Time-dependent oxidative stress responses after acute exposure to toxic cyanobacterial cells containing microcystins in tilapia fish (Oreochromis niloticus) under laboratory conditions

Ultrastructural, molecular and haemato-immunological changes: Multifaceted toxicological effects of microcystin-LR in rohu, Labeo rohita

No water body is resilient to afflicts of algal bloom, if goes unmanaged. With the increasing trend of intensification, eutrophication and climate change, Labeo rohita (rohu) is highly anticipated to suffer from the deleterious effects of bloom and eventually its toxins. A comprehensive study was conducted to understand the toxicopathological effects of microcystin-LR (MC-LR) in rohu following intraperitoneal injection of 96 h-LD50 dose i.e., 713 μg kg-1. Substantial changes in micro- and ultrastructural level were evident in histopathology and transmission electron microscope (TEM) study. The haematological, biochemical, cellular and humoral innate immune biomarkers were significantly altered (p < 0.05) in MC-LR treated fish. The mRNA transcript levels of IL-1β, IL-10, IgM and IgZ in liver and kidney tissues were significantly up-regulated in 12 hpi and declined in 96 hpi MC-LR exposed fish. The relative mRNA expression of caspase 9 in the liver and kidney indicates mitochondrial-mediated apoptosis which was strongly supported by TEM study. In a nutshell, our study illustrates for the first time MC-LR induced toxicological implications in rohu displaying immunosuppression, enhanced oxidative stress, pathophysiology, modulation in mRNA transcription, genotoxicity, structural and ultrastructural alterations signifying it as a vulnerable species for MC-LR intoxication.

Metal-amino acid complexes (Zn, Se, Cu, Fe, and Mn) enhance immune response, antioxidant capacity, liver function enzymes, and expression of cytokine genes in Nile Tilapia reared under field conditions

OBJECTIVES

In the present study, we investigated the effects of partial or total replacement of dietary inorganic trace materials (ITM) with metal-amino acid complexes (MAACs) on immune response, antioxidant capacity, cytokine genes expression, and overall health status of Nile Tilapia Oreochromis niloticus reared in in-pond hapas (mesh cages) under field conditions.

METHODS

All-male Nile Tilapia with an average initial weight of about 90 g fish-1 were stocked into the hapas, in quadruplicates, at a density of 60 fish per hapa (30 fish m-3 ). The fish in each hapa were acclimatized to culture conditions and test diets for 1 week. Water quality parameters, including temperature (°C), pH, dissolved oxygen (mg L-1 ), and total ammonia (mg L-1 ), were monitored regularly. The MAACs were formulated to contain the same mineral concentrations found in the inorganic premix. Metal-amino acid complexes replaced the ITM premix at 0 (control), 25, 50, 75, and 100% levels (Table 1). The diets were fed to caged Nile Tilapia twice a day, for 80 days, at a daily rate of 3% of their body weights. The fish were weighed every 10 days, and the daily rations were readjusted. At harvest, fish in each hapa were collected, counted, and weighed collectively. Five fish from each hapa were rapidly anesthetized, and used for chemical and physiological analyses, including antioxidant and immune response analyses, liver function analysis, and gene expression.

RESULT

The activities of lysozyme, respiratory burst (%), alternative complement (ACH50), phagocytic cells, phenoloxidase, superoxide dismutase, glutathione peroxidase, and liver function enzymes were all improved with increasing supplemental MAACs up to the 50% substitution level. The expression of cytokine genes, including interferon, tumor necrosis factor, interleukin-1, serum alkaline phosphatase, the integrated microbial genomes, chloramphenicol acetyltransferase, and transforming growth factor genes, was significantly upregulated in fish fed on MAAC-supplemented diets compared with the control group. The 50% MAAC level produced the highest upregulation of these genes, whereas gene expression decreased with increasing dietary MAAC levels to 75% and 100%. The quadratic regression analysis indicated that about 60-65% MAAC is required for maximum promotion of immunological and oxidative stress responses, gene expression, and overall health status of Nile Tilapia reared in in-pond hapas under field conditions.

CONCLUSION

Replacement of the ITM premix with a MAAC premix enhanced the immune and antioxidant responses of Nile Tilapia.

Oxidative Stress Parameters and Morphological Changes in Japanese Medaka (Oryzias latipes) after Acute Exposure to OA-Group Toxins

Toxins of the OA-group (okadaic acid, OA; dinophysistoxin-1, DTX-1) are the most prevalent in the fjords of southern Chile, and are characterized by their potential harmful effects on aquatic organisms. The present study was carried out to determine the acute toxicity of OA/DTX-1 on oxidative stress parameters in medaka (Oryzias latipes) larvae. Medaka larvae were exposed to different concentrations (1.0-30 μg/mL) of OA/DTX-1 for 96 h to determine the median lethal concentration. The LC₅₀ value after 96 h was 23.5 μg/mL for OA and 16.3 μg/mL for DTX-1 (95% confidence interval, CI was 22.56, 24.43 for OA and 15.42, 17.17 for DTX-1). Subsequently, larvae at 121 hpf were exposed to acute doses (10, 15 and 20 μg/mL OA and 5.0, 7.5 and 11.0 μg/mL DTX-1) for 96 h and every 6 h the corresponding group of larvae was euthanized in order to measure the activity levels of biochemical biomarkers (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPx; and glutathione reductase, GR) as well as the levels of oxidative damage (malondialdehyde, MDA; and carbonyl content). Our results showed that acute doses caused a decrease in SOD (≈25%), CAT (≈55%), and GPx and GR (≈35%) activities, while MDA levels and carbonyl content increased significantly at the same OA/DTX-1 concentrations. This study shows that acute exposure to OA-group toxins tends to simultaneously alter the oxidative parameters that induce sustained morphological damage in medaka larvae. DTX-1 stands out as producing greater inhibition of the antioxidant system, leading to increased oxidative damage in medaka larvae. Considering that DTX-1 is the most prevalent HAB toxin in southern Chile, these findings raise the possibility of an important environmental impact on the larval stages of different fish species present in the southern fjords of the South Pacific.

Toxicity of the microcystin-producing cyanobacteria Microcystis aeruginosa to shrimp Litopenaeus vannamei

Microcystis aeruginosa is reported to cause cyanobacterial blooms in shrimp breeding ponds, which can result in significant shrimp mortality. However, the toxic effects of M. aeruginosa on Litopenaeus vannamei are still not completely understood. In this paper, the toxicity of M. aeruginosa cells to L. vannamei was examined, and the toxic components in the cells were analyzed through high-pressure liquid chromatography (HLPC). In addition, the immune response of shrimp to the M. aeruginosa cell extract was assessed by measuring the activity of immune-related enzymes, as well as the transcription of the relevant genes. The results showed that M. aeruginosa cells, extract and cell-free cultured medium resulted in a 100%, 98.3%, and 1.7% mortality rate in shrimp, respectively. HPLC analysis results revealed the presence of microcystin-LR (MC-LR) at a concentration of 190.40 mg/kg of cells. In addition, the activity and gene transcription of two immune related enzymes, SOD and LZM, were both significantly reduced in shrimp hepatopancreas (p < 0.05) after injection with extract. However, reduced glutathione (GSH) content was slightly increased, but the ratio of GSH to GSSG decreased. The transcription of gst gene function as detoxification, was significantly downregulated (p < 0.05). The results demonstrated that M. aeruginosa cell extract was highly toxic to L. vannamei, and exerted a negative effect on shrimp immunity including reduction of antioxidant capacity, antibacterial activity and detoxification activity, due to toxins including microcystin-LR.

Biochemical indices, gene expression, and SNPs associated with salinity adaptation in juvenile chum salmon (Oncorhynchus keta) as determined by comparative transcriptome analysis

Chum salmon (Oncorhynchus keta) migrate from freshwater to saltwater, and incur developmental, physiological and molecular adaptations as the salinity changes. The molecular regulation for salinity adaptation in chum salmon is currently not well defined. In this study, 1-g salmon were cultured under 0 (control group, D0), 8‰ (D8), 16‰ (D16), and 24‰ (D24) salinity conditions for 42 days. Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities in the gill first increased and then decreased in response to higher salinity environments where D8 exhibited the highest Na⁺/K⁺ATPase and Ca²⁺/Mg²⁺-ATPase activity and D24 exhibited the lowest. Alkaline phosphatase (AKP) activity was elevated in all salinity treatment groups relative to controls, while no significant difference in acid phosphatase (ACP) activity was observed across treatment groups. De novo transcriptome sequencing in the D0 and D24 groups using RNA-Seq analysis identified 187,836 unigenes, of which 2,143 were differentially expressed in response to environmental salinity (71 up-regulated and 2,072 down-regulated). A total of 56,020 putative single nucleotide polymorphisms (SNPs) were also identified. The growth, development, osmoregulation and maturation factors of N-methyl-D-aspartate receptors (nmdas) expressed in memory formation, as well as insulin-like growth factor 1 (igf-1) and igf-binding proteins (igfbps) were further investigated using targeted qRT-PCR. The lowest expression of all these genes occurred in the low salinity environments (D8 or D16), while their highest expression occurred in the high salinity environments (D24). These results provide preliminary insight into salinity adaptation in chum salmon and a foundation for the development of marker-assisted breeding for this species.

