Evaluation of mitochondrial toxicity of cadmium in clam Ruditapes philippinarum using iTRAQ-based proteomics

Toxic mechanisms of nanoplastics exposure at environmental concentrations on juvenile red swamp crayfish (Procambarus clarkii): From multiple perspectives

Nanoplastics pollution has emerged as a global issue due to its widespread potential toxicity. This study delved in to toxic effects of nanoplastics on juvenile P. clarkii and molecular mechanisms from perspectives of growth, biochemical, histopathological analysis and transcriptome level for the first time. The findings of this study indicated that nanoplastics of different concentrations have varying influence mechanisms on juvenile P. clarkii. Nanoplastics have inhibitory effects on growth of juvenile P. clarkii, can induce oxidative stress. The biochemical analysis and transcriptome results indicated that 10 mg/L nanoplastics can activate the antioxidant defense system and non-specific immune system in juvenile P. clarkii, and affect energy metabolism and oxidative phosphorylation. While 20 mg/L and 40 mg/L have a destructive influence on the immune function in juvenile P. clarkii, leading to lipid peroxidation and oxidative damage, and induce apoptosis, can affect ion transport and osmotic pressure regulation. The findings of this study can offer foundational data for delving further into impacts of nanoplastics on crustaceans and toxicity mechanism.

Cadmium Highlights Common and Specific Responses of Two Freshwater Sentinel Species, Dreissena polymorpha and Dreissena rostriformis bugensis

Zebra mussel (ZM), Dreissena polymorpha, commonly used as a sentinel species in freshwater biomonitoring, is now in competition for habitat with quagga mussel (QM), Dreissena rostriformis bugensis. This raises the question of the quagga mussel's use in environmental survey. To better characterise QM response to stress compared with ZM, both species were exposed to cadmium (100 µg·L-1), a classic pollutant, for 7 days under controlled conditions. The gill proteomes were analysed using two-dimensional electrophoresis coupled with mass spectrometry. For ZM, 81 out of 88 proteoforms of variable abundance were identified using mass spectrometry, and for QM, 105 out of 134. Interestingly, the proteomic response amplitude varied drastically, with 5.6% of proteoforms of variable abundance (DAPs) in ZM versus 9.4% in QM. QM also exhibited greater cadmium accumulation. Only 12 common DAPs were observed. Several short proteoforms were detected, suggesting proteolysis. Functional analysis is consistent with the pleiotropic effects of the toxic metal ion cadmium, with alterations in sulphur and glutathione metabolisms, cellular calcium signalling, cytoskeletal dynamics, energy production, chaperone activation, and membrane events with numerous proteins involved in trafficking and endocytosis/exocytosis processes. Beyond common responses, the sister species display distinct reactions, with cellular response to stress being the main category involved in ZM as opposed to calcium and cytoskeleton alterations in QM. Moreover, QM exhibited greater evidence of proteolysis and cell death. Overall, these results suggest that QM has a weaker stress response capacity than ZM.

Chronic cadmium exposure impairs flight behavior by dampening flight muscle carbon metabolism in bumblebees

Cadmium pollution affects the global ecosystem because cadmium can be transferred up the food chain. The bumblebee, Bombus terrestris, is an important insect pollinator. Their foraging activity on flowers exposes them to harmful heavy metals, which damages their health and leads to massive population declines. However, the effects of chronic exposure to heavy metals on the flight performance of bumblebees have not yet been characterized. Here, we studied variation in the flight capacity of bumblebees induced by chronic cadmium exposure at field-realistic concentrations using behavioral, physiological, and molecular approaches. Chronic cadmium exposure caused a significant reduction in the duration, distance, and mean velocity of bumblebee flight. Transcriptome analysis showed that the impairment of carbon metabolism and mitochondrial dysfunction in the flight muscle were the primary causes. Physiological, biochemical, and metabolomic analyses validated disruptions in energy metabolism, and impairments in mitochondrial respiratory chain complexes activities. Histological analysis revealed muscle fiber damage and mitochondrial loss. Exogenous decanoic acid or citric acid partially restored sustained flight ability of bumblebees by mitigating muscle fiber damage and increasing energy generation. These findings provide insights into how long-term cadmium stress affects the flight ability of insects and will aid human muscle or exercise-related disease research.

Alterations in mitochondrial structure and function in response to environmental temperature changes in Apostichopus japonicus

