Ozarelix

We investigated how the structure of nanofibers, resulting from interactions between anionic polyelectrolytes and cationic peptides, relies on the properties of the polyelectrolyte component. By using hyaluronate (H), carboxymethylcellulose (CMC), xanthan (X), and ozarelix (O), a cationic decapeptide, we determined the influence of characteristic polyelectrolyte parameters such as size and charge density on the formation of polyelectrolyte-peptide complexes. Transmission electron microscopy of unstained, frozen hydrated, or negatively stained samples revealed that the interaction between different anionic polyelectrolytes and ozarelix led to the formation of distinctly shaped nanofibers. CMC formed rather flexible structures with alternating thin and thick segments within the nanofibers with diameters ranging from 10 to 16 nm and a length of up to 1 μm. Hyaluronate, a high-molecular-mass molecule, formed extra-long aggregates of more than 5 μm. Individual fibers with a diameter of 8 nm aggregated to bigger strands. The nonlinear polysaccharide xanthan gum led to highly coiled structures. The diameter of the respective nanofibers varied between 15 and 25 nm. Isothermal titration calorimetry was used to determine the binding constants and the thermodynamic parameters of the different polyelectrolyte-peptide complexes. The binding constant, which was of the order of 10(6) M(-1) , indicated a strong binding affinity, but also showed differences among the polyelectrolytes. These differences might be useful for prospective applications as drug delivery systems.

We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems.