Brain as a critical target of mercury in environmentally exposed fish (Dicentrarchus labrax)--bioaccumulation and oxidative stress profiles

Influence of acute heat shock on antioxidant defense of tropical fish, Psalidodon bifasciatus

Psalidodon bifasciatus is a fish species sensitive to physical and chemical changes in water. It serves as a good bioindicator of temperature variations and is utilized in environmental monitoring studies in Brazilian rivers. The objective of this study was to evaluate antioxidant defense biomarkers in the heart, brain, and muscle of P. bifasciatus exposed to a 10 °C thermal increase. P. bifasciatus were collected and divided into a control group (21 °C) and groups subjected to thermal shock (31 °C) for periods of 2, 6, 12, 24, and 48h. Two-way ANOVA indicated that a 10 °C temperature increase caused oxidative stress in P. bifasciatus. This was evidenced by altered levels of lipid peroxidation (LPO), carbonylated proteins (PCO), and glutathione peroxidase (GPx) in the heart, catalase (CAT) and LPO in the brain, and LPO in the muscle. Principal component analysis (PCA) and integrated biomarker response (IBR) analysis indicated that, compared to the heart and muscle, the brain exhibited a greater activation of the antioxidant response. Sensitivity analysis indicated that the muscle was the most sensitive organ, followed by the brain and heart. Our results indicate that the stress response is tissue-specific through the activation of distinct mechanisms. These responses may be associated with the tissue's function as well as its energy demand. As expected, P. bifasciatus showed changes in response to thermal stress, with the brain showing the greatest alteration in antioxidant defenses and the muscle being the most sensitive tissue.

Mercury chloride causes cognitive impairment, oxidative stress and neuroinflammation in male Wistar rats: The potential protective effect of 6-gingerol-rich fraction of Zingiber officinale via regulation of antioxidant defence system and reversal of pro-inflammatory markers increase

This study investigated the effects of 6-gingerol-rich fraction of Zingiber officinale (6-GIRIFZO) on mercury chloride (HgCl2)-induced neurotoxicity in Wistar rats. Thirty -five male Wistar rats weighing between (150-200 g) were divided randomly into five groups (n = 7): group 1: control, received 0.5 mL of normal saline, group 2: received HgCl2 (5 mg/kg), group 3: received N-acetylcysteine (NAC) (50 mg/kg) as well as HgCl2 (5 mg/kg), group 4: received 6-GIRIFZO (100 mg/kg) and HgCl2 (5 mg/kg), group 5: had 6-GIRIFZO (200 mg/kg) and HgCl2 (5 mg/kg), consecutively for 14 days. On the day14, the rats were subjected to behavioural tests using a Morris water maze and novel object recognition tests. The rats were then euthanized to obtain brain samples for the determination of biochemical parameters (acetylcholinesterase (AchE), nitric oxide (NO), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione (GSH), tumor necrosis factor- alpha (TNF-α), nuclear factor kappa-B (NF-κB), interleukin-1β (IL-1β) and interleukin-6 (IL-6)) using standard methods. The result revealed a significant increase in escape latency and a significant decrease in recognition ratio in the rats that were exposed to HgCl2 only. However, 6-GIRIFZO produced a significant reduction in the escape latency and (p < 0.05) increase in the recognition ratio. Similarly, HgCl2 exposure caused a significant (p < 0.05) decrease in the brain SOD, GPx, CAT, GSH with increased brain levels of MDA, NO, AchE, TNF-α, NF-κB, IL-1β and IL-6. Similarly to the standard drug, NAC, 6-GIRIFZO (100 and 200 mg/kg) significantly (p < 0.05) increased brain SOD, GPx, CAT, and GSH levels with decreased concentrations of MDA, NO, AchE, TNF-α, NF-κB, IL-1β and IL-6. Also, pre-treatment with 6-GIRIFZO prevented the HgCl2-induced morphological aberrations in the rats. This study concludes that 6-GIRIFZO prevents HgCl2-induced cognitive deficit via reduction of brain inflammation as well as oxidative stress in rats.

Mercury transformations in algae, plants, and animals: The occurrence, mechanisms, and gaps

Mercury (Hg) is a global pollutant showing potent toxicity to living organisms. The transformations of Hg are critical to global Hg cycling and Hg exposure risks, considering Hg mobilities and toxicities vary depending on Hg speciation. Though currently well understood in ambient environments, Hg transformations are inadequately explored in non-microbial organisms. The primary drivers of in vivo Hg transformations are far from clear, and the impacts of these processes on global Hg cycling and Hg associated health risks are not well understood. This hinders a comprehensive understanding of global Hg cycling and the effective mitigation of Hg exposure risks. Here, we focused on Hg transformations in non-microbial organisms, particularly algae, plants, and animals. The process of Hg oxidation/reduction and methylation/demethylation in organisms were reviewed since these processes are the key transformations between the dominant Hg species, i.e., elemental Hg (Hg0), divalent inorganic Hg (IHgII), and methylmercury (MeHg). By summarizing the current knowledge of Hg transformations in organisms, we proposed the potential yet overlooked drivers of these processes, along with potential challenges that hinder a full understanding of in vivo Hg transformations. Knowledge summarized in this review would help achieve a comprehensive understanding of the fate and toxicity of Hg in organisms, providing a basis for predicting Hg cycles and mitigating human exposure.

Andrographis paniculata protects against brain hippocampus and cerebellum from mercury chloride induced damage by attenuating oxidative stress

Mercury chloride (HgCl2) is a neurotoxicant that remains a health hazard despite numerous efforts to reduce its levels in the environment. The use of medicinal plants in treating various diseases and other toxic agents has grown popular owing to their effectiveness and affordable rates. Andrographis paniculata (A. paniculata) is a plant with astringent and detoxifying characteristics and is widely used worldwide for its medicinal and antioxidant benefits. This study aimed to investigate the possible protective effects of A. paniculata aqueous extract against HgCl2-induced memory impairment, oxidative stress, and brain damage. Twenty-five adult Wistar rats were randomly divided into five groups: control, HgCl2 0.5 mg/kg, HgCl2+AP 250 mg/kg, HgCl2+AP 500 mg/kg, or HgCl2+Ascorbic acid 200 mg/kg. For 28 days, administrations were given through oral gavage once a day. HgCl2 injection resulted in memory impairment, increased glutamate concentrations in the brain, and the production of oxidative stress. Memory impairment was prevented in A. paniculata-treated groups by balancing the levels of AChE and dopamine activities, which then lowered glutamate concentration, avoided oxidative stress, and improved histopathological alterations in the brain. A. paniculata alleviated HgCl2-induced memory impairment in Wistar rats by increasing the memory index, regulating neurotransmitter levels, and reducing oxidative stress.

