Biochemical response of the copepod Tigriopus japonicus Mori experimentally exposed to cadmium

Oxidative Stress and Neurotoxicity of Cadmium and Zinc on Artemia franciscana

Despite not being redox-active metals, Cd and Zn can disrupt cellular redox homeostasis by acting pro-oxidatively. The aim of this study was to examine the effects of exposure to Zn (14 and 72 mg/L) and Cd (7.7 and 77 mg/L) for 24 and 48 h on oxidative and antioxidative parameters and the activity of glutathione-S-transferase in Artemia franciscana tissue. In addition, the neurotoxicity of the metals was examined by determining the activity of acetylcholinesterase (AChE). In A. franciscana tissue, Cd (0.0026 ± 0.0001 mg/L) was detected only after 48 h of exposure to 77 mg/L Cd. After 24 h, the 14- and 72-mg/L Zn treatments resulted in significant increases in the Zn concentration (0.54 ± 0.026 mg/L (p < 0.01) and 0.68 ± 0.035 (p < 0.0001), respectively) in A. franciscana tissue compared with the control level, and significant increases were also detected after 48 h (0.59 ± 0.02 (p < 0.0001) and 0.79 ± 0.015 (p < 0.0001), respectively). The malondialdehyde (MDA) concentration in the metal-treated samples was increased after 24 h of exposure, whereas after 48 h, an increase in the MDA concentration was detected only with 7.7. mg/L Cd. A significant increase in the H₂O₂ concentration after 24 h was measured only after treatment with 72 mg/L Zn. The treatment with 7.7 mg/L Cd for 24 h induced a significant increase in the AChE activity, whereas 48 h of treatment with 77 mg/L Cd and 14 mg/L Zn significantly inhibited AChE. The results indicate that lipid peroxidation resulting from metal toxicity may constitute the basis of neurotoxicity.

Diel Fluctuation Superimposed on Steady High pCO2 Generates the Most Serious Cadmium Toxicity to Marine Copepods

Coastal systems experience diel fluctuation of pCO₂ and cadmium (Cd) pollution; nevertheless, the effect of fluctuating pCO₂ on Cd biotoxicity is poorly known. In this study, we initially performed the isotopically enriched organism bioassay to label Tigriopus japonicus with ¹¹³Cd (5 μg/L) to determine the Cd accumulation rate constant (k_accu) under ambient (400 μatm) and steadily (1000 μatm) and fluctuatingly elevated (1000 ± 600 μatm) pCO₂ conditions for 48 h. Next, T. japonicus was interactively subjected to the above pCO₂ exposures at Cd (control, 5, and 500 μg/L) treatments for 7 d. Biochemical and physiological responses for copepods were analyzed. The results showed that steadily increased pCO₂ facilitated Cd bioaccumulation compared to ambient pCO₂, and it was more under fluctuating acidification conditions. Despite compensatory reactions (e.g., increased energy production), Cd ultimately induced oxidative damage and apoptosis. Meanwhile, combined treatment exhibited higher toxicity (e.g., increased apoptosis) relative to Cd exposure, and even more if fluctuating acidification was considered. Intriguingly, fluctuating acidification inhibited Cd exclusion in Cd-treated copepods compared to steady acidification, linking to higher Cd k_accu and bioaccumulation. Collectively, CO₂-driven acidification could aggravate Cd toxicity, providing a mechanistic understanding of the interaction between seawater acidification and Cd pollution in marine copepods.

Biochemical response and metals bioaccumulation in planktonic communities from marine areas impacted by the Fundão mine dam rupture (southeast Brazil)

