO₂ (400 mg L^-1) attenuated the toxicity of Cd towards the algae for reducing the intracellular Cd contents, and the former was more pronounced. QD (0.5 mg L^-1) increased the toxicity of Cd to algae, but n-Ag (0.2 mg L^-1) had no significant influence on the Cd toxicity to algae. The microscopic observations on the ultrastructure of algae cells presented the same phenomena and n-TiO₂, n-SiO₂ aggregations were clearly observed outside the cell wall. Furthermore, the regulation of NPs to the Cd toxicity towards algae was related to the intracellular nitric oxide (NO), an important signaling molecule, rather than the phototaxis of algae. Above all, this study provided a basic understanding about the difference in joint toxicity of different kinds of NPs and Cd to aquatic organisms.

Comparative effects of graphene and graphene oxide on copper toxicity to Daphnia magna: Role of surface oxygenic functional groups

Although the risk of graphene materials to aquatic organisms has drawn wide attention, the combined effects of graphene materials with other contaminants such as toxic metals, which may bring about more serious effects than graphene materials alone, have seldom been explored. Herein, the effects of graphene (GN) and graphene oxide (GO, an important oxidized derivative of graphene) on copper (Cu) toxicity to Daphnia magna were systematically investigated. The results indicated that GN remarkably increased the Cu accumulation in D. magna and enhanced the oxidative stress injury caused by Cu, whereas did not significantly alter D. magna acute mortality within the tested Cu concentrations (0-200 μg L^-1). On the contrary, GO significantly decreased the Cu accumulation in D. magna and alleviated the oxidative stress injury caused by Cu. Meanwhile, the presence of GO significantly reduced the mortality of D. magna when Cu concentration exceeded 50 μg L^-1. The different effects of GN and GO on Cu toxicity were possibly dependent on the action of surface oxygenic functional group. Because of the introduction of surface oxygenic functional groups, the adsorption ability to metal ions, stability in water and interaction mode with organisms of GO are quite different from that of GN, causing different effects on Cu toxicity. This study provides important information on the bioavailability and toxicity of heavy metals as affected by graphene materials in natural water.

Binary effect of titanium dioxide nanoparticles (nTio2) and phosphorus on microalgae (Chlorella 'Ellipsoides Gerneck, 1907)

The wide application of titanium dioxide nanoparticles and phosphorus in the manufacturing of many industrial products mainly used in agricultural sector has resulted in the release of considerable amounts of these compounds into freshwater aquatic ecosystem. These compounds may cause some unexpected effects to aquatic organisms. This study assessed the binary effects of Titanium nanoparticles (nTiO₂) and Phosphorus on Chlorella ellipsoides. Toxicological assay test of the compounds nTiO₂ (1.25 μM) alone and the combination of Titanium dioxide (1.25 μM) and Phosphorus (16, 32, 80, 160, 240 μM) was assessed, after 96 h exposures, for optical density (OD₆₈₀), specific growth rate, chlorophyll levels and lipid peroxidation via Malondialdehyde (MDA) activity. Superoxide dismutase (SOD), peroxidase (POD) and glutathione-s-transferase (GST) activities were also measured. Two-way ANOVA showed a significant interaction (P < 0.05) between binary mixture. Co-exposure showed a decreased phosphorus bioconcentration in the microalgae with significant increase (P < 0.05) in chlorophyll a/b and total chlorophyll contents. A significant decrease (P < 0.05) in specific growth rate and optical density were recorded whereas, antioxidant enzymes (MDA, SOD, POD, GST) activities were significantly (P < 0.05) increased. These results showed that the addition of nTiO₂ to Phosphorus affected the physiology of microalgae and should be of great concern for freshwater biodiversity.

A critical review of histopathological findings associated with endocrine and non-endocrine hepatic toxicity in fish models

Although frequently examined as a target organ for non-endocrine toxicity, histopathological evaluation of the liver is becoming a routine component of endocrine disruption studies that utilize various fish species as test subjects. However, the interpretation of microscopic liver findings can be challenging, especially when attempting to distinguish adverse changes associated with endocrine disrupting substances from those caused by systemic or direct hepatic toxicity. The purpose of this project was to conduct a critical assessment of the available peer-reviewed and grey literature concerning the histopathologic effects of reproductive endocrine active substances (EAS) and non-endocrine acting substances in the livers of fish models, and to determine if liver histopathology can be used to reliably distinguish endocrine from non-endocrine etiologies. The results of this review suggest that few compound-specific histopathologic liver effects have been identified, among which are estrogen agonist-induced increases in hepatocyte basophilia and proteinaceous intravascular fluid in adult male teleosts, and potentially, decreased hepatocyte basophilia in female fish exposed to substances that possess androgenic, anti-estrogenic, or aromatase inhibitory activity. This review also used published standardized methodology to assess the credibility of the histopathology data in each of the 117 articles that reported liver effects of treatment, and consequently it was determined that in only 37% of those papers were the data considered either highly credible or credible. The outcome of this work highlights the value of histopathologic liver evaluation as an investigative tool for EAS studies, and provides information that may have implications for EAS hazard assessment.

