Effects of copper on cortisol receptor and metallothionein expression in gills of Oncorhynchus mykiss

Effects of salinity stress on antioxidant status and inflammatory responses in females of a "Near Threatened" economically important fish species Notopterus chitala: a mechanistic approach

In the present study, acute stress responses of adult female Notopterus chitala were scrutinized by antioxidant status and inflammation reaction in the gill and liver at five different salinity exposures (0, 3, 6, 9, 12 ppt). Oxidative defense was assessed by determining superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase, and glutathione reductase activities, while malondialdehyde (MDA), glutathione, and xanthine oxidase levels were determined as indicators of oxidative load. Pro-inflammatory cytokines (IL-1β, IL-6, IL-10, and TNFα) and caspase 1 levels were also analyzed. Expression levels of transcription factors (NRF2 and NF-κB) and molecular chaperons (HSF, HSP70, and HSP90) were estimated to evaluate their relative contribution to overcome salinity stress. MDA showed a significant (P < 0.05) increase (gill, + 25.35-90.14%; liver, + 23.88-80.59%) with salinity; SOD (+ 13.72-45.09%) and CAT (+ 12.73-33.96%) exhibited a sharp increase until 9 ppt, followed by a decrease at the highest salinity (12 ppt) (gill, - 3.92%; liver, - 2.18%). Levels of cytokines were observed to increase (+ 52.8-127.42%) in a parallel pattern with increased salinity. HSP70 and HSP90 expressions were higher in gill tissues than those in liver tissues. NRF2 played pivotal role in reducing salinity-induced oxidative load in both the liver and gills. Serum cortisol and carbonic anhydrase were measured and noted to be significantly (P < 0.05) upregulated in salinity stressed groups. Gill Na⁺-K⁺-ATPase activity decreased significantly (P < 0.05) in fish exposed to 6, 9, and 12 ppt compared to control. Present study suggests that a hyperosmotic environment induces acute oxidative stress and inflammation, which in turn causes cellular death and impairs tissue functions in freshwater fish species such as Notopterus chitala.

Life-time exposure to waterborne copper II: Patterns of tissue accumulation and gene expression of the metal-transport proteins ctr1 and atp7b in the killifish Poecilia vivipara

The involvement of transporting proteins on copper (Cu) bioaccumulation was evaluated in the killifish Poecilia vivipara chronically exposed to environmentally relevant concentrations of waterborne Cu. Fish (<24 h-old) were maintained under control condition or exposed to different waterborne Cu concentrations (5, 9 and 20 μg/L) for 28 and 345 days in saltwater. Following exposure periods, Cu accumulation and the expression of genes encoding for the high affinity Cu-transporter (ctr1) and the P-type Cu-ATPase (atp7b) were evaluated. Whole-body metal accumulation and gene expression were evaluated in fish exposed to 28 days. Similarly, in fish exposed to 345 days, liver, gills and gut were also evaluated. No fish survival was observed after exposure to 20 μg/L for 345 days. Whole-body Cu accumulation was significantly higher in fish exposed to 20 μg/L Cu for 28 days and in fish exposed to 9 μg/L for 345 days in comparison to control animals. Similarly, tissue Cu accumulation was significantly higher in fish exposed to 9 μg/L for 345 days in comparison to control animal. However, no significant accumulation was observed in fish muscle. Following exposure for 28 days, whole-body ctr1 expression was slightly induced in fish exposed to 9 μg/L. In turn, no significant change in ctr1 expression was observed following exposure to Cu for 345 days. Differently, whole-body atp7b expression was markedly up-regulated in the whole-body of fish exposed Cu for 28 days and in tissues of fish exposed to Cu for 345 days. These findings indicate the expression of atp7b is more responsive to Cu accumulation in P. vivipara than ctr1 expression and, therefore, more suitable to be used as a biomarker of exposure to this metal. Also, we argue that the expression of atp7b is sustained at elevated levels for as much time as fish are maintained in Cu contaminated water.

Effects of life-time exposure to waterborne copper on the somatotropic axis of the viviparous fish Poecilia vivipara

