Detoxification and oxidative stress responses along with microcystins accumulation in Japanese quail exposed to cyanobacterial biomass

Prolonged exposure to environmental levels of microcystin-LR triggers ferroptosis in brain via the activation of Erk/MAPK signaling pathway

While existing research has illuminated the environmental dangers and neurotoxic effects of MC-LR exposure, the molecular underpinnings of brain damage from environmentally-relevant MC-LR exposure remain elusive. Employing a comprehensive approach involving RNA sequencing, histopathological examination, and biochemical analyses, we discovered genes differentially expressed and enriched in the ferroptosis pathway. This finding was associated with mitochondrial structural impairment and downregulation of Gpx4 and Slc7a11 in mice brains subjected to low-dose MC-LR over 180 days. Mirroring these findings, we noted reduced cell viability and GSH/GSSH ratio, along with an increased ROS level, in HT-22, BV-2, and bEnd.3 cells following MC-LR exposure. Intriguingly, MC-LR also amplified phospho-Erk levels in both in vivo and in vitro settings, and the effects were mitigated by treatment with PD98059, an Erk inhibitor. Taken together, our findings implicate the activation of the Erk/MAPK signaling pathway in MC-LR-induced ferroptosis, shedding valuable light on the neurotoxic mechanisms of MC-LR. These insights could guide future strategies to prevent MC-induced neurodegenerative diseases.

Oxidative damage varies in response to bacterial, fungal and viral antigen challenges in bats

The immune system plays an important role in defending against pathogens and regulating physiological homeostasis, but the strength of the immune responses depends on the type of pathogen. The immune system of bats shows a high variability in responsiveness towards various pathogens; they can safely harbor certain pathogens that are highly lethal to other mammals. Oxidative stress may act as a pathophysiological cellular mechanism mediating the immunological function of bats because of its potentially detrimental effects on physiological homeostasis, fertility and longevity. By experimentally exposing greater mouse-eared bats (Myotis myotis) to three antigens, it was previously shown that animals reacted immunologically most strongly to bacterial and viral antigens, but not to fungal ones. As a follow up, in this study we observed that both bacterial and fungal antigens induced a significant increase of plasma oxidative damage, whereas viral antigens did not cause any increase of plasma oxidative damage at all albeit the mild immune response. Thus, experimental bats were able to avoid oxidative stress only in the face of a viral antigen, possibly by dampening inflammatory signalling. Bats may be able to handle viral infections and live well beyond expectations by reducing the detrimental effects of molecular oxidation.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

State-of-the-art review on the ecotoxicology, health hazards, and economic loss of the impact of microcystins and their ultrastructural cellular changes

Cyanobacteria are ubiquitously globally present in both freshwater and marine environments. Ample reports have been documented by researchers worldwide for pros and cons of cyanobacterial toxins. The implications of cyanobacterial toxin on health have received much attention in recent decades. Microcystins (MCs) represent the unique class of toxic metabolites produced by cyanobacteria. Although the beneficial aspects of cyanobacterial are numerous, the deleterious effect of MCs overlooked. Several studies on MCs evidently reported that MCs exhibit a plethora of harmful effect on animals, plants, and cell lines. Accordingly, numerous histopathological studies have also found that MCs cause detrimental effects to cells by damaging cellular organelles, including nuclear envelope, Golgi apparatus, endoplasmic reticulum, mitochondria, plastids, flagellum, pilus membrane structures and integrity, vesicle structures, and autolysosomes and autophagosomes. Such ultrastructural cellular damages holistically influence the morphological, biochemical, physiological, and genetic status of the host. Indeed, MCs have also been found to cause the deleterious effect to different animals and plants. Such deleterious effects of MCs have greater impact on agriculture, public health which in turn influences ecotoxicology and economic consequences. The impairments correspond to oxidative stress, organ failure, carcinogenesis, aquaculture loss, with an emphasis for blooms and respective bioaccumulation prospects. The preservation of mortality among life forms is addressed in a critical cellular perspective for multitude benefits. The comprehensive cellular assessment could provide opportunity to develop strategy for therapeutic implications.

Review of harmful algal bloom effects on birds with implications for avian wildlife in the Chesapeake Bay region

The Chesapeake Bay, along the mid-Atlantic coast of North America, is the largest estuary in the United States and provides critical habitat for wildlife. In contrast to point and non-point source release of pesticides, metals, and industrial, personal care and household use chemicals on biota in this watershed, there has only been scant attention to potential exposure and effects of algal toxins on wildlife in the Chesapeake Bay region. As background, we first review the scientific literature on algal toxins and harmful algal bloom (HAB) events in various regions of the world that principally affected birds, and to a lesser degree other wildlife. To examine the situation for the Chesapeake, we compiled information from government reports and databases summarizing wildlife mortality events for 2000 through 2020 that were associated with potentially toxic algae and HAB events. Summary findings indicate that there have been few wildlife mortality incidents definitively linked to HABs, other mortality events that were suspected to be related to HABs, and more instances in which HABs may have indirectly contributed to or occurred coincident with wildlife mortality. The dominant toxins found in the Chesapeake Bay drainage that could potentially affect wildlife are microcystins, with concentrations in water approaching or exceeding human-based thresholds for ceasing recreational use and drinking water at a number of locations. As an increasing trend in HAB events in the U.S. and in the Chesapeake Bay have been reported, additional information on HAB toxin exposure routes, comparative sensitivity among species, consequences of sublethal exposure, and better diagnostic and risk criteria would greatly assist in predicting algal toxin hazard and risks to wildlife.

