Alteration and recovery of the antioxidant system induced by sub-chronic exposure to microcystin-LR in mice: Its relation to liver lipid composition

Microcystin-LR induces fatty liver metabolic disease in zebrafish through the PPARα-NOD1 pathway: In vivo, in vitro, and in silico investigations

Hepatic lipid metabolism dysfunction caused by cyanobacteria bloom-released microcystin-LR (MC-LR) contributes to the development of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis (NASH), thereby severely impacting the health and safety of animals and humans. In this study, the effects and mechanisms of different environmental concentrations of MC-LR (0, 0.1, 1, and 10 μg/L) on fatty liver metabolic disease in zebrafish were investigated using in vivo, in vitro, and in silico models. Exposure to 10 μg/L of MC-LR-induced NASH in zebrafish, characterized by hepatic steatosis, toxic saturated fatty acid (SFA) accumulation, and inflammation. Analyses of the liver transcriptome, molecular docking, molecular dynamics simulation, and in vitro experiments indicated that PPARα might be a key molecular target in MC-LR-induced steatosis and in toxic-SFA accumulation. The results obtained from molecular docking, molecular dynamics simulation, and NOD1-inhibitor experiments further revealed that MC-LR-derived SFAs, such as palmitic acid, could target the NOD1 protein to initiate hepatitis in zebrafish. The benchmark dose model identified palmitic acid as a sensitive indicator of MC-LR-induced NASH, and the point of departure value was estimated to be 1.634 μg/L. In conclusion, our findings offer new insights into the mechanism of MC-LR-induced NASH and aid in the prognosis and treatment of MC-LR-related liver metabolic diseases, as well as in assessing the health risks associated with cyanobacterial blooms.

Involvement of reactive oxygen species (ROS) in the hepatopancreatic cytotoxicity, oxidative stress, and apoptosis induced by microcystin-LR in Eriocheir sinensis

There is limited knowledge about the toxicity of Microcystin-LR (MC-LR) in crustaceans, despite its high toxicity to aquatic organisms. This research aimed to explore the effects of MC-LR on cytotoxicity, oxidative stress, and apoptosis in the hepatopancreas of Eriocheir sinensis, as well as elucidate the involvement of reactive oxygen species (ROS) and potential mechanisms of toxicity. In vivo and in vitro exposures of crabs to MC-LR and N-acetylcysteine (NAC) were performed, followed by assessments of cell morphology, viability, tissue pathology, biochemical indicators, gene expression, and hepatopancreatic transcriptome. Results revealed that MC-LR facilitated the entry of the MC-LR transporter oatp3a into hepatopancreatic cells, leading to upregulated expression of phase I detoxification enzyme genes (cyp4c, cyp2e1, and cyp3) and downregulated the phase II enzyme genes (gst1, gpx, gsr2, gclc, and nqo1), resulting in increased ROS levels and cytotoxic effects. MC-LR exhibited cytotoxicity, reducing cell viability and inducing abnormal nuclear morphology with a 48 h-IC50 value of approximately 120 μm. MC-LR exposure caused biochemical changes indicative of oxidative stress damage and evident hepatopancreatic lesions. Additionally, MC-LR exposure regulated the levels of bax and bcl-2 expression, activating caspase 3 and 6 to induce cell apoptosis. Intervention with NAC attenuated MC-LR-induced ROS production and associated toxic effects. Transcriptome analysis revealed enrichment of differentially expressed genes in pathways related to cytochrome P450-mediated xenobiotic metabolism and the FoxO signaling pathway. These findings shed light on the potential mechanisms underlying MC-LR toxicity and provide valuable references for further research and conservation efforts regarding the health of aquatic animals.

Cyanotoxins Increase Cytotoxicity and Promote Nonalcoholic Fatty Liver Disease Progression by Enhancing Cell Steatosis

Freshwater prokaryotic cyanobacteria within harmful algal blooms produce cyanotoxins which are considered major pollutants in the aquatic system. Direct exposure to cyanotoxins through inhalation, skin contact, or ingestion of contaminated drinking water can target the liver and may cause hepatotoxicity. In the current study, we investigated the effect of low concentrations of cyanotoxins on cytotoxicity, inflammation, modulation of unfolded protein response (UPR), steatosis, and fibrosis signaling in human hepatocytes and liver cell models. Exposure to low concentrations of microcystin-LR (MC-LR), microcystin-RR (MC-RR), nodularin (NOD), and cylindrospermopsin (CYN) in human bipotent progenitor cell line HepaRG and hepatocellular carcinoma (HCC) cell lines HepG2 and SK-Hep1 resulted in increased cell toxicity. MC-LR, NOD, and CYN differentially regulated inflammatory signaling, activated UPR signaling and lipogenic gene expression, and induced cellular steatosis and fibrotic signaling in HCC cells. MC-LR, NOD, and CYN also regulated AKT/mTOR signaling and inhibited autophagy. Chronic exposure to MC-LR, NOD, and CYN upregulated the expression of lipogenic and fibrosis biomarkers. Moreover, RNA sequencing (RNA seq) data suggested that exposure of human hepatocytes, HepaRG, and HCC HepG2 cells to MC-LR and CYN modulated expression levels of several genes that regulate non-alcoholic fatty liver disease (NAFLD). Our data suggest that low concentrations of cyanotoxins can cause hepatotoxicity and cell steatosis and promote NAFLD progression.

