Stabilization and encapsulation of human immunoglobulin G into biodegradable microspheres

The instability of protein during preparation, storage, and release has become a major concern in recent years in the encapsulation of proteins into biodegradable polymers for controlled release systems. The present investigation was performed to study the mechanism of degradation of human immunoglobulin G (IgG) in double emulsion and solid-in-oil-in-water (S/O/W) encapsulation processes. The stabilizing effects of various excipients during the period of protein atomization using spray freeze-drying and subsequent encapsulation into polylactide-co-glycolide (PLGA) microspheres were explored. The size-exclusion high-performance liquid chromatography (SEC-HPLC) results showed that ultrasonication did not change the primary structure of IgG significantly. However, enzyme-linked immunosorbent assay (ELISA) revealed that the subsequent double-emulsion solvent evaporation process denatured nearly 80% of the total amount of IgG. This was possibly due to the adsorption, unfolding, and aggregation of IgG at the water/organic solvent interface. Both mannitol and trehalose could stabilize IgG during spray freeze-drying, with over 90% retention of its molecular integrity and immunoactivity, which were verified using SEC-HPLC and ELISA. Solid protein microparticles were further entrapped into monolithic-type microspheres of PLGA using the S/O/W method. FTIR results suggested that the incomplete release that is often observed in the formulation of controlled protein release systems may be due to the degradation or aggregation of protein in the solid polymer matrix.