The toxic effects of microcystin-LR on mouse lungs and alveolar type II epithelial cells

A novel multitargeted self-assembling peptide-siRNA complex for simultaneous inhibition of SARS-CoV-2-host cell interaction and replication

Effective therapeutics are necessary for managing severe COVID-19 disease despite the availability of vaccines. Small interfering RNA (siRNA) can silence viral genes and restrict SARS-CoV-2 replication. Cell-penetrating peptides is a robust method for siRNA delivery, enhancing siRNA stability and targeting specific receptors. We developed a peptide HE25 that blocks SARS-CoV-2 replication by various mechanisms, including the binding of multiple receptors involved in the virus's internalization, such as ACE2, integrins and NRP1. HE25 not only acts as a vehicle to deliver the SARS-CoV-2 RNA-dependent RNA polymerase siRNA into cells but also facilitates their internalization through endocytosis. Once inside endosomes, the siRNA is released into the cytoplasm through the Histidine-proton sponge effect and the selective cleavage of HE25 by cathepsin B. These mechanisms effectively inhibited the replication of the ancestral SARS-CoV-2 and the Omicron variant BA.5 in vitro. When HE25 was administered in vivo, either by intravenous injection or inhalation, it accumulated in lungs, veins and arteries, endothelium, or bronchial structure depending on the route. Furthermore, the siRNA/HE25 complex caused gene silencing in lung cells in vitro. The SARS-CoV-2 siRNA/HE25 complex is a promising therapeutic for COVID-19, and a similar strategy can be employed to combat future emerging viral diseases.

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.

Toxic effects of three variants of microcystins on the intestinal histology, physiological and metabolic response of Litopenaeus vannamei

Microcystins (MCs) are harmful substances to the health of cultured shrimp, and there are many variants of MCs. Intestinal is the immune and metabolic center of the shrimp, and is also the target organ for MCs toxicity. In this study, the shrimp Litopenaeus vannamei juvenile were separately exposed to 1 μg/L of three MCs variants (LR, YR, RR) for 72 h respectively, and the changes of intestinal morphology, physiological response and metabolic function were analyzed. The results showed the three MCs variants stress caused intestinal mucosal damage and disordered the homeostasis of antimicrobial genes (ALF and Lys) expression. The mRNA expression levels of antioxidant genes (Nrf2 and GPx) and apoptosis factors (CytC and Casp-3) were increased, but that of detoxification gene (CYP450) was decreased. Furthermore, the intestinal metabolic pattern was also influenced by stresses, among which MC-LR induced more differential metabolites than that of MC-YR and MC-RR. The function of purine metabolism was highly influenced by the stress of three MCs variants, followed by amino acid metabolism, but there were differences in the types of amino acids. The metabolites citric acid, L-glutamine, L-tryptophan, spermine, UMP, and indole contributed to the metabolic pathway network. Nineteen stress-related metabolites were identified as candidates for subsequent screening of potential biomarkers. These results revealed the toxic effects of three MCs variants on the intestinal physiological and metabolic homeostasis of the shrimp.

Advances in investigating microcystin-induced liver toxicity and underlying mechanisms

Microcystins (MCs) are a class of biologically active cyclic heptapeptide pollutants produced by the freshwater alga Microcystis aeruginosa. With increased environmental pollution, MCs have become a popular research topic. In recent years, the hepatotoxicity of MCs and associated effects and mechanisms have been studied extensively. Current epidemiological data indicate that long-term human exposure to MCs can lead to severe liver toxicity, acute toxicity, and death. In addition, current toxicological studies on the liver, a vital target organ of MCs, indicate that MC contamination is associated with the development of liver cancer, nonalcoholic fatty liver, and liver fibrosis. MCs produce hepatotoxicity that affects the metabolic homeostasis of the liver, induces apoptosis, and acts as a pro-cancer factor, leading to liver lesions. MCs mainly mediate the activation of signaling pathways, such as the ERK/JNK/p38 MAPK and IL-6-STAT3 pathways, which leads to oxidative damage and even carcinogenesis. Moreover, MCs can act synergistically with other pollutants to produce combined toxicity. However, few systematic reviews have been performed on these new findings. This review systematically summarizes the toxic effects and mechanisms of MCs on the liver and discusses the combined liver toxicity effects of MCs and other pollutants to provide reference for subsequent research. The toxicity of different MC isomers deserves further study. The detection methods and limit standards of MCs in agricultural and aquatic products will represent important research directions in the future. Standard protocols for fish sampling during harmful algal blooms or to evaluate the degree of MC toxicity in nature are lacking. In future, bioinformatics can be applied to offer insights into MC toxicology research and potential drug development for MC poisoning. Further research is essential to understand the molecular mechanisms of liver function damage in combined-exposure toxicology studies to establish treatment for MC-induced liver damage.

