CYTOTOXIC EFFECTS OF IODIDE ON THYROID-CELLS - DIFFERENCE BETWEEN RAT-THYROID FRTL-5 CELL AND PRIMARY DOG THYROCYTE RESPONSIVENESS

In order to investigate whether the cytotoxic effect of iodide observe d in the thyroid gland represented an apoptotic phenomenon, in vitro e xperiments were performed using the FRTL-5 thyroid cell line and dog t hyrocytes in primary culture. These cells were exposed to iodide under various incubation conditions. Apoptosis was assessed through the ana lysis of DNA breakdown, i.e. the electrophoresis of internucleosomal D NA fragments generating a typical ''ladder'' and quantification of pre labelled DNA cleavage products, The FRTL-5 cells appeared to be sensit ive only to high doses of iodide, far in excess of physiological level s. They exhibited the different characteristics of two different cell death phenomena: apoptosis and necrosis. The toxicity of iodide appear ed to be partially relieved by anti-thyroid agents. This effect consti tutes an additional example of the general paradigm of iodide action t hrough oxidized intermediates. In contrast dog thyrocytes in primary c ulture did not appear to be sensitive to iodide under similar incubati on conditions; species differences and/or types of culture could accou nt for these discrepant effects.