Guidance values for microcystins in water and cyanobacterial supplement products (blue-green algal supplements): a reasonable or misguided approach?

Blue revolution turning green? A global concern of cyanobacteria and cyanotoxins in freshwater aquaculture: A literature review

To enhance productivity, aquaculture is intensifying, with high-density fish ponds and increased feed input, contributing to nutrient load and eutrophication. Climate change further exacerbates cyanobacterial blooms and cyanotoxin production that affect aquatic organisms and consumers. A review was conducted to outline this issue from its inception - eutrophication, cyanobacterial blooms, their harmful metabolites and consequential effects (health and economic) in aquacultures. The strength of evidence regarding the relationship between cyanobacteria/cyanotoxins and potential consequences in freshwater aquacultures (fish production) globally were assessed as well, while identifying knowledge gaps and suggesting future research directions. With that aim several online databases were searched through June 2023 (from 2000), and accessible publications conducted in aquacultures with organisms for human consumption, reflecting cyanotoxin exposure, were selected. Data on cyanobacteria/cyanotoxins in aquacultures and its products worldwide were extracted and analyzed. Selected 63 papers from 22 countries were conducted in Asia (48%), Africa (22%), America (22%) and Europe (8%). Microcystis aeruginosa was most frequent, among over 150 cyanobacterial species. Cyanobacterial metabolites (mostly microcystins) were found in aquaculture water and fish from 18 countries (42 and 33 papers respectively). The most affected were small and shallow fish ponds, and omnivorous or carnivorous fish species. Cyanotoxins were detected in various fish organs, including muscles, with levels exceeding the tolerable daily intake in 60% of the studies. The majority of research was done in developing countries, employing less precise detection methods, making the obtained values estimates. To assess the risk of human exposure, the precise levels of all cyanotoxins, not just microcystins are needed, including monitoring their fate in aquatic food chains and during food processing. Epidemiological research on health consequences, setting guideline values, and continuous monitoring are necessary as well. Further efforts should focus on methods for elimination, prevention, and education.

Alleviation of microcystin-leucine arginine -induced hepatotoxicity: An updated overview

OBJECTIVES

Contamination of surface waters is a major health threat for all living creatures. Some types of blue-green algae that naturally occur in fresh water, are able to produce various toxins, like Microcystins (MCs). Microcystin-leucine arginine (MC-LR) produced by Microcystis aeruginosa is the most toxic and abundant isoforms of MCs, and it causes hepatotoxicity. The present article reviews preclinical experiments examined different treatments, including herbal derivatives, dietary supplements and drugs against MC-LR hepatotoxicity.

METHODS

We searched scientific databases Web of Science, Embase, Medline (PubMed), Scopus, and Google Scholar using relevant keywords to find suitable studies until November 2023.

RESULTS

MC-LR through Organic anion transporting polypeptide superfamily transporters (OATPs) penetrates and accumulates in hepatocytes, and it inhibits protein phosphatases (PP1 and PP2A). Consequently, MC-LR disturbs many signaling pathways and induces oxidative stress thus damages cellular macromolecules. Some protective agents, especially plants rich in flavonoids, and natural supplements, as well as chemoprotectants were shown to diminish MC-LR hepatotoxicity.

CONCLUSION

The reviewed agents through blocking the OATP transporters (nontoxic nostocyclopeptide-M1, captopril, and naringin), then inhibition of MC-LR uptake (naringin, rifampin, cyclosporin-A, silymarin and captopril), and finally at restoration of PPAse activity (silybin, quercetin, morin, naringin, rifampin, captopril, azo dyes) exert hepatoprotective effect against MC-LR.

Microcystin-LR improves anti-tumor efficacy of oxaliplatin through induction of M1 macrophage polarization

Tumor-associated macrophages within the tumor microenvironment play an immunosuppressive role by promoting tumor growth and immune evasion. Macrophages are highly plastic and can be stimulated to adopt an anti-tumor M1 phenotype. In this study, we used microcystin-LR (MC-LR), a cyclic heptapeptide produced by cyanobacteria, to induce in vitro macrophage innate immunity and transition into the anti-tumor M1 phenotype. MC-LR was also tested in vivo in a mouse model of colorectal cancer. An intraperitoneal injection of MC-LR increased the proportion of CD86⁺ M1 macrophages and triggered the maturation of CD11c⁺ dendritic cells within tumor tissues. MC-LR combined with the chemotherapeutic drug oxaliplatin significantly inhibited tumor growth in vivo. Flow cytometry analysis revealed increased infiltration of activated cytotoxic (CD8⁺, PD-1⁺) T-cells and anti-tumor cytokines (IFNγ and Granzyme B) in the tumor tissues of the combination therapy group, suggesting that this may be the primary mechanism behind the anti-tumor effect of the combination treatment. These findings indicate that MC-LR regulates the immune stimulation of macrophage polarization and dendritic cell maturation, effectively reversing tumor immunosuppression, activating an anti-tumor immune response, and enhancing tumor therapy.

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

Systematic analysis, aggregation and visualisation of interaction fingerprints for molecular dynamics simulation data

Computational methods such as molecular docking or molecular dynamics (MD) simulations have been developed to simulate and explore the interactions between biomolecules. However, the interactions obtained using these methods are difficult to analyse and evaluate. Interaction fingerprints (IFPs) have been proposed to derive interactions from static 3D coordinates and transform them into 1D bit vectors. More recently, the concept has been applied to derive IFPs from MD simulations, which adds a layer of complexity by adding the temporal motion and dynamics of a system. As a result, many IFPs are obtained from one MD simulation, resulting in a large number of individual IFPs that are difficult to analyse compared to IFPs derived from static 3D structures. Scientific contribution: We introduce a new method to systematically aggregate IFPs derived from MD simulation data. In addition, we propose visualisations to effectively analyse and compare IFPs derived from MD simulation data to account for the temporal evolution of interactions and to compare IFPs across different MD simulations. This has been implemented as a freely available Python library and can therefore be easily adopted by other researchers and to different MD simulation datasets.

Microcystin-LR-induced epithelial-mesenchymal transition-like cells acquire resistance to multi-toxins

The protein phosphatase inhibitor microcystin-LR (MC-LR), a hepatocyte-selective cyanotoxin, induces phenotypic changes in HEK293 OATP1B3-expressing (HEK293-OATP1B3) cells, which include cytoskeletal reorganization (HEK293-OATP1B3-AD) and anoikis resistance (HEK293-OATP1B3-FL) transformed cells, respectively. These cells acquire resistance to MC-LR and partial epithelial-mesenchymal transition (EMT) characteristics. In cancer cells, EMT is generally involved in multi-drug resistance. Here, we focused on the multi-drug resistance of HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. The MTT assay and immunoblotting were conducted to examine the responses of HEK293-OATP1B3, HEK293-OATP1B3-AD, and HEK293-OATP1B3-FL cells to multiple toxins and drugs that function as substrates for OATP1B3, including MC-LR, nodularin (Nod), okadaic acid (OA), and cisplatin (CDDP). HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells were more resistant to MC-LR, Nod, and OA than HEK293-OATP1B3 cells. Conversely, the three cell types were equivalently sensitive to CDDP. By using protein phosphatase assay, the reduction of the inhibitory effect of MC-LR and Nod on phosphatase activity might be one reason for the resistance to MC-LR and Nod in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. Furthermore, the parental HEK293-OATP1B3 cells showed enhanced p53 phosphorylation and stabilization after MC-LR exposure, while p53 phosphorylation was attenuated in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells. Moreover, in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells, AKT phosphorylation was higher than that of the parental HEK293-OATP1B3 cell line. These results suggest that the multi-toxin resistance observed in HEK293-OATP1B3-AD and HEK293-OATP1B3-FL cells is associated with AKT activation and p53 inactivation.

