Comparative study of 17 β-estradiol on endocrine disruption and biotransformation in fingerlings and juveniles of Japanese sea bass Lateolabrax japonicus

Sensitivity of cholinesterases and carboxylesterases to pharmaceutical products in Tinca tinca

Discharges to the aquatic environment of pharmaceuticals represent a hazard to the aquatic organisms. Subchronic assay with 17-alpha-ethinylestradiol (EE2) and in vitro essays with pharmaceuticals of environmental concern were conducted to examine the sensitivity of tissue acetylcholinesterase (AChE) and carboxylesterase (CbE) activities of Tinca tinca to them. Subchronic exposure to 17-alpha-EE2 caused significant effects on brain, liver, and muscle CbE, but no on AChE activities. Most of the pharmaceuticals tested in vitro were considered as weak inhibitors of tissular AChE activity. Depending on the tissues, some compounds were classified as moderate inhibitors of CbE activity while other were categorized as weak enzymatic inhibitors. An opposite trend was observed depending on the tissue, while brain and liver CbE activities were inhibited, the muscle CbE activity was induced. Changes experienced on enzymatic activities after exposure to pharmaceuticals might affect the physiological functions in which these enzymes are involved. In vitro exposure to 17-alpha-EE2 in tench could be an informative, but not a surrogate model to know the effect of this synthetic estrogen on AChE and CbE activities.

Chronic exposure to tris (2-chloroethyl) phosphate (TCEP) induces brain structural and functional changes in zebrafish (Danio rerio): A comparative study on the environmental and LC50 concentrations of TCEP

Tris (2-chloroethyl) phosphate (TCEP) is a crucial organophosphorus flame retardant widely used in many industrial and commercial products. Available reports reported that TCEP could cause various toxicological effects on organisms, including humans. Unfortunately, toxicity data for TCEP (particularly on neurotoxicity) on aquatic organisms are lacking. In the present study, Danio rerio were exposed to different concentrations of TCEP for 42 days (chronic exposure), and oxidative stress, neurotoxicity, sodium, potassium-adenosine triphosphatase (Na+, K+-ATPase) activity, and histopathological changes were evaluated in the brain. The results showed that TCEP (100 and 1500 µg L-1) induced oxidative stress and significantly decreased the activities of antioxidant enzymes (SOD, CAT and GR) in the brain tissue of zebrafish. In contrast, the lipid peroxidation (LPO) level was increased compared to the control group. Exposure to TCEP inhibited the acetylcholinesterase (AChE) and Na+,K+-ATPase activities in the brain tissue. Brain histopathology after 42 days of exposure to TCEP showed cytoplasmic vacuolation, inflammatory cell infiltration, degenerated neurons, degenerated purkinje cells and binucleate. Furthermore, TCEP exposure leads to significant changes in dopamine and 5-HT levels in the brain of zebrafish. The data in the present study suggest that high concentrations of TCEP might affect the fish by altering oxidative balance and inducing marked pathological changes in the brain of zebrafish. These findings indicate that chronic exposure to TCEP may cause a neurotoxic effect in zebrafish.

The influence of 17β-oestradiol on lymphopoiesis and immune system ontogenesis in juvenile sea bass, Dicentrarchus labrax

