Dahlin D C, Miwa G T, Lu A Y, Nelson S D
Proc Natl Acad Sci U S A. 1984 Mar;81(5):1327-31. doi: 10.1073/pnas.81.5.1327.
N-acetyl-p-benzoquinone imine (NAPQI) has been proposed as the toxic metabolite of acetaminophen for the past 10 years, although it has never been detected as an enzymatic oxidation product of acetaminophen. We report (i) direct detection of NAPQI formed as an oxidation product of acetaminophen by cytochrome P-450 and cumene hydroperoxide and (ii) indirect evidence that is compelling for NAPQI formation from acetaminophen by cytochrome P-450, NADPH, and NADPH-cytochrome P-450 reductase. Evidence is provided for the rapid reduction of NAPQI back to acetaminophen by NADPH and NADPH-cytochrome P-450 reductase such that steady-state levels of NAPQI were below our detection limits of 6.7 X 10(-8) M. In mouse liver microsomal incubations, radiolabeled analogs of both NAPQI and acetaminophen bound covalently to microsomal protein with the loss of approximately equal to 20% of the acetyl group as acetamide. The binding in each case was decreased by glutathione with concomitant formation of 3-S-glutathionylacetaminophen. The binding also was decreased by L-ascorbic acid, NADPH, and NADH with reduction of NAPQI to acetaminophen. Results of partitioning experiments indicate that NAPQI is a major metabolite of acetaminophen, a considerable fraction of which is rapidly reduced back to acetaminophen.
在过去十年中，N - 乙酰 - 对 - 苯醌亚胺（NAPQI）一直被认为是对乙酰氨基酚的有毒代谢产物，尽管它从未被检测为对乙酰氨基酚的酶促氧化产物。我们报告：（i）直接检测到细胞色素P - 450和氢过氧化异丙苯将对乙酰氨基酚氧化生成的NAPQI；（ii）有间接证据强有力地表明细胞色素P - 450、NADPH和NADPH - 细胞色素P - 450还原酶可将对乙酰氨基酚转化为NAPQI。有证据表明NADPH和NADPH - 细胞色素P - 450还原酶可将NAPQI迅速还原回对乙酰氨基酚，使得NAPQI的稳态水平低于我们6.7×10⁻⁸ M的检测限。在小鼠肝微粒体孵育实验中，NAPQI和对乙酰氨基酚的放射性标记类似物均与微粒体蛋白共价结合，同时约20%的乙酰基以乙酰胺形式丢失。在每种情况下，谷胱甘肽均可减少这种结合，并伴随生成3 - S - 谷胱甘肽酰对乙酰氨基酚。L - 抗坏血酸、NADPH和NADH也可减少这种结合，同时将NAPQI还原为对乙酰氨基酚。分配实验结果表明，NAPQI是对乙酰氨基酚的主要代谢产物，其中相当一部分会迅速还原回对乙酰氨基酚。
