In vivo studies on the toxic effects of microcystins on mitochondrial electron transport chain and ion regulation in liver and heart of rabbit

Polystyrene microplastics enhance microcystin-LR-induced cardiovascular toxicity and oxidative stress in zebrafish embryos

The health risks associated with combined exposure to microplastics (MPs) and cyanobacteria toxins have gained increasing attention due to the large-scale prevalence of cyanobacterial blooms and accumulation of MPs in aquatic environments. Therefore, we explored the cardiovascular toxic effects of microcystin-LR (MC-LR, 1, 10, 100 μg/L) in the presence of 5 μm polystyrene microplastics (PS-MPs, 100 μg/L) and 80 nm polystyrene nanoplastics (PS-NPs, 100 μg/L) in zebrafish models. Embryos were exposed to certain PS-MPs and PS-NPs conditions in water between 3 h post-fertilization (hpf) and 168 hpf. Compared to MC-LR alone, a significant decrease in heart rate was observed as well as notable pericardial edema in the MC-LR + PS-MPs/NPs groups. At the same time, sinus venosus and bulbus arteriosus (SV-BA) distances were significantly increased. Furthermore, the addition of PS-MPs/NPs caused thrombosis in the caudal vein and more severe vascular damage in zebrafish larvae compared to MC-LR alone. Our findings revealed that combined exposure to PS-NPs and MC-LR could significantly decreased the expression of genes associated with cardiovascular development (myh6, nkx2.5, tnnt2a, and vegfaa), ATPase (atp1a3b, atp1b2b, atp2a1l, atp2b1a, and atp2b4), and the calcium channel (cacna1ab and ryr2a) compared to exposure to MC-LR alone. In addition, co-exposure with PS-MPs/NPs exacerbated the MC-LR-induced reactive oxygen species (ROS) production, as well as the ROS-stimulated apoptosis and heightened inflammation. We also discovered that astaxanthin (ASTA) treatment partially attenuated these cardiovascular toxic effects. Our findings confirm that exposure to MC-LR and PS-MPs/NPs affects cardiovascular development through calcium signaling interference and ROS-induced cardiovascular cell apoptosis. This study highlights the potential environmental risks of the co-existence of MC-LR and PS-MPs/NPs for fetal health, particularly cardiovascular development.

Cardiac Toxicity Induced by Long-Term Environmental Levels of MC-LR Exposure in Mice

Cyanobacterial blooms are considered a serious global environmental problem. Recent studies provided evidence for a positive association between exposure to microcystin-LR (MC-LR) and cardiotoxicity, posing a threat to human cardiovascular health. However, there are few studies on the cardiotoxic effects and mechanisms of long-term low-dose MC-LR exposure. Therefore, this study explored the long-term toxic effects and toxic mechanisms of MC-LR on the heart and provided evidence for the induction of cardiovascular disease by MC-LR. C57BL/6 mice were exposed to 0, 1, 30, 60, 90, and 120 μg/L MC-LR via drinking water for 9 months and subsequently necropsied to examine the hearts for microstructural changes using H&E and Masson staining. The results demonstrated fibrotic changes, and qPCR and Western blots showed a significant up-regulation of the markers of myocardial fibrosis, including TGF-β1, α-SMA, COL1, and MMP9. Through the screening of signaling pathways, it was found the expression of PI3K/AKT/mTOR signaling pathway proteins was up-regulated. These data first suggested MC-LR may induce myocardial fibrosis by activating the PI3K/AKT/mTOR signaling pathway. This study explored the toxicity of microcystins to the heart and preliminarily explored the toxic mechanisms of long-term toxicity for the first time, providing a theoretical reference for preventing cardiovascular diseases caused by MC-LR.

