Methionine-enkephalin-and Dynorphin A-release from immune cells and control of inflammatory pain


Methionine-enkephalin-and Dynorphin A-release from immune cells and control of inflammatory pain


Cabot PJ; Carter L; Schafer M; Stein C






Humans; Male; Animals; Rats; Biomarkers of Pain; Dose-Response Relationship; Drug; Enkephalin; Biomarkers Reference List; Wistar; Antibodies/pharmacology; Corticotropin-Releasing Hormone/antagonists & inhibitors/pharmacology/therapeutic use; Dynorphins/immunology/secretion; Inflammation/drug therapy/immunology/metabolism; Interleukin-2/pharmacology; Lymphocytes/drug effects/immunology/secretion; Methionine/immunology/metabolism; Pain/drug therapy/immunology/metabolism


We have previously shown that beta-endorphin (END) is contained and released from memory-type T-cells within inflamed tissue and that it is capable to control pain (J Clin Invest 100(1) (1997) 142). Methionine-enkephalin (MET) and Dynorphin-A (DYN) are endogenous opioids with preference for delta- and kappa-opioid receptors, respectively. Both MET and DYN are produced and contained within immune cells. The goal of this study was to determine the release characteristics of MET and DYN in a rat model of localized hindpaw inflammation and to examine the antinociceptive role of MET and DYN in a Freund's adjuvant induced model of inflammatory pain. We found that corticotropin-releasing factor (CRF) can stimulate the release of both MET and DYN from lymphocytes. This release is dose-dependent and reversible by the selective CRF antagonist alpha-helical-CRF. Furthermore, CRF (1.5 ng) produces analgesia when injected into the inflamed paw, which is reversible by direct co-administration of antibodies to MET. Lymphocyte content of MET was 7.0+/-1.4 ng/million cells, whilst DYN content was ~30-fold lower. Both END and DYN, but not MET, were released by IL-1. Consistently, IL-1 produced peripheral analgesic effects which were not reversed by antibodies to MET. These results indicate that both MET and DYN play a role in peripheral analgesia but have different characteristics of release. These studies further support a role of the immune system in the control of inflammatory pain. This may be particularly important in patients suffering from compromised immune systems as with cancer and AIDS.


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Cabot PJ; Carter L; Schafer M; Stein C, “Methionine-enkephalin-and Dynorphin A-release from immune cells and control of inflammatory pain,” Pediatric Palliative Care Library, accessed December 1, 2023,