Insight into the Molecular Mechanism for the Discrepant Inhibition of Microcystins (MCLR, LA, LF, LW, LY) on Protein Phosphatase 2A

Microcystins (MCs) exhibit diversified inhibition effects on protein phosphatases (PPs) due to their structural differences. To fully evaluate the potential mechanism for the discrepant inhibition effects, the five most frequent MCs with varying residues at position Z4 were selected as the tested toxins. Their inhibition sequence on PP2A was detected as follows: MCLR > MCLW > MCLA > MCLF > MCLY. Combined with homology modeling and molecular docking technology, the major interaction parameters between the MCs and PP2A were obtained. The correlation analysis for the major interaction parameters and inhibition effects showed that the hydrophobicity of Z4 had an important influence on the interaction of the MCs to PP2A. The introduction of hydrophobic Z4 directly weakened hydrogen bonds Z4→Pro213 and Z4←Arg214, indirectly weakened hydrogen bonds Adda5←Asn117, Glu6←Arg89, and MeAsp3←Arg89, but indirectly enhanced ionic bonds Glu6←Arg89, Glu6-Mn12+, and Glu6-Mn22+. In this way, the combination of the MCs with PP2A was blocked, and thus, the interactions between PP2A and the Mn2+ ions (in the catalytic center) were further affected; metal bonds Asp85-Mn12+ and Asp85-Mn22+ were weakened, while metal bond His241-Mn12+ was enhanced. As a result, the interactions in the catalytic center were inhibited to varying degrees, resulting in the reduced toxicity of MCs.

MCLR-elicited hepatic fibrosis and carcinogenic gene expression changes persist in rats with diet-induced nonalcoholic steatohepatitis through a 4-week recovery period

Nonalcoholic steatohepatitis (NASH) causes liver extracellular matrix (ECM) remodeling and is a risk factor for fibrosis and hepatocellular carcinoma (HCC). Microcystin-LR (MCLR) is a hepatotoxin produced by fresh-water cyanobacteria that causes a NASH-like phenotype, liver fibrosis, and is also a risk factor for HCC. The focus of the current study was to investigate and compare hepatic recovery after cessation of MCLR exposure in healthy versus NASH animals. Male Sprague-Dawley rats were fed either a control or a high fat/high cholesterol (HFHC) diet for eight weeks. Animals received either vehicle or 30 μg/kg MCLR (i.p: 2 weeks, alternate days). Animals were euthanized at one of three time points: at the completion of the MCLR exposure period and after 2 and 4 weeks of recovery. Histological staining suggested that after four weeks of recovery the MCLR-exposed HFHC group had less steatosis and more fibrosis compared to the vehicle-exposed HFHC group and MCLR-exposed control group. RNA-Seq analysis revealed dysregulation of ECM genes after MCLR exposure in both control and HFHC groups that persisted only in the HFHC groups during recovery. After 4 weeks of recovery, MCLR hepatotoxicity in pre-existing NASH persistently dysregulated genes related to cellular differentiation and HCC. These data demonstrate impaired hepatic recovery and persistent carcinogenic changes after MCLR toxicity in pre-existing NASH.

A Review of Nephrotoxicity of Microcystins

Cyanobacterial blooms triggered by eutrophication and climate change have become a global public health issue. The toxic metabolites microcystins (MCs) generated by cyanobacteria can accumulate in food chain and contaminate water, thus posing a potential threat to human and animals health. Studies have suggested that aside liver, the kidney may be another target organ of MCs intoxication. Therefore, this review provides various evidences on the nephrotoxicity of MCs. The review concludes that nephrotoxicity of MCs may be related to inhibition of protein phosphatases and excessive production of reactive oxygen species, cytoskeleton disruption, endoplasmic reticulum stress, DNA damage and cell apoptosis. To protect human from MCs toxic consequences, this paper also puts forward some directions for further research.