A review and assessment of cyanobacterial toxins as cardiovascular health hazards

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

Effects of chronic exposure to microcystin-LR on life-history traits, intestinal microbiota and transcriptomic responses in Chironomus pallidivittatus

Microcystins (MCs) are the most widely distributed cyanobacterial toxins that can exert adverse effects on aquatic organisms, but aside from the study of the harmful effect of cyanobacterial blooms, little is known about the effect of released MCs on the growth and development of chironomid larvae. To assess the harmful effect and the toxic mechanism of MCs on midges, the life-history traits, intestinal microbiota, and transcriptome of Chironomus pallidivittatus were analyzed after chronic exposure to 30 μg/L of MC-LR. Exposure inhibited larvae body length by 35.61% and wet weight by 21.92%, increased emergence time of midges, damaged mitochondria in the intestine, promoted oxidative stress, dysregulated lipid metabolism of chironomid larvae, and increased detoxification enzymes glutathione S-transferase (GST) and superoxide dismutase (SOD) by 32.44% and 17.41%, respectively. Exposure also altered the diversity and abundance of the intestinal microbiota, favoring pathogenic and MC degradation bacteria. RNA sequencing identified 261 differentially expressed genes under MC-LR stress, suggesting that impairment of the peroxisome proliferator-activated receptor signaling pathway upregulated fatty acid biosynthesis and elongation to promote lipid accumulation. In addition, exposure-induced detoxification and antioxidant responses, indicating that the chironomid larvae had the potential ability to resist MC-LR. To our knowledge, this is the first time that lipid accumulation, oxidative stress, and detoxification have been studied in this organism at the environmentally relevant concentration of MC-LR; the information may assist in ecological risk assessment of cyanobacterial toxins and their effects on benthic organisms.

Update on the adverse effects of microcystins on the liver

Microcystins (MCs) are the most common cyanobacteria toxins in eutrophic water, which have strong hepatotoxicity. In the past decade, epidemiological and toxicological studies on liver damage caused by MCs have proliferated, and new mechanisms of hepatotoxicity induced by MCs have also been discovered and confirmed. However, there has not been a comprehensive and systematic review of these new findings. Therefore, this paper summarizes the latest advances in studies on the hepatotoxicity of MCs to reveal the effects and mechanisms of hepatotoxicity induced by MCs. Current epidemiological studies have confirmed that symptoms or signs of liver damage appear after human exposure to MCs, and a long time of exposure can even lead to liver cancer. Toxicological studies have shown that MCs can affect the expression of oncogenes by activating cell proliferation pathways such as MAPK and Akt, thereby promoting the occurrence and development of cancer. The latest evidence shows that epigenetic modifications may play an important role in MCs-induced liver cancer. MCs can cause damage to the liver by inducing hepatocyte death, mainly manifested as apoptosis and necrosis. The imbalance of liver metabolic homeostasis may be involved in hepatotoxicity induced by MCs. In addition, the combined toxicity of MCs and other toxins are also discussed in this article. This detailed information will be a valuable reference for further exploring of MCs-induced hepatotoxicity.

Differences in Abnormal Water Metabolism between SD Rats and KM Mice Intoxicated by Microcystin-RR

The effects of microcystin-RR (MC-RR) on water metabolism were studied on Sprague-Dawley (SD) rats and KunMing (KM) mice. In the single dose toxicity test, polydipsia, polyuria, hematuria and proteinuria were found in group of rats receiving a MC-RR dose of 574.7 μg/kg, and could be relieved by dexamethasone (DXM). Gradient damage was observed in kidney and liver in rats with gradient MC-RR doses of 574.7, 287.3, and 143.7 μg/kg. No significant water metabolic changes or kidney injuries were observed in mice treated with MC-RR doses of 210.0, 105.0, and 52.5 μg/kg. In the continuous exposure test, in which mice were administrated with 140.0, 70.0, and 35.0 μg/kg MC-RR for 28 days, mice in the 140.0 μg/kg group presented increasing polydipsia, polyuria, and liver damage. However, no anatomic or histological changes, including related serological and urinary indices, were found in the kidney. In summary, abnormal water metabolism can be induced by MC-RR in rats through kidney injury in single dose exposure; the kidney of SD rats is more sensitive to MC-RR than that of KM mouse; and polydipsia and polyuria in mice exposed to MC-RR for 28 days occurred but could not be attributed to kidney damage.

[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.

Development and Application of Extraction Methods for LC-MS Quantification of Microcystins in Liver Tissue

A method was developed to extract and quantify microcystins (MCs) from mouse liver with limits of quantification (LOQs) lower than previously reported. MCs were extracted from 40-mg liver samples using 85:15 (v:v) CH₃CN:H₂O containing 200 mM ZnSO₄ and 1% formic acid. Solid-phase extraction with a C18 cartridge was used for sample cleanup. MCs were detected and quantified using HPLC-orbitrap-MS with simultaneous MS/MS detection of the 135.08 m/z fragment from the conserved Adda amino acid for structural confirmation. The method was used to extract six MCs (MC-LR, MC-RR, MC-YR, MC-LA, MC-LF, and MC-LW) from spiked liver tissue and the MC-LR cysteine adduct (MC-LR-Cys) created by the glutathione detoxification pathway. Matrix-matched internal standard calibration curves were constructed for each MC (R² ≥ 0.993), with LOQs between 0.25 ng per g of liver tissue (ng/g) and 0.75 ng/g for MC-LR, MC-RR, MC-YR, MC-LA, and MC-LR-Cys, and 2.5 ng/g for MC-LF and MC-LW. The protocol was applied to extract and quantify MC-LR and MC-LR-Cys from the liver of mice that had been gavaged with 50 µg or 100 µg of MC-LR per kg bodyweight and were euthanized 2 h, 4 h, or 48 h after final gavage. C57Bl/6J (wild type, control) and Lepr^db/J (experiment) mice were used as a model to study non-alcoholic fatty liver disease. The Lepr^db/J mice were relatively inefficient in metabolizing MC-LR into MC-LR-Cys, which is an important defense mechanism against MC-LR exposure. Trends were also observed as a function of MC-LR gavage amount and time between final MC-LR gavage and euthanasia/organ harvest.

A Review of Cardiovascular Toxicity of Microcystins

The mortality rate of cardiovascular diseases (CVD) in China is on the rise. The increasing burden of CVD in China has become a major public health problem. Cyanobacterial blooms have been recently considered a global environmental concern. Microcystins (MCs) are the secondary products of cyanobacteria metabolism and the most harmful cyanotoxin found in water bodies. Recent studies provide strong evidence of positive associations between MC exposure and cardiotoxicity, representing a threat to human cardiovascular health. This review focuses on the effects of MCs on the cardiovascular system and provides some evidence that CVD could be induced by MCs. We summarized the current knowledge of the cardiovascular toxicity of MCs, with regard to direct cardiovascular toxicity and indirect cardiovascular toxicity. Toxicity of MCs is mainly governed by the increasing level of reactive oxygen species (ROS), oxidative stress in mitochondria and endoplasmic reticulum, the inhibition activities of serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) and the destruction of cytoskeletons, which finally induce the occurrence of CVD. To protect human health from the threat of MCs, this paper also puts forward some directions for further research.

Chronic Low Dose Oral Exposure to Microcystin-LR Exacerbates Hepatic Injury in a Murine Model of Non-Alcoholic Fatty Liver Disease

Microcystins are potent hepatotoxins that have become a global health concern in recent years. Their actions in at-risk populations with pre-existing liver disease is unknown. We tested the hypothesis that the No Observed Adverse Effect Level (NOAEL) of Microcystin-LR (MC-LR) established in healthy mice would cause exacerbation of hepatic injury in a murine model (Lepr^db/J) of Non-alcoholic Fatty Liver Disease (NAFLD). Ten-week-old male Lepr^db/J mice were gavaged with 50 μg/kg, 100 μg/kg MC-LR or vehicle every 48 h for 4 weeks (n = 15–17 mice/group). Early mortality was observed in both the 50 μg/kg (1/17, 6%), and 100 μg/kg (3/17, 18%) MC-LR exposed mice. MC-LR exposure resulted in significant increases in circulating alkaline phosphatase levels, and histopathological markers of hepatic injury as well as significant upregulation of genes associated with hepatotoxicity, necrosis, nongenotoxic hepatocarcinogenicity and oxidative stress response. In addition, we observed exposure dependent changes in protein phosphorylation sites in pathways involved in inflammation, immune function, and response to oxidative stress. These results demonstrate that exposure to MC-LR at levels that are below the NOAEL established in healthy animals results in significant exacerbation of hepatic injury that is accompanied by genetic and phosphoproteomic dysregulation in key signaling pathways in the livers of NAFLD mice.

