Critical role of bile acid (BA) in the cellular entry and permissiveness of Hepatitis B virus in vitro

Background: Lack of universal replication system for hepatitis B virus with narrow host range and organ tropism has hampered to uncover the pathogenesis of HBV. Previously, we reported the essentiality of humoral milieu and its components toward HBV and hepatitis C virus survival/viability in vitro. Of these components, the precise role of enterohepatic humoral milieu such as bile acid (BA) on HBV cultivation in vitro and in vivo is unknown. Objective: We explored whether BA, specifically taurochenodeoxycholic acid (tCDCA) would directly regulate the viral DNA and surface antigen expression of HBV in vitro, consequently rendering HBV to enter into human or murine immortalized hepatocytes, and non-hepatocytes. Result: We found that higher concentration of taurochenodeoxycholic acid (tCDCA) is able to preserve the genomic stability of HBV in cell-free DMEM, showing higher the surface antigenicity than taurocholic acid (tCA). In line, we found that in vitro cell culture condition (100 μmol/L of tCDCA coupled with 1 × 10⁸ g e/mL HBV) would be optimal for HBV entry into target cells. Using this, human (HepG2, Huh7), and rodent (Hepa1c1c7, H4-II-E) hepatoma cell lines were infected by HBV, as evidenced by the presence of HBV biomarkers (HBsAg, and HBV DNA in culture supernatant, as well as HBcAg in cell). Further, cellular entry test revealed that HBV is able to infect 12 different non-hepatic cell lines regardless of species, and organ/tissue, consequently reproducing progeny as confirmed by HBV biomarkers. Last, reinfection test showed that the progenies of HBV from immortalized HepG2, and Hepa1c1c7 cells are able to enter into each or vice versa naïve HepG2, and Hepa1c1c7 cells with or without BA. Conclusion: This study demonstrates that enterohepatic humoral milieu such as BA, specifically tCDCA would directly regulate HBV DNA and its surface antigen expression in vitro, consequently rendering HBV to enter into human or murine immortalized hepatocytes, and non-hepatocytes. This is the first note to render HBV permissive to human or rodent hepatic and non-hepatic cells via sole manipulation of humoral milieu, thus establishing the platform for in vitro robust replication system of HBV.