(232i) Nanocrystalline Insulin: Molecular Mechanism of Poly Vinyl Alcohol (PVA) Induced Crystallinity

Diabetes treatment (insulin dependent diabetes mellitus – IDDM) requires administration of multiple dose of insulin, a 51 amino acid dual chain hormone which is normally stored in pancreatic β-cells. Though protein therapeutics can be administered by oral, subcutaneous, intravenous and aerosol but daily subcutaneous injection is most preferred route of insulin administration. However, inadequate control of blood glucose and poor patient compliance are associated drawbacks with this treatment. Furthermore, most protein drugs are unstable in biological fluids and have short half lives and are not fully absorbed from their route of administration because of their relatively high molecular weights. Protein nanocrystals are expected to be useable for alternative, more attractive delivery forms such as sustained release formulation. However, formulation of biological macromolecules like insulin, that has an inherent tendency to undergo degradation processes, such as aggregation, oxidation, hydrolysis, and deamidation, for sustained release as stable and structurally integrated active protein constitutes a challenge Various polymers with different physicochemical properties have been explored for the crystallization behavior. The formulation of excipients favoring crystallization of a protein in encapsulated biopharmaceuticals is still a challenge. In the present study the Poly-(D, L lactide-co-glycolide) (PLGA) based nanoparticles formulation of bovine insulin has been prepared. The use of poly vinyl alcohol (PVA) as a surfactant in inner aqueous phase has been explored for imparting the crystallinity to the prepared formulation. The prepared nanoparticles were analyzed for size and morphology by dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM studies of prepared formulation, analyzed by electron diffraction, showed the crystalline behavior. The powder X-ray diffraction (PXRD) studies of lyophilized formulation further supported the crystallinity of the formulation.   Differential scanning calorimetry (DSC) of lyophilized formulation showed the increase in enthalpy of fusion on increasing the PVA concentration in inner aqueous phase. On analyzing the released insulin by TEM and HRTEM (high resolution) the nanocrystalline insulin was observed. In in vitro release studies the released crystalline insulin was found to be conformationally and thermally stable using circular dichroism (CD) and   differential scanning calorimetry (DSC). The results in detail will be presented.