Dysregulation of lipid metabolism in the pseudolobule promotes region-specific autophagy in hepatitis B liver cirrhosis

BACKGROUND

Chronic hepatitis B (CHB) infection leads to liver cirrhosis (LC), the end stage of liver fibrosis. The precise diagnosis and effective therapy for hepatitis B cirrhosis are still lacking. It is highly necessary to elucidate the metabolic alteration, especially the spatial distribution of metabolites, in LC progression.

METHODS

In this study, LC-MS/MS together with an airflow-assisted ionization mass spectrometry imaging system was applied to analyze and compare the metabolites' spatial distribution in healthy control (HC) and hepatitis B LC tissue samples. The liver samples were further divided into several subregions in HC and LC groups based on the anatomical characteristics and clinical features.

RESULTS

Both the LC-MS/MS and mass spectrometry imaging results indicated separated metabolite clusters between the HC and LC groups. The differential metabolites were mainly concentrated in lipid-like molecules and amino acids. The phosphatidylcholines (PCs), lysoPCs, several fatty acids, and amino acids reduced expression in the LC group with region specific. Acyl-CoA thioesterase 2 and choline/ethanolamine phosphotransferase 1, which regulate PC and fatty acid metabolism, were significantly decreased in the pseudolobule. Meanwhile, the increased expression of LC3B and p62 in the pseudolobule indicated the upregulation of autophagy.

CONCLUSIONS

Hepatitis B LC induced region-specific autophagy by increasing the expression of LC3B and p62 in the pseudolobule and by dysregulation of unsaturated fatty acids, amino acids, and PC metabolism. The mass spectrometry imaging system provided additional metabolites' spatial information, which can promote biomarker screening technology and support the exploration of novel mechanisms in LC.

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.

Cyanobacteria, cyanotoxins and lipopolysaccharides in aerosols from inland freshwater bodies and their effects on human bronchial cells

Components of cyanobacterial water blooms were quantified in aerosols above agitated water surfaces of five freshwater bodies. The thoracic and respirable aerosol fraction (0.1-10 µm) was sampled using a high-volume sampler. Cyanotoxins microcystins were detected by LC-MS/MS at levels 0.3-13.5 ng/mL (water) and < 35-415 fg/m³ (aerosol). Lipopolysaccharides (endotoxins) were quantified by Pyrogene rFC assay at levels < 10-119 EU/mL (water) and 0.13-0.64 EU/m³ (aerosol). Cyanobacterial DNA was detected by qPCR at concentrations corresponding to 10⁴-10⁵ cells eq./mL (water) and 10¹-10³ cells eq./m³ (aerosol). Lipopolysaccharides isolated from bloom samples induced IL-6 and IL-8 cytokine release in human bronchial epithelial cells Beas-2B, while extracted cyanobacterial metabolites induced both pro-inflammatory and cytotoxic effects. Bloom components detected in aerosols and their bioactivities observed in upper respiratory airway epithelial cells together indicate that aerosols formed during cyanobacterial water blooms could induce respiratory irritation and inflammatory injuries, and thus present an inhalation health risk.

