Effects of cylindrospermopsin on cultured immortalized human airway epithelial cells

Impact of long-term cyanotoxin exposure on cattle: Biochemical, histological, and oxidative stress assessment

Background and Aim

Cyanobacterial blooms, driven by anthropogenic and climatic changes, pose significant ecological and health threats. This study investigates the long-term effects of microcystins (MCs), potent cyanotoxins, on cattle at Lake des Oiseaux, a Ramsar-listed wetland in Algeria. Aligning with the "One Health" framework, the research evaluates the biochemical, histological, and oxidative stress impacts of MCs on livestock as environmental sentinels.

Materials and Methods

A herd of 40 cattle (20 exposed and 20 non-exposed) was studied during the summer bloom period of 2019. Blood and liver samples were analyzed to assess biochemical markers (ALT, AST, ALP, GGT, etc.), histopathological changes, and oxidative stress parameters (GPx, CAT, SOD, LPO and GSH).

Results

Exposed cattle exhibited significant elevations in liver enzymes and oxidative stress markers, indicating hepatic inflammation and redox imbalance. Histological analysis revealed macrovacuolar steatosis, fibrosis, and bile duct dilatation. Antioxidant enzyme activities (GPx, CAT and SOD) were reduced, with notable depletion of GSH levels and increased lipid peroxidation. These findings reflect the cumulative cytotoxic effects of MC exposure. Non-exposed cattle showed no such changes.

Conclusion

Long-term MC exposure disrupts liver function and induces oxidative stress in cattle, implicating significant risks for both animal and human health. The bioaccumulation of cyanotoxins in livestock emphasizes the urgent need for preventive measures, including water monitoring, restricted livestock access to contaminated sites, and farmer education. These strategies are vital to mitigate risks under the "One Health" approach, ensuring sustainable livestock and public health.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Effects of all-trans and 9-cis retinoic acid on differentiating human neural stem cells in vitro

Cyanobacterial blooms are known sources of environmentally-occurring retinoid compounds, including all-trans and 9-cis retinoic acids (RAs). The developmental hazard for aquatic organisms has been described, while the implications for human health hazard assessment are not yet sufficiently characterized. Here, we employ a human neural stem cell model that can differentiate in vitro into a mixed culture of neurons and glia. Cells were exposed to non-cytotoxic 8-1000 nM all-trans or 9-cis RA for 9-18 days (DIV13 and DIV22, respectively). Impact on biomarkers was analyzed on gene expression (RT-qPCR) and protein level (western blot and proteomics) at both time points; network patterning (immunofluorescence) on DIV22. RA exposure significantly concentration-dependently increased gene expression of retinoic acid receptors and the metabolizing enzyme CYP26A1, confirming the chemical-specific response of the model. Expression of thyroid hormone signaling-related genes remained mostly unchanged. Markers of neural progenitors/stem cells (PAX6, SOX1, SOX2, NESTIN) were decreased with increasing RA concentrations, though a basal population remained. Neural markers (DCX, TUJ1, MAP2, NeuN, SYP) remained unchanged or were decreased at high concentrations (200-1000 nM). Conversely, (astro-)glial marker S100β was increased concentration-dependently on DIV22. Together, the biomarker analysis indicates an RA-dependent promotion of glial cell fates over neural differentiation, despite the increased abundance of neural protein biomarkers during differentiation. Interestingly, RA exposure induced substantial changes to the cell culture morphology: while low concentrations resulted in a network-like differentiation pattern, high concentrations (200-1000 nM RA) almost completely prevented such network patterning. After functional confirmation for implications in network function, such morphological features could present a proxy for network formation assessment, an apical key event in (neuro-)developmental Adverse Outcome Pathways. The described application of a human in vitro model for (developmental) neurotoxicity to emerging environmentally-relevant retinoids contributes to the evidence-base for the use of differentiating human in vitro models for human health hazard and risk assessment.

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.

