Neurotoxicity induced by microcystins and cylindrospermopsin: A review

Toxicity assessment of microcystin-leucine arginine in planarian Dugesia japonica

Microcystin-leucine arginine (MC-LR), a representative cyanobacterial toxin, poses an increasing and serious threat to aquatic ecosystems. Despite investigating its toxic effects in various organisms and cells, the toxicity to tissue regeneration and stem cells in vivo still needs to be explored. Planarians are ideal regeneration and toxicology research models and have profound implications in ecotoxicology evaluation. This study conducted a systemic toxicity evaluation of MC-LR, including morphological changes, growth, regeneration, and the underlying cellular and molecular changes after MC-LR exposure, which were investigated in planarians. The results showed that exposure to MC-LR led to time- and dose-dependent lethal morphological changes, tissue damage, degrowth, and delayed regeneration in planarians. Furthermore, MC-LR exposure disturbed the activities of antioxidants, including total superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, and total antioxidant capacity, leading to oxidative stress and DNA damage, and then reduced the number of dividing neoblasts and promoted apoptosis. The results demonstrated that oxidative stress and DNA damage induced by MC-LR exposure caused apoptosis. Excessive apoptosis and suppressed neoblast activity led to severe homeostasis imbalance. This study explores the underlying mechanism of MC-LR toxicity in planarians and provides a basis for the toxicity assessment of MC-LR to aquatic organisms and ecological risk evaluation.

Behavioral Responses of Chironomus aprilinus Larvae as Proxies for Cyanobacterial Metabolite Interactions: Insights from Ternary Combinations

This study aimed to assess the behavioral responses (immobilization, horizontal and vertical motility, and response to light) of Chironomus aprilinus larvae exposed to individual cyanobacterial metabolites aeruginosin 98B (AER-B), anabaenopeptin-B (ANA-B), and cylindrospermopsin (CYL), and their binary and ternary mixtures. The investigation revealed that single metabolites ANA-B and CYL exhibited the highest potency in immobilizing the larvae. Notably, the binary mixture AER-B+CYL induced a remarkably strong synergistic interaction, while other tested binary and ternary mixtures demonstrated antagonistic effects. Both individual metabolites and their mixtures led to a decrease in larval movement speed, with the AER-B+CYL combination showing a very synergistic effect, and strong antagonistic interactions between the oligopeptides in the ternary mixture. Conversely, while AER-B and the binary mixture ANA-B+CYL stimulated vertical movement, other single metabolites and binary and ternary mixtures decreased this parameter. Antagonistic interactions were observed in all mixtures. ANA-B emerged as the most potent inhibitor, yet all tested metabolites and their mixtures decreased larval response to light, displaying synergistic interactions, except for the AER-B+ANA-B mixture at 250 μg L-1 + 250 μg L-1. These findings underscore the sensitivity of Chironomus larvae behavioral parameters as indicators of environmental stressors and mixtures. Consequently, they are recommended for assessing toxic effects induced by cyanobacterial products and other bioactive chemicals.

MC-LR disrupts dopamine synthesis in the substantia nigra of midbrain by enhancing the chaperone-mediated autophagy pathway through direct binding to ERK2

Microcystins are environmental toxins produced by freshwater cyanobacteria. Microcystin-LR (MC-LR) is one of the most abundant and harmful isomers. MC-LR poses a serious threat to human health. MC-LR could penetrate the blood-brain barrier of mice and accumulate in the substantia nigra (SN) of the midbrain, leading to a reduction in dopamine levels and Parkinson's disease (PD)-like motor dysfunction in mice. The reduction in dopamine levels is a key factor contributing to movement disorders in humans with PD. Dopamine is synthesized in the dopaminergic neurons of the SN by the actions of tyrosine hydroxylase (TH) and dihydroxyphenylalanine decarboxylase (DDC). In this study, we found that MC-LR could enter dopaminergic neurons in the SN and directly bound to extracellular signal-regulated kinase 2 (ERK2), enhancing ERK2 stability. ERK2 further enhanced the transcriptional activity of Heat Shock Protein Family A Member 8 (HSPA8) and promoted the expression of Heat shock cognate 71 kDa protein (HSC70), which in turn amplified the chaperone-mediated autophagy (CMA) pathway and accelerated the degradation of TH and DDC. This affected the dopamine synthesis process, resulting in a significant reduction in dopamine levels. The study is the first to reveal that ERK2 was a direct target of MC-LR, and further enhanced CMA affecting dopamine synthesis, which has important theoretical and practical significance for environmental safety management.

Enhanced inhibitory efficiency against toxic bloom forming Raphidiopsis raciborskii by Streptomyces sp. HY through triple algicidal modes: Direct and indirect attacks combined with bioflocculation

Raphidiopsis raciborskii (R. raciborskii) forms harmful cyanobacterial blooms globally, and poses a great threat to the safety of drinking water and public health. There is a great need to develop eco-friendly biological alternative measures to mitigate mass blooms of R. raciborskii. However, previous rare studies on algicidal microorganisms against R. raciborskii restricted this aim. Recently, an algicidal bacterium Streptomyces sp. HY (designated HY) was identified with flavones producing ability, and could remove up to 98.73 % of R. raciborskii biomass within 48 h by directly attacking the cyanobacterium and release of algicidal substances (i.e., flavonoids) with a inoculum ratio of 5 %. Algicidal rate of HY was enhanced by 88.05 %, 89.33 % under dark and light, and full-light conditions respectively, when compared with the dark condition. Its algicidal substances were stable in a broad range of temperature (-80-55 °C) and pH (3-11) conditions, and all treated groups exhibited ≈ 100 % algicidal rate at day 3. HY treatment disrupted the photosynthesis system and triggered serious oxidative stress resulting in severe morphological injury. Thereby, HY treatment significantly affected expression levels of several essential genes (i.e., psbA, psaB, rbcL, ftsZ, recA, grpE), and simultaneously inhibited the biosynthesis and release of cylindrospermopsin. Yet, HY treatment didn't show any toxicity to zebrafish test embryos. Such results indicate that HY is a promising algicidal candidate strain to control global R. raciborskii blooms, and holds great promises for an effective biological measure to sustain water safety.

Cyanobacterial Cyclic Peptides Can Disrupt Cytoskeleton Organization in Human Astrocytes-A Contribution to the Understanding of the Systemic Toxicity of Cyanotoxins

The systemic toxicity of cyclic peptides produced by cyanobacteria (CCPs) is not yet completely understood. Apart from the most known damages to the liver and kidneys, symptoms of their neurotoxicity have also been reported. Hepatotoxic CCPs, like microcystins, as well as non-hepatotoxic anabaenopeptins and planktopeptins, all exhibit cytotoxic and cytostatic effects on mammalian cells. However, responses of different cell types to CCPs depend on their specific modes of interaction with cell membranes. This study demonstrates that non-hepatotoxic planktopeptin BL1125 and anabaenopeptins B and F, at concentrations up to 10 µM, affect normal and tumor human astrocytes (NHA and U87-GM) in vitro by their almost immediate insertion into the lipid monolayer. Like microcystin-LR (up to 1 µM), they inhibit Ser/Thr phosphatases and reorganize cytoskeletal elements, with modest effects on their gene expression. Based on the observed effects on intermediate filaments and intermediate filament linkage elements, their direct or indirect influence on tubulin cytoskeletons via post-translational modifications, we conclude that the basic mechanism of CCP toxicities is the induction of inter- and intracellular communication failure. The assessed inhibitory activity on Ser/Thr phosphatases is also crucial since the signal transduction cascades are modulated by phosphorylation/dephosphorylation processes.

Nodding syndrome: A role for environmental biotoxins that dysregulate MECP2 expression?

Nodding syndrome is an epileptic encephalopathy associated with neuroinflammation and tauopathy. This initially pediatric brain disease, which has some clinical overlap with Methyl-CpG-binding protein 2 (MECP2) Duplication Syndrome, has impacted certain impoverished East African communities coincident with local civil conflict and internal displacement, conditions that forced dependence on contaminated food and water. A potential role in Nodding syndrome for certain biotoxins (freshwater cyanotoxins plus/minus mycotoxins) with neuroinflammatory, excitotoxic, tauopathic, and MECP2-dysregulating properties, is considered here for the first time.

