Effects of pH on molecular mechanisms of chitosan-integrin interactions and resulting tight-junction disruptions

Chitosan (CS) is a potential paracellular permeation enhancer for trans-epithelial drug delivery; however, its ability to enhance epithelial permeability in a pH-dependent manner remains unclear. This study was designed to explore the underlying molecular mechanisms with regard to the effect of CS on tight junction (TJ) disruption at different pH environments in Caco-2 cell monolayers. The experimental results revealed that the direct interaction between CS and integrin α_Vβ₃ on cell surfaces has a crucial role in CS-induced TJ opening, an indication of receptor activation. The mechanism of action appeared to be the electrostatic interaction between the positively-charged CS and the negatively-charged integrin α_Vβ₃. This electrostatic interaction led to the conformation change of integrin α_Vβ₃ and its clustering along the cell border, F-actin reorganization, and CLDN4 down-regulation, eventually resulting in the disruption of TJs and an increase in paracellular permeability. The above observations were all in a pH-dependent manner. As pH increased, CS became less positively charged, thereby losing its capability to interact with integrin α_Vβ₃ and failing to induce the TJ opening. These consequences might help to better understand the molecular mechanism of TJ opening mediated by CS, thereby facilitating the use of CS for trans-epithelial drug delivery.