Reduced fish growth following chronic exposure to dissolved copper (Cu) is well reported in the literature. Nevertheless, information on the mechanism(s) involved in this process is scarce. Therefore, we evaluated growth, gene expression and concentrations of proteins related to growth regulation in the viviparous guppy Poecilia vivipara chronically exposed to dissolved Cu. Newborn (<24 h after birth) fish were kept under control conditions or exposed to environmentally relevant concentrations of Cu (5 and 9 μg/L) in salt water (24 ppt) for 345 days. After exposure, fish growth was evaluated based on body weight and length. Also, growth hormone (gh) mRNA expression was evaluated in brain, while growth hormone receptor 1 (ghr1) and 2 (ghr2) mRNA expressions were analyzed in brain, skeletal muscle and liver. In turn, insulin-like growth factor 1 (igf1) and 2 (igf2) mRNA expressions were evaluated in skeletal muscle and liver. Additionally, Gh concentration was assessed in brain, while Ghr concentration was evaluated in skeletal muscle and liver. Exposure to 9 μg/L Cu reduced fish body weigh and length. Metal exposure affected mRNA expression only in skeletal muscle. Reduced ghr2 mRNA expression was observed in guppies exposed to 5 and 9 μg/L Cu. Additionally, reduced igf1 and igf2 mRNA expressions were observed in guppies exposed to 9 μg/L Cu. However, no significant change in Ghr concentration was observed. The reduced ghr2 mRNA expression suggests that chronic Cu exposure induced an insensitivity of the skeletal muscle to Gh, thus resulting in reduced igf1 and igf2 mRNA expression which lead to reduced fish growth. These findings indicate that chronic exposure to dissolved Cu disrupts the somatotropic axis regulation, thus helping to elucidate the mechanism underlying the Cu-dependent inhibition of growth observed in the viviparous fish P. vivipara.

EROD activity and cytochrome P4501A induction in liver and gills of Senegal sole Solea senegalensis from a polluted Huelva estuary (SW Spain)

EROD activity and induction cytochrome P4501A in liver and gills of Senegal sole, Solea senegalensis, from a heavy metal and PAH polluted estuary, was studied. Liver and gill CYP1A catalytic activity was assessed at the enzyme activity level-measured as 7-ethoxyresorufin-O-deethylase and cellular localization of CYP1A in the liver was studied using immunohistochemistry. Liver EROD was correlated with phenanthrene-type metabolites in liver and copper concentrations in water. Strong CYP1A occurrence was observed in acinar pancreatic cells, pancreatic duct epithelium and vascular system endothelium and negative/rare induction were observed in hepatocytes and sinusoidal endothelium. In gills, EROD activity showed a significant correlation with different fractions of heavy metals in sediment but no correlation was observed between EROD activity and PAHs. Strongly positive CYP1A associated staining of the vascular system endothelia and primary filament cells and a moderate staining of pillar cells in gills were observed. The results substantiated the utility of EROD activity and CYP1A induction measurement as biomarkers for use by aquatic toxicologists and indicate that catalytic assays and immunohistochemical assays appear to be sensitive to different kinds of pollutants being the use of both methods recommended for monitoring programs.

Chronic exposure to a low dose of ingested petroleum disrupts corticosterone receptor signalling in a tissue-specific manner in the house sparrow (Passer domesticus)

Stress-induced concentrations of glucocorticoid hormones (including corticosterone, CORT) can be suppressed by chronic exposure to a low dose of ingested petroleum. However, endocrine-disrupting chemicals could interfere with CORT signalling beyond the disruption of hormone titres, including effects on receptors in different target tissues. In this study, we examined the effects of 6 weeks of exposure to a petroleum-laced diet (1% oil weight:food weight) on tissue mass and intracellular CORT receptors in liver, fat, muscle and kidney (metabolic tissues), spleen (an immune tissue) and testes (a reproductive tissue). In the laboratory, male house sparrows were fed either a 1% weathered crude oil (n = 12) or a control diet (n = 12); glucocorticoid receptors and mineralocorticoid receptors were quantified using radioligand binding assays. In oil-exposed birds, glucocorticoid receptors were lower in one metabolic tissue (liver), higher in another metabolic tissue (fat) and unchanged in four other tissues (kidney, muscle, spleen and testes) compared with control birds. We saw no differences in mineralocorticoid receptors between groups. We also saw a trend towards reduced mass of the testes in oil-exposed birds compared with controls, but no differences in fat, kidney, liver, muscle or spleen mass between the two groups. This is the first study to examine the effects of petroleum on CORT receptor density in more than one or two target tissues. Given that a chronic low dose of ingested petroleum can affect stress-induced CORT titres as well as receptor density, this demonstrates that oil can act at multiple levels to disrupt an animal's response to environmental stressors. This also highlights the potential usefulness of the stress response as a bioindicator of chronic crude oil exposure.

Salinity acclimation modulates copper toxicity in the sheepshead minnow, Cyprinodon variegatus

The sheepshead minnow (Cyprinodon variegatus) is able to withstand a wide range of salinities. Salinity acclimation involves physiological and biochemical changes, which may influence how organisms respond to a stressor. The present study investigated effects of salinity acclimation on subsequent Cu toxicity. In experiment 1, fish were acclimated to a hyposmotic, isosmotic, or hyperosmotic salinity for 14 d and then exposed at these salinities to 16.6 µM Cu(2+) for 12 h. Survival differed during this Cu challenge; fish acclimated to 2.5 ppt salinity were much more sensitive to Cu than those acclimated to 10.5 or 18.5 ppt seawater. In experiment 2, fish were exposed to 14.6 µM Cu(2+) for 6 h after the 14-d salinity acclimation. Whole-body Cu, whole-body Na, liver lipid peroxidation (LPO), liver catalase activity, and liver glucose levels were determined before and after Cu exposure. Prior to Cu exposure, the acclimation groups differed only for liver glucose levels, which were higher in the 2.5 ppt acclimated fish than in the others. These same 2.5 ppt acclimated fish were markedly affected by Cu, having increased whole-body Cu and liver LPO and decreased whole-body Na levels. Copper exposure had generally insignificant effects for the 10.5 ppt and the 18.5 ppt acclimated fish. This study showed that even in euryhaline fish, salinity acclimation can have a drastic effect on Cu toxicity.

