Antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae under methylmercury exposure

Bioaccumulation of manganese and its effects on oxidative stress and immune response in juvenile groupers (Epinephelus moara ♀ × E. lanceolatus ♂)

We evaluated the effects of Mn in juvenile Yunlong groupers (Epinephelus moara ♀ × E. lanceolatus ♂). The groupers were exposed to Mn²⁺ (0, 0.5, 1, 2, and 4 mg/L) for 30 days after which they were assessed. The results indicate the accumulation of Mn in fish depended on dose and time. Mn²⁺ accumulation in tissues occurred in the following order: liver > gills > intestine > muscle. The concentrations of SOD and CAT in the fish significantly increased after 10 and 20 days of treatment with 4 mg/L Mn²⁺ but decreased after 30 days. Similarly, GSH and GPx levels increased after 10 days of exposure to 2 and 4 mg/L Mn²⁺ but decreased after 20 and 30 days of exposure. Additionally, malondialdehyde levels significantly increased after exposing the fish to 2 and 4 mg/L Mn²⁺ for 10, 20, and 30 days. In addition, liver HSP70 and HSP90 levels significantly increased at days 20 and 30 in all fish exposed to Mn²⁺. In addition, when Mn²⁺ concentration was 1, 2, and 4 mg/L, liver C3 and C4 levels were significantly increased after 10, 20, and 30 days. Conversely, the levels of LZM and IgM significantly decreased. Mn²⁺ also significantly upregulated the expression of genes associated with immunity (tlr3, tnf-α, il-1β, and il-6) in the fish, which suggests that it induces immunotoxicity by altering the immune response. Overall, the findings showed that Mn²⁺ can disrupt grouper health by bioaccumulating in the fish and subsequently inducing oxidative stress and immune responses. These results can help elucidate the mechanism by which manganese induces toxicity in marine fish. Additionally, they provide a new perspective regarding the detrimental effects of heavy metals in fish.

Toxic Effects on Oxidative Stress, Neurotoxicity, Stress, and Immune Responses in Juvenile Olive Flounder, Paralichthys olivaceus, Exposed to Waterborne Hexavalent Chromium

Simple Summary

Metals such as chromium can be exposed at high levels in the marine environment, and exposure to these heavy metals can have a direct effect on marine organisms. High levels of chromium exposure can have a direct impact on organisms in a coastal cage and terrestrial aquaculture. Hexavalent chromium exposure of more than 1.0 and 2.0 mg Cr⁶⁺/L induced physiological responses such as antioxidant, neurotransmitter, immune, and stress indicators in Paralichthys olivaceus. Therefore, this study will provide a reference indicator for stable aquaculture production through reference indicators for toxicity due to chromium exposure that may exist in the marine environment.

Abstract

Juvenile Paralichthys olivaceus were exposed to waterborne hexavalent chromium at various concentrations (0, 0.5, 1.0, and 2.0 mg/L) for 10 days. After chromium exposure, the activities of superoxide dismutase and glutathione S-transferase, which are oxidative stress indicators, were significantly increased; however, the glutathione level was significantly reduced. Acetylcholinesterase activity as a neurotoxicity marker was significantly inhibited upon chromium exposure. Other stress indicators, including plasma cortisol and heat shock protein 70, were significantly increased. The immune response markers (lysozyme and immunoglobulin M) were significantly decreased after chromium exposure. These results suggest that exposure to environmental toxicity in the form of waterborne chromium at concentrations higher than 1.0 mg/L causes significant alterations in antioxidant responses, neurotransmitters, stress, and immune responses in juvenile olive flounders. This study will provide a basis for an accurate assessment of the toxic effects of hexavalent chromium on aquatic organisms.

Toxicological effects of cadmium on the immune response and biomineralization of larval flounder Paralichthys olivaceus under seawater acidification

Seawater acidification can cause threats to both calcifying and uncalcifying marine organisms, affecting their acid-base regulatory functions, immune system and biomineralization. Marine pollutants, such as cadmium (Cd) that is globally distributed in coastal ecosystems, do not affect organisms alone but commonly as combined stressors. To investigate the toxicological effects of Cd on the immune and biomineralization of marine fishes under seawater acidification, flounder Paralichthys olivaceus was exposed to seawater acidification (control (pH 8.10), 7.70 and 7.30) and Cd exposure (control (0.36 μg L^-1), 0.01 and 0.15 mg L^-1 Cd) for 49 days from embryonic stage until they became settled. Immune and biomineralization-related biomarkers of flounder at the end of exposure were investigated. Results showed that single seawater acidification and Cd exposure or combined exposure significantly affected the immune system-related enzyme activities. Specifically, lysozyme (LZM) activity was significantly inhibited by single seawater acidification and Cd exposure, indicating innate immunosuppression under two stressors. Contents of IgM, HSP70 and MT were induced by seawater acidification or Cd exposure, indicating a detoxification mechanism that responded to the stressors. The expressions of immune-related genes were upregulated (hsp70 and mt) or downregulated (lzm) under Cd exposure. Of the biomineralization-related enzymes, activities of carbonic anhydrase (CA), Na⁺/K⁺-ATPase and Ca²⁺-ATPase increased under seawater acidification and Cd exposure, a potential mechanism in response to changes of acid-base balance induced by the stressors. Generally, immune and biomineralization of the flounder responded more sensitively to Cd exposure than seawater acidification. Seawater acidification aggravated the toxicological effects of Cd exposure on the two physiological functions, while high Cd exposure augmented their responses to seawater acidification.