Global temperatures have risen as a result of climate change, and the resulting warmer seawater will exert physiological stresses on many aquatic animals, including Apostichopus japonicus. It has been suggested that the sensitivity of aquatic poikilothermal animals to climate change is closely related to mitochondrial function. Therefore, understanding the interaction between elevated temperature and mitochondrial functioning is key to characterizing organisms' responses to heat stress. However, little is known about the mitochondrial response to heat stress in A. japonicus. In this work, we investigated the morphological and functional changes of A. japonicus mitochondria under three representative temperatures, control temperature (18 °C), aestivation temperature (25 °C) and heat stress temperature (32 °C) temperatures using transmission electron microscopy (TEM) observation of mitochondrial morphology combined with proteomics and metabolomics techniques. The results showed that the mitochondrial morphology of A. japonicus was altered, with decreases in the number of mitochondrial cristae at 25 °C and mitochondrial lysis, fracture, and vacuolization at 32 °C. Proteomic and metabolomic analyses revealed 103 differentially expressed proteins and 161 differential metabolites at 25 °C. At 32 °C, the levels of 214 proteins and 172 metabolites were significantly altered. These proteins and metabolites were involved in the tricarboxylic acid (TCA) cycle, substance transport, membrane potential homeostasis, anti-stress processes, mitochondrial autophagy, and apoptosis. Furthermore, a hypothetical network of proteins and metabolites in A. japonicus mitochondria in response to temperature changes was constructed based on proteomic and metabolomic data. These results suggest that the dynamic regulation of mitochondrial energy metabolism, resistance to oxidative stress, autophagy, apoptosis, and mitochondrial morphology in A. japonicus may play important roles in the response to elevated temperatures. In summary, this study describes the response of A. japonicus mitochondria to temperature changes from the perspectives of morphology, proteins, and metabolites, which provided a better understanding the mechanisms of mitochondrial regulation under environment stress in marine echinoderms.

Ameliorative effects of silybin against avermectin-triggered carp spleen mitochondrial dysfunction and apoptosis through inhibition of PERK-ATF4-CHOP signaling pathway

The aim of this study was to investigate the splenic tissue damage of environmental biological drug avermectin to freshwater cultured carp and to evaluate the effect of silybin on the splenic tissue damage of carp induced by avermectin. A total of 60 carp were divided into 4 groups with 15 carp in each group, including the control group fed with basic diet, experimental group fed with basal diet and exposed to avermectin (avermectin group), experimental group fed with basal diet supplement silybin (silybin group), and experimental group fed with basal diet supplement silybin and exposed to avermectin (silybin + avermectin group). The whole test period lasted for 30 days, and spleen tissue was collected for analysis. In this study, H&E staining, mitochondrial purification and membrane potential detection, ATP detection, DHE staining, biochemical tests, qPCR, immunohistochemistry, and apoptosis staining were used to evaluate the biological processes of spleen tissue injury, mitochondrial function, oxidative stress, apoptosis, and endoplasmic reticulum stress. The results show that silybin protected carp splenic tissue damage caused by chronic avermectin exposure, decreased mitochondrial membrane potential, decreased ATP content, ROS accumulation, oxidative stress, apoptosis, and endoplasmic reticulum stress. Silybin may ameliorate the splenic tissue damage of cultured freshwater carp caused by environmental biopesticide avermectin by alleviating mitochondrial dysfunction and inhibiting PERK-ATF4-CHOP-driven mitochondrial apoptosis. Adding silybin into the diet becomes a feasible strategy to resist the pollution of avermectin and provides a theoretical basis for creating a good living environment for freshwater carp.

Effect of cadmium in the gonads of mussel (Mytilus coruscus): an ionomics and proteomics study

The mussel Mytilus coruscus is an important and very popular seafood in China and widespread along the eastern coast of China. In this study, we investigated the molecular response of mussel gonads to cadmium accumulation at two concentrations (80 and 200 µg/L) for 30 days using ionomics and proteomics techniques. The shrinkage of the cells and moderate hemocytic infiltration were observed in the Cd-treated groups. The strontium, selenium (Se), and zinc contents were significantly altered, and the relationships between iron, copper, Se, manganese, calcium, sodium, and magnesium were also significantly altered. Label-free quantitative proteomics analysis revealed a total of 227 differentially expressed proteins. These proteins were associated with multiple biological processes, including the tricarboxylic acid cycle, structural reorganization of cells, biosynthesis of amino acids, inflammatory response of cells, and tumorigenesis. Nonetheless, our ionomics and proteomics analysis revealed that mussels could partly alleviate the adverse effects of Cd by altering the metal contents and correlations between minerals, thereby enhancing the biosynthesis of some amino acids and activity of antioxidant enzymes. Overall, this study provides an insight into the mechanism underlying Cd toxicity in mussel gonads from a metal and protein perspective.

Effect of heat and hypoxia stress on mitochondrion and energy metabolism in the gill of hard clam

Aquatic animals suffer from heat and hypoxia stress more frequently due to global climate change and other anthropogenic activities. Heat and hypoxia stress can significantly affect mitochondrial function and energy metabolism. Here, the response and adaptation characteristics of mitochondria and energy metabolism in the gill of the hard clam Mercenaria mercenaria under heat (35 °C), hypoxia (0.2 mg/L), and heat plus hypoxia stress (35 °C, 0.2 mg/L) after 48 h exposure were investigated. Mitochondrial membrane potentials were depolarized under environmental stress. Mitochondrial fusion, fission and mitophagy played a key role in maintain mitochondrion function. The AMPK subunits showed different expression under environmental stress. Acceleration of enzyme activities (phosphofructokinase, pyruvate kinase and lactic dehydrogenase) and accumulation of anaerobic metabolites in glycolysis and TCA cycle implied that the anaerobic metabolism might play a key role in providing energy. Accumulation of amino acids might help to increase tolerance under heat and heat combined hypoxia stress. In addition, urea cycle played a key role in amino acid metabolism to prevent ammonia/nitrogen toxicity. This study improved our understanding of the mitochondrial and energy metabolism responses of marine bivalves exposed to environmental stress.