Microcystin-LR aerosol induces inflammatory responses in healthy human primary airway epithelium

Harmful algal blooms plague bodies of freshwater globally. These blooms are often composed of outgrowths of cyanobacteria capable of producing the heptapeptide Microcystin-LR (MC-LR) which is a well-known hepatotoxin. Recently, MC-LR has been detected in aerosols generated from lake water. However, the risk for human health effects due to MC-LR inhalation exposure have not been extensively investigated. In this study, we exposed a fully differentiated 3D human airway epithelium derived from 14 healthy donors to MC-LR-containing aerosol once a day for 3 days. Concentrations of MC-LR ranged from 100 pM to 1 µM. Although there were little to no detrimental alterations in measures of the airway epithelial function (i.e. cell survival, tissue integrity, mucociliary clearance, or cilia beating frequency), a distinct shift in the transcriptional activity was found. Genes related to inflammation were found to be upregulated such as C-C motif chemokine 5 (CCL5; log2FC = 0.57, p = 0.03) and C-C chemokine receptor type 7 (CCR7; log2FC = 0.84, p = 0.03). Functionally, conditioned media from MC-LR exposed airway epithelium was also found to have significant chemo-attractive properties for primary human neutrophils. Additionally, increases were found in the concentration of secreted chemokine proteins in the conditioned media such as CCL1 (log2FC = 5.07, p = 0.0001) and CCL5 (log2FC = 1.02, p = 0.046). These results suggest that MC-LR exposure to the human airway epithelium is capable of inducing an inflammatory response that may potentiate acute or chronic disease.

Microcystin-LR in Primary Liver Cancers: An Overview

The cyanobacterial blooms produced by eutrophic water bodies have become a serious environmental issue around the world. After cellular lysing or algaecide treatment, microcystins (MCs), which are regarded as the most frequently encountered cyanobacterial toxins in fresh water, are released into water. Among all the variants of MCs, MC-LR has been widely studied due to its severe hepatotoxicity. Since 1992, various studies have identified the important roles of MC-LR in the origin and progression of primary liver cancers (PLCs), although few reviews have focused on it. Therefore, this review aims to summarize the major achievements and shortcomings observed in the past few years. Based on the available literature, the mechanisms of how MC-LR induces or promotes PLCs are elucidated in this review. This review aims to enhance our understanding of the role that MC-LR plays in PLCs and provides a rational approach for future applications.

The Toxicity Testing of Cyanobacterial Toxins In Vivo and In Vitro by Mouse Bioassay: A Review

Different biological methods based on bioactivity are available to detect cyanotoxins, including neurotoxicity, immunological interactions, hepatotoxicity, cytotoxicity, and enzymatic activity. The mouse bioassay is the first test employed in laboratory cultures, cell extracts, and water bloom materials to detect toxins. It is also used as a traditional method to estimate the LD50. Concerning the ease of access and low cost, it is the most common method for this purpose. In this method, a sample is injected intraperitoneally into adult mice, and accordingly, they are assayed and monitored for about 24 hours for toxic symptoms. The toxin can be detected using this method from minutes to a few hours; its type, e.g., hepatotoxin, neurotoxin, etc., can also be determined. However, this method is nonspecific, fails to detect low amounts, and cannot distinguish between homologues. Although the mouse bioassay is gradually replaced with new chemical and immunological methods, it is still the main technique to detect the bioactivity and efficacy of cyanotoxins using LD50 determined based on the survival time of animals exposed to the toxin. In addition, some countries oppose animal use in toxicity studies. However, high cost, ethical considerations, low-sensitivity, non-specificity, and prolonged processes persuade researchers to employ chemical and functional analysis techniques. The qualitative and quantitative analyses, as well as high specificity and sensitivity, are among the advantages of cytotoxicity tests to investigate cyanotoxins. The present study aimed at reviewing the results obtained from in-vitro and in-vivo investigations of the mouse bioassay to detect cyanotoxins, including microcystins, cylindrospermopsin, saxitoxins, etc.

Salton Sea aerosol exposure in mice induces a pulmonary response distinct from allergic inflammation

In communities surrounding the Salton Sea, high rates of asthma are associated with high aerosol dust levels. However, the Salton Sea itself may play an additional role in pulmonary health. Therefore, to investigate a potential role of the Salton Sea on pulmonary health, we exposed mice to aerosolized Salton Sea water for 7 days and assessed tissue responses, including cellular infiltration and gene expression changes. For reference, mice were also exposed to aerosolized fungal allergen (Alternaria sp.) and Pacific Ocean aerosols. Exposure to aerosolized Alternaria sp. induced dramatic allergic inflammation, including neutrophil and eosinophil recruitment to the bronchoalveolar lavage fluid (BALF) and lung tissue. By contrast, Salton Sea "spray" induced only B cell recruitment to the lung tissue without increased inflammatory cell numbers in BALF. However, there were consistent gene expression changes suggestive of an inflammatory response. The response to the Salton Sea spray was notably distinct from the response to Pacific Ocean water, which induced some B cell recruitment but without an inflammatory gene expression profile. Our studies suggest that soluble components in Salton Sea water promote induction of a unique inflammation-associated response, though any relationship to asthma remains to be explored.

