Immunohistochemical localization of microcystin-LR in the liver of mice: a study on the pathogenesis of microcystin-LR-induced hepatotoxicity

Immunotoxicity of cynobacterial toxin Microcystin-LR is mitigated by Quercitin and himalaya tonic Liv52

Microcystin-LR (MC-LR) has received worldwide concern for its hepatotoxicity with maximum acceptable daily intake of 0.0015 mg/L (1.5 μg/L) [Federal-Provinicial-Territorial-Committee-on-drinking-water-2002]. Comprehensive immunotoxicity data is still deficient with MC-LR. To curb the menace of MC-LR, Quercitin (QE), himalaya made hepatotonic Liv52 were studied. To investigate the immunotoxic properties of MC-LR, QE and Liv52, primary splenocyte cells prepared, cultured, and immunoproliferation assay with mitogens lipopolysaccharide (LPS) or concanavalin A, (Con A) was done for, immunophenotyping, cell cycle and apoptotic studies. In current study, we have divided the splenocytes into 4 groups, i.e., Group I: Normal saline, Group II: MC-LR (0.1 μM), Group III: MC-LR (0.1 μM) + QE (20 μM), and Group IV: MC-LR (0.1 μM) + Liv52 (25 μg/ml) and treated with maximum < CC50 concentration. MC-LR enhanced proliferation of Con A and LPS stirred splenocytes at 24 h, whereas QE and Liv52 both act as antimitogenic. With combined mixture of MC-LR + QE, a significant increase in proliferation compared to mitogen or MC-LR was observed. MC-LR down-regulated expression of CD19+, CD3e+, CD4+, CD8+, (1.05%), (18.9%), (8.9%), and (7.8%) respectively in comparison to Group I. Down-regulation of 10% and 28% is observed in CD19+ and CD4+ populations with MC-LR and QE. The Liv52 addition concealed MC-LR adverse properties in most effective way. MC-LR induced G1-phase significant declined cell cycle arrest at S phase (9.26%) and G2/M phase (26.31%) was observed. QE and Liv52 mask the activity of MC-LR. Further apoptotic study revealed that MC-LR treatment decreases late apoptotic cells compared to control with no significant change in live and early apoptotic cells. Although QE increased live cells and Liv52 significantly increased late apoptotic cells, these results suggest that a Collapse

Key Words

• Cynobacterial toxin
• FACS analysis
• Immunomodulation
• Immunophenotyping
• MC-LR

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MESH Headings

• Lipopolysaccharides
• Microcystins/toxicity
• Cell Cycle

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Grants Collapse

Affiliation(s)

Kriti Shrinet School of Biotechnology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, 221005, India; School of Biotechnology, IFTM University, Moradabad, Uttar Pradesh, 244102, India
Arvind Kumar School of Biotechnology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, 221005, India.

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Microcystin Toxicokinetics, Molecular Toxicology, and Pathophysiology in Preclinical Rodent Models and Humans

Microcystins are ubiquitous toxins produced by photoautotrophic cyanobacteria. Human exposures to microcystins occur through the consumption of contaminated drinking water, fish and shellfish, vegetables, and algal dietary supplements and through recreational activities. Microcystin-leucine-arginine (MCLR) is the prototypical microcystin because it is reported to be the most common and toxic variant and is the only microcystin with an established tolerable daily intake of 0.04 µg/kg. Microcystin toxicokinetics is characterized by low intestinal absorption, rapid and specific distribution to the liver, moderate metabolism to glutathione and cysteinyl conjugates, and low urinary and fecal excretion. Molecular toxicology involves covalent binding to and inhibition of protein phosphatases, oxidative stress, cell death (autophagy, apoptosis, necrosis), and cytoskeleton disruption. These molecular and cellular effects are interconnected and are commonly observed together. The main target organs for microcystin toxicity are the intestine, liver, and kidney. Preclinical data indicate microcystins may also have nervous, pulmonary, cardiac, and reproductive system toxicities. Recent evidence suggests that exposure to other hepatotoxic insults could potentiate microcystin toxicity and increase the risk for chronic diseases. This review summarizes the current knowledge for microcystin toxicokinetics, molecular toxicology, and pathophysiology in preclinical rodent models and humans. More research is needed to better understand human toxicokinetics and how multifactorial exposures contribute to disease pathogenesis and progression.

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.

Global transcriptomic profiling of microcystin-LR or -RR treated hepatocytes (HepaRG)

The canonical mode of action (MOA) of microcystins (MC) is the inhibition of protein phosphatases, but complete characterization of toxicity pathways is lacking. The existence of over 200 MC congeners complicates risk estimates worldwide. This work employed RNA-seq to provide an unbiased and comprehensive characterization of cellular targets and impacted cellular processes of hepatocytes exposed to either MC-LR or MC-RR congeners. The human hepatocyte cell line, HepaRG, was treated with three concentrations of MC-LR or -RR for 2 h. Significant reduction in cell survival was observed in LR1000 and LR100 treatments whereas no acute toxicity was observed in any MR-RR treatment. RNA-seq was performed on all treatments of MC-LR and -RR. Differentially expressed genes and pathways associated with oxidative and endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) were highly enriched by both congeners as were inflammatory pathways. Genes associated with both apoptotic and inflammatory pathways were enriched in LR1000. We present a model of MC toxicity that immediately causes oxidative stress and leads to ER stress and the activation of the UPR. Differential activation of the three arms of the UPR and the kinetics of JNK activation ultimately determine whether cell survival or apoptosis is favored. Extracellular exosomes were enrichment of by both congeners, suggesting a previously unidentified mechanism for MC-dependent extracellular signaling. The complement system was enriched only in MC-RR treatments, suggesting congener-specific differences in cellular effects. This study provided an unbiased snapshot of the early systemic hepatocyte response to MC-LR and MC-RR congeners and may explain differences in toxicity among MC congeners.

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Microcystin-LR and microcystin-RR have similar transcriptional responses.

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Genes associated with oxidative stress and the unfolded protein response were enriched by congeners.

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Genes associated with extracellular exosomes were enriched, suggesting a potential new mechanism for cell signaling.

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Complement associated genes were strongly enriched only by microcystin-RR.

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Identified a potential molecular mechanism underlying the cellular fate of hepatocyte.

Possible Pathways of Hepatotoxicity Caused by Chemical Agents

BACKGROUND

Liver injury induced by drugs has become a primary reason for acute liver disease and therefore posed a potential regulatory and clinical challenge over the past few decades and has gained much attention. It also remains the most common cause of failure of drugs during clinical trials. In 50% of all acute liver failure cases, drug-induced hepatoxicity is the primary factor and 5% of all hospital admissions.

