Effects on Inflammation of Newly-Synthesized Hexapeptide with Affinity to Opioid and Nociceptin Receptors

Following the discovery of the N/OFQ/NOP system and its modulatory role in physiological and pathophysiological processes, intensive study has started to find selective NOP ligands with hypothetic therapeutic potential. Among the agonists, a hexapeptide Ac-RYYRWK-NH₂ has been identified. It expresses high NOP receptor affinity and selectivity. Its molecule was used as a template, in which Tyr⁵ was substituted by original β²-tryptophan analogue (S)-2-(1-methyl-1H-indol-3-yl)propionic residue (compound HP3) The new compound activates both NOP and opioid receptors. Having in mind that classical opioids, as well as nociceptin, are involved in modulating pain and inflammation, we examined the anti-inflammatory effect of newly-synthesized peptide HP3 on carrageenan-induced peripheral inflammation, and compared it with that of indomethacin (3 mg/kg). It was found that HP3 in dose 40 μg/kg exerts weaker anti-inflammatory action in the first 180 min of the experiment, but is equally effective with indomethacin 3 mg/kg at the end of the observation. The HP3 effect is due mainly of the activation of opioid receptors.