The rupture of the Fundão dam (Mariana, MG, southeast Brazil) released a huge flood of mine tailings to Doce river basin and its adjacent coastal area, in November 2015. This catastrophic event exposed aquatic communities to metal contamination related to mine tailings, but its biological effects are still poorly understood. This study investigates how biochemical response related to metal exposure vary between locations and seasons during the years of 2018-2020, in planktonic communities (micro and mesoplankton). Marine microplankton collected in sectors in front and south of the Doce river mouth presented the highest lipid peroxidation (LPO) and induction of metallothioneins (MT). Mesoplankton collected in sectors in front and north of the Doce river mouth presented highest LPO, while MT in this size class did not respond to a clear spatial pattern. Our results showed that metals affected biomarkers in a non-linear pattern and highlighted the complex relationship between metals, biochemical parameters, and seasonality. The variation in biochemical biomarkers indicates physiological stress related to metals, once sectors contaminated by metals, especially Fe, Mn and Cd, presented stronger biochemical responses. Comparison of metal levels with bioaccumulation data collected before the impact indicates Fe, Cd, Cr and Cu more than 2-fold higher after disaster in sectors closer to the river. Literature showed that these sectors present zooplanktonic assemblages with lower biomass and biodiversity, suggesting that the opportunistic species that thrives in the area are also under biochemical stress, but possibly relies on repair or defense mechanisms. The physiological stress detected by this study is possibly related to the mine tailings, considering the metals that stood out and the proximity with the Doce river mouth. This suggests that the impacts related to the failure of Fundão dam are still affecting the marine planktonic community even three to four years after the environmental disaster.

Glutathione S-Transferases in Marine Copepods

The glutathione S-transferase (GST) is a complex family of phase II detoxification enzymes, known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to a wide variety of endogenous and exogenous electrophilic compounds for detoxification purposes. In marine environments, copepods are constantly exposed to multiple exogenous stressors, thus their capability of detoxification is key for survival. Full identification of the GST family in copepods has been limited only to few species. As for insects, the GST family includes a wide range of genes that, based on their cellular localization, can be divided in three classes: cytosolic, microsomal, and mitochondrial. The role of GSTs might have class-specific features, thus understanding the nature of the GST family has become crucial. This paper covers information of the GST activity in marine copepods based on studies investigating gene expression, protein content, and enzymatic activity. Using published literature and mining new publicly available transcriptomes, we characterized the multiplicity of the GST family in copepods from different orders and families, highlighting the possible role of these genes as biomarker for ocean health status monitoring.

Differential gene expression profile of male and female copepods in response to cadmium exposure

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 μg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Seasonal ecotoxicological monitoring of freshwater zooplankton in Bir Mcherga dam (Tunisia)

Dams represent large semi-closed reservoirs of pesticides and various organic and inorganic pollutants from agricultural and human activities, and their monitoring should receive special attention. This study evaluated the environmental health status of Bir Mcherga dam using zooplankton species. The dam has a capacity of 130 Mm³ and its waters are used for irrigation, water drinking supply, and fishery. Copepods and cladocerans (crustaceans) were collected in situ monthly between October and August 2012. Oxidative stress (CAT, MDA), neurotoxicity (AChE), and genotoxicity (micronucleus test) biomarkers were analyzed in two zooplankton species: Acanthocyclops robustus and Diaphanosoma mongolianum. High values of cells with a micronucleus were observed during summer. AChE activities were inhibited during early winter and summer. The high seasonal variability of CAT and MDA levels indicates that zooplankton is continuously exposed to different oxidative stresses. These results suggest that there is an obvious and continuous multi-faceted stress in Bir Mcherga reservoir and, consequently, an urgent monitoring of freshwater environments in Tunisia is needed, particularly those intended for human consumption and irrigation.

Effect of metals of treated electroplating industrial effluents on antioxidant defense system in the microalga Chlorella vulgaris

The microalga Chlorella vulgaris is one of the prominent and most widely distributed green microalgae found in aquatic environments, often used in toxicity tests due to its sensitivity to various pollutants. To examine the toxicity of metals found in the effluent discharges from an electroplating industry, physicochemical parameters in the microalga C. vulgaris were measured. pH, turbidity, total dissolved solids, color, and the concentrations of metals such as chromium (1.97 mg/L), mercury (104.2 mg/L), and zinc (167.25 mg/L) were found exceeding the permissible limits. Several endpoints such as total protein content, reactive oxygen species (ROS) production, photosynthetic pigment contents, and antioxidant enzymatic activities, including those of superoxide dismutase (SOD) and catalase (CAT), were measured in C. vulgaris in response to treated electroplating industrial effluent (TEPIE). In addition, concentration-dependent morphological changes were also observed in response to TEPIE. Under both acute and chronic TEPIE exposure, increase in the ROS level was observed indicating increased production of ROS in C. vulgaris cells. The total protein and chlorophyll contents were found to be gradually decreasing in an effluent concentration-dependent manner. Moreover, lower concentrations of effluent stimulated the antioxidant enzyme systems. A concentration-dependent increase was observed in both SOD and CAT enzymatic activities. The results indicated toxic impairments by the effluent on the function of C. vulgaris in response to both acute and chronic exposure, indicating an urgent need of proper treatment processes/modification of the existing one of TEPIE, with continuous monitoring of the discharge of the pollutants into the aquatic ecosystems using biological assays.

