Inhibition of goldfish mitochondrial metabolism by in vitro exposure to Cd, Cu and Ni

Combined Effects of Fluoride and Arsenic on Mitochondrial Function in the Liver of Rat

Biochemical and/or molecular mechanisms of arsenic or fluoride toxicity in experimental animals have been widely investigated in the recent past. However, their combined effects on target cells/organelle are poorly understood. The present study was executed to delineate their combined effects on mitochondrial function in the liver of rat. Female Wistar rats (140 ± 20 g) were force fed individually or in combination with sodium arsenate (4 mg/kg body weight) and sodium fluoride (4 mg/kg body weight) for 90 days. Thereafter, established markers of mitochondrial function viz. mitochondrial lipid peroxidation, oxidative phosphorylation, ATPase, succinic dehydrogenase, and caspase-3 activity were determined. Cytochrome C release and oxidative DNA damage were also estimated in the liver of respective groups of rats. The study showed significant differences in these results amongst the three groups. Observations on parameters viz. LPO, cytochrome-C, caspase-3, and 8-OHdG suggested an antagonistic relationship between these two elements. Results on ATPase, SDH, and ADP:O ratio indicated synergism. It is concluded that AsIII + F in combination may express differential effects on signalling pathways and proapoptotic/antiapoptotic proteins/genes that contribute to liver cell death. Interaction of As and F with mitochondria.

A first study on the bioaccumulation of trace metals in Rhyssoplax olivacea (Mediterranean Polyplacophora)

This study investigates, for the first time, the bioaccumulation of trace metals in the chiton Rhyssoplax olivacea. Fe, Cu, Co, Cr and Cd were measured in the shell and soft tissue of R. olivacea sampled in five sites along the Algerian west coast during the cold and hot seasons. Physiological and contamination indices were calculated. The condition index provides information on habitat quality and on R. olivacea reproductive performance and physiological status. The metal/shell-weight index informs on the bioavailability of trace metals. The trace element pollution index is used to assign a global contamination status to the studied sites. The trace element spatial variation index ranks Cd and Cr as trace metals of primary environmental concern based on the overall variability of their levels. An exhaustive review compiling data on trace element bioaccumulation in chitons is performed. The potential use of R. olivacea as bioindicator species is discussed.

Thermal modulation of mitochondrial function is affected by environmental nickel in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the combined effects of temperature and nickel (Ni) contamination on liver mitochondria electron transport system (ETS) enzymes, citrate synthase (CS), phospholipid fatty acid composition and lipid peroxidation in rainbow trout (Oncorhynchus mykiss). Juvenile trout were acclimated for two weeks to two different temperatures (5˚C and 15˚C) and exposed to nickel (Ni; 520 μg/L) for three weeks. Using ratios of ETS enzymes and CS activities, our data suggest that Ni and an elevated temperature acted synergistically to induce a higher capacity for reduction status of the ETS. The response of phospholipid fatty acid profiles to thermal variation was also altered under nickel exposure. In control conditions, the proportion of saturated fatty acids (SFA) was higher at 15˚C than at 5˚C, while the opposite was observed for monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). However, in nickel contaminated fish, the proportion of SFA was higher at 5˚C than at 15˚C, while PUFA and MUFA followed the opposite direction. A higher PUFA ratio is associated with higher vulnerability to lipid peroxidation. Thiobarbituric Acid Reactive Substances (TBARS) content was higher when the PUFA were in higher proportions, except for Ni-exposed, warm-acclimated fish, in which we reported the lowest level of TBARS but the highest proportion of PUFA. We suspect that the interaction of nickel and temperature on lipid peroxidation is due to their synergistic effects on aerobic energy metabolism, as supported by the decrease in the activity of complex IV of the ETS enzyme activity in those fish, or on antioxidant enzymes and pathways. Overall, our study demonstrates that Ni exposure in heat-challenged fish can lead to the remodelling of the mitochondrial phenotype and potentially stimulate alternative antioxidant mechanisms.

Integration of proteomic and metabolomic analyses: New insights for mapping informal workers exposed to potentially toxic elements

Occupational exposure to potentially toxic elements (PTEs) is a concerning reality of informal workers engaged in the jewelry production chain that can lead to adverse health effects. In this study, untargeted proteomic and metabolomic analyses were employed to assess the impact of these exposures on informal workers' exposome in Limeira city, São Paulo state, Brazil. PTE levels (Cr, Mn, Ni, Cu, Zn, As, Cd, Sn, Sb, Hg, and Pb) were determined in blood, proteomic analyses were performed for saliva samples (n = 26), and metabolomic analyses in plasma (n = 145) using ultra-high performance liquid chromatography (UHPLC) coupled with quadrupole-time-of-flight (Q-TOF) mass spectrometry. Blood PTE levels of workers, controls, and their family members were determined by inductively coupled plasma-mass spectrometry (ICP-MS). High concentration levels of Sn and Cu were detected in welders' blood (p < 0.001). Statistical analyses were performed using MetaboAnalyst 4.0. The results showed that 26 proteins were upregulated, and 14 proteins downregulated on the welder group, and thirty of these proteins were also correlated with blood Pb, Cu, Sb, and Sn blood levels in the welder group (p < 0.05). Using gene ontology analysis of these 40 proteins revealed the biological processes related to the upregulated proteins were translational initiation, SRP-dependent co-translational protein targeting to membrane, and viral transcription. A Metabolome-Wide Association Study (MWAS) was performed to search for associations between blood metabolites and exposure groups. A pathway enrichment analysis of significant features from the MWAS was then conducted with Mummichog. A total of 73 metabolomic compounds and 40 proteins up or down-regulated in welders were used to perform a multi-omics analysis, disclosing seven metabolic pathways potentially disturbed by the informal work: valine leucine and isoleucine biosynthesis, valine leucine and isoleucine degradation, arginine and proline metabolism, ABC transporters, central carbon metabolism in cancer, arachidonic acid metabolism and cysteine and methionine metabolism. The majority of the proteins found to be statistically up or downregulated in welders also correlated with at least one blood PTE level, providing insights into the biological responses to PTE exposures in the informal work exposure scenario. These findings shed new light on the effects of occupational activity on workers' exposome, underscoring the harmful effects of PTE.

