Microcystin-LR induced liver injury in mice and in primary human hepatocytes is caused by oncotic necrosis

Microcystin-LR and its health impacts: Chemistry, transmission routes, mechanisms of toxicity and target organs

Microcystin-LR, a hepatotoxin produced by cyanobacteria, poses significant health risks to humans and other animals through various routes of exposure. This review comprehensively explores the chemistry, transmission pathways, mechanisms of toxicity, and target organs affected by MC-LR to provide a detailed understanding of its health impacts on animals and humans. MC-LR exposure occurs through different transmission routes, including ingesting contaminated water and food, algal dietary supplements, direct body contact with harmful algal blooms, and inhalation of aerosolized toxins. In this review, we explored that the toxic effects of MC-LR are mediated through multiple complex mechanisms. A key mechanism of its toxicity is the inhibition of protein phosphatases PP1 and PP2A which results in abnormal cellular signalling pathways. Additionally, MC-LR induces oxidative stress and disrupts cellular homeostasis. The findings suggest that MC-LR modulates the activity of various antioxidant enzymes and also activates apoptosis pathways by different mechanisms. It also induces cytoskeletal disruption, ultimately compromising cellular integrity and function. MC-LR also induces activation of oncogenes such as Gankyrin, PI3K/AKT, HIF-1α, RAC1/JNK and NEK2 pathway and upregulates the inflammatory molecules such as NF-κβ, and TNF-α, hence leading to carcinogenesis. MC-LR has toxicological effects on multiple organs. The liver is the primary target, where MC-LR accumulates and causes hepatotoxicity, but other organs are affected as well. MC-LR shows neurotoxicity, nephrotoxicity, cardiotoxicity and reproductive toxicity.

Oxidative stress and mitochondrial dysfunctions induced by cyanobacterial microcystin-LR in primary grass carp hepatocytes

Microcystin-LR (MC-LR), a cyclic heptapeptide produced by freshwater cyanobacteria, induces a range of liver injuries. However, the mechanisms underlying MC-LR toxicity in primary hepatocytes of aquatic organisms remains poorly understood. In this study, we investigated the effects of MC-LR on oxidative stress and mitochondrial function using primarily cultured grass carp hepatocytes. The results revealed that IC50 of MC-LR on grass carp primary liver cells for 24 hours was 2.40 μmol/L. Based on 24h-IC50, concentrations of 0, 0.30, 0.60, and 1.20 μmol/L were used in subsequent experiments. MC-LR exposure led to a significant reduction in cell viability, induced abnormal cell morphology, and caused plasma membrane rupture, as indicated by elevated LDH activity in a concentration-dependent manner. Additionally, MC-LR exposure induced oxidative stress, resulting in increased ROS levels and downregulation of genes associated with oxidative stress, including keap1, nrf2, cat, sod1, gpx, gst, and gr (P<0.05). Furthermore, the electron microscopy results showed that MC-LR caused damage to the ultrastructure of primary hepatocytes, including mitochondrial membrane rupture, vacuolation, and induction of mitochondrial autophagy. Moreover, MC-LR exposure elevated intracellular Ca2+ concentration, reduced MMP and ATP levels, and inhibited mitochondrial respiratory chain complex I activity (P<0.05). qRT-PCR analysis demonstrated that MC-LR treatment significantly decreased the transcriptional levels of genes related to mitochondrial quality control including pgc-1α, tfam, nrf1, drp1, opa1, mfn1, and mfn2 (P<0.05). Collectively, our findings highlight that MC-LR causes oxidative stress and impairs mitochondrial function, leading to further hepatocyte damage, which provides insights into the mechanisms of MC-LR-induced hepatotoxicity and offers valuable references for further investigations.

Aerosolized Harmful Algal Bloom Toxin Microcystin-LR Induces Type 1/Type 17 Inflammation of Murine Airways

Harmful algal blooms are increasing globally and pose serious health concerns releasing cyanotoxins. Microcystin-LR (MC-LR), one of the most frequently produced cyanotoxins, has recently been detected in aerosols generated by the normal motions of affected bodies of water. MC-LR aerosol exposure has been linked to a pro-inflammatory influence on the airways of mice; however, little is understood about the underlying mechanism or the potential consequences. This study aimed to investigate the pro-inflammatory effects of aerosolized MC-LR on murine airways. C57BL/6 and BALB/c mice were exposed to MC-LR aerosols, as these strains are predisposed to type 1/type 17 and type 2 immune responses, respectively. Exposure to MC-LR induced granulocytic inflammation in C57BL/6 but not BALB/c mice, as observed by increased expression of cytokines MIP-1α, CXCL1, CCL2, and GM-CSF compared with their respective vehicle controls. Furthermore, the upregulation of interleukins IL-17A and IL-12 is consistent with Th1- and Th17-driven type 1/type 17 inflammation. Histological analysis confirmed inflammation in the C57BL/6 lungs, with elevated neutrophils and macrophages in the bronchoalveolar lavage fluid and increased pro-inflammatory and pro-resolving oxidized lipids. In contrast, BALB/c mice showed no significant airway inflammation. These results highlight the ability of aerosolized MC-LR to trigger harmful airway inflammation, requiring further research, particularly into populations with predispositions to type 1/type 17 inflammation.

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.

