Effect of PLGA as a polymeric emulsifier on preparation of hydrophilic protein-loaded solid lipid nanoparticles
Introduction
In recent years, many new pharmaceutically active polypeptides have been developed due to the progress of biotechnological techniques and genetic engineering. These new therapeutic biomolecules are usually characterized by large size, short plasma half-life, limited ability to cross cell membranes and frequent injection of drugs over a long therapeutic period [1], [2], [3], [4]. Therefore, the therapeutic potential of peptide and protein drugs, as well as their clinical application, is often hampered by a number of obstacles to their successful delivery [2], [4]. Such disadvantages have provided the impetus for the development of pharmaceutical formulation of peptides and proteins.
Many colloidal carriers of proteins, such as liposomes [5], [6], microemulsions [7] and nanoparticles [8], [9] have been studied as delivery systems to obtain better therapeutic efficacy. Among them, solid lipid nanoparticles (SLN) have attracted increasing attention in the past decades as an alternative dosage form to microemulsions, liposomes, and polymeric nanoparticles, because of the possibility of combining the advantages of other colloidal carriers but at the same time avoiding some of their disadvantages, such as good biocompatibility, biodegradability, high bioavailability, low toxicity, good storage capability, protecting chemically labile drugs from degradation, offering sustained release, can readily be produced in large scale [10], [11].
Therapeutically relevant peptides (e.g. calcitonin, cyclosporine A, insulin, LHRH), protein antigens (e.g. hepatitis B and malaria antigens) and model proteins (e.g. bovine serum albumin (BSA) and lysozyme) have been incorporated into or adsorbed onto SLN and further administered by parenteral routes or by alternative routes such as oral, nasal, pulmonary, ocular, and rectal routes [4], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21].
Lipophilic proteins can be incorporated easily into SLN due to the highly hydrophobic nature of the lipid matrices. However, due to their hydrophilic nature, most proteins were poorly microencapsulated into the hydrophobic matrix of SLN, tending to partition in the water phase during the preparation process, so the encapsulation efficiencies were generally low or proteins adsorbed onto the surface rather than encapsulated within SLN [16], [20], [22]. Therefore, optimum SLN systems need to be developed to improve the encapsulation efficiency (EE) and loading capacity (LC).
Poly (lactic-co-glycolic acid, PLGA) is an FDA approved biodegradable and biocompatible polymer which has been used in human clinic for years [23], [24], [25]. PLGA copolymers are composed of different ratios of lactic acid and glycolic acid. The lactic acid is hydrophobic, while the glycolic acid is hydrophilic [25], [26]. Therefore, the copolymer has a dual nature in structure, similar to an amphiphile, with part of the molecule exhibiting lipophilicity and another part exhibiting hydrophilicity, which is necessary for use as a surface-active agent. PLGA (50:50) was used as a novel emulsifier in current work to prepare hydrophilic protein-loaded SLN for enhanced encapsulation efficiency and loading capacity.
Section snippets
Materials
Hydrogenated castor oil (HCO) was purchased from Tongliao Tonghua Castor Chemical Co., Ltd. (Inner Mongolia, China). Bovine serum albumin, lysozyme, insulin and poly vinyl alcohol (PVA) were purchased from Sigma (St. Louis, MO, USA). Fluorescein isothiocyanate (FITC)–anti-rabbit IgG (H + L) and the reagents used in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) were bought from Beijing Dingguo Tech. Co., Ltd. (Beijing, China). PLGA (50:50, IV 0.26–0.54) was obtained from
Effect of PLGA on the primary w/o emulsification
The effect of PLGA on the primary w/o emulsification was assessed with different model proteins (BSA, lysozyme and insulin). When the oil phase contained HCO alone, phase separation occurred immediately after sonication, and the protein was denatured and floated in the upper aqueous phase. When an appropriate amount of PLGA was added to the lipid phase, stable w/o emulsions were formed. The minimum content of PLGA to form stable emulsion for different formulations was shown in Table 1.
Effect of PLGA on the stabilization of the w/o emulsion
Three
Discussion
In this work, the effect of PLGA as a novel polymeric emulsifier for preparation of hydrophilic protein-loaded SLN has been investigated. PLGA used for encapsulating protein within biodegradable polymeric nano- and microparticles has gained some popularity, because of their noteworthy properties in terms of tissue compatibility and biodegradability [30]. PLGA copolymers are composed of different ratios of lactic acid and glycolic acid, the former is hydrophobic and the latter is responsible for
Conclusion
This work proved that PLGA is a highly efficient emulsifier for preparation of hydrophilic protein-loaded SLN with enhanced encapsulation efficiency and loading capacity. The strategy using PLGA as a novel emulsifier could be an effective way to overcome the difficulties of encapsulating hydrophilic proteins in SLN and extend the therapeutic potential of hydrophilic peptide and protein drugs.
Acknowledgement
This work was supported by the National High Technology Research and Development Program (“863” Program) of China (2006AA10A2030).
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