A review and assessment of cyanobacterial toxins as cardiovascular health hazards

Eutrophicated waters frequently support bloom-forming cyanobacteria, many of which produce potent cyanobacterial toxins (cyanotoxins). Cyanotoxins can cause adverse health effects in a wide range of organisms where the toxins may target the liver, other internal organs, mucous surfaces and the skin and nervous system. This review surveyed more than 100 studies concerning the cardiovascular toxicity of cyanotoxins and related topics. Over 60 studies have described various negative effects on the cardiovascular system by seven major types of cyanotoxins, i.e. the microcystin (MC), nodularin (NOD), cylindrospermopsin (CYN), anatoxin (ATX), guanitoxin (GNTX), saxitoxin (STX) and lyngbyatoxin (LTX) groups. Much of the research was done on rodents and fish using high, acutely toxin concentrations and unnatural exposure routes (such as intraperitoneal injection), and it is thus concluded that the emphasis in future studies should be on oral, chronic exposure of mammalian species at environmentally relevant concentrations. It is also suggested that future in vivo studies are conducted in parallel with studies on cells and tissues. In the light of the presented evidence, it is likely that cyanotoxins do not constitute a major risk to cardiovascular health under ordinary conditions met in everyday life. The risk of illnesses in other organs, in particular the liver, is higher under the same exposure conditions. However, adverse cardiovascular effects can be expected due to indirect effects arising from damage in other organs. In addition to risks related to extraordinary concentrations of the cyanotoxins and atypical exposure routes, chronic exposure together with co-existing diseases could make some of the cyanotoxins more dangerous to cardiovascular health.

Challenges of using blooms of Microcystis spp. in animal feeds: A comprehensive review of nutritional, toxicological and microbial health evaluation

Microcystis spp., are Gram-negative, oxygenic, photosynthetic prokaryotes which use solar energy to convert carbon dioxide (CO₂) and minerals into organic compounds and biomass. Eutrophication, rising CO₂ concentrations and global warming are increasing Microcystis blooms globally. Due to its high availability and protein content, Microcystis biomass has been suggested as a protein source for animal feeds. This would reduce dependency on soybean and other agricultural crops and could make use of "waste" biomass when Microcystis scums and blooms are harvested. Besides proteins, Microcystis contain further nutrients including lipids, carbohydrates, vitamins and minerals. However, Microcystis produce cyanobacterial toxins, including microcystins (MCs) and other bioactive metabolites, which present health hazards. In this review, challenges of using Microcystis blooms in feeds are identified. First, nutritional and toxicological (nutri-toxicogical) data, including toxicity of Microcystis to mollusks, crustaceans, fish, amphibians, mammals and birds, is reviewed. Inclusion of Microcystis in diets caused greater mortality, lesser growth, cachexia, histopathological changes and oxidative stress in liver, kidney, gill, intestine and spleen of several fish species. Estimated daily intake (EDI) of MCs in muscle of fish fed Microcystis might exceed the provisional tolerable daily intake (TDI) for humans, 0.04 μg/kg body mass (bm)/day, as established by the World Health Organization (WHO), and is thus not safe. Muscle of fish fed M. aeruginosa is of low nutritional value and exhibits poor palatability/taste. Microcystis also causes hepatotoxicity, reproductive toxicity, cardiotoxicity, neurotoxicity and immunotoxicity to mollusks, crustaceans, amphibians, mammals and birds. Microbial pathogens can also occur in blooms of Microcystis. Thus, cyanotoxins/xenobiotics/pathogens in Microcystis biomass should be removed/degraded/inactivated sufficiently to assure safety for use of the biomass as a primary/main/supplemental ingredient in animal feed. As an ameliorative measure, antidotes/detoxicants can be used to avoid/reduce the toxic effects. Before using Microcystis in feed ingredients/supplements, further screening for health protection and cost control is required.

BMAA and MCLR Interact to Modulate Behavior and Exacerbate Molecular Changes Related to Neurodegeneration in Larval Zebrafish