Cyanobacteria and cyanotoxins in the environment and water intakes: Reports, diversity of congeners, detection by mass spectrometry and their impact on health

Cyanobacteria are aquatic microorganisms of high interest for research due to the production of secondary metabolites, among which the most popular are cyanotoxins, responsible for causing severe poisoning in humans and animals through ingestion or contact with contaminated water bodies. Monitoring the number of cyanobacteria in water and concentrations of secreted cyanotoxins with the aid of sensitive and reliable methods is considered the primary action for evaluating potentially toxic blooms. There is a great diversity of methods to detect and identify these types of micro contaminants in water, differing by the degree of sophistication and information provided. Mass Spectrometry stands out for its accuracy and sensitivity in identifying toxins, making it possible to identify and characterize toxins produced by individual species of cyanobacteria, in low quantities. In this review, we seek to update some information about cyanobacterial peptides, their effects on biological systems, and the importance of the main Mass Spectrometry methods used for detection, extraction, identification and monitoring of cyanotoxins.

Microcystins in water containers used in the home: A review of their potential health effects

Cyanobacteria produce toxins that are harmful to humans. They are found mostly in surface water, which is the main water source for drinking water before treatment. However, most of the water treatment plants are inadequate to treat toxins such as microcystins in raw water sources from contaminated surface water that has blooming and/or decaying cyanobacteria. Microcystins are harmful toxins produced by cyanobacteria that cause both acute and chronic health problems in humans. However, little is known about microcystins in water containers at the household level. This article therefore focuses on a review of the effects of microcystins in drinking water containers at the household level, including types of microcystins, their health effects, and cases reported in both animals and humans. Therefore, there is a need to develop the water quality management for cyanobacteria toxins, particularly microcystins in household containers.

Cyanotoxins in African waterbodies: occurrence, adverse effects, and potential risk to animal and human health

Public concerns about cyanotoxins production in water and its detrimental impacts on human and animal health are growing primarily due to the widespread eutrophication observed in aquatic ecosystems. A review of relevant literature was done to determine the degree of cyanotoxin occurrence and its harmful effects in African waterbodies. Data were extracted from 64 published studies from 1990 to 2022 that quantified the concentration of cyanotoxins in African aquatic ecosystems. Cyanotoxins have been reported in 95 waterbodies (29 lakes, 41 reservoirs, 10 ponds, 9 rivers, 5 coastal waters, and 1 irrigation canal) from 15 African countries. Cyanotoxins were documented in all the regions of Africa except the central region. Microcystins have been reported in nearly all waterbodies (98.9%), but anatoxin-a (5.3%), cylindrospermopsin (2.1%), nodularins (2.1%), homoanatoxin-a (1.1%), and β-N-methylamino-L-alanine (1.1%) were encountered in a small number of water ecosystems, homoanatoxin-a and β-N-methylamino-L-alanine each occurred in one waterbody. The largest concentrations of microcystins and nodularins were reported in South African Lakes Nhlanganzwani (49,410 μg L-1) and Zeekoevlei (347,000 μg g-1). Microcystin concentrations exceeding the WHO guideline for lifetime drinking water (1 μg L-1) were reported in 63% of the aquatic ecosystems surveyed. The most frequently reported toxin-producing cyanobacteria genus is Microcystis spp. (73.7%), followed by Oscillatoria spp. (35.8%) and Dolichospermum spp. (33.7%). Cyanotoxin-related animal mortality and human illness were reported in the continent. Consequently, it is necessary to regularly monitor the level of nutrients, cyanobacteria, and cyanotoxins in African waterbodies in an integrated manner to devise a sustainable water resources management.

Transformation of Algal Toxins during the Oxidation/Disinfection Processes of Drinking Water: From Structure to Toxicity

With the increase of algal blooms worldwide, drinking water resources are threatened by the release of various algal toxins, which can be hepatotoxic, cytotoxic, or neurotoxic. Because of their ubiquitous occurrence in global waters and incomplete removal in conventional drinking water treatment, oxidation/disinfection processes have become promising alternative treatment options to destroy both the structures and toxicity of algal toxins. This Review first summarizes the occurrence and regulation of algal toxins in source water and drinking water. Then, the transformation kinetics, disinfection byproducts (DBPs)/transformation products (TPs), pathways, and toxicity of algal toxins in water oxidation/disinfection processes, including treatment by ozonation, chlorination, chloramination, ultraviolet-based advanced oxidation process, and permanganate, are reviewed. For most algal toxins, hydroxyl radicals (HO•) exhibit the highest oxidation rate, followed by ozone and free chlorine. Under practical applications, ozone and chlorine can degrade most algal toxins to meet water quality standards. However, the transformation of the parent structures of algal toxins by oxidation/disinfection processes does not guarantee a reduction in toxicity, and the formation of toxic TPs should also be considered, especially during chlorination. Notably, the toxicity variation of algal toxins is associated with the chemical moiety responsible for toxicity (e.g., Adda moiety in microcystin-LR and uracil moiety in cylindrospermopsin). Moreover, the formation of known halogenated DBPs after chlorination indicates that toxicity in drinking water may shift from toxicity contributed by algal toxins to toxicity contributed by DBPs. To achieve the simultaneous toxicity reduction of algal toxins and their TPs, optimized oxidation/disinfection processes are warranted in future research, not only for meeting water quality standards but also for effective reduction of toxicity of algal toxins.

Biotests in Cyanobacterial Toxicity Assessment-Efficient Enough or Not?

Cyanobacteria are a diverse group of organisms known for producing highly potent cyanotoxins that pose a threat to human, animal, and environmental health. These toxins have varying chemical structures and toxicity mechanisms and several toxin classes can be present simultaneously, making it difficult to assess their toxic effects using physico-chemical methods, even when the producing organism and its abundance are identified. To address these challenges, alternative organisms among aquatic vertebrates and invertebrates are being explored as more assays evolve and diverge from the initially established and routinely used mouse bioassay. However, detecting cyanotoxins in complex environmental samples and characterizing their toxic modes of action remain major challenges. This review provides a systematic overview of the use of some of these alternative models and their responses to harmful cyanobacterial metabolites. It also assesses the general usefulness, sensitivity, and efficiency of these models in investigating the mechanisms of cyanotoxicity expressed at different levels of biological organization. From the reported findings, it is clear that cyanotoxin testing requires a multi-level approach. While studying changes at the whole-organism level is essential, as the complexities of whole organisms are still beyond the reach of in vitro methodologies, understanding cyanotoxicity at the molecular and biochemical levels is necessary for meaningful toxicity evaluations. Further research is needed to refine and optimize bioassays for cyanotoxicity testing, which includes developing standardized protocols and identifying novel model organisms for improved understanding of the mechanisms with fewer ethical concerns. In vitro models and computational modeling can complement vertebrate bioassays and reduce animal use, leading to better risk assessment and characterization of cyanotoxins.