Impact of nickel mining in New Caledonia on marbled eels Anguilla marmorata

New Caledonia is particularly affected by nickel open pit mining activities because of the presence of ultramafic soils rich in metals. The particles dispersed by atmospheric transport and soil erosion during the excavation of nickel end up by deposition or leaching in rivers where they may be bioaccumulated by organisms living downstream the mines. Despite alarming freshwater metals concentrations, no study investigated the level of their bioaccumulation in eels, and if high bioaccumulation levels occur, the potential consequences on their health. The aim of this study was to determine how eels Anguilla marmorata are impacted in situ by metals issued from mining activity by measuring: morphometric parameters; metal concentrations in tissues and organs and transcription levels of target genes encoding proteins involved in several metabolic key functions. Among organs, liver was found to be the most affected by mining with average nickel concentrations of 5.14 mg/kg versus 1.63 mg/kg for eels away from mines leading to dysregulation of numerous genes involved in oxidative stress, DNA repair, apoptosis, reproduction and both lipid and mitochondrial metabolisms. This study should allow us to define in an integrated way if metals released by mining activities influence metals bioaccumulation in eels and induce biological effects.

Effects of waterborne cadmium exposure on Spinibarbus sinensis hepatopancreas and kidney: Mitochondrial cadmium accumulation and respiratory metabolism

To examine the relationship between heavy metal accumulation in mitochondria and their respiration function in fish during in vivo exposure, juvenile Spinibarbus sinensis were exposed to different waterborne cadmium (Cd) concentrations for up to 28 days. We measured the state III respiration rate and cytochrome c oxidase (CCO) activity of mitochondria in hepatopancreas and kidney and the accumulated Cd concentrations in mitochondria and heat-stable protein (HSP) fractions. Dose- and time-dependent Cd accumulation occurred at different levels in both organs, but was lower in hepatopancreas. When hepatopancreas mitochondrial Cd concentrations in Cd-exposed groups were > 5.5 μg/g dwt, their state III respiration rates were significantly lower than the control. CCO activity of hepatopancreas mitochondria exhibited decreasing dose- and time-dependent trends. However, kidney mitochondria respiratory activities were not affected significantly by Cd exposure. Cd concentrations in kidney HSP fraction were 2-5 times higher than in hepatopancreas under all exposure conditions, and were mainly present as non-deleterious metallothionein (MT)-Cd complexes. These results suggest that Cd accumulation occurred in hepatopancreas and kidney mitochondria of S. sinensis following waterborne Cd exposure, which significantly inhibited the respiration function of hepatopancreas mitochondria but did not have a deleterious effect on kidney mitochondria. The inhibitory pattern of hepatopancreas mitochondrial Cd concentrations related to function exhibited threshold and saturation effects, suggesting the capacity of S. sinensis to manage Cd toxicity. The difference in the relative proportion of Cd occurring as MT-Cd complexes in organs likely causes the organ-specific effects of Cd on hepatopancreas and kidney mitochondrial function.

"Nanosize effect" in the metal-handling strategy of the bivalve Scrobicularia plana exposed to CuO nanoparticles and copper ions in whole-sediment toxicity tests

To date, the occurrence, fate and toxicity of metal-based NPs in the environment is under investigated. Their unique physicochemical, biological and optical properties, responsible for their advantageous application, make them intrinsically different from their bulk counterpart, raising the issue of their potential toxic specificity or "nanosize effect". The aim of this study was to investigate copper bioaccumulation, subcellular distribution and toxic effect in the marine benthic species Scrobicularia plana exposed to two forms of sediment-associated copper, as nanoparticles (CuO NPs) and as soluble ions (CuCl₂). Results showed that the exposure to different copper forms activated specific organism's metal handling strategies. Clams bioaccumulated soluble copper at higher concentrations than those exposed to sediment spiked with CuO NPs. Moreover, CuO NPs exposure elicited a stronger detoxification response mediated by a prompt mobilization of CuO NPs to metal-containing granules as well as a delayed induction of MT-like proteins, which conversely, sequestered soluble copper since the beginning of the exposure at levels significantly different from the control. Eventually, exposure to high concentrations of either copper form led to the same acute toxic effect (100% mortality) but the outcome was delayed in bivalves exposed to CuO NPs suggesting that the mechanisms underlying toxicity were copper form-specific. Indeed, while most of soluble copper was associated to the mitochondrial fraction suggesting an impairment of the ATP synthesis capacity at mitochondrial level, CuO NPs toxicity was most likely caused by the oxidative stress mediated by their bioaccumulation in the enzymatic and mitochondrial metabolically available fractions.

Metabolic status of the coral Mussismilia harttii in field conditions and the effects of copper exposure in vitro

It is widely known that metals can alter enzyme functioning, however, little is known about the mechanisms of metal toxicity in energy metabolism enzymes of corals. Thus, the present study had two objectives: firstly, we evaluated the activity of eight metabolic enzymes of the coral Mussismilia harttii to clarify metabolic functioning under field conditions. After that, we investigated the in vitro effect of copper (Cu) exposure in the activity of an enzyme representative of each metabolism stage. We evaluated enzymes involved in glycolysis (hexokinase, HK; phosphofructokinase, PFK; pyruvate kinase, PK and lactate dehydrogenase, LDH), Krebs cycle (citrate synthase, CS and isocitrate dehydrogenase, IDH), electron transport chain (electron transport system activity, ETS) and pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH). The in vitro tests were performed through contamination of the reaction medium using Cu concentrations of 0, 1.4, 3.7 and 14.2 μg L^-1. The results showed that M. harttii has elevated activity of HK, PK and CS in field conditions compared to the activity of other energy metabolism enzymes evaluated. Moreover, lower activities of LDH and ETS in exposed samples were observed. In conclusion, in field conditions this species has elevated aerobic metabolism and glucose may be an important energetic fuel. Also, exposure to Cu in vitro caused inhibition of LDH and ETS by direct binding.

Copper exposure alters the metabolism of the blue crab Callinectes sapidus submitted to osmotic shock

Copper (Cu) is an essential metal capable to alter many metabolic and physiological processes in animal species, depending on the environmental concentration and salinity. The present study evaluated the effects of Cu exposure on the metabolism of the blue crab Callinectes sapidus under different osmotic situations. Crabs were acclimated at two different salinities conditions (30 and 2). Subsequently, they were exposed to Cu during 96 h at each salinity and under hypo-osmotic shock. Results demonstrated that Cu exposure increased whole-body oxygen consumption. In addition, the activity of LDH decreased while citrate synthase increased in anterior gills from animals submitted to hypo-osmotic shock. This scenario indicates extra stress caused by sudden environmental osmotic changes, as commonly observed in estuarine environments, when combined with copper exposure. Therefore, the activity of LDH and citrate synthase enzymes might be sensitive indicators for aquatic toxicology studies approaching Cu contamination in estuarine environments.

