Cyclosporin A--a chemoprotectant against microcystin-LR toxicity

The role of IL-8/CXCR2 signaling in microcystin-LR triggered endothelial cell activation and increased vascular permeability

Microcystins are a family of cyclic heptapeptide toxins naturally produced by freshwater cyanobacteria. Microcystin-LR (MCLR) is believed to be the most toxic and common one with various pathological effects on human and mammals. However, the effects of MCLR on endothelial cells and vascular homeostasis have been largely unknown. We explored the mRNA and protein expression changes of several pro-inflammatory mediators in human umbilical vein endothelial cells (HUVECs) and C57BC/6 mice exposed to MCLR. Tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), especially interleukin-8 (IL-8) were remarkably upregulated both in endothelial cells and in serum. Increased endothelial permeability in vitro and chronic microvascular permeability in animals were also observed. Silencing the IL-8 gene with siRNA or blocking its cognate receptor, CXC-chemokine receptor type 2 (CXCR2), by a specific inhibitor efficiently prevented the MCLR induced leakage. These observations indicate a novel insight of inflammation triggered property of MCLR via IL-8/CXCR2 signaling, suggesting CXCR2 as a target molecule in protective strategy against the wide range pollution of microcystin.

Repeated five-day administration of L-BMAA, microcystin-LR, or as mixture, in adult C57BL/6 mice - lack of adverse cognitive effects

The cyanobacterial toxins β-methylamino-L-alanine (L-BMAA) and microcystin-LR (MC-LR; a potent liver toxin) are suspected to cause neurological disorders. Adult male C57BL/6JOlaHsd mice aged approximately 11 months were subcutaneously injected for five consecutive days with L-BMAA and microcystin-LR alone, or as a mixture. A dose-range study determined a tolerable daily dose to be ~31 µg MC-LR/kg BW/day based on survival, serum liver status enzymes, and relative liver and kidney weight. Mice tolerating the first one-two doses also tolerated the subsequent three-four doses indicating adaptation. The LD50 was 43-50 μg MC-LR/kg BW. Long-term effects (up to 10 weeks) on spatial learning and memory performance was investigated using a Barnes maze, were mice were given 30 µg MC-LR/kg BW and/or 30 mg L-BMAA/kg BW either alone or in mixture for five consecutive days. Anxiety, general locomotor activity, willingness to explore, hippocampal and peri-postrhinal cortex dependent memory was investigated after eight weeks using Open field combined with Novel location/Novel object recognition tests. Toxin exposed animals did not perform worse than controls, and MC-LR exposed animals performed somewhat better during the first Barnes maze re-test session. MC-LR exposed mice rapidly lost up to ~5% body weight, but regained weight from day eight.

Microcystin-LR exposure induces oxidative damage in Caenorhabditis elegans: Protective effect of lutein extracted from marigold flowers

Microcystin-LR (MIC-LR) is a hepatotoxin, with toxicity mechanisms linked to oxidative stress. Besides, neurotoxic effects of MIC-LR have recently been described. Herein, we evaluated the effects of environmentally important concentrations of MIC-LR (1, 10, 100, 250, and 500 μg/L) on oxidative stress markers and the survival rate of the nematode Caenorhabditis elegans (C. elegans). In addition, a possible protective effect of the carotenoid lutein (LUT) extracted from marigold flowers against MIC-LR toxicity was investigated. Higher concentrations (250 and 500 μg/L) of MIC-LR induced the generation of reactive oxygen species (ROS) and resulted in a survival loss in C elegans. Meanwhile, all MIC-LR concentrations caused an increase in the superoxide dismutase (SOD) expression, while catalase (CAT) expression was only affected at 500 μg/L. The carotenoid LUT prevented the ROS generation, impairment in the CAT expression, and the survival loss induced by MIC-LR in C. elegans. Our results confirm the toxicity of MIC-LR even in a liver-lacking invertebrate and the involvement of oxidative events in this response. Additionally, LUT appears to be able to mitigate the MIC-LR toxic effects.

Potential Use of Chemoprotectants against the Toxic Effects of Cyanotoxins: A Review

Cyanobacterial toxins, particularly microcystins (MCs) and cylindrospermopsin (CYN), are responsible for toxic effects in humans and wildlife. In order to counteract or prevent their toxicity, various strategies have been followed, such as the potential application of chemoprotectants. A review of the main substances evaluated for this aim, as well as the doses and their influence on cyanotoxin-induced toxicity, has been performed. A search of the literature shows that research on MCs is much more abundant than research on CYN. Among chemoprotectants, antioxidant compounds are the most extensively studied, probably because it is well known that oxidative stress is one of the toxic mechanisms common to both toxins. In this group, vitamin E seems to have the strongest protectant effect for both cyanotoxins. Transport inhibitors have also been studied in the case of MCs, as CYN cellular uptake is not yet fully elucidated. Further research is needed because systematic studies are lacking. Moreover, more realistic exposure scenarios, including cyanotoxin mixtures and the concomitant use of chemoprotectants, should be considered.

Liver failure in a dog following suspected ingestion of blue-green algae (Microcystis spp.): a case report and review of the toxin

A 2.5 yr old spayed female Weimaraner presented after ingestion of blue-green algae (Microcystis spp.). One day prior to presentation, the patient was swimming at a local lake known to be contaminated with high levels of blue-green algae that was responsible for deaths of several other dogs the same summer. The patient presented 24 hr after exposure with vomiting, inappetence, weakness, and lethargy. Blood work at the time of admission was consistent with acute hepatic failure, characteristic findings of intoxication by Microcystis spp. Diagnosis was suspected by analyzing a water sample from the location where the patient was swimming. Supportive care including fluids, fresh frozen plasma, whole blood, vitamin K, B complex vitamins, S-adenosyl methionine, and Silybum marianum were started. The patient was discharged on supportive medications, and follow-up blood work showed continued improvement. Ingestion is typically fatal for most patients. This is the first canine to be reported in the literature to survive treatment after known exposure.

κ-Selenocarrageenan prevents microcystin-LR-induced hepatotoxicity in BALB/c mice

Microcystins (MCs) are a family of cyclic heptapeptides that are produced by blooming algae Microcystis. MCs have been implicated in the development of liver cancer, necrosis and even intrahepatic bleeding. Effective prophylactic approaches and complete removal of MCs are urgently needed. Accumulating evidence suggests that microcystin-LR (MC-LR)-induced damage is accompanied by oxidative stress. Supplementation of Se can enhance resistance to oxidative stress. Therefore, in the present study, we investigated the protective effects of κ-Selenocarrageenan (Se-Car), a kind of organic Se compound, in Balb/c mice exposed to MC-LR. Our results proved that Se-Car could significantly ameliorate the hepatic damage induced by MC-LR, including serum markers of liver dysfunction, oxidative damages and histological alterations. Furthermore, Se-Car could significantly alleviate the up-regulation of the molecular targets indicating mitochondrial dysfunction and endoplasmic reticulum stress induced by MC-LR. In conclusion, Se-Car showed clear protection against toxicity induced by MC-LR. Thus, Se-Car could be useful as a new category of anti-MC-LR toxicity reagent.

Hepatoprotective efficacy of certain flavonoids against microcystin induced toxicity in mice

