Self-assembled peptide nanotubes as potential nanocarriers for drug delivery

The self-assembly of amphiphilic peptide I3K (Ac-I3K-NH2) and its potential application as a drug nanocarrier have been investigated. I3K monomers and nanotubular segments were initially the dominant species in aqueous solution and they gradually self-assembled into mature nanotubes with heights of approximately 12 nm and lengths of more than 1 mu m. The encapsulation properties of the self-assembled peptide nanotubes were then investigated using model compound guests, including anionic hydrophilic methyl orange (MO) and hydrophobic oil red. It revealed that the model compounds could be efficiently encapsulated by I3K assemblies via electrostatic and hydrophobic interactions, respectively. Atomic force microscopy images demonstrated that variations in drug concentration did not significantly alter the structures of the peptide assemblies but could affect their sizes. Circular dichroism analyses indicated the predominance of beta-sheet conformation associated with the self-assembled system regardless of drug concentrations. The in vitro releasing behavior of the encapsulated model drugs was also studied by the techniques of dialysis. The entrapped model drug MO exhibited an accelerated release as the solution pH was either decreased to 2.0-3.0 or increased to 10.0-11.0 but revealed a sustained release at physiological pH. These results demonstrated that these self-assembled peptide nanotubes could serve as potential drug nanocarriers with efficient encapsulation ability, and sustained and pH-responsive release properties.