Dispersed liquid crystals as pH-adjustable antimicrobial peptide nanocarriers

pH-responsive nanocarriers have the potential to provide targeted delivery of antimicrobial peptides (AMPs) to sites of bacterial infection with typically abnormal pH levels in the body. However, the local pH of the infected sites varies substantially among different infection-related diseases, calling for the development of delivery systems capable of targeting local pathological conditions in an adjustable pH range.

In this study, a highly versatile pH-responsive nanocarrier platform, based on dispersions of oleic acid (OA) and glycerol monooleate (GMO) self-assemblies with the human cathelicidin AMP LL-37, was designed and characterized.

A detailed pH-composition phase diagram was constructed from small angle X-ray scattering and cryogenic transmission electron microscopy data. In addition, the protonation state and apparent pK_a of OA embedded in these nano-self-assemblies were investigated by electrophoretic mobility measurements at different pHs and found to be strongly dependent on nanocarrier composition. By varying composition of these nanocarriers, the apparent pK_a of embedded OA molecules could be tuned from 7.8 to 6.3, shifting the range of nanocarriers' pH-response. The study advances our fundamental understanding of self-assembly and pH-responsiveness in lipid-peptide systems containing monounsaturated long-chain fatty acids. The results may guide the future design of highly adaptable nanocarriers for patient-optimized pH-targeted AMP delivery.