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The cyanobacterial toxin cylindrospermopsin (CYN) is a widely distributed contaminant of freshwater systems with the consequent risk for human and wildlife, particularly fish. However, CYN toxicity data on fish are still scarce. It is known that CYN inhibits glutathione synthesis and this could contribute to oxidative damage. In the present work tilapia (Oreochromis niloticus) were exposed by gavage to 200 and 400 μg/kg bw of pure CYN and sacrificed after 24 h. The activity and relative mRNA expression by real-time PCR of antioxidant enzymes glutathione peroxidase (GPx) and soluble glutathione-S-transferases (sGST) and the sGST protein abundance by Western blot analysis were evaluated in liver and kidney. Also the induction of lipid peroxidation (LPO) was assayed. Results show an increase of LPO products in both organs. Moreover, CYN altered the activity, gene expression and protein abundance of the enzymes, indicating the importance of GPx and sGST in CYN pathogenicity. This is the first time that CYN is reported to affect these enzymes in fish and they have shown to be responsive biomarkers of CYN toxicity.

The incorporation of the natural mineral clay montmorillonite into polymeric systems enhances their barrier properties as well as their thermal and mechanical resistance, making them suitable for a wide range of industrial applications, e.g., in the food industry. Considering humans could easily be exposed to these clays due to migration into food, toxicological and health effects of clay exposure should be studied. In the present work, the cytotoxic effects induced by two different clays (the unmodified clay Cloisite(®) Na(+) , and the organically modified Cloisite(®) 30B) on Caco-2 cells were studied after 24 and 48 h of exposure. The basal cytotoxicity endpoints assessed were total protein content, neutral red uptake and a tetrazolium salt reduction. Our results showed that only Cloisite(®) 30B induced toxic effects. Therefore, the effects of subcytotoxic concentrations of this clay on the generation of intracellular reactive oxygen species, glutathione content and DNA damage (comet assay) were investigated. Results indicate that oxidative stress may be implicated in the toxicity induced by Closite(®) 30B, in regards of the increases in intracellular reactive oxygen species production and glutathione content at the highest concentration assayed, while no damage was observed in DNA. The most remarkable morphological alterations observed were dilated cisternae edge in the Golgi apparatus and nucleolar segregation, suggesting impairment in the secretory functions, which could be related to inhibition in the synthesis of proteins.

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