The effect and mechanism of combined exposure of MC-LR and NaNO2 on liver lipid metabolism

Microcystin-LR (MC-LR) and sodium nitrite (NaNO2) co-exist in the environment and are hepatotoxic. The liver has the function of lipid metabolism, but the impacts and mechanisms of MC-LR and NaNO2 on liver lipid metabolism are unclear. Therefore, we established a chronic exposure model of Balb/c mice and used LO2 cells for in vitro verification to investigate the effects and mechanisms of liver lipid metabolism caused by MC-LR and NaNO2. The results showed that after 6 months of exposure to MC-LR and NaNO2, the lipid droplets content was increased, and the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were raised in the liver (P < 0.05). Moreover, MC-LR and NaNO2 synergistically induced hepatic oxidative stress by decreasing total superoxide dismutase (T-SOD) activity and glutathione (GSH) levels and increasing malondialdehyde (MDA) content levels. In addition, the levels of Nrf2, HO-1, NQO1 and P-AMPK was decreased and Keap1 was increased in the Nrf2/HO-1 pathway. The key factors of lipid metabolism, SREBP-1c, FASN and ACC, were up-regulated in the liver. More importantly, there was a combined effect on lipid deposition of MC-LR and NaNO2 co-exposure. In vitro experiments, MC-LR and NaNO2-induced lipid deposition and changes in lipid metabolism-related changes were mitigated after activation of the Nrf2/HO-1 signaling pathway by the Nrf2 activator tertiary butylhydroquinone (TBHQ). Additionally, TBHQ alleviated the rise of reactive oxygen species (ROS) in LO2 cells induced by MC-LR and NaNO2. Overall, our findings indicated that MC-LR and NaNO2 can cause abnormal liver lipid metabolism, and the combined effects were observed after MC-LR and NaNO2 co-exposure. The Nrf2/HO-1 signal pathway may be a potential target for prevention and control of liver toxicity caused by MC-LR and NaNO2.

CXCL1/IGHG1 signaling enhances crosstalk between tumor cells and tumor-associated macrophages to promote MC-LR-induced colorectal cancer progression

Microcystin-leucine arginine (MC-LR) is a common cyantotoxin produced by hazardous cyanobacterial blooms, and eutrophication is increasing the contamination level of MC-LR in drinking water supplies and aquatic foods. MC-LR has been linked to colorectal cancer (CRC) progression associated with tumor microenvironment, however, the underlying mechanism is not clearly understood. In present study, by using GEO, KEGG, GESA and ImmPort database, MC-LR related differentially expressed genes (DEGs) and pathway- and gene set-enrichment analysis were performed. Of the three identified DEGs (CXCL1, GUCA2A and GDF15), CXCL1 was shown a positive association with tumor infiltration, and was validated to have a dominantly higher upregulation in MC-LR-treated tumor-associated macrophages (TAMs) rather than in MC-LR-treated CRC cells. Both CRC cell/macrophage co-culture and xenograft mouse models indicated that MC-LR stimulated TAMs to secrete CXCL1 resulting in promoted proliferation, migration, and invasion capability of CRC cells. Furtherly, IP-MS assay found that interaction between TAMs-derived CXCL1 and CRC cell-derived IGHG1 may enhance CRC cell proliferation and migration after MC-LR treatment, and this effect can be attenuated by silencing IGHG1 in CRC cell. In addition, molecular docking analysis, co-immunoprecipitation and immunofluorescence further proved the interactions between CXCL1 and IGHG1. In conclusion, CXCL1 secreted by TAMs can trigger IGHG1 expression in CRC cells, which provides a new clue in elucidating the mechanism of MC-LR-mediated CRC progression.

Modifying luteolin's algicidal effect on Microcystis by virgin and diversely-aged polystyrene microplastics: Unveiling novel mechanisms through microalgal adaptive strategies

Luteolin has shown great potential in inhibiting Microcystis-dominated cyanobacterial blooms. However, widespread microplastics (MPs) in natural aquatic systems often serve as substrates for cyanobacterial growth, which could impact cyanobacterial resistance to external stresses and interfere with luteolin's algicidal effect. This study explored the influence of virgin and diversely-aged polystyrene microplastics (PS-MPs) on inhibitory effect of luteolin on Microcystis growth and its microcystins (MCs) production/release. Moreover, the underlying mechanisms were also revealed by jointly analyzing SEM image, antioxidant response, exopolymeric substances (EPSs) production, and functional gene expression. Results suggested that 0.5, 5, and 50 mg/L virgin and diversely-aged PS-MPs almost weakened growth inhibition and oxidative damage of two doses of luteolin against Microcystisby stimulating its EPSs production and inducing self-aggregation of Microcystis cells and/or hetero-aggregation between Microcystis cells and PS-MPs. Compared to virgin PS-MPs, photo-aged PS-MPs possessed rougher flaky surfaces, and hydrothermal-aged PS-MPs showed internal cracking. These characteristics led to greater stimulation of EPS production and exhibited more significant protective effects on Microcystis. Notably, PS-MPs also decreased MCs content in aqueous phase, likely because they adsorbed some MCs. Such toxigenic hetero-aggregates formed by MCs, MPs, and Microcystis cells would directly poison grazing organisms that consume them and create more pathways for MCs into food web, posing greater eco-risks. This is the first study to clarify the influence and mechanisms of virgin and diversely-aged MPs on allelopathic algicidal effects from the perspective of microalgal inherent adaptive strategies.

Exposure to microcystin-LR promotes astrocyte proliferation both in vitro and in vivo via Hippo signaling pathway

Microcystins (MCs) are toxic to the central nervous system of mammals. However, the direct toxicity of MCs on mammalian brain cells and the involved molecular mechanisms are not fully elucidated. Here, we incubated primary astrocytes, the major glial cell-type in the brain, with 0-12.5 μM concentrations of MC-LR for 48 h, and the impairment was evaluated. We found that MC-LR caused significant increases in the cell viability at the range of 0.05-1 μM concentrations with the highest density at 0.1 μM concentration. Treatment with 0.1 μM MC-LR induced YAP nuclear translocation and decreased the ratio of p-YAP to YAP. It also decreased mRNA levels of the upstream regulator (AMOT), and enhanced expressions of YAP interacted genes (Egfr, Tead1, and Ctgf) in primary astrocytes. Overexpression of AMOT significantly attenuated the increase of MC-LR-induced astrocyte proliferation and the expression of YAP downstream genes. These results indicate that Hippo signaling contributed to MC-LR-caused astrocyte proliferation. Further, reactive astrogliosis was observed in the mice brain after MC-LR exposure to environmentally relevant concentrations (20 or 100 μg/L) through drinking water for 16 weeks. Pathological observations revealed that 100 μg/L MC-LR exposure caused neuronal damages with characteristics of shrunken or vacuolation in the region of the cerebral cortex, striatum and cerebellum. These results were accompanied with increased oxidative stress and inflammatory response. Our data reveal the potential astrocytic mechanisms in MC-induced neurotoxicity and raise an alarm for neurodegenerative disease risk following daily exposure to MC-LR.

Urolithin a Partially Protects against Oxidative Damage Induced for Microcistyn-lr in C6 Cells

Microcystin-LR (MIC-LR) is a toxin which the mechanism of intoxication involves oxidative stress. Urolithin A (URO-A) is a metabolic product from the colonic fermentation of ellagic acid with antioxidant potential. This study aimed to evaluate the putative protective effect of URO-A against MIC-LR toxicity in C6 cells. C6 cells were incubated with MIC-LR (1 and 10 μM) and/or URO-A (3, 30, 60 and 100 μM) for 24 h. MIC-LR induced reactive species (RS) generation, depletion of total thiol (SH) groups, and survival loss when compared with the control group. Also, at 10 μM, MIC-LR induced CAT activity inhibition. URO-A caused CAT activity inhibition and showed a trend to increase RS generation (60 and 100 μM) per se. URO-A at 3 μM completely attenuated the RS generation and the impairment in SH groups caused by MIC-LR. Our results demonstrated that URO-A might offer a protective effect against toxicity caused by MIC-LR in glial cells by restoring the levels of RS and thiol groups.

