Formulation of protein-loaded nanoparticles via freeze-drying

Several nanotechnology-based formulation strategies have been reported for the oral administration of biological drugs. However, a prerequisite often overlooked in developing these formulations is their adaptation to a solid dosage form. This study aimed to incorporate a freeze-drying step, using either mannitol or sucrose laurate (SLAE), into the formulation of new insulin-zinc nanocomplexes to render them resistant to intestinal fluids while maintaining a high protein loading. The resulting freeze-dried insulin-zinc nanocomplexes exhibited physicochemical properties consistent with the target product profile, including a particle size of ∼ 100 nm, a zeta potential close to neutrality (∼ -15 mV) and a high association efficiency (> 90%). Importantly, integrating the freeze-drying step in the formulation significantly improved the colloidal stability of the system and preserved the stability of the insulin molecules. Results from in vitro and in vivo studies indicated that the insulin activity remained fully retained throughout the entire formulation and freeze-drying processes. In brief, we present a novel protein formulation strategy that incorporates a critical freeze-drying step, resulting in a dry powder enabling efficient protein complexation with zinc and optimized for oral administration.