Dexamethasone modulates expression of genes involved in the innate immune system, growth and stress and increases susceptibility to bacterial disease in Senegalese sole (Solea senegalensis Kaup, 1858)

Oral cortisol and dexamethasone intake: Differential physiology and transcriptional responses in the marine juvenile Sparus aurata

This study approached the long-term oral administration of cortisol (F) and dexamethasone (DEX), two synthetic glucocorticoids, compared to a control group (CT) in the juveniles of a marine teleost, the gilthead seabream (Sparus aurata). Physiologically, DEX treatment impaired growth, which appears to be linked to carbohydrate allocation in muscle and liver, hepatic triglycerides depletion, and reduced hematocrit. Hypophyseal gh mRNA expression was 2-fold higher in DEX than in CT or F groups. Similarly, hypothalamic trh and hypophyseal pomcb followed this pattern. Plasma cortisol levels were significantly lower in DEX than in CT, while F presented intermediate levels. In the posterior intestine, measured short circuit-current (Isc) was more anion absorptive in CT and F compared to the DEX group, whereas Isc remained unaffected in the anterior intestine. The derived transepithelial electric resistance (TEER) significantly differed between intestinal regions in the DEX group. These results provide new insights to understand better potential targeted biomarkers indicative of the differential glucocorticoid or mineralocorticoid-receptors activation in fish.

Chitooligosaccharide boosts the immunity of immunosuppressed blunt snout bream against bacterial infections

The immunosuppression hazard of fish brought by intensive aquaculture needs to be addressed urgently, while chitooligosaccharide (COS) shows the potential application in the prevention the immunosuppression of fish due to its superior biological properties. In this study, COS reversed the cortisol-induced immunosuppression of macrophages and improved the immune activity of macrophages in vitro, promoting the expression of inflammatory genes (TNF-α, IL-1β, iNOS) and NO production, and increasing the phagocytic activity of macrophages. In vivo, the oral COS was absorbed directly through the intestine, significantly ameliorating the innate immunity of cortisol-induced immunosuppression of blunt snout bream (Megalobrama amblycephala). Such as facilitated the gene expression of inflammatory cytokines (TNF-α, IL-1β, IL-6) and pattern recognition receptors (TLR4, MR) and potentiated bacterial clearance, resulting in an effective improvement in survival and tissue damage. Altogether, this study demonstrates that COS offers potential strategies in the application of immunosuppression prevention and control in fish.

Stocking density mediated stress modulates growth attributes in cage reared Labeo rohita (Hamilton) using multifarious biomarker approach

The present study was conducted for 240 days to evaluate the effects of stocking density based on growth attributes, digestive enzymes, muscular composition, biochemical and physiological responses of Labeo rohita fingerlings in tropical inland open water cages. L. rohita (30.35 ± 1.08 g) were randomly distributed into three treatments, namely low stocking density, LSD (10 m-3), medium stocking density, MSD (20 m-3) and high stocking density, HSD (30 m-3) in triplicates. Fish were fed twice daily with CIFRI CAGEGROW® floating feed (crude protein-28%, crude fat-4%). Fish growth and feed efficiency were higher (p < 0.05) in LSD, however, MSD registered a higher yield. Amylase and protease activity reduced whereas lipase activity increased with increasing stocking density. Muscle crude protein and crude fat formed an inverse correlation. The fillet quality deteriorated at higher stocking densities based on Muscle pH, drip loss and frozen leakage rate. The stress biomarkers level (glucose, cortisol, superoxide dismutase and catalase) increased in serum under crowding conditions. Glutamate oxaloacetate transaminase and glutamate pyruvate transaminase in serum were significantly increased in HSD. Serum protein levels decreased with the increase in stocking densities. Body ionic imbalance (Na+, Cl- and K+) was observed under crowding stress. Based on growth attributes and multiple biomarker responses, L. rohita @ 10 m-3 was found to be the optimum density for inland open water cage culture.

Oxidation of Aqueous Dexamethasone Solution by Gas-Phase Pulsed Corona Discharge

The most widely used anti-inflammatory corticosteroid dexamethasone (DXM), frequently detected in waterbodies due to its massive consumption and incomplete removal in wastewater treatment processes, was experimentally studied for oxidation with gas-phase pulsed corona discharge (PCD) varied in pulse repetition frequency, pH, DXM initial concentration and additions of surfactant sodium dodecyl sulphate (SDS) and tert-butyl alcohol (TBA). The experimental study also included ozonation as compared to PCD in energy efficiency. The advantageous energy efficiency of PCD was observed in wide spans of pH and DXM initial concentrations surpassing ozonation by about 2.4 times. Identified transformation by- and end-products (fluoride and acetate), as well as the impact of radical scavengers, point to the prevalent radical oxidation of DXM. Somewhat increased toxicity observed on the course of PCD-treatment of high DXM concentrations presents a subject for further studies.

Short-term exposure to pharmaceuticals negatively impacts marine flatfish species: Histological, biochemical and molecular clues for an integrated ecosystem risk assessment

The marine habitat and its biodiversity can be impacted by released pharmaceuticals. The short-term (7 days) effect of 3 commonly used drugs - warfarin, dexamethasone and imidazole - on Senegalese sole (Solea senegalensis) juveniles was investigated. Occurrence of hemorrhages, histopathological alterations, antioxidant status, activity of antioxidant enzymes and expression of genes involved in the xenobiotic response (pxr, abcb1 and cyp1a), were evaluated. The results showed a time and drug-dependent effect. Warfarin exposure induced hemorrhages, hepatocyte vacuolar degeneration, and altered the activity of glutathione peroxidase (GPx) and the expression of all the studied genes. Dexamethasone exposure increased liver glycogen content, altered antioxidant status, GPx and superoxide dismutase activities, as well as abcb1 and cyp1a expression. Imidazole induced hepatocyte vacuolar degeneration and ballooning, and altered the antioxidant status and expression of the tested genes. The present work anticipates a deeper impact of pharmaceuticals on the aquatic environment than previously reported, thus underlining the urgent need for an integrated risk assessment.

