Preparation, complexation mechanism and properties of nano-complexes of Astragalus polysaccharide and amphiphilic chitosan derivatives

To improve the small intestinal absorption efficacy of Astragalus polysaccharides (APS) through oral administration, amphiphilic chitosan derivatives conjugated with deoxycholic acid residues in the absence and presence of vitamin B 12 residues (DA-Chit and VB 12 -DA-Chit, respectively) were synthesized and characterized by FTIR and NMR spectroscopy. APS and the amphiphilic chitosan derivatives formed the nano-complexes with positive zeta potentials in the size of 100–150   nm observed using scanning electron microscopy. To investigate the fluorescent properties of APS, a Congo red residue-conjugated APS derivative (CR-APS) was synthesized. Fluorescence spectroscopy and resonance light scattering spectroscopy confirmed the formation of the CR-APS/DA-Chit nano-complex as a result of electrostatic interaction. The APS/DA-Chit and APS/VB 12 -DA-Chit nano-complexes were not toxic against the human colon adenocarcinoma (Caco-2) cells. The APS/VB 12 -DA-Chit nano-complex exhibited high permeation through intestinal enterocytes using the Caco-2 cell model, which could be beneficial to small intestinal absorption of humans.