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

Hepatotoxicity of cyanotoxin microcystin-LR in human: Insights into mechanisms of action in the 3D culture model Hepoid-HepaRG

Microcystin-LR (MC-LR) is a potent hepatotoxin produced by harmful cyanobacterial blooms (CyanoHABs). MC-LR targets highly differentiated hepatocytes expressing organic anion transporting polypeptides OATP1B1 and OATP1B3 that are responsible for hepatocellular uptake of the toxin. The present study utilized an advanced 3D in vitro human liver model Hepoid-HepaRG based on the cultivation of collagen-matrix embedded multicellular spheroids composed of highly differentiated and polarized hepatocyte-like cells. 14-d-old Hepoid-HepaRG cultures showed increased expression of OATP1B1/1B3 and sensitivity to MC-LR cytotoxicity at concentrations >10 nM (48 h exposure, EC20 = 26 nM). MC-LR induced neither caspase 3/7 activity nor expression of the endoplasmic reticulum stress marker gene BiP/GRP78, but increased release of pro-inflammatory cytokine IL-8, indicating a necrotic type of cell death. Subcytotoxic (10 nM) and cytotoxic (≥100 nM) MC-LR concentrations disrupted hepatocyte functions, such as xenobiotic metabolism phase-I enzyme activities (cytochrome P450 1A/1B) and albumin secretion, along with reduced expression of CYP1A2 and ALB genes. MC-LR also decreased expression of HNF4A gene, a critical regulator of hepatocyte differentiation and function. Genes encoding hepatobiliary membrane transporters (OATP1B1, BSEP, NTCP), hepatocyte gap junctional gene connexin 32 and the epithelial cell marker E-cadherin were also downregulated. Simultaneous upregulation of connexin 43 gene, primarily expressed by liver progenitor and non-parenchymal cells, indicated a disruption of tissue homeostasis. This was associated with a shift in the expression ratio of E-cadherin to N-cadherin towards the mesenchymal cell marker, a process linked to epithelial-mesenchymal transition (EMT) and hepatocarcinogenesis. The effects observed in the human liver cell in vitro model revealed mechanisms that can potentially contribute to the MC-LR-induced promotion and progression of hepatocellular carcinoma (HCC). Hepoid-HepaRG cultures provide a robust, accessible and versatile in vitro model, capable of sensitively detecting hepatotoxic effects at toxicologically relevant concentrations, allowing for assessing hepatotoxicity mechanisms, human health hazards and impacts of environmental hepatotoxins, such as MC-LR.

Morchella Effectively Removes Microcystins Produced by Microcystis aeruginosa

Microcystins (MCs) produced by Microcystis aeruginosa are harmful to animal and human health, and there is currently no effective method for their removal. Therefore, the development of biological approaches that inhibit cyanobacteria and remove MCs is needed. We identified strain MB1, confirmed as Morchella, using morphological and mole-cular evolution methods. To assess the impact of strain MB1 on M. aeruginosa, we conducted an experiment in which we inoculated M. aeruginosa with Morchella strain MB1. After their co-cultivation for 4‍ ‍d, the inoculation with 0.9696‍ ‍g MB1 completely inhibited and removed M. aeruginosa while concurrently removing up to 95% of the MC content. Moreover, within 3‍ ‍d of their co-cultivation, MB1 removed more than 50% of nitrogen and phosphorus from the M. aeruginosa solution. Therefore, the development of effective biological techniques for MC removal is paramount in safeguarding both the environment and human well-being. We herein successfully isolated MB1 from its natural habitat. This strain effectively inhibited and removed M. aeruginosa and also reduced the content of nitrogen and phosphorus in the M. aeruginosa solution. Most importantly, it exhibited a robust capability to eliminate MCs. The present results offer a new method and technical reference for mitigating harmful algal blooms.

Hepatic NLRP3-Derived Hsp70 Binding to TLR4 Mediates MASLD to MASH Progression upon Inhibition of PP2A by Harmful Algal Bloom Toxin Microcystin, a Second Hit

Harmful algal bloom toxin microcystin has been associated with metabolic dysfunction-associated steatotic liver disease (MASLD) progression and hepatocellular carcinoma, though the mechanisms remain unclear. Using an established mouse model of MASLD, we show that the NLRP3-Hsp70-TLR4 axis drives in part the inflammation of the liver lobule that results in the progression of MASLD to metabolic dysfunction-associated steatohepatitis (MASH). Results showed that mice deficient in NLRP3 exhibited decreased MASH pathology, blocked Hsp70 expression, and co-binding with NLRP3, a crucial protein component of the liver inflammasome. Hsp70, both in the liver lobule and extracellularly released in the liver vasculature, acted as a ligand to TLR4 in the liver, primarily in hepatocytes to activate the NF-κB pathway, ultimately leading to hepatic cell death and necroptosis, a crucial pathology of MASH progression. The above studies show a novel insight into an inflammasome-triggered Hsp70-mediated inflammation that may have broader implications in MASLD pathology. MASLD to MASH progression often requires multiple hits. One of the mediators of progressive MASLD is environmental toxins. In this research report, we show for the first time a novel mechanism where microcystin-LR, an environmental toxin, advances MASLD to MASH by triggering the release of Hsp70 as a DAMP to activate TLR4-induced inflammation in the liver.