Microcystin-LR induces angiodysplasia and vascular dysfunction through promoting cell apoptosis by the mitochondrial signaling pathway

The harmful algal blooms are becoming increasingly problematic in the regions that drinking water production depends on surface waters. With a global occurrence, microcystins are toxic peptides produced by multiple cyanobacterial genera in the harmful algal blooms. In this study, we examined the effects of microcystin-LR (MC-LR), a representative toxin of the microcystin family, on vascular development in zebrafish and the apoptosis of human umbilical vein endothelial cells (HUVECs). In zebrafish larvae, MC-LR induced angiodysplasia, damaged vascular structures and reduced lumen size at 0.1 μM and 1 μM, leading to the decrease of the blood flow area in the blood vessels and brain hemorrhage, which showed that MC-LR could dose-dependently inhibit vascular development and cause vascular dysfunction. In MC-LR treated HUVECs, the proportion of early apoptosis and late apoptosis cells increased in a concentration-dependent manner. Different concentrations of MC-LR could also activate caspase 3/9 in HUVECs, increase the level of mitochondrial ROS and reduce mitochondrial membrane potential. Additionally, MC-LR could promote the expression of p53 and inhibit the expression of PCNA. The findings showed that MC-LR could promote apoptosis of HUVECs through the mitochondrial signaling pathway. Combined with these results, MC-LR may promote vascular endothelial cell apoptosis through mitochondrial signaling pathway, leading to angiodysplasia and vascular dysfunction.

Microcystin-RR: Occurrence, content in water and food and toxicological studies. A review

Microcystins (MCs) are hepatotoxins, produced by various species of cyanobacteria, whose occurrence is increasing worldwide owing to climate change and anthropogenic activities. More than 100 variants have been reported, and among them MC-LR is the most extensively studied, but there are other MC congeners that deserve to be investigated. The need for data to characterize the toxicological profile of MC variants other than MC-LR has been identified in order to improve risk assessment in humans and wildlife. Accordingly, the aim of this study was to evaluate the information available in the scientific literature dealing with MC-RR, as this congener is the second most common cyanotoxin in the environment. The review focuses on aspects such as occurrence in water and food, and toxicity studies both in vitro and in vivo. It reveals that, although MC-RR is a real hazard with a high exposure potential in some countries, little is known yet about its specific toxicological properties that differ from those of MC-LR, and important aspects such as genotoxicity and chronic effects have not yet been sufficiently addressed.

Impairment of endoplasmic reticulum is involved in β-cell dysfunction induced by microcystin-LR

Microcystins (MCs) widely distributed in freshwaters have posed a significant risk to human health. Previous studies have demonstrated that exposure to MC-LR impairs pancreatic islet function, however, the underlying mechanisms still remain unclear. In the present study, we explored the role of endoplasmic reticulum (ER) impairment in β-cell dysfunction caused by MC-LR. The result showed that MC-LR modified ER morphology evidenced by increased ER amount and size at low doses (15, 30 or 60 μM) and vacuolar and dilated ER ultrastructure at high doses (100 or 200 μM). Also, insulin content showed increased at 15 or 30 μM but declined at 60, 100, or 200 μM, which was highly accordant with ER morphological alteration. Transcriptomic analysis identified a number of factors and several pathways associated with ER protein processing, ER stress, apoptosis, and diabetes mellitus in the cells treated with MC-LR compared with non-treated cells. Furthermore, MC-LR-induced ER stress significantly promoted the expression of PERK/eIF2α and their downstream targets (ATF4, CHOP, and Gadd34), which indicates that PERK-eIF2α-ATF4 pathway is involved in MC-LR-induced insulin deficiency. These results suggest that ER impairment is an important contributor to MC-LR-caused β-cell failure and provide a new insight into the association between MCs contamination and the occurrence of human diseases.

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.