Enhanced bio-concentration of tris(1,3-dichloro-2-propyl) phosphate in the presence of nano-TiO2 can lead to adverse reproductive outcomes in zebrafish

Interactions between organic toxicants and nano-particles in the aquatic environment may modify toxicant bioavailability and consequently the toxicant's fate and toxicity. To evaluate the potential impact of nano-titanium dioxide (TiO₂) on the bio-concentration and reproductive endocrine disruption of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) in fish, a comparative bioaccumulation study was conducted on zebrafish (Danio rerio, AB strain) treated with 0, 5.74, 23.6, or 90.7 μg L^-1 TDCIPP alone or co-exposed to TDCIPP and 0.09 mg L^-1 nano-TiO₂ for 21 days. Nano-TiO₂ can absorb TDCIPP and nano-TiO₂ is taken up into zebrafish. Chemical measurements showed that TDCIPP was bio-concentrated in zebrafish, and the highest level was detected in the liver, followed by the brain and gonads. Compared with TDCIPP treatment, increased tissue burdens of both TDCIPP were observed in the liver, brain, and gonads suggesting that nano-TiO₂ adsorbed TDCIPP and acted as a carrier facilitating the uptake and translocation of TDCIPP in tissues. Higher bio-concentration in the presence of nano-TiO₂ resulted in a significant decrease in the hepatic-somatic index, gonad-somatic index and brain-somatic index in F0 females but not F0 males. Moreover, a further gender-dependent reduction in testosterone (T), estradiol (E2), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and induction of plasma vitellogenin (VTG) concentrations in adults were observed following co-exposure. Co-exposure also inhibited egg production and caused significant developmental toxicity in F1 larvae. The results obtained using this multi-marker approach suggested that nano-TiO₂ is a carrier of TDCIPP and accelerated its bio-concentration in adult zebrafish, resulting in adverse reproduction outcomes.

Responses of growth, malformation, and thyroid hormone-dependent genes expression in Bufo gargarizans embryos following chronic exposure to Pb2

The aim of this study was to examine the adverse effects of lead (Pb) exposure on Bufo gargarizans embryos. The 96 h-LC₅₀ of Pb²⁺ for B. gargarizans embryos was determined to be 26.6 mg L^-1 after an acute test. In the chronic test, B. gargarizans embryos at Gosner stage 3 were exposed to 10~2000 μg Pb²⁺ L^-1 during embryogenesis. Total length, weight, developmental stage, and malformation were monitored. In addition, the transcript levels of type II and type III iodothyronine deiodinase (Dio2 and Dio3) and thyroid hormone receptors (TRα and TRβ) were determined to assess the thyroid-disrupting effects of Pb²⁺. Slightly increased growth and development of B. gargarizans embryos were observed at low concentrations of Pb²⁺ (10, 50, and 100 μg L^-1), while retarded growth and development were found at high concentrations of Pb²⁺ (1000 and 2000 μg L^-1). In addition, Pb²⁺ exposure induced morphological abnormalities, which were characterized by edema at tail, wavy fin, abdominal edema, stunted growth, hyperplasia, and axial flexures in B. gargarizans embryos. Furthermore, our results showed that exposure to 2000 μg Pb²⁺ L^-1 decreased the transcript levels of Dio2, TRα, and TRβ, but it increased Dio3 mRNA level. In contrast, exposure to 50 μg Pb²⁺ L^-1 increased TRα mRNA level and decreased Dio3 mRNA level. These results suggested that Pb²⁺ might have thyroid-disrupting effects, leading to the disruption of growth and development in B. gargarizans embryos.

