Nociceptin/orphanin FQ metabolism and bioactive metabolites

Nocistatin and Products of Its Proteolysis Are Dual Modulators of Type 3 Acid-Sensing Ion Channels (ASIC3) with Algesic and Analgesic Properties

The neuropeptide nocistatin (NS) is expressed by the nervous system cells and neutrophils as a part of a precursor protein and can undergo stepwise limited proteolysis. Previously, it was shown that rat NS (rNS) is able to activate acid-sensing ion channels (ASICs) and that this effect correlates with the acidic nature of NS. Here, we investigated changes in the properties of rNS in the course of its proteolytic degradation by comparing the effects of the full-size rNS and its two cleavage fragments on the rat isoform 3 ASICs (ASIC3) expressed in X. laevis oocytes and pain perception in mice. The rNS acted as both positive and negative modulator by lowering the steady-state desensitization of ASIC3 at pH 6.8-7.0 and reducing the channel's response to stimuli at pH 6.0-6.9, respectively. The truncated rNSΔ21 peptide lacking 21 amino acid residues from the N-terminus retained the positive modulatory activity, while the C-terminal pentapeptide (rNSΔ30) acted only as a negative ASIC3 modulator. The effects of the studied peptides were confirmed in animal tests: rNS and rNSΔ21 induced a pain-related behavior, whereas rNSΔ30 showed the analgesic effect. Therefore, we have shown that the mode of rNS action changes during its stepwise degradation, from an algesic molecule through a pain enhancer to a pain reliever (rNSΔ30 pentapeptide), which can be considered as a promising drug candidate.

Copper-Mediated Radiocyanation of Unprotected Amino Acids and Peptides

This report describes a copper-mediated radiocyanation of aryl halides that is applicable to complex molecules. This transformation tolerates an exceptionally wide range of functional groups, including unprotected amino acids. As such, it enables the site-specific introduction of [¹¹C]CN into peptides at an iodophenylalanine residue. The use of a diamine-ligated copper(I) mediator is crucial for achieving high radiochemical yield under relatively mild conditions, thus limiting racemization and competing side reactions of other amino acid side chains. The reaction has been scaled and automated to deliver radiolabeled peptides, including analogues of adrenocorticotropic hormone 1-27 (ACTH) and nociceptin (NOP). For instance, this Cu-mediated radiocyanation was leveraged to prepare >40 mCi of [¹¹C]cyano-NOP to evaluate biodistribution in a primate using positron emission tomography. This investigation provides preliminary evidence that nociceptin crosses the blood-brain barrier and shows uptake across all brain regions (SUV > 1 at 60 min post injection), consistent with the known distribution of NOP receptors in the rhesus brain.

[The role of nociceptin in opioid regulation of brain functions]

This review discusses our current knowledge on the nociceptin/orphanin (N/OFQ) system regarding its role in regulation of brain functions. Nociceptin receptor (NOPr) was identified in 1994 [Bunzow et al., 1994; Mollereau et al., 1994]. In 1995 a 17 amino acid endogenous peptide was found to be the high-affinity ligand for the NOPr [Reinscheid et al., 1995]. N/OFQ has a broad spectrum of activity and can act as on opioid-like as well as an anti-opioid peptide. Considering high level of N/OFQ and NOPr mRNA expression in the limbic brain regions, the N/OFQ/NOP system is suggested to be involved in regulation of emotions, resward, pain sensitivity, stress responsibility, sexual behavior, aggression, drug abuse and addiction. However it is still not well understood whether an increased vulnerability to drugs of abuse may be associated with dysregulation of N/OFQ/NOP system. Current review further highlights a need for further research on N/OFQ/NOP system as it could have clinical utility for substance abuse, depression, and anxiety pharmacotherapy.

Aminopeptidase T of M29 Family Acts as A Novel Intracellular Virulence Factor for Listeria monocytogenes Infection

The foodborne pathogen Listeria monocytogenes employs a number of virulence determinants including metalloproteases to infect hosts. Here for the first time, we identified an M29 family aminopeptidase T (encoded by lmo1603) from L. monocytogenes that possesses a typical feature to catalyze the cleavage of amino acids from peptide substrates, with a preference for arginine. The purified recombinant Lmo1603 was activated by Fe³⁺, Zn²⁺ and Mn²⁺, but strongly stimulated by Co²⁺, indicating that Lmo1603 is a cobalt-dependent aminopeptidase. Single mutation at any of the Glu216, Glu281, His308, Tyr315, His327, and Asp329 completely abolished the enzymatic activity of Lmo1603. More importantly, we showed that Lmo1603 was mainly involved in Listeria infection, but not required for growth in rich laboratory medium and minimal defined medium. Disruption of Lmo1603 resulted in almost complete attenuation of Listeria virulence in a mouse infection model. In addition, we demonstrated that Lmo1603 was mainly localized in the bacterial cytosol and required for invasion and survival inside human epithelial cells and murine macrophages. We conclude that Lmo1603 encodes a functional aminopeptidase T of M29 family, which acts as a novel intracellular virulence factor essential in the successful establishment of L. monocytogenes infections in a mouse model.

The biology of Nociceptin/Orphanin FQ (N/OFQ) related to obesity, stress, anxiety, mood, and drug dependence

Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide that was deorphanized in 1995. The generation of specific agonists, antagonists and receptor deficient mice and rats has enabled progress in elucidating the biological functions of N/OFQ. Additionally, radio-imaging technologies have been advanced for investigation of this system in animals and humans. Together with traditional neurobehavioral techniques, these tools have been utilized to identify the biological significance of the N/OFQ system and its interacting partners. The present review focuses on the role of N/OFQ in the regulation of feeding, body weight homeostasis, stress, the stress-related psychiatric disorders of depression and anxiety, and in drug and alcohol dependence. Critical evaluation of the current scientific preclinical literature suggests that small molecule modulators of nociceptin opioid peptide receptors (NOP) might be useful in the treatment of diseases related to these biological functions. In particular, the literature data suggest that antagonism of NOP receptors will produce anti-obesity and antidepressant activities in humans. However, there are also contradictory data discussed. The current literature on the role of N/OFQ in anxiety and addiction, on the other hand points primarily to a role of agonist modulation being potentially therapeutic. Some drug-like molecules that function either as agonists or antagonists of NOP receptors have been optimized for human clinical study to test some of these hypotheses. The discovery of PET ligands for NOP receptors, combined with the pharmacological tools and burgeoning preclinical data set discussed here bodes well for a rapid advancement of clinical understanding and potential therapeutic benefit.