Toxic cyanobacteria (blue-green algae) water blooms have become a serious problem in several industrialized areas of the world. Microcystin-LR (MC-LR) is a cyanobacterial heptapeptide that represents acute and chronic hazards to animal and human health. Identification of suitable chemprotectants against microcystin is essential considering human health hazards. In the present study, we have evaluated the protective efficacy of three flavanoids namely quercetin (200 mg/kg), silybin (400 mg/kg), and morin (400 mg/kg)] pretreatment against microcystin toxicity (0.75 LD(50), 57.5 microg/kg) in mice. Various biochemical variables were measured to study the recovery profile of protected animals at 1- and 3-days post-toxin treatment. The serum alanine amino transferase (ALT) shows 17-fold increase in MC-LR treated animals compared with control group at 1 day. The silybin and quercetin group showed a decrease in level of ALT compared with MC-LR group but still higher than control group. No significant protection was observed with aspartate aminotransaminase (AST) and lactate dehydrogenase (LDH) levels in flavanoid-treated groups at 1-day post-treatment. But at 3 days, the serum levels of AST and ALT were normalized to control values, but the serum LDH levels were still significantly higher than the control group. No significant changes were observed in glutathione peroxidase and reduced glutathione levels at both 1- and 3-day postexposure. The catalase activity shows a significant decrease in quercetin-treated animals at 3-day postexposure. The protein phosphatase was significantly inhibited in MC-LR group compared to control. The silybin pretreated group showed recovery after 1 day. At 3 days, the PPAse activity was reversed to control values in all the flavanoid-treated groups. Immunoblotting analysis showed microcystin-PPAse adduct in liver tissues of toxin-treated as well as flavanoid-treated mice even after 3 days. The results of this study show that flavanoids, quercetin, silybin, and morin could reverse the hepatotoxic effects of MC-LR in vivo.

Ecotoxicological effects of selected cyanobacterial secondary metabolites: a short review

Cyanobacteria are one of the most diverse groups of gram-negative photosynthetic prokaryotes. Many of them are able to produce a wide range of toxic secondary metabolites. These cyanobacterial toxins can be classified in five different groups: hepatotoxins, neurotoxins, cytotoxins, dermatotoxins, and irritant toxins (lipopolysaccharides). Cyanobacterial blooms are hazardous due to this production of secondary metabolites and endotoxins, which could be toxic to animals and plants. Many of the freshwater cyanobacterial blooms include species of the toxigenic genera Microcystis, Anabaena, or Plankthotrix. These compounds differ in mechanisms of uptake, affected organs, and molecular mode of action. In this review, the main focus is the aquatic environment and the effects of these toxins to the organisms living there. Some basic toxic mechanisms will be discussed in comparison to the mammalian system.

Protective efficacy and the recovery profile of certain chemoprotectants against lethal poisoning by microcystin-LR 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. Development of suitable chemoprotectants against microcystin is essential considering the human health importance. In the present study, three agents cyclosporin-A (10mg/kg), rifampin (25mg/kg) and silymarin (400mg/kg) pre-treatment gave 100% protection against lethal dose of microcystin-LR (100 microg/kg). Various biochemical parameters were evaluated to study the recovery profile of protected animals at 1, 3, 7 and 14 days post-toxin treatment. There was significant depletion of hepatic glutathione in protected animals compared to control group till 7 days post-treatment but normalised by 14 days. Similarly enhanced hepatic lipid peroxidation, inhibition of protein phosphatase activity was observed till 3-7 days post-treatment in protected animals. Elevated levels of enzymes alanine amino transferase, lactate dehydrogenase and sorbitol dehydrogenase were observed in serum at 1 day post-treatment. All the biochemical variables reached control levels by 14 day post-treatment. Immunoblotting analyses of liver homogenates showed microcystin-protein phosphatase adduct in liver samples of toxin treated as well as antidote-protected animals. The adduct could be seen even after 14 days post-toxin treatment. The study shows that though cyclosporin-A, rifampin and silymarin could offer 100% protection against microcystin-LR induced lethality many of the toxic manifestations are persistent and could not be reversed till 7 days.

Therapy and prophylaxis of inhaled biological toxins

This review highlights the current lack of therapeutic and prophylactic treatments for use against inhaled biological toxins, especially those considered as potential biological warfare (BW) or terrorist threats. Although vaccine development remains a priority, the use of rapidly deployable adjunctive therapeutic or prophylactic drugs could be life-saving in severe cases of intoxication or where vaccination has not been possible or immunity not established. The current lack of such drugs is due to many factors. Thus, methods involving molecular modelling are limited by the extent to which the cellular receptor sites and mode of action and structure of a toxin need to be known. There is also our general lack of knowledge of what effect individual toxins will have when inhaled into the lungs - whether and to what extent the action will be cell specific and cytotoxic or rather an acute inflammatory response requiring the use of immunomodulators. Possible sources of specific high-affinity toxin antagonists being investigated include monoclonal antibodies, selected oligonucleotides (aptamers) and derivatized dendritic polymers (dendrimers). The initial selection of suitable agents of these kinds can be made using cytotoxicity assays involving cultured normal human lung cells and a range of suitable indicators. The possibility that a mixture of selected antibody, aptamer or dendrimer-based materials for one or more toxins could be delivered simultaneously as injections or as inhaled aerosol sprays should be investigated.