Purification and Activity of the Second Recombinant Enzyme for Biodegrading Linearized Microcystins by Sphingopyxis sp. USTB-05

Hepatotoxic microcystins (MCs) are produced and released by the harmful bloom-forming cyanobacteria, which severely threaten drinking water safety and human health due to their high toxicity, widespread distribution, and structural stability. The linearized microcystinase (MlrB) further hydrolyses the poisonous linearized MCs produced by the microcystinase-catalysed MCs to form tetrapeptides. Here, the purification and activity of MlrB were investigated. The results showed that the linearized products generated by 12.5 mg/L MC-LR and MC-RR were removed by purified recombinant MlrB at a protein concentration of 1 mg/L within 30 min. The high catalytic activity of MlrB can be obtained via heterologous expression and affinity purification, which lays the foundation for further studies on the properties and mechanism of MCs biodegradation enzymes.

Behavioral disturbances induced by cyanobacterial oligopeptides microginin-FR1, anabaenopeptin-A and microcystin-LR are associated with neuromotoric and cytotoxic changes in Brachionus calyciflorus

Aquatic animals are exposed to various cyanobacterial products released concomitantly to the environment by decaying blooms. Although there exist results on the toxicity of cyanobacterial extracts little is known on the influence of pure oligopeptides or their mixtures and elucidated mechanisms of behavioral toxicity in zooplanktonic organisms. Therefore, the aim of the present study was to assess the effects of single and mixed pure cyanobacterial oligopeptides: microginin FR-1 (MG-FR1), anabaenopeptin-A (ANA-A) and microcystin-LR (MC-LR) at various concentrations on the swimming behavior and catecholamine neurotransmitter activity, muscular F-actin structure, DNA nuclear content and cell viability of a model rotifer Brachionus calyciflorus. Swimming behavior was analyzed with the use of video digital analysis. Fluorescent microscopy imaging was used to analyze neuromotoric biomarkers in the whole organisms: neuromediator release (by staining with EC517 probe), muscle F-actin filaments (by staining with blue phalloidin dye). DNA content and cytotoxicity was also determined by Hoechst 34580 and propidium iodide double staining, respectively. The results showed that single oligopeptides inhibited all the tested endpoints. The binary mixtures induced synergistic interaction on swimming speed except for MG-FR1 +MC-LR which was nearly additive. Both binary and ternary mixtures also synergistically degraded F-actin and triggered cytotoxic effects visible in the whole organisms. Antagonistic inhibitory effects of all the binary mixtures were found on catecholamine neurotransmitter activity, however the ternary mixture induced additive toxicity. Antagonistic effects of both binary and ternary mixtures were also noted on nuclear DNA content. The results of the study suggest that both depression of neurotransmission and impairment of muscle F-actin structure in muscles may contribute to mechanisms of Brachionus swimming speed inhibition by the tested single cyanobacterial oligopeptides and their mixtures. The study also showed that natural exposure of rotifers to mixtures of these cyanobacterial metabolites may result in different level of interactive toxicity with antagonistic, additive synergistic effects depending on the variants and concentrations present in the environment.

Impact of Cyanotoxin Ingestion on Liver Cancer Development Using an At-Risk Two-Staged Model of Mouse Hepatocarcinogenesis

Exposure to cyanobacterial hepatotoxins has been linked to the promotion and increased incidence of liver cancer in pre-clinical and epidemiologic studies. The family of hepatotoxins, microcystins (MCs), are produced by over 40 cyanobacterial species found in harmful algal blooms (HABs) worldwide, with MC-LR being the most common and potent MC congener. In the current study, we hypothesized that the low-dose chronic ingestion of Microcystis cyanotoxins via drinking water would promote liver carcinogenesis in pre-initiated mice. Four groups of C3H/HeJ mice received one intraperitoneal (i.p.) injection of diethylnitrosamine (DEN) at 4 weeks of age. Three weeks later, the mice were administered ad libitum drinking water containing one of the following: (1) reverse osmosis, deionized water; (2) water containing 500 mg/L phenobarbital (PB500); (3) water with purified MC-LR (10 µg/L) added; or (4) water containing lysed Microcystis aeruginosa (lysate; 10 µg/L total MCs). The exposure concentrations were based on environmentally relevant concentrations and previously established Ohio EPA recreational water MC guidelines. Throughout the 30-week exposure, mouse weights, food consumption, and water consumption were not significantly impacted by toxin ingestion. We found no significant differences in the number of gross and histopathologic liver lesion counts across the treatment groups, but we did note that the PB500 group developed lesion densities too numerous to count. Additionally, the proportion of lesions classified as hepatocellular carcinomas in the MC-LR group (44.5%; p < 0.05) and lysate group (55%; p < 0.01) was significantly higher compared to the control group (14.9%). Over the course of the study, the mice ingesting the lysate also had a significantly lower survival probability (64.4%; p < 0.001) compared to water (96.8%), PB500 (95.0%), and MC-LR (95.7%) exposures. Using cyanotoxin levels at common recreational water concentration levels, we demonstrate the cancer-promoting effects of a single cyanotoxin MC congener (MC-LR). Furthermore, we show enhanced hepatocarcinogenesis and significant mortality associated with combinatorial exposure to the multiple MCs and bioactive compounds present in lysed cyanobacterial cells—a scenario representative of the ingestion exposure route, such as HAB-contaminated water and food.