Microbiota and Cyanotoxin Content of Retail Spirulina Supplements and Spirulina Supplemented Foods

Cyanobacterial biomass such as spirulina (Arthrospira spp.) is widely available as a food supplement and can also be added to foods as a nutritionally beneficial ingredient. Spirulina is often produced in open ponds, which are vulnerable to contamination by various microorganisms, including some toxin-producing cyanobacteria. This study examined the microbial population of commercially available spirulina products including for the presence of cyanobacterial toxins. Five products (two supplements, three foods) were examined. The microbial populations were determined by culture methods, followed by identification of isolates using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF), and by 16S rRNA amplicon sequencing of the products themselves and of the total growth on the enumeration plates. Toxin analysis was carried out by enzyme-linked immunosorbent assay (ELISA). Several potentially pathogenic bacteria were detected in the products, including Bacillus cereus and Klebsiella pneumoniae. Microcystin toxins were detected in all the products at levels that could lead to consumers exceeding their recommended daily limits. Substantial differences were observed in the identifications obtained using amplicon sequencing and MALDI-TOF, particularly between closely related Bacillus spp. The study showed that there are microbiological safety issues associated with commercial spirulina products that should be addressed, and these are most likely associated with the normal means of production in open ponds.

16S-rRNA-Based Metagenomic Profiling of the Bacterial Communities in Traditional Bulgarian Sourdoughs

Sourdoughs (SDs) are spontaneously formed microbial ecosystems composed of various species of lactic acid bacteria (LAB) and acid-tolerant yeasts in food matrices of cereal flours mixed with water. To date, more than 90 LAB species have been isolated, significantly impacting the organoleptic characteristics, shelf life, and health properties of bakery products. To learn more about the unique bacterial communities involved in creating regional Bulgarian sourdoughs, we examined the metacommunities of five sourdoughs produced by spontaneous fermentation and maintained by backslopping in bakeries from three geographic locations. The 16S rRNA gene amplicon sequencing showed that the former genus Lactobacillus was predominant in the studied sourdoughs (51.0-78.9%). Weissella (0.9-42.8%), Herbaspirillum (1.6-3.8%), Serratia (0.1-11.7%), Pediococcus (0.2-7.5%), Bacteroides (0.1-1.3%), and Sphingomonas (0.1-0.5%) were also found in all 5 samples. Genera Leuconostoc, Enterococcus, Bacillus, and Asaia were sample-specific. It is interesting to note that the genus Weissella was more abundant in wholegrain samples. The greatest diversity at the species level was found in the former genus Lactobacillus, presented in the sourdough samples with 13 species. The UPGMA cluster analysis clearly demonstrated similarity in species' relative abundance between samples from the same location. In addition, we can conclude that the presence of two main clusters-one including samples from mountainous places (the cities of Smolyan and Bansko) and the other including samples from the city of Ruse (the banks of the Danube River)-may indicate the impact of climate and geographic location (e.g., terrain, elevation, land use, and nearby water bodies and their streams) on the abundance of microbiome taxa. As the bacterial population is crucial for bread standardization, we expect the local bakery sector to be interested in the relationship between process variables and their effect on bacterial dynamics described in this research study.

Dietary Thymoquinone Alone or Combined with Swimming Exercise Protect against Microcystin-LR-Induced Oxidative Injury in Mice

Microcystin-leucine-arginine (MCLR) is the most abundant cyanotoxin produced by cyanobacteria. It induces potent cytotoxicity through oxidative stress and DNA damage. Thymoquinone (TQ) is a natural nutraceutical antioxidant derived from black cumin (Nigella sativa). Physical exercise (EX) improves whole-body metabolic homeostasis. Therefore, this study examined the protective role of swimming exercise and TQ against MC-induced toxicity in mice. Fifty-six healthy adult male albino mice (25-30 g) were randomized into seven groups; group (I) was the negative control and received oral physiological saline for 21 days; group (II) received water EX for 30 min daily; group (III) was intraperitoneally injected with TQ (5 mg/kg daily, for 21 days); group (IV) was intraperitoneally administered MC (10 μg/kg daily, for 14 days) and acted as the positive toxic control; group (V) was treated with MC and water EX; group (VI) was injected with MC and TQ; finally, group (VII) was treated with MC with TQ and water EX. In comparison with the control group, the results showed hepatic, renal, and cardiac toxicity in the MCLR-treated group, indicated by a significant increase (p < 0.05) in serum levels of alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine transferase (ALT), cholesterol, lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase-myocardial band (CK-MB), urea, creatinine, interleukin-6, interleukin -1β, and tumor necrosis factor-α levels. In addition, there were significant elevations (p < 0.05) in malondialdehyde (MDA) and nitric oxide (NO) levels and a significant decrease in reduced glutathione (GSH), glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD) in hepatic, cardiac, and renal tissues. Treatment with either TQ or water EX significantly improved (p < 0.05) the MC-induced toxicity with superiority of the TQ group in the restoration of normal ranges; however, cotreatment with both TQ and swimming EX showed the most improvement and restoration to normal ranges as a result of increasing EX clinical efficacy by TQ.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (Klarite^TM substrate), hydrophobic Tienta^® SpecTrim^TM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the Klarite^TM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10^-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Variability of Microcystin-LR Standards Available from Seven Commercial Vendors

Microcystins (MCs) are a large group of heptapeptide cyanobacterial toxins commonly produced in harmful algal blooms (HABs) and associated with adverse health effects in wildlife, livestock, pets, and humans. MC chemical standards are extracted from cyanobacteria biomass rather than produced synthetically and are used in water assessment methods and toxicological studies. MC standards are generally supplied in less than 1 mg quantities, and verification of the mass can only be accomplished by analytical chemistry methods using a certified reference of the specific MC for comparison. Analytical quantification of MCs in environmental samples and toxicology studies using accurate doses of test chemicals administered to experimental animals rely on the availability and accuracy of chemical standards. To check the accuracy and purity of available standards, seven individual microcystin-LR (MCLR) standards were purchased from separate commercial vendors and analyzed to determine the actual mass supplied and identify the presence of potential contaminants. To determine the effect of varying toxin mass in toxicological studies, each MCLR standard was administered to CD-1 mice in doses based on mass purchased, by a single 40 µg/kg intraperitoneal injection. The measured mass purchased varied from the vendor label mass by more than 35% for two of the seven MCLR standards. Contaminants, including trifluoroacetic acid (TFA), were identified in four of the seven samples. Comparative in vivo hepatotoxicity between vendor samples closely reflected the actual amount of MCLR present in each standard and demonstrated the toxicological impact of varying cyanotoxin mass.

LC-MS/MS Validation and Quantification of Cyanotoxins in Algal Food Supplements from the Belgium Market and Their Molecular Origins

Food supplements are gaining popularity worldwide. However, harmful natural compounds can contaminate these products. In the case of algae-based products, the presence of toxin-producing cyanobacteria may cause health risks. However, data about the prevalence of algal food supplements on the Belgian market and possible contaminations with cyanotoxins are scarce. Therefore, we optimized and validated a method based on Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry to quantify eight microcystin congeners and nodularin in algal food supplements. Our analytical method was successfully validated and applied on 35 food supplement samples. Nine out of these samples contained microcystin congeners, of which three exceeded 1 µg g−1, a previously proposed guideline value. Additionally, the mcyE gene was amplified and sequenced in ten products to identify the taxon responsible for the toxin production. For seven out of these ten samples, the mcyE gene could be amplified and associated to Microcystis sp. EFSA and posology consumption data for algal-based food supplements were both combined with our toxin prevalence data to establish different toxin exposure scenarios to assess health risks and propose new guideline values.