Acute and sublethal effects in an Indian major carp Cirrhinus mrigala exposed to silver nitrate: Gill Na+/K+-ATPase, plasma electrolytes and biochemical alterations

Due to prolonged use of silver in many applications, it enters into the freshwater and affects the aquatic organisms. Fingerlings of Cirrhinus mrigala were exposed to acute and sublethal concentrations of silver nitrate and the alterations of gill Na(+)/K(+)-ATPase, plasma electrolytes and biochemical parameters were assessed. The median lethal concentration of silver nitrate to the fish C. mrigala for 96 h was found to be 0.107 mg/l (with 95% confidence limits). 1/10th of LC 50 96 h value (0.0107 mg/l) was selected for sublethal study. During acute treatment branchial Na(+)/K(+)-ATPase activity was inhibited approximately 44.34% after 96 h of exposure. In sublethal treatment, silver nitrate could not produce a significant change in the activity of the enzyme at the end of 7th day. However, after 14th day, significant (p < 0.05) decrease was noted showing 22.52%-49.11% in rest of the study period. Silver intoxication resulted hyponatremia, hypokalemia, hypochloremia, and hypoproteinemia in both the treatments. Despite the decrease in these parameters, plasma glucose level was found to be increased in both the treatments to endure the silver toxicity. We suggest that the alterations in branchial Na(+)/K(+)-ATPase activity, plasma electrolytes, and biochemical parameters of fish may be useful in environmental biomonitoring and to assess the health of fish in freshwater habitat contaminated with silver.

Effects of copper on the acute cortisol response and associated physiology in rainbow trout

The aim of this study was to determine the effects of chronic waterborne copper (Cu) exposure on the acute stress-induced cortisol response and associated physiological consequences in rainbow trout (Oncorhynchus mykiss). Trout were exposed to 30 μg Cu/L in moderately hard water (120 mg/L as CaCO(3)) for 40 days, following which time the acute cortisol response was examined with a series of stressors. At 40 days, a 65% increase in Cu was observed in the gill, but no accumulation was observed in the liver, brain or head kidney. Stressors such as air exposure or confinement did not elicit an increase in circulating cortisol levels for Cu-exposed fish, in contrast to controls. However, this inhibitory effect on the acute cortisol response appeared to have few implications on the ability of Cu-exposed fish to maintain ion and carbohydrate homeostasis. For example, plasma Na(+), Ca(2+) and glucose levels as well as hepatic glycogen levels were the same post-stress in control and Cu-exposed fish. Trout were also challenged with exposure to 50% seawater for 48 h, where Cu-exposed trout maintained plasma Na(+), glucose and hepatic glycogen levels. However, Cu-exposed fish experienced decreased plasma K(+) levels throughout the Cu exposure and stress tests. In conclusion, chronic Cu exposure resulted in the abolition of an acute cortisol response post-stress. There was no Cu accumulation in the hypothalamus-pituitary-interrenal axis (HPI axis) suggesting this was not a direct toxic effect of Cu on the cortisol regulatory pathway. However, the lack of an acute cortisol response in Cu-exposed fish did not impair the ability of the fish to maintain ion and carbohydrate homeostasis. This effect on cortisol may be a strategy to reduce costs during the chronic stress of Cu exposure, and not endocrine disruption as a result of toxic injury.

Metallothionein biosynthesis as a detoxification mechanism in mercury exposure in fish, spotted scat (Scatophagus argus)

It is of crucial importance to study on the biomarkers types to assess the specification of the pollutants and health status of marine ecosystems in environmental evaluation projects. In this respect, total metallothionein biosynthesis and mercury bioaccumulation in the liver and gills under acute mercury exposure were investigated in fish, Scat (Scatophagus argus). Spotted scat was exposed to different mercury concentrations (0, 10, 20, 30) for 24, 48, 72 h. Total MT levels were determined by enzyme-linked immunosorbent assay (ELISA) method. Mercury contents were determined through cold vapor atomic absorption spectrometry (CVAAS). Induction of MT during exposure was tissue specific, displaying different response pattern in gills and liver. Mercury accumulated in liver much higher than in gills and the latter also showed lower MT level (P<0.05). MT biosynthesis in liver showed a significant (P<0.05) increase after exposure to different mercury concentration with increase in exposure time, whereas total MT content did not significantly (P>0.05) change in gills except for 72 h exposure at 30 μg l(-1). Nonetheless, the relationship between MT biosynthesis and Mercury bioaccumulation in both tissues was significant (P<0.05). The results suggest that this form of MT in S. argus was Hg inducible and could be extended as a biomarker of mercury pollution in marine ecosystems.

