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

Exploring the neurotoxic effects of cylindrospermopsin in early development of zebrafish: An integrated impact of oxidative stress, inflammatory response, and apoptosis

The increasing global spread of cyanobacteria and their toxin Cylindrospermopsin (CYN) is a growing concern.This study aimed to examine the toxic effects of CYN on the early neurodevelopment of zebrafish, and to identify the underlying mechanisms. The findings indicated that zebrafish exposed to varying concentrations of CYN exhibited general developmental toxicity, including typical malformations, diminished embryonic movement, and shortened body length. The length of zebrafish larvae was shortened by 4.8 and 6.1 % in the 0.2 and 2 μm exposure groups, Furthermore, CYN was observed to impede neuronal development and motor behaviour in zebrafish. Concomitantly, CYN markedly elevated reactive oxygen species (ROS) levels and modified catalase (CAT) and superoxide dismutase (SOD) activities. Compared with the control group, zebrafish larvae in the 0.2 and 2 μm exposure groups showed a significant decrease of 17.7 and 43.2 % in CAT activity and a significant increase of 51.4 and 84.4 % in SOD activity, indicating that CYN induces oxidative stress. Furthermore, the fluorescence quantification and acridine orange staining assay conducted on additional Tg(lyz:dsRed) transgenic lines provided further evidence that CYN induced an inflammatory response and apoptosis, a finding that was also verified at the gene level. This study not only provides new insights into the mechanisms of CYN toxicity, but also provides important scientific evidence for risk assessment of environmental pollutants and the conservation of aquatic organisms.

Assessment of the Effects of Anatoxin-a In Vitro: Cytotoxicity and Uptake

Anatoxin-a (ATX-a) is a cyanotoxin whose toxicological profile has been underinvestigated in comparison to other cyanotoxins such as microcystins (MCs) or cylindrospermopsin (CYN). However, its wide distribution, occurrence, and toxic episodes justify more attention. It is classified as a neurotoxin, but it has also been reported to affect other organs and systems. Thus, the aim of this study was to establish, as a first tier in its toxicological evaluation, its cytotoxicity in a wide range of cell lines representative of potential target organs (N2a, SH-SY5Y, HepG2, Caco2, L5178Y Tk+/-, THP-1 and Jurkat). As limited effects were observed after exposure to up to 200 µg/mL of ATX-a for 24 h (only Jurkat and THP-1 cells showed reduced cell viability), cell uptake experiments were performed by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The results showed that the immune system cells had the highest percentage of ATX-a in the intracellular fraction, followed by neuronal cells and finally Caco-2 and HepG2 cells. Moreover, the expression of genes related to cell death mechanisms in THP-1 cells was also analyzed by polymerase chain reaction (PCR) and showed no changes under the conditions tested. Further research is required on ATX-a's toxic effects and toxicokinetics to contribute to its risk assessment.

Invitro evaluation of interactions between cylindrospermopsin and water contaminants, arsenic and cadmium, in two human immune cell lines

Cylindrospermopsin (CYN), a cyanotoxin with worldwide distribution, is gaining increased attention due to its bioaccumulation potential and toxicological effects. Previous research suggests that CYN may interact with other environmental contaminants, potentially amplifying its toxicity. To address this concern, the present study investigated the combined effects of CYN with arsenic (As) and cadmium (Cd) on human immune cell lines, Jurkat and THP-1. Cytotoxicity tests showed that As and Cd significantly decreased the viability of both cell lines after 24 and 48 h of exposure. The EC50 (24 h) values for Jurkat cells were 13.15 ± 1.97 (As) and 36.92 ± 3.77 μM (Cd), respectively, while for THP-1, the EC50 (24 h) values were 46.48 ± 0.17 for As and 55.09 ± 4.98 μM for Cd. Furthermore, individual contaminants and their mixtures with CYN impaired monocyte differentiation into macrophages. The effect on mRNA expression of some cytokines (TNF-α, INF-γ, IL-2, IL-6 and IL-8) was also assessed. In the Jurkat cell line, As upregulated IL-8 expression while Cd increased the expression of all interleukins. Exposure to binary combinations (CYN + As, and CYN + Cd) increased IL-2 and INF-γ expression. In THP-1 cells, As elevated IL-8 and INF-γ expression, whereas Cd caused an increase in TNF-α and INF-γ expression. Exposure to CYN + As up-regulated IL-8 and INF-γ expression, while the CYN + Cd combination down-regulated TNF-α expression. These findings highlight the complex interactions between contaminants, emphasizing the need for evaluating combined effects in risk assessments.

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

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.

Microcystis sp. AE03 strain in Dal Lake harbors cylindrospermopsin and microcystin synthetase gene cluster

Cyanobacterial harmful algal blooms (CHABs) are increasing at an alarming rate in different water bodies worldwide. In India, CHAB events in water bodies such as Dal Lake have been sporadically reported with no study done to characterize the cyanobacterial species and their associated toxins. We hypothesized that this Lake is contaminated with toxic cyanobacterial species with the possibility of the presence of cyanotoxin biosynthetic genes. We, therefore, used some of the molecular tools such as 16S ribosomal DNA, PCR, and phylogenetic analysis to explore cyanobacterial species and their associated toxins. A 3-year (2018–2020) survey was conducted at three different sampling sites of Dal Lake namely, Grand Palace Gath (S1), Nigeen basin (S2), and Gagribal basin (S3). Two strains of Dolichospermum sp. AE01 and AE02 (S3 and S1 site) and one strain of Microcystis sp. AE03 (S2 site) was isolated, cultured, and characterized phylogenetically by 16S ribosomal DNA sequencing. The presence of cyanotoxin genes from the isolates was evaluated by PCR of microcystins (mcyB), anatoxins (anaC), and cylindrospermopsins (pks) biosynthesis genes. Results revealed the presence of both mcyB and pks gene in Microcystis sp. AE03, and only anaC gene in Dolichospermum sp. AE02 strain. However, Dolichospermum sp. AE01 strain was not found to harbor any such genes. Our findings, for the first time, reported the coexistence of pks and mcyB in a Microcystis AE03 strain. This study has opened a new door to further characterize the unexplored cyanobacterial species, their associated cyanotoxin biosynthetic genes, and the intervention of high-end proteomic techniques to characterize the cyanotoxins.