In vitro study of polyoxyethylene alkyl ether niosomes for delivery of insulin

Abstract

In this study, niosomes of polyoxyethylene alkyl ethers (Brij™) were prepared for encapsulation of insulin by film hydration method. Without cholesterol, brij 35 and brij 58 did not form niosomes, apparently because of relatively large polar head groups in comparison with their alkyl chains. The size of vesicles depended on the cholesterol content, charge incorporation or hydrophilicity of surfactants. Entrapment of insulin in bilayer structure of niosomes protected it against proteolytic activity of α-chymotrypsin, trypsin and pepsin in vitro. The maximum protection activity was seen in brij 92/cholesterol (7:3 molar ratios) in which only 26.3 ± 3.98% of entrapped insulin was released during 24 h in simulated intestinal fluid (SIF). The kinetic of drug release for most formulations could be best described by Baker and Lonsdale equation indicating diffusion based delivery mechanism. These results indicate that niosomes could be developed as sustained release oral dosage forms for delivery of peptides and proteins such as insulin.

Introduction

The delivery of protein pharmaceuticals to the systemic circulation through oral administration is hindered by numerous barriers, including proteolytic enzymes, sharp pH gradients and low epithelial permeability (Lee and Yamamoto, 1990). Recently, different systems and technologies such as enteric-coated capsules (Hosny et al., 2002), gel beads (Sriamornsak, 1998), intestinal patches (Whitehead et al., 2004), liposomes (Takeuchi et al., 1996, Kim et al., 1999, Iwanaga et al., 1999, Kisel et al., 2001, Wu et al., 2004), microparticles (Agarwal et al., 2001, Morcol et al., 2004, Morishita et al., 2004), microspheres (Morishita et al., 1992), mucoadhesive tablets (Caliceti et al., 2004, Krauland et al., 2004), nanocubicles (Chung et al., 2002), nanospheres (Damge et al., 1997, Carino et al., 2000, Foss et al., 2004), and non-ionic surfactant vesicles (Yoshida et al., 1992) have been used to overcome these barriers and improve protein absorption following oral delivery. Among these, vesicular systems such as liposomes have been investigated more than the other systems. Unfortunately, a number of serious limitations exist with the use of liposomes such as in vitro (Ausborn et al., 1992) and in vivo (Poste, 1983) instability.

One alternative of phospholipids, the main constituents of liposomes, is the hydrated mixture of cholesterol and non-ionic surfactants such as alkyl ethers, alkyl esters or alkyl amides non-ionic surfactants (Manosroi et al., 2003). This type of vesicle formed from the above mixtures has been known as niosomes or non-ionic surfactant vesicles (NSVs). The low cost, greater stability, ease of storage and also large numbers of available vesicle forming non-ionic surfactants make these vesicles more attractive than liposomes for industrial production both in pharmaceutical and cosmetic applications (Uchegbu and Vyas, 1998).

Both hydrophilic and hydrophobic substances can be embedded in niosomal vesicles. Some proteins and peptides such as alpha-interferon (Niemiec et al., 1995), bovine serum albumin (Brewer and Alexander, 1992, Murdan et al., 1999), cyclosporine A (Niemiec et al., 1995, Waranuch et al., 1998), 9-desglycinamide-8-arginine vasopressin [DGAVP] (Yoshida et al., 1992), GnRH-based anti-fertility immunogen (Ferro et al., 2004), haemagglutinin (Murdan et al., 1999), influenza viral antigens (Chattaraj and Das, 2003), insulin (Khaksa et al., 2000, Varshosaz et al., 2003), luteinizing hormone releasing hormone [LHRH] (Arunothayanun et al., 1999), ovalbumin (Brewer et al., 1998, Rentel et al., 1999) and recombinant human granulocyte-macrophage colony stimulating factor [rhGM-CSF] (Memisoglu et al., 1997) have been successfully encapsulated in niosomes. The encapsulation of pharmaceutical materials in niosomes can decrease drug toxicity, increase drug absorption, stability or activity and retard removal of drug from the circulation due to slow drug release.

In previous article we reported the encapsulation of insulin in sorbitan ester vesicles which led to protection of protein against proteolytic enzymes and sustained release of insulin (Varshosaz et al., 2003). In this study, the ability of polyoxyethylene alkyl ethers (C_nEO_m, Brij™) mixed with cholesterol to form bilayer vesicles and encapsulate recombinant human insulin was studied. Furthermore, encapsulation efficiency of insulin, protection against enzymes, thermal analysis and size distribution study of vesicles and characterization of niosomes with optical microscope were carried out.