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

The mechanisms of microcystin-LR-induced genotoxicity and neurotoxicity in fish and mammals: Bibliometric analysis and meta-analysis

Microcystin-leucine arginine (MC-LR) is a typical cyanobacterial toxin, and the threat of this toxin is increasing among organisms. Despite extensive toxicological studies on MC-LR, there is no comprehensive analysis based on previously published data. Therefore, we conducted bibliometric analysis and meta-analysis to identify research hotspots and to elucidate the key mechanism of the relationship between MC-LR and genotoxicity and neurotoxicity among fish and mammals. One of the hotspots is toxic mechanisms (indicated by the frequent appearance of oxidative stress, DNA damage, apoptosis, neurotoxicity, genotoxicity, ROS, comet assay, signalling pathway, and gene expression indicate as keywords). The density visualization shows a high frequency of "microcystin-LR" and "toxicology," and the overlay visualization emphasizes the prominence of "neurotoxicity" in recent years. These findings confirm the importance of studying MC-LR toxicity. Meta-analysis indicated that in both fish and mammals, MC-LR exposure increased ROS levels by 294 % and increased DNA damage biomarkers by 174 % but decreased neurotoxicity biomarkers by 9 %. Intergroup comparisons revealed that the exposure concentration of MC-LR was significantly correlated with genotoxicity and neurotoxicity levels in both fish and mammals (p < 0.05). Furthermore, the random forest (RF) model revealed that exposure concentration was the primary determinant associated with the induction of ROS, genotoxicity, and neurotoxicity induced by MC-LR. This is likely the dominant mechanism by which excessive ROS production induced by MC-LR causes oxidative stress, ultimately leading to genotoxicity and neurotoxicity in both fish and mammals.

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.

Immunomodulatory Effects of Pure Cylindrospermopsin in Rats Orally Exposed for 28 Days

Cylindrospermopsin (CYN) is a ubiquitous cyanotoxin showing increasing incidence worldwide. CYN has been classified as a cytotoxin and, among its toxic effects, its immunotoxicity is scarcely studied. This work investigates for the first time the influence of oral CYN exposure (18.75; 37.5 and 75 µg/kg b.w./day, for 28 days) on the mRNA expression of selected interleukin (IL) genes (IL-1β, IL-2, IL-6, Tumor Necrosis Factor alpha (TNF-α), Interferon gamma (IFN-γ)) in the thymus and the spleen of male and female rats, by quantitative real-time polymerase chain reaction (RT-qPCR). Moreover, their serum levels were also measured by a multiplex-bead-based immunoassay, and a histopathological study was performed. CYN produced immunomodulation mainly in the thymus of rats exposed to 75 μg CYN/kg b.w./day in both sexes. However, in the spleen only IL-1β and IL-2 (males), and TNF-α and IFN-γ (females) expression was modified after CYN exposure. Only female rats exposed to 18.75 μg CYN/kg b.w./day showed a significant decrease in TNF-α serum levels. There were no significant differences in the weight or histopathology in the organs studied. Further research is needed to obtain a deeper view of the molecular mechanisms involved in CYN immunotoxicity and its consequences on long-term exposures.

Immunotoxic Effects Induced by Microcystins and Cylindrospermopsin: A Review

Cyanotoxin occurrence is gaining importance due to anthropogenic activities, climate change and eutrophication. Among them, Microcystins (MCs) and Cylindrospermopsin (CYN) are the most frequently studied due to their ubiquity and toxicity. Although MCs are primary classified as hepatotoxins and CYN as a cytotoxin, they have been shown to induce deleterious effects in a wide range of organs. However, their effects on the immune system are as yet scarcely investigated. Thus, to know the impact of cyanotoxins on the immune system, due to its importance in organisms’ homeostasis, is considered of interest. A review of the scientific literature dealing with the immunotoxicity of MCs and CYN has been performed, and both in vitro and in vivo studies have been considered. Results have confirmed the scarcity of reports on the topic, particularly for CYN. Decreased cell viability, apoptosis or altered functions of immune cells, and changed levels and mRNA expression of cytokines are among the most common effects reported. Underlying mechanisms, however, are still not yet fully elucidated. Further research is needed in order to have a full picture of cyanotoxin immunotoxicity.

