Gastrointestinal toxicity induced by microcystins

A proteomic study on gastric impairment in rats caused by microcystin-LR

Microcystins (MCs) are the most common cyanobacterial toxins. Epidemiological investigation showed that exposure to MCs can cause gastro-intestinal symptoms, gastroenteritis and gastric cancer. MCs can also accumulate in and cause histopathological damage to stomach. However, the exact mechanisms by which MCs cause gastric injury were unclear. In this study, Wistar rats were administrated 50, 75 or 100 μg microcystin-LR (MC-LR)/kg, body mass (bm) via tail vein, and histopathology, response of anti-oxidant system and the proteome of gastric tissues at 24 h after exposure were studied. Bleeding of fore-stomach and gastric corpus, inflammation and necrosis in gastric corpus and exfoliation of mucosal epithelial cells in gastric antrum were observed following acute MC-LR exposure. Compared with controls, activities of superoxide dismutase (SOD) were significantly greater in gastric tissues of exposed rats, while activities of catalase (CAT) were less in rats administrated 50 μg MC-LR/kg, bm, and concentrations of glutathione (GSH) and malondialdehyde (MDA) were greater in rats administrated 75 or 100 μg MC-LR/kg, bm. These results indicated that MC-LR could disrupt the anti-oxidant system and cause oxidative stress. The proteomic results revealed that MC-LR could affect expressions of proteins related to cytoskeleton, immune system, gastric functions, and some signaling pathways, including platelet activation, complement and coagulation cascades, and ferroptosis. Quantitative real-time PCR (qRT-PCR) analysis showed that transcriptions of genes for ferroptosis and gastric function were altered, which confirmed results of proteomics. Overall, this study illustrated that MC-LR could induce gastric dysfunction, and ferroptosis might be involved in MC-LR-induced gastric injury. This study provided novel insights into mechanisms of digestive diseases induced by MCs.

Symptom frequency and exposure to a cyanobacteria bloom in Florida

This investigation was undertaken to characterize health effects associated with a major bloom of blue-green algae due to the proliferation Microcystis aeruginosa that occurred in Florida in 2018. Cyanobacteria produce multiple toxins, including the potent hepatotoxic microcystins (MCs), that have been reported to cause illness in exposed persons worldwide. Widespread exposure to toxins released by blue-green algae during the 2018 bloom was shown by the presence of MCs in the nasal passages of 95 percent of the individuals studied previously in south Florida (Schaefer et al., 2020). The current analyses were conducted to determine whether self-reported symptoms were associated with activity patterns, direct contact with water, residential, recreational, and occupational exposure. The 125 persons who participated in the initial study reported an average of 4.94 (± 4.87) symptoms. Those reported most commonly included rhinorrhea, sneezing, headache, sore throat and dry cough. Respiratory symptoms were reported by 74%, ocular symptoms by 62%, and gastrointestinal symptoms by 35% of respondents. Residential and recreational exposures were associated with increased risks of respiratory, gastrointestinal, or ocular symptoms in univariate and adjusted multivariable analyses. Residential exposure was significantly associated with increased reporting of dry cough (p = 0.03), dyspnea (p < 0.01) and wheezy respirations (p = 0.04). Among persons reporting gastrointestinal symptoms, nausea (p = 0.02) and abdominal pain (p < 0.01) were significantly associated with residential exposure. Recreational exposure was significantly associated with sore throat and eye irritation. The findings add to the evidence that exposure to cyanobacteria at concentrations encountered during an algal bloom is associated with a diverse array of symptoms and that inhalation of aerosols constitutes an important exposure pathway.