Biophysical characterization of a recombinant aminopeptidase II from the thermophilic bacterium Bacillus stearothermophilus

In the present study, the biophysical properties of His6-tagged Bacillus stearothermophilus aminopeptidase II (His6-tagged BsAmpII) are characterized in detail by gel-filtration, analytical ultracentrifugation, and various spectroscopic techniques. Using size-exclusion chromatography and analytical ultracentrifugation, we demonstrate that His6-tagged BsAmpII exists predominantly as a dimer in solution. The enzyme is active and stable at pHs ranging from 6.5 to 8.5. Far-UV circular dichroism analysis reveals that the secondary structures of His6-tagged BsAmpII are significantly altered in the presence of SDS, whereas the presence of 5-10% acetone and ethanol was harmless to the folding of the enzyme. Thermal unfolding of His6-tagged BsAmpII was found to be irreversible and led to the formation of aggregates. The native enzyme started to unfold beyond 0.6 M guanidine hydrochloride and had a midpoint of denaturation at 1.34 M. This protein remained active at concentrations of urea below 2.7 M but experienced an irreversible unfolding by >5 M denaturant. Taken together, this work lays a foundation for potential biotechnological applications of His6-tagged BsAmpII.

Acute and subchronic treatments with selective serotonin reuptake inhibitors increase Nociceptin/Orphanin FQ (NOP) receptor density in the rat dorsal raphe nucleus; interactions between nociceptin/NOP system and serotonin

Nociceptin/Orphanin FQ is the endogenous ligand of NOP receptor, formerly referred to as the Opioid Receptor-Like 1 receptor. We have previously shown that NOP receptors were located on serotonergic neurons in the rat dorsal raphe nucleus, suggesting possible direct interactions between nociceptin and serotonin in this region, which is a target for antidepressant action. In the present study, we investigated further the link between Selective Serotonin Reuptake Inhibitor (SSRI) antidepressant treatments and the nociceptin/NOP receptor system. Intraperitoneal administration of the SSRI citalopram induced an increase in NOP-receptor density, measured by autoradiographic [(3)H] nociceptin binding, in the rat dorsal raphe nucleus, from the first to the 21st day of treatment. This effect was also observed with other SSRIs (sertraline, fluoxetine), but not with two tricyclic antidepressants (imipramine, clomipramine) and was abolished by pre-treatment with para-chlorophenylalanine, an inhibitor of serotonin synthesis. Using microdialysis experiments, we demonstrated that NOP-receptor activation by infusion of nociceptin 10(-6) M or 10(-5) M increased the level of extracellular serotonin in the dorsal raphe nucleus. This effect was abolished by co-infusion of the NOP-receptor antagonist UFP 101. These results confirm the existence of reciprocal interactions between serotonin and nociceptin/NOP transmissions in the dorsal raphe nucleus.

Sex differences in the Nociceptin/Orphanin FQ system in rat spinal cord following chronic morphine treatment

Nociceptin/Orphanin FQ (N/OFQ) appears to contribute to the development of morphine tolerance, as blockade of its actions will block or reverse the process. To better understand the contribution of N/OFQ to the development of morphine tolerance, this study examined the effect of chronic morphine treatment on levels of N/OFQ and levels and activity of the N/OFQ peptide (NOP) receptor in spinal cord (SC) from male and female rats. Both male and female Wistar rats showed less responsiveness to morphine after subcutaneous injection of escalating doses of morphine (10, 20, 40, 60 and 80 mg/kg, respectively) twice daily for five consecutive days. Male rats were more tolerant to the antinociceptive actions of morphine than females. The N/OFQ content of SC extracts was higher in females than in males, regardless of treatment; following chronic morphine treatment the difference in N/OFQ levels between males and females was more pronounced. N/OFQ content in cerebrospinal fluid (CSF) was reduced 40% in male and 16% in female rats with chronic morphine exposure, but increased in periaqueductal grey of both sexes. Chronic morphine treatment increased NOP receptor levels 173% in males and 137% in females, while decreasing affinity in both. Chronic morphine increased the efficacy of N/OFQ-stimulated [³⁵S]GTPγS binding to SC membranes from male rats, consistent with increased receptor levels. Taken together, these findings demonstrate sex differences in N/OFQ-NOP receptor expression and NOP receptor activity following chronic morphine treatment. They also suggest interplay between endogenous N/OFQ and chronic morphine treatment that results in nociceptive modulation.

Production of leucine amino peptidase in lab scale bioreactors using Streptomyces gedanensis

Studies were conducted on the production of leucine amino peptidase (LAP) by Streptomyces gedanensis to ascertain the performance of the process in shake flask, parallel fermenter and 5-L fermenter utilizing soy bean meal as the carbon source. Experiments were conducted to analyze the effects of aeration and agitation rate on cell growth and LAP production. The results unveiled that an agitation rate of 300 rpm, 50% dissolved oxygen (DO) upholding and 0.15 vvm strategies were the optimal for the enzyme production, yielding 22.72 ± 0.11 IU/mL LAP in parallel fermenter which was comparable to flask level (24.65 ± 0.12 IU/mL LAP) fermentation. Further scale-up, in 5-L fermenter showed 50% DO and 1 vvm aeration rate was the best, producing optimum and the production was 20.09 ± 0.06 IU/mL LAP. The information obtained could be useful to design a strategy to improve a large-scale bioreactor cultivation of cells and production of LAP.

Antinociceptive effects of spinally administered nociceptin/orphanin FQ and its N-terminal fragments on capsaicin-induced nociception

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand for the N/OFQ peptide (NOP) receptors, has been shown to be metabolized into some fragments. We examined to determine whether intrathecal (i.t.) N/OFQ (1-13), (1-11) and (1-7) have antinociceptive activity in the pain-related behavior after intraplantar injection of capsaicin. The i.t. administration of N/OFQ (0.3-1.2 nmol) produced an appreciable and dose-dependent inhibition of capsaicin-induced paw-licking/biting response. The N-terminal fragments of N/OFQ, (1-13) and (1-11), were antinociceptive with a potency lower than N/OFQ. Calculated ID₅₀ values (nmol, i.t.) were 0.83 for N/OFQ, 2.5 for N/OFQ (1-13) and 4.75 for N/OFQ (1-11), respectively. The time-course effect revealed that the antinociceptive effects of these N-terminal fragments lasted longer than those of N/OFQ. Removal of amino acids down to N/OFQ (1-7) led to be less potent than N/OFQ and its fragments, (1-13) and (1-11). Antinociception induced by N/OFQ or N/OFQ (1-13) was reversed significantly by i.t. co-injection of [Nphe¹]N/OFQ (1-13)NH₂, a peptidergic antagonist for NOP receptors, whereas i.t. injection of the antagonist did not interfere with the action of N/OFQ (1-11) and (1-7). Pretreatment with the opioid receptor antagonist naloxone hydrochloride did not affect the antinociception induced by N/OFQ and its N-terminal fragments. These results suggest that N-terminal fragments of N/OFQ are active metabolites and may modulate the antinociceptive effect of N/OFQ in the spinal cord. The results also indicate that N/OFQ (1-13) still possess antinociceptive activity through NOP receptors.