Acute microcystin exposure induces reversible histopathological changes in Chinook Salmon (Oncorhynchus tshawytscha) and Atlantic Salmon (Salmo salar)

Atlantic Salmon (Salmo salar) and Chinook Salmon (Oncorhynchus tshawytscha) develop a severe liver disease called net-pen liver disease (NPLD), which is characterized by hepatic lesions that include megalocytosis and loss of gross liver structure. Based on studies where salmonids have been exposed to microcystin (MC) via intraperitoneal injection, NPLD is believed to be caused by MC exposure, a hepatotoxin produced by cyanobacteria. Despite the link between MC and NPLD, it remains uncertain if environmentally relevant MC exposure is responsible for NPLD. To determine if we could produce histopathology consistent with NPLD, we compared the response of Atlantic and Chinook Salmon sub-lethal MC exposure. Salmon were orally gavaged with saline or MC containing algal paste and sampled over 2 weeks post-exposure. Liver lesions appeared by 6 h but were resolved 2-weeks post-exposure; histopathological changes observed in other tissues were not as widespread, nor was their severity as great as those in the liver. There was no evidence for NPLD due to the absence of hepatic megalocytosis. These results indicate that the development of NPLD is not due to acute MC exposure but may be associated with higher MC concentration occurring in food, long-term exposure through drinking of contaminated seawater and/or interactions with other marine toxins.

Inonotus obliquus aqueous extract prevents histopathological alterations in liver induced by environmental toxicant Microcystin

Environmental toxicants like microcystins are known to adversely impact liver physiology and lead to the increased risk for abnormal liver function and even liver carcinoma. Chaga mushroom (Inonotus obliquus) is reported for various properties mainly antibacterial, antiallergic, anti-inflammatory, antioxidant, and anticancer properties. This study was aimed to assess the effect microcystin (MC-LR) on histopathology of liver in mice and a preventive measure by using aqueous extract of Inonotus obliquus (IOAE). Adult Balb/c mice were administered with MC-LR at 20 ​μg/kg body weight, per day, intraperitoneal (i.p.) for 4 weeks. IOAE was treated to one group of MC-LR mice at 200 ​mg/kg body weight, per oral, for 4 weeks. Histological staining for liver structural details and biochemical assays for functions were assessed. The results of the study showed that MC-LR drastically reduced the body weight of mice which were restored close to the range of control by IOAE treatment. MC-LR exposed mice showed 1.9, 1.7 and 2.2-fold increase in the levels of SGOT, SGPT and LDH which were restored by IOAE treatment as compared to control (one-fold). MC-LR exposed mice showed reduced level of GSH (19.83 ​± ​3.3 ​μM) which were regained by IOAE treatment (50.83 ​± ​3.0 ​μM). Similar observations were noted for catalase activity. Histological examinations show that MC-LR exposed degenerative changes in the liver sections which were restored by IOAE supplementation. The immunofluorescence analysis of caspase-3 counterstained with DAPI showed that MC-LR led to the increased expression of caspase-3 which were comparatively reduced by IOAE treatment. The cell viability decreased on increasing the concentration of MC-LR with 5% cell viability at concentration of 10 ​μg MC-LR/mL as that of control 100% Cell viability. The IC₅₀ was calculated to be 3.6 ​μg/ml, indicating that MC-LR is chronic toxic to AML12 mouse hepatocytes. The molecular docking interaction of NF-κB-NIK with ergosterol peroxidase showed binding interaction between the two and showed the plausible molecular basis for the effects of IOAE in MC-LR induced liver injury. Collectively, this study revealed the deleterious effects of MC-LR on liver through generation of oxidative stress and activation of caspase-3, which were prevented by treatment with IOAE.

•

Microcystin-LR is a potent hepatotoxic agent acting by inducing lipid peroxidation and oxidative damages.

•

MC-LR exhibited significant deleterious alteration in liver by histopathological and biochemical signatures.

•

Inonotus obliquus aqueous extract (IOAE) suppressed inflammation and oxidative damage in the liver induced by microcystin-LR.

•

IOAE suppressed caspase-3 and p53 expression in MC-LR-induced liver.

•

Chaga mushroom is suggested for using as a supplement in prevention of liver toxicity and inflammation.

Functional analysis of co-expression networks of zebrafish ace2 reveals enrichment of pathways associated with development and disease

Human Angiotensin I Converting Enzyme 2 (ACE2) plays an essential role in blood pressure regulation and SARS-CoV-2 entry. ACE2 has a highly conserved, one-to-one ortholog (ace2) in zebrafish, which is an important model for human diseases. However, the zebrafish ace2 expression profile has not yet been studied during early development, between genders, across different genotypes, or in disease. Moreover, a network-based meta-analysis for the extraction of functionally enriched pathways associated with differential ace2 expression is lacking in the literature. Herein, we first identified significant development-, tissue-, genotype-, and gender-specific modulations in ace2 expression via meta-analysis of zebrafish Affymetrix transcriptomics datasets (n_datasets = 107); and the correlation analysis of ace2 meta-differential expression profile revealed distinct positively and negatively correlated local functionally enriched gene networks. Moreover, we demonstrated that ace2 expression was significantly modulated under different physiological and pathological conditions related to development, tissue, gender, diet, infection, and inflammation using additional RNA-seq datasets. Our findings implicate a novel translational role for zebrafish ace2 in organ differentiation and pathologies observed in the intestines and liver.

A Brief Review of the Structure, Cytotoxicity, Synthesis, and Biodegradation of Microcystins

Harmful cyanobacterial blooms pose an environmental health hazard due to the release of water-soluble cyanotoxins. One of the most prevalent cyanotoxins in nature is microcystins (MCs), a class of cyclic heptapeptide hepatotoxins, and they are produced by several common cyanobacteria in aquatic environments. Once released from cyanobacterial cells, MCs are subjected to physical chemical and biological transformations in natural environments. MCs can also be taken up and accumulated in aquatic organisms and their grazers/predators and induce toxic effects in several organisms, including humans. This brief review aimed to summarize our current understanding on the chemical structure, exposure pathway, cytotoxicity, biosynthesis, and environmental transformation of microcystins.

