Selection of an optimal culture medium and the most responsive viability assay to assess AgNPs toxicity with primary cultures of Eisenia fetida coelomocytes

Coupled Lipidomics and Digital Pathology as an Effective Strategy to Identify Novel Adverse Outcome Pathways in Eisenia fetida Exposed to MoS2 Nanosheets and Ionic Mo

Molybdenum disulfide (MoS₂) nanosheets are increasingly applied in several fields, but effective and accurate strategies to fully characterize potential risks to soil ecosystems are lacking. We introduce a coelomocyte-based in vivo exposure strategy to identify novel adverse outcome pathways (AOPs) and molecular endpoints from nontransformed (NTMoS₂) and ultraviolet-transformed (UTMoS₂) MoS₂ nanosheets (10 and 100 mg Mo/L) on the earthworm Eisenia fetida using nontargeted lipidomics integrated with transcriptomics. Machine learning-based digital pathology analysis coupled with phenotypic monitoring was further used to establish the correlation between lipid profiling and whole organism effects. As an ionic control, Na₂MoO₄ exposure significantly reduced (61.2-79.5%) the cellular contents of membrane-associated lipids (glycerophospholipids) in earthworm coelomocytes. Downregulation of the unsaturated fatty acid synthesis pathway and leakage of lactate dehydrogenase (LDH) verified the Na₂MoO₄-induced membrane stress. Compared to conventional molybdate, NTMoS₂ inhibited genes related to transmembrane transport and caused the differential upregulation of phospholipid content. Unlike NTMoS₂, UTMoS₂ specifically upregulated the glyceride metabolism (10.3-179%) and lipid peroxidation degree (50.4-69.4%). Consequently, lipolytic pathways were activated to compensate for the potential energy deprivation. With pathology image quantification, we report that UTMoS₂ caused more severe epithelial damage and intestinal steatosis than NTMoS₂, which is attributed to the edge effect and higher Mo release upon UV irradiation. Our results reveal differential AOPs involving soil sentinel organisms exposed to different Mo forms, demonstrating the potential of liposome analysis to identify novel AOPs and furthermore accurate soil risk assessment strategies for emerging contaminants.

Chlorine substitution-dependent toxicities of polychlorinated biphenyls to the earthworm Eisenia fetida in soil

Polychlorinated biphenyls (PCBs) with different chlorine substitution patterns often coexist in e-waste-processing sites. However, the single and combined toxicity of PCBs to soil organisms and the influence of chlorine substitution patterns remain largely unknown. Herein, we evaluated the distinct in vivo toxicity of PCB28 (a trichlorinated PCB), PCB52 (a tetrachlorinated PCB), PCB101 (a pentachlorinated PCB), and their mixture to earthworm Eisenia fetida in soil, and looked into the underlining mechanisms in an in vitro test using coelomocytes. After a 28-days exposure, all PCBs (up to 10 mg/kg) were not fatal to earthworms, but could induce intestinal histopathological changes and microbial community alterations in the drilosphere system, along with a significant weight loss. Notably, pentachlorinated PCBs with a low bioaccumulation ability showed greater inhibitory effects on the growth of earthworm than lowly chlorinated PCBs, suggesting that bioaccumulation was not the main determinant of chlorine substitution-dependent toxicity. Furthermore, in vitro assays showed that the highly chlorinated PCBs induced a high-percentage apoptosis of eleocytes in the coelomocytes and significantly activated antioxidant enzymes, indicating that the distinct cellular vulnerability to lowly/highly chlorinated PCBs was the main contributor to the PCBs toxicity. These findings emphasize the specific advantage of using earthworms in the control of lowly chlorinated PCBs in soil due to their high tolerance and accumulation ability.