Prenatal antioxidant-enriched and pro-oxidant-contained food, IL4 and IL13 pathway genes, and cord blood IgE

Prenatal oxidative balance might influence cord blood IgE (cIgE) levels. We aimed to explore if certain prenatal dietary sources of antioxidants and pro-oxidants are associated with cIgE elevation and if they interact with IL4 and IL13 pathway genes. A structured questionnaire was completed during the third trimester of pregnancy for 1107 full-term newborns. Surveyed antioxidant-enriched food included fish, shellfish, and fruit, whereas surveyed pro-oxidant-contained food included fried fish sticks and canned fish. Cord blood was collected for measuring cIgE levels and genotyping IL13 rs1800925, rs20541, rs848, IL4 rs2243250, and STAT6 rs324011. Fairly lean fish consumption showed protection against cIgE elevation (odds ratio [OR] 0.66; 95% CI 0.49–0.90) in the whole sample, while daily fruit (OR 0.46; 95% CI 0.27–0.79) and ≥ monthly canned fish (OR 2.81; 95% CI 1.24–6.36) exhibited associations only in genetically susceptible babies. A prenatal food protective index, comprising any fairly lean fish, daily fruit, and the absence of any canned fish, exerted dose–response protection against cIgE elevation in babies carrying the IL13 rs20541 GA or AA genotype (P for trend < 0.0001; P for interaction = 0.004). We concluded that prenatal antioxidant-enriched and pro-oxidant-contained food consumption may influence cIgE, especially in genetically susceptible babies.

Nannochloropsis oculata feed additive alleviates mercuric chloride-induced toxicity in Nile tilapia (Oreochromis niloticus)

Using microalgae to alleviate the adverse effects of aquaculture pollutants, including metals, has recently gained much attention. In this context, bioaccumulation, hematological indices, oxidative and antioxidant responses, and histopathological alterations were investigated in Nile tilapia (Oreochromis niloticus) fed with either a control diet or diets containing Nannochloropsis oculata (N. oculata) after exposure to mercuric chloride in order to evaluate the role of this microalgae in protecting against mercury-induced toxicity. Fish exposed to HgCl2 at a dose of ¼ LC50 (0.3 mg/L) (Hg group) for 7-21 days exhibited a significant increase in total mercury concentration with a bioaccumulation pattern of liver>gills>muscle, and a significant decrease in all blood indices except mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), monocyte counts, and neutrophil counts. Malondialdehyde (MDA) levels were significantly increased in the Hg group at all time points relative to the control. Glutathione peroxidase (GPx) activity was significantly increased at days 14 and 21, while catalase (CAT) and GPx activities increased and decreased, respectively, at day 7 compared to the control. Additionally, lysozyme activity and immunoglobulin M (IgM) were significantly decreased in the Hg-exposed group. Severe histopathological alterations were evident in the liver, kidneys, and gills. However, supplementation with N. oculata at a low (5%, 50 g/kg feed) or high (10%, 100 g/kg feed) dose stabilized all parameters and reduced the severity of the histopathological alterations with the high N. oculata diet showing more prominent effects. These results suggest that feeding N. oculata protects Nile tilapia against mercuric chloride-induced toxicity.

Immune, inflammatory, autophagic and DNA damage responses to long-term H2O2 exposure in different tissues of common carp (Cyprinus carpio)