Comparative toxicology of algal cell extracts and pure cyanotoxins: insights into toxic effects and mechanisms of harmful cyanobacteria Raphidiopsis raciborskii

Ongoing research on cyanotoxins, driven by the socioeconomic impact of harmful algal blooms, emphasizes the critical necessity of elucidating the toxicological profiles of algal cell extracts and pure toxins. This study comprehensively compares Raphidiopsis raciborskii dissolved extract (RDE) and cylindrospermopsin (CYN) based on Daphnia magna assays. Both RDE and CYN target vital organs and disrupt reproduction, development, and digestion, thereby causing acute and chronic toxicity. Disturbances in locomotion, reduced behavioral activity, and weakened swimming capability in D. magna have also been reported for both RDE and CYN, indicating the insufficiency of conventional toxicity evaluation parameters for distinguishing between the toxic effects of algal extracts and pure cyanotoxins. Additionally, chemical profiling revealed the presence of highly active tryptophan-, humic acid-, and fulvic acid-like fluorescence compounds in the RDE, along with the active constituents of CYN, within a 15-day period, demonstrating the chemical complexity and dynamics of the RDE. Transcriptomics was used to further elucidate the distinct molecular mechanisms of RDE and CYN. They act diversely in terms of cytotoxicity, involving oxidative stress and response, protein content, and energy metabolism, and demonstrate distinct modes of action in neurofunctions. In essence, this study underscores the distinct toxicity mechanisms of RDE and CYN and emphasizes the necessity for context- and objective-specific toxicity assessments, advocating nuanced approaches to evaluate the ecological and health implications of cyanotoxins, thereby contributing to the precision of environmental risk assessments.

Effects of cylindrospermopsin, chlorpyrifos and their combination in a SH-SY5Y cell model concerning developmental neurotoxicity

The cyanotoxin cylindrospermopsin (CYN) has been postulated to cause neurotoxicity, although the studies in this concern are very few. In addition, some studies in vitro indicate its possible effects on development. Furthermore, pesticides can be present in the same environmental samples as cyanotoxins. Therefore, chlorpyrifos (CPF) has been one of the most common pesticides used worldwide. The aim of this report was to study the effects of CYN, isolated and in combination with CPF, in a developmental neurotoxicity in vitro model. The human neuroblastoma SH-SY5Y cell line was exposed during 6 days of differentiation to both toxics to study their effects on cell viability and neurite outgrowth. To further evaluate effects of both toxicants on cholinergic signaling, their agonistic and antagonistic activities on the α7 homomeric nicotinic acetylcholine receptor (nAChR) were studied upon acute exposure. Moreover, a transcriptomic analysis by qPCR was performed after 6 days of CYN-exposure during differentiation. The results showed a concentration-dependent decrease on both cell viability and neurite outgrowth for both toxics isolated, leading to effective concentration 20 (EC20) values of 0.35 µM and 0.097 µM for CYN on cell viability and neurite outgrowth, respectively, and 100 µM and 58 µM for CPF, while the combination demonstrated no significant variations. In addition, 95 µM and 285 µM CPF demonstrated to act as an antagonist to nicotine on the nAChR, although CYN up to 2.4 µM had no effect on the efficacy of these receptors. Additionally, the EC20 for CYN (0.097 µM) on neurite outgrowth downregulated expression of the 5 genes NTNG2 (netrin G2), KCNJ11 (potassium channel), SLC18A3 (vesicular acetylcholine transporter), APOE (apolipoprotein E), and SEMA6B (semaphorin 6B), that are all important for neuronal development. Thus, this study points out the importance of studying the effects of CYN in terms of neurotoxicity and developmental neurotoxicity.

Spatio-temporal variation of toxin-producing gene abundance in Microcystis aeruginosa from Poyang Lake

Microcystis aeruginosa (M. aeruginosa) causes massive blooms in eutrophic freshwater and releases microcystin. Poyang Lake is the largest freshwater lake in China and has kept a mid-nutrient level in recent years. However, there is little research on microcystin production in Poyang Lake. In this study, water and sediment samples from ten sampling sites in Poyang Lake were collected from May to December in 2020, and from January to April in 2021 respectively. Microcystis genes (mcyA, mcyB, 16 s rDNA) were quantified by real-time fluorescence quantitative PCR analysis, and then the spatial and temporal variation of mcy genes, physicochemical factors, and bacterial population structure in the lake was analyzed. The relationship between the abundance of mcy genes and physicochemical factors in water column was also revealed. Results indicated that the microcystin-producing genes mcyA and mcyB showed significant differences in spatial and temporal levels as well, which is closely related to the physicochemical factors especially the water temperature (p < 0.05) and the nitrogen content (p < 0.05). The abundance of mcy genes in the sediment in December affected the abundance of mcy genes in the water column in the next year, while the toxic Microcystis would accumulate in the sediment. In addition to the toxic Microcystis, we also found a large number of non-toxic Microcystis in the water column and sediment, and the ratio of toxic to non-toxic species can also affect the toxicity production of M. aeruginosa. Overall, the results showed that M. aeruginosa toxin-producing genes in Poyang Lake distributed spatially and temporally which related to the physicochemical factors of Poyang Lake.

A Direct Analysis of β-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks

Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid β-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer's. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as β-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

Transmission of Microcystins in Natural Systems and Resource Processes: A Review of Potential Risks to Humans Health

The rapid rise of microcystins (MCs) poses a serious threat to global freshwater ecosystems and has become an important issue of global public health. MCs have considerable stability and are the most widely distributed hepatotoxins. It cannot only accumulate in aquatic organisms and transfer to higher nutrients and levels, but also be degraded or transferred during the resource utilization of cyanobacteria. No matter which enrichment method, it will lead to the risk of human exposure. This review summarizes the research status of MCs, and introduces the distribution of MCs in different components of aquatic ecosystems. The distribution of MCs in different aquatic organisms was summarized, and the potential risks of MCs in the environment to human safety were summarized. MCs have polluted all areas of aquatic ecosystems. In order to protect human life from the health threats caused by MCs, this paper also proposes some future research directions to promote MCs control and reduce human exposure to MCs.

First insights into region-specific lipidome alterations of prefrontal cortex and hippocampus of mice exposed chronically to microcystins

Microcystins (MCs), a group of most widespread freshwater cyanotoxins that possess strong neurotoxicity, can adversely affect brain structures and functions and are linked to neurodegenerative diseases. Despite the essential role of lipids in brain structures and functions, the brain lipidome profile of mammals exposed to MCs remains unexplored, hindering a clear understanding of the neurotoxic effects of MCs and underlying mechanisms. In this study, we performed untargeted lipidomic profiling using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) on the prefrontal cortex and hippocampus of mice orally exposed to 30 and 300 μg/kg body mass/day of microcystin-leucine arginine (MC-LR) for 180 days to evaluate the impacts of MC-LR on the brain lipidome profile and functions. Our results show that MC-LR resulted in a decline in cognitive parameters, as assessed by the Morris water maze test. Interestingly, apparent neurodegenerative changes were observed in the prefrontal cortex, but not in the hippocampus. Comprehensive lipidomic analyses uncovered profound, region-specific changes in the phospholipid and sphingolipid profile at the levels of lipid subclasses, lipid species, and fatty acyl composition. These changes showed overall decrease trends of lipid content in the prefrontal cortex yet increasing trends in the hippocampus. We identified distinct transcriptional regulations of lipid metabolism and apoptosis by MC-LR in the two regions, which appeared to underlie the neurodegenerative changes. Collectively, this study uncovers region-specific changes in the brain lipidome profile and functions induced by MCs, shedding light on the role of lipid dysfunction in neurotoxicity mechanism of MCs.

