Different pathways of canalicular secretion of sulfated and non-sulfated fluorescent bile acids: a study in isolated hepatocyte couplets and TR- rats

Background/Aims: Fluorescent bile acids have proved useful for characterizi ng bile salt transport mechanisms, The aim of this study was to further val idate the use of lysyl-fluorescein conjugated bile acid analogues as surrog ate bile acids, Methods: We analyzed biliary excretion kinetics of cholyl lysyl fluorescein (CLF), lithocholyl lysyl fluorescein (LLF) and sulfo-lithocholyl lysyl flu orescein (sLLF), both in the isolated rat hepatocyte couplet model and in T R- rats with a selective canalicular transport defect of non-bile acid orga nic anions, Results: CLF and LLF, which like their natural nonsulfated bile acid congen ers are expected to be handled by the canalicular bile salt export pump, we re transferred into the bile canaliculus much faster than sLLF, a putative substrate for the canalicular multispecific organic anion transporter in bo th the in who and the in vitro models employed, The contention that differe nt transport systems are involved in sulfated and non-sulfated lysyl fluore scein conjugated bile acids biliary excretion was supported further by stud ies using TR- rats, in which the cumulative biliary excretion of sLLF was r educed to 6% as compared with that of normal Wistar rats, in good agreement with values for its naturally-occurring radio-labeled parent compound sulf oglycolithocholate. In contrast, CLF and LLF were reduced to 66% and 52%, s imilar values to these for their congeners, [C-14] glycocholate and [14C] l ithocholate, Conclusion: The close similarity in behavior of lysyl fluorescein conjugate d bile acids to that of their naturally-occurring parent compounds in these different models gives support for both sulfated and nonsulfated lysyl flu orescein conjugated bile acids as substitute molecules for studies of bile acid transport.