Acute waterborne cadmium toxicity in the estuarine pulmonate mud snail, Amphibola crenata

Effects of cadmium exposure on metabolism, antioxidant defense, immune function, and the hepatopancreas transcriptome of Cipangopaludina cathayensis

Cadmium (Cd) is a common contaminant in aquatic environments. However, little is known about the mechanisms underlying Cd toxicity in the freshwater snail Cipangopaludina cathayensis (Heude, 1890). This study to investigate the toxic effects of Cd on the standard metabolism, antioxidant activities, immune function, and hepatopancreas transcriptome profiles of C. cathayensis. C. cathayensis was exposed to 0.25, 0.5, 1.0, or 1.5 mg/L Cd for 3 h, with results showing that Cd significantly inhibited oxygen consumption and ammonia excretion and disrupted the respiratory metabolism of C. cathayensis. In addition, the O:N ratio dropped below 7, indicating that C. cathayensis may rely exclusively on proteins as an energy source under Cd stress. To understand how Cd impacts the antioxidant activities, immune function, and transcriptional profiles, C. cathayensis were exposed to 0.5 (low exposure, L14) or 1.5 (high exposure, H14) mg/L Cd for 14 days. Our results indicate that Cd exposure leads to oxidative stress and immunosuppression, with the latter effect being larger for exposure to higher Cd concentrations. A total of 2172 differentially expressed genes (DEGs) were identified by transcriptome analysis of the hepatopancreas, of which 885 were upregulated and 1287 were downregulated. Gene ontology and KEGG analyses revealed that the DEGs in the H14 group are enriched for energy generation terms and the "oxidative phosphorylation" pathway, respectively. Therefore, up-regulation of energy metabolism may be an adaptive strategy under Cd stress. Moreover, several genes involved in antioxidant activity were downregulated, whereas genes related to reactive oxygen species generation were upregulated. In addition, many immunity-related genes were identified within the DEGs, indicating that Cd toxicity may affect immune defense. Further, DEGs in the H14 group were enriched for disease-associated pathways. Taken together, our results indicate that Cd exposure leads to metabolic disorders, oxidative stress, and immunosuppression and thus may potentially contribute to disease outbreaks.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Physiological and biochemical responses of the estuarine pulmonate mud snail, Amphibola crenata, sub-chronically exposed to waterborne cadmium

Physiological and biochemical responses of the pulmonate mud snail, Amphibola crenata, to waterborne cadmium (Cd) were investigated to determine the mechanisms of toxicity and impacts of a 21-d Cd exposure. Mud snails were exposed to nominal Cd concentrations of 0, 0.2, 4 and 8 mg L ^- 1 and bioaccumulation, whole animal physiological (oxygen consumption, ammonia excretion and oxygen:nitrogen), and tissue level biochemical (catalase activity, lipid peroxidation, glycogen, glucose and protein) endpoints were measured every 7 days. At the two highest Cd exposure concentrations complete mortality was observed over 21-d. In surviving animals, oxygen consumption declined and ammonia excretion rate increased with Cd exposure concentration and duration. The increased ammonia excretion likely reflected enhanced protein metabolism as suggested by a reduced oxygen:nitrogen (O:N). Increasing waterborne Cd concentration and exposure time led to increasing metal accumulation in all tissues. The snail viscera showed the highest Cd accumulation. Both catalase activity and lipid peroxidation in the viscera significantly increased with Cd exposure concentration and time, whereas, the foot muscle and remaining tissues (kidney, mantle, remaining digestive tissues and heart) showed increased catalase activity and lipid peroxidation at higher Cd concentrations (4 and 8 mg L ^- 1), suggestive of an effect of Cd on oxidative stress. Over the course of 21 days, Cd exposure resulted in significantly lower levels of glycogen in viscera relative to Cd-free controls, reflecting an increased energy demand. Haemolymph glucose rose initially and then fell with increased exposure duration, while haemolymph protein generally exhibited an increased concentration in Cd-exposure groups, reflecting the changes in energy substrates noted for somatic tissues. These results suggest that the physiological and biochemical responses of A. crenata to Cd are conserved relative to other aquatic animals, and were tissue-specific, dose- and time-dependant.

The relationship between population attributes of the mud snail Amphibola crenata and sediment contamination: A multi-estuary assessment

This study assessed the potential of the New Zealand mud snail Amphibola crenata to act as a bioindicator of contaminated estuarine sediment. Seventeen sites with varying contaminant burdens were identified within six New Zealand regions. Attributes (population density, individual length distribution and individual dry weight condition index) were measured for field-collected A. crenata, and related to measurements of sediment trace metals and nutrients. Population density of the mud snail was relatively high in sites with elevated nutrients and organic matter. The length distribution of A. crenata showed significant regional and site-specific variations. Minimum, mean, and median shell length of A. crenata were positively correlated with sediment cadmium and zinc concentration. Overall, the sites were able to be distinguished by A. crenata population attributes and the sediment metal and nutrient content. These results suggest that A. crenata population information has potential value for assessing estuarine sediment metal and nutrient contamination.