Hydrogen peroxide (H₂O₂) is a stable reactive oxygen species (ROS) in aquatic environment, and high concentration of ambient H₂O₂ may directly or indirectly affect aquatic animal health. However, the response mechanism of fish to ambient H₂O₂ has not been well studied yet. Therefore, the aim of the study was to investigate the immune, inflammatory, autophagic and DNA damage responses to long-term H₂O₂ exposure in different tissues of common carp. The results showed that H₂O₂ exposure induced a significant immune response, with alterations in the levels of immune parameters including AKP, ACP, LZM, C3, HSP90 and HSP70 in different tissues. The inflammatory response evoked by H₂O₂ exposure was associated with the activations of TLRs and NF-κB (P65) in the majority of tested tissues. The autophagy process was significantly affected by H₂O₂ exposure, evidenced by the upregulations of the autophagy-related genes in liver, gills, muscle, intestines, heart and spleen and the downregulations in kidney. Meanwhile, the mRNA level of atm, a primary transducer of DNA damage response, was upregulated in liver, gills, intestines and spleen, and the DNA damage was evidenced by increased 8-OHdG level in intestines after H₂O₂ exposure. Moreover, cell cycle regulation-related genes, including cyclin A1, B and/or E1, highly expressed in all tested tissues except heart after H₂O₂ exposure. Interestingly, IBR analysis exhibited that immune, inflammatory, autophagic and DNA damage responses to H₂O₂ exposure were in a dose-dependent and tissue-specific manner. These data may contribute to understanding H₂O₂ toxicity for fish and assessing potential risk of H₂O₂ in aquatic environment.

Inorganic mercury effects on biomarker gene expressions of a freshwater amphipod at two temperatures

Mercury (Hg) is a global contaminant resulting of both natural processes and human activities. In aquatic environments, studies conducted on vertebrates highlighted changes of gene expression or activity of antitoxic and oxidative enzymes. However, although Hg is a highly toxic compound in aquatic environments, only a few studies have evaluated the lethal and sublethal effects of inorganic Hg on Gammarus sp. Therefore, this study aimed at evaluating the effects of inorganic Hg (HgCl₂) on the expression of 17 genes involved in crucial biological functions or mechanisms for organisms, namely respiration, osmoregulation, apoptosis, immune and endocrine system, and antioxidative and antitoxic defence systems. The study was performed in males of the freshwater amphipod Gammarus pulex exposed to two environmentally relevant concentrations (50 and 500 ng/L) at two temperature regime fluctuations (16 °C and 20 °C +/-2 °C) for 7 and 21 days. Results showed that G. pulex mortality was dependent on Hg concentration and temperature; the higher the concentration and temperature, the higher the mortality rate. In addition, the Integrated Biomarker Response emphasized that HgCl₂ toxicity was dependent on the concentration, time and temperature of exposure. Overall, antioxidant and antitoxic defences, as well as the endocrine and immune systems, were the biological functions most impacted by Hg exposure (based on the concentration, duration, and temperature tested). Conversely, osmoregulation was the least affected biological function. The results also demonstrated a possible adaptation of G. pulex after 21 days at 500 ng/L, regardless of the exposure temperature. This study allowed us to show that Hg deregulates many crucial biological functions after a short exposure, but that during a long exposure, an adaptation phenomenon could occur, regardless of temperature.

Neurobehavioral and immune-toxic impairments induced by organic methyl mercury dietary exposure in Nile tilapia Oreochromis niloticus

Although substantial knowledge of mercury toxicity in fish has been assembled; until now, studies investigating the toxic impacts in Nile tilapia (Oreochromis niloticus) following dietary exposure to organic methyl mercury (MeHg) are less prolific. Accordingly, the current study aimed to evaluate the impacts of MeHg on neurobehavioral and immune integrity in Nile tilapia after dietary exposure. Two hundred and twenty-five juvenile Nile tilapia (19.99 ± 0.33 g) were allocated into five groups in triplicates (15 fish/replicate). G1, G2, G3, G4, and G5. O. niloticus were fed corresponding basal diets containing 0, 0.5, 1, 1.5, and 2 mg/kg diet MeHg chloride (MeHgCl) daily for 30 days, zero value represented the control G1 group. The results showed that MeHg induced significant alterations in O. niloticus behavior, the swimming behavior was significantly decreased, while scratching, biting, and fin tugging behaviors were significantly augmented. Moreover; chasing, mouth pushing, and butting behaviors were significantly increased in all the exposed groups. MeHg significantly decreased brain acetylcholine esterase (AChE) and serum immunoglobulin M (IgM) levels in all the exposed groups. Meanwhile, serum levels of lysozyme (LYZ), nitric oxide (NO), superoxide dismutase (SOD) malondialdehyde (MDA), protein carbonyl (PCO), and 8 hydroxy 2 deoxyguanosine (8OH2dG) were significantly elevated in all the exposed groups except for serum reduced glutathione (GSH) content was significantly decreased implying oxidative stress (OS), lipid peroxidation (LPO), protein, DNA damage and impaired immune response of the exposed tilapia. MeHg significantly altered transcriptional expression of immune-related genes including (TNF-α, IL-1β, and IL-8, and IL-10) in all the exposed groups. From the obtained outcomes, the present research is the premier to investigate that dietary MeHg exposure in O. niloticus significantly induced neurobehavioral and immune defense impairments in a dose-related manner. This study exhibits that dietary MeHg may pose a potential threat to the O. niloticus populations.

