Immunofluorescence detection and localization of B[a]P and TCDD in earthworm tissues

Bioaccumulation and biological effects of hydrogenated cement particles in the marine bivalve, Mytilusgalloprovincialis

The decommissioning and normal functioning of nuclear facilities can result in the production and release of airborne particles in the environment. Aquatic biota are expected to be exposed to these particles considering that nuclear facilities are often located near water bodies. Aerosols, such as cement dust, can interact with radionuclides as well as with heavy metals, and therefore elicit not only radiological impacts but also chemical toxicity. In the present study, we aimed to determine the effects of hydrogenated cement particles (HCPs) as a first step before evaluating any radiotoxicity of tritiated cement particles in the marine mussels, Mytilus galloprovincialis. Responses at different levels of biological organisation were assessed, including clearance rate (CR), tissue specific accumulation, DNA damage and transcriptional expression of key stress related genes. Acute (5 h) and medium-term, chronic (11 d) exposures to 1000 μg L-1 HCPs showed that bioaccumulation, assessed using Cu as a proxy and determined by inductively coupled plasma mass spectrometry, was time and tissue dependent. The highest levels of Cu were found in the digestive gland (DG) after 11 d. HCP exposure caused changes in the expression of oxidative and other stress-related genes, including mt20 in DG and gst and sod in the gill after 5 h exposure, while an overexpression of hsp70 in the gill was observed after 11 d. Genotoxic effects in haemocytes were observed after 11 d of HCP exposure. Multivariate analysis indicated that oxidative stress is the most probable factor contributing to overall physiological dysfunction. Our results provide a baseline to perform further studies employing tritiated cement particles. Specifically, future work should focus on the DG since only this tissue showed significant bioaccumulation when compared to the negative control.

AhR-mediated lipid peroxidation contributes to TCDD-induced cardiac defects in zebrafish

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a persistent environmental contaminant that activates the aryl hydrocarbon receptor (AhR) pathway, has been reported to cause cardiac damage. However, the mechanism underlying AhR-induced cardiac defects in response to TCDD exposure remains unclear. In this study, we characterized the impacts of TCDD exposure on heart morphology and cardiac function in zebrafish. TCDD exposure in the early developmental stage of zebrafish embryos led to morphological heart malformation and pericardial edema, concomitant with reduced cardiac function. These cardiac defects were attenuated by inhibiting AhR activity with CH223191. Transcriptome profiling showed that, along with an upregulation of the AhR signaling pathway by TCDD treatment, the expression of pro-ferroptotic genes was upregulated, while that of genes implicated in glutathione metabolism were downregulated. Moreover, lipid peroxidation, as indicated by malonaldehyde (MDA) production, was increased in TCDD-exposed cardiac tissue. Accordingly, inhibiting lipid peroxidation with liproxstatin-1 reversed the adverse cardiac effects induced by TCDD treatment. Taken together, our findings demonstrate that AhR-mediated lipid peroxidation contributes to cardiac defects in the early developmental stage in zebrafish embryos exposed to TCDD.

Immunofluorescence Visualization of Polycyclic Aromatic Hydrocarbon Mixtures in the Eastern Oyster Crassostrea virginica

Bivalve mollusks including oysters have low metabolic potential and are therefore susceptible to accumulating high levels of lipophilic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs). Human exposure to PAHs via consumption of this important commercial shellfish can be a serious public health concern in areas where high PAH contamination exists. Previous PAH immunohistochemical studies have been limited to laboratory-based exposures focusing on one or a few individual PAH compounds. To date, such studies have yet to explore PAH accumulation in oysters, known to have some of the highest levels of PAHs across different food products. Using a monoclonal antibody selective for a range of three- to five-ring PAHs, we present a method to detect and localize complex mixtures of PAHs in oyster tissues via fluorescent immunohistochemistry. Observed immunofluorescence intensity followed a similar trend as measured levels of PAHs in oyster interstitial fluid from PAH-contaminated sites and oysters exposed to the water accommodated fraction of crude oil. This method will be valuable in understanding internal partitioning mechanisms of PAH-exposed oysters and will have important applications in studies on PAH distribution in the tissues of additional organisms for environmental, medical, or veterinary purposes. Environ Toxicol Chem 2023;42:475-480. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