Dose- and age-specific antioxidant responses of the mysid crustacean Neomysis awatschensis to metal exposure

Waterborne metals can adversely affect an organism's innate defenses through oxidative stress. In the present study, the marine mysid Neomysis awatchensis was exposed to sublethal concentrations (1/10 and 1/5 of the median LC50s) of As, Cd, Cu, Pb, and Zn for 48 or 96 h at the juvenile and adult developmental stages, and the dose- and age-specific antioxidant defense system responses were characterized. Metal accumulation and modulation of four key antioxidant biomarkers, malondialdehyde (MDA), glutathione (GSH), superoxide dismutase, and catalase, were measured in juvenile and adult mysids. Based on LC50, level of metal toxicity was dependent on metal concentration, developmental stage, and the exposure duration. Intracellular MDA content was increased in the As-, Cu-, Pb-, and Zn-exposed juvenile mysids after exposure for 48 and/or 96 h, while increases in MDA content were observed in adult mysids following Cu and Zn exposure. Interestingly, GSH content was differentially modulated, where intracellular GSH levels decreased in juvenile mysids following Cd, Cu, Pb, and Zn exposure, but significantly increased in metal-exposed adult mysids, except for Pb exposure. The catalase and superoxide dismutase activities displayed similar stage-specific increases or decreases as also observed for the different GSH levels, suggesting that the susceptibility to and defense against metal-induced oxidative stress differed based on stage. Modulations in MDA and GSH content and enzymatic activity of the antioxidant defense system indicate that mysid antioxidant defense system factors are intimately connected during control of oxidative imbalances with different capacities at different developmental stages.

Bioaccumulation and physiological effects of copepods sp. (Eucyclop sp.) fed Chlorella ellipsoides exposed to titanium dioxide (TiO2) nanoparticles and lead (Pb2+)

The demand for manufactured products and the derivatives of nanomaterials and non essential metals continue to increase, and as a consequence their presence in fisheries and aquaculture has therefore become a major concern for the risks to which our environment is exposed. The bioaccumulation profile of binary compounds (Titanium dioxide nanoparticles and lead) and their effects on the feeding behaviour of copepods were assessed in a simplified food chain including, the freshwater alga Chlorella ellipsoides and the cyclopoids copepods sp. Our results indicated that Pb and TiO₂ NPs individually and mixed can be transferred from alga to copepods via dietary pathway. The highest bioconcentration factor (748.5) was recorded for Pb in the combined compounds (Pb15 + Ti16.5) μg L^-1 and the highest BCF (5.57) recorded for TiO₂ NPs was found in TiO₂ NPs (16.5) alone. Ingestion and filtration rate decreased significantly (p < 0.05) in all treatments. Analysis of variance (ANOVA) showed that the combination of these metals significantly (p < 0.05) decreased ingestion and filtration rate. In addition, the individual compounds and their combinations significantly (p < 0.05) increased carbohydrate and total lipid content. The antioxidant activities showed significant (p < 0.05) effect of Glutathione peroxidase (GPx), Glutathione reductase (GR), catalase (CAT) however, SOD and MDA were not significant (p > 0.05) in both single and binary treatments. The results demonstrate that the co-exposure of TiO₂ NPs and Pb inhibit the ingestion and filtration of microalgae by cyclopoid copepods sp. and also induce increase of carbohydrate, lipid; GPx, GR and CAT due to stress.

The combined effects of elevated pCO2 and food availability on Tigriopus japonicus Mori larval development, reproduction, and superoxide dismutase activity

Previous studies have shown that ocean acidification has little effect on adult Tigriopus japonicus copepods, and mainly impairs the early development and reproduction of females. This study investigated the possible interactive effect between CO₂-induced seawater acidification and food availability on larval development and reproductive output in T. japonicus. Copepods were exposed to either pH8.1 or pH7.3 under different food concentrations (0.5×10⁴-80.0×10⁴cells/mL). Both the development of nauplii and copepodites was delayed at pH7.3 with a greater effect at lower food concentrations. The reproductive output followed a bell-shaped curve with the highest reproductive output at food concentrations between 30×10⁴ and 40×10⁴cells/mL. As an indicator of oxidative stress, the activity of superoxide dismutase increased at lower pH, with a greater increase at lower food concentrations. Therefore, the effect of elevated pCO₂ on T. japonicus was food dependent.

