Effects of Extremely Low Frequency Elecromagnetic Fields on Thyroid Carcinogenesis Induced by N-bis(2-hydroxypropyl)nitrosamine and Sulfadimethoxine

Abstract

Purpose: Long-term exposure to extremely low-frequency (60 ㎐) electromagnetic fields (ELF-EMF) raises the questions of the induction of biological effects including tumorigenesis. One mechanism through which ELF-MFS could influence neoplastic development is the imbalance of cellular proliferation and cell apoptosis. The present study investigated the effect of ELF-EMF on chemically-induced thyroid carcinogenesis in a rat. Methods: We examined cellular proliferation index measured by anti-Ki-67 antigen, apoptosis, apoptosis related proteins such as caspase 3 and p53, and cell cycle-related proteins (cyclin D1 and p21 WAF1 /Cip1). Forty Male F344 rats received a subcutaneous N-bis(2-hydroxypropyl)nitrosamine (DHPN, 2,800 ㎎/㎏) injection, and 1 week later were allowed free access to drinking water containing sulfadimethoxine (0.1%) for 12 weeks. Twenty rats were exposed by ELF-EMF. During the carcinogenesis, sequential histological changes from hyperplasia, adenoma, and ultimately to overt carcinomas were noted. Results: The exposure group of ELF-EMF, significantly increases the number size of carcinomas. Also, the proliferative and apoptotic indices were significantly increased in the ELF-EMF exposure group than in the control group. The caspase 3 protein expression did not show any significant changes between ELF-EMF group and control group. The p53 protein was not detected in both ELF-EMF exposure and control group. Among the cell cycle related proteins, cyclin D1, not p21 WAF1 /Cip1, was significantly increased in adenomas and carcinomas in ELF-EMF exposure group compared with the control group. Conclusion: Exposure of ELF-EMF effects on chemically-induced rat thyroid carcinogenesis as results of altered increase of cellular proliferation, apoptosis, and cyclin D1 expression.