Repeated intranasal exposure to microcystin-LR affects lungs but not nasal epithelium in mice

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

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

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.

Chronic Exposure to Environmentally Relevant Concentrations of Microcystin-Leucine Arginine Causes Lung Barrier Damage through PP2A Activity Inhibition and Claudin1 Ubiquitination

Microcystin-leucine arginine (MC-LR), ubiquitous in water and food, is a threat to public health. In the present study, after C57BL/6J mice were fed with environmental concentrations of MC-LR (0, 1, 30, 60, 90, and 120 μg/L) for 6, 9, and 12 months, it was found that MC-LR could enter into mouse lung tissues and cause microstructural damage, as shown by western blotting and HE staining. Electron microscopy examination showed that MC-LR could damage the lung barrier by disruption of the tight junctions, which was confirmed by the decreased expression of tight junction markers, including Occludin, Claudin1, and ZO-1. In addition, MC-LR also increased the ubiquitination of Claudin1, indicating that MC-LR could disrupt tight junctions by promoting the degradation of Claudin1. Furthermore, MC-LR increased the levels of TNF-α and IL-6 in mouse lung tissues, leading to pneumonia. Importantly, pretreatment with PP2A activator D-erythro-sphingosine (DES) was found to significantly alleviate MC-LR-induced decrease of Occludin and Claudin1 by inhibiting the P-AKT/Snail pathway in vitro. Together, this study revealed that chronic exposure to MC-LR causes lung barrier damage, which involves PP2A activity inhibition and enhancement of Claudin1 ubiquitination. This study broadens the awareness of the toxic effects of MC-LR on the respiratory system, which has deep implications for public health.

Subacute and sublethal ingestion of microcystin-LR impairs lung mitochondrial function by an oligomycin-like effect

Microcystin-LR (MC-LR) is a potent cyanotoxin that can reach several organs. However subacute exposure to sublethal doses of MC-LR has not yet well been studied. Herein, we evaluated the outcomes of subacute and sublethal MC-LR exposure on lungs. Male BALB/c mice were exposed to MC-LR by gavage (30 µg/kg) for 20 consecutive days, whereas CTRL mice received filtered water. Respiratory mechanics was not altered in MC-LR group, but histopathology disclosed increased collagen deposition, immunological cell infiltration, and higher percentage of collapsed alveoli. Mitochondrial function was extensively affected in MC-LR animals. Additionally, a direct in vitro titration of MC-LR revealed impaired mitochondrial function. In conclusion, MC-LR presented an intense deleterious effect on lung mitochondrial function and histology. Furthermore, MC-LR seems to exert an oligomycin-like effect in lung mitochondria. This study opens new perspectives for the understanding of the putative pulmonary initial mechanisms of damage resulting from oral MC-LR intoxication.

As We Drink and Breathe: Adverse Health Effects of Microcystins and Other Harmful Algal Bloom Toxins in the Liver, Gut, Lungs and Beyond

Freshwater harmful algal blooms (HABs) are increasing in number and severity worldwide. These HABs are chiefly composed of one or more species of cyanobacteria, also known as blue-green algae, such as Microcystis and Anabaena. Numerous HAB cyanobacterial species produce toxins (e.g., microcystin and anatoxin—collectively referred to as HAB toxins) that disrupt ecosystems, impact water and air quality, and deter recreation because they are harmful to both human and animal health. Exposure to these toxins can occur through ingestion, inhalation, or skin contact. Acute health effects of HAB toxins have been well documented and include symptoms such as nausea, vomiting, abdominal pain and diarrhea, headache, fever, and skin rashes. While these adverse effects typically increase with amount, duration, and frequency of exposure, susceptibility to HAB toxins may also be increased by the presence of comorbidities. The emerging science on potential long-term or chronic effects of HAB toxins with a particular emphasis on microcystins, especially in vulnerable populations such as those with pre-existing liver or gastrointestinal disease, is summarized herein. This review suggests additional research is needed to define at-risk populations who may be helped by preventative measures. Furthermore, studies are required to develop a mechanistic understanding of chronic, low-dose exposure to HAB toxins so that appropriate preventative, diagnostic, and therapeutic strategies can be created in a targeted fashion.

New insights into toxicity of microcystins produced by cyanobacteria using in silico ADMET prediction

In silico methodologies can be used in the discovery of new drugs for measuring toxicity, predicting effects of substances not yet analyzed by in vivo methodologies. The ADMET Predictor® software (absorption, distribution, metabolism, elimination, and toxicity [ADMET]) was used in this work to predict toxic effects of microcystin variants MC-LR, MC-YR, MC-RR, and MC-HarHar. In the case of rodents, predictive results for all analyzed variants indicated carcinogenic potential. The predictive model of respiratory sensitivity in this group differentiated microcystins into 2 categories: sensitizer (MC-LR and -YR) and non-sensitizer (MC-HarHar and -RR). Predictive results for humans indicated that MC-LR and -RR are phospholipidosis inducers; on the other hand, MC-LR showed the highest predictive value of permeability in rabbit cornea and probability of crossing lipoprotein barriers (MC-LR>-YR>-HarHar>-RR). Considering bioavailable fractions, microcystins are more likely to cause biological effects in rats than humans, showing significant differences between models. The results of ADMET predictions add valuable information on microcystin toxicity, especially in the case of variants not yet studied experimentally.

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.

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.

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.

