Oral Delivery of Pathogens from the Intestine to the Nervous System

SNAC for Enhanced Oral Bioavailability: An Updated Review

The delivery of proteins and peptides via an oral route poses numerous challenges to improve the oral bioavailability and patient compliance. To overcome these challenges, as well as to improve the permeation of proteins and peptides via intestinal mucosa, several chemicals have been studied such as surfactants, fatty acids, bile salts, pH modifiers, and chelating agents, amongst these medium chain fatty acid like C10 (sodium caprate) and Sodium N-[8-(2-hydroxybenzoyl) amino] caprylate (SNAC) and its derivatives that have been well studied from a clinical perspective. This current review enumerates the challenges involved in protein and peptide delivery via the oral route, i.e., non-invasive routes of protein and peptide administration. This review also covers the chemistry behind SNAC and toxicity as well as mechanisms to enhance the oral delivery of clinically proven molecules like simaglutide and other small molecules under clinical development, as well as other permeation enhancers for efficient delivery of proteins and peptides.

Development of a versatile in vitro method for understanding the migration of Fasciola hepatica newly excysted juveniles

Fasciola hepatica is a parasitic trematode that causes serious losses to livestock producers, and also zoonotic disease. The limitations of chemotherapy for the control of fasciolosis have led to significant interest in the development of vaccines to protect cattle and sheep from infection. However, relatively few studies have concentrated on the mechanisms of invasion of the gut by newly excysted juvenile liver flukes (NEJ) and the host response triggered by this event. The aim of this work was to develop an in vitro model to study invasion by NEJ, while also reducing the requirement for challenge infections of experimental animals. Fasciola hepatica metacercariae were excysted in vitro and placed into compartments containing rat distal jejunal sheets. Variations in incubation medium, chamber size and incubation temperature were used to identify optimal conditions for NEJ migration across the gut. Histological examination showed increased migration until 120 min post-incubation. The use of RPMI, without gassing at 39 °C, as the incubation medium was found to be optimal, with 40·5% of NEJ migrating after 150 min. This study describes a readily-reproducible method for studying the migration of F. hepatica NEJ within the definitive host. It will be useful for identifying potential drug and vaccine targets.

Eosinophil-nerve interactions and neuronal plasticity in rat gut associated lymphoid tissue (GALT) in response to enteric parasitism

Intestinal lymphoid tissues and Peyer's patches (PP) are innervated sites of immune surveillance in the gastrointestinal tract. Following infection with F. hepatica, neuronal hyperplasia and significantly increased eosinophil and mast cell trafficking to colonic PP sites were evident in rat tissues. Nerve-eosinophil associations were significantly elevated in infected colon and colonic PP, as were colonic tissue levels of the circulatory recruitment factors IL-5 and eotaxin. Increased immunoreactivity for neuronal plasticity markers GAP-43 and neural cell adhesion molecule (NCAM) was also found in infected tissues. Such neuronal alterations in the PP during enteric parasitism may have functional consequences on particular or pathogen uptake.

Oral Delivery of Peptide Drugs

A wide variety of peptide drugs are now produced on a commercial scale as a result of advances in the biotechnology field. Most of these therapeutic peptides are still administered by the parenteral route because of insufficient absorption from the gastrointestinal tract. Peptide drugs are usually indicated for chronic conditions, and the use of injections on a daily basis during long-term treatment has obvious drawbacks. In contrast to this inconvenient and potentially problematic method of drug administration, the oral route offers the advantages of self-administration with a high degree of patient acceptability and compliance. The main reasons for the low oral bioavailability of peptide drugs are pre-systemic enzymatic degradation and poor penetration of the intestinal mucosa. A considerable amount of research has focused on overcoming the challenges presented by these intestinal absorption barriers to provide effective oral delivery of peptide and protein drugs. Attempts to improve the oral bioavailability of peptide drugs have ranged from changing the physicochemical properties of peptide molecules to the inclusion of functional excipients in specially adapted drug delivery systems. However, the progress in developing an effective peptide delivery system has been hampered by factors such as the inherent toxicities of absorption-enhancing excipients, variation in absorption between individuals, and potentially high manufacturing costs. This review focuses on the intestinal barriers that compromise the systemic absorption of intact peptide and protein molecules and on the advanced technologies that have been developed to overcome the barriers to peptide drug absorption.