Long-Term Exposure to Microcystin-LR Induces Gastric Toxicity by Activating the Mitogen-Activated Protein Kinase Signaling Pathway

Previous studies have primarily concentrated on the hepatotoxicity of MC-LR, whereas its gastric toxicity effects and mechanisms of long-term exposure under low dosage remain unknown. Herein, the gastric tissue from C57BL/6 mice fed with drinking water contaminated by low-dose MC-LR (including 1, 60, and 120 μg/L) was investigated. The results obtained showed that exposure to different concentrations of MC-LR resulted in significant shedding and necrosis of gastric epithelial cells in mice, and a down-regulation of tight junction markers, including ZO-1, Claudin1, and Occludin in the stomach, which might lead to increased permeability of the gastric mucosa. Moreover, the protein expression levels of p-RAF/RAF, p-ERK1/2/ERK1/2, Pink1, Parkin, and LC3-II/LC-3-I were increased in the gastric tissue of mice exposed to 120 μg/L of MC-LR, while the protein expression level of P62 was significantly decreased. Furthermore, we found that pro-inflammatory factors, including IL-6 and TNF-ɑ, were dramatically increased, while the anti-inflammatory factor IL-10 was significantly decreased in the gastric tissue of MC-LR-exposed mice. The activation of the MAPK signaling pathway and mitophagy might contribute to the development of gastric damage by promoting inflammation. We first reported that long-term exposure to MC-LR induced gastric toxicity by activating the MAPK signaling pathway, providing a new insight into the gastric toxic mechanisms caused by MC-LR.

A review of adsorption techniques for removal of phosphates from wastewater

Phosphate is considered the main cause of eutrophication and has received considerable attention recently. Several methods have been used for removal of phosphates in water and these include biological treatment, membrane filtration processes, chemical precipitation, and adsorption. Adsorption technology is highly effective in the removal of phosphate from wastewater even at low phosphate concentrations. Nanomaterials/nanoparticles, carbon-based materials (activated carbon and biochar), and their composites have been widely employed for the adsorptive removal and recovery of phosphate from wastewater due to their exceptional properties such as high surface area and high phosphate adsorption properties. This article is a review of the recently reported literature in the field of nanotechnology and activated carbon for the adsorption of phosphate from wastewater. Highlights of the adsorption mechanisms, adsorption behaviour, experimental parameters, effects of co-existing ions, and adsorbent modifications are also discussed.

Prior exposure to microcystin alters host gut resistome and is associated with dysregulated immune homeostasis in translatable mouse models

A strong association between exposure to the common harmful algal bloom toxin microcystin and the altered host gut microbiome has been shown. We tested the hypothesis that prior exposure to the cyanotoxin microcystin-LR may alter the host resistome. We show that the mice exposed to microcystin-LR had an altered microbiome signature that harbored antibiotic resistance genes. Host resistome genotypes such as mefA, msrD, mel, ant6, and tet40 increased in diversity and relative abundance following microcystin-LR exposure. Interestingly, the increased abundance of these genes was traced to resistance to common antibiotics such as tetracycline, macrolides, glycopeptide, and aminoglycosides, crucial for modern-day treatment of several diseases. Increased abundance of these genes was positively associated with increased expression of PD1, a T-cell homeostasis marker, and pleiotropic inflammatory cytokine IL-6 with a concomitant negative association with immunosurveillance markers IL-7 and TLR2. Microcystin-LR exposure also caused decreased TLR2, TLR4, and REG3G expressions, increased immunosenescence, and higher systemic levels of IL-6 in both wild-type and humanized mice. In conclusion, the results show a first-ever characterization of the host resistome following microcystin-LR exposure and its connection to host immune status and antimicrobial resistance that can be crucial to understand treatment options with antibiotics in microcystin-exposed subjects in clinical settings.

Pollution Indicators and HAB-Associated Halophilic Bacteria Alongside Harmful Cyanobacteria in the Largest Mussel Cultivation Area in Greece

Taking into consideration the essential contribution of Mytilus galloprovincialis farming, it is of rising importance to add knowledge regarding bacterial species occurrence in water samples from aquaculture zones from the point of view of both the organism and public health. In the present study, we investigated the bacterial community existing in water samples from six Mytilus galloprovincialis aquaculture areas in the Thermaikos gulf, northern Greece, that may provoke toxicity in aquatic organisms and humans and may indicate environmental pollution in mussel production as well as algal blooms. Bacterial species were identified molecularly by sequencing of a partial 16s rRNA segment and were analyzed phylogenetically for the confirmation of the bacterial taxonomy. The results obtained revealed the presence of four bacterial genera (Halomonas sp., Planococcus sp., Sulfitobacter sp., and Synechocystis sp.). Members of the Halomonas and Sulfitobacter genera have been isolated from highly polluted sites, Planococcus bacteria have been identified in samples derived directly from plastic debris, and Synechocystis bacteria are in line with microcystin detection. In this context, the monitoring of the bacteria community in mussel aquaculture water samples from the Thermaikos gulf, the largest mussel cultivation area in Greece, represents an indicator of water pollution, microplastics presence, algal blooms, and toxin presence.