Microcystin-LR inhibits testosterone synthesis via reactive oxygen species-mediated GCN2/eIF2α pathway in mouse testes

Previous studies demonstrated that microcystin-leucine-arginine (MC-LR) disrupted testosterone (T) synthesis, but the underlying mechanisms are not entirely elucidated. This study aims to explore the role of reactive oxygen species (ROS)-mediated GCN2/eIF2α activation on MC-LR-induced disruption of testicular T synthesis. Male mice were intraperitoneally injected with MC-LR (0 or 20 μg/kg) daily for 5 weeks. Serum T was decreased in MC-LR-exposed mice (0.626 ± 0.122 vs 24.565 ± 8.486 ng/ml, P < 0.01), so did testicular T (0.667 ± 0.15 vs 8.317 ± 1.387 ng/mg protein, P < 0.01). Steroidogenic proteins including StAR, CYP11A1 and CYP17A1 were downregulated in MC-LR-exposed mouse testes and TM3 cells. Mechanistically, p-GCN2 and p-eIF2α were elevated in MC-LR-exposed TM3 cells. GCN2iB attenuated MC-LR-induced GCN2 and eIF2α phosphorylation in TM3 cells. Moreover, GCN2iB attenuated MC-LR-induced downregulation of steroidogenic proteins in TM3 cells. Further analysis found that cellular ROS were elevated and HO-1 was upregulated in MC-LR-exposed TM3 cells. PBN rescued MC-LR-induced activation of GCN2/eIF2α signaling in TM3 cells. Additionally, pretreatment with PBN attenuated MC-LR induced downregulation of steroidogenic proteins and synthases in TM3 cells. These results suggest that ROS-mediated GCN2/eIF2α activation contributes partially to MC-LR-caused downregulation of steroidogenic proteins and synthases. The present study provides a new clue for understanding the mechanism of MC-LR-induced endocrine disruption.

Microcystin-leucine arginine exposure contributes to apoptosis and follicular atresia in mice ovaries by endoplasmic reticulum stress-upregulated Ddit3

Microcystin-leucine arginine (MC-LR), an intracellular toxin to cause reproduction toxicity, is produced by blooming cyanobacteria and widely distributed in eutrophic waters. It is revealed that MC-LR-induced female reproductive toxicity is more severe than male reproductive toxicity. Previous studies mainly focused on male reproductive toxicity, and the molecular mechanisms of MC-LR-induced apoptosis, follicular atresia and infertility in female remain largely unclear. Here, it was found that MC-LR treatment could induce apoptosis, inflammation, follicular atresia, and decrease of gonadal index in mice ovaries. RNA-Seq data showed that the up-regulation of DNA-damage inducible transcript 3 (Ddit3) under endoplasmic reticulum (ER) stress had predominantly regulatory role in MC-LR-induced apoptotic pathway. Furthermore, MC-LR exposure promoted cleavage of activating transcription factor 6 (ATF6, 50kd), inositol-requiring enzyme 1 (Ire1) expression, phosphorylation of IRE1, mitogen-activated protein kinase 5 (Map3k5) and Ddit3 expression, which was accompanied by the upregulation of death receptor 5 (Dr5) and active-caspase-3, and a decrease in Bcl-2 expression. ER stress inhibitor 4-Phenyl butyric acid (4-PBA) ameliorated these MC-LR-induced changes in protein or mRNA level. More importantly, knockdown of Ddit3 suppressed MC-LR-induced cell apoptosis and follicular atresia by directly regulating Dr5 and Bcl-2. Additionally, it was also found that MC-LR increased Map3k5 phosphorylation by inhibiting protein phosphatase 2A (PP2A) activity, and then promoted Ddit3 expression. In short, our data suggests that Ddit3 promotes MC-LR-induced mice ovarian cells apoptosis and follicular atresia via ER stress activation, which provides a new insight into the relation between infertility in females and the emerging water pollutant MC-LR.

MicroRNA-181a regulates endoplasmic reticulum stress in offspring of mice following prenatal microcystin-LR exposure

Microcystin-LR (MCLR) was commonly regarded as a potent hepatotoxin and has been reported to cause neurotoxicity. This study was aimed to investigate how maternal MCLR exposure during pregnancy alters behavioral responses in offspring mice and the possible molecular mechanism involved in this procedure. Three doses of MCLR solutions (0, 3 or 15 μg/kg body weight) were administered subcutaneously to pregnant C57bl/6 from gestation day (GD) 6-19. Our results showed that MCLR prenatal exposure led to the impairment of learning and memory function in offspring on postnatal days (PND) 35, accompanied by endoplasmic reticulum (ER) stress and neuronal apoptosis in hippocampal CA1 regions of mice. Sixteen miRNAs in hippocampus of pups on PND 35 were significantly affected by MCLR exposure with the markedly decreased transcription of miR-181a-5p. We then found that miR-181a-5p was down-regulated, accompanied by activation of ER stress after prenatal exposure to MCLR using qPCR analysis. Furthermore, glucose-regulated protein, 78kDa/binding immunoglobulin protein (Grp78/BIP), a major ER chaperone and signaling regulator, was identified as a target of miR-181a-5p. Our study showed that miR-181a could lead to a decrease in the mRNA expression and protein levels of Grp78 by directly binding to its 3'-untranslated region (3'-UTR) in primary hippocampal neurons. Our findings indicate that the up-regulation of Grp78 mediated by inhibition of miR-181a-5p is a possible mechanism resulting in ER stress and cognitive impairment in pups following prenatal MCLR exposure.

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.

