Copper exposure affects hemocyte apoptosis and Perkinsus marinus infection in eastern oysters Crassostrea virginica (Gmelin)

Copper induces cytotoxicity in freshwater bivalve Anodonta woodiana hemocytes

Hemocytes of freshwater bivalves are an important target model for evaluating copper (Cu) toxicity in vitro, with excess Cu causing adverse responses in these organisms. Despite this, the mechanisms underlying cytotoxicity remain poorly understood. The freshwater bivalve Anodonta woodiana, employed as a model organism in freshwater environments, was utilized in this study. Hemocytes of A. woodiana were exposed to various aqueous Cu treatments (0.001, 0.01, 0.1, 1, and 10 mg/L), and a control group (no Cu added) for 3 h to investigate the cytotoxic mechanisms of Cu. The results showed a significant increase in the production of reactive oxygen species in hemocytes of all Cu exposed groups compared to the control (p < 0.05). Remarkably, Cu treatments disrupted the cellular membrane (p < 0.05) but did not induce significant changes in the stability of the lysosomal membrane. Cu targeted the mitochondria, leading to a reduction in mitochondrial membrane potential. Additionally, all Cu treatments significantly increased the degree of DNA damage (p < 0.05). Cellular damage and a significant decline in cell viability were observed when the Cu exposure concentration reached 0.1, 1, and 10 mg/L (p < 0.05). Our study provides new insights into the cytotoxicity mechanisms triggered by Cu in hemocytes of the freshwater bivalve A. woodiana, even under environmentally relevant conditions of 0.01 mg/L exposure.

Lysosomal Cu(I)/Cu(II) Dependence of Antimicrobial Ability of Oyster Hemocytes and Regulation of Phagolysosomal System

Copper (Cu) is hyperaccumulated in oyster hemocytes and is an essential trace metal indispensable for diverse innate immune functions. However, the roles of Cu in oyster immune defense are still unclear. In this study, Cu exposure enhanced the phagocytosis of zymosan by increasing the number and length of filopodia, as well as mitochondrial ROS (mitoROS) production mainly in granulocytes, followed by semigranulocytes and agranulocytes. The intracellular calcium level increased to promote the phagosome-lysosome fusion after Cu exposure. The enhancement of phagosomal acidification and mitochondrion-phagosome juxtaposition were also found in granulocytes after Cu exposure. These results indicated that Cu could regulate the phagolysosomal system to enhance the antimicrobial ability of oyster hemocytes with the assistance of mitoROS. Furthermore, Cu(I) and Cu(II) were predominately located in lysosomes, and degranulation may provide a mechanism for exposing Cu to bacteria to prevent their survival and proliferation. Specifically, we showed that the newly formed Cu(I) arising from lysosomal Cu(II) moved to lysosomes and mitochondria in activated hemocytes to induce strong immune responses. The ability of the transformation of Cu(I) from Cu(II) followed granulocytes > semigranlocytes > agranulocytes, indicating that granulocytes played important roles in immune functions of oysters. Our results provided new insights into the understanding of antimicrobial effects of Cu in oyster hemocytes.

Effects of Dietary Copper and Escherichia coli Challenge on the Immune Response and Gill Oxidative Balance in the Freshwater Mussel Diplodon chilensis

Copper is a water and sediment pollutant that can be biomagnified by phytoplankton, and it often co-occurs with fecal bacteria. We addressed the combined effects of copper and Escherichia coli on the immune response and gill oxidative balance of the freshwater mussel Diplodon chilensis. Bivalves were sorted into four groups fed with 1) control algae, 2) bacteria (E. coli), 3) copper-enriched algae (Cu²⁺ ) algae, and 4) copper-enriched algae followed by bacteria (Cu²⁺  + E. coli). Cellular and humoral immune and cytotoxic variables were analyzed in hemolymph, and detoxifying/antioxidant enzyme activities (glutathione S-transferase [GST] and catalase [CAT]) and lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) were studied in gill tissue. The total hemocyte number increased after Cu²⁺ exposure, independently of the E. coli challenge. The proportion of hyalinocytes significantly diminished in the E. coli and Cu²⁺ groups but not in Cu²⁺  + E. coli groups; granulocytes significantly increased with E. coli but not with Cu²⁺  + E. coli treatments. Phagocytic activity was higher in all treatments than in control mussels. Acid phosphatase activity was increased by E. coli and inhibited by Cu²⁺ and Cu²⁺  + E. coli. Both E. coli and Cu²⁺ but not Cu²⁺  + E. coli augmented alkaline phosphatase activity. The Cu²⁺ and Cu²⁺  + E. coli treatments reduced the lysosomal membrane stability and cell viability. Humoral bacteriolytic and phenol oxidase activities were not affected by any treatment. The Cu²⁺ treatment induced gill CAT and GST activities and increased TBARS levels. The Cu²⁺  + E. coli treatment reversed this CAT and GST stimulation and increased the Cu²⁺ effect on TBARS. Dietary Cu²⁺ affects bivalves' immunological and oxidative status and impairs defensive responses against bacteria. In turn, E. coli potentiates the gill oxidative effects of Cu²⁺ . Environ Toxicol Chem 2023;42:154-165. © 2022 SETAC.