In Vitro Toxicity Evaluation of Cyanotoxins Cylindrospermopsin and Microcystin-LR on Human Kidney HEK293 Cells

Cyanotoxins are secondary metabolites produced by different types of cyanobacteria. Among them, Cylindrospermopsin (CYN) and Microcystins (MCs) stand out due to their wide geographical distribution and toxicity in various organs, including the kidney, which is involved in their distribution and elimination. However, the renal toxicity caused by CYN and MCs has hardly been studied. The aim of this work was to assess the cytotoxicity effects caused by CYN and MC-LR in the renal cell line HEK293, and for the first time, the influence of CYN on the gene expression of selected genes in these cells by quantitative real-time PCR (qRT-PCR). CYN caused an upregulation in the gene expression after exposure to the highest concentration (5 µg/mL) and the longest time of exposure (24 h). Moreover, shotgun proteomic analysis was used to assess the molecular responses of HEK293 cells after exposure to the individuals and combinations of CYN + MC-LR. The simultaneous exposure to both cyanotoxins caused a greater number of alterations in protein expression compared to single toxins, causing changes in the cellular, lipid and protein metabolism and in protein synthesis and transport. Further studies are needed to complete the toxicity molecular mechanisms of both CYN and MC-LR at the renal level.

Neurotoxicity induced by combined exposure of microcystin-LR and nitrite in male zebrafish (Danio rerio): Effects of oxidant-antioxidant system and neurotransmitter system

With the intensification of water eutrophication around the world, cyanobacterial blooms have been becoming a common environmental pollution problem. The levels of microcystin-LR (MC-LR) and nitrite rise sharply during the cyanobacterial bloom period, which may have potential joint toxicity on aquatic organisms. In this study, adult male zebrafish were immersed into different joint solutions of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 days to explore the neurotoxic effects and underlying mechanisms. The results showed that single factor MC-LR or nitrite caused a concentration-dependent damage in brain ultrastructure and the effects of their joint exposure were much more intense. Downregulated expression of mbp and bdnf associated with myelination of nerve fibers further confirmed that MC-LR and nitrite could damage the structure and function of neuron. The decreases in dopamine content, acetylcholinesterase activity and related gene mRNA levels indicated that MC-LR and nitrite adversely affected the normal function of the dopaminergic and cholinergic systems in zebrafish brain. In addition, the significant increase in malondialdehyde content suggested the occurrence of oxidative stress caused by MC-LR, nitrite and their joint-exposure, which paralleled a significant decrease in antioxidant enzyme‑manganese superoxide dismutase activity and its transcription level. In conclusion, MC-LR + Nitrite joint-exposure has synergistic neurotoxic effects on the structure and neurotransmitter systems of fish brain, and antioxidant capacity disruption caused by these two factors might be one of the underlying synergistic mechanisms. Therefore, there is a risk of being induced neurotoxicity in fish during sustained cyanobacterial bloom events.

Effects of Dufulin on Oxidative Stress and Metabolomic Profile of Tubifex

Dufulin is a highly effective antiviral pesticide used in plants. In this study, a seven-day experiment was conducted to evaluate the effects of Dufulin at five different concentrations (1 × 10⁻⁴, 1 × 10⁻³, 1 × 10⁻², 0.1, and 1 mg/L) on Tubifex. LC-MS-based metabolome analysis detected a total of 5356 features in positive and 9110 features in negative, of which 41 showed significant changes and were identified as differential metabolites. Four metabolic pathways were selected for further study. Detailed analysis revealed that Dufulin exposure affected the urea cycle of Tubifex, probably via argininosuccinate lyase (ASL) inhibition. It also affected the fatty acid metabolism, leading to changes in the concentration of free fatty acids in Tubifex. Furthermore, the changes in metabolites after exposure to Dufulin at 1 × 10⁻² mg/L were different from those at the other concentrations.

Comparison of toxicokinetics and toxic effects of PFOS and its novel alternative OBS in zebrafish larvae

Sodium p-perfluorous nonenoxybenzene sulfonate (OBS), a novel alternative to perfluorooctanesulfonate (PFOS), is widely used in industry as a surfactant, firefighting foam and photographic material. The occurrence of OBS in the aquatic environment has been recently reported, but little information is available on its accumulation and toxic effects in aquatic organisms. In this study, zebrafish larvae (3 d post-fertilization) were subjected to OBS (10, 100 μg/L) and PFOS (10 μg/L) for a period of 48 h, followed by a 24 h of depuration period. The bioconcentration and depuration kinetics, oxidative stress and possible molecular mechanisms of OBS and PFOS were investigated in zebrafish larvae. Our results showed that the uptake and depuration of both OBS and PFOS fitted well with a first-order kinetic model. The uptake rate constant of OBS was similar to that of PFOS, but the depuration rate constant was much higher than PFOS with a half-life of 69.7-85 h for OBS and 222.2 h for PFOS. The calculated BCFs of OBS and PFOS were 238.0-242.5 and 644.2, respectively. In our acute toxicity assay, the enhanced expression of Nrf2 protein accompanied by the upregulation of CAT and SOD protein expressions indicated OBS and PFOS induced oxidative stress in zebrafish larvae, and the Nrf2-ARE signaling pathway was involved in this process. Collectively, OBS has a lower bioconcentration potential than PFOS, but its toxic effect on oxidative stress was comparable to PFOS in zebrafish larvae.

In Vivo and In Vitro Toxicity Testing of Cyanobacterial Toxins: A Mini-Review

Harmful cyanobacterial blooms are increasing and becoming a worldwide concern as many bloom-forming cyanobacterial species can produce toxic metabolites named cyanotoxins. These include microcystins, saxitoxins, anatoxins, nodularins, and cylindrospermopsins, which can adversely affect humans, animals, and the environment. Different methods to assess these classes of compounds in vitro and in vivo include biological, biochemical, molecular, and physicochemical techniques. Furthermore, toxic effects not attributable to known cyanotoxins can be observed when assessing bloom material. In order to determine exposures to cyanotoxins and to monitor compliance with drinking and bathing water guidelines, it is necessary to have reliable and effective methods for the analysis of these compounds. Many relatively simple low-cost methods can be employed to rapidly evaluate the potential hazard. The main objective of this mini-review is to describe the assessment of toxic cyanobacterial samples using in vitro and in vivo bioassays. Newly emerging cyanotoxins, the toxicity of analogs, or the interaction of cyanobacteria and cyanotoxins with other toxicants, among others, still requires bioassay assessment. This review focuses on some biological and biochemical assays (MTT assay, Immunohistochemistry, Micronucleus Assay, Artemia salina assay, Daphnia magna test, Radionuclide recovery, Neutral red cytotoxicity and Comet assay, Enzyme-Linked Immunosorbent Assay (ELISA), Annexin V-FITC assay and Protein Phosphatase Inhibition Assay (PPIA)) for the detection and measurement of cyanotoxins including microcystins, cylindrospermopsins, anatoxin-a, saxitoxins, and nodularins. Although most bioassay analyses often confirm the presence of cyanotoxins at low concentrations, such bioassays can be used to determine whether some strains or blooms of cyanobacteria may produce other, as yet unknown toxic metabolites. This review also aims to identify research needs and data gaps concerning the toxicity assessment of cyanobacteria.

