Analytical Sciences

A Screening Method for Estrogens Using an Array-Type DNA Glass Slide

Sung Bae KIM, Takeaki OZAWA, and Yoshio UMEZAWA 

Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

A new screening assay was described for the determination of endocrine disrupting chemicals (EDCs), such as synthetic estrogens, with an array-type DNA glass slide having characteristics of 1) a high sample throughput, 2) a compact size allowing a small sample volume, and 3) a sensitive determination based on the estrogen-dependent binding of the human estrogen receptor α(hERα) with its estrogen responsive element (ERE; Vit. A₂ gene promoter). We devised a glass slide on which a thin agarose gel was mounted. Avidin was then covalently immobilized on each well of the glass slide after the gel was activated by a NaIO₄ solution. Also, the biotinylated ERE as a DNA probe was immobilized on the gel layer through avidin-biotin binding. After the estrogen-dependent binding of a yellow fluorescent protein-fused hERα (YFP-hERα) to ERE on the gel layer, the fluorescence intensity of YFP-hERα quantitatively extracted into the gel was directly determined with a fluorescence microplate reader. Pre-incubation of YFP-hERα with estrogen at 37°C for 30 min enhanced the estrogen-dependent hERα-ERE binding. The determined hormonal activities of estrogens on the interaction of YFP-hERα with ERE were as follows in their decreasing order: diethylstilbestrol (DES) > 17β-estradiol (E₂) = ethynylestradiol (EE₂) > 4-hydroxy tamoxifen (OHT) > clomiphene (Clo). The present method provides a sensitive estrogen-dependent dose-response curve down to ∼10^-13 M in the case of DES. This method will become a competitive alternative to the conventional in vitro assays, such as a DNA-binding assay using radioisotopes.

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