Effect of extracellular proteins on Cd(II) adsorption in fungus and algae symbiotic system

Fungus-algae symbiotic systems (FASS) are typically used to assist in the immobilization of algae and strengthen the adsorption of heavy metals. However, the adsorption behavior of the symbiotic system and the molecular regulation mechanism of extracellular proteins in the adsorption of heavy metals have not been reported in detail. In this study, a stable FCSS (fungus-cyanobacterium symbiotic system) was used to study Cd(II) adsorption behavior. The fixation efficiency of fungus to cyanobacterium reached more than 95% at pH7.0, 30 °C, 150 rpm, and a medium ratio of 100%. The biomass, chlorophyll content, and total fatty acid content of the symbiotic system were much higher than those of cyanobacterium and fungus alone. The photosynthetic fluorescence parameters showed that the presence of fungus enhanced the light tolerance of cyanobacterium. The original light energy conversion efficiency and potential activity of PSII were enhanced, indicating that symbiosis could promote the photosynthetic process of cyanobacterium. The Cd(II) adsorption efficiency can achieve 90%. The system maintained excellent adsorption after six adsorption cycles. Differential proteins were mainly enriched in areas such as metabolism, ABC transport system, and pressure response. Cd(II) stress promotes an increase in efflux proteins. Moreover, cadmium can be fixed as much as possible by secreting extracellular proteins, and the toxicity of cadmium to cells can be alleviated by regulating the metabolism of glutathione, reducing oxidative phosphorylation level, and reducing oxidative stress, thus improving the resistance to Cd(II). Meanwhile, the expression of enzymes involved in glycolysis and the pentose phosphate pathway was upregulated, while the expression of those in the TCA cycle was downregulated. The expression of substances related to PSI and PSII in the photosynthetic system and rubisco, a key enzyme in the Calvin cycle, was significantly upregulated, indicating that the glucose metabolism and photosynthetic pathways of the symbiotic system were involved in resistance to Cd toxicity. This revealed the response mechanism of the fungus-algal symbiotic system in the process of Cd adsorption, and also provided reference value for industrial application in water treatment.

Toxicological effects of cadmium on the immune response and biomineralization of larval flounder Paralichthys olivaceus under seawater acidification

Seawater acidification can cause threats to both calcifying and uncalcifying marine organisms, affecting their acid-base regulatory functions, immune system and biomineralization. Marine pollutants, such as cadmium (Cd) that is globally distributed in coastal ecosystems, do not affect organisms alone but commonly as combined stressors. To investigate the toxicological effects of Cd on the immune and biomineralization of marine fishes under seawater acidification, flounder Paralichthys olivaceus was exposed to seawater acidification (control (pH 8.10), 7.70 and 7.30) and Cd exposure (control (0.36 μg L^-1), 0.01 and 0.15 mg L^-1 Cd) for 49 days from embryonic stage until they became settled. Immune and biomineralization-related biomarkers of flounder at the end of exposure were investigated. Results showed that single seawater acidification and Cd exposure or combined exposure significantly affected the immune system-related enzyme activities. Specifically, lysozyme (LZM) activity was significantly inhibited by single seawater acidification and Cd exposure, indicating innate immunosuppression under two stressors. Contents of IgM, HSP70 and MT were induced by seawater acidification or Cd exposure, indicating a detoxification mechanism that responded to the stressors. The expressions of immune-related genes were upregulated (hsp70 and mt) or downregulated (lzm) under Cd exposure. Of the biomineralization-related enzymes, activities of carbonic anhydrase (CA), Na⁺/K⁺-ATPase and Ca²⁺-ATPase increased under seawater acidification and Cd exposure, a potential mechanism in response to changes of acid-base balance induced by the stressors. Generally, immune and biomineralization of the flounder responded more sensitively to Cd exposure than seawater acidification. Seawater acidification aggravated the toxicological effects of Cd exposure on the two physiological functions, while high Cd exposure augmented their responses to seawater acidification.

Finding Biomarkers in Antioxidant Molecular Mechanisms for Ensuring Food Safety of Bivalves Threatened by Marine Pollution

Aquaculture production as an important source of protein for our diet is sure to continue in the coming years. However, marine pollution will also likely give rise to serious problems for the food safety of molluscs. Seafood is widely recognized for its high nutritional value in our diet, leading to major health benefits. However, the threat of marine pollution including heavy metals, persistent organic pollutants and other emerging pollutants is of ever-growing importance and seafood safety may not be guaranteed. New approaches for the search of biomarkers would help us to monitor pollutants and move towards a more global point of view; protocols for the aquaculture industry would also be improved. Rapid and accurate detection of food safety problems in bivalves could be carried out easily by protein biomarkers. Hence, proteomic technologies could be considered as a useful tool for the discovery of protein biomarkers as a first step to improve the protocols of seafood safety. It has been demonstrated that marine pollutants are altering the bivalve proteome, affecting many biological processes and molecular functions. The main response mechanism of bivalves in a polluted marine environment is based on the antioxidant defense system against oxidative stress. All these proteomic data provided from the literature suggest that alterations in oxidative stress due to marine pollution are closely linked to robust and confident biomarkers for seafood safety.