Renal effects of supernatant from rat peritoneal macrophages activated by microcystin-LR: role protein mediators

We have demonstrated previously that microcystin-LR promoted some renal alterations using the isolated perfused rat kidney preparation. However, these effects were not proved to be direct or indirect. The aim of the current work is to examine the renal effects promoted by supernatants from rat macrophages stimulated with microcystin-LR and the role of inflammatory mediators. Peritoneal macrophages were collected previously and were incubated for 1h in fresh medium (control) and in medium containing microcystin-LR. Dexamethasone, quinacrine, thalidomide and cycloheximide were administered 30 min before microcystin-LR. Supernatants of macrophages stimulated with or without pharmacological inhibitors were added on the perfused rat kidney model. The infusion of macrophages supernatants stimulated by microcystin-LR caused significant increases in renal vascular resistance (C: 4.93+/-0.33 vs T: 5.15+/-0.21), glomerular filtration rate (C: 0.559+/-0.008 vs T: 0.978+/-0.15) and urinary flow (C: 0.16+/-0.01 vs T: 0.23+/-0.03). Cycloheximide, quinacrine and dexamethasone blocked these effects and thalidomide blocked renal vascular resistance. Macrophages stimulated by microcystin-LR release mediators capable of promoting nephotoxicity in isolated perfused rat kidney. Phospholipase A(2), TNF-alpha and other protein mediators appear to be involved on its renal toxic mechanism.

The toxicology of microcystins

Microcystins are a family of more than 50 structurally similar hepatotoxins produced by species of freshwater cyanobacteria, primarily Microcystis aeruginosa. They are monocyclic heptapeptides, characterised by some invariant amino acids, including one of unusual structure which is essential for expression of toxicity. Microcystins are chemically stable, but suffer biodegradation in reservoir waters. The most common member of the family, microcystin-LR (L and R identifying the 2 variable amino acids, in this case leucine and arginine respectively) has an LD50 in mice and rats of 36-122 microg/kg by various routes, including aerosol inhalation. Although human illnesses attributed to microcystins include gastroenteritis and allergic/irritation reactions, the primary target of the toxin is the liver, where disruption of the cytoskeleton, consequent on inhibition of protein phosphatases 1 and 2A, causes massive hepatic haemorrhage. Microcystins are tight-binding inhibitors of these protein phosphatases, with inhibition constants in the nanomolar range or lower. Uptake of microcystins into the liver occurs via a carrier-mediated transport system, and several inhibitors of uptake can antagonise the toxic effects of microcystins. The most effective of these is the antibiotic rifampin (a drug approved for clinical use), which protects mice and rats against microcystin-induced lethality when given prophylactically and, in some cases, therapeutically.