Hormonal and ion regulatory response in three freshwater fish species following waterborne copper exposure

We evaluated effects of sublethal copper exposure in 3 different freshwater fish: rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio). In a first experiment we exposed these fishes to an equally toxic Cu dose, a Cu level 10 times lower than their 96 h LC50 value: 20, 65, and 150 microg/L Cu. In a second series we exposed them to the same Cu concentration (50 microg/L). Na+/K+-ATPase activity in gill tissue was disturbed differently in rainbow trout then in common and gibel carp. Rainbow trout showed a thorough disruption of plasma ion levels at the beginning of both exposures, whereas common carp and gibel carp displayed effects only after 3 days. Rainbow trout and common carp thyroid hormones experienced adverse effects in the beginning of the exposure. The involvement of prolactin in handling metal stress was reflected in changes of mRNA prolactin receptor concentrations in gill tissue, with an up regulation of this mRNA in rainbow trout and a down regulation in gibel carp, which was more pronounced in the latter. Overall, rainbow trout appeared more sensitive in the beginning of the exposure, however, when it overcame this first challenge, it handled copper exposure in a better manner then common and gibel carp as they showed more long term impacts of Cu exposure.

Early subcellular partitioning of cadmium in gill and liver of rainbow trout (Oncorhynchus mykiss) following low-to-near-lethal waterborne cadmium exposure

Non-essential metals such as cadmium (Cd) accumulated in animal cells are envisaged to partition into potentially metal-sensitive compartments when detoxification capacity is exceeded. An understanding of intracellular metal partitioning is therefore important in delineation of the toxicologically relevant metal fraction for accurate tissue residue-based assessment of toxicity. In the present study, the early intracellular Cd accumulation was studied to test the prediction that it conforms to the spillover model of metal toxicity. Juvenile rainbow trout (10-15g) were exposed for 96h to three doses of cadmium (5, 25 and 50microg/l) and a control (nominal 0microg/l Cd) in hard water followed by measurement of the changes in intracellular Cd concentrations in the gill and liver, and carcass calcium (Ca) levels. There were dose-dependent increases in Cd concentration in both organs but the accumulation pattern over time was linear in the liver and biphasic in the gill. The Cd accumulation was associated with carcass Ca loss after 48h. Comparatively, the gill accumulated 2-4x more Cd than the liver and generally the subcellular compartments reflected the organ-level patterns of accumulation. For the gill the rank of Cd accumulation in subcellular fractions was: heat-stable proteins (HSP)>heat-labile proteins (HLP)>nuclei>microsomes-lysosomes (ML)>/=mitochondria>resistant fraction while for the liver it was HSP>HLP>ML>mitochondria>nuclei>resistant fraction. Contrary to the spillover hypothesis there was no exposure concentration or internal accumulation at which Cd was not found in potentially metal-sensitive compartments. The proportion of Cd bound to the metabolically active pool (MAP) increased while that bound to the metabolically detoxified pool (MDP) decreased in gills of Cd-exposed fish but remained unchanged in the liver. Because the Cd concentration increased in all subcellular compartments while their contribution to the total increased, decreased or remained unchanged following Cd exposure, use of percentage data to infer spillover requires caution.

Bioaccumulation and subcellular partitioning of zinc in rainbow trout (Oncorhynchus mykiss): cross-talk between waterborne and dietary uptake

Zinc homeostasis was studied at the tissue and gill subcellular levels in rainbow trout (Oncorhynchus mykiss) following waterborne and dietary exposures, singly and in combination. Juvenile rainbow trout were exposed to 150 or 600microgl(-1) waterborne Zn, 1500 or 4500microgg(-1) dietary Zn, and a combination of 150microgl(-1) waterborne and 1500microgg(-1) dietary Zn for 40 days. Accumulation of Zn in tissues and gill subcellular fractions was measured. At the tissue level, the carcass acted as the main Zn depot containing 84-90% of whole body Zn burden whereas the gill held 4-6%. At the subcellular level, the majority of gill Zn was bioavailable with the estimated metabolically active pool being 81-90%. Interestingly, the nuclei-cellular debris fraction bound the highest amount (40%) of the gill Zn burden. There was low partitioning of Zn into the detoxified pool (10-19%) suggesting that sequestration and chelation are not major mechanisms of cellular Zn homeostasis in rainbow trout. Further, the subcellular partitioning of Zn did not conform to the spill-over model of metal toxicity because Zn binding was indiscriminate irrespective of exposure concentration and duration. The contribution of the branchial and gastrointestinal uptake pathways to Zn accumulation depended on the tissue. Specifically, in plasma, blood cells, and gill, uptake from water was dominant whereas both pathways appeared to contribute equally to Zn accumulation in the carcass. Subcellularly, additive uptake from the two pathways was observed in the heat-stable proteins (HSP) fraction. Toxicologically, Zn exposure caused minimal adverse effects manifested by a transitory inhibition of protein synthesis in gills in the waterborne exposure. Overall, subcellular fractionation appears to have value in the quest for a better understanding of Zn homeostasis and interactions between branchial and gastrointestinal uptake pathways.