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.

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.

Multibiomarker-based assessment of toxicity of central European strains of filamentous cyanobacteria Aphanizomenon gracile and Raphidiopsis raciborskii to zebrafish Danio rerio

The global increase in cyanobacterial blooms poses environmental and health threats. Selected cyanobacterial strains reveal toxicities despite a lack of synthesis of known toxic metabolites, and the mechanisms of these toxicities are not well understood. Here we investigated the toxicity of non-cylindrospermopsin and non-microcystin producing Aphanizomenon gracile and Raphidiopsis raciborskii of Central European origin to zebrafish exposed for 14 days to their extracts. Toxicological screening revealed the presence of anabaenopeptins and a lack of anatoxin-a, ß-methylamino-L-alanine or saxitoxins in examined extracts. The responses were compared to 20 μg L^-1 of common cyanobacterial toxins cylindrospermopsin (CYN) and microcystin-LR (MC-LR). The expression of the marker genes involved in apoptosis (caspase 3a and 3b, Bcl-2, BAX, p53, MAPK, Nrf2), DNA damage detection and repair (GADD45, RAD51, JUN, XPC), detoxification (CYP1A, CYP26, EPHX1), lipid metabolism (PPARa, FABP1, PLA2), phosphorylation/dephosphorylation (PPP6C, PPM1) and cytoskeleton (actin, tubulin) were examined using targeted transcriptomics. Cellular stress and toxicity biomarkers (oxidative injury, antioxidant enzymes, thiol pool status, and lactate dehydrogenase activity) were measured in the liver, and acetylcholinesterase activity was determined as an index of neurotoxicity in the brain. The extracts of three cyanobacterial strains that produce no known cyanotoxins caused marked toxicity in D. rerio, and the biomarker profiles indicate different toxic mechanisms between the bioactive compounds extracted from these strains and the purified cyanotoxins. All studied cyanobacterial extracts and purified cyanotoxins induced oxidative stress and neurotoxicity, downregulated Nrf2 and CYP26B1, disrupted phosphorylation/dephosphorylation processes and actin/tubulin cytoskeleton and upregulated apoptotic activity in the liver. The tested strains and purified toxins displayed distinctively different effects on lipid metabolism. Unlike CYN and MC-LR, the Central European strain of A. gracile and R. raciborskii did not reveal a genotoxic potential. These findings help to further understand the ecotoxicological consequences of toxic cyanobacterial blooms in freshwater ecosystems.

Toxic Cyanobacteria: A Growing Threat to Water and Air Quality

The global expansion of harmful cyanobacterial blooms (CyanoHABs) poses an increasing threat to public health. CyanoHABs are characterized by the production of toxic metabolites known as cyanotoxins. Human exposure to cyanotoxins is challenging to forecast, and perhaps the least understood exposure route is via inhalation. While the aerosolization of toxins from marine harmful algal blooms (HABs) has been well documented, the aerosolization of cyanotoxins in freshwater systems remains understudied. In recent years, spray aerosol (SA) produced in the airshed of the Laurentian Great Lakes (United States and Canada) has been characterized, suggesting that freshwater systems may impact atmospheric aerosol loading more than previously understood. Therefore, further investigation regarding the impact of CyanoHABs on human respiratory health is warranted. This review examines current research on the incorporation of cyanobacterial cells and cyanotoxins into SA of aquatic ecosystems which experience HABs. We present an overview of cyanotoxin fate in the environment, biological incorporation into SA, existing data on cyanotoxins in SA, relevant collection methods, and adverse health outcomes associated with cyanotoxin inhalation.

