FRET-based dual-emission and pH-responsive nanocarriers for enhanced delivery of protein across intestinal epithelial cell barrier.

The oral route is a convenient and commonly employed way for drug delivery. However, therapeutic proteins have poor bioavailability upon oral administration due to the impermeable barrier from intestinal epithelial tight junction (TJ). Moreover, the pH of the small intestine varies among different regions of the intestinal tract where digestion and absorption occur at different levels. In this study, a tunable dual-emitting and pH-responsive nanocarrier that can alter the fluorescent color and emission intensity in response to pH changes and can trigger the opening of intestinal epithelial TJ at different levels were developed from chitosan-N-arginine and poly(γ-glutamic acid)-taurine conjugates. As pH increased from 6.0 to 8.0, the binding affinity of the oppositely charged polyions decreased, whereas the ratio of the intensity of the donor-to-acceptor emission intensity (ID/IA) increased by 27-fold. The fluorescent and pH-responsive nanocarrier was able to monitor the pH change of intestinal environment and to control the release of an anti-angiogenic protein in response to the pH gradient. The nanocarrier triggered the opening of intestinal epithelial TJ and consequently enhanced the permeation of the released protein through the intestinal epithelial barrier model (Caco-2 cell monolayer) to inhibit tube formation of human umbilical vein endothelial cells.