Preparation and properties of pH-responsive, self-assembled colloidal nanoparticles from guanidine-containing polypeptide and chitosan for antibiotic delivery

Amoxicillin is a traditional antibiotic used to treat Helicobacter pylori (H. pylori). However, the clinical applicability was limited by low local concentrations of amoxicillin that are reached at the sites of H. pylori infection. In this study, a pH-sensitive, guanidine-containing polypeptide composed of poly(γ-glutamic acid) (γ-PGA) and arginine (Arg) were synthesized. The γ-PGA-g-Arg polypeptide can self-assemble into colloidal nanoparticles at pH lower than 3.0, and the morphological changes are reversibly switched by elevating the pH of the colloidal suspension. The chemo-physical properties of the γ-PGA-g-Arg polypeptide were investigated by proton nuclear magnetic resonance (¹H NMR), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The γ-PGA-g-Arg colloidal nanoparticles were modified with a guanidinylated polymer, the chitosan (CS)-arginine(Ag) conjugate (CS-N-Arg). The effect of electrostatic complexation between γ-PGA-g-Arg polypeptide and CS-N-Arg conjugate extends the stable range of the self-assembled nanoparticles to a higher pH (pH>6.0), and the surface charge density changes from negative to positive. The morphological changes of the CS-N-Arg/γ-PGA-g-Arg complex nanoparticles in response to environmental pH were investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Amoxicillin release from the CS-N-Arg/γ-PGA-g-Arg NPs was reduced at pH 2.5 (gastric fluid, fasted state) and 4.5 (the gastric mucosal surface), but the antibiotic released rapidly from the nanoparticles at pH 7.0 (the sites of H. pylori infection). The amoxicillin-loaded CS-N-Arg/γ-PGA-g-Arg complex nanoparticles showed a superior antibacterial activity against the growth of H. pylori.