Endomorphins as agents for the treatment of chronic inflammatory disease

Endomorphin (EM)-1 and EM-2 are tetrapeptides located within the mammalian central nervous system and immune tissues, with high affinity and specificity for [micro]-opioid receptors. Most of the literature has focused on the analgesic properties of EM-1 and EM-2 in animal models of neuropathic or neurogenic pain, but there is persuasive evidence emerging that EMs can also exert potent anti-inflammatory effects in both acute and chronic peripheral inflammation. The purpose of this review is to present and evaluate the evidence for anti-inflammatory properties of EM-1 and EM-2 with a view to their potential for use in chronic human inflammatory disease. Distribution of EMs within the immune system and functional roles as immunomodulatory agents are summarized and discussed. Possible milestones to be met revolve around issues of peptide stability, biodegradability problems and optimal route and method of delivery. The potential for delivery of a low-cost drug with both peripheral anti-inflammatory and analgesic properties, effective in low doses, and targeted to the site of inflammation, should focus our attention on further development of EMs as potent therapeutic agents in chronic inflammation.