Hemocytes of bivalve mollusks as cellular models in toxicological studies of metals and metal-based nanomaterials

Understanding the impacts of environmental pollutants on immune systems is indispensable in ecological and health risk assessments due to the significance of normal immunological functions in all living organisms. Bivalves as sentinel organisms with vital ecological importance are widely distributed in aquatic environments and their innate immune systems are the sensitive targets of environmental pollutants. As the central component of innate immunity, bivalve hemocytes are endowed with specialized endolysosomal systems for particle internalization and metal detoxification. These intrinsic biological features make them a unique cellular model for metal- and nano-immunotoxicology research. In this review, we firstly provided a general overview of bivalve's innate immunity and the classification and immune functions of hemocytes. We then summarized the recent progress on the interactions of metals and nanoparticles with bivalve hemocytes, with emphasis on the involvement of hemocytes in metal regulation and detoxification, the interactions of hemocytes and nanoparticles at eco/bio-nano interface and hemocyte-mediated immune responses to the exposure of metals and nanoparticles. Finally, we proposed the key knowledge gaps and future research priorities in deciphering the fundamental biological processes of the interactions of environmental pollutants with the innate immune system of bivalves as well as in developing bivalve hemocytes into a promising cellular model for nano-immuno-safety assessment.

Exploration of immune response mechanisms in cadmium and copper co-exposed juvenile golden cuttlefish (Sepia esculenta) based on transcriptome profiling

Sepia esculenta is a popular economic cephalopod with high yield, delicious meat, and rich nutrition. With the rapid development of heavy industry and medical industry, a large amount of waste has been released into the ocean recklessly in recent years, inducing a significant increase in the content of heavy metals, especially cadmium (Cd) and copper (Cu), in the ocean. This phenomenon significantly affects the growth and development of S. esculenta, causing a serious blow to its artificial breeding. In this study, transcriptome analysis is used to initially explore immune response mechanisms of Cd and Cu co-exposed juvenile S. esculenta. The results show that 1,088 differentially expressed genes (DEGs) are identified. And DEGs functional enrichment analysis results suggests that co-exposure may promote inflammatory and innate immune responses in juvenile S. esculenta. Fifteen key genes that might regulate the immunity of S. esculenta are identified using protein-protein interaction (PPI) network and KEGG enrichment analyses, of which the three genes with the highest number of interactions or involve in more KEGG pathways are identified as hub genes that might significantly affect the immune response processes. Comprehensive analysis of PPI network and KEGG signaling pathway is used for the first time to explore co-exposed S. esculenta juvenile immune response processes. Our results preliminarily reveal immune response mechanisms of cephalopods exposed to heavy metals and provide a valuable resource for further understanding of mollusk immunity.

Proteomic changes associated with predator-induced morphological defenses in oysters

Inducible prey defenses occur when organisms undergo plastic changes in phenotype to reduce predation risk. When predation pressure varies persistently over space or time, such as when predator and prey co-occur over only part of their biogeographic ranges, prey populations can become locally adapted in their inducible defenses. In California estuaries, native Olympia oyster (Ostrea lurida) populations have evolved disparate phenotypic responses to an invasive predator, the Atlantic oyster drill (Urosalpinx cinerea). In this study, oysters from an estuary with drills, and oysters from an estuary without drills, were reared for two generations in a laboratory common garden, and subsequently exposed to cues from Atlantic drills. Comparative proteomics was then used to investigate molecular mechanisms underlying conserved and divergent aspects of their inducible defenses. Both populations developed smaller, thicker, and harder shells after drill exposure, and these changes in shell phenotype were associated with up-regulation of calcium transport proteins that could influence biomineralization. Inducible defenses evolve in part because defended phenotypes incur fitness costs when predation risk is low. Immune proteins were down-regulated by both oyster populations after exposure to drills, implying a trade-off between biomineralization and immune function. Following drill exposure, oysters from the population that co-occurs with drills grew smaller shells than oysters inhabiting the estuary not yet invaded by the predator. Variation in the response to drills between populations was associated with isoform-specific protein expression. This trend suggests that a stronger inducible defense response evolved in oysters that co-occur with drills through modification of an existing mechanism.