Life-time exposure to waterborne copper IV: Sperm quality parameters are negatively affected in the killifish Poecilia vivipara

In previous studies, we have shown that copper (Cu) is significantly accumulated in various tissues of killifish Poecilia vivipara following chronic exposure. Also, we showed that chronic metal exposure disrupted energy production and growth in this species. In the present study, we aimed to evaluate if chronic exposure to this metal could also affect reproductive parameters of P. vivipara males (sperm quality). In order to test that, newborn (<24 h-old) fish were exposed to two concentrations of waterborne Cu (5 and 9 μg/L) for 345 days. After exposure, fish were euthanized and the testes were collected for sperm analysis. We could observe that exposed animals had reduced sperm motility and period of motility. Also, the sperm of exposed fish had reduced plasma membrane integrity, mitochondrial functionality and DNA integrity when compared to sperm of control animals. It is suggested that the well-known association of Cu with elevated oxidative damage, endocrine disruption and energetic disturbance are involved with the observed outcomes. The results obtained in the present study show that chronic exposure to environmentally relevant concentrations of waterborne Cu caused reductions in all parameters used to evaluate sperm quality. Therefore, it is concluded that life-time exposure to this metal may disrupt fish reproduction and negatively affect the maintenance of its populations.

Life-time exposure to waterborne copper III: Effects on the energy metabolism of the killifish Poecilia vivipara

Copper ions (Cu) are essential to life maintenance, nonetheless, elevated concentrations can be hazardous. Acute and sub-chronic toxic effects of this metal are well known and are usually related to enzymatic inhibition, elevated ROS production and dysfunction of energy metabolism. Despite that, chronic studies are extremely rare. Therefore, the aim of this study was to assess the effects of chronic exposure to 5, 9 and 20 μg/L Cu (28 ad 345 days) on the energy metabolism and survival of the killifish Poecilia vivipara. To accomplish that, we evaluated the activity of enzymes related to aerobic (pyruvate kinase (PK); citrate synthase (CS)) and anaerobic metabolism (lactate dehydrogenase (LDH)) in whole-body (28 days) or in gills, liver and muscle (345 days) of exposed fish. Additionally, whole-body oxygen consumption was evaluated in fish exposed for 28 days and hepatic and muscular expression of genes involved in mitochondrial metabolism (cox I, II and III and atp5a1) was assessed in animals exposed for 345 days. Finally, final survival was evaluated. Following 28 days, Cu did not affect survival neither enzyme activities. However, increased whole-body oxygen consumption was observed in comparison to control condition. After 345 days, 76.8%, 63.9%, 60.9% and 0% survival were observed for control, 5, 9 and 20 μg/L groups, respectively. Animals exposed to 5 and 9 μg/L had a significant reduction in branchial and muscular LDH activity and in hepatic PK activity. Also, exposure to 9 μg/L significantly increased hepatic CS activity. For gene expression, Cu down-regulated muscular cox II (9 μg/L) and III (5 and 9 μg/L), and up-regulated hepatic atp5a1 (9 μg/L). Findings reported in the present study indicate that chronic exposure to Cu induces tissue-specific responses in key aspects of the energetic metabolism. In gills and muscle, Cu leads to reduced energy production through inhibition of anaerobic pathways and mitochondrial respiratory chain. This effect is paralleled by an increased ATP consumption in the liver, characterized by the augmented CS activity and atp5a1 expression. Finally, reduced PK activity indicate that oxidative stress may be involved with the observed outcomes.

Overview of the toxic effects of titanium dioxide nanoparticles in blood, liver, muscles, and brain of a Neotropical detritivorous fish

The toxicity of titanium dioxide nanoparticles (TiO₂ -NP) in the blood, liver, muscle, and brain of a Neotropical detritivorous fish, Prochilodus lineatus, was tested. Juvenile fish were exposed to 0, 1, 5, 10, and 50 mg L^-1 of TiO₂ -NP for 48 hours (acute exposure) or 14 days (subchronic exposure) to evaluate changes in hematology, red blood cell (RBC) genotoxicity/mutagenicity, liver function (reactive oxygen species (ROS) production, antioxidant responses, detoxification, and histopathology), acetylcholinesterase (AChE) activity in muscles and brain, and Ti bioaccumulation. TiO₂ -NP did not cause genetic damage to RBC, but acutely decreased white blood cells (WBC) and increased monocytes. Subchronically, RBC decreased, mean cell volume and hemoglobin increased, and WBC and lymphocytes decreased. Therefore, NP has the potential to affect immune system and increase energy expenditure, reducing the fish's ability to avoid predator and to resist pathogens. In the liver, acute exposure decreased ROS and increased glutathione (GSH) content, while subchronic exposure decreased superoxide dismutase activity and increased glutathione-S-transferase (GST) activity and GSH content. GSH and GST seem to play an essential role in metabolizing NP and ROS, likely increasing hepatocytes' metabolic rate, which may be the cause of observed cell hypertrophy, disarrangement of hepatic cords and degenerative morphological alterations. Although most studies indicate that the kidney is responsible for metabolizing and/or eliminating TiO₂ -NP, this study shows that the liver also has a main role in these processes. Nevertheless, Ti still accumulated in the liver, muscle, and brain and decreased muscular AChE activity after acute exposure, showing neurotoxic potential. More studies are needed to better understand the biochemical pathways TiO₂ -NP are metabolized and how its bioaccumulation may affect fish homeostasis and survival in the environment.

Inconsistent responses of liver mitochondria metabolism and standard metabolism in Silurus meridionalis when exposed to waterborne cadmium

We investigated the standard metabolic rate and liver mitochondria metabolism of the southern catfish when exposed to waterborne cadmium. Juvenile southern catfish were exposed to waterborne cadmium concentrations (0, 62.5, 125, 250 and 500 μg/L, respectively) for 8 weeks, and the final body mass, the standard metabolic rate, the state III respiration rate, the activity of cytochrome C oxidase (CCO) of liver mitochondria, and the hepatosomatic index (HSI) were determined. The results showed that the 62.5 μg/L, 125 μg/L, and 250 μg/L experiment groups had a significantly higher standard metabolic rate than that of the control group. Standard metabolic rate in the 500 μg/L experiment group did not differ from the control group. State III respiration rate of liver mitochondria decreased with an increase in cadmium concentration. The 125 μg/L, 250 μg/L, and 500 μg/L experiment groups had a significantly lower state III respiration rate than that of the control group. The activity of CCO in the 500 μg/L experiment group was significantly lower than that of the control group. These results suggest that at low cadmium concentrations, the southern catfish could continuously improve the standard metabolism to provide extra energy in response to the cadmium stress. Cadmium exposures caused damage to the structure and function of liver mitochondria and decreased the activity of mitochondria enzymes, which results in a decrease in the energy of the liver metabolism. The adjustment of the metabolism of liver mitochondria in southern catfish was inconsistent with the adjustment of individual standard metabolism.

