Non-opioid actions of opioid peptides

Addiction and the cerebellum with a focus on actions of opioid receptors

Increasing evidence suggests that the cerebellum could play a role in the higher cognitive processes involved in addiction as the cerebellum contains anatomical and functional pathways to circuitry controlling motivation and saliency. In addition, the cerebellum exhibits a widespread presence of receptors, including opioid receptors which are known to play a prominent role in synaptic and circuit mechanisms of plasticity associated with drug use and development of addiction to opioids and other drugs of abuse. Further, the presence of perineural nets (PNNs) in the cerebellum which contain proteins known to alter synaptic plasticity could contribute to addiction. The role the cerebellum plays in processes of addiction is likely complex, and could depend on the particular drug of abuse, the pattern of use, and the stage of the user within the addiction cycle. In this review, we discuss functional and structural modifications shown to be produced in the cerebellum by opioids that exhibit dependency-inducing properties which provide support for the conclusion that the cerebellum plays a role in addiction.

Dynorphin Neuropeptides Decrease Apparent Proton Affinity of ASIC1a by Occluding the Acidic Pocket

Prolonged acidosis, as it occurs during ischemic stroke, induces neuronal death via acid-sensing ion channel 1a (ASIC1a). Concomitantly, it desensitizes ASIC1a, highlighting the pathophysiological significance of modulators of ASIC1a acid sensitivity. One such modulator is the opioid neuropeptide big dynorphin (Big Dyn) which binds to ASIC1a and enhances its activity during prolonged acidosis. The molecular determinants and dynamics of this interaction remain unclear, however. Here, we present a molecular interaction model showing a dynorphin peptide inserting deep into the acidic pocket of ASIC1a. We confirmed experimentally that the interaction is predominantly driven by electrostatic forces, and using noncanonical amino acids as photo-cross-linkers, we identified 16 residues in ASIC1a contributing to Big Dyn binding. Covalently tethering Big Dyn to its ASIC1a binding site dramatically decreased the proton sensitivity of channel activation, suggesting that Big Dyn stabilizes a resting conformation of ASIC1a and dissociates from its binding site during channel opening.

Perinatal exposure to a glyphosate-based herbicide causes dysregulation of dynorphins and an increase of neural precursor cells in the brain of adult male rats

Glyphosate, the most used herbicide worldwide, has been suggested to induce neurotoxicity and behavioral changes in rats after developmental exposure. Studies of human glyphosate intoxication have reported adverse effects on the nervous system, particularly in substantia nigra (SN). Here we used matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) to study persistent changes in peptide expression in the SN of 90-day-old adult male Wistar rats. The animals were perinatally exposed to 3 % GBH (glyphosate-based herbicide) in drinking water (corresponding to 0.36 % of glyphosate) starting at gestational day 5 and continued up to postnatal day 15 (PND15). Peptides are present in the central nervous system before birth and play a critical role in the development and survival of neurons, therefore, observed neuropeptide changes could provide better understanding of the GBH-induced long term effects on SN. The results revealed 188 significantly altered mass peaks in SN of animals perinatally exposed to GBH. A significant reduction of the peak intensity (P < 0.05) of several peptides from the opioid-related dynorphin family such as dynorphin B (57 %), alpha-neoendorphin (50 %), and its endogenous metabolite des-tyrosine alpha-neoendorphin (39 %) was detected in the GBH group. Immunohistochemical analysis confirmed a decreased dynorphin expression and showed a reduction of the total area of dynorphin immunoreactive fibers in the SN of the GBH group. In addition, a small reduction of dynorphin immunoreactivity associated with non-neuronal cells was seen in the hilus of the hippocampal dentate gyrus. Perinatal exposure to GBH also induced an increase in the number of nestin-positive cells in the subgranular zone of the dentate gyrus. In conclusion, the results demonstrate long-term changes in the adult male rat SN and hippocampus following a perinatal GBH exposure suggesting that this glyphosate-based formulation may perturb critical neurodevelopmental processes.

The atypical chemokine receptor ACKR3/CXCR7 is a broad-spectrum scavenger for opioid peptides

Endogenous opioid peptides and prescription opioid drugs modulate pain, anxiety and stress by activating opioid receptors, currently classified into four subtypes. Here we demonstrate that ACKR3/CXCR7, hitherto known as an atypical scavenger receptor for chemokines, is a broad-spectrum scavenger of opioid peptides. Phylogenetically, ACKR3 is intermediate between chemokine and opioid receptors and is present in various brain regions together with classical opioid receptors. Functionally, ACKR3 is a scavenger receptor for a wide variety of opioid peptides, especially enkephalins and dynorphins, reducing their availability for the classical opioid receptors. ACKR3 is not modulated by prescription opioids, but we show that an ACKR3-selective subnanomolar competitor peptide, LIH383, can restrain ACKR3’s negative regulatory function on opioid peptides in rat brain and potentiate their activity towards classical receptors, which may open alternative therapeutic avenues for opioid-related disorders. Altogether, our results reveal that ACKR3 is an atypical opioid receptor with cross-family ligand selectivity.

Opioids modulate pain, anxiety and stress by activating four subtypes of opioid receptors. The authors show that atypical chemokine receptor 3 (ACKR3) is a scavenger for various endogenous opioid peptides regulating their availability without activating downstream signaling.

Mechanism and site of action of big dynorphin on ASIC1a

Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there is a great interest in understanding the in vivo regulation of ASICs, especially by endogenous neuropeptides that potently modulate ASICs. The most potent endogenous ASIC modulator known to date is the opioid neuropeptide big dynorphin (BigDyn). BigDyn is up-regulated in chronic pain and increases ASIC-mediated neuronal death during acidosis. Understanding the mechanism and site of action of BigDyn on ASICs could thus enable the rational design of compounds potentially useful in the treatment of pain and ischemic stroke. To this end, we employ a combination of electrophysiology, voltage-clamp fluorometry, synthetic BigDyn analogs, and noncanonical amino acid-mediated photocrosslinking. We demonstrate that BigDyn binding results in an ASIC1a closed resting conformation that is distinct from open and desensitized states induced by protons. Using alanine-substituted BigDyn analogs, we find that the BigDyn modulation of ASIC1a is primarily mediated through electrostatic interactions of basic amino acids in the BigDyn N terminus. Furthermore, neutralizing acidic amino acids in the ASIC1a extracellular domain reduces BigDyn effects, suggesting a binding site at the acidic pocket. This is confirmed by photocrosslinking using the noncanonical amino acid azidophenylalanine. Overall, our data define the mechanism of how BigDyn modulates ASIC1a, identify the acidic pocket as the binding site for BigDyn, and thus highlight this cavity as an important site for the development of ASIC-targeting therapeutics.