Evaluation of metallothionein expression as a biomarker of mercury exposure in Scatophagus argus

The effect of mercury exposure to total Metallothionein (MT) response and bioaccumulation under control and acute mercury exposure were investigated in scats (Scatophagus argus). Scats were exposed to different mercury concentrations (10, 20 and 30 microg Hg L(-1)) for 24, 48 and 72 h. Total MT levels were determined by Enzyme-Linked Immunosorbent Assay (ELISA) method. Mercury contents were determined through cold Vapour atomic Absorption spectrometry. Induction of MT during exposure was tissue specific, displaying different response pattern in gill and liver. Mercury accumulated much stronger in liver than gill and the latter also showed lower MT level. MT biosynthesis in liver showed a significant increase after exposure to different mercury concentration during different times. This increase was significantly correlated with mercury bioaccumulation. In contrast, presence of different mercury concentration during different times did not significantly modify total MT except for 72 h exposure at 30 microg L(-1) in gills. The results suggest that this form of MT existing in S. argus was Hg-inducible and could be extended the as a biomarker of mercury pollution in ecosystems.

Juvenile tilapia (Oreochromis mossambicus) strive to maintain physiological functions after waterborne copper exposure

Juvenile tilapia were acutely exposed to 0.2 and 2 mg/L Cu(2+) for up to 144 h. The Na(+)-K(+)-ATPase (NKA)-specific activity in the gills of tilapia exposed to 0.2 mg/L Cu(2+) significantly decreased over 48-72 h and was restored to the control level after 96 h, but was again depressed during 120-144 h. The whole-body Cl(-) levels significantly decreased after 48 h, but recovered shortly afterwards and continued to do so until 144 h with 0.2 mg/L Cu exposure. During 48-72 h, the numbers of the wavy-convex type of mitochondria-rich (MR) cells appeared to significantly increase and the cortisol content also significantly increased. Changes in MR cell morphology might be necessary in order to enhance Cl(-) uptake, and this might be related to changes in cortisol levels. Whole-body Na(+) concentrations had significantly decreased by 72 h, but recovered during 96-144 h. Whole-body Cu(2+) concentrations also significantly increased compared to the initial concentration during 72-144 h of Cu exposure. All measured parameters (NKA activity, Na(+) concentration, and MR cell numbers) significantly decreased in fish exposed to 2 mg/L Cu, and no recovery was observed. These data demonstrate that juvenile tilapia strived to maintain physiological functions after exposure to sub-lethal concentrations of Cu.

Opercular epithelial cells: a simple approach for in vitro studies of cellular responses in fish

This study evaluated the efficacy of fish opercular external (skin) and inner (opercular membrane) epithelium as an in vitro model for toxic and other substances studies. The rainbow trout (Oncorhynchus mykiss) operculum was cultured in 12-well dishes containing sterile Leibovitz 15 (L-15) supplemented with glutamine medium during 24h at 9 degrees C, and the effect of copper, a toxic agent, and/or cortisol, an endogenous agent, on the epithelial cells was analyzed using light microscopy techniques. The opercula were submitted to four treatments: (i) control (Cont), L-15 medium only, (ii) 0.28 microM cortisol (Cort), (iii) 100 microM CuSO(4) (Cu), and (iv) 0.28 microM cortisol+100 microM CuSO(4) (Cort-Cu). The tissue condition after 24h incubation was analyzed by staining the mucous cells for neutral and acid mucosubstances. Cellular necrosis was evaluated by measuring the lactate dehydrogenase (LDH) leakage at 12 and 24h incubation. Cellular proliferation, apoptosis, metallothionein (MT) and glucocorticoid receptor (GR) expression were evaluated by immunohistochemistry. The LDH leakage was higher and the proliferating cell nuclear antigen (PCNA) positive-stained cells were lower in Cu treatment in both, epidermis and opercular membrane. Apoptotic cells in the opercular membrane were higher in the Cort and Cort-Cu treatments while, in the epidermis, they were higher in Cu and Cort-Cu treatments. GR-positive stained cells decreased significantly in all treatments in both epithelia and the MT-positive cells increased in the Cu and Cort-Cu treated groups. Copper showed to be a potent toxic stressor killing the cells via necrosis, decreasing the number of PCNA-positive cells and inducing MT synthesis while cortisol did not affect the MT synthesis, although it might stimulate apoptosis. The results are evidence that the opercular epithelia serve as a suitable model for studying in vitro effects of toxic agents, as well as endogenous factors on the cellular responses without interference of the physiological state of fish being useful to predict in vivo toxicity.