METHODS

The various hepatotoxins used to induce hepatotoxicity in experimental animals include paracetamol, CCl4, isoniazid, thioacetamide, erythromycin, diclofenac, alcohol, etc. Among the various models used to induce hepatotoxicity in rats, every hepatotoxin causes toxicity by different mechanisms.

RESULTS

The drug-induced hepatotoxicity caused by paracetamol accounts for 39% of the cases and 13% hepatotoxicity is triggered by other hepatotoxic inducing agents.

CONCLUSION

Research carried out and the published papers revealed that hepatotoxins such as paracetamol and carbon- tetrachloride are widely used for experimental induction of hepatotoxicity in rats.

Subcellular localization of microcystin in the liver and the gonads of medaka fish acutely exposed to microcystin-LR

Among the diverse toxic components produced by cyanobacteria, microcystins (MCs) are one of the most toxic and notorious cyanotoxin groups. Besides their potent hepatotoxicity, MCs have been revealed to induce potential reproductive toxicity in various animal studies. However, little is still known regarding the distribution of MCs in the reproductive organ, which could directly affect reproductive cells. In order to respond to this question, an acute study was conducted in adult medaka fish (model animal) gavaged with 10 μg.g^-1 body weight of pure MC-LR. The histological and immunohistochemical examinations reveal an intense distribution of MC-LR within hepatocytes along with a severe liver lesion in the toxin-treated female and male fish. Besides being accumulated in the hepatocytes, MC-LR was also found in the connective tissue of the ovary and the testis, as well as in oocytes and degenerative spermatocyte-like structures but not spermatocytes. Both liver and gonad play important roles in the reproductive process of oviparous vertebrates. This observation constitutes the first observation of the presence of MC-LR in reproductive cells (female, oocytes) of a vertebrate model with in vivo study. Our results, which provide intracellular localization of MC-LR in the gonad, advance our understanding of the potential reproductive toxicity of MC-LR in fish.

Novel Role of ER Stress and Autophagy in Microcystin-LR Induced Apoptosis in Chinese Hamster Ovary Cells

Microcystin-LR (MC-LR) is a ubiquitous peptide that exhibits strong reproductive toxicity, although the mechanistic basis for such toxicity remains largely unknown. The present study was conducted to investigate the mechanisms underlying the adverse effects of exposure to MC-LR in Chinese hamster ovary (CHO) cells. The results showed that MC-LR inhibited the in vitro proliferation of CHO cells significantly, with an IC₅₀ of 10 μM. Moreover, MC-LR-treated CHO cells revealed strong induction of cell cycle arrest and apoptosis. Additionally, exposure of CHO cells to MC-LR resulted in excess reactive oxygen species production and intracellular calcium release, with resultant endoplasmic reticulum stress (ERs). There was also extensive accumulation of autophagic vacuoles with the highest concentration of MC-LR used (10 μM). Furthermore, the expression of ERs (GRP78, ATF-6, PERK, IRE1, CHOP) and autophagy (Beclin1 and LC3II) proteins was increased, with concomitantly reduced expression of LC3I suggesting that ERs and autophagy were induced in CHO cells by MC-LR treatment. Conversely, pretreatment of CHO cells with 4-Phenyl butyric acid, the ERs inhibitor reduced the MC-LR-induced apoptotic cell death and cellular autophagy as evidenced by the reduced expression of Beclin1 and LC3II. Similarly, MC-LR treatment in combination with an autophagy inhibitor (3-methyladenine) increased apoptotic cell death compared with MC-LR alone, and induced ERs via upregulating ERs proteins. The overall results indicated that activation of ERs and autophagy are both associated with MC-LR-induced apoptosis in CHO cells. ERs may be a trigger of autophagy in this process.

PUMA and survivin are involved in the apoptosis of HepG2 cells induced by microcystin-LR via mitochondria-mediated pathway

The present study aimed to determine the cytotoxicity of microcystin-LR (MC-LR) on the human hepatocellular carcinoma (HepG2) cells in order to elucidate the mechanism of apoptosis induced by MC-LR. Morphological evaluation results showed that MC-LR induced time- and concentration-dependent apoptosis in HepG2 cells. The biochemical assays revealed that MC-LR-exposure caused overproduction of reactive oxygen species (ROS), cyclooxygenase-2 activity alteration, cytochrome c release, and remarkable activation of caspase-3 and caspase-9 in HepG2 cells, indicating that MC-LR-induced apoptosis is mediated by mitochondrial pathway. Moreover, we also found that p53 and Bax might play an important role in MC-LR-induced apoptosis in HepG2 cells in which PUMA and survivin were involved. However, further studies are necessary to elucidate the possible functions of PUMA and survivin in MC-LR-induced apoptosis in HepG2 cells.

Hepatic Gene Expression Changes in Mice Associated with Prolonged Sublethal Microcystin Exposure

Microcystin-LR (MCLR) is an acute hepatotoxicant and suspected carcinogen. Previous chronic studies have individually described hepatic morphologic changes, or alterations in the cytoskeleton, cell signaling or redox pathways. The objective of this study was to characterize chronic effects of MCLR in wild-type mice utilizing gene array analysis, morphology, and plasma chemistries. MCLR was given daily for up to 28 days. RNA from the 28-day study was hybridized onto mouse genechip arrays. RNA from 4 hours, 24 hours, 4 days, 1 day, and 28 days for selected genes was processed for quantitative-PCR. Increases in plasma hepatic enzyme activities and decreases in total protein, albumin and glucose concentrations were identified in MCLR-treated groups at 14 and 28 days. Histologically, marked hepatokaryomegaly was identified in the 14-day MCLR group with the addition of giant cells at 28 days. Major gene transcript changes were identified in the actin organization, cell cycle, apoptotic, cellular redox, cell signaling, albumin metabolism, and glucose homeostasis pathways, and the organic anion transport polypeptide system. Using toxicogenomics, we have identified key molecular pathways involved in chronic sublethal MCLR exposure in wild-type mice, genes participating in those critical pathways and related them to cellular and morphologic alterations seen in this and other studies.

