在多細胞生物的生長發育和維持恆定的過程中，細胞死亡和細胞增生具有相同的重要性。細胞凋亡是一種擁有獨特生化機制和形態變化的細胞死亡模式，又稱為細胞程式化死亡。細胞凋亡可以防止變異或不需要的細胞增生，但在調控機轉異常情況下，將導致細胞不受控制的增長，這也是癌症難以治療的原因。
乙醇是酒精飲料中主要的成分，在人體飲入的乙醇主要是經由醇及醛脫氫酶 (ADH、ALDH) 所分解代謝，兩種酶族在細胞中扮演解毒酶的角色，它們均有多種同功酶存在，在組織的活性和表現與乙醇的代謝效應有關，並進而影響乙醇對器官傷害的發生。乙醇會抑制細胞正常的生理功能與細胞生長，促使細胞走向凋亡的路徑；乙醇代謝的產物乙醛，是主要具有細胞毒性與致癌性的化合物，它可以與DNA共價形成加成產物，誘發基因突變；另外，乙醇氧化時，所產生的氧化壓力傷害也會影響與細胞凋亡相關基因的表現。
本研究目的為以人類口腔癌細胞 (OEC-M1) 及皮膚角化細胞 (HaCaT) 為實驗對象，探討經乙醇處理後，乙醇與其代謝產物乙醛及代謝過程產生之氧化壓力，所造成的細胞凋亡效應。並進一步了解代謝過程中ADH及ALDH在細胞凋亡效應下所扮演的角色。
聚丙烯醯胺膠等電焦集電泳、西方點墨法結果顯示人類口腔癌細胞在ADH酶族中主要表現ADH4；在ALDH酶族方面，ALDH2為主要表現型，ALDH3A1次之，ALDH1A1則最弱。西方點墨法分析，發現乙醇會誘使細胞產生凋亡反應，其中HaCaT 細胞凋亡蛋白表現量相較於OEC-M1來的高。另外在加入ADH及ALDH抑制劑後，結果顯示細胞代謝過程主要是由於乙醛的堆積造成細胞產生凋亡反應。螢光冷光儀分析結果顯示乙醇氧化代謝所產生的活性氧化物，會造成細胞受到氧化壓力的傷害，進而產生細胞凋亡效應。特別在細胞經乙醇處理後並抑制ALDH代謝條件下，有大量的活性氧化物產生，細胞凋亡蛋白大量的表現。然而這個機轉會因為加入活性氧化物清除劑 (Dithiothreitol, DTT) 而受到抑制，因此，研究結果顯示針對OEC-M1、HaCaT這兩株細胞中，乙醇經由ADH代謝成乙醛會產生氧化壓力並對細胞產生凋亡反應，而乙醛的堆積亦是主要誘導細胞產生凋亡反應的原因。

Apoptosis, also known as programmed cell death, plays an important role to maintain the proper numbers and type of cells. It is belived that cancer cells not only gain DNA mutation but also are resistant to apoptosis. Ethanol is the main ingredient of alcoholic beverages. Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the main enzymes responsible for ethanol metabolism. Ethanol can inhibit cell growth and physiological functions of cells and further induce apoptosis. Acetaldehyde, the major metabolic intermediate of ethanol, is the main cytotoxic and carcinogenic molecule to trigger the formation to DNA adducts and DNA mutation. Therefore ethanol could play a crucial role in oral cancer formation.
The purpose of this thesis is focusing on the effects driven by ethanol and its metabolites in oral cancer cells. Our results demonstrate that ADH4 and ALDH2 are the major isozymes in oral cancer cells (OEC-M1) by isoelectric focusing and western blotting. ALDH1A1 and ALDH3A1 also are detected weakly in OEC-M1. Western blot showed that ethanol can induce cells to undergo apoptosis, however the percentage of apoptosis is higher in HaCaT cells than in OEC-M1 cells. When adding ADH and ALDH inhibitors, the accumulation of acetaldehyde could enhance the amount of apoptosis. Fluorescent analysis results also indicate that ROS is induced by ethanol and further induce apoptosis in OEC-M1 and HaCaT cells because of oxidative stress. Especially, after treatment of ethanol and ADH inhibitor, there will be a dramatic elevation of reactive oxidative species and apoptosis. However, the induction can be suppressed by ROS scavenger (Dithiothreitol, DTT). We conclude that in OEC-M1 and HaCaT cells, ethanol can induce cells to undergo apoptosis through ROS which is generated by ethanol and its metabolite, acetaldehyde.

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