Exposure to toxins produced by cyanobacteria (ie, cyanotoxins) is an emerging health concern due to their increasing prevalence and previous associations with neurodegenerative diseases including amyotrophic lateral sclerosis. The objective of this study was to evaluate the neurotoxic effects of a mixture of two co-occurring cyanotoxins, β-methylamino-l-alanine (BMAA) and microcystin leucine and arginine (MCLR), using the larval zebrafish model. We combined high-throughput behavior-based toxicity assays with discovery proteomic techniques to identify behavioral and molecular changes following 6 days of exposure. Although neither toxin caused mortality, morphological defects, nor altered general locomotor behavior in zebrafish larvae, both toxins increased acoustic startle sensitivity in a dose-dependent manner by at least 40% (p < .0001). Furthermore, startle sensitivity was enhanced by an additional 40% in larvae exposed to the BMAA/MCLR mixture relative to those exposed to the individual toxins. Supporting these behavioral results, our proteomic analysis revealed a 4-fold increase in the number of differentially expressed proteins in the mixture-exposed group. Additionally, prediction analysis reveals activation and/or inhibition of 8 enriched canonical pathways (enrichment p-value < .01; z-score≥|2|), including ILK, Rho Family GTPase, RhoGDI, and calcium signaling pathways, which have been implicated in neurodegeneration. We also found that expression of TDP-43, of which cytoplasmic aggregates are a hallmark of amyotrophic lateral sclerosis pathology, was significantly upregulated by 5.7-fold following BMAA/MCLR mixture exposure. Together, our results emphasize the importance of including mixtures of cyanotoxins when investigating the link between environmental cyanotoxins and neurodegeneration as we reveal that BMAA and MCLR interact in vivo to enhance neurotoxicity.

Ecotoxicological profiling of selected cyanobacterial strains using multi-endpoint effect-directed analysis

The main goal of this study was to perform an ecotoxicological profiling of terrestrial and aquatic cyanobacterial strains found in different soils or in toxic cyanobacterial blooms in Vojvodina region, Serbia, using the effect-directed analysis (EDA) approach. The applied procedure was based on a series of in vitro or small-scale bioassays covering multiple endpoints in combination with advanced chemical analytical protocols. Non-selective and non-target preparation techniques were used for the extraction of a broad range of chemical compounds present in three terrestrial (Anabaena Č2, Anabaena Č5, Nostoc S8) and three aquatic (Nostoc Z1, Phormidium Z2, Oscillatoria K3) strains. Ecotoxicological endpoints addressed included evaluation of the fish cytotoxicity in vitro (acute toxicity), algal growth inhibition (chronic toxicity), and interaction with cellular detoxification mechanisms. All cyanobacterial strains tested in the 1^st tier EDA showed significant effects in terms of chronic toxicity and interaction with cellular detoxification. Three major fractions of different polarities were further tested in the 2^nd tier, using bioassays which showed the strongest response: induction of CYP1A1 biotransformation enzyme and inhibition of zebrafish organic anion (Oatp1d1) and cation (Oct1) uptake transporters. Oscillatoria K3 strain was selected for a more detailed 3^rd tier EDA, and the obtained results revealed that positive sub-fractions possess polar anion and cation compounds that are reactive to both uptake transporters, and compounds responsible for the strongest effects have a pronounced lipophilic character. Apart from lipophilic non-polar compounds that represent typical phase I substrates, sub-fractions that contained polar substances are also shown to significantly induce CYP1A1.

Neurotoxicity induced by microcystins and cylindrospermopsin: A review

Microcystins (MCs) and cylindrospermopsin (CYN) are among the most frequent toxins produced by cyanobacteria. These toxic secondary metabolites are classified as hepatotoxins and cytotoxin, respectively. Furthermore, both may present the ability to induce damage to the nervous system. In this sense, there are many studies manifesting the potential of MCs to cause neurotoxicity both in vitro and in vivo, due to their probable capacity to cross the blood-brain-barrier through organic anion transporting polypeptides. Moreover, the presence of MCs has been detected in brain of several experimental models. Among the neurological effects, histopathological brain changes, deregulation of biochemical parameters in brain (production of oxidative stress and inhibition of protein phosphatases) and behavioral alterations have been described. It is noteworthy that minority variants such as MC-LF and -LW have demonstrated to exert higher neurotoxic effects compared to the most studied congener, MC-LR. By contrast, the available studies concerning CYN-neurotoxic effects are very scarce, mostly showing inflammation and apoptosis in neural murine cell lines, oxidative stress, and alteration of the acetylcholinesterase activity in vivo. However, more studies are required in order to clarify the neurotoxic potential of both toxins, as well as their possible contribution to neurodegenerative diseases.

Occurrence and toxicity of microcystin congeners other than MC-LR and MC-RR: A review

The occurrence of cyanobacterial toxins is being increasingly reported. This is a reason for concern as they can induce toxic effects both in humans and in the environment. Among them, microcystins (MCs) are the best described and most diverse group of cyanobacterial toxins, and MC-LR and MC-RR are the congeners most widely investigated. However, the number of MC variants has also increased in recent years. Some of these minority variants have been shown to have a different toxicokinetic and toxicodynamic profile, but research focused on them is still limited. Moreover, in some water bodies these minority variants can be the predominant toxins. Nonetheless, MC-LR is the only one used for risk evaluation purposes at present. In order to contribute to more realistic risk assessments in the future, the aim of this review was to compile the available information in the scientific literature regarding the occurrence and concentration of minority MCs in water and food samples, and their toxic effects. The data retrieved demonstrate the congener-specific toxicity of MCs, as well as many data gaps in relation to analytical or mechanistic aspects, among others. Therefore, further research is needed to improve the toxicological characterization of these toxins and the exposure scenarios.