Mechanism of Action of Shenerjiangzhi Formulation on Hyperlipidemia Induced by Consumption of a High-Fat Diet in Rats Using Network Pharmacology and Analyses of the Gut Microbiota

Shenerjiangzhi formulation (SEJZ) is a new traditional Chinese medicine formulation (patent number: CN110680850A). SEJZ contains Eleutherococcus senticosus (Rupr. and Maxim.), Maxim (Araliaceae; E. senticosus radix and rhizome), Lonicera japonica Thunb (Caprifoliaceae; Lonicera japonica branch, stem), Crataegus pinnatifida Bunge (Rosaceae; Crataegus pinnatifida fruit), and Auricularia auricula. SEJZ has been designed to treat hyperlipidemia. Despite the therapeutic benefits of SEJZ, its underlying mechanism of action is not known. We explored the efficacy of SEJZ against hyperlipidemia by integrating network pharmacology and 16S rRNA gene sequencing and elucidated its mechanism of action. First, SEJZ targets were found through the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform and from the literature. Hyperlipidemia-related therapeutic targets were obtained from GeneCards, Online Mendelian Inheritance in Man, and DrugBank databases. Then, Search Tool for the Retrieval of Interacting Genes/Proteins and Cytoscape were applied for the analyses and construction of a protein–protein interaction (PPI) network. The Kyoto Encyclopedia of Genes and Genomes database was employed to identify signaling pathways that were enriched. Second, the therapeutic effects of SEJZ against hyperlipidemia induced by consumption of a high-fat diet in rats were evaluated by measuring body weight changes and biochemical tests. SEJZ treatment was found to alleviate obesity and hyperlipidemia in rats. Finally, 16S rRNA gene sequencing showed that SEJZ could significantly increase the abundance of short-chain fatty acid-producing bacteria, restore the intestinal barrier, and maintain intestinal-flora homeostasis. Using PICRUSt2, six metabolic pathways were found to be consistent with the results of network pharmacology: “African trypanosomiasis”, “amoebiasis”, “arginine and proline metabolism”, “calcium signaling pathway”, “NOD-like receptor signaling pathway”, and “tryptophan metabolism”. These pathways might represent how SEJZ works against hyperlipidemia. Moreover, the “African trypanosomiasis pathway” had the highest association with core genes. These results aid understanding of how SEJZ works against dyslipidemia and provide a reference for further studies.

Microcystin-LR incorporated into colonic cells through probenecid-sensitive transporters leads to upregulated MCP-1 expression induced by JNK activation

Harmful algae that inhabit eutrophic lakes produce cyanotoxic microcystins. Therefore, the relationship between chronic exposure to microcystins via drinking water and organ disorders has been investigated. The present study aimed to determine whether representative microcystin-LR is involved in increased monocyte chemoattractant protein-1 (MCP-1) expression in rat colonic mucosa and enterocyte-like differentiated Caco-2 cells. The mRNA expression of MCP-1 was increased in the colons of rats administered with microcystin-LR, compared with controls. Furthermore, mRNA levels of MCP-1 expression significantly and positively correlated with those of Adhesion G Protein-Coupled Receptor E1 (ADGRE1; EMR1; F4/80), an indicator of macrophage infiltration, suggesting that increased MCP-1 expression induced by microcystin-LR promotes macrophage infiltration into the colon. Microcystin-LR increased MCP-1 expression in enterocyte-like differentiated Caco-2 cells, by activating c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinase (ERK) or p38. The findings of transporter inhibitors indicated that microcystin-LR is incorporated into cells via ATP Binding Cassette (ABC) or solute carrier (SLC) transporters other than the organic anion transporting polypeptides (OATPs)1B1, 1B3, 2B1, and 1A2, which this leads to increased MCP-1 expression in the colon through activating JNK. Thus, increased MCP-1 expression induced by microcystin-LR might be a trigger for initiating tumorigenesis with inflammation in the colon because increased MCP-1 expression induces inflammation associated with macrophage infiltration into the colon, and chronic inflammation is associated with the initiation of tumorigenesis.