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.

The role of DRP1- PINK1-Parkin-mediated mitophagy in early cadmium-induced liver damage

Cadmium (Cd) is an important environmental pollutant that causes varying degrees of damage to multiple systems of the body. However, the specific mechanism of Cd-induced liver mitophagy remains unclear. In the present study, 5-week-old BALB/c mice and a mouse liver parenchyma cell line (AML12) were studied using a combination of in vivo and in vitro studies. We found that Cd damaged liver cells, destroy the structure and function of mitochondria, and increased the production of superoxide anions. This study further examined the effect of Cd on mitochondrial dynamics and mitophagy and showed that Cd increased mitochondrial division and induced mitophagy. The PINK1-Parkin pathway is a classical mitophagy pathway. Cd-induced mitophagy was inhibited after significantly knocking down Pink1. Mdivi-1 can effectively inhibit mitochondrial division. In this study, Mdivi-1 inhibited the expression of DRP1 and significantly inhibited the occurrence of mitophagy induced by Cd. We further examined the effect of Cd on mitophagy flux. Cd did not increase lysosomal colocalization with mitochondria. In summary, Cd increase the level of oxidative stress, destroy the structure and function of mitochondria, destroy the homeostasis of mitochondrial division and fusion, induce mitophagy through the PINK1-Parkin pathway. Mitophagy plays a protective role in early cadmium-induced liver damage.

Cadmium-induced oxidative stress in Meretrix meretrix gills leads to mitochondria-mediated apoptosis

Cadmium (Cd) is one of the most important marine environmental pollutants that can cause oxidative damage and apoptosis in living organisms, and mitochondria are the key cell organelles affected by Cd toxicity. In this study, we investigated the effect of Cd on the mitochondria in the gill cells of the clam Meretrix meretrix and the underlying mechanism of mitochondria-mediated apoptosis following exposure to the metal. Exposure of the clams to artificial seawater containing 1.5, 3, 6 and 12 mg L^-1 Cd²⁺ led to swollen mitochondria compared with the untreated clams. The mitochondria also became vacuolated at the higher Cd²⁺ concentrations. Biochemical assays showed that monoamine oxidase (MAO) activity and mitochondrial membrane potential (Δψm) increased at 1.5 mg L^-1 Cd²⁺, but decreased at higher Cd²⁺ concentrations, while the activities of malate dehydrogenase (MDH) and cytochrome oxidase (CCO) and the scavenging capacities of anti-superoxide anion (ASA) and anti-hydroxy radical (AHR) all decreased with increasing Cd²⁺ concentrations. Significant increases in the levels of malondialdehyde (MDA) and H₂O₂ as well as in the activity levels of caspase-3, -8, and -9 were also observed in the Cd²⁺-treated clams. The results implied that Cd might induce apoptosis in M. meretrix via the mitochondrial caspase-dependent pathway.

Metabolomic Alterations in the Digestive System of the Mantis Shrimp Oratosquilla oratoria Following Short-Term Exposure to Cadmium

Mantis shrimp Oratosquilla oratoria is an economically critical aquatic species along the coast of China but strongly accumulates marine pollutant cadmium (Cd) in its digestive system. It is necessary to characterize the toxicity of Cd in the digestive system of mantis shrimp. The metabolic process is an essential target of Cd toxicity response. In this work, we used ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC-TOF-MS) for untargeted metabolomics to characterize the metabolic changes in the digestive system of O. oratoria, exposed to 0.05 mg/L for 96 h. The aim of this study was to further investigate the effect of O. oratoria on Cd response to toxicity and develop biomarkers. Metabolomics analysis showed the alteration of metabolism in the digestive system of mantis shrimp under Cd stress. A total of 91 metabolites were differentially expressed and their main functions were classified into amino acids, phospholipids, and fatty acid esters. The enrichment results of differential metabolite functional pathways showed that biological processes such as amino acid metabolism, transmembrane transport, energy metabolism, and signal transduction are significantly affected. Based on the above results, the Cd-induced oxidative stress and energy metabolism disorders were characterized by the differential expression of amino acids and ADP in mantis shrimp, while the interference of transmembrane transport and signal transduction was due to the differential expression of phospholipids. Overall, this work initially discussed the toxicological response of Cd stress to O. oratoria from the metabolic level and provided new insights into the mechanism.

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.

Assessment spermatogenic cell apoptosis and the transcript levels of metallothionein and p53 in Meretrix meretrix induced by cadmium