Discovery of 1-[1-(1-methylcyclooctyl)-4-piperidinyl]-2-[(3R)-3-piperidinyl]-1H-benzimidazole: integrated drug-design and structure-activity relationships for orally potent, metabolically stable and potential-risk reduced novel non-peptide nociceptin/orphanin FQ receptor agonist as antianxiety drug

Anxiety disorders, caused by continuous or acute stress or fear, have been highly prevailing psychiatric disorders. For the acute treatment of the disorders, benzodiazepines have been widely used despite having liabilities that limit their utility. Alternatively, endogenous nociceptin/orphanin FQ and nociceptin/orphanin FQ peptide receptor (or opioid-receptor-like-1 receptor) have important roles in the integration of emotional components, e.g. anxiolytic activity is the key behavioral action of nociceptin/orphanin FQ in brain. In our preceding study, various structurally novel 1,2-disubstituted benzimidazole derivatives were designed and synthesized as highly potent nociceptin/orphanin FQ peptide receptor selective full agonists in vitro with high or moderate nociceptin/orphanin FQ peptide receptor occupancy in the mice brain per os based on appropriate physicochemical properties for the oral brain activity [Hayashi et al. (2009) J Med Chem;52:610-625]. In the present study, drug design and structure-activity relationships for Vogel anticonflict activities in mice per os, metabolic stabilities in human liver microsome, CYP2D6 inhibitions, serum protein bindings, and human ether-a-go-go related gene binding affinities of novel nociceptin/orphanin FQ peptide receptor agonists were investigated. Through the series of coherent drug discovery studies, the strongest nociceptin/orphanin FQ peptide receptor agonist, 1-[1-(1-methylcyclooctyl)-4-piperidinyl]-2-[(3R)-3-piperidinyl]-1H-benzimidazole was designed and identified as a new-class orally potent anxiolytic with little side-effects, as significant findings.

In vivo effects of N/OFQ(1–13)NH2 and its structural analogue [ORN9]N/OFQ(1–13)NH2 on carrageenan-induced inflammation: rat-paw oedema and antioxidant status

The effects of nociceptin(1–13)NH2 (N/OFQ(1–13)NH2) and its structural analogue [Orn9]N/OFQ(1–13)NH2 on acute carrageenan (CG)-induced peripheral inflammation and paw antioxidant status were studied. CG was injected intraplantarly in the right hind paw of rats and the volume of the inflamed paw was measured each 30 min for a period of 4h. When administered simultaneously with CG, N/OFQ(1–13)NH2 decreased the paw volume, whereas if injected 15 min before CG it had no effect. [Orn9]N/OFQ(1–13)NH2 produced the opposite effects at the same time-intervals of its administration. We also investigated whether these neuropeptides influence CG-induced changes in cell antioxidant system, especially at the 4th hour of CG administration. CG alone decreased the glutathione level and superoxide dismutase activity, as measured in post-nuclear homogenate of the inflamed paw. However, CG injection increased glutathione peroxidase and glucose-6-phospate dehydrogenase activities, while the activity of glutathione reductase was unchanged. The peptides themselves did not change all measured parameters. Moreover, neither N/OFQ(1–13)NH2 nor [Orn9]N/OFQ(1–13)NH2 modified CG-induced changes in the antioxidant status, regardless of the time of their injection (simultaneously or 15 min before CG). The present results suggest that N/OFQ(1–13)NH2 and [Orn9]N/OFQ(1–13)NH2 most likely affect the neuronal inflammation, rather than act as pro- or antioxidants.

Psychiatric research: psychoproteomics, degradomics and systems biology

While proteomics has excelled in several disciplines in biology (cancer, injury and aging), neuroscience and psychiatryproteomic studies are still in their infancy. Several proteomic studies have been conducted in different areas of psychiatric disorders, including drug abuse (morphine, alcohol and methamphetamine) and other psychiatric disorders (depression, schizophrenia and psychosis). However, the exact cellular and molecular mechanisms underlying these conditions have not been fully investigated. Thus, one of the primary objectives of this review is to discuss psychoproteomic application in the area of psychiatric disorders, with special focus on substance- and drug-abuse research. In addition, we illustrate the potential role of degradomic utility in the area of psychiatric research and its application in establishing and identifying biomarkers relevant to neurotoxicity as a consequence of drug abuse. Finally, we will discuss the emerging role of systems biology and its current use in the field of neuroscience and its integral role in establishing a comprehensive understanding of specific brain disorders and brain function in general.

Human peripheral blood mononuclear cells produce pre-pro-nociceptin/orphanin FQ mRNA

BACKGROUND

Peripheral blood mononuclear cells (PBMC) transcribe mRNA for the nonclassical opioid nociceptin/orphanin FQ (N/OFQ) receptor (NOP). We probed for the N/OFQ precursor, pre-pro-N/OFQ (ppN/OFQ).

METHODS

Using PBMC from 10 healthy volunteers we probed for ppN/OFQ using polymerase chain reaction (PCR) based experimental paradigms.

RESULTS

In gel-based PCR, we detected amplicons consistent with ppN/OFQ mRNA in all samples. This was confirmed in quantitative real-time PCR with cycle thresholds (representing quantity of mRNA) of 30.91 +/- 0.18 (n = 10).

CONCLUSIONS

These data indicate that PBMCs transcribe ppN/OFQ which, coupled with NOP expression, suggest NOP may be involved in the autoregulation of PBMCs.

In vitro pharmacological characterisation of a novel cyclic nociceptin/orphanin FQ analogue c[Cys(7,10)]N/OFQ(1-13)NH (2)

Nociceptin/orphanin FQ (N/OFQ) is the endogenous 17 amino acid peptide ligand for the G(i)-protein-coupled N/OFQ receptor (NOP). In an attempt to improve the metabolic stability of N/OFQ, we have produced a truncated cyclic analogue with cysteine residues at positions 7 and 10, c[Cys(7,10)]N/OFQ(1-13)NH(2) (c[Cys(7,10)]). c[Cys(7,10)], the template N/OFQ(1-13)NH(2) and N/OFQ displaced the binding of [(3)H]N/OFQ to Chinese hamster ovary cells expressing recombinant human NOP (CHO(hNOP)) with pK ( i ) values of 9.98, 9.83 and 9.18, respectively. In addition, c[Cys(7,10)], N/OFQ(1-13)NH(2) and N/OFQ stimulated the binding of guanosine triphosphate gamma [(35)S] to CHO(hNOP) cells with pEC(50)/E (max) (stimulation factor) of 9.16/5.5, 9.11/4.9 and 8.35/5.5, respectively. c[Cys(7,10)], N/OFQ(1-13)NH(2) and N/OFQ inhibited forskolin-stimulated cyclic adenosine monophosphate (cAMP) formation with pEC(50) values of 10.08, 10.11 and 9.78, respectively. All ligands produced complete inhibition of cAMP formation. In both functional assays, c[Cys(7,10)] was a full agonist. In a series of metabolism experiments, incubation of 1 nM c[Cys(7,10)], N/OFQ(1-13)NH(2) and N/OFQ with a rat brain homogenate produced a time-dependent loss of peptide that was greatest for the native peptide N/OFQ. Amidation in N/OFQ(1-13)NH(2) produced some metabolic protection, but this was not significantly improved by further inclusion of c[Cys(7,10)]. In summary, c[Cys(7,10)] is a high-affinity, high-potency full agonist of the NOP receptor. However, we were unable to demonstrate clear metabolic protection.