A nationwide survey of trace metals and Zn isotopic signatures in mussels (Mytilus edulis) and oysters (Crassostrea gigas) from the coast of South Korea

Thirteen trace metals and Zn isotopic signatures were investigated in mussels and oysters collected from the coast of South Korea to evaluate their bioavailability in bivalve mollusks. The average Cu, Zn, and Cd concentrations were 2.6-17.7 times higher in oysters than mussels, and high biota sediment accumulation factors (>30) were observed for these metals in oysters. Except for Pb in mussels, most metals had no correlation with total sediment concentrations. In oysters, Fe, V, Cu, Zn, Sn, and Pb concentrations were significantly correlated with sediments. The average values of δ⁶⁶Zn_IRMM3702 in mussels, oyster, and sediments were +0.09‰, +0.12‰, and -0.06‰, respectively. Soft tissues of mussels and oysters with high Zn concentrations tended to contain lighter Zn isotopes. The results indicate that oysters are a better biomonitoring organism for metal contamination than mussels and can be used in the monitoring and management of coastal environments and ecosystems.

Interactive effects of salinity variation and exposure to ZnO nanoparticles on the innate immune system of a sentinel marine bivalve, Mytilus edulis

ZnO nanoparticles (nZnO) are released into the coastal environment from multiple sources, yet their toxicity to marine organisms is not well understood. We investigated the interactive effects of salinity (normal 15, low 5, and fluctuating 5-15) and nZnO (100 μg l-1) on innate immunity of the blue mussels Mytilus edulis from a brackish area of the Baltic Sea. Exposure to ionic Zn (100 μg l-1) was used to test whether the toxic effects of nZnO can be attributed to the potential release of Zn2+. Functional parameters and the expression of key immune-related genes were investigated in the mussels exposed to nZnO or ionic Zn under different salinity regimes for 21 days. nZnO exposures elevated hemocyte mortality, suppressed adhesion, stimulated phagocytosis, and led to an apparent increase in lysosomal volume. At salinity 15, nZnO suppressed the mRNA expression of the Toll-like receptors TLRb and c, C-lectin, and the complement system component C3q indicating impaired ability for pathogen recognition. In contrast, the mRNA levels of an antimicrobial peptide defensin increased during nZnO exposure at salinity 15. At fluctuating salinity (5-15), nZnO exposure increased expression of multiple immune-related genes in hemocytes including the complement system components C1 and C3q, and the Toll-like receptors TLRa, b and c. Low salinity (5) had strong immunosuppressive effects on the functional and molecular immune traits of M. edulis that overshadowed the effects of nZnO. The salinity-dependent modulation of immune response to nZnO cannot be attributed to the differences in the aggregation or solubility of nZnO, and likely reflects the interaction of the toxic effects of nanoparticles and physiological effects of the osmotic stress. These findings have implications for the environmental risk assessment of nanomaterials and the development of the context-specific biomarker baselines for coastal pollution monitoring.

The role of copper and zinc accumulation in defense against bacterial pathogen in the fujian oyster (Crassostrea angulata)

Cu and Zn are hyper-accumulated in oysters, and the accumulation of these metals increases host resistance to pathogens. However, the role of Cu/Zn in oyster immune defense remains unclear. In this study, Crassostrea angulata with different levels of Cu and Zn were obtained through metal exposure or selective breeding. Both in vivo and in vitro experiments showed that oysters accumulating more Cu/Zn exhibited stronger antibacterial abilities. Vibrio harveyi infection significantly promoted the metal redistribution in oysters: Cu and Zn concentrations decreased in the mantle, but increased in the plasma and hemocytes. This redistribution was accompanied by changes in the expression levels of Cu and Zn transporter genes (CTR1, ATP7A, ZIP1, and ZNT2), suggesting that the Cu/Zn burst observed in the hemocytes was likely due to the transfer of heavy metals from plasma (mediated by the metal importer proteins) or released from intracellular stores. The degree to which Cu/Zn concentration increased in the plasma and hemocytes was more dramatic in oysters with high levels of Cu/Zn accumulation. In vitro, Cu and Zn both inhibited the growth of V. harveyi, while Cu plus H₂O₂ was lethal to the bacteria. The strength of the growth-inhibition and lethal effects depended on the metal dose. In addition to these effects, increases in Cu concentration increased the activity levels of PO in the oyster plasma and hemocytes in vivo and in vitro. However, SOD activity was not affected by Cu or Zn accumulation. Thus, our results suggested that the Cu/Zn burst in the hemolymph was an important factor in the oyster immune reaction, creating a toxic internal environment for the pathogen, as well as catalyzing inorganic or enzymatic reactions to strengthen bacteriostasis. By determining the extent of Cu/Zn burst in the immune response, Cu/Zn accumulated levels could affect the resistance of oysters to pathogens.