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Microcystin-LR upregulated colonic MCP-1 expression in rats.

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Increased MCP-1 expression correlated with accumulated macrophages in rat colon.

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Microcystin-LR evoked MCP-1 expression by activating JNK in cultured colon cells.

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Rifampicin was not involved in microcystin-LR-induced JNK activation.

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Probenecid suppressed JNK/MCP-1 pathway activation induced by microcystin-LR.

Microcystin-LR induces ferroptosis in intestine of common carp (Cyprinus carpio)

Previous studies provide comprehensive evidence of the environmental hazards and intestinal toxicity of microcystin-LR (MC-LR) exposure. However, little is known about the mechanisms underlying the injury of intestine exposed to MC-LR. Juvenile common carp (Cyprinus carpio) were exposed to MC-LR (0 and 10 μg/L) for 15 days. The results suggest that organic anion-transporting polypeptides 3a1, 4a1, 2b1, and 1d1 mediate MC-LR entry into intestinal tissues. Lesion morphological features (vacuolization, deformation and dilation of the endoplasmic reticulum [ER], absence of mitochondrial cristae in mid-intestine), up-regulated mRNA expressions of ER stress (eukaryotic translation initiation factor 2-alpha kinase 3, endoplasmic reticulum to nucleus signaling 1, activating transcription factor [ATF] 6, ATF4, DNA damage-inducible transcript 3), iron accumulation, and down-regulated activity of glutathione peroxidase (GPx) and glutathione (GSH) content were all typical characteristics of ferroptosis in intestinal tissue following MC-LR exposure. GSH levels in intestinal tissue corroborated as the most influential GSH/GPx 4- related metabolic pathway in response to MC-LR exposure. Verrucomicrobiota, Planctomycetes, Bdellovibrionota, Firmicutes and Cyanobacteria were correlated with the ferroptosis-related GSH following MC-LR exposure. These findings provide new perspectives of the ferroptosis mechanism of MC-LR-induced intestinal injury in the common carp.

Advances in the toxicology research of microcystins based on Omics approaches

Microcystins (MCs) are the most widely distributed cyanotoxins, which can be ingested by animals and human body in multiple ways, resulting in a threat to human health and the biodiversity of wildlife. Therefore, the study on toxic effects and mechanisms of MCs is one of the focuses of attention. Recently, the Omics techniques, i.e. genomics, transcriptomics, proteomics and metabolomics, have significantly contributed to the comprehensive understanding and revealing of the molecular mechanisms about the toxicity of MCs. This paper mainly reviews current literature using the Omics approaches to explore the toxicity mechanism of MCs in liver, gonad, spleen, brain, intestine and lung of multiple species. It was found that MCs can exert strong toxic effects on various metabolic activities and cell signal transduction in cell cycle, apoptosis, destruction of cell cytoskeleton and redox disorder, at protein, transcription and metabolism level. Meanwhile, it was also revealed that the alteration of non-coding RNAs (miRNA, circRNA and lncRNA, etc.) and gut microbiota plays an essential regulatory role in the toxic effects of MCs, especially in hepatotoxicity and reproductive toxicity. In addition, we summarized current research gaps and pointed out the future directions for research. The detailed information in this paper shows that the application and development of Omics techniques have significantly promoted the research on MCs toxicity, and it is also a valuable resource for exploring the toxic mechanism of MCs.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

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

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

Acute cyanotoxin poisoning reveals a marginal effect on mouse gut microbiome composition but indicates metabolic shifts related to liver and gut inflammation