Metabolic Costs of Exposure to Wastewater Effluent Lead to Compensatory Adjustments in Respiratory Physiology in Bluegill Sunfish

Municipal wastewater effluent is a major source of aquatic pollution and has potential to impact cellular energy metabolism. However, it is poorly understood whether wastewater exposure impacts whole-animal metabolism and whether this can be accommodated with adjustments in respiratory physiology. We caged bluegill sunfish (Lepomis macrochirus) for 21 days at two sites downstream (either 50 or 830 m) from a wastewater treatment plant (WWTP). Survival was reduced in fish caged at both downstream sites compared to an uncontaminated reference site. Standard rates of O₂ consumption increased in fish at contaminated sites, reflecting a metabolic cost of wastewater exposure. Several physiological adjustments accompanied this metabolic cost, including an expansion of the gill surface area available for gas exchange (reduced interlamellar cell mass), a decreased blood-O₂ affinity (which likely facilitates O₂ unloading at respiring tissues), increased respiratory capacities for oxidative phosphorylation in isolated liver mitochondria (supported by increased succinate dehydrogenase, but not citrate synthase, activity), and decreased mitochondrial emission of reactive oxygen species (ROS). We conclude that exposure to wastewater effluent invokes a metabolic cost that leads to compensatory respiratory improvements in O₂ uptake, delivery, and utilization.

Combined effects of cadmium, temperature and hypoxia-reoxygenation on mitochondrial function in rainbow trout (Oncorhynchus mykiss)

Although aquatic organisms face multiple environmental stressors that may interact to alter adverse outcomes, our knowledge of stressor-stressor interaction on cellular function is limited. We investigated the combined effects of cadmium (Cd), hypoxia-reoxygenation (H-R) and temperature on mitochondrial function. Liver mitochondria from juvenile rainbow trout were exposed to Cd (0-20μM) and H-R (0 and 5min) at 5, 13 and 25°C followed by measurements of mitochondrial Cd load, volume, complex І active (A)↔deactive (D) transition, membrane potential, ROS release and ultrastructural changes. At high temperature Cd exacerbated H-R-imposed reduction of maximal complex I (CI) respiration whereas at low temperature 5 and 10μM stimulated maximal CI respiration post H-R. The basal respiration showed a biphasic response at high temperatures with low Cd concentrations reducing the stimulatory effect of H-R and high concentrations enhancing this effect. At low temperature Cd monotonically enhanced H-R-induced stimulation of basal respiration. Cd and H-R reduced both the P/O ratio and the RCR at all 3 temperatures. Temperature rise alone increased mitochondrial Cd load and toxicity, but combined H-R and temperature exposure reduced mitochondrial Cd load but surprisingly exacerbated the mitochondrial dysfunction. Mitochondrial dysfunction induced by H-R was associated with swelling of the organelle and blocking of conversion of CІ D to A form. However, low amounts of Cd protected against H-R induced swelling and prevented the inhibition of H-R-induced CI D to A transition. Both H-R and Cd dissipated mitochondrial membrane potential Δψ_m and damaged mitochondrial structure. We observed increased reactive oxygen species (H₂O₂) release that together with the protection afforded by EGTA, vitamin E and N-acetylcysteine against the Δψ_m dissipation suggested direct involvement of Cd and oxidative stress. Overall, our findings indicate that mitochondrial sensitivity to Cd toxicity was enhanced by the effects of H-R and temperature, and changes in mitochondrial Cd load did not always explain this effect.

Response of selenium-dependent glutathione peroxidase in the freshwater bivalve Anodonta woodiana exposed to 2,4-dichlorophenol,2,4,6-trichlorophenol and pentachlorophenol

2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) pose a health risk to aquatic organism and humans, and are recognized as persistent priority pollutants. Selenium dependent glutathione peroxidase (Se-GPx) belongs to the family of selenoprotein, which acts mainly as an antioxidant role in the cellular defense system. In the current study, a Se-GPx full length cDNA was cloned from Anodonta woodiana and named as AwSeGPx. It had a characteristic codon at 165TGA167 that corresponds to selenocysteine(Sec) amino acid as U44. The full length cDNA consists of 870 bp, an open reading frame (ORF) of 585 bp encoded a polypeptide of 195 amino in which conserved domain (68LGFPCNQF75) and a glutathione peroxide-1 GPx active site (32GKVILVENVASLUGTT47) were observed. Additionally, the eukaryotic selenocysteine insertion sequence (SECIS) was conserved in the 3'UTR. The AwSeGPx amino acid sequence exhibited a high similarity with that of other Se-GPx. Real-time PCR analysis revealed that AwSeGPx mRNA had a widely distribution, but the highest level was observed in hepatopancreas. AwSeGPx mRNA expression was significantly up-regulated in hepatopancreas, gill and hemocytes after 2,4-DCP, 2,4,6-TCP and PCP exposure. Under similar environment, clams A. woodiana showed a more sensitive to PCP than that of 2,4-DCP and 2,4,6-TCP. These results indicate that AwSeGPx plays a protective role in eliminating oxidative stress derived from 2,4-DCP, 2,4,6-TCP and PCP treatment.

Effects of copper, hypoxia and acute temperature shifts on mitochondrial oxidation in rainbow trout (Oncorhynchus mykiss) acclimated to warm temperature

Temperature fluctuations, hypoxia and metals pollution frequently occur simultaneously or sequentially in aquatic systems and their interactions may confound interpretation of their biological impacts. With a focus on energy homeostasis, the present study examined how warm acclimation influences the responses and interactions of acute temperature shift, hypoxia and copper (Cu) exposure in fish. Rainbow trout (Oncorhynchus mykiss) were acclimated to cold (11°C; control) and warm (20°C) temperature for 3 weeks followed by exposure to environmentally realistic levels of Cu and hypoxia for 24h. Subsequently, mitochondrial electron transport system (ETS) respiratory activity supported by complexes I-IV (CI-IV), plasma metabolites and condition indices were measured. Warm acclimation reduced fish condition, induced aerobic metabolism and altered the responses of fish to acute temperature shift, hypoxia and Cu. Whereas warm acclimation decelerated the ETS and increased the sensitivity of maximal oxidation rates of the proximal (CI and II) complexes to acute temperature shift, it reduced the thermal sensitivity of state 4 (proton leak). Effects of Cu with and without hypoxia were variable depending on the acclimation status and functional index. Notably, Cu stimulated respiratory activity in the proximal ETS segments, while hypoxia was mostly inhibitory and minimized the stimulatory effect of Cu. The effects of Cu and hypoxia were modified by temperature and showed reciprocal antagonistic interaction on the ETS and plasma metabolites, with modest additive actions limited to CII and IV state 4. Overall, our results indicate that warm acclimation came at a cost of reduced ETS efficiency and increased sensitivity to added stressors.

