Background: Nociceptin/orphanin FQ and its receptor (NOP) are involved in immune responses, inflammation and pain processing. The aim of this study was to investigate the modulation of NOP and prepro-nociceptin (PNoc), the precursor of nociceptin, by inflammatory mediators in human whole blood.
Methods: Peripheral blood from healthy volunteers was cultured for 0, 3, 6 and 24 hrs with or without lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-10 or interferon (IFN)-γ. NOP and PNoc mRNA of peripheral white blood cells were detected by quantitative RT-PCR. Cytokine concentrations in supernatants of whole blood cultures were measured using ELISA. In addition, an intervention experiment using anti-cytokine antibodies was conducted to evaluate possible mechanisms involved in the modulation of NOP and PNoc by LPS. The primary goal was to investigate NOP and PNoc mRNA expression in human peripheral blood under inflammatory conditions.
Results: LPS significantly suppressed NOP (median area under the mRNA-expression-time curve (1(st)/3(rd) quartile): 5.4 (4.6/6.6) normalized ratio · hr) and PNoc expression (40.8 (34.4/49.5)) compared to baseline measures (NOP: 22.7 (17.1/25.3); PNoc: 69.9 (58.4/89.2), both p<0.001). LPS incubation induced cytokine concentrations (TNF-α, IL-1β, IL-10 and IFN-γ) in whole blood cultures. Incubation with TNF-α, IL-1β, IL-10 or IFN-γ decreased NOP mRNA levels to varying extents (p<0.05 for all). In contrast, PNoc mRNA expression was decreased by IL-10 only (p = 0.018). The LPS effect on NOP expression could be antagonized by anti-TNF-α and anti-IL-1β, whereas anti-IL-10 and anti-INF-γ had no effect. There was no change of PNoc expression when LPS induced cytokines were antagonized by the respective antibodies.
Conclusions: LPS as well as cytokines suppress mainly NOP and, in part, PNoc mRNA expression in human whole blood cultures. This may represent a negative feedback loop to the previously described upregulation of cytokines by PNoc.