Sublethal exposure to Microcystis aeruginosa extracts during embryonic development reduces aerobic swimming capacity in juvenile zebrafish

In the last decades, cyanobacterial harmful algal blooms (CyanoHABs) pose an intensifying ecological threat. Microcystis aeruginosa is a common CyanoHAB species in freshwater ecosystems, with severe toxic effects in a wide range of organisms. In the present paper we examined whether transient and short (48 h) exposure of fish embryos to sublethal levels of M. aeruginosa crude extract (200 mg biomass dw L^-1) affects swimming performance at later life stages (end of metamorphosis, ca 12 mm TL, 22,23 days post-fertilization). Pre-exposed metamorphosing larvae presented a significant decrease in swimming performance (9.7 ± 1.6 vs 11.4 ± 1.7 TL s^-1 in the control group, p < 0.01), and a significant decrease in the ventricle length-to-depth ratio (1.23 ± 0.15 vs 1.42 ± 0.15 in control fish, p < 0.05). In addition, extract-exposed fish presented significantly elevated rates of vertebral abnormalities (82 ± 13% vs 7 ± 4% in the control group), mainly consisting of the presence of extra neural and haemal processes. No significant differences between groups were detected in survival and growth rates. Results are discussed in respect to the mechanisms that might mediate the detected cyanobacterial effects. This is the first evidence of a direct link between sublethal exposure to M. aeruginosa during the embryonic period and swimming performance at later life-stages. Decreased swimming performance, altered cardiac shape, and elevated vertebral abnormalities in response to early exposure to M. aeruginosa could have significant effects on fish populations in the wild.

A Summer of Cyanobacterial Blooms in Belgian Waterbodies: Microcystin Quantification and Molecular Characterizations

In the context of increasing occurrences of toxic cyanobacterial blooms worldwide, their monitoring in Belgium is currently performed by regional environmental agencies (in two of three regions) using different protocols and is restricted to some selected recreational ponds and lakes. Therefore, a global assessment based on the comparison of existing datasets is not possible. For this study, 79 water samples from a monitoring of five lakes in Wallonia and occasional blooms in Flanders and Brussels, including a canal, were analyzed. A Liquid Chromatography with tandem mass spectrometry (LC-MS/MS) method allowed to detect and quantify eight microcystin congeners. The mcyE gene was detected using PCR, while dominant cyanobacterial species were identified using 16S RNA amplification and direct sequencing. The cyanobacterial diversity for two water samples was characterized with amplicon sequencing. Microcystins were detected above limit of quantification (LOQ) in 68 water samples, and the World Health Organization (WHO) recommended guideline value for microcystins in recreational water (24 µg L⁻¹) was surpassed in 18 samples. The microcystin concentrations ranged from 0.11 µg L⁻¹ to 2798.81 µg L⁻¹ total microcystin. For 45 samples, the dominance of the genera Microcystis sp., Dolichospermum sp., Aphanizomenon sp., Cyanobium/Synechococcus sp., Planktothrix sp., Romeria sp., Cyanodictyon sp., and Phormidium sp. was shown. Moreover, the mcyE gene was detected in 75.71% of all the water samples.

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

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

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

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

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

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

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

Negative impacts of microcystin-LR and glyphosate on zebrafish intestine: Linked with gut microbiota and microRNAs?

Microcystin-LR (MC-LR) and glyphosate (GLY) have been classified as a Group 2B and Group 2A carcinogens for humans, respectively, and frequently found in aquatic ecosystems. However, data on the potential hazard of MC-LR and GLY exposure to the fish gut are relatively scarce. In the current study, a subacute toxicity test of zebrafish exposed to MC-LR (35 μg L-1) and GLY (3.5 mg L-1), either alone or in combination was performed for 21 d. The results showed that MC-LR or/and GLY treatment reduced the mRNA levels of tight junction genes (claudin-5, occludin, and zonula occludens-1) and altered the levels of diamine oxidase and D-lactic, indicating increased intestinal permeability in zebrafish. Furthermore, MC-LR and/or GLY treatment remarkably increased the levels of intestinal IL-1β and IL-8 but decreased the levels of IL-10 and TGF-β, indicating that MC-LR and/or GLY exposure induced an inflammatory response in the fish gut. MC-LR and/or GLY exposure also activated superoxide dismutase and catalase, generally upregulated the levels of p53, bax, bcl-2, caspase-3, and caspase-9, downregulated the levels of caspase-8 and caused notable histological injury in the fish gut. Moreover, MC-LR and/or GLY exposure also significantly altered the microbial community in the zebrafish gut and the expression of miRNAs (miR-146a, miR-155, miR-16, miR-21, and miR-223). Chronic exposure to MC-LR and/or GLY can induce intestinal damage in zebrafish, and this study is the first to demonstrate an altered gut microbiome and miRNAs in the zebrafish gut after MC-LR and GLY exposure.

Evaluation of cyanobacterial toxicity using different biotests and protein phosphatase inhibition assay

Cyanobacteria are prolific producers of numerous toxic compounds, among which microcystins (hepatotoxins) are the most frequently found. Cyanobacterial bloom in freshwaters is an increasing problem, and there is still a need for rapid and reliable methods for the detection of toxic cyanobacterial samples. In the present study, the toxicity of crude extracts of 11 cyanobacterial strains from different genera has been assessed on two cell lines (human hepatocellular carcinoma HepG2 and rainbow trout (Oncorhynchus mykiss) liver-derived RTL-W1 cells), crustaceans (Daphnia magna and Artemia salina), and zebrafish (Danio rerio) embryos, as well as by protein phosphatase 1 (PP1) inhibition assay and ELISA test to determine whether the toxicity could be due to the presence of hepatotoxins/microcystins. All the tested strains exhibited toxicity on HepG2 cell line (IC₅₀ from 35 to 702 μg mL^-1), including Arthrospira (Spirulina) strains, while toxicity against the RTL-W1 cells was detected only in the positive reference Microcystis PCC 7806 and Nostoc 2S9B. Tested strains expressed higher toxicity to D. magna and zebrafish embryos in comparison to A. salina, whereby Nostoc LC1B and Nostoc S8 belonged to the most toxic strains. The PP1-inhibiting compounds have been detected by PP1 assay only in four strains (Microcystis PCC 7806, Oscillatoria K3, Nostoc LC1B, and Nostoc S8), indicating that their toxic potency can be attributed to these compounds. On the other hand, very low levels of microcystins, as confirmed by ELISA, were insufficient to explain toxicity and different toxic potencies of tested cyanobacteria. Results presented in this study suggested HepG2 cell line as a particularly suitable model for cyanobacterial toxicity assessment. In addition, they highlight terrestrial cyanobacterial strains as potent producers of toxic compounds.

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

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

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.

Environmental Risk Factors Implicated in Liver Disease: A Mini-Review

Liver disease is a global health issue, resulting in about two million deaths per year. It encompasses a wide spectrum of varied or unknown etiologies, ranging from lifestyle choices to pre-existing comorbidities. In recent decades, exposure to environmental toxins and subsequent liver health outcomes have captured public interest, due to the extensive application of pesticides, consumption of aflatoxin contaminated foodstuff, and cyanobacterial harmful algae blooms in endemic regions of liver disease. Hepatocellular carcinoma is a serious and debilitating condition of the liver, characterized by abdominal pain and unexplained weight loss. Established risk factors for hepatocellular carcinoma include alcohol consumption, cigarette smoking, and viral infections of hepatitis B and C. However, mounting evidence suggests that environmental toxins may represent an important contributing factor in hepatocellular carcinoma development. This mini-review synthesizes epidemiological investigations, providing evidence for environmental toxins as one potential risk factor for liver disease.

