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Toxicological Sciences 57, 54-60 (2000)
Copyright © 2000 by the Society of Toxicology

Endocrine Toxicology

Lack of Significant Estrogenic or Antiestrogenic Activity of Pyrethroid Insecticides in Three in Vitro Assays Based on Classic Estrogen Receptor {alpha}-Mediated Mechanisms

Koichi Saito1, Yoshitaka Tomigahara, Norihisa Ohe, Naohiko Isobe, Iwao Nakatsuka and Hideo Kaneko

Environmental Health Science Laboratory, Sumitomo Chemical Company, Limited., 1-98, 3-Chome, Kasugade-Naka, Konohana-Ku, Osaka 554-8558, Japan

Estrogenic and antiestrogenic activity of pyrethroid insecticides (d-trans-allethrin, cypermethrin, empenthrin, fenvalerate, imiprothrin, permethrin, d-phenothrin and prallethrin) was evaluated using a suite of three in vitro assays based on classic human estrogen receptor {alpha} (hER{alpha})-mediated mechanisms. A mammalian cell-based luciferase reporter gene assay was developed for examining effects on hER{alpha}-mediated gene activation. hER{alpha}-independent effects on the gene activation were examined using control cells with constitutive luciferase activation by a herpes simplex virus thymidine kinase (HSV-TK) promoter for determining appropriate dose levels of test chemicals. Moreover, the test chemical-dependent interaction between hER{alpha} and a coactivator (transcriptional intermediary factor 2: TIF2) was analyzed by a yeast two-hybrid method, competitive binding to hER{alpha} being assayed by a fluorescence polarization method. Significant (p < 0.05) positive effects of estrogenic substances (E2/estradiol, diethylstilbestrol, and p-nonylphenol) were detected in all assays. An antiestrogen, 4-hydroxytamoxifen, significantly inhibited E2-mediated transactivation and interaction between hER{alpha} and TIF2 through hER{alpha} binding (p < 0.05). However, none of the pyrethroids tested showed significant (p < 0.05) estrogenic or antiestrogenic effects (100 nM–10 µM), indicating that they do not impact on the classic hER{alpha}-mediated activation pathway in vitro.

Key Words: estrogen receptor; pyrethroid insecticides; reporter gene assay; yeast two-hybrid assay; competitive ligand-binding assay.


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