Molecular mechanisms underlying the effects of temperature increase on Mytilus sp. and their hybrids at early larval stages

The present work aims to investigate the effects of water temperature increase on Mytilus galloprovincilis and Mytilus edulis pure larvae (PG, PE) and their hybrids (HFG, HFE). D-larvae were maintained at 18 °C or exposed to a higher temperature of 22 °C for 48 h. Initially, Embryotoxicity test was evaluated. Second, a transcriptomic analysis using a recently developed microarray platform was applied to determine the main biological processes involved in early life stages responses to temperature increase. Finally, an immunofluorescence investigation was performed to bridge the gap between transcriptomic regulation and the real changes at cellular/tissue levels. Embryotoxicity test revealed a higher sensitivity of M. edulis (PE) D-larvae as well as hybrids from females M. edulis (HFE) to temperature increase, with the highest rate of larval malformations. Transcriptomic results indicated a lack of an adequate heat shock protein (Hsp) response in PE and HFE larvae (the high expression was observed in PG larvae); the differential expression of gene involved in translation, energy metabolism and oxidative stress response may contribute to explain the observed complex alterations in the studied conditions. As revealed by immunohistochemistry, cytoskeleton proteins changes associated with a drastic decrease of Histidine-Rich Glycoprotein (HRG) may elucidate the larval abnormalities in shell development observed for PE and HFE larvae. Overall, the results indicate that each type of pure larva (PG and PE) and their respective female hybrid (HFG and HFE) react similarly to the temperature increase. Our data should be carefully considered in view of the water temperature increase in marine ecosystems and especially for the mussel's species in confluence zones.

Application of a new targeted low density microarray and conventional biomarkers to evaluate the health status of marine mussels: A field study in Sardinian coast, Italy

In the present study, we investigated the health status of marine mussels (Mytilus galloprovincialis) caged and deployed at three different sites on the Sardinian coastline characterized by different levels of contamination: Fornelli (F, the reference site), Cala Real (CR), and Porto Torres (PT). A new low density oligonucleotide microarray was used to investigate global gene expression in the digestive gland of mussels. Target genes were selected to cover most of the biological processes involved in the stress response in bivalve mollusks (e.g. DNA metabolism, translation, immune response, cytoskeleton organization). A battery of classical biomarkers was also employed to complement the gene expression analyses. Chemical analysis revealed higher loads of heavy metals (Pb and Cu) and total polycyclic aromatic hydrocarbons (PAHs) at PT compared to the other sites. In mussels deployed at CR, functional genomics analysis of the microarray data rendered 78 differentially expressed genes (DEGs) involved in 11 biological processes. Animals exposed at PT had 105 DEGs that were characterized by the regulation of 14 biological processes, including mitochondrial activity, adhesion to substrate, DNA metabolism, translation, metal resistance, and cytoskeleton organization. Biomarker data (lysosomal membrane stability, lysosomal/cytoplasm volume ratio, lipofuscin accumulation, metallothionein content, micronucleus frequency, and cytoskeleton alteration) were in trend with transcriptomic output. Biomarker data were integrated using the Mussel Expert System (MES), allowing defining the area in which the presence of chemicals is toxic for mussels. Our study provides the opportunity to adopt a new approach of integrating transcriptomic (microarray) results with classical biomarkers to assess the impact of pollutants on marine mussels in biomonitoring programs.

Role of mTOR in autophagic and lysosomal reactions to environmental stressors in molluscs