Copper-induced immunomodulation in mussel (Perna canaliculus) haemocytes

Copper is a common contaminant in aquatic environments, which may cause physiological dysfunction in marine organisms. However, the toxicity mechanisms of copper in marine bivalves is not fully understood. In this study, we applied an integrated approach that combines flow cytometry and Gas Chromatography-Mass Spectrometry (GC-MS)-based metabolomics to characterize cellular and molecular mechanisms of copper immunotoxicity in New Zealand Greenshell™ mussel (Perna canaliculus) haemolymph. Flow cytometric results showed significant increases in haemocyte mortality, production of reactive oxygen species and apoptosis (via alteration of caspase 3/7 and mitochondrial membrane potential) of haemocytes exposed to increasing total concentrations of Cu2+ (62.5, 125.0 and 187.5 μM) compared to a low Cu2+ concentration (25.0 μM) and control (0.0 μM). In addition to flow cytometric data, our metabolomics results showed alterations of 25 metabolites within the metabolite profile of Cu2+-exposed haemolymph (125 μM) compared to those of control samples. Changes in levels of these metabolites may be considered important signatures of oxidative stress (e.g., glutathione) and apoptosis processes (e.g., alanine, glutamic acid). This study provides insights into the cellular and molecular mechanisms of oxidative stress and apoptosis in marine bivalves and highlights the applicability and reliability of metabolomic techniques for immunotoxicological studies in marine organisms.

Potential trade-offs between biomineralization and immunity revealed by shell properties and gene expression profiles of two closely related Crassostrea species

Species of the Ostreidae family are key ecosystem engineers and many of them - including Crassostrea gigas and Crassostreavirginica - are commercially important aquaculture species. Despite similarities in their morphology and ecology, these two species differ in their ability to defend against pathogens, potentially reflecting species-specific differential specialization of hemocytes on immune defense versus biomineralization. To test this hypothesis, we investigated the expression levels of immune- and biomineralization-related genes as well as mineralogical and mechanical properties of the shells and the calcium sequestration ability of the hemocytes of C. gigas and C. virginica The expression of biomineralization-related genes was higher in C. virginica than in C. gigas in multiple tissues including the mantle edge and hemocytes, while the expression of immune genes was higher in the hemocytes of C. gigas Hemocytes of C. virginica contained more calcium (stored intracellularly as calcium carbonate mineral) compared with those of C. gigas Analysis of the adult shells showed that the crystallinity of calcite was higher and the laths of the foliated layer of the shell were thicker in C. virginica than in C. gigas Mechanically, the shells of C. virginica were stiffer, harder and stronger than those of C. gigas Taken together, our results show that the species-specific differences in physiology (such as disease resistance and exoskeleton properties) are reflected at the cellular and molecular levels in the differential specialization of hemocytes on potentially competing functions (immunity and biomineralization) as well as different expression profiles of other tissues involved in biomineralization (such as the mantle edge).

Effects of food contaminated with cadmium and copper on hemocytes of Steatoda grossa (Araneae: Theridiidae)

The aim of this study was to evaluate the metabolic condition of Steatoda grossa (Theridiidae) spider, from their hemocytes, after a short-term (four-week) exposure to cadmium and copper in sublethal doses by administering them into the body of the preys. The ultrastructure of the dominant types of hemocytes, such as granulocytes, plasmatocytes and prohemocytes, was evaluated using transmission electron microscope (TEM). Quantitative evaluation of apoptotic and necrotic cells, as well as the ones with depolarized mitochondria in hemolymph, was performed using flow cytometry, while ATP concentration and ADP/ATP ratio in hemocytes were measured by luminescent methods. Cadmium, unlike copper, demonstrated proapoptotic and pronecrotic activity. Low ATP levels and high ADP/ATP ratio in hemocytes indicate a disturbance in the energy metabolism of cells and may account for their qualitative and quantitative degenerative changes. The intensification of death processes in hemocytes after an exposure to cadmium-contaminated food may impair the ability of these cells to fight infectious diseases. Copper at the applied dosage was safe for the spiders without causing visible changes in the hemocyte ultrastructure and in the level of analyzed cell death indices.

Effects of elevated CO2 levels on subcellular distribution of trace metals (Cd and Cu) in marine bivalves