Evaluation of an in vitro assay to screen for the immunotoxic potential of chemicals to fish

A wide variety of environmental contaminants has been shown to disrupt immune functions of fish and may compromise their defense capability against pathogens. Immunotoxic effects, however, are rarely considered in ecotoxicological testing strategies. The aim of this study was to systematically evaluate the suitability of an in vitro immuno-assay using selected fish immune parameters to screen for chemicals with known immunotoxic potential and to differentiate them from non-immunotoxicants. Non-stimulated and lipopolysaccharide-stimulated head kidney leukocytes of rainbow trout (Oncorhynchus mykiss) were exposed for 3 h or 19 h to chemicals with different modes of action. As immune parameters, phagocytosis activity, oxidative burst activity and cytokine transcription (IL-1β, TNFα, IL-10) were examined, accompanied by in silico modelling. The immunotoxicants dexamethasone, benzo(a)pyrene, ethinylestradiol and bisphenol A significantly altered the immune parameters at non-cytotoxic concentrations whereas diclofenac had only weak effects. However, the two baseline chemicals with no known immunotoxic potential, butanol and ethylene glycol, caused significant effects, too. From our results it appears that the in vitro fish leukocyte assay as performed in the present study has only a limited capacity for discriminating between immunotoxicants and non-immunotoxicants.

Effects of dietary baicalin supplementation on growth performance, antioxidative status and protection against oxidative stress-induced liver injury in GIFT tilapia (Oreochromis niloticus)

Baicalin, a main bioactive compound of Scutellaria baicalensis, has a variety of pharmacological activities including antioxidation, anti-inflammation and hepatoprotection. However, there are few reports on these biological activities in fish. Therefore, the aim of this study was to assess the effects of baicalin on growth performance, antioxidative status and hepatoprotection in tilapia. The fish were fed on different doses of baicalin (0, 0.4, 0.8 and 1.6 g/kg diet). After feeding 60 days, parts of fishes were netted, and the blood, liver, gills and muscle tissues were collected to analyze the antioxidative effect. The remaining fishes were injected with saline or hydrogen peroxide (H₂O₂) for challenge test. The results showed that the specific growth rate of fish was slightly increased in three baicalin treatments, and the feed efficiency was clearly improved in 0.4 g/kg baicalin treatment. Meanwhile, the antioxidative capacity in blood, liver and/or gill was enhanced in treatments with 0.4, 0.8 and/or 1.6 g/kg baicalin. After challenge test, the pre-treatments with baicalin effectively alleviated H₂O₂-induced liver injury. In serum and liver, pre-treatments with 0.8 and/or 1.6 g/kg baicalin suppressed the oxidative damage induced by H₂O₂, as evidenced by improvement of the levels of SOD, T-AOC and GSH and the decline of MDA level. More important, pre-treatments with 0.4, 0.8 and/or 1.6 g/kg baicalin blocked the upregulation of mRNA levels of tlr1, myd88, irak4, rela, tnf-α and il-1β in H₂O₂-induced liver injury. In summary, dietary baicalin supplementation could improve feed efficiency, enhance antioxidative ability and alleviate oxidative stress-induced hepatotoxicity in tilapia.

Morphological and histological abnormalities of the neotropical toad, Rhinella arenarum (Anura: Bufonidae) larvae exposed to dexamethasone

Dexamethasone (DEX) is a glucocorticoid highly effective as an anti-inflammatory, immunosuppressant and decongestant drug. In the present study, a preliminary acute toxicity test was assayed in order to determinate DEX median-lethal, lowest-observed-effect and the no-observed-effect concentrations (LC₅₀, LOEC and NOEC, respectively) on the common toad embryos (Rhinella arenarum). Also, morphological and histological abnormalities from five body larval regions, liver melanomacrophages (MM) and glutathione S-transferase (GST) activity were evaluated in the toad larvae to characterize the chronic sublethal effects of DEX (1-1,000 µg L^-L). Results of the acute test showed that the LC₅₀ of DEX at 96 h of exposure for the toad embryos (GS 18-20) was 10.720 mg L^-g, and the LOEC was 1 µg L^-g. In the chronic assay, the larval development and body length were significantly affected. DEX exposition also induced teratogenic effects. Most frequent external abnormalities observed in DEX-treated larvae included abdominal edema and swollen body, abnormal gut coiling and visceral congestion. Intestinal dysplasia was recurrent in cross-section of all DEX-treated larvae. Neural, conjunctive and renal epithelial cells were also affected. Significant increase in liver MM number and size, and GST activity levels were also registered in DEX treatments with respect to controls. The evaluation of a variety of biomarkers provided clear evidence of toad larvae sensitivity to DEX, and the ecotoxicological risk of these pharmaceuticals, commonly found in different water bodies worldwide on aquatic animals.

Genome and Phylogenetic Analysis of Genes Involved in the Immune System of Solea senegalensis - Potential Applications in Aquaculture

Global aquaculture production continues to increase rapidly. One of the most important species of marine fish currently cultivated in Southern Europe is Solea senegalensis, reaching more than 300 Tn in 2017. In the present work, 14 Bacterial Artificial Chromosome (BAC) clones containing candidate genes involved in the immune system (b2m, il10, tlr3, tap1, tnfα, tlr8, trim25, lysg, irf5, hmgb2, calr, trim16, and mx), were examined and compared with other species using multicolor Fluorescence in situ Hybridization (mFISH), massive sequencing and bioinformatic analysis to determine the genomic surroundings and syntenic chromosomal conservation of the genomic region contained in each BAC clone. The mFISH showed that the groups of genes hmgb2-trim25-irf5-b2m; tlr3-lysg; tnfα-tap1, and il10-mx-trim16 were co-localized on the same chromosomes. Synteny results suggested that the studied BACs are placed in a smaller number of chromosomes in S. senegalensis that in other species. Phylogenetic analyses suggested that the evolutionary rate of immune system genes studied is similar among the taxa studied, given that the clustering obtained was in accordance with the accepted phylogenetic relationships among these species. This study contributes to a better understanding of the structure and function of the immune system of the Senegalese sole, which is essential for the development of new technologies and products to improve fish health and productivity.

