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-NH(2)), 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-NH(2) being the most potent analgesic (from 25 µmol · kg(-1)). In vitro, IbKTP-NH(2) caused the biggest shift in the membrane surface charge of BBB endothelial cells, as quantified using zeta-potential dynamic light scattering. Our results suggest that IbKTP-NH(2) crosses the BBB and acts by activating both opioid dependent and independent pathways.