Systematic identification of seven ribosomal protein genes in bighead carp and their expression in response to microcystin-LR

Microcystin-LR (MCLR) is one of the most toxic cyanotoxins produced in algal blooms. The toxic effects of MCLR on the expression of some organelles genes (mitochondrion, endoplasmic reticulum, and cytoskeleton etc) have been widely investigated, but little is known how it impacts on the expression of ribosomal genes. In this study we identified seven ribosomal protein genes RPS6, RPS12, RPS24, RPS27a, RPL12, RPL27 and RPL29 in bighead carp (Aristichthys nobilis), whose expression was regulated by MCLR. The amino acid sequences of those 7 genes shared more than 90% identity with corresponding sequences from zebrafish, and were well conserved throughout evolution. The 3D structure prediction showed that the structures of these ribosomal proteins were conserved, but had species specificity. Q-PCR analysis revealed that expression of seven genes changed dramatically at 3 hr, then went back to a moderate change- level at 24 hr in almost all tested tissues (liver, kidney, intestine, heart, spleen and gill) post MCLR injection, but in brain expression of the seven genes stayed same as the normal level. This study will help us to know not only about the evolution and functions of ribosomal proteins in anti-MCLR response in bighead carp, but also about the MCLR toxicity and its impact on aquaculture and human health.

Microcystin-LR induces mitochondria-mediated apoptosis in human bronchial epithelial cells

The present study aimed to investigate the toxicity of microcystin-LR (MC-LR) and to explore the mechanism of MC-LR-induced apoptosis in human bronchial epithelial (HBE) cells. HBE cells were treated with MC-LR (1, 10, 20, 30 and 40 µg/ml) alone or with MC-LR (0, 2.5, 5 and 10 µg/ml) and Z-VAD-FMK (0, 10, 20, 40, 60, 80, 100, 120 and 140 µM), which is a caspase inhibitor, for 24 and 48 h. Cell viability was assessed via an MTT assay and the half maximal effective concentration of MC-LR was determined. The optimal concentration of Z-VAD-FMK was established as 50 µm, which was then used in the subsequent experiments. MC-LR significantly inhibited cell viability and induced apoptosis of HBE cells in a dose-dependent manner, as detected by an Annexin V/propidium iodide assay. MC-LR induced cell apoptosis, excess reactive oxygen species production and mitochondrial membrane potential collapse, upregulated Bax expression and downregulated B-cell lymphoma-2 expression in HBE cells. Moreover, western blot analysis demonstrated that MC-LR increased the activity levels of caspase-3 and caspase-9 and induced cytochrome c release into the cytoplasm, suggesting that MC-LR-induced apoptosis is associated with the mitochondrial pathway. Furthermore, pretreatment with Z-VAD-FMK reduced MC-LR-induced apoptosis by blocking caspase activation in HBE cells. Therefore, the results of the present study suggested that MC-LR is capable of significantly inhibiting the viability of HBE cells by inducing apoptosis in a mitochondria-dependent manner. The present study provides a foundation for further understanding the mechanism underlying the toxicity of MC-LR in the respiratory system.

The interactive effects of cytoskeleton disruption and mitochondria dysfunction lead to reproductive toxicity induced by microcystin-LR

The worldwide occurrence of cyanobacterial blooms evokes profound concerns. The presence of microcystins (MCs) in waters and aquatic food increases the risk to human health. Some recent studies have suggested that the gonad is the second most important target organ of MCs, however, the potential toxicity mechanisms are still unclear. For a better understanding of reproductive toxicity of MCs on animals, we conducted the present experimental investigation. Male rats were intraperitoneally injected with MC-LR for 50 d with the doses of 1 and 10 µg/kg body weight per day. After prolonged exposure to MC-LR, the testes index significantly decreased in 10 µg/kg group. Light microscope observation indicated that the space between the seminiferous tubules was increased. Ultrastructural observation showed some histopathological characteristics, including cytoplasmic shrinkage, cell membrane blebbing, swollen mitochondria and deformed nucleus. Using Q-PCR methods, the transcriptional levels of some cytoskeletal and mitochondrial genes were determined. MC-LR exposure affected the homeostasis of the expression of cytoskeletal genes, causing possible dysfunction of cytoskeleton assembly. In MC-LR treatments, all the 8 mitochondrial genes related with oxidative phosphorylation (OXPHOS) significantly increased. The reactive oxygen species (ROS) level significantly increased in 10 µg/kg group. The mitochondria swelling and DNA damage were also determined in 10 µg/kg group. Hormone levels of testis significantly changed. The present study verified that both cytoskeleton disruption possibly due to cytoskeletal reorganization or depolymerization and mitochondria dysfunction interact with each other through inducing of reactive oxygen species and oxidative phosphorylation, and jointly result in testis impairment after exposure to MC-LR.

