An integrated approach to determine interactive genotoxic and global gene expression effects of multiwalled carbon nanotubes (MWCNTs) and benzo[a]pyrene (BaP) on marine mussels: evidence of reverse ‘Trojan Horse’ effects

Fate and effects of graphene oxide alone and with sorbed benzo(a)pyrene in mussels Mytilus galloprovincialis

Graphene oxide (GO) has gained a great scientific and economic interest due to its unique properties. As incorporation of GO in consumer products is rising, it is expected that GO will end up in oceans. Due to its high surface to volume ratio, GO can adsorb persistent organic pollutants (POPs), such as benzo(a)pyrene (BaP), and act as carrier of POPs, increasing their bioavailability to marine organisms. Thus, uptake and effects of GO in marine biota represent a major concern. This work aimed to assess the potential hazards of GO, alone or with sorbed BaP (GO+BaP), and BaP alone in marine mussels after 7 days of exposure. GO was detected through Raman spectroscopy in the lumen of the digestive tract and in feces of mussels exposed to GO and GO+BaP while BaP was bioaccumulated in mussels exposed to GO+BaP, but especially in those exposed to BaP. Overall, GO acted as a carrier of BaP to mussels but GO appeared to protect mussels towards BaP accumulation. Some effects observed in mussels exposed to GO+BaP were due to BaP carried onto GO nanoplatelets. Enhanced toxicity of GO+BaP with respect to GO and/or BaP or to controls were identified for other biological responses, demonstrating the complexity of interactions between GO and BaP.

An Insight into the Combined Toxicity of 3,4-Dichloroaniline with Two-Dimensional Nanomaterials: From Classical Mixture Theory to Structure-Activity Relationship

The assessment and prediction of the toxicity of engineered nanomaterials (NMs) present in mixtures is a challenging research issue. Herein, the toxicity of three advanced two-dimensional nanomaterials (TDNMs), in combination with an organic chemical (3,4-dichloroaniline, DCA) to two freshwater microalgae (Scenedesmus obliquus and Chlorella pyrenoidosa), was assessed and predicted not only from classical mixture theory but also from structure-activity relationships. The TDNMs included two layered double hydroxides (Mg-Al-LDH and Zn-Al-LDH) and a graphene nanoplatelet (GNP). The toxicity of DCA varied with the type and concentration of TDNMs, as well as the species. The combination of DCA and TDNMs exhibited additive, antagonistic, and synergistic effects. There is a linear relationship between the different levels (10, 50, and 90%) of effect concentrations and a Freundlich adsorption coefficient (K_F) calculated by isotherm models and adsorption energy (E_a) obtained in molecular simulations, respectively. The prediction model incorporating both parameters K_F and E_a had a higher predictive power for the combined toxicity than the classical mixture model. Our findings provide new insights for the development of strategies aimed at evaluating the ecotoxicological risk of NMs towards combined pollution situations.

Exposure to dibutyl phthalate adsorbed to multi-walled carbon nanotubes causes neurotoxicity in mice by inducing the release of BDNF

Multi-walled carbon nanotubes (MWCNTs) and dibutyl phthalate (DBP) exist extensively in the environment, and they are easy to form compound pollution through π-π interactions in the environment. We investigate whether DBP, an environmental hormone disruptor, mediated by CNTs can more easily cross the blood-brain barrier, and whether DBP entering the brain has neurotoxic effects on the cells in the brain. Experimental subjects were 40 male Kunming (KM) mice randomly divided into 4 groups: the control group; the MWCNTs group; the DBP group; and the MWCNTs+DBP group. The mice were exposed via tail intravenous injection once every 3 days for 21 days, following which toxicology studies were carried out. The results of behavioral experiments showed that the mice in the combined exposure group (MWCNTs+DBP) exhibited spatial learning and memory impairment, and anxiety-like behavior. Staining of hippocampal sections of mouse brain tissue showed that, in the CA1, CA2, and DG areas, the number of neurons decreased, the nucleus was pyknotic, the cell body was atrophied, and levels of the microglia marker Iba-1 increased. By proteomic KEGG analysis, we found that the DEPs were mainly those related to neurodegenerative diseases. Immunohistochemistry in the hippocampus indicated that the level of brain-derived neurotrophic factor (BDNF) in the DG region was significantly increased. RT-PCR results revealed that the expression levels of P53, caspase3, and Bax genes related to apoptosis were up-regulated. The experimental results demonstrated that the mechanism of the combined-exposure injury to neurons in the hippocampus of mice may be that MWCNTs with adsorbed DBP can induce the release of BDNF, accelerate the apoptosis of neurons, and reduce the number of nerve cells, which activates microglia, causing neuroinflammation and nervous system toxicity.