Long-term exposure of the binary mixture of cadmium and mercury damages the developed ovary of adult zebrafish

The toxicity of the binary mixture of cadmium (Cd) and mercury (Hg) on the ovary of adult zebrafish was evaluated in the present study. Adult female zebrafish were exposed to cadmium chloride (1 mg/L), mercury chloride (30 µg/L), and a binary mixture of both metals for 21 days. The toxic effects of both metals on the ovary were investigated by evaluating the oxidative stress markers and related gene expression in ovarian tissue along with the histopathological examination. The significantly decreased level of GSH and increased level of MDA in ovarian tissue of adult female zebrafish exposed to Cd + Hg indicated that the exposure of binary mixture of Cd and Hg caused more lipid peroxidation in the ovary. The significant changes in expression of mRNA of catalase (CAT) and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) were not observed in the ovary of zebrafish exposed to the binary mixture. Upon histological evaluation, a decreased number of full-growth (mature) oocytes along with degenerative changes due to Cd exposure were noticed, while ovary of zebrafish of the Hg-exposed group had shown a decreased number of pre-and early vitellogenic oocytes along with atretic previtellogenic oocytes compared to the control group. The ovary of zebrafish of the Cd + Hg-exposed group had shown a decreased number of previtellogenic oocytes with marked pathological changes in mature oocytes. Present findings elucidate that simultaneous long-term exposure of Cd and Hg compared to individual exposure significantly damaged the various stages of oocytes of an ovary of adult zebrafish.

Chronic Toxic Effects of Waterborne Mercury on Silver Carp (Hypophthalmichthys molitrix) Larvae

Mercury (Hg) is a kind of heavy metal pollutant widely existing in the aquatic environment, and it is also recognized to have a highly toxic effect on fish. In this study, silver carp (Hypophthalmichthys molitrix) larvae were exposed to 0 (control), 1, 5, and 10 μg/L Hg2+ for 2 weeks. Antioxidant ability, neurotoxicity, and thyroid hormones (THs) content were evaluated. In comparison with the control, the superoxide dismutase (SOD) activity and the glutathione (GSH) activity were lower in silver carp exposed to 10 μg/L Hg2+. The lowest catalase (CAT) activity was found in the 10 μg/L Hg2+, while malondialdehyde (MDA) content was not significantly different among all groups. Compared with the control, monoamine oxidase (MAO) activity and nitric oxide (NO) content were significantly higher in the 10 μg/L Hg2+, while acetylcholinesterase (AChE) activity significantly decreased. Compared with the control, triiodothyronine (T3) content was significantly higher in the 1 μg/L Hg2+ and significantly lower in the 10 μg/L Hg2+; the 1 μg/L and 5 μg/L Hg2+ groups had significantly higher thyroxine (T4) content than the other groups. In the 1 μg/L Hg2+, the integrated biomarker response (IBR) index value was the highest. In summary, exposure to Hg could decrease the antioxidant ability, cause changes in neurotoxic parameters, and induce disorders of the thyroid hormone system in silver carp larvae. The results of this study may contribute to the understanding of the adverse effects of chronic mercury poisoning on fish.

Tissue Distribution of Mercury and Its Relationship with Selenium in Atlantic Bluefin Tuna (Thunnus thynnus L.)

Mercury (Hg) is an important heavy metal to consider in marine predators, while selenium (Se) has a natural antagonistic effect on this metal in fish. The Atlantic bluefin tuna (ABFT, Thunnus thynnus) is a pelagic top-level predator of the trophic web and their Hg muscular content is an object of concern in food safety. Nevertheless, little is known about levels of this metal in remaining tissues, which may be important as by-product source, and its relationship with Se. Thus, concentration of both elements in liver, kidney, brain, gill and bone, in addition to muscle, of ABFT were determined. The kidney was the tissue with the highest concentration of Hg (Total-Hg, THg) and Se, and the Se/THg concentration ratio was similar in all tissues, except bone and muscle. The Selenium Health Benefit Value (HBV_Se) was positive in each specimen and tissue, indicating that the Se plays an important role against Hg not only in the muscle.

CoNaMad-Cohorte de Nacimiento de Madre de Dios/Madre de Dios Birth Cohort to Study Effects of in-utero Trace Metals Exposure in the Southern Peruvian Amazon

Background:

In-utero exposure to mercury and other trace metals pose a significant threat to child health and development, but exposures and health impacts in artisanal and small-scale gold mining (ASGM) environments are poorly defined.

Objectives:

We describe the CONAMAD study design, a prospective birth cohort consisting of multiparous women (18 and over) living in rural and peri-urban Peruvian Amazon communities exposed to ASGM.

Methods:

Pregnant women are enrolled from health posts across four zones of Madre de Dios, Peru. Data are collected at enrollment, childbirth, and (planned) 36-48 months. At enrollment, hair samples for mercury assessment, demographic and clinical data are obtained. At birth, we obtain venous and cord blood, placenta, hair, toenails, and saliva.

Findings:

Two hundred seventy mothers were enrolled at an average 20 weeks gestational age with no differences in maternal characteristics across zones. Two hundred fifteen mothers were successfully followed at birth. We obtained 214 maternal and cord blood samples, 211 maternal and 212 infant hair samples, 212 placenta samples, 210 infant saliva samples, and 214 infant dried blood spots. Data collected will allow for testing our primary hypotheses of maternal malnutrition modifying ratios of cord:maternal blood total mercury (tHg), cord blood:maternal hair tHg, and infant:maternal hair tHg, and whether chemical mixtures (Hg, Pb, Cd) have synergistic effects on infant neurodevelopment.

Conclusions:

CONAMAD is designed to collect and store samples for future processing and hypothesis testing associated with in-utero mercury exposure and child development. We have completed the exposure assessments and will conduct a follow-up of mothers to evaluate early child development outcomes, including developmental delay and growth. These data offer insights into disease mechanisms, exposure prevention, and policy guidance for countries where ASGM is prevalent.

Oxidative stress, metabolic activity and mercury concentrations in Antarctic krill Euphausia superba and myctophid fish of the Southern Ocean

Indicators of oxidative stress and metabolic capacity are key factors in understanding the fitness of wild populations. In the present study, these factors were evaluated in the pelagic Southern Ocean taxa Antarctic krill (Euphausia superba) and myctophid fish (Electrona antarctica, Gymnoscopelus braueri and G. nicholsi) to establish a baseline record for future studies. Mercury (Hg) concentrations were also analysed to evaluate its potential impacts on species biochemical performance. E. superba had higher metabolic activity than most of the myctophid species, which may explain the comparatively lower energy reserves found in the former. The activity of antioxidant enzymes showed, generally, a lower level in E. superba than in the myctophid species. The lack of any relationship between Hg concentrations and organisms' antioxidant and biotransformation defence mechanisms indicate that levels of Hg accumulated in the studied species were not high enough to affect their biochemical processes adversely.

Mercury in the tissues of five cephalopods species: First data on the nervous system

Mercury (Hg), one of the elements most toxic to biota, accumulates within organisms throughout their lifespan and biomagnifies along trophic chain. Due to their key role in marine systems, cephalopods constitute a major vector of Hg in predators. Further, they grow rapidly and display complex behaviours, which can be altered by neurotoxic Hg. This study investigated Hg concentrations within 81 cephalopod specimens sampled in the Bay of Biscay, which belonged to five species: Eledone cirrhosa, Sepia officinalis, Loligo vulgaris, Todaropsis eblanae and Illex coindetii. Hg concentrations were measured in the digestive gland, the mantle muscle and the optic lobes of the brain. The digestive gland and the mantle were tissues with the most concentrated Hg among all species considered (up to 1.50 μg.g^-1 dw), except E. cirrhosa. This benthic cephalopod had 1.3-fold higher Hg concentrations in the brain (up to 1.89 μg.g^-1 dw) than in the mantle, while other species had 2-fold lower concentrations of Hg in the brain than in the mantle. Brain-Hg concentrations can be predicted from muscle-Hg concentrations for a given species, which facilitates the assessment of Hg toxicokinetics in cephalopods. In the most contaminated E. cirrhosa individual, the chemical form of Hg in its digestive gland, mantle muscle and optic lobes, was determined using High energy-Resolution X-ray Absorption Near Edge Structure (HR XANES) spectroscopy. In the digestive gland, 33 ± 11% of total Hg was inorganic Hg speciated as a dicysteinate complex (Hg(Cys)₂), which suggested that the demethylation of dietary MeHg occurs in this organ. All Hg found in the mantle muscle and the optic lobes is methylated and bound to one cysteinyl group (MeHgCys complex), which implies that dietary MeHg is distributed to these tissues via the bloodstream. These results raised the questions regarding interspecific differences observed regarding Hg brain concentrations and the possible effect of Hg on cephalopod functional brain plasticity and behaviour.

