The anti-inflammatory action of the analgesic kyotorphin neuropeptide derivatives: insights of a lipid-mediated mechanism

Recently, a designed class of efficient analgesic drugs derived from an endogenous neuropeptide, kyotorphin (KTP, Tyr-Arg) combining C-terminal amidation (KTP-NH 2 ) and N-terminal conjugation to ibuprofen (Ib), IbKTP-NH 2 , was developed. The Ib moiety is an enhancer of KTP-NH 2 analgesic action. In the present study, we have tested the hypothesis that KTP-NH 2 is an enhancer of the Ib anti-inflammatory action. Moreover, the impact of the IbKTP-NH 2 conjugation on microcirculation was also evaluated by a unified approach based on intravital microscopy in the murine cremasteric muscle. Our data show that KTP-NH 2 and conjugates do not cause damage on microcirculatory environment and efficiently decrease the number of leukocyte rolling induced by lipopolysaccharide (LPS). Isothermal titration calorimetry showed that the drugs bind to LPS directly thus contributing to LPS aggregation and subsequent elimination. In a parallel study, molecular dynamics simulations and NMR data showed that the IbKTP-NH 2 tandem adopts a preferential “stretched” conformation in lipid bilayers and micelles, with the simulations indicating that the Ib moiety is anchored in the hydrophobic core, which explains the improved partition of IbKTP-NH 2 to membranes and the permeability of lipid bilayers to this conjugate relative to KTP-NH 2 . The ability to bind glycolipids concomitant to the anchoring in the lipid membranes through the Ib residue explains the analgesic potency of IbKTP-NH 2 given the enriched glycocalyx of the blood–brain barrier cells. Accumulation of IbKTP-NH 2 in the membrane favors both direct permeation and local interaction with putative receptors as the location of the KTP-NH 2 residue of IbKTP-NH 2 and free KTP-NH 2 in lipid membranes is the same.