Ocean acidification, hypoxia and warming impair digestive parameters of marine mussels

Global change and anthropogenic activities have driven marine environment changes dramatically during the past century, and hypoxia, acidification and warming have received much attention recently. Yet, the interactive effects among these stressors on marine organisms are extremely complex and not accurately clarified. Here, we evaluated the combined effects of low dissolved oxygen (DO), low pH and warming on the digestive enzyme activities of the mussel Mytilus coruscus. In this experiment, mussels were exposed to eight treatments, including two degrees of pH (8.1, 7.7), DO (6, 2 mg/l) and temperature (30 °C and 20 °C) for 30 days. Amylase (AMS), lipase (LPS), trypsin (TRY), trehalase (TREH) and lysozyme (LZM) activities were measured in the digestive glands of mussels. All the tested stress conditions showed significant effects on the enzymatic activities. AMS, LPS, TRY, TREH showed throughout decreased trend in their activities due to low pH, low DO, increased temperature and different combinations of these three stressors with time but LZM showed increased and then decreased trend in their activities. Hypoxia and warming showed almost similar effects on the enzymatic activities. PCA showed a positive correlation among all measured biochemical parameters. Therefore, the fitness of mussel is likely impaired by such marine environmental changes and their population may be affected under the global change scenarios.

Toxicity and differential oxidative stress effects on zebrafish larvae following exposure to toxins from the okadaic acid group

Okadaic acid-group (OA-group) is a set of lipophilic toxins produced only in seawater by species of the Dinophysis and Prorocentrum genera, and characterized globally by being associated with harmful algal blooms (HABs). The diarrhetic shellfish poisoning toxins okadaic acid (OA) and dinophysistoxin-1 (DTX-1) are the most prevalent toxic analogues making up the OA-group, which jeopardize environmental safety and human health through consumption of hydrobiological organisms contaminated with these toxins that produce diarrhetic shellfish poisoning (DSP) syndrome in humans. Consequently, a regulatory limit of 160 μg of OA-group/kg was established for marine resources (bivalves). The aim of this study was to investigate effects varying concentrations of 1-15 μg/ml OA or DTX-1 on toxicity, development, and oxidative damage in zebrafish larvae (Danio rerio). After determining the lethal concentration 50 (LC₅₀) in zebrafish larvae of 10 and 7 μg/ml (24 h) and effective concentration 50 (EC₅₀) of 8 and 6 μg/ml (24 h), different concentrations (5, 6.5, or 8 μg/ml of OA and 4, 4.5, or 6 μg/ml of DTX-1) were used to examine the effects of these toxins on oxidative damage to larvae at different time points between 24 and 120 hpf. Macroscopic evaluation during the exposure period showed alterations in zebrafish including pericardial edema, cyclopia, shortening in the anteroposterior axis, and developmental delay. The activity levels of biochemical biomarkers superoxide dismutase (SOD) and catalase (CAT) demonstrated a concentration-dependent decrease while glutathione peroxidase (GPx) and glutathione reductase (GR) were markedly elevated. In addition, increased levels of oxidative damage (malondialdehyde and carbonyl content) were detected following toxin exposure. Data demonstrate that high concentrations of OA and DTX-1produced pathological damage in the early stages of development <48 h post-fertilization (hpf) associated with oxidative damage.

Biotransformations, Antioxidant System Responses, and Histopathological Indexes in the Liver of Fish Exposed to Cyanobacterial Extract

Radiocystis fernandoi, a microcystin (MC) producer, has been common in cyanobacterial blooms in tropical regions. Microcystin is a hepatotoxin that causes tissue damage and even death in animals, including humans; its detoxification process may involve biotransformation and activation of the antioxidant defense system. We evaluated the detoxification pathway, examined the antioxidant defense system responses, and determined the alterations and the organ histopathological indexes in the liver of the tropical fish Hoplias malabaricus after acute and subchronic intraperitoneal exposure to microcystin. The crude microcystin extract of R. fernandoi had predominantly MC-RR and MC-YR. The detoxification process was activated by increasing ethoxyresorufin-O-deethylase activity, whereas glutathione S-transferase was inhibited. The activity of the antioxidant defense enzymes superoxide dismutase (SOD) and glutathione peroxidase decreased after acute exposure; the SOD-catalase system and the glutathione level increased after subchronic exposure. The carbonyl protein level, lipid peroxidation (LPO), and DNA damage were unchanged after acute exposure, whereas protein carbonyl was unchanged, LPO decreased, and DNA damage increased after subchronic exposure. Histopathological alteration indexes differed between acute and subchronic exposure, but the histopathological organ indexes indicate liver dysfunction in both exposure periods. We conclude that MC-RR and MC-YR induce different liver responses depending on the time of exposure, and the antioxidant defense responses after subchronic exposure may help to partially restore the liver function. Environ Toxicol Chem 2020;39:1041-1051. © 2020 SETAC.

Biochemical parameters in skin and muscle of Pelophylax kl. esculentus frogs: Influence of a cyanobacterial bloom in situ

There is little information in scientific literature as to how conditions created by a microcystin (MC) producing cyanobacterial bloom affect the oxidant/antioxidant, biotransformation and neurotoxicity parameters in adult frogs in situ. We investigated biochemical parameters in the skin and muscle of Pelophylax kl. esculentus from Lake Ludaš (Serbia) by comparing frogs that live on the northern bloom side (BS) of the lake with those that inhabit the southern no-bloom side (NBS). A higher protein carbonylation level and lower antioxidant defense system capability in the skin of frogs living in conditions of the cyanobacterial bloom were observed. Inhibition of glutathione-dependent machinery was the major mechanism responsible for the induction of cyanobacterial bloom-mediated oxidative stress in frog skin. On the other hand, the detected higher ability of muscle to overcome bloom prooxidant toxicity was linked to a higher efficiency of the biotransformation system through glutathione-S-transferase activity and/or was the consequence of indirect exposure of the tissue to the bloom. Our results have also revealed that the cyanobacterial bloom conditions induced the cholinergic neurotransmitter system in both tissues. This study provides a better understanding of the ecotoxicological impact of the MC producing cyanobacterial bloom on frogs in situ. However, further investigations of the complex mechanism involved in cyanobacterial bloom toxicity in real environmental conditions are required.

Protected Freshwater Ecosystem with Incessant Cyanobacterial Blooming Awaiting a Resolution

For 50 years persistent cyanobacterial blooms have been observed in Lake Ludoš (Serbia), a wetland area of international significance listed as a Ramsar site. Cyanobacteria and cyanotoxins can affect many organisms, including valuable flora and fauna, such as rare and endangered bird species living or visiting the lake. The aim was to carry out monitoring, estimate the current status of the lake, and discuss potential resolutions. Results obtained showed: (a) the poor chemical state of the lake; (b) the presence of potentially toxic (genera Dolichospermum, Microcystis, Planktothrix, Chroococcus, Oscillatoria, Woronichinia and dominant species Limnothrix redekei and Pseudanabaena limnetica) and invasive cyanobacterial species Raphidiopsis raciborskii; (c) the detection of microcystin (MC) and saxitoxin (STX) coding genes in biomass samples; (d) the detection of several microcystin variants (MC-LR, MC-dmLR, MC-RR, MC-dmRR, MC-LF) in water samples; (e) histopathological alterations in fish liver, kidney and gills. The potential health risk to all organisms in the ecosystem and the ecosystem itself is thus still real and present. Although there is still no resolution in sight, urgent remediation measures are needed to alleviate the incessant cyanobacterial problem in Lake Ludoš to break this ecosystem out of the perpetual state of limbo in which it has been trapped for quite some time.

Protective effects of melatonin and N-acetyl cysteine against oxidative stress induced by microcystin-LR on cardiac muscle tissue

Microcystin Leucine-Arginine (MC-LR) is a toxin produced by the cyanobacteria Microcystis aeruginosa. It is the most encountered and toxic type of cyanotoxins. Oxidative stress was shown to play a role in the pathogenesis of microcystin LR by the induction of intracellular reactive oxygen species (ROS) formation that oxidize and damage cellular macromolecules. In the present study we examined the effect of acute MC-LR dose on the cardiac muscle of BALB/c mice. Afterwards, melatonin and N-acetyl cysteine (NAC) were assayed and evaluated as potential protective and antioxidant agents against damages generated by MC-LR. For this purpose, thirty mice were assigned into six groups of five mice each. The effect of MC-LR was first compared to the control group supplied with distilled water, then compared to the other groups supplied with melatonin and NAC. The experiment lasted 10 days after which animals were euthanized. Biomarkers of toxicity such as alkaline phosphatase activity, lipid peroxidation, protein carbonyl content, reduced glutathione content, serum lactate dehydrogenase and serum sorbitol dehydrogenase were assayed. Results showed that toxin treated mice have experienced significant oxidative damage in their myocardial tissue as revealed by noticeable levels of oxidative stress biomarkers and by the reduction in alkaline phosphatase activity. Whereas, melatonin and NAC treated mice manifested lesser oxidative damages. Our findings suggest a potential therapeutic use of melatonin and N-acetyl cysteine as antioxidant protective agents against oxidative damage induced by MC-LR.