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.

Microcystin-LR Induces NLRP3 Inflammasome Activation via FOXO1 Phosphorylation, Resulting in Interleukin-1β Secretion and Pyroptosis in Hepatocytes

Microcystin-LR (MC-LR), the most common and toxic microcystin (MC) present in freshwater, poses a substantial threat to human health, especially hepatotoxicity. Recent evidence reveals that the NLRP3 inflammasome plays an important role in liver injury by activating caspase-1 to promote interleukin-1β (IL-1β) secretion. In this study, we investigated the possible role of NLRP3 inflammasome activation in MC-LR-induced mouse liver inflammatory injury. We found that MC-LR administered to mice by oral gavage mainly accumulated in liver and induced the activation of the NLRP3 inflammasome and production of mature IL-1β. Additionally, we observed an increase in the levels of NLRP3 inflammasome-related proteins and the proportion of pyroptosis in MC-LR-treated AML-12 cells. We also found that inhibition of NLRP3 in mice attenuated MC-LR-induced IL-1β production, indicating an essential role for NLRP3 in MC-LR-induced liver inflammatory injury. In addition, we found that inhibition of FOXO1 by AKT-mediated hyperphosphorylation, due to protein phosphatase 2A (PP2A) inhibition, is required for MC-LR-induced expression of NLRP3. Taken together, our in vivo and in vitro findings suggest a model in which the NLRP3 inflammasome activation, a result of AKT-mediated hyperphosphorylation of FOXO1 through inhibition of PP2A, plays a key role in MC-LR-induced liver inflammatory injury via IL-1β secretion and pyroptotic cell death.

Extraction, Properties, and Applications of Bioactive Compounds Obtained from Microalgae

With the increase in the global population, getting new sources of food is essential. One of the solutions can be found in the oceans due to algae. Microalgae are aquatic photosynthetic organisms used mainly due to their variety of bioactive compounds. The consumption of microalgae has been carried out for centuries and is recommended by organizations, such as OMS and FAO, due to its nutritional value and its properties. Based on the existing literature, there is substantial evidence of the nutritional quality of the algae as well as their functional elements. However, much quantification is still necessary, as well as studying possible adverse effects. The present review describes the compounds of alimentary interest present in these algae as well as different extraction techniques assisted by different energetic mechanisms (such as heat, supercritical-fluid, microwave, ultrasound, enzymes, electric field, high hydrostatic pressure, among others). The most challenging and crucial issues are reducing microalgae growth cost and optimizing extraction techniques. This review aimed a better understanding of the uses of microalgae for new researches in nutrition. Since the use of microalgae is still a field in which there is much to discover, it is likely that more benefits will be found in its consumption.

Properties of CaO2 for H2O2 release and phosphate removal and its feasibility in controlling Microcystis blooms

Calcium peroxide (CP) has been widely applied in environmental remediation, but few studies have reported its application in controlling Microcystis blooms. To recognize its feasibility for mitigating Microcystis blooms, the properties of CP in terms of hydrogen peroxide (HP) release and phosphate removal were investigated at different CP doses, temperatures, and initial pH values. HP release kinetics followed the Higuchi model. Batch experiments conducted in this study suggested that the HP yield and release rate were positively correlated with the CP dose. Increasing temperature decreased the HP yield but accelerated the HP release rate. The phosphate removal kinetics were well simulated by the pseudo-second-order model. The batch experiments suggested that an increased CP dose enhanced the phosphate removal capacity, but it did not affect the phosphate removal rate. Moreover, increased temperature accelerated both phosphate removal capacity and rate. However, the initial pH of low-buffer-capacity solutions did not notably affect HP release and phosphate removal. According to laboratory experiments, HP released from CP could impair photosynthetic activity, resulting in Microcystis mortality. Furthermore, the reduced phosphate concentration in the solutions suggested that CP could facilitate the control of eutrophication, which directly reduced bloom formation. Hence, our results confirmed CP as a promising algicide for Microcystis bloom control, and it is worthwhile to develop novel methods for bloom mitigation based on CP. Graphic abstract.

Microcystin-LR exposure results in aberrant spindles and induces apoptosis in porcine oocytes

Microcystin-LR (MC-LR), as a well-known hepatotoxin, was recently found to accumulate in gonads and induce a variety of reproductive damages in zebrafish, mice and other model organisms, however, little information is available on whether MC-LR has toxic effects on the mammalian oocytes, especially in livestock species. In this study, the effects of MC-LR on meiotic maturation of porcine oocytes were investigated, and the potential mechanism of MC-LR toxicity was explored. Germinal vesicle (GV)-stage oocytes were exposed to 0, 20, 40 and 60 μM MC-LR, respectively, during the in vitro maturation for 44 h, and the results showed that the first polar body (PbI) extrusion rate of the oocytes decreased significantly when the MC-LR concentration reached 40 (P < 0.01) or 60 μM (P < 0.001). After treated with 60 μM MC-LR for 44 h, a significant higher percentage of the oocytes arrested at anaphase-telophase I (ATI) stage (P < 0.01). Laser scanning confocal results further confirmed that a significantly larger proportion of the 60 μM MC-LR-treated oocytes exhibited aberrant spindles and misaligned chromosomes, suggesting a failure of spindle assembly and homologous chromosome segregation during the ATI stage. Furthermore, the ROS levels in the 60 μM MC-LR-exposed oocytes were significantly higher than the control group (P < 0.01), while the expression of antioxidant related genes (SOD1, CAT and GPX) were much lower compared with control group, indicating that oxidative stress was induced and the antioxidant capacity of oocytes was depleted by 60 μM MC-LR treatment. Additionally, markedly decreased mitochondrial membrane potential (MMP) (P < 0.01) and significantly higher incidence of early apoptosis (P < 0.01) were observed in the 60 μM MC-LR-treated oocytes, suggesting that MC-LR exposure induced apoptosis in porcine oocytes. Moreover, the protein expression of PP2A was remarkably inhibited, whereas the expression of p53, BAX, Caspase3 and Cleaved-caspase3 were prominently increased in the 60 μM MC-LR-exposed oocytes. Together, these results suggested that 60 μM of MC-LR exposure can induce oxidative stress, and lead to aberrant spindles, impaired MMP, and trigger apoptosis, which eventually result in failure of porcine oocyte maturation.