Feed and immersion challenges with lymphocystis disease virus (LCDV) reveals specific mechanisms for horizontal transmission and immune response in senegalese sole post-larvae

The horizontal transmission of lymphocystis disease virus (LCDV) through contaminated water and feed (using artemia as vehicle) and the associated immune gene expression profiles in Senegalese sole post-larvae were investigated. All specimens analyzed were positive for LCDV DNA detection at 1-day post-challenge (1 dpc) with the highest viral levels in specimens infected through the immersion route. However, the percentage of LCDV-positive animals and number of viral DNA copies dropped progressively at 2 and 7 dpc. The histological analysis identified structural changes in the skin, muscle and gills of sole post-larvae LCDV-challenged by immersion. In situ hybridization confirmed a wide distribution of LCDV in the skin, gut, surrounding vessels in trunk muscle and head kidney in the immersion route, while the signals were restricted to the liver and lamina propria in the feeding treatment. Expression analysis using a set of 22 genes related to innate immune defense system demonstrated clear differences in the time-course response to LCDV as function of the infection route. Most antiviral defense genes, the proinflammatory cytokines, the complement c3, g-type lysozyme and T-cell markers cd4 and cd8a were rapidly induced in the feeding-infected post-larvae, and they were remained activated at 2 dpc. In contrast, in the immersion-infected post-larvae the induction of most defensive genes was delayed, with a low intensity at 2 dpc. All these data demonstrate that LCDV can horizontally infect Senegalese sole post-larvae through the water or feed although with different patterns of histopathological disorders, virus distribution and route-specific expression profiles.

Effects of stocking density on growth, stress, and immune responses of juvenile Chinese sturgeon (Acipenser sinensis) in a recirculating aquaculture system

The present study was to investigate the effects of stocking density on the welfare of juvenile Chinese sturgeon (Acipenser sinensis) cultured in a recirculating aquaculture system (RAS) for three months. Fish (average weight 760.86 g) were reared in triplicate under three densities: low density (4.80 kg m^-2), medium density (8.99 kg m^-2), and high density (12.68 kg m^-2). The results showed that the 12.68 kg m^-2 treatment significantly suppressed fish growth, gene expression of glutathione-s-transferase (GST), and enhanced serum adrenocorticotropic hormone (ACTH), cortisol, glucose, lactate levels, and the heat shock protein 70 (HSP70) mRNA level (P < 0.05). Additionally, the 12.68 kg m^-2 treatment significantly decreased serum glutathione peroxidase and superoxide dismutase activities, and increased the formation of malondialdehyde (P < 0.05). Serum immunoglobulin M (IgM), lysozyme, alkaline phosphatase, and acid phosphatase activities showed a significant decline in this group (P < 0.05). Transcriptions of immune-related genes, including lysozyme, hepcidin antimicrobial peptide 1 (HAMP1), tumor necrosis factor-ɑ (TNF-ɑ), interleukin 1β, and interleukin 8 significantly reduced in the 12.68 kg m^-2 group (P < 0.05). In the somatotropic axis, both the serum values and gene expressions of growth hormone (GH) and insulin-like growth factor-I (IGF-I) resulted in a down-regulation in the 12.68 kg m^-2 group (P < 0.05). Overall, these results suggest that high stocking density could negatively influence the growth, stress, and immune responses of juvenile Chinese sturgeon. Consequently, the appropriate stocking density recommended for culturing juvenile Chinese sturgeon in an RAS is between 4.80 kg m^-2 and 8.99 kg m^-2.

Modulation of stress and innate immune response by corticosteroids in pacu (Piaractus mesopotamicus)

Understanding how stress and corticosteroid modulates the innate immune response is one of the keys to improving productivity and reducing losses in intensive aquaculture. Thus, we investigated the effects of dietary corticosteroids (7 days; long-term exposure) and transport (4 h; short-term stress) on stress and innate immune response in pacu. For this end, fish were fed with diets containing dexamethasone (100 mg kg^-1) or hydrocortisone (200 mg kg^-1), followed by transport, and then were intraperitoneally inoculated with heat-killed Aeromonas hydrophila or PBS (sham-inoculation). Fish were sampled after a 7-day feeding period, immediately post-transport and 24 h post-transport and inoculation. The dietary treatment of corticosteroids decreased resting cortisol levels by inhibiting the production of cortisol on the hypothalamus pituitary interrenal-axis. Further, both corticosteroids reduced hematocrit, red blood cells, haemoglobin and hemolytic activity of the complement, while they increased glucose levels and serum lysozyme concentrations. The transport increased cortisol and glucose levels and reduced the humoral immune defenses such as serum lysozyme concentration and hemolytic activity of the complement system. Interestingly, the hemolytic activity of the complement system increased sharply in fish fed with corticosteroids immediately post-transport, when they had their HPI-axis partially suppressed by the corticosteroids. This finding suggests a stimulatory effect of the catecholamines released during the transport on the activity of the complement system. Our results are highly valuable to understanding the stress and innate immune responses to long-term exposure to corticosteroids and short-term stress in fish and may provide insights into how corticosteroids modulate the innate immune system.

What can we learn from glucocorticoid administration in fish? Effects of cortisol and dexamethasone on intermediary metabolism of gilthead seabream (Sparus aurata L.)

In aquaculture facilities fish welfare could be compromised due to stressors. Fish deal with stress, inter alia, through the activation of the hypothalamic-pituitary-interrenal endocrine axis and, as a result, corticosteroids are released into the blood. Recent studies have described that corticosteroids actions depend on the specific affinities to their receptors, and the subsequent differentiated responses. Cortisol is the main corticosteroid hormone in teleost fish, being its actions dependent on the intensity and time of exposure to stressors. Short-term effects of corticosteroids are well described, but long-term effects, including changes in the energy management directly affecting growth and survival, are less understood in fish. Here we show the effects of chronic oral administration of cortisol and the synthetic glucocorticoid dexamethasone (DXM) on the intermediary metabolism of the gilthead seabream (Sparus aurata). We described a higher energy expenditure associated to both corticosteroids resulting in lower growth rates of fish. Moreover, the effects of these compounds were tissue-dependant, with differences between both hormones. Thus, cortisol-fed animals accumulated triglycerides in the liver, while DXM treatment led to glycogen storage. Cortisol and DXM stimulated amino acids catabolism and gluconeogenic pathways in muscle and gills, but the effects were significantly enhanced in DXM-fed fish. The described effects highlighted differentiated mechanisms of action associated to both corticosteroids under chronic stress conditions. Further studies should aim at describing those pathways in detail, with special attention to the functionality of glucocorticoid receptor isoforms. The effects described here for S. aurata juveniles, may serve as a basis to assess long-term stress in future comparative studies with other aquaculture species.