Effects of Cyanobacterial Harmful Algal Bloom Toxin Microcystin-LR on Gonadotropin-Dependent Ovarian Follicle Maturation and Ovulation in Mice

BACKGROUND

Cyanobacterial harmful algal blooms (CyanoHABs) originate from the excessive growth or bloom of cyanobacteria often referred to as blue-green algae. They have been on the rise globally in both marine and freshwaters in recently years with increasing frequency and severity owing to the rising temperature associated with climate change and increasing anthropogenic eutrophication from agricultural runoff and urbanization. Humans are at a great risk of exposure to toxins released from CyanoHABs through drinking water, food, and recreational activities, making CyanoHAB toxins a new class of contaminants of emerging concern.

OBJECTIVES

We investigated the toxic effects and mechanisms of microcystin-LR (MC-LR), the most prevalent CyanoHAB toxin, on the ovary and associated reproductive functions.

METHODS

Mouse models with either chronic daily oral or acute intraperitoneal exposure, an engineered three-dimensional ovarian follicle culture system, and human primary ovarian granulosa cells were tested with MC-LR of various dose levels. Single-follicle RNA sequencing, reverse transcription-quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, immunohistochemistry (IHC), and benchmark dose modeling were used to examine the effects of MC-LR on follicle maturation, hormone secretion, ovulation, and luteinization.

RESULTS

Mice exposed long term to low-dose MC-LR did not exhibit any differences in the kinetics of folliculogenesis, but they had significantly fewer corpora lutea compared with control mice. Superovulation models further showed that mice exposed to MC-LR during the follicle maturation window had significantly fewer ovulated oocytes. IHC results revealed ovarian distribution of MC-LR, and mice exposed to MC-LR had significantly lower expression of key follicle maturation mediators. Mechanistically, in both murine and human granulosa cells exposed to MC-LR, there was reduced protein phosphatase 1 (PP1) activity, disrupted PP1-mediated PI3K/AKT/FOXO1 signaling, and less expression of follicle maturation-related genes.

DISCUSSION

Using both in vivo and in vitro murine and human model systems, we provide data suggesting that environmentally relevant exposure to the CyanoHAB toxin MC-LR interfered with gonadotropin-dependent follicle maturation and ovulation. We conclude that MC-LR may pose a nonnegligible risk to women's reproductive health by heightening the probability of irregular menstrual cycles and infertility related to ovulatory disorders. https://doi.org/10.1289/EHP12034.

Cyanobacterial metabolites: aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin and their mixtures affect behavioral and physiological responses of Daphnia magna

We determined the effects influence of cyanobacterial products metabolites: aeruginosin-A (AER-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A), cylindrospermopsin (CYL) and their binary and quadruple mixtures on swimming behavior, heart rate, thoracic limb activity, oxygen consumption and in vivo cell health of Daphnia magna. The study showed that CYL induced mortality of daphnids at the highest concentrations, however three oligopeptides had no lethal effect. All the tested Each single metabolites inhibited swimming speed. The mixtures AER+MG-FR1 and AER-A+ANA-A induced antagonistic and the quadruple mixture synergistic effects. Physiological endpoints were depressed by CYL, however they were simulated by the oligopeptides and their binary mixtures. The quadruple mixture inhibited the physiological parameters with antagonistic interactions between the components were antagonistic. Single CYL, MG-FR1 and ANA-A induced cytotoxicity with synergistic interactions and the metabolites in mixtures showed. The study suggests that swimming behavior and physiological parameters may be affected by single cyanobacterial oligopeptides, however their mixtures may induce different total effects.

Combined methods elucidate the multi-organ toxicity of cylindrospermopsin (CYN) on Daphnia magna

Global water bodies are now at risk from inevitable cyanobacterial blooms and their production of multiple cyanotoxins, in particular cylindrospermopsin (CYN). However, research on the CYN toxicity and its molecular mechanisms is still limited, whilst the responses of aquatic species against CYN are uncovered. By integrating behavioral observations, chemical detections and transcriptome analysis, this study demonstrated that CYN exerted multi-organ toxicity to model species, Daphnia magna. The present study confirmed that CYN could cause protein inhibition by undermining total protein contents, and altered the gene expression related to proteolysis. Meantime, CYN induced oxidative stress by increasing reactive oxygen species (ROS) level, decreasing the glutathione (GSH) concentration, and interfered with protoheme formation process molecularly. Neurotoxicity led by CYN was solidly determined by abnormal swimming patterns, reduced acetylcholinesterase (AChE), and downward expression of muscarinic acetylcholine receptor (CHRM). Importantly, for the first time, this research determined CYN directly interfered with energy metabolism in cladocerans. CYN distinctively reduced filtration and ingestion rate by targeting on heart and thoracic limbs, which declined the energy intake, and could be further displayed by the reduction of motional strength and the trypsin concentration. These phenotypic alterations were supported by transcriptomic profile, including the down-regulation of oxidative phosphorylation and ATP synthesis. Moreover, CYN was speculated to trigger the self-defense responses of D. magna, known as "abandon-ship" by moderating lipid metabolism and distribution. This study, overall, comprehensively demonstrated the CYN toxicity and the responses of D. magna against it, which is of great significance to the advancements of CYN toxicity knowledge.

Cyanobacterial Harmful Algal Bloom Toxin Microcystin and Increased Vibrio Occurrence as Climate-Change-Induced Biological Co-Stressors: Exposure and Disease Outcomes via Their Interaction with Gut-Liver-Brain Axis

The effects of global warming are not limited to rising global temperatures and have set in motion a complex chain of events contributing to climate change. A consequence of global warming and the resultant climate change is the rise in cyanobacterial harmful algal blooms (cyano-HABs) across the world, which pose a threat to public health, aquatic biodiversity, and the livelihood of communities that depend on these water systems, such as farmers and fishers. An increase in cyano-HABs and their intensity is associated with an increase in the leakage of cyanotoxins. Microcystins (MCs) are hepatotoxins produced by some cyanobacterial species, and their organ toxicology has been extensively studied. Recent mouse studies suggest that MCs can induce gut resistome changes. Opportunistic pathogens such as Vibrios are abundantly found in the same habitat as phytoplankton, such as cyanobacteria. Further, MCs can complicate human disorders such as heat stress, cardiovascular diseases, type II diabetes, and non-alcoholic fatty liver disease. Firstly, this review describes how climate change mediates the rise in cyanobacterial harmful algal blooms in freshwater, causing increased levels of MCs. In the later sections, we aim to untangle the ways in which MCs can impact various public health concerns, either solely or in combination with other factors resulting from climate change. In conclusion, this review helps researchers understand the multiple challenges brought forth by a changing climate and the complex relationships between microcystin, Vibrios, and various environmental factors and their effect on human health and disease.

Phosphorus level impacts luteolin effect on Microcystis aeruginosa growth and microcystin-pollution risk - Novel perspective from correlation between exopolymers substances fractions and microcystin-production/release

Luteolin as a phytogenic algicide can inhibit the growth and microcystins (MCs) release of Microcystis, a dominant genus during cyanobacterial blooms, but how phosphorus (P) level impacts luteolin effect on its growth and MC-pollution risk is unclear. By employing Microcystis aeruginosa as test alga, this study addressed this concern and explored response mechanisms from novel insights of relationship between extracellular polysaccharide (ex-poly) and protein (ex-pro) contents and MC-production/release. At each P level (0.05-5 mg/L), rising luteolin dose more greatly inhibited Microcystis growth and MC-pollution risk, with growth inhibition ratio of around 10%-30%, 20%-50% and 40%-90% for 3, 6 and 12 mg/L luteolin, respectively, but almost increasingly enhanced cellular ability of MC-production/conservation and total and bound ex-poly/ex-pro production. Rising P level promoted Microcystis growth and intracellular/extracellular MCs content (IMC, EMC) in test system at each luteolin dose, thus higher P level weakened algicidal and MC-removal effects of luteolin, indicating that P-decrease was required for stronger application outcome of luteolin. Total and bound ex-poly/ex-pro amount were positively correlated with cellular MC-production/conservation ability, IMC and EMC, which constituted cooperative stress-defense of Microcystis at each P level. Besides, rising luteolin dose posed stronger algicidal effect by inactivating gene expression involving peroxidase synthesis (especially at P-limitation), photosynthesis and P acquisition, while rising P level alleviated algicidal and MC-pollution inhibition effects of luteolin by enhancing gene expression involving N acquisition and peroxidase synthesis. This study shed novel insights for P-dependent effect and mechanisms of luteolin on toxigenic Microcystis growth and MC-pollution control, which guided to mitigating toxigenic Microcystis-dominated cyanobacterial blooms in different P-level water areas.