Oxidative damage of 18S and 5S ribosomal RNA in digestive gland of mussels exposed to trace metals

Numerous studies have shown the ability of trace metals to accumulate in marine organisms and cause oxidative stress that leads to perturbations in many important intracellular processes, including protein synthesis. This study is mainly focused on the exploration of structural changes, like base modifications, scissions, and conformational changes, caused in 18S and 5S ribosomal RNA (rRNA) isolated from the mussel Mytilus galloprovincialis exposed to 40μg/L Cu, 30μg/L Hg, or 100μg/L Cd, for 5 or 15days. 18S rRNA and 5S rRNA are components of the small and large ribosomal subunit, respectively, found in complex with ribosomal proteins, translation factors and other auxiliary components (metal ions, toxins etc). 18S rRNA plays crucial roles in all stages of protein synthesis, while 5S rRNA serves as a master signal transducer between several functional regions of 28S rRNA. Therefore, structural changes in these ribosomal constituents could affect the basic functions of ribosomes and hence the normal metabolism of cells. Especially, 18S rRNA along with ribosomal proteins forms the decoding centre that ensures the correct codon-anticodon pairing. As exemplified by ELISA, primer extension analysis and DMS footprinting analysis, each metal caused oxidative damage to rRNA, depending on the nature of metal ion and the duration of exposure. Interestingly, exposure of mussels to Cu or Hg caused structural alterations in 5S rRNA, localized in paired regions and within loops A, B, C, and E, leading to a continuous progressive loss of the 5S RNA structural integrity. In contrast, structural impairments of 5S rRNA in mussels exposed to Cd were accumulating for the initial 5days, and then progressively decreased to almost the normal level by day 15, probably due to the parallel elevation of metallothionein content that depletes the pools of free Cd. Regions of interest in 18S rRNA, such as the decoding centre, sites implicated in the binding of tRNAs (A- and P-sites) or translation factors, and areas related to translation fidelity, were found to undergo significant metal-induced conformational alterations, leading either to loosening of their structure or to more compact folding. These modifications were associated with parallel alterations in the translation process at multiple levels, a fact suggesting that structural perturbations in ribosomes, caused by metals, pose significant hurdles in translational efficiency and fidelity.

Assessing the relevance of a multiplexed methodology for proteomic biomarker measurement in the invertebrate species Gammarus fossarum: A physiological and ecotoxicological study

Recently, a protein sequence database was built specifically for the sentinel non-model species Gammarus fossarum using a proteogenomics approach. A quantitative multiplexed targeted proteomics assay (using Selected Reaction Monitoring mass spectrometry) was then developed for a fast and simultaneous quantification of dozens of biomarker peptides specific of this freshwater sentinel crustacean species. In order to assess the relevance of this breakthrough methodology in ecotoxicology, the response patterns of a panel of 26 peptides reporting for 20 proteins from the Gammarus fossarum proteome with putative key functional roles (homeostasis, osmoregulation, nutrition, reproduction, molting,…) were recorded through male and female reproductive cycles and after exposure to environmental concentrations of cadmium and lead in laboratory-controlled conditions. Based on these results, we validated the implication of annotated vtg-like peptides in the oogenesis process, and the implication of Na⁺/K⁺ ATPase proteins in the molt cycle of organisms. Upon metal (cadmium and lead) contamination, peptides belonging to proteins annotated as involved in antioxidant and detoxification functions, immunity and molting were significantly down-regulated. Overall, this multiplex assay allowed gaining relevant insights upon disruption of different main functions in the sentinel species Gammarus fossarum. This breakthrough methodology in ecotoxicology offers a valid and high throughput alternative to currently used protocols, paving the way for future practical applications of proteogenomics-derived protein biomarkers in chemical risk assessment and environmental monitoring.

Toxicity assessment of cadmium chloride on planktonic copepods Centropages ponticus using biochemical markers

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Ecotoxicological effects of cadmium chloride were tested in planktonic copepods Centropages ponticus.

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Cadmium chloride toxicity influenced enzymatic activity and proteins synthesis in treated groups.

