Effective activation of antioxidant system by immune-relevant factors reversely correlates with apoptosis of Eisenia andrei coelomocytes

A multi-biomarker approach to verify chronic effects on Eisenia andrei earthworms exposed to tailings from one of the world's largest mining disasters

Mining is of great relevance to the global economy, but its activities are challenging due to socio-environmental impacts. In January 2019, an iron ore tailings dam collapsed in Brumadinho (Minas Gerais, Brazil) releasing 12 × 106 m3 of tailings, causing human losses and devastation around 3.13 × 106 m2 of a watershed. In this context, the present study aimed to investigate the potential toxic effects of tailings from the collapsed dam using earthworms Eisenia andrei as a model organism for terrestrial environments. An extensive set of tests was performed, including behavioral (avoidance), acute (mortality and biomass) and chronic tests, such as biomass, reproduction and cytotoxicity (viability and cell density and change in coelomocyte pattern). The physical-chemical characterization revealed a higher density of the tailings in relation to the control soil, which can result in physical changes, such as soil compaction and surface sealing. Aluminum, Ca, Fe, Hg, Mg, Mn, K, Na and P registered higher concentrations in the tailings compared to the control soil, while Total Nitrogen, Total Organic Carbon and Organic Matter were higher in the natural soil. Based on the avoidance test, an EC50 of 27.18 ± 2.83% was estimated. No lethality was observed in the acute exposure, nor variations in biomass in the acute and chronic assays. However, there was a tendency to reduce the number of juveniles in relation to cocoons in the proportions of 3125; 12.5 and 25%. Significant changes in viability, cell density and pattern of amebocytes and eleocytes were observed up to the 35th day of exposure. A multi-biomarker approach (Integrated Biological Response version 2) indicated concentration-dependent effects and attenuation of cellular changes over time. These are the first results of chronic effects on earthworms exposed to tailings from the B1 dam. Despite being conclusive, we highlight the possible heterogeneity of the tailings and the necessary care in extrapolating the results.

New insights into vermiremediation of sewage sludge: The effect of earthworms on micropollutants and vice versa

Vermicomposting represents an environmentally friendly method for the treatment of various types of biowastes, including sewage sludge (SS), as documented in numerous studies. However, there are few papers providing insights into the mechanisms and toxicity effects involved in SS vermicomposting to present a comprehensive overview of the process. In this work, the vermiremediation of SS containing various micropollutants, including pharmaceuticals, personal care products, endocrine disruptors, and per/polyfluoroalkyl substances, was studied. Two SSs originating from different wastewater treatment plants (WWTP1 and WWTP2) were mixed with a bulking agent, moistened straw, at ratios of 0, 25, 50, and 75% SS. Eisenia andrei earthworms were introduced into the mixtures, and after six weeks, the resulting materials were subjected to various types of chemical and toxicological analyses, including conventional assays (mortality, weight) as well as tissue- and cell-level assays, such as malondialdehyde production, cytotoxicity tests and gene expression assays. Through the vermiremediation process significant removal of diclofenac (90%), metoprolol (88%), telmisartan (62%), and triclosan (81%) was achieved. Although the concentrations of micropollutants were substantially different in the original SS samples, the micropollutants vermiaccumulated to a similar extent over the incubation period. The earthworms substantially eliminated the present bacterial populations, especially in the 75% SS treatments, in which the average declines were 90 and 79% for WWTP1 and WWTP2, respectively. To the best of our knowledge, this is the first study to investigate the vermiremediation of such a large group of micropollutants in real SS samples and provide a thorough evaluation of the effect of SS on earthworms at tissue and cellular level.