Mechanisms underlying δ- and μ-opioid receptor agonist-induced increases in extracellular dopamine level in the nucleus accumbens of freely moving rats

The nucleus accumbens is a terminal area of the mesolimbic dopaminergic system that arises in the ventral tegmental area. Opioids are thought to enhance dopaminergic activity in the nucleus accumbens by activating δ- and μ-opioid receptors in the ventral tegmental area. However, δ- and μ-opioid receptor agonists increase extracellular levels of accumbal dopamine when infused directly into the nucleus accumbens of rats. Therefore, the roles of δ- and μ-opioid receptors in regulation of accumbal dopaminergic neural activity have been analyzed by using δ- and μ-opioid receptor ligands. This review describes the mechanisms underlying the stimulatory effects on accumbal dopamine efflux, which are induced by local administration of δ- and μ-opioid receptor agonists into the nucleus accumbens of freely moving rats. The focus of this article is neurochemical studies that use in vivo microdialysis techniques. Taken together, the in vivo neurochemical evidence from these studies indicates that δ- and μ-opioid receptor agonists increase accumbal dopamine efflux by activating naloxone-sensitive opioid receptors, and by mechanisms independent of naloxone-sensitive opioid receptors, in the nucleus accumbens.

Cyclic mu-opioid receptor ligands containing multiple N-methylated amino acid residues

In this study we report the in vitro activities of four cyclic opioid peptides with various sequence length/macrocycle size and N-methylamino acid residue content. N-Methylated amino acids were incorporated and cyclization was employed to enhance conformational rigidity to various extent. The effect of such modifications on ligand structure and binding properties were studied. The pentapeptide containing one endocyclic and one exocyclic N-methylated amino acid displayed the highest affinity to the mu-opioid receptor. This peptide was also shown to be a full agonist, while the other analogs failed to activate the mu opioid receptor. Results of molecular docking studies provided rationale for the explanation of binding properties on a structural basis.

Role of the non-opioid dynorphin peptide des-Tyr-dynorphin (DYN-A(2-17)) in food intake and physical activity, and its interaction with orexin-A

Food intake and physical activity are regulated by multiple neuropeptides, including orexin and dynorphin (DYN). Orexin-A (OXA) is one of two orexin peptides with robust roles in regulation of food intake and spontaneous physical activity (SPA). DYN collectively refers to several peptides, some of which act through opioid receptors (opioid DYN) and some whose biological effects are not mediated by opioid receptors (non-opioid DYN). While opioid DYN is known to increase food intake, the effects of non-opioid DYN peptides on food intake and SPA are unknown. Neurons that co-express and release OXA and DYN are located within the lateral hypothalamus. Limited evidence suggests that OXA and opioid DYN peptides can interact to modulate some aspects of behaviors classically related to orexin peptide function. The paraventricular hypothalamic nucleus (PVN) is a brain area where OXA and DYN peptides might interact to modulate food intake and SPA. We demonstrate that injection of des-Tyr-dynorphin (DYN-A(2-17), a non opioid DYN peptide) into the PVN increases food intake and SPA in adult mice. Co-injection of DYN-A(2-17) and OXA in the PVN further increases food intake compared to DYN-A(2-17) or OXA alone. This is the first report describing the effects of non-opioid DYN-A(2-17) on food intake and SPA, and suggests that DYN-A(2-17) interacts with OXA in the PVN to modulate food intake. Our data suggest a novel function for non-opioid DYN-A(2-17) on food intake, supporting the concept that some behavioral effects of the orexin neurons result from combined actions of the orexin and DYN peptides.

Dynorphin A analogs for the treatment of chronic neuropathic pain

Chronic pain is one of the most ubiquitous diseases in the world, but treatment is difficult with conventional methods, due to undesirable side effects of treatments and unknown mechanisms of pathological pain states. The endogenous peptide, dynorphin A has long been established as a target for the treatment of pain. Interestingly, this unique peptide has both inhibitory (opioid in nature) and excitatory activities (nonopioid) in the CNS. Both of these effects have been found to play a role in pain and much work has been done to develop therapeutics to enhance the inhibitory effects. Here we will review the dynorphin A compounds that have been designed for the modulation of pain and will discuss where the field stands today.

Nociceptin receptor activation does not alter acquisition, expression, extinction and reinstatement of conditioned cocaine preference in mice

Growing evidence indicates that targeting nociceptin receptor (NOP) signaling may have therapeutic efficacy in treating alcohol and opioid addiction. However, little is known about the therapeutic value of selective NOP agonists for the treatment of cocaine dependence. Recently, we identified a highly selective, brain-penetrant NOP small molecule agonist (SR-8993), and using this compound, we previously showed that nociceptin receptor activation attenuated consolidation of fear-related memories. Here, we sought to determine whether SR-8993 also affects the rewarding properties of cocaine. Using a conditioned place preference (CPP) procedure, we show that SR-8993 (3 or 10 mg/kg) failed to disrupt acquisition or expression of cocaine CPP (7.5 or 15 mg/kg) in C57BL/6 mice. Additionally, SR-8993 did not affect rate of extinction or reinstatement (yohimbine- and cocaine-induced) of cocaine CPP. These studies indicate that selective activation of NOP may not be sufficient in reducing behavioral responses to cocaine.

Monitoring β-arrestin recruitment via β-lactamase enzyme fragment complementation: purification of peptide E as a low-affinity ligand for mammalian bombesin receptors

Identification of cognate ligands for G protein-coupled receptors (GPCRs) provides a starting point for understanding novel regulatory mechanisms. Although GPCR ligands have typically been evaluated through the activation of heterotrimeric G proteins, recent studies have shown that GPCRs signal not only through G proteins but also through β-arrestins. As such, monitoring β-arrestin signaling instead of G protein signaling will increase the likelihood of identifying currently unknown ligands, including β-arrestin-biased agonists. Here, we developed a cell-based assay for monitoring ligand-dependent GPCR-β-arrestin interaction via β-lactamase enzyme fragment complementation. Inter alia, β-lactamase is a superior reporter enzyme because of its cell-permeable fluorescent substrate. This substrate makes the assay non-destructive and compatible with fluorescence-activated cell sorting (FACS). In a reporter cell, complementary fragments of β-lactamase (α and ω) were fused to β-arrestin 2 and GPCR, respectively. Ligand stimulation initiated the interaction of these chimeric proteins (β-arrestin-α and GPCR-ω), and this inducible interaction was measured through reconstituted β-lactamase activity. Utilizing this system, we screened various mammalian tissue extracts for agonistic activities on human bombesin receptor subtype 3 (hBRS3). We purified peptide E as a low-affinity ligand for hBRS3, which was also found to be an agonist for the other two mammalian bombesin receptors such as gastrin-releasing peptide receptor (GRPR) and neuromedin B receptor (NMBR). Successful purification of peptide E has validated the robustness of this assay. We conclude that our newly developed system will facilitate the discovery of GPCR ligands.

