Liposomal formulations
represent attractive biocompatible and tunable
drug delivery systems for peptide drugs. Among the tools to analyze
their physicochemical properties, nuclear magnetic resonance (NMR)
spectroscopy, despite being an obligatory technique to characterize
molecular structure and dynamics in chemistry as well as in structural
biology, yet appears to be rather sparsely used to study drug-liposome
formulations. In this work, we exploited several facets of liquid-state
NMR spectroscopy to characterize liposomal delivery systems for the
apelin-derived K14P peptide and K14P modified by Nα-fatty acylation.
Various liposome compositions and preparation modes were analyzed.
Using NMR, in combination with cryo-electron microscopy and dynamic
light scattering, we determined structural, dynamic, and self-association
properties of these peptides in solution and probed their interactions
with liposomes. Using 31P and 1H NMR, we characterized
membrane fluidity and thermotropic phase transitions in empty and
loaded liposomes. Based on diffusion and 1H NMR experiments,
we localized and quantified peptides with respect to the interior/exterior
of liposomes and changes over time and upon thermal treatments. Finally,
we assessed the release kinetics of several solutes and compared various
formulations. Taken together, this work shows that NMR has the potential
to assist the design of peptide/liposome systems and more generally
drug delivery systems.