Impairment of mitochondrial energy metabolism of two marine fish by in vitro mercuric chloride exposure

The goal of this work was to understand the extent of mercury toxic effects in liver metabolism under an episode of acute contamination. Hence, the effects of in vitro mercuric chloride in liver mitochondria were assessed in two commercial marine fish: Senegalese sole (Solea senegalensis) and gilthead seabream (Sparus aurata). Liver mitochondria were exposed to 0.2mgL(-1) of mercury, the average concentration found in fish inhabiting contaminated areas. Mercuric chloride depressed mitochondrial respiration state 3 and the maximal oxygen consumption in the presence of FCCP indicating inhibitory effects on the oxidative phosphorylation and on the electron transport chain, respectively. The inhibition of F1Fo-ATPase and succinate-dehydrogenase activities also corroborated the ability of mercury to inhibit ADP phosphorylation and the electron transport chain. This study brings new understanding on the mercury levels able to impair fish mitochondrial function, reinforcing the need for further assessing bioenergetics as a proxy for fish health status.

Assessment of the European flounder responses to chemical stress in the English Channel, considering biomarkers and life history traits

A multi-biomarker approach was developed to evaluate responses of European flounder (Platichthys flesus) in three contrasted estuaries over the English Channel: the Canche (pristine site), Tamar (heavy metals and PAHs contamination) and Seine (heavily pollution with a complex cocktail of contaminants). The condition factor and several biomarkers of the immune system, antioxidant enzymes, energetic metabolism and detoxification processes were investigated in young-of-the-year (0+) and one-year-old (1+) flounder. Results underlined the difference between the pristine site and the Seine estuary which showed a lower condition factor, a modulation of the immune system, a higher Cytochrome C oxidase activity, and an up-regulation of BHMT expression. The moderate biomarker responses in the Tamar fish could be linked to the specific contamination context of this estuary. Flounder life history traits were analyzed by otolith microchemistry, in order to depict how the fish use their habitat and thus respond to chemical stress in estuaries.

Bioassessment of trace element contamination of Mediterranean coastal waters using the seagrass Posidonia oceanica

A large scale survey of the trace element (TE) contamination of Mediterranean coastal waters was performed from the analysis of Ag, As, Cd, Cu, Hg, Ni and Pb in the bioindicator Posidonia oceanica, sampled at 110 sites differing by their levels of exposure to contaminants. The holistic approach developed in this study, based on the combined utilization of several complementary monitoring tools, i.e. water quality scale, pollution index and spatial analysis, accurately assessed the TE contamination rate of Mediterranean coastal waters. In particular, the mapping of the TE contamination according to a new proposed 5-level water quality scale precisely outlined the contamination severity along Mediterranean coasts and facilitated interregional comparisons. Finally, the reliability of the use of P. oceanica as bioindicator species was again demonstrated through several global, regional and local detailed case studies. NB: The designations employed and the presentation of the information in this document do not imply the expression of any opinion whatsoever on the part of the authors concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

Interactions of copper and thermal stress on mitochondrial bioenergetics in rainbow trout, Oncorhynchus mykiss

Thermal stress may influence how organisms respond to concurrent or subsequent chemical, physical and biotic stressors. To unveil the potential mechanisms via which thermal stress modulates metals-induced bioenergetic disturbances, the interacting effects of temperature and copper (Cu) were investigated in vitro. Mitochondria isolated from rainbow trout livers were exposed to a range of Cu concentrations at three temperatures (5, 15 and 25 °C) with measurement of mitochondrial complex I (mtCI)-driven respiratory flux indices and uncoupler-stimulated respiration. Additional studies assessed effects of temperature and Cu on mtCI enzyme activity, induction of mitochondrial permeability transition pore (MPTP), swelling kinetics and mitochondrial membrane potential (MMP). Maximal and basal respiration rates, as well as the proton leak, increased with temperature with the Q10 effects being higher at lower temperatures. The effect of Cu depended on the mitochondrial functional state in that the maximal respiration was monotonically inhibited by Cu exposure while low and high Cu concentrations stimulated and inhibited the basal respiration/proton leak, respectively. Importantly, temperature exacerbated the effects of Cu by lowering the concentration of the metal required for toxicity and causing loss of thermal dependence of mitochondrial respiration. Mitochondrial complex I activity was inhibited by Cu but was not affected by incubation temperature. Compared with the calcium (Ca) positive control, Cu-imposed mitochondrial swelling exhibited variable kinetics depending on the inducing conditions, and was highly temperature-sensitive. A partial reversal of the Cu-induced swelling by cyclosporine A was observed suggesting that it is in part mediated by MPTP. Interestingly, the combination of high Cu and high temperature not only completely inhibited mitochondrial swelling but also greatly increased the respiratory control ratio (RCR) relative to the controls. Copper exposure also caused marked MMP dissipation which was reversed by N-acetyl cysteine and vitamin E suggesting a role of reactive oxygen species (ROS) in this response. Taken together, Cu impairs oxidative phosphorylation in part by inhibiting the electron transport chain (ETC), stimulating proton leak, inducing MPTP and dissipating MMP, with high temperature exacerbating these effects. Thus environmental temperature rise due to natural phenomenon or global climate change may sensitize fish to Cu toxicity by exacerbating mitochondrial dysfunction.

Effects of environmentally relevant concentrations of metallic compounds on the flatfish Scophthalmus maximus: biomarkers of neurotoxicity, oxidative stress and metabolism

Flatfish species, such as the turbot (Scophthalmus maximus), are common targets for toxic effects, since they are exposed through the food chain (ingestion of contaminated preys) and are in direct contact with the waterborne contaminant and sediments. Furthermore, these fish species live in close proximity to interstitial water that frequently dissolves high amounts of contaminants, including metals. Despite this significant set of characteristics, the present knowledge concerning flatfish contamination and toxicity by metals is still scarce. To attain the objective of assessing the effects of metals on a flatfish species, S. maximus specimens were chronically exposed to lead, copper and zinc, at ecologically relevant concentrations, and biochemical (oxidative stress: catalase and glutathione S-transferases activities, and lipid peroxidation; neurotoxicity: cholinesterase activity) parameters were assessed on selected tissues (gills and liver). Copper had no significant effects on all tested parameters; lead was causative of significant increases in liver GSTs activities and also in lipoperoxidation of gill tissue; exposure to zinc caused a significant increase in catalase activity of gill tissue. None of the tested metals elicited noteworthy effects in terms of neurotoxicity. The obtained results showed that only the metal lead is of some environmental importance, since it was able to cause deleterious modifications of oxidative nature at relevant concentrations.

Copper alters the effect of temperature on mitochondrial bioenergetics in rainbow trout, Oncorhynchus mykiss

We investigated the interaction of temperature and copper (Cu) on mitochondrial bioenergetics to gain insight into how temperature fluctuations imposed by natural phenomena or anthropogenic activities would modulate the effects of Cu on cellular energy homeostasis. Mitochondria were isolated from rainbow trout livers and, in the first set of experiments, exposed to Cu (0-2.5 mM) at 5, 11, and 25 °C with measurement of mitochondrial complex II (mtCII)-driven respiration. In the second set of experiments, unenergized mitochondria were incubated for 30 or 60 min with lower concentrations (0-160 μM) of Cu to measure the effects on mtCII enzyme activity. Whereas maximal (state 3) respiration was inhibited by high Cu exposure, low Cu doses stimulated and high Cu doses inhibited resting (state 4) and 4ol (proton leak) respirations. High temperature alone increased mitochondrial respiration in all states. The Q10 values for state 3, state 4, and proton leak respirations suggested active processes with state 4 respiration and proton leak exhibiting greater thermal sensitivity than state 3 respiration. The differential thermal sensitivity of resting relative to phosphorylating mitochondrial state led to uncoupling and limitation of mitochondrial oxidative capacity at both high temperature and doses of Cu. Moreover, exposure to high Cu caused loss of thermal dependence of the mitochondrial bioenergetics culminating in Q10 values well below unity and decreased activation energies (E a) for both maximal and resting respiration rates. In addition, mtCII activity was increased by low and decreased by high doses of Cu indicating that direct effects on this enzyme contribute to Cu-induced mitochondrial dysfunction. Taken together, it appears that the substrate oxidation (electron transport chain and tricarboxylic acid cycle) and proton leak subsystems are targets of the deleterious effects of Cu and increased temperature on mitochondrial bioenergetics. However, mitochondrial effects of Cu and temperature may not be easily distinguished because they are generally qualitatively similar.

Effects of chronic exposure to lead, copper, zinc, and cadmium on biomarkers of the European eel, Anguilla anguilla

Exposure to specific metallic compounds can cause severe deleterious modifications in organisms. Fishes are particularly prone to toxic effects from exposure to metallic compounds via their environment. Species that inhabit estuaries or freshwater environments can be chronically affected by persistent exposure to a large number of metallic compounds, particularly those released by industrial activities. In this study, we exposed yellow eels (European eel, Anguilla anguilla) for 28 days to environmentally relevant concentrations of four specific metals; lead (300, 600, and 1,200 μg/l), copper (40, 120, and 360 μg/l), zinc (30, 60, and 120 μg/l) and cadmium (50, 150, and 450 μg/l). The selected endpoints to assess the toxicological effects were neurotransmission (cholinesterasic activity in nervous tissue), antioxidant defense, and phase II metabolism (glutathione-S-transferase [GST] activity, in both gills and liver tissues), and peroxidative damage. The results showed an overall lack of effects on acetylcholinesterase for all tested metals. Lead, copper, and cadmium exposure caused a significant, dose-dependent, increase in GST activity in gill tissue. However, liver GST only significantly increased following zinc exposure. No statistically significant effects were observed for the thiobarbituric acid reactive substances assay, indicating the absence of peroxidative damage. These findings suggest that, despite the occurrence of an oxidative-based response after exposure to lead, copper, and cadmium, this had no consequence in terms of peroxidative membrane damage; furthermore, cholinergic neurotoxicity caused by lead, copper, and cadmium did not occur. The implications of these results are further discussed.

Sublethal Cd-induced cellular damage and metabolic changes in the freshwater crab Sinopotamon henanense

To explore whether sublethal cadmium (Cd) exposure causes branchial cellular damages and affects the metabolic activity in brachyuran crustaceans, the freshwater crab Sinopotamon henanense was exposed to 0.71, 1.43, and 2.86 mg/L Cd(2+) for 3 weeks. Gill morphology, metabolic activity (activities of isocitrate dehydrogenase (IDH), cytochrome c oxidase (CCO) and lactate dehydrogenase (LDH), mRNA expression of CCO active subunit 1 (cco-1) and ldh, as well as ATP levels) in crab muscle were investigated. The results showed that sublethal Cd exposure caused profound morphological damages in the gills. The branchial epithelial cells were disorganized and vacuolized. Ultrastructurally, a decrease in number of apical microvilli, vacuolized mitochondria, and condensed chromatin were observed in gill epithelial cells. Correspondingly, the Cd exposure also induced downregulations of cco-1 and ldh mRNA expression and reduced activities of IDH, CCO, and LDH, in accordance with the lower ATP level in crab muscle. These results led to the conclusion that gill damage caused by sublethal Cd exposure could lead to an impairment of oxygen uptake of S. henanense, and the inhibition of metabolic activity decreases the oxygen demand of the crab and assists them to survive under the condition of lower oxygen availability. These effects add to our understanding on toxic effects of Cd and survival management of S. henanense subchronically exposed to sublethal Cd.

Effects of anthropogenic metallic contamination on cholinesterases of Gambusia holbrooki

Metal contamination causes multiple biological dysfunctions, including impairment of key physiological functions by targeting enzymes. This feature is a matter of concern, since it may imply significant disturbances in energy allocation, behaviour, reproduction, and survival. Inhibition of the cholinesterase (ChE) activity of aquatic organisms by metals has been described, and systematically used in biomonitoring studies as effect criterion of environmental exposure to these compounds. The present paper addresses the feasibility of using ChE inhibition to quantify the adverse acute and chronic effects of metals (copper, zinc, lead, and cadmium) on nervous tissue of Gambusia holbrooki. With the exception of acute exposure to copper, ChE activity was not significantly impaired. The meanings of the reported findings are further discussed, aiming at a more comprehensive use of this biomarker in environmental assessment. Based on the obtained results, the role of ChE inhibition in environmental metal contamination scenarios should be questioned or even discarded.

