Estrogenic activity and metabolism of N-butyl benzyl phthalate in vitro: Identification of the active molecule(s)

Some phthalates are suspected to disrupt the endocrine system, especially b y mimicking estrogens. N-butyl benzyl phthalate (BBP) has estrogenic effect s in vitro but not in vivo. The aim of this study was to identify the activ e molecule(s) (parent compound and/or metabolite(s)) involved in the estrog enic activities of BBP. The estrogenic effects of BBP and its in vivo metab olites were assessed using the following tests: E-Screen, ER binding, and P R induction tests on the human breast cancer cell line MCF-7 (ER+). BBP, th e parent compound, was a partial agonist. It stimulated MCF-7 proliferation in the E-Screen assay and increased cytosolic progesterone receptors (PR) levels in a concentration-dependent manner. No BBP metabolites were active except hippuric acid (HA), which had a weak effect at very high concentrati ons. BBP and HA stimulatory effects on MCF-7 proliferation were antagonized by tamoxifen. However, no competition was observed between BBP or HA and 1 7 beta -estradiol for binding to the estrogen receptor (ER). BBP metabolism by MCF-7 cells was also investigated. After a 48-h incubation, only 10% of the initial BBP remained in the culture medium, demonstrating that BBP was extensively metabolized by the MCF-7 cells. The radioactivity recovered in the medium was represented by: mono-n-butyl phthalate (MBuP, 25%) and mono -n-benzyl phthalate (MBeP, 48%), phthalic acid (6%), and benzoic acid (3%). Since none of these metabolites had estrogenic activities, this study demo nstrates that the parent compound was the active molecule involved in the i n vitro estrogenic effects of BBP. (C) 2001 Academic Press.