Activation of the nociceptin opioid system in rat sensory neurons produces antinociceptive effects in inflammatory pain: involvement of inflammatory mediators

Despite a large body of literature on the nociceptin (NC) opioid system in pain modulation, the mechanism of action of NC remains largely unexplored. Here, we investigated the role and mode of action of the spinal NC system in inflammatory pain. Preemptive intrathecal administration of NC attenuated thermal hyperalgesia and mechanical allodynia in rats with intraplantar complete Freund's adjuvant (CFA) injection. By using immunohistochemistry in L4 dorsal root ganglion (DRG) neurons, a marked increase of NC and ORL1 receptor immunoreactivity was detected following CFA. Intrathecal administration of NC attenuated the CFA-induced increases of calcitonin gene-related peptide, transient receptor potential vanilloid-1, and tumor necrosis factor-alpha in DRG neurons. Real-time reverse transcription-polymerase chain reaction showed that NC reduced the up-regulation of inducible nitric oxide synthase mRNA but not that of neuronal nitric oxide synthase mRNA in spinal cord segments after CFA. Furthermore, [Nphe1]NC(1-13)NH2, a selective opioid receptor-like 1 (ORL1) receptor antagonist, significantly antagonized the effects of NC on pain modulation and on the expression of inflammatory mediators, indicating a specific NC action through the ORL1 receptor. Together, these findings reveal novel mechanisms by which the NC system produces analgesia.

Possible involvement of endogenous nociceptin/orphanin FQ in the pain-related behavioral responses induced by its own metabolite, nociceptin/orphanin FQ(14-17)

Nociceptin/orphanin FQ(14-17) (N/OFQ(14-17)) is one of the major fragments that are released from N/OFQ, an endogenous ligand for the opioid receptor like-1 (ORL-1) receptor by endopeptidase 24.11. In the present study, we determined the pharmacological profiles of N/OFQ(14-17) on pain-related behavioral responses in the mouse. Intrathecal (i.t.) administration of N/OFQ(14-17) (5-160 pmol) evoked pain-related behaviors, and these behavioral responses were reduced by i.t. co-administration of an ORL-1 receptor antagonist, [Nphe(1)]N/OFQ(1-13)NH2 (4 pmol). However, in the ligand-binding receptor assay, N/OFQ(14-17) had no affinity for the ORL-1 receptor. Furthermore, i.t. pretreatment with an antiserum against N/OFQ (1:50) diminished the N/OFQ(14-17)-induced pain-related behaviors, suggesting that endogenous N/OFQ is involved in their expression. Therefore, N/OFQ(14-17)-induced pain-related behaviors may be mediated through the release of endogenous N/OFQ in the mouse spinal cord.

Residues threonine 346 and leucine 352 are critical for the proper function of Bacillus kaustophilus leucine aminopeptidase

The importance of Thr-346 and Leu-352 residues in Bacillus kaustophilus leucine aminopeptidase (BkLAP) was explored by site-directed mutagenesis. The impact of substitutions at these positions was evaluated with His6-BkLAP fusion proteins expressed in Escherichia coli. Substitution of Thr-346 with Tyr, Arg, and Leu, respectively, resulted in a dramatic reduction in LAP activity. A complete loss of activity was observed in L352E and L352R variants with the exception of L352 V, which retained approximately 60% of the wild-type activity. Zinc content analysis and protein modeling suggested that Thr-346 and Leu-352 of BkLAP play a role in maintaining the coordination environment for the zinc-binding residues.

Effects of intrathecally administered nociceptin/orphanin FQ in monkeys: behavioral and mass spectrometric studies

Nociceptin/orphanin FQ (N/OFQ) is a heptadecapeptide that is an endogenous ligand for the N/OFQ peptide (NOP) receptor. The aim of this study was to investigate the behavioral responses of N/OFQ and its major fragment N/OFQ(2-17) in monkeys following i.t. administration. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to quantify the amounts of N/OFQ and N/OFQ(2-17) in the cerebrospinal fluid at specific time points when effects of i.t. N/OFQ were sustained and disappeared. Intrathecal administration of N/OFQ dose dependently (10-100 nmol) produced long-lasting antinociception against a noxious stimulus, 50 degrees C water, and did not elicit itch/scratching responses in monkeys. Subcutaneous pretreatment with a selective NOP receptor antagonist, (+)J-113397 [(1-[3R,4R)-1-cyclooctymethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3,-dihydro-2H-benzimidazol-2-one] (0.1 mg/kg), completely blocked i.t. N/OFQ (100 nmol)-induced antinociception. In contrast, a classic opioid receptor antagonist, naltrexone (0.01 and 1 mg/kg), failed to reverse i.t. N/OFQ-induced antinociception. MALDI-TOF-MS showed that the amount of N/OFQ(2-17) was 4-fold higher than that of N/OFQ at 1.5 h after i.t. administration of 100 nmol N/OFQ. Intrathecal N/OFQ-induced antinociception disappeared at 4.5 h, which corresponded to nearly undetectable cerebrospinal fluid levels of N/OFQ. No other metabolite of N/OFQ was detected at appreciable levels at either the 1.5- or 4.5-h time points. Although significant amounts of N/OFQ(2-17) were detected at the 1.5- and 4.5-h time points, 100 nmol N/OFQ(2-17) i.t. was inactive in changing the monkeys' nociceptive threshold. These results provide the first functional evidence of spinal N/OFQ-induced antinociception in primates and indicate that activation of spinal NOP receptors may be a potential target for spinal analgesics.

Identification of glutamate residues important for catalytic activity of Bacillus stearothermophilus leucine aminopeptidase II

Each of four conserved glutamate residues of Bacillus stearothermophilus leucine aminopeptidase II (BsLAPII) was replaced with aspartate, lysine, and leucine respectively by site-directed mutagenesis. The over-expressed wild-type and mutant enzymes were purified to homogeneity by nickel-chelate chromatography and the molecular mass of the subunit was determined to be 44.5 kDa by SDS-PAGE. The specific activity for the Glu-316 and Glu-340 mutants was completely abolished, while Glu-249 mutants showed comparable activity to that of the wild-type BsLAPII. Compared with the wild-type enzyme, the E250D and E250L mutant enzymes retained less than 18% of the enzyme activity and exhibited a dramatic decrease in the value of k (cat)/K (m). These observations indicate that Glu-250, Glu-316, and Glu-340 residues are critical for the catalytic activity of BsLAPII.