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Synthesis of proteins, together with changes in antioxidant enzymes activity, could be used as biomarkers for further studies of copepods species.

Pollution of the aquatic environment by heavy metals has become a worldwide problem. Most heavy metals exhibit toxic waste on aquatic organisms. Cadmium (Cd) is a highly toxic metal which affects aquatic organisms acutely and chronically. Planktonic calanoid copepods are the secondary dominant producers of pelagic ecosystems and play a considerable role in the transfer of energy and organic matter from primary producers to higher trophic levels. We investigated the effect of cadmium chloride on biochemical responses of the planktonic calanoid copepods Centropages ponticus which is a key species in the Mediterranean Sea. The response of copepods to cadmium chloride was examined under laboratory-controlled conditions during a 72-h exposure. Catalase (CAT), Glutathion Reductase (GR), Glutathione Peroxidase (GPx), Glutathione-S-Transferase (GST) and Acetylcholinesterase (AChE) were analyzed for cadmium chloride treatments (0, 0.2 and 0.4 μg/L) after 24, 48 and 72 h. Additionally, the thiobarbituric reactive species assay was used to evaluate lipid peroxidation (LPO) level of the copepod. In this study, it is observed that contents of protein increased gradually with an increase in concentrations of metals and exposure time. Our findings showed that cadmium chloride directly influenced malondialdehyde (MDA) levels in the treated copepods hinting that the copepods had suffered from oxidative damage. During exposure, the Cd treatments significantly influenced the biochemical markers (CAT, GR, GPx, GST and AChE). Thus, Centropages ponticus could be used as a suitable bioindicator of exposure to Cd using biochemicals markers.

Combined effects of temperature and metal exposure on the fatty acid composition of cell membranes, antioxidant enzyme activities and lipid peroxidation in yellow perch (Perca flavescens)

The aim of this study was to investigate the combined effects of temperature and metal contamination (cadmium and nickel) on phospholipid fatty acid composition, antioxidant enzyme activities and lipid peroxidation in fish. Yellow perch were acclimated to two different temperatures (9°C and 28°C) and exposed either to Cd or Ni (respectively 4μg/L and 600μg/L) for seven weeks. Superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase activities and glutathione concentration were measured as indicators of antioxidant capacities, while malondialdehyde concentration was used as an indicator of lipid peroxidation. Poikilotherms including fish counteract the effects of temperature on phospholipid fatty acid ordering by remodelling their composition to maintain optimal fluidity. Accordingly, in our study, the fatty acid composition of yellow perch muscle at 9°C was enhanced in monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) compared to fish maintained at 28°C, in agreement with the theory of homeoviscous adaptation. Using ratios of various fatty acids as surrogates for desaturase and elongase activities, our data suggests that modification of the activity of these enzymes is responsible for the thermal acclimation of phospholipid fatty acid profiles. However, this response was altered under Ni and Cd exposure: PUFA decreased (specifically n-6 PUFA) while the proportion of saturated fatty acids increased at 9°C, whereas at 28°C, PUFA increased to proportions exceeding those observed at 9°C. Lipid peroxidation could be observed under all experimental conditions. Both enzymatic and non-enzymatic antioxidant defense systems acted cooperatively to cope with oxidative stress leading to lipid peroxidation, which was not affected by temperature acclimation as indicated by malondialdehyde concentration, in spite of a higher polyinsaturation in cold-acclimated fish which would be predicted to increase their vulnerability to peroxidation. However, in warm-acclimated, Ni-exposed fish, in which the highest proportion of PUFA was observed, lower concentrations of malondialdehyde were measured, suggesting an overcompensation of antioxidant mechanisms in these fish which could represent a substantial metabolic cost and explain their lower condition.