Silver nanoparticles cause osmoregulatory impairment and oxidative stress in Caspian kutum (Rutilus kutum, Kamensky 1901)

Silver nanoparticles (AgNPs) are increasingly used in several industrial and household products because of their antibacterial and antifungal properties. Hence, there is an inevitable risk that these chemicals may end up in aquatic biotopes and have adverse effects on the fauna. In order to assess potential health effects on aquatic organisms, this study evaluated the effects of waterborne AgNP exposure for 7 days on a set of critical stress parameters in juvenile Caspian kutum (Rutilus kutum), an economically important fish in the Caspian Sea. The applied level 11 μg/l of AgNP is high compared to reported water concentrations and corresponds to 40% of the 96 h LC₅₀ value, initially determined to be 28 μg/l. Gill heat shock protein 70 (hsp70) mRNA expression, Na⁺/K⁺-ATPase activity and enzymatic activities of liver superoxide dismutase (SOD), glutathione peroxidase (Gpx), lactate dehyrogenase (LDH) and alkaline phosphatase (ALP), and whole-body cortisol and thyroid hormones (T3 and T4) were measured as endpoints. Gill hsp70 mRNA expression increased and gill Na⁺/K⁺-ATPase activity decreased in AgNP-exposed fish compared to controls. The specific activities of all liver enzymes decreased significantly compared to controls. Whole-body cortisol and thyroid hormones decreased compared to controls. In conclusion, the study demonstrates that AgNPs cause oxidative stress and gill osmoregulatory disruption in Caspian kutum juveniles.

Silica nanoparticles and lead acetate co-exposure triggered synergistic cytotoxicity in A549 cells through potentiation of mitochondria-dependent apoptosis induction

The adverse effects of PM2.5 are the results of combined toxicities of finer particles and their adsorbed toxic pollutants. Nevertheless, the combined toxicity of finer particles and air pollutants still remains unclear. The present study was therefore undertaken to investigate the combined cytotoxicity of silica nanoparticles (nano-SiO₂, a typical atmospheric ultrafine particle) and lead acetate (Pb, a representative air pollutant) in A549 cells focusing on mitochondria-dependent apoptosis induction. The results showed that Pb exposure alone induced mitochondria-dependent apoptosis in A549 cells, as evidenced by increased apoptotic rate and Bax/Bcl-2 ratio, up-regulated caspases 3 and 9 expressions as well as decreased mitochondrial membrane potential. Non-cytotoxic concentration of nano-SiO₂ exposure alone did not trigger apoptosis in A549 cells, but potentialized the apoptotic changes when co-exposure with Pb. Factorial analyses revealed synergistic interactions were responsible for the potentiation of joint apoptotic responses.

Effects of titanium dioxide nanoparticles exposure on parkinsonism in zebrafish larvae and PC12

Nanomaterials hold significant potential for industrial and biomedical application these years. Therefore, the relationship between nanoparticles and neurodegenerative disease is of enormous interest. In this contribution, zebrafish embryos and PC12 cell lines were selected for studying neurotoxicity of titanium dioxide nanoparticles (TiO₂ NPs). After exposure of different concentrations of TiO₂ NPs to embryos from fertilization to 96 hpf, the hatching time of zebrafish was decreased, accompanied by an increase in malformation rate. However, no significant increases in mortality relative to control were observed. These results indicated that TiO₂ NPs exposure hold a risk for premature of zebrafish embryos, but not fatal. The further investigation confirmed that TiO₂ NPs could accumulate in the brain of zebrafish larvae, resulting in reactive oxygen species (ROS) generation and cell death of hypothalamus. Meanwhile, q-PCR analysis showed that TiO₂ NPs exposure increased the pink1, parkin, α-syn and uchl1 gene expression, which are related with the formation of Lewy bodies. We also observed loss of dopaminergic neurons in zebrafish and in vitro. These remarkable hallmarks are all linked to these Parkinson's disease (PD) symptoms. Our results indicate that TiO₂NPs exposure induces neurotoxicity in vivo and in vitro, which poses a significant risk factor for the development of PD.

Assessment of thyroid endocrine system impairment and oxidative stress mediated by cobalt ferrite (CoFe2 O4 ) nanoparticles in zebrafish larvae

Fascinating super paramagnetic uniqueness of iron oxide particles at nano-scale level make them extremely useful in the state of the art therapies, equipments, and techniques. Cobalt ferrite (CoFe₂ O₄ ) magnetic nanoparticles (MNPs) are extensively used in nano-based medicine and electronics, results in extensive discharge and accumulation into the environment. However, very limited information is available for their endocrine disrupting potential in aquatic organisms. In this study, the thyroid endocrine disrupting ability of CoFe₂ O₄ NPs in Zebrafish larvae for 168-h post fertilization (hpf) was evaluated. The results showed the elevated amounts of T4 and T3 hormones by malformation of hypothalamus pituitary axis in zebrafish larvae. These elevated levels of whole body THs leads to delayed hatching, head and eye malformation, arrested development, and alterations in metabolism. The influence of THs disruption on ROS production and change in activities of catalase (CAT), mu-glutathione s-transferase (mu-GST), and acid phosphatase (AP) were also studied. The production of significantly higher amounts of in vivo generation of ROS leads to membrane damage and oxidative stress. Presences of NPs and NPs agglomerates/aggregates were also the contributing factors in mechanical damaging the membranes and physiological structure of thyroid axis. The increased activities of CAT, mu-GST, and AP confirmed the increased oxidative stress, possible DNA, and metabolic alterations, respectively. The excessive production of in vivo ROS leads to severe apoptosis in head, eye, and heart region confirming that malformation leads to malfunctioning of hypothalamus pituitary axis. ROS-induced oxidative DNA damage by formation of 8-OHdG DNA adducts elaborates the genotoxicity potential of CoFe₂ O₄ NPs. This study will help us to better understand the risk and assessment of endocrine disrupting potential of nanoparticles. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 2068-2080, 2016.

