The encapsulation of active ingredients in liposomes is used in several domains such as food, pharmaceutical and cosmetic industries. Liposomes are drug delivery systems (DDS) used both for lipophilic cargos and for hydrophilic cargos. Such encapsulation allows a controlled release of active ingredients over time .
To increase the efficiency of peptide drugs, we aim at designing optimized liposomes by playing both on peptide structure and liposome composition. Potential parameters to be improved are peptide-liposome interactions, encapsulation efficiency and release kinetics. To reach this goal, we explored the potentiality of Nuclear Magnetic Resonance (NMR) spectroscopy to characterize peptides, liposomes and their behavior during release. The active ingredients used in this study are apelin-derived peptides used in cardiovascular diseases for their role in cardiovascular homeostasis regulation .
Liposome and peptide structures as well as their interactions were characterized by 1H, 31P NMR and cryo-EM. We also used Diffusion Ordered SpectroscopY (DOSY) to discriminate between the inner and the outer space of liposomes. This method allows determining the translational diffusion coefficient (D) of molecules that reports on their apparent size. Significant differences were observed for D of free and encapsulated peptides, due to the difference of molar mass between peptide and liposome, allowing distinguishing encapsulated and released peptides. We then investigated the potentiality of DOSY for peptide incorporation and real-time release quantification. Moreover, 1H NMR spectra were used to monitor and quantify peptide release kinetics by spectral integration.
To conclude, we showed that liquid-state NMR can be used to follow the release kinetics of peptides in liposomal formulation in-situ and in real-time without perturbing the process. This approach could certainly be extended to other active ingredients and DDS used for pharmaceutical and cosmetic applications.
 Sercombe L.et al. Frontiers in Pharmacology. 2015, 6, 286.
 Japp AG, Newby DE. Biochemical Pharmacology 2008;75:1882-92