Immunohistochemical approach to study cylindrospermopsin distribution in tilapia (Oreochromis niloticus) under different exposure conditions

Cylindrospermopsin (CYN) is a cytotoxic cyanotoxin produced by several species of freshwater cyanobacteria (i.e., Aphanizomenon ovalisporum). CYN is a tricyclic alkaloid combined with a guanidine moiety. It is well known that CYN inhibits both protein and glutathione synthesis, and also induces genotoxicity and the alteration of different oxidative stress biomarkers. Although the liver and kidney appear to be the main target organs for this toxin based on previous studies, CYN also affects other organs. In the present study, we studied the distribution of CYN in fish (Oreochromis niloticus) under two different exposure scenarios using immunohistochemical (IHC) techniques. In the first method, fish were exposed acutely by intraperitoneal injection or by gavage to 200 µg pure CYN/Kg body weight (bw), and euthanized after 24 h or five days of exposure. In the second method, fish were exposed by immersion to lyophilized A. ovalisporum CYN-producing cells using two concentration levels (10 or 100 µg/L) for two different exposure times (7 or 14 days). The IHC was carried out in liver, kidney, intestine, and gills of fish. Results demonstrated a similar pattern of CYN distribution in both experimental methods. The organ that presented the most immunopositive results was the liver, followed by the kidney, intestine, and gills. Moreover, the immunolabeling signal intensified with increasing time in both assays, confirming the delayed toxicity of CYN, and also with the increment of the dose, as it is shown in the sub-chronic assay. Thus, IHC is shown to be a valuable technique to study CYN distribution in these organisms.

Histopathological and immunohistochemical analysis of Tilapia (Oreochromis niloticus) exposed to cylindrospermopsin and the effectiveness of N-Acetylcysteine to prevent its toxic effects

Cylindrospermopsin (CYN) is a cytotoxic cyanotoxin produced by several cyanobacteria species. It has been demonstrated that CYN is a potent protein and glutathione synthesis inhibitor, and induces genotoxicity and oxidative stress. The present study investigated the protective role of two different doses of N-Acetylcysteine (NAC) (22 and 45 mg/fish/day) against the pathological changes induced in tilapia (Oreochromis niloticus) orally exposed to a single dose of pure CYN or CYN from an Aphanizomenon ovalisporum CYN-producer strain (200 μg/kg of CYN in both cases). Moreover, an immunohistochemical (IHC) analysis was carried out in order to elucidate the CYN distribution in exposed fish. The histological findings were more pronounced when fish were intoxicated with CYN from the cyanobacterial strain, being liver and kidney the main targets for CYN toxicity. NAC pre-treatment was effective reducing the damage induced by CYN, especially at the highest dose employed (45 mg/fish/day), with a total prevention in all organs. The IHC analysis showed that CYN-antigen appeared mainly in the liver and gastrointestinal tract, although it was also present in kidney and gills. In this case, the immunopositive results were more abundant in those fish exposed to pure CYN. NAC reduced the number of immunopositive cases in a dose-dependent way. Therefore, NAC can be considered a useful chemoprotectant in the prophylaxis and treatment of CYN-related intoxications in fish.

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.

Comparison of response indices to toxic microcystin-LR in blood of mice

In order to investigate the response indices to toxic microcystin-LR (MC-LR) in blood of mice, concentrations of free and total MC-LR in blood and tissues, accompanied by serous parameters in series including some enzymatic activities, hematology and the function of leukocytes, were determined in mice exposed to the toxin ranging from 3.125 to 25.000 μg kg(-1)day(-1) by intraperitoneal injection for 7 days. On the 7th day, the ratios of mass of free MC-LR in serum to the mass of MC-LR in given dose were 3.843-4.555%, while the ratios of total MC-LR in liver were 34.465-38.567%. Comparing the overall experimental results, the three most sensitive indices are total MC-LR in the liver, the phagocytic index and reactive oxygen species (ROS) which have shown significant differences between the lowest dose group and the control group. Alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase had proportional correlations with the MC-LR exposure doses, and the hematology of the majority of blood cells and the volume of erythrocytes were also influenced by the toxin. The alterations of some cytokines and the ROS of leukocytes were observed. The results of the studies suggest that measurement of MC-LR in blood is powerful and clear evidence to indicate that subjects have been exposed to MC-LR and can be used to discriminate from other causes leading to hepatic lesions although it is not as sensitive as other indices that are usually as useful complements to reflect the liver function.

Integrated Histopathological and Urinary Metabonomic Investigation of the Pathogenesis of Microcystin-LR Toxicosis

Patterns of change of endogenous metabolites may closely reflect systemic and organ-specific toxic changes. The authors examined the metabolic effects of the cyanobacterial (blue-green algal) toxin microcystin-LR by 1H-nuclear magnetic resonance (NMR) analysis of urinary endogenous metabolites. Rats were treated with a single sublethal dose, either 20 or 80 µg/kg intraperitoneally, and sacrificed at 2 or 7 days post dosing. Changes in the high-dose, 2-day sacrifice group included centrilobular hepatic necrosis and congestion, accompanied in some animals by regeneration and neovascularization. By 7 days, animals had recovered, the necrotizing process had ended, and the centrilobular areas had been replaced by regenerative, usually hypertrophic hepatocytes. There was considerable interanimal variation in the histologic process and severity, which correlated with the changes in patterns of endogenous metabolites in the urine, thus providing additional validation of the biomarker and biochemical changes. Similarity of the shape of the metabolic trajectories suggests that the mechanisms of toxic effects and recovery are similar among the individual animals, albeit that the magnitude and timing are different for the individual animals. Initial decreases in urinary citrate, 2-oxoglutarate, succinate, and hippurate concentrations were accompanied by a temporary increase in betaine and taurine, then creatine from 24 to 48 hours. Further changes were an increase in guanidinoacetate, dimethylglycine, urocanic acid, and bile acids. As a tool, urine can be repeatedly and noninvasively sampled and metabonomics utilized to study the onset and recovery after toxicity, thus identifying time points of maximal effect. This can help to employ histopathological examination in a guided and effective fashion.

Cyanobacterial cyclopeptides as lead compounds to novel targeted cancer drugs

Cyanobacterial cyclopeptides, including microcystins and nodularins, are considered a health hazard to humans due to the possible toxic effects of high consumption. From a pharmacological standpoint, microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cellular damage following uptake via organic anion-transporting polypeptides (OATP). Their intracellular biological effects involve inhibition of catalytic subunits of protein phosphatase 1 (PP1) and PP2, glutathione depletion and generation of reactive oxygen species (ROS). Interestingly, certain OATPs are prominently expressed in cancers as compared to normal tissues, qualifying MC as potential candidates for cancer drug development. In the era of targeted cancer therapy, cyanotoxins comprise a rich source of natural cytotoxic compounds with a potential to target cancers expressing specific uptake transporters. Moreover, their structure offers opportunities for combinatorial engineering to enhance the therapeutic index and resolve organ-specific toxicity issues. In this article, we revisit cyanobacterial cyclopeptides as potential novel targets for anticancer drugs by summarizing existing biomedical evidence, presenting structure-activity data and discussing developmental perspectives.