Innovative in vivo and in vitro bioassays for the establishment of toxicity thresholds of pollutants in sediment quality assessment using polychaetes and their immune cells

Sediment toxicity testing has become a crucial component for assessing the risks posed by contaminated sediments and for the development of sediment quality assessment strategies. Commonly used organisms for bioassays with estuarine sediments include amphipods, Arenicola marina polychaetes and echinoids. Among the latter, the Sea Urchin Embryo test (SET) is the most widely used. However, one relevant limitation of this bioassay is the unavailability of gametes all year-round, particularly outside the natural spawning seasons. Consequently, the establishment of an appropriate and complementary model organism for a continuous assessment of sediment quality is recommended. A reliable assessment of the hazards resulting from pollutants in sediments or pore water, can be achieved with ecologically relevant species of sediment such as the polychaete Hediste diversicolor, which is widespread in estuaries and has the capacity to accumulate pollutants. The aim of this work was to develop reliable in vivo and in vitro bioassays with H. diversicolor and its coelomocytes (immune cells) to determine the toxicity thresholds of different contaminants bounded to sediments or resuspended into water. Polychaetes were exposed to sublethal concentrations of CuCl₂ (in vivo) and a non-invasive method for collection of polychaetes coelomocytes was applied for the in vitro bioassay, exposing cells to a series of CuCl₂ and AgNPs concentrations. Same reference toxicants were used to expose Paracentrotus lividus following the SET (ICES Nº 51; Beiras et al., 2012) and obtained toxicity thresholds were compared between the two species. In vivo exposure of polychaetes to high concentrations of Cu produced weight loss and histopathological alterations. After in vitro approaches, a significant decrease in coelomocytes viability was recorded for both toxicants, in a monotonic dose-response curve, at very short-exposure times (2 h). The toxicity thresholds obtained with polychaetes were in line with the ones obtained with the SET, concluding that their sensitivity is similar. In conclusion, in vivo and in vitro bioassays developed with H. diversicolor are accurate toxicity screenings of pollutants that could be bounded to sediments or dissolved in the pore water, and may complement the SET outside the spawning period of the echinoderms. The bioassays herein developed could be applied not only to establish the toxicity thresholds of individual compounds or mixtures, but also to assess the toxicity of field collected sediments.

Effects of silver sulfide nanoparticles on the earthworm Eisenia andrei

The massive production and use of silver nanoparticles (Ag NPs) have led to their increasing release into the environment. Even though the antimicrobial and cytotoxic effects of native nanoparticles have been well studied, the environmental impacts of transformation products such as silver sulfide nanoparticles (Ag₂S NPs) have not been elucidated. In the present study, we assessed the toxicity of Ag₂S NPs and silver nitrate (AgNO₃), as a source of Ag, to the earthworm Eisenia andrei using a nominal concentration of 5 mg Ag kg^-1 soil. We used the OECD guidelines to assess effects on weight loss and mortality for 14 days. After exposure, we also extracted the immune effector cells (coelomocytes) and conducted a battery of biomarker tests. To ensure the quality of the toxicological results, the structural changes of NPs during the experiment and the uptake of silver by the earthworms were monitored. During the experiment, mortality effects were not detected, but a weight loss was observed in the earthworms exposed to Ag₂S NPs. Altough Ag₂S NPs were engulfed by E. andrei cells, neither phenoloxidase activity nor lipid peroxidation differed from the untreated control group. Cells from earthworms treated with Ag₂S NPs exerted very broad value range of nitric oxide (NO) generation, suggesting an imbalance in the NO metabolism. Overall, this study suggests minimal risks associated with Ag₂S NPs exposure to earthworms. However, further studies are needed to assure no immunotoxicological or chronic effects on a wider range of terrestrial organisms.