Interactive effects of pH and metals on mitochondrial functions of intertidal bivalves Crassostrea virginica and Mercenaria mercenaria

Intertidal bivalves experience broad fluctuations of environmental temperature, pH and oxygen content which could change their intracellular pH. They are also exposed to trace metals such as cadmium (Cd) and copper (Cu) that accumulate in their tissues and may negatively affect mitochondrial functions and bioenergetics. We determined the interactive effects of pH and trace metals (25 μM Cd or Cu) on mitochondrial functions (including respiration and membrane potentials in both ADP-stimulated (state 3) and resting (state 4) states) of two common marine bivalves, the hard clams (Mercenaria mercenaria) and eastern oysters (Crassostrea virginica). In the absence of the trace metals, mitochondrial functions of C. virginica and M. mercenaria were insensitive to pH in a broad physiologically relevant range (6.6-7.8). Mitochondrial respiration was generally suppressed by 25 μM Cd or Cu (with the stronger effects observed for ADP-stimulated compared to the resting respiration) while the mitochondrial membrane potential was unaffected. pH modulated the effects of Cu and Cd on mitochondrial respiration of the bivalves. In oysters, Cu suppressed ADP-stimulated mitochondrial respiration at high and low pH values (6.6 and 7.8, respectively), but had no effect in the intermediate pH range (7.0-7.4). In clams, the negative effect of Cu on ADP-stimulated respiration was only observed at extremely high pH (7.8). A decrease in pH was also protective against Cd in mitochondria of clams and oysters. In clams, 25 μM Cd suppressed ADP-stimulated respiration at all pH; however, at low pH (6.6-7.0) this suppression was paralleled by a decrease in the rates of proton leak thereby effectively restoring mitochondrial coupling. In oysters, the inhibitory effects of Cd on ADP-stimulated respiration were fully abolished at low pH (6.6-7.0). This indicates that moderate acidosis (such as occurs during exposure to air, extreme salinities or elevated CO2 levels in the intertidal zone) may have a beneficial side-effect of protecting mitochondria of clams and oysters against the toxic effects of trace metals in polluted estuaries.

Cadmium-induced apoptosis in primary rat cerebral cortical neurons culture is mediated by a calcium signaling pathway

Cadmium (Cd) is an extremely toxic metal, capable of severely damaging several organs, including the brain. Studies have shown that Cd disrupts intracellular free calcium ([Ca²⁺]_i) homeostasis, leading to apoptosis in a variety of cells including primary murine neurons. Calcium is a ubiquitous intracellular ion which acts as a signaling mediator in numerous cellular processes including cell proliferation, differentiation, and survival/death. However, little is known about the role of calcium signaling in Cd-induced apoptosis in neuronal cells. Thus we investigated the role of calcium signaling in Cd-induced apoptosis in primary rat cerebral cortical neurons. Consistent with known toxic properties of Cd, exposure of cerebral cortical neurons to Cd caused morphological changes indicative of apoptosis and cell death. It also induced elevation of [Ca²⁺]_i and inhibition of Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities. This Cd-induced elevation of [Ca²⁺]_i was suppressed by an IP₃R inhibitor, 2-APB, suggesting that ER-regulated Ca²⁺ is involved. In addition, we observed elevation of reactive oxygen species (ROS) levels, dysfunction of cytochrome oxidase subunits (COX-I/II/III), depletion of mitochondrial membrane potential (ΔΨm), and cleavage of caspase-9, caspase-3 and poly (ADP-ribose) polymerase (PARP) during Cd exposure. Z-VAD-fmk, a pan caspase inhibitor, partially prevented Cd-induced apoptosis and cell death. Interestingly, apoptosis, cell death and these cellular events induced by Cd were blocked by BAPTA-AM, a specific intracellular Ca²⁺ chelator. Furthermore, western blot analysis revealed an up-regulated expression of Bcl-2 and down-regulated expression of Bax. However, these were not blocked by BAPTA-AM. Thus Cd toxicity is in part due to its disruption of intracellular Ca²⁺ homeostasis, by compromising ATPases activities and ER-regulated Ca²⁺, and this elevation in Ca²⁺ triggers the activation of the Ca²⁺-mitochondria apoptotic signaling pathway. This study clarifies the signaling events underlying Cd neurotoxicity, and suggests that regulation of Cd-disrupted [Ca²⁺]_i homeostasis may be a new strategy for prevention of Cd-induced neurodegenerative diseases.

Influence of a step-change in metal exposure (Cd, Cu, Zn) on metal accumulation and subcellular partitioning in a freshwater bivalve, Pyganodon grandis: a long-term transplantation experiment between lakes with contrasting ambient metal levels

The objective of the present field experiment was to identify detoxification responses in the gills and digestive gland of a freshwater unionid bivalve, Pyganodon grandis, subjected to a step-change in metal exposure. Adult bivalves were transferred from a reference site (Lake Opasatica) and a metal-contaminated lake (Lake Héva) to a second contaminated lake (Lake Vaudray) in northwestern Quebec, Canada. Changes in organ metal concentrations, in the subcellular distribution of metals and in metallothionein concentrations were followed over time (t=0, 132, (400) and 860 days). At each collection time and for each bivalve, the gills and digestive gland were excised and gently homogenized; six sub-cellular fractions were separated by differential centrifugation and analyzed for their Cd, Cu and Zn content, and metallothionein was quantified independently. Metal detoxification strategies were shown to differ between target organs: in the gills, incoming metals were sequestered largely in the granules, whereas in the digestive gland the same metals primarily accumulated in the cytosol, in the metallothionein-like protein fraction. These metal-handling strategies, as employed by the metal-naïve bivalves originating in the reference lake, closely resemble those identified in free-living P. grandis chronically exposed in the metal-contaminated lake, suggesting that the ability to handle incoming metals (Cd in particular) is inherent in P. grandis and is not a trait acquired after long-term adaptation of the bivalve to metal-contaminated environments. The bivalves transplanted from both Lakes Opasatica and Héva were able to tolerate their new surroundings during the first 400 days of the transplant experiment, as indicated by the absence of mortality and the presence of gravid animals. Over the final 460 days, mortality remained low for the bivalves transplanted from the reference lake (20%) but reached 100% in the transplanted group from the contaminated lake. It would seem that the Lake Héva bivalves were compromised by their initial exposure to metals in their home lake and that the added stress of being transplanted to and caged in a lake with comparable or slightly higher concentrations of metals was sufficient to cause mortality.

Mitochondria as a target of environmental toxicants

Enormous strides have recently been made in our understanding of the biology and pathobiology of mitochondria. Many diseases have been identified as caused by mitochondrial dysfunction, and many pharmaceuticals have been identified as previously unrecognized mitochondrial toxicants. A much smaller but growing literature indicates that mitochondria are also targeted by environmental pollutants. We briefly review the importance of mitochondrial function and maintenance for health based on the genetics of mitochondrial diseases and the toxicities resulting from pharmaceutical exposure. We then discuss how the principles of mitochondrial vulnerability illustrated by those fields might apply to environmental contaminants, with particular attention to factors that may modulate vulnerability including genetic differences, epigenetic interactions, tissue characteristics, and developmental stage. Finally, we review the literature related to environmental mitochondrial toxicants, with a particular focus on those toxicants that target mitochondrial DNA. We conclude that the fields of environmental toxicology and environmental health should focus more strongly on mitochondria.