CD40 Receptor Knockout Protects against Microcystin-LR (MC-LR) Prolongation and Exacerbation of Dextran Sulfate Sodium (DSS)-Induced Colitis

Inflammatory Bowel Disease (IBD) is one of the most common gastrointestinal (GI) disorders around the world, and includes diagnoses such as Crohn’s disease and ulcerative colitis. The etiology of IBD is influenced by genetic and environmental factors. One environmental perturbagen that is not well studied within the intestines is microcystin-leucine arginine (MC-LR), which is a toxin produced by cyanobacteria in freshwater environments around the world. We recently reported that MC-LR has limited effects within the intestines of healthy mice, yet interestingly has significant toxicity within the intestines of mice with pre-existing colitis induced by dextran sulfate sodium (DSS). MC-LR was found to prolong DSS-induced weight loss, prolong DSS-induced bloody stools, exacerbate DSS-induced colonic shortening, exacerbate DSS-induced colonic ulceration, and exacerbate DSS-induced inflammatory cytokine upregulation. In addition, we previously reported a significant increase in expression of the pro-inflammatory receptor CD40 in the colons of these mice, along with downstream products of CD40 activation, including plasminogen activator inhibitor-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1). In the current study, we demonstrate that knocking out CD40 attenuates the effects of MC-LR in mice with pre-existing colitis by decreasing the severity of weight loss, allowing a full recovery in bloody stools, preventing the exacerbation of colonic shortening, preventing the exacerbation of colonic ulceration, and preventing the upregulation of the pro-inflammatory and pro-fibrotic cytokines IL-1β, MCP-1, and PAI-1. We also demonstrate the promising efficacy of a CD40 receptor blocking peptide to ameliorate the effects of MC-LR exposure in a proof-of-concept study. Our findings suggest for the first time that MC-LR acts through a CD40-dependent mechanism to exacerbate colitis.

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.

Harmful algal blooms and liver diseases: focusing on the areas near the four major rivers in South Korea

Freshwater harmful algal blooms (HABs) have become a global concern because blooms contain cyanotoxins that can cause liver damage and other negative health impacts. In South Korea, HABs have been frequently observed along the major rivers (Han, Geum, Nakdong, and Youngsan) in recent years. However, there are hardly any studies that report a linkage between HABs and human health, especially along the four major rivers where dams, weirs, and reservoirs were constructed, and sediments were dredged under the Four Major Rivers Project (FMRP) that ended in 2012. The goals of this study were to summarize spatial distribution patterns of HABs and investigate a potential association between HABs and liver diseases. Chlorophyll-a concentration was used to estimate bloom intensity since it was the only available bloom-related parameter that covers the entire rivers. Liver disease data (ICD-10 codes: K71-K77) were sorted by administrative districts. Generalized linear mixed model was used to analyze the bloom, liver diseases, and population data (2005-2016). The results show that chlorophyll-a levels significantly increased since 2013, except Han River region. There was a significant association between HAB intensity and incidence rate of liver diseases, except Han River area, and the extent of association significantly increased after the completion of the FMRP. For future studies, more in-depth epidemiological investigations are warranted in those areas to accurately determine more specific associations between HABs and liver diseases as well as other bloom-related diseases and symptoms. In addition, identification of major exposure pathways to cyanotoxins is needed to better protect public health in those bloom-affected areas.

Characterization of microcystin-induced apoptosis in HepG2 hepatoma cells

Microcystins (MCs) are a class of hepatotoxins that are commonly produced by freshwater cyanobacteria. MCs harm liver cells through inhibiting protein phosphatases 1 and 2A (PP1 and PP2A) and can produce dualistic effects, i.e., cell death and uncontrolled cellular proliferation. The induction of programmed cell death, i.e., apoptosis, in MC treated hepatic cells has been described previously; however, its exact pathway remains unclear. To address this, HepG2 human hepatoma cells were exposed to MC-LR, the most prevalent isomer of MCs, and morphological and physiological responses were examined. Microscopy and Alamar Blue assay showed that HepG2 cells responded to MC-LR treatment with apoptosis characteristics, such as clumping and shrinking of cells and detachment from the monolayer culture surface. A fluorescent caspase activation assay further revealed activation of all tested apoptosis-dependent caspases (i.e., caspase-3/7, 8 and 9) after 24 h of MC-LR treatment. Furthermore, caspase-8 was found being activated 4 h after MC-LR treatment, earlier than observed activation of caspase-9 (8 h after MC-LR treatment). These data demonstrated that MC-LR can induce apoptosis of HepG2 cells through both extrinsic and intrinsic pathways and that the extrinsic pathway may be activated before the intrinsic pathway. This indicates that extrinsic pathway is more sensitive than intrinsic pathway in MC induced apoptosis. This knowledge contributes to a better understanding of MC hepatotoxicity and can be further used for developing treatments for MC exposed hepatic cells.

