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

Toxicol Appl Pharmacol. 2001 Apr 15;172(2):108-18. doi: 10.1006/taap.2001.9141.

Abstract

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.

MeSH terms

  • Binding, Competitive
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cell Division / drug effects
  • Cytosol / metabolism
  • Estradiol / metabolism
  • Estradiol / toxicity
  • Estrogen Receptor Modulators / pharmacology
  • Estrogens, Non-Steroidal / metabolism*
  • Estrogens, Non-Steroidal / toxicity*
  • Gas Chromatography-Mass Spectrometry
  • Hippurates / pharmacology
  • Humans
  • Molecular Mimicry
  • Phthalic Acids / metabolism*
  • Phthalic Acids / toxicity*
  • Receptors, Estrogen / metabolism
  • Receptors, Progesterone / biosynthesis
  • Tamoxifen / pharmacology
  • Tumor Cells, Cultured

Substances

  • Estrogen Receptor Modulators
  • Estrogens, Non-Steroidal
  • Hippurates
  • Phthalic Acids
  • Receptors, Estrogen
  • Receptors, Progesterone
  • Tamoxifen
  • Estradiol
  • hippuric acid
  • butylbenzyl phthalate