Functional and Pharmacological Comparison of Human and Mouse Na+/Taurocholate Cotransporting Polypeptide (NTCP)

Role of sodium taurocholate cotransporting polypeptide (NTCP) in HBV-induced hepatitis: Opportunities for developing novel therapeutics

Hepatitis B is an infectious disease caused by the HBV virus. It presents a significant challenge for treatment due to its chronic nature and the potential for developing severe complications, including hepatocirrhosis and hepatocellular carcinoma. These complications not only cause physical and psychological distress to patients but also impose substantial economic and social burdens on both individuals and society as a whole. The internalization of HBV relies on endocytosis and necessitates the involvement of various proteins, including heparin sulfate proteoglycans, epidermal growth factor receptors, and NTCP. Among these proteins, NTCP is pivotal in HBV internalization and is primarily located in the liver's basement membrane. As a transporter of bile acids, NTCP also serves as a receptor facilitating HBV entry into cells. Numerous molecules have been identified to thwart HBV infection by stifling NTCP activity, although only a handful exhibit low IC50 values. In this systematic review, our primary focus dwells on the structure and regulation of NTCP, as well as the mechanism involved in HBV internalization. We underscore recent drug breakthroughs that specifically target NTCP to combat HBV infection. By shedding light on these advances, this review contributes novel insights into developing effective anti-HBV medications.

Investigations with Drugs and Pesticides Revealed New Species- and Substrate-Dependent Inhibition by Elacridar and Imazalil in Human and Mouse Organic Cation Transporter OCT2

Multiple drugs are used to treat various indications as well as pesticides that are ingested unintentionally and enter the bloodstream. The residence time or bioavailability of these substances in circulation depends on several mechanisms, such as drug−drug interaction (DDI), drug−pesticide interaction, metabolizing enzymes and the hepatic and renal transport systems, involved in the elimination of the compounds from the body. One of these transporters is the Organic Cation Transporter 2 (OCT2) member of the solute carrier (SLC22) transporter family. OCT2 is highly expressed in the proximal tubule epithelial cells in human and mouse kidney, where it mediates the uptake of endogenous organic cations as well as numerous drugs and xenobiotics, and contributes to the first step of renal clearance. In this study, we examined OCT2 on two subjects: First, the transferability of data from mouse to human, since mice are initially examined in the development of new drugs to assess the renal excretion of organic cations. Second, to what extent the choice of substrate affects the properties of an inhibitor. For this purpose, the functional properties of hOCT2 and mOct2 were validated under the same experimental conditions with the known substrates metformin and 1-Methyl-4-phenylpyridinium iodide (MPP). While hOCT2 and mOct2 showed very low affinities for metformin with Km values of 3.9 mM and 3.5 mM, the affinity of hOCT2 and mOct2 for MPP (62 and 40 µM) was 64- and 89-fold higher, respectively. For our positive control inhibitor decynium22, we determined the following IC50 values for hOCT2 and mOct2: 2.2 and 2.6 µM for metformin uptake, and 16 and 6.9 µM for MPP uptake. A correlation analysis of the inhibitory effects of 13 drugs and 9 pesticides on hOCT2- and mOct2-mediated transport of metformin showed a correlation coefficient R2 of 0.88, indicating good interspecies correlation. Nevertheless, the bioenhancer elacridar and the fungicide imazalil showed species-dependent inhibitory potentials. Concentration-dependent inhibition of hOCT2- and mOct2-mediated metformin uptake by elacridar showed IC50 values of 20 µM and 1.9 µM and by imazalil 4.7 µM and 0.58 µM, respectively. In conclusion, although our data show comparable species-independent interactions for most compounds, there can be large species−specific differences in the interactions of individual compounds, which should be considered when extrapolating data from mice to humans. Furthermore, a comparison of the inhibitory potential of elacridar and imazalil on metformin uptake with that on MPP uptake reveals substrate-dependent differences in hOCT2 and mOct2 for both inhibitors. Therefore, it might be useful to test two different substrates in inhibition studies.

Multitasking Na+/Taurocholate Cotransporting Polypeptide (NTCP) as a Drug Target for HBV Infection: From Protein Engineering to Drug Discovery

Hepatitis B virus (HBV) infections are among the major public health concerns worldwide with more than 250 million of chronically ill individuals. Many of them are additionally infected with the Hepatitis D virus, a satellite virus to HBV. Chronic infection frequently leads to serious liver diseases including cirrhosis and hepatocellular carcinoma, the most common type of liver cancer. Although current antiviral therapies can control HBV replication and slow down disease progress, there is an unmet medical need to identify therapies to cure this chronic infectious disease. Lately, a noteworthy progress in fighting against HBV has been made by identification of the high-affinity hepatic host receptor for HBV and HDV, namely Na⁺/taurocholate cotransporting polypeptide (NTCP, gene symbol SLC10A1). Next to its primary function as hepatic uptake transporter for bile acids, NTCP is essential for the cellular entry of HBV and HDV into hepatocytes. Due to this high-ranking discovery, NTCP has become a valuable target for drug development strategies for HBV/HDV-infected patients. In this review, we will focus on a newly predicted three-dimensional NTCP model that was generated using computational approaches and discuss its value in understanding the NTCP’s membrane topology, substrate and virus binding taking place in plasma membranes. We will review existing data on structural, functional, and biological consequences of amino acid residue changes and mutations that lead to loss of NTCP’s transport and virus receptor functions. Finally, we will discuss new directions for future investigations aiming at development of new NTCP-based HBV entry blockers that inhibit HBV tropism in human hepatocytes.