[D-Leu1]MC-LR Has Lower PP1 Inhibitory Capability and Greater Toxic Potency than MC-LR in Animal and Plant Tissues

Two microcystins, MC-LR and [D-Leu¹]MC-LR, present in La Plata Basin blooms, are differentiated by substitution of D-Alanine for D-Leucine at position 1. Our objective was to evaluate acute toxicity of [D-Leu¹]MC-LR and MC-LR in mice (N:NIH Swiss) and beans (Phaseolus vulgaris). We observed variations in [D-Leu¹]MC-LR lethal doses with respect to those reported for MC-LR (100 μg/kg), with an increased liver/body weight ratio and intrahepatic hemorrhages in mice exposed to 50–200 μg [D-Leu¹]MC-LR/kg and slight steatosis after a single 25 μg [D-Leu¹]MC-LR/kg i.p. dose. Our study in the plant model showed alterations in germination, development, morphology and TBARs levels after a single contact with the toxins during imbibition (3.5 and 15 µg/mL), those treated with [D-Leu¹]MC-LR being more affected than those treated with the same concentration of MC-LR. Protein phosphatase 1 (PP1) IC₅₀ values were 40.6 nM and 5.3 nM for [D-Leu¹]MC-LR and MC-LR, respectively. However, the total phosphatase activity test in root homogenate showed 60% inhibition for [D-Leu¹]MC-LR and 12% for MC-LR. In mouse liver homogenate, 50% inhibition was observed for [D-Leu¹]MC-LR and 40% for MC-LR. Our findings indicate the need for further research into [D-Leu¹]MC-LR toxicity since together with oxidative stress, the possible inhibition of other phosphatases could explain the differences detected in the potency of the two toxins.

[D-Leu1]MC-LR and MC-LR: A Small-Large Difference: Significantly Different Effects on Phaseolus vulgaris L. (Fabaceae) Growth and Phototropic Response after Single Contact during Imbibition with Each of These Microcystin Variants

[D-Leu¹]MC-LR and MC-LR, two microcystins differing in one amino acid, constitute a sanitary and environmental problem owing to their frequent and concomitant presence in water bodies of the Americas and their association with human intoxication during recreational exposure to cyanobacterial bloom. Present in reservoirs used for irrigation as well, they can generate problems in the development of crops such as Phaseolus vulgaris, of nutritional and economic interest to the region. Although numerous works address the toxic effects of MC-LR, information on the toxicity of [D-Leu¹]MC-LR is limited. Our objective was to study the toxic effects of [D-Leu¹]MC-LR and MC-LR (3.5 µg/ml) on P. vulgaris after a single contact at the imbibition stage. Our findings indicate that 10 days post treatment, [D-Leu¹]MC-LR generates morphological and physiological alterations more pronounced than those caused by MC-LR. In addition to the alterations produced by [D-Leu¹]MC-LR in the development of seedlings and the structure of the leaves, roots and stems, we also found alterations in leaf stomatal density and conductivity, a longer delay in the phototropic response and a decrease in the maximum curvature angles achieved with respect to that observed for MC-LR. Our findings indicate that these alterations are linked to the greater inhibition of phosphatase activity generated by [D-Leu¹]MC-LR, rather than to oxidative damage. We observed that 30 days after treatment with MC-LR, plants presented better development and recovery than those treated with [D-Leu¹]MC-LR. Further studies are required on [D-Leu¹]MC-LR and MC-LR toxicity and their underlying mechanisms of action.

Cylindrospermopsin-Microcystin-LR Combinations May Induce Genotoxic and Histopathological Damage in Rats

Cylindrospermopsin (CYN) and microcystins (MC) are cyanotoxins that can occur simultaneously in contaminated water and food. CYN/MC-LR mixtures previously investigated in vitro showed an induction of micronucleus (MN) formation only in the presence of the metabolic fraction S9. When this is the case, the European Food Safety Authority recommends a follow up to in vivo testing. Thus, rats were orally exposed to 7.5 + 75, 23.7 + 237, and 75 + 750 μg CYN/MC-LR/kg body weight (b.w.). The MN test in bone marrow was performed, and the standard and modified comet assays were carried out to measure DNA strand breaks or oxidative DNA damage in stomach, liver, and blood cells. The results revealed an increase in MN formation in bone marrow, at all the assayed doses. However, no DNA strand breaks nor oxidative DNA damage were induced, as shown in the comet assays. The histopathological study indicated alterations only in the highest dose group. Liver was the target organ showing fatty degeneration and necrotic hepatocytes in centrilobular areas, as well as a light mononuclear inflammatory periportal infiltrate. Additionally, the stomach had flaking epithelium and mild necrosis of epithelial cells. Therefore, the combined exposure to cyanotoxins may induce genotoxic and histopathological damage in vivo.

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

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

Sub-Chronic Microcystin-LR Liver Toxicity in Preexisting Diet-Induced Nonalcoholic Steatohepatitis in Rats

Microcystin-LR (MCLR) is a hepatotoxic cyanotoxin reported to cause a phenotype similar to nonalcoholic steatohepatitis (NASH). NASH is a common progressive liver disease that advances in severity due to exogenous stressors such as poor diet and toxicant exposure. Our objective was to determine how sub-chronic MCLR toxicity affects preexisting diet-induced NASH. Sprague-Dawley rats were fed one of three diets for 10 weeks: control, methionine and choline deficient (MCD), or high fat/high cholesterol (HFHC). After six weeks of diet, animals received vehicle, 10 µg/kg, or 30 µg/kg MCLR via intraperitoneal injection every other day for the final 4 weeks. Incidence and severity scoring of histopathology endpoints suggested that MCLR toxicity drove NASH to a less fatty and more fibrotic state. In general, expression of genes involved in de novo lipogenesis and fatty acid esterification were altered in favor of decreased steatosis. The higher MCLR dose increased expression of genes involved in fibrosis and inflammation in the control and HFHC groups. These data suggest MCLR toxicity in the context of preexisting NASH may drive the liver to a more severe phenotype that resembles burnt-out NASH.

