Inhibitory Effects of 2-iodohexadecanal on Thyroid Cell Proliferation.

THOMASZ, L; ROSSICH, L; OGLIO, R; DAGROSA, MA; PISAREV , M; JUVENAL, G

Paris

Congreso; 14th International Thyroid Congress; 2010

American Thyroid Association (ATA)

Introduction: Although thyroid gland function is mainly under the control of pituitary TSH, other factors, such as iodine play a role in this process. The thyroid is capable of producing different iodolipids such as 6-iodo-deltalactone and 2-iodohexadecanal (2-IHDA). It was shown that these iodolipids mimic some of the inhibitory effects of excess iodide on several thyroid parameters. Objectives: To studied the effect of 2-IHDA on cell proliferation and apoptosis in FRTL-5 cells. Results: FRTL-5 cells were grown in the presence of TSH and treated with increasing concentrations of KI and 2-IHDA (0.5, 5, 10 and 33 ìM) for 24, 48 and 72 h. Cell proliferation was measured using the MTT assay and is expressed as % of inhibition versus TSH. Whereas KI inhibited cell proliferation only at 33 ìM after 72 h of treatment (24 % p<0.01), 2-IHDA inhibited in a time and dose dependent manner. Analysis of cell cycle by flow cytometric DNA analysis revealed an accumulation of cells in G1 phase induced by 2-IHDA: TSH G1: 54.5%, 2-IHDA 33 ìM G1: 65,3% (p<0.01), 2-IHDA 10 ìM G1: 63%, (p<0.01).We found that treatment with 2-IHDA caused a decreased of intracellular ROS production (20% p <0.01), assayed by fluorescence analysis using 2’-7’-dichlorofluorescein diacetate and catalase activity (UE/mg protein): TSH: 0.21, 2-IHDA 33 ìM: 0.14 (p <0.01), 2-IHDA 10 ìM: 0.17 (p <0.01), no significant effects of KI on ROS production and catalase activity was observed. We also observed evidences of a pro-apoptotic effect of 2-IHDA. After 6 h of 33 ìM 2-IHDA treatment, it increased significantly caspase-3 activity (pmolpNA/min/ml): 2-IHDA (0 h): 21, 2-IHDA (1 h): 19, 2-IHDA (3 h): 15, 2-IHDA (6 h): 44 (p<0.001), 2-IHDA (24 h): 62 (p<0.001), whereas no significant effect of 5 ìM or 33 ìM  KI was observed. In order to see if 2-IHDA can acts downstream of the TSH receptor-adenylyl cyclase system, or inhibiting other regulatory cascades, the effect of 2-IHDA on dbcAMP or TPA (which activates PKC enzyme) induced cell proliferation was studied (results are expressed as % of inhibition versus dbcAMP or TPA. Conclusion: These results suggest that the inhibitory effects of 2-IHDA on FRTL-5 thyroid cell proliferation are mediated by cell cycle arrest and apoptosis