Thermodynamic stabilization of von Willebrand factor A1 domain induces protein loss of function.

The von Willebrand disease (vWD) is the most common hereditary bleeding disorder caused by defects of the von Willebrand Factor (vWF), a large extracellular protein in charge of adhering platelets to sites of vascular lesions. vWF performs this essential homeostatic task via specific protein-protein interactions between the vWF A1 domain and the platelet receptor, the glycoprotein Ib alpha (GPIBα). The two naturally occurring vWF A1 domain mutations G1324A and G1324S, near the GPIBα binding site, induce a dramatic decrease in platelet adhesion, resulting in a bleeding disorder classified as type 2M vWD. However, the reason for the drastic phenotypic response induced by these two supposedly minor modifications remains unclear. We addressed this question using a combination of equilibrium-molecular dynamics (MD) and nonequilibrium MD-based free energy simulations. Our data confirms that both mutations maintain the highly stable Rossmann fold of the vWF A1 domain. G1324A and G1324S mutations hardly changed the per-residue flexibility of the A1 domain but induced a global conformational change affecting the region near the binding site to GPIBα. Furthermore, we observed two significant changes in the vWF A1 domain upon mutation, the global redistribution of the internal mechanical stress and the increased thermodynamic stability of the A1 domain. These observations are consistent with previously reported mutations increasing the melting temperature. Overall, our results support the idea of thermodynamic conformational restriction of A1-before the binding to GPIBα-as a crucial factor determining the loss-of-function of the G1324A(S) vWD mutants.

Development of self-nanoemulsifying tablet (SNET) for bioavailability enhancement of sertraline

The purpose of the study was to combine the advantages of self-nanoemulsifying drug delivery systems and tablets as a conventional dosage form. Self-nanoemulsifying drug delivery system (SNEDDS) was prepared to enhance the solubility and thus oral bioavailability of sertraline. Aqueous titration method was used to prepare the liquid SNEDDS; ternary phase diagrams were constructed and based on smaller droplet size (24.8 nm), minimum viscosity (153.63 cP) and polydispersity index (0.182), higher percentage transmittance (95%) and in vitro drug release (97%), an optimum system was designated. Liquid SNEDDS was transformed into free-flowing powder by solid adsorption technique followed by compression into tablets. In vitro release of sertraline from liquid and solid SNEDDS was found to be highly significant compared to plain sertraline (p<0.01). Pharmacokinetic studies after oral administration of liquid and solid SNEDDS in rats showed about 6-and 5-fold increased absorption of sertraline compared to the aqueous suspension of sertraline. These studies demonstrate that the solid SNEDDS are promising strategies for successful delivery of poorly water-soluble drug like sertraline