Freshwater harmful algal blooms (HABs) are a major environmental health problem worldwide. HABs are caused by a predominance of cyanobacteria, some of which produce potent toxins. The most ubiquitous cyanotoxin is microcystin (MC) and the congener MC-LR is the most studied due to its toxicity. Short-term exposure to toxins can cause gut microbiome disturbances, but this has not been well described with MC-LR exposure. This study investigated the gut microbial communities of mice from a prior study, which identified significant liver toxicity from ingestion of MC-LR daily for 8 days. CD-1 mice were divided into three dosage groups: control, low exposure (sub-lethal MC-LR concentration), and high exposure (near-lethal MC-LR concentration). Fecal samples were analyzed using 16S rRNA sequencing. Results revealed that at population level, there were no significant shifts in bacterial diversity or the microbial community structure over the exposure period. However, there were significant differences between male and female mice. Predictive functional gene analysis indicated that several metabolic pathways were significantly different in the high dose group before exposure and following 7 doses of MC-LR, as well as between the control and high dose groups on Day 8. Significant differentially abundant taxa were also identified contributing to these pathways. Several pathways, including superpathway of N-acetylneuraminate degradation, were related to liver and gut inflammation. The outcome of this study suggests a need for in-depth investigation of metabolic activity and other functions in the gut in future studies, as well as potential consideration of the role of sex in MC-LR toxicity.

Risk prediction of microcystins based on water quality surrogates: A case study in a eutrophicated urban river network

Microcystins (MCs), the toxic by-products from harmful algal bloom (HAB), have caused world-wide concern due to their acute toxicity in freshwater ecosystems. Most studies on HAB have been conducted for shallow freshwater lakes, such as Taihu Lake in China. However, algal blooms in urban rivers located downstream of eutrophicated lakes are also a serious problem for local administrators. It is important for them to know the current and potential risk level of MCs. This environmental issue is rarely reported or discussed. Within this context, we monitored MC concentrations in the Binhu River Network (BRN) in the algal bloom season (Aug, Sep, and Oct) in 2019. To note if the MC concentrations were dangerous, we used 1.0 μg/L suggested by the World Health Organization as the standard value. The proportions of MC samples violating the standard value were 31.78% (Aug), 21.14% (Sep) and 30.77% (Oct). We also designed two statistical models to predict MC concentrations and the possibility to exceed the standard level based on 10 water quality surrogates: Artificial Neural Network (ANN) and Logistic Regression (LR) models. These two models were trained and validated by the monitoring dataset (n = 224). Both models had good performances during training and testing. Although the water quality varied diversely both in spatial and temporal scale, Cluster Analysis (CA) could detect similarities among the samples and separated them into 3 classes, with each class denoting different types of rivers based on the 10 water quality surrogates. Then the ANN and LR were applied as a function of chl-a in each class; by gradually increasing chl-a concentration, we detected chl-a thresholds in class 1, 2, 3 were 25.5, 224, and 109.5 μg/L, respectively, when MCs have a 50% possibility to exceed standard level. The threshold values provided important implications for MC management in the BRN.

Effects of fulvic acid size on microcystin-LR photodegradation and detoxification in the chlorine/UV process

Microcystin-LR (MC-LR), a polypeptide toxin generated by cyanobacteria, threatens the safety of drinking water supplies. In this study, fulvic acid (FA) was separated into two molecular weight (MW) ranges to evaluate the effects of FA size on MC-LR degradation in the chlorine/UV process. The rates of MC-LR degradation were significantly reduced in FA-containing water (3.7 × 10^-3 s^-1 for small MW FA; 4.3 × 10^-3 s^-1 for large MW FA) as compared with FA free water (4.9 × 10^-3 s^-1). The contributions of ClO• to MC-LR degradation were dramatically lower in small MW FA water (0.4%) than large MW FA (13.9%) and FA free water (17.4%), suggesting inhibition by lignin-like substances in FA in the transformation of Cl• to ClO• and scavenging ClO•. Monochlorination and hydroxylation occurred in the first step of the MC-LR degradation process. The accumulation of intermediate products in the chlorine/UV process indicated that small MW FA inhibited further degradation of MC-LR. Small MW FA, rather than MC-LR degradation, was the dominant factor in minimizing MC-LR cytotoxicity toward a human intestinal epithelial cell line.