Oxidative imbalance in mice intoxicated by microcystin-LR can be minimized

Microcystins-LR (MC-LR) is a cyanotoxin produced by cyanobacteria. We evaluated the antioxidant potential of LASSBio-596 (LB-596, inhibitor of phosphodiesterases 4 and 5), per os, and biochemical markers involved in lung and liver injury induced by exposure to sublethal dose of MC-LR. Fifty male Swiss mice received an intraperitoneal injection of 60 μL of saline (CTRL group, n = 20) or a sublethal dose of MC-LR (40 μg/kg, TOX group, n = 20). After 6 h the animals received either saline (TOX and CTRL groups) or LB-596 (50 mg/kg, TOX + LASS group, n = 10) by gavage. At 6 h after exposure, respiratory mechanics was evaluated in 10 CTRL and 10 TOX mice: there was a significant increase of all lung mechanics parameters (static elastance, viscoelastic component of elastance and lung resistive and viscoelastic/inhomogeneous pressures) in TOX compared to CTRL. 8 h after saline or MC-LR administration, i.e., 2 h after treatment with LB-596, blood serum levels of alanine aminotransferase and aspartate aminotransferase, activity of superoxide dismutase, catalase, and content of malondialdehyde and carbonyl in lung and liver, NADPH oxidase 2 and 4 mRNA expressions, dual oxidase enzyme activity and H₂O₂ generation were analyzed in lung homogenates. All parameters were significantly higher in TOX than in the other groups. There was no significant difference between CTRL and TOX + LASS. MC-LR deteriorated lung and liver functions and induced redox imbalance in them, which was prevented by oral administration of LB-596.

Environmental Microcystin Exposure Increases Liver Injury Risk Induced by Hepatitis B Virus Combined with Aflatoxin: A Cross-Sectional Study in Southwest China

Three liver hazards, two confirmed-hepatitis B virus (HBV) and aflatoxin (AFB), and one rarely studied in populations-microcystin (MC), simultaneously exist in tropical and humid areas; however, there are no epidemiological data on their risks in the same population. We conducted a community-based cross-sectional survey among 5493 adults in two rural towns and statistically analyzed the comparative and combinative effects of the three factors after detecting HBsAg and HBV DNA titers, determining estimated daily intakes (EDIs) of AFB1 and MC-LR and testing serum AST and ALT as liver injury markers for each participant. We observed a HBsAg(+) rate of 7.6%, a relatively high AFB1 exposure level (mean EDI_AFB1 = 471.30 ng/d), and a relatively low MC-LR exposure level (mean EDI_MC-LR = 228.25 ng/d). ORs for abnormal AST (2.42, 95%CI = 1.69-3.45) and ALT (2.87, 95%CI = 1.91-4.29) increased in HBV infections compared with HBV-unexposed participants but did not increase in participants with separate or combined exposure to AFB1 and MC-LR (EDIs ≥ mean). Meanwhile, after adjustment for confounding factors, means of AST and ALT and ORs of abnormal AST and ALT were successively elevated after exposure to HBV, HBV&AFB1 (or HBV&MC-LR), and HBV&AFB1&MC-LR, especially in the group with detectable HBV DNA (AST: OR = 11.38, 95%CI = 3.91-33.17; ALT: OR = 17.09, 95%CI = 5.36-54.53). Notably, ORs for abnormal AST and ALT in the HBV exposed group were not significantly different from those in HBV&AFB1 or in the HBV&MC-LR exposed group but were significantly higher in the HBV&AFB1&MC-LR exposed group (P = 0.029 and P = 0.037, respectively). Our study indicated that microcystin may have the potential to increase the risk of liver injury induced by combined exposure to HBV and aflatoxin. However, in consideration of the uncertainties in the detection of the toxins and evaluation of the EDIs, more epidemiological data are expected to determine the increasing toxic effects of microcystins.

Organ-dependent response in antioxidants, myoglobin and neuroglobin in goldfish (Carassius auratus) exposed to MC-RR under varying oxygen level

Cyanobacterial bloom, a common phenomenon nowadays often results in the depletion of dissolved oxygen (hypoxia) and releases microcystin-RR (MC-RR) in the water. Information on the combined effects of MC-RR and hypoxia on the goldfish is lacking, therefore, this study is aimed at evaluating the effect of two doses of MC-RR on the antioxidants and globin mRNA of goldfish under normoxia, hypoxia and reoxygenation. The result showed that MC-RR at both doses (50 and 200 μg kg(-1) body weight) significantly (p<0.05) induced superoxide dismutase activities in the liver and kidney but catalase activities and total antioxidant capacity were low in these organs during hypoxia and reoxygenation compared to normoxia and control. Myoglobin and neuroglobin mRNAs in MC-RR group were significantly induced in the brain only and are believed to protect the brain from oxidative damage. However, other organs were unprotected and extensive damage was observed in the liver cells. Our results clearly demonstrated that MC-RR and hypoxia-reoxygenation transitions were synergistically harmful to the goldfish and could impair its adaptation to hypoxia, especially during reoxygenation.