Miles Kristini K, Kessler Fay K, Webb Laura J, Smith Philip C, Ritter Joseph K
Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA 23298, USA.
J Pharmacol Exp Ther. 2006 Sep;318(3):1240-7. doi: 10.1124/jpet.106.104810. Epub 2006 Jun 8.
The Gunn rat has been a valuable model for investigating the effect of UDP-glucuronosyltransferase 1A (UGT1A) deficiencies on drug metabolism and toxicity, but it is limited in some aspects. For example, the native Gunn rat model cannot distinguish between hepatic and extrahepatic UGT1A deficiencies in toxicological mechanisms. To extend the model's utility, we investigated the use of replication-defective recombinant UGT1A adenoviruses for the purpose of selectively restoring hepatic UGT1A function. Mycophenolic acid, the active metabolite of the anti-transplant rejection drug mycophenolate mofetil and suspected gastrointestinal toxicant, was used as a model UGT1A-dependent substrate. Treatment with UGT1A adenoviruses normalized the plasma mycophenolic acid and 7-O-mycophenolate glucuronide (MPAG) (concentration-time curves after mycophenolic acid administration (80 mg/kg intraperitoneally). Functional reconstitution was also apparent in the correction of the mycophenolic acid t(1/2alpha) and the area under the curve (AUC)(MPA,0-8 h)/AUC(MPAG,0-8 h) ratio. Twenty-four hours after administration of mycophenolic acid, severe signs of toxicity were noted in the naive Gunn group, including reduced food consumption. The effect on food consumption was reduced but not completely prevented in the UGT adenovirus-treated Gunn rats. In vitro analyses indicated adenovirus dose-dependent reconstitution of mycophenolic acid UGT activities and UGT1A contents in liver but not intestinal microsomes. In the highest adenovirus dose group, the liver microsomal UGT1A markers exceeded those of the heterozygote controls. The ability to selectively manipulate multiple hepatic UGT1A enzymes in Gunn rats should provide a novel way to assess the importance of intestinal or other extrahepatic UGT1A enzymes in toxicities induced by mycophenolic acid and other cytotoxic drugs and dietary agents.
冈恩大鼠一直是研究尿苷二磷酸葡萄糖醛酸基转移酶1A（UGT1A）缺陷对药物代谢和毒性影响的重要模型，但它在某些方面存在局限性。例如，天然的冈恩大鼠模型无法在毒理学机制上区分肝脏和肝外UGT1A缺陷。为了扩展该模型的用途，我们研究了使用复制缺陷型重组UGT1A腺病毒来选择性恢复肝脏UGT1A功能。霉酚酸是抗移植排斥药物霉酚酸酯的活性代谢产物，也是可疑的胃肠道毒物，被用作UGT1A依赖性模型底物。用UGT1A腺病毒治疗可使血浆霉酚酸和7 - O - 霉酚酸葡萄糖醛酸（MPAG）正常化（腹腔注射80 mg/kg霉酚酸后的浓度 - 时间曲线）。在霉酚酸t(1/2α)的校正以及曲线下面积（AUC）（MPA，0 - 8小时）/AUC（MPAG，0 - 8小时）比值方面，功能重建也很明显。在给予霉酚酸24小时后，未处理的冈恩组出现了严重的毒性迹象，包括食物摄入量减少。在经UGT腺病毒治疗的冈恩大鼠中，对食物摄入量的影响有所减轻，但并未完全消除。体外分析表明，腺病毒剂量依赖性地重建了肝脏而非肠道微粒体中的霉酚酸UGT活性和UGT1A含量。在最高腺病毒剂量组中，肝脏微粒体UGT1A标志物超过了杂合子对照组。在冈恩大鼠中选择性操纵多种肝脏UGT1A酶的能力，应该为评估肠道或其他肝外UGT1A酶在霉酚酸和其他细胞毒性药物及膳食剂诱导的毒性中的重要性提供一种新方法。
