Effect of Pharmacological Modulation of Liver P-Glycoproteins on Cyclosporin A Biliary Excretion and Cholestasis A Study in Isolated Perfused Rat Liver MARCO DELLE MONACHE, MD, ALESSANDRO GIGLIOZZI, MD, ANTONIO BENEDETTI, MD, LUCA MARUCCI, MD, ADRIANO BINI, MD, CHIARA FRANCIA, MD, EMANUELA PAPA, MD, EMANUELE DI COSIMO, MD, FLAVIA FRAIOLI, MD, ANNE MARIE JEZEQUEL, MD, and DOMENICO ALVARO, MD In different cell types P-glycoproteins (P-gp) are involved in the transport of cyclosporin A (CyA). The aim of this study was to evaluate the effect of the pharmacological modulation of the hepatic P-gp on biliary secretion of CyA and on cholestasis induced by acute adminis- tration of CyA in the isolate d perfused rat liver (IPRL). Verapamil was used as a P-gp speci®c inhibitor and acetylamino¯uorene (AAF) as a P-gp inducer. CyA biliary excretion was determined by administe ring in the IPRL a tracer dose of [ 3 H]CyA with or without verapamil or AAF. The effect on bile ¯ow was evaluated by administe ring increasing doses of CyA (2.8, 8, and 20 mg/kg body wt) in the IPRL. Morphological evidence of damage was evaluated by optical and electron microscopy in the liver as well as in primary culture of rat hepatocytes exposed to CyA 6 verapamil. Verapamil signi®cantly inhibite d the biliary excretion of a tracer dose of [ 3 H]CyA (0.15 6 0.04 vs 0.33 6 0.07% ; P , 0.05). In contrast, pretreatment with AAF signi®cantly increased the biliary excretion of [ 3 H]CyA, (0.61 6 0.10 vs 0.33 6 0.07% ; P , 0.05). CyA induced a dose-dependent inhibition of bile ¯ow with a maximal effect at 20 mg/kg CyA ( 249.3 6 4.5% decrease of basal bile ¯ow). CyA cholestasis was signi®cantly worsened by the P-gp inhibitor, verapamil ( 275.5 6 7.5% ; P , 0.05), but it was unaffected by induction of P-gp via AAF pretreatment ( 244.9 6 1.7% ). During CyA cholestasis, the cumulative biliary excretion of [ 3 H]CyA was lower than in the absence of cholestasis (0.22 6 0.05 vs 0.33 6 0.07% ; P , 0.05), was inhibited by verapamil (0.08 6 0.01% ; P , 0.05), but was unaffected by AAF (0.23 6 0.05% ). No morphological evidence of damage was observed in the liver, and no evidence of cytoskeleton derangement was seen in primary cultures of rat hepatocyte s exposed to CyA 6 verapamil. We demonstrated that pharmacological modula- tion of P-gp may in¯uence the biliary excretion of CyA. The acute cholestatic effect of CyA is worsened by P-gp inhibitors, while it is unaffected by P-gp inducers. This indicates CyA should not be given with other P-gp substrates or inhibitors. KEY WORDS: cyclosporin; P-glycoproteins; bile secretion; cholestasis. Manuscript received December 18, 1998; revised manuscript received April 6, 1999; accepted May 24, 1999. From the II Division of Gastroenterology, Department of Clin- ical Medicine, University of Rome ªLa Sapienza,º Viale dell’UniversitaÁ 37, 00185 Rome, Italy; and Department of Gastro- enterology, University of Ancona, 60020 Ancona, Italy. Address for reprint requests: Dr. Domenico Alvaro, Via Val- solda 45/i, 00141 Rome, Italy. Digestive Diseases and Sciences, Vol. 44, No. 11 (November 1999), pp. 2196±2204 2196 Digestive Diseases and Sciences, Vol. 44, No. 11 (November 1999) 0163-2116/99/1100-2196$16.00/0 Ñ 1999 Plenum Publishing Corporation