Immunotoxic responses of chronic exposure to cypermethrin in common carp

In the current study, laboratory evaluations were made to assess the immunomodulatory effect of cypermethrin on fingerlings of common carp (Cyprinus carpio L.). Results showed that 96-h LC50 of cypermethrin in common carp was estimated at 0.85 μg/L. Fish were exposed for 21 days to cypermethrin at three sub-lethal concentrations of 0.042, 0.085, and 0.17 μg/L that represented 5, 10, and 20%, respectively, of the 96-h LC50 of the pesticide for this fish species. Blood samples were taken after 7, 14, and 21 days of exposure. Immunological indices and resistance against bacterial infection were determined. Compared to the control group, the fish exposed to cypermethrin showed a significant increase in neutrophil ratio but exhibited a significant decrease in leukocyte number and lymphocyte ratio in treatments exposed to 0.17 and/or 0.085 μg/L after 21 days of exposure (p < 0.05). Serum protein level was significantly decreased in group exposed to 0.17 μg/L on day 14 and also in groups exposed to 0.085 and 0.17 μg/L on day 21 (p < 0.05). Immunoglobulin value was significantly reduced in groups exposed to 0.085 and 0.17 μg/L after 21 days of exposure (p < 0.05). Serum lysozyme activity and phagocytic activity were significantly decreased following exposure to 0.17 μg/L determined on days 14 and 21, post-exposure (p < 0.05). Mortality rate following the challenge with Aeromonas hydrophila significantly increased in fish exposed to 0.17 μg/L of cypermethrin. Overall, the present results indicate severe immunotoxicological effects of cypermethrin in common carp. Therefore, the use of cypermethrin in the proximities of common carp farms should be carefully considered.

Use of common carp (Cyprinus carpio) and Aeromonas salmonicida for detection of immunomodulatory effects of chemicals on fish

To develop a test for assessing the immunomodulatory effects of chemical pollutants on fish, we evaluated the effects of dexamethasone on the natural host-pathogen interaction between common carp (Cyprinus carpio) and Aeromonas salmonicida. Carp were exposed to 1mgL^-1 dexamethasone for the entire experimental period. One week after the exposure test started, the exposed fish, as well as unexposed fish, were bath-infected with A. salmonicida. One hundred percent mortality was observed in bacteria-infected fish exposed to dexamethasone, whereas no infection-associated mortality was observed in infected fish in the absence of dexamethasone exposure. In a separate experiment, dexamethasone exposure significantly suppressed hemolytic complement activity in bacteria-infected fish. These results clearly indicate that exposure to a high concentration of dexamethasone suppressed the carp immune system and caused subsequent mortality. Thus, this proposed test method is likely to be useful for evaluating the immunomodulatory effects of chemicals in fish.

Dexamethasone-induced hepatomegaly and steatosis in larval zebrafish

Fish hepatobiliary syndrome, characterized by hepatomegaly and fatty liver, has been frequently reported in many cultured fish species and has caused a dramatic economic loss in China. Glucocorticoids are thought to be important non-nutritional factors for hepatomegaly and fatty liver development. In the present study, a dexamethasone-induced zebrafish model of fatty liver and hepatomegaly was established, and the role of glucocorticoid receptor (GR) in the development of hepatomegaly and fatty liver was investigated using developing zebrafish. Exposure of larval zebrafish at 5 days post fertilization (dpf) to dexamethasone for 24 hr caused significant increases of liver size and number of fish with hepatic steatosis at 6 dpf. The increase of liver size caused by dexamethasone was significantly reversed by treatment with RU486, a GR antagonist, and by gene knock-down with a morpholino against the GR. The dexamethasone-induced hepatic steatosis was also inhibited by treatment with RU486. Overall, the results highlight larval zebrafish as a useful model for stress-induced liver failure.

Effects of thermal stress on the expression of glucocorticoid receptor complex linked genes in Senegalese sole (Solea senegalensis): Acute and adaptive stress responses

The present study examined the short and mid-term effects of a rise in temperature from 18°C to 24°C on the expression of genes related to the stress response regulation in juveniles of Senegalese sole, Solea senegalensis. The animals were exposed to a temperature increase of 6°C, after 1month of acclimation at 18°C. After this process, samples of different tissues were collected from a total of 96 fish at four sampling points: 1h, 24h, 3days and 1week. The transcript levels of a set of genes involved in the stress response such as glucocorticoid receptors 1 and 2, corticotrophin-releasing factor, corticotrophin-releasing factor binding proteins, proopiomelanocortin A and B, and cellular stress defense (heat shock protein 70, 90AA and 90AB) were quantified at these sampling points. Additionally, blood samples were also taken to measure the circulating plasma cortisol concentration. Thermal stress induced by increasing temperature prompted an elevation of plasma cortisol levels in juvenile Senegalese sole after 1h as a short-term response, and a consecutive increase after one week, as a mid-term response. Senegalese sole seemed to respond positively in terms of adaptive mechanisms, with a rapid over-expression of grs and hsps in liver and brain, significantly higher after one hour post stress, denoting the fast and acute response of those tissues to a rapid change on temperature. The ratio hsp90/gr also increased 24h after thermal shock, ratio proposed to be an adaptive mechanism to prevent proteosomal degradation of GR. As a mid-term response, the elevation of brain crfbp gene expression one week after thermal shock could be an adaptive mechanism of negative feedback on HPI axis. Taken together, these data suggested an initial up-regulation of the glucocorticoid receptor complex linked genes in response to a temperature increase in Senegalese sole, with heat shock protein 90 potentially being a regulatory factor for the glucocorticoid receptor in the presence of cortisol.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Clobetasol propionate causes immunosuppression in zebrafish (Danio rerio) at environmentally relevant concentrations