Permeability of the Cyanotoxin Microcystin-RR across a Caco-2 Cells Monolayer

Microcystins (MCs) are toxins produced by several cyanobacterial species found worldwide. While MCs have a common structure, the variation of two amino acids in their structure affects their toxicity. As toxicodynamics are very similar between the MC variants, their differential toxicity could rather be explained by toxicokinetic parameters. Microcystin-RR (MC-RR) is the second most abundant congener and induces toxicity through oral exposure. As intestinal permeability is a key parameter of oral toxicokinetics, the apparent permeability of MC-RR across a differentiated intestinal Caco-2 cell monolayer was investigated. We observed a rapid and large decrease of MC-RR levels in the donor compartment. However, irrespective of the loaded concentration and exposure time, the permeabilities were very low from apical to basolateral compartments (from 4 to 15 × 10⁻⁸ cm·s⁻¹) and from basolateral to apical compartments (from 2 to 37 × 10⁻⁸ cm·s⁻¹). Our results suggested that MC-RR would be poorly absorbed orally. As similar low permeability was reported for the most abundant congener microcystin-LR, and this variant presented a greater acute oral toxicity than MC-RR, we concluded that the intestinal permeability was probably not involved in the differential toxicity between them, in contrast to the hepatic uptake and metabolism.

Joint effects of naphthalene and microcystin-LR on physiological responses and toxin bioaccumulation of Landoltia punctata

The co-contamination of naphthalene (NAP) and microcystin-LR (MC-LR) commonly occurs in eutrophic waters. However, the joint effects of NAP and MC-LR on plants in aquatic environments remain unknown. Landoltia punctata is characterized by high starch yields and high biomass in polluted waters and has been proven to be a bioenergy crop and phytoremediation plant. In this study, L. punctata was cultured in a nutrient medium with environmentally relevant NAP (0.1, 1, 3, 5, and 10 μg/L) and MC-LR (5, 10, 25, 50, and 100 μg/L) to determine individual and joint toxic effects. The effects of NAP and MC-LR on physiological responses of L. punctata, including growth, starch accumulation, and antioxidant responses, were studied. Bioaccumulation of MC-LR in L. punctata, with or without NAP, was also examined. The results showed that growth and chlorophyll-a contents of L. punctata were reduced at high concentrations of MC-LR (≥ 25 μg/L), NAP (≥ 10 μg/L) and their mixture (≥ 10 + 1 μg/L) after exposure for 7 d. Starch accumulation in L. punctata did not decrease when exposed to NAP and MC-LR, and higher starch content of 29.8 % ± 2.7 % DW could be due to the destruction of starch-degrading enzymes. The antioxidant responses of L. punctata were stronger after exposure to MC-LR + NAP than when exposed to a single pollutant, although not enough to avoid oxidative damage. NAP enhanced the bioaccumulation of MC-LR in L. punctata when NAP concentration was higher than 5 μg/L, suggesting that higher potentials of MC-LR phytoremediation with L. punctata may be observed in NAP and MC-LR co-concomitant waters. This study provides theoretical support for the application of duckweed in eutrophic waters containing organic chemical pollutants.

Impedimetric Microcystin-LR Aptasensor Prepared with Sulfonated Poly(2,5-dimethoxyaniline)–Silver Nanocomposite

This paper presents a novel impedimetric aptasensor for cyanobacterial microcystin-LR (L, l-leucine; R, l-arginine) (MC-LR) containing a 5′ thiolated 60-mer DNA aptamer (i.e., 5′-SH-(CH2)6GGCGCCAAACAGGACCACCATGACAATTACCCATACCACCTCATTATGCCCCATCT CCGC-3′). A nanocomposite electrode platform comprising biocompatible poly(2,5-dimethoxyaniline) (PDMA)-poly(vinylsulfonate) (PVS) and silver nanoparticle (Ag0) on a glassy carbon electrode (GCE), i.e., (GCE/PDMA–PVS–Ag0) was used in the biosensor development. Small-angle X-ray scattering (SAXS) spectroscopic analysis revealed that the PDMA–PVS–Ag0 nanocomposites were polydispersed and contained embedded Ag0. Electrochemical impedance spectroscopy (EIS) responses of the aptasensor gave a dynamic linear range (DLR) and limit of detection (LOD) values of 0.01–0.1 ng L−1 MC-LR and 0.003 ng L−1 MC-LR, respectively. The cross-reactivity studies, which was validated with enzyme-linked immunosorbent assay (ELISA), showed that the aptasensor possesses excellent selectivity for MC-LR.

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Chronic exposure to microcystin-LR increases the risk of prostate cancer and induces malignant transformation of human prostate epithelial cells

Microcystins-LR (MC-LR) acts as a possible carcinogen for humans and causes a serious risk to public environmental health. The current study aimed to evaluate the interaction between MC-LR exposure and prostate cancer development and elucidate the underlying mechanism. In this study, mice were exposed to MC-LR at various doses for 180 days. MC-LR was able to induce the progression of prostatic intraepithelial neoplasia (PIN) and microinvasion. Furthermore, MC-LR notably increased angiogenesis and susceptibility to prostate cancer in vivo. In vitro, over 25 weeks of MC-LR exposure, normal human prostate epithelial (RWPE-1) cells increased secretion of matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9), and colony formation, features typical for cancer cells. These MC-LR-transformed prostate epithelial cells displayed increased expression of forkhead box M1 (FOXM1) and cyclooxygenase-2 (COX-2); abrogation of FOXM1 or COX-2 activity by specific inhibitors could abolish the invasion and migration of MC-LR-treated cells. In conclusion, we have provided compelling evidence demonstrating the induction of a malignant phenotype in human prostate epithelial cells and the in vivo development of prostate cancer by exposure to MC-LR, which might be a potential tumor promoter in the progression of prostate cancer.

Toxic compounds produced by cyanobacteria belonging to several species of the order Nostocales: A review

Cyanobacteria are well recognised as producers of a wide range of natural compounds that are in turn recognised as toxins that have potential and useful applications in the future as pharmaceutical agents. The order Nostocales, which is largely overlooked in this regard, has become increasingly recognised as a source of toxin producers including Anabaena, Nostoc, Hapalosiphon, Fischerella, Anabaenopsis, Aphanizomenon, Gloeotrichia, Cylindrospermopsis, Scytonema, Raphidiopsis, Cuspidothrix, Nodularia, Stigonema, Calothrix, Cylindrospermum and Desmonostoc species. The toxin compounds (i.e., microcystins, nodularin, anatoxins, ambiguines, fischerindoles and welwitindolinones) and metabolites are about to have a destructive effect on both inland and aquatic environment aspects. The present review gives an overview of the various toxins that are extracted by the order Nostocales. The current research suggests that these compounds that are produced by cyanobacterial species have promising future considerations as potentially harmful algae and as promising leads for drug discovery.