Nonalcoholic fatty liver disease alters microcystin-LR toxicokinetics and acute toxicity

Microcystin-LR (MCLR) is a cyanotoxin produced by blue-green algae that causes liver and kidney toxicities. MCLR toxicity is dependent on cellular uptake through the organic anion transporting polypeptide (OATP) transporters. Nonalcoholic fatty liver disease (NAFLD) progresses through multiple stages, alters expression of hepatic OATPs, and is associated with chronic kidney disease. The purpose of this study was to determine whether NAFLD increases systemic exposure to MCLR and influences acute liver and kidney toxicities. Rats were fed a control diet or two dietary models of NAFLD; methionine and choline deficient (MCD) or high fat/high cholesterol (HFHC). Two studies were performed in these groups: 1) a single dose intravenous toxicokinetic study (20 μg/kg), and 2) a single dose intraperitoneal toxicity study (60 μg/kg). Compared to control rats, plasma MCLR area under the concentration-time curve (AUC) in MCD rats doubled, whereas biliary clearance (Clbil) was unchanged; in contrast, plasma AUC in HFHC rats was unchanged, whereas Clbil approximately doubled. Less MCLR bound to PP2A was observed in the liver of MCD rats. This shift in exposure decreased the severity of liver pathology only in the MCD rats after a single toxic dose of MCLR (60 μg/kg). In contrast, the single toxic dose of MCLR increased hepatic inflammation, plasma cholesterol, proteinuria, and urinary KIM1 in HFHC rats more than MCLR exposed control rats. In conclusion, rodent models of NAFLD alter MCLR toxicokinetics and acute toxicity and may have implications for liver and kidney pathologies in NAFLD patients.

Amelioratory effect of coenzyme Q10 on potential human carcinogen Microcystin-LR induced toxicity in mice

Microcystins are a group of cyclic heptapeptide toxins produced by cyanobacteria. More than 100 microcystin analogues have been detected, among which microcystin-LR is the most abundant and toxic variant. Present study was designed to reveal whether potential human carcinogen microcystin-LR could imbalance the glycolytic-oxidative-nitrosative status of heart, kidney and spleen of mice and also to explore the amelioratory effect of coenzyme Q10 on microcystin-LR induced toxicity. Microcystin-LR was administered at a dose of 10 μg/kg bw/day, ip for 14 days in male mice. In microcystin-LR treated mice as compared to control, significant increase in the level of lipid peroxidation, hydrogen peroxide, lactate dehydrogenase, nitric oxide with a concomitant decrease in the level of glutathione was observed, suggesting microcystin-LR induced toxicity via induction of oxidative-nitrosative-glycolytic pathway. Although several studies have evaluated numerous antioxidants but still there is no effective chemoprotectant against microcystin-LR induced toxicity. When microcystin-LR treated mice were co-administered coenzyme Q10 (10 mg/kg bw/day, im) for 14 days, it was observed that coenzyme Q10 ameliorates microcystin-LR induced toxicity via modulation of glycolytic-oxidative-nitrosative stress pathway. Thus, the results suggest that coenzyme Q10 has a potential to be developed as preventive agent against microcystin-LR induced toxicity.

Chemical proteomic analysis of the potential toxicological mechanisms of microcystin-RR in zebrafish (Danio rerio) liver

Microcystins (MCs) are common toxins produced by freshwater cyanobacteria, and they represent a potential health risk to aquatic organisms and animals, including humans. Specific inhibition of protein phosphatases 1 and 2A is considered the typical mechanism of MCs toxicity, but the exact mechanism has not been fully elucidated. To further our understanding of the toxicological mechanisms induced by MCs, this study is the first to use a chemical proteomic approach to screen proteins that exhibit special interactions with MC-arginine-arginine (MC-RR) from zebrafish (Danio rerio) liver. Seventeen proteins were identified via affinity blocking test. Integration of the results of previous studies and this study revealed that these proteins play a crucial role in various toxic phenomena of liver induced by MCs, such as the disruption of cytoskeleton assembly, oxidative stress, and metabolic disorder. Moreover, in addition to inhibition of protein phosphate activity, the overall toxicity of MCs was simultaneously modulated by the distribution of MCs in cells and their interactions with other target proteins. These results provide new insight into the mechanisms of hepatotoxicity induced by MCs. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1206-1216, 2016.