Lung and liver responses to 1- and 7-day treatments with LASSBio-596 in mice subchronically intoxicated by microcystin-LR

Microcystin-LR (MC-LR) can cause serious injuries upon short- and long-term exposures that can be prevented by LASSBio-596 (LB-596), an anti-inflammatory compound. We aimed to test LB-596 following subchronic exposure to MC-LR. Swiss mice received 10 intraperitoneal injections of distilled water (DW) or MC-LR (20 μg/kg bw) every 2 days. On the 10th injection animals receiving DW were gavaged with DW or 50 mg/kg bw of LB-596 for 1 or 7 days (C1D, C7D, CL1D and CL7D groups), whereas those exposed to MC-LR received either DW or 50 mg/kg of LB-596 for 1 or 7 days (T1D, T7D, TL1D and TL7D groups). Twelve hours after the last gavage we assessed respiratory mechanics, and extracted lung and liver for histology, apoptosis, inflammatory biomarkers and MC-LR content. C1D, C7D, CL1D and CL7D were all similar. Mechanical parameters were significantly higher in T1D and T7D compared to the other groups. LB-596 reversed these changes on day 1 of administration. LB-596 reduced inflammatory mediators in lung and liver on day 1 of treatment. On day 7 apoptosis in liver and lung fell even more. Briefly, 7-day administration completely reversed lung and liver changes.

Epigallocatechin-3-gallate attenuates microcystin-LR induced oxidative stress and inflammation in human umbilical vein endothelial cells

Epigallocatechin-3-gallate (EGCG) has been shown to possess anti-inflammatory effects. Microcystin-LR (MC-LR) is a potent toxin and our past research suggested that it also mediated human umbilical vein endothelial cell (HUVEC) injury. The aim of this study was to investigate the effects of EGCG on MC-LR-induced oxidative stress and inflammatory responses in HUVECs. HUVECs were stimulated with MC-LR in the presence or absence of EGCG. MC-LR (40 μM) significantly increased cell death and decreased cell viability, migration, and tube formation, whereas EGCG (50 μM) inhibited these effects. Furthermore, the results indicated that EGCG inhibited the production of reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) in MC-LR-stimulated HUVECs. Compared with MC-LR, EGCG significantly increased superoxide dismutase (SOD) and glutathione (GSH) levels and decreased malondialdehyde (MDA) levels. Moreover, the analysis indicated that EGCG suppressed MC-LR-induced NF-κB activation. In conclusion, the effects of EGCG were associated with inhibition of the NF-κB signaling pathway, which resulted in decreased ROS and TNF-α, thereby attenuating MC-LR-mediated oxidative and inflammatory responses.

Microcystin-LR induces mitochondria-mediated apoptosis in human bronchial epithelial cells

The present study aimed to investigate the toxicity of microcystin-LR (MC-LR) and to explore the mechanism of MC-LR-induced apoptosis in human bronchial epithelial (HBE) cells. HBE cells were treated with MC-LR (1, 10, 20, 30 and 40 µg/ml) alone or with MC-LR (0, 2.5, 5 and 10 µg/ml) and Z-VAD-FMK (0, 10, 20, 40, 60, 80, 100, 120 and 140 µM), which is a caspase inhibitor, for 24 and 48 h. Cell viability was assessed via an MTT assay and the half maximal effective concentration of MC-LR was determined. The optimal concentration of Z-VAD-FMK was established as 50 µm, which was then used in the subsequent experiments. MC-LR significantly inhibited cell viability and induced apoptosis of HBE cells in a dose-dependent manner, as detected by an Annexin V/propidium iodide assay. MC-LR induced cell apoptosis, excess reactive oxygen species production and mitochondrial membrane potential collapse, upregulated Bax expression and downregulated B-cell lymphoma-2 expression in HBE cells. Moreover, western blot analysis demonstrated that MC-LR increased the activity levels of caspase-3 and caspase-9 and induced cytochrome c release into the cytoplasm, suggesting that MC-LR-induced apoptosis is associated with the mitochondrial pathway. Furthermore, pretreatment with Z-VAD-FMK reduced MC-LR-induced apoptosis by blocking caspase activation in HBE cells. Therefore, the results of the present study suggested that MC-LR is capable of significantly inhibiting the viability of HBE cells by inducing apoptosis in a mitochondria-dependent manner. The present study provides a foundation for further understanding the mechanism underlying the toxicity of MC-LR in the respiratory system.

Pulmonary and hepatic injury after sub-chronic exposure to sublethal doses of microcystin-LR

We had previously shown that microcystin-LR (MCLR) could induce lung and liver inflammation after acute exposure. The biological outcomes following prolonged exposure to MCLR, although more frequent, are still poorly understood. Thus, we aimed to verify whether repeated doses of MCLR could damage lung and liver and evaluate the dose-dependence of the results. Male Swiss mice received 10 intraperitoneal injections (i.p.) of distilled water (60 μL, CTRL) or different doses of MCLR (5 μg/kg, TOX5), 10 μg/kg (TOX10), 15 μg/kg (TOX15) and 20 μg/kg (TOX20) every other day. On the tenth injection respiratory mechanics (lung resistive and viscoelastic/inhomogeneous pressures, static elastance, and viscoelastic component of elastance) was measured. Lungs and liver were prepared for histology (morphometry and cellularity) and inflammatory mediators (KC and MIP-2) determination. All mechanical parameters and alveolar collapse were significantly higher in TOX5, 10, 15 and 20 than CTRL, but did not differ among them. Lung inflammatory cell content increased dose-dependently in all TOX groups in relation to CTRL, being TOX20 the largest. The production of KC was increased in lung and liver homogenates. MIP-2 increased in the liver of all TOX groups, but in lung homogenates it was significantly higher only in TOX20 group. All TOX mice livers showed steatosis, necrosis, inflammatory foci and a high degree of binucleated hepatocytes. In conclusion, sub-chronic exposure to MCLR damaged lung and liver in all doses, with a more important lung inflammation in TOX20 group.