Analysis of free and metabolized microcystins in samples following a bird mortality event

In the summer of 2012, over 750 dead and dying birds were observed at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island, Maryland, USA (Chesapeake Bay). Clinical signs suggested avian botulism, but an ongoing dense Microcystis bloom was present in an impoundment on the island. Enzyme-linked immunosorbent assay (ELISA) analysis of a water sample indicated 6000 ng mL^-1 of microcystins (MCs). LC-UV/MS analysis confirmed the presence of MC-LR and a high concentration of an unknown MC congener (m/z 1037.5). The unknown MC was purified and confirmed to be [D-Leu¹]MC-LR using NMR spectroscopy, LC-HRMS and LC-MS², which slowly converted to [D-Leu¹,Glu(OMe)⁶]MC-LR during storage in MeOH. Lyophilized algal material from the bloom was further characterized using LC-HRMS and LC-MS² in combination with chemical derivatizations, and an additional 24 variants were detected, including MCs conjugated to Cys, GSH and γ-GluCys and their corresponding sulfoxides. Mallard (Anas platyrhynchos) livers were tested to confirm MC exposure. Two broad-specificity MC ELISAs and LC-MS² were used to measure free MCs, while 'total' MCs were estimated by both MMPB (3-methoxy-2-methyl-4-phenylbutyric acid) and thiol de-conjugation techniques. Free microcystins in the livers (63-112 ng g^-1) accounted for 33-41% of total microcystins detected by de-conjugation and MMPB techniques. Free [D-Leu¹]MC-LR was quantitated in tissues at 25-67 ng g^-1 (LC-MS²). The levels of microcystin varied based on analytical method used, highlighting the need to develop a comprehensive analysis strategy to elucidate the etiology of bird mortality events when microcystin-producing HABs are present.

Cyanobacterial effects in Lake Ludoš, Serbia - Is preservation of a degraded aquatic ecosystem justified?

Cyanobacteria are present in many aquatic ecosystems in Serbia. Lake Ludoš, a wetland area of international significance and an important habitat for waterbirds, has become the subject of intense research interest because of practically continuous blooming of cyanobacteria. Analyses of water samples indicated a deterioration of ecological condition and water quality, and the presence of toxin-producing cyanobacteria (the most abundant Limnothrix redekei, Pseudanabaena limnetica, Planktothrix agardhii and Microcystis spp.). Furthermore, microcystins were detected in plants and animals from the lake: in macrophyte rhizomes (Phragmites communis, Typha latifolia and Nymphaea elegans), and in the muscle, intestines, kidneys, gonads and gills of fish (Carassius gibelio). Moreover, histopathological deleterious effects (liver, kidney, gills and intestines) and DNA damage (liver and gills) were observed in fish. A potential treatment for the reduction of cyanobacterial populations employing hydrogen peroxide was tested during this study. The treatment was not effective in laboratory tests although further in-lake trials are needed to make final conclusions about the applicability of the method. Based on our observations of the cyanobacterial populations and cyanotoxins in the water, as well as other aquatic organisms and, a survey of historical data on Lake Ludoš, it can be concluded that the lake is continuously in a poor ecological state. Conservation of the lake in order to protect the waterbirds (without urgent control of eutrophication) actually endangers them and the rest of the biota in this wetland habitat, and possibly other ecosystems. Thus, urgent measures for restoration are required, so that the preservation of this Ramsar site would be meaningful.

Cyanotoxins as the "common suspects" for the Dalmatian pelican (Pelecanus crispus) deaths in a Mediterranean reconstructed reservoir

Toxic cyanobacterial blooms have been implicated for their negative consequences on many terrestrial and aquatic organisms. Water birds belong to the most common members of the freshwater food chains and are most likely to be affected by the consumption of toxic cyanobacteria as food. However, the contribution of cyanotoxins in bird mortalities is under-studied. The aim of the study was to investigate the likely role of cyanotoxins in a mass mortality event of the Dalmatian pelican (Pelecanus crispus) in the Karla Reservoir, in Greece. Water, scum, tissues and stomach content of dead birds were examined for the presence of microcystins, cylindrospermopsins and saxitoxins by an enzyme-linked immunosorbent assay. High abundances of potential toxic cyanobacterial species and significant concentrations of cyanotoxins were recorded in the reservoir water. All examined tissues and stomach content of the Dalmatian pelicans contained significant concentrations of microcystins and saxitoxins. Cylindrospermopsin concentrations were detected in all tissues except from the brain. Our results suggest that cyanotoxins are a plausible cause for this bird mass mortality episode in the Karla Reservoir.

A review of neurotoxicity of microcystins

Cyanobacterial blooms-produced microcystins are secondary metabolites which can accumulate in the food chain and contaminate water, thus posing a potential threat to the health of aquatic animals and even humans. Microcystin toxicity affects not only the liver but also the other organs, i.e., the brain. The serious neurotoxicity effects caused by microcystins then lead to various symptoms. This review focuses on the neurotoxicity of microcystins. Microcystins can cross blood-brain barrier with the transport of Oatps/OATPs, causing neurostructural, functional, and behavioral changes. In this review, potential uptake mechanisms and neurotoxicity mechanisms are summarized, including neurotransmissions, neurochannels, signal transduction, oxidative stress, and cytoskeleton disruption. However, further researches are needed for detailed studies on signaling pathways and the downstream pathways of neurotoxicity of microcystins.

