Ultrastructural damage to heart tissue from repeated oral exposure to yessotoxin resolves in 3 months

Yessotoxin (YTX), an algal toxin contaminating edible shellfish, was previously shown to induce ultrastructural changes in some cardiac muscle cells of mice after acute (1 and 2 mg/kg) or daily repeated oral exposure (1 and 2 mg/kg/day, for 7 days). Therefore, the temporal evolution of the ultrastructural myocardial alterations and the development of other signs of toxicity induced by a repeated daily oral administration of YTX (1 mg/kg/day, for 7 days) to mice were evaluated within 3 months after the treatment. Symptoms, food consumption, body weight, gross pathology and histopathology of the main organs and tissues were observed, and plasma levels of transaminases, lactate dehydrogenase, creatinine and creatinine phosphokinase were measured. Heart, liver, kidneys and cerebellum were also analysed by transmission electron microscopy. In addition, the blood concentration of YTX was determined by a direct enzyme linked immunosorbent assay (ELISA) 24 h after the last toxin administration.No mortality or other treatment-related changes, including histological or hematoclinical parameters, were recorded in mice administered with YTX. Similarly, electron microscopy did not reveal any ultrastructural alteration in the liver, kidneys, and cerebellum associated with YTX treatment. In contrast, changes in cardiac muscle cells near to the capillaries (clusters of rounded mitochondria and disorganization of myofibrils) were observed 24 h after the treatment. These changes were also noted 30 days after the toxin administration, while after 90 days no differences in cardiac muscle cells between control and YTX-treated mice were observed, which indicated a recovery of the ultrastructural alterations induced by the toxin.