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標題: | 不同價態鉈之穩定性與對青鱂魚毒性機制探討 Investigation of stability and toxicity mechanisms of monovalent and trivalent thallium to medaka (Oryzias latipes) |
作者: | Ching-Hsin Yang 楊景昕 |
指導教授: | 陳佩貞 |
關鍵字: | 一價鉈,三價鉈,青?魚,氧化壓力,次世代定序,一級代謝,膽固醇,皮質醇, Thallous [Tl(I)],Thallic [Tl(III)],Medaka (Oryzias latipes),Oxidative stress,Next generation sequencing,Phase I metabolism,Cholesterol,Cortisol, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 鉈 (Thallium, Tl) 為3A族之稀有元素,其對哺乳動物具高毒性,因而被美國環保署列為優先列管毒害污染物 (Priority pollutant)。鉈於水體環境中主要以一價Tl(I)及三價Tl(III)存在,Tl(III)具有高氧化還原電位,環境中應以Tl(I)為主要價態,然而部分文獻研究則指出三價鉈為表層水中主要之價態,然而目前對於三價鉈如何穩定存在於水中的原因仍不清楚。此外,關於鉈毒性之研究目前多以一價鉈為主,對於不同價態鉈之毒性研究有限。本篇研究首先探討Tl(III)在水中之穩定性與價數之動力變化,並以青鱂魚 (Oryzias latipes) 為模式生物探討不同價態鉈之毒性效應及致毒機制。Tl(III)在水中不穩定,24小時內多已還原成Tl(I),但< pH 5及添加DTPA (Diethylenetriaminepentaacetic acid) 可以有效穩定Tl(III)。本研究毒性試驗除Tl(I)及Tl(III)處理外,額外增加DTPA-Tl(III)處理組比較未穩定Tl(III)及穩定化Tl(III)的毒性差異。青鱂魚七日急毒性 (30-400 μg/L) 大小依序為Tl(I) > Tl(III) > DTPA-Tl(III)。氧化壓力指標則顯示Tl(I)及Tl(III)誘發氧化壓力的機制有所不同,Tl(I)及Tl(III)抑制CAT活性;Tl(III)及DTPA-Tl(III)抑制SOD活性;DTPA-Tl(III)則誘導MDA含量。滲透壓調節指標鈉鉀幫浦活性則是只受DTPA-Tl(III)所抑制。青鱂魚暴露14天不同鉈溶液 (15-30 μg/L) 後,生物累積性大小為Tl(I) > Tl(III) > DTPA-Tl(III),與七日急毒性具相同之趨勢。以次世代定序基因表達分析發現膽固醇生合成及一級代謝途徑相關基因表達可能會受到Tl(I) (50 μg/L) 所影響。以即時聚合酶連鎖反應進行基因表達分析 (15-30 μg/L) 則顯示一級代謝基因關cyp3a38及cyp3a40表達量顯著受到Tl(I)及Tl(III) 誘導,pxr則是受Tl(I)及Tl(III) 抑制。CYP1A活性則是顯著受到三種鉈處理所誘導。膽固醇合成重要指標基因hmgr顯著受到三種鉈處理誘導,但魚體膽固醇含量則無受到影響。固醇激素皮質醇 (Cortisol) 合成相關基因cyp21表達量受Tl(I)及Tl(III)抑制,代謝基因hsd11b2則受誘導,但魚體固醇激素皮質醇的含量則不受影響。綜合上述結果,Tl(I)相較於Tl(III)對青鱂魚有較高之急毒性及生物累積性,且皆會造成氧化壓力及誘導一級代謝途徑,但不同鉈物種對青鱂魚的毒性機制差異仍需更進一步研究。 Thallium (Tl) is a trace element with high toxicity to mammals and classified as a priority pollutant by the U.S. EPA. Tl exists in the environment as monovalent Tl(I) and trivalent Tl(III) states. Tl(I) is thought to be more thermodynamically stable than Tl(III); but, recent studies indicate that Tl(III) may persistently exist in surface water. However, environmental transformation between Tl(I) and Tl(III) and their toxicities to higher tropic levels of aquatic organisms such as fish remain unclear. In this study, we aim to understand the stability and redox dynamics of Tl(III) in EPA dilution water. The toxic effect of three different Tl species [Tl(I), Tl(III) and DTPA-Tl(III)] and associated modes of toxic action are investigated using medaka (Oryzias latipes). Tl(III) is unstable in EPA dilution water, but it can be stabilized in EPA dilution water of < pH 5 or with addtion of DTPA in EPA dilution water. Our results showed that Tl(I) and Tl(III) caused greatest and less acute mortality in medaka larvae and DTPA-Tl(III) had the least mortality with 7 day exposure at 30-400 μg/L. The MDA content was significantly induced in the DTPA-Tl(III) group. The CAT activity was suppressed in either Tl(I) or Tl(III) groups, whereas both Tl(III) and DTPA-Tl(III) suppressed the SOD activity. The osmoregulation biomarker Na-K ATPase was only suppressed by DTPA-Tl(III). After 14 day exposure to 3 Tl species (15-30 μg/L), the trend of Tl content in fish was similar to acute mortality. Next generation sequencing (NGS) differential gene expression (DGE) profiles showed that Tl(I) (50 μg/L) significantly induced alteration in cholesterol synthesis, steroid hormone metabolism and phase I metabolism related genes. These Tl-induced transcriptional alteration was confirmed by qPCR analysis and related enzymatic assays. Phase I metabolism related gene (cyp3a38 and cyp3a40) expression were significantly induced by Tl(I) and Tl(III). However, pxr was significantlty suppressed by Tl(I) and Tl(III). The CYP1A activity was also induced in three kinds of Tl treatment. Cholesterol synthesis related gene (hmgr) expression was significantly induced by three Tl species, but cholesterol content in fish body was not altered by all treatments. Tl(I) and Tl(III) suppressed steroid hormone cortisol synthesis related gene (cyp21) expression, but induced degradation gene (hsd11b), whereas cortisol content in fish body was not altered. In the summary, Tl(I) has higher acute toxicity and bioaccumulation potential to medaka than Tl(III). Both Tl(I) and Tl(III) induce oxidative stress and phase I metabolism, but they may have different toxicity mechanisms which need for further investigation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/67448 |
DOI: | 10.6342/NTU201702469 |
全文授權: | 有償授權 |
顯示於系所單位: | 農業化學系 |
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