Opposites Attract: Electrostatically Driven Loading of Antimicrobial Peptides into Phytoglycogen Nanocarriers

Abstract

Antimicrobial peptides, such as GL13K, have a high binding selectivity toward bacterial membranes, while not affecting healthy mammalian cells at therapeutic concentrations. However, delivery of these peptides is challenging since they are susceptible to proteolytic hydrolysis and exhibit poor cellular uptake. A protective nanocarrier is thus proposed to overcome these obstacles. We investigate the potential to employ biodegradable phytoglycogen nanoparticles as carriers for GL13K using a simple loading protocol based on electrostatic association rather than chemical conjugation, eliminating the need for control of chemical cleavage for release of the peptide in situ. Both the native (quasineutral) and carboxymethylated (anionic) phytoglycogen were evaluated for their colloidal stability, loading capacity, and release characteristics. We show that the anionic nanophytoglycogen carries a greater cationic GL13K load and exhibits slower release kinetics than native nanophytoglycogen. Isotope exchange measurements demonstrate that the antimicrobial peptide is entrapped in the pores of the dendritic-like macromolecule, which should provide the necessary protection for delivery. Importantly, the nanoformulations are active against a Pseudomonas aeruginosa clinical isolate at concentrations comparable to those of the free peptide and representative, small molecule antibiotics. The colloidal nanocarrier preserves peptide stability and antimicrobial activity, even after long periods of storage (at least 8 months).

Gas-Phase Functionalization of Phytoglycogen Nanoparticles and the Role of Reagent Structure in the Formation of Self-Limiting Hydrophobic Shells

“…23,24 Some anionic modifications to PhG have resulted in superior uptake of cationic peptides. 25 More recently, PhG NPs have been conjugated with bioactive molecules to generate stimuli-responsive nanoconjugates for biomedical applications. 26 For glucosic materials such as PhG, the extent of modification is quantitatively represented in terms of the degree of substitution (DS), which corresponds to the number of substituted hydroxyl groups per glucose monomer unit with a maximum value of three.…”

“…For example, cationic groups can be introduced through a reaction with 3-chloro-2-hydroxypropyl trimethylammonium chloride. , This positive charge enables PhG NPs to act as vaccine adjuvants , and to deliver payloads such as dsRNA , and selenium to cells, although the mechanism of cellular uptake remains unclear . Amphiphilic modifications of PhG NPs have also been explored to improve encapsulation and delivery of lipophilic pharmaceuticals, , such as anticancer agents, , and natural products such as curcumin. , Some anionic modifications to PhG have resulted in superior uptake of cationic peptides . More recently, PhG NPs have been conjugated with bioactive molecules to generate stimuli-responsive nanoconjugates for biomedical applications .…”