Background: The sodium-taurocholate cotransporting polypeptide (NTCP), a bile acids (BA) transporter mediating uptake of BA into hepatocytes, has been found to be an essential receptor for hepatitis B virus (HBV) and hepatitis D virus (HDV). To what extent BA affect HBV/HDV cell entry and whether the BA transport function is linked to HBV/HDV receptor function is unknown.
Methods: We stably expressed NTCP in Huh-7 cells. Huh-7/NTCP cells were then infected with in vitro generated HDV particles and the effects of BA on infectivity were assessed using immunofluorescence staining for HDV antigen and standard 50% tissue culture infectious dose (TCDI50) assays. Moreover, the effect of chenodeoxycolic acid that is licensed for the treatment of certain gall stones was assessed in vivo.
Results: As expected, upon expression of NTCP Huh-7 cells became readily infectable with HDV while untransduced cells were resistant to infection. Addition of primary (e.g., cholic acid, chenodeoxycholic acid) or conjugated BA (e.g., sodium chenodeoxycholic acid) resulted in a dose dependent reduction in the number of infected cells while secondary BA (e.g., deoxycholic acid, lithocholic acid) had no detectable effect. However, inhibition was incomplete and less dramatic than that achievable with Myrcludex-B, a lipopeptide consisting of amino acids 2 – 48 of the HBV L protein. Later replication cycle steps such as replication and particle assembly and release were unaffected. When chenodeoxycolic acid (15 mg per kg body weight) was administered to n = 3 chronically HDV infected individuals over a period of 8 days we observed no clear change in viral load.
Conclusion: Primary and conjugated BA inhibit NTCP-mediated HDV entry into hepatocytes providing new evidence for an essential role of NTCP in HBV/HDV cell entry. However, the primary BA chenodeoxycolic acid does not alter viral load suggesting that inhibitory effect may be to subtle to significantly alter viral load in the setting of established chronic infection in vivo.
