Evaluation of the alcohol-related cancer using aldehyde dehydrogenase 2 knock-out mice exposed to acetaldehyde or ethanol.

前言：乙醛脱氢酶-2(ALDH2)将乙醇生成的乙醛代谢成乙酸乙酯，在体内乙醛的氧化过程中起着重要作用。一半的日本人患有不活跃的ALDH2。我们通过基因打靶的方法获得了ALDH2缺失(ALDH2 KO)小鼠。为了研究乙醛的致突变性，对ALDH2KO小鼠和野生型(ALDH2WT)小鼠进行了乙醛和乙醇的体内微核试验和T细胞受体基因突变试验。方法：将扩散管产生的乙醛引入不锈钢曝光室(体积为100 L)的顶部。小鼠连续两周暴露于500ppm乙醛蒸气或100 mg/kg po。染毒后立即处死小鼠，用流式细胞仪检测网织红细胞微核率。结果：乙醛暴露后，ALDH2 KO小鼠网织红细胞微核率显著增加，而ALDH2 WT小鼠微核率无明显变化。此外，ALDH2 KO小鼠的微核率、TCR突变率和尿8-羟基-2‘-脱氧鸟苷(8OHdG)水平均显著高于ALDH2 WT小鼠，即使在对照组也是如此。我们还观察了100 mg/kg乙醛对ALDH2 KO小鼠TCR突变的促进作用。讨论：在MN试验中，ALDH2 KO小鼠对乙醛的敏感性高于ALDH2 WT小鼠。这意味着酒精饮用者没有ALDH活性，会增加致癌风险。即使在对照组，ALDH2 KO小鼠的MN和TCR基因突变也显著高于ALDH2 WT小鼠。这些结果表明，ALDH2不仅在乙醛解毒中发挥重要作用，而且在小鼠的氧化应激中也起着重要作用。

Introduction : Aldehyde dehydrogenase-2 (ALDH2) metabolizes acetaldehyde produced from ethanol into acetate and plays a major role in the oxidation of acetaldehyde in vivo. Half of Japanese have inactive ALDH2. We generated Aldh2 null (Aldh2 KO) mice by gene targeting knockout. In order to investigate the mutagenicity of acetaldehyde, micronucleus (MN) assay and T cell receptor (TCR) gene mutation assay were performed in Aldh2 KO mice and wild type (Aldh2 WT) mice exposed to acetaldehyde or ethanol in vivo.Methods : Acetaldehyde vapor, obtained by a diffusion tube, was introduced into the top of an exposure chamber (volume 100 l) made of stainless steel. The mice were exposed to 500ppm acetaldehyde vapour or 100mg/kg po for two weeks continuously. Just after exposure, mice were sacrificed and the frequency of micronucleated reticulocytes was measured by flowcytometry. We also observed the incidence of TCR gene mutation in T-lymphocytes evaluated by measuring the variant CD3^-4^+ expression by flowcytometry.Results : Frequencies of micronuclei in reticulocytes significantly increased by acetaldehyde exposure in Aldh2 KO mice, but not in Aldh2 WT mice. In addition, frequencies of micronuclei, TCR mutation, and 8-hydroxy-2'-deoxyguanosine (8OHdG) levels in urine were significantly high in Aldh2 KO mice than in Aldh2 WT mice even in control groups. We also observed the increase of TCR mutation in Aldh2 KO mice administered acetaldehyde at the dose of 100mg/kg.Discussion : In the MN assay, Aldh2 KO mice showed the high sensitivity compared to Aldh2 WT mice, when exposed to acetaldehyde. It means that alcohol drinkers, who have no ALDH activity, increase the risk of carcinogenesis. Aldh2 KO mice also showed significantly high in MN and TCR gene mutation compared to Aldh2 WT mice even in control. These results indicate that Aldh2 plays a major role not only in acetaldehyde detoxification but also in oxidative stress in mice.