Accumulation and detoxification dynamics of microcystin-LR and antioxidant responses in male red swamp crayfish Procambarus clarkii

MC-LR is one of major microcystin isoforms with potent hepatotoxicity. In the present study, we aim to: 1) explore the dynamics of MC-LR accumulation and elimination in different tissues of male red swamp crayfish Procambarus clarkii; 2) reveal the mechanisms underlying hepatic antioxidation and detoxification. In the semi-static toxicity tests under the water temperature of 25±2°C, P. clarkii were exposed to 0.1, 1, 10 and 100μg/L MC-LR for 7days for accumulation and subsequently relocated to freshwater for another 7days to depurate MC-LR. MC-LR was measured in the hepatopancreas, intestine, abdominal muscle and gill by HPLC. The enzyme activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST), content of glutathione (GSH), and transcripts of Mn-sod, cat, gpx1, Mu-gst, heat shock protein90 (hsp90), hsp70 and hsp60 in hepatopancreas were detected. The results showed that P. clarkii accumulated more MC-LR in intestine, and less in abdominal muscle and gill during accumulation period and eliminated the toxin more quickly in gill and abdominal muscle, and comparatively slowly in intestine during depuration period. The fast increase of SOD and CAT activities at early stage, subsequent decrease at later stage of accumulation period and then fast increase during depuration period were partially consistent with the transcriptional changes of their respective genes. GPx was activated by longer MC-LR exposure and gpx1 mRNA expression showed uncoordinated regulation pattern compared with its enzyme. Hsp genes were up-regulated when P. clarkii was exposed to MC-LR.

Effects of microcystin-LR on gut microflora in different gut regions of mice

To reveal the toxicological effects of the hepatotoxic microcystin-leucine arginine (MC-LR) on gut microbial community composition in different gut regions, we conducted a subchronic exposure of BALB/c mice to MC-LR via intragastric administration. Denaturing gradient gel electrophoresis (DGGE) was employed to profile the shifts of microbes after MC-LR treatment in the jejuno-ileum, caecum and colon. DGGE profiles analysis showed that MC-LR increased the microbial species richness (number of microbial bands) in the caecum and colon as well as microbial diversity (Shannon-Wiener index) in the caecum. The cluster analysis of DGGE profiles indicated that the microbial structures in the caecum and colon shifted significantly after MC-LR treatment, while that in the jejuno-ileum did not. All the relatively decreased gut microbes belonged to Clostridia in the Firmicutes phylum, and most of them were Lachnospiraceae. The increased ones derived from a variety of microbes including species from Porphyromonadaceae and Prevotellaceae in the Bacteroidetes phylum, as well as Lachnospiraceae and Ruminococcaceae in the Firmicutes phylum, and among which, the increase of Barnesiella in Porphyromonadaceae was most remarkable. In conclusion, subchronic exposure to MC-LR could disturb the balance of gut microbes in mice, and its toxicological effects varied between the jejuno-ileum and the other two gut regions.

The role of glutathione detoxification pathway in MCLR-induced hepatotoxicity in SD rats

In the present study, we investigated the role of glutathione (GSH) and its related enzymes in Sprague Dawley (SD) rats subjected to microcystin-leucine-arginine (MCLR)-induced hepatotoxicity. SD rats were intraperitoneally (i.p.) injected with MCLR after pretreating with or without buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis. The depletion of GSH with BSO enhanced MCLR-induced oxidative stress, resulting in more severe liver damage and higher MCLR accumulation. Similarly, the contents of malondialdehyde (MDA), total GSH (T-GSH), oxidized GSH (GSSG) and GSH were significantly enhanced in BSO pretreated rats following MCLR treatment. The study showed that the transcription of GSH-related enzymes such as glutathione-S-transferase (GST), γ-glutamylcysteine synthetase (γ-GCS), glutathione reductase (GR) varied in different ways (expect for glutathione peroxidase (GPx), whose gene expression was induced in all treated groups) with or without BSO pretreatment before MCLR exposure, suggesting an adaptative response of GSH-related enzymes at transcription level to combat enhancement of oxidative stress induced by MCLR when pretreated with BSO. These data suggested the tissues with low GSH concentration are highly vulnerable to MCLR toxicity and GSH was critical for the detoxification in MCLR-induced hepatotoxicity in vivo.

Are fish fed with cyanobacteria safe, nutritious and delicious? A laboratory study

Toxic cyanobacterial blooms, which produce cyclic heptapeptide toxins known as microcystins, are worldwide environmental problems. On the other hand, the cyanobacteria protein (30–50%) has been recommended as substitute protein for aquaculture. The present laboratory study verified the feasibility of cyanobacteria protein substitution and risk assessment. Goldfish were fed diets supplemented lyophilised cyanobacteria powder for 16 weeks with the various doses: 0% (control), 10%, 20%, 30% and 40%. Low doses (10% and 20%) promoted growth whereas high doses (30% and 40%) inhibited growth. In cyanobacteria treated fish, the proximate composition of ash, crude fat content and crude protein content decreased in 16 weeks; the saturated fatty acid (SFA) content significantly increased; the n-3 polyunsaturated fatty acid content, collagen content and muscle pH significantly decreased; cooking loss percents increased significantly. Muscle fiber diameter and myofibril length were negatively correlation. Additionally, flavour compounds (e.g., amino acids, nucleotides, organic acids and carnosine) changed significantly in the treated fish, and odour compounds geosmin and 2-methylisoborneol increased significantly. The estimated daily intake (EDI) of microcystins in muscle was close to or exceeded the World Health Organization (WHO) tolerable daily intake (TDI), representing a great health risk. Cyanobacterie is not feasible for protein sources use in aquaculture.