Insight into the Mechanisms of Combined Toxicity of Single-Walled Carbon Nanotubes and Nickel Ions in Macrophages: Role of P2X7 Receptor

Coexistence of nanomaterials and environmental pollutants requires in-depth understanding of combined toxicity and underlying mechanism. In this work, we found that coexposure to the mixture of noncytotoxic level of single-walled carbon nanotubes (SWCNTs) (10 μg/mL) and Ni²⁺ (20 μM) induced significant cytotoxicity in macrophages. However, almost equal amount of intracellular Ni²⁺ was detected after Ni²⁺/SWCNT coexposure or Ni²⁺ single exposure, indicating no enhanced cellular uptake of Ni²⁺ occurred. SDS-PAGE analysis revealed 50% more SWCNTs retained in Ni²⁺/SWCNT exposed cells than that with SWCNT exposure alone, regardless of the exposure sequence (coexposure, Ni²⁺ pre- or post-treatment), suggesting inhibited SWCNT exocytosis by Ni²⁺. The increased cellular dose of SWCNTs could quantitatively account for the elevated toxicity of Ni²⁺/SWCNT mixture to cells. It was then found that agonist (ATP) and antagonist (o-ATP) of P2X₇R could regulate intracellular SWCNT amount and the cytotoxicity accordingly. In addition, inhibition of P2X₇R by P2X₇-targeting siRNA diminished the inhibitory effect of Ni²⁺. It was therefore concluded that Ni²⁺ impeded SWCNT exocytosis by inhibiting P2X₇R, leading to higher intracellular retention of SWCNTs and elevated cytotoxicity. Our work identified exocytosis inhibition as an important mechanism for SWCNT/Ni²⁺ toxicity, and revealed the crucial role of P2X₇R in mediating such inhibitory effect.

Effect of titanium dioxide nanoparticles on copper toxicity to Daphnia magna in water: Role of organic matter

Inevitably released into natural water, titanium dioxide nanoparticles (nano-TiO₂) may affect the toxicity of other contaminants. Ubiquitous organic matter (OM) may influence their combined toxicity, which has been rarely reported. This study investigated the effect of nano-TiO₂ on Cu toxicity to Daphnia magna and the role of OM (dissolved or particle surface bound) in inducing combined effects. The effect of nano-TiO₂ on heavy metal accumulation depended on the adsorption capacity for heavy metals of nano-TiO₂ and the uptake of nano-TiO₂-metal complexes by organisms. Nano-TiO₂ significantly decreased Cu accumulation in D. magna, but the reducing effect of nano-TiO₂ was eliminated in the presence of humic acid (HA, a model OM). In the Cu and HA solution, nano-TiO₂ slightly affected the bioavailability of Cu²⁺ and Cu-HA complexes and thus slightly influenced Cu toxicity. The nanoparticle surface-bound HA reduced the effect of nano-TiO₂ on the speciation of the accumulated Cu; therefore, the combined effects of nano-TiO₂ and Cu on biomarkers similarly weakened. HA-altered Cu speciation may be the main factor responsible for the influence of HA on the combined effects of nano-TiO₂ and Cu. This study provides insights into the combined effects of nano-TiO₂ and heavy metals in natural water.