Localization of microcystin-LR in medaka fish tissues after cyanotoxin gavage

Microcystins (MCs) are toxic monocyclic heptapeptides produced by many cyanobacteria. Over 70 MCs have been successfully isolated and identified, of which MC-LR is the most commonly occurring toxin. Microcystins, especially MC-LR, cause toxic effects in mammals, birds and fish and are a recognized potent cause of environmental stress and pose a potential health hazard in aquatic ecosystems when heavy blooms of cyanobacteria appear. They also constitute a public health threat to people via drinking water and food chains. The concentrations of MC-LR can be very low, even in fish displaying severely disrupted tissues, which makes it essential to devise selective and sensitive histochemical methods for identifying and localizing MC-LR in target organs, such as liver and intestine. The aim of the study reported here was to analyze the presence of MC-LR in contaminated fish tissues using immunohistochemical methods. The present experiment involving subacute exposure confirmed our initial hypothesis that subacute and acute exposure to microcystin contamination can exacerbate physiological stress, induce sustained pathological damage, and affect the immune response in exposed medaka fish.

Cyanobacterial toxins and liver diseaseThis article is one of a selection of papers published in a special issue celebrating the 125th anniversary of the Faculty of Medicine at the University of Manitoba

Blue-green algae, also known as cyanobacteria, produce a variety of toxins, some of which have been implicated in the pathogenesis of severe and potentially life-threatening diseases in humans. As the growth of cyanobacteria within freshwater lakes increases worldwide, it is important to review our present understanding of their toxicity and potential carcinogenicity to gain insight into how these organisms impact human health. This review addresses each of these topics, with special emphasis given to cyanobacterial hepatotoxins within freshwater environments.

Gene expression profiles in liver of zebrafish treated with microcystin-LR

Microcystin-LR (MC-LR) is the most frequently studied cyclic heptatoxin produced by cyanobacteria, which has tremendous negative impacts on fish, while its molecular mechanism behind remained unclear at present. Here, Affymetrix Zebrafish GeneChip was used to identify alterations in gene expression of zebrafish (Danio rerio) after MC-LR exposure. Among the 14,900 transcripts in the microarray, 273 genes were differentially expressed, in which 243 genes were elevated and 30 were decreased. According to GOstat analysis, MC-LR mainly influenced the cell cycle and mitogen-activated protein kinases (MAPK) signaling pathways. In addition, many immune-related genes were also influenced. These data suggest that MC-LR could promote tumorigenesis and cause immunotoxicity in fish.

Mitochondria a key role in microcystin-LR kidney intoxication

Microcystins (MCs) are a group of closely related cyclic heptapeptides produced by a variety of common cyanobacteria. These toxins have been implicated in both human and livestock mortality. Microcystin-LR could affect renal physiology by altering vascular, glomerular and urinary parameters, indicating that MC-LR could act directly on the kidney. The aim of the current work was to examine the effect of MC-LR on mitochondrial oxidative phosphorylation of rat kidney isolated mitochondria.Furthermore, microcystin-LR decreased both state 3 and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP)-uncoupled respiration. The transmembrane potential was strongly depressed by MC-LR in a concentration dependent manner, pointing to an uncoupling effect; however, microcystin-LR did not increase the permeability of the inner mitochondria membrane to protons. Therefore, the transmembrane decrease was a consequence of a strong inhibitory effect on redox complexes. The addition of uncoupling concentrations of MC-LR to Ca(2+)-loaded mitochondria treated with ruthenium red resulted in mitochondrial permeability transition pore (MPTP) opening, as evidenced by mitochondrial swelling in isosmotic sucrose medium. Mitochondrial swelling in the presence of Ca(2+) was prevented by cyclosporin A and was drastically inhibited by catalase and dithiothreitol, indicating the participation of mitochondrial generated reactive oxygen species in this process. From this study it can be concluded that the bioenergetic lesion promoted by microcystin-LR seems to be sufficient to explain renal injury.

Biomonitoring Of Cyanobacterial Blooms In Polish Water Reservoir And The Cytotoxicity And Genotoxicity Of Selected Cyanobacterial Extracts

OBJECTIVES

Water pollution with toxic cyanobacterial blooms is a worldwide problem. Cyanobacteria species that mainly produce microcystins predominate in Polish water reservoirs.

MATERIALS AND METHODS

In our study, cyanobacterial blooms were monitored during summer of 2004 in the Sulejów reservoir. The concentration of microcystins in water and cyanobacterial cells were determined using liquid chromatography and immunobiotests, while the biological activity of microcystic cyanobacterial extracts was assessed using bacterial tests (SOS Chromotest, UMU test), the comet assay and micronucleus test with human lymphocytes.

RESULTS

It was revealed that cyanobacterial bloom was most intensive in mid August and lasted until the end of September. Microcystis aeruginosa and Aphanizomenon flos-aquae dominated in the blooms. The highest concentration of microcystins in cyanobacterial cells was also observed at that time. The concentration of microcystins in water did not exceed 1 microg/l. All cyanobacterial extracts showed weak genotoxicity only for Escherichia coli PQ37. The cyanobacterial extracts prepared at the beginning of September were most toxic to human lymphocytes, the effective microcystin extracts (EC50) concentration was about two or three times lower compared to the other extracts. The level of DNA damage in lymphocytes after short exposure to microcystic extracts (3 and 6 h) was significantly higher than respective levels after longer exposure. The microcystins of cyanobacterial blooms induced a slight increase in micronuclei frequencies in human lymphocytes.

CONCLUSION

Phytoplankton biomass and the genotoxicity of massive cyanobacterial blooms should be assessed for eucariotic cells in the Sulejów reservoir to avoid the hazard induced by cyanobacterial blooms.

Rapid Analytical Detection of Microcystins Using Gold Colloidal Immunochromatographic Strip

Routine monitoring of microcystin in natural waters is difficult because the concentration of the toxin is low and the detection method is usually complicated. We developed a rapid analytical detection method of microcystins gold colloidal immunochromatogeraphic strip. The sensitivity of the strip is about 1 ng/mL for microcystin LR; it is able to distinguish visually among different concentrations of microcystin solutions. The developed gold colloidal strip can detect microcystins within 15 min and does not require either a complicated extraction system, or trained or qualified experts.

