Disposition of gemfibrozil and gemfibrozil acyl glucuronide in the rat isolated perfused liver

Acyl glucuronides are reactive electrophilic metabolites and in vivo are readily hydrolyzed, undergo intramolecular rearrangement, and bind covalently to proteins. The isolated perfused liver preparation, using male Sprague-Dawley rats, was used to examine the hepatic disposition of the fibrate hypolipidemic agent gemfibrozil and its acyl glucuronide metabolite, 1-O-gemfibrozil-beta-D-glucuronide. Using a recirculating design, erythrocyte-free perfusion medium containing 1% (w/v) albumin was delivered to the liver via the portal vein at a flow rate of 30 ml/min, and for each experiment was spiked with either gemfibrozil (N = 4) or 1-O-gemfibrozil-beta-D-glucuronide (N = 4) at initial concentrations of 120 microM and 21 microM, respectively. In the gemfibrozil perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio of gemfibrozil, and the fraction of eliminated gemfibrozil excreted in bile as the glucuronide conjugate were 2.73 (0.30) ml/min, 76.9 (5.6) min, 0.091 (0.012), and 0.347 (0.154), respectively. In the 1-O-gemfibrozil-beta-D-glucuronide perfusions, the mean (SD) total perfusate clearance, half-life, hepatic extraction ratio, and fraction excreted in bile as the glucuronide conjugate were 19.5 (2.1) ml/min, 8.7 (0.9) min, 0.649 (0.068), and 0.534 (0.077), respectively. The higher hepatic extraction ratio for 1-O-gemfibrozil-beta-D-glucuronide could mostly be attributed to its higher unbound fraction in perfusate (0.182), compared with that of the parent drug (0.004), because the conjugate had a lower intrinsic clearance (305 ml/min) compared with the aglycone (751 ml/min). Control perfusions, conducted in the absence of a liver, showed negligible degradation of 1-O-gemfibrozil-beta-D-glucuronide over 90 min. However, in the presence of a liver, approximately 25% of 1-O-gemfibrozil-beta-D-glucuronide added to perfusate was hydrolyzed to gemfibrozil over 90 min. The study demonstrates the importance of the liver in the formation, uptake, hydrolysis, and excretion of 1-O-gemfibrozil-beta-D-glucuronide.Benedetta C. Sallustio, Barbara A. Fairchild, Kathryn Shanahan, Allan M. Evans, and Roger L. Natio