Water temperature modulates mercury accumulation and oxidative stress status of common goby (Pomatoschistus microps)

Mercury (Hg) is a widespread pollutant across estuarine and coastal areas, raising concern on its potential impact on aquatic organisms. Hg may origin from natural and anthropogenic sources, being persistent and potentially toxic to biota, ultimately representing a serious risk to human health. Hg accumulation and toxicity may also induce reactive oxygen species (ROS) production in marine organisms, responsible for cell and tissue damage. Additionally, the temperature is undoubtedly an important environmental factor to consider regarding accumulation, due to its marked influence on the physiology and ecology of aquatic organisms. This study aimed to investigate the effect of different temperature scenarios (15, 20 and 25 °C) on the Hg accumulation in Pomatoschistus microps (Krøyer, 1838) liver and muscle, as well as on oxidative stress responses and energy metabolism, after short-term exposure to a naturally contaminated sediment with an environmentally relevant [Hg] (1.2 μg g^-1). The results showed that Hg accumulation tends to increase along the temperature gradient with higher values of Hg accumulated in liver than in muscle tissue. The action of antioxidant enzymes and stress proteins seems to be effective in combating oxidative stress in the liver. Despite the action of antioxidant defences in the muscle, oxidative damage was observed at the protein level concomitantly with a decrease in aerobic energy production after exposure to Hg at higher temperatures. These findings are ecologically relevant and highlight the importance of further investigation of combined effects of Hg and other stressors, especially in a scenario of a changing climate where events leading to rapid alterations on water parameters are more frequent.

Mercury Accumulation and Effects in the Brain of the Atlantic Sharpnose Shark (Rhizoprionodon terraenovae)

Few published studies have examined whether the elevated concentrations of the nonessential toxic metal mercury (Hg) often observed in shark muscle also occur in the shark brain or whether Hg accumulation affects shark neurophysiology. Therefore, this study examined accumulation and distribution of Hg in the shark brain, as well as effects of Hg on oxidative stress in the shark central nervous system, with particular focus on the Atlantic sharpnose shark (Rhizoprionodon terraenovae). Sharks were collected along the southeastern U.S. coast throughout most of this species' U.S. geographical range. Total Hg (THg) concentrations were measured in and compared between shark muscle and brain, whereas known biomarkers of Hg-induced neurological effects, including glutathione depletion, lipid peroxidation, and concentrations of a protein marker of glial cell damage (S100b), were measured in shark cerebrospinal fluid. Brain THg concentrations were correlated with muscle THg levels but were significantly lower and did not exceed most published thresholds for neurological effects, suggesting limited potential for detrimental responses. Biomarker concentrations supported this premise, because these data were not correlated with brain THg levels. Hg speciation also was examined. Unlike muscle, methylmercury (MeHg) did not comprise a high percentage of THg in the brain, suggesting that differential uptake or loss of organic and inorganic Hg and/or demethylation of MeHg may occur in this organ. Although Hg accumulation in the shark brain generally fell below toxicity thresholds, higher THg levels were measured in the shark forebrain compared with the midbrain and hindbrain. Therefore, there is potential for selective effects on certain aspects of shark neurophysiology if brain Hg accumulation is increased.

Oxidative stress, histopathological alterations and anti-oxidant capacity in different tissues of largemouth bass (Micropterus salmoides) exposed to a newly developed sodium carbonate peroxyhydrate granular algaecide formulated with hydrogen peroxide

Various strategies exist to control noxious cyanobacterial populations, although the application of a newly developed granular compound (sodium carbonate peroxyhydrate 'SCP', trade name 'PAK® 27' algaecide) containing hydrogen peroxide (H₂O₂) as the active ingredient, has been recently proven as an effective and ecofriendly treatment. However, in aquaculture settings the application of SCP to treat cynobacterial blooms may affect non-targeted biota, such as fish due to H₂O₂ being known to elicit toxic oxidative stress. Consequently, a better understanding of the side effects as a function of dosing concentrations would help to improve treatment efficacy and fish welfare. Thus, the aim of the current study is to assess the potential risks of SCP to largemouth bass (Micropterus salmoides), a high priced fish in the U.S. To this end, fish were exposed to two recommended doses of SCP corresponding to either 2.5 or 4.0 mg/L H₂O₂ for 6 days, with a control group in parallel. After 6 days, the effect of SCP exposure on oxidative stress, histopathological changes and anti-oxidant potential in the brain, liver, gills and muscle were investigated. Results show that exposure to 4.0 mg/L H₂O₂ -SCP incited oxidative damage, evidenced by an over-accumulation of H₂O₂ and malondialdehyde (MDA) in the brain and liver, which were accompanied by an increment in xanthine oxidase activity. Unlike 4.0 mg/L H₂O₂, these oxidative stress biomarkers in the brain and liver tissue of 2.5 mg/L H₂O₂-SCP exposed fish were restrained within control levels and concomitant with an increase in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-s-transferase (GST) activity. In contrast, many of these anti-oxidants sentinels in the 4.0 mg/L H₂O₂ exposed fish were either unaffected or significantly inhibited, which resulted in over-accumulation of H₂O₂ and MDA. In addition, a series of histopathological alterations were observed, and the most severe brain injuries and liver inflammation were recorded in 4.0 mg/L H₂O₂-SCP exposed fish. Based on oxidative parameters, both SCP doses resulted in a relatively mild oxidative stress in gills but no effect in muscle, probably explaining the modest anti-oxidative responses in the former and almost complete lack of anti-oxidative responses in the latter. Overall, our findings suggests that the application of SCP at 4.0 mg/L H₂O₂ to control cyanobacterial blooms in aquaculture settings can possess potential risks to the farmed fish.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior

BACKGROUND

Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms.

SCOPE OF REVIEW

A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed.

MAJOR CONCLUSIONS

Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed.

GENERAL SIGNIFICANCE

Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.

Metals(loids) targeting fish eyes and brain in a contaminated estuary - Uncovering neurosensory (un)susceptibility through bioaccumulation, antioxidant and morphometric profiles

This study examined the susceptibility of fish (Liza aurata) eyes and brain to metals(loids) contamination under realistic exposure conditions. A multidimensional approach was applied to fish caught at a chronically contaminated site (BAR) and at a reference site of the Tagus estuary (Portugal), which comprised metals(loids) accumulation in eyes and brain together with a battery of enzymatic and non-enzymatic antioxidants, as well as brain morphometry (i.e. cell density). Trace element levels in the blood, gills, liver and kidney allowed interpretations on their preferential pathway(s) to the eyes and brain. Metals(loids) accumulation pointed out the elevated vulnerability of the fish eyes at BAR, probably related with the direct waterborne uptake. Pb uptake in L. aurata eyes could be associated both with water and indirect pathways. At the most contaminated site, metals(loids) were on the basis of pro-oxidant conditions in the ocular tissues, while no indication of toxicity was recorded in the brain. Overall, the results disclosed a differential bioaccumulation among fish organs, suggesting that, in the L. aurata population studied, metal organotropism underlie the lower susceptibility of the brain comparing to the eyes. However, mechanisms remain little understood and further work is needed.

