Papers of the Week

Little is known about the mechanisms involved in the regulation of nociceptin and its receptor (NOP) in response to inflammation and pain in humans. In this study, specific signaling path-ways contributing to the regulation of nociceptin and NOP in human peripheral blood leuko-cytes were investigated. After approval by the ethics committee, peripheral blood obtained from healthy donors was cultured with or without phorbol-12-myristate-13-acetate (PMA). Prepronociceptin (ppNOC) and NOP mRNA were analyzed by real-time quantitative PCR, and nociceptin concentrations in culture supernatants by fluorescent enzyme immunoassay. Nociceptin and NOP protein levels in blood leukocyte subsets were determined using flow cytometry. To examine the contribution of signaling pathways to ppNOC and NOP regulation, blood was pre-treated with kinase inhibitors specific for ERK, JNK, p38 and NFκB pathways prior to culturing with or without PMA. PMA dose-dependently upregulated ppNOC mRNA but downregulated NOP mRNA in human peripheral blood leukocytes. PMA 10 ng/ml increased ppNOC after 6 hours and suppressed NOP after 3 hours compared to controls (both P <0.005). Nociceptin concentrations were increased in supernatants of PMA-induced blood samples after 24 hours (P <0.005), whereas expression of cell-membrane NOP was de-creased by PMA in blood leukocyte subsets (all P <0.05). Blockade of ERK or p38 pathways partially prevented PMA effects on ppNOC and NOP mRNA (all P <0.05). The combination of ERK and p38 inhibitors completely reversed the effects of PMA (P <0.05). ERK and p38 are two major signaling pathways regulating nociceptin and its receptor in human peripheral blood leukocytes under inflammatory conditions.