Toxic effects of the cylindrospermopsin and chlorpyrifos combination on the differentiated SH-SY5Y human neuroblastoma cell line

Due to climate change and anthropogenic activities, the levels of pollution of aquatic and terrestrial environments have increased in the last decades. In this sense, the rise of cyanobacterial blooms, which release secondary metabolites with toxic properties, and the global use of pesticides for agricultural purposes have a negative impact on ecosystems. Thus, it would be interesting to study the concomitance of both types of toxicants in the same sample, since it is possible that they appear together. The aim of the present work was to state the effects of the interaction between the cyanotoxin cylindrospermopsin and the pesticide chlorpyrifos in differentiated SH-SY5Y neuronal cells to assess how they could affect the nervous system. To this end, cytotoxicity, morphological, and acetylcholinesterase activity studies were performed during 24 and 48 h. The results revealed a concentration-dependent decrease in viability and interaction between both toxicants, together with clear signs of apoptosis and necrosis induction. In this sense, different stages on the differentiation process would lead to differences in the toxicity exerted by the compounds both isolated as in combination, which it is not observed in non-differentiated cells. Additionally, the acetylcholinesterase activity appeared not to be affected, which is a clear difference compared to non-differentiated cells. These results show the importance of studying not only the toxicants themselves, but also in combination, to assess their possible effects in a more realistic scenario.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

Potential Endocrine Disruption of Cyanobacterial Toxins, Microcystins and Cylindrospermopsin: A Review

Microcystins (MCs) and cylindrospermopsin (CYN), although classified as hepatotoxins and cytotoxins, respectively, have been shown to also induce toxic effects in many other systems and organs. Among them, their potential endocrine disruption (ED) activity has been scarcely investigated. Considering the increasing relevance of ED on humans, mammals, and aquatic organisms, this work aimed to review the state-of-the-art regarding the toxic effects of MCs and CYN at this level. It has been evidenced that MCs have been more extensively investigated than CYN. Reported results are contradictory, with the presence or absence of effects, but experimental conditions also vary to a great extent. In general, both toxins have shown ED activity mediated by very different mechanisms, such as estrogenic responses via a binding estrogen receptor (ER), pathological changes in several organs and cells (testis, ovarian cells), and a decreased gonad-somatic index. Moreover, toxic effects mediated by reactive oxygen species (ROS), changes in transcriptional responses on several endocrine axes and steroidogenesis-related genes, and changes in hormone levels have also been reported. Further research is required in a risk assessment frame because official protocols for assessment of endocrine disrupters have not been used. Moreover, the use of advanced techniques would aid in deciphering cyanotoxins dose-response relationships in relation to their ED potential.

Subchronic Oral Cylindrospermopsin Exposure Alters the Host Gut Microbiome and Is Associated with Progressive Hepatic Inflammation, Stellate Cell Activation, and Mild Fibrosis in a Preclinical Study

Epidemiological studies have reported a strong association between liver injury and incidences of hepatocellular carcinoma in sections of humans globally. Several preclinical studies have shown a strong link between cyanotoxin exposure and the development of nonalcoholic steatohepatitis, a precursor of hepatocellular carcinoma. Among the emerging threats from cyanotoxins, new evidence shows cylindrospermopsin release in freshwater lakes. A known hepatotoxin in higher concentrations, we examined the possible role of cylindrospermopsin in causing host gut dysbiosis and its association with liver pathology in a mouse model of toxico-pharmacokinetics and hepatic pathology. The results showed that oral exposure to cylindrospermopsin caused decreased diversity of gut bacteria phyla accompanied by an increased abundance of Clostridioides difficile and decreased abundance of probiotic flora such as Roseburia, Akkermanssia, and Bacteroides&nbsp;thetaiotamicron, a signature most often associated with intestinal and hepatic pathology and underlying gastrointestinal disease. The altered gut dysbiosis was also associated with increased Claudin2 protein in the intestinal lumen, a marker of gut leaching and endotoxemia. The study of liver pathology showed marked liver inflammation, the release of damage-associated molecular patterns, and activation of toll-like receptors, a hallmark of consistent and progressive liver damage. Hepatic pathology was also linked to increased Kupffer cell activation and stellate cell activation, markers of progressive liver damage often linked to the development of liver fibrosis and carcinoma. In conclusion, the present study provides additional evidence of cylindrospermopsin-linked progressive liver pathology that may be very well-linked to gut dysbiosis, though definitive evidence involving this link needs to be studied further.

Reduced Fitness and Elevated Oxidative Stress in the Marine Copepod Tigriopus japonicus Exposed to the Toxic Dinoflagellate Karenia mikimotoi

Blooms of the toxic dinoflagellate Karenia mikimotoi cause devastation to marine life, including declines of fitness and population recruitment. However, little is known about the effects of them on benthic copepods. Here, we assessed the acute and chronic effects of K. mikimotoi on the marine benthic copepod Tigriopus japonicus. Results showed that adult females maintained high survival (>85%) throughout 14-d incubation, but time-dependent reduction of survival was detected in the highest K. mikimotoi concentration, and nauplii and copepodites were more vulnerable compared to adults. Ingestion of K. mikimotoi depressed the grazing of copepods but significantly induced the generation of reactive oxygen species (ROS), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and acetylcholinesterase. Under sublethal concentrations for two generations, K. mikimotoi reduced the fitness of copepods by prolonging development time and decreasing successful development rate, egg production, and the number of clutches. Our findings suggest that the bloom of K. mikimotoi may threaten copepod population recruitment, and its adverse effects are associated with oxidative stress.

Microcystins in Water: Detection, Microbial Degradation Strategies, and Mechanisms

Microcystins are secondary metabolites produced by some cyanobacteria, a class of cyclic heptapeptide toxins that are stable in the environment. Microcystins can create a variety of adverse health effects in humans, animals, and plants through contaminated water. Effective methods to degrade them are required. Microorganisms are considered to be a promising method to degrade microcystins due to their high efficiency, low cost, and environmental friendliness. This review focuses on perspectives on the frontiers of microcystin biodegradation. It has been reported that bacteria and fungi play an important contribution to degradation. Analysis of the biodegradation mechanism and pathway is an important part of the research. Microcystin biodegradation has been extensively studied in the existing research. This review provides an overview of (1) pollution assessment strategies and hazards of microcystins in water bodies and (2) the important contributions of various bacteria and fungi in the biodegradation of microcystins and their degradation mechanisms, including mlr gene-induced (gene cluster expressing microcystinase) degradation. The application of biodegradable technology still needs development. Further, a robust regulatory oversight is required to monitor and minimize MC contamination. This review aims to provide more references regarding the detection and removal of microcystins in aqueous environments and to promote the application of biodegradation techniques for the purification of microcystin-contaminated water.