Brain morphometric profiles and their seasonal modulation in fish (Liza aurata) inhabiting a mercury contaminated estuary

Mercury (Hg) is a potent neurotoxicant known to induce important adverse effects on fish, but a deeper understanding is lacking regarding how environmental exposure affects the brain morphology and neural plasticity of specific brain regions in wild specimens. In this work, it was evaluated the relative volume and cell density of the lateral pallium, hypothalamus, optic tectum and molecular layer of the cerebellum on wild Liza aurata captured in Hg-contaminated (LAR) and non-contaminated (SJ) sites of a coastal system (Ria de Aveiro, Portugal). Given the season-related variations in the environment that fish are naturally exposed, this assessment was performed in the winter and summer. Hg triggered a deficit in cell density of hypothalamus during the winter that could lead to hormonal dysfunctions, while in the summer Hg promoted larger volumes of the optic tectum and cerebellum, indicating the warm period as the most critical for the manifestation of putative changes in visual acuity and motor-dependent tasks. Moreover, in fish from the SJ site, the lateral pallium relative volume and the cell density of the hypothalamus and optic tectum were higher in the winter than in summer. Thus, season-related stimuli strongly influence the size and/or cell density of specific brain regions in the non-contaminated area, pointing out the ability of fish to adapt to environmental and physiological demands. Conversely, fish from the Hg-contaminated site showed a distinct seasonal profile of brain morphology, presenting a larger optic tectum in the summer, as well as a larger molecular layer of the cerebellum with higher cell density. Moreover, Hg exposure impaired the winter-summer variation of the lateral pallium relative size (as observed at SJ). Altogether, seasonal variations in fish neural morphology and physiology should be considered when performing ecotoxicological studies in order to better discriminate the Hg neurotoxicity.

Impaired intestinal immune barrier and physical barrier function by phosphorus deficiency: Regulation of TOR, NF-κB, MLCK, JNK and Nrf2 signalling in grass carp (Ctenopharyngodon idella) after infection with Aeromonas hydrophila

In aquaculture, the occurrence of enteritis has increased and dietary nutrition is considered as one of the major strategies to solve this problem. In the present study, we assume that dietary phosphorus might enhance intestinal immune barrier and physical barrier function to reduce the occurrence of enteritis in fish. To test this assumption, a total of 540 grass carp (Ctenopharyngodon idella) were investigated by feeding graded levels of available phosphorus (0.95-8.75 g/kg diet) and then infection with Aeromonas hydrophila. The results firstly showed that phosphorus deficiency decreased the ability to combat enteritis, which might be related to the impairment of intestinal immune barrier and physical barrier function. Compared with optimal phosphorus level, phosphorus deficiency decreased fish intestinal antimicrobial substances activities or contents and down-regulated antimicrobial peptides mRNA levels leading to the impairment of intestinal immune response. Phosphorus deficiency down-regulated fish intestinal anti-inflammatory cytokines mRNA levels and up-regulated the mRNA levels of pro-inflammatory cytokines [except IL-1β and IL-12p35 in distal intestine (DI) and IL-12p40] causing aggravated of intestinal inflammatory responses, which might be related to the signalling molecules target of rapamycin and nuclear factor kappa B. In addition, phosphorus deficiency disturbed fish intestinal tight junction function and induced cell apoptosis as well as oxidative damage leading to impaired of fish intestinal physical barrier function, which might be partially associated with the signalling molecules myosin light chain kinase, c-Jun N-terminal protein kinase and NF-E2-related factor 2, respectively. Finally, based on the ability to combat enteritis, dietary available phosphorus requirement for grass carp (254.56-898.23 g) was estimated to be 4.68 g/kg diet.

Seasonal changes in stress biomarkers of an exotic coastal species - Chaetopleura angulata (Polyplacophora) - Implications for biomonitoring

Knowledge on baseline values of stress biomarkers in natural conditions is urgent due to the need of reference values for monitoring purposes. Here we assessed the cellular stress response of the chiton Chaetopleura angulata in situ. Biomarkers commonly used in environmental monitoring (heat shock protein 70kDa, total ubiquitin, catalase, glutathione-S-transferase, superoxide-dismutase, lipid peroxidation) were analyzed in the digestive system, gills and muscle of C. angulata, under spring and summer conditions in order to assess seasonal tissue-specific responses. Season had an effect on all targeted organs, especially affecting the digestive system which displayed clear seasonal clusters. The respective Integrated Biomarker Response (IBR) showed a 7.2-fold seasonal difference. Muscle and gills showed similar IBRs between seasons making them appropriate organs to monitor chemical pollution as they were less responsive to seasonal variation. The most stable biomarkers in these organs were ubiquitin and superoxide-dismutase thus being reliable for monitoring purposes.

Unveiling the neurotoxicity of methylmercury in fish (Diplodus sargus) through a regional morphometric analysis of brain and swimming behavior assessment

The current study aims to shed light on the neurotoxicity of MeHg in fish (white seabream - Diplodus sargus) by the combined assessment of: (i) MeHg toxicokinetics in the brain, (ii) brain morphometry (volume and number of neurons plus glial cells in specific brain regions) and (iii) fish swimming behavior (endpoints associated with the motor performance and the fear/anxiety-like status). Fish were surveyed for all the components after 7 (E7) and 14 (E14) days of dietary exposure to MeHg (8.7μgg^-1), as well as after a post-exposure period of 28days (PE28). MeHg was accumulated in the brain of D. sargus after a short time (E7) and reached a maximum at the end of the exposure period (E14), suggesting an efficient transport of this toxicant into fish brain. Divalent inorganic Hg was also detected in fish brain along the experiment (indicating demethylation reactions), although levels were 100-200 times lower than MeHg, which pinpoints the organic counterpart as the great liable for the recorded effects. In this regard, a decreased number of cells in medial pallium and optic tectum, as well as an increased hypothalamic volume, occurred at E7. Such morphometric alterations were followed by an impairment of fish motor condition as evidenced by a decrease in the total swimming time, while the fear/anxiety-like status was not altered. Moreover, at E14 fish swam a greater distance, although no morphometric alterations were found in any of the brain areas, probably due to compensatory mechanisms. Additionally, although MeHg decreased almost two-fold in the brain during post-exposure, the levels were still high and led to a loss of cells in the optic tectum at PE28. This is an interesting result that highlights the optic tectum as particularly vulnerable to MeHg exposure in fish. Despite the morphometric alterations reported in the optic tectum at PE28, no significant changes were found in fish behavior. Globally, the effects of MeHg followed a multiphasic profile, where homeostatic mechanisms prevented circumstantially morphometric alterations in the brain and behavioral shifts. Although it has become clear the complexity of matching brain morphometric changes and behavioral shifts, motor-related alterations induced by MeHg seem to depend on a combination of disruptions in different brain regions.