Toxic potential of microcystin-containing cyanobacterial extracts from three Romanian freshwaters

The aim of this study was to characterise for the first time the toxin profile and in vivo/in vitro toxicological effects of cyanobacteria obtained from three Romanian freshwater blooms. Two strains of Microcystis aeruginosa were isolated from blooms occurring in different fish ponds. As well, a complex bloom sample obtained from a recreational lake area and dominated by Microcystis aeruginosa and Microcystis viridis was explored. The morphological identity of the cyanobacterial species could be confirmed by sequence analysis of the intergenic spacer region of the phycocyanin operon, PC-IGS. As well, both the strains and the field sample were confirmed to possess mcyA and mcyB genes, which correlated with the formation of several microcystins (MCYSTs). A number of cyanopeptolins and a new aeruginosin were also found. Despite these mixtures of compounds, in vivo as well as in vitro toxicological responses resembled those previously found for MCYST-LR. These include strong hepatotoxicity in mice with parenchymal disintegration and the emergence of haemorrhagic centres, a lack of responsiveness of human and fish cell lines most likely due to a lack of active transport systems, and a significant subcellular damage most prominent on the level of the lysosomes in primary hepatocytes of mice and rainbow trout. We thus conclude that the formation of blooms in the Romanian fish ponds and the recreational area may impact on animal and human health. A broader survey of cyanotoxin occurrence and related toxicity is necessary in Romania in order to assess the extent of this animal and human health hazard.

Recovery of MC-LR in fish liver tissue

Cyanotoxins, particularly microcystins (MCs), have been shown to be a hazard to human health. MCs accumulate in aquatic organisms probably as a result of irreversible binding to liver protein phosphatases. The aim of this study was to describe the recovery of MC from fish liver using various detection methods, with MC-LR as the representative congener. These findings are discussed in conjunction with the current procedures and limit values used for human risk assessment. Following incubation of liver homogenates with various MC-LR concentrations, the homogenates were extracted by a water/methanol/butanol mixture via different treatments and subsequently analyzed via the colorimetric protein phosphatase inhibition assay (cPPA), HPLC, and anti-Adda ELISA. Detection via cPPA appeared to yield the highest recovery of MC-LR, although the presence of unspecific background may have resulted in overestimation of the true recovery. The recoveries determined via HPLC and anti-Adda ELISA were comparable to each other. The limits of detection were 0.01-2.4 microg MC-LR/g liver tissue, depending on the method used. Maximum MC-LR recovery from samples incubated with 10 and 100 microg MC-LR/g ranged between 44% and 101%. Recovery from samples incubated with 1 microg MC-LR/g liver tissue was below 3%. Lower recovery is assumed to result from irreversible, covalent MC protein binding, as confirmed by Western blotting of liver homogenates with anti-Adda immunoprobing. The results demonstrate that further investigation of and improvement in routinely applied MC methods for fish tissue and/or food analyses are needed for a reliable risk assessment.

Decomposition of microcystin-LR, microcystin-RR, and microcystin-YR in water samples submitted to in vitro dissolution tests

The presence of cyanobacterial toxins (microcystins) in waters and food increases the risk of toxicity to animal and human health. These toxins can degrade in the human gastrointestinal tract before they are absorbed. To evaluate this possible degradation, water samples spiked with known concentrations of microcystins MC-LR, MC-RR, and MC-YR, which are the toxins most commonly produced by such toxic cyanobacteria as Microcystis aeruginosa, Oscillatoria spp., and Nostoc spp., were submitted to a dissolution test that used gastric and intestinal fluids according to U.S. Pharmacopeia conditions. HPLC with UV detection was used to determine the toxins before and after treatments. This study revealed enzymatic alterations in gastric conditions for all the toxins assayed. MC-RR was the toxin most affected: its range of inactivation was 49-64%. The percentage of degradation for MC-YR and MC-LR was around 30%. However, none was degraded by intestinal digestion.

Proteomics approach on microcystin binding proteins in mouse liver for investigation of microcystin toxicity

Microcystins (MC) produced by freshwater cyanobacteria are potent hepatotoxins. MC inhibit protein phosphatases (PP) 1 and 2A. MC and okadaic acid (OA), which is a similar PP inhibitor whereas it has a less affinity to PP1 than PP2A, behave similarly to primary culture hepatocytes, with inducements of phosphorylations of cytoskeleton, morphological changes and apoptosis. Although the distribution of OA in mouse liver was observed immunohistochemically, no OA injury was found. The purpose of this study was therefore to determine why only MC has specific toxicities on the liver. A systematic process of MC affinity chromatography and proteomics, using two-dimensional gel electrophoresis and MALDI-TOFMS, indicated the existence of some MC-binding proteins including the complexes of PP1, PP2A, and PP4 with their own regulatory subunits in mouse liver extracts. The competitive inhibition experiments using affinity chromatography with OA showed that two of the three protein complexes strongly interacted with OA, whereas only the complex of PP1 with the inhibitory subunit NIPP1 did not strongly interacted with OA. These results suggest that the PP1 complex is not related to the common behavior of MC and OA of primary culture hepatocytes, and is related to the specific hepatotoxicities of MC.

DNA damage and repair in human peripheral blood lymphocytes following treatment with microcystin-LR

The purpose of this study was to find a possible explanation of the inconsistency of data regarding the genotoxicity of microcystin-LR (MC-LR). We compared the results of the comet assay with the results of the analysis of chromosome aberrations and apoptosis. In order to investigate the influence of MC-LR on DNA damage in human lymphocytes, cells were treated with MC-LR at different concentrations (1, 10 and 25 microg/ml) for 6, 12, 18 and 24 h. Analyses of Olive Tail Moment (OTM) as an indicator of DNA damage showed that MC-LR treatment induced DNA damage in a time-dependent manner, reaching its maximum after 18 h. The lowest values of OTM were observed after 24 h. MC-LR had no effect on the frequency of chromosome aberrations in lymphocytes. Since some data available in the literature indicate that apoptosis may lead to overestimated or false positive results regarding the genotoxicity of mutagens in the comet assay, we measured the frequency of late apoptotic cells by use of the comet assay and the frequency of early apoptotic cells with the TUNEL method. The comet assay results revealed that the highest level of apoptosis was observed after 24 h and the lowest after 18 h. The comparison of the frequency of apoptotic cells determined by the comet assay with DNA damage (OTM) examined by the comet assay revealed a statistically significant, negative correlation. The TUNEL results showed that the frequency of apoptotic cells progressively increased in a dose- and time-dependent manner. The comparison of the frequency of apoptotic cells determined by TUNEL method with DNA damage (OTM) examined by the comet assay showed a significant positive correlation for lymphocytes treated with MC-LR for 6, 12 and 18 h. Therefore, our findings indicate that microcystin-LR-induced DNA damage observed in the comet assay may be related to the early stages of apoptosis due to cytotoxicity but not genotoxicity. In addition, we examined the DNA repair kinetics in lymphocytes following treatment with microcystin-LR and ionizing radiation. Our results indicate that MC-LR has an inhibiting effect on the repair of radiation-induced damage.