Enantioselective neurotoxicity and oxidative stress effects of paclobutrazol in zebrafish (Danio rerio)

Paclobutrazol is a widely used chiral plant growth regulator and its enantioselective toxicity in aquatic organisms is less explored till now. Herein, the enantioselective neurotoxicity of paclobutrazol mediated by oxidative stress in zebrafish were investigated. The oxidative stress parameters and neurotoxic biomarkers changed significantly in each exposure group, and paclobutrazol showed enantioselective toxicity in zebrafish. Firstly, (2R, 3R)-paclobutrazol exhibited a stronger oxidative stress in zebrafish than (2S, 3S)-enantiomer (P < 0.05). Then, activities of acetylcholinesterase, calcineurin, and total nitric oxide synthase in (2R, 3R)-paclobutrazol treatments were 0.61-0.89, 1.24-1.53, and 1.21-1.35-fold stronger (P < 0.05) than those in (2S, 3S)-enantiomer treatments, respectively. Next, the content variations of four neurotransmitters in zebrafish exposed to (2R, 3R)-paclobutrazol were significantly larger than those in (2S, 3S)-enantiomer treatments (P < 0.05). Moreover, (2R, 3R)-paclobutrazol had stronger binding with the receptors than (2S, 3S)-enantiomer through molecular docking. The integrated biomarker response values further demonstrated that (2R, 3R)-paclobutrazol showed stronger toxicity to zebrafish than (2S, 3S)-enantiomer. Furthermore, the neurotoxicity of paclobutrazol can be interpreted as the mediating effect of oxidative stress in zebrafish through correlation analysis, and an adverse outcome pathway for the nervous system in zebrafish induced by paclobutrazol was proposed. This work will greatly extend our understanding on the enantioselective toxic effects of paclobutrazol in aquatic organisms.

In Vitro Toxicity Evaluation of Cyanotoxins Cylindrospermopsin and Microcystin-LR on Human Kidney HEK293 Cells

Cyanotoxins are secondary metabolites produced by different types of cyanobacteria. Among them, Cylindrospermopsin (CYN) and Microcystins (MCs) stand out due to their wide geographical distribution and toxicity in various organs, including the kidney, which is involved in their distribution and elimination. However, the renal toxicity caused by CYN and MCs has hardly been studied. The aim of this work was to assess the cytotoxicity effects caused by CYN and MC-LR in the renal cell line HEK293, and for the first time, the influence of CYN on the gene expression of selected genes in these cells by quantitative real-time PCR (qRT-PCR). CYN caused an upregulation in the gene expression after exposure to the highest concentration (5 µg/mL) and the longest time of exposure (24 h). Moreover, shotgun proteomic analysis was used to assess the molecular responses of HEK293 cells after exposure to the individuals and combinations of CYN + MC-LR. The simultaneous exposure to both cyanotoxins caused a greater number of alterations in protein expression compared to single toxins, causing changes in the cellular, lipid and protein metabolism and in protein synthesis and transport. Further studies are needed to complete the toxicity molecular mechanisms of both CYN and MC-LR at the renal level.

Microcystin-LR induces apoptosis in Juvenile Eriocheir sinensis via the mitochondrial pathway

Microcystin-LR (MC-LR), the toxic substance of cyanobacteria secondary metabolism, widely exists in water environments and poses great risks to living organisms. Some toxicological assessments of MC-LR have performed at physiological and biochemical levels. However, plenty of blanks about the potential mechanism in aquatic crustacean remains. In this study, we firstly assessed the exposure toxicity of MC-LR to juvenile E. sinensis and clarified that the 96 h LD50 of MC-LR was 73.23 μg/kg. Then, hepatopancreas transcriptome profiles of MC-LR stressed crabs were constructed at 6 h post-injection and 37 differential expressed genes (DEGs) were identified. These DEGs were enriched in cytoskeleton, peroxisome and apoptosis pathways. To further reveal the toxicity of MC-LR, oxidative stress parameters (SOD, CAT, GSH-px and MDA), apoptosis genes (caspase 3, bcl-2 and bax) and apoptotic cells were detected. Significant accumulated MDA and rise-fall enzyme activities verified the oxidative stress caused by MC-LR. It is noteworthy that quantitative real-time PCR and TUNEL assay indicated that MC-LR stress-induced apoptosis via the mitochondrial pathway. Interestingly, activator protein-1 may play a crucial role in mediating the hepatotoxicity of MC-LR by regulating apoptosis and oxidative stress. Taken together, our study investigated the toxic effects and the potential molecular mechanisms of MC-LR on juvenile E. sinensis. It provided useful data for exploring the toxicity of MC-LR to aquatic crustaceans at molecular levels.

Sorption of microcystin-RR onto surface soils: Characteristics and influencing factors

Microcystins are frequently detected in cyanobacterial bloom-impacted sites; however, their mobility potential in soils is poorly understood. This study aimed to elucidate the sorption behaviors of microcystin-RR (MC-RR) in heterogeneous soils and evaluate critical affecting factors. MC-RR sorption followed the pseudo-second-order kinetics and Freundlich model. All isotherms (n = 0.83-1.03) had no or minor deviations from linearity. The linear distribution coefficients (K_d) varied from 2.64 to 15.2 across soils, depending mainly on OM and CEC. Stepwise regression analysis indicated that the K_d was predictable by the fitting formula of: K_d = 2.56 + 0.15OM + 0.28CEC (R² = 0.45). The sorption was an endothermic physisorption process, involving electrostatic forces, cation exchange and bridging, H-bonding, ligand exchange, and van der Waals forces. The sorption of MC-RR (dominantly behaved as electroneutral zwitterions) at pH > 5 was insensitive to pH change, while more MC-RR (anionic species) was adsorbed at lower pH and in the presence of Ca²⁺. The study provides insights into the sorption of MC-RR across a range of soil properties and water chemistry for the first time, which is of importance for a better understanding of the mobility potential of microcystins in the terrestrial systems.

Algicide capacity of Paucibacter aquatile DH15 on Microcystis aeruginosa by attachment and non-attachment effects

The excessive proliferation of Microcystis aeruginosa can lead to ecological damage, economic losses, and threaten animal and human health. For controlling Microcystis blooms, microorganism-based methods have attracted much attention from researchers because of their eco-friendliness and species-specificity. Herein, we first found that a Paucibacter strain exhibits algicidal activity against M. aeruginosa and microcystin degradation capability. The algicidal activity of DH15 (2.1 × 10⁴ CFU/ml) against M. aeruginosa (2 × 10⁶ cells/ml) was 94.9% within 36 h of exposure. DH15 also degraded microcystin (1.6 mg/L) up to 62.5% after 72 h. We demonstrated that the algicidal activity of DH15 against M. aeruginosa can be mediated by physical attachment and indirect attack: (1) Both washed cells and cell-free supernatant could kill M. aeruginosa efficiently; (2) Treatment with DH15 cell-free supernatants caused oxidative stress, altered the fatty acid profile, and damaged photosynthetic system, carbohydrate, and protein metabolism in M. aeruginosa. The combination of direct and indirect attacks supported that strain DH15 exerts high algicidal activity against M. aeruginosa. The expression of most key genes responsible for photosynthesis, antioxidant activity, microcystin synthesis, and other metabolic pathways in M. aeruginosa was downregulated. Strain DH15, with its microcystin degradation capacity, can overcome the trade-off between controlling Microcystis blooms and increasing microcystin concentration. Our findings suggest that strain DH15 possesses great potential to control outbreaks of Microcystis blooms.

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.

Neurotoxicity induced by combined exposure of microcystin-LR and nitrite in male zebrafish (Danio rerio): Effects of oxidant-antioxidant system and neurotransmitter system

With the intensification of water eutrophication around the world, cyanobacterial blooms have been becoming a common environmental pollution problem. The levels of microcystin-LR (MC-LR) and nitrite rise sharply during the cyanobacterial bloom period, which may have potential joint toxicity on aquatic organisms. In this study, adult male zebrafish were immersed into different joint solutions of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 days to explore the neurotoxic effects and underlying mechanisms. The results showed that single factor MC-LR or nitrite caused a concentration-dependent damage in brain ultrastructure and the effects of their joint exposure were much more intense. Downregulated expression of mbp and bdnf associated with myelination of nerve fibers further confirmed that MC-LR and nitrite could damage the structure and function of neuron. The decreases in dopamine content, acetylcholinesterase activity and related gene mRNA levels indicated that MC-LR and nitrite adversely affected the normal function of the dopaminergic and cholinergic systems in zebrafish brain. In addition, the significant increase in malondialdehyde content suggested the occurrence of oxidative stress caused by MC-LR, nitrite and their joint-exposure, which paralleled a significant decrease in antioxidant enzyme‑manganese superoxide dismutase activity and its transcription level. In conclusion, MC-LR + Nitrite joint-exposure has synergistic neurotoxic effects on the structure and neurotransmitter systems of fish brain, and antioxidant capacity disruption caused by these two factors might be one of the underlying synergistic mechanisms. Therefore, there is a risk of being induced neurotoxicity in fish during sustained cyanobacterial bloom events.