The effect of selected immunostimulants on hemocytes of the false black widow Steatoda grossa (Theridiidae) spiders under chronic exposition to cadmium

The aim of this study was to analyze whether, and to what extent, long-term exposure to cadmium, administered in sublethal concentrations by the oral route, caused changes in the immune potential of hemocytes in adult female Steatoda grossa spiders. We used artificial and natural immunostimulants, namely phorbol 12-myristate 13-acetate (PMA) and bacterial cell suspension based on Gram-positive (G+, Staphylococcus aureus) and Gram-negative (G-, Pseudomonas fluorescens) bacteria, to compare the status of hemocytes in nonstimulated individuals and those subjected to immunostimulation. After cadmium exposure, the percentage of small nongranular hemocytes in response to G+ cell suspension and PMA mitogen was decreased. Furthermore, in the cadmium-intoxicated spiders the percentage of plasmatocytes after immunostimulation remained lower compared to the complementary control group. Exposure to cadmium also induced several degenerative changes, including typical apoptotic and necrotic changes, in the analyzed types of cells. Immunostimulation by PMA mitogen and G+ bacterial suspension resulted in an increase in the number of cisterns in the rough endoplasmic reticulum of granulocytes, in both the control group and cadmium-treated individuals. These changes were accompanied with a low level of metallothioneins in hemolymph. Chronic cadmium exposure may significantly weaken the immune defense system of spiders during infections.

Arginase Activity in Eisenia andrei Coelomocytes: Function in the Earthworm Innate Response

Arginase is the manganese metalloenzyme catalyzing the conversion of l-arginine to l-ornithine and urea. In vertebrates, arginase is involved in the immune response, tissue regeneration, and wound healing and is an important marker of alternative anti-inflammatory polarization of macrophages. In invertebrates, data concerning the role of arginase in these processes are very limited. Therefore, in the present study, we focused on the changes in arginase activity in the coelomocytes of Eisenia andrei. We studied the effects of lipopolysaccharide (LPS), hydrogen peroxide (H₂O₂), heavy metals ions (e.g., Mn²⁺), parasite infection, wound healing, and short-term fasting (5 days) on arginase activity. For the first time in earthworms, we described arginase activity in the coelomocytes and found that it can be up-regulated upon in vitro stimulation with LPS and H₂O₂ and in the presence of Mn²⁺ ions. Moreover, arginase activity was also up-regulated in animals in vivo infected with nematodes or experiencing segment amputation, but not in fasting earthworms. Furthermore, we confirmed that the activity of coelomocyte arginase can be suppressed by l-norvaline. Our studies strongly suggest that similarly to the vertebrates, also in the earthworms, coelomocyte arginase is an important element of the immune response and wound healing processes.

Comparative response of Spodoptera litura challenged per os with Serratia marcescens strains differing in virulence

Host plays an important role in influencing virulence of a pathogen and efficacy of a biopesticide. The present study was aimed to characterize the possible factors present in Spodoptera litura that influenced pathogenecity of orally ingested S. marcescens strains, differing in their virulence. Fifth instar larvae of S. litura responded differently as challenged by two Serratia marcescens strains, SEN (virulent strain, LC₅₀ 7.02 10³ cfu/ml) and ICC-4 (non-virulent strain, LC₅₀ 1.19 10¹² cfu/ml). Considerable increase in activity of lytic enzymes protease and phospholipase was recorded in the gut and hemolymph of larvae fed on diet supplemented with S. marcescens strain ICC-4 as compared to the larvae treated with S. marcescens strain SEN. However, a significant up-regulation of antioxidative enzymes SOD (in foregut and midgut), CAT (in the midgut) and GST (in the foregut and hemolymph) was recorded in larvae fed on diet treated with the virulent S. marcescens strain SEN in comparison to larvae fed on diet treated with the non-virulent S. marcescens strain ICC-4. Activity of defense related enzymes lysozyme and phenoloxidase activity were also higher in the hemolymph of larvae fed with diet treated with S. marcescens strain SEN as compared to hemolymph of S. marcescens strain ICC-4 treated larvae. More number of over-expressed proteins was observed in the gut and hemolymph of S. marcescens strains ICC-4 and SEN treated larvae, respectively. Identification of the selected differentially expressed proteins indicated induction of proteins involved in insect innate immune response (Immunoglobulin I-set domain, Apolipophorin III, leucine rich repeat and Titin) in S. marcescens strain SEN treated larvae. Over-expression of two proteins, actin related protein and mt DNA helicase, were noted in S. marcescens treated larvae with very high levels observed in the non-virulent strain. Up-regulation of homeobox protein was noted only in S. marcescens strain ICC-4 challenged larvae. This study indicated that ingestion of non-virulent S. marcescens strain ICC-4 induced strong immune response in insect gut while there was weak response to the virulent S. marcescens strain SEN which probably resulted in difference in their virulence.

