Permeation enhancer decorated nanoparticles for oral delivery of insulin: manipulating the surface density of borneol and PEG for absorption barriers

Oral protein drugs’ delivery faces challenges due to multiple absorption barriers for macromolecules. Co-administration with permeation enhancers and encapsulation in nano-carriers are two promising strategies to enhance their oral absorption. Herein, the poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are decorated with polyethylene glycol (PEG) and a traditional Chinese medicine-derived permeation enhancer borneol (BO) for oral insulin delivery. Compared with a physical mixture of BO and PEG-decorated PLGA NPs, PLGA–PEG–BO NPs significantly facilitate insulin permeation across intestinal epithelia through various transcytosis pathways. The relationship among the BO surface density, physico-chemical properties and multiple barriers penetration ability is further investigated. Increasing the BO density boosts penetration through the epithelial cell layer but reduces enzyme and mucus barrier penetration. When the surface PEG density is at 90% and BO density is at 10%, the NPs possess the strongest overall ability to overcome both the mucus layer barrier and epithelial cell barrier, as illustrated by the highest permeation efficiency through Caco-2/HT29-MTX cell co-cultural monolayers. In diabetic rodents, PLGA–PEG90%–BO10% NPs exhibit high intestinal safety and a substantial hypoglycemic effect, with insulin availability at 6.22 ± 2.30%, double that of orally delivered insulin PLGA–PEG NPs and far superior to a physical mixture with BO. This study reveals the importance of tailored absorption enhancer decoration for oral protein delivery.