2,4-Dichlorophenoxyacetic acid (2,4-D) affects DNA integrity and retina structure in zebrafish larvae

Monitoring the potential risk of herbicides in non-target organisms is a crucial issue for environmental safety. 2,4-D is an herbicide of high environmental relevance that has been shown to exert toxic effects to soil and aquatic biota. In the present study, we investigated the possible genotoxic and retinal development effects of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in early life stages zebrafish (Danio rerio). Genotoxicity was evaluated by measuring DNA damage using the comet assay and also by the mRNA expression of genes implicated in apoptosis and/or DNA repair. Retinal development toxicity was evaluated with histological approach. The results obtained revealed that 2,4-D alters DNA integrity of zebrafish larvae. Moreover, transcriptomic data showed a significant induction of p-53 and casp-3 genes and a significant decrease of lig-4 in larvae exposed to the highest tested concentration of 2,4-D (0.8 mg/L). This suggested that p-53 gene regulates the process of DNA repair and apoptosis with increased levels of 2,4-D. The histopathological analysis revealed that early exposure to 2,4-D damaged the structure of larvae retina. Overall, this study is the first to report the DNA damage, casp-3, lig-4 and p-53 regulation, as well as the ocular developmental toxicity in zebrafish larvae at environmentally relevant concentrations of 2,4-D herbicide.

Antagonistic cytoprotective effects of C60 fullerene nanoparticles in simultaneous exposure to benzo[a]pyrene in a molluscan animal model

The hypothesis that C₆₀ fullerene nanoparticles (C₆₀) exert an antagonistic interactive effect on the toxicity of benzo[a]pyrene (BaP) has been supported by this investigation. Mussels were exposed to BaP (5, 50 & 100μg/L) and C₆₀ (C₆₀-1mg/L) separately and in combination. Both BaP and C₆₀ were shown to co-localize in the secondary lysosomes of the hepatopancreatic digestive cells in the digestive gland where they reduced lysosomal membrane stability (LMS) or increased membrane permeability, while BaP also induced increased lysosomal lipid and lipofuscin, indicative of oxidative cell injury and autophagic dysfunction. Combinations of BaP and C₆₀ showed antagonistic effects for lysosomal stability, mTORC1 (mechanistic target of rapamycin complex 1) inhibition and intralysosomal lipid (5 & 50μg/L BaP). The biomarker data (i.e., LMS, lysosomal lipidosis and lipofuscin accumulation; lysosomal/cell volume and dephosphorylation of mTORC1) were further analysed using multivariate statistics. Principal component and cluster analysis clearly indicated that BaP on its own was more injurious than in combination with C₆₀. Use of a network model that integrated the biomarker data for the cell pathophysiological processes, indicated that there were significant antagonistic interactions in network complexity (% connectance) at all BaP concentrations for the combined treatments. Loss of lysosomal membrane stability probably causes the release of intralysosomal iron and hydrolases into the cytosol, where iron can generate harmful reactive oxygen species (ROS). It was inferred that this adverse oxidative reaction induced by BaP was ameliorated in the combination treatments by the ROS scavenging property of intralysosomal C₆₀, thus limiting the injury to the lysosomal membrane; and reducing the oxidative damage in the cytosol and to the nuclear DNA. The ROS scavenging by C₆₀, in combination with enhanced autophagic turnover of damaged cell constituents, appeared to have a cytoprotective effect against the toxic reaction to BaP in the combined treatments.

Evaluation of interactive effects of phosphorus-32 and copper on marine and freshwater bivalve mollusks

PURPOSE

Contaminants seldom occur in isolation in the aquatic environment. While pollution of coastal and inland water bodies has received considerable attention to date, there is limited information on potential interactive effects between radionuclides and metals. Whether by accidental or controlled release, such contaminants co-exist in aquatic ecosystems and can pose an enhanced threat to biota. Using a range of biological responses, the study aimed to evaluate relative interactive effects on representative freshwater and marine bivalve species.

METHODS

An integrated, multi-biomarker approach was adopted to investigate response to copper (Cu, 18 μg L^-1), a known environmentally relevant genotoxic metal and differing concentrations of phosphorus-32 (³²P; 0.1 and 1 mGy d^-1), alone and in combination in marine (Mytilus galloprovincialis) and freshwater (Dreissena polymorpha) mussels. Genetic and molecular biomarkers were determined post-exposure and included DNA damage (as measured by the comet assay), micronuclei (MN) formation, γ-H2AX foci induction and the expression of key stress-related genes (i.e. hsp70/90, sod, cat, gst).

RESULTS

Overall, using a tissue-specific (i.e. gill and digestive gland) approach, genotoxic response was reflective of exposures where Cu had a slight additive effect on ³²P-induced damage across the species (but not all), cell types and dose rates. Multivariate analysis found significant correlations between comet and γ-H2AX assays, across both the tissues. Transcriptional expression of selected genes were generally unaltered in response to contaminant exposures, independent of species or tissues.