Reversed-phase liquid chromatographic–mass spectrometric determination of microcystin-LR in cyanobacteria blooms under alkaline conditions

Reversed-phase HPLC coupled to the atmospheric pressure ionization-electrospray ionization (API-ESI) MS was used for microcystin-LR detection and quantitation in samples of dried Microcystis aeruginosa cells. An alkaline linear gradient (20 mmol/l ammonium hydroxide-acetonitrile, pH 9.7) was used for elution of the toxic peptides. Limit of detection was 1 microg/ml (20 ng per injection) in the scan mode of MS and 0.1 microg/ml (2 ng per injection) in the case of selective ion monitoring.

Microcystin-LR and okadaic acid-induced cellular effects: a dualistic response

Microcystins, potent heptapeptide hepatotoxins produced by certain bloom-forming cyanobacteria, are strong protein phosphatase inhibitors. They covalently bind the serine/threonine protein phosphatases 1 and 2A (PP1 and PP2A), thereby influencing regulation of cellular protein phosphorylation. The paralytic shellfish poison, okadaic acid, is also a potent inhibitor of these PPs. Inhibition of PP1 and PP2A has a dualistic effect on cells exposed to okadaic acid or microcystin-LR, with both apoptosis and increased cellular proliferation being reported. This review summarises the existing data on the molecular effects of microcystin-LR inhibition of PP1 and PP2A both in vivo and in vitro, and where possible, compares this to the action of okadaic acid.

Comparative toxicity evaluation of cyanobacterial cyclic peptide toxin microcystin variants (LR, RR, YR) in mice

The cyclic peptide toxins microcystins and nodularins are the most common and abundant cyanotoxins present in diverse water systems. They have been the cause of human and animal health hazards and even death. Over 60 microcystin variants have been reported so far. We report here the results of our study on comparative toxicity evaluation of three most predominant microcystins, MC-LR, MC-RR and MC-YR in mice. The mice were administered one LD(50) dose of MC-LR, RR and YR (43, 235.4 and 110.6 micro g/kg body weight, respectively), and biochemical and histological variables were determined at 30 min post-treatment and mean time to death (MTD). Significant increase in liver body weight index was induced by all three variants. There was marginal increase in serum levels of hepatic enzymes viz. AST, ALT and gamma-GT at 30 min post-treatment but 3-4 fold increase was observed at MTD. In contrast, enhanced LDH leakage, DNA fragmentation and depletion of hepatic glutathione was observed at 30 min post treatment in all three variants. There was no change in levels of serum protein, albumin and albumin/globulin ratio. Liver histology showed time dependent severe pathological lesions like congestion, haemorrhage, portal mononuclear cell infiltration and obliteration of chromatin material. Lung lesions were predominantly in bronchi and parenchyma. Though qualitatively lesions were identical in all three microcystin variants, degree of liver and lung lesions varied quantitatively with the toxin. The breathing pattern and respiratory frequency of the mice after i.p. administration of the toxin showed uniform pattern for 90 min followed by abrupt change in the respiratory pattern and instantaneous death. Based on biochemical and histological studies, MC-LR was found to be the most potent toxin followed by MC-YR and MC-RR.

Inhibition of nuclear protein phosphatase activity in mouse hepatocytes by the cyanobacterial toxin microcystin-LR

Microcystin-LR (MCLR) is a cyanobacterial hepatotoxin and protein phosphatase inhibitor that contaminates water reservoirs worldwide. MCLR localizes to the cytosol of hepatocytes, however, immunohistochemical studies indicate that it accumulates in the nucleus. MCLR toxicosis is associated with decreased hepatic protein phosphatase activity, but effects in nuclear protein phosphatase activity have not been investigated. Balb/c mice were given lethal (100 microg/kg) or sublethal (12, 23 and 45 microg/kg) i.p. doses of MCLR and hepatic nuclear extracts were analyzed for protein phosphatase 1 and 2A activity. There was profound inhibition of nuclear protein phosphatase activity within 50 min of lethal dosing, however an inhibition was not detected with sublethal doses. MCLR immunohistochemistry revealed widespread lobular staining in the lethal group and centrilobular staining in the sublethal groups. At the cellular level there was nuclear and cytoplasmic staining of equal intensity. As an indicator of nuclear protein phosphatase activity, the phosphorylation of p53, a nuclear phosphoprotein and known substrate for protein phosphatases 1 and 2A, was evaluated. Balb/c mice were treated with sublethal doses of MCLR or saline vehicle after induction of hepatic p53 by the DNA damaging agent diethylnitrosamine (DEN). P53 was immunoprecipitated and probed with phosphoserine specific antibodies by Western blotting. There was greater phosphoserine reactivity of p53 protein in animals treated with MCLR relative to saline treated controls, consistent with increased phosphorylation of serine sites. It is concluded that an interaction of this toxin with nuclear protein phosphatases occurs within 50 min of lethal dosing, which leads to a profound inhibition of enzymatic activity. Even sublethal doses of MCLR that do not result in significant inhibition of activity in bulk nuclei, result in detectable changes in phosphorylation of p53.

Development of an ultrarapid one-step fluorescence immunochromatographic assay system for the quantification of microcystins

Microcystins are a family of potent toxic oligopeptides produced by freshwater cyanobacteria genera and have been a great threat to the welfare of humans and animals. There has been a great demand for developing a fast and convenient analytical method to detect microcystins. Recently, direct competition ELISA using monoclonal or polyclonal antibody has become the prevailing method for detecting microcystins. In this study, we report rapid quantification methods of microcystins using fluorescence for a detection signal and a lateral-flow-type immunochromatography as a separation system. The assay systems consist of a test strip housed in a disposable cartridge and a portable laser-fluorescence scanner. The components of a test strip are as follows: a nitrocellulose membrane, a sample pad, an absorption pad, and a backing card. A fluorescence scanner was designed to fit the cartridge and to quantify the distribution of the fluorescence intensity along the strip. When the calibration curve for an antibody-immobilized system was determined, a good linearity was displayed in the range from 125 to 2000 pg/mL of microcystin-LR. The linear-regression coefficient (R) was 0.938 between relative fluorescence intensity and the microcystin concentration. The limit of detection was determined to be 95.38 pg/mL. We then designed another biosensor system by changing an experimental format from the competition type to the inhibition type. When compared to the antibody-immobilized system, the antigen-immobilized assay detected a lower level of microcystin but did not discern microcystin-LR above 1000 pg/mL. The detection of limit for the antigen-immobilized system was 47.23 pg/mL. The linear regression coefficient (R) in the antigen-immobilized system equaled to 0.927. The reproducibility in the antigen-immobilized system was good through the entire range. The reproducibility in the antibody-immobilized system was relatively poor when compared to a MC-immobilized system. However, it still registered in the acceptable range of 7.32-9.91% except for the extreme ends of the MC concentration. Finally, surface water was tested to check for potential matrix interference. The calibration curve displayed a similar pattern as did those for other matrixes, including PBS and tap water, although its sensitivity was a little less due to the interference with certain components in the surface water. Overall, either of the biosensor systems can be used as a useful on-site detection tool for checking drinking water or surface water for microcystins. The laser-fluorescence scanner we developed is relatively small, transportable, and easy to use. Thus, the samples can be analyzed for microcystins at the test site using a real-time base within 15 min without having to bring the samples back to the laboratory.