p53-Dependent pathway and the opening of mPTP mediate the apoptosis of co-cultured Sertoli-germ cells induced by microcystin-LR

Microcystin-LR (MC-LR), a potent endotoxin, can induce reproductive toxicity. In order to investigate the role and mechanisms of apoptosis (p53-dependent and mitochondrial pathways) of germ cells induced by MC-LR, the co-cultured primary Sertoli-germ cells from Sprague-Dawley rats were used for the experiments. Expression levels of proteins, genes, and mitochondrial membrane potential (MMP) were obtained after exposing co-cultured Sertoli-germ cells to MC-LR with or without the addition of the p53 inhibitor, pifithrin-α (PFT-α), and MMP inhibitor, cyclosporin A (CsA). Results indicated that MC-LR could activate p53-dependent pathway-associated proteins in Sertoli-germ cells, leading to a decrease in MMP (indicating the opening of mitochondrial permeability transition pore [mPTP] and the release of Cytochrome-c [Cyt-c]) from the mitochondria into the cytoplasm and eventually the induction of apoptosis. PFT-α inhibited the expression ofp53, ameliorated the MMP of the co-cultured Sertoli-germ cells, and prevented the release of Cyt-c from the mitochondria into the cytoplasm, which reduces the occurrence of apoptosis. Similarly, the decreased release of Cyt-c from the mitochondria into the cytoplasm and the declined level of apoptosis in Sertoli-germ cells induced by MC-LR were observed after the addition of CsA. These results indicated that the apoptosis of the co-cultured Sertoli-germ cells induced by MC-LR was mediated by the p53-dependent pathway, with the involvement of the opening of mPTP.

Physiological characteristics and toxin production of Microcystis aeruginosa (Cyanobacterium) in response to DOM in anaerobic digestion effluent

The ecological implications of livestock production intensification have received sustained attention across the globe. Anaerobic digestion is the main process for livestock waste treatment. However, the ecological consequences of dissolved organic matter originating from anaerobic digestion (AD-DOM) in eutrophic water bodies remain elusive. In this study, the physiological responses of a bloom-forming cyanobacterium, Microcystis aeruginosa, to AD-DOM were investigated. Moreover, the composition of AD-DOM was identified by using thermochemolysis followed by gas chromatography-mass spectrometry (GC-MS) analysis. The growth of M. aeruginosa FACHB905 was not sensitive to low levels (0.625-1.25%, V/V) of AD-DOM but was inhibited by high levels (2.5-5%, V/V) of AD-DOM, resulting from photoinhibition damage to photosystem II (PSII). The main target of AD-DOM in PSII was the electron accepting side (ψ₀) or the electron donor side (φ P₀), depending on time variables. The reactive oxygen species (ROS) level showed a positive correlation with AD-DOM addition; however, it was higher than that of the control for 3.75-5% AD-DOM on the 6th day. The intracellular microcystin contents (including MC-LR and Dha⁷-MC-LR) decreased in response to AD-DOM addition, but extracellular microcystin increased after 6 days of exposure. In addition, GC-MS detection showed that AD-DOM is mainly composed of lignin-derived aromatic compounds, alkanes/alkene, nitrogen-containing compounds, and sterols. The results presented in this study suggested that AD-DOM released from the livestock industry may play a subtle role in affecting harmful algal blooms through level-dependent variables. In addition, the ecological consequences of microcystin released by toxin-producing species under AD-DOM stress are still worth considering.

Exogenous PP2A inhibitor exacerbates the progression of nonalcoholic fatty liver disease via NOX2-dependent activation of miR21

Nonalcoholic fatty liver disease (NAFLD) is an emerging global pandemic. Though significant progress has been made in unraveling the pathophysiology of the disease, the role of protein phosphatase 2A (PP2A) and its subsequent inhibition by environmental and genetic factors in NAFLD pathophysiology remains unclear. The present report tests the hypothesis that an exogenous PP2A inhibitor leads to hepatic inflammation and fibrogenesis via an NADPH oxidase 2 (NOX2)-dependent pathway in NAFLD. Results showed that microcystin (MC) administration, a potent PP2A inhibitor found in environmental exposure, led to an exacerbation of NAFLD pathology with increased CD68 immunoreactivity, the release of proinflammatory cytokines, and stellate cell activation, a process that was attenuated in mice that lacked the p47phox gene and miR21 knockout mice. Mechanistically, leptin-primed immortalized Kupffer cells (a mimicked model for an NAFLD condition) treated with apocynin or nitrone spin trap 5,5 dimethyl-1- pyrroline N-oxide (DMPO) had significantly decreased CD68 and decreased miR21 and α-smooth muscle actin levels, suggesting the role of NOX2-dependent reactive oxygen species in miR21-induced Kupffer cell activation and stellate cell pathology. Furthermore, NOX2-dependent peroxynitrite generation was primarily responsible for cellular events observed following MC exposure since incubation with phenylboronic acid attenuated miR21 levels, Kupffer cell activation, and inflammatory cytokine release. Furthermore, blocking of the AKT pathway attenuated PP2A inhibitor-induced NOX2 activation and miR21 upregulation. Taken together, we show that PP2A may have protective roles, and its inhibition exacerbates NAFLD pathology via activating NOX2-dependent peroxynitrite generation, thus increasing miR21-induced pathology.NEW & NOTEWORTHY Protein phosphatase 2A inhibition causes nonalcoholic steatohepatitis (NASH) progression via NADPH oxidase 2. In addition to a novel emchanism of action, we describe a new tool to describe NASH histopathology.

