The role of Peyer's patches in intestinal humoral immune responses is limited to memory formation

Nanoencapsulation II. Biomedical applications and current status of peptide and protein nanoparticulate delivery systems

The concept of polymeric nanoparticles for the design of new drug delivery systems emerged a few years ago, and recent rapid advances in nanotechnology have offered a wealth of new opportunities for diagnosis and therapy of various diseases. Recent progress has made possible the engineering of nanoparticles to allow the site-specific delivery of drugs and to improve the pharmacokinetic profile of numerous compounds with biomedical applications such as peptide and protein drugs. Biologically active peptides and their analogues are becoming an increasingly important class of drugs. Their use for human and animal treatment is problematic, however, because some of these drugs are generally ineffective when taken orally and thus have been administered chiefly by the parenteral route. This review covers some of the historical and recent advances of nanotechnology and concludes that polymeric nanoparticles show great promise as a tool for the development of peptide drug delivery systems.

Polymeric particulates to improve oral bioavailability of peptide drugs

Oral administration remains the most convenient way of delivering drugs. Recent advances in biotechnology have produced highly potent new molecules such as peptides, proteins and nucleic acids. Due to their sensitivity to chemical and enzymatic hydrolysis as well as a poor cellular uptake, their oral bioavailability remains very low. Despite sophisticated new delivery systems, the development of a satisfactory oral formulation remains a challenge. Among the possible strategies to improve the absorption of drugs, micro- and nanoparticles represent an exciting approach to enhance the uptake and transport of orally administered molecules. Increasing attention has been paid to their potential use as carriers for peptide drugs for oral administration.

This article reviews the most common manufacturing methods for polymeric particles and the physiology of particle absorption from the gastrointestinal (GI) tract. In a second part, the use of polymeric particulate systems to improve the oral absorption of insulin is discussed.

Comparison of poly(DL-lactide-co-glycolide) and polystyrene microsphere targeting to intestinal M cells

The interaction of poly(DL-lactide-co-glycolide) (PLG) and polystyrene microspheres with the follicle-associated epithelium (FAE) of rabbit Peyer's patches was compared. Binding by PLG microspheres to the FAE was an order of magnitude lower than that of polystyrene microspheres of equivalent size (0.5-0.6 microns diameter). Although PLG microspheres are not selectively targeted to the M cell surface, as is the case with polystyrene microspheres, a high proportion of those that bind to M cells are transcytosed, resulting in the transepithelial delivery of 1.5 x 10(4) PLG microspheres/mm2 FAE. This represents the first direct demonstration of transepithelial delivery of PLG microspheres by M cells, which is crucial to the potential use of such vehicles for the oral delivery of drugs and vaccines. As native PLG microspheres are not optimally targeted to the M cell surface, there is scope for the further improvement of their efficacy by surface modifications.

Anti-TNP-forming cells in rats after different routes of priming with TNP-LPS followed by intranasal boosting with the same antigen

To study the reactivity of nasal-associated lymphoid tissue (NALT) and its position in the mucosal immune system, rats were intranasally challenged with 200 micrograms TNP-LPS. Priming had occurred 15 days previous to the challenge with the same antigen and dose, either intranasally, intratracheally, subcutaneously in the cheek or intraperitoneally. The number of anti-TNP antibody-forming cells (AFC) was determined in various tissues using the conjugate TNP/alkaline phosphatase. Generally, anti-TNP AFC were predominantly found in the posterior cervical lymph nodes, while NALT contained hardly any such AFC. The highest response in the posterior cervical lymph nodes occurred on day 5, after subcutaneous priming and intranasal boosting. This also evoked peak responses in several other tissues. The highest response in spleen and lung occurred on day 7 after intraperitoneal priming and intranasal boosting. Irrespective of the immunization route, IgA was the least produced isotype in the spleen as compared to antigen-specific IgG and IgM. In the posterior cervical lymph nodes, besides specific IgG and IgM, a considerable proportion of specific IgA was produced. All four immunization routes yielded anti-TNP antibodies in serum. As for the non-lymphoid cells, the intratracheal-intranasal immunization protocol induced an increase in pulmonary macrophages on days 3 and 5. The immunological role of lung macrophages is discussed.