Short-Term Study Investigating the Estrogenic Potency of Diethylstilbesterol in the Fathead Minnow (Pimephales promelas)

Diethylstilbestrol (DES) is a synthetic estrogen that
has been
banned for use in humans, but still is employed in livestock and aquaculture
operations in some parts of the world. Detectable concentrations of
DES in effluent and surface waters have been reported to range from
slightly below 1 to greater than 10 ng/L. Little is known, however,
concerning the toxicological potency of DES in fish. In this study,
sexually mature fathead minnows (Pimephales promelas) of both sexes were exposed to 1, 10, or 100 ng of DES/L of water
in a flow-through system. Tissue concentrations of DES and changes
in a number of estrogen-responsive end points were measured in the
fish at the end of a 4 d exposure and after a 4 d depuration/recovery
period in clean water. Accumulation of DES was sex-dependent, with
females exhibiting higher tissue residues than males after the 4 d
exposure. The observed bioconcentration of DES in the fish was about
1 order of magnitude lower than that predicted on the basis of the
octanol–water partition coefficient of the chemical, suggesting
relatively efficient metabolic clearance by the fish. Exposure to
1, 10, or 100 ng of DES/L caused decreased testis weight and morphological
demasculinization of males (regression of dorsal nuptial tubercles).
Diethylstilbesterol induced plasma vitellogenin (VTG) in both sexes
at water concentrations ≥10 ng/L; this response (especially
in males) persisted through the end of the 4 d recovery period. Hepatic
transcripts of VTG and estrogen receptor-α also were affected
at DES concentrations ≥10 ng/L. Evaluation of transcript profiles
in the liver of females using a 15K-gene fathead minnow microarray
revealed a concentration-dependent change in gene expression, with
mostly up-regulated transcripts after the exposure and substantial
numbers of down-regulated gene products after depuration. Genes previously
identified as vitellogenesis-related and regulated by 17β-estradiol
were significantly enriched among those differentially expressed following
exposure to DES. Overall, our studies show that DES causes a range
of responses in fish at water concentrations comparable to those reported
in the environment and that in vivo potency of the estrogen is on
par with that of the better-studied estrogenic contaminant 17α-ethinylestradiol.

己烯雌酚（Diethylstilbestrol, DES）是一种合成雌激素，已被禁止用于人类，但在全球部分地区仍被应用于畜禽养殖与水产养殖作业。有研究报道，废水中及地表水中可检测到的DES浓度范围为略低于1ng/L至超过10ng/L。然而，目前关于DES对鱼类的毒理效力的认知仍较为匮乏。
在本研究中，研究人员将性成熟的雌雄胖头鲦鱼（Pimephales promelas）置于流水养殖系统中，使其暴露于1、10或100ng/L的DES水溶液中。在4天暴露结束后，以及在清洁水中经历4天净化/恢复周期后，检测了鱼类体内的DES组织浓度以及多项雌激素响应终点的变化。
DES的生物富集具有性别依赖性：4天暴露结束后，雌性鱼类的组织残留量高于雄性。本研究观测到的鱼类体内DES生物富集量较基于该化学品的辛醇-水分配系数（octanol–water partition coefficient）预测值低约一个数量级，这表明鱼类对DES的代谢清除效率相对较高。暴露于1、10或100ng/L的DES会导致雄性精巢重量降低，并引发形态学去雄性化反应（背侧生殖结节退化）。
当水体DES浓度≥10ng/L时，己烯雌酚可诱导雌雄鱼血浆中的卵黄蛋白原（vitellogenin, VTG）生成；该响应（尤其在雄性个体中）在4天净化周期结束后仍持续存在。当DES浓度≥10ng/L时，肝脏中VTG与雌激素受体α（estrogen receptor-α）的转录水平也会受到影响。
使用搭载15K个基因的胖头鲦鱼微阵列（microarray）对雌性肝脏的转录谱进行分析后发现，基因表达呈现浓度依赖性变化：暴露阶段主要为转录本上调，而净化阶段则有大量基因产物出现下调。此前已鉴定的与卵黄生成相关且受17β-雌二醇（17β-estradiol）调控的基因，在DES暴露后的差异表达基因中显著富集。
总体而言，本研究表明，在与环境中已报道浓度相当的水体DES浓度下，该物质会在鱼类体内引发一系列响应，且该雌激素的体内活性与研究较为充分的雌激素类污染物17α-乙炔基雌二醇（17α-ethinylestradiol）相当。