Nagel S C, vom Saal F S, Welshons W V
Division of Biological Sciences, University of Missouri-Columbia, 65211, USA.
J Steroid Biochem Mol Biol. 1999 Apr-Jun;69(1-6):343-57. doi: 10.1016/s0960-0760(99)00078-3.
Many estrogenic chemicals found in the environment (xenoestrogens) show a lower affinity for plasma estrogen binding proteins relative to the natural estrogens such as estradiol. These binding proteins, which include alphafetoprotein in rats and mice, sex hormone binding globulin in humans, and albumin in all species, regulate estrogen uptake into tissues. Therefore, the in vivo estrogenic potency relative to estradiol of xenoestrogens that show lower binding to these serum proteins will thus be underestimated in assays that compare the potency of xenoestrogens to estradiol and do not take serum binding into account. We have examined the effects of the binding components in serum on the uptake of a number of xenoestrogens into intact MCF-7 human breast cancer cells. Since most estrogenic chemicals are not available in radiolabeled form, their uptake is determined by competition with [3H]estradiol for binding to estrogen receptors (ER) in an 18-h assay. Serum modified access (SMA) of cell uptake of xenoestrogens is calculated as the RBA in serum-free-medium divided by the RBA in serum, and the bioactive free fraction of xenoestrogen in serum is then also calculated. We predicted the concentration of two xenoestrogens, bisphenol A and octylphenol, required to alter development of the prostate in male mouse fetuses. Whereas octylphenol was predicted to be a more potent estrogen than bisphenol A when tested in serum-free medium, our assay predicted that bisphenol A would be over 500-times more potent than octylphenol in fetal mice. The finding that administration of bisphenol A at a physiologically relevant dose predicted from our in vitro assay to pregnant mice from gestation day 11 to 17 increased adult prostate weight in male offspring relative to controls (similar to the effect of estradiol), while the same doses of octylphenol did not alter prostate development, provided support for our hypothesis.
环境中发现的许多具有雌激素活性的化学物质（外源性雌激素）与血浆雌激素结合蛋白的亲和力相对于天然雌激素（如雌二醇）较低。这些结合蛋白包括大鼠和小鼠体内的甲胎蛋白、人类的性激素结合球蛋白以及所有物种体内的白蛋白，它们调节雌激素进入组织的过程。因此，在比较外源性雌激素与雌二醇的效力且未考虑血清结合情况的检测中，与这些血清蛋白结合能力较低的外源性雌激素相对于雌二醇的体内雌激素活性会被低估。我们研究了血清中的结合成分对多种外源性雌激素进入完整的MCF-7人乳腺癌细胞的摄取的影响。由于大多数具有雌激素活性的化学物质没有放射性标记形式，它们的摄取是通过在18小时的检测中与[3H]雌二醇竞争结合雌激素受体（ER）来确定的。外源性雌激素细胞摄取的血清修饰通路（SMA）通过无血清培养基中的相对结合活性（RBA）除以血清中的RBA来计算，然后还可计算血清中外源性雌激素的生物活性游离部分。我们预测了改变雄性小鼠胎儿前列腺发育所需的两种外源性雌激素双酚A和辛基酚的浓度。在无血清培养基中测试时，辛基酚被预测为比双酚A更有效的雌激素，但我们的检测预测在胎儿小鼠中双酚A的效力比辛基酚高500倍以上。从我们的体外检测预测，在妊娠第11天至17天给怀孕小鼠施用生理相关剂量的双酚A，相对于对照组增加了雄性后代的成年前列腺重量（类似于雌二醇的作用），而相同剂量的辛基酚并未改变前列腺发育，这一发现为我们的假设提供了支持。