Cloning, Functional Characterization and Response to Cadmium Stress of the Thioredoxin-like Protein 1 Gene from Phascolosoma esculenta

Cadmium (Cd) is a heavy metal toxicant and is widely distributed in aquatic environments. It can cause excessive production of reactive oxygen species (ROS) in the organism, which in turn leads to a series of oxidative damages. Thioredoxin (Trx), a highly conserved disulfide reductase, plays an important role in maintaining the intracellular redox homeostasis in eukaryotes and prokaryotes. Phascolosoma esculenta is an edible marine worm, an invertebrate that is extensively found on the mudflats of coastal China. To explore the molecular response of Trx in mudflat organisms under Cd stress, we identified a new Trx isoform (Trx-like protein 1 gene) from P. esculenta for the first time, designated as PeTrxl. Molecular and structural characterization, as well as multiple sequence and phylogenetic tree analysis, demonstrated that PeTrxl belongs to the Trx superfamily. PeTrxl transcripts were found to be ubiquitous in all tissues, and the highest expression level occurred in the coelomic fluid. Exposure to three sublethal concentrations of Cd resulted in the upregulation and then downregulation of PeTrxl expression levels over time in coelomic fluid of P. esculenta. The significant elevation of PeTrxl expression after 12 and 24 h of Cd exposure at 6 and 96 mg/L, respectively, might reflect its important role in the resistance to Cd stress. Recombinant PeTrxl (rPeTrxl) showed prominent dose-dependent insulin-reducing and ABTS free radical-scavenging abilities. After exposure to 96 mg/L Cd for 24 h, the ROS level increased significantly in the coelomic fluid, suggesting that Cd induced oxidative stress in P. esculenta. Furthermore, the injection of rPeTrxl during Cd exposure significantly reduced the ROS in the coelomic fluid. Our data suggest that PeTrxl has significant antioxidant capacity and can protect P. esculenta from Cd-induced oxidative stress.

Acute Cd Toxicity, Metal Accumulation, and Ion Loss in Southern Catfish (Silurus meridionalis Chen)

The amounts of cadmium in multiple organs and the amounts of Na⁺ and Ca²⁺ in the carcass were measured in dead and surviving southern catfish exposed to different concentrations of Cd. The 96 h median lethal concentration was 6.85 mg/L. The Cd content and Cd accumulation rate were positively correlated with Cd exposure concentrations, and there were significant differences between dead and surviving individuals, indicating that both Cd content in tissues and Cd accumulation rates were correlated with mortality. Cd levels in the liver of dead fish were saturated. A lethal threshold for Cd concentration in the whole fish was obtained. Bioconcentration factors for Cd did not decrease with increasing exposure. Acute exposure to waterborne Cd caused a significant decrease in the ion content of the fish carcass. There was a significant difference between the Na⁺ content of the carcass of dead fish (34.54 μmol/g wet weight) and surviving fish (59.34 μmol/g wet weight), which was not the case with the Ca²⁺ content, indicating that the lethal toxicity of Cd was probably related to the decrease in Na⁺ content. Collectively, these results suggest that whole-fish Cd concentration and carcass Na⁺ content can be useful indicators of fish acutely exposed to Cd.

Sub-lethal effects of dimethoate alone and in combination with cadmium on biochemical parameters in freshwater snail, Galba truncatula

The objective of the present study was to evaluate the influence of the organophosphorus pesticide dimethoate and cadmium on biochemical parameters of a freshwater snail, Galba truncatula, in laboratory conditions. In 14 days, snails were exposed to 0, 100, 200, and 400 μg L^-1 of dimethoate and 0.0 and 1000 μg L^-1 of cadmium chloride. The results evidenced that dimethoate induces oxidative stress and alters biochemical parameters in freshwater snails. Cadmium also induced significant changes in biochemical parameters. The combination of the dimethoate and cadmium markedly increased the effects on G. truncatula. Dimethoate and cadmium mixture caused a decrease in Acetylcholinesterase (AChE), and Glucose-6-phosphate dehydrogenase (G6PDH) activities, glycogen, and total antioxidant capacity (TAN) levels, and increased aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), glutathione peroxidase (GPx), and catalase (CAT) activities, and malondialdehyde (MDA) level in exposed snails. The increased toxicity and bioaccumulation of cadmium after the exposure to the highest concentration of dimethoate indicates a synergistic effect leading to a reduced performance of the detoxification system in the snail. Dimethoate contributed to the bioconcentration of cadmium in snails and increased its toxic effects evidenced in biomarkers of oxidative stress and cell damage.

Dose-dependent effects induced by cadmium in polychaete Perinereis aibuhitensis

Cadmium is a known metal contaminant in the Bohai Sea. In this study, the dose-dependent responses induced by Cd were characterized in marine polychaete Perinereis aibuhitensis using the endpoints, including activities of enzymes, expression levels of stress-responsive genes and metabolic responses. Both enzyme activities and gene expression levels exhibited the hormetic effects induced by Cd in P. aibuhitensis, as shown by the typical U-shaped or inverted U-shaped response profiles. The highest concentration (1280 µg/L) of Cd exposure induced obvious oxidative stresses. NMR-based metabolomics revealed that Cd induced both linear dose-dependent effects (69.13% of the total variation) and a relatively slight hormesis (5.54% of the total variation) in energy metabolism in P. aibuhitensis at metabolite level. In details, Cd exposures linearly reduced the consumption of amino acids and enhanced the consumption of glucose for energy supply, resulting in elevated contents of amino acids and depleted contents of glucose. Additionally, Cd treatments induced hormesis in the conversion of ATP hydrolysis to AMP. This work suggested that the hormetic effects should be considered in the ecological risk assessment for the environmental pollutants.