Nicholls A W, Caddick S, Wilson I D, Farrant R D, Lindon J C, Nicholson J K
Department of Chemistry, Birkbeck College, University of London, U.K.
Biochem Pharmacol. 1995 Apr 18;49(8):1155-64. doi: 10.1016/0006-2952(95)98513-9.
Paracetamol (4-hydroxyacetanilide, acetaminophen) was synthesized with the acetyl group labelled with C2H3 (paracetamol-C2H3), and dosed to rats i.p. at 25 mg/kg (N = 5) and 40 mg/kg (N = 3) body weight. Paracetamol, with a 13CH3 in the acetyl group (paracetamol-13CH3) was also synthesized and dosed to rats i.p. at 40 mg/kg (N = 3). The metabolism and excretion of the 2H-labelled compound was followed in the rat using 600 MHz 1H and 92.1 MHz 2H NMR spectroscopy of urine collected 0-8, 8-24, 24-32 and 32-48 hr post-dosing. The metabolism of paracetamol-13CH3 was also monitored using 600 MHz 1H NMR spectroscopy of urine collected 0-8, 8-24 and 24-48 hr post-dosing. For paracetamol-C2H3 the total recovery of the sulphate, glucuronide and N-acetyl cysteinyl metabolites via the urine accounted for 61.2 +/- 14.1% of the 25 mg/kg dose and 61.4 +/- 8.8% of the 40 mg/kg dose. For paracetamol-13CH3 the recovery was 102.7 +/- 3.7% indicating that the low % urinary recovery with the C2H3-labelled drug is the result of isotope effects on the disposition of paracetamol. In the case of the paracetamol-C2H3, quantitative 1H NMR analysis of urine showed that 13.3 +/- 0.5 and 10.0 +/- 1.2 mole % (25 and 40 mg/kg, respectively) of the urinary paracetamol sulphate recovered following dosing of the deuterium labelled drug had the C2H3 acetyl groups replaced by C1H3 acetyl groups from endogenous sources. In the case of the paracetamol-13CH3 8.9 +/- 0.7 mole % of the sulphate conjugate had also been transacetylated to paracetamol-12CH3. There was no significant difference between the level of futile deacetylation observed for the deuterated and 13C-labelled drug. Overall these data indicate a high level of deacetylation followed by reacetylation (i.e. futile deacetylation) prior to excretion of paracetamol via the nephrotoxic intermediate 4-aminophenol. The level of deacetylation is much higher than has previously been thought which may cast new light on the role of 4-aminophenol in the development of paracetamol induced nephrotoxicity.
对乙酰氨基酚（4-羟基乙酰苯胺，醋氨酚）通过用C₂H₃标记乙酰基来合成（对乙酰氨基酚-C₂H₃），并以25mg/kg（N = 5）和40mg/kg（N = 3）的体重腹腔注射给大鼠。还合成了乙酰基带有¹³CH₃的对乙酰氨基酚（对乙酰氨基酚-¹³CH₃），并以40mg/kg（N = 3）腹腔注射给大鼠。使用600MHz ¹H和92.1MHz ²H核磁共振波谱对给药后0 - 8、8 - 24、24 - 32和32 - 48小时收集的大鼠尿液进行分析，以追踪²H标记化合物的代谢和排泄情况。对乙酰氨基酚-¹³CH₃的代谢也通过给药后0 - 8、8 - 24和24 - 48小时收集的尿液的600MHz ¹H核磁共振波谱进行监测。对于对乙酰氨基酚-C₂H₃，经尿液排出的硫酸盐、葡萄糖醛酸和N-乙酰半胱氨酸代谢物的总回收率分别占25mg/kg剂量的61.2±14.1%和40mg/kg剂量的61.4±8.8%。对于对乙酰氨基酚-¹³CH₃，回收率为102.7±3.7%，这表明用C₂H₃标记药物时尿液回收率较低是对乙酰氨基酚处置过程中同位素效应的结果。在对乙酰氨基酚-C₂H₃的情况下，尿液的定量¹H核磁共振分析表明，给药氘标记药物后回收的尿液对乙酰氨基酚硫酸盐中，分别有13.3±0.5和10.0±1.2摩尔%（分别对应25mg/kg和40mg/kg）的C₂H₃乙酰基被内源性来源的C₁H₃乙酰基取代。在对乙酰氨基酚-¹³CH₃的情况下，8.9±0.7摩尔%的硫酸盐共轭物也已转乙酰化为对乙酰氨基酚-¹²CH₃。氘标记药物和¹³C标记药物观察到的无效脱乙酰化水平之间没有显著差异。总体而言，这些数据表明在对乙酰氨基酚通过肾毒性中间体4-氨基酚排泄之前，存在高水平的脱乙酰化然后再乙酰化（即无效脱乙酰化）。脱乙酰化水平比之前认为的要高得多，这可能为4-氨基酚在对乙酰氨基酚诱导的肾毒性发展中的作用提供新的线索。