Role of oxidative stress and mitochondrial changes in cyanobacteria-induced apoptosis and hepatotoxicity

Microcystins produced by cyanobacteria are potent and specific hepatotoxins; however, the mechanisms of microcystin-induced hepatotoxicity have not been fully elucidated. The induction of free radical formation and mitochondrial alterations are two major events found in microcystin-treated cultured rat hepatocytes. The mitochondrial alterations, i.e. loss of mitochondrial membrane potential and mitochondria permeability transition are now recognized as key steps in apoptosis. The activation of calpain and Ca(2+)/calmodulin-dependent protein kinase II is believed to be critical in the microcystin-induced apoptotic process.

Synthesis and organotropism of 3H-dihydro derivatives of the cyanobacterial peptide hepatotoxin nodularin

Tritium-labelled dihydro derivatives of the cyanobacterial peptide hepatotoxin nodularin were prepared by reduction with sodium boro[3H]hydride. The optimised reaction gave two dihydronodularin stereoisomers which were purified by high-performance liquid chromatography with a mobile phase of methanol-0.7% sodium sulfate (6:4) and a C(18) stationary phase. The specific activities of the stereoisomers were 1780-1807 dis min(-1) ng(-1). The radiolabelled dihydronodularins were tested for stability and used for toxicokinetic studies in mice. Liver was the main site of toxin accumulation.

Identification of ATP-synthase as a novel intracellular target for microcystin-LR

Microcystins (MCs) are a group of closely related cyclic heptapeptides produced by a variety of common cyanobacteria. These are potent and highly specific hepatotoxins, the toxicity of which is based upon their inhibition of type-1 (PP1) and type-2A (PP2A) protein phosphatases. Apart from protein phosphatases, it is not known whether these phosphatase-inhibiting peptides could bind any other cellular proteins. We wanted to determine whether any possible unknown MC-adducts could explain the apoptotic effects observed at high concentrations of MCs. The question of other possible cellular proteins binding to MCs is also relevant when these compounds are employed for affinity purification of protein phosphatases. In MC-treated cell lysates, antibodies to MC recognized three protein adducts of 35-37 and 55 kD. By immunochemical and proteomics approaches, these proteins were identified as the catalytic subunits of type-1 and type-2A protein phosphatases and the ATP-synthase beta-subunit. The latter target could be associated with the suggested apoptosis-inducing potential of MCs.

Immunohistochemistry of fumonisin in poultry using avidin-biotin-peroxidase system

Using monoclonal anti-fumonisin B1 antibody (anti-FB1) and avidin-biotin-peroxidase system, liver and kidneys of broiler chicks were evaluated for the detection and distribution of fumonisins (FBs). One hundred and fifty micrograms of FB1 or culture extract of Fusarium moniliforme str. 113F containing 150 microg of FB1 and 4 microg of FB2 were administered into the vitelline sac of 1-day old, specific pathogen-free chicks. The animals were killed 24 h after injection, and renal and hepatic tissues submitted for immunohistochemical analysis. FBs were detected in the epithelial cells of convoluted distal and proximal tubules of the kidneys, as well as in the cytoplasm of hepatocytes. This novel immunohistochemical method developed is expected to be an efficient way for monitoring the target of the FB toxins in tissues.

Characterization of sublethal microcystin-LR exposure in mice

Microcystin-LR (MCLR) is a potent hepatotoxin produced by the cyanobacterium Microcystis aeruginosa. The histology of acute lethal toxicity has been well characterized, but histology is limited regarding sublethal exposure. Balb/C mice were given a single sublethal dose of MCLR (45 microg/kg) and euthanized at 2, 4, 12, and 24 hours after exposure. Centrilobular to midzonal hepatocellular hypertrophy with loss of cytosolic vacuolation consistent with glycogen depletion occurred at 2 hours. At 4 hours, central lobular hepatocytes exhibited eccentric areas of eosinophilic cytoplasmic condensation that were partially aggregated around the outer nuclear membrane. The areas were weakly positive for cytokeratin and somewhat resembled the Mallory bodies of alcoholic human hepatitis. Small numbers of apoptotic hepatocytes were seen at 24 hours. The toxin was detectable by immunohistochemistry (IHC) as early as 2 hours and was colocalized with the areas of hepatocellular hypertrophy. Intense nuclear staining occurred at 4 hours; this was no longer evident after 12 hours. Strong staining of apoptotic bodies occurred at 24 hours. Mice that received two daily doses had a marked increase in apoptotic hepatocytes in the centrilobular areas. Lesions at four and seven doses consisted of marked hepatocytomegaly and karyomegaly with parenchymal disarray and cytosolic vacuolation. IHC revealed diffuse staining throughout the liver parenchyma consistent with toxin accumulation. An anti-MCLR monoclonal antibody detected bands at the 40-kDa mark in nuclear extracts that were identified as protein phosphatases 1 and 2A by western blotting, consistent with a covalent interaction between MCLR and nuclear protein phosphatases.

Lack of teratogenicity of microcystin-LR in the mouse and toad

Microcystin-LR (MC-LR) is a cyanobacterial toxin generated by the organism Microcystis aeruginosa. Although the hepatotoxicity of this chemical has been characterized, the potential developmental toxicity in vertebrates has not been well studied. The purpose of this study was to elucidate the effects of this toxin on the in vivo and in vitro development of mammals and the development of an Anuran (toad). Initial acute toxicity experiments with female CD-1 mice were accomplished with MC-LR administered i.p. in saline. Lethality occurred at 128 and 160 microg kg (-1) and histopathology revealed massive hepatic necrosis with diffuse hemorrhage. Developmental toxicity studies were done with MC-LR administered i.p. for 2-day periods: gestation days 7-8, 9-10 or 11-12. Doses used ranged from 2 to 128 microg kg(-1). On gestation day 17, fetuses were weighed and analyzed for gross morphological and skeletal defects. No treatment-related differences were seen in litter size, viability, weight or the incidence of anomalies. Groups of dams dosed with 32-128 microg kg(-1) on gestation days 7-8, 9-10 or 11-12 were allowed to give birth and the growth and development of their pups were followed postnatally. There were no significant effects noted in the offspring of the treated dams. Neurulation-staged CD-1 mouse conceptuses were exposed to 50-1000 nM MC-LR in whole embryo culture for 24 h. No significant increase in abnormalities or developmental delays was observed. Finally, exposure of the developing toad. Bufo arenarum was done from stage 17 (tail bud) for 10 days at concentrations of 1-20 mg l(-1). No effect on morphological development or survival was noted in any exposed groups. These data indicate that microcystin does not appear to affect development adversely in the mouse (in vivo or in vitro) or the toad at the doses and exposure parameters used.