Lysosomal membrane stability (LMS) has been used in various organisms as a very sensitive biomarker of stress. However, despite the abundance of data about regulation of the autophagic process in mammals, in the invertebrates there is only limited mechanistic understanding. Marine mussels (Mytilus galloprovincialis Lam.) are bivalve molluscs, widely used as models in ecotoxicology and as environmental bioindicators of sea water quality. In order to elucidate this fundamental process, in the present study, mussels were exposed for 3 days to a "priority", ubiquitous environmental contaminant, benzo[a]pyrene (B[a]P) at different concentrations (i.e. 5, 50, 100 μg/L seawater). B[a]P accumulated in lysosomes of digestive tubule epithelial cells (digestive cells) and in enlarged lipid-rich lysosomes (autolysosomes) as detected by immunofluorescence and UV-fluorescence. B[a]P also activated the autophagic process with a marked decrease of LMS and concurrent increase in lysosomal/cytoplasmic volume ratio. Dephosphorylation of mTOR contributes to increased lysosomal membrane permeability and induced autophagy. B[a]P induced a decrease in phosphorylated (active form) mTOR. The probable role of mTOR in cell signalling and the regulation of the cellular responses to the contaminants has been also confirmed in a field study, where there was significant inactivation of mTOR in stressed animals. Statistical and network modelling supported the empirical investigations of autophagy and mTOR; and was used to integrate the mechanistic biomarker data with chemical analysis and DNA damage.

Effects of Cr(VI) on Ca2+-ATPase activity in the earthworm Eisenia andrei

The effect of Cr(VI) as a soil contaminant on the edaphic worm Eisenia andrei was studied by evaluating the activity of Ca²⁺-ATPase in the intestinal mucosa. In eukaryotes, Ca²⁺-ATPase is a key mediator of cell signaling although comparatively little is known about its activity in earthworms. Size and anatomical constraints (i.e. small and complex) led us to develop and optimize a cyto-biochemical method to measure Ca²⁺-ATPase activity in earthworms. The principal site of enzyme activity was found to be the post clitellar intestinal tract; immunohistochemistry then identified plasma membrane Ca²⁺-ATPase (PMCA ATPase) in the apical area of the intestinal epithelium. Earthworms exposed for 28days to OECD soil contaminated with 1, 2, and 15mg/Kg Cr(VI) demonstrated about 70% inhibition of Ca²⁺-ATPase activity at the low Cr (VI) concentration (the half of the Italian law limit for residential areas), rising to approximately 84% inhibition at the highest concentration. Reduced enzyme activity was accompanied by decreased enzyme content and reduced lysosomal membrane stability (LMS), which is a well established early warning biomarker of stress. These data demonstrate the potential utility of Ca²⁺-ATPase activity as a sensitive parameter with which to detect environmental stress in earthworms.

Exposure to lethal levels of benzo[a]pyrene or cadmium trigger distinct protein expression patterns in earthworms (Eisenia fetida)

Different pollutants induce distinct toxic responses in earthworms (Eisenia fetida). Here, we used proteomics techniques to compare the responses of E. fetida to exposure to the 10% lethal concentration (14d-LC₁₀) of benzo[a]pyrene (BaP) or cadmium (Cd) in natural red soil (China). BaP exposure markedly induced the expression of oxidation-reduction proteins, whereas Cd exposure mainly induced the expression of proteins involved in transcription- and translation-related processes. Furthermore, calmodulin-binding proteins were differentially expressed upon exposure to different pollutants. The calcium (Ca²⁺)-binding cytoskeletal element myosin was down-regulated upon BaP treatment, whereas the Ca²⁺-binding cytoskeletal element tropomyosin-1 was up-regulated upon Cd treatment. Some proteins exhibited opposite responses to the two pollutants. For instance, catalase (CAT) and heat shock protein 70 were up-regulated upon BaP treatment and down-regulated upon Cd treatment. A significant (p<0.05, one-way ANOVA with least-significant difference (LSD) test) increase in the level of reactive oxygen species (ROS) and CAT activity further showed that BaP mainly induces oxidative stress. Real-time PCR analysis showed that mRNA expression often did not correlate well with protein expression in earthworms subjected to Cd or BaP treatment. In addition, the expression of the gene encoding the protein metallothionein, which was not detected in the protein analysis, was induced upon Cd treatment, but slightly reduced upon BaP treatment. Therefore, BaP and Cd have distinct effects on the protein profile of E. Fetida with BaP markedly inducing ROS activity, and Cd mainly triggering genotoxicity.

CAPSULE SUMMARY

Distinct patterns of protein expression are induced in earthworms upon exposure to different pollutants; BaP markedly induces high levels of ROS, while Cd resultes in genotoxicity.

