title: Oestrogenic activity of isobutylparaben in vitro and in vivo.
abstract: The alkyl esters of p-hydroxybenzoic acid (parabens) are used widely as preservatives in foods, pharmaceuticals and cosmetics to which the human population is exposed. Recent studies have reported that methylparaben, ethylparaben, n-propylparaben and n-butylparaben all possess oestrogenic activity in several in vitro assays and in animal models in vivo. This study reports on the oestrogenic activity of isobutylparaben in a panel of assays in vitro and in vivo. Isobutylparaben was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor alpha of MCF7 human breast cancer cells by 81% at 100 000-fold molar excess. Using a clonal line of MCF7 cells containing a stably transfected oestrogen-responsive ERE-CAT reporter gene, CAT gene expression could be increased by isobutylparaben such that the magnitude of the response was the same at 10(-5) M isobutylparaben as with 10(-8) M 17beta-oestradiol. Isobutylparaben could also increase expression of the endogenous oestrogen-responsive pS2 gene in MCF7 cells and maximal expression at 10(-5) M isobutylparaben could be inhibited with the anti-oestrogen ICI 182 780. The proliferation of two oestrogen-dependent human breast cancer cell lines MCF7 and ZR-75-1 could be increased with isobutylparaben such that at concentrations of 10(-5) M the proliferation response was of the same magnitude as with 10(-8) M 17beta-oestradiol. Evidence for oestrogen receptor mediation of proliferation effects was provided by the inability of isobutylparaben to influence the growth of oestrogen-unresponsive MDA-MB-231 human breast cancer cells and by the ability of the anti-oestrogen ICI 182 780 to inhibit the isobutylparaben effects on MCF7 cell growth. The proliferation response to 10(-10) M 17beta-oestradiol was not antagonized with isobutylparaben at any concentration from 10(-9) M to 10(-4) M in either MCF7 or ZR-75-1 cells. Finally, subcutaneous administration of isobutylparaben was able to increase the uterine weight in the immature mouse after three daily doses of 1.2 or 12.0 mg per mouse. Previous work using linear-alkyl-chain parabens has shown that oestrogenic activity increases with alkyl chain length from methylparaben to n-butylparaben. The results here show that branching of the alkyl chain to isobutylparaben increases oestrogenic activity beyond that of the equivalent length linear alkyl chain in n-butylparaben.
authors.affiliation: Division of Cell and Molecular Biology, School of Animal and Microbial Sciences, University of Reading, UK. p.d.darbre@reading.ac.uk
authors.forename: P D
authors.initials: PD
authors.lastname: Darbre
authors.forename: J R
authors.initials: JR
authors.lastname: Byford
authors.forename: L E
authors.initials: LE
authors.lastname: Shaw
authors.forename: R A
authors.initials: RA
authors.lastname: Horton
authors.forename: G S
authors.initials: GS
authors.lastname: Pope
authors.forename: M J
authors.initials: MJ
authors.lastname: Sauer
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism; D002455:Cell Division; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D004968:Estrogens, Non-Steroidal / Q000037:antagonists & inhibitors / Q000633:toxicity*; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008024:Ligands; D051379:Mice; D008815:Mice, Inbred Strains; D009929:Organ Size / Q000187:drug effects; D010226:Parabens / Q000633:toxicity*; D011485:Protein Binding; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011960:Receptors, Estrogen / Q000378:metabolism; D000071163:Trefoil Factor-1; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins; D014599:Uterus / Q000187:drug effects / Q000473:pathology
chemical_list: D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D004968:Estrogens, Non-Steroidal; D008024:Ligands; D010226:Parabens; D011506:Proteins; D012333:RNA, Messenger; D011960:Receptors, Estrogen; C051838:TFF1 protein, human; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; C471067:isobutylparaben; D000077267:Fulvestrant; D004958:Estradiol