Dynamic measurement of extracellular opioid activity: status quo, challenges, and significance in rewarded behaviors

Opioid peptides are the endogenous ligands of opioid receptors, which are also the molecular target of naturally occurring and synthetic opiates, such as morphine and heroin. Since their discovery in the 1970s, opioid peptides, which are found widely throughout the central nervous system and the periphery, have been intensely studied because of their involvement in pain and pleasure. Over the years, our understanding of opioid peptides has widened to cover a multitude of functions, including learning and memory, affective state, gastrointestinal transit, feeding, immune function, and metabolism. Unsurprisingly, aberrant opioid activity is implicated in numerous pathologies, including drug addiction, overeating, pain, depression, and obesity. To date, virtually all preclinical and clinical studies aimed at understanding the function of endogenous opioids have relied upon manipulating endogenous opioid fluxes using opioid receptor ligands or genetic manipulations of opioid receptors and endogenous opioids. Difficulties in directly monitoring endogenous opioid fluxes, particularly in the central nervous system, have presented a major obstacle to fully understanding endogenous opioid function. This review summarizes these challenges and offers suggestions for future goals while focusing on the neurobiology of reward, specifically drawing attention to studies that have succeeded in dynamically measuring opioid peptides.

Membrane interactions in small fast-tumbling bicelles as studied by 31P NMR

Small fast-tumbling bicelles are ideal for studies of membrane interactions at molecular level; they allow analysis of lipid properties using solution-state NMR. In the present study we used 31P NMR relaxation to obtain detailed information on lipid head-group dynamics. We explored the effect of two topologically different membrane-interacting peptides on bicelles containing either dimyristoylphosphocholine (DMPC), or a mixture of DMPC and dimyristoylphosphoglycerol (DMPG), and dihexanoylphosphocholine (DHPC). KALP21 is a model transmembrane peptide, designed to span a DMPC bilayer and dynorphin B is a membrane surface active neuropeptide. KALP21 causes significant increase in bicelle size, as evidenced by both dynamic light scattering and 31P T2 relaxation measurements. The effect of dynorphin B on bicelle size is more modest, although significant effects on T2 relaxation are observed at higher temperatures. A comparison of 31P T1 values for the lipids with and without the peptides showed that dynorphin B has a greater effect on lipid head-group dynamics than KALP21, especially at elevated temperatures. From the field-dependence of T1 relaxation data, a correlation time describing the overall lipid motion was derived. Results indicate that the positively charged dynorphin B decreases the mobility of the lipid molecules--in particular for the negatively charged DMPG--while KALP21 has a more modest influence. Our results demonstrate that while a transmembrane peptide has severe effects on overall bilayer properties, the surface bound peptide has a more dramatic effect in reducing lipid head-group mobility. These observations may be of general importance for understanding peptide-membrane interactions.

Epigenetic regulation of spinal cord gene expression controls opioid-induced hyperalgesia

Background

The long term use of opioids for the treatment of pain leads to a group of maladaptations which includes opioid-induced hyperalgesia (OIH). OIH typically resolves within few days after cessation of morphine treatment in mice but is prolonged for weeks if histone deacetylase (HDAC) activity is inhibited during opioid treatment. The present work seeks to identify gene targets supporting the epigenetic effects responsible for OIH prolongation.

Results

Mice were treated with morphine according to an ascending dose protocol. Some mice also received the selective HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) additionally. Chronic morphine treatment with simultaneous HDAC inhibition enhanced OIH, and several spinal cord genes were up-regulated. The expression of Bdnf (Brain-derived neurotrophic factor) and Pdyn (Prodynorphin) were most closely related to the observed behavioral changes. ChIP (Chromatin immuoprecipation) assays demonstrated that promoter regions of Pdyn and Bdnf were strongly associated with aceH3K9 (Acetylated histone H3 Lysine9) after morphine and SAHA treatment. Furthermore, morphine treatment caused an increase in spinal BDNF and dynorphin levels, and these levels were further increased in SAHA treated mice. The selective TrkB (tropomyosin-receptor-kinase) antagonist ANA-12 reduced OIH when given one or seven days after cessation of morphine. Treatment with the selective kappa opioid receptor antagonist nor-BNI also reduced established OIH. The co-administration of either receptor antagonist agent daily with morphine resulted in attenuation of hyperalgesia present one day after cessation of treatment. Additionally, repeated morphine exposure induced a rise in BDNF expression that was associated with an increased number of BDNF⁺ cells in the spinal cord dorsal horn, showing strong co-localization with aceH3K9 in neuronal cells. Lastly, spinal application of low dose BDNF or Dynorphin A after resolution of OIH produced mechanical hypersensitivity, with no effect in controls.

Conclusions

The present study identified two genes whose expression is regulated by epigenetic mechanisms during morphine exposure. Treatments aimed at preventing the acetylation of histones or blocking BDNF and dynorphin signaling may reduce OIH and improve long-term pain using opioids.

Endomorphins and ohmefentanyl in the inhibition of immunosuppressant function in rat peritoneal macrophages: An experimental in vitro study

BACKGROUND

The potential immunosuppressant effects of opioids might have clinical implications. The effects of endomorphins (EMs) and ohmefentanyl (OMF) on cultured rat peritoneal macrophages remain unclear.

OBJECTIVE

The aim of this study was to investigate the immunosuppressant effects of EMs and OMF on cultured rat peritoneal macrophages in vitro.

METHODS

Purified rat peritoneal macrophages, from healthy adult male Sprague-Dawley rats, were cultured with EM-1 (EM-1 group), EM-2 (EM-2 group), OMF (OMF group), and saline (saline group). We measured the concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-β in supernatant when macrophages were cultured with 10(-6) mol/L of EM-1, EM-2, OMF, or saline for 0, 6, 12, and 24 hours (time-effect relationship) or with 10(-10), 10(-9), 10(-8), 10(-7), and 10(-6) mol/L of these substances for 24 hours (concentration-effect relationship). We also determined the phagocytic and bactericidal activities of macrophages using isotope markers when macrophages were cultured with 10(-6) mol/L of EM-1, EM-2, OMF, or saline for 24 hours.

