Wang M, Dickinson R G
Department of Medicine of The University of Queensland at Royal Brisbane Hospital, Australia.
Drug Metab Dispos. 1998 Feb;26(2):98-104.
Acyl glucuronides are intrinsically reactive metabolites of carboxylate drugs, capable of undergoing hydrolysis, intramolecular rearrangement (isomerization via acyl migration), and intermolecular transacylation reactions. Transacylation with nucleophilic groups located on protein molecules leads to covalent drug-protein adducts. Protein adducts can also form from the rearrangement isomers via a glycation mechanism. In this study, the isolated perfused rat liver preparation was used to separately trace the dispositions of the nonsteroidal anti-inflammatory drug diflunisal (DF), its reactive acyl glucuronide metabolite (DAG), and a mixture of DAG rearrangement isomers (iso-DAG), each administered at 30-microg DF equivalents/ml perfusate (four recirculating perfusions each group). After administration of DF, the drug was eliminated in a log linear manner over 3 hr, with apparent elimination half-life (t1/2) of 2.6 +/- 0.4 hr. The sulfate conjugate (DS), excreted almost exclusively into perfusate, accounted for 14.2% of the dose, with the phenolic glucuronide (DPG) and DAG (11.1 and 7.9% of dose, respectively) excreted primarily in bile. Only a small portion (2.3%) of the dose was recovered as novel "diglucuronides" (D-2G, arising from phenolic glucuronidation of iso-DAG), excreted exclusively in bile. Covalent DF-protein adducts were found in both perfusate (0.98%) and liver (0. 14%). After administration of DAG, rapid hydrolysis occurred (initial DAG t1/2 17.3 +/- 4.2 min). At 3 hr, recoveries (in comparison to DF-dosed perfusions) were similar for DF (51.7%) and DAG (8.3%), significantly decreased for DS (10.6%) and DPG (6.4%), and significantly increased for iso-DAG (0.8%), D-2G (9.1%), and covalent adducts in perfusate (1.49%) and liver (0.30%). After administration of iso-DAG, elimination from perfusate was slower (t1/2 55 +/- 15 min), and hydrolysis to DF was modest by comparison with DAG-dosed perfusions. Recoveries as iso-DAG and D-2G in bile were greatly enhanced (8.2 and 36.4%, respectively). Adduct formation was higher in liver (0.76% of dose) but not in perfusate (1.03%). Immunoblots of liver homogenates revealed drug-modified proteins at ca. 110 and 120 kDa. The results show that (a) DAG undergoes avid systemic deconjugation-conjugation cycling and isomerization to iso-DAG; (b) iso-DAG is more resistant to hydrolysis, is readily taken up by hepatocytes and undergoes novel metabolism (phenolic glucuronidation); and (c) the glycation pathway (i.e. using iso-DAG as substrate) plays a major role in formation of covalent DF-protein adducts in liver.
酰基葡糖醛酸是羧酸类药物的固有反应性代谢产物，能够发生水解、分子内重排（通过酰基迁移进行异构化）和分子间转酰基反应。与蛋白质分子上的亲核基团发生转酰基反应会导致形成共价药物 - 蛋白质加合物。蛋白质加合物也可通过糖基化机制由重排异构体形成。在本研究中，使用离体灌注大鼠肝脏制剂分别追踪非甾体抗炎药二氟尼柳（DF）、其反应性酰基葡糖醛酸代谢产物（DAG）以及DAG重排异构体混合物（异 - DAG）的处置情况，每组均以30μg DF当量/毫升灌注液给药（每组进行四次再循环灌注）。给予DF后，药物在3小时内以对数线性方式消除，表观消除半衰期（t1/2）为2.6±0.4小时。几乎完全排泄到灌注液中的硫酸酯共轭物（DS）占剂量的14.2%，酚葡糖醛酸酯（DPG）和DAG（分别占剂量的11.1%和7.9%）主要经胆汁排泄。仅一小部分（2.3%）剂量以新型“二葡糖醛酸酯”（D - 2G，由异 - DAG的酚葡糖醛酸化产生）形式回收，仅经胆汁排泄。在灌注液（0.98%）和肝脏（0.14%）中均发现了共价DF - 蛋白质加合物。给予DAG后，迅速发生水解（初始DAG t1/2为17.3±4.2分钟）。3小时时，与给予DF的灌注相比，DF（51.7%）和DAG（8.3%）的回收率相似，DS（10.6%）和DPG（6.4%）显著降低，而异 - DAG（0.8%）、D - 2G（9.1%）以及灌注液（1.49%）和肝脏（0.30%）中的共价加合物显著增加。给予异 - DAG后，从灌注液中的消除较慢（t1/2为55±15分钟），与给予DAG的灌注相比，水解为DF的程度适中。胆汁中异 - DAG和D - 2G的回收率大大提高（分别为8.2%和36.4%）。肝脏中的加合物形成较高（占剂量的0.76%），但灌注液中则不然（1.03%）。肝脏匀浆的免疫印迹显示在约110和120 kDa处有药物修饰的蛋白质。结果表明：（a）DAG经历活跃的全身去共轭 - 共轭循环并异构化为异 - DAG；（b）异 - DAG对水解更具抗性，易被肝细胞摄取并经历新型代谢（酚葡糖醛酸化）；（c）糖基化途径（即以异 - DAG为底物）在肝脏中共价DF - 蛋白质加合物的形成中起主要作用。
