Department of Biochemistry and Microbiology, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada.
Arch Environ Contam Toxicol. 2021 May;80(4):735-744. doi: 10.1007/s00244-021-00838-y. Epub 2021 Mar 31.
Nonnutritive sweeteners used in food and beverage products are widespread, persistent aquatic pollutants. Despite this, their impact on aquatic organisms, particularly vertebrates, is not well-studied. Recent findings in rodents suggest sucralose, a chlorinated disaccharide, alters thyroid hormone (TH) metabolism. Because amphibian tadpole metamorphosis is TH-dependent, we hypothesized sucralose may alter signaling for this postembryonic developmental process. The present study used the American bullfrog, Rana (Lithobates) catesbeiana, as a sensitive, environmentally relevant model for testing TH disruption in the absence and presence of thyroxine (T), a hormone that induces metamorphosis. Premetamorphic R. catesbeiana tadpoles were immersed in 1-, 15-, and 32-mg/L sucralose solutions ± 5 nM (3.9 µg/L) thyroxine (T) for 48 h. RNA transcripts encoding thyroid hormone receptors alpha and beta (thra and thrb) and TH-induced basic region leucine zipper protein (thibz) were analyzed in four tissues: back skin, liver, olfactory epithelium, and tail fin, using reverse transcription quantitative real-time PCR (RT-qPCR). We found that sucralose altered the expression of fundamental TH-response genes involved in anuran metamorphosis in a tissue- and TH-status dependent manner. As organochlorines induce xenobiotic metabolism, we isolated and characterized three novel R. catesbeiana gene transcripts involved in xenobiotic metabolism: pregnane X receptor (nr1i2), constitutive androstane receptor (nr1i3), and cytochrome p450 3a4 (cyp3a4). We analyzed their expression using RT-qPCR and found evidence of their modulation by sucralose. To our knowledge, these data are the first to show xenobiotic and thyroid-disrupting activities in amphibians and further investigations into cumulative effects of environmental sucralose exposure are warranted.
食品和饮料产品中使用的非营养性甜味剂是广泛存在且持久的水生污染物。尽管如此，它们对水生生物，特别是脊椎动物的影响尚未得到充分研究。最近在啮齿动物中的发现表明，三氯蔗糖（一种氯化二糖）会改变甲状腺激素（TH）代谢。由于两栖动物蝌蚪变态是 TH 依赖性的，我们假设三氯蔗糖可能会改变这个胚胎后发育过程的信号。本研究使用美国牛蛙（Rana (Lithobates) catesbeiana）作为一种敏感且具有环境相关性的模型，用于测试在缺乏和存在甲状腺素（T）的情况下 TH 破坏的情况，T 是一种诱导变态的激素。在 48 小时内，将处于前变态期的 R. catesbeiana 蝌蚪浸入 1、15 和 32mg/L 三氯蔗糖溶液中，同时加入 5nM（3.9µg/L）甲状腺素（T）。使用逆转录定量实时 PCR（RT-qPCR）分析了四个组织（背部皮肤、肝脏、嗅上皮和尾鳍）中编码甲状腺激素受体 alpha 和 beta（thra 和 thrb）和 TH 诱导的碱性亮氨酸拉链蛋白（thibz）的 RNA 转录物。我们发现，三氯蔗糖以组织和 TH 状态依赖的方式改变了参与无尾目变态的基本 TH 反应基因的表达。由于有机氯会诱导外源性代谢，我们分离并鉴定了三个涉及外源性代谢的新的 R. catesbeiana 基因转录物：孕烷 X 受体（nr1i2）、组成型雄烷受体（nr1i3）和细胞色素 P450 3a4（cyp3a4）。我们使用 RT-qPCR 分析了它们的表达，并发现了三氯蔗糖对它们的调节证据。据我们所知，这些数据是首次表明外源性代谢和甲状腺破坏活性在两栖动物中的作用，并且需要进一步研究环境中三氯蔗糖暴露的累积效应。