Effects of cylindrospermopsin, its decomposition products, and anatoxin-a on human keratinocytes

Toxins produced by cyanobacteria (cyanotoxins) are among the most dangerous natural compounds. In recent years, there have been many published papers related to the toxic alkaloids cylindrospermopsin (CYN) and anatoxin-a (ANTX-a), which are synthesized by several freshwater species of cyanobacteria (i.e. Raphidiopsis raciborskii and Anabaena flos-aquae) and are some of the most common cyanotoxins in aquatic reservoirs. The harmful properties of CYN are wide and primarily include cytotoxicity. To date, several analogs and decomposition products of CYN have been described, which can potentially increase its toxic effects in living organisms. The mode of action of ANTX-a is different than that observed after CYN exposure and involves structures in the nervous system. One of the most frequent situations in which cyanotoxins are introduced into the human body is by skin contact with contaminated water, i.e., during water sports, fishing or agriculture. Unfortunately, to date, knowledge on the influence of CYN, its decomposition products, and ANTX-a on human skin is limited. In this paper, we investigated the impact of CYN, its decomposition products, and ANTX-a on the proliferation of human keratinocytes, which provide a protective barrier on the skin. Moreover, we described the cytotoxic effects developed in the selected cell type and estimated the ability of the keratinocytes to migrate under the influence of the studied cyanotoxins. The obtained results suggest that CYN and its decomposition products at concentrations corresponding to that determined for CYN in nature (1 μg·mL^-1) are strong inhibitors of keratinocyte proliferation (70% inhibition within 24 h for pure CYN). The cytotoxic effects of CYN and the CYN decomposition products on keratinocytes was also significant, and the pure toxin (1 μg·mL^-1) was estimated to be 35% after 24 h of exposure. Similarly, harmful effects caused by CYN and its byproducts were observed during keratinocyte migration, and the initial form of the toxin (1 μg·mL^-1) showed 40% inhibition within 16 h. Different results were obtained for ANTX-a. The toxic effects of this compound on human keratinocytes estimated by the applied tests was observed only at the highest tested concentration (10 μg·mL^-1) and after a long period of exposure. The results presented in this paper are, to the best of our knowledge, the first description of the influence of CYN, CYN decomposition products, and ANTX-a on human epidermal cells. Clearly, CYN and its decomposition products are serious threats not only when acting on internal organs but also during the skin contact stage. Further studies on cyanotoxins should focus on the determination of their decomposition products and ecotoxicology in natural aquatic environments.

Four decades of progress in cylindrospermopsin research: The ins and outs of a potent cyanotoxin

The cyanotoxin cylindrospermopsin (CYN), a toxic metabolite from cyanobacteria, is of particular concern due to its cosmopolitan occurrence, aquatic bioaccumulation, and multi-organ toxicity. CYN is the second most often recorded cyanotoxin worldwide, and cases of human morbidity and animal mortality are associated with ingestion of CYN contaminated water. The toxin poses a great challenge for drinking water treatment plants and public health authorities. CYN, with the major toxicity manifested in the liver, is cytotoxic, genotoxic, immunotoxic, neurotoxic and may be carcinogenic. Adverse effects are also reported for endocrine and developmental processes. We present a comprehensive review of CYN over the past four decades since its first reported poisoning event, highlighting its global occurrence, biosynthesis, toxicology, removal, and monitoring. In addition, current data gaps are identified, and future directions for CYN research are outlined. This review is beneficial for understanding the ins and outs of this environmental pollutant, and for robustly assessing health hazards posed by CYN exposure to humans and other organisms.

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.

Cylindrospermopsin induces cellular stress and activation of ERK1/2 and p38 MAPK pathways in adult human liver stem cells

Cyanobacterial toxin cylindrospermopsin (CYN) is an emerging freshwater contaminant, whose expanding environmental occurrence might result into increased human health risks. CYN is potent hepatotoxin, with cytotoxicity and genotoxicity documented in primary hepatocytes or hepatoma cell lines. However, there is only limited information about CYN effects on adult human liver stem cells (LSCs), which play an important role in liver tissue development, regeneration and repair. In our study with human liver cell line HL1-hT1 which expresses characteristics of LSCs, CYN was found to be cytotoxic and increasing cell death after 24-48 h exposure to concentrations >1 μM. Subcytotoxic 1 μM concentration did not induce cell death or membrane damage, but inhibited cellular processes related to energy production, leading to a growth stagnation after >72 h. Interestingly, these effects were not associated with increased DNA damage, reactive oxygen species production, or endoplasmic reticulum stress. However, CYN induced a sustained (24-48 h) activation of mitogen-activated protein kinases ERK1/2 and p38, and increased expression of stress-related transcription factor ATF3. Thus, LSCs were not primarily affected by CYN-induced genotoxicity and oxidative stress, but via activation of signaling and transcriptional pathways critical for regulation of cell proliferation, stress responses, cell survival and inflammation. Alterations of LSCs during CYN-induced liver injury, including the role of nongenotoxic mechanisms, should be therefore considered in mechanistic assessments of chronic CYN hepatotoxicity and hepatocarcinogenicity.