Oxidative stress and liver damage in birds exposed to diclofenac and lead

Responses of wildlife to multiple stressors fit in the ecological concept of trade-off. While toxicity of non-steroidal anti-inflammatory drugs and heavy metals for free-ranging birds has been shown in single exposures, the present study aims to evaluate oxidative stress, and liver and kidney damage caused by single and combined effects of diclofenac and lead in the Japanese quail. Forty Japanese quail (Coturnix coturnix japonica) were divided into equal groups of controls, diclofenac, Pb, and Pb+diclofenac exposures. The birds were exposed to the respective chemicals through insertion of lead shots (1.5 g) into the crop on day 0 of the experiment and/or administration of 5 mg/kg of diclofenac intramuscularly in two treatments on days 0 and 5. Groups in liver and kidney tissues of birds were then compared after 10 days using histopathology and biochemistry markers such as glutathione reductase (GR), ferric reducing antioxidant power (FRAP), and lipid peroxidation measured as total thiobarbituric acid reactive species (TBARS). The liver damage score gradient was Pb+diclofenac exposure group > Pb exposure group > diclofenac exposure group and hepatic TBARS values were significantly increased in the group of birds exposed to a combination of diclofenac and lead compared to the healthy control group. The study has shown that, apart from the reported nephrotoxicity of diclofenac, hepatic toxicity should also be considered. Avian clinicians should be cautious when selecting drugs for therapy of wild birds with unknown history of exposure to toxic substances.

Immunoassays and biosensors for the detection of cyanobacterial toxins in water

Algal blooms are a frequent phenomenon in nearly all kinds of fresh water. Global warming and eutrophication by waste water, air pollution and fertilizers seem to lead to an increased frequency of occurrence. Many cyanobacteria produce hazardous and quite persistent toxins, which can contaminate the respective water bodies. This may limit the use of the raw water for many purposes. The purification of the contaminated water might be quite costly, which makes a continuous and large scale treatment economically unfeasible in many cases. Due to the obvious risks of algal toxins, an online or mobile detection method would be highly desirable. Several biosensor systems have been presented in the literature for this purpose. In this review, their mode of operation, performance and general suitability for the intended purpose will be described and critically discussed. Finally, an outlook on current developments and future prospects will be given.

Presence of UV filters in surface water and the effects of phenylbenzimidazole sulfonic acid on rainbow trout (Oncorhynchus mykiss) following a chronic toxicity test

UV filters belong to a group of compounds that are used by humans and are present in municipal waste-waters, effluents from sewage treatment plants and surface waters. Current information regarding UV filters and their effects on fish is limited. In this study, the occurrence of three commonly used UV filters - 2-phenylbenzimidazole-5-sulfonic acid (PBSA), 2-hydroxy-4-methoxybenzophenone (benzophenone-3, BP-3) and 5-benzoyl-4-hydroxy-2-methoxy-benzenesulfonic acid (benzophenone-4, BP-4) - in South Bohemia (Czech Republic) surface waters is presented. PBSA concentrations (up to 13μgL(-1)) were significantly greater than BP-3 or BP-4 concentrations (up to 620 and 390ngL(-1), respectively). On the basis of these results, PBSA was selected for use in a toxicity test utilizing the common model organism rainbow trout (Oncorhynchus mykiss). Fish were exposed to three concentrations of PBSA (1, 10 and 1000µgL(-1)) for 21 and 42 days. The PBSA concentrations in the fish plasma, liver and kidneys were elevated after 21 and 42 days of exposure. PBSA increased activity of certain P450 cytochromes. Exposure to PBSA also changed various biochemical parameters and enzyme activities in the fish plasma. However, no pathological changes were obvious in the liver or gonads.

In situ studies on growth, oxidative stress responses, and gene expression of juvenile bighead carp (Hypophthalmichthys nobilis) to eutrophic lake water dominated by cyanobacterial blooms

Cyanobacterial blooms have received increasing attention as a public biohazard for human and animal health. To assess the effect of cyanobacteria-dominant lake water on juvenile fish, we measured the responses of specific growth rate, condition factor, body weight and body length, oxidative stress, and related gene expression of juvenile bighead carp Hypophthalmichthys nobilis exposed to in situ eutrophic lake (Chl a was around 7.0μgL(-1)). Results showed in situ cyanobacteria-dominant lake water had no effect on the growth performance, but significantly elevated the contents of malondialdehyde, the expression of heat shock protein 70, and the activity of superoxide dismutase, indicating that oxidative stress occurred. Meanwhile in situ lake water significantly decreased the expression of catalase and glutathione S-transferase genes. We conclude that in situ cyanobacteria-dominated lake water was harmful to juvenile bighead carp based on the oxidative stress and changes in the related gene expression levels.

