A delta-2 opioid agonist inhibits p38 MAPK and suppresses inflammatory activation of murine macrophages

Abstract

Abstract Introduction: Delta opioid agonists may represent a novel approach to attenuate organ dysfunction following ischemia-reperfusion injury associated with organ transplantation. Activation of macrophages is a key component of this injury. However, whether signaling through delta opioid receptors (delta-1 or delta-2) alters macrophage function has not been investigated. We sought to determine if the delta opioids, [D-Ala2, D-Leu5]-enkephalin (DADLE, a nonspecific delta opioid receptor agonist), [D2,5Pen]-enkephalin (DPDPE, a specific delta-1 opioid receptor agonist) or deltorphin-D (a specific delta-2 opioid receptor agonist) could attenuate proinflammatory cytokine production by macrophages after activation with lipopolysaccharide (LPS). Methods: Murine macrophages, RAW 264.7, were pretreated for 4 hours with media, DADLE, DPDPE, or deltorphin-D, and then incubated with LPS for 4 hours. TNF-alpha and macrophage inflammatory protein-2 (MIP-2) secretion were measured by ELISA. Additionally, after 1 hour of LPS, activation of NF-kB, AP-1 and p38 MAPK were assessed by EMSA and Western blot. Results: LPS induced significant increases in TNF-alpha and MIP-2 production. Pretreatment with media, DADLE or DPDPE had no effect on cytokine secretion. However, deltorphin-D in a dose-dependent fashion, caused a 3.5–5-fold reduction in TNF-alpha and MIP-2 (p Conclusions: Delta-2 but not delta-1 opioid agonists appear to suppress inflammatory activation of macrophages in a p38 MAPK-dependent fashion. Further examination of the molecular mechanism by which these agonists confer protection may provide important information allowing their use in the clinical setting.