Cadmium (Cd) has been widely used in industry and can accumulate in the water, soil, and food. Meretrix meretrix is one of the marine shellfishes cultivated for economic purpose in China. The increasing Cd levels in coastal marine water could adversely affect the economic benefits of shellfish cultivation. In the present study, M. meretrix were exposed to different Cd²⁺ concentrations (0, 1.5, 3, 6, and 12 mg L^-1) for 5 d to evaluate the effects of Cd on spermatogenic cell. The Cd accumulation, survival rate and the indices of oxidative stress and apoptosis were determined in the spermatogenic cells of M. meretrix. The expression levels of p53 and metallothionein (MT) mRNA were also measured in the spermatogenic cells. Cd accumulation and the mortality rate of spermatogenic cells were found to increase in a dose-response manner with Cd²⁺ concentrations. Histopathology changes, especially the damage of membranous structure, were more severe as the Cd²⁺ levels in the testis became higher. The indexes of oxidative stress, including reactive oxygen species, malondialdehyde, protein carbonyl derivates and DNA-protein crosslinks all increased after exposure to Cd²⁺. However, the total antioxidant capacity gradually decreased with the increasing Cd²⁺ concentration. In addition, exposure to Cd²⁺ increased the apoptotic rate and caspase-3 and 9 activities but decreased the level of mitochondrial membrane potential and cytochrome C oxidase in the spermatogenic cells. MT mRNA expression increased in lower Cd²⁺ concentration treated groups whereas decreased in higher groups, while the p53 mRNA expression increased in a dose-response manner with Cd²⁺ and was positively correlated with the oxidative damage indices. These results indicated that Cd²⁺ caused oxidative stress and p53 induced apoptosis in the spermatogenic cells, and thus decreased the survival rate of sperm cells. This finding highlights that Cd can reduce the reproductive capacity of M. meretrix, thus threatening to wild shellfish populations and reducing the efficiency of shellfish farming.

Development of an adverse outcome pathway for nanoplastic toxicity in Daphnia pulex using proteomics

Nanoplastics are a growing environmental and public health concern. However, the toxic mechanisms of nanoplastics are poorly understood. Here, we evaluated the effects of spherical polystyrene nanoplastics on reproduction of Daphnia pulex and analyzed the proteome of whole animals followed by molecular and biochemical analyses for the development of an adverse outcome pathway (AOP) for these contaminants of emerging concern. Animals were exposed to polystyrene nanoplastics (0, 0.1, 0.5, 1 and 2 mg/L) via water for 21 days. Nanoplastics negatively impacted cumulative offspring production. A total of 327 differentially expressed proteins (DEPs) were identified in response to nanoplastics which were further validated from gene expression and enzyme activity data. Based on these results, we propose an AOP for nanoplastics, including radical oxygen species production and oxidative stress as the molecular initiating event (MIE); followed by changes in specific signaling pathways (Jak-STAT, mTOR and FoxO) and in the metabolism of glutathione, protein, lipids, and molting proteins; with an end result of growth inhibition and decrease reproductive output. This study serves as a foundation for the development of a mechanistic understanding of nanoplastic toxicity in crustaceans and perhaps other aquatic organisms.

The role of Nrf2 in mitigating cadmium-induced oxidative stress of Marsupenaeus japonicus

Nuclear factor-erythroid 2-related factor-2 (Nrf2) is an important modulator of cellular responses against Cd in mammalian cells. However, whether such modulation is conserved in Marsupenaeus japonicas remains unknown.In our study, the shrimps were injected with dsRNA targeting Nrf2 at 4 μg g^-1 body weight (b.w.) or sulforaphane (SFN) at 5 μg g^-1 b.w., and then were exposed to 40 mg L^-1 CdCl₂ for 48 h. After Nrf2 knockdown, the Cd content increased, but decreased in the SFN group. This suggested that Nrf2 could promote Cd excretion. A terminal deoxynulceotidyl transferase nick-end-labeling (TUNEL) assay revealed that the Nrf2 knockdown increased the number of apoptotic cells in M. japonicas, while SFN decreased the number of apoptotic cells. After Nrf2 knockdown, the total antioxidant capacity (T-AOC), superoxide dismutase (Sod) activity, and related gene expression decreased significantly, while the malondialdehyde (MDA) content increased remarkably. By contrast, SFN injection alleviated the oxidative stress, as evidenced by increased T-AOC, Sod activity, sod mRNA expression and a reduced MDA content. Similarly, detoxification related enzyme activities (ethoxyresorufin O-deethylase and glutathione-S-transferase (GST)) and their corresponding gene expressions (cyp3a (cytochrome P450 family 3 subfamily A) and gst) were suppressed in the ds-Nrf2 injection group, while they were elevated in the SFN group. In addition, ds-Nrf2 activated mitochondrial apoptotic pathway, as evidenced the mRNA and protein levels of caspase-3, Bcl2 associated X protein (Bax), and p53, while SFN treatment suppressed them. These results displayed that in M. japonicus Cd-induced cellular oxidative damage probably acts via the Nrf2 pathway.