RESULTS

Compared with the saline group, TNF-α concentration decreased significantly in the OMF, EM-2, and EM-1 groups at 12 hours (P < 0.05, P < 0.05, and P < 0.01, respectively) and at 24 hours (P < 0.05, P < 0.01, and P < 0.01, respectively). Compared with the saline group, IL-1β concentration decreased signifcantly in the OMF, EM-2, and EM-1 groups at 12 hours (P < 0.05, P < 0.05, and P < 0.01, respectively) and at 24 hours (P < 0.05, P < 0.01, and P < 0.01, respectively). Decreased TNF-α and IL-1β concentrations were observed in the supernatant at 24 hours when cultured with 10(-8), 10(-7), and 10(-6) mol/L in the OMF and EM-2 groups (all, P < 0.05) and in the EM-1 group (all, P < 0.01). Compared with the saline group, macrophage phagocytic activity (all, P < 0.05) and macrophage bactericidal activity (all, P < 0.01) were significantly lower in the 3 experimental groups compared with the saline group.

CONCLUSION

In this in vitro experiment, EM-1, EM-2, and OMF inhibited the immunosuppressant function of cultured rat peritoneal macrophages, including decreasing TNF-α and IL-1β concentrations and phagocytic and bactericidal activities.

Highlights in opioid agonists and antagonists

This review highlights new insights in to opioid agonists and antagonists, focusing on their mechanism of action with spinal and systemic administration, chronic use and main adverse effects. Short-cuts on some opioid agonists and antagonists of clinical interest are also presented, revealing potential clinical implications and future clinical directions as part of multimodal analgesia.

The mechanism of effective electroacupuncture on T cell response in rats with experimental autoimmune encephalomyelitis

Previously, we demonstrated that electroacupuncture (EA) decreased lymphocyte infiltration into the spinal cords of rats presenting with experimental autoimmune encephalomyelitis (EAE), a disease model used in the study of multiple sclerosis (MS). The aim of this study was to characterize the effects of EA on the EAE. Female Lewis rats were divided into either CFA, EAE, EA, or injection with naloxone after electroacupuncture (NAL) groups. Electroacupuncture was administered every day for 21 days. To evaluate proliferation and apoptosis, lymphocytes from rats presenting with EAE were collected and cultured with β-endorphin. Immunohistochemisty, flow cytometry and radio-immunity methods were applied to detect the expression of β-endorphin. Results presented in this report demonstrate that the beneficial anti-inflammatory effects of EA on EAE were related to β-endorphin production that balances the Thl/Th2 and Th17/Treg responses. These results suggest that β-endorphin could be an important component in the development of EA-based therapies used for the treatment of EAE.

A systematic literature review of cerebrospinal fluid biomarkers in delirium

BACKGROUND

Cerebrospinal fluid (CSF) analysis has great potential to advance understanding of delirium pathophysiology.

METHODS

A systematic literature review of CSF studies of DSM or ICD delirium was performed.

RESULTS

In 8 studies of 235 patients, delirium was associated with: elevated serotonin metabolites, interleukin-8, cortisol, lactate and protein, and reduced somatostatin, β-endorphin and neuron-specific enolase. Elevated acetylcholinesterase predicted poor outcome after delirium and higher dopamine metabolites were associated with psychotic features.

CONCLUSIONS

No clear conclusions emerged, but the current literature suggests multiple areas for further investigation with more detailed studies.

Nonopioid effect of β-endorphin

This review presents the generalized literature data and the results of our own research of the nonopioid effect of β-endorphin, an opioid neuropeptide interacting not only with opioid but also with nonopioid (insensitive to the opioid antagonist naloxone) receptors. The roles of the hormone and its receptors in regulation of the immune, nervous, and endocrine systems are discussed. The effect of neuromediator on the immune system mediated by both opioid and nonopioid receptors is considered in detail. The data on distribution and function of the nonopioid β-endorphin receptor in human and animal organisms are presented. All available data on the characteristics of the nonopioid β-endorphin receptor obtained by means of radioligand analysis are given. The discussed information is supposed to extend our conceptions of the role of β-endorphin in mammals and to be of extensive use in medicine and pharmacology.

Mu opioid receptor and inflammatory bowel disease

The mu opioid receptor (MOR), a member of G protein-coupled receptors, plays a pleiotropic role in various physiological and pathological processes, such as pain, inflammation, and immune modulation. MOR is expressed abundantly in both central and peripheral tissues and plays a significant role in peristalsis and secretion. It has been documented that MOR agonists are potentially valuable agents for the treatment of inflammatory bowel disease (IBD). This paper will explore the link between MOR and IBD, aiming at providing a theoretical basis for future development of new treatments for IBD.

Internalization of the opioid growth factor, [Met5]-enkephalin, is dependent on clathrin-mediated endocytosis for downregulation of cell proliferation

The opioid growth factor (OGF; [Met(5)]-enkephalin), a constitutively expressed and tonically active inhibitory peptide, interacts with the OGF receptor (OGFr) to form an endogenous growth-regulating pathway in homeostasis. Amplification of OGF-OGFr interfacing in animal and clinical studies depresses development, neoplasia, angiogenesis, and immunity. Disruption of the OGF-OGFr axis accelerates cell proliferation and has been particularly important in wound repair. To investigate how OGF enters cells, OGF was labeled with 5,6-tetramethylrhodamine OGF (RhoOGF) to study its uptake in live cells. African green monkey kidney cells (COS-7) incubated with RhoOGF exhibited a temperature-dependent course of entry, being internalized at 37 degrees C but not at 4 degrees C. RhoOGF was detected in the cytoplasm 15 min after initial exposure, observed in both cytoplasm and nucleus within 30 min, and remained in the cells for as long as 5 h. A 100-fold excess of OGF or the opioid antagonist naltrexone, but not other opioid ligands (some selective for classic opioid receptors), markedly reduced entry of RhoOGF into cells. RhoOGF was functional because DNA synthesis in cells incubated with RhoOGF (10(-5) to 10(-8) M) was decreased 24-36%, and was comparable to cells treated with unlabeled OGF (reductions of 26-39%). OGF internalization was dependent on clathrin-mediated endocytosis, with addition of clathrin siRNA diminishing the uptake of RhoOGF and upregulating DNA synthesis. RhoOGF clathrin-mediated endocytosis was unrelated to endosomal or Golgi pathways. Taken together, these results suggest that OGF enters cells by active transport in a saturable manner that requires clathrin-mediated endocytosis.