Hypercapnia (elevated CO₂ levels) and pollution with trace metals such as Cu and Cd are common stressors in estuarine habitats that can negatively affect physiology and health of marine organisms. Hypercapnia can modulate toxicity of trace metals including Cu and Cd; however, the physiological and cellular mechanisms of the metal-CO₂ interactions are not well understood. We investigated the effects of elevated P_CO2 (∼800 and 2000μatm) and metal exposure (50μgl^-1 of Cu or Cd) on subcellular distribution of metals in two common species of marine bivalves, Eastern oysters Crassostrea virginica and hard shell clams Mercenaria mercenaria. Oysters accumulated higher burdens of Cu and Cd in the gill tissues compared to clams. In both studied species, Cu was predominantly associated with the metabolically active cell compartments (mitochondria, lysosomes, microsomes and cytosolic enzymes), with a modest fraction sequestered by metallothioneins (∼30%) and the insoluble metal-containing granules (MCG) (∼15-20%). Unlike Cu, Cd was largely sequestered by metallothioneins (∼60-70%), with a relatively small fraction associated with the organelles and the cytosolic enzymes. Mitochondria were the main intracellular target for trace metals accumulating higher concentrations of Cd (and in the case of oysters - of Cu) than other organelles or cytosolic enzymes. Cu accumulation in the metabolically active cellular compartments was independent of the CO₂ levels, while Cd content of the organelles and cytosolic enzymes increased at elevated P_CO2 in both studied species indicating that hypercapnia may enhance cellular toxicity of Cd in bivalves. Hypercapnia suppressed the sequestration capacity of metallothioneins for Cu and Cd in oysters but increased Cu and Cd load in clam metallothioneins. Thus, metal-induced metabolic injury in oysters may be exaggerated by hypercapnia which enhances metal accumulation in the potentially sensitive intracellular fractions and suppresses the metal detoxification capacity. In contrast, clams appear to be more resistant to the combined effects of hypercapnia and metal exposure reflecting more efficient and robust detoxification mechanisms of this species.

Conservation and divergence of mitochondrial apoptosis pathway in the Pacific oyster, Crassostrea gigas

Apoptosis is considered a crucial part of the host defense system in oysters according to previous reports; however, the exact process by which this occurs remains unclear. Besides, mitochondrial apoptosis is the primary method of apoptosis in vertebrate cells, but has been poorly studied in invertebrates and is quite controversial. In this study, we investigated the molecular mechanism of mitochondrial apoptosis in the Pacific oyster Crassostrea gigas. Notably, we show that most key elements involved in the vertebrate mitochondrial apoptosis pathway – including mitochondrial outer membrane permeabilization, cytochrome c release, and caspase activation – are also present in C. gigas. In contrast, the lack of Bcl-2 homology 3-only subfamily members and apoptotic protease activating factor-1 (APAF-1) protein revealed evolutionary diversity from other phyla. Our results support that mitochondrial apoptosis in animals predates the emergence of vertebrates, but suggest that an unexpectedly diverse mitochondrial apoptosis pathway may exist in invertebrates. In addition, our work provided new clues for an improved understanding of how bivalve acclimate themselves to an inconstant environment.

Can ecological history influence response to pollutants? Transcriptomic analysis of Manila clam collected in different Venice lagoon areas and exposed to heavy metal

Chronic exposure to environmental pollutants can exert strong selective pressures on natural populations, favoring the transmission over generations of traits that enable individuals to survive and thrive in highly impacted environments. The lagoon of Venice is an ecosystem subject to heavy anthropogenic impact, mainly due to the industrial activities of Porto Marghera (PM), which led to a severe chemical contamination of soil, groundwater, and sediments. Gene expression analysis on wild Manila clams collected in different Venice lagoon areas enabled to identify differences in gene expression profiles between clams collected in PM and those sampled in clean areas, and the definition of molecular signatures of chemical stress. However, it remains largely unexplored to which extent modifications of gene expression patterns persists after removing the source of contamination. It is also relatively unknown whether chronic exposure to xenobiotics affects the response to other chemical pollutants. To start exploring such issues, in the present study a common-garden experiment was coupled with transcriptomic analysis, to compare gene expression profiles of PM clams with those of clams collected in the less impacted area of Chioggia (CH) during a period under the same control conditions. Part of the two experimental groups were also exposed to copper for seven days to assess whether different "ecological history" does influence response to such pollutant. The results obtained suggest that the chronic exposure to chemical pollution generated a response at the transcriptional level that persists after removal for the contaminated site. These transcriptional changes are centered on key biological processes, such as defense against either oxidative stress or tissue/protein damage, and detoxification, suggesting an adaptive strategy for surviving in the deeply impacted environment of Porto Marghera. On the other hand, CH clams appeared to respond more effectively to copper exposure than PM animals, proposing that chronic exposure to chemical toxicants either lowers the sensitivity to additional toxicants or blunts the capacity to respond to novel chemical challenges in PM clams.

Interactive effects of copper exposure and environmental hypercapnia on immune functions of marine bivalves Crassostrea virginica and Mercenaria mercenaria

