Aim: Drug-induced hyperbilirubinemia has been shown to often be derived from modulation of the expression and activity of hepatobiliary transporters. In this study we examined the interactions of some therapeutic agents, which have been shown to cause cholestasis, with the elimination of bilirubin-glucuronides, in order to clarify whether these drugs modify the activity of Mrp2 and Mrp3 directly.
Methods: The modulation of bilirubin-glucuronide elimination with rifampicin, probenecid, indomethacin and benzbromarone was assayed in sandwich cultured rat hepatocytes.
Results: All the drugs studied decreased the canalicular transport, but modified the sinusoidal efflux differently. Rifampicin and probenecid stimulated the sinusoidal efflux, shifting the elimination of bilirubin-glucuronides to the sinusoidal domain (biliary excretion index: 3.9 +/- 1.2; 22.7 +/- 7.4 vs. 56.6 +/- 1.5 and 56.8 +/- 5.5). However, the overall elimination of bilirubin-glucuronides did not change significantly. In contrast, indomethacin and benzbromarone inhibited bothtransport processes, resulting in the decrease of the overall bilirubin-glucuronide elimination (61 +/- 22; 56 +/- 5% of the control). Rifampicin, indomethacin and benzbromarone decreased 5,(6)-carboxy-2',7'-dichlorofluorescein transport by multidrug resistance-associated protein (Mrp)2 as visualized by confocal laser microscopy and in vesicular transport experiments. Interestingly, rifampicin decreased the MRP3 activity in vesicular transport experiments using 17-beta-estradiol-17-beta-D-glucuronide as substrate, in contrast to that observed in bilirubin-glucuronide transport experiments.
Conclusion: Here we show that the interactions of drugs on hepatobiliary transporter proteins may be identified in vitro in a sandwich culture of hepatocytes, in which canalicular and sinusoidal transport can be studied separately.