From Species to Regional and Local Specialization of Intestinal Macrophages

Initially intended for nutrient uptake, phagocytosis represents a central mechanism of debris removal and host defense against invading pathogens through the entire animal kingdom. In vertebrates and also many invertebrates, macrophages (MFs) and MF-like cells (e.g., coelomocytes and hemocytes) are professional phagocytic cells that seed tissues to maintain homeostasis through pathogen killing, efferocytosis and tissue shaping, repair, and remodeling. Some MF functions are common to all species and tissues, whereas others are specific to their homing tissue. Indeed, shaped by their microenvironment, MFs become adapted to perform particular functions, highlighting their great plasticity and giving rise to high population diversity. Interestingly, the gut displays several anatomic and functional compartments with large pools of strikingly diversified MF populations. This review focuses on recent advances on intestinal MFs in several species, which have allowed to infer their specificity and functions.

In Vitro Interactions of TiO2 Nanoparticles with Earthworm Coelomocytes: Immunotoxicity Assessment

Titanium dioxide nanoparticles (TiO₂ NPs) are manufactured worldwide. Once they arrive in the soil environment, they can endanger living organisms. Hence, monitoring and assessing the effects of these nanoparticles is required. We focus on the Eisenia andrei earthworm immune cells exposed to sublethal concentrations of TiO₂ NPs (1, 10, and 100 µg/mL) for 2, 6, and 24 h. TiO₂ NPs at all concentrations did not affect cell viability. Further, TiO₂ NPs did not cause changes in reactive oxygen species (ROS) production, malondialdehyde (MDA) production, and phagocytic activity. Similarly, they did not elicit DNA damage. Overall, we did not detect any toxic effects of TiO₂ NPs at the cellular level. At the gene expression level, slight changes were detected. Metallothionein, fetidin/lysenin, lumbricin and MEK kinase I were upregulated in coelomocytes after exposure to 10 µg/mL TiO₂ NPs for 6 h. Antioxidant enzyme expression was similar in exposed and control cells. TiO₂ NPs were detected on coelomocyte membranes. However, our results do not show any strong effects of these nanoparticles on coelomocytes at both the cellular and molecular levels.

Enhanced Antioxidant and Cytotoxic Potentials of Lipopolysaccharides-Injected Musca domestica Larvae

The usage of insects as a sustainable and functional natural products resource is a new promise in complementary and alternative medicine. The present study aimed to investigate the ability of Musca domestica (housefly) larval hemolymph (insect blood) to display the enhanced in vitro antioxidant and cytotoxic effects. The oxidative stress (OS) was elicited by inducing lipopolysaccharides (LPS) treatment as an exogenous stressor. Determination of superoxide dismutase 1 (SOD1), glutathione (GSH), malondialdehyde (MDA) and total antioxidant capacity (TAC), and mRNA and protein expressions of SOD1, was investigated as confirmatory markers of oxidative stress induction. Cytotoxicity on cancerous MCF-7 and normal Vero cells were also evaluated using an MTT assay at 24 h post-injection. The injection of LPS induced a significant (p < 0.05) increase in SOD, GSH and TAC, whereas, the MDA was diminished. Hemolymph was collected from normal and treated larvae after 6, 12 and 24 h. The M. domestica superoxide dismutase (MdSOD1) transcripts were significantly (p < 0.05) upregulated 6 and 12 h post-treatment, while a significant downregulation was observed after 24 h. Western blot analysis showed that MdSOD1 was expressed in the hemolymph of the treated larvae with an increase of 1.2 folds at 6 and 12 h and 1.6 folds at 24 h relative to the control group. LPS-treated larval hemolymphs exhibited significant cytotoxicity with respect to the untreated ones against MCF-7 while Vero cells showed no cytotoxicity for both hemolymphs. The DPPH free radical scavenging activity was examined and a significant antioxidant potential potency was observed at 6 h (50% maximal inhibitory concentration (IC50): 63.3 ± 3.51 µg/mL) when compared to the control M. domestica larval hemolymph (IC50: 611.7 ± 10.41 µg/mL). Taken together, M. domestica larval hemolymph exhibited enhanced antioxidant and consequently increased cytotoxic capacities under stressed conditions.

Mutual interactions of E. andrei earthworm and pathogens during the process of vermicomposting

Vermicomposting is a process by which earthworms together with microorganisms degrade organic wastes into a humus-like material called vermicompost. This process does not include a thermophilic stage, and therefore, the possible presence of pathogens represents a potential health hazard. To elucidate the effect of earthworms in the selective reduction of pathogens, grape marc substrate was artificially inoculated with Escherichia coli, Enterococcus spp., thermotolerant coliform bacteria (TCB), and Salmonella spp., and their reduction during vermicomposting was monitored. Various defense mechanisms eliminating microorganisms in the earthworm gut were assumed to be involved in the process of pathogen reduction. Therefore, we followed the expression of three pattern recognition receptors (coelomic cytolytic factor (CCF), lipopolysaccharide-binding protein (LBP), and Toll-like receptor (v-TLR)), two antimicrobial molecules (fetidin/lysenins and lysozyme), and heat shock protein HSP70. We detected the significant decrease of some defense molecules (fetidin/lysenins and LBP) in all pathogen-inoculated substrates, and the increase of CCF and LBP in the Salmonella spp.-inoculated substrate. At the same time, the reduction of pathogens during vermicomposting was assessed. We observed the accelerated reduction of E. coli, Enterococcus spp., and TCB in pathogen-inoculated substrates with earthworms compared to that without earthworms. Moreover, the differences between the microbiome of grape marc substrate and earthworm intestines were determined by high throughput sequencing. This analysis revealed that the bacterial composition of grape marc substrate differed from the composition of the content of earthworm intestines, suggesting the elimination of specific bacterial species during food passage through the gut.

Transcriptomic analysis of oligochaete immune responses to myxosporeans infection: Branchiura sowerbyi infected with Myxobolus cultus

The Myxozoa are endoparasites characterized by a two-host life cycle that typically involves invertebrates and vertebrates as definitive and intermediate hosts, respectively. However, little is known about invertebrate-myxosporean interactions, particularly about patterns of host immune defense. We used RNA-sequencing to identify genes that are possibly involved in the immune responses of the oligochaete Branchiura sowerbyi naturally infected with Myxobolus cultus. De novo assembly of the B. sowerbyi transcriptome yielded 119,031 unigenes, with an average length of 896 bp and an N50 length of 1754 bp. Comparative transcriptome analysis revealed 4059 differentially expressed genes (DEGs) between M. cultus-infected and uninfected B. sowerbyi groups, including 3802 upregulated genes and 257 downregulated genes. Among the B. sowerbyi immune factors implicated in the responses to M. cultus infection, DEGs related to lectins, ubiquitin-mediated proteolysis, phagocytosis, oxidative-antioxidative responses, proteases, and protease inhibitors were upregulated. The expression of some immune-related molecules such as calmodulin, heat shock proteins, antimicrobial peptides, lysenin, and serum amyoid A protein were also significantly upregulated. The expression patterns of 14 immune-related DEGs identified by RNA-seq were validated by quantitative real-time polymerase chain reaction. This study is the first attempt to characterize the B. sowerbyi transcriptome and identify immune-related molecules possibly associated with M. cultus infection. It is also the first report of invertebrate host-myxosporean interactions at the transcriptomic level. Our results will facilitate the elucidation of adaptive evolution mechanisms of myxosporean parasites in the definitive host and the genetic basis for differences in resistance of invertebrate hosts of different genotypes to a myxosporean species.

Construction of a cDNA library and preliminary analysis of the expressed sequence tags of the earthworm Eisenia fetida (Savigny, 1826)

Earthworms are useful indicator organisms of soil health and Eisenia fetida have been extensively used as test organisms in ecotoxicological studies. In order to gain insight into the gene expression profiles associated with physiological functions of earthworms, a full-length enriched cDNA library of the Eisenia fetida genome was successfully constructed using Switching Mechanism at 5′End of RNA Template technology. Construction of a cDNA library and analysis of Expressed Sequence Tags (ESTs) are efficient approaches for collecting genomic information and identifying genes important for a given biological process. Furthermore, analysis of the expression abundance of ESTs was performed with the aim of providing genetic and transcriptomic information on the development and regenerative process of earthworms. Phrep and Crossmatch were used to process EST data and a total of 1,140 high-quality EST sequences were determined by sequencing random cDNA clones from the library. Clustering analysis of sequences revealed a total of 593 unique sequences including 225 contiguous and 368 singleton sequences. Basic Local Alignment Search Tool analysis against the Kyoto Encyclopedia of Genes and Genomes database resulted in 593 significant hits (P-value <1×10⁻⁸), of which 168 were annotated through Gene Ontology analysis. The STRING database was used to determine relationships among the 168 ESTs, identifying associated genes involved in protein-protein interactions and gene expression regulation. Based on nucleic acid and protein sequence homology, the mutual relationships between 287 genes could be obtained, which identified a portion of the ESTs as known genes. The present study reports on the construction of a high-quality cDNA library representative of adult earthworms, on a preliminary analysis of ESTs and on a putative functional analysis of ESTs. The present study is expected to enhance our understanding of the molecular basis underlying the biological development of earthworms.

Acute toxicity of selenate and selenite and their impacts on oxidative status, efflux pump activity, cellular and genetic parameters in earthworm Eisenia andrei

Selenium (Se) is an essential element for humans, animals, and certain lower plants, but can be toxic at high concentration. Even though Se is potentially toxic, little information is available about the effects of Se on soil animals. The aim of this study was to assess the impact of different concentrations of two Se forms, selenate and selenite, on earthworm Eisenia andrei. In order to obtain comprehensive overview on the Se effects, different parameters were measured. Namely, acute toxicity, apoptosis, efflux pump activity, different enzymatic and non-enzymatic biomarkers (acetylcholinesterase, carboxylesterase, glutathione S-transferase, catalase, glutathione reductase and superoxide dismutase activities, lipid peroxidation level and GSH/GSSG ratio) and expression of genes involved in oxidative and immune response have been investigated. Additionally, measurement of metallothioneins concentration and concentration of Se in exposed earthworms has been also performed. The assessment of acute toxicity showed a greater sensitivity of E. andrei to selenite exposure, whereas Se concentration measurements in earthworms showed higher accumulation of selenate form. Both Se forms caused inhibition of the efflux pump activity. Decrease in superoxide dismutase activity and increase in lipid peroxidation and glutathione reductase activity indicate that Se has a significant impact on the oxidative status of earthworms. Selenate exposure caused an apoptotic-like cell death in the coelomocytes of exposed earthworms, whereas decreased mRNA levels of stress-related genes and antimicrobial factors were observed upon the exposure to selenite. The obtained data give insight into the effects of two most common forms of Se in soil on the earthworm E. andrei.

Earthworm coelomocyte extracellular traps: structural and functional similarities with neutrophil NETs

Invertebrate immunity is associated with natural mechanisms that include cellular and humoral elements, similar to those that play a role in vertebrate innate immune responses. Formation of extracellular traps (ETs) is a newly discovered mechanism to combat pathogens, operating not only in vertebrate leucocytes but also in invertebrate immune cells. The ET components include extracellular DNA (exDNA), antimicrobial proteins and histones. Formation of mammalian ETs depends on enzymes such as neutrophil elastase, myeloperoxidase, the citrullination of histones and protease activity. It was confirmed that coelomocytes-immunocompetent cells of the earthworm Eisenia andrei-are also able to release ETs in a protease-dependent manner, dependent or independent of the formation of reactive oxygen species and rearrangement of the cell cytoskeleton. Similar to vertebrate leukocytes (e.g., neutrophil), coelomocytes are responsible for many immune functions like phagocytosis, cytotoxicity and secretion of humoral factors. ETs formed by coelomocyte analogues to neutrophil ETs consist of exDNA, histone H3 and attached to these structures proteins, e.g., heat shock proteins HSP27. The latter fact confirms that mechanisms of ET release are conserved in evolution. The study on Annelida adds this animal group to the list of invertebrates capable of ET release, but most importantly provides insides into innate mechanisms of ET formation in lower animal taxa.

Environmental pollutants, pathogens and immune system in earthworms

Earthworms also known as farmer's friends are natural tillers of soil. They belong to Phylum Annelida and class Oligochaeta. Acid soils with organic matter and surface humus maintain the largest fauna of worms and earthworms. Due to their habitat in soil, they are constantly exposed to microbes and pollution generated by anthropogenic sources. Studies have revealed that damage of the immune system of earthworms can lead to alterations of both morphological and cellular characteristics of worms, activation of signalling pathways and can strongly influence their survival. Therefore, the understanding of the robust immune system in earthworms has become very important from the point of view of understanding its role in combating pathogens and pollutants and its role in indicating the soil pollution. In this article, we have outlined the (i) components of the immune system and (ii) their function of immunological responses on exposure to pollutants and pathogens. This study finds importance from the point of view of ecotoxicology and monitoring of earthworm health and exploring the scope of earthworm immune system components as biomarkers of pollutants and environmental toxicity. The future scope of this review remains in understanding the earthworm immunobiology and indicating strong biomarkers for pollution.

Conservative Mechanisms of Extracellular Trap Formation by Annelida Eisenia andrei: Serine Protease Activity Requirement

Formation of extracellular traps (ETs) capturing and immobilizing pathogens is now a well-established defense mechanism added to the repertoire of vertebrate phagocytes. These ETs are composed of extracellular DNA (extDNA), histones and antimicrobial proteins. Formation of mouse and human ETs depends on enzymes (i) facilitating decondensation of chromatin by citrullination of histones, and (ii) serine proteases degrading histones. In invertebrates, initial reports revealed existence of ETs composed of extDNA and histones, and here we document for the first time that also coelomocytes, immunocompetent cells of an earthworm Eisenia andrei, cast ETs which successfully trap bacteria in a reactive oxygen species (ROS)-dependent and -independent manner. Importantly, the formation of ETs was observed not only when coelomocytes were studied ex vivo, but also in vivo, directly in the earthworm coelom. These ETs were composed of extDNA, heat shock proteins (HSP27) and H3 histones. Furthermore, the formation of E. andrei ETs depended on activity of serine proteases, including elastase-like activity. Moreover, ETs interconnected and hold together aggregating coelomocytes, a processes proceeding encapsulation. In conclusion, the study confirms ET formation by earthworms, and unravels mechanisms leading to ET formation and encapsulation in invertebrates.