Estuarine organisms such as bivalves are commonly exposed to trace metals such as copper (Cu) and hypercapnia (elevated CO2 levels) in their habitats, which may affect their physiology and immune function. This study investigated the combined effects of elevated CO2 levels (∼800-2000 μatm PCO2, such as predicted by the near-future scenarios of global climate change) and Cu (50 μg l(-1)) on immune functions of the sediment dwelling hard clams Mercenaria mercenaria and an epifaunal bivalve, the eastern oyster Crassostrea virginica. Clams and oysters were exposed for 4 weeks to different CO2 and Cu levels, and tissue Cu burdens and immune parameters were assessed to test the hypothesis that hypercapnia will enhance Cu uptake due to the higher bioavailability of free Cu(2+) and increase the immunomodulatory effects of Cu. Exposure to Cu stimulated key immune parameters of clams and oysters leading to increased number of circulating hemocytes, higher phagocytosis and adhesion ability of hemocytes, as well as enhanced antiparasitic and antibacterial properties of the hemolymph reflected in higher activities of lysozyme and inhibitors of cysteine proteases. Lysozyme activation by Cu exposure was most prominent in normocapnia (∼400 μatm PCO2) and an increase in the levels of the protease inhibitors was strongest in hypercapnia (∼800-2000 μatm PCO2), but other immunostimulatory effects of Cu were evident in all PCO2 exposures. Metabolic activity of hemocytes of clams and oysters (measured as routine and mitochondrial oxygen consumption rates) was suppressed by Cu exposure likely reflecting lower rates of ATP synthesis and/or turnover. However, this metabolic suppression had no negative effects of the studied immune functions of hemocytes such as phagocytosis or adhesion capacity. Hypercapnia (∼800-2000 μatm PCO2) slightly but significantly enhanced accumulation of Cu in hemocytes, consistent with higher Cu(2+) bioavailability in CO2-acidified water, but had little effect on cellular and humoral immune traits of clams and oysters. These findings indicate that low levels of Cu contamination may enhance immunity of estuarine bivalves while moderate hypercapnia (such as predicted by the near future scenarios of the global climate change) does not strongly affect their immune parameters.

Morphological alteration, lysosomal membrane fragility and apoptosis of the cells of Indian freshwater sponge exposed to washing soda (sodium carbonate)

Washing soda is chemically known as sodium carbonate and is a component of laundry detergent. Domestic effluent, drain water and various anthropogenic activities have been identified as major routes of sodium carbonate contamination of the freshwater ecosystem. The freshwater sponge, Eunapius carteri, bears ecological and evolutionary significance and is considered as a bioresource in aquatic ecosystems. The present study involves estimation of morphological damage, lysosomal membrane integrity, activity of phosphatases and apoptosis in the cells of E. carteri under the environmentally realistic concentrations of washing soda. Exposure to washing soda resulted in severe morphological alterations and damages in cells of E. carteri. Fragility and destabilization of lysosomal membranes of E. carteri under the sublethal exposure was indicative to toxin induced physiological stress in sponge. Prolonged exposure to sodium carbonate resulted a reduction in the activity of acid and alkaline phosphatases in the cells of E. carteri. Experimental concentration of 8 mg/l of washing soda for 192 h yielded an increase in the physiological level of cellular apoptosis among the semigranulocytes and granulocytes of E. carteri, which was suggestive to possible shift in apoptosis mediated immunoprotection. The results were indicative of an undesirable shift in the immune status of sponge. Contamination of the freshwater aquifers by washing soda thus poses an alarming ecotoxicological threat to sponges.

Immunotoxicological effects of environmental contaminants on marine bivalves

Coastal areas are complex environments frequently contaminated by numerous pollutants that represent a potential threat to marine organisms, especially bivalves. These pollutants may have major ecological consequences. Although effects of different environmental contaminants on the immune system in marine bivalves have been already reported, a few of reviews summarizes these effects. The main purpose of this chapter relies on summarizing recent body of data on immunotoxicity in bivalves subjected to contaminants. Immune effects of heavy metals, pesticides, HAP, PCB and pharmaceuticals are presented and discussed and a particular section is devoted to nanoparticle effects. A large body of literature is now available on this topic. Finally, the urgent need of a better understanding of complex interactions between contaminants, marine bivalves and infectious diseases is noticed.

Effects of environmental hypercapnia and metal (Cd and Cu) exposure on acid-base and metal homeostasis of marine bivalves

Elevated CO2 levels reduce seawater pH and may affect bioavailability of trace metals in estuaries. We studied the interactive effects of common metal pollutants (50 μg l(-1) Cd or Cu) and PCO2 (~395, 800 and 2000 μatm) on metal levels, intracellular pH, expression of metal binding proteins and stress biomarkers in estuarine bivalves Crassostrea virginica (oysters) and Mercenaria mercenaria (hard clams). Cd (but not Cu or hypercapnia) exposure affected the acid-base balance of hemocytes resulting in elevated intracellular pH. Cd and Cu exposure led to the increase in the tissue metal burdens, and metal accumulation was reduced by elevated PCO2 in the mantle but not hemocytes. No change was found in the intracellular free Cd(2+), Cu(2+) or Fe(2+) during Cu or Cd exposure indicating that these metals are bound to intracellular ligands. Free Zn(2+) content in oyster hemocytes was suppressed by Cd and Cu exposure and below the detection limits in clam hemocytes, which went hand-in-hand with the elevated mRNA expression of metallothioneins and ferritin in Cd- and Cu-exposed bivalves, enhanced by hypercapnia. The metal-binding and antioxidant mechanisms of oysters and clams were sufficient to effectively maintain intracellular redox status, even though metal exposure combined with moderate hypercapnia (~800 μatm PCO2) led to the elevated production of reactive oxygen species in hemocytes. Overall, while hypercapnia modulates metal accumulation, binding capacity and oxidative stress in estuarine bivalves, the physiological effects of elevated CO2 are mild compared to the effects of other common stressors.

