Paracellular enhancers Chitosan and EDTA increase intestinal permeability of Hexarelin and Enalaprilat in rats
Background
Effective oral delivery of peptide drugs like hexarelin and enalaprilat is a significant challenge due to their poor intestinal permeability. While transcellular permeation enhancers have shown some success with smaller peptides like enalaprilat (349 Da), they are ineffective for larger ones like hexarelin (887 Da). This gap necessitates exploring alternative pathways for absorption. The paracellular pathway, which involves transport through the tight junctions between intestinal cells, represents a promising route. This study investigates whether specific paracellular enhancers can open these junctions to facilitate the absorption of both small and large hydrophilic peptides, potentially overcoming the limitations of transcellular strategies.
Study Design
The study utilized a rat single-pass intestinal perfusion model with concomitant blood sampling to investigate intestinal permeation. Researchers perfused the rat intestine with solutions containing the peptides hexarelin and enalaprilat, alongside several paracellular permeation enhancers. The enhancers tested were chitosan (5 mg/mL) and ethylenediaminetetraacetate (EDTA) at two concentrations, 1 mg/mL and 5 mg/mL. They also tested the effect of a low luminal tonicity solution (100 mOsm) with and without lidocaine. The primary endpoint was the change in lumen-to-blood permeability of the two peptides. Mucosal barrier integrity was assessed by measuring the blood-to-lumen clearance of 51chromium-labeled EDTA (CLCr-EDTA).
Results
The two paracellular permeation enhancers, chitosan and EDTA, successfully increased the mucosal permeability of both hexarelin and enalaprilat. The study noted that the increase in permeability was similar for both peptide drugs, despite their significant difference in molecular weight. The mucosal blood-to-lumen flux of 51Cr-EDTA, a marker for mucosal barrier compromise, was also increased by both chitosan and EDTA, confirming their mechanism of action on the paracellular pathway.
In contrast, luminal hypotonicity (100 mOsm) did not affect the lumen-to-blood transport of either enalaprilat or hexarelin.
This suggests that while hypotonicity does affect paracellular transport, it primarily impacts the mucosal crypt region, which is less accessible to luminal contents. The findings support the hypothesis that paracellular enhancers are more effective for increasing the intestinal absorption of hydrophilic peptides compared to transcellular enhancers, especially for larger molecules.
Key Findings
- Paracellular permeation enhancers chitosan (5 mg/mL) and EDTA (1 and 5 mg/mL) increased the mucosal permeability of both hexarelin and enalaprilat.
- The increase in permeability for both peptides was of a similar extent, despite their different molecular weights (887 Da vs 349 Da).
- Luminal hypotonicity (100 mOsm) did not affect the lumen-to-blood transport of enalaprilat or hexarelin.
- Both chitosan and EDTA, as well as luminal hypotonicity, increased the blood-to-lumen clearance of 51Cr-EDTA, a marker of mucosal barrier opening.
Why It Matters
This research provides a proof-of-concept for improving the oral bioavailability of larger peptides like hexarelin by targeting the paracellular pathway. For individuals using oral peptide formulations, this suggests that co-administration with specific enhancers like chitosan or EDTA could significantly boost absorption and efficacy. The key takeaway is that paracellular enhancement is a viable strategy for peptides that are too large for transcellular routes. This work is still preclinical (in rats) and far from a human-ready protocol; safety and optimal dosing of these enhancers in humans need extensive investigation. However, it opens the door for developing more effective oral peptide delivery systems by combining the peptide with a suitable absorption enhancer in a single formulation.
hexarelin
enalaprilat
peptide
oral bioavailability
drug delivery
permeability enhancer