Tissue-Specific Accumulation and Antioxidant Defenses in Flounder (Paralichthys olivaceus) Juveniles Experimentally Exposed to Methylmercury

Methylmercury (MeHg) is the most toxic form of mercury and can accumulate in the cells of marine organisms, such as fish, causing adverse effects on various physiological functions. This study examined MeHg accumulation and its toxicological role in antioxidant defenses in tissues, including the liver, gills, and muscle of flounder (Paralichthys olivaceus) juveniles. After 30 d of MeHg exposure (0, 0.1, 1.0, 10.0, and 20.0 µg L^-1), the accumulation of MeHg in the three tissues correlated positively with the concentration of MeHg and exhibited tissue specificity in the order of liver > gills > muscle. Among the antioxidant markers, the activities of SOD (superoxide dismutase) and GST (glutathione S-transferase) as well as the content of glutathione (GSH) in the liver and gills were induced at 0.1-10.0 µg L^-1 but repressed at 20.0 µg L^-1. The activities of SOD and GST and the content of GSH in the muscle significantly increased with increasing MeHg concentration. Catalase (CAT) activity in the liver was induced at 0.1-1.0 µg L^-1 but inhibited at 10.0-20.0 µg L^-1, whereas exposure to MeHg did not remarkably affect CAT activity in the gills and muscle. The levels of lipid peroxidation (LPO) increased dose dependently, showing tissue specificity with the highest level in the liver, then the gills, followed by muscles. Overall, higher sensitivity to oxidative stress induced by MeHg was detected in the liver than the gills and muscle. These findings improve our understanding of the tissue-specific accumulation of heavy metals and their roles in antioxidant responses in marine fish subjected to MeHg exposure.

Differential micropollutants bioaccumulation in European hake and their parasites Anisakis sp

Organisms are exposed to various stressors including parasites and micropollutants. Their combined effects are hard to predict. This study assessed the trophic relationship, micropollutants bioaccumulation and infection degree in a host-parasite couple. Carbon and nitrogen isotopic ratios were determined in hake Merluccius merluccius muscle and in its parasite Anisakis sp.. Concentrations of both priority (mercury species and polychlorinated biphenyls congeners) and emerging (musks and sunscreens) micropollutants were also measured for the parasite and its host, to detect potential transfer of contaminants between the two species. The results showed partial trophic interaction between the parasite and its host, in accordance with the Anisakis sp. life encysted in hake viscera cavity. PCB transfer between the two species may result from some lipids uptake by the parasite, while no relation occurred for the two other contaminants. Finally, a positive correlation was found between the number of Anisakis sp. larvae and the methylmercury contamination for hake, emphasizing the assumption that the contamination level in methylmercury can weaken immune system of the host enough to affect parasite infection degree.

Effects of seawater acidification and cadmium on the antioxidant defense of flounder Paralichthys olivaceus larvae

Increasing atmospheric carbon dioxide has led to a decrease in the pH of the ocean, which influences the speciation of heavy metals and consequently affects metal toxicity in marine organisms. To investigate the effects of seawater acidification and metals on the antioxidant defenses of marine fishes, the flounder Paralichthys olivaceus, was continuously exposed to cadmium (Cd; control, 0.01 and 0.15 mg L^-1) and acidified seawater (control (pH 8.10), 7.70 and 7.30) for 49 days from embryogenesis to settlement. The results demonstrated that both Cd and acidified seawater could induce oxidative stress and consequently cause lipid peroxidation (LPO) in the larvae. Antioxidants (i.e., superoxide dismutase, SOD; catalase, CAT; reduced glutathione, GSH; glutathione S-transferase, GST; glutathione peroxidase, GPx; and glutathione reductase, GR) functioned to defend the larvae against oxidative damage. Overall, Cd induced (SOD, GST and GSH) or inhibited (CAT and GPx) the enzymatic activities or contents of all the selected antioxidants except for GR. The antioxidants responded differently to seawater acidification, depending on their interaction with the metal. Similarly, the mRNA expressions of the antioxidant-related genes were upregulated (sod, gr and gst) or downregulated (cat and gpx) in response to increasing Cd exposure. Seawater acidification did not necessarily affect all of the biomarkers; in some cases (e.g., SOD and sod, GR and gr), Cd stress may have exceeded and masked the stress from seawater acidification in regulating the antioxidant defense of the larvae. The integrated biomarker response (IBR) was enhanced with increasing levels of the stressors. These findings support the hypothesis that seawater acidification not only directly affects the antioxidant defense in flounder larvae but also interacts with Cd to further regulate this defense. This study has ecological significance for assessing the long-term impacts of ocean acidification and metal pollution on the recruitment of fish populations in the wild.