Effects of copper on CYP1A activity and epithelial barrier properties in the rainbow trout gill

The effects of copper on beta-naphthoflavone (betaNF)-induced ethoxyresorufin O-deethylase (EROD) activity were studied in rainbow trout (Oncorhynchus mykiss) gill filaments (after in vivo exposure) and in gill cells cultured as both primary cultures and as polarised epithelia, i.e. with water in the apical compartment and culture medium in the basolateral compartment. In the in vivo study betaNF and copper were added to the water, in primary cultures both chemicals were added to the culture medium and in cultured epithelia copper was added to the apical water whilst betaNF was added to the basolateral culture medium. In primary cultures this investigation was repeated with and without foetal bovine serum (FBS) supplementation of the culture media. Gill barrier properties, specifically polyethylene glycol (PEG-4000) permeability (i.e. paracellular permeability), sodium efflux and transepithelial electrical resistance (TER) were also investigated in cultured gill cell epithelia after apical treatment with copper. Two micromolar copper had no effect on EROD activity in gill filaments in vivo irrespective of whether EROD was induced by 0.01, 0.1 or 1.0 microM betaNF. Similarly, 0.5-100 microM copper had no effect on EROD induction in cultured epithelia. In primary cultures copper did reduce EROD induction but the effective concentration was dependent on whether the cells were supplemented with FBS, i.e. EROD activity was reduced by all copper concentrations of 5 and above if FBS was included, but only by 1000 microM if FBS was omitted. In cultured epithelia PEG-4000 permeability increased, whilst sodium efflux and TER were unaffected following treatment with 75 microM copper. Based on these results we conclude that the branchial monooxygenase system is a less sensitive target for copper than the barrier properties of the gill. Indeed, these data suggest the apical membrane of the gill epithelial cells minimises the uptake of waterborne copper and therefore protects the intracellular environment, including the CYP1A system. This could enable the freshwater fish gill to retain their potential of first-pass metabolism of waterborne organic compounds whilst simultaneously being exposed to waterborne copper.

Copper induced alterations of biochemical parameters in the gill and plasma of Oreochromis niloticus

The main objective of this study was to determine the effects of copper exposure on copper accumulated in branchial tissue, gill Na+/K+-ATPase activity and plasma Na+, Cl-, osmolality, protein, glucose and cortisol, in Oreochromis niloticus. Fish were experimentally exposed to 40 and 400 microg L(-1) of waterborne copper and sacrified after 0, 3, 7, 14 and 21 days. Copper accumulation and Na+/K+-ATPase activity were determined in branchial tissue, whereas osmolality, Na+, Cl-, protein, glucose and cortisol concentrations were measured in plasma samples. Gill copper accumulation increased linearly with exposure time and concentration, whereas gill Na+/K+-ATPase activity was maximally inhibited after 3 days of exposure and showed a significant negative correlation with copper tissue levels. Plasma Cl- values decreased with time of exposure but only at 400 microg L(-1) of copper. Plasma Na+, protein and osmolality decreased with exposure time at the highest copper concentration tested, whereas at 40 microg L(-1) of copper this effect was only observed after 21 days of exposure. Plasma glucose and cortisol levels increased in a dose and time dependent manner, while showing complex fluctuations during the intermediate exposure times. In conclusion, copper induces an early maximum inhibition of gill Na+/K+-ATPase activity in O. niloticus. The subsequent slow decrease in ion plasma levels was related to compensatory mechanisms involving a non-specific stress response that appeared overcome at long-term exposures.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

A short-term in vitro gill culture system to study the effects of toxic (copper) and non-toxic (cortisol) stressors on the rainbow trout, Oncorhynchus mykiss (Walbaum)

A short-term (24 h) method of gill filament culture system was developed to predict the effects of environmental contamination and stress in fish. Gill culture system containing two or three rainbow trout gill filaments in sterile glutamine supplemented Leibovitz 15 (L-15) media was submitted for 24 h to six different treatments: (i) CONT (control, medium only); (ii) CORT (cortisol, 0.28 microM cortisol); (iii) BLOCK (glucocorticoid receptor blocker, 14 microM RU 486); (iv) CORT+BLOCK (cortisol and blocker, 0.28 microM cortisol+14 microM RU 486); (v) CORT+CU (cortisol and copper, 100 microM CuSO4+0.28 microM cortisol); (vi) CU (copper, 100 microM CuSO4). After 24 h, the overall gill structure and cellular components resembled those of salmonids in vivo. Lactate dehydrogenase (LDH) activity in the culture media increased in the CORT+CU and CU groups but was significantly lower in the CORT+CU compared to CU group. Apoptotic cells increased in the CORT and CORT+BLOCK. The numbers of glucocorticoid (GR) receptor-positive cells were lower in the CU group. This short-term culture system seems to be suitable for studying the effects of both external and internal stress effectors (toxicants and hormones respectively), as it contains all cell types found in the gills and the cells give similar biological response as in vivo.