Dynorphin opioid peptides enhance acid-sensing ion channel 1a activity and acidosis-induced neuronal death

Acid-sensing ion channel 1a (ASIC1a) promotes neuronal damage during pathological acidosis. ASIC1a undergoes a process called steady-state desensitization in which incremental pH reductions desensitize the channel and prevent activation when the threshold for acid-dependent activation is reached. We find that dynorphin A and big dynorphin limit steady-state desensitization of ASIC1a and acid-activated currents in cortical neurons. Dynorphin potentiation of ASIC1a activity is independent of opioid or bradykinin receptor activation but is prevented in the presence of PcTx1, a peptide which is known to bind the extracellular domain of ASIC1a. This suggests that dynorphins interact directly with ASIC1a to enhance channel activity. Inducing steady-state desensitization prevents ASIC1a-mediated cell death during prolonged acidosis. This neuroprotection is abolished in the presence of dynorphins. Together, these results define ASIC1a as a new nonopioid target for dynorphin action and suggest that dynorphins enhance neuronal damage following ischemia by preventing steady-state desensitization of ASIC1a.

Opioid growth factor suppresses expression of experimental autoimmune encephalomyelitis

Naltrexone, an opioid antagonist, has been shown to modulate expression of experimental autoimmune encephalomyelitis (EAE), an animal model of MS, suggesting that endogenous opioids are inhibitory trophic factors in EAE. In the present study, we investigated the effects of one native opioid peptide, opioid growth factor ([Met(5)]-enkephalin), on the onset and progression of EAE. C57Bl/6 mice injected with myelin oligodendrocyte glycoprotein (MOG) received daily injections of 10 mg/kg OGF (MOG+OGF) or saline (MOG+Vehicle). Over 60% of the MOG+OGF animals did not exhibit behavioral signs of disease (EAE) in contrast to 100% of the mice in the MOG+Vehicle group. The severity and disease indices of EAE in the OGF-treated mice were markedly reduced from MOG+Vehicle cohorts. By day 30, 60% of MOG+OGF mice had a remission, relative to 4% in the MOG+Vehicle group. MOG-injected mice receiving OGF had significant reductions in activated astrocytes and damaged neurons compared to MOG+Vehicle animals. Unlike MOG+Vehicle and MOG+OGF mice with behavioral signs of disease, MOG+OGF animals without manifestation of disease had no lumbar spinal cord demyelination. Both OGF and OGF receptor were detected in splenic-derived T lymphocytes by immunohistochemistry. OGF treatment decreased both DNA synthesis and cell proliferation in comparison to vehicle-treated T cell lymphocyte cultures. These results indicate that an endogenous opioid, OGF, inhibits the onset and progression of EAE, and suggest that clinical studies on the use of OGF treatment for MS are merited.

Endogenous Opioids Regulate Expression of Experimental Autoimmune Encephalomyelitis: A New Paradigm for the Treatment of Multiple Sclerosis

Preclinical investigations utilizing murine experimental auto-immune encephalomyelitis (EAE), as well as clinical observations in patients with multiple sclerosis (MS), may suggest alteration of endogenous opioid systems in MS. In this study we used the opioid antagonist naltrexone (NTX) to invoke a continuous (High Dose NTX, HDN) or intermittent (Low Dose NTX, LDN) opioid receptor blockade in order to elucidate the role of native opioid peptides in EAE. A mouse model of myelin oligodendrocyte glycoprotein (MOG)-induced EAE was employed in conjunction with daily treatment of LDN (0.1 mg/kg, NTX), HDN (10 mg/kg NTX), or vehicle (saline). No differences in neurological status (incidence, severity, disease index), or neuropathological assessment (activated astrocytes, demyelination, neuronal injury), were noted between MOG-induced mice receiving HDN or vehicle. Over 33% of the MOG-treated animals receiving LDN did not exhibit behavioral signs of disease, and the severity and disease index of the LDN-treated mice were markedly reduced from cohorts injected with vehicle. Although all LDN animals demonstrated neuropathological signs of EAE, LDN-treated mice without behavioral signs of disease had markedly lower levels of activated astrocytes and demyelination than LDN- or vehicle-treated animals with disease. These results imply that endogenous opioids, evoked by treatment with LDN and acting in the rebound period from drug exposure, are inhibitory to the onset and progression of EAE, and suggest that clinical studies of LDN are merited in MS and possibly in other autoimmune disorders.

Prodynorphin-derived peptides are critical modulators of anxiety and regulate neurochemistry and corticosterone

Stress and anxiety are mainly regulated by amygdala and hypothalamic circuitries involving several neurotransmitter systems and providing physiological responses to peripheral organs via the hypothalamic-pituitary-adrenal axis and other pathways. The role of endogenous opioid peptides in this process is largely unknown. Here we show for the first time that anxiolytic parameters of explorative behavior in mice lacking prodynorphin were increased 2-4-fold in the open field, the elevated plus maze and the light-dark test. Consistent with this, treatment of wild-type mice with selective kappa-opioid receptor antagonists GNTI or norbinaltorphimine showed the same effects. Furthermore, treatment of prodynorphin knockout animals with U-50488H, a selective kappa-opioid receptor agonist, fully reversed their anxiolytic phenotype. These behavioral data are supported by an approximal 30% reduction in corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus and central amygdala and an accompanying 30-40% decrease in corticosterone serum levels in prodynorphin knockout mice. Although stress-induced increases in corticosterone levels were attenuated in prodynorphin knockout mice, they were associated with minor increases in depression-like behavior in the tail suspension and forced swim tests. Taken together, our data suggest a pronounced impact of endogenous prodynorphin-derived peptides on anxiety, but not stress coping ability and that these effects are mediated via kappa-opioid receptors. The delay in the behavioral response to kappa-opioid receptor agonists and antagonist treatment suggests an indirect control level for the action of dynorphin, probably by modulating the expression of CRH or neuropeptide Y, and subsequently influencing behavior.

