Microsomal triglyceride transfer protein (MTP) is a lipid transfer protein that is required for the assembly and secretion of very low density lipoproteins by the liver and chylomicrons by the intestine. To further elucidate the nature of the lipid molecule binding and transport site on MTP, we have studied the relative rates at which MTP transports different lipid species. Assay conditions were chosen in which there were minimal changes in the physical properties of the substrate membranes so that transfer rates would reflect MTP-lipid interactions at a membrane surface. Lipid transport rates decreased in order of triglyceride > cholesteryl ester > diglyceride > cholesterol > phosphatidylcholine. Changes in the hydrophobic nature of a lipid molecule by the addition of a fatty acid, modulated the ability of MTP to transport it. Addition of one acyl chain from diglyceride to triglyceride, lysophosphatidylcholine to phosphatidylcholine, or cholesterol to cholesteryl ester increased the rate of MTP-mediated transport 10-fold. In contrast, the lipid transport rate was insensitive to the changes in the structure or charge of the polar head group on phospholipid substrates. Zwitterionic, net negative, or net positive charged phospholipid molecules were all transported at a comparable rate. The ability of MTP to transport lipids is strongly correlated to the binding of these lipids to MTP. Thus, MTP has a specific preference for binding and transporting nonpolar lipid compared with phospholipids, and within a class of lipid molecules, a decrease in polarity increases its tendency to be transported.

BMS-200475 was recently shown to have potent antiviral activity against hepatitis B virus (50% effective concentration ‫؍‬ 3.7 nM; 50% cytotoxic concentration ‫؍‬ 30 M). In metabolic studies in both HepG2 and hepatitis B virus-transfected 2.2.15 human hepatoma cell lines, the metabolism was similar, the primary products being the di-and triphosphates. The accumulation of triphosphate was rapid and detectable down to a 5 nM concentration of added drug. When cells were labeled at 25 M, the intracellular triphosphate concentration attained 30 pmol/10 6 cells (ϳ30 M). The intracellular half-life of the triphosphate was about 15 h. Compared with five other nucleoside analogs of medical interest (lamivudine, penciclovir, ganciclovir, acyclovir, and lobucavir), BMS-200475 was most efficiently phosphorylated to the triphosphate in HepG2 cells.

No abstract

This article is available online at http://dmd.aspetjournals.org

No abstract