Effect of pharmacological modulation of liver P-glycoproteins on cyclosporin A biliary excretion and cholestasis - A study in isolated perfused rat liver

In different cell types P-glycoproteins (P-gp) are involved in the transpor t 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 administration of CyA in the iso lated perfused rat liver (IPRL). Verapamil was used as a P-gp specific inhi bitor and acetylaminofluorene (AAF) as a P-gp inducer. CyA biliary excretio n was determined by administering in the IPRL a tracer dose of [H-3]CyA wit h or without verapamil or AAF. The effect on bile flow was evaluated by adm inistering increasing doses of CyA (2.8, 8, and 20 mg/kg body wt) in the IP RL. Morphological evidence of damage was evaluated by optical and electron microscopy in the liver as well as in primary culture of rat hepatocytes ex posed to CyA +/- verapamil. Verapamil significantly inhibited the biliary e xcretion of a tracer dose of [H-3]CyA (0.15 +/- 0.04 vs 0.33 +/- 0.07%; P < 0.05). In contrast, pretreatment with AAF significantly increased the bili ary excretion of [H-3]CyA, (0.61 +/- 0.10 vs 0.33 +/- 0.07%; P < 0.05). CyA induced a dose-dependent inhibition of bile how with a maximal effect at 2 0 mg/kg CyA (-493 +/- 4.5% decrease of basal bile flow). CyA cholestasis wa s significantly worsened by the P-gp inhibitor, verapamil (-75.5 +/- 7.5%; P < 0.05), but it was unaffected by induction of P-gp via AAF pretreatment (-44.9 +/- 1.7%). During CyA cholestasis, the cumulative biliary excretion of [H-3]CyA was lower than in the absence of cholestasis (0.22 +/- 0.05 vs 0.33 +/- 0.07%; P < 0.05), was inhibited by verapamil (0.08 +/- 0.01%; P < 0.05), but was unaffected by AAF (0.23 +/- 0.05%). No morphological evidenc e of damage was observed in the liver, and no evidence of cytoskeleton dera ngement was seen in primary cultures of rat hepatocytes exposed to CyA +/- verapamil. We demonstrated that pharmacological modulation of P-gp may infl uence the biliary excretion of CyA. The acute cholestatic effect of CLA 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.