The female sex steroid 17β-oestradiol (E2) is involved in the regulation of numerous physiological functions, including the immune system development and performance. The role of oestrogens during ontogenesis is, however, not well studied. In rodents and fish, thymus maturation appears to be oestrogen-dependent. Nevertheless, little is known about the function of oestrogen in immune system development. To further the understanding of the role of oestrogens in fish immune system ontogenesis, fingerlings of European sea bass (Dicentrarchus labrax) were exposed for 30 days to 20 ng E2·L^-1, at two ages tightly related to thymic maturation, i.e., 60 or 90 days post hatch (dph). The expression of nuclear and membrane oestrogen receptors was measured in the thymus and spleen, and the expression of several T cell-related gene markers was studied in both immune organs, as well as in the liver. Waterborne E2-exposure at 20.2 ± 2.1 (S.E.) ng·L^-1 was confirmed by radioimmunoassay, leading to significantly higher E2-contents in the liver of exposed fish. The majority of gene markers presented age-dependent dynamics in at least one of the organs, confirming thymus maturation, but also suggesting a critical ontogenetic window for the implementation of liver resident γδ and αβ T cells. The oestrogen receptors, however, remained unchanged over the age and treatment comparisons with the exception of esr2b, which was modulated by E2 in the younger cohort and increased its expression with age in the thymus of the older cohort, as did the membrane oestrogen receptor gpera. These results confirm that oestrogen-signalling is involved in thymus maturation in European sea bass, as it is in mammals. This suggests that esr2b and gpera play key roles during thymus ontogenesis, particularly during medulla maturation. In contrast, the spleen expressed low or non-detectable levels of oestrogen receptors. The E2-exposure decreased the expression of tcrγ in the liver in the cohort exposed from 93 to 122 dph, but not the expression of any other immune-related gene analysed. These results indicate that the proliferation/migration of these innate-like T cell populations is oestrogen-sensitive. In regard to the apparent prominent role of oestrogen-signalling in the late thymus maturation stage, the thymic differentiation of the corresponding subpopulations of T cells might be regulated by oestrogen. To the best of our knowledge, this is the first study investigating the dynamics of both nuclear and membrane oestrogen receptors in specific immune organs in a teleost fish at very early stages of immune system development as well as to examine thymic function in sea bass after an exposure to E2 during ontogenesis.

Brain Aromatase Modulates Serotonergic Neuron by Regulating Serotonin Levels in Zebrafish Embryos and Larvae

Teleost fish are known to express two isoforms of P450 aromatase, a key enzyme for estrogen synthesis. One of the isoforms, brain aromatase (AroB), cyp19a1b, is highly expressed during early development of zebrafish, thereby suggesting its role in brain development. On the other hand, early development of serotonergic neuron, one of the major monoamine neurons, is considered to play an important role in neurogenesis. Therefore, in this study, we investigated the role of AroB in development of serotonergic neuron by testing the effects of (1) estradiol (E₂) exposure and (2) morpholino (MO)-mediated AroB knockdown. When embryos were exposed to E₂, the effects were biphasic. The low dose of E₂ (0.005 µM) significantly increased serotonin (5-HT) positive area at 48 hour post-fertilization (hpf) detected by immunohistochemistry and relative mRNA levels of tryptophan hydroxylase isoforms (tph1a, tph1b, and tph2) at 96 hpf measured by semi-quantitative PCR. To test the effects on serotonin transmission, heart rate and thigmotaxis, an indicator of anxiety, were analyzed. The low dose also significantly increased heart rate at 48 hpf and decreased thigmotaxis. The high dose of E₂ (1 µM) exhibited opposite effects in all parameters. The effects of both low and high doses were reversed by addition of estrogen receptor (ER) blocker, ICI 182,780, thereby suggesting that the effects were mediated through ER. When AroB MO was injected to fertilized eggs, 5-HT-positive area was significantly decreased, while the significant decrease in relative tph mRNA levels was found only with tph2 but not with two other isoforms. AroB MO also decreased heart rate and increased thigmotaxis. All the effects were rescued by co-injection with AroB mRNA and by exposure to E₂. Taken together, this study demonstrates the role of brain aromatase in development of serotonergic neuron in zebrafish embryos and larvae, implying that brain-formed estrogen is an important factor to sustain early development of serotonergic neuron.

