亞砷酸鈉增加人類細胞活性氧的壓迫

Abstract

砷是廣泛的分佈於自然界中的一種重金屬元素，它也是生命體內微量的必需元素。流行病學的研究指出，慢性砷暴露能增加人類某些疾病及癌症的機率。關於砷的致毒性及致癌性也一直被深入的研究，但真正的作用機制尚不清楚。許多研究結果指出，遊離基的產生可能參與其間，例如：砷增加脂肪的過氧化；及在砷處理的細胞內，姊妹染色體互換頻率的增加能被抗氧化物catalase及SOD減少等。我們的結果發現，砷處理過的KB細胞內，砷能增加80％ GSH的含量；且能隨砷處理劑量的增加，誘發heme oxygenase蛋白質的合成，然而heme oxygenase的抑制劑SnPP能增加砷處理細胞的毒性；且發現在砷處理的細胞內，誘發的heme oxygenase能在後處理SnPP的過程中，迅速的被破壞；另外，砷不會改變SOD的活性，但能減少40％ catalase的活性。在不同時間的砷處理KB細胞內發現，砷處理能在前4小時迅速的增加GSH的含量；4到6小時有最大的增加Heme oxygenase合成；然而catalase的活性能隨處理時間的增加而減少。從這些結果顯示，砷能擾亂細胞內抗氧化物的表現；且誘發性的Heme oxygenase在砷處理的細胞內，可能扮演一種保護的角色。 進一步的利用DCF螢光分析儀測量細胞內過氧化氫的含量，結果顯示砷能增加過量的過氧化氫堆積於人類口腔表皮癌細胞（KB cell）及淋巴球癌細胞（HL60 cell）。此外catalase不能顯著提升砷處理細胞的存活率；從以上的結果顯示，砷可擾亂細胞內抗氧化物的表現；且能造成過氧化氫的堆積；而過氧化氫的堆積可能與砷的細胞毒性無關。

Many experimental evidences have supported that arsenite-induced toxicity is associated with the generation of free radicals, e.g. arsenic induces lipid peroxidation, sister chromatid exchanges, heme oxygenase (HO), glutathione S-transferase and glutathione (GSH). In our experiments, antioxidants were assessed in arsenite-treated KB cells. GSH contents was increased to 180% of the control and it was rapidly increased during early 4 h treatment. HO was induced in a dose-dependent way and the maximal induction of HO was observed during 4 to 6 h treatment. Moreover, tin-protoporphyrin (SnPP), an HO inhibitor, can enhanced the cytotoxicity of arsenite, indicating that HO may play an important role in reducing the cytotoxicity of arsenite. In arsenite-treated KB cells, induced HO can be degraded very rapidly by posttreatment of SnPP. Superoxide dismutase (SOD) activity was not changed. Catalase activity was decreased to 60% of the control and it was decreased by time-dependently. These results indicated that arsenite may result in the imbalance of free radicals in cells. In addition, our results have also shown that arsenite can induce the accumulation of H2O2 in human KB and HL60 cells by using dichlorofluorescein (DCF) fluorescence spectrophotometry. However, the survival of arsenite-treated cells can not be notablely raised by catalase. These results suggested that arsenite may caused disturbances of cellular antioxidants and result in the accumulation of H2O2 which may not involved in arsenite cytotoxicity.