Taxonomic and Genotypical Heterogeneity of Microcystin degrading Bacterioplankton in Western Lake Erie

Microcystins (MCs) are among the predominant cyanotoxins that are primarily degraded by heterotrophic bacteria in various freshwater environments, including Lake Erie, a Laurentian Great Lake. However, despite the prevalence of MCs in Lake Erie basins, our knowledge about the taxonomic diversity of local MC-degrading bacteria is largely limited. The current study obtained thirty-four MC-degrading bacterial pure isolates from Lake Erie surface water and characterized their taxonomical and phenotypic identities as well as their MC-degradation rates under different pH, temperature, availability of organic substrates and with other MC-degrading isolates. Obtained MC-degrading isolates included both Gram-positive (18 isolates of Actinobacteria and Firmicutes) and Gram-negative bacteria (16 isolates of Gamma-proteobacteria); and 7 of these isolates were motile, and 13 had the capacity to form biofilms. In general, MC-degradation rates of the isolates were impacted by temperature and pH but insensitive to the presence of cyanobacterial exudates. At the optimal temperature (30-35°C) and pH (7-8), individual isolates degraded MC-LR, the most abundant MC isomer, at an average of 0.20 µg/mL/hr. With additions of cyanobacterial exudates, only Pseudomonas sp. LEw-2029, a non-motile biofilm maker, showed increased MC degradation (0.25 µg/mL/hr). Five out of nine tested dual culture mixtures showed rises in MC degradation rates than their corresponding monocultures; the highest rate reached 0.40 µg/mL/hr for the pair LEw-(1132 + 2029). PCR amplification of mlrA genes yielded negative results for all isolates; subsequent enzyme assay-Mass Spectrum analysis identified no product associated with the mlr gene-based MC degradation pathway. Collectively, our results demonstrated that a diversity of indigenous Lake Erie bacteria can degrade MCs via a novel mlr-independent pathway. Obtained MC degraders, especially Pseudomonas sp. LEw-2029, may serve as candidates for the development of biological filters to remove cyanotoxins in water treatment systems.

Are Cyanotoxins the Only Toxic Compound Potentially Present in Microalgae Supplements? Results from a Study of Ecological and Non-Ecological Products

Food supplements with microalgae are becoming increasingly abundant and can be easily found anywhere. The most popular products are based on cyanophytes, such as Aphanizomenon flos-aquae, Arthrospira platensis and Limnospira maxima, or on chlorophytes, such as Chlorella or Haematoccus. Although they are all advertised as being very beneficial for health, these products might be harmful because they may contain cyanotoxins and other contaminants, and no information on production methods or strain origins is usually provided. While legislation on the presence of microcystins in waters for different uses is clear, toxicological analyses are not compulsory for food supplements, nor for analyzing anatoxins. Given the potential risk of eating contaminated food, cyanotoxins, heavy metals and the presence of other contaminant organisms were analyzed in 10 microalgae food supplements. Microcystin-LR and anatoxin-a were detected in three analyzed products, and in both cyanophyte- and chlorophyte-based products. The light microscope study revealed the presence of different potentially harmful microbial contaminants. The ICP (OES) analyses detected high concentrations of some heavy metals, especially Pb. The results emphasize the need to promote the better control of food products containing microalgae, and to develop standard methodologies to analyze cyanotoxins and potential toxic compounds to protect consumer health.

Ecotoxicological profiling of selected cyanobacterial strains using multi-endpoint effect-directed analysis

The main goal of this study was to perform an ecotoxicological profiling of terrestrial and aquatic cyanobacterial strains found in different soils or in toxic cyanobacterial blooms in Vojvodina region, Serbia, using the effect-directed analysis (EDA) approach. The applied procedure was based on a series of in vitro or small-scale bioassays covering multiple endpoints in combination with advanced chemical analytical protocols. Non-selective and non-target preparation techniques were used for the extraction of a broad range of chemical compounds present in three terrestrial (Anabaena Č2, Anabaena Č5, Nostoc S8) and three aquatic (Nostoc Z1, Phormidium Z2, Oscillatoria K3) strains. Ecotoxicological endpoints addressed included evaluation of the fish cytotoxicity in vitro (acute toxicity), algal growth inhibition (chronic toxicity), and interaction with cellular detoxification mechanisms. All cyanobacterial strains tested in the 1^st tier EDA showed significant effects in terms of chronic toxicity and interaction with cellular detoxification. Three major fractions of different polarities were further tested in the 2^nd tier, using bioassays which showed the strongest response: induction of CYP1A1 biotransformation enzyme and inhibition of zebrafish organic anion (Oatp1d1) and cation (Oct1) uptake transporters. Oscillatoria K3 strain was selected for a more detailed 3^rd tier EDA, and the obtained results revealed that positive sub-fractions possess polar anion and cation compounds that are reactive to both uptake transporters, and compounds responsible for the strongest effects have a pronounced lipophilic character. Apart from lipophilic non-polar compounds that represent typical phase I substrates, sub-fractions that contained polar substances are also shown to significantly induce CYP1A1.

α-Lipoic acid protects against microcystin-LR induced hepatotoxicity through regeneration of glutathione via activation of Nrf2

Microcystins (MCs), as the most dominant bloom-forming strains in eutrophic surface water, can induce hepatotoxicity by oxidative stress. Alpha-lipoic acid (α-LA) is a super antioxidant that can induce the synthesis of antioxidants, such as glutathione (GSH), by nuclear factor erythroid 2-related factor 2 (Nrf2). However, the potential molecular mechanism of α-LA regeneration of GSH remains unclear. The present study aimed to investigate whether α-LA could reduce the toxicity of MCs induced in human hepatoma (HepG2), Bel7420 cells, and BALB/c mice by activating Nrf2 to regenerate GSH. Results showed that exposure to 10 μM microcystin-leucine arginine (MC-LR) reduced viability of HepG2 and Bel7402 cells and promoted the formation of reactive oxygen species (ROS) compared with untreated cells. Moreover, the protection of α-LA included reducing the level of ROS, increasing superoxide dismutase activity, and decreasing malondialdehyde. Levels of reduced glutathione (rGSH) and rGSH/oxidized glutathione were significantly increased in cells cotreated with α-LA and MC-LR compared to those treated with MC-LR alone, indicating an ability of α-LA to attenuate oxidative stress and MC-LR-induced cytotoxicity by increasing the amount of rGSH. α-LA can mediate GSH regeneration through the Nrf2 pathway under the action of glutathione reductase in MC-LR cell lines. Furthermore, the data also showed that α-LA-induced cytoprotection against MC-LR is associated with Nrf2 mediate pathway in vivo. These findings demonstrated the potential of α-LA to resist MC-LR-induced oxidative damage of liver.

Low-dose microcystin-LR antagonizes aflatoxin B1 induced hepatocarcinogenesis through decreasing cytochrome P450 1A2 expression and aflatoxin B1-DNA adduct generation

Aflatoxin B1 (AFB1) and microcystin-LR (MC-LR) co-existed in food and water, and were associated with hepatocellular carcinoma (HCC). AFB1 induced HCC by activating oxidative stress and generating AFB1-DNA adducts, while MC-LR could promote HCC progression. However, whether they have co-effects in HCC progression remains uncertain. In this study, we found the antagonistic effects of MC-LR on AFB1 induced HCC when they were exposed simultaneously. Compared with single exposure to AFB1, co-exposed to MC-LR significantly repressed the AFB1 induced malignant transformation of human hepatic cells and the glutathione S-transferase Pi positive foci formation in rat livers. MC-LR inhibited AFB1 induced upregulation of cytochrome P450 family 1 subfamily A member 2 (CYP1A2) and reduced the AFB1-DNA adducts generation in both human hepatic cells and rat livers. These results suggest that when co-exposure with AFB1, MC-LR might repress hepatocarcinogenicity of AFB1, which might be associated with its repression on AFB1 induced CYP1A2 upregulation and activation.