Lead toxicosis of captive vultures: case description and responses to chelation therapy

Background

Lead, a serious threat for raptors, can hamper the success of their conservation. This study reports on experience with accidental lead intoxication and responses to chelation therapy in captive Cinereous (Aegypius monachus) and Egyptian (Neophron percnopterus) Vultures.

Results

Soil contamination by lead-based paint sanded off the steel aviary resulted in poisoning of eight Cinereous and two Egyptian Vultures. A male Egyptian Vulture developed signs of apathy, polydipsia, polyuria, regurgitation, and stupor, and died on the next day. Liver, kidney and blood lead concentrations were 12.2, 8.16 and 2.66 μg/g, respectively. Laboratory analyses confirmed severe liver and kidney damage and anaemia. Blood Pb levels of Pb-exposed Cinereous Vultures were 1.571 ± 0.510 μg/g shortly after intoxication, decreased to 0.530 ± 0.165 μg/g without any therapy in a month and to 0.254 ± 0.097 μg/g one month after CaNa₂EDTA administration. Eight months later, blood lead levels decreased to close to the background of the control group. Blood parameters of healthy Pb-non-exposed Cinereous Vultures were compared with those of the exposed group prior to and after chelation therapy. Iron levels in the lead-exposed pre-treatment birds significantly decreased after chelation. Haematocrit levels in Pb-exposed birds were significantly lower than those of the controls and improved one month after chelation. Creatine kinase was higher in pre-treatment birds than in the controls but normalised after therapy. Alkaline phosphatase increased after chelation. A marked increase in the level of lipid peroxidation measured as thiobarbituric acid reactive species was demonstrated in birds both prior to and after chelation. The ferric reducing antioxidant power was significantly lower in pre-treatment vultures and returned to normal following chelation therapy. Blood metallothionein levels in lead-exposed birds were higher than in controls. Reduced glutathione dropped after CaNa₂EDTA therapy, while oxidised glutathione was significantly lower in both pre- and post-treatment birds. A chick in an egg produced by a Cinereous Vulture female two months after lead toxicosis died on day 40 of artificial incubation. Lead concentrations in foetal tissues were consistent with levels causing avian mortality.

Conclusions

The reported blood parameters and reproduction impairment in captive birds may have implications for professionals dealing with lead exposure in wild birds.

Biochemical and genetic alterations in the freshwater neotropical fish Prochilodus lineatus after acute exposure to Microcystis aeruginosa

Microcystins are secondary metabolites produced by different species of cyanobacteria, such as Microcystis aeruginosa (MA). In this study, the biochemical and genetic effects of lyophilized MA were evaluated in the neotropical fish Prochilodus lineatus exposed to 1 or 2 mg L-1 lyophilized MA (treated group) or only water (control group) in static toxicity tests for 24 and 96 h. The gills and liver were used in the analysis of biotransformation enzymes and antioxidant defenses, blood and gill cells in genetic analysis and in brain and muscle it was determined the activity of acetylcholinesterase (AChE). The results showed the biotransformation pathway activation due to the increase in hepatic CYP1A and in branchial and hepatic glutathione S-transferase (GST). The antioxidant defense proved to be greatly affected by MA exposure leading to changes, both in gills and liver, in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and in the content of tripeptide glutathione (GSH). Lipid peroxidation was not detected, but damage to DNA molecule was observed in blood cells. In conclusion, it can be state the lyophilized MA is able to promote changes in the biochemical and genetic parameters of P. lineatus.

Oxidative stress and detoxification biomarker responses in aquatic freshwater vertebrates exposed to microcystins and cyanobacterial biomass

Cyanobacterial blooms represent a serious threat to the aquatic environment. Among other effects, biochemical markers have been studied in aquatic vertebrates after exposures to toxic cyanobacteria. Some parameters such as protein phosphatases may serve as selective markers of exposure to microcystins, but under natural conditions, fish are exposed to complex mixtures, which affect the overall biomarker response. This review aims to provide a critical summary of biomarker responses in aquatic vertebrates (mostly fish) to toxic cyanobacteria with a special focus on detoxification and oxidative stress. Detoxification biomarkers such as glutathione (GSH) and glutathione-S-transferase (GST) showed very high variability with poor general trends. Often, stimulations and/or inhibitions and/or no effects at GSH or GST have been reported, even within a single study, depending on many variables, including time, dose, tissue, species, etc. Most of the oxidative stress biomarkers (e.g., superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) provided more consistent responses, but only lipid peroxidation (LPO) seemed to fulfill the criteria needed for biomarkers, i.e., a sufficiently long half-life and systematic response. Indeed, reviewed papers demonstrated that toxic cyanobacteria systematically elevate levels of LPO, which indicates the important role of oxidative damage in cyanobacterial toxicity. In summary, the measurement of biochemical changes under laboratory conditions may provide information on the mode of toxic action. However, comparison of different studies is very difficult, and the practical use of detoxification or oxidative stress biomarkers as diagnostic tools or early warnings of cyanobacterial toxicity is questionable.