Synthesis of enzymatically resistant nociceptin-related peptides containing a carbamic acid residue

Nociceptin, a 17-amino acid peptide (FGGFTGARKSARKLANQ, N/OFQ), is the endogenous ligand of the nociceptin/orphanin FQ (NOP) receptor. This receptor-ligand system is involved in various physiological as well as pathophysiological mechanisms, but owing to the peptidic structure, it is rapidly degraded by enzymes. The enzymatic digestion of nociceptin involves mainly aminopeptidases and yields Noc(2-17)-OH and other smaller fragments. We aimed at increasing the enzymatic stability against aminopeptidases in the case of peptide Noc(1-13)-NH(2), which possesses the minimum sequence capable of interacting with the NOP receptor. Therefore we developed a new procedure for the synthesis of peptides with the carbamic acid residue [...-NH-CH(R)-CO-NH-CO-NH-CH(Q)-CO-.]. A set of four carbamic acid-nociceptin derivatives were produced. The carbamic acid residue was incorporated into the inner part of the peptides, building on solid phase, by using a suitable dipeptide fragment with carbamic acid residue produced by a simple and efficient three-step solution phase procedure. Enzymatic stability of carbamic acid peptides was studied in the presence of aminopeptidase M (AP-M) and in rat brain membrane homogenate. The receptor-binding properties were also studied by radioligand binding assay on crude rat brain membranes and the activity of the ligands were analyzed on isolated mouse vas deferens (MVD) tissues. We found that incorporation of the carbamic acid residue into the N-terminal part of nociceptin significantly increases the resistance against AP-M. We observed the decrease of binding affinities to the NOP receptor in case of the peptides modified in the N-terminal portion. Consequently, the incorporation of the carbamic acid residue into peptides can be proposed as a promising and reasonable tool for increasing enzymatic stability, where the native molecule is less sensitive for carbamic acid residue-related structural change.

Effects of intraplantar injections of nociceptin and its N-terminal fragments on nociceptive and desensitized responses induced by capsaicin in mice

Injection of capsaicin into the hindpaw has been employed as a model of chemogenic nociception in mice. Intraplantar injection of nociceptin (30-240 pmol) produced a significant and dose-dependent antinociceptive activity in the capsaicin test. The nociceptin N-terminal fragments, (1-11) and (1-13), were also active with a potency higher than nociceptin and comparable to nociceptin, respectively. Intraplantar injection of the nociceptin (1-7) fragment had no effect on capsaicin-induced nociception. Antinociception induced by nociceptin or nociceptin (1-13) was reversed significantly by intraplantar co-injection of [Nphe1]nociceptin (1-13)NH2, an orphan opioid receptor-like 1 (ORL1) receptor antagonist, whereas local injection of the antagonist did not interfere with the action of nociceptin (1-11). Nociceptin (1-11) was approximately 2.0-fold more potent than naturally occurring peptide nociceptin, and 10-fold more active than intraplantar morphine. Nociceptive licking/biting response to intraplantar injection of capsaicin was desensitized by repeated injections of capsaicin at the interval of 15 min. Desensitization induced by capsaicin was attenuated significantly by co-injection of nociceptin at much lower doses than antinociceptive ED50 for nociceptin. Capsaicin desensitization was also decreased by co-injection of nociceptin (1-11) and (1-13) to a similar extent. The present results indicate that not only nociceptin but also the N-terminal fragment (1-13) possesses a local peripheral antinociceptive action, which may be mediated by peripheral ORL1 receptors. In addition, the difference of the effective doses suggests that the antinociceptive action and inhibition of capsaicin-induced desenitization by nociceptin, nociceptin (1-11) and (1-13), may involve distinct mechanisms at the level of the peripheral nerve terminal.

Histidines 345 and 378 of Bacillus stearothermophilus leucine aminopeptidase II are essential for the catalytic activity of the enzyme

The conserved histidine residues, His-191, His-227, His-345, and His-378, in Bacillus stearothermophilus leucine aminopeptidase II (LAPII) were replaced with leucine by site-directed mutagenesis. The overexpressed wild-type and mutant enzymes have been purified by nickel-chelate chromatography and their molecular masses were approximately 44.5 kDa. Under assay conditions, no LAP activity was detected in H345L and H378L. Although the Km value for H191L increased more than 30% with respect to the wild-type LAPII, alteration in this residue did not lead to a significant change on the catalytic efficiency. The 39% decrease in Kcat/Km for H227L was partly caused by a 3.9-fold increase in Km value. Based on these results, it is suggested that His-345 and His-378 play a crucial role in the catalytic reaction of B. stearothermophilus LAPII.

Functional selectivity of nociceptin/orphanin FQ peptide receptor partial agonists on cardiovascular and renal function

The opioid-like peptide nociceptin/orphanin FQ (N/OFQ) produces marked cardiovascular and renal responses after central or peripheral administration in rats. Due to their ability to behave as full/partial agonists or antagonists in different cellular and tissue assays, the present studies were performed to determine how compounds classified as N/OFQ peptide (NOP) receptor partial agonists ([F/G]N/OFQ(1-13)-NH(2), Ac-RYYRIK-NH(2), and Ac-RYYRWK-NH(2)) affect cardiovascular and renal function in vivo. In conscious Sprague-Dawley rats, intracerebroventricular (i.c.v.) administration of each of the three NOP receptor ligands produced profound cardiovascular (depressor), renal excretory (water diuresis), and renal sympathetic nerve activity (inhibitory) responses that were similar to those produced by i.c.v. injection of the native ligand N/OFQ. In contrast, in other groups of rats, the intravenous (i.v.) bolus injection of these same NOP receptor ligands produced responses unlike N/OFQ; N/OFQ evoked an immediate and profound bradycardia and hypotension with no change in urine output, whereas all purported NOP receptor partial agonists elicited a subtle slow onset hypotension, no change in heart rate, and a marked water diuresis. In other studies, i.v. bolus pretreatment of rats with NOP receptor partial agonists prevented/attenuated the cardiovascular depressor effects produced by a subsequent i.v. bolus N/OFQ challenge without affecting the cardiovascular responses to i.c.v. N/OFQ. Together, these findings demonstrate that in conscious rats, NOP receptor partial agonists produce functionally selective effects on cardiovascular and renal function ranging from full agonist (i.c.v., cardiovascular depressor; i.c.v. and i.v., water diuresis), partial agonist (i.v., submaximal hypotension) to antagonist (i.v., blockade of N/OFQ-evoked bradycardia and hypotension) behavior.