Discovery and validation of novel peptide agonists for G-protein-coupled receptors

G-protein-coupled receptors (GPCRs) represent an important group of targets for pharmaceutical therapeutics. The completion of the human genome revealed a large number of putative GPCRs. However, the identification of their natural ligands, and especially peptides, suffers from low discovery rates, thus impeding development of therapeutics based on these potential drug targets. We describe the discovery of novel GPCR ligands encrypted in the human proteome. Hundreds of potential peptide ligands were predicted by machine learning algorithms. In vitro screening of selected 33 peptides on a set of 152 GPCRs, including a group of designated orphan receptors, was conducted by intracellular calcium measurements and cAMP assays. The screening revealed eight novel peptides as potential agonists that specifically activated six different receptors in a dose-dependent manner. Most of the peptides showed distinct stimulatory patterns targeted at designated and orphan GPCRs. Further analysis demonstrated a significant in vivo effect for one of the peptides in a mouse inflammation model.

Capsaicin inhibits the in vitro binding of peptides selective for mu- and kappa-opioid, and nociceptin-receptors

Capsaicin inhibited the equilibrium specific binding of endogenous opioid-like peptide ligands such as endomorphin-1, nociceptin, and dynorphin((1-17)) in rat brain membrane preparations. We studied the in vitro effect of capsaicin (1-10 microM) on homologous and heterologous competitive binding of opioid ligands, using unlabeled synthetic peptides and the following tritiated compounds: [(3)H]endomorphin-1, [(3)H]endomorphin-2, [(3)H]nociceptin((1-17)) and [(3)H]dynorphin((1-17)). Capsaicin-dependent inhibition was also observed in [(35)S]GTPgammaS stimulation assays in the presence of certain opioid peptides. The inhibition of opioid binding was further investigated using other synthetic and natural mu-opioid ligands such as [D-Ala(2),(NMe)Phe(4),Gly(5)-ol]enkephalin (DAMGO), morphine and naloxone. The decrease in opioid ligand affinity upon capsaicin treatments was most apparent with endomorphin-1, followed by nociceptin and dynorphin. The binding of other investigated opioids were not affected in the presence of capsaicin. In [(3)H]endomorphin-1 binding assays, capsazepine antagonized the inhibitory effect of capsaicin in rat brain membranes suggesting the involvement of TRPV1 receptors. In Chinese hamster ovary (CHO) cells stably expressing mu-opioid receptors, but lacking vanilloid receptors, the inhibition by capsaicin on the binding of [(3)H]endomorphin-1 was not present. It is concluded that the inhibitory effect of capsaicin on the receptor binding affinity of endogenous opioid peptides in brain membrane preparations seems not to be a direct effect, it is rather a negative feedback interaction with opioid receptors.

Hepatic fibrogenesis in response to chronic liver injury: novel insights on the role of cell-to-cell interaction and transition

Hepatic fibrosis represents the wound-healing response process of the liver to chronic injury, independently from aetiology. Advanced liver fibrosis results in cirrhosis that can lead to liver failure, portal hypertension and hepatocellular carcinoma. Currently, no effective therapies are available for hepatic fibrosis. After the definition of hepatic stellate cells (HSCs) as the main liver extracellular matrix-producing cells in the 1980s, the subsequent decade was dedicated to determine the role of specific cytokines and growth factors. Fibrotic progression of chronic liver diseases can be nowadays considered as a dynamic and highly integrated process of cellular response to chronic liver injury. The present review is dedicated to the novel mechanisms of cellular response to chronic liver injury leading to hepatic myofibroblasts' activation. The understanding of the cellular and molecular pathways regulating their function is crucial to counteract therapeutically the organ dysfunction caused by myofibroblasts' activation.

Joint capsule treatment with enkephalin-encoding HSV-1 recombinant vector reduces inflammatory damage and behavioural sequelae in rat CFA monoarthritis

This study assessed enkephalin expression induced by intra-articular application of recombinant, enkephalin-encoding herpes virus (HSV-1) and the impact of expression on nociceptive behaviours and synovial lining inflammation in arthritic rats. Replication-conditional HSV-1 recombinant vectors with cDNA encoding preproenkephalin (HSV-ENK), or control transgene beta-galactosidase cDNA (HSV-beta-gal; control) were injected into knee joints with complete Freund's adjuvant (CFA). Joint temperatures, circumferences and nociceptive behaviours were monitored on days 0, 7, 14 and 21 post CFA and vector treatments. Lumbar (L4-6) dorsal root ganglia (DRG) and spinal cords were immunostained for met-enkephalin (met-ENK), beta-gal, HSV-1 proteins and Fos. Joint tissues were immunostained for met-ENK, HSV-1 proteins, and inflammatory mediators Regulated on Activation, Normal T-cell Expressed and Secreted (RANTES) and cyclo-oxygenase-2, or stained with haematoxylin and eosin for histopathology. Compared to exuberant synovial hypertrophy and inflammatory cell infiltration seen in arthritic rats treated with CFA only or CFA and HSV-beta-gal, the CFA- and HSV-ENK-treated arthritic rats had: (i) striking preservation of synovial membrane cytoarchitecture with minimal inflammatory cell infiltrates; (ii) significantly improved nociceptive behavioural responses to mechanical and thermal stimuli; (iii) normalized Fos staining in lumbar dorsal horn; and (iv) significantly increased met-ENK staining in ipsilateral synovial tissue, lumbar DRG and spinal cord. The HSV-1 and transgene product expression were confined to ipsilateral lumbar DRG (HSV-1, met-ENK, beta-gal). Only transgene product (met-ENK and beta-gal) was seen in lumbar spinal cord sections. Targeted delivery of enkephalin-encoding HSV-1 vector generated safe, sustained opioid-induced analgesia with protective anti-inflammatory blunting in rat inflammatory arthritis.

Enkephalin-encoding herpes simplex virus-1 decreases inflammation and hotplate sensitivity in a chronic pancreatitis model

Background

A chronic pancreatitis model was developed in young male Lewis rats fed a high-fat and alcohol liquid diet beginning at three weeks. The model was used to assess time course and efficacy of a replication defective herpes simplex virus type 1 vector construct delivering human cDNA encoding preproenkephalin (HSV-ENK).

Results

Most surprising was the relative lack of inflammation and tissue disruption after HSV-ENK treatment compared to the histopathology consistent with pancreatitis (inflammatory cell infiltration, edema, acinar cell hypertrophy, fibrosis) present as a result of the high-fat and alcohol diet in controls. The HSV-ENK vector delivered to the pancreatic surface at week 3 reversed pancreatitis-associated hotplate hypersensitive responses for 4–6 weeks, while control virus encoding β-galactosidase cDNA (HSV-β-gal) had no effect. Increased Fos expression seen bilaterally in pain processing regions in control animals with pancreatitis was absent in HSV-ENK-treated animals. Increased met-enkephalin staining was evident in pancreas and lower thoracic spinal cord laminae I–II in the HSV-ENK-treated rats.

