Surfactant-free Formulation of Poly(Lactic/Glycolic) Acid Nanoparticles Encapsulating Functional Polypeptide: A Technical Note

Abstract

Therapeutic proteins or polypeptides can be formulated into various particulate delivery systems including the polymeric carriers to avoid rapid degradation and to maintain the sustained release for better therapeutic effects (1). Poly(lactic/glycolic) acid (PLGA) micro/nanoparticle is a widely used formulation agent because of its good biodegradability, biocompatibility, and approved clinical usage, which have been available in the market to treat prostate cancer, acromegaly, periodontal disease, and pediatric growth hormone deficiency (2). The sustaining and complete release of proteins in their native or active forms from the PLGA micro/nanoparticles is often a challenging task (3). Proteins are generally formulated into PLGA nanoparticles by water/oil/water double-emulsion–solvent evaporation method, which generates hydrophilic/hydrophobic interface that may result in the unfolding or denaturing of protein molecules (4). Thus, polymeric surfactants are usually used to lower surface tension of protein solutions and to prevent aggregation of protein molecules at hydrophobic surface (1). Polyvinyl alcohol (PVA) is a widely used polymeric surfactant in the exterior aqueous phase as an emulsifier. However, the safety of PVA still appears to be a concern from the previous literature reports (5,6). Following repeated subcutaneous or intravenous administrations of PVA, various organ lesions and hypertension have been reported in rats, and central nervous system depression and anemia followed by renal damage have also been reported in beagle dogs; whereas, orally administered PVA is relatively harmless in mice or rat (5,6). Therefore, residual PVA was always removed by washing procedures such as repetitive centrifugation (7) or filtration (8), which removes not only the PVA but also the unencapsulated proteins or polypeptides, which might be often valuable or hard to collect. Hence, a few substituting emulsifiers have been studied. For example, poly(ethylene glycol) (PEG) was used successfully as the stabilizer to prepare enzyme-loaded PLGA microparticles (9). Besides, surfactant-free formulation was achieved by nanoprecipitation/solvent-displacement method that would not alter surface properties of PLGA nanoparticles, but this method may suffer the low encapsulation efficiency when low protein concentration solution is to be used (10). In the present study, we introduced another surfactant-free method to prepare PLGA nanoparticles encapsulating polypeptides by double-emulsion–solvent evaporation method. We used sucrose as the stabilizer of the exterior aqueous phase to prevent aggregation of PLGA nanoparticles during formulation process. Nerve growth factor (NGF), a small secreted protein which can induce the differentiation and survival of particular target neurons, was used as the model protein. As sucrose is a nontoxic material, additional washing procedures are not necessarily needed for NGF-loaded PLGA nanoparticles, and thus, the valuable NGF loss can be minimized. The release of functional NGF molecules from these nanoparticles was verified by either the antibody recognition in enzyme-linked immunosorbent assay (ELISA) method or the induction on the neurite outgrowth of PC-12 cells.