[Expression und function of the ORL-1 receptor on human leukocytes]

Nociceptin/Orphanin FQ (N/OFQ) conjugated to ATTO594: a novel fluorescent probe for the N/OFQ (NOP) receptor

BACKGROUND AND PURPOSE

The nociceptin/orphanin FQ (N/OFQ) receptor (NOP) is a member of the opioid receptor family and is involved in a number of physiological responses, pain and immune regulation as examples. In this study, we conjugated a red fluorophore-ATTO594 to the peptide ligand N/OFQ (N/OFQATTO594 ) for the NOP receptor and explored NOP receptor function at high (in recombinant systems) and low (on immune cells) expression.

EXPERIMENTAL APPROACH

We assessed N/OFQATTO594 receptor binding, selectivity and functional activity in recombinant (CHO) cell lines. Live cell N/OFQATTO594 binding was measured in (i) HEK cells expressing NOP and NOPGFP receptors, (ii) CHO cells expressing the hNOPGαqi5 chimera (to force coupling to measurable Ca2+ responses) and (iii) freshly isolated human polymorphonuclear cells (PMN).

KEY RESULTS

N/OFQATTO594 bound to NOP receptor with nM affinity and high selectivity. N/OFQATTO594 activated NOP receptor by reducing cAMP formation and increasing Ca2+ levels in CHOhNOPGαqi5 cells. N/OFQATTO594 was also able to visualize NOP receptors at low expression levels on PMN cells. In NOP-GFP-tagged receptors, N/OFQATTO594 was used in a FRET protocol where GFP emission activated ATTO, visualizing ligand-receptor interaction. When the NOPGFP receptor is activated by N/OFQATTO594 , movement of ligand and receptor from the cell surface to the cytosol can be measured.

CONCLUSIONS AND IMPLICATIONS

In the absence of validated NOP receptor antibodies and issues surrounding the use of radiolabels (especially in low expression systems), these data indicate the utility of N/OFQATTO594 to study a wide range of N/OFQ-driven cellular responses.

Elevated methylation of OPRM1 and OPRL1 genes in Alzheimer's disease

Previous studies have suggested that increased opioid receptor κ1 (OPRK1) and opioid receptor δ1 (OPRD1) methylation levels are involved in Alzheimer's disease (AD). In the present study, the methylation levels of two opioid receptor genes, opioid receptor µ1 (OPRM1) and opioid related nociceptin receptor 1 (OPRL1), were analyzed for their association with AD. Gene methylation levels were measured using bisulfite pyrosequencing in DNA samples derived from blood samples of 51 AD patients and 63 controls. The results indicated that there were significantly elevated promoter methylation levels of OPRM1 and OPRL1 in AD (OPRM1: P=0.007; OPRL1: P=2.987×10⁻⁶). Dual-luciferase reporter gene assays demonstrated that the promoter fragments of these two genes were able to promote gene expression (OPRM1: Fold-change=2.616, P=0.003; OPRL1: Fold change=11.395, P=0.007). In addition, receiver operating characteristic analyses further indicated that a methylation panel of four opioid receptor genes (area under the curve=0.848, sensitivity=0.723, and specificity=0.879) performed well in the prediction of AD. These results suggested that opioid receptor genes may be used as potential methylation biomarkers for the diagnosis of AD.

Phorbol-12-myristate-13-acetate induces nociceptin in human Mono Mac 6 cells via multiple transduction signalling pathways

BACKGROUND

Nociceptin in the peripheral circulation has been proposed to have an immunoregulatory role with regards to inflammation and pain. However, the mechanisms involved in its regulation are still not clear. The aim of this study was to investigate signalling pathways contributing to the regulation of the expression of nociceptin under inflammatory conditions.

METHODS

Mono Mac 6 cells (MM6) were cultured with or without phorbol-12-myristate-13-acetate (PMA). Prepronociceptin (ppNOC) mRNA was detected by RT-qPCR and extracellular nociceptin by fluorescent-enzyme immunoassay. Intracellular nociceptin and phosphorylated kinases were measured using flow cytometry. To evaluate the contribution of various signalling pathways to the regulation of ppNOC mRNA and nociceptin protein, cells were pre-treated with specific kinase inhibitors before co-culturing with PMA.

RESULTS

ppNOC mRNA was expressed in untreated MM6 at low concentrations. Exposure of cells to PMA upregulated ppNOC after nine h compared with controls without PMA (median normalized ratio with IQR: 0.18 (0.15-0.26) vs. 0 (0-0.02), P<0.01). Inhibition of mitogen-activated protein kinases specific for signal transduction reversed the PMA effects (all P<0.001). Induction of nociceptin protein concentrations in PMA stimulated MM6 was prevented predominantly by identity of ERK inhibitor (P<0.05).

CONCLUSIONS

Upregulation of nociceptin expression by PMA in MM6 cells involves several pathways. Underlying mechanisms involved in nociceptin expression may lead to new insights in the treatment of pain and inflammatory diseases.

Inflammatory mediators influence the expression of nociceptin and its receptor in human whole blood cultures

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.

Extending pharmacological spectrum of opioids beyond analgesia: multifunctional aspects in different pathophysiological states

Opioids are well known to exert potent central analgesic actions. In recent years, the numerous studies have unfolded the critical role of opioids in the pathophysiology of various diseases as well as in biological phenomenon of therapeutic interest. The endogenous ligands of opioid receptors are derived from three independent genes and their appropriate processing yields the major representative opioid peptides beta-endorphin, met-enkephalin, leu-enkephalin and dynorphin, respectively. These peptides and their derivatives exhibit different affinity and selectivity for the mu-, delta- and kappa-receptors located on the central and the peripheral neurons, neuroendocrine, immune, and mucosal cells and on many other organ systems. The present review article highlights the role of these peptides in central nervous system disorders such as depression, anxiety, epilepsy, and stress; gastrointestinal disorders such as diarrhea, postoperative ileus, ulceration, and irritable bowel syndrome; immune system and related inflammatory disorders such as osteoarthritis and rheumatoid arthritis; and others including respiratory, alcoholism and obesity/binge eating. Furthermore, the key role of opioids in different forms of pre- and post-conditioning including ischemic and pharmacological along with in remote preconditioning has also been described.

Nociceptin/orphanin FQ suppresses adaptive immune responses in vivo and at picomolar levels in vitro

Nociceptin/orphanin FQ (N/OFQ), added in vitro to murine spleen cells in the picomolar range, suppressed antibody formation to sheep red blood cells in a primary and a secondary plaque-forming cell assay. The activity of the peptide was maximal at 10(-12) M, with an asymmetric U-shaped dose-response curve that extended activity to 10(-14) M. Suppression was not blocked by pretreatment with naloxone. Specificity of the suppressive response was shown using affinity-purified rabbit antibodies against two N/OFQ peptides and with a pharmacological antagonist. Antisera against both peptides were active, in a dose-related manner, in neutralizing N/OFQ-mediated immunosuppression, when the peptide was used at concentrations from 10(-12.3) to 10(-11.6) M. In addition, nociceptin given in vivo by osmotic pump for 48 h suppressed the capacity of spleen cells placed ex vivo to make an anti-sheep red blood cell response. These studies show that nociceptin directly inhibits an adaptive immune response, i.e., antibody formation, both in vitro and in vivo.