Data from: Metabolites of n-Butylparaben and iso-Butylparaben exhibit estrogenic properties in MCF-7 and T47D human breast cancer cell lines

Two oxidized metabolites of n-butylparaben (BuP) and iso-butylparaben (IsoBuP) discovered in human urine samples exhibit structural similarity to endogenous estrogens. We hypothesized that these metabolites bind to the human estrogen receptor (ER) and promote estrogen signaling. We tested this using models of ER-mediated cellular proliferation. The estrogenic properties of 3-hydroxy n-butyl 4-hydroxybenzoate (3OH) and 2-hydroxy iso-butyl 4-hydroxybenzoate (2OH) were determined using the ER-positive, estrogen-dependent human breast cancer cell lines MCF-7, and T47D. The 3OH metabolite induced cellular proliferation with EC50 of 8.2 µM in MCF-7 cells. The EC50 for 3OH in T47D cells could not be reached. The 2OH metabolite induced proliferation with EC50 of 2.2 µM and 43.0 µM in MCF-7 and T47D cells, respectively. The EC50 for the parental IsoBuP and BuP was 0.30 and 1.2 µM in MCF-7 cells, respectively. The expression of a pro-proliferative, estrogen-inducible gene (GREB1) was induced by these compounds and blocked by co-administration of an ER antagonist (ICI 182, 780), confirming the ER-dependence of these effects. The metabolites promoted significant ER-dependent transcriptional activity of an ERE-luciferase reporter construct at 10 and 20 µM for 2OH and 10 µM for 3OH. Computational docking studies showed that the paraben compounds exhibited the potential for favorable ligand-binding domain interactions with human ERα in a manner similar to known x-ray crystal structures of 17ß-estradiol in complex with ERα. We conclude that the hydroxylated metabolites of BuP and IsoBuP are weak estrogens and should be considered as additional components of potential endocrine disrupting effects upon paraben exposure.本研究在人体尿液样本中发现的尼泊金正丁酯（n-butylparaben, BuP）与尼泊金异丁酯（iso-butylparaben, IsoBuP）的两种氧化代谢产物，其结构与内源性雌激素具有高度相似性。我们提出假说：此类代谢物可结合人类雌激素受体（estrogen receptor, ER）并激活雌激素信号通路。为验证该假说，我们采用雌激素受体介导的细胞增殖模型开展了系列实验。 本研究通过ER阳性、雌激素依赖型人乳腺癌细胞系MCF-7与T47D，测定了3-羟基对羟基苯甲酸正丁酯（3-hydroxy n-butyl 4-hydroxybenzoate, 3OH）与2-羟基对羟基苯甲酸异丁酯（2-hydroxy iso-butyl 4-hydroxybenzoate, 2OH）的雌激素活性。结果显示，3OH代谢物在MCF-7细胞中可诱导细胞增殖，半数效应浓度（EC50）为8.2 μM；而在T47D细胞中未测得3OH的EC50值。2OH代谢物则分别在MCF-7和T47D细胞中诱导细胞增殖，其EC50值依次为2.2 μM与43.0 μM。原型化合物IsoBuP与BuP在MCF-7细胞中的EC50值分别为0.30 μM与1.2 μM。 此类化合物可诱导促增殖型雌激素诱导基因GREB1的表达，且该效应可被雌激素受体拮抗剂ICI 182,780联合给药所阻断，证实了上述效应的雌激素受体依赖性。此外，在10 μM与20 μM浓度下（2OH）、10 μM浓度下（3OH），代谢物均可显著激活雌激素反应元件（estrogen response element, ERE）-荧光素酶报告基因载体的ER依赖性转录活性。分子对接研究表明，尼泊金酯类化合物可与人类雌激素受体α（ERα）的配体结合域形成稳定相互作用，其结合模式与已知的17β-雌二醇与ERα复合物的X射线晶体结构高度相似。 综上，本研究证实BuP与IsoBuP的羟基化代谢物属于弱雌激素类物质，在接触尼泊金酯类物质时，这类代谢物应被视为潜在内分泌干扰效应的额外贡献组分。