Progress in the Molecular Characterization of Hepatobiliary Transporters.

Over the last 25 years, our understanding of the driving forces for hepatobiliary elimination and knowledge of the molecular basis of uptake and efflux transport in hepatocytes have undergone fundamental changes. This refers to bile acids and many other endogenous substances as well as to drugs that are eliminated on the hepatobiliary route. In this development, not only molecular cloning, functional characterization, and localization of transporters were decisive, but also the discovery of hereditary mutations in genes encoding sinusoidal uptake transporters and canalicular export pumps in humans and rodents.

Retroviral expression of human cystatin genes in HeLa cells.

Retroviral gene transfer is a highly efficient and effective method of stably introducing genetic material into the genome of specific cell types. The process involves the transfection of retroviral expression vectors into a packaging cell line, the isolation of viral particles, and the infection of target cell lines. Compared to traditional gene transfer methods such as liposome-mediated transfection, retroviral gene transfer allows for stable gene expression in cell populations without the need for lengthy selection and cloning procedures.

The roles of MRP2, MRP3, OATP1B1, and OATP1B3 in conjugated hyperbilirubinemia.

Increased concentrations of bilirubin glucuronides in blood plasma indicate hepatocellular dysfunction. Elucidation of the transport processes of bilirubin conjugates across the basolateral (sinusoidal) and the canalicular plasma membrane domains of hepatocytes has decisively contributed to our current understanding of the molecular basis of conjugated hyperbilirubinemia in human liver diseases. Under normal conditions, unconjugated bilirubin is taken up into hepatocytes by transporters of the organic anion-transporting polypeptide (OATP) family, followed by conjugation with glucuronic acid, and ATP-dependent transport into bile.

In vitro methods to support transporter evaluation in drug discovery and development.

This white paper addresses current approaches and knowledge gaps concerning methods to assess the role of transport proteins in drug/metabolite disposition in humans. The discussion focuses on in vitro tools to address key questions in drug development, including vesicle- and cell-based systems. How these methods can be used to assess the liability of compounds for transporter-based drug-drug interactions (DDIs) in vivo is also explored.