Global characterization of dose-dependent effects of cadmium in clam Ruditapes philippinarum

Cadmium (Cd) is being frequently detected in marine organisms. However, dose-dependent effects of Cd challenged unraveling the toxicological mechanisms of Cd to marine organisms and developing biomarkers. Here, the dose-dependent effects of Cd on clams Ruditapes philippinarum following exposure to 5 doses of Cd (3, 9, 27, 81, 243 μg/L) were investigated using benchmark dose (BMD) method. By model fitting, calculation of BMD values was performed on transcriptomic profiles, metals concentrations, and antioxidant indices. Cd exposure induced not only significant Cd accumulation in clams, but also marked alterations of essential metals such as Ca, Cu, Zn, Mn, and Fe. Gene regulation posed little influence on essential metal homeostasis, indicated by poor enrichment of differentially expressed genes (DEGs) associated with metal binding and metal transport in lower concentrations of Cd-treated groups. BMD analysis on biological processes and pathways showed that peptide cross-linking was the most sensitive biological process to Cd exposure, followed by focal adhesion, ubiquitin mediated proteolysis, and apoptosis. Occurrence of apoptosis was also confirmed by TUENL-positive staining in gills and hepatopancreas of clams treated with Cd. Furthermore, many DEGs, such as transglutaminases (TGs), metallothionein (MT), STEAP2-like and laccase, which presented linear or monotonic curves and relatively low BMD values, were potentially preferable biomarkers in clams to Cd. Overall, BMD analysis on transcriptomic profiles, metals concentrations and biochemical endpoints unraveled the sensitiveness of key events in response to Cd treatments, which provided new insights in exploring the toxicological mechanisms of Cd in clams as well as biomarker selection.

Effect of cadmium in the microalga Chlorella sorokiniana: A proteomic study

Cadmium is one of the most common heavy metals in contaminated aquatic environments and one of the most toxic contaminants for phytoplankton. Nevertheless, there are not enough studies focused on the effect of this metal in algae. Through a proteomic approach, this work shows how Cd can alter the growth, cell morphology and metabolism of the microalga Chlorella sorokiniana. Using the sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS), we concluded that exposure of Chlorella sorokiniana to 250 μM Cd²⁺ for 40 h caused downregulation of different metabolic pathways, such as photosynthesis, oxidative phosphorylation, glycolysis, TCA cycle and ribosomal proteins biosynthesis. However, photorespiration, antioxidant enzymes, gluconeogenesis, starch catabolism, and biosynthesis of glutamate, cysteine, glycine and serine were upregulated, under the same conditions. Finally, exposure to Cd also led to changes in the metabolism of carotenoids and lipids. In addition, the high tolerance of Chlorella sorokiniana to Cd points to this microalga as a potential microorganism to be used in bioremediation processes.

Are we forgetting the "proteomics" in multi-omics ecotoxicology?

Proteomics plays a significant role in discerning the effects of chemical exposures in animal taxa. Multi-omics applications have become more pervasive in toxicology, however questions remain about whether proteomics is being utilized by the community to its full potential - are we placing too much stock in transcriptomics and other omics approaches for developing adverse outcome pathways? Proteins are more relevant than transcripts because they are direct mediators of the resulting phenotype. There is also rarely perfect stoichiometry between transcript and protein abundance and transcript abundance may not accurately predict physiologic response. Proteins direct all levels of phenotype: structural proteins dictate physical form, enzymes catalyze biochemical reactions, and proteins act as signaling proteins, antibodies, transporters, ion pumps, and transcription factors to control gene expression. Molecular initiating events (MIEs) of AOPs predominantly occur at the level of the protein (e.g. ligand-receptor binding) and proteomics can elucidate novel MIEs and mapping KEs in AOPs. This critical review highlights the need for proteomics in multi-omics studies in environmental toxicology and outlines steps required for inclusion and wider acceptance in chemical risk assessment. We also present case studies of multi-omics approaches that utilize proteomics and discuss some of the challenges and opportunities for proteomics in comparative ecotoxicology. Our intention is not to minimize the importance of other omics technologies, as each has strengths and limitations, but rather to encourage researchers to consider proteomics-based methods in multi-omics studies and AOP development.

Mechanism of Action of Novel Pyrazole Carboxamide Containing a Diarylamine Scaffold against Rhizoctonia solani

In the last few decades, Rhizoctonia solani causing rice sheath blight has resulted in a lot of economic losses in the world. Therefore, many novel pyrazole carboxamide fungicides have been intensively researched and employed to fight against it. In this regard, in recent years, our group reported a novel pyrazole carboxamide containing a diarylamine scaffold with good antifungal activity against rice sheath blight in the pot test and field trial. Following this project, the antifungal mechanism of action of the pyrazole carboxamide has been elucidated in this work. The antifungal result showed that compound SCU2028, N-[2-[(3-chlorophenyl)amino]-phenyl]-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, was equivalent to the commercial fungicide thifluzamide and its EC₅₀ value was 0.022 mg/L against R. solani. Also, the observation results by scanning electron microscopy and transmission electron microscopy showed that it could destroy the fungus' cell walls or membranes and result in the leakage of contents and increase of the number of mitochondria and abnormal morphology. Meanwhile, the result on the mitochondrial membrane potential (MMP) showed that it could decrease R. solani's MMP. Furthermore, the results by label-free quantitative proteomic analysis showed that 1153 proteins were found after R. solani was treated with compound SCU2028, including 212 proteins in the control group and 257 proteins in the treatment group. A total of 142 differential proteins were obtained, of which 92 proteins were upregulated and 50 proteins were downregulated. The differentially expressed proteins affected a series of physiological and biochemical pathways in the mitochondria, endoplasmic reticulum, ribosome, and other related GO and KEGG pathways. In particular, the inhibition of the respiratory chain caused by the TCA cycle and oxidative phosphorylation KEGG pathway indicated that complex II (succinate dehydrogenase) and complex IV (cytochrome oxidase) might be compound SCU2028's main action targets. In addition, multiple experiments of qRT-PCR, enzyme activity detection, and molecular docking confirmed complex II and complex IV as targets. It could be seen that these findings provided a theoretical support for further research and development of the pyrazole carboxamide fungicides.