Cyanotoxins: bioaccumulation and effects on aquatic animals

Cyanobacteria are photosynthetic prokaryotes with wide geographic distribution that can produce secondary metabolites named cyanotoxins. These toxins can be classified into three main types according to their mechanism of action in vertebrates: hepatotoxins, dermatotoxins and neurotoxins. Many studies on the effects of cyanobacteria and their toxins over a wide range of aquatic organisms, including invertebrates and vertebrates, have reported acute effects (e.g., reduction in survivorship, feeding inhibition, paralysis), chronic effects (e.g., reduction in growth and fecundity), biochemical alterations (e.g., activity of phosphatases, GST, AChE, proteases), and behavioral alterations. Research has also focused on the potential for bioaccumulation and transferring of these toxins through the food chain. Although the herbivorous zooplankton is hypothesized as the main target of cyanotoxins, there is not unquestionable evidence of the deleterious effects of cyanobacteria and their toxins on these organisms. Also, the low toxin burden in secondary consumers points towards biodilution of microcystins in the food web as the predominant process. In this broad review we discuss important issues on bioaccumulation and the effects of cyanotoxins, with emphasis on microcystins, as well as drawbacks and future needs in this field of research.

Combined exposure of Japanese quails to cyanotoxins, Newcastle virus and lead: oxidative stress responses

Wild birds are continually exposed to many anthropogenic and natural stressors in their habitats. Over the last decades, mass mortalities of wild birds constitute a serious problem and may possibly have more causations such as natural toxins including cyanotoxins, parasitic diseases, industrial chemicals and other anthropogenic contaminants. This study brings new knowledge on the effects of controlled exposure to multiple stressors in birds. The aim was to test the hypothesis that influence of cyanobacterial biomass, lead and antigenic load may combine to enhance the effects on birds, including modulation of antioxidative and detoxification responses. Eight treatment groups of model species Japanese quail (Coturnix coturnix japonica) were exposed to various combinations of these stressors. The parameters of detoxification and oxidative stress were studied in liver and heart after 30 days of exposure. The antioxidative enzymatic defense in birds seems to be activated quite efficiently, which was documented by the elevated levels and activities of antioxidative and detoxification compounds and by the low incidence of damage to lipid membranes. The greatest modulations of glutathione level and activities of glutathione-S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase and lipid peroxidation were shown mostly in the groups with combined multiple exposures. The results indicate that the antioxidative system plays an important role in the protective response of the tissues to applied stressors and that its greater induction helps to protect the birds from more serious damage. Most significant changes of these "defense" parameters in case of multiple stressors suggest activation of this universal mechanism in situation with complex exposure and its crucial role in protection of the bird health in the environment.

Mycoplasma gallisepticum infection in the grey partridge Perdix perdix: outbreak description, histopathology, biochemistry and antioxidant parameters

Background

The grey partridge is an important game bird in Europe that has declined considerably over the last decades. The production and release of farm-bred birds can be threatened by infectious agents. The objective of this study was to describe the outbreak, pathology, and blood and tissue biochemical responses in a flock of grey partridges naturally infected with Mycoplasma gallisepticum.

Results

Morbidity and mortality rates were 100% and 60%, respectively. Necropsy revealed an accumulation of caseous exudate within the infraorbital sinuses, tracheitis, pneumonia and airsacculitis. There were significant increases in activities of lactate dehydrogenase, creatine kinase and amylase, and levels of total protein and glucose in Mycoplasma-infected birds when compared to control. Catalase showed significantly lower activity in the heart, lungs, liver and gonads of Mycoplasma-infected birds. Glutathione-S-transferase activity was elevated in the eye and the associated infraorbital sinus and kidneys, and decreased in the liver. Decreased levels of reduced glutathione were found in the heart, kidneys, liver and gonads. The activity of glutathione reductase was lower only in the lungs. Compared to healthy birds, mycoplasmosis in the grey partridge caused significant differences in the level of lipid peroxidation in lungs and plasma (p < 0.05), while the ferric reducing antioxidant power was lower in the heart and kidneys (p < 0.01). Significant correlations among responses of the antioxidant parameters were found namely in the heart, lungs, spleen, liver and plasma. There were also numerous significant inter-tissue correlations of all the studied antioxidant parameters.

Conclusions

The present study demonstrates the high susceptibility of grey partridges to natural infection by M. gallisepticum, the severity of the disease based on histopathology, and the modulation of blood chemical profiles and oxidative stress-associated parameters in the avian hosts, thus enhancing the understanding of the pathogenesis of mycoplasmosis in birds. Moreover, the reported reference values can be useful for the evaluation of the state of health in grey partridges.

Biochemical responses and oxidative stress in Francisella tularensis infection: a European brown hare model

BACKGROUND

The aim of the present study was to investigate biochemical and oxidative stress responses to experimental F. tularensis infection in European brown hares, an important source of human tularemia infections.

METHODS

For these purposes we compared the development of an array of biochemical parameters measured in blood plasma using standard procedures of dry chemistry as well as electrochemical devices following a subcutaneous infection with a wild Francisella tularensis subsp. holarctica strain (a single dose of 2.6 × 10⁹ CFU pro toto).

