Oral delivery of microencapsulated proteins

Significant systemic and mucosal immune response induced on oral delivery of diphtheria toxoid using nano-bilosomes

BACKGROUND AND PURPOSE

Over the last decade apprehension has been growing over the effectiveness of existing parenteral vaccines for diphtheria and has created an interest in the development of a mucosally active vaccine. Oral immunization appears to be an effective alternative, but is not without the inherent disadvantages of antigen destruction and tolerance. Therefore, our objective was to investigate the incorporation of diphtheria toxoid (DTx) into bilosomes, which could provide protection as well as aid transmucosal uptake and subsequent immunization. Another objective was to determine the oral dose that will produce serum antibody titres comparable with those produced by i.m. doses of DTx.

EXPERIMENTAL APPROACH

Bilosomes containing DTx were prepared by thin film hydration and characterized in vitro for their shape, size, percent antigen entrapment and stability. In the in vivo study the anti-DTx IgG and anti-DTx sIgA response was estimated using elisa, in serum and in various body secretions, respectively, following oral immunization with different doses of DTx entrapped in nano-bilosomes.

KEY RESULTS

High dose loaded nano-bilosomes (DTxNB3, 2Lf) produced comparable anti-DTx IgG levels in serum to those induced by i.m. alum-adsorbed DTx (0.5Lf). In addition, all the nano-bilosomal preparations elicited a measurable anti-DTx sIgA response in mucosal secretion, whereas i.m. alum-adsorbed DTx (0.5Lf) was unable to elicit this response.

CONCLUSIONS AND IMPLICATIONS

The orally administered nano-bilosomal DTx formulation produced comparable serum antibody titres to i.m.alum-adsorbed DTx, at a fourfold higher dose and without the induction of tolerance. This approach will provide an effective and comprehensive immune protection against diphtheria with better patient compliance.

M-cell targeted delivery of recombinant hepatitis B surface antigen using cholera toxin B subunit conjugated bilosomes

The present study aims to improve upon our earlier findings with bilosomes as potential delivery vehicle through oral route for recombinant hepatitis B surface antigen (HBsAg). The work entails the conjugation of bilosomal system with cholera toxin B subunit (CTB) to increase transmucosal uptake via M-cell specific delivery approach. The study encompasses the development and characterization of HBsAg-loaded CTB-conjugated system for percent antigen entrapment, size, shape, and stability in SGF (USP, pH 1.2), SIF (USP, pH 7.5) and in bile salt solutions. Biological activity of CTB, subsequent to conjugation, was verified by hemagglutination test. Anti-HBsAg IgG response in serum and anti-HBsAg sIgA in various body secretions were estimated using ELISA, following oral immunization with 10 microg dose-loaded CTB-conjugated bilosomes (CTB2) and 20 microg dose-loaded CTB-conjugated bilosomes (CTB1) in BALB/c mice. The results showed that CTB1 produced anti-HBsAg IgG antibody titre response comparable to that of the intramuscular (i.m.) injection of 10 microg of alum-adsorbed HBsAg. Moreover, all the bilosomal preparations elicited measurable sIgA vis-à-vis negligible response with i.m. administered HBsAg. Thus, HBsAg-loaded CTB-conjugated bilosomes provide a promising potential for targeted oral immunization against hepatitis B.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

M cell targeting by lectins: a strategy for mucosal vaccination and drug delivery

Bioadhesins are a recognised method of enhancing the absorption of drugs and vaccines at mucosal surfaces. Additionally, bioadhesins allow for cell specific targeting. Lectin-mediated targeting and delivery exploits unique surface carbohydrates on mucosal epithelial cells. The antigen-sampling M cells offer a portal for absorption of colloidal and particulate delivery vehicles, including bacteria, viruses and inert microparticles. We review work supporting the use of lectins to aid targeting to intestinal M cells. Consideration is also given to lectin-mediated targeting in non-intestinal sites and to the potential application of other bioadhesins to enhance M cell transport. While substantial hurdles must be overcome before mucosal bioadhesins can guarantee consistent, safe, effective mucosal delivery, this strategy offers novel opportunities for drug and vaccine formulation.

Protein drug oral delivery: the recent progress

Rapid development in molecular biology and recent advancement in recombinant technology increase identification and commercialization of potential protein drugs. Traditional forms of administrations for the peptide and protein drugs often rely on their parenteral injection, since the bioavailability of these therapeutic agents is poor when administered nonparenterally. Tremendous efforts by numerous investigators in the world have been put to improve protein formulations and as a result, a few successful formulations have been developed including sustained-release human growth hormone. For a promising protein delivery technology, efficacy and safety are the first requirement to meet. However, these systems still require periodic injection and increase the incidence of patient compliance. The development of an oral dosage form that improves the absorption of peptide and especially protein drugs is the most desirable formulation but one of the greatest challenges in the pharmaceutical field. The major barriers to developing oral formulations for peptides and proteins are metabolic enzymes and impermeable mucosal tissues in the intestine. Furthermore, chemical and conformational instability of protein drugs is not a small issue in protein pharmaceuticals. Conventional pharmaceutical approaches to address these barriers, which have been successful with traditional organic drug molecules, have not been effective for peptide and protein formulations. It is likely that effective oral formulations for peptides and proteins will remain highly compound specific. A number of innovative oral drug delivery approaches have been recently developed, including the drug entrapment within small vesicles or their passage through the intestinal paracellular pathway. This review provides a summary of the novel approaches currently in progress in the protein oral delivery followed by factors affecting protein oral absorption.

Lectin-mediated mucosal delivery of drugs and microparticles

Absorption of drugs and vaccines at mucosal surfaces may be enhanced by conjugation to appropriate bioadhesins which bind to mucosal epithelia. Bioadhesins might also permit cell- and site-selective targeting. One approach is to exploit surface carbohydrates on mucosal epithelial cells for lectin-mediated delivery. We review work supporting the use of lectins as mucosal bioadhesins in the gastrointestinal and respiratory tracts, the oral cavity and the eye. The gastrointestinal tract is particularly favoured for mucosal delivery. Many studies have demonstrated that the antigen sampling intestinal M cells offer a portal for absorption of colloidal delivery vehicles. Evidence is presented that M cell targeting may be achieved using M cell-specific lectins, microbial adhesins or immunoglobulins. While many hurdles must be overcome before mucosal bioadhesins can guarantee consistent, safe, effective mucosal delivery, this is an exciting area of research that has important implications for future drug and vaccine formulation.