NMR Study on the Aggregation Behavior of the Therapeutic Peptide Carbetocin

Sammanfattning: Carbetocin is an uncharged cyclic therapeutic peptide with a tendency to aggregate in solution. Aggregation is undesirable since it, for example, can lead to loss of pharmaceutical effects. To gain a better understanding of peptide aggregation, along with a potential to develop better drug formulations, aggregation of carbetocin was studied. In focus were soluble aggregates in contrast to phase-separated aggregates. The behavior of these soluble aggregates was studied with NMR spectroscopy. NMR diffusometry and 1 H NMR spectroscopy were used as the main analytic methods. Aqueous solutions of carbetocin at different concentrations alone, and with added sodium dodecyl sulfate (SDS) and pentaethylene glycol monododecyl ether (C12E5) were analyzed using these methods. The peptide has an increased self-aggregation in solution at higher peptide concentrations, with a distinct increase in aggregation at around 15-20 mM carbetocin. Hydrophobic interactions and hydrogen bonding are suggested to be the major attractive forces in the aggregation mechanism based on that the chemical shifts of hydrophobic and hydrogen-bonding sites in carbetocin show significant changes at higher peptide concentrations. Surfactants significantly affect the aggregation behavior of carbetocin and co-aggregates are formed. To fully understand the aggregation behavior of carbetocin and other peptides, more research has to be conducted.