Synthetic glucocorticoids (GCs) are potential endocrine disrupting compounds that have been detected in the aquatic environment around the world in the low ng/L (nanomolar) range. GCs are used as immunosuppressants in medicine. It is of high interest whether clobetasol propionate (CP), a highly potent GC, suppresses the inflammatory response in fish after exposure to environmentally relevant concentrations. Bacterial lipopolysaccharide (LPS) challenge was used to induce inflammation and thus mimic pathogen infection. Zebrafish embryos were exposed to ≤1000nM CP from ~1h post fertilization (hpf) to 96 hpf, and CP uptake, survival after LPS challenge, and expression of inflammation-related genes were examined. Our initial experiments were carried out using 0.001% DMSO as a solvent vehicle, but we observed that DMSO interfered with the LPS challenge assay, and thus masked the effects of CP. Therefore, DMSO was not used in the subsequent experiments. The internal CP concentration was quantifiable after exposure to ≥10nM CP for 96h. The bioconcentration factor (BCF) of CP was determined to be between 16 and 33 in zebrafish embryos. CP-exposed embryos showed a significantly higher survival rate in the LPS challenge assay after exposure to ≥0.1nM in a dose dependent manner. This effect is an indication of immunosuppression. Furthermore, the regulation pattern of several genes related to LPS challenge in mammals supported our results, providing evidence that LPS-mediated inflammatory pathways are conserved from mammals to teleost fish. Anxa1b, a GC-action related anti-inflammatory gene, was significantly down-regulated after exposure to ≥0.05nM CP. Our results show for the first time that synthetic GCs can suppress the innate immune system of fish at environmentally relevant concentrations. This may reduce the chances of fish to survive in the environment, as their defense against pathogens is weakened.

Dexamethasone treatment decreases replication of viral hemorrhagic septicemia virus in Epithelioma papulosum cyprini cells

The expression of Mx1 in EPC cells after treatment with poly(I:C) or infection with viral hemorrhagic septicemia virus (VHSV) was significantly suppressed by treatment with dexamethasone. However, the titer of VHSV did not increase but instead decreased after dexamethasone treatment. This suggests that dexamethasone not only downregulates type I IFN but also affects certain factors that are necessary for VHSV replication. An important effect of HSP90 on replication of RNA viruses and downregulation of HSP90 by glucocorticoids have been reported. In this study, dexamethasone downregulated HSP90α expression in EPC cells that were stimulated with poly(I:C) or infected with VHSV. Furthermore, cells treated with an HSP90 inhibitor, geldanamycin, showed significantly decreased titers of VHSV, suggesting that HSP90 may be an important host component involved in VHSV replication, and HSP90 inhibition might be one of the causes for the observed reduction in viral titer caused by dexamethasone treatment.

Dose-dependent effects of morphine on lipopolysaccharide (LPS)-induced inflammation, and involvement of multixenobiotic resistance (MXR) transporters in LPS efflux in teleost fish

Opioid drugs, such as morphine (MO), detected in aquatic environments worldwide, may harm fish due to their semi-persistence and ability to potently interact with molecular targets conserved across vertebrates. Here, we established a waterborne bacterial lipopolysaccharide (LPS) challenge assay with zebrafish embryos as a model to investigate chemically-induced disruption of the innate immune system, and used it to study the effects of MO exposure. Exposure to 1 mg/L MO resulted in pronounced immunosuppression, reflected in downregulation of several inflammation-related genes, including myd88, trif, traf6, p38, nfκb2, il-1β, il-8 and ccl34a. Fish exposed to 1 mg/L MO accumulated 11.7 ng/g (wet weight) of MO, a concentration comparable to that reported in blood of chronic drug abusers subject to higher infection rates. Surprisingly, exposure to lower MO concentrations (100 ng/L-100 μg/L) led to exacerbation of LPS-induced inflammation. Two ATP-binding cassette (ABC) transporters known to be involved in the xenobiotic efflux - abcb4 and abcc2, also known as multixenobiotic resistance (MXR) transporters - were downregulated at 100 ng/L MO. We hypothesized that ABC/MXR transporters could modulate the severity of inflammation by being involved in efflux of LPS, thus regulating its accumulation in the organism. Indeed, we could demonstrate that blocking of ABC/MXR transporters by an inhibitor, cyclosporine A, results in stronger inflammation, coinciding with higher LPS accumulation, as visualized with fluorescently labeled LPS. Our work demonstrates that MO can disrupt fish innate immune responses at environmentally relevant concentrations. We also provide evidence for a role of ABC/MXR transporters in LPS efflux in fish. These finding may be applicable across other taxa, as ABC transporters are evolutionary conserved. Since diverse environmentally present chemicals are known to interfere with ABC/MXR transporters' expression or activity, our discovery raises concerns about potential adverse effects of such compounds on the immune system responses in aquatic organisms.

Preliminary study on the relationship between dexamethasone and pathogen susceptibility on crucian carp (Carassius auratus)

Dexamethasone, a known immunosuppressant, can inhibit the immune response and increase the amount of pathogen in body, but the role of dexamethasone affecting susceptibility of crucian carp (Carassius auratus) to pathogen is unclear. The effects of dexamethasone on susceptibility of crucian carp to Aeromonas hydrophila were investigated in this study. The fish were divided into four groups randomly and injected intraperitoneally by dexamethasone for 0 day (group D), 3 days (group C), 6 days (group B), and 9 days (group A), respectively. The serum lysozyme activity was significantly declined in group A, B and C. Relative immune gene expression such as il-1β, cxcl-8, tnfα and crp in kidney were down-regulation compared to group D. After that crucian carp were infected with A. hydrophila, crucian carp treated by dexamethasone had higher mortality (group A 95%, group B 76%, group C 31%) when compared to group D (4% mortality); the amount of pathogen in was significantly increased (P < 0.05) in liver, kidney and spleen of fish in group A-C compared to group D. These results implicated that higher susceptibility caused by dexamethasone may be induced by the decrease of lysozyme activity and the down-regulation of some immune genes.