17β-Estradiol induces cyto-genotoxicity on blood cells of common carp (Cyprinus carpio)

17β-Estradiol, a natural hormone present at high concentrations in aquatic ecosystems, affects and modifies endocrine function in animals. In recent years research workers have expressed concern over its potential effects on aquatic organisms; however, little is known about its capacity to induce genetic damage or the pro-apoptotic effects of such damage on fish. Therefore, this study aimed to evaluate 17β-estradiol-induced cyto-genotoxicity in blood cells of the common carp Cyprinus carpio exposed to different concentrations (1 ng, 1 μg and 1 mg L^-1). Peripheral blood samples were collected and evaluated by comet assay, micronucleus test, determination of caspase-3 activity and TUNEL assay at 12, 24, 48, 72 and 96 h of exposure. Increases in frequency of micronuclei, TUNEL-positive cells and caspase-3 activity were observed, particularly at the highest concentration. In contrast, the comet assay detected significant increases at 24 and 96 h with the 1 μg and 1 ng L^-1 concentrations respectively. The set of assays used in the present study constitutes a reliable early warning biomarker for evaluating the toxicity induced by this type of emerging contaminants on aquatic species.

The chronic effects of lignin-derived bisphenol and bisphenol A in Japanese medaka Oryzias latipes

One of the ultimate goals of green chemistry is to produce greener and more environmentally friendly chemicals to replace the existing toxic chemicals. In this study, Japanese medaka were exposed to 1.5mg/L of bisphenol A or lignin-derived bisphenol for 60 days, and the expressions of various biochemical markers, effects on reproduction, and histopathology were evaluated. The results showed that concentrations of liver vitellogenin of LD-BP exposed males were approximately 125% higher compared to the control males. Total number of eggs from the BPA and LD-BP exposed fish was approximately 47% (p<0.001) and 25% (p<0.05) less than the control fish, respectively. Total number of brood was lower from the BPA (46%, p<0.05) and LD-BP (17%, p<0.05) exposed fish than that of the control fish. Relative to the control fish, catalase and glutathione-S-transferase were significantly affected by the two chemicals in all tested tissues. BPA and LD-BP caused lipid peroxidation in all the tested tissues. Furthermore, acetylcholinesterase and α-glucosidase activity were significantly inhibited. Histopathological analysis showed that both the testis and ovary were mildly damaged by both chemicals. LD-BP affected medaka slightly more severe than BPA except on the reproduction, which was most likely due to different uptake, translocation, binding to targets and metabolism. Our results demonstrated that chronic exposure to both chemicals caused several adverse effects to medaka. Further research on the toxicity of LD-BP to other aquatic organisms is needed before substitution of traditional BPA with LD-BP can be recommended.

Biochemical responses in the gills of Meretrix meretrix after exposure to treated municipal effluent

The biochemical effects in marine bivalves exposed to increasing concentrations of treated municipal effluent (TME), as discharged into receiving marine waters, are investigated. The effluent was collected from a municipal sewage treatment plant (STP) in Qingdao (China). Meretrix meretrix were exposed to effluent volume ratio (EVR, ratio of effluent volume accounted for tailwater seawater mixture) 0%, 1%, 5%, 10%, and 20% (v/v) TME for 15 days and the following biochemical responses in gills were measured: (1) the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione (GSH) content, and lipid peroxidation levels of malondialdehyde (MDA), as oxidative stress biomarkers; (2) the activity of 7-ethoxyresorufin O-deethylase (EROD) and gluthathione S-transferase (GST), as phase I and phase II conjugation enzymes, respectively; (3) acetylcholinesterase (AChE), as a biomarker of neurotoxicity, and (4) metallothioneins (MTs), as proteins strongly induced by heavy metals. Most of the biochemical indices present high and significant variation frequency (above 50%). There is enhancement in the antioxidant enzymes, EROD, GST, AChE, and MTs, as well as consumption of GSH. The current experimental results suggest that effluent with concentrations less than 20% (v/v) do not cause lipid peroxidation damage. This implies that the activated defense is sufficient to protect the bivalves' gill tissues from cytotoxicity produced by the effluent. Furthermore, GSH, GPx, MTs, and GR are suitable, and sufficiently sensitive, biomarkers to indicate the pollution levels in marine environments receiving such effluent.