Cytotoxicity and Effects on the Synapsis Induced by Pure Cylindrospermopsin in an E17 Embryonic Murine Primary Neuronal Culture in a Concentration- and Time-Dependent Manner

Cylindrospermopsin (CYN) is a cyanotoxin whose incidence has been increasing in the last decades. Due to its capacity to exert damage at different levels of the organism, it is considered a cytotoxin. Although the main target organ is the liver, recent studies indicate that CYN has potential toxic effects on the nervous system, both in vitro and in vivo. Thus, the aim of the present work was to study the effects of this cyanotoxin on neuronal viability and synaptic integrity in murine primary cultures of neurons exposed to environmentally relevant concentrations (0–1 µg/mL CYN) for 12, 24, and 48 h. The results demonstrate a concentration- and time-dependent decrease in cell viability; no cytotoxicity was detected after exposure to the cyanotoxin for 12 h, while all of the concentrations assayed decreased this parameter after 48 h. Furthermore, CYN was also demonstrated to exert damage at the synaptic level in a murine primary neuronal culture in a concentration- and time-dependent manner. These data highlight the importance of studying the neurotoxic properties of this cyanotoxin in different experimental models.

Immunoassay technology: Research progress in microcystin-LR detection in water samples

Increasing global warming and eutrophication have led to frequent outbreaks of cyanobacteria blooms in freshwater. Cyanobacteria blooms cause the death of aquatic and terrestrial organisms and have attracted considerable attention since the 19th century. Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins. Therefore, the fast, sensitive, and accurate determination of MC-LR plays an important role in the health of humans and animals. Immunoassay refers to a method that uses the principle of immunology to determine the content of the tested substance in a sample using the tested substance as an antigen or antibody. In analytical applications, the immunoassay technology could use the specific recognition of antibodies for MC-LR detection. In this review, we firstly highlight the immunoassay detection of MC-LR over the past two decades, including classical enzyme-link immunosorbent assay (ELISA), modern immunoassay with optical signal, and modern immunoassay with electrical signal. Among these detection methods, the water environment was used as the main detection system. The advantages and disadvantages of the different detection methods were compared and analyzed, and the principles and applications of immunoassays in water samples were elaborated. Furthermore, the current challenges and developmental trends in immunoassay were systematically introduced to enhance MC-LR detection performance, and some critical points were given to deal with current challenges. This review provides novel insight into MC-LR detection based on immunoassay method.

Microcystins can be extracted from Microcystis aeruginosa using amino acid-derived biosurfactants

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

Microcystin-leucine arginine (MC-LR) induces mouse ovarian inflammation by promoting granulosa cells to produce inflammatory cytokine via activation of cGAS-STING signaling

Early experimental studies have demonstrated that microcystin-leucine arginine (MC-LR) is able to induce multiple organ damage. Female reproductive disorders caused by MC-LR have attracted increased attention in recent years. However, the underlying mechanisms of female reproductive malfunctions are not yet fully understood. Our previous study confirmed that MC-LR could enter mice ovary, induce apoptosis of ovarian granulosa cell and lead to follicular atresia. Research shows that ovary inflammation is positively related to the decline of female reproductive function. This study was aimed to find out the relationship between inflammation response and ovarian injury caused by MC-LR. MC-LR were administrated at 0, 7.5, 22.5 and 45 µg/kg for two weeks by intraperitoneal injection in female BALB/c mice. Histopathological analysis of ovary was performed. We found that MC-LR exposure induced inflammation response and fibrosis in ovary. In the present study, we observed that MC-LR could enter ovary and was mainly distributed in mGCs (mouse ovarian granulosa cells), but not in the theca-interstitial cells. We isolated and cultured mGCs with different concentrations of MC-LR at 0, 0.01, 0.1, 1 and 10 µM. MC-LR exposure caused mitochondrial DNA (mtDNA) leakage which was detected by qPCR andimmunofluorescence staining. Subsequently, mtDNA leakage activated cGAS-STING signaling, leading to elevated production of inflammatory cytokines TNF-α in mGCs.Diffusion of TNF-α in ovary resulted in inflammatory cell infiltration and interstitial cell proliferation. Ovarian inflammation provides a new perspective to explore the underlying mechanisms associated with MC-LR-induced female reproductive dysfunction.

Synergistic toxicity of some cyanobacterial oligopeptides to physiological activities of Daphnia magna (Crustacea)

Anabaenopeptins and microcystins are oligopeptides produced by bloom-forming cyanobacteria. We determined in vivo effects of anabaenopeptin-B (AN-B) and two variants of microcystins of different hydrophobicity (MC-LR and MC-LF) on the physiology of Daphnia magna. Heart rate, thoracic limb activity and post-abdominal claw activity were determined by digital video analysis and oxygen consumption by Oxygraph + system. EC50 calculation and isobole methodology for interactive effects of AN-B and MC-LR mixture were used. Daphnids' responses to all three oligopeptides were concentration- and time-dependent. MC-LF was the most potent inhibitor of heart rate, thoracic limb activity, post-abdominal claw activity and oxygen consumption. AN-B was more toxic than MC-LR toward oxygen consumption; it inhibited the movements of limbs and post-abdominal claw similarly to MC-LR, but did not inhibit heart rate. The strongest toxic effects were induced by the binary mixture of AN-B with MC-LR at the sum concentration equal to the concentration of the single compounds. First time direct synergistic toxic effects of the cyanopeptides on all the physiological parameters were found. The obtained results explain stronger disturbances in aquatic organisms caused by cyanobacterial cell contents than the individual cyanopeptides present even at higher concentrations. Other metabolites and their interactions need further studies.

Characterization and Diversity of Microcystins Produced by Cyanobacteria from the Curonian Lagoon (SE Baltic Sea)

Microcystins (MCs) are the most widely distributed and structurally diverse cyanotoxins that can have significant health impacts on living organisms, including humans. The identification of MC variants and their quantification is very important for toxicological assessment. Within this study, we explored the diversity of MCs and their potential producers from the Curonian Lagoon. MC profiles were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, while the potential producers were detected based on the presence of genus-specific mcyE gene sequences. Among the numerous MCs detected, one new potential MC variant with m/z 1057 was partially characterized. Moreover, two other MCs with m/z 1075 and m/z 1068 might belong to new variants with serine (Ser), rarely detected in position one of the peptides. They might also represent MC-Y(OMe)R and MC-WR, respectively. However, the application of a low-resolution MS/MS system made the unambiguous identification of the MCs impossible. Based on this example, the problems of peptide structure identification are discussed in the work. Genetic analysis revealed that potential MCs producers include Dolichospermum/Anabaena, Microcystis spp., and Planktothrix agardhii. The diversity and temporal variations in MC profiles may indicate the presence of several chemotypes of cyanobacteria in the Curonian Lagoon.

Chronic MC-LR exposure promoted Aβ and p-tau accumulation via regulating Akt/GSK-3β signal pathway

It has been reported that microcystin-leucine-arginine (MC-LR) can enter into the brain and demonstrate neurotoxicity resulting in learning and memory deficits. While, there is still a lack of clear understanding of the related molecular mechanisms. In this study, we observed β-amyloid (Aβ) accumulation and tau hyperphosphorylation (p-tau) at sites of Ser396 and Thr205 in mouse hippocampus and cortex, Alzheimer's disease (AD) like changes, after chronic exposure to MC-LR at different concentrations (1, 7.5, 15 and 30 μg/L) for 180 days. The hallmarks of AD are characterized by senile plaques and neurofibrillary tangles (NFT), with associated loss of neurons, resulting in cognitive impairment and dementia. Similarly, the production of Aβ and tau hyperphosphorylation was also detected in HT-22 cells treated with MC-LR. In addition, MC-LR promoted increased expressions of BACE1 and PS1, but reduced mRNA expressions of ADAM family members both in vivo and in vitro, promoting the Aβ production. Moreover, we identified Akt/GSK-3β signal pathway mediated the Aβ and p-tau accumulation, bringing about Alzheimer's disease-like changes. Furthermore, microglial cells were activated in those mice exposed to MC-LR. Inflammatory cytokines were also found being activated to release in vitro. In conclusion, this study could provide a clue for MC-LR-induced neurotoxicity, which gave insights into the environmental risks of Alzheimer's disease.