Stress and immune responses in skin of turbot (Scophthalmus maximus) under different stocking densities

Fish skin and its mucus provide the first line of defense against chemical, physical and biological stressors, but little is known about the role of skin and its mucus in immune response to crowding stress. In the present study, we investigated the stress and immune responses in skin of turbot (Scophthalmus maximus) under different stocking densities. Turbot (average weight 185.4 g) were reared for 120 days under three densities: low density (LD), medium density (MD), and high density (HD). After 120 days, fish were weighed and sampled to obtain blood, mucus and skin tissues which were used for analyses of biochemical parameters and genes expression. The results showed HD treatment significantly suppressed growth and enhanced plasma cortisol and glucose levels (P < 0.05). In mucus, the activities of lysozyme (LZM), alkaline phosphatase (ALP) and esterase in HD treatment were lower than LD and MD treatments (P < 0.05) In skin, HD treatment resulted in up-regulation in malondialdehyde (MDA) formation and heat shock protein 70 (HSP 70) mRNA level, and down-regulation in activity of superoxide dismutase (SOD) and the transcriptions of glutathione-s-transferase (GST), interleukin-1β (IL-1β), tumor necrosis factor -α (TNF-α), insulin-like growth factor- (IGF-) and LZM (P < 0.05). Overall, the data suggested that overly high stocking density was a stressor which caused an immunosuppression in skin of turbot. Moreover, this information would help to understand the skin immunity and their relation with stress and disease in fish.

Occurrence of glucocorticoids discharged from a sewage treatment plant in Japan and the effects of clobetasol propionate exposure on the immune responses of common carp (Cyprinus carpio) to bacterial infection

The present study evaluated the environmental risks to common carp (Cyprinus carpio) posed by glucocorticoids present in sewage treatment plant (STP) effluent. To gather information on the seasonal variations in glucocorticoid concentration, the authors sampled the effluent of a Japanese STP every other week for 12 mo. Six of 9 selected glucocorticoids were detected in the effluent, with clobetasol propionate and betamethasone 17-valerate detected at the highest concentrations and frequencies. The present study's results indicated that effluent glucocorticoid concentration may depend on water temperature, which is closely related to the removal efficiency of the STP or to seasonal variations in the public's use of glucocorticoids. In a separate experiment, to clarify whether glucocorticoids in environmental water increase susceptibility to bacterial infection in fish, the authors examined the responses to bacterial infection (Aeromonas veronii) of common carp exposed to clobetasol propionate. Clobetasol propionate exposure did not affect bacterial infection-associated mortality. In fish infected with A. veronii but not exposed to clobetasol propionate, head kidney weight and number of leukocytes in the head kidney were significantly increased (p < 0.05), whereas these effects were not observed in infected fish exposed to clobetasol. This suggests that clobetasol propionate alleviated bacterial infection-associated inflammation. Together, these results indicate that susceptibility to bacterial infection in common carp is not affected by exposure to glucocorticoids at environmentally relevant concentrations.

The role of adjunctive dexamethasone in the treatment of bacterial meningitis: an updated systematic meta-analysis

BACKGROUND

Bacterial meningitis is a serious infection in children and adults worldwide, with considerable morbidity, mortality, and severe neurological sequelae. Dexamethasone is often used before antibiotics in cases of this disease, and improves outcomes.

OBJECTIVE

Although several studies have identified the role of adjunctive dexamethasone therapy in the treatment of bacterial meningitis, the results are still inconclusive. The aim of this study was to systematically evaluate the therapeutic and adverse effect of adjunctive dexa-methasone in patients with bacterial meningitis.

MATERIALS AND METHODS

Relevant randomized, double-blind, placebo-controlled trials of dexamethasone in bacterial meningitis published between 2000 and 2016 were retrieved from the common electronic databases. The odds ratio (OR) and risk ratio (RR) with their 95% confidence interval (CI) were employed to calculate the effect.

RESULTS

A total of ten articles including 2,459 bacterial meningitis patients (1,245 in the dex-amethasone group and 1,214 in the placebo group) were included in this meta-analysis. Our result found that dexamethasone was not associated with a significant reduction in follow-up mortality (292 of 1,245 on dexamethasone versus 314 of 1,214 on placebo; OR =0.91, 95% CI =0.80-1.03, P=0.14) and severe neurological sequelae (22.4% versus 24.1%, OR =0.84, 95% CI =0.54-1.29, P=0.42). However, dexamethasone seemed to reduce hearing loss among survivors (21.2% versus 26.1%; OR =0.76, 95% CI =0.59-0.98, P=0.03). No significant difference was found between these two groups in adverse events.

CONCLUSION

Our results suggested that adjunctive dexamethasone might not be beneficial in the treatment of bacterial meningitis. Future studies with more data are needed to further prove the role of dexamethasone in bacterial meningitis.

Dietary administration of the probiotic SpPdp11: Effects on the intestinal microbiota and immune-related gene expression of farmed Solea senegalensis treated with oxytetracycline

Few antimicrobials are currently authorised in the aquaculture industry to treat infectious diseases. Among them, oxytetracycline (OTC) is one of the first-choice drugs for nearly all bacterial diseases. The objective of this study was to evaluate the effect of the dietary administration of OTC both alone and jointly with the probiotic Shewanella putrefaciens Pdp11 (SpPdp11) on the intestinal microbiota and hepatic expression of genes related to immunity in Senegalese sole (Solea senegalensis) juveniles. The results demonstrated that the richness and diversity of the intestinal microbiota of fish treated with OTC decreased compared with those of the control group but that these effects were lessened by the simultaneous administration of SpPdp11. In addition, specimens that received OTC and SpPdp11 jointly showed a decreased intensity of the Denaturing Gradient Gel Electrophoresis (DGGE) bands related to Vibrio genus and the presence of DGGE bands related to Lactobacillus and Shewanella genera. The relationship among the intestinal microbiota of fish fed with control and OTC diets and the expression of the NADPH oxidase and CASPASE-6 genes was demonstrated by a Principal Components Analysis (PCA) carried out in this study. In contrast, a close relationship between the transcription of genes, such as NKEF, IGF-β, HSP70 and GP96, and the DGGE bands of fish treated jointly with OTC and SpPdp11 was observed in the PCA study. In summary, the results obtained in this study demonstrate that the administration of OTC results in the up-regulation of genes related to apoptosis but that the joint administration of OTC and S. putrefaciens Pdp11 increases the transcription of genes related to antiapoptotic effects and oxidative stress regulation. Further, a clear relationship between these changes and those detected in the intestinal microbiota is established.