Mode of action of Cr(VI) in immunocytes of earthworms: Implications for animal health

Chromium (Cr) is one of the major and most detrimental pollutant, widely present in the environment as a result of several anthropogenic activities. In mammalian cells, Cr(VI) is known to enhance reactive oxygen species (ROS) production and to cause toxic and genotoxic effects. Less commonly investigated are the effects and mode of action of this contaminant in invertebrates, particularly in soil organisms. In this work, earthworms of the species Eisenia andrei were exposed for 1 and 3 days to various sublethal concentrations of Cr(VI) (2, 15, 30µgmL^-1) using the paper contact toxicity test. In amoeboid leukocytes we investigated intracellular ROS and lipoperoxide production, oxidative DNA damage, and the effects on different cell functions. The analysis of the results shows that Cr(VI) triggered severe adverse reactions; the first events were an increase of intracellular ROS levels, generating in the cells oxidative stress conditions leading to membrane lipid peroxidation and oxidative DNA damage. Lysosomes showed relevant changes such as a strong membrane destabilization, which was accompanied by an increased catabolism of cytoplasmic proteins and accumulation of lipofuscin. With an increase in the dose and/or time of exposure, the physiological status of intracellular organelles (such as lysosomes, nucleus and mitochondria) showed further impairment and amoebocyte immune functions were adversely affected, as shown by the decrease of the phagocytic activity. By mapping the responses of the different parameters evaluated, diagnostic of (oxidative) stress events, against lysosomal membrane stability, a "health status" indicator (able to describe the stress syndrome from its early phase to pathology), we have shown that this biomarker is suitable as a prognostic test for health of earthworms. This is viewed as a crucial step toward the derivation of explanatory frameworks for prediction of pollutant impact on animal health.

Molecular and cellular response of earthworm Eisenia andrei (Oligochaeta, Lumbricidae) to PCDD/Fs exposure

The acute toxicity of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) was investigated in the earthworm Eisenia andrei using filter paper toxicity test. Protein content, catalase (CAT) activity, and histology of intestinal wall (chloragogen cells and intestinal epithelium) were investigated in earthworms exposed for 48 h to 0 (control), 0.5, 1.0, and 1.5 ng/cm² PCDD/Fs. The results showed an increase in the total protein content 1.56- (p = 0.104), 1.66- (p = 0.042), and 2.26-fold (p < 0.001), respectively, compared to control. The average ± standard deviation of tissular CAT activity showed no significant differences; it was 36.01 ± 7.65, 36.17 ± 9.45, 36.08 ± 9.80, and 40.01 ± 6.98 U/g tissue, respectively. However, the average specific activity of CAT ± standard deviation was significantly decreased (p < 0.001) at all doses compared to control; it was 2.93 ± 0.42, 1.93 ± 0.53, 1.80 ± 0.38, and 1.53 ± 0.44 U/mg protein, respectively. There was a progressive damage in both of the intestinal villi and the chloragogenous tissue associated with the incrementing doses. Since the toxic mixture altered the investigated biomarkers of E. andrei within 48 h, the cellular and molecular alterations resulted from the filter paper contact test could be utilized as a rapid toxicity assessment tool of environmental contamination with dioxins/furans and to assess consequent potential adverse effects on soil biota and other organisms in the ecosystem.

Combined effects of n-TiO2 and 2,3,7,8-TCDD in Mytilus galloprovincialis digestive gland: A transcriptomic and immunohistochemical study

