Abstract
對砷化物敏感的細胞株D21 ，是Sun(1993)以無機三價砷化物(As II)處理 CHO-K1細胞後，再以BUdR-light的方法，所篩選出來的敏感細胞株。由細 胞群落形成法得知此篩選得之敏感細胞株D21，以無機三價砷處理 4小時 較CHO-K1敏感7倍(結果由LD50比值估計)。 除此之外，對無機三價砷化物 的代謝產物--有機砷化物DMA(Dimethylarsenicacid)並不特別敏感，其敏 感程度與母細胞株CHO-K1相似。處理無機三價砷化物的時間到24小時，發 現D21細胞對於無機三價砷化物的敏感性更加提高。已發表的研究報告認 為：三價及五價無機砷化物，會經由生物體內甲基轉移酵素(Methylt ansferase，MT) 的作用，而代謝成較不具毒性的有機態砷化物MMA (Monoethylarsonic acid)及DMA 。D21~化物敏感，而對有機 砷化物DMA 伅□W長增加敏感性，表示此細胞可能無法有效的將無機砷化物甲基化。 細胞對抗砷毒性的第一道防線，已知與麩胱甘胜(glutathione,SH)的含量 及麩胱甘胜轉移酵素 (glutathione S-transferase, GST)的活呇釩颩垠n 的關係。 本研究發現前兩者不論在細胞內的含量或經由無機三顴~四小時 處理後的含量均無太大差異。 另一種抗活性氧的酵素--過氧化B酵素( catalase) 也與其母細胞株沒有差異。使用甲基轉移酵素MT的抑制烈AD (peroxidate-oxidized adenosine)處理D21與母細胞株CHO-K1 ，檢d兩者 的甲基轉移酵素是否有差異。我們發現敏感細胞株對三價無機砷化物的敏 感程度，並不會受外加抑制劑PAD的影響。但是在母細胞株，則會隨著抑 制劑加入濃度的升高 ，對三價無機砷化物的敏感程度，也隨之增加。這 個結果建議 ：甲基轉移酵素MT，對三價無機砷化物的解毒是很重要的， 而敏感細胞株D21，由於可能進行甲基化的功能較差，所以加入PAD並不會 明顯改變其對無機砷化物的敏感程度。 The sensitive cell line, D21 cells were isolated by meansf a modified cell suicide method through ethylnitrosourea(ENU)tagen treatment in Chinese hamster ovary (CHO-K1) cells. Thesels showed 7-fold susceptibility to sodium arsenite (SA) thanK1 cells by calulating LD50 values. Besides, the D21 cellsed markedly cross-sensitive to mercury chloride. They chloride had several charact eristics resemble to SA,including oxidative stress and methylationmation within cells. There were no significantetween D21 and CHO-K1 cells in the sensitivity tots (UV,r-ray, methyl methanesulfonate), freeor (H2O2), and heavy metal (FeSO4). From previous studies, two major SA detoxificationathways were processed in cells. One of them was methylated tonomethylarsonic acid and dimethylarsenic acid (DMA) byenosyl-methionine dependent methyltransferase, theselisms were less toxic than SA. The second pathway wasione (GSH) level and glutathione S-transferase (GST)were convened as to protect cells against arsenico signigicant different GSH level and GST activity werehese two cell lines. Although, D21 cells were, both of these cells owned the similarDMA, the one of arsenic metabolites. In thehyltransferaseinhibitor (periodate oxidizedincrease of SA cytotoxicity was observed in CHO-K1in D21 cells. Since the methylation biotransformation is important for SAetoxification in cells, these results suggested that D21 cellsnot methylate inorganic arsenic efficiently or partially losehylation activity.