Immunopharmacologic agents in the amelioration of hepatic injuries

A number of immunomodulating agents of different origin have been shown to reduce liver injury of various etiologies. Immunostimulants like levamisole, BCG, a protein polysaccharide from myceria Coriolus vesicolor PS-K, a streptoccocal preparation OK-432 and immunomodulators like N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) and its analogs. Selective T-cell suppressors like the polypeptide cyclosporine A (CsA) and the macrolide FK 506 (tacrolimus) have also been claimed to possess hepatoprotrophic or hepatoprotective properties at low doses. The aim of this review article is to highlight the interplay between the administration of immunomodulating agents and the amelioration of hepatic injuries. Hepatic effects of exogenous immunomodulators are discussed with special focus on the most widely used immunosuppressive agents, CsA and tacrolimus. An important question exists as to whether these potential hepatoprotective effects are related mechanistically to the immune system or are working at different levels. Due to the differences in effects and modes of actions of various immunoactive substances presented herein, a common mechanism for their cytoprotective effects cannot be formulated at this stage. Levamisole and cyanidanol may protect cells against necrosis by acting as free radical scavengers. MDP and its analogs reduce carbon tetrachloride-elevated (CCl4) lipid peroxides and their protective effects are primarily on hepatic cytoplasmic membranes where lipid peroxidation and calcium homeostasis interact. MDP reduced CCl4-elevated calcium in both intact hepatocytes and in the post microsomal supernatant suggest that the influx of extracellular calcium across plasma membrane is affected. Elevations of intracellular calcium above a threshold are involved in: the stimulation of Ca2+-sensitive enzymes such as phospholipase A2, endonucleases and proteases, the conversion of xanthine dehydrogenase to xanthine oxidase and the formation of free radicals, all of which disturb biomembranes. MDP and its analogs, in a specific dose range, may act to maintain intracellular calcium within physiological ranges. Highly complex cellular signalling systems, including calcium, are involved in the explanation of the mechanism of the immunosuppressive effect of CsA and tacrolimus. The hepatoprotective effects of these selective immunosuppressive agents, however, are independent of the inhibition of T-cell activation. The cyclophilin and tacrolimus binding proteins of the mitochondria are the receptors for these compounds and play a key role in the regulation of mitochondrial permeability transition pores. CsA or tacrolimus inhibition of mitochondrial permeability transition pores does not require interaction with calcineurin, indicating a dissociation between immunosuppression and mitochondrial protection. The involvement of intracellular or intramitochondrial proteins in the modulation of mitochondrial permeability transition pores with the creation of a partially impermeable state for Ca2+ movement in drug-treated mitochondria and the dissociation of this effect from immunomodulatory actions potentially offers new and promising approaches for the development of new pharmacologicals targeted at therapeutic intervention. Clinical trials of these drugs as hepatoprotective agents are limited. Use of CsA in patients with primary biliary cirrhosis and autoimmune chronic hepatitis and in cirrhotic animal models produced by chronic administration of CCl4 have yielded encouraging results. It seems that this class of compounds may be of substantial benefit in liver protection against many pathological conditions where disturbance in mitochondrial function and in Ca2+ homeostasis appear to be prerequisites for cell injury.

Cyclosporin-mediated inhibition of bovine calcineurin by cyclophilins A and B

The Ca(2+)- and calmodulin-dependent protein phosphatase calcineurin is inhibited by the immunosuppressant drug cyclosporin A in the presence of cyclophilin A or B. Of the two isoforms, cyclophilin B is more potent by a factor of 2-5 when either the phosphoprotein [32P]casein or the [32P]phosphoserine [Ser(32P)] form of the 19-residue bovine cardiac cAMP-dependent protein kinase regulatory subunit peptide RII, [Ser(32P)15]RII, is used as substrate. With [Ser(32P15]RII as substrate, the concentrations of the cyclosporin A.cyclophilin A and cyclosporin A.cyclophilin B complexes, which cause 50% inhibition of calcineurin activity, are 120 and 50 nM, respectively. Lowering the concentration of calcineurin 80% with [32P]casein as substrate lowered the apparent inhibition constant for each complex even further; 50% inhibition of calcineurin was observed at 40 nM for cyclosporin A.cyclophilin A, whereas it was less than 10 nM for cyclosporin A.cyclophilin B. In all inhibition assays with [32P]casein or [Ser(32P)15]RII, the concentration of calcineurin required for measurable phosphatase activity is such that these complexes behave as tight-binding inhibitors of calcineurin, and steady-state kinetics cannot be used to assess inhibition patterns or Ki values. Limited trypsinization of calcineurin produces a fragment that is still inhibited, indicating that the interaction of cyclosporin.cyclophilin with calcineurin does not require either calmodulin or Ca2+.