Differential metallothionein induction patterns in three freshwater fish during sublethal copper exposure

We assessed whether fish that tolerate higher levels of Cu exposure have a higher capacity to induce metallothionein (MT) synthesis than other, more sensitive, fish species. Furthermore, we examined if a correlation could be found between tissue Cu accumulation and MT levels. Cu accumulation and MT concentrations in gill, liver, kidney and muscle of rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio) were measured during a 1 week exposure to a sublethal Cu (1 microM). Different patterns were observed for the three species regarding Cu accumulation as well as MT induction. Virtually no Cu accumulation was seen in rainbow trout gill, while in both cyprinid species gill Cu levels increased three- to four-fold. Cu accumulated fast in common carp (within the first day), but slow in gibel carp (1 week). Gill MT induction was obvious in gibel carp only, with an increase of 156% after 1 week of exposure. Liver accumulated most Cu in rainbow trout (235% increase) and common carp (144% increase), with Cu levels in liver being significantly higher in rainbow trout compared to the carp species from the start. MT induction was pronounced in common carp liver only (138% increase). In gibel carp liver, there was no clear Cu accumulation or MT induction. In contrast, gibel carp was the only species to show Cu accumulation in kidney after 3 days of exposure (83% increase), after which levels returned to normal. Concomitantly, gibel carp kidney was also the only kidney tissue to show MT induction (192-195% increase after 3 and 7 days). In common carp, a significant decrease of kidney MT levels was observed from day 1 onwards. In muscle, Cu accumulation was clear for the two cyprinid species (three- to four-fold increase) but not for rainbow trout. Of the species studied, gibel carp is the most resistant to copper polluted environments, and showed a positive significant relationship between tissue copper concentrations and MT levels in gill, liver and muscle tissues. Common carp showed an intermediate response, with significant correlations in liver and muscle tissue. In contrast, we found low MT induction in rainbow trout, the most sensitive species, and no correlation at all between MT concentrations and tissue copper contents. Possibly, the regulatory capacity for copper homeostasis was exceeded in rainbow trout, and MT synthesis inhibited.

Chronic effects of copper exposure versus endocrine toxicity: two sides of the same toxicological process?

Chronic sub-lethal exposure to copper (Cu) causes a series of cellular and physiological changes in fish that enable the animal to survive. Copper is also an endocrine disrupting metal in the aquatic environment, and has a number of normal neuro-endocrine roles in vertebrates. This paper explores whether the chronic effects of Cu exposure can be explained by the effects of Cu on neuro-endocrine functions in fish. Chronic Cu exposure involves complex physiological adjustments in many body systems, including increased oxygen consumption, reduced mean swimming speed, up-regulation of ionic regulation, decreasing lymphocyte levels and increasing neutrophils, altered immunity, modulation of Cu-dependent and independent enzyme activities, and proliferation of epithelial cells in gills or intestine. These responses can occur with exposure via the food or the water and can be rationalised into three major categories: (1) up-regulation of enzymes/metabolism (2) altered haematopoietic responses and (3) altered cellularity (cell type, turnover or size) in tissues. Some of these responses can be explained by stimulation of general stress responses, including the adrenergic response and stimulated cortisol release via the hypothalamic-pituitary-interrenal axis. This can occur despite evidence of vacuolation and foci of necrosis in the brain, and increased macrophage activity, in the kidney of fish exposed to dietary Cu. In addition to generic stress responses, Cu regulates specific neuro-endocrine functions, including the loss of circadian rhythm during dietary Cu exposure that involves the failure to respond to circulating melatonin and a loss of circulating serotonin. We conclude that the chronic physiological effects of Cu and apparent endocrine disrupting effects of Cu are two sides of the same toxicological process.

The influence of ration size on copper homeostasis during sublethal dietary copper exposure in juvenile rainbow trout, Oncorhynchus mykiss

The influence of ration size on homeostasis and sublethal toxicity of copper (Cu) was assessed in rainbow trout (Oncorhynchus mykiss) during dietary Cu exposure in synthetic soft water. A constant dietary dose of 0.24 micromol Cu per g fish per day as CuSO(4).5H(2)O was delivered via diets containing 15.75, 7.87, and 5.24 micromol Cu g(-1) fed at 1.5, 3.0, and 4.5% wet body weight daily ration, respectively. Juvenile rainbow trout showed clear effects of ration but not Cu on growth suggesting that growth is hardly a sensitive endpoint for detection of sublethal dietary Cu exposure. All Cu-exposed fish accumulated the same total metal load when expressed on a per fish basis. This suggests that differences in tissue and whole-body Cu concentrations among the treatments reflected the differences in the fish size rather than total Cu accumulation, and demonstrate that absorption and accumulation of Cu from the gut during dietary exposure are independent of the food quantity in which the Cu is delivered. Fish fed a high ration exhibited greater mass-specific unidirectional uptake of waterborne Cu than fish fed a low ration indicating an increased need for Cu for growth processes in rapidly growing fish. Stimulated excretion of Cu was indicated by greater Cu accumulation in the bile of the Cu-exposed fish. Branchial Na(+), K(+)-ATPase was not affected by dietary Cu exposure or ration but gut Na(+), K(+)-ATPase activities showed stimulatory effects of increasing ration but not of Cu exposure. The 96-h LC50 for waterborne Cu (range 0.17-0.21 micromol l(-1) (10.52-13.20 microg l(-1)) was the same in all treatment groups indicating that ration size was unimportant and that dietary Cu did not induce an increase in tolerance to waterborne Cu. Taken together these results suggest that the nutritional status, fish size, and growth rates should be considered when comparing whole-body and tissue Cu concentration data for biomonitoring and risk assessment. Moreover, expressing the exposure as total metal dose rather than metal concentration in the diet is more appropriate.