CONCLUSIONS

Our study is the first to explore the interactive effects of ionizing radiation (IR) and Cu on two bivalve species representing two ecological habitats. The complexity of IR-metal interactions demonstrate that extrapolation of findings obtained from single stressor studies into field conditions could be misrepresentative of real-world environments. In turn, environmental protective strategies deemed suitable in protecting biota from a single, isolated stressor may not be wholly adequate.

Will temperature rise change the biochemical alterations induced in Mytilus galloprovincialis by cerium oxide nanoparticles and mercury?

It is known that, for marine coastal ecosystems, pollution and global warming are among the most threatening factors. Among emerging pollutants, nanoparticles (NPs) deserve particular attention as their possible adverse effects are significantly influenced by environmental factors such as salinity, pH and temperature, as well as by their ability to interact with other contaminants. In this framework, the present study aimed to evaluate the potential interactions between CeO₂ NPs and the toxic classic metal mercury (Hg), under current and warming conditions. The marine bivalve Mytilus galloprovincialis was used as biological model and exposed to CeO₂ NPs and Hg, either alone or in combination, for 28 day at 17 °C and 22 °C. A suite of biomarkers related to energetic metabolism, oxidative stress/damage, redox balance, and neurotoxicity was applied in exposed and non-exposed (control) mussels. The Hg and Ce accumulation was also assessed. Results showed that the exposure to CeO₂ NPs alone did not induce toxic effects in M. galloprovincialis. On the contrary, Hg exposure determined a significant loss of energetic metabolism and a general impairment in biochemical performances. Hg accumulation in mussels was not modified by the presence of CeO₂ NPs, while the biochemical alterations induced by Hg alone were partially canceled upon co-exposure with CeO₂ NPs. The temperature increase induced loss of metabolic and biochemical functions and the effects of temperature prevailed on mussels exposed to pollutants acting alone or combined.

Mathematical Modeling Approaches for Assessing the Joint Toxicity of Chemical Mixtures Based on Luminescent Bacteria: A Systematic Review

Developments in industrial applications inevitably accelerate the discharge of enormous substances into the environment, whereas multi-component mixtures commonly cause joint toxicity which is distinct from the simple sum of independent effect. Thus, ecotoxicological assessment, by luminescent bioassays has recently brought increasing attention to overcome the environmental risks. Based on the above viewpoint, this review included a brief introduction to the occurrence and characteristics of toxic bioassay based on the luminescent bacteria. In order to assess the environmental risk of mixtures, a series of models for the prediction of the joint effect of multi-component mixtures have been summarized and discussed in-depth. Among them, Quantitative Structure-Activity Relationship (QSAR) method which was widely applied in silico has been described in detail. Furthermore, the reported potential mechanisms of joint toxicity on the luminescent bacteria were also overviewed, including the Trojan-horse type mechanism, funnel hypothesis, and fishing hypothesis. The future perspectives toward the development and application of toxicity assessment based on luminescent bacteria were proposed.

Effects of fullerene C60 in blue mussels: Role of mTOR in autophagy related cellular/tissue alterations

The effects of C₆₀ on mTOR (mechanistic Target of Rapamycin) activity in mussel digestive gland were investigated. mTOR is a kinase that senses physiological and environmental signals to control eukaryotic cell growth. mTOR is present in two complexes: the phosphorylated mTORC1 regulates cell growth by activating anabolic processes, and by inhibiting catabolic processes (i.e. autophagy); mTORC2 also modulates actin cytoskeleton organization. Mussels were exposed to C₆₀ (0.01, 0.1 and 1 mg/L) for 72 h. Immunocytochemical analysis using a specific antibody revealed the cellular distribution of C₆₀ in mussel digestive gland, already at the lowest concentration. In exposed mussels, the dephosphorylation of mTORC1 and mTORC2 may explain the C₆₀ effects, i.e. the reduction of lysosomal membrane stability, the enhancement of LC3B protein, and the increase of lysosomal/cytoplasmic volume ratio; as well the cytoskeletal alterations. No oxidative stress was observed. Multivariate analysis was used to facilitate the interpretation of the biomarker data. Finally, a low density oligo-microarray was used to understand the cellular responses to fullerene. Transcriptomics identified a number of differentially expressed genes (DEGs) showing a maximum in animals exposed to 0.1 mg/L C₆₀. The most affected processes are associated with energy metabolism, lysosomal activity and cytoskeleton organization. In this study, we report the first data on the subcellular distribution of C₆₀ in mussel's cells; and on the involvement of mTOR inhibition in the alterations due to nanoparticle accumulation. Overall, mTOR deregulation, by affecting protein synthesis, energy metabolism and autophagy, may reduce the capacity of the organisms to effectively grow and reproduce.