Partial D-amino acid substitution: Improved enzymatic stability and preserved Ab recognition of a MUC2 epitope peptide

The stability of an immunogen against enzymatic degradation is considered an important factor for the design of synthetic vaccines. For our studies, we have selected an epitope from the tandem-repeat unit of the high-molecular-weight MUC2 mucin glycoprotein, which can be underglycosylated in case of colon cancer. In this study, we prepared a MUC2 peptide containing the PTGTQ epitope of a MUC2 protein backbone-specific mAb 996 and its derivatives. In these peptides, the N- and C-terminal flanking regions were systematically substituted by up to three d-amino acids. Peptides prepared by solid-phase synthesis were tested for their mAb 996 binding in competitive ELISA experiments, and their stability was studied in serum and lysosomal preparation. Our data show that the epitope function of peptide (15)TPTPTGTQTPT(25) is retained even in the presence of two d-amino acid residues at its N-terminal flanking region and up to three at its C-terminal flanking region (tpTPTGTQtpt). Also, this partly d peptide shows high resistance against proteolytic degradation in diluted human serum and in lysosomal preparation. These findings suggest that, by appropriate combination of structural modifications (namely, d-amino acid substitution) in the flanks of an Ab epitope, it is feasible to construct a synthetic antigen with preserved recognition properties and high stability against enzymatic degradation. Peptides tPTPTGTQTpt and tpTPTGTQTpt derived from this study can be used for immunization experiments and as potential components of synthetic vaccines for tumor therapy.

The effect of cyclization on the enzymatic degradation of herpes simplex virus glycoprotein D derived epitope peptide

One linear and three cyclic peptides corresponding to the 278-287 ((278)LLEDPVGTVA(287)) sequence of glycoprotein D (gD-1) of herpes simplex virus were synthesized for the analysis of the effect of cyclization on protection against enzymatic degradation. In this design, the turn-forming motif ((281)DPVG(284)) was positioned in the central part of the peptide and elongated by three amino acids at both termini. Cyclopeptide formation was achieved by the introduction of a peptide bond, a disulfide bridge or a thioether link. The stability of these peptides was compared in human serum and also in rat lysosomal preparations. The data obtained in 10% and 50% human serum show that all three types of cyclization enhanced the stability, but at different levels. Complete stability was only achieved by the introduction of a thioether link, while the presence of a disulfide or peptide bond resulted in improved, but partial resistance against hydrolytic decomposition. In lysosomal preparations the presence of cyclic primary structure provided full protection against enzymatic hydrolysis. Taken together, these findings indicate that by appropriate structural modification it is feasible to construct a synthetic antigen with high stability against enzymatic degradation in complex biological fluids. Further studies are in progress to identify enzymes responsible for degradation in diluted human sera as well as in the lysosomal preparations and to gain more detailed information on the mechanism of action.

Cerebrospinal fluid levels of opioid peptides in fibromyalgia and chronic low back pain

BACKGROUND

The mechanism(s) of nociceptive dysfunction and potential roles of opioid neurotransmitters are unresolved in the chronic pain syndromes of fibromyalgia and chronic low back pain.

METHODS

History and physical examinations, tender point examinations, and questionnaires were used to identify 14 fibromyalgia, 10 chronic low back pain and 6 normal control subjects. Lumbar punctures were performed. Met-enkephalin-Arg6-Phe7 (MEAP) and nociceptin immunoreactive materials were measured in the cerebrospinal fluid by radioimmunoassays.

RESULTS

Fibromyalgia (117.6 pg/ml; 85.9 to 149.4; mean, 95% C.I.; p = 0.009) and low back pain (92.3 pg/ml; 56.9 to 127.7; p = 0.049) groups had significantly higher MEAP than the normal control group (35.7 pg/ml; 15.0 to 56.5). MEAP was inversely correlated to systemic pain thresholds. Nociceptin was not different between groups. Systemic Complaints questionnaire responses were significantly ranked as fibromyalgia > back pain > normal. SF-36 domains demonstrated severe disability for the low back pain group, intermediate results in fibromyalgia, and high function in the normal group.

CONCLUSIONS

Fibromyalgia was distinguished by higher cerebrospinal fluid MEAP, systemic complaints, and manual tender points; intermediate SF-36 scores; and lower pain thresholds compared to the low back pain and normal groups. MEAP and systemic pain thresholds were inversely correlated in low back pain subjects. Central nervous system opioid dysfunction may contribute to pain in fibromyalgia.

Increased nociceptin/orphanin FQ plasma levels in hepatocellular carcinoma

AIM

The heptadecapeptide nociceptin alias orphanin FQ is the endogenous agonist of opioid receptor-like1 receptor. It is involved in modulation of pain and cognition. High blood level was reported in patients with acute and chronic pain, and in Wilson disease. An accidental observation led us to investigate nociceptin in hepatocellular carcinoma.

METHODS

Plasma nociceptin level was measured by radioimmunoassay, aprotinin was used as protease inhibitor. Hepatocellular carcinoma was diagnosed by laboratory, ultrasound, other imaging, and confirmed by fine needle biopsy. Results were compared to healthy controls and patients with other chronic liver diseases.

RESULTS

Although nociceptin levels were elevated in patients with Wilson disease (14.0+/-2.7 pg/mL, n=26), primary biliary cirrhosis (12.1+/-3.2 pg/mL, n=21) and liver cirrhosis (12.8+/-4.0 pg/mL, n=15) compared to the healthy controls (9.2+/-1.8 pg/mL, n=29, P<0.001 for each), in patients with hepatocellular carcinoma a ten-fold increase was found (105.9+/-14.4 pg/mL, n=29, P<0.0001). High plasma levels were found in each hepatocellular carcinoma patient including those with normal alpha fetoprotein and those with pain (104.9+/-14.9 pg/mL, n=12) and without (107.7+/-14.5 pg/mL, n=6).

CONCLUSION

A very high nociceptin plasma level seems to be an indicator for hepatocellular carcinoma. Further research is needed to clarify the mechanism and clinical significance of this novel finding.

Generating oxidation-resistant variants of Bacillus kaustophilus leucine aminopeptidase by substitution of the critical methionine residues with leucine

Bacillus kaustophilus leucine aminopeptidase (bkLAP) was sensitive to oxidative damage by hydrogen peroxide. To improve its oxidative stability, the oxidation-sensitive methionine residues in the enzyme were replaced with leucine by site-directed mutagenesis. The variants, each with an apparent molecular mass of approximately 54 kDa, were overexpressed in recombinant Escherichia coli M15 cells and purified to homogeneity by nickel-chelate chromatography. The specific activity for M282L, M285L, M289L and M321L decreased by more than 43%, while M400L, M426L, M445L, and M485L showed 191, 79, 313, and 103%, respectively, higher activity than the wild-type enzyme. Although the mutations did not cause significant changes in the K(m) value, more than 67.8% increase in the value of k(cat)/K(m) was observed in the M400L, M426L, M445L and M485L. In the presence of 50 mM H2O2, most variants were more stable with respect to the wild-type enzyme, indicating that the oxidative stability of the enzyme can be improved by engineering the methionine residues.