Combined effects of toxic Microcystis aeruginosa and hypoxia on the digestive enzyme activities of the triangle sail mussel Hyriopsis cumingii

Nowadays, eutrophication is a very popular environmental problem in numerous waters around the world. The main reason of eutrophication is the enrichment of the nutrient, which results in the excessive growth of phytoplankton and some of them are toxic and harmful. Fortunately, some studies have shown that some bivalves can filter the overgrown phytoplankton in water, which may alleviate water eutrophication. However, the physiological effects of toxic cyanobacteria on filter feeding animal have not been clarified very well. In this experiment, digestive enzyme activities in Hyriopsis cumingii exposed to different concentrations of the toxic Microcystis aeruginosa (0, 5 * 10⁵ and 5 *10⁶ cell ml^-1) at two dissolved oxygen (DO) levels (6 and 2 mg l^-1) for 14 days were investigated. Toxic M. aeruginosa significantly affected all digestive enzyme activities throughout the experiment. At high toxic M. aeruginosa concentration, the activities of cellulase, amylase and lipase in digestive gland and stomach were significantly increased (P<0.05). However, hypoxia reduced the activities of cellulase, amylase and lipase in digestive gland and stomach. Conflicting effects were observed between toxic M. aeruginosa and DO in most digestive enzyme activities during the exposure period. Therefore, it is not conducive for the digestion and absorption of M. aeruginosa in H. cumingii under hypoxic conditions. H. cumingii is tolerant to toxic M. aeruginosa and may remove toxic cyanobacteria from waters under normal DO conditions.

Bioaccumulation of microcystins in seston, zooplankton and fish: A case study in Lake Zumpango, Mexico

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii, Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g^-1 on sestonic samples; in zooplankton they were in the range of 0.0070-0.29 μg g^-1. The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg^-1 d^-1) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote.

Effects of microcystin-LR on the immune dysfunction and ultrastructure of hepatopancreas in giant freshwater prawn Macrobrachium rosenbergii

Microcystins (MCs), produced by cyanobacteria, can strongly inhibit the activity of protein phosphatase, and exhibit strong hepatotoxicity. Macrobrachium rosenbergii is an important aquaculture economic species. Cyanobacterial blooms occur frequently during the culture of M. rosenbergii. However, the effects of MCs on the M. rosenbergii immune function have not been studied. In the present study, M. rosenbergii were exposed to environment-related concentrations of MC-LR type (0.5 and 5 μg/L) for 3 weeks. Hepatopancreatic histology was investigated, and antioxidant enzymes activity, acid phosphatase, alkaline phosphatase and lysozyme activity in hepatopancreas were also analyzed. Results showed that MC-LR could damage M. rosenbergii hepatopancreas, induce hepatopancreatic apoptosis and antioxidant dysfunctions. The expression profiles of major immune-related genes after MC-LR exposure were also detected. Some genes with antibacterial functions were suppressed, and the expression of apoptosis-related genes were up-regulated. After MC-LR exposure, the cumulative mortality of M. rosenbergii infected with Vibrio vulnificus and Aeromonas hydrophila were much higher than the control in a time-dose dependent manner. These results indicated the potential negative influence of MC-LR on the immune function of M. rosenbergii.

Microcystin - LR exposure causes cardiorespiratory impairments and tissue oxidative damage in trahira, Hoplias malabaricus

This study investigated the effect of microcystin-LR (MC-LR) on in vivo cardiorespiratory function and on tissue biomarkers of oxidative stress in gills and liver of the trahira, a neotropical freshwater fish. Trahira were treated with an intraperitoneal injection of 100 µg MC-LR.kg^-1 body mass or a saline, with the toxic effects of MC-LR then evaluated after 48 h. Rates of oxygen uptake (V̇O₂) did not differ significantly between Control and the exposed group (Mcys), but exposure to MC-LR significantly reduced O₂ extraction in the Mcys group at all O₂ tensions. This was associated with higher gill ventilation volume (V̇_G) in the Mcys group at all O₂ tensions except 140 and 120 mmHg, and a higher tidal volume (V_T) of the Mcys group at all tensions except 140 mmHg. Heart rate was also higher in the Mcys group, significantly so at an O₂ tension of 40 mmHg. In the liver of trahira, exposure to MC-LR has significant effects on antioxidant defense systems, inducing a significant increase in the activity of the (GPx) glutathione peroxidase enzyme (100%) and in the reduced glutathione (GSH) content (70%) compared to the control group, but no effects on superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) enzymes. The liver showed no oxidative damage, when measured as lipid peroxidation (LPO) levels and protein carbonyl (PC) content. In the gills SOD and GPx enzyme activity increased significantly in the Mcys group (98% and 73% respectively) compared to the controls, although GSH, CAT and GST did not differ between groups. There was also no significant difference in GSH in this tissue. Levels of lipid peroxidation in the gills were 53% higher in the Mcys group, although carbonyl protein levels did not differ. In conclusion, these data show that MC-LR leads to development of hyperventilation and increased activity of the detoxification system and that this species was able to compensate the deleterious effects of microcystin on its vital functions. The antioxidant defense in the liver was able to contain the propagation of LPO and prevent the oxidation of proteins, although the gills of the fishes exposed to MC-LR were not able to contain the formation of reactive oxygen species and LPO, which led to the establishment of oxidative stress which impaired gill function.

Toxicokinetics and toxic effects of a Chinese PFOS alternative F-53B in adult zebrafish

6:2 chlorinated polyfluorinated ether sulfonate (F-53B), a Chinese PFOS alternative, has recently been identified in river water, sewage sludge, wildlife and humans, causing great concerns about its potential toxic effects. Here, we report the first investigation of the toxicokinetics and oxidative stress of F-53B in adult zebrafish. Adult male and female zebrafish were exposed to 10 and 100 μg/L of F-53B for 7 days followed by a 5-d depuration period to examine bioaccumulation, distribution, and depuration of F-53B in fish. The results showed that F-53B was readily accumulated in fish tissues with log BCF values of 2.36-3.65, but was eliminated slowly (t_1/2 = 152.4-358.5 h). F-53B accumulation was greater in males than in females and the concentration in tissues decreased in the following order: gonad ≈ liver ≫ gill ≫ brain in females and liver ≈ gill ≫ gonad ≫ brain in males, showing sex- and tissue- specific accumulation of F-53B in fish. After chronic exposure to F-53B for 28 days, a significant dose-dependent increase in histopathological changes in the liver were mainly manifested by vacuolation. Furthermore, F-53B also significantly reduced the enzyme activity (or content) of most of the measured oxidative stress-related markers (e.g., SOD, CAT and MDA) except for an increase in GSH-Px activity, indicating that oxidative stress was induced in zebrafish after treatment with F-53B. The results of this study provide important information on the toxicokinetics and toxic effects of F-53B, which will contribute to the ecological risk assessments of F-53B released into surface waters.

Chronic Toxic Effects of Flutolanil on the Liver of Zebrafish ( Danio rerio)

Flutolanil is a broad-spectrum amide fungicide that is widely used to prevent fungal pathogens in agriculture. However, its usage may have a potential environmental impact on organisms. So far, few literatures have investigated the chronic toxicity of flutolanil at concentrations relevant to environmental conditions in the nontarget aquatic organisms. This study was aimed at evaluating whether the long-term exposure of flutolanil affects oxidative stress, immune response, and apoptosis in the liver of zebrafish ( Danio rerio). The results showed that the activity of catalase (CAT) was significantly decreased in the liver in all flutolanil-treated groups. Interestingly, the malondialdehyde (MDA) contents were remarkably increased following the flutolanil exposure. Deoxyribonucleic acid (DNA) damage was increased with a concentration-dependent manner. The transcription level of genes involved in apoptosis and the immune system were significantly altered following flutolanil chronic exposure in zebrafish liver. Furthermore, the caspase-3 enzyme activity was significantly increased. Taken together, this study demonstrated that the resulting effects on oxidative stress, immune toxicity, and apoptosis may be responsible for the pathological alterations in zebrafish liver after flutolanil exposure at concentrations relevant to environmental conditions, advancing the knowledge of pesticide environmental risk assessment.