Effects of Microcystis aeruginosa and microcystin-LR on intestinal histology, immune response, and microbial community in Litopenaeus vannamei

Microcystis aeruginosa (MA) is a primary hazardous cyanobacteria species in aquatic ecosystems that can produce microcystin-LR (MC-LR), which harms aquatic animals. The intestine is an important target tissue for MA and MC-LR. In this study, we investigated the effects of MA and MC-LR exposure on the intestinal microbiota variation and immune responses of Litopenaeus vannamei. Shrimp were experimentally exposed to MA and MC-LR for 72 h. The results showed that both MA and MC-LR exposure caused marked histological variation and apoptosis characteristics and increased oxidative stress in the intestine. Furthermore, the relative expression levels of antimicrobial peptide genes (ALF, Crus, Pen-3) decreased, while those of pro-inflammatory cytokines (MyD88, Rel, TNF-a), a pattern-recognition receptor (TLR4) and a mediator of apoptosis (Casp-3) increased. MA and MC-LR exposure also caused intestinal microbiota variation, including decreasing microbial diversity and disturbing microbial composition. Specifically, the relative abundance of Proteobacteria decreased in the two stress groups; that of Bacteroidetes decreased in the MA group but increased in the MC-LR group, while Tenericutes varied inversely with Bacteroidetes. Our results indicate that MA and MC-LR exposure causes intestinal histopathological and microbiota variations and induces oxidative stress and immune responses in L. vannamei. In conclusion, this study reveals the negative effects of MA and MC-LR on the intestinal health of shrimp, which should be considered in aquaculture.

Microcystin-leucine-arginine induces liver fibrosis by activating the Hedgehog pathway in hepatic stellate cells

Microcystin-leucine-arginine (MC-LR), produced by cyanobacteria, accumulates in the liver through blood circulation. We investigated the impact of MC-LR on liver fibrosis. Mice received a daily injection of MC-LR at various concentrations for 14 consecutive days aa and then mouse liver was obtained for histopathological and immunoblot analysis. Next, a human hepatic stellate cell line (LX-2) was treated with MC-LR at various concentrations followed by measurement of cell viability, cell cycle and relevant protein expression levels. Our data confirmed the induction of mouse liver fibrosis after exposure to MC-LR at 15 μg/kg and 30 μg/kg. Furthermore, we demonstrated that LX-2 cells could uptake MC-LR, resulting in cell proliferation and differentiation through impacting the Hedgehog signaling after the treatment of MC-LR at 50 nM. Our data supported that MC-LR could induce liver fibrosis by modulating the expression of the transcription factor Gli2 in the Hedgehog signaling in hepatic stellate cells.

The mechanisms in the altered ontogenetic development and lung-related pathology in microcystin-leucine arginine (MC-LR)-paternal-exposed offspring mice

A father's lifetime experience is a major risk factor for a range of diseases in an individual, and the consequences of the exposure can also be transmitted to his offspring. Our previous work has demonstrated that damage to testicular structures and decline in sperm quality in male mice can be caused by microcystin-leucine arginine (MC-LR), but the overall effects of the scope and extent of paternal exposure on health and disease in the offspring remain underexplored. Here, we report that MC-LR-paternal-exposed offspring mice showed reduced litter size and body weight accompanied by increased abnormalities in the lung. Analyses of the small noncoding RNAs (sncRNAs) in the sperm from MC-LR-exposed males demonstrated the downregulation of a wide range of piRNAs enriched for those target genes involved in the regulation of the embryo implantation pathways. Gene and protein expression analyses, as well as biochemical and functional studies, revealed suppressed expression of Hsp90α in testicular tissues from MC-LR-exposed males. Decreased Hsp90α in testicular tissues impaired the development of the offspring. In this study, we revealed that MC-LR alters the expression of Hsp90α in testicular tissues to cause changes in the expression profiles of sperm piRNAs produced by paternal mice. These changes lead to aberrant activation of the Wnt/β-catenin signaling pathway in pulmonary tissues of offspring mice, causing lung tissue damage and abnormal development. We hereby confirmed that MC-LR-induced alterations in epigenetic inheritance are capable of contributing to intergenerational developmental defects in paternal-exposed offspring mice.

A Mini Review on Microcystins and Bacterial Degradation

Microcystins (MCs) classified as hepatotoxic and carcinogenic are the most commonly reported cyanobacterial toxins found in the environment. Microcystis sp. possessing a series of MC synthesis genes (mcyA-mcyJ) are well documented for their excessive abundance, numerous bloom occurrences and MC producing capacity. About 246 variants of MC which exert severe animal and human health hazards through the inhibition of protein phosphatases (PP1 and PP2A) have been characterized. To minimize and prevent MC health consequences, the World Health Organization proposed 1 µg/L MC guidelines for safe drinking water quality. Further the utilization of bacteria that represent a promising biological treatment approach to degrade and remove MC from water bodies without harming the environment has gained global attention. Thus the present review described toxic effects and bacterial degradation of MCs.