HIFs genes expression and hematology indices responses to different oxygen treatments in an ovoviviparous teleost species Sebastes schlegelii

Hypoxia-inducible factors (HIFs) are transcription factors considered as a respond factor to oxygen tension. By using quantitative real-time PCR, expression files of HIF-1α and HIF-2α mRNA were detected in the Korean rockfish ovary, liver, gill and spleen after 30 min and 60 min acute hypoxia exposure. Meanwhile, the cortisol levels, white blood cells and several serum biochemical values of Korean rockfish under different oxygen concentration treatments were also detected. All the results might be helpful for further understanding of the potential effect of hypoxia in ovoviviparous fish.

AealRACK1 expression and localization in response to stress in C6/36 HT mosquito cells

The Receptor for Activated C Kinase 1 (RACK1), a scaffold protein member of the tryptophan-aspartate (WD) repeat family, folds in a seven-bladed β-propeller structure that permits the association of proteins to form active complexes. Mosquitoes of the genus Aedes sp., are vectors of virus producing important diseases such as: dengue, chikungunya and yellow fever. Based on the highly conserved gene sequence of AeaeRACK1 of the mosquito Aedes aegypti we characterized the mRNA and protein of the homologous AealRACK1 from the Ae. albopictus-derived cell line C6/36 HT. Two protein species differing in MW/pI values were observed at 35kDa/8.0 and 36kDa/6.5. The behavior of AealRACK1 was studied inducing stress with serum deprivation and the glucocorticoid dexamethasone. Both stressors induced increase of the expression of AealRACK1 mRNA and proteins. In serum-deprived cells AealRACK1 protein was located cortically near the plasma membrane in contrast to dexamethasone-treated cells where the protein formed a dotted pattern in the cytoplasm. In addition, 33 protein partners were identified by immunoprecipitation and mass spectrometry. Most of the identified proteins were ribosomal, involved in signaling pathways and stress responses. Our results suggest that AealRACK1 in C6/36 HT cells respond to stress increasing its synthesis and producing phosphorylated activated form.

BIOLOGICAL SIGNIFICANCE

Insect cells adapt to numerous environmental stressors, including chemicals and invasion of pathogenic microorganisms among others, coordinating cellular and organismal responses. Individual cells sense the environment using receptors that trigger signaling pathways that regulate expression of specific effector proteins and/or cellular responses as movement or secretion. In the coordination of responses to stress, scaffold proteins are pivotal molecules that recruit other proteins forming active complexes. The Receptor for Activated C Kinase 1 (RACK1) is the best studied member of the conserved tryptophan-aspartate (WD) repeat family. RACK1 folds in a seven-bladed β-propeller structure and it could be activated during stress, participating in different signaling pathways. The presence and activities of RACK1 in mosquitoes had not been documented before, in this work the molecule is demonstrated in an Aedes albopictus-derived cell line and its reaction to stress is observed under the effect of serum deprivation and the presence of glucocorticoid analog dexamethasone, a chemical used to cause stress in vitro.

Endocrine disrupting compounds affecting corticosteroid signaling pathways in Czech and Swiss waters: potential impact on fish

This study investigated the occurrence of corticosteroid signaling disruptors in wastewaters and rivers in the Czech Republic and in Switzerland. 36 target compounds were detected using HPLC-MS/MS, with up to 6.4 μg/L for azole antifungals that indirectly affect corticosteroid signaling. Glucocorticoid receptor (GR)-mediated activity was determined using the GR-CALUX bioassay with dexamethasone equivalent concentrations ranging from <LOD-2.6, 19-37, and 78-542 ng/L for river water, treated, and untreated wastewater, respectively. For most samples, the chemically predicted GR-mediated response was higher than that determined by the bioassay. Correspondingly, antiglucocorticoid activity was observed in some fractions. The fish plasma model (FPM), which predicts plasma concentrations, was applied to evaluate the potential of detected pharmaceuticals to cause receptor-mediated effects in fish. With one exception, medroxyprogesterone, the FPM applied to individual compounds predicted fish plasma concentrations to be below the level of human therapeutic plasma concentrations. To account for the activity of the sum of GR-active compounds, we introduce the "cortisol equivalents fish plasma concentration" approach, through which an increase in fish glucocorticoid plasma levels comparable to 0.9-83 ng/mL cortisol after exposure to the analyzed river waters was estimated. The results suggest that these chemicals may impact wild fish.

Uptake and biological effects of synthetic glucocorticoids in common carp (Cyprinus carpio)

Uptake and biological effects of synthetic glucocorticoids (GCs) were analyzed using common carp (Cyprinus carpio). Fish were exposed to clobetasol propionate (CP) or clobetasone butyrate (CB) individually or in mixture at 1 μg L(-1) for 21 days. Bioconcentration factor (BCF) of CB was calculated as 100, and BCF of CP was less than 16. No effects were found in fish erythrocyte and leukocyte numbers and serum glucose levels after exposure to the selected GCs. On the other hand, serum concentrations of free amino acids significantly increased in GC-exposed groups. Thus, exposures to synthetic GCs at relatively low concentrations seemed to cause enhancement of protein degradation and subsequent increase of serum free amino acids without a corresponding increase in serum glucose levels, an effect which might be related to partial induction of gluconeogenesis by GC.

Impairment of the immune system in GH-overexpressing transgenic zebrafish (Danio rerio)

Growth hormone (GH) is an important regulator of immune functions in vertebrates, and it has been intensively reported a series of stimulatory actions of this hormone over on the immune system. Within aquaculture, overexpression of GH has been considered a promising alternative for promoting higher growth rates in organisms of commercial interest. Considering the various pleiotropic effects of GH, there are still few studies that aim to understand the consequences of the excess of GH on the physiological systems. In this context, our goal was to present the effects of the overexpression of GH on immune parameters using a model of zebrafish (Danio rerio) that overexpress this hormone. The results showed that GH transgenic zebrafish had 100% of mortality when immunosuppressed with dexamethasone, revealing a prior weakening of the immune system in this lineage. Morphometric analysis of thymus and head kidney revealed a reduction in the area of these structures in transgenic zebrafish. Moreover, the phenotypic expression of CD3 and CD4 thymocytes was also depreciated in transgenic zebrafish. Furthermore, a decrease was noted in the expression of genes RAG-1 (60%), IKAROS (50%), IL-1β (55%), CD4 (60%) and CD247 (40%), indicating that development parameters, of innate and acquired immunity, are being harmed. Based on these results, it can be concluded that the excess of GH impairs the immune functions in GH transgenic zebrafish, indicating that the maintenance of normal levels of this hormone is essential for the functioning of immunological activities.

