Hepatobiliary Efflux: Using a Model that Can Separate Basolateral from Biliary Efflux

Hepatic models, such as those that utilize B-CLEAR® technology, are integral tools in the drug development process and can impact the clinical and commercial success of any development program. Hepatic models assess compounds for:


Inaccurate models put drug developers at major risk of basing development plans on faulty information, creating liabilities that may include improperly dosing trial participants and patients and missing predictable toxicities or drug-drug related adverse events. Accurate models and accurate data arm researchers with the proper information to anticipate challenges and plan for success.

Qualyst Transporter Solutions has developed a physiologically relevant, hepatobiliary method called B-CLEAR®. This technology is a proprietary parallel incubation methodology that provides more accurate data than any other hepatic system available as it can uniquely separate and quantitate uptake, basolateral efflux, and biliary efflux.

Figure 1. A fully functioning model system maintains all major clearance pathways which include: uptake, basolateral efflux, biliary efflux, and metabolism. In addition to acute assessment of these pathways (e.g., inhibition, transport), a physiologic model should be able to be used under chronic conditions where key regulatory pathways are understood and functioning (e.g. AhR, CAR, PXR, FXR).

What is different about B-CLEAR® technology?

The B-CLEAR® technology was developed through more than a decade of research and incorporates culturing and assay methods utilizing a Transporter Certified™ sandwich-cultured hepatocyte (SCH) platform. Transporter function requires 3-5 days in culture to allow time for the re-polarization of transport proteins and the re-formation of bile canaliculi. Our technology allows for this, and therefore provides more physiologic transporter and metabolism function, resulting in in vivo-relevant intracellular concentrations. Finally, our patented methodology is the only way to separately measure both basolateral and biliary efflux. No other model, system, or technology can provide this level of confidence and detail (Figure 2).

Other hepatic models use culture systems or hepatocytes that lack physiologic transporter function. These notably include hepatocytes in suspension and hepatocytes plated on a single layer of collagen (short or long-term cultures). Other companies claim to measure biliary transport in their systems but are actually measuring both basolateral and biliary efflux together! We have patented the only system certified for transporter function and the ability to distinguish and independently measure both basolateral and biliary efflux.

Figure 2. An appropriate hepatobiliary system has physiologic transporter function. (A) For accurate transport and clearance measurements, a technology like B-CLEAR® is needed that can separately measure basolateral efflux. (B) Methodology that other companies employ to measure biliary excretion (i.e. single measurement methods) cannot distinguish between basolateral and biliary efflux, and report a combined value of the two pathways - giving you inaccurate information. (C) Incorrectly, some researchers use hepatocytes in suspension to estimate biliary efflux, when in fact, there is no canalicular membrane, and canalicular transporters are internalized and non-functional, therefore no biliary efflux can occur. In this case, measurements reflect only basolateral efflux.

What is basolateral efflux and why is it important?

In vitro biliary clearance, defined as the elimination of a compound into the bile pocket, is an essential and challenging step in the execution of accurate hepatic models. However, the contribution of basolateral efflux in these models has previously been underappreciated. Basolateral efflux transporters can play a significant role in the removal of many compounds and drugs from the hepatocyte. Methodologies that do not separate basolateral efflux from biliary efflux result in inaccurate biliary efflux measurements. This overestimation of biliary clearance could lead to the false assumption that compounds are being eliminated from the body, when in fact, they are being excreted into the systemic circulation, potentially leading to increased systemic exposures. Essentially, hepatic models that do not use the B-CLEAR® technology can yield faulty predictions and inaccurate clinical conclusions.

Relevance of basolateral efflux in published studies

HEPATIC BASOLATERAL EFFLUX CONTRIBUTES SIGNIFICANTLY TO ROSUVASTATIN DISPOSITION

In a paper published in 2013, researchers from the University of North Carolina studied and established the importance of basolateral efflux in the clearance of rosuvastatin, using rat and human hepatocytes.1 This study was the first to specifically examine the role of basolateral transporters in the hepatobiliary disposition of rosuvastatin. The researchers found that basolateral efflux was approximately equal to the canalicular efflux. This study has added to the growing interest in the scientific community regarding the importance of basolateral efflux in the in vivo disposition of drugs and metabolites.

SPECIES DIFFERENCES IN HEPATOBILIARY DISPOSITION OF TAUROCHOLIC ACID IN HUMAN AND RAT SANDWICH-CULTURED HEPATOCYTES:

In a paper published in 2015, researchers from the University of North Carolina used pharmacokinetic modeling to evaluate species differences in the hepatic transport of taurocholic acid in order to better understand bile acid homeostasis and its implications for drug-induced liver injury.2 The basolateral clearance for taurocholic acid was approximately 25-30% of the canalicular clearance, and is likely mediated by MRP3 and MRP4 basolateral transport.

Both of these examples clearly highlight the importance of basolateral efflux and its emergence as a competing and compensatory mechanism of clearance. Inhibitory effects of a drug on bile acid transport mediated by multiple efflux pathways (basolateral and canalicular) should be considered when evaluating the hepatotoxic potential of drugs.

In addition, using transporter-impaired systems such as suspension hepatocytes or unproven and inaccurate methodologies that combine basolateral and biliary efflux together will result in grossly overestimated hepatic clearance data and generally inaccurate conclusions.

How can you obtain products and services that use B-CLEAR® technology?

The B-CLEAR® technology is exclusively provided by Qualyst Transporter Solutions and available in our products and contract research services. These products and services allow you to accurately assess induction, hepatotoxicity, cholestasis, clearance, and/or drug interactions by combining physiologic transporter function with a proven method that can separately measure both basolateral and biliary efflux.

Please call us at (919) 313-6500 or Contact Us for more information.

References

1. Hepatic Basolateral Efflux Contributes Significantly to Rosuvastatin Disposition: Characterization of Basolateral Versus Biliary Clearance Using a Novel Protocol in Sandwich-Cultured Hepatocytes. Nathan D. Pfeifer, Kyunghee Yang, and Kim L. R. Brouwer. J Pharmacol Exp Ther 347:727-736, December 2013.

2. Species Differences in Hepatobiliary Disposition of Taurocholic Acid in Human and Rat Sandwich-Cultured Hepatocytes: Implications for Drug-Induced Liver Injury. Kyunghee Yang, Nathan D. Pfeifer, Kathleen Kock, and Kim L. R. Brouwer, Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina. J Pharmacol Exp Ther 353:415-423, May 2015. Received November 29, 2014; accepted February 20, 2015.

Copyright 2011-2012 Qualyst Transporter Solutions, LLC. All Rights Reserved. B-CLEAR is a registered trademark of Qualyst Transporter Solutions, LLC.
*B-CLEAR® is covered by US Patent 6,780,580 and other worldwide patents issued & pending.