Conclusion

Thus, clear evidence is provided that site specific HSV-mediated transgene delivery of human cDNA encoding preproenkephalin ameliorates pancreatic inflammation and significantly reduces hypersensitive hotplate responses for an extended time consistent with HSV mediated overexpression, without tolerance or evidence of other opiate related side effects.

Electroacupuncture attenuates bone-cancer-induced hyperalgesia and inhibits spinal preprodynorphin expression in a rat model

Cancer pain impairs the quality of life of cancer patients, but opioid intervention can cause significant side effects that further decrease quality of life. Although electroacupuncture (EA) has been used to treat cancer pain, its mechanisms are largely unknown. To examine its effects and underlying mechanisms on cancer pain, we injected AT-3.1 prostate cancer cells into the tibia to induce bone cancer in the male Copenhagen rat. The resulting pain was treated with 10Hz/2mA/0.4ms pulse EA for 30min daily at the point equivalent to the human acupoint GB30 (Huantiao) between days 14 and 18 after the injection. For sham control, EA needles were inserted into GB30 without stimulation. Thermal hyperalgesia, a decrease in paw withdrawal latency (PWL) to a noxious thermal stimulus, and mechanical hyperalgesia, a decrease in paw withdrawal pressure threshold (PWPT), was measured at baseline and 20min after the EA treatment. Preprodynorphin mRNA and dynorphin were determined by RT-PCR and immunohistochemistry, respectively. Thermal and mechanical hyperalgesia developed ipsilaterally between days 12 and 18 after cancer cell inoculation. EA significantly (P<0.05) attenuated this hyperalgesia, as shown by increased PWL and PWPT, and inhibited up-regulation of preprodynorphin mRNA and dynorphin compared to sham control. Intrathecal injection of antiserum against dynorphin A (1-17) also significantly inhibited the cancer-induced hyperalgesia. These results suggest that EA alleviates bone cancer pain at least in part by suppressing dynorphin expression, and they support the clinical use of EA in the treatment of cancer pain.

beta-Endorphin regulates diverse functions of splenic phagocytes through different opioid receptors in freshwater fish Channa punctatus (Bloch): an in vitro study

In this in vitro study, the role of beta-endorphin in the control of phagocytic and cytotoxic activities of fish splenic phagocytes was investigated. Further, the involvement of specific opioid receptor was explored. beta-Endorphin stimulated phagocytosis, whereas inhibited nitric oxide production as assessed by nitrite release. However, it had concentration-related biphasic effects on superoxide production, stimulatory at low and inhibitory at high concentration. Naltrexone, non-selective opioid receptor antagonist, antagonized the effect of beta-endorphin on phagocyte functions. Moreover, CTAP, selective mu-receptor antagonist, completely blocked the effect of beta-endorphin on phagocytosis and nitrite release. With regard to superoxide production, CTAP blocked the stimulatory effect of beta-endorphin at low concentration, while the inhibitory effect at high concentration was completely antagonized by selective delta-receptor antagonist, NTI. In conclusion, beta-endorphin acting via mu-receptor stimulated phagocytosis and inhibited nitric oxide production, while its biphasic effect on superoxide production seems to be mediated by mu- and delta-receptors.

Effect of exogenous catecholamines on tumor necrosis factor alpha, interleukin-6, interleukin-10 and beta-endorphin levels following severe trauma

Cytokines and endogenous opioids are mediators of the post traumatic inflammatory response. The aim of this study was to determine the effect of exogenous catecholamines on tumor necrosis factor alpha (TNFa), interleukin-6 (IL-6), interleukin-10 (IL-10) and beta(beta)-endorphin levels in patients with severe trauma, during the first 24 h after injury. Forty four traumatized patients with haemorrhage class III and IV were included in the study. Patients were divided in two groups: Group 1 (adrenergic, n=22) and Group 2 (non adrenergic, n=22), depending on the use of exogenous catecholamines. Blood samples were collected at 0, 2, 4 and 24 h time points. Baseline values were different between the two groups, but an altered pattern of release was observed for TNFa, IL-6, IL-10 and beta-endorphin levels in patients treated with catecholamines. ICU stay was longer for the adrenergic group, while survival after 1 month was significantly lower. Findings support an altered pattern of cytokine release during the early phase after trauma, probably due to catecholamine presence.

Structure−Activity Relationships of αS1-Casomorphin Using AM1 Calculations and Molecular Dynamics Simulations

This paper investigates the structure-activity relationships of alphaS1-casomorphin (alphaS1-CM) using AM1 calculations and molecular dynamics (MD) simulations. Previous studies have shown that this peptide has remarkable opioid actions, and not only has a high affinity toward all three subtypes (kappa1-kappa3) of the kappa-opioid sites, but also inhibits the proliferation of the T47D human breast cancer cell line. The systematic conformer search performed by the AM1 calculations is based on the torsional angles of the Val2-Pro3 (omega2) and Phe4-Pro5 (omega4) amide bonds. The AM1 results reveal that the alphaS1-CM conformers strongly favor the cis/cis pair of the omega2/omega4 amide bonds in the minimized energy state. Furthermore, the picture of these stable conformers is found to be a strong interaction of the coulomb's force between two terminuses. MD simulations are performed to investigate the features of both the structural stability and pharmacological activity of alphaS1-CM in aqueous solution. The simulation results reveal that the omega2/omega4 amide bonds favor the cis/cis status in the stable state. Furthermore, the pharmacophoric distance between two aromatic rings is found to be 5.0 approximately 5.4A. The chi1 rotamers of the Tyr and Phe residues show a preference for gauche (-) and trans, respectively. The side chain rotamers of alphaS1-CM are competed to those of other opioid ligands with a known potency and selectivity for delta- and mu-opioid receptors. Finally, we address a likely kappa pharmacophore model compared to the delta pharmacophore model.