Uptake and elimination of emerging polyfluoroalkyl substance F-53B in zebrafish larvae: Response of oxidative stress biomarkers

6:2 chlorinated polyfluorinated ether sulfonate (F-53B) has been widely applied as a mist suppressant to replace perfluorooctane sulfonate (PFOS) in the metal plating industry in China for decades. Recently, F-53B has been frequently identified in the aquatic environment and wild-caught fish. However, studies on the uptake and elimination kinetics, and the toxicological effects of F-53B were very scarce. In this study, zebrafish larvae (72 h post fertilization, hpf) were exposed to F-53B (10, 100 μg/L) for 48 h, followed by a 24 h of depuration to examine both the dynamics of accumulation and elimination of F-53B and responses of antoxidant defense system in fish. The results showed that F-53B rapidly accumulated in zebrafish larvae in a concentration and time-dependent manner with BCF values of 3612-3615, but was eliminated slowly (half-life ranged from 241.5 to 258.6 h). F-53B exposure induced oxidative stress in zebrafish larvae, as reflected by the reduction in the GSH and MDA contents, CAT, SOD, CuZn-SOD, and GSH-ST activities, and the increase in GSH-Px activity as well as CAT and SOD protein levels. However, these oxidative stress markers were restored to control levels except for a decrease in protein level of SOD after depuration. Collectively, the results of this work indicate that F-53B behaves like PFOS and is bioaccumulative and persistent in zebrafish larvae, and further induced oxidative stress responses.

Effect of crude extracts from Nodularia spumigena on round goby (Neogobius melanostomus)

Nodularia spumigena is a nitrogen-fixing filamentous cyanobacteria in the Baltic Sea. Nodularin (NOD), the hepatotoxic peptide produced by this cyanobacterium, accumulates in the organisms from different trophic levels. In this paper, the effects of N. spumigena cell extract on the round goby (Neogobius melanostomus) was investigated under laboratory conditions. This benthic fish species feed on mussels in which nodularin accumulation was well documented. In current study a sharp increase in the NOD concentration in analyzed organs was observed after 24 h (PPIA) after 72 h of exposure (LC/MS). To determine the direction and strength of the changes induced in the fish by the toxin, several biochemical markers of exposure such as concentration of glutathione and activities of catalase, guaiacol peroxidase and glutathione S-transferase were used. In analyzed organs (liver, gills and muscle) of the round goby, the activity of these enzymes were suppressed. Higher GSH/protein amount and CAT and POD activity in gills than in liver reflects the importance of gills in NOD entering into analyzed fish body when exposed to toxin. The results indicate that the round goby (Neogobius melanostomus) exposed to extracts from N. spumigena cells triggered a defense system in a time-dependent manner. The obtained results contribute to a better understanding of fish response to the presence of compounds produced by N. spumigena.

Effects of Dietary Astaxanthin Supplementation on Energy Budget and Bioaccumulation in Procambarus clarkii (Girard, 1852) Crayfish under Microcystin-LR Stress

This research aimed to study the effects of astaxanthin on energy budget and bioaccumulation of microcystin-leucine-arginine (microcystin-LR) in the crayfish Procambarus clarkii (Girard, 1852). The crayfish (21.13 ± 4.6 g) were cultured under microcystin-LR stress (0.025 mg/L) and were fed with fodders containing astaxanthin (0, 3, 6, 9, and 12 mg/g) for 8 weeks in glass tanks (350 mm × 450 mm × 150 mm). Accumulations of microcystin-LR were measured in different organs of P. clarkii. The results suggested that astaxanthin can significantly improve the survival rate and specific growth rate (SGR) of P. clarkii (p < 0.05). The dietary astaxanthin supplement seems to block the bioaccumulation of microcystin-LR in the hepatopancreas and ovaries of P. clarkii to some extent (p < 0.05). Astaxanthin content of 9⁻12 mg/g in fodder can be a practical and economic choice.

The synergistic effects of waterborne microcystin-LR and nitrite on hepatic pathological damage, lipid peroxidation and antioxidant responses of male zebrafish

Hazardous materials from decaying cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite pose serious challenges to aquatic organisms. To assess combined toxic effects of MC-LR and nitrite on hepatic pathology, lipid peroxidation and antioxidant responses of fish, adult male zebrafish (Danio rerio) were exposed to solutions with different combined concentrations of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 d. The results showed that hepatic pathological lesions progressed in severity and extent with increasing concentration of single factor MC-LR or nitrite and became more severe in co-exposure groups. Concurrently, significant increases in malondialdehyde (MDA) revealed the occurrence of oxidative stress caused by MC-LR, nitrite and both of them, which was indirectly verified by remarkable decreases in the total antioxidant capacity (T-AOC) as well as the transcription and activity of antioxidant enzymes (CAT and GPx). Hepatic mitochondria were damaged as the common action site of MC-LR and nitrite, suggesting that oxidative stress played a significant role in the mechanisms of the hepatotoxicity of MC-LR and nitrite. The depletion of hepatic glutathione (GSH) indicated the importance of GSH/glutathione-S-transferases (GST) system in these two chemicals detoxification. These results clearly illustrated that MC-LR and nitrite have synergistic effects on the histostructure, antioxidant capacity and detoxification capability in the liver of zebrafish. Therefore, the combined pollution of MC-LR and nitrite in eutrophic lakes can reduce the defense mechanism of the fish and accelerate the consumption of GSH, which compromise the survival of the fish during prolonged cyanobacterial blooms episodes.

Toxicological and biochemical responses of the earthworm Eisenia fetida to cyanobacteria toxins

Irrigation with eutrophic water containing cyanobacteria toxins poses a potential risk to soil animals. To evaluate ecotoxicological effect of microcystins (MCs) on earthworms, filter paper acute toxicity test, avoidance test and a 14-d artificial soil test were carried out. No acute toxicity was found in the filter paper test, and earthworms showed no avoidance response to MCs exposure. In the artificial soil test, Eisenia fetida were allowed to grow in presence or absence of MCs (0, 1, 10, 100, 1000 μg kg⁻¹ of soil) for 1, 7, and 14 d. Results showed that MCs could bioaccumulated in earthworm. A stimulatory effect on catalase and glutathione oxidase activities induced by MCs was found on day 1, and both of them were significantly inhibited at 100 and 1000 μg kg⁻¹ on days 14. The superoxide dismutase activity was relatively insensitive. Significant increase of malondialdehyde content and decrease of neutral red retention time were observed at 100 and 1000 μg kg⁻¹ on days 7 and 14. Our results suggest that MCs induces oxidative stress on earthworms, which leads to disruption of the antioxidant system and lipid peroxidation, as well as alterations in lysosomal membrane stability.

Microcystin-LR leads to oxidative damage and alterations in antioxidant defense system in liver and gills of Brycon amazonicus (SPIX & AGASSIZ, 1829)

Microcystin's (MCs) are toxins produced by several groups of cyanobacteria, in water bodies throughout the world, in a process which is being intensified by human action. Among the variants of MCs, MC-LR stands out for its distribution and toxicity. MCs are potent inhibitors of protein phosphatases 1 and 2 A, which causes disruption of the cytoskeleton and consequent cell death. They can also alter the antioxidant system and induce oxidative stress in various organs of many species. There is, however, a lack of information about the effects of MCs on the antioxidant system and oxidative damage in Brazilian fishes. This study evaluated the effect of microcystin-LR on the antioxidant system in liver and gills of the Brazilian fish Brycon amazonicus, after 48 h of i.p injection of 100 μg MC-LR.kg^-1 body mass. The liver exhibited increases in the activity of GST (74%) and GPx (217%), and a 47% decrease in SOD activity, with no changes in CAT values. In the gills of fish exposed to MC-LR, CAT and GPx activities did not show significant changes, while SOD and GST activity decreased by 66% and 37%, respectively. The GSH content did not change significantly in the liver, however, a decrease of 43% was observed in the gills. Oxidative damage measured by protein oxidation (PC) and lipoperoxidation (LPO) showed significant effects in both tissues. In hepatic tissue, there was no change in PC levels but LPO increased by 116%. Conversely, in the gills LPO levels did not change but PC increased by 317%. In conclusion, these data show that MC-LR induces oxidative damage in both tissues but in different ways, with being liver most sensitive to LPO and gills to PC. This also suggests that the gills are most sensitive to oxidative stress than liver, due to the inhibition of its antioxidant responses following MC-LR exposure.

Subchronic toxicity of Nile tilapia with different exposure routes to Microcystis aeruginosa: Histopathology, liver functions, and oxidative stress biomarkers

BACKGROUND

Toxic cyanobacterial blooms (Microcystis aeruginosa contains microcystins [MCs]) have been reported to induce clinicopathological alterations as well as different oxidative stress in aquatic biota.