Potential of environmental concentrations of the musks galaxolide and tonalide to induce oxidative stress and genotoxicity in the marine environment

Polycyclic musk compounds have been identified in environmental matrices (water, sediment and air) and in biological tissues in the last decade, yet only minimal attention has been paid to their chronic toxicity in the marine environment. In the present research, the clams Ruditapes philippinarum were exposed to 0.005, 0.05, 0.5, 5 and 50 μg/L of the fragrances Galaxolide® (HHCB) and Tonalide® (AHTN) for 21 days. A battery of biomarkers related with xenobiotics biotransformation (EROD and GST), oxidative stress (GPx, GR and LPO) and genotoxicity (DNA damage) were measured in digestive gland tissues. HHCB and AHTN significantly (p < 0.05) induced EROD and GST enzymatic activities at environmental concentrations. Both fragrances also induced GPx activity. All concentrations of both compounds induced an increase of LPO and DNA damage on day 21. Although these substances have been reported as not acutely toxic, this study shows that they might induce oxidative stress and genotoxicity in marine organisms.

Metal pollution and its biological effects in swimming crab Portunus trituberculatus by NMR-based metabolomics

Metal pollution in the Bohai Sea in China has posed a potential risk on marine organisms. In this work, crabs (Portunus trituberculatus) were sampled from four sites, namely a reference (site 3934) and three metal-polluted (sites 6151, 6351, and 3562) sites, located in the Bohai Sea. Metal concentrations in crab gill tissues were measured using inductively coupled plasma mass spectrometry. Cu, Zn, and Cd in crab samples from S3562 presented the highest concentrations. Particularly, Cu concentration exceeded the marine biological quality standard II. Cd contents in crab samples from all metal-polluted sites exceeded the marine biological quality standard I. Nuclear magnetic resonance-based metabolomics indicated metal pollution-induced immune stresses in crab samples from all metal-polluted sites. Metal pollution in S6151 and S6351 disturbed energy metabolism through differential pathways. For crab samples from S3562, the metabolic profile suggested that metal pollution mainly induced osmotic stress.

Global responses to tris(1-chloro-2-propyl)phosphate (TCPP) in rockfish Sebastes schlegeli using integrated proteomic and metabolomic approach

As alternatives of brominated flame retardants, organophosphate flame retardants (OPFRs) can be detected in multiple marine environmental media. Tris(1-chloro-2-propyl)phosphate (TCPP) was one of the most frequently and abundantly detected OPFRs in the Bohai Sea. Exposure to TCPP has been shown to induce abnormal behavior in zebrafish as well as neurotoxicity in Caenorhabditis elegans. However, there is a lack of mechanism investigations on the toxic effects of TCPP at molecular levels. In this work, proteomics and metabolomics were integrated to analyze the proteome and metabolome responses in rockfish Sebastes schlegeli treated with TCPP (10 and 100 nM) for 15 days. A total of 143 proteins and 8 metabolites were significantly altered in rockfish following TCPP treatments. The responsive proteins and metabolites were predominantly involved in neurotransmission, neurodevelopment, signal transduction, cellular transport, cholesterol metabolism, bile acid synthesis, and detoxification. Furthermore, a hypothesized network of proteins, metabolites, and pathways in rockfish was summarized based on the combination of proteomic and metabolomic results, showing some key molecular events in response to TCPP. Overall, the present study unraveled the molecular responses at protein and metabolite levels, which provided a better understanding of toxicological effects and mechanisms of TCPP in marine teleost.

iTRAQ-based proteomic analysis on the mitochondrial responses in gill tissues of juvenile olive flounder Paralichthys olivaceus exposed to cadmium

Cadmium (Cd) is an important heavy metal pollutant in the Bohai Sea. Mitochondria are recognized as the key target for Cd toxicity. However, mitochondrial responses to Cd have not been fully investigated in marine fishes. In this study, the mitochondrial responses were characterized in gills of juvenile flounder Paralichthys olivaceus treated with two environmentally relevant concentrations (5 and 50 μg/L) of Cd for 14 days by determination of mitochondrial membrane potential (MMP), observation of mitochondrial morphology and quantitative proteomic analysis. Both Cd treatments significantly decreased MMPs of mitochondria from flounder gills. Mitochondrial morphologies were altered in Cd-treated flounder samples, indicated by more and smaller mitochondria. iTRAQ-based proteomic analysis indicated that a total of 128 proteins were differentially expressed in both Cd treatments. These proteins were basically involved in various biological processes in gill mitochondria, including mitochondrial morphology and import, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), primary bile acid biosynthesis, stress resistance and apoptosis. These results indicated that dynamic regulations of energy homeostasis, cholesterol metabolism, stress resistance, apoptosis, and mitochondrial morphology in gill mitochondria might play significant roles in response to Cd toxicity. Overall, this study provided a global view on mitochondrial toxicity of Cd in flounder gills using iTRAQ-based proteomics.