Long-term exposure to gold nanoparticles accelerates larval metamorphosis without affecting mass in wood frogs (Lithobates sylvaticus) at environmentally relevant concentrations

Nanoparticles are environmental contaminants of emerging concern. Exposure to engineered nanoparticles has been shown to have detrimental effects on aquatic organisms. The authors synthesized gold nanoparticles (18.1 ± 3.5 nm) and tested their effects on time to and weight at metamorphosis in wood frog (Lithobates sylvaticus) tadpoles, a species known to be sensitive to environmental stressors. Continuous exposure to all concentrations of gold nanoparticles (0.05 pM, 0.5 pM, and 5 pM in particles) for up to 55 d significantly reduced time to metamorphosis by as much as an average of 3 d (p < 0.05). However, exposure to gold nanoparticles had no effect on tadpole mass at metamorphosis. The approximately 18-nm gold nanoparticles used were metastable in dechlorinated tap water, resulting in a change in surface charge and aggregation over time, leading to negatively charged aggregates that were on the order of 60 nm to 110 nm. Nanoparticle aggregation could exacerbate the effect on time to metamorphosis. To the authors' knowledge, the present study is the first report on the effect of engineered nanoparticles of any kind on life-history variables in an amphibian, a taxonomic group that has been declining globally for at least 25 yr. Environ Toxicol Chem 2016;35:2304-2310. © 2016 SETAC.

Zebrafish: A complete animal model to enumerate the nanoparticle toxicity

Presently, nanotechnology is a multi-trillion dollar business sector that covers a wide range of industries, such as medicine, electronics and chemistry. In the current era, the commercial transition of nanotechnology from research level to industrial level is stimulating the world’s total economic growth. However, commercialization of nanoparticles might offer possible risks once they are liberated in the environment. In recent years, the use of zebrafish (Danio rerio) as an established animal model system for nanoparticle toxicity assay is growing exponentially. In the current in-depth review, we discuss the recent research approaches employing adult zebrafish and their embryos for nanoparticle toxicity assessment. Different types of parameters are being discussed here which are used to evaluate nanoparticle toxicity such as hatching achievement rate, developmental malformation of organs, damage in gill and skin, abnormal behavior (movement impairment), immunotoxicity, genotoxicity or gene expression, neurotoxicity, endocrine system disruption, reproduction toxicity and finally mortality. Furthermore, we have also highlighted the toxic effect of different nanoparticles such as silver nanoparticle, gold nanoparticle, and metal oxide nanoparticles (TiO₂, Al2O₃, CuO, NiO and ZnO). At the end, future directions of zebrafish model and relevant assays to study nanoparticle toxicity have also been argued.

Permethrin is a potential thyroid-disrupting chemical: In vivo and in silico envidence

Permethrin (PM), one of the most heavily used synthetic pyrethroids, has the potential to interfere with thyroid hormones in mammals, however, the effect is poorly recognized in aquatic organisms. Herein, embryonic zebrafish were exposed to PM (0, 1, 3 and 10μg/L) until 72h post-fertilization. We demonstrated that PM readily accumulated in larvae with a preference for cis-PM, inhibited development and increased thyroxine and 3,5,3'-triiodothyronine levels accompanying increase in the transcription of most target genes, i.e., thyroid-stimulating hormone β, deiodinases, thyroid receptors, involved in the hypothalamic-pituitary-thyroid axis. Further Western blot analysis indicated that transthyretin (TTR) protein was significantly increased. Molecular docking analysis and molecular dynamics simulations revealed that PM fits into three hydrophobic binding pocket of TTR, one of the molecular targets of thyroid hormone disrupting chemicals (THDCs), and forms strong van der Waals interactions with six resides of TTR, including Leu8, Leu 101, Leu125, Thr214, Leu218 and Val229, thus altering TTR activity. Both in vivo and in silico studies clearly disclosed that PM potentially disrupts the thyroid endocrine system in fish. This study provides a rapid and cost-effective approach for identifying THDCs and the underlying mechanisms.

Synthesis of Luminescent Graphene Quantum Dots with High Quantum Yield and Their Toxicity Study

High fluorescence quantum yield graphene quantum dots (GQDs) have showed up as a new generation for bioimaging. In this work, luminescent GQDs were prepared by an ameliorative photo-Fenton reaction and a subsequent hydrothermal process using graphene oxide sheets as the precursor. The as-prepared GQDs were nanomaterials with size ranging from 2.3 to 6.4 nm and emitted intense green luminescence in water. The fluorescence quantum yield was as high as 24.6% (excited at 340 nm) and the fluorescence was strongest at pH 7. Moreover, the influences of low-concentration (12.5, 25 μg/mL) GQDs on the morphology, viability, membrane integrity, internal cellular reactive oxygen species level and mortality of HeLa cells were relatively weak, and the in vitro imaging demonstrated GQDs were mainly in the cytoplasm region. More strikingly, zebrafish embryos were co-cultured with GQDs for in vivo imaging, and the results of heart rate test showed the intake of small amounts of GQDs brought little harm to the cardiovascular of zebrafish. GQDs with high quantum yield and strong photoluminescence show good biocompatibility, thus they show good promising for cell imaging, biolabeling and other biomedical applications.