Bioavailability and toxicity of dietborne copper and zinc to fish

To date, most researchers have used dietborne metal concentrations rather than daily doses to define metal exposure and this has resulted in contradictory data within and between fish species. It has also resulted in the impression that high concentrations of dietborne Cu and Zn (e.g. > 900 mg kg(-1) dry diet) are relatively non-toxic to fish. We re-analyzed existing data using rations and dietborne metal concentrations and used daily dose, species and life stage to define the toxicity of dietborne Cu and Zn to fish. Partly because of insufficient information we were unable to find consistent relationships between metal toxicity in laboratory-prepared diets and any other factor including, supplemented metal compound (e.g. CuSO(4) or CuCl(2)), duration of metal exposure, diet type (i.e. practical, purified or live diets), or water quality (flow rates, temperature, hardness, pH, alkalinity). For laboratory-prepared diets, dietborne Cu toxicity occurred at daily doses of > 1 mg kg(-1) body weight d(-1) for channel catfish (Ictalurus punctatus), 1-15 mg kg(-1) body weight d(-1) (depending on life stage) for Atlantic salmon (Salmo salar) and 35-45 mg kg(-1) body weight d(-1) for rainbow trout (Oncorhynchus mykiss). We found that dietborne Zn toxicity has not yet been demonstrated in rainbow trout or turbot (Scophthalmus maximus) probably because these species have been exposed to relatively low doses of metal ( < 90 mg kg(-1) body weight d(-1)) and effects on growth and reproduction have not been analyzed. However, daily doses of 9-12 mg Zn kg(-1) body weight d(-1) in laboratory-prepared diets were toxic to three other species, carp Cyprinus carpio, Nile tilapia Oreochromis niloticus, and guppy Poecilia reticulata. Limited research indicates that biological incorporation of Cu or Zn into a natural diet can either increase or decrease metal bioavailability, and the relationship between bioavailability and toxicity remains unclear. We have resolved the contradictory data surrounding the effect of organic chelation on metal bioavailability. Increased bioavailability of dietborne Cu and Zn is detectable when the metal is both organically chelated and provided in very low daily doses. We have summarized the information available on the effect of phosphates, phytate and calcium on dietborne Zn bioavailability. We also explored a rationale to understand the relative importance of exposure to waterborne or dietborne Cu and Zn with a view to finding an approach useful to regulatory agencies. Contrary to popular belief, the relative efficiency of Cu uptake from water and diet is very similar when daily doses are compared rather than Cu concentrations in each media. The ratio of dietborne dose:waterborne dose is a good discriminator of the relative importance of exposure to dietborne or waterborne Zn. We discuss gaps in existing data, suggest improvements for experimental design, and indicate directions for future research.

Gill cellular changes induced by copper exposure in the South American tropical freshwater fish Prochilodus scrofa

The cellular changes in gill tissue induced by exposure to copper were studied in the tropical freshwater fish Prochilodus scrofa, with emphasis on chloride and pavement cells. Damage to gills included epithelial changes such as lifting, rupture, peeling of lamellar epithelium, lamellar fusion, hyperplasia, and cellular hypertrophy. Cell degeneration by necrosis and apoptosis was intense in fish exposed to 25 and 29 microg Cu L-1. Pavement cells showed microridge reduction on their surface. Chloride cells proliferated in the lamellar epithelia close to the onset of the lamellae. However, no changes in total chloride cell density in contact with the water were observed. The chloride cell apical area of fish exposed to copper increased, but only fish exposed to 25 microg Cu L-1 showed significant increase in the chloride cell fractional area. At this water copper concentration, almost 60% of the chloride cells were apoptotic. Necrotic chloride cells increased with copper in water, reaching 70% in fish exposed to 29 microg Cu L-1 (=LC50 calculated for this species). Pavement and chloride cell proliferation and hypertrophy on lamellar epithelia increased the thickness of the water-blood barrier. Our findings suggest severe impairment of ion regulation and gas transfer of fish exposed to copper.