Estrogenic activity of an antioxidant, nordihydroguaiaretic acid (NDGA).
Nordihydroguaiaretic acid (NDGA), an antioxidant which has been used to preserve oils and foods, has recently become well known as a putative anticancer agent. Although NDGA is a member of the lignan family, its hormonal activities have not been well investigated. Here we show that NDGA has in vitro estrogenic activity in the ERE-luc reporter system using NIH3T3 cells, and in the estrogen-responsive cell growth assay in a pituitary cell line, MtT/E-2. Uterotropic assay in rats indicated that NDGA has estrogenic activity in vivo as well, albeit weak. Interestingly it preferentially induced ERalpha mediated ERE-luc activity, although it showed similar binding affinity to both ERalpha and ERbeta. With ERbeta, on the other hand, NDGA showed only weak agonistic action, and antagonized the estrogenic action of 17beta-estradiol when the two were coadministered. These data suggest that NDGA is an estrogenic agonist for ERalpha : ERE transcription and a mixed agonist/antagonist for ERbeta mediated ERE transactivation.