Oral exposure to cylindrospermopsin in pregnant rats: reproduction and foetal toxicity studies

Cylindrospermopsin induces oocyte maturation and disrupts gene expression in zebrafish ovarian follicles

There is evidence that cylindrospermopsin (CYN) exerts reproductive toxicity in mice. However, little information is available concerning the toxicity of CYN in nonmammalian vertebrates. Here, we investigated the direct action of CYN on female reproduction by studying germinal vesicle breakdown, transcript abundance, caspase-3 activity, and testosterone production using cultured follicle-enclosed zebrafish oocytes as a model system. Treatment of follicles with 1,000 μg/L CYN significantly increased GVBD, Caspase-3 activity, and hCG-induced testosterone secretion. Exposure to CYN also reduced the abundance of 3βhsd as well as hCG-induced fshr and era transcripts and increased cyp19a1 mRNA levels. In summary, this study provides a framework for a better understanding of the adverse action of CYN on female reproduction in zebrafish and other vertebrate species. The findings are also relevant to developing valid biomarkers for CYN by measuring zebrafish oocyte maturation and gene expression.

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.

Cylindrospermopsin-Microcystin-LR Combinations May Induce Genotoxic and Histopathological Damage in Rats

Cylindrospermopsin (CYN) and microcystins (MC) are cyanotoxins that can occur simultaneously in contaminated water and food. CYN/MC-LR mixtures previously investigated in vitro showed an induction of micronucleus (MN) formation only in the presence of the metabolic fraction S9. When this is the case, the European Food Safety Authority recommends a follow up to in vivo testing. Thus, rats were orally exposed to 7.5 + 75, 23.7 + 237, and 75 + 750 μg CYN/MC-LR/kg body weight (b.w.). The MN test in bone marrow was performed, and the standard and modified comet assays were carried out to measure DNA strand breaks or oxidative DNA damage in stomach, liver, and blood cells. The results revealed an increase in MN formation in bone marrow, at all the assayed doses. However, no DNA strand breaks nor oxidative DNA damage were induced, as shown in the comet assays. The histopathological study indicated alterations only in the highest dose group. Liver was the target organ showing fatty degeneration and necrotic hepatocytes in centrilobular areas, as well as a light mononuclear inflammatory periportal infiltrate. Additionally, the stomach had flaking epithelium and mild necrosis of epithelial cells. Therefore, the combined exposure to cyanotoxins may induce genotoxic and histopathological damage in vivo.

In vivo genotoxicity evaluation of cylindrospermopsin in rats using a combined micronucleus and comet assay

Cylindrospermopsin (CYN) is a potent cyanotoxin recognized as an emerging human threat due to its cytotoxicity and potential carcinogenicity. Although the genotoxicity of CYN has been extensively studied in vitro, limited data are available on its in vivo genotoxicity. The aim of this study was to evaluate the in vivo genotoxicity of pure CYN (7.5-75 μg/kg body weight) after oral exposure of rats through a combined assay of the micronucleus test (MN) in bone marrow, and the standard and modified comet assay in stomach, liver and blood. Also, histopathological changes in stomach and liver were evaluated. Positive results in the MN test were observed in bone marrow in the exposed rats at all the tested concentrations. However, the comet assay revealed that CYN did not induce DNA strand breaks nor oxidative DNA damage in any of the tissues investigated. Finally, histopathological changes were observed in stomach and liver (7.5-75 μg/kg) in intoxicated rats. These results could indicate that CYN is able to induce irritation in stomach before its biotransformation in rats orally exposed, and genotoxicity in bone marrow.

Potential Use of Chemoprotectants against the Toxic Effects of Cyanotoxins: A Review

Cyanobacterial toxins, particularly microcystins (MCs) and cylindrospermopsin (CYN), are responsible for toxic effects in humans and wildlife. In order to counteract or prevent their toxicity, various strategies have been followed, such as the potential application of chemoprotectants. A review of the main substances evaluated for this aim, as well as the doses and their influence on cyanotoxin-induced toxicity, has been performed. A search of the literature shows that research on MCs is much more abundant than research on CYN. Among chemoprotectants, antioxidant compounds are the most extensively studied, probably because it is well known that oxidative stress is one of the toxic mechanisms common to both toxins. In this group, vitamin E seems to have the strongest protectant effect for both cyanotoxins. Transport inhibitors have also been studied in the case of MCs, as CYN cellular uptake is not yet fully elucidated. Further research is needed because systematic studies are lacking. Moreover, more realistic exposure scenarios, including cyanotoxin mixtures and the concomitant use of chemoprotectants, should be considered.