Hepatic and intestine alterations in mice after prolonged exposure to low oral doses of Microcystin-LR

Oral intake of Microcystin-LR (MC-LR) is the principal route of exposure to this toxin, with prolonged exposure leading to liver damage of unspecific symptomatology. The aim of the present paper was therefore to investigate the liver and intestine damage generated by prolonged oral exposure to low MC-LR doses (50 and 100 μg MC-LR/kg body weight, administrated every 48 h during a month) in a murine model. We found alterations in TBARS, SOD activity and glutathione content in liver and intestine of mice exposed to both doses of MC-LR. Furthermore, the presence of MC-LR was detected in both organs. We also found hepatic steatosis (3.6 ± 0.6% and 15.3 ± 1.6%) and a decrease in intraepithelial lymphocytes (28.7 ± 5.0% and 44.2 ± 8.7%) in intestine of 50- and 100-μg MC-LR/kg treated animals, respectively. This result could have important implications for mucosal immunity, since intraepithelial lymphocytes are the principal effectors of this system. Our results indicate that prolonged oral exposure at 50 μg MC-LR/kg every 48 h generates significant damage not only in liver but also in intestine. This finding calls for a re-appraisal of the currently accepted NOAEL (No Observed Adverse Effect Level), 40 μg MC-LR/kg body weight, used to derive the guideline value for MC-LR in drinking water.

Hepatopathy following consumption of a commercially available blue-green algae dietary supplement in a dog

Background

Dietary supplement use in both human and animals to augment overall health continues to increase and represents a potential health risk due to the lack of safety regulations imposed on the manufacturers. Because there are no requirements for demonstrating safety and efficacy prior to marketing, dietary supplements may contain potentially toxic contaminants such as hepatotoxic microcystins produced by several species of blue-green algae.

Case presentation

An 11-year-old female spayed 8.95 kg Pug dog was initially presented for poor appetite, lethargy polyuria, polydipsia, and an inability to get comfortable. Markedly increased liver enzyme activities were detected with no corresponding abnormalities evident on abdominal ultrasound. A few days later the liver enzyme activities were persistently increased and the dog was coagulopathic indicating substantial liver dysfunction. The dog was hospitalized for further care consisting of oral S-adenosylmethionine, silybin, vitamin K, and ursodeoxycholic acid, as well as intravenous ampicillin sodium/sulbactam sodium, dolasetron, N-acetylcysteine, metoclopramide, and intravenous fluids. Improvement of the hepatopathy and the dog’s clinical status was noted over the next three days. Assessment of the dog’s diet revealed the use of a commercially available blue-green algae dietary supplement for three-and-a-half weeks prior to hospitalization. The supplement was submitted for toxicology testing and revealed the presence of hepatotoxic microcystins (MCs), MC-LR and MC-LA. Use of the supplement was discontinued and follow-up evaluation over the next few weeks revealed a complete resolution of the hepatopathy.

Conclusions

To the authors’ knowledge, this is the first case report of microcystin intoxication in a dog after using a commercially available blue-green algae dietary supplement. Veterinarians should recognize the potential harm that these supplements may cause and know that with intervention, recovery is possible. In addition, more prudent oversight of dietary supplement use is recommended for our companion animals to prevent adverse events/intoxications.

Oxidative damage and apoptosis induced by microcystin-LR in the liver of Rana nigromaculata in vivo

Microcystins (MCs) are hepatotoxins with potent inhibitor activity of protein phosphatases PP1 and PP2A. The present study shows that MC-LR can induce severe oxidative damage and apoptosis in the livers of frogs (Rana nigromaculata) exposed to 1μg/L MC-LR for 7 and 14d in vivo. Ultrastructural observation showed the apoptotic morphology of perinuclear chromatin margination and swollen mitochondria, indicating that MC-LR can significantly damage frog liver. Reactive oxygen species (ROS) production and malondialdehyde (MDA) content were positively correlated with exposure time. Meanwhile, reduced glutathione (GSH) content and GSH peroxidase (GPx) activity rapidly decreased after prolonged exposure to 1μg/L MC-LR in a time-dependent manner. These results imply that the antioxidant defense systems of the liver were damaged. Enhanced apoptosis of cells in the livers of MC-treated frogs was detected by terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labeling (TUNEL) associated with up-regulation of the mitochondrial system. MC-LR significantly stimulated the livers to release cytochrome c, which improved the protein expressions of Bax, caspase-3, and caspase-9 (p<0.01) and inhibited the protein expression of Bcl-2 with prolonged exposure (p<0.01) via the mitochondrial pathway. These results imply that the mitochondrial pathway has a key function in toxin-induced liver cell apoptosis. The expression of caspase-8 was induced significantly (p<0.01), which illustrates the mechanism that the death receptor pathway is also involved in apoptosis. The present findings show that MC-LR can induce apoptosis in frog liver, which may be related with the decline of amphibian populations. The World Health Organization-recommended drinking water limit for MC-LR in water may be not safe for amphibians.