In vitro cultivation of primary intestinal cells from Eisenia fetida as basis for ecotoxicological studies

The earthworm Eisenia fetida is a commonly used model organism for unspecific soil feeders in ecotoxicological studies. Its intestinal cells are the first to encounter possible pollutants co-ingested by the earthworm, which makes them prime candidates for studies of toxic effects of environmental pollutants on the cellular as compared to the organismic level. In this context, the aim of this study was to demonstrate the suitability of preparations of primary intestinal E. fetida cells for in vitro ecotoxicological studies. For this purpose, a suitable isolation and cultivation protocol was established. Cells were isolated directly from the intestine, maintaining >85% viability during subsequent cultivations (up to 144 h). Exposure to established pollutants and soil elutriates comprising silver nanoparticles and metal ions (Cu²⁺, Cd²⁺) induced a significant decrease in the metabolic activity of the cells. In case of microplastic particles (MP particles), namely 0.2, 0.5, 2.0, and 3.0 µm diameter polystyrene (PS) beads as well as 0.5 and 2.0 µm diameter polylactic acid (PLA) beads, no active uptake was observed. Slight positive as well as negative dose and size dependent effects on the metabolism were seen, which to some extent might correlate with effects on the organismic level.

Cross-Species Comparisons of Nanoparticle Interactions with Innate Immune Systems: A Methodological Review

Many components of the innate immune system are evolutionarily conserved and shared across many living organisms, from plants and invertebrates to humans. Therefore, these shared features can allow the comparative study of potentially dangerous substances, such as engineered nanoparticles (NPs). However, differences of methodology and procedure between diverse species and models make comparison of innate immune responses to NPs between organisms difficult in many cases. To this aim, this review provides an overview of suitable methods and assays that can be used to measure NP immune interactions across species in a multidisciplinary approach. The first part of this review describes the main innate immune defense characteristics of the selected models that can be associated to NPs exposure. In the second part, the different modes of exposure to NPs across models (considering isolated cells or whole organisms) and the main endpoints measured are discussed. In this synergistic perspective, we provide an overview of the current state of important cross-disciplinary immunological models to study NP-immune interactions and identify future research needs. As such, this paper could be used as a methodological reference point for future nano-immunosafety studies.

Combined toxicity of functionalized nano-carbon black and cadmium on Eisenia fetida coelomocytes: The role of adsorption

Little is known about the potential threats of functionalized nano-carbon black (FNCB) combined with cadmium (Cd) to soil invertebrates. In this study, immunocompetent coelomocytes from Eisenia fetida are harnessed, and the joint cytotoxicity types of FNCB and Cd co-exposure are analyzed. The extracellular interaction mechanisms of FNCB and Cd were completely explored using adsorption kinetics and thermodynamics accompanied by isotherm batch experiments and Fourier infrared spectroscopy. The results indicated that functional amorphous carbon nanoparticles up to certain dose may injure cells due to their surface oxygen-containing groups. The MIXTOX model and the combination index suggested that the combined action of FNCB and Cd exhibited antagonism at the low dose/effect-level and synergism at the high dose/effect-level. FNCB decreased the intracellular free Cd²⁺ content at a low mixture dose, while it increased it at a high mixture dose. The adsorption of Cd on FNCB followed pseudo-second-kinetics and the Langmuir isotherm, hence better indicating a chemisorption, which was also supported by the activation energy (E_a = 36.6 kJ/mol), enthalpy change (ΔH = -98.4 kJ/mol), and functional group changes. Coordination binding should be responsible for the subsequent interaction of toxicity.

Transcriptome, bioaccumulation and toxicity analyses of earthworms (Eisenia fetida) affected by trifloxystrobin and trifloxystrobin acid