Identification of pathways, gene networks, and paralogous gene families in Daphnia pulex responding to exposure to the toxic cyanobacterium Microcystis aeruginosa

Although cyanobacteria produce a wide range of natural toxins that impact aquatic organisms, food webs, and water quality, the mechanisms of toxicity are still insufficiently understood. Here, we implemented a whole-genome expression microarray to identify pathways, gene networks, and paralogous gene families responsive to Microcystis stress in Daphnia pulex . Therefore, neonates of a sensitive isolate were given a diet contaminated with Microcystis to contrast with those given a control diet for 16 days. The microarray revealed 2247 differentially expressed (DE) genes (7.6% of the array) in response to Microcystis , of which 17% are lineage-specific (i.e., these genes have no detectable homology to any other gene in currently available databases) and 49% are gene duplicates (paralogues). We identified four pathways/gene networks and eight paralogous gene families affected by Microcystis . Differential regulation of the ribosome, including three paralogous gene families encoding 40S, 60S, and mitochondrial ribosomal proteins, suggests an impact of Microcystis on protein synthesis of D. pulex . In addition, differential regulation of the oxidative phosphorylation pathway (including the NADH:ubquinone oxidoreductase gene family) and the trypsin paralogous gene family (a major component of the digestive system in D. pulex ) could explain why fitness is reduced based on energy budget considerations.

Laboratory exposure of Oreochromis niloticus to crude microcystins (containing microcystin-LR) extracted from Egyptian locally isolated strain (Microcystis aeruginosa Kützing): biological and biochemical studies

Cyanobacterial blooms exert negative impacts on fisheries and water management authorities. Recently, it has gained global attention, as elevated earth warming and environmental pollution are accelerating algal growth. Oreochromis niloticus (O. niloticus) is a worldwide and the most commonly cultured fish in Egypt. The biological interaction of the living organisms to the surrounding environment must continuously be assessed to predict future effects of the ongoing hazards on fish. The study was designed to examine the possible biological and biochemical response of O. niloticus exposed to different concentrations of microcystins crude extract (containing microcystin-LR). Three equal groups of O. niloticus were assigned for intraperitoneal injection of three different doses: 100, 200, and 400 μg m(-1) dried aqueous microcystins extract, for 10 days. Clinical, condition factor (K) and hepatosomatic index (HIS) were estimated. Biochemical alterations were evaluated via lipid peroxidation, DNA fragmentation assay and electrophoretic analysis of fragmented DNA using agarose gel electrophoresis. The results showed that there were discernible behavioral and clinical alterations. Significant differences in K and HIS were observed between treatments. Also, significant elevations were observed in lipid peroxidation level and in the DNA fragmentation percentage in the exposed fish to the doses of 200 and 400 μg m(-1) of microcystins crude extract. The current study addresses the possible toxic effects of microcystins crude extract to O. niloticus. The results cleared that microcystins crude extract (containing MC-LR) is toxic to O. niloticus in time- and dose-dependent manners.

In vivo studies on the immunotoxic effects of microcystins on rabbit

Microcystins (MCs) are the toxic molecules produced by common cyanobacterium in freshwater blooms. Their toxicities raise severe health issues in livestock and human beings. In current study, the immunotoxic effects of MC-LR were investigated in rabbit through evaluating the dynamics of white blood cell (WBC) numbers and cytokine production such as interleukin-3 (IL-3), IL-4, IL-6, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α). MCs at the high dose (50 μg MC-LReq kg(-1) ) significantly induced increase in the WBC number but decrease in the Th1 (IFN-γ, TNF-α) and Th2 (IL-3, IL-4, IL-6) production. In the low dose group(12.5 μg MC-LReq kg(-1) ), the number of WBC and the production of IFN-γ, IFN-α, IL-4, IL-3, and IL-6 increased gradually in first 12 h, reach the peaks at 12 h, and dropped after 24 h. Significantly positive correlations were found between the cytokines production of IL-4 and IL-6, IFN-γ and IFN-α, or IL-4 and IFN-γ. In conclusion, MC-LR is able to disturb the rabbit immune system and there exists time-dose response relationship in the MC-LR-eliciting perturbation, which probably give a better insight into investigating the immunotoxicity mechanisms of MCs in vivo. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.