Reproductive toxicity of inorganic mercury exposure in adult zebrafish: Histological damage, oxidative stress, and alterations of sex hormone and gene expression in the hypothalamic-pituitary-gonadal axis

Mercury (Hg) is a prominent environmental contaminant that causes a variety of adverse effects on aquatic organisms. However, the mechanisms underlying inorganic Hg-induced reproductive impairment in fish remains largely unknown. In this study, adult zebrafish were exposed to 0 (control), 15 and 30μg Hg/l (added as mercuric chloride, HgCl2) for 30days, and the effects on histological structure, antioxidant status and sex hormone levels in the ovary and testis, as well as the mRNA expression of genes involved in the hypothalamic-pituitary-gonadal (HPG) axis were analyzed. Exposure to Hg caused pathological lesions in zebrafish gonads, and changed the activities and mRNA levels of antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx)) as well as the content of glutathione (GSH) and malondialdehyde (MDA). In females, although ovarian 17β-estradiol (E2) content remained relatively stable, significant down-regulation of lhβ, gnrh2, gnrh3, lhr and erα were observed. In males, testosterone (T) levels in the testis significantly decreased after Hg exposure, accompanied by down-regulated expression of gnrh2, gnrh3, fshβ and lhβ in the brain as well as fshr, lhr, ar, cyp17 and cyp11b in the testis. Thus, our study indicated that waterborne inorganic Hg exposure caused histological damage and oxidative stress in the gonads of zebrafish, and altered sex hormone levels by disrupting the transcription of related HPG-axis genes, which could subsequently impair the reproduction of fish. Different response of the antioxidant defense system, sex hormone and HPG-axis genes between females and males exposed to inorganic Hg indicated the gender-specific regulatory effect by Hg. To our knowledge, this is the first time to explore the effects and mechanisms of inorganic Hg exposure on reproduction at the histological, enzymatic and molecular levels, which will greatly extend our understanding on the mechanisms underlying of reproductive toxicity of inorganic Hg in fish.

Insights into the mechanisms underlying mercury-induced oxidative stress in gills of wild fish (Liza aurata) combining (1)H NMR metabolomics and conventional biochemical assays

Oxidative stress has been described as a key pathway to initiate mercury (Hg) toxicity in fish. However, the mechanisms underlying Hg-induced oxidative stress in fish still need to be clarified. To this aim, environmental metabolomics in combination with a battery of conventional oxidative stress biomarkers were applied to the gills of golden grey mullet (Liza aurata) collected from Largo do Laranjo (LAR), a confined Hg contaminated area, and São Jacinto (SJ), selected as reference site (Aveiro Lagoon, Portugal). Higher accumulation of inorganic Hg and methylmercury was found in gills of fish from LAR relative to SJ. Nuclear magnetic resonance (NMR)-based metabolomics revealed changes in metabolites related to antioxidant protection, namely depletion of reduced glutathione (GSH) and its constituent amino acids, glutamate and glycine. The interference of Hg with the antioxidant protection of gills was corroborated through oxidative stress endpoints, namely the depletion of glutathione peroxidase and superoxide dismutase activities at LAR. The increase of total glutathione content (reduced glutathione+oxidized glutathione) at LAR, in parallel with GSH depletion aforementioned, indicates the occurrence of massive GSH oxidation under Hg stress, and an inability to carry out its regeneration (glutathione reductase activity was unaltered) or de novo synthesis. Nevertheless, the results suggest the occurrence of alternative mechanisms for preventing lipid peroxidative damage, which may be associated with the enhancement of membrane stabilization/repair processes resulting from depletion in the precursors of phosphatidylcholine (phosphocholine and glycerophosphocholine), as highlighted by NMR spectroscopy. However, the observed decrease in taurine may be attributable to alterations in the structure of cell membranes or interference in osmoregulatory processes. Overall, the novel concurrent use of metabolomics and conventional oxidative stress endpoints demonstrated to be sensitive and effective towards a mechanistically based assessment of Hg toxicity in gills of wild fish, providing new insights into the toxicological pathways underlying the oxidative stress.

Effect of diets enriched with rutin on blood parameters, oxidative biomarkers and pituitary hormone expression in silver catfish (Rhamdia quelen)

The effects of adding rutin to the diet (0, 0.15 or 0.30%) of silver catfish for 21 days on blood parameters, oxidative stress biomarkers and pituitary hormones expression were investigated. Fish that received the diet containing 0.15% rutin exhibited reduced plasma cortisol levels. The levels of lipid peroxidation were lowered in the all tissues of animals receiving the diet containing rutin. Rutin increased the activity of the superoxide dismutase (SOD), catalase (CAT), nonprotein thiols (NPSH), ascorbic acid content (AA) and total reactive antioxidant potential (TRAP) in the brain; glutathione S-transferase (GST) activity and TRAP in the gills; SOD, CAT and GST activity, NPSH, AA levels and TRAP in the liver; CAT and GST activity and TRAP levels in the kidneys; and glutathione peroxidase activity, NPSH, AA levels and TRAP in the muscle. There were no changes regarding the expression of growth hormone, prolactin and somatolactin in fish fed with the diet containing rutin when compared with the control. The supplementation of rutin to the diet of fish is beneficial because it increases the antioxidant responses of tissues.

Insights into neurosensory toxicity of mercury in fish eyes stemming from tissue burdens, oxidative stress and synaptic transmission profiles

This study aims to contribute to fill a knowledge gap related with Hg effects in fish eyes. As a pioneering strategy, Hg bioaccumulation in eye wall of the wild grey mullet (Liza aurata) was assessed, together with oxidative stress and synaptic transmission profiles. This approach was complemented by the characterisation of environmental contamination (both in water and sediment). Sampling was conducted in winter and summer in two sites of a Portuguese coastal lagoon (Aveiro lagoon): Largo do Laranjo (LAR) - located in an Hg contaminated/confined area; São Jacinto (SJ) - closer to the lagoon inlet and selected as reference site. Levels of total Hg (tHg), inorganic Hg (iHg) and methylmercury (MeHg) in eye wall were higher at LAR than SJ, both in winter and summer, reflecting the environmental contamination patterns. Moreover, fish caught at LAR in winter showed a significant decrease of catalase and superoxide dismutase activities, in line with the occurrence of peroxidative damage. A different spatial pattern was recorded in summer, being characterised by the increment of glutathione peroxidase and glutathione reductase activities at LAR, as well as total glutathione content, preventing the occurrence of lipid peroxidation. Also in summer, a significant decrease of acetylcholinesterase activity was recorded in fish eyes at LAR, pointed out Hg as an anticholinergic agent. Besides Hg, water salinity had probably an indirect effect on spatial and winter-summer variation patterns of AChE. Current data pointed out that Hg (in iHg and MeHg forms) could exert ocular toxicity both by the promotion of oxidative stress and by the interference with neurotransmission processes.

Inorganic mercury accumulation in brain following waterborne exposure elicits a deficit on the number of brain cells and impairs swimming behavior in fish (white seabream-Diplodus sargus)

The current study contributes to fill the knowledge gap on the neurotoxicity of inorganic mercury (iHg) in fish through the implementation of a combined evaluation of brain morphometric alterations (volume and total number of neurons plus glial cells in specific regions of the brain) and swimming behavior (endpoints related with the motor activity and mood/anxiety-like status). White seabream (Diplodus sargus) was exposed to realistic levels of iHg in water (2μgL(-1)) during 7 (E7) and 14 days (E14). After that, fish were allowed to recover for 28 days (PE28) in order to evaluate brain regeneration and reversibility of behavioral syndromes. A significant reduction in the number of cells in hypothalamus, optic tectum and cerebellum was found at E7, accompanied by relevant changes on swimming behavior. Moreover, the decrease in the number of neurons and glia in the molecular layer of the cerebellum was followed by a contraction of its volume. This is the first time that a deficit on the number of cells is reported in fish brain after iHg exposure. Interestingly, a recovery of hypothalamus and cerebellum occurred at E14, as evidenced by the identical number of cells found in exposed and control fish, and volume of cerebellum, which might be associated with an adaptive phenomenon. After 28 days post-exposure, the optic tectum continued to show a decrease in the number of cells, pointing out a higher vulnerability of this region. These morphometric alterations coincided with numerous changes on swimming behavior, related both with fish motor function and mood/anxiety-like status. Overall, current data pointed out the iHg potential to induce brain morphometric alterations, emphasizing a long-lasting neurobehavioral hazard.

Factors Affecting Antioxidant Response in Fish from a Long-term Mercury-Contaminated Reservoir

The objective of this work was to evaluate antioxidant defence and oxidative damage in organs (liver, gills, kidney, and brain) of five fish species (Aspius aspius, Esox lucius, Sander lucioperca, Abramis brama, Rutilus rutilus) from the long-term mercury-contaminated Skalka Reservoir in the Czech Republic. Special emphasis was placed on a comprehensive assessment of the factors that may affect the antioxidant response to mercury in fish. Antioxidant enzymes (glutathione reductase, glutathione peroxidase, and glutathione-S-transferase) did not significantly respond to mercury contamination. Levels of the analysed enzymes and oxidative damage to lipids were predominantly determined by a separate organ factor or species factor, or by the combination of both (p < 0.001). Levels of total glutathione and the reduced/oxidized glutathione ratio were influenced by mercury contamination in combination with their specific organ distribution (p < 0.001). Our results suggest that species and type of organ alone or in combination are more important factors than chronic exposure to mercury contamination with respect to effects on antioxidant defence in fish under field conditions. Our findings suggest that the main antioxidant defensive mechanism in fish from the studied long-term mercury contaminated site was the inter-tissue distribution of glutathione.

High environmental ammonia elicits differential oxidative stress and antioxidant responses in five different organs of a model estuarine teleost (Dicentrarchus labrax)

We investigated oxidative status and antioxidant profile in five tissues (brain, liver, gills, muscle and kidney) of European sea bass (Dicentrarchus labrax) when exposed to high environmental ammonia (HEA, 20 mg/L~1.18 mM as NH4HCO3) for 12 h, 2 days, 3.5 days, 7.5 days and 10 days. Results show that HEA triggered ammonia accumulation and induced oxidative stress in all tissues. Unlike other organs, hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation in liver were restored to control levels. This recovery was associated with a concomitant augmentation in superoxide dismutase (SOD), catalase (CAT), components of glutathione redox cycle (glutathione peroxidase GPX, glutathione reductase, reduced glutathione), ascorbate peroxidase activity and reduced ascorbate content. On the contrary, in brain during prolonged exposure many of these anti-oxidant enzymes were either unaffected or inhibited, which resulted in persistent over-accumulation of H2O2 and MDA. Branchial and renal tissue both involved in osmo-regulation, revealed an entirely dissimilar compensatory response; the former rely mainly on the ascorbate dependent defensive system while the glutathione catalytic pathway was activated in the latter. In muscle, GPX activity first rose (3.5 days) followed by a subsequent drop, counterbalanced by simultaneous increment of CAT. HEA resulted in a relatively mild oxidative stress in the muscle and kidney, probably explaining the modest anti-oxidative responses. Our findings exemplify that oxidative stress as well as antioxidant potential are qualitatively diverse amongst different tissues, thereby demonstrating that for biomonitoring studies the screening of adaptive responses at organ level should be preferred over whole body response.

The neuroprotective effect of berberine in mercury-induced neurotoxicity in rats

The central nervous system is one of the most vulnerable organs affected by mercury toxicity. Both acute and chronic exposure to mercury is also known to cause a variety of neurological or psychiatric disorders. Here, the neuroprotective effect of berberine (BN; 100 mg/kg bwt) on mercuric chloride (HgCl2; 0.4 mg/kg bwt) induced neurotoxicity and oxidative stress was examined in rats. Adult male albino Wistar rats were injected with HgCl2 for 7 days. HgCl2 treatment induced oxidative stress by increasing lipid peroxidation (LPO) and nitrite/nitrate (nitric oxide; NO) production along with a concomitant decrease in glutathione (GSH) and various antioxidant enzymes, namely superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. Pre-treatment of rats with BN inhibited LPO and NO production, whereas it increased GSH content. Activities of antioxidant enzymes were also restored concomitantly when compared to the control rats after BN administration. Berberine also caused decrease in TNF-α level and caspase-3 activity which was higher with HgCl2. Furthermore, treatment with BN inhibited apoptosis, as indicated by the reduction of Bax/Bcl-2 ratio in brain tissue. These data indicated that BN augments antioxidant defense with anti-inflammatory and anti-apoptotic activities against HgCl2-induced neurotoxicity and provides evidence that it has a therapeutic potential as neuroprotective agent.

Risk Assessment of Heavy Metals in Imported Frozen Fish Scomber scombrus Species Sold in Nigeria: A Case Study in Zaria Metropolis

This study assesses the likely health risks to human contamination of heavy metals from fish consumption. The analysis of the idea of fish destination and status (fishing area) for heavy metals was determined by the assessment of its risk limits (daily intake of metal and health risk index). Variations in the accumulation of heavy metals concentrations were between various tissues/organs (skin, muscle, gills, liver, intestine, kidneys, brain, and bones) across the batches of two fishing origins. Post hoc (Duncan) multicomparison shows that there are significant differences (P<0.05) across batches. The concentrations of heavy metals analyzed, in the investigated tissues of Scomber scombrus, showed higher levels of heavy metals accumulations in the order: Fe>Hg>Pb>Cd>Ni and were above the recommended safety limits outlined by FAO/WHO. However, the consumer’s health risk with the consumption of fish muscles tissues shows that there are greater tendencies for cadmium, lead, and mercury exposure. Also consumption of Scomber scombrus species above the recommended daily intake (stated in this study) might lead to ingestion of heavy metals at unacceptable concentrations.

A new page on the road book of inorganic mercury in fish body – tissue distribution and elimination following waterborne exposure and post-exposure periods

Time-related accumulation/distribution of inorganic Hg upon exposure and post-exposure periods. Body compartments selected: gills, eye wall, lens, blood, liver, brain and bile.