First report of detection of microcystins in farmed mediterranean mussels Mytilus galloprovincialis in Thermaikos gulf in Greece

BACKGROUND

Microcystins are emerging marine biotoxins, produced by potentially toxic cyanobacteria. Their presence has been reported in aquatic animals in Greek freshwater, while data are few in marine environments. Since the climate change induces eutrophication and harmful algal blooms in coastal marine ecosystems affecting the public health, further research on microcystins' presence in marine waters is required. The aim of this study was to examine the potential presence of microcystins in mussels Mytilus galloprovincialis in the largest farming areas in Thermaikos gulf, in Northern Greece, and to investigate their temporal and spatial distribution, adding to the knowledge of microcystins presence in Greek Mediterranean mussels.

RESULTS

A 4-year microcystins' assessment was conducted from 2013 to 2016, in farmed Mediterranean mussels M. galloprovincialis, in five sampling areas in Thermaikos gulf, in northern Greece, where the 90% of the Greek mussels' farming activities is located. The isolation of potentially toxic cyanobacteria was confirmed by molecular methods. An initial screening was performed with a qualitative and quantitative direct monoclonal (DM) ELISA and results above 1 ng g-1 were confirmed for the occurrence of the most common microcystins-RR, -LR and -YR, by Ultra High Performance Liquid Chromatography (UHPLC) coupled with a high- resolution mass spectrometer (HRMS) (Orbitrap analyzer). Microcystin-RR and microcystin-LR were detected, while the intensity of microcystin-YR was below the method detection limit. Most samples that exhibited concentrations above 1 ng g-1 were detected during the warm seasons of the year and especially in spring. Results indicated an overestimation of the ELISA method, since concentrations ranged between 0.70 ± 0.15 ng g-1 and 53.90 ± 3.18 ng g-1, while the confirmation denoted that the levels of microcystins were 6 to 22 times lower.

CONCLUSIONS

Microcystin-RR and microcystin-LR were detected for the first time in mussel M. galloprovincialis, harvested from farms in Thermaikos gulf, in Central Macedonia, Greece. Their presence was linked to potentially toxic cyanobacteria. Bioaccumulation was observed in digestive gland, while the concentrations in muscles were found extremely low. Samples with levels above 1 ng g-1 were observed mostly during spring, confirming the seasonal distribution of microcystins. The comparison of the results by the ELISA and the LC-Orbitrap MS method indicated an overestimation of concentration by the ELISA method.

IRE1 and CaMKKβ pathways to reveal the mechanism involved in microcystin-LR-induced autophagy in mouse ovarian cells

Microcystin-LR (MC-LR) is an emerging water pollutant produced by blooming cyanobacteria. It could be absorbed into human body via contaminated food and drinking water causing severe reproductive toxicity. Previous studies showed that MC-LR could regulate autophagy by inducing endoplasmic reticulum (ER) stress thereby causing female reproductive toxicity. However, the molecular mechanisms of MC-LR-induced autophagy remain to be elucidated. It is known that IRE1 and CaMKKβ pathways are two important pathways involved in autophagy induced by ER stress. Hence, this study investigated the roles of both pathways in MC-LR-induced autophagy in mouse ovarian cells. The results showed that MC-LR significantly up-regulated the expression of autophagy marker proteins LC3Ⅱ and BECLIN1 and down-regulated the expression of P62 in vivo and in vitro. MC-LR-caused increase of autophagosomes could be observed in KK-1 cells by MDC staining. MC-LR induced the formation of autolysosomes as indicated by the overlap of LAMP1 and LC3. Meanwhile, MC-LR significantly activated the proteins in IRE1 pathway (IRE1, XBP1 and JNK) and in CaMKKβ pathway (CaMKKβ, AMPK, mTOR). Furthermore, MC-LR caused weight loss and ovarian histopathological damage in mice. In contrast, after the expression and function of IRE1 and CaMKKβ were inhibited with siRNA in vitro and by inhibitors (4μ8C and STO-609, respectively) in vivo, the up-regulation of LC3Ⅱ and BECLIN1 and the degradation of P62 induced by MC-LR were significantly suppressed. MC-LR-induced autophagosomes in KK-1 cells and autolysosomes in mouse ovarian cells were also decreased. Moreover, the knockdown of IRE1 and CaMKKβ relieved MC-LR-induced histopathological injury to mouse ovaries. These results indicated that MC-LR induced ovarian cell autophagy and ovarian injury via IRE1 and CaMKKβ pathways. This study is the first study revealing the molecular mechanisms of MC-LR-induced autophagy of ovarian cells and providing new insights into the female reproductive toxicity of MC-LR.

