Mechanism of charge self-reversal nano-nutrient delivery system to overcome the mucosal barrier

Abstract

When delivering hydrophobic nutrients such as curcumin (Cur) in the gastrointestinal tract (GIT), oral protein nanoparticles (NPs) will encounter several physiological barriers, including gastric acidity, digestive enzymes, mucus, and the epithelial layer. It is worth noting that overcoming both mucus and epithelial barriers requires NPs with completely opposite surface properties. To address this challenge, this study developed enzyme-responsive NPs using chitosan (CS) and tripolyphosphate (TPP) co-modification of zein (Cur/ZCT NPs). Three types of ZCT NPs were studied: positively charged NPs (Cur/ZCT0.2), neutrally charged NPs (Cur/ZCT0.8), and negatively charged NPs (Cur/ZCT3.0), which exhibit good stability in GIT while preserving the bioactivity of Cur. ZCT0.8 (0.86 ± 3.86 mV) and ZCT3.0 (–32.75 ± 1.07 mV) demonstrated superior mucus penetration capabilities. ZCT NPs were shown to effectively undergo charge reversal in the presence of intestinal alkaline phosphatase (IAP). The enhanced cellular uptake of ZCT NPs compared to zein NPs can be attributed to two factors: (1) enzyme-responsive dephosphorylation leading to a hydrophobic and positively charged surface, and (2) the ability of NPs to enter cells via transcellular and paracellular pathways. In vivo experiments revealed that ZCT0.8 and ZCT3.0 NPs exhibited extended retention times in the small intestine and higher uptake by epithelial cells compared to other samples. In conclusion, the enzyme-responsive charge reversal mechanism in ZCT3.0 NPs results in enhancing stability and enabling effective traversal of mucus and epithelial barriers. Consequently, they exhibit significant potential as a nutrient delivery system.