Nodularin induced oxidative stress contributes to developmental toxicity in zebrafish embryos

Nodularin (NOD) is a kind of cyanobacterial toxins. It is of concern due to elicit severe genotoxicity in humans and animals. The comprehensive evaluation of NOD-induced adverse effects in living organisms is urgently needed. This study is aimed to report the developmental toxicity and molecular mechanism using zebrafish embryos exposed to NOD. The embryonic toxicity induced by NOD is demonstrated by inhibition of embryo hatching, increase in mortality rate, abnormal heart rate, embryonic malformation as well as defects in angiogenesis and common cardinal vein remodeling. NOD triggered a decreased rate of angiogenesis through inhibiting endothelial cells migration. NOD induced embryonic cell apoptosis and DNA damage, which can be alleviated by antioxidant N-acetyl-L-cysteine. NOD significantly caused oxidative damage as indicated by changes in reactive oxygen species, superoxide dismutase, catalase, glutathione and malondialdehyde. NOD also altered the expression of vascular development-genes (DLL4, CDH5, VEGFA, VEGFC) and apoptosis-related genes (BAX, BCL-2, P53, CASPASE 3). Taken together, NOD induced adverse effect on zebrafish embryos development, which may be associated with oxidative stress and apoptosis through the activation of P53-BAX/BCL-2-CASPASE 3-mediated pathway.

The effects of Microcystis aeruginosa cells lysate containing microcystins on physiological and molecular responses in the nematode Caenorhabditis elegans

Microcystins (MCs) are potent toxins produced by environmental cyanobacterial blooms. The present study evaluated the effects of a Microcystis aeruginosa cyanobacterial lysate containing 0.1, 1, and 10 μg L^-1 MC-LR equivalent in the C. elegans Bristol N2 wild-type and the effects caused by equivalent concentrations of a MC-LR standard. The lysate was prepared from a culture of toxic strain (RST9501) originated from the Patos Lagoon Estuary (RS, Brazil). The minimal concentration necessary to cause significant effects in C. elegans under exposure to M. aeruginosa lysate or to MC-LR standard were, respectively, 10 and 0.1 μg L^-1 MC-LR equivalent for growth and 10 and 1 μg L^-1 MC-LR equivalent for fertility. Reproduction (ie, brood size) was only affected by the exposure to 10 μg L^-1 MC-LR standard and was not affected by the lysate. The nematodes that were exposed to lysate containing 1 μg L^-1 MC-LR equivalent or MC-LR were also analyzed for pharyngeal pumping and gene expression using RT-qPCR. The worms' rhythmic contractions of the pharynx were similarly affected by the lysate containing 1 μg L^-1 of MC-LR equivalent and the MC-LR standard. The MC-LR standard caused down-regulation of genes related to growth (daf-16), fertility (spe-10), and biotransformation (gst-2). This is the first study to evaluate the effects of a toxic cyanobacterial lysate using the C. elegans model. This study suggests the organism as a potential biotest to evaluate toxicity of natural waters containing M. aeruginosa cells and to environmental risk assessment associated to cyanobacterial bloom events.

Toxicological effects of marine seaweeds: a cautious insight for human consumption

Marine environment is a rich and diverse source for many biologically active substances including functional foods and nutraceuticals. It is well exploited for useful compounds, natural products and aquaculture industry; and seaweeds is one of the major contributors in terms of both food security and healthy nutrition. They are well-known due to their enormous benefits and is consumed globally in many countries. However, there is lack of attention toward their toxicity reports which might be due toxic chemical compounds from seaweed, epiphytic bacteria or harmful algal bloom and absorbed heavy metals from seawater. The excess of these components might lead to harmful interactions with drugs and hormone levels in the human body. Due to their global consumption and to meet increasing demands, it is necessary to address their hazardous and toxic aspects. In this review, we have done extensive literature for healthy seaweeds, their nutritional composition while summarizing the toxic effects of selected seaweeds from red, brown and green group which includes- Gracilaria, Acanthophora, Caulerpa, Cladosiphon, and Laminaria sp. Spirulina, a microalgae (cyanobacteria) biomass is also included in toxicity discussion as it an important food supplement and many times shows adverse reactions and drug interactions. The identified compounds from seaweeds were concluded to be toxic to humans, though they exhibited certain beneficial effects too. They have an easy access in food chain and thus invade the higher trophic level organisms. This review will create an awareness among scientific and nonscientific community, as well as government organization to regulate edible seaweed consumption and keep them under surveillance for their beneficial and safe consumption.

Waterborne exposure to microcystin-LR alters thyroid hormone levels, iodothyronine deiodinase activities, and gene transcriptions in juvenile zebrafish (Danio rerio)

This study investigated the effects of microcystin (MC) on the regulation of thyroid hormone (TH) metabolism in juvenile zebrafish exposed to MC-LR. The results showed that acute MC-LR exposure at concentrations ranging from 50 μg/L to 400 μg/L led to significant reductions in thyroxine (T4) and triiodothyronine (T3) levels in juvenile zebrafish. The transcription levels of genes involved in TH synthesis, such as corticotropin-releasing hormone (crh), thyroid-stimulating hormone (tsh), thyroid peroxidase (tpo) and transthyretin (ttr), were significantly decreased followed by an increase after MC-LR exposure. Transcription of the TH nuclear receptors (tr-α and tr-β) was significantly reduced during the exposure period. Moreover, the activities of iodothyronine deiodinase type Ⅰ (ID1) and iodothyronine deiodinase type Ⅱ (ID2) showed initially decreased and then increased trend, while the activity of iodothyronine deiodinase type Ⅲ (ID3) significantly decreased during MC-LR exposure. In addition, the effect of MC-LR on deiodinase activities and T4 contents were important causes of the decreased T3 at the early exposure stage. These results indicated that acute MC-LR exposure significantly interfered with the transcription of genes related to TH synthesis, transport and metabolism, and affected normal function of the thyroid which leads to decrease of T4 and T3 in juvenile zebrafish. Therefore, the thyroid function is susceptible to interference by MC-LR, and it may cause adverse effects on the growth and development of juvenile zebrafish.

Histone acetylation plays an important role in MC-LR-induced apoptosis and cycle disorder in SD rat testicular cells

Microcystin-leucine arginine (MC-LR) is a variant of microcystins (MCs), which poses a serious threat to the reproductive system. Histone acetylation modification can regulate the expressions of apoptosis-related genes. However the mechanisms of histone acetylation involving MC-LR-induced apoptosis were not understood. This study investigated the change of histone acetylation and its role in apoptosis and cell cycle arrest induced by MC-LR. MC-LR enhanced the activity of histone deacetylase (HDAC), decreased the activity of histone acetylase (HAT), up-regulated the expression of HDAC1, and down-regulated the expressions of Ac-H3 and Ac-H4 in vitro and vivo. Meanwhile, MC-LR induced testicular tissue injury and increased the expressions of apoptosis-related genes, such as Bax, Caspase3 and Caspase8, ultimately causing cells apoptosis in testicular tissues. Furthermore, MC-LR also induced cell cycle arrest in S phase, increased the expression of P21^Wif1/Cip1, and inhibited the expressions of cyclinD1, cyclinE1, CDK2 and E2F1. Importantly, HDAC inhibitor Trichostatin A (TSA) could ameliorate MC-LR-induced apoptosis and cell cycle arrest by reverse-regulating the expressions of these proteins. These results indicated that MC-LR could activate the mitochondrial apoptotic pathway and disorder the cell cycle pathway to induce the cell apoptosis by enhancing HDAC activity and reducing histone acetylation of normal testicular cells in SD rats. Hence, histone acetylation has a vital function in MC-LR-induced apoptosis in SD rat testicular cells, which provides a new insight on the reproductive toxicity of male induced by MC-LR.