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

Cyanotoxins have gained global public interest due to their potential to bioaccumulate in food, which threatens human health. Bloom formation is usually enhanced under Mediterranean, subtropical and tropical climates which are the dominant climate types in developing countries. In this context, we present an up-to-date overview of cyanotoxins (types, toxic effects, analysis, occurrence, and mitigation) with a special focus on their contamination in (sea)food from all the developing countries in Africa, Asia, and Latin America as this has received less attention. A total of 65 publications have been found (from 2000 until October 2021) reporting the contamination by one or more cyanotoxins in seafood and edible plants (five papers). Only Brazil and China conducted more research on cyanotoxin contamination in food in comparison to other countries. The majority of research focused on the detection of microcystins using different analytical methods. The detected levels mostly surpassed the provisional tolerable daily intake limit set by the World Health Organization, indicating a real risk to the exposed population. Assessment of cyanotoxin contamination in foods from developing countries still requires further investigations by conducting more survey studies, especially the simultaneous detection of multiple categories of cyanotoxins in food.

Paternal exposure to microcystin-LR induces fetal growth restriction partially through inhibiting cell proliferation and vascular development in placental labyrinth

Microcystin-leucine arginine (MC-LR) has reproductive and developmental toxicities. Previous studies indicated that gestational exposure to MC-LR induced fetal growth restriction in mice. The aim of this study was to further evaluate the effect of paternal MC-LR exposure before mating on fetal development. Male mice were intraperitoneally injected with either normal saline or MC-LR (10 μg/kg) daily for 35 days. Male mouse was then mated with female mice with 1:1 ratio. There was no significant difference on the rates of mating and pregnancy between MC-LR-exposed male mice and controls. Body weight and crown-rump length were reduced in fetuses whose fathers were exposed to MC-LR. Despite no difference on relative thickness of labyrinthine layer, cell proliferation, as measured by Ki67 immunostaining, was reduced in labyrinth layer of MC-LR-exposed mice. Moreover, blood sinusoid area in labyrinth layer was decreased in the fetus whose father was exposed to MC-LR before mating. Correspondingly, cross-sectional area of CD34-positive blood vessel in labyrinth layer was lower in fetuses whose fathers were exposed to MC-LR than in controls. These results provide evidence that paternal MC-LR exposure before mating induces fetal growth restriction partially through inhibiting cell proliferation and vascular development in labyrinth layer.

Effects of microcystin-producing and non-microcystin-producing Microcystis on the behavior and life history traits of Chironomus pallidivittatus

Species of the genus Microcystis are among the most notorious cyanobacteria in eutrophic lakes worldwide, with ability present adverse effects on many aquatic organisms. In the surface sediments, Microcystis can be ingested by benthic macroinvertebrates such as Chironomus. However, the potential negative effects of Microcystis on Chironomus life history traits remain unclear. In the present study, we investigated the effect of different Microcystis diets on specific behaviors (burrowing activity, locomotion ability) and life history traits of Chironomus pallidivittatus (Diptera, Chironomidae). We also studied the interactive effects of microcystin-producing M. aeruginosa and temperature (15, 20, and 25 °C) stress on chironomid larvae. The results showed that the inhibitory effect on the cumulative emergence and burrowing activity of larvae was more severe when they were fed M. aeruginosa among the three Microcystis diets groups. Locomotion ability (i.e., locomotor distance and velocity) and adult dry weight decreased significantly in the group fed M. aeruginosa. Locomotion was significantly inhibited and mortality increased when the larvae were fed a mixture of M. aeruginosa and M. wesenbergii, which may have been the result of additive or synergistic effect of the toxins. Under the stress of lower temperature, C. pallidivittatus larvae exhibited weaker locomotion and growth ability, and the emerging adults were mostly male. At both the lower and higher temperature conditions, M. aeruginosa cause cumulative emergence decreased, and sex ratio imbalance, which inhibited the reproduction of larvae from the population perspective. The fourth-instar larvae showed better adaption to Microcystis than did the other instars. This study thus highlights the adverse effects of microcystin-producing M. aeruginosa on Chironomus. It also provides a novel perspective on how environmental factors may influence the behavior and life history traits of chironomid larvae, and how they may respond to cyanobacterial blooms and global warming.

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.

Cyanotoxins and the Nervous System

Cyanobacteria are capable of producing a wide range of bioactive compounds with many considered to be toxins. Although there are a number of toxicological outcomes with respect to cyanobacterial exposure, this review aims to examine those which affect the central nervous system (CNS) or have neurotoxicological properties. Such exposures can be acute or chronic, and we detail issues concerning CNS entry, detection and remediation. Exposure can occur through a variety of media but, increasingly, exposure through air via inhalation may have greater significance and requires further investigation. Even though cyanobacterial toxins have traditionally been classified based on their primary mode of toxicity, increasing evidence suggests that some also possess neurotoxic properties and include known cyanotoxins and unknown compounds. Furthermore, chronic long-term exposure to these compounds is increasingly being identified as adversely affecting human health.

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.

Harmful algal bloom resources for livestock veterinarians

Harmful algal blooms can have deleterious effects on animal and human health as well as the environment and are anticipated to become more frequent and intensified in the future because of climate change. Veterinarians are well positioned to diagnose and treat animals affected by HABs and to educate livestock owners and the public about health risks and environmental issues associated with those toxic events. Pets, livestock, wildlife, and marine life can all be affected by HABs. Information about HABs is becoming increasingly assessable as a result of ongoing research into the structure, properties, toxic mechanisms, and geographic distribution of toxins found in HABs. The AVMA's multi-entity working group on HABs is comprised of members from the Aquatic Veterinary Medicine Committee, Committee on Environmental Issues, and Council on Public Health and is working to make more information and resources regarding HABs available to practicing veterinarians. The present article is the first of those resources and provides a review of HABs, with a focus on livestock. It includes background material about bloom formation, appearance, and persistence as well as descriptions of clinical observations from early field cases and more recent information about the causative organisms and toxins to provide livestock veterinarians a foundation for understanding HABs. Reporting of HABs and prevention and mitigation strategies for livestock owners are also discussed.

Histological and chemical damage induced by microcystin-LR and microcystin-RR on land snail Helix aspersa tissues after acute exposure

Microcystins (MCs) are the most common cyanotoxins with more than 200 variants. Among these cyanotoxins, microcystin-LR (MC-LR) and microcystin-RR (MC-RR) are the most studied congeners due to their high toxicity and frequent occurrence in surface waters. MC-LR has been detected in more than 75% of natural cyanobacteria bloom, along with other toxic and less toxic congeners. Accumulation of several microcystins variants (MC-LR and MC-RR) has been confirmed in aquatic snails exposed naturally or in the laboratory to toxic blooms. Thus, this paper aims to compare the biochemical and histological impact of both toxic variants (microcystin-LR and microcystin-RR) and their mixed form on a bioindicator, the land snail Helix aspersa. During experiments, snails were gavaged with a single acute dose (0.5 μg/g) of purified MC-LR, MC-RR, or mixed MC-LR + MC-RR (0.25 + 0.25 μg/g). After 96 h of exposure, effects on the hepatopancreas, kidney, intestine and lungs were assessed by histological observations and analysis of oxidative stress biomarkers. The results show that a small dose of MCs variants can increase the non-enzymatic antioxidant glutathione (GSH), inhibit glutathione-s-transferase (GST) level and trigger a defense system by activating glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD). Microcystin-RR causes serious anomalies in the hepatopancreas and kidney than Microcystin-LR. The organ most affected is the kidney. The damage caused by MC-LR + MC-RR is greater than that caused by single variants.