Pharmacological profile of the cyclic nociceptin/orphanin FQ analogues c[Cys10,14]N/OFQ(1-14)NH2 and c[Nphe1,Cys10,14]N/OFQ(1-14)NH2

In this study we describe the activity of two cyclic nociceptin/orphanin FQ (N/OFQ) peptides; c[Cys(10,14)]N/OFQ(1-14)NH(2) (c[Cys(10,14)]) and its [Nphe(1)] derivative c[Nphe(1),Cys(10,14)]N/OFQ(1-14)NH(2) (c[Nphe(1),Cys(10,14)]) in native rat and mouse and recombinant human N/OFQ receptors (NOP). Cyclisation may protect the peptide from metabolic degradation. In competition binding studies of rat, mouse and human NOP the following rank order pK(i) was obtained: N/OFQ(1-13)NH(2)(reference agonist)>N/OFQ=c[Cys(10,14)]>>c[Nphe(1)Cys(10,14)]. In GTPgamma(35)S studies of Chinese hamster ovary cells expressing human NOP (CHO(hNOP)) c[Cys(10,14)] (pEC(50) 8.29) and N/OFQ(1-13)NH(2) (pEC(50) 8.57) were full agonists whilst c[Nphe(1)Cys(10,14)] alone was inactive. Following 30 min pre-incubation c[Nphe(1)Cys(10,14)] competitively antagonised the effects of N/OFQ(1-13)NH(2) with a pA(2) and slope factor of 6.92 and 1.01 respectively. In cAMP assays c[Cys(10,14)] (pEC(50) 9.29, E(max) 102% inhibition of the forskolin stimulated response), N/OFQ(1-13)NH(2) (pEC(50) 10.16, E(max) 103% inhibition) and c[Nphe(1)Cys(10,14)] (~80% inhibition at 10 microM) displayed agonist activity. In the mouse vas deferens c[Cys(10,14)] (pEC(50) 6.82, E(max) 89% inhibition of electrically evoked contractions) and N/OFQ(1-13)NH(2) (pEC(50) 7.47, E(max) 93% inhibition) were full agonists whilst c[Nphe(1)Cys(10,14)] alone was inactive. c[Nphe(1)Cys(10,14)] (10 microM) competitively antagonised the effects of N/OFQ(1-13)NH(2) with a pK(B) of 5.66. In a crude attempt to assess metabolic stability, c[Cys(10,14)] was incubated with rat brain membranes and then the supernatant assayed for remaining peptide. Following 60 min incubation 64% of the 1 nM added peptide was metabolised (compared with 54% for N/OFQ-NH(2)). In summary, we report that c[Cys(10,14)] is a full agonist with a small reduction in potency but no improvement in stability whilst c[Nphe(1)Cys(10,14)] displays tissue (antagonist in the vas deferens) and assay (antagonist in the GTPgamma(35)S assay and agonist in cAMP assay) dependent activity.

Cardiovascular responses to microinjections of nociceptin into a midline area in the commissural subnucleus of the nucleus tractus solitarius of the rat

Immunoreactivity for nociceptin, an endogenous ligand for the ORL1 opioid receptors, has been reported in the nucleus tractus solitarius (nTS). A midline area in the commissural subnucleus (nCom) of nTS is the site of peripheral chemoreceptor projections. This investigation was carried out in urethane-anesthetized, artificially ventilated, adult male Wistar rats, to study the cardiovascular effects of the activation of ORL1 receptors in a midline area of the nCom. Microinjections (30 nl) of nociceptin (0.15-0.62 mM) into the nCom elicited depressor and bradycardic responses. Prior microinjections of [N-Phe(1)]-nociceptin-(1-13)-NH(2) (4.5 mM), a specific antagonist for ORL1 opioid receptors, into the nCom blocked the effects of nociceptin (0.31 mM, the maximally effective concentration), but not endomorphin-2 (0.6 mM; an endogenous ligand for micro -opioid receptors). On of other hand, naloxone (0.125 mM; an antagonist for classical opioid receptors) did not block the effects of nociceptin, while it did block the effects of endomorphin-2. The blockade of nociceptin effects by [N-Phe(1)]-nociceptin-(1-13)-NH(2) and endomorphin-2 by naloxone, was not due to some nonspecific effects because the responses to L-Glu (5 mM) remained unaltered after the microinjection of these antagonists. These results indicate that activation of ORL1 receptors in the nCom may play a role in the regulation of cardiovascular function.

Nociceptin/orphanin FQ: actions within the brain

A peptide termed nociceptin/orphanin FQ (N/OFQ) was recently identified as an endogenous agonist for the opioid receptor-like receptor currently specified as NOP receptor. Despite many structural homologies to the opioid system, the NOP receptor shows low-affinity binding to selective opioid agonists or antagonists. Vice versa, N/OFQ selectively activates the NOP receptor but not any opioid receptor subtype. This novel receptor/ligand system is widely expressed in the brain. At the cellular level, the actions of N/OFQ resemble those elicited by opioid peptides. The NOP receptor is coupled to G-proteins, whose activation results in inhibition of adenylate cyclase, modulation of calcium and potassium conductances, and regulation of transmitter systems. At the behavioral level, systemic application of N/OFQ elicits a unique range of responses, including a wide range of effects on pain processing such as hyperalgesia, analgesia, and allodynia, as well as anxiolytic actions, modulation of opioid-mediated processes, and influences on learning and memory.

The Drosophila slamdance gene: a mutation in an aminopeptidase can cause seizure, paralysis and neuronal failure

We report here the characterization of slamdance (sda), a Drosophila melanogaster "bang-sensitive" (BS) paralytic mutant. This mutant exhibits hyperactive behavior and paralysis following a mechanical "bang" or electrical shock. Electrophysiological analyses have shown that this mutant is much more prone to seizure episodes than normal flies because it has a drastically lowered seizure threshold. Through genetic mapping, molecular cloning, and RNA interference, we have demonstrated that the sda phenotype can be attributed to a mutation in the Drosophila homolog of the human aminopeptidase N (APN) gene. Furthermore, using mRNA in situ hybridization and LacZ staining, we have found that the sda gene is expressed specifically in the central nervous system at particular developmental stages. Together, these results suggest that the bang sensitivity in sda mutants is caused by a defective APN gene that somehow increases seizure susceptibility. Finally, by using the sda mutation as a sensitized background, we have been able to identify a rich variety of sda enhancers and other independent BS mutations.