Immunomodulation by the interactive effects of cadmium and hypercapnia in marine bivalves Crassostrea virginica and Mercenaria mercenaria

Estuarine organisms are exposed to multiple stressors including large fluctuations in partial pressure of carbon dioxide (P2CO) and concentrations of trace metals such as cadmium (Cd) that can affect their survival and fitness. Ocean acidification due to the increasing atmospheric (P2CO) leads to a decrease in pH and shifts in the carbonate chemistry of seawater which can change bioavailability and toxicity of metals. We studied the interactive effects of (P2CO) and Cd exposure on metal levels, metabolism and immune-related functions in hemocytes of two ecologically and economically important bivalve species, Mercenaria mercenaria (hard shell clam) and Crassostrea virginica (Eastern oyster). Clams and oysters were exposed to combinations of three (P2CO) levels (∼400, 800 and 2000 μatm (P2CO), corresponding to the present day conditions and the projections for the years 2100 and 2250, respectively) and two Cd concentrations (0 and 50 μg l(-1)) in seawater. Following four weeks of exposure to Cd, hemolymph of both species contained similar Cd levels (50-70 μg l(-1)), whereas hemocytes accumulated intracellular Cd burdens up to 15-42 mg l(-1), regardless of the exposure P2CO. Clam hemocytes had considerably lower Cd burdens than those of oysters (0.7-1 ng 10(-6) cells vs. 4-6 ng 10(-6) cells, respectively). Cd exposure suppressed hemocyte metabolism and increased the rates of mitochondrial proton leak in normocapnia indicating partial mitochondrial uncoupling. This Cd-induced mitochondrial uncoupling was alleviated in hypercapnia. Cd exposure suppressed immune-related functions in hemocytes of clams and oysters, and these effects were exacerbated at elevated (P2CO). Thus, elevated (P2CO) combined with Cd exposure resulted in decrease in phagocytic activity and adhesion capacity as well as lower expression of mRNA for lectin and heat shock protein (HSP70) in clam and oyster hemocytes. In oysters, combined exposure to elevated (P2CO) and Cd also led to reduced activity of lysozyme in hemocytes and hemolymph. Overall, our study shows that moderately elevated (P2CO) (∼800-2000 μatm P2CO) potentiates the negative effects of Cd on immunity and thus may sensitize clams and oysters to pathogens and diseases during seasonal hypercapnia and/or ocean acidification in polluted estuaries.

Immunomodulating effects of environmentally realistic copper concentrations in Mytilus edulis adapted to naturally low salinities

The monitoring of organisms' health conditions by the assessment of their immunocompetence may serve as an important criterion for the achievement of the Good Environmental Status (GES) as defined in the Marine Strategy Framework Directive (EU). In this context, the complex role of natural environmental stressors, e.g. salinity, and interfering or superimposing effects of anthropogenic chemicals, should be carefully considered, especially in scenarios of low to moderate contamination. Organisms from the Baltic Sea have adapted to the ambient salinity regime, however energetically costly osmoregulating processes may have an impact on the capability to respond to additional stress such as contamination. The assessment of multiple stressors, encompassing natural and anthropogenic factors, influencing an organisms' health was the main aim of the present study. Immune responses of Mytilus edulis, collected and kept at natural salinities of 12‰ (LS) and 20‰ (MS), respectively, were compared after short-term exposure (1, 7 and 13 days) to low copper concentrations (5, 9 and 16 μg/L Cu). A significant interaction of salinity and copper exposure was observed in copper accumulation. LS mussels accumulated markedly more copper than MS mussels. No combined effects were detected in cellular responses. Bacterial clearance was mostly achieved by phagocytosis, as revealed by a strong positive correlation between bacterial counts and phagocytic activity, which was particularly pronounced in LS mussels. MS mussels, on the other hand, seemingly accomplished bacterial clearance by employing additional humoral factors (16 μg/L Cu). The greatest separating factor in the PCA biplot between LS and MS mussels was the proportion of granulocytes and hyalinocytes while functional parameters (phagocytic activity and bacterial clearance) were hardly affected by salinity, but rather by copper exposure. In conclusion, immune responses of the blue mussel may be suitable and sensitive biomarkers for the assessment of ecosystem health in brackish waters (10-20‰S).