Biomarkers of prolonged exposure to microcystin-LR in mice

The effects of prolonged exposure to microcystins (MCs) on health are not yet sufficiently understood and this type of poisoning is often undiagnosed. Even though chronic exposure has been linked with liver cancer and alterations have been described in liver damage marker enzymes in exposed populations, there are not profile parameters that indicate prolonged exposure to microcystins. The aim of this work is to determine, based on an animal model of prolonged exposure to successive i.p. doses of 25 μg MC-LR/kg body weight, several plasma parameters which could be useful as exposure biomarkers. Hemoglobin (Hb) and methemoglobin (MetHb) levels were determined on blood samples. We also studied plasma levels of hydroperoxides (ROOHs), α-tocopherol, glutathione and lipid profile as well as superoxide dismutase (SOD) and catalase (CAT) erythrocyte activities. In addition, the determination of MC-LR levels in liver, kidney, plasma, urine and feces of treated mice was carried out. We found that alteration in MetHb, ROOHs, glutathione, α-tocopherol levels, SOD activity and plasma lipid profile, correlates with those expected if the alteration derived from hepatic damage. The alterated plasma paramenters together with MC-LR determination could be used as biomarkers, helpful tools in screening and epidemiological studies.

Expression profiling in vivo demonstrates rapid changes in liver microRNA levels of whitefish (Coregonus lavaretus) following microcystin-LR exposure

At present, little is known about the role of miRNAs in liver response of fish to the cyanobacterial hepatotoxin microcystin-LR (MC-LR) treatment, despite the fact that the exposure is thought to underlie multiple acute and chronic effects. To address this question, we used the Real-Time PCR method to examine the differential expression of 6 miRNAs putatively playing roles in signal transduction (let-7c, miR-9b), apoptosis and cell cycle (miR-16a, miR-21a, miR-34a) and fatty acid metabolism (miR-122) in whitefish (Coregonus lavaretus) liver, during the first 48h after intraperitoneal injection of MC-LR (100 μg/kg body weight). In addition, we analyzed expression levels of 8 mRNAs and p53 protein, known to be involved in the cell response on the exposure to environmental stressors. Following the challenge we observed a rapid and transient increase in the mean (n=5) levels of individual miRNA expression (from 2.7-fold for miR-122 to 6.8-fold for let-7c), compared to the respective levels in control fish, which mostly peaked at 24h of the experiment. This increase was correlated with a reduction in the expression of mRNAs of genes coding for ferritin H (frih) and HNK Ras -like protein (p-ras) and an overexpression of mRNAs of genes coding for bcl2-associated X protein (bax), cyclin dependent kinase inhibitor 1a (cdkn1a), dicer (dcr), histone 2A (h2a) and p53. Expression of the remaining caspase 6 (cas6) mRNA did not change over 48 h of the treatment. Moreover, exposure to MC-LR did not alter whitefish p53 protein levels. Bearing in mind a variety of likely silencing targets for, and the onset of, the aberrant miRNA expression it may be concluded that they are involved in molecular pathways, such as liver cell metabolism, cell cycle regulation and apoptosis, and may contribute to the early phase of MC-LR induced hepatotoxicity.

Effects of a toxic cyanobacterial bloom (Planktothrix agardhii) on fish: insights from histopathological and quantitative proteomic assessments following the oral exposure of medaka fish (Oryzias latipes)

Cyanobacterial toxic blooms often occur in freshwater lakes and constitute a potential health risk to human populations, as well as to fish and other aquatic organisms. Microcystin-LR (the cyanotoxin most commonly detected in the freshwater environment) is a potent hepatotoxin, deregulating the kinase pathway by inhibiting phosphatases 1 and 2A. Although toxicological effects have been clearly linked to the in vitro exposure of fish to purified microcystins, cyanotoxins are produced by the cyanobacteria together with numerous other potentially toxic molecules, and their overall and specific implications for the health of fish have still not been clearly established and remain puzzlingly difficult to assess. The medaka fish (Oryzias latipes) was chosen as an in vitro model for studying the effects of a cyanobacterial bloom on liver protein contents using a gel free quantitative approach, iTRAQ, in addition to pathology examinations on histological preparations. Fish were gavaged with 5 μL cyanobacterial extracts (Planktothrix agardhii) from a natural bloom (La Grande Paroisse, France) containing 2.5 μg equiv. MC-LR. 2h after exposure, the fish were sacrificed and livers were collected for analysis. Histological observations indicate that hepatocytes present glycogen storage loss, and cellular damages, together with immunological localization of MCs. Using a proteomic approach, 304 proteins were identified in the fish livers, 147 of them with a high degree of identification confidence. Fifteen of these proteins were statistically significantly different from those of controls (gavaged with water only). Overall, these protein regulation discrepancies clearly indicate that oxidative stress and lipid regulation had occurred in the livers of the exposed medaka fish. In contrast to previous pure microcystin-LR gavage experiments, marked induction of vitellogenin 1 protein was observed for the first time with a cyanobacterial extract. This finding was confirmed by ELISA quantification of vitellogenin liver content, suggesting that the Planktothrix bloom extract had induced the occurrence of an endocrine-disrupting effect.

