Chemical Conjugation of the Neuropeptide Kyotorphin and Ibuprofen Enhances Brain Targeting and Analgesia

The pharmaceutical potential of natural analgesic peptides is mainly hampered by their inability to cross the blood–brain barrier, BBB. Increasing peptide–cell membrane affinity through drug design is a promising strategy to overcome this limitation. To address this challenge, we grafted ibuprofen (IBP), a nonsteroidal anti-inflammatory drug, to kyotorphin (l-Tyr-l-Arg, KTP), an analgesic neuropeptide unable to cross BBB. Two new KTP derivatives, IBP-KTP (IbKTP-OH) and IBP-KTP-amide (IbKTP-NH2), were synthesized and characterized for membrane interaction, analgesic activity and mechanism of action. Ibuprofen enhanced peptide–membrane interaction, endowing a specificity for anionic fluid bilayers. A direct correlation between anionic lipid affinity and analgesic effect was established, IbKTP-NH2 being the most potent analgesic (from 25 μmol·kg–1). In vitro, IbKTP-NH2 caused the biggest shift in the membrane surface charge of BBB endothelial cells, as quantified using zeta-potential dynamic light scattering...