AIM

Three-week subchronic exposure experiment was carried out on Nile tilapia, to determine their effects on fish behavior, tissues, liver functions, antioxidant enzymes, and lipid peroxidation.

MATERIALS AND METHODS

Fish were exposed to four main treatments; orally fed diet plus toxic cells of M. aeruginosa (containing 3500 µg/g MC-LR), immersion in 500 µg MC-LR/L, intraperitoneal injection of M. aeruginosa MC-LR with a dose of 0.1 ml of extracted toxin at a dose of 200 μg/kg bwt, and the fourth one served as a control group, then the fish were sacrificed at the end of 3^rd week of exposure.

RESULTS

The results revealed no recorded mortality with obvious behavioral changes and an enlarged liver with the congested gall bladder. Histopathology demonstrated fragmentation, hyalinization, and necrosis of the subcutaneous musculature marked fatty degeneration, and vacuolation of hepatopancreatic cells with adhesion of the secondary gill lamellae associated with severe leukocytic infiltration. Furthermore, liver functions enzymes (aspartate aminotransferase and alanine aminotransferase, and the activities of glutathione peroxidase, glutathione reductase, lipid peroxidase, and catalase enzymes) were significantly increased in all treatments starting from the 2^nd week as compared to the control levels.

CONCLUSION

In this context, the study addresses the possible toxicological impacts of toxic M. aeruginosa contain MC-LR to Nile tilapia, and the results investigated that MC-LR is toxic to Nile tilapia in different routes of exposure as well as different doses.

Modulatory role of L-carnitine against microcystin-LR-induced immunotoxicity and oxidative stress in common carp

Microcystin-LR (MCLR), one of the most popular microcystins (MCs) found in many field water bodies around the world, poses great health risks to animals and humans. In the present study, healthy common carp (initial weight 24.8 ± 2.3 g) were randomly assigned to five groups. Group I was fed on normal diet as control. Group II was maintained on normal diet and received MCLR intraperitoneal injection (150 μg kg^-1 BW). Common carp in groups III, IV, and V were daily pretreated with L-carnitine (LC) at doses of 0.5, 1.0, and 2.0 g kg^-1 of the diet for 4 weeks prior to MCLR intraperitoneal injection. The results showed that MCLR alone led to a significant downregulation in immune response, including serum complement C3, lysozyme, and bactericidal activity. However, oxidative stress response: catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GPx), and lipid peroxidation (LPO) levels were significantly increased. Similarly, gene expressions of inflammatory IL-1β, TNF-α, IFN I, and heat shock proteins (HSP70 and HSP90) were also upregulated after challenged with MCLR. However, LC pretreated group caused a significant elevation in immune response (C3, lysozyme, and bactericidal activity) and gene expressions of inflammatory IL-1β, TNF-α, IFN I, and heat shock proteins (HSP70 and HSP90) after MCLR stress. Antioxidant activities (CAT, SOD, GSH, GPx, and LPO) were returned to background levels at 96 h after MCLR challenge. Strikingly, LC supplementation at 2.0 g kg^-1 has been considered the optimum for common carp since it exhibited enhancement of immune response and antioxidant activity over the level 0.5 and 1.0 g kg^-1, and even better than that of control level. It was concluded that LC as a functional feed additive significantly inhibited the progression of MCLR-induced immunotoxicity and oxidative stress in common carp.

Vitamin E pretreatment prevents histopathological effects in tilapia (Oreochromis niloticus) acutely exposed to cylindrospermopsin

Cylindrospermopsin (CYN) is a cyanotoxin frequently involved in blooms with a predominantly extracellular availability, which makes it easily taken up by a variety of aquatic organisms. CYN is a potent protein and glutathione synthesis inhibitor, and also induces genotoxicity, oxidative stress and several histopathological lesions. The present study investigates the protective role of a vitamin E pretreatment (700 mg vit E/kg fish bw/day, for 7 days) on the histopathological alterations induced in different organs of tilapia (Oreochromis niloticus) acutely exposed to a single oral dose of 400 µg pure CYN/kg bw fish. The major histological changes observed were degenerative glucogenic process and loss of the hepatic structure in the liver, glomerulopathy and tubular tumefaction in the kidney, myofibrolysis and edema in the heart, catarrhal enteritis and necrosis in the gastrointestinal tract, hyperemic processes in the gill lamellae, and high basophilia, degeneration and tumefaction of granular neurons in the brain. Vitamin E pretreatment was effective in preventing or ameliorating the abovementioned alterations induced by CYN. In addition, a morphometric study indicated that the average nuclear diameter of hepatocytes, and cross-sections of proximal and distal convoluted tubules, together with the cardiac fiber and capillaries diameters represent a useful tool to evaluate the damage induced by CYN. This is the first study reporting vitamin E prevention of histopathological damage in tissues (liver, kidney, heart, gastrointestinal tract, gills and brain) of fish intoxicated with CYN. Therefore, vitamin E can be considered a useful chemoprotectant in the treatment of histopathological changes induced in CYN-intoxicated fish. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1469-1485, 2016.

In vivo effects of Aphanizomenon flos-aquae DC-1 aphantoxins on gas exchange and ion equilibrium in the zebrafish gill

Aphantoxins, neurotoxins or paralytic shellfish poisons (PSPs) generated by Aphanizomenon flos-aquae, are a threat to environmental safety and human health in eutrophic waters worldwide. The molecular mechanisms of neurotoxin function have been studied; however, the effects of these neurotoxins on oxidative stress, ion transport, gas exchange, and branchial ultrastructure in fish gills are not fully understood. Aphantoxins extracted from A. flos-aquae DC-1 were detected by high-performance liquid chromatography. The major ingredients were gonyautoxins 1 and 5 and neosaxitoxin, which comprised 34.04%, 21.28%, and 12.77% of the total, respectively. Zebrafish (Danio rerio) were administered A. flos-aquae DC-1 aphantoxins at 5.3 or 7.61μg saxitoxin equivalents (eq)/kg (low and high doses, respectively) by intraperitoneal injection. The activities of Na(+)-K(+)-ATPase (NKA), carbonic anhydrase (CA), and lactate dehydrogenase (LDH), ultrastructural alterations in chloride and epithelial cells, and reactive oxygen species (ROS) and total antioxidative capacity (T-AOC) were investigated in the gills during the first 24h after exposure. Aphantoxins significantly increased the level of ROS and decreased the T-AOC in zebrafish gills from 3 to 12h post-exposure, suggesting an induction of oxidative stress and inhibition of antioxidant capacity. Reduced activities of NKA and CA demonstrated abnormal ion transport and gas exchange in the gills of aphantoxin-treated fish. Toxin administration also resulted in increased LDH activity and ultrastructural alterations in chloride and epithelial cells, suggesting a disruption of function and structure in zebrafish gills. The observed abnormalities in zebrafish gills occurred in a time- and dose-dependent manner. These findings demonstrate that aphantoxins or PSPs may inhibit ion transport and gas exchange, increase LDH activity, and result in ultrastructural damage to the gills through elevations in oxidative stress and reduced antioxidant capacity. These effects of aphantoxins in the gills of zebrafish suggest an induction of respiratory toxicity. The parameters investigated in this study may be also considered as biomarkers for studying aphantoxin/PSP exposure and cyanobacterial blooms in nature.

Activity and Transcriptional Responses of Hepatopancreatic Biotransformation and Antioxidant Enzymes in the Oriental River Prawn Macrobrachium nipponense Exposed to Microcystin-LR

Microcystins (MCs) are a major group of cyanotoxins with side effects in many organisms; thus, compounds in this group are recognized as potent stressors and health hazards in aquatic ecosystems. In order to assess the toxicity of MCs and detoxification mechanism of freshwater shrimp Macrobrachium nipponense, the full-length cDNAs of the glutathione S-transferase (gst) and catalase (cat) genes were isolated from the hepatopancreas. The transcription level and activity changes in the biotransformation enzyme (glutathione S-transferase (GST)) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)) in the hepatopancreas of M. nipponense exposed to MC-LR (0.2, 1, 5, and 25 μg/L) for 12, 24, 72 and 96 h were analyzed. The results showed that the isolated full-length cDNAs of cat and gst genes from M. nipponense displayed a high similarity to other crustaceans, and their mRNAs were mainly expressed in the hepatopancreas. MC-LR caused significant increase of GST activity following 48-96 h (p < 0.05) and an increase in SOD activity especially in 24- and 48-h exposures. CAT activity was activated when exposed to MC-LR in 12-, 24- and 48-h exposures and then it was inhibited at 96-h exposure. There was no significant effect on GPx activity after the 12- and 24-h exposures, whereas it was significantly stimulated after the 72- and 96-h exposures (p < 0.05). The transcription was altered similarly to enzyme activity, but the transcriptional response was generally more immediate and had greater amplitude than enzymatic response, particularly for GST. All of the results suggested that MC-LR can induce antioxidative modulation variations in M. nipponense hepatopancreas in order to eliminate oxidative damage.

