Hepatitis B virus envelope L protein-derived bio-nanocapsules: mechanisms of cellular attachment and entry into human hepatic cells.

A bio-nanocapsule (BNC) is a hollow nanoparticle consisting of an approximately 100-nm-diameter liposome with about 110 molecules of hepatitis B virus (HBV) surface antigen L protein embedded as a transmembrane protein. BNC can encapsulate various drugs and genes and deliver them specifically to human hepatic cells based on the ability of HBV to recognize human hepatocyte, which is integrated in the N-terminal region of L protein. However, it is elusive whether the cellular attachment and entry into hepatic cells of BNC utilize the early infection mechanism of HBV. In this study, we have found that while all human hepatic cells show distinct affinities for BNC compared to non-hepatic cells, primary hepatocytes shows the highest efficiency for cellular binding and incorporation of BNC. Amounts of BNCs bound weakly and strongly to cell membranes and those entered into the cells varied significantly depending on the types of human hepatic cells. The weak and strong binding modes of BNC are likely mediated through binding to two distinct HBV receptors (heparin-mediated low-affinity and unidentified high-affinity receptors), which play major roles in the early infection mechanism of HBV. The rates of cellular uptake of BNC are similar to those reported for HBV. The BNCs incorporated into the cells are swiftly sorted to either early endosomes or macropinosomes and then to late endosomes and/or lysosomes. These findings strongly suggest that BNC is bound to and incorporated into human hepatic cells according to the early infection mechanism of HBV.