Environmental stress-induced testis differentiation: androgen as a by-product of cortisol inactivation

This review deals with the gonadal masculinization induced by thermal stress in fish with focus on the action of 11β-hydroxysteroid dehydrogenase (11β-HSD) as this mechanism key transducer. High temperatures have been reported to produce male-skewed sex ratios in several species with TSD (temperature-dependent sex determination), and in some of them, this process was reported to be associated with high levels of cortisol, the hormone-related stress in vertebrates, during early gonad development. In addition, in pejerrey larvae reared at high-masculinizing temperatures, 11-ketotestosterone (11-KT), the main and most potent androgen in fish, was also detected at high levels. In testicular explants, cortisol induced the synthesis of 11-KT, suggesting that its synthesis could be under the control of the stress axis at the time of gonadal fate determination. 11β-HSD is one of the enzymes shared by the glucocorticoid and androgen pathways; this enzyme converts cortisol to cortisone and also participates in the finals steps of the synthesis of the 11-oxigenated androgens. Based on these data and literature information, here we propose that the masculinization induced by thermal stress can be considered as a consequence of cortisol inactivation and the concomitant synthesis of 11-KT and discussing this as a possible mechanism of masculinization induced by different types of environmental stressors.

Effects of praziquantel and sanguinarine on expression of immune genes and susceptibility to Aeromonas hydrophila in goldfish (Carassius auratus) infected with Dactylogyrus intermedius

Praziquantel and sanguinarine have been demonstrated positive therapeutic effects on monogenean Dactylogyrus intermedius; however, few studies have considered the post impacts of these antiparasitic chemicals on host after repelling the parasites. The changes of expression of selected immune genes (CCL-1, CXCL-8, IL-1β-1, IL-1β-2, TNFα-1, TNFα-2 and TGF-β) in gill, kidney and spleen and bacterial loads of Aeromonas hydrophila in gill, kidney, spleen and liver following bath administration of these antiparasitic chemicals were evaluated. The results showed that praziquantel and sanguinarine up-regulated to varying degrees of CXCL-8, IL-1β-1, IL-1β-2, TNFα-1 and TNFα-2 in gill, kidney and spleen. They both decreased the CCL-1 expression in gill while increased it in kidney and spleen. However, in all the tested tissues, the expression of TGF-β decreased in praziquantel treated goldfish whereas that increased in sanguinarine treated goldfish. The A. hydrophila challenge test showed that the praziquantel treatment enhanced the susceptibility to A. hydrophila while sanguinarine treatment decreased the susceptibility, as compared with the non-treated group. Overall, the results indicate that bath administration of praziquantel and sanguinarine modulates the immune related genes in goldfish and these may, to some extent, affect their ability to resist bacterial pathogens.

Effects of dietary arachidonic acid on cortisol production and gene expression in stress response in Senegalese sole (Solea senegalensis) post-larvae

Dietary fatty acids, particularly arachidonic acid (ARA), affect cortisol and may influence the expression of genes involved in stress response in fish. The involvement of ARA on stress, lipid, and eicosanoid metabolism genes, in Senegalese sole, was tested. Post-larvae were fed Artemia presenting graded ARA levels (0.1, 0.4, 0.8, 1.7, and 2.3%, dry matter basis), from 22 to 35 days after hatch. Whole-body cortisol levels were determined, before and 3 h after a 2 min air exposure, as well as the expression of phospholipase A2 (PLA 2 ), cyclooxygenase-2 (COX-2), steroidogenic acute regulatory protein (StAR), glucocorticoid receptors (GRs), phosphoenolpyruvate carboxykinase (PEPCK), and peroxisome proliferator-activated receptor alpha (PPARα). Relative growth rate (6.0-7.8% day(-1)) and survival at the end of the experiment (91-96%) and after stress (100%) were unaffected. Fish reflected dietary ARA content and post-stress cortisol increased with ARA supply up to 1.7%, whereas 2.3% ARA seemed to enhance basal cortisol slightly and alter the response to stress. Results suggested that elevating StAR transcription might not be necessary for a short-term response to acute stress. Basal cortisol and PLA 2 expression were strongly correlated, indicating a potential role for this enzyme in steroidogenesis. Under basal conditions, larval ARA was associated with GR1 expression, whereas the glucocorticoid responsive gene PEPCK was strongly related with cortisol but not GR1 mRNA levels, suggesting the latter might not reflect the amount of GR1 protein in sole. Furthermore, a possible role for PPARα in the expression of PEPCK following acute stress is proposed.

Effects of Cortisol Administered through Slow-Release Implants on Innate Immune Responses in Rainbow Trout (Oncorhynchus mykiss)

Cortisol is a key hormone in the fish stress response with a well-known ability to regulate several physiological functions, including energy metabolism and the immune system. However, data concerning cortisol effects on fish innate immune system using a more controlled increase in cortisol levels isolated from any other stress related signaling is scarce. The present study describes the effect of doses of cortisol corresponding to acute and chronic levels on the complement and lysozyme activity in plasma of the rainbow trout (Oncorhynchus mykiss). We also evaluated the effects of these cortisol levels (from intraperitoneally implanted hydrocortisone) on the mRNA levels quantified by RT-qPCR of selected key immune-related genes in the liver, head kidney, and spleen. For that purpose, 60 specimens of rainbow trout were divided in to two groups: a control group injected with a coconut oil implant and another group injected with the same implant and cortisol (50 μg cortisol/g body weight). Our results demonstrate the role of cortisol as a modulator of the innate immune response without the direct contribution of other stress axes. Our results also show a relationship between the complement and lysozyme activity in plasma and mRNA levels in liver, supporting the important role of this organ in producing these immune system proteins after a rise of cortisol in the fish plasma.