A δ2-opioid agonist inhibits p38 MAPK and suppresses activation of murine macrophages

Background. delta-Opioid agonists have been shown to attenuate ischemic organ injury in multiple models. The purpose of the present study was to determine if delta-opioid agonists could inhibit proinflammatory cytokine production by macrophages. Material and methods. Murine macrophages (RAW 264.7) were pretreated for 4 h with media, a dose range (10(-4) to 10(-7) M) of DADLE ([D-Ala(2)], D-Leu(5)]-enkephalin, a nonspecific delta-opioid receptor agonist), a dose range (10-4 to 10-7 M) of DPDPE ([D(2,5)Pen]-enkephalin, a specific delta(1)-opioid receptor agonist), or a dose range (10-4 to 10(-7) M) of Deltorphin-D-variant (a specific delta(2) opioid receptor agonist) and then incubated with 0.1 mu g/ml lipopolysaccharide (LPS) for 1 or 4 h. Cytokine levels were measured by enzyme-linked immunosorbent assay. Activation of NF-kappa B, AP-1, and p38 MAPK were determined by mobility shift assays and Western blot. Results. LPS induced significant increases in TNF alpha and MIP-2 production. Deltorphin-D-variant, but not DADLE or DPDPE, dose-dependently reduced both TNF alpha and MIP-2 production. Deltorphin-D-variant did not alter activation of the transcription factors NF-kappa B or AP-1, but greatly reduced activation of p38 MAPK. Conclusions. The data show that delta(2)- but not delta(1)-opioid agonists suppress LPS-induced p38 MAPK activation and expression of TNF alpha and MIP-2. (c) 2005 Elsevier Inc. All rights reserved.