Effect of early acute high concentrations of iodide exposure on mitochondrial superoxide production in FRTL cells

• Published in: Free radical biology & medicine 2012-04, Vol.52 (8), p.1343-1352
• Main Authors: Yao, Xiaomei, Li, Min, He, Jing, Zhang, Guiqin, Wang, Min, Ma, Jun, Sun, Yun, Zhang, Wanqi, Li, Lanying
• Format: Article
• Language: English
• Subjects: Animals; apoptosis; Cell Line; cell membranes; cytochrome c; Cytochromes c - metabolism; cytotoxicity; DNA; DNA fragmentation; DNA Fragmentation - drug effects; droplets; Enzyme-Linked Immunosorbent Assay; Fischer rat thyroid cell line (FRTL); Flow Cytometry; fluorescence; Fluorescent Dyes; Hydrogen Peroxide - metabolism; Immunohistochemistry; Iodide excess; iodides; Iodides - administration & dosage; Iodides - pharmacology; lactate dehydrogenase; lipid bodies; lipid peroxidation; Mice; Microscopy, Electron, Transmission; mitochondria; Mitochondria - drug effects; Mitochondria - enzymology; Mitochondria - metabolism; Mitochondria - ultrastructure; Mitochondrial superoxide production; oxidative stress; rats; Superoxides - metabolism; thyrotropin; transmission electron microscopy
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2012.02.002

Excessive oxidative stress has been suggested as one of the underlying mechanisms in the development of thyroid cytotoxicity. Although the involvement of mitochondria has been hypothesized, the effect of early acute high concentrations of iodide on mitochondrial superoxide production remains largely unknown, especially within a 24h time frame. By using a novel fluorescent probe, MitoSOX Red, we demonstrated the concentration response and time-course response of KI-induced mitochondrial superoxide production in the Fischer rat thyroid cell line (FRTL). A strong increase of MitoSOX Red fluorescence intensity in FRTL cells can be seen at 2h following high concentrations of iodide exposure. Besides, we indicated that 6-propyl-2-thiouracil (PTU, 300μM), thyroid-stimulating hormone (TSH, 10mU/ml), and perchlorate (KClO4, 30μM) can inhibit excessive iodide-induced strong mitochondrial superoxide production; however, diethyldithiocarbamic acid (DETC, 2mM) can further increase excessive iodide-induced mitochondrial superoxide production. By using transmission electron microscopy (TEM), we noted accumulated myelinoid bodies with lipid droplets and numerous apoptotic nuclear bodies at 24h in FRTL cells. In addition, we demonstrated a significant decrease in cytochrome c (cyt c) content in the mitochondria by enzyme linked immunosorbent assay (ELISA), and DNA fragments and significant increases in lactate dehydrogenase (LDH) activity were detected. We propose a sequence of events mediated by a strong mitochondrial superoxide production at 2h, followed by lipid peroxidation, cell membrane damage with significant cyt c release, culminating in DNA fragmentation and apoptotic nuclear formation at 24h, which may partly contribute to the underlying mechanisms of early acute iodide excess. ► The concentration response and time-course response of iodide-induced mitochondrial superoxide production in FRTL cells were demonstrated. ► The strong mitochondrial superoxide production induced by excessive iodide can be inhibited by 6-propyl-2-thiouracil (PTU), thyroid-stimulating hormone (TSH), or perchlorate (KClO4). ► The strong mitochondrial superoxide production induced by excessive iodide can be increased by diethyldithiocarbamic acid (DETC). ► A sequence of events induced by early acute iodide excess within 24h was proposed.