Apoptotic effect of cyanobacterial extract on rat hepatocytes and human lymphocytes

Toxic cyanobacterial blooms are an increasing problem in Poland. The production of cyanobacterial toxins and their presence in drinking and recreational waters represent a growing danger to human and animal health. This is connected with the increase of cyanobacterial biomass caused by excessive eutrophication of the water ecosystem. There is evidence that cyanobacterial hepatotoxins can act as a potent promoter of primary liver cancer. The apoptotic effect of microcystins in Polish cyanobacterial bloom samples on rat hepatocytes and human lymphocytes was observed using light and fluorescence microscopy, flow cytometry, and electrophoretic analysis. The incubation time needed to observe the first morphological apoptotic changes in hepatocytes was approximately 30 min; however, the characteristic biochemical changes in DNA were not observed even after 120 min. In lymphocyte cultures the morphological changes characteristic for apoptosis were observed after 24 h of incubation and a 48-h incubation was found to be optimal for analysis of internucleosomal DNA fragmentation, which is one of the main biochemical hallmarks of programmed cell death. These cells are an easily isolated and inexpensive material for medical diagnostics. Therefore the apoptotic changes, together with the clastogenic effect seen in lymphocyte cultures, are proposed as a future analytical method for these toxins.

Intratracheal administration of microcystin-LR, and its distribution

Microcystin-LR (MCLR) was injected into mice intratracheally, absorption from the lungs was easy and it was confirmed that both the cause of death and lethality dose level were the same as by intraperitoneal injection treatment. An immunostaining method revealed that there was a time lag of about 60 min before accumulation of MCLR, and that it caused bleeding in the liver. Clearance from internal organs took about 2 weeks; during the initial stage (the first 2 days), the small intestine, kidney, cecum and large intestine were already involved. However, even after 2 weeks, small amounts of MCLR were still present in epithelial cells in the gastrointestinal mucosa.

Fulminant hepatocyte apoptosis in vivo following microcystin-LR administration to rats

Microcystin-LR (MCLR) is a cyanobacterial toxin responsible for human and livestock deaths worldwide. MCLR has also been implicated as a contributing factor in hepatocellular carcinoma. Following absorption, MCLR is taken up via a hepatocyte-specific bile acid carrier. Inside hepatocytes, MCLR selectively binds to protein phosphatases 1 and 2A, resulting in rapid, massive liver damage. However, the apoptotic nature of this toxicosis in rats has not been fully characterized as such at appropriate time points utilizing light and electron microscopy, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), and electrophoresis of hepatic DNA. Rats were administered intraperitoneal saline or MCLR at 500 microg/kg (0.5 micromol/kg) and necropsied at 3 or 9 hours. Light microscopy at 3 hours revealed massive, widespread apoptotic necrosis of the majority of hepatocytes. Hepatocytes were rounded and disassociated, with cell shrinkage, increased eosinophilia, and margination of nuclear chromatin or pyknosis. The apoptotic index increased from 0.03% +/- 0.02% in controls to 205% +/- 12% in MCLR-treated animals (p < or = 0.0001). At 3 hours, transmission electron microscopy revealed hepatocellular changes typical of apoptotic necrosis: rounding and disassociation of hepatocytes, loss of microvilli, and margination and condensation of nuclear chromatin. Laddering of hepatic DNA by electrophoresis and widespread TUNEL staining of hepatocytes were consistent with apoptosis. These results demonstrate that in rats, hepatic damage caused by MCLR is due to extremely rapid induction and progression of apoptosis in virtually every hepatocyte in the liver. This model of fulminant hepatic necrosis should be useful for increased characterization and understanding of the relationship between protein phosphatase inhibition and apoptosis.

Immunoaffinity column as clean-up tool for determination of trace amounts of microcystins in tap water

Trace amounts of microcystins (MCs) in drinking water should be monitored because of their potential hazard for human health as an environmental tumor promoter. We describe here a new clean-up tool with immunoaffinity column (IAC) for determination of trace amounts of MCs (from pg to microg/litre) in tap water. The water samples were concentrated with IAC clean-up and MCs levels were determined by HPLC with UV detection or enzyme-linked immunosorbent assay (ELISA). In the combination with HPLC analysis, mean recovery of microcystin-LR (MCLR),-RR and-YR spiked to tap water were 91.8%, 77.3% and 86.4%, respectively, in the range 2.5-100 microg/litre. The chromatogram of MCs-spiked tap water sample cleaned up with IAC showed effective elimination of the impurities compared to that with octadecyl silanized cartridge, which had been cleaned up with a conventional method. Also, in the combination with highly sensitive ELISA, mean recovery of MCLR spiked to tap water was 80% in the range 0.1-1000 ng/litre. The combined methods developed here can detect pg to microg/litre of MCs in tap water. The overall results indicated that IAC will be suitable as a clean-up tool for trace amounts of MCs in tap water.

First report on the distribution of orally administered microcystin-LR in mouse tissue using an immunostaining method

The purpose of this study was to investigate the distribution of microcystin-LR (MCLR) orally administered to mice using an immunostaining method. MCLR was orally dosed at 500 microg/kg to aged Balb/C and ICR mice and their lethality was 23.9%. The former was more sensitive to MCLR than the latter, suggesting that oral toxicity by MCLR is related to the animal strains tested, although the pathological and immunostaining changes were essentially the same in both strains. According to this method the distribution of MCLR and related compounds were indicated as the red staining. Particularly, livers of dead aged mice were intensively stained. The main route of absorption was considered to be the small intestine because the villi contained a large amount of MCLR in both surface epithelial cells and lamina propria, resulting in erosion. The absorbed MCLR was contained in blood plasma and moved to the liver, lung, and heart, and finally to capillaries of the whole body. Excretion of MCLR was shown in the mucous from goblet cells in both the small intestine and large intestine.