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.

Effects of Chronic Exposure to Microcystin-LR on Kidney in Mice

Microcystin-LR (MC-LR) is a potent hepatotoxin, but a few studies suggested that it might also induce nephrotoxicity. However, nephrotoxicity induced by prolonged oral exposure to MC-LR is unknown. The aim of this study was to evaluate the potential influence of MC-LR on the kidney in mice following chronic exposure to MC-LR. In this study, we evaluated the nephrotoxicity of MC-LR in mice drinking water at different concentrations (1, 30, 60, 90, and 120 μg/L) for 6 months for the first time. The results showed that the kidney weights and the kidney indexes of mice were not altered in the MC-LR treated mice, compared with the control group. In addition, the renal function indicators revealed that the serum creatinine (SCr) levels were not significant changes after exposure to MC-LR. The blood urea nitrogen (BUN) levels were markedly decreased after exposure to 90 and 120 μg/L MC-LR for 3 months. The BUN levels were lower than that of the control group after exposure to 120 μg/L MC-LR for 6 months. The histopathological investigation revealed enlarged renal corpuscles, widened of kidney tubules, and lymphocyte infiltration in the interstitial tissue and the renal pelvis after exposure to 60, 90, and 120 μg/L MC-LR. Consequently, our results suggested that long-term exposure to MC-LR might be one important risk of kidney injury, which will provide important clues for the prevention of renal impairment.

Effects of microcystins-LR on genotoxic responses in human intestinal epithelial cells (NCM460)

Microcystin-LR (MC-LR), a cyclic heptapeptide toxin produced by cyanobacteria, was found to induce genotoxic actions in various types of cells. Some investigators reported that microcystin-LR acted as tumor initiator in the observed genotoxic action mediated by this cyanotoxin. However, the underlying mechanisms underlying MC-induced DNA damage in the human intestine epithelium cell line (NCM460) are not known. The purpose of this study was to examine the influence of 24 hr exposure to 5 or 10 µM MC-LR on intestinal DNA damage using NCM460 intestine cell line as a model. Data showed that MC-LR increased Olive tail moment (OTM) as evidenced by the comet assay, inhibited protein phosphatase 2A (PP2A) activity, elevated reactive oxygen species levels (ROS) and enhanced γ-H2AX and p-p53 protein expression levels. Results indicated that MC-LR produced intestinal DNA damage by inhibiting PP2A activity, activating p53 protein and subsequently initiating excess generation of ROS. These observations suggest that MC-LR-induced intestinal DNA damage involves a complex series of events that include oxidant stress, PP2A enzymic inhibition and activation of p53 protein.

Effects of Microcystin-LR on the Microstructure and Inflammation-Related Factors of Jejunum in Mice

The increasing cyanobacterial blooms have recently been considered a severe environmental problem. Microcystin-leucine arginine (MC-LR) is one of the secondary products of cyanobacteria metabolism and most harmful cyanotoxins found in water bodies. Studies show MC-LR negatively affects various human organs when exposed to it. The phenotype of the jejunal chronic toxicity induced by MC-LR has not been well described. The aim of this paper was to investigate the effects of MC-LR on the jejunal microstructure and expression level of inflammatory-related factors in jejunum. Mice were treated with different doses (1, 30, 60, 90 and 120 μg/L) of MC-LR for six months. The microstructure and mRNA expression levels of inflammation-related factors in jejunum were analyzed. Results showed that the microstructure of the jejunum was destroyed and expression levels of inflammation-related factors interleukin (IL)-1β, interleukin (IL)-8, tumor necrosis factor alpha, transforming growth factor-β1 and interleukin (IL)-10 were altered at different MC-LR concentrations. To the best of our knowledge, this is the first study that mice were exposed to a high dose of MC-LR for six months. Our data demonstrated MC-LR had the potential to cause intestinal toxicity by destroying the microstructure of the jejunum and inducing an inflammatory response in mice, which provided new insight into understanding the prevention and diagnosis of the intestinal diseases caused by MC-LR.