RESULTS

Subcutaneous inoculation of a single dose with 2.6 × 10⁹ colony forming units of a wild F. tularensis strain pro toto resulted in the death of two out of five hares. Plasma chemistry profiles were examined on days 2 to 35 post-infection. When compared to controls, the total protein, urea, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase were increased, while albumin, glucose and amylase were decreased. Both uric and ascorbic acids and glutathione dropped on day 2 and then increased significantly on days 6 to 12 and 6 to 14 post-inoculation, respectively. There was a two-fold increase in lipid peroxidation on days 4 to 8 post-inoculation.

CONCLUSIONS

Contrary to all expectations, the present study demonstrates that the European brown hare shows relatively low susceptibility to tularemia. Therefore, the circumstances of tularemia in hares under natural conditions should be further studied.

Combined exposure to cyanobacterial biomass, lead and the Newcastle virus enhances avian toxicity

Under environmental conditions, wild birds can be exposed to multiple stressors including natural toxins, anthropogenic pollutants and infectious agents at the same time. This experimental study was successful in testing the hypothesis that adverse effects of cyanotoxins, heavy metals and a non-pathogenic immunological challenge combine to enhance avian toxicity. Mortality occurred in combined exposures to naturally occurring cyanobacterial biomass and lead shots, lead shots and Newcastle vaccination as well as in single lead shot exposure. Mostly acute effects around day 10 were observed. On day 30 of exposure, there were no differences in the liver accumulation of lead in single and combined exposure groups. Interestingly, liver microcystin levels were elevated in birds co-exposed to cyanobacterial biomass together with lead or lead and the Newcastle virus. Significant differences in body weights between all Pb-exposed and Pb-non-exposed birds were found on days 10 and 20. Single exposure to cyanobacterial biomass resulted in hepatic vacuolar dystrophy, whereas co-exposure with lead led to more severe granular dystrophy. Haematological changes were associated with lead exposure, in particular. Biochemical analysis revealed a decrease in glucose and an increase in lactate dehydrogenase in single and combined cyanobacterial and lead exposures, which also showed a decreased antibody response to vaccination. The combined exposure of experimental birds to sub-lethal doses of individual stressors is ecologically realistic. It brings together new pieces of knowledge on avian health. In light of this study, investigators of wild bird die-offs should be circumspect when evaluating findings of low concentrations of contaminants that would not result in mortality on a separate basis. As such it has implications for wildlife biologists, veterinarians and conservationists of avian biodiversity.

Ferric reducing antioxidant power and square wave voltammetry for assay of low molecular weight antioxidants in blood plasma: performance and comparison of methods

The purpose of the present study was to employ two methods—square wave voltammetry (SWV) performed on screen printed sensors and ferric reducing antioxidant power (FRAP)—as suitable tools for the assay of low-molecular-weight antioxidants (LMWAs). LMWAs were assayed by both methods and the resulting data were statistically compared. Plasma samples from five Cinereous vultures accidentally intoxicated with lead were used to represent real biological matrices with different levels of LMWAs. Blood was collected from the birds prior to and one month after treatment with Ca-EDTA. SWV resulted in two peaks. The first peak, with the potential value of 466 ± 15 mV, was recognized as ascorbic and uric acids, while the second one (743 ± 30 mV) represented glutathione, tocopherol, ascorbic acid and in a minor effect by uric acid, too. Contribution of individual antioxidants was recognized by separate assays of LMWA standards. Correlation between peaks 1 and 2 as well as the sum of the two peaks and FRAP was analysed. While peak 1 and the sum of peaks were in close correlation to FRAP results (correlation coefficient of 0.97), the relation between peak 2 and FRAP may be expressed using a correlation coefficient of 0.64. The determination of thiols by the Ellman assay confirmed the accuracy of SWV. Levels of glutathione and other similar structures were stable in the chosen model and it may be concluded that SWV is appropriate for assay of LMWAs in plasma samples. The methods employed in the study were advantageous in minimal sample volume consumption and fast acquisition of results.

Morphological and ultrastructural changes in tobacco BY-2 cells exposed to microcystin-RR

Tobacco BY-2 cells were exposed to microcystin-RR (MC-RR) at two concentrations, 60 microg mL(-1) and 120 microg mL(-1), to study the changes in morphology and ultrastructure of cells as a result of the exposure. Exposure to the lower concentration for 5 d led to typical apoptotic morphological changes including condensation of nuclear chromatin, creation of a characteristic 'half moon' structure, and cytoplasm shrinkage and decreased cell volume, as revealed through light microscopy, fluorescence microscopy, and transmission electron microscopy, respectively. Exposure to the higher concentration, on the other hand, led to morphological and ultrastructural changes typical of necrosis, such as rupture of the plasma membrane and the nuclear membrane and a marked swelling of cells. The presence of many vacuoles containing unusual deposits points to the involvement of vacuoles in detoxifying MC-RR. Results of the present study indicate that exposure of tobacco BY-2 cells to MC-RR at a lower concentration (60 microg mL(-1)) results in apoptosis and that to a higher concentration (120 microg mL(-1)), in necrosis.