Copper exposure induces oxidative injury, disturbs the antioxidant system and changes the Nrf2/ARE (CuZnSOD) signaling in the fish brain: protective effects of myo-inositol

The brain is the center of the nervous system in all vertebrates, and homeostasis of the brain is crucial for fish survival. Copper (Cu) is essential for normal cellular processes in most eukaryotic organisms but is toxic in excess. Although Cu is indicated as a potent neurotoxicant, information regarding its threat to fish brain and underlying mechanisms is still scarce. In accordance, the objective of this study was to assess the effects and the potential mechanism of Cu toxicity by evaluating brain oxidative status, the enzymatic and mRNA levels of antioxidant genes, as well as the Nrf2/ARE signaling in the brain of fish after Cu exposure. The protective effects of myo-inositol (MI) against subsequent Cu exposure were also investigated. The results indicate that induction of oxidative stress by Cu is shown by increases in brain ROS production, lipid peroxidation and protein oxidation, which are accompanied by depletions of antioxidants, including total superoxide dismutase (T-SOD), CuZnSOD, glutathione-S-transferase (GST) and glutathione reductase (GR) activities and glutathione (GSH) content. Cu exposure increased the catalase (CAT) and glutathione peroxidase (GPx) activities. Further molecular results showed that Cu exposure up-regulated CuZnSOD, GPx1a and GR mRNA levels, suggesting an adaptive mechanism against stress. Moreover, Cu exposure increased fish brain Nrf2 nuclear accumulation and increased its ability of binding to ARE (CuZnSOD), which supported the increased CuZnSOD mRNA levels. In addition, Cu exposure caused increases of the expression of the Nrf2, Maf G1 (rather than Maf G2 gene) and PKCd genes, suggesting that de novo synthesis of those factors is required for the protracted induction of such antioxidant genes. However, the modulation of Keap1a (rather than Keap1b) of fish brain under Cu exposure might be used to turn off of the signaling cascade and avoid harmful effects. Interestingly, pre-treatment of fish with MI prevented the fish brain from Cu-induced oxidative damages mainly by increasing the GSH content and CuZnSOD and GST activities. Summarily, this study indicates that although Cu stimulates adaptive increases in the expression of some antioxidant enzyme genes through Nrf2/ARE signaling, it also induces oxidation and the depletion of most of antioxidant enzyme activities and GSH content due to the increase of ROS production, and MI protects the fish brain against Cu toxicity.

Fish eyes and brain as primary targets for mercury accumulation - a new insight on environmental risk assessment

Fish eyes and brain are highly susceptible to environmental Hg exposure but this issue is still scarcely investigated, mainly regarding methylmercury (MeHg) accumulation. Yet, Hg levels in fish lens have not been previously examined under field conditions. Total Hg (tHg), MeHg and inorganic Hg (iHg) levels were assessed in the brain, eye wall and lens of the golden grey mullet (Liza aurata) from an Hg contaminated area, both in winter and summer, together with water and sediment levels. Sampling was performed at Aveiro lagoon (Portugal) where a confined area (LAR) is severely contaminated by Hg. Fish brain, eye wall and lens accumulated higher levels of tHg, MeHg and iHg at LAR than the reference site, reflecting faithfully environmental spatial differences. The brain and eye wall responded also to the winter-summer changes found in water and sediment, accumulating higher levels of MeHg (and tHg) in winter. Contrarily, lens was unable to reflect seasonal changes, probably due to its composition and structural stability over time. The three neurosensory structures accumulated preferentially MeHg than iHg (MeHg was higher than 77% of tHg). Lens exhibited a higher retention capacity of MeHg (mean around 1 μg g(-1) at LAR), accumulating higher levels than the other two tissues. Interestingly, MeHg and iHg levels were significantly correlated for the brain and eye wall but poorly associated within the two analysed eye components. The high levels of MeHg found in the brain, eye wall and lens could compromise their functions and this needs further research.

Mercury accumulation and tissue-specific antioxidant efficiency in the wild European sea bass (Dicentrarchus labrax) with emphasis on seasonality

The main goal of this study was to assess both mercury (Hg) accumulation and organs' specific oxidative stress responses of gills, liver and kidney of Dicentrarchus labrax with emphasis on seasonality. Fish were collected in cold and warm periods in three stations: reference, moderated and highly contaminated sites. Our results showed that seasonal factors slightly influenced Hg accumulation between year periods (cold and warm) and strongly affected organs' response basal levels. In contrast, seasonality seemed not to influence oxidative stress responses, since similar response patterns were obtained for both year periods, and moderate degree of antioxidant responses was obtained. Moreover, the oxidative stress profile may be attributed to Hg contamination degree, which showed organ-specific response and accumulation patterns. Hence, gills showed to be able to adapt to Hg contamination, and in opposition, kidney and liver demonstrated some vulnerability to Hg toxicity. The critical Hg concentrations indicated specific threshold limits for each organ. Overall, seasonality should be taken into account in monitoring programmes, helping to characterize the individuals' reference values of response and thus to discriminate between the effects induced by natural causes or by contamination.

Effect of increasing temperature in the differential activity of oxidative stress biomarkers in various tissues of the Rock goby, Gobius paganellus

Oxidative stress biomarkers have been widely used in the development of ecological indices and in the assessment of exposure of aquatic organisms to contaminants from agricultural, industrial and urban pollution. However, temperature is known to also have a significant effect on oxidative stress biomarkers. This way, temperature is a confounding factor that may result in difficulties in the interpretation of oxidative stress biomarkers response patterns. Since climate change is expected to result in more frequent and intense heat wave events it is pertinent to investigate the effect of increasing temperature in the oxidative stress response of common aquatic organisms. It is also important to assess the differential response of different body tissues, given that they are differently exposed to temperature depending on their location and physiological function. This study investigates the effect of increasing temperature (20 °C-34 °C) in the response of multiple biomarkers of oxidative stress: lipid peroxidation, glutathione-S-transferase, superoxide dismutase and catalase activities, in the muscle, liver and gills of a common coastal fish, the Rock goby, Gobius paganellus. The response of the oxidative stress biomarkers analysed were always higher in the gills than in the other tissues. Muscle generally presented the lower levels of any of the biomarkers tested when compared to other tissues. Nevertheless, muscle tissue always responded significantly to temperature, as did the liver, while the gills were unresponsive in terms of lipid peroxidation and glutathione-S-transferase. Unresponsive tissues to temperature may be particularly interesting as indicators of pollution, given that temperature will not be a confounding variable in their oxidative stress response.

Effect of temperature in multiple biomarkers of oxidative stress in coastal shrimp

Various studies in captivity and in the wild have pointed to the effect of season, and temperature in particular, in the levels of the oxidative stress biomarkers currently used for environmental quality assessment. However, knowledge on how temperature affects the oxidative stress response is unavailable for most species. This study investigated the effect of increasing temperature on lipid peroxidation, catalase activity, superoxide dismutase and glutathione-S-transferase in the shrimps, Palaemon elegans and Palaemon serratus. It was concluded that increasing temperatures significantly affect all the biomarkers tested in both species, with the exception of superoxide dismutase in P. serratus which was not affected by temperature. The oxidative stress response was more intense in P. elegans, than in P. serratus, producing higher peaks of all biomarkers at temperatures between 22°C and 26°C, followed by low levels at higher temperatures. It was concluded that monitoring of ecosystems using oxidative stress biomarkers should take into account the species and thermal history of the organisms. Sampling should be avoided during heat waves and immediately after heat waves.

Glutathione and its dependent enzymes' modulatory responses to toxic metals and metalloids in fish--a review

Toxic metals and metalloid are being rapidly added from multiple pathways to aquatic ecosystem and causing severe threats to inhabiting fauna including fish. Being common in all the type of aquatic ecosystems such as freshwater, marine and brackish water fish are the first to get prone to toxic metals and metalloids. In addition to a number of physiological/biochemical alterations, toxic metals and metalloids cause enhanced generation of varied reactive oxygen species (ROS) ultimately leading to a situation called oxidative stress. However, as an important component of antioxidant defence system in fish, the tripeptide glutathione (GSH) directly or indirectly regulates the scavenging of ROS and their reaction products. Additionally, several other GSH-associated enzymes such as GSH reductase (GR, EC 1.6.4.2), GSH peroxidase (EC 1.11.1.9), and GSH sulfotransferase (glutathione-S-transferase (GST), EC 2.5.1.18) cumulatively protect fish against ROS and their reaction products accrued anomalies under toxic metals and metalloids stress conditions. The current review highlights recent research findings on the modulation of GSH, its redox couple (reduced glutathione/oxidised glutathione), and other GSH-related enzymes (GR, glutathione peroxidase, GST) involved in the detoxification of harmful ROS and their reaction products in toxic metals and metalloids-exposed fish.

