Chapter 15 Mucosal Delivery of Liposome–Chitosan Nanoparticle Complexes

Abstract

Designing adequate drug carriers has long been a major challenge for those working in drug delivery. Since drug delivery strategies have evolved for mucosal delivery as the outstanding alternative to parenteral administration, many new drug delivery systems have been developed which evidence promising properties to address specific issues. Colloidal carriers, such as nanoparticles and liposomes, have been referred to as the most valuable approaches, but still have some limitations that can become more inconvenient as a function of the specific characteristics of administration routes. To overcome these limitations, we developed a new drug delivery system that results from the combination of chitosan nanoparticles and liposomes, in an approach of combining their advantages, while avoiding their individual limitations. These lipid/chitosan nanoparticle complexes are, thus, expected to protect the encapsulated drug from harsh environmental conditions, while concomitantly providing its controlled release. To prepare these assemblies, two different strategies have been applied: one focusing on the simple hydration of a previously formed dry lipid film with a suspension of chitosan nanoparticles, and the other relying on the lyophilization of both basic structures (nanoparticles and liposomes) with a subsequent step of hydration with water. The developed systems are able to provide a controlled release of the encapsulated model peptide, insulin, evidencing release profiles that are dependent on their lipid composition. Moreover, satisfactory in vivo results have been obtained, confirming the potential of these newly developed drug delivery systems as drug carriers through distinct mucosal routes.

Introduction

The efficient delivery of therapeutic peptides and proteins through routes other than the parenteral has been one of the major scientific challenges in drug delivery research. Mucosal administration of these molecules has a number of advantages, and many design strategies have been explored to administer these biomacromolecules by routes such as the oral, pulmonary, and ocular (Jorgensen et al., 2006). The most valuable approach to address this purpose consists of the application of colloidal carriers like nanoparticles and liposomes (de la Fuente et al., 2008).

Polymeric nanoparticles have reduced dimensions that provide them with extremely increased surface-to-volume ratio and surface functionality (Silva et al., 2007). Furthermore, they have been reported to increase drug absorption by reducing the resistance of the epithelium to drug transport in a localized area or by carrying the drug itself across the epithelium (Csaba et al., 2006). In this context, mucoadhesive polymers, such as chitosan, have been proven adequate materials to design suitable nanoparticulate carriers, facilitating their interaction with mucosal surfaces (Takeuchi et al., 2001b). Chitosan is a polysaccharide with reported ability to improve the permeation of macromolecules across epithelial barriers and chitosan nanoparticles (CS-NP) have demonstrated excellent capacity for protein entrapment and to increase their absorption through the nasal, intestinal, and ocular mucosa (Alonso and Sánchez, 2003, De Campos et al., 2001, Fernández-Urrusuno et al., 1999a, Paolicelli et al., 2009). However, one of the major limitations of these nanoparticles is their limited stability in biological fluids, such as the gastrointestinal media (Issa et al., 2005).

Liposomes are versatile structures that enable the protection of the encapsulated material and tend to be relatively innocuous, because they comprise naturally occurring lipids that are metabolized at endogenous level (Jiang et al., 2007, Torchilin, 2005). Their organized structure (an aqueous core enclosed within one or more phospholipid bilayers) permits the association of drugs with both the aqueous and lipid compartments, and drug release can usually be controlled, depending on the bilayer number and composition (Courrier et al., 2002, Kirby and Gregoriadis, 1999). Moreover, their aqueous core ensures the preservation of protein structure and conformation, while the external lipids might help to improve absorption across biological barriers (El-Maghrabya et al., 2008, Fenske et al., 2008, Gregoriadis, 1988). Nevertheless, one of the most reported problems of liposomes is their lack of stability in terms of leakage of the encapsulated drug (Gabizon, 1995). In fact, if liposomes' inner core was solid instead of liquid, leakage would decrease dramatically, since drug release would imply an extra step of release from the solid core, followed by the traditional diffusion across the lipid bilayer (Campbell et al., 2004, Huang et al., 2005).

We have therefore decided to combine the advantages of each of the described colloidal systems under the form of a single and new drug delivery system, which assembles the chitosan nanoparticles in lipid vesicles (liposome–chitosan nanoparticle, L/CS-NP, complexes) (Carvalho et al., 2001). This system should permit an efficient encapsulation of therapeutic macromolecules, ensuring at the same time their stability and, ideally, providing a controlled release. As expected, as the phospholipid bilayer comprises an extra barrier that should be overcome before release, phospholipids provided a controlled release of the encapsulated model protein, insulin (Grenha et al., 2008a), and also provided stability in biological fluids. Moreover, the complexes demonstrated very low toxicity in ocular epithelial cells (Diebold et al., 2007).

Depending on the administration objective (oral, ocular, or lung delivery), different methodologies have been established to prepare the lipid/chitosan nanoparticle complexes, which are described in detail in this chapter.