Degradation of nociceptin (orphanin FQ) by mouse spinal cord synaptic membranes is triggered by endopeptidase-24.11: an in vitro and in vivo study

We analyzed spinal metabolic pathway of nociceptin/orphanin FQ related to pain-transmission or modulation in the both in vitro and in vivo experiments. Nociceptin was degraded by spinal synaptic membranes. Major metabolites of nociceptin were free phenylalanine, nociceptin (1-13) and nociceptin (14-17). Both the degradation of nociceptin and the accumulation of the major cleavage metabolites, nociceptin (1-13) and nociceptin (14-17), were strongly inhibited by a metal chelator and also by specific inhibitors of endopeptidase-24.11, thiorphan and phosphoramidon. Furthermore, purified endopeptidase-24.11 hydrolyzed nociceptin at the cleavage site (Lys(13)-Leu(14) bond) identical to that by spinal synaptic membranes. Recently, we have found that nociceptin, injected intrathecally at small doses (fmol order) elicits a behavioral response consisting of scratching, biting and licking in mice. In the present study, we have examined the effect of peptidase inhibitors on the behavioral response elicited by intrathecal injection of nociceptin in mice. Phosphoramidon simultaneously injected with nociceptin additively enhanced nociceptin-induced behavioral response, whereas the nociceptin-induced behavioral response was unaffected by either bestatin, an aminopeptidase inhibitor or captopril, an angiotensin-converting enzyme inhibitor. However, the nociceptin effect was potentiated by combined injection of phosphoramidon and bestatin, indicating that inhibition of aminopeptidase may also contribute to inducing the behavioral response to nociceptin. These data suggest that endopeptidase-24.11 plays a major role in initial stage of nociceptin metabolism at the spinal cord level in mice.

Novel orphanin FQ/nociceptin transcripts are expressed in human immune cells

The opioid-like receptor (NOP) is widely expressed throughout the human immune system. Here, we report that human peripheral blood lymphocytes (PBLs) express transcripts encoding the NOP receptor agonist, orphanin FQ/nociceptin (OFQ/N). OFQ/N transcripts in resting PBLs were restricted to CD19+B cells and contained a novel 5' exon (ImEx2b), replacing exons 1 and 2 found in neuronal transcripts. Translation of ImEx2b-containing transcripts resulted in truncated OFQ/N precursors lacking a classical signal peptide. Mitogen activation of PBLs dramatically up-regulated neuronal-like transcripts, predominantly in CD3+T cells. Overall, this suggests different promoters direct specific OFQ/N transcript expression in immune cells.

Effects of chronic nociceptin/orphanin FQ exposure on cAMP accumulation and receptor density in Chinese hamster ovary cells expressing human nociceptin/orphanin FQ receptors

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the G(i)-coupled N/OFQ receptor (NOP). We have examined the effects of chronic exposure of Chinese hamster ovary cells expressing the recombinant human NOP receptor (CHO(hNOP)) to 1 nM N/OFQ for up to 48 h in the absence and presence of the NOP selective antagonist [Nphe(1)]N/OFQ (1-13)NH(2) ([Nphe(1)]). Then, either a concentration-response curve for N/OFQ inhibition of cAMP formation was constructed or the cells were homogenized and membrane receptor density was determined using [(125)I]Y(14)N/OFQ. There was a time-dependent reduction in pEC(50) (without a change in maximum) for N/OFQ with significant differences observed following >24 h of exposure (control pEC(50) approximately 9.5; 48 h pretreatment approximately 8.7). In cells co-exposed to N/OFQ+[Nphe(1)] for 48 h, there was no reduction in pEC(50). There was a compensatory (approximately 2.5-fold), [Nphe(1)]-sensitive increase in cAMP mass in cells exposed to N/OFQ for 24-48 h. N/OFQ pretreatment also resulted in a time-dependent [Nphe(1)]-sensitive loss of cell surface receptors. At 48 h, B(max) was reduced from approximately 2.0 to approximately 1.3 pmol mg(-1) protein without a change in pK(d) for N/OFQ. There was a positive correlation between pEC(50) for cAMP inhibition and B(max). The lack of effect on maximum cAMP response probably results from receptor overexpression and the creation of a receptor reserve.

Comparison of the ORL1 receptor-mediated inhibition of noradrenaline release in human and rat neocortical slices

The effects of nociceptin/orphanin (N/OFQ) and the selective ORL1 antagonist J-113397 (1-[(3R,4R)-1-cyclo-octylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) were studied on electrically-evoked release of [(3)H]-noradrenaline ([(3)H]-NA) from human and rat neocortical slices. Specimens of human tissue were obtained during neurosurgery. Slices were preincubated with 0.1 microM [(3)H]-NA, superfused in the presence of desipramine, idazoxan, and naloxone (1 microM each), and stimulated electrically up to three times under conditions (4 pulses, 100 Hz, 2 ms, 60 mA) that prevent inhibition of evoked [(3)H]-NA release by endogenous modulators accumulating during ongoing stimulation. N/OFQ decreased electrically-evoked [(3)H]-NA release in both human and rat neocortical slices in a concentration-dependent manner. The respective pEC(50) values were 7.74 [CI(95): 7.47, 8.04] and 7.64 [CI(95): 7.48, 7.77], and the maximal inhibitions were 36.9% [CI(95): 32.4%, 41.8%] and 66.4% [CI(95): 61.7%, 72.7%]. N/OFQ (1 microM) inhibited K(+) (15 mM)-evoked [(3)H]-NA release from neocortical slices of both species by a similar magnitude, either in the presence or absence of tetrodotoxin. The nonpeptide ORL1 antagonist J-113397 competitively attenuated, with similar potency, the inhibition of electrically-evoked [(3)H]-NA release by N/OFQ in both species (pA(2) values: human, 8.16 [CI(95): 7.64, 8.64]; rat, 8.47 [CI(95): 8.27, 8.67]). J-113397 (0.1 microM) by itself did not alter either the evoked or spontaneous [(3)H]-NA release, suggesting that presynaptic ORL1 receptors are not activated by endogenous N/OFQ under the stimulation conditions employed. This study provides the first evidence that N/OFQ modulates [(3)H]-NA release in human neocortex via specific ORL1 receptors most likely located on noradrenergic axon terminals.

Recent advances in opioid pharmacology

Despite their many and sometimes life-threatening side-effects, opioids in general and morphine in particular are valuable and potent painkillers. This article describes recent developments in sex-related differences in opioid (morphine) pharmacodynamics, morphine metabolites, the nociceptin/orphanin FQ receptor system, acute opioid tolerance and opioid-induced side-effects, such as opioid-induced respiratory depression and itch, and P-glycoprotein modulation of opioid effect.