As a promising fungicide, the potential environmental risk of trifloxystrobin (TFS) and its main metabolism trifloxystrobin acid (TFSA) in soil environment should be given special attention. The present study investigated the potential risks of TFS and TFSA in soil environment to earthworms (Eisenia fetida) through measuring several biomarkers. Residual analysis showed that TFSA was more stable than TFS in artificial soil with half-lives ranging from 138.6 to 231.0 d and 20.4-24.7 d, respectively. Additionally, the accumulation of TFS in earthworms increased in the beginning and then decreased from day 14, while that of TFSA continuously increased. At concentrations of 4.0 mg/kg and 10.0 mg/kg, the weight and lysosomal membrane stability of earthworms were reduced; however, the superoxide dismutase (SOD) activity, glutathione-S-transferase (GST) activity and malondialdehyde (MDA) content in earthworms were enhanced by TFS and TFSA. Moreover, the growth inhibition effect and the oxidative damage level induced by TFSA to earthworms were higher than those induced by TFS. The transcriptome analysis date indicated that the differentially expressed genes (DEGs) in both TFS and TFSA treatments were mainly enriched in ribosome pathway and lysosome pathway, finally affecting the protein synthesis and proteolysis in earthworms. The findings of the present study indicated that TFSA may pose a higher risk in the soil environment than TFS.

Nanomaterials and Annelid Immunity: A Comparative Survey to Reveal the Common Stress and Defense Responses of Two Sentinel Species to Nanomaterials in the Environment

Simple Summary

Nanotechnology is a dynamically developing field producing large amounts of nanocompounds that are applied in industry, daily life, and health care. During production, use, and waste these materials could end up in water or soil. Large scale contaminations of our environment are a threat to public health. Pollution can have harmful effects on the immune system, as revealed by numerous studies in humans and other vertebrates. The relative simplicity of invertebrate immune functions offers potentially sensitive and accessible means of monitoring the effects and complex interactions of nanoparticles which ultimately affect host resistance. Among terrestrial and freshwater invertebrates, earthworms and leeches are the “keystone” species to evaluate the health of our ecosystems. In this review we compare the conserved stress and immune responses of these invertebrate model organisms toward nanoparticles. The obtained knowledge provides exciting insights into the conserved molecular and cellular mechanisms of nanomaterial-related toxicity in invertebrates and vertebrates. Understanding the unique characteristics of engineered nanoproducts and their interactions with biological systems in our environment is essential to the safe realization of these materials in novel biomedical applications.

Abstract

Earthworms and leeches are sentinel animals that represent the annelid phylum within terrestrial and freshwater ecosystems, respectively. One early stress signal in these organisms is related to innate immunity, but how nanomaterials affect it is poorly characterized. In this survey, we compare the latest literature on earthworm and leeches with examples of their molecular/cellular responses to inorganic (silver nanoparticles) and organic (carbon nanotubes) nanomaterials. A special focus is placed on the role of annelid immunocytes in the evolutionarily conserved antioxidant and immune mechanisms and protein corona formation and probable endocytosis pathways involved in nanomaterial uptake. Our summary helps to realize why these environmental sentinels are beneficial to study the potential detrimental effects of nanomaterials.

The Effects of In Vivo Exposure to Copper Oxide Nanoparticles on the Gut Microbiome, Host Immunity, and Susceptibility to a Bacterial Infection in Earthworms

Nanomaterials (NMs) can interact with the innate immunity of organisms. It remains, however, unclear whether these interactions can compromise the immune functioning of the host when faced with a disease threat. Co-exposure with pathogens is thus a powerful approach to assess the immuno-safety of NMs. In this paper, we studied the impacts of in vivo exposure to a biocidal NM on the gut microbiome, host immune responses, and susceptibility of the host to a bacterial challenge in an earthworm. Eisenia fetida were exposed to CuO-nanoparticles in soil for 28 days, after which the earthworms were challenged with the soil bacterium Bacillus subtilis. Immune responses were monitored by measuring mRNA levels of known earthworm immune genes. Effects of treatments on the gut microbiome were also assessed to link microbiome changes to immune responses. Treatments caused a shift in the earthworm gut microbiome. Despite these effects, no impacts of treatment on the expression of earthworm immune markers were recorded. The methodological approach applied in this paper provides a useful framework for improved assessment of immuno-safety of NMs. In addition, we highlight the need to investigate time as a factor in earthworm immune responses to NM exposure.