N-Acetyl-β-D-glucosaminidase activity in feral Carcinus maenas exposed to cadmium

Cadmium is a priority hazardous substance, persistent in the aquatic environment, with the capacity to interfere with crustacean moulting. Moulting is a vital process dictating crustacean growth, reproduction and metamorphosis. However, for many organisms, moult disruption is difficult to evaluate in the short term, what limits its inclusion in monitoring programmes. N-acetyl-β-D-glucosaminidase (NAGase) is an enzyme acting in the final steps of the endocrine-regulated moulting cascade, allowing for the cast off of the old exoskeleton, with potential interest as a biomarker of moult disruption. This study investigated responses to waterborne cadmium of NAGase activity of Carcinus maenas originating from estuaries with different histories of anthropogenic contamination: a low impacted and a moderately polluted one. Crabs from both sites were individually exposed for seven days to cadmium concentrations ranging from 1.3 to 2000 μg/L. At the end of the assays, NAGase activity was assessed in the epidermis and digestive gland. Detoxification, antioxidant, energy production, and oxidative stress biomarkers implicated in cadmium metabolism and tolerance were also assessed to better understand differential NAGase responses: activity of glutathione S-transferases (GST), glutathione peroxidase (GPx) glutathione reductase (GR), levels of total glutathiones (TG), lipid peroxidation (LPO), lactate dehydrogenase (LDH), and NADP(+)-dependent isocitrate dehydrogenase (IDH). Animals from the moderately polluted estuary had lower NAGase activity both in the epidermis and digestive gland than in the low impacted site. NAGase activity in the epidermis and digestive gland of C. maenas from both estuaries was sensitive to cadmium exposure suggesting its usefulness for inclusion in monitoring programmes. However, in the digestive gland NAGase inhibition was found in crabs from the less impacted site but not in those from the moderately contaminated one. Altered glutathione levels were observed in cadmium-treated crabs from the contaminated site possibly conferring enhanced tolerance to these animals through its chelator action. Investigation of enhanced tolerance should thus be accounted for in monitoring programmes employing NAGase as biomarker to avoid data misinterpretation.

Heavy metals induce oxidative stress and trigger oxidative stress-mediated heat shock protein (hsp) modulation in the intertidal copepod Tigriopus japonicus

Heat shock proteins (hsps) are induced by a wide range of environmental stressors including heavy metals in aquatic organisms. However, the effect of heavy metals on zooplankton at the molecular level remains still unclear. In this study, we measured the intracellular reactive oxygen species (ROS) level and the antioxidant enzyme activities for 96 h after exposure to five heavy metals: arsenic (As), cadmium (Cd), copper (Cu), silver (Ag), and zinc (Zn) in the intertidal copepod Tigriopus japonicus. Activities of the antioxidant enzymes were highly elevated in metal-exposed copepods, indicating that heavy metals can induce oxidative stress by generating ROS, and stimulate the involvement of antioxidant enzymes as cellular defense mechanisms. Subsequently, transcriptional changes in hsp gene families were further investigated in the metal-exposed groups for 96 h. The ROS level and glutathione (GSH) content were significantly increased in Ag-, As-, and Cu-exposed copepods, while they were only slightly elevated in Cd- and Zn-exposed groups. Based on the numbers of significantly modulated hsp genes and their expression levels for 96 h, we measured the effect of heavy metals to stress genes of T. japonicus in the following order: Cu > Zn > Ag > As > Cd, implying that Cu acts as a stronger oxidative stress inducer than other heavy metals. Of them, the expression of hsp20 and hsp70 genes was substantially modulated by exposure to heavy metals, indicating that these genes would provide a sensitive molecular biomarker for aquatic monitoring of heavy metal pollution.

Changes of polyamine pattern in digestive glands of mussel Mytilus galloprovincialis under exposure to cadmium

Polyamines, in particular spermidine and spermine, have been identified as important antioxidants, highly induced by oxidative stress in a variety of organisms. However, little is known about changes in polyamine content of metal-stressed marine organisms. In the present study, mussels (Mytilus galloprovincialis) were experimentally exposed to 25 μg/L Cd(2+) or 100 μg/L Cd(2+) for up to 15 days. Cd(2+) was progressively accumulated in mussel tissues, leading to a characteristic oxidative-stress status. Free putrescine (PUT) production was noticeably induced in response to Cd(2+) at day 5 and then declined. In contrast, free spermidine (SPD) content was gradually reduced, whereas the concentration of free spermine (SPM) increased. In combination, these changes led to a 69% or 88% reduction in the ratio of (SPD+SPM)/PUT at day 5, dependent on the Cd(2+) concentration used, which subsequently followed an upward trend in values, albeit not reaching those of controls. Conjugated polyamines constantly increased, in particular conjugated spermidine and spermine, tagging along with metallothionein production. Acetylated polyamines showed a diverse profile of changes, but their content was generally kept at low levels throughout the exposure period. Collectively, our results suggest that certain polyamine compounds could play a significant role in the tolerance of mussels against Cd(2+)-mediated stress, and that the ratio (SPD+SPM)/PUT could be a good indicator of the metal-stress status.

