Biochemical and pathological toxic effects induced by the cyanotoxin Cylindrospermopsin on the human cell line Caco-2.

Cylindrospermopsin (CYN), a cyanotoxin produced by several freshwater cyanobacteria, causes human intoxications and animal mortalities. The present study focuses on the cytotoxic effects of CYN on Caco-2 cells at 24 and 48 h. The basal cytotoxicity endpoints studied were total protein content (TP), neutral red uptake (NR) and reduction of the tetrazolium salt (MTS). The effect of non-cytotoxic concentrations of CYN on the generation of intracellular reactive oxygen species (ROS), γ-glutamylcysteine synthetase (GCS) activity and glutathione (GSH) content was also studied and the morphological alterations in the Caco-2 cells subsequent to CYN exposure were recorded. The most sensitive endpoint - the reduction of MTS - showed that the viability of Caco-2 cells after exposure to the highest concentration assayed (40 μg/mL CYN) was reduced by about 90%. Intracellular ROS production increased only when exposed to a concentration of 1.25 μg/mL CYN, while GSH content and GCS activity increased when exposed to 2.5 μg/mL CYN. The main insights provided by the present study are the ultrastructural alterations, which reveal lipid degeneration, mitochondrial damage and nucleolar segregation with altered nuclei. Therefore, it has been demonstrated that CYN can induce toxic effects in Caco-2 cells in a time-concentration dependent manner. Moreover, unlike the cytotoxic and biochemical alterations, which were only evident at higher concentrations, morphological damage at the ultrastructural level was noticeable even at the lowest concentration used.