Assessment of Hepatotoxic Potential of Cyanobacterial Toxins Using 3D In Vitro Model of Adult Human Liver Stem Cells

Cyanotoxins microcystin-LR (MC-LR) and cylindrospermopsin (CYN) represent hazardous waterborne contaminants and potent human hepatotoxins. However, in vitro monolayer cultures of hepatic cell lines were found to recapitulate, poorly, major hepatocyte-specific functions and inadequately predict hepatotoxic effects of MC-LR and CYN. We utilized 3-dimensional (3D), scaffold-free spheroid cultures of human telomerase-immortalized adult liver stem cells HL1-hT1 to evaluate hepatotoxic potential of MC-LR and CYN. In monolayer cultures of HL1-hT1 cells, MC-LR did not induce cytotoxic effects (EC₅₀ > 10 micromol/L), while CYN inhibited cell growth and viability (48h-96h EC₅₀ ≈ 5.5-0.6 micromol/L). Growth and viability of small growing spheroids were inhibited by both cyanotoxins (≥0.1 micromol/L) and were associated with blebbing and disintegration at the spheroid surface. Hepatospheroid damage and viability reduction were observed also in large mature spheroids, with viability 96h-EC₅₀ values being 0.04 micromol/L for MC-LR and 0.1 micromol/L for CYN, and No Observed Effect Concentrations <0.01 micromol/L. Spheroid cultures of adult human liver stem cells HL1-hT1 exhibit sensitivity comparable to cultures of primary hepatocytes and provide a simple, practical, and cost-effective tool, which can be effectively used in environmental and toxicological research, including assessment of hepatotoxic potential and effect-based monitoring of various samples contaminated with toxic cyanobacteria.

Resveratrol Ameliorates Microcystin-LR-Induced Testis Germ Cell Apoptosis in Rats via SIRT1 Signaling Pathway Activation

Microcystin-leucine arginine (MC-LR), a cyclic heptapeptide produced by cyanobacteria, is a strong reproductive toxin. Studies performed in rat Sertoli cells and Chinese hamster ovary cells have demonstrated typical apoptosis after MC-LR exposure. However, little is known on how to protect against the reproductive toxicity induced by MC-LR. The present study aimed to explore the possible molecular mechanism underlying the anti-apoptosis and protective effects of resveratrol (RES) on the co-culture of Sertoli–germ cells and rat testes. The results demonstrated that MC-LR treatment inhibited the proliferation of Sertoli–germ cells and induced apoptosis. Furthermore, sirtuin 1 (SIRT1) and Bcl-2 were inhibited, while p53 and Ku70 acetylation, Bax expression, and cleaved caspase-3 were upregulated by MC-LR. However, RES pretreatment ameliorated MC-LR-induced apoptosis and SIRT1 inhibition, and downregulated the MC-LR-induced increase in p53 and Ku70 acetylation, Bax expression, and caspase-3 activation. In addition, RES reversed the MC-LR-mediated reduction in Ku70 binding to Bax. The present study indicated that the administration of RES could ameliorate MC-LR-induced Sertoli–germ cell apoptosis and protect against reproductive toxicity in rats by stimulating the SIRT1/p53 pathway, suppressing p53 and Ku70 acetylation and enhancing the binding of Ku70 to Bax.

Tumor-promoting cyanotoxin microcystin-LR does not induce procarcinogenic events in adult human liver stem cells

HL1-hT1 cell line represents adult human liver stem cells (LSCs) immortalized with human telomerase reverse transcriptase. In this study, HL1-hT1 cells were found to express mesenchymal markers (vimentin, CD73, CD90/THY-1 and CD105) and an early hepatic endoderm marker FOXA2, while not expressing hepatic progenitor (HNF4A, LGR5, α-fetoprotein) or differentiated hepatocyte markers (albumin, transthyretin, connexin 32). In response to microcystin-LR (MC-LR), a time- and concentration-dependent formation of MC-positive protein bands in HL1-hT1 cells was observed. Cellular accumulation of MC-LR occurred most likely via mechanisms independent on organic anion transporting polypeptides (OATPs) or multidrug resistance (MDR) proteins, as indicated (a) by a gene expression analysis of 11 human OATP genes and 4 major MDR genes (MDR1/P-glycoprotein, MRP1, MRP2 and BCRP); (b) by non-significant effects of OATP or MDR1 inhibitors on MC-LR uptake. Accumulation of MC-positive protein bands in HL1-hT1 cells was associated neither with alterations of cell viability and growth, dysregulations of ERK1/2 and p38 kinases, reactive oxygen species formation, induction of double-stranded DNA breaks nor modulations of stress-inducible genes (ATF3, HSP5). It suggests that LSCs might have a selective, MDR1-independent, survival advantage and higher tolerance towards MC-induced cytotoxic, genotoxic or cancer-related events than differentiated adult hepatocytes, fetal hepatocyte or malignant liver cell lines. HL1-hT1 cells provide a valuable in vitro tool for studying effects of toxicants and pharmaceuticals on LSCs, whose important role in the development of chronic toxicities and liver diseases is being increasingly recognized.