Despite the growing concern over the potential biological impact of nanoparticles (NPs) in the aquatic environment, little is known about their interactions with other pollutants. In the marine mussel Mytilus galloprovincialis, exposure to nanosized titanium dioxide (n-TiO2), one of the most widespread type of NPs in use, in combination with and 2,3,7,8-tetrachlorodibenzo-p-dioxins (TCDD), chosen as model organic xenobiotic, was shown to induce significant changes in different biomarkers in hemocytes, gills and digestive gland, with distinct effects depending on cell/tissue and type of response measured. In this work, the interactive effects of n-TiO2 and TCDD at the tissue level were further investigated in mussel digestive gland using an integrated approach transcriptomics/immunohistochemistry. Mussels were exposed to n-TiO2 (100μgL(-1)) and TCDD (0.25μgL(-1)), alone and in combination, for 96h. Transcriptomic analysis identified 48-, 49- and 62 Differentially Expressed Genes (DEGs) in response to n-TiO2, TCDD and n-TiO2/TCDD, respectively. Gene Ontology (GO) term analysis revealed distinct biological processes affected in different experimental conditions. n-TiO2 mainly up-regulated cytoskeletal genes, while TCDD up-regulated endocrine and signal transduction related processes. Co-exposure induced transcriptional changes common to individual treatments, and identified a newly generated process, response to chemical stimulus. Transcription of selected genes was verified by qPCR. Moreover, expression of tubulin, as an example of target protein of interest identified by gene transcription data, was evaluated in tissue sections by immunolabelling. Tissue TCDD accumulation was evaluated by immunofluorescence with an anti-dioxins antibody. The results demonstrate both distinct and interactive effects of n-TiO2 and TCDD in mussel digestive gland at the molecular and tissue level, identify the main molecular targets involved, and underline how exposure to the n-TiO2/TCDD mixture does not result in increased TCDD accumulation and overall stressful conditions in the tissue. These represent the first data on transcriptional responses of marine invertebrates to exposure not only to n-TiO2 as a model of NP, but also to a legacy contaminant like TCDD.

Effects of PAHs and dioxins on the earthworm Eisenia andrei: a multivariate approach for biomarker interpretation

In this study, a battery of biomarkers was utilised to evaluate the stress syndrome induced in the earthworm Eisenia andrei by exposure to environmentally realistic concentrations of benzo[a]pyrene (B[a]P) and 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) in OECD soil. The set of tests was then employed to assess the toxicity of field soils contaminated with organic xenobiotic compounds (such as PAHs, dioxins and PCBs). The results highlighted an impairment of immune and metabolic functions and genotoxic damage in worms exposed also to lower bioavailable concentrations of toxic chemicals. Multivariate analysis of biomarker data showed that all different contaminated soils had a detrimental effect on the earthworms. A separation between temporal and concentration factors was also evident for B[a]P and TCDD treatments; and field contaminated soils were further differentiated reflecting a diverse contamination. Multivariate analysis also demonstrated that lysosomal membrane stability can be considered a prognostic indicator for worm health status.

Inhibition of cathepsin B activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent toxic isomer in the dioxin-like family. Due to its resistance to metabolic degradation, this ubiquitous environmental pollutant readily accumulates in multiple organs. Cathepsin B is a lysosomal cysteine protease playing an essential role in the intracellular protein turnover. Alterations in its expression, activity, and localization may facilitate the development of many pathologies, including cancer. TCDD, due to its extremely lipophilic nature, may diffuse through biological membranes and affect lysosomal enzymes, including cathepsins. Therefore, in this study we performed two enzymatic assays, spectrofluorimetry and gelatin zymography, in order to evaluate the effect of TCDD on purified bovine cathepsin B. We showed that the dioxin decreases the enzyme's activity in a dose-dependent manner. The reversibility of TCDD-induced inhibition of the protease was also examined, suggesting that TCDD does not bind covalently to the enzyme's active site, acting rather as a reversible inhibitor.

The effect of dibenzo-p-dioxin- and dibenzofuran-contaminated soil on the earthworm Eisenia andrei

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) belong to the group of persistent organic pollutants, highly toxic environmental pollutants that include hydrophobic compounds with the tendency to bioaccumulate. Earthworms (Eisenia andrei) were exposed to PCDD/Fs-contaminated soil, and changes in their lipophilic structures and the gene expression of their defense molecules were followed. Damage to the intestinal wall and adjacent chloragogenous tissue was observed. Further, the up-regulation of the expression of several genes was detected. On the basis of these results, the mechanism of the impact of PCDD/Fs on earthworms has been proposed. Dioxins that accumulate in the lipophilic structures cause an increase in reactive oxidative species that triggers oxidative stress followed by the gene expression of two molecules that play a role in protection against oxidant toxicity, calreticulin (CRT) and Hsp70. Moreover, the effect of microbial biomass on the expression of coelomic cytolytic factor (CCF), a pattern recognition receptor, was also observed.