Microcystin-LR Does Not Alter Cell Survival and Intracellular Signaling in Human Bronchial Epithelial Cells

Changes in ecological and environmental factors lead to an increased occurrence of cyanobacterial water blooms, while secondary metabolites-producing cyanobacteria pose a threat to both environmental and human health. Apart from oral and dermal exposure, humans may be exposed via inhalation and/or swallowing of contaminated water and aerosols. Although many studies deal with liver toxicity, less information about the effects in the respiratory system is available. We investigated the effects of a prevalent cyanotoxin, microcystin-LR (MC-LR), using respiratory system-relevant human bronchial epithelial (HBE) cells. The expression of specific organic-anion-transporting polypeptides was evaluated, and the western blot analysis revealed the formation and accumulation of MC-LR protein adducts in exposed cells. However, MC-LR up to 20 μM neither caused significant cytotoxic effects according to multiple viability endpoints after 48-h exposure, nor reduced impedance (cell layer integrity) over 96 h. Time-dependent increase of putative MC-LR adducts with protein phosphatases was not associated with activation of mitogen-activated protein kinases ERK1/2 and p38 during 48-h exposure in HBE cells. Future studies addressing human health risks associated with inhalation of toxic cyanobacteria and cyanotoxins should focus on complex environmental samples of cyanobacterial blooms and alterations of additional non-cytotoxic endpoints while adopting more advanced in vitro models.

Microcystin-LR induced oxidative stress, inflammation, and apoptosis in alveolar type II epithelial cells of ICR mice in vitro

Previous studies have shown that microcystin-LR (MC-LR) produced by toxic cyanobacterial blooms could inflict damage to the lung. However, the mechanisms underlying MC-induced pulmonary toxicity are not fully described. In this study, the primary' fetal alveolar type II epithelial cells (AEC II) from ICR mice, which are involved in formation of bioactive component of pulmonary epithelium and secretion of pulmonary surfactants, were exposed to MC-LR at different concentrations (0, 0.625, 1.25, 2.5, 5, 10, 20 μg/mL) for different time (12, 24, 36 h). Results showed that the viabilities of AEC II exposed to 10 and 20 μg MC-LR/mL were significantly decreased compared with the control group. Furthermore, MC-LR exposure resulted in overproduction of reactive oxygen species (ROS) and induced a significant reduction in superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Expressions of apoptosis-related proteins including bax, cyt-c, and caspase-9 were significantly up-regulated by exposure to 2.5, 5, 10, or 20 μg MC-LR/mL. When exposed to 5, 10, or 20 μg MC-LR/mL, expressions of proteins involved in inflammatory, p-65 and iNOS were significantly greater than those of the controls. In conclusion, inflammation and apoptosis might be responsible for MC-LR-induced pulmonary injury.

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

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

Microcystins in water and in microalgae: Do microcystins as microalgae contaminants warrant the current public alarm?

Microcystins have been the subject of increasingly alarming popular and scientific articles, which have taken as their unquestionable foundation the provisional Guideline of 1 μg/L established by the WHO Panel on microcystins levels in water, and mechanically translated by the Oregon government as 1 μg/g of Klamath Aphanizomenon flos aquae microalgae. This article underlines the significant limitations and ultimately scientific untenability of the WHO Guideline on microcystins in water, for being based on testing methodologies which may lead to a significant overestimation of the toxicity of microcystins. I propose criteria for the realization of new experimental studies on the toxicity of microcystins, based on the essential understanding that drinking water is contaminated by whole cyanobacterial microalgae rather than purified microcystins, while it is important to differentiate between water and cyanobacterial supplements. It is indeed a mistake to automatically apply standards that are proper for water to cyanobacterial supplements, as they have different concentrations of the antioxidant substances that inactivate or significantly reduce the toxicity of microcystins, a fact that also require that each cyanobacterial supplement be tested individually and through realistic testing methodologies.