Evaluation of metal pollution-induced biological effects in Chinese shrimp Fenneropenaeus chinensis by NMR-based metabolomics

Metal pollution in Laizhou Bay along the Bohai Sea in China has been posing a risk on fishery species and hence may affect seafood quality. In this work, shrimps Fenneropenaeus chinensis were sampled from three sites, namely, a reference (site 6334) and two metal-polluted (sites 6262 and 7262) sites, located in Laizhou Bay. The metal concentrations in shrimp muscle tissues were tested using the ICP-MS technique. The Cr and Cu concentrations were the highest in the shrimp samples from site 7262, exceeding the national seafood safety standard Ⅱ, and the As concentration was much higher than the national seafood safety standard Ⅲ. NMR-based metabolomics indicated that metal pollution induced oxidative and immune stresses, damaged the muscular structure, and disrupted energy metabolism in shrimps at sites 6262 and 7262, in particular disturbed osmotic regulation in shrimps at site 7262. Glycine and serine could serve as biomarkers for Cd in F. chinensis.

Toxicological effects of As (V) in juvenile rockfish Sebastes schlegelii by a combined metabolomic and proteomic approach

Arsenic (As) is a metalloid element that is ubiquitous in the marine environment and its contamination has received worldwide attention due to its potential toxicity. Arsenic can induce multiple adverse effects, such as lipid metabolism disorder, immune system dysfunction, oxidative stress and carcinogenesis, in animals. Inorganic arsenic includes two chemical forms, arsenite (As (III)) and arsenate (As (V)), in natural environment. As (V) is the dominant form in natural waters. In the present study, metabolomic and proteomic alterations were investigated in juvenile rockfish Sebastes schlegelii exposed to environmentally relevant concentrations of As (V) for 14 d. The analysis of iTRAQ-based proteomics combined with untargeted NMR-based metabolomics indicated apparent toxicological effects induced by As (V) in juvenile rockfish. In details, the metabolites, including lactate, alanine, ATP, inosine and phosphocholine were significantly altered in As-treated groups. Proteomic responses suggested that As (V) could not only affected energy and primary metabolisms and signal transduction, but also influenced cytoskeleton structure in juvenile rockfish. This work suggested that the combined proteomic and metabolomic approach could shed light on the toxicological effects of pollutants in rockfish S. schlegelii.

Epigenetic inheritance and intergenerational effects in mollusks

Recent insights in evolutionary biology have shed light on epigenetic variation that interacts with genetic variation to convey heritable information. An important characteristic of epigenetic changes is that they can be produced in response to environmental cues and passed on to later generations, potentially facilitating later genetic adaptation. While our understanding of epigenetic mechanisms in vertebrates is rapidly growing, our knowledge about invertebrates remains lower, or is restricted to model organisms. Mollusks in particular, are a large group of invertebrates, with several species important for ecosystem function, human economy and health. In this review, we attempt to summarize the literature on epigenetic and intergenerational studies in mollusk species, with potential importance for adaptive evolution. Our review highlights that two molecular bearers of epigenetic information, DNA methylation and histone modifications, are key features for development in mollusk species, and both are sensitive to environmental conditions to which developing individuals are exposed. Further, although studies are still scarce, various environmental factors (e.g. predator cues, chemicals, parasites) can induce intergenerational effects on the phenotype (life-history traits, morphology, behaviour) of several mollusk taxa. More work is needed to better understand whether environmentally-induced changes in DNA methylation and histone modifications have phenotypic impacts, whether they can be inherited through generations and their role in intergenerational effects on phenotype. Such work may bring insights into the potential role of epigenetic in adaptation and evolution in mollusks.

Bioaccumulation and physiological responses in juvenile Marsupenaeus japonicus exposed to cadmium

The heavy metal cadmium readily accumulates in organisms, causing damage. In this study, juvenile marine shrimp Marsupenaeus japonicus were exposed to cadmium (Cd²⁺; 5, 50 and 500 μg L^-1). Cd accumulation and antioxidant-related indices were determined, and damage to biomolecules was assessed, after 24, 48 and 96 h. Cd bioaccumulation in M. japonicus increased with exposure time and concentration, which reached the highest value at 96 h. The data showed that 5, 50 and 500 μg L^-1 Cd increased glutathione (GSH) content and the activities of superoxide dismutase (SOD) and glutathione S-transferase (GST) in a Cd-dose-dependent manner, but 5 and 50 μg L^-1 Cd had no effect on caspase-3 activity. The expression levels of SOD, GST, heat shock protein 70 (HSP70), metallothionein (MT), p53 and caspase-3 genes were rapidly increased after 50 and 500 μg L^-1 Cd exposure, and remained at a significantly higher level than in the control after 96 h of exposure. After exposure to 5, 50 and 500 μg L^-1 Cd, F-value (the ratio between double-stranded DNA and total DNA) remained high at 24 h, however, as the exposure time increased, the F-value decreased in a dose-dependent manner. An increase in malondialdehyde content was also observed following exposure to 50 and 500 μg L^-1 Cd. Our data suggest that Cd induces oxidative stress, molecular damage and apoptosis in juvenile M. japonicus in a concentration- and time-dependent manner.