A Review on the Study of Cyanotoxins in Paleolimnological Research: Current Knowledge and Future Needs

Cyanobacterial metabolites are increasingly studied, in regards to their biosynthesis, ecological role, toxicity, and potential biomedical applications. However, the history of cyanotoxins prior to the last few decades is virtually unknown. Only a few paleolimnological studies have been undertaken to date, and these have focused exclusively on microcystins and cylindrospermopsins, both successfully identified in lake sediments up to 200 and 4700 years old, respectively. In this paper, we review direct extraction, quantification, and application of cyanotoxins in sediment cores, and put forward future research prospects in this field. Cyanobacterial toxin research is also compared to other paleo-cyanobacteria tools, such as sedimentary pigments, akinetes, and ancient DNA isolation, to identify the role of each tool in reproducing the history of cyanobacteria. Such investigations may also be beneficial for further elucidation of the biological role of cyanotoxins, particularly if coupled with analyses of other abiotic and biotic sedimentary features. In addition, we identify current limitations as well as future directions for applications in the field of paleolimnological studies on cyanotoxins.

The mechanism of Oatp1a5-mediated microcystin-leucine arginine entering into GnRH neurons

Microcystin-leucine arginine (MC-LR) enters into gonadotropin-releasing hormone (GnRH) neurons and induces decline of serum GnRH levels resulting in male reproductive toxicity via hypothalamic-pituitary-testis axis. The organic anion transporting polypeptide 1a5 (Oatp1a5) is a critical transporter for the uptake of MC-LR by GnRH neurons. However, the underlying molecular mechanisms of the transport process are still elusive. In this study, we found that the transmembrane domains 2, 8, and 9 played important roles in transporting function of Oatp1a5. In addition, our data demonstrated that N-linked glycosylation was involved in the transport of MC-LR by Oatp1a5. Moreover, we showed that N-linked glycosylation sites Asn483 and Asn492 were vital for the transport function of Oatp1a5. In summary, the study furthered our understanding of mechanisms that the uptake of MC-LR by GnRH neurons and laid a theoretical foundation for preventing MC-LR from injuring male reproductive health.

Current Effects of Cyanobacteria Toxin in Water Sources and Containers in the Hartbeespoort Dam Area, South Africa

The study investigated the effects of cyanobacteria toxins such as microcystins in water sources and water stored in containers during its blooming and decaying seasons. Samples from water sources and containers near the Hartbeespoort Dam in South Africa were analysed using a microcystin ELIZA test kit. Microcystins were present in water sources used by the community, with an average of 4.3 μg/L in communal tap water and 4.8 μg/L in the water stored in tanks. The concentration of microcystins was lower in groundwater in the decaying season (0.38 μg/L) than in the blooming season (1.4 μg/L). Although microcystins were present in the storage containers, the average levels in all water samples were below the acceptable limit of 1 μg/L. The present study confirmed the presence of microcystins in the water storage containers. Therefore, it is suggested that water used for drinking from community water sources should be treated before storage to eliminate microcystins.

Harmful algal bloom and associated health risks among users of Lake Victoria freshwater: Ukerewe Island, Tanzania

There is a global concern regarding the occurrences of harmful algal blooms (HABs) and their effects on human health. Lake Victoria (LV) has been reported to face eutrophication challenges, resulting in an increase of bloom-forming cyanobacteria. This study is aimed at understanding the association of HABs and health risks at Ukerewe Island. A cross-sectional study conducted on 432 study subjects and water samples for cyanobacteria species identification were collected at LV shores. The results reveal that concentrations of cyanobacteria cells are beyond (WHO) acceptable limits; species of Microcystis aeruginosa range from 90,361.63 to 3,032.031.65 cells/mL and Anabaena spp. range from 13,310.00 to 4,814,702 cells/mL. Water usage indicates that 31% use lake water, 53% well water and 16% treated supplied pipe water. Vomiting and throat irritation was highly reported by lake water users as compared to wells and pipe water (P < 0.001). Gastrointestinal illness (GI) was significantly elevated among lake water users as compared to pipe and well water users (P < 0.001). Visible blooms in lake water were associated with GI, skin irritation and vomiting as compared to water without visible blooms (P < 0.001). The concentration of cyanobacteria blooms poses greater risks when water is used without treatment.

Assessment of microcystin contamination of Amaranthus hybridus, Brassica oleracea, and Lactuca sativa sold in markets: a case study of Zaria, Nigeria

Microcystins (MCs) are toxic secondary metabolites produced by several cyanobacteria genera that have been implicated in human cancer cases and deaths. Human exposure routes include direct contact with contaminated water and the consumption of contaminated food. The present study investigated the presence of MCs in three commonly consumed vegetables at the point of sale in market places as a means of assessing the direct human health risk of buying vegetables. Overall, 53% of the vegetables obtained from different markets had levels of MCs that were higher than 1.00 μg/g. Amaranthus hybridus L. (smooth amaranth) had the highest MC concentration (4.79 μg/g) in samples obtained from Sabon Gari Market, while Lactuca sativa L. (garden lettuce) had the lowest concentration (0.17 μg/g) in samples obtained from Dan-Magaji Market. The highest total daily intake (TDI) of MCs by an adult weighing 60 kg was 3.19 μg/kg for A. hybridus, 1.41 μg/kg for Brassica oleracea L. (cabbage), and 2.94 μg/kg for L. sativa. The highest TDI of MCs for a child weighing 25 kg was highest in A. hybridus (1.91 μg/kg), followed by L. sativa (1.77 μg/kg). These results revealed that the consumption of vegetables sold in markets in Zaria, Nigeria, during the dry season represents a major exposure route to MCs. There is, therefore, an urgent need to develop policies and monitoring strategies to tackle this problem in developing countries.

Economic impact of harmful algal blooms on human health: a systematic review

Harmful algal blooms (HABs) damage human activities and health. While there is wide literature on economic losses, little is known about the economic impact on human health. In this review, we systematically retrieved papers which presented health costs following exposure to HABs. A systematic review was conducted up to January 2019 in databases such as ScienceDirect and PubMed, and 16 studies were selected. Health costs included healthcare and medication expenses, loss of income due to illness, cost of pain and suffering, and cost of death. Two categories of illness (digestive and respiratory) were considered for health costs. For digestive illness cost, we found $86, $1,015 and $12,605, respectively, for mild, moderate and severe cases. For respiratory illness, costs were $86, $1,235 and $14,600, respectively, for mild, moderate and severe cases. We used Quality-Adjusted Life Years (QALYs) to access the loss of well-being due to illness caused by HABs. We found that breathing difficulty causes the most loss of QALYs, especially in children, with a loss of between 0.16 and 0.771 per child. Having gastroenteritis could cause a loss of between 2.2 and 7.1 QALYs per 1,000 children. Misleading symptoms of illness following exposure to HABs could cause bias in health costs estimations.