Exposure routes and health effects of microcystins on animals and humans: A mini-review

Microcystins (MCs) pollution has quickly risen in infamy and has become a major problem to public health worldwide. MCs are a group of monocyclic hepatotoxic peptides, which are produced by some bloom-forming cyanobacteria in water. More than 100 different MCs variants posing a great threat to animals and humans due to their potential carcinogenicity have been reported. To reduce MCs risks, the World Health Organization has set a provisional guideline of 1 μg/L MCs in human's drinking water. This paper provides an overview of exposure routes of MCs into the human system and health effects on different organs after MCs exposure including the liver, intestine, brain, kidney, lung, heart and reproductive system. In addition, some evidences on human poisoning and deaths associated with MCs exposure are presented. Finally, in order to protect human life against the health threats posed by MCs, this paper also suggests some directions for future research that can advance MCs control and minimize human exposure to MCs.

A proteomic study of the pulmonary injury induced by microcystin-LR in mice

MCLR has been shown to act as potent hepatotoxin, and recent studies showed that MCs can accumulate in lung tissue and exert adverse effects. However, the exact mechanism still remain unclear. The present study mainly focuses on the impairments of respiratory system after MCLR exposure in mice. After intratracheal instillation with MCLR (0, 10 and 25 μg/kg bw), histological change was examined in MCLR exposure groups. Results indicated that exposure of MCLR led to serious histopathology alteration and apoptosis in lung of mice. To further our understanding of the toxic effects of MCLR on the lung, we employed a proteomic method to search the mechanisms behind MCLR-induced pulmonary injury. In total, 38 proteins were identified to be significantly altered after MCLR exposure. These proteins involved in inflammatory response, apoptosis, cytoskeleton, and energetic metabolism, suggesting MCLR exerts complex toxic effects contributing to pulmonary injury. Furthermore, MCLR also induced pulmonary inflammation, as manifested by up-regulating the protein levels of interleukin-1β (IL-1β) and p65 subunit. Our results indicated that MCLR exerts lung injury mainly by generating inflammation and apoptosis.

Toxic mechanisms of microcystins in mammals

Microcystins, such as microcystin-leucine arginine (MC-LR), are some of the most toxic and prevalent cyanotoxins produced by cyanobacteria in freshwater and saltwater algal blooms worldwide. Acute and chronic exposures to microcystins are primarily known to cause hepatotoxicity; cellular damage and genotoxicity within mammalian livers. However, in vivo studies indicate that similar damage may occur in other mammalian organs and tissues, such as the kidney, heart, reproductive systems, and lungs - particularly following chronic low-dose exposures. Mechanisms of toxicity of mycrocystins are reviewed herein; including cellular uptake, interaction with protein phosphatases PP1 and PP2A, cytoskeletal effects, formation of oxidative stress and induction of apoptosis. In general, the mode of action of toxicity by MCs in mammalian organs are similar to those that have been observed in liver tissues. A comprehensive understanding of the toxic mechanisms of microcystins in mammalian tissues and organs will assist in the development of risk assessment approaches to public health protection strategies and the development of robust drinking water policies.

Development of Toxicological Risk Assessment Models for Acute and Chronic Exposure to Pollutants

Alert level frameworks advise agencies on a sequence of monitoring and management actions, and are implemented so as to reduce the risk of the public coming into contact with hazardous substances. Their effectiveness relies on the detection of the hazard, but with many systems not receiving any regular monitoring, pollution events often go undetected. We developed toxicological risk assessment models for acute and chronic exposure to pollutants that incorporate the probabilities that the public will come into contact with undetected pollution events, to identify the level of risk a system poses in regards to the pollutant. As a proof of concept, we successfully demonstrated that the models could be applied to determine probabilities of acute and chronic illness types related to recreational activities in waterbodies containing cyanotoxins. Using the acute model, we identified lakes that present a ‘high’ risk to develop Day Away From Work illness, and lakes that present a ‘low’ or ‘medium’ risk to develop First Aid Cases when used for swimming. The developed risk models succeeded in categorising lakes according to their risk level to the public in an objective way. Modelling by how much the probability of public exposure has to decrease to lower the risks to acceptable levels will enable authorities to identify suitable control measures and monitoring strategies. We suggest broadening the application of these models to other contaminants.