Adenovirus-Mediated Gene Therapy to Restore Expression and Functionality of Multiple UDP-Glucuronosyltransferase 1A Enzymes in Gunn Rat Liver

Abstract

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_½α 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.