PT  - JOURNAL ARTICLE
AU  - Jennifer Ryan
AU  - Ryan E Morgan
AU  - Yuan Chen
AU  - Laurie Volak
AU  - Robert T Dunn
AU  - Kenneth W Dunn
TI  - Intravital multiphoton microscopy with fluorescent bile salts in rats as an in vivo biomarker for hepatobiliary transport inhibition
AID  - 10.1124/dmd.117.079277
DP  - 2018 Jan 01
TA  - Drug Metabolism and Disposition
PG  - dmd.117.079277
4099  - http://dmd.aspetjournals.org/content/early/2018/02/21/dmd.117.079277.short
4100  - http://dmd.aspetjournals.org/content/early/2018/02/21/dmd.117.079277.full
AB  - The bile salt export pump (BSEP) is expressed at the canalicular domain of hepatocytes, where it mediates the elimination of monovalent bile salts into the bile. Inhibition of BSEP is considered a susceptibility factor for drug-induced liver injury (DILI) that often goes undetected during non-clinical testing. Although in vitro assays exist for screening BSEP inhibition, a reliable and specific method for confirming Bsep inhibition in vivo would be a valuable follow-up to a BSEP screening strategy, helping to put a translatable context around in vitro inhibition data, incorporating processes such as metabolism, protein binding, and other exposure properties that are lacking in most in vitro BSEP models. Here, we describe studies in which methods of quantitative intravital microscopy were used to identify dose-dependent effects of two known BSEP/Bsep inhibitors, AMG 009 and bosentan, on hepatocellular transport of the fluorescent bile salts, cholylglycyl amidofluorescein (CGamF) and cholyl-lysyl-fluorescein (CLF) in rats. Results of these studies demonstrate that the intravital microscopy approach is capable of detecting Bsep inhibition at drug doses well below those found to increase serum bile acid levels, and also indicate that basolateral efflux transporters play a significant role in preventing cytosolic accumulation of bile acids under conditions of Bsep inhibition in rats. Studies of this kind can both improve our understanding of exposures needed to inhibit Bsep in vivo, but also provide unique insights into drug effects in ways that can improve our ability interpret animal studies for the prediction of human drug hepatotoxicity.