Oxidative effects and toxin bioaccumulation after dietary microcystin intoxication in the hepatopancreas of the crab Neohelice (Chasmagnathus) granulata

We studied the accumulation and depuration of microcystin-LR (MCLR) in the hepatopancreas of the crab Neohelice granulata fed twice weekly with either non toxic or MCLR-producing Microcystis aeruginosa (strain NPDC1 or NPJB, respectively) during seven weeks. We also analyzed MCLR effects on the oxidative stress- and detoxification-related variables, superoxide dismutase and glutathione-S-transferase activities, and the levels of reduced glutathione and lipid peroxidation (as thiobarbituric acid reactive substances, TBARS). Hepatopancreas MCLR content slightly increased during the first three weeks, up to 8.81±1.84ngg(-1) wet tissue mass (WTM) and then started to decrease to a minimum of 1.57±0.74ngg(-1) WTM at the seventh week (p<0.05 with respect to that in the first week). TBARS levels were about 55% higher in treated than in control N. granulata (p<0.001 and p<0.05) during the first three weeks of the experimental period. GSH content became 50% lower than in control individuals (p<0.01) during weeks 6 and 7. SOD activity was increased by about 2-fold (p<0.05 or p<0.001) from week 3 to 7 in treated crabs with respect to control ones, while GST activity was about 70% higher in treated than in control crabs from week 4 to week 7 (p<0.05). Our data suggest that in the hepatopancreas of N. granulata MCLR accumulation and oxidative damage are limited and reversed by detoxification-excretion and antioxidant mechanisms. The activation of these defensive mechanisms becomes evident at 3-4 weeks after the start of the intoxication.

Biomarkers involved in energy metabolism and oxidative stress response in the liver of Goodea gracilis Hubbs and Turner, 1939 exposed to the microcystin-producing Microcystis aeruginosa LB85 strain

Goodea gracilis is an endemic fish that only habitats in some water bodies of Central Mexico that are contaminated with cyanobacteria-producing microcystins (MC); however, a lack of information on this topic prevails. With the aim to generate the first approximation about the physiological changes elicited by cyanobacterium that produce MC congeners in this fish species, specimens born in the laboratory was exposed for 96 h to cell densities of 572.5, 1145, 2290, 4580, and 9160 × 10(6) cells of Microcystis aeruginosa strain LB85/L, and a set of novel endpoint related to hepatic gluconeogenesis (ADH/LDH) and pro-oxidant forces O2., H2 O2 ) in addition to biomarkers of oxidative damage and antioxidant response was evaluated in the liver. Results suggest that high inhibition of protein serine/threonine phosphatase (PP) may trigger many metabolic processes, such as those related to hepatic gluconeogenesis (ADH/LDH) and pro-oxidant O2⋅, H2 O2 , TBARS, ROOH, RC=O) as well as antioxidant (SOD, CAT, GPx) response to oxidative stress. Particularly, we observed that inhibition of LDH and PP, and H2 O2 increase and TBARS production were the key damages induced by high densities of M. aeruginosa. However, changes between aerobic and anaerobic metabolism related with ROS metabolism and ADH/LDH balance are apparently an acclimation of this fish species to exposure to cyanobacteria or their MCs. Fish species living in environments potentially contaminated with cyanobacteria or their MCs possess mechanisms of acclimation that allow them to offset the damage induced, even in the case of fish that have never been exposed to MCs.

Transcriptional responses of glutathione transferase genes in Ruditapes philippinarum exposed to microcystin-LR

Glutathione Transferases (GSTs) are phase II detoxification enzymes known to be involved in the molecular response against microcystins (MCs) induced toxicity. However, the individual role of the several GST isoforms in the MC detoxification process is still unknown. In this study, the time-dependent changes on gene expression of several GST isoforms (pi, mu, sigma 1, sigma 2) in parallel with enzymatic activity of total GST were investigated in gills and hepatopancreas of the bivalve Ruditapes philippinarum exposed to pure MC-LR (10 and 100 µg/L). No significant changes in GST enzyme activities were found on both organs. In contrast, MC-LR affected the transcriptional activities of these detoxification enzymes both in gills and hepatopancreas. GST transcriptional changes in gills promoted by MC-LR were characterized by an early (12 h) induction of mu and sigma 1 transcripts. On the other hand, the GST transcriptional changes in hepatopancreas were characterized by a later induction (48 h) of mu transcript, but also by an early inhibition (6 h) of the four transcripts. The different transcription patterns obtained for the tested GST isoforms in this study highlight the potential divergent physiological roles played by these isoenzymes during the detoxification of MC-LR.

Hepatic positive and negative antioxidant responses in zebrafish after intraperitoneal administration of toxic microcystin-LR

Microcystin-LR (MC-LR) is the most toxic and common among microcystins. In order to understand the possible molecular mechanisms of hepatic antioxidation and detoxification, the activities and transcriptional levels of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferases (GST), and glutathione (GSH) contents as well as histopathological changes were studied in the liver of female zebrafish injected intraperitoneally (i.p.) at doses of 50 and 200 μg MC-LR kg(-1) body weight (BW) respectively. In the low dose group (50 μg MC-LR kg(-1)), zebrafish displayed a little unease at the initial 1h post-injection (hpi), slight hepatic injury and quick recovery, and enhanced enzymatic activities and up-regulated gene expression of antioxidant enzymes. In contrast, high dose of MC-LR (200 μg MC-LR kg(-1)) resulted in uneasiness and frantic swimming, severe hepatic injury, and suppressed enzymatic activities and down-regulated gene expression of antioxidant enzymes. GSH depletion in both dose groups may be explained by enhanced antioxidant reactions and higher rates of MC conjugation, suggesting the crucial roles of GSH in both cellular antioxidant protection and MC-LR detoxification. This study demonstrated that administration of MC-LR caused a positive response in the low dose group but a negative response in the high dose group. Hepatic positive/negative responses in the low/high dose group might result from an increased/decreased synthesis of antioxidant enzymes at the molecular level, respectively. These results illustrated that antioxidant status played an important role in zebrafish protection against MC-LR-caused oxidative stress through regulating antioxidant enzyme gene expression and activities.

Exposure of Lycopersicon esculentum to microcystin-LR: effects in the leaf proteome and toxin translocation from water to leaves and fruits

Natural toxins such as those produced by freshwater cyanobacteria have been regarded as an emergent environmental threat. However, the impact of these water contaminants in agriculture is not yet fully understood. The aim of this work was to investigate microcystin-LR (MC-LR) toxicity in Lycopersicon esculentum and the toxin accumulation in this horticultural crop. Adult plants (2 month-old) grown in a greenhouse environment were exposed for 2 weeks to either pure MC-LR (100 μg/L) or Microcystis aeruginosa crude extracts containing 100 μg/L MC-LR. Chlorophyll fluorescence was measured, leaf proteome investigated with two-dimensional gel electrophoresis and Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF)/TOF, and toxin bioaccumulation assessed by liquid chromatography-mass spectrometry (LC-MS)/MS. Variations in several protein markers (ATP synthase subunits, Cytochrome b6-f complex iron-sulfur, oxygen-evolving enhancer proteins) highlight the decrease of the capacity of plants to synthesize ATP and to perform photosynthesis, whereas variations in other proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit and ribose-5-phosphate isomerase) suggest an increase of carbon fixation and decrease of carbohydrate metabolism reactions in plants exposed to pure MC-LR and cyanobacterial extracts, respectively. MC-LR was found in roots (1635.21 μg/kg fw), green tomatoes (5.15–5.41 μg/kg fw), mature tomatoes (10.52–10.83 μg/kg fw), and leaves (12,298.18 μg/kg fw). The results raise concerns relative to food safety and point to the necessity of monitoring the bioaccumulation of water toxins in agricultural systems affected by cyanotoxin contamination.