Effects of microcystin-LR exposure on matrix metalloproteinase-2/-9 expression and cancer cell migration

This study assessed the effects of microcystin-LR (MC-LR) exposure on matrix metalloproteinases (MMPs) expression and cancer cell migration. After male mice were orally administered with different concentrations of MC-LR for 270 d, histopathologic observation revealed an obvious hepatic lymphocyte infiltration or fatty degeneration. Immunohistochemical staining and enzyme-linked immunosorbent assay demonstrated that MC-LR treatment (even at 1 nM) caused up-regulated expressions of hepatic MMP-2/-9. Quantitative reverse-transcriptase PCR showed that the exposure to 80 nM MC-LR induced an increase of MMP-2/-9 mRNA levels by 1.0 and 1.9 fold. Breast cancer cells (MDA-MB-435s) were also cultured with MC-LR solutions and a wound healing assay demonstrated that MC-LR posed a time/dose-dependent stimulation effect on migration of the cancer cells. Gelatin electrophoresis and quantitative PCR showed significant increases in cellular MMP-2/-9 expressions after MC-LR exposure. This study indicated that chronic exposure to MC-LR could alter MMP-2/-9 expressions and stimulate cancer cell migration.

Microcystin-LR induced DNA damage in human peripheral blood lymphocytes

Human exposure to microcystins, which are produced by freshwater cyanobacterial species, is of growing concern due to increasing appearance of cyanobacterial blooms as a consequence of global warming and increasing water eutrophication. Although microcystins are considered to be liver-specific, there is evidence that they may also affect other tissues. These substances have been shown to induce DNA damage in vitro and in vivo, but the mechanisms of their genotoxic activity remain unclear. In human peripheral blood lymphocytes (HPBLs) exposure to non-cytotoxic concentrations (0, 0.1, 1 and 10μg/ml) of microcystin-LR (MCLR) induced a dose- and time-dependent increase in DNA damage, as measured with the comet assay. Digestion of DNA from MCLR-treated HPBLs with purified formamidopyrimidine-DNA glycosylase (Fpg) displayed a greater number of DNA strand-breaks than non-digested DNA, confirming the evidence that MCLR induces oxidative DNA damage. With the cytokinesis-block micronucleus assay no statistically significant induction of micronuclei, nucleoplasmic bridges and nuclear buds was observed after a 24-h exposure to MCLR. At the molecular level, no changes in the expression of selected genes involved in the cellular response to DNA damage and oxidative stress were observed after a 4-h exposure to MCLR (1μg/ml). After 24h, DNA damage-responsive genes (p53, mdm2, gadd45a, cdkn1a), a gene involved in apoptosis (bax) and oxidative stress-responsive genes (cat, gpx1, sod1, gsr, gclc) were up-regulated. These results provide strong support that MCLR is an indirectly genotoxic agent, acting via induction of oxidative stress, and that lymphocytes are also the target of microcystin-induced toxicity.

Microcystin accumulation and antioxidant responses in the freshwater clam Diplodon chilensis patagonicus upon subchronic exposure to toxic Microcystis aeruginosa

We investigated the accumulation and toxicity of microcystin-LR (MCLR) in the digestive gland of the freshwater clam Diplodon chilensis patagonicus. Treated clams were fed with a toxic strain of Microcystis aeruginosa (NPJB1) during 6 weeks and control clams received the non-toxic strain NPDC1. Filtration rate was estimated for both groups. Toxic effects were evaluated through the hepatosomatic index (HSI) and different oxidative stress biomarkers, lipid peroxidation (content of thiobarbituric reactive substances-TBARS), protein oxidation (carbonyl groups) and reduced glutathione (GSH) levels, and enzymatic activities of superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST). The extractable MCLR measured by ELISA in digestive gland extracts showed little or no change during the first 3 weeks and increased significantly at weeks 5 and 6. HSI was reduced by 30% in treated clams at weeks 5 and 6. No significant oxidative damage to lipids or proteins was. All the antioxidant defense parameters analyzed were significantly increased at week 5 or 6. GSH increased in treated clams at week 5, reaching 62% increase at week 6. SOD, CAT and GST activities were significantly increased in treated clams by 50%, 66% and 60%, respectively, at the end of the experiment. D. chilensis patagonicus can be exposed to prolonged cyanobacterial blooms accumulating significant quantities of MCLR, which could be a risk for mammals and birds, which feed on this species and, in a lesser extent, to humans.