Mitochondrial gene expression, antioxidant responses, and histopathology after cadmium exposure

The present study investigates cadmium effects on the transcription of mitochondrial genes of Procambarus clarkii after acute (0.05, 0.5, and 5 mg Cd/L; 4-10 days) and chronic exposures (10 μg Cd/L; 30-60 days). Transcriptional responses of cox1, atp6, and 12S using quantitative real-time RT-PCR were assessed in gills and hepatopancreas. Additionally, the expression levels of genes involved in detoxification and/or oxidative stress responses [mt, sod(Mn)] and enzymatic activities of antioxidants (SOD, CAT, GPX, and GST) were analyzed. The histopathological effects in hepatopancreas of crayfish were evaluated by light microscopy. Relationships between endpoints at different levels of biological organization and Cd bioaccumulation were also examined. Cd induced high levels of bioaccumulation, which was followed by mitochondrial dysfunction and histological alterations in both experiments. Moreover, perturbations in the defence mechanisms against oxidative stress tended to increase with time. Results also showed that molecular responses can vary depending on the intensity and duration of the chemical stress applied to the organisms and that the study of mt gene expression levels seemed to be the best tool to assess Cd intoxication.

Role of crustacean hyperglycemic hormone (CHH) in the environmental stressor-exposed intertidal copepod Tigriopus japonicus

To identify and characterize CHH (TJ-CHH) gene in the copepod Tigriopus japonicus, we analyzed the full-length cDNA sequence, genomic structure, and promoter region. The full-length TJ-CHH cDNA was 716 bp in length, encoding 136 amino acid residues. The deduced amino acid sequences of TJ-CHH showed a high similarity of the CHH mature domain to other crustaceans. Six conserved cysteine residues and five conserved structural motifs in the CHH mature peptide domain were also observed. The genomic structure of the TJ-CHH gene contained three exons and two introns in its open reading frame (ORF), and several transcriptional elements were detected in the promoter region of the TJ-CHH gene. To investigate transcriptional change of TJ-CHH under environmental stress, T. japonicus were exposed to heat treatment, UV-B radiation, heavy metals, and water-accommodated fractions (WAFs) of Iranian crude oil. Upon heat stress, TJ-CHH transcripts were elevated at 30 °C and 35 °C for 96 h in a time-course experiment. UV-B radiation led to a decreased pattern of the TJ-CHH transcript 48 h and more after radiation (12 kJ/m(2)). After exposure of a fixed dose (12 kJ/m(2)) in a time-course experiment, TJ-CHH transcript was down-regulated in time-dependent manner with a lowest value at 12h. However, the TJ-CHH transcript level was increased in response to five heavy metal exposures for 96 h. Also, the level of the TJ-CHH transcript was significantly up-regulated at 20% of WAFs after exposure to WAFs for 48 h and then remarkably reduced in a dose-dependent manner. These findings suggest that the enhanced TJ-CHH transcript level is associated with a cellular stress response of the TJ-CHH gene as shown in decapod crustaceans. This study is also helpful for a better understanding of the detrimental effects of environmental changes on the CHH-triggered copepod metabolism.

Effects of multigenerational cadmium exposure of insects (Spodoptera exigua larvae) on anti-oxidant response in haemolymph and developmental parameters

Biochemical and organismal indices of metal tolerance were studied in Spodoptera exigua exposed to a cadmium-contaminated diet for one or many (33 or 61) generations. Reduced and oxidised glutathione, protein thiols, total anti-oxidant capacity level, glutathione transferase activity, and Cd accumulation were assayed in the haemolymph of the last instar larvae. The cadmium concentration in the whole larval body as well as larval survival, larval duration time and last instar body weight were also measured. Elevated cadmium concentration in the whole body, higher mortality and longer duration of the larval stage in one-generation exposed insects in comparison with those exposed for many generations suggest that metal tolerance builds over time. For the larvae from multigeneration metal treatment, the higher cadmium concentration in larval haemolymph positively correlated with glutathione oxidation and total anti-oxidant capacity. One-generation exposed insects had lower metal concentration in haemolymph than did 33-generation exposed insects.