Short-term acute hypercapnia affects cellular responses to trace metals in the hard clams Mercenaria mercenaria

Estuarine and coastal habitats experience large fluctuations of environmental factors such as temperature, salinity, partial pressure of CO2 ( [Formula: see text] ) and pH; they also serve as the natural sinks for trace metals. Benthic filter-feeding organisms such as bivalves are exposed to the elevated concentrations of metals in estuarine water and sediments that can strongly affect their physiology. The effects of metals on estuarine organisms may be exacerbated by other environmental factors. Thus, a decrease in pH caused by high [Formula: see text] (hypercapnia) can modulate the effects of trace metals by affecting metal bioavailability, accumulation or binding. To better understand the cellular mechanisms of interactions between [Formula: see text] and trace metals in marine bivalves, we exposed isolated mantle cells of the hard clams (Mercenaria mercenaria) to different levels of [Formula: see text] (0.05, 1.52 and 3.01 kPa) and two major trace metal pollutants - cadmium (Cd) and copper (Cu). Elevated [Formula: see text] resulted in a decrease in intracellular pH (pHi) of the isolated mantle cells from 7.8 to 7.4. Elevated [Formula: see text] significantly but differently affected the trace metal accumulation by the cells. Cd uptake was suppressed at elevated [Formula: see text] levels while Cu accumulation has greatly accelerated under hypercapnic conditions. Interestingly, at higher extracellular Cd levels, labile intracellular Cd(2+) concentration remained the same, while intracellular levels of free Zn(2+) increased suggesting that Cd(2+) substitutes bound Zn(2+) in these cells. In contrast, Cu exposure did not affect intracellular Zn(2+) but led to a profound increase in the intracellular levels of labile Cu(2+) and Fe(2+). An increase in the extracellular concentrations of Cd and Cu led to the elevated production of reactive oxygen species under the normocapnic conditions (0.05 kPa [Formula: see text] ); surprisingly, this effect was mitigated in hypercapnia (1.52 and 3.01 kPa). Overall, our data reveal complex and metal-specific interactions between the cellular effects of trace metals and [Formula: see text] in clams and indicate that variations in environmental [Formula: see text] may modulate the biological effects of trace metals in marine organisms.

Density shift, morphological damage, lysosomal fragility and apoptosis of hemocytes of Indian molluscs exposed to pyrethroid pesticides

Bellamya bengalensis (Gastropoda: Prosobranchia) and Lamellidens marginalis (Bivalvia: Eulamellibranchiata) are the molluscs of Indian freshwater ecosystem and important biological resources. These edible species bear economical, ecological, nutritional and medicinal importance. Natural habitat of these organisms is under the ecological threat of contamination by cypermethrin and fenvalerate, the common pyrethroid pesticides of India. Hemocytes are chief immunoeffector cells of molluscs which exhibit responsiveness against environmental toxins and perform diverse immunological functions including phagocytosis, encapsulation and cytotoxicity. Experimental exposure of cypermethrin and fenvalerate resulted in significant shift in density and morphological damage in hemocytes of B. bengalensis and L. marginalis respectively. Pyrethroid induced fragility and destabilization of hemocyte lysosomal membrane was recorded and proposed as an indication of toxin induced stress in molluscs. Apoptosis is an immunologically important cellular response which is modulated by environmental toxins. Pyrethroid exposure suppressed the physiological level of apoptosis and necrosis in hemocytes of B. bengalensis and L. marginalis indicating possible impairment of apoptosis mediated immunoprotection. Differential responses of B. bengalensis and L. marginalis hemocytes may be due to species specificity, toxin specificity, nonidentical immune strategies of Gastropoda and Bivalvia, specific habitat preference and related ecological niches.

Can ecological history influence immunomarker responses and antioxidant enzyme activities in bivalves that have been experimentally exposed to contaminants? A new subject for discussion in "eco-immunology" studies

Numerous studies have demonstrated that environmental parameters affect bivalve immunomarkers. In the present study, we tested the hypothesis that clams (Venerupis philippinarum) collected in sites with different environmental conditions respond differently to experimental contaminant exposure. Clams were collected at two sites within the Lagoon of Venice that are influenced differently by both anthropogenic impact and natural conditions: Marghera, which is characterised by relatively high contamination levels and restricted clam fishing, and Chioggia, which is inside a licensed clam culture area that is characterised by lower contamination levels. Total haemocyte count, haemocyte diameter and volume, lysozyme activity in both haemocyte lysate and cell-free haemolymph, superoxide dismutase and catalase activities in gills and digestive glands were measured at time 0 (clam sampling time), after 7 days of acclimation in the laboratory and after 1, 3 and 7 days of copper exposure. Interestingly, statistical analyses (three-way ANOVA and Canonical Correlation Analysis) revealed persistent differences in the biological responses of clams from the two sampling sites before and after copper exposure. Conversely, the influence of copper on cellular and biochemical parameters was negligible. Overall, the results obtained indicated that animals with a different ecological history respond differently to experimental contaminant exposure. In addition, this study suggested that immunomarkers and other biomarkers might be used to determine the origin of fishing products.