Some phthalates are suspected to disrupt the endocrine system, especially by mimicking
estrogens. N-
butyl benzyl phthalate (
BBP) has
estrogenic effects in vitro but not in vivo. The aim of this study was to identify the active molecule(s) (parent compound and/or metabolite(s)) involved in the estrogenic activities of
BBP. The
estrogenic effects of
BBP and its in vivo metabolites were assessed using the following tests: E-Screen, ER binding, and PR induction tests on the human
breast cancer cell line MCF-7 (ER(+)).
BBP, the 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 concentrations.
BBP and HA stimulatory effects on MCF-7 proliferation were antagonized by
tamoxifen. However, no competition was observed between
BBP or HA and 17beta-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 demonstrates that the parent compound was the active molecule involved in the in vitro
estrogenic effects of
BBP.