Oxidative stress parameters and anti-apoptotic response to hydroxyl radicals in fish erythrocytes: protective effects of glutamine, alanine, citrulline and proline

The present study explored the protective effects of glutamine (Gln), alanine (Ala), citrulline (Cit) and proline (Pro) on hydroxyl radical (·OH)-induced apoptosis in isolated carp erythrocytes. Hydroxyl radicals were generated by ferrous ion (Fe(2+))-mediated decomposition of hydrogen peroxide (H(2)O(2)) (Fenton reaction). In order to select an optimal ·OH concentration to induce apoptosis, cultures were treated with different concentrations of FeSO(4)/H(2)O(2) (0 μM/0 μM-50 μM/25 μM). The results showed that exposure to FeSO(4)/H(2)O(2) (0 μM/0 μM-40 μM/20 μM) increased apoptosis in a dose-dependent manner. Moreover, apoptosis was at its highest level at 40 μM FeSO(4)/20 μM H(2)O(2). We then examined the cytoprotective effects of Gln, Ala, Cit, Pro or the combination of Ala, Cit and Pro under conditions of apoptosis. Carp erythrocytes were treated with the substances listed above in the presence of 40 μM FeSO(4)/20 μM H(2)O(2) for 9 h. The controls were grown in Gln, Ala, Cit, Pro-free culture medium. The results showed that Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro effectively protected against annexin binding, decrease of forward scatter and DNA fragmentation in carp erythrocytes induced by ·OH. Furthermore, Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro effectively blocked ·OH-stimulated erythrocyte hemolysis, reduced the increase of superoxide anion and H(2)O(2) concentrations, inhibited the formation of malondialdehyde, protein carbonyls and met-hemoglobin, and prevented the decrease of superoxide dismutase, catalase and glutathione peroxidase activities and glutathione content in carp erythrocytes induced by ·OH. In addition, the results suggest that the combination of Ala, Cit and Pro produces a greater anti-apoptotic and anti-oxidative effect than their individual effects at the same concentrations. Taken together, the results showed that ·OH induces apoptosis and oxidative damage in carp erythrocytes. In addition to inhibiting apoptosis, Gln, Ala, Cit, Pro and the combination of Ala, Cit and Pro protected carp erythrocytes against oxidative damage induced by ·OH, which may be a major factor in the protection of erythrocytes from apoptosis.

Mercury and selenium interaction in vivo: effects on thioredoxin reductase and glutathione peroxidase

Mercury compounds exert toxic effects via interaction with many vital enzymes involved in antioxidant regulation, such as selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). Selenium supplementation can reactivate the mercury-inhibited TrxR and recover the cell viability in vitro. To gain an insight on how selenium supplementation affects mercury toxicity in vertebrates, we investigated the effects of selenium on the mercury accumulation and TrxR and GPx activities in a fish model. Juvenile zebra-seabreams were exposed either to methylmercury (MeHg) or inorganic mercury (Hg(2+)) in the presence or absence of sodium selenite (Se) for 28 days followed by 14 days of depuration. Mercury accumulation was found to be 10-fold higher under MeHg exposure than under Hg(2+) exposure. Selenium supplementation caused a half decrease of the accumulation of MeHg but did not influence Hg(2+) accumulation. Exposure to both mercurials led to a decrease of the activity of TrxR (<50% of control) in all organs. Se supplementation coincident with Hg(2+) exposure protected the thioredoxin system in fish liver. However, supplementation of Se during the depuration phase had no effects. The activity of GPx was only affected in the brain of fishes upon the exposure to MeHg and coexposure to MeHg and Se. Selenium supplementation has a limited capacity to prevent mercury effects in brain and kidney. These results demonstrate that Se supplementation plays a protective role in a tissue-specific manner and also highlight the importance of TrxR as a main target for mercurials in vivo.

Oxidative stress in neurodegenerative diseases: mechanisms and therapeutic perspectives

The incidence and prevalence of neurodegenerative diseases (ND) increase with life expectancy. This paper reviews the role of oxidative stress (OS) in ND and pharmacological attempts to fight against reactive oxygen species (ROS)-induced neurodegeneration. Several mechanisms involved in ROS generation in neurodegeneration have been proposed. Recent articles about molecular pathways involved in ROS generation were reviewed. The progress in the development of neuroprotective therapies has been hampered because it is difficult to define targets for treatment and determine what should be considered as neuroprotective. Therefore, the attention was focused on researches about pharmacological targets that could protect neurons against OS. Since it is necessary to look for genes as the ultimate controllers of all biological processes, this paper also tried to identify gerontogenes involved in OS and neurodegeneration. Since neurons depend on glial cells to survive, recent articles about the functioning of these cells in aging and ND were also reviewed. Finally, clinical trials testing potential neuroprotective agents were critically reviewed. Although several potential drugs have been screened in in vitro and in vivo models of ND, these results were not translated in benefit of patients, and disappointing results were obtained in the majority of clinical trials.

Myo-inositol prevents copper-induced oxidative damage and changes in antioxidant capacity in various organs and the enterocytes of juvenile Jian carp (Cyprinus carpio var. Jian)

Although oxidative stress has been demonstrated to be involved in copper (Cu)-induced toxicity, information regarding the effect of antioxidants on Cu toxicity is still scarce. This study assessed the possible protective effects of myo-inositol (MI) against subsequent Cu exposure in juvenile Jian carp (Cyprinus carpio var. Jian) in vivo and in their enterocytes in vitro. First, oxidative stress was established by exposing fish to different concentrations of Cu (0-7.2 mg Cu/L water) for 4 days. Next, the protective effects of MI (administered as a dietary supplement for 60 days) against subsequent Cu exposure (0.6 mg Cu/L water for 4 days) were studied in fish. The third trial determined the effects of Cu exposure (0-6.0 mg Cu/L of medium for 24h) on enterocytes in vitro. Finally, enterocytes were pre-incubated with graded levels of MI (0-75 mg MI/L of medium) for 72 h and exposed to 6.0 mg Cu/L of medium for 24h. The results indicated that ≥ 0.6 mg Cu/L water could induce oxidative stress in fish (P<0.05). Cu exposure significantly induced increases in lipid peroxidation and protein oxidation in the gill, hepatopancreas and intestine in fish. However, these oxidative effects were prevented by MI pre-supplementation. MI also prevented the toxic effects of Cu on anti-superoxide anion (ASA), anti-hydroxyl radical (AHR), superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and glutathione reductase (GR) activities and glutathione (GSH) content in these organs. In vitro, enterocytes exposed to Cu displayed a dose-dependent injury. Moreover, cell viability, protein retention (PR), alkaline phosphatase, total-SOD (T-SOD) and Cu/ZnSOD activities were all depressed by Cu (P<0.05). Interestingly, the final experiment showed that MI pre-supplementation could block the toxic effects of Cu on the antioxidant system, and thus protect enterocytes from Cu-induced oxidative damage. All of these results indicated that the induction of key antioxidant defenses by MI pre-supplementation, including SOD, CAT, GPx, GST and GSH, may play an important role in the protection of fish against oxidative stress.