Delker D A, McKnight S J, Rosenberg D W
Department of Pharmaceutical Sciences, University of Connecticut, Storrs 06269-2092, USA.
Toxicol Sci. 1998 Sep;45(1):66-71. doi: 10.1006/toxs.1998.2499.
The aim of this study was to determine whether the cytosolic enzyme alcohol dehydrogenase (ADH) activates methylazoxymethanol (MAM) in the mouse colon and whether differential tumor susceptibility in the mouse is dependent, in part, on strain-related differences in MAM metabolism by ADH. Liver and colon cytosols were isolated from 7-week-old male tumor-susceptible (SWR/J) and -resistant (AKR/J) mice. Minimal reduction of NAD+ was found in colon cytosols from AKR/J mice at the highest concentration (2 mM) of MAM tested. In liver cytosols, only SWR was capable of sustaining NAD+ reduction with MAM, although at very low levels. Despite minimal reactivity with MAM, however, mouse cytosols did effectively reduce NAD+ in the presence of the common ADH subrates ethanol and benzyl alcohol. NAD(+)-coupled oxidation of benzyl alcohol was significantly higher (two- to three-fold, p < 0.05) in mouse colon cytosols compared to activity present within corresponding rat tissues. Incubation of colon and liver cytosols with the ADH-3 inhibitor 4-methylpyrazole markedly (95-100% of controls) reduced ethanol oxidation in both strains. However, 4-methylpyrazole was a less effective inhibitor of benzyl alcohol oxidation in AKR/J colons, suggesting a different ADH isoform complement. An opposite inhibition pattern of benzyl alcohol oxidation was seen in the liver, where 4-methylpyrazole produced a greater inhibition in SWR/J mice. These studies suggest that the metabolism of the proximate mutagen MAM occurs by processes in the mouse that are independent of ADH.
本研究的目的是确定胞质酶乙醇脱氢酶（ADH）是否在小鼠结肠中激活甲基偶氮甲醇（MAM），以及小鼠中不同的肿瘤易感性是否部分取决于ADH对MAM代谢的品系相关差异。从7周龄雄性肿瘤易感（SWR/J）和抗性（AKR/J）小鼠中分离出肝脏和结肠胞质溶胶。在测试的最高浓度（2 mM）的MAM下，AKR/J小鼠的结肠胞质溶胶中NAD+的还原极少。在肝脏胞质溶胶中，只有SWR能够用MAM维持NAD+的还原，尽管水平非常低。然而，尽管与MAM的反应性极小，但在常见的ADH底物乙醇和苯甲醇存在的情况下，小鼠胞质溶胶确实有效地还原了NAD+。与相应大鼠组织中的活性相比，小鼠结肠胞质溶胶中苯甲醇的NAD(+)-偶联氧化显著更高（两到三倍，p < 0.05）。用ADH-3抑制剂4-甲基吡唑孵育结肠和肝脏胞质溶胶，显著（对照组的95-100%）降低了两个品系中的乙醇氧化。然而，4-甲基吡唑对AKR/J结肠中苯甲醇氧化的抑制作用较小，表明ADH同工型组成不同。在肝脏中观察到苯甲醇氧化的相反抑制模式，其中4-甲基吡唑在SWR/J小鼠中产生了更大的抑制作用。这些研究表明，近端诱变剂MAM的代谢在小鼠中通过与ADH无关的过程发生。