Exposure to the cyanotoxin microcystin arising from interspecific differences in feeding habits among fish and shellfish in the James River Estuary, Virginia

The cyanotoxin, microcystin (MC), is known to accumulate in the tissues of diverse aquatic biota although factors influencing exposure, such as feeding habits and seasonal patterns in toxin production, are poorly known. We analyzed seasonal variation in the MC content of primary and secondary consumers, and used dietary analysis (gut contents and stable isotopes) to improve understanding of cyanotoxin transport in food webs. Periods of elevated toxin concentration were associated with peaks in the abundance of genes specific to Microcystis and MC toxin production (mcyD). Peak toxin levels in consumer tissues coincided with peak MC concentrations in seston. However, toxins in tissues persisted in overwintering populations suggesting that potential health impacts may not be limited to bloom periods. Interspecific differences in tissue MC concentrations were related to feeding habits and organic matter sources as pelagic fishes ingested a greater proportion of algae in their diet, which resulted in greater MC content in liver and muscle tissues. Sediments contained a greater proportion of allochthonous (terrestrial) organic matter and lower concentrations of MC, resulting in lower toxin concentrations among benthic detritivores. Among shellfish, the benthic suspension feeder Rangia cuneata (wedge clam) showed seasonal avoidance of toxin ingestion due to low feeding rates during periods of elevated MC. Among predators, adult Blue Catfish had low MC concentrations, whereas Blue Crabs exhibited high levels of MC in both muscle and viscera.

Acute exposure to pure cylindrospermopsin results in oxidative stress and pathological alterations in tilapia (Oreochromis niloticus)

Cylindrospermopsin (CYN) is increasingly recognized as a potential threat to drinking water safety, due to its ubiquity. This cyanotoxin has been found to cause toxic effects in mammals, and although fish could be in contact with this toxin, acute toxicity studies on fish are nonexistent. This is the first study showing that single doses of CYN pure standard (200 or 400 μg CYN/kg fish bw) by oral route (gavage) generate histopathological effects in fish (Tilapia-Oreochromis niloticus) exposed to the toxin under laboratory condition. Among the morphological changes, disorganized parenchymal architecture in the liver, dilated Bowman's space in the kidney, fibrolysis in the heart, necrotic enteritis in the intestines, and hemorrhages in the gills, were observed. Moreover, some oxidative stress biomarkers in the liver and kidney of tilapias were altered. Thus, CYN exposure induced increased protein oxidation products in both organs, NADPH oxidase activity was significantly increased with the kidney being the most affected organ, and decreased GSH contents were also detected in both organs, at the higher dose assayed.

Effects of depuration on oxidative biomarkers in tilapia (Oreochromis niloticus) after subchronic exposure to cyanobacterium producing cylindrospermopsin

Cylindrospermopsin (CYN) is a cytotoxic polyketide-derived alkaloid produced by several freshwater cyanobacterial species. It is now considered the second most studied cyanotoxin worldwide. Among the toxic mechanisms suggested for CYN pathogenicity are inhibition of protein and glutathione synthesis, genotoxicity by DNA fragmentation, and oxidative stress. The study of depuration of cyanobacterial toxins by aquatic organisms, particularly by fish, is important for fish economy and public health, but in the case of CYN is practically nonexistent. In this work, we investigated the efficiency of two distinct depuration periods, 3 or 7d, in a clean environment, as a mean of restoring the levels of several oxidative stress biomarkers in tilapia (Oreochromis niloticus) subchronically exposed to CYN by immersion in an Aphanizomenon ovalisporum culture (by adding 10 μg CYN/L every two days during 14 d). Lipid peroxidation (LPO) and DNA oxidation returned to normal values after 7d of depuration, whereas the time needed for restoring of the oxidatively damaged proteins was longer. Superoxide dismutase (SOD) and gamma-glutamyl-cysteine-synthetase (γ-GCS) activities recovered after just 3d of depuration, while catalase (CAT) activity needed up to 7d to return to control values. Ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) returned to control levels after 7d of depuration in both organs. These results validate the depuration process as a very effective practice for detoxification in fish contaminated with these toxins.

Lipid peroxidation and antioxidant responses in zebrafish brain induced by Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae is a cyanobacterium that is frequently encountered in eutrophic waters worldwide. It is source of neurotoxins known as aphantoxins or paralytic shellfish poisons (PSPs), which present a major threat to the environment and human health. The molecular mechanism of PSP action is known, however the in vivo effects of this neurotoxin on oxidative stress, lipid peroxidation and the antioxidant defense responses in zebrafish brain remain to be understood. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed using high performance liquid chromatography. The major components of the toxins were gonyautoxins 1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and neosaxitoxin (neoSTX, 12.77%). Zebrafish (Danio rerio) were injected intraperitoneally with 7.73 μg/kg (low dose) and 11.13 μg/kg (high dose) of A. flos-aquae DC-1 aphantoxins. Oxidative stress, lipid peroxidation and antioxidant defense responses in the zebrafish brain were investigated at various timepoints at 1-24h post-exposure. Aphantoxin exposure was associated with significantly increased (>1-2 times) reactive oxygen species (ROS) and malondialdehyde (MDA) in zebrafish brain compared with the controls at 1-12h postexposure, suggestive of oxidative stress and lipid peroxidation. In contrast, reduced glutathione (GSH) levels in the zebrafish brain exposed to high or low doses of aphantoxins decreased by 44.88% and 41.33%, respectively, after 1-12h compared with the controls, suggesting that GSH participated in detoxification to ROS and MDA. Further analysis showed a significant increase in the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) compared with the controls, suggesting elimination of oxidative stress by the antioxidant response in zebrafish brain. All these changes were dose and time dependent. These results suggested that aphantoxins or PSPs increased ROS and MDA and decreased GSH in zebrafish brain, and these changes induced oxidative stress. The increased activity of SOD, CAT and GPx demonstrated that these antioxidant enzymes could play important roles in eliminating excess ROS and MDA. These results also suggest that MDA, ROS, GSH and these three antioxidant enzymes in the brain of zebrafish may act as bioindicators for investigating A. flos-aquae DC-1 aphantoxins or PSPs and algal blooms in nature.

Toxicological evaluation of microcystins in aquatic fish species: current knowledge and future directions

Microcystins (MCs) are algal toxins produced intracellularly within the algal cells, and are subsequently released into the aquatic systems. An increase in the frequency and intensity of occurrence of harmful algal blooms has directed the global attention towards the presence of MCs in aquatic systems. The effects of MCs on fish have been verified in a number of studies including histological, biochemical and behavioral effects. The toxicological effects of MCs on different organs of fish are related to the exposure route (intraperitoneal injection, feeding or immersion), the mode of uptake (passive or active transport) as well as biotransformation and bioaccumulation capabilities by different organs. This paper reviews the rapidly expanding literature on the toxicological evaluation of MCs in fish from both field studies and controlled laboratory experimental investigations, integrates the current knowledge available about the mechanisms involved in MC-induced effects on fish, and points out future research directions from a cross-disciplinary perspective. In addition, the need to carry out systematic fish toxicity studies to account for possible interactions between MCs and other environmental pollutants in aquatic systems is discussed.

Regulation of nodularin-induced apoptosis by epigallocatechin-3-gallate on fish lymphocytes in vitro

Nodularin is one of the most conspicuous and widespread pollutants that elicit water ecological hazards to fish, causing serious damage on the immune system and physiological functions. Nodularin can cause oxidative stress-induced apoptosis on fish lymphocytes. The regulatory effects of epigallocatechin-3-gallate (EGCG) at 10, 100, and 1000 μg/L levels on the antioxidant defense system and apoptosis of Carassius auratus lymphocytes exposed to a high dose of nodularin (100 μg/L) were quantified in vitro. EGCG reduced nodularin-induced oxidative damage on fish immune cells. This compound significantly increased the activities of superoxide dismutase and catalase and the level of glutathione but decreased the levels of intracellular reactive oxygen species and malondialdehyde. Flow cytometry results showed that the percentages of apoptotic cells after treatment with 10, 100, and 1000 μg/L EGCG for 12 h reached 27.9%, 19.1%, and 13.7%, respectively. By contrast, the nodularin alone-induced group showed a high percentage of apoptosis (44.2%). Western blot analysis showed the increased expression of bcl-2 and the decreased expression of bax and caspase-3 in EGCG-treated fish lymphocytes. EGCG also inhibited the potential collapse of the mitochondrial membrane. Overall, EGCG can inhibit nodularin-induced apoptosis and protect the normal immunity of fish by regulating bax/bcl-2 and blocking the downstream of mitochondrial apoptosis pathway with increased intracellular antioxidant enzyme activity.