Ghrelin–liposome interactions: Characterization of liposomal formulations of an acylated 28‐amino acid peptide using CE

Abstract

Ghrelin is a pharmacologically interesting peptide hormone due to its effects on appetite and metabolism. The cationic, octanoylated 28 amino acid peptide has a short biological half-life; thus, prolonged release formulations are of interest. Acylated peptides have been suggested to bind to or be incorporated into liposomes. Formulations based on neutral dipalmitoylphosphatidylcholine (DPPC) liposomes and phosphatidylcholine:cholesterol (70:30 mol%) liposomes, and negatively charged dipalmitoylphosphatidylcholine:dipalmitoylphosphatidylserine (DPPC:DPPS) (70:30 mol%) liposomes (2 mM total lipid concentration) were characterized using ACE. Pre-equilibrium CZE and frontal analysis CE methods circumventing capillary wall adsorption of the peptide and the liposomes and suitable for characterizing ghrelin-liposome interactions were developed. The cationic peptide exhibited low affinity (<10% bound) for DPPC and phosphatidylcholine:cholesterol (70:30 mol%) liposomes whereas electrostatic interactions caused a higher affinity for DPPC:DPPS (70:30 mol%) liposomes. Studies on desacyl ghrelin instead of ghrelin demonstrated the significance of the n-octanoyl side chain as an affinity providing moiety towards DPPC:DPPS liposomes (48 and 73% bound peptide, respectively). CE experiments showed that the binding was characterized by rapid dissociation kinetics.

Development of coated liposomes loaded with ghrelin for nose-to-brain delivery for the treatment of cachexia

“…In both theoretical localizations, the octanoyl fatty-acid group is inserted in the lipid structure. This interaction has already been described in other studies, 37,38 and shown to provide significant protection to the octanoyl group, which is essential for preserving the physiological activity of Ghrl. 34 …”

“…36,37 However, when looking at EE, it can be seen that electrostatic interactions have a clear impact in the case of Ghrl. 38 By providing a negative charge to ALs, the percentage of Ghrl loaded in ALs was fivefold higher compared to CLs (Table 2). This resulted in EE of 56.1%±7.8%, 21.3%±4.1%, and 9.8%±3.7% for ALs, NLs and CLs, respectively.…”

Recent developments in CE and CEC of peptides (2009–2011)

“…Interactions of ghrelin, a pharmacologically interesting appetite‐stimulating peptide hormone, with neutral dipalmitoylphosphatidylcholine liposomes and negatively charged phosphatidylcholine/cholesterol (70/30 mol%) liposomes were investigated by CZE with UV‐detection at 200 nm in BGE containing 10 mM HEPES and 50 mM KCl, pH 5.50 241, 242. About 75% cationic ghrelin was bound to anionic phosphatidylcholine/cholesterol (70/30 mol%) liposomes but only 5–10% was bound to neutral dipalmitoylphosphatidylcholine liposomes.…”

Capillary electromigration techniques for studying interactions between analytes and lipid dispersions

“…To note is that the drug to liposome interactions were found to depend on the drug concentrations and neutral drugs could not be analyzed by CE‐FA due to co‐elution with the EOF. The potential of CE to study a liposomal drug formulation was revealed in . Interactions of the 28 amino acid peptide ghrelin and its n ‐octanoyl analogue with neutral 1,2‐dipalmitoyl‐ sn ‐glycero‐3‐phosphocholine (DPPC), DPPC/cholesterol, and net negative DPPC/1,2‐dipalmitoyl‐ sn ‐glycero‐3‐phospho‐L‐serine liposomes were investigated by CE‐FA using fused silica, poly(dimethyldiallylammonium chloride), and poly(vinyl alcohol)‐coated capillaries.…”

“…In this section, we will go through studies where liposomes prepared from different kinds of phospholipids and cholesterol have been applied in interaction studies with compounds. The techniques include conventional EKC , PF‐EKC , and CE‐FA .…”