Endogenous dynorphin in epileptogenesis and epilepsy: anticonvulsant net effect via kappa opioid receptors

Neuropsychiatric disorders are one of the main challenges of human medicine with epilepsy being one of the most common serious disorders of the brain. Increasing evidence suggest neuropeptides, particularly the opioids, play an important role in epilepsy. However, little is known about the mechanisms of the endogenous opioid system in epileptogenesis and epilepsy. Therefore, we investigated the role of endogenous prodynorphin-derived peptides in epileptogenesis, acute seizure behaviour and epilepsy in prodynorphin-deficient mice. Compared with wild-type littermates, prodynorphin knockout mice displayed a significantly reduced seizure threshold as assessed by tail-vein infusion of the GABA(A) antagonist pentylenetetrazole. This phenotype could be entirely rescued by the kappa receptor-specific agonist U-50488, but not by the mu receptor-specific agonist DAMGO. The delta-specific agonist SNC80 decreased seizure threshold in both genotypes, wild-type and knockout. Pre-treatment with the kappa selective antagonist GNTI completely blocked the rescue effect of U-50488. Consistent with the reduced seizure threshold, prodynorphin knockout mice showed faster seizure onset and a prolonged time of seizure activity after intracisternal injection of kainic acid. Three weeks after local injection of kainic acid into the stratum radiatum CA1 of the dorsal hippocampus, prodynorphin knockout mice displayed an increased extent of granule cell layer dispersion and neuronal loss along the rostrocaudal axis of the ipsi- and partially also of the contralateral hippocampus. In the classical pentylenetetrazole kindling model, dynorphin-deficient mice showed significantly faster kindling progression with six out of eight animals displaying clonic seizures, while none of the nine wild-types exceeded rating 3 (forelimb clonus). Taken together, our data strongly support a critical role for dynorphin in the regulation of hippocampal excitability, indicating an anticonvulsant role of kappa opioid receptors, thereby providing a potential target for antiepileptic drugs.

Organization of endogenous opioids in the rostral agranular insular cortex of the rat

The rostral agranular insular cortex (RAIC) of rats has opioid receptors and has been implicated in the analgesic and reinforcing effects of opiates. To help in understanding the function of endogenous opioids in this structure, we sought to identify and describe the opioid peptides intrinsic to the RAIC by using immunohistochemical methods. Immunolabeling for proopiomelanocortin (POMC), the precursor to beta-endorphin, and endomorphin 1 and 2 on sectioned rat forebrain revealed limited labeling consisting of individual varicose fibers. Immunolabeling for prodynorphin and enkephalin revealed numerous immunopositive cell bodies and fibers with distribution and morphology unique to each. Prodynorphin-immunopositive cell bodies consisted of two types: large, lightly labeled, pyramidal-shaped cell bodies in lamina V and more intensely labeled, small, ovoid cell bodies scattered in other lamina. Axonal fibers immunolabeled for prodynorphin varied in size and were found in all lamina. Immunolabeling for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) was rarely found in dynorphin-containing cell bodies (6%, 10/167) but was visible within a subpopulation of axons. Enkephalin immunolabeling was detected within a single morphological subpopulation of nonpyramidal neurons located predominantly in lamina II/III, 30% (33/109) of which were also GABA immunopositive. Axons immunolabeled for enkephalin were also abundant in lamina II/III. These results suggest that dynorphin and enkephalin peptides are the predominant endogenous opioids in the RAIC and their distinct distributions suggest divergent functional roles. The localization of prodynorphin immunoreactivity to pyramidal cells suggests the possibility that this neuropeptide may be used in RAIC projection neurons, whereas enkephalin distribution was more characteristic of a role in local networks.

Beta-endorphin differentially affects inflammation in two inbred rat strains

It has been shown that inflammation of rat paws elicits accumulation of opioid peptide beta-endorphin-containing immune cells in the inflamed subcutaneous tissue, contributing to immunocyte-produced pain suppression. However, the possible mechanisms involved in the pharmacological application of beta-endorphin in rat paw inflammation have not been investigated. The present study was set up to explore the effects of intraplantar injection of beta-endorphin on Concanavalin A-induced paw edema in two inbred rat strains, Albino Oxford (AO) and Dark Agouti (DA). Both high dose-induced suppression and low dose-induced potentiation of edema development in AO and DA rats, respectively, were blocked with antagonists specific for delta (naltrindole) and kappa (nor-binaltorphimine) opioid receptors. beta-endorphin in vitro decreased phagocytosis and increased nitric oxide (NO) production in air pouch granulocytes obtained from AO rats. However, in cells from DA rat strain beta-endorphin modulated both phagocytosis and NO production in a concentration-dependent manner. It could be concluded that the strain-dependent opposing effects of beta-endorphin on paw inflammation are mediated through delta and kappa opioid receptors and probably involve changes in the production of reactive oxygen species by inflammatory cells. Our results point to the importance of genotype for pharmacological manipulations and the development of inflammation.

Effects of orphanin FQ on colonic motility of rats

AIM: To investigate the role of ORL1 (opioid receptor-like 1) receptor in the colon movement.

METHODS: The test for tension of colonic muscle strips in vitro and the colonic myoelectrical activity in vivo as well as the charcoal suspension pushing test were performed to evaluate the effect of orphanin FQ (OFQ) on the motility of colon.

RESULTS: NOFQ (1-1000 nmol/L) caused an immediate tonic contraction in the isolated colon in a concentration-dependent manner. In anesthetized rats, intravenous administration of OFQ (1 mg/kg) caused phasic contractions in the proximal colon (t = 2.41, P = 0.02), and this contraction was not inhibited by classical opioid receptor antagonist, naloxone. Subcutaneous administration of OFQ (3 nmol/kg) accelerated the colonic transit of charcoal suspension in vivo (48.0 ± 1.24 vs 43.5 ± 2.63, t = -4.5, P = 0.008).

CONCLUSION: OFQ is a brain-gut peptide and plays a role in the modulation of gastrointestinal functions.

Endogenous opioids modulate the growth of the biliary tree in the course of cholestasis

BACKGROUND & AIMS

There is poor knowledge on the factors that modulate the growth of cholangiocytes, the epithelial cell target of cholangiopathies, which are diseases leading to progressive loss of bile ducts and liver failure. Endogenous opioids are known to modulate cell growth. In the course of cholestasis, the opioidergic system is hyperactive, and in cholangiocytes a higher expression of opioid peptide messenger RNA has been described. This study aimed to verify if such events affect the cholangiocyte proliferative response to cholestasis.

METHODS

The presence of the delta opioid receptor (OR), muOR, and kappaOR was evaluated. The effects on cholangiocyte proliferation of the in vitro and in vivo exposure to their selective agonists, together with the intracellular signals, were then studied. The effects of the OR antagonist naloxone on cell growth were also tested both in vivo and in vitro.

RESULTS

Cholangiocytes express all 3 receptors studied. deltaOR activation strongly diminished the proliferative and functional response of cholangiocytes to cholestasis, whereas muOR resulted in a slight increase in cell growth. The deltaOR signal is mediated by the IP3/CamKIIalpha/PKCalpha pathway, which inhibits the cAMP/PