Kawamoto T, Hobara T, Kobayashi H, Iwamoto S, Sakai T, Takano T, Miyazaki Y
Pharmacol Toxicol. 1987 May;60(5):325-9. doi: 10.1111/j.1600-0773.1987.tb01519.x.
Chloral hydrate (CH), an intermediate metabolite of trichloroethylene, is reduced to trichloroethanol (TCE) by alcohol dehydrogenase and aldehyde reductase, and is also oxidized to trichloroacetic acid (TCA) by the nicotinamide adenine dinucleotide (NAD)-dependent enzyme, CH dehydrogenase. Alcohol dehydrogenase requires reduced NAD (NADH), aldehyde reductase requires reduced nicotinamide adenine dinucleotide phosphate (NADPH) and CH dehydrogenase requires NAD to complete the reaction. It is unclear which reaction is predominant at the physiological redox level in intact liver cells. To study this question, we perfused the livers of well-fed rats with Krebs-Ringer buffer solution containing 0.1 mM pyruvate/1.0 mM lactate. The levels of TCE and TCA in the effluent were measured by gas chromatography, and the fluorescence of reduced pyridine nucleotides was measured with a surface fluorometer. When a low concentration (below 0.25 mM) of CH was administered, more TCA than TCE was produced. When a high concentration of CH was administered (over 0.5 mM), TCE production was greater. Reduced pyridine nucleotides decreased inversely with the CH concentration. Even at low CH concentrations, pyridine nucleotides were not reduced. When 10 mM lactate was added to the perfusate in order to reduce the pyridine nucleotides in the liver cells, the TCE/TCA ratio increased. On the other hand, the TCE/TCA ratio tended to fall following the addition of 5.0 mM pyruvate. In conclusion, the TCE/TCA ratio was altered according to the concentration of CH, and to the redox level of pyridine nucleotides in the liver.
水合氯醛（CH）是三氯乙烯的一种中间代谢产物，可被乙醇脱氢酶和醛还原酶还原为三氯乙醇（TCE），也可被烟酰胺腺嘌呤二核苷酸（NAD）依赖性酶CH脱氢酶氧化为三氯乙酸（TCA）。乙醇脱氢酶需要还原型NAD（NADH），醛还原酶需要还原型烟酰胺腺嘌呤二核苷酸磷酸（NADPH），而CH脱氢酶需要NAD来完成反应。目前尚不清楚在完整肝细胞的生理氧化还原水平下哪种反应占主导地位。为了研究这个问题，我们用含有0.1 mM丙酮酸/1.0 mM乳酸的Krebs-Ringer缓冲溶液灌注饱食大鼠的肝脏。通过气相色谱法测量流出液中TCE和TCA的水平，并用表面荧光计测量还原型吡啶核苷酸的荧光。当给予低浓度（低于0.25 mM）的CH时，产生的TCA比TCE多。当给予高浓度的CH（超过0.5 mM）时，TCE的产生量更大。还原型吡啶核苷酸与CH浓度呈反比下降。即使在低CH浓度下，吡啶核苷酸也不会被还原。当向灌注液中加入10 mM乳酸以降低肝细胞中的吡啶核苷酸时，TCE/TCA比值增加。另一方面，加入5.0 mM丙酮酸后，TCE/TCA比值趋于下降。总之，TCE/TCA比值根据CH的浓度以及肝脏中吡啶核苷酸的氧化还原水平而改变。