Oxygen consumption and metabolic responses of freshwater crab Sinopotamon henanense to acute and sub-chronic cadmium exposure

To explore the respiratory and metabolic responses of the freshwater crab (Sinopotamon henanense) to Cd exposure, crabs were acutely exposed to 7.14, 14.28, 28.55 mg/L Cd for 96 h and subchronically exposed to 0.71, 1.43, 2.86 mg/L for three weeks. The oxygen consumption, concentrations of oxyhemocyanin, hemolymph protein, the activities of respiratory enzymes, i.e. lactate dehydrogenase (LDH), NAD-isocitrate dehydrogenase (IDH), cytochrome c oxidase (CCO), as well as cco-1(CCO active subunit 1) and ldh mRNA expression level and adenosine triphosphate (ATP) content in crab heart were assessed. Oxygen consumption, concentration of oxyhemocyanin and oxyhemocyanin/blood protein proportion were increased during acute exposure and decreased during sub-chronic exposure. Both exposure schemes induced downregulation of cco-1 gene expression and lowered CCO activity. For acute exposure, tissue ATP level was increased, in association with increased IDH activity and decreased LDH activity, whereas subchronic exposure caused decreased IDH activity accompanied with increased ldh gene expression and LDH activity, resulting in lowered ATP level. By coupling gene expression to biochemical and physiological endpoints, this work provides new insights into the mechanisms involved in metal stress and the differential respiratory and metabolic responses of S. henanense to acute and subchronic Cd exposure.

Zebrafish: a model animal for analyzing the impact of environmental pollutants on muscle and brain mitochondrial bioenergetics

Mercury, anthropogenic release of uranium (U), and nanoparticles constitute hazardous environmental pollutants able to accumulate along the aquatic food chain with severe risk for animal and human health. The impact of such pollutants on living organisms has been up to now approached by classical toxicology in which huge doses of toxic compounds, environmentally irrelevant, are displayed through routes that never occur in the lifespan of organisms (for instance injecting a bolus of mercury to an animal although the main route is through prey and fish eating). We wanted to address the effect of such pollutants on the muscle and brain mitochondrial bioenergetics under realistic conditions, at unprecedented low doses, using an aquatic model animal, the zebrafish Danio rerio. We developed an original method to measure brain mitochondrial respiration: a single brain was put in 1.5 mL conical tube containing a respiratory buffer. Brains were gently homogenized by 13 strokes with a conical plastic pestle, and the homogenates were immediately used for respiration measurements. Skinned muscle fibers were prepared by saponin permeabilization. Zebrafish were contaminated with food containing 13 μg of methylmercury (MeHg)/g, an environmentally relevant dose. In permeabilized muscle fibers, we observed a strong inhibition of both state 3 mitochondrial respiration and cytochrome c oxidase activity after 49 days of MeHg exposure. We measured a dramatic decrease in the rate of ATP release by skinned muscle fibers. Contrarily to muscles, brain mitochondrial respiration was not modified by MeHg exposure although brain accumulated twice as much MeHg than muscles. When zebrafish were exposed to 30 μg/L of waterborne U, the basal mitochondrial respiratory control ratio was decreased in muscles after 28 days of exposure. This was due to an increase of the inner mitochondrial membrane permeability. The impact of a daily ration of food containing gold nanoparticles of two sizes (12 and 50 nm) was investigated at a very low dose for 60 days (40 ng gold/fish/day). Mitochondrial dysfunctions appeared in brain and muscle for both tested sizes. In conclusion, at low environmental doses, dietary or waterborne heavy metals impinged on zebrafish tissue mitochondrial respiration. Due to its incredible simplicity avoiding tedious and time-consuming mitochondria isolation, our one-pot method allowing brain respiratory analysis should give colleagues the incentive to use zebrafish brain as a model in bioenergetics. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Effects of uranium uptake on transcriptional responses, histological structures and survival rate of the crayfish Procambarus clarkii

This work aims to investigate the accumulation levels and effects (transcriptional responses, histopathology and survival rate) associated with a wide range of dissolved uranium (U) concentrations (0, 0.03, 0.6, 4 and 8 mg/L of U) on adult male crayfish Procambarus clarkii during 4 (T4) and 10 (T10) days of exposure. The follow-up of the crayfish mortality showed that P. clarkii was highly resistant to U. Increasing waterborne U concentrations led to increasing bioaccumulation in key crayfish organs and increasing histological damages. U distribution in tissues was also evaluated using transmission electron microscopy and showed the presence of a detoxified form of U in the gill's epithelium in the shape of flakes. Expression levels of mitochondrial genes (cox1, atp6 and 12S gene) and genes involved in oxidative stress (sod(Mn) and mt) were examined together with the housekeeping gene 18S. atp6 and mt genes of P. clarkii were cloned and sequenced before analysis. Significant correlations were observed between U bioaccumulation and the down-regulation of both cox1 and sod(Mn) genes. This work provides a first U toxicogenomic and histopathological pattern of P. clarkii, identify U biomarkers and associate gene expression endpoints to accumulation levels. It also provides new insights into the mechanisms involved in U stress.

Effects of chronic metal exposure on wild fish populations revealed by high-throughput cDNA sequencing

Given the inherent variability of aquatic systems, predicting the in situ effects of contaminants on such ecosystems still represents a major challenge for ecotoxicology. In this context, transcriptomic tools can help identify and investigate the mechanisms of toxicity beyond the traditional morphometric, physiological and population-level endpoints. In this study, we used the 454 sequencing technology to examine the in situ effects of chronic metal (Cd, Cu) exposure on the yellow perch (Perca flavescens) transcriptome. Total hepatic mRNA from fish sampled along a polymetallic gradient was extracted, reverse transcribed, labeled with unique barcode sequences and sequenced. This approach allowed us to identify correlations between the transcription level of single genes and the hepatic concentrations of individual metals; 71% of the correlations established were negative. Chronic metal exposure was thus associated with a decrease in the transcription levels of numerous genes involved in protein biosynthesis, in the immune system, and in lipid and energy metabolism. Our results suggest that this marked decrease could result from an impairment of bile acid metabolism by Cd and energy restriction but also from the recruitment of several genes involved in epigenetic modifications of histones and DNA that lead to gene silencing.