The role of GST omega in metabolism and detoxification of arsenic in clam Ruditapes philippinarum

Biochemical response and tissue-specific accumulation of scallop Aequipecten tehuelchus from Patagonia, Argentina after exposure to inorganic arsenic

This study investigates the effects of different inorganic arsenic (As III) concentrations (0, 125, 500 and 1000 μg As/L) following two exposure times (7 and 14 days) on gills, digestive gland and muscle of scallop Aequipecten tehuelchus from Patagonia, Argentina. A biochemical approach was used to investigate oxidative stress-related parameters after different As concentrations and exposure times. Although the accumulation of As was of the same order of magnitude in all tissues, the results showed distinct tissue-specific oxidative responses to this metalloid. Furthermore, the variation in exposure time had no significant effect on As accumulation in any of the three tissues. In gills, despite no reactive oxygen and nitrogen species (RONS) were detected, there was an increase in catalase (CAT) activity and metallothionein (MT) levels. Conversely, digestive gland showed RONS production without a rise in CAT and glutathione S-transferases (GST) activities, but with an increase in MT levels. In muscle, RONS production and CAT activity kept constant or decreased, while MT levels remained unchanged. In addition, exposure time demonstrated its critical role in gills by influencing the response of CAT, GST and MT, particularly at high As concentrations, while exposure time did not affect the biochemical stress parameters in the digestive gland and muscle. Interestingly, neither concentration of As produced lipid damage, showing the effectiveness of the antioxidant mechanisms to avoid it. These results emphasize that A. tehuelchus exhibited no time-dependent effects in response to As exposure, while showing tissue-specific responses characterized by significant concentration-dependent effects of As. This study provides a comprehensive insight by considering the combined effects of time and concentration of a contaminant and distinguishing its effects on specific tissues, a dimension often overlooked in the existing literature. Subsequent studies should prioritize the analysis of additional contaminants in species with increased sensitivity.

Integrating chemical and biological data by chemometrics to evaluate detoxification responses of a neotropical bivalve to metal and metalloid contamination

Mangroves represent a challenge in monitoring studies due to their physical and chemical conditions under constant marine and anthropogenic influences. This study investigated metals/metalloids whole-body bioaccumulation (soft tissues) and the risk associated with their uptake, biochemical and morphological detoxification processes in gills and metals/metalloids immobilisation in shells of the neotropical sentinel oyster Crassostrea rhizophorae from two Brazilian estuarine sites. Biochemical and morphological responses indicated three main mechanisms: (1) catalase, superoxide dismutase and glutathione played important roles as the first defence against reactive oxygen species; (2) antioxidant capacity against peroxyl radicals, glutathione S-transferase, metallothionein prevent protein damage and (3) metals/metalloids sequestration into oyster shells as a mechanism of oyster detoxification. However, the estimated daily intake, target hazard quotient, and hazard index showed that the human consumption of oysters would not represent a human health risk. Among 14 analysed metals/metalloids, chemometrics indicate that Mn, As, Pb, Zn and Fe overload the antioxidant system leading to morphological alterations in gills. Overall, results indicated cellular vacuolization and increases in mucous cell density as defence mechanisms to prevent metals/metalloids accumulation and the reduction in gill cilia; these have long-term implications in respiration and feeding and, consequently, for growth and development. The integration of data from different sites and environmental conditions using chemometrics highlights the main biological patterns of detoxification from a neotropical estuarine bivalve, indicating the way in which species can cope with metals/metalloids contamination and its ecological consequences.

Transcriptional Responses as Biomarkers of General Toxicity: A Systematic Review and Meta-analysis on Metal-Exposed Bivalves

Through a systematic review and a series of meta-analyses, we evaluated the general responsiveness of putative transcriptional biomarkers of general toxicity and chemical stress. We targeted metal exposures performed on bivalves under controlled laboratory conditions and selected six transcripts associated with general toxicity for evaluation: catalase, glutathione-S-transferase, heat shock proteins 70 and 90, metallothionein, and superoxide dismutase. Transcriptional responses (n = 396) were extracted from published scientific articles (k = 22) and converted to log response ratios (lnRRs). By estimating toxic units, we normalized different metal exposures to a common scale, as a proxy of concentration. Using Bayesian hierarchical random effect models, we then tested the effects of metal exposure on lnRR, both for metal exposure in general and in meta-regressions using toxic unit and exposure time as independent variables. Corresponding analyses were also repeated with transcript and tissue as additional moderators. Observed patterns were similar for general and for transcript- and tissue-specific responses. The expected overall response to arbitrary metal exposure was an lnRR of 0.50, corresponding to a 65% increase relative to a nonexposed control. However, when accounting for publication bias, the estimated "true" response showed no such effect. Furthermore, expected response magnitude increased slightly with exposure time, but there was little support for general monotonic concentration dependence with regard to toxic unit. Altogether, the present study reveals potential limitations that need consideration prior to applying the selected transcripts as biomarkers in environmental risk assessment. Environ Toxicol Chem 2023;42:628-641. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Differential susceptibility to arsenic in glutathione S-transferase omega 2 (GST-O2)-targeted freshwater water flea Daphnia magna mutants

To examine the role of glutathione S-transferase omega class (GST-O2) genes in the biotransformation and detoxification in Daphnia magna, various responses such as in vivo endpoints, arsenic speciation, enzymatic activities, and gene expression pathways related to arsenic metabolism were investigated in wild-type (WT) and GST-O2-mutant-type (MT) fleas produced by CRISPR/Cas9. Sensitivity to arsenic in MT fleas was higher than in WT fleas. Also, the reduction rate of arsenate (As^V) to arsenite (As^III) in the MT group was significantly lower and led to accumulation of higher arsenic concentrations, resulting in decreased protection against arsenic toxicity. Relative mRNA expression of other GST genes in the GST-O2-targeted MT group generally increased but the enzymatic activity of GST decreased compared with the WT group. Oxidative stress on arsenic exposure was more strongly induced in the MT group compared with the WT group, resulting in a decrease in the ability to defend against toxicity in GST-O2-targeted mutant D. magna. Our results suggest that GST-O2 plays an important role in arsenic biotransformation and detoxification functions in D. magna.

Analyzing toxicological effects of AsIII and AsV to Chlamys farreri by integrating transcriptomic and metabolomic approaches

Inorganic arsenic (iAs) is a widespread contaminant in marine environments, which is present in two different oxidation states (arsenate (AsV) and arsenite (AsIII)) that have complex toxic effects on marine organisms. The scallop Chlamys farreri (C. farreri) accumulates high levels of As and is a suitable bioindicator of As. In this report, we integrated transcriptomics and metabolomics to investigate genetic and metabolite changes and functional physiological disturbances in C. farreri exposured to inorganic arsenic. Physiological indicators antioxidant factors and cell apoptosis analysis macroscopically corroborated the toxic effects of inorganic arsenic revealed by omics results. Toxic effects of inorganic arsenic on C. farreri were signaling-mediated, causing interference with a variety of cell growth and small molecule metabolism. The results provide evidence that inorganic arsenic disrupts the physiological functions of bivalves, highlighting the correlations between different metabolic pathways and providing new insights into the toxic effects of environmental pollutants on marine organisms.

Biodegradation of arsenobetaine to inorganic arsenic regulated by specific microorganisms and metabolites in mice

Arsenobetaine (AsB) is a primary arsenic (As) compound found in marine organisms. However, in mammals, the metabolic mechanism of AsB remains indistinct. Therefore, in this study, we investigated the biotransformation and regulatory mechanism of AsB, particularly the biodegradation process, in a mouse model to assess the underlying health hazards of AsB. We studied the biotransformation process of AsB in mice through the food chain [AsB feed-marine fish (Epinephelus fuscoguttatus)-mice (Mus musculus)]. Our results showed the significant bioaccumulation of total As, AsB, and, in particular, arsenate [As(V)] through biodegradation in mice tissues. As the abundance of Staphylococcus and Blautia (phylum, Firmicutes) increased, the expression of aqp7 (absorption) and methyltransferase (as3mt) (methylation) was upregulated. In contrast, the expression of S-adenosyl methionine (sam) (methylation) was downregulated. These findings suggest that demethylation and methylation occurred simultaneously in the intestines, with demethylation capacity being greater than that of methylation. Furthermore, Firmicutes such as Staphylococcus and Blautia showed a significant inverse relationship with arachidonic acid, choline, and sphingosine. Gene, microbiome, and metabolomics analyses indicated that Staphylococcus and Blautia and arachidonic acid, choline, and sphingosine participated in the degradation of AsB to As(V) in mouse intestines. Therefore, long-term AsB ingestion through marine fish consumption could cause potential health hazards in humans.

Genome-Wide Identification, Evolution and Expression Analysis of the Glutathione S-Transferase Supergene Family in Euphorbiaceae

Euphorbiaceae, a family of plants mainly grown in the tropics and subtropics, is also widely distributed all over the world and is well known for being rich in rubber, oil, medicinal materials, starch, wood and other economically important plant products. Glutathione S-transferases (GSTs) constitute a family of proteins encoded by a large supergene family and are widely expressed in animals, bacteria, fungi and plants, but with few reports of them in Euphorbiaceae plants. These proteins participate in and regulate the detoxification and oxidative stress response of heterogeneous organisms, resistance to stress, growth and development, signal transduction and other related processes. In this study, we identified and analyzed the whole genomes of four species of Euphorbiaceae, namely Ricinus communis, Jatropha curcas, Hevea brasiliensis, and Manihot esculenta, which have high economic and practical value. A total of 244 GST genes were identified. Based on their sequence characteristics and conserved domain types, the GST supergene family in Euphorbiaceae was classified into 10 subfamilies. The GST supergene families of Euphorbiaceae and Arabidopsis have been found to be highly conserved in evolution, and tandem repeats and translocations in these genes have made the greatest contributions to gene amplification here and have experienced strong purification selection. An evolutionary analysis showed that Euphorbiaceae GST genes have also evolved into new subtribes (GSTO, EF1BG, MAPEG), which may play a specific role in Euphorbiaceae. An analysis of expression patterns of the GST supergene family in Euphorbiaceae revealed the functions of these GSTs in different tissues, including resistance to stress and participation in herbicide detoxification. In addition, an interaction analysis was performed to determine the GST gene regulatory mechanism. The results of this study have laid a foundation for further analysis of the functions of the GST supergene family in Euphorbiaceae, especially in stress and herbicide detoxification. The results have also provided new ideas for the study of the regulatory mechanism of the GST supergene family, and have provided a reference for follow-up genetics and breeding work.

Toxicity mechanisms of arsenic compounds in aquatic organisms

Arsenic is a toxic metalloid that is widely distributed in the environment due to its persistence and accumulative properties. The occurrence, distribution, and biological effects of arsenic in aquatic environments have been extensively studied. Acute and chronic toxicities to arsenic are associated with fatal effects at the individual and molecular levels. The toxicity of arsenic in aquatic organisms depends on its speciation and concentration. In aquatic environments, inorganic arsenic is the dominant form. While trivalent arsenicals have greater toxicity compared with pentavalent arsenicals, inorganic arsenic can assume a variety of forms through biotransformation in aquatic organisms. Biotransformation mechanisms and speciation of arsenic have been studied, but few reports have addressed the relationships among speciation, toxicity, and bioavailability in biological systems. This paper reviews the modes of action of arsenic along with its toxic effects and distribution in an attempt to improve our understanding of the mechanisms of arsenic toxicity in aquatic organisms.

Dose-dependent responses of metabolism and tissue injuries in clam Ruditapes philippinarum after subchronic exposure to cadmium

Marine cadmium (Cd) pollution has been globally occurring, which creates a pressing need to characterize toxicological effects and develop biomarkers for Cd. However, the dose-response relationships challenge toxicity characterization and biomarkers selection. Metabolic processes have been frequently targeted by Cd. In this work, we investigated the dose-dependent effects of Cd on metabolic endpoints in whole soft tissues as well as gill and hepatopancreas injuries in clam Ruditapes philippinarum, aiming to better understand the metabolic responses and develop biomarkers. Nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted on clam whole soft tissues to identify metabolites. The enzymes and metabolites associated with tricarboxylic acid (TCA) cycle, glycolysis, and oxidative phosphorylation showed both monotonic and non-monotonic curves with the increase of Cd dose. In details, glutamine, glucose-1-phosphate, hexokinase (HK), and citrate synthase (CS) presented monotonic decreases with the increase of Cd dose, among which glutamine and CS were preferable biomarkers to Cd exposure based on lower benchmark dose (BMD) values. The monotonic decreases of HK and CS activities suggested Cd exposure potentially disrupted glycolysis and TCA cycle via inhibiting rate-limiting enzymes. In contrast, the non-monotonic responses of succinate dehydrogenase (SDH), alanine aminotransferase (ALT), and their substrates (succinate and alanine) were approximate to U- or J-shaped curves, suggesting the adaptive strategy of metabolic responses to different degrees of Cd stress, like induction of anaerobiosis as energy compensation. Especially, the alterations of succinate and SDH presented typical hormetic dose-response curves. What is more, clam hepatopancreas was more sensitive to Cd than gill in terms of injury occurrence. Overall, characterization of dose-dependent effect of Cd on metabolism and tissue injuries provides a new insight into understanding the metabolic adaptation in marine clams and risk assessment of Cd pollution.

Arsenic exposure combined with nano- or microplastic induces different effects in the marine rotifer Brachionus plicatilis

Besides the adverse biological effects induced by microplastics (MPs), the effects associated with sorption of ambient pollutants on MPs are considered as an emerging environmental problem as MPs act as a mediator of pollutants. The present study examines the combined effects of nano(micro)plastics (NMPs) and arsenic (As) by exposing the marine rotifer Brachionus plicatilis to MP particles at the micro-scale (6 μm) and nano-scale (nanoplastics, NPs) (50 nm) along with As. In vivo toxicity, bioaccumulation, and biochemical reactions were used to examine the effects of combined exposure. The results of in vivo experiments showed that As toxicity increased with NP exposure, whereas toxicity was alleviated by MPs, indicating a different mode of action between NPs and MPs in combination with As. The highest level of As bioaccumulation was detected in NP + As groups, and followed by MP + As and As-only exposure groups, whereas no significant difference between groups was shown for As metabolites. In addition, the activity of several ATP-binding cassette proteins that confer multixenobiotic resistance, which is responsible for efflux of As, was activated by As but significantly inhibited by NP exposure, supporting the findings of in vivo experiments. Our results show that the effects of combining exposure to As with NP and MPs differ depending on particle size and provide an in-depth understanding of both environmental pollutants.

Arsenic in shellfish: A systematic review of its dynamics and potential health risks

Arsenic is the most toxic element for humans. Presenting naturally in aquatic ecosystems and due to anthropogenic action, this semi-metal transfers to shellfish through the food chain. This systematic review aims to explain the dynamic of arsenic in the marine aquatic system, investigating factors that affect its bioaccumulation. A total of 64 articles were considered from three databases. The key abiotic factor influencing the presence of arsenic in shellfish is anthropogenic contamination, followed by geographic location. The crucial biotic factor is the genetics of each species of shellfish, including their diet habits, habitat close to the sediment, metabolic abilities, physiological activities of organisms, and metal levels in their habitats and food. Finally, arsenic presents an affinity for specific tissues in shellfish. Despite containing mostly less toxic organic arsenic, shellfish are a relevant source of arsenic in the human diet.

Subcellular metal distribution in two deep-sea mollusks: Insight of metal adaptation and detoxification near hydrothermal vents

In this study, we determined the concentrations of Cu, Zn, Ni, Cd, Pb and As and their subcellular distributions within the tissues of mussels (Bathymodiolus marisindicus) and snails (Gigantopelta aegis) from two hydrothermal vent regions, i.e., Tiancheng and Longqi, at Southwest Indian Ridge. Mussels collected from the two venting regions showed comparable concentrations for Ni and Pb, but Cu, Zn, Cd and As concentrations were significantly different in mussel gills between the two vent regions. Similar ranges of metal concentrations were found in the snails as those in the mussels, but most of the metals were mainly accumulated in the viscera, except for Ni. Similar subcellular partitioning of Cu, Zn and Cd was documented in different mussel tissues, with cellular debris (50%) being the predominant fraction, followed by equivalent values in other fractions. Lead was distributed in both cellular debris and metal-rich granules (MRG) fraction, whereas Ni was predominantly distributed in MRG (90%). Arsenic was mainly partitioned in cellular debris and metallothionein-like protein. However, deep-sea snails displayed elevated subcellular partitioning of Cu in the organelles (up to 60%) and may be more susceptible to Cu stress than the mussels. Our results demonstrated the metal-specificity of detoxification strategies in these deep-sea hydrothermal vent mollusks, and the mussels may be more adaptable to high metal exposures than the snails at hydrothermal vent.

Co-exposure to nTiO2 impairs arsenic metabolism and affects antioxidant capacity in the marine shrimp Litopenaeus vannamei

Aquatic animals are vulnerable to arsenic (As) toxicity. However, rarely does a contaminant occur alone in the aquatic environment. For this reason, this study was conducted to evaluate whether titanium dioxide nanoparticles (nTiO₂) can interfere with the effects induced by As in Litopenaeus vannamei. Arsenic accumulation and metabolic capacity; expression and enzymatic activity of GSTΩ (glutathione-S-transferase omega isoform); antioxidant responses such as GSH, GR, and GST (reduced glutathione levels, glutathione reductase, and glutathione-S-transferase activity, respectively); and lipid peroxidation in the gills and hepatopancreas of shrimp were evaluated. The results are summarized as follows: (1) higher accumulation of As occurred in both tissues after exposure to As alone; (2) co-exposure to nTiO₂ affected the capacity to metabolize As; (3) GSTΩ gene expression was not modified, but its activity was decreased by co-exposure to both contaminants; (4) As alone increased the GSH levels in the hepatopancreas, and co-exposure to nTiO₂ reduced these levels in both tissues; (5) a decrease in the GST activity in the gills occurred with all treatments; (6) in the gills, GR activity was increased by As, and nTiO₂ reversed this increase, whereas in the hepatopancreas co-exposure inhibited enzyme activity; (7) only in the hepatopancreas lipid damage was observed when animals were exposed to As or nTiO₂ but not in co-exposure. The results showed that the As induces toxic effects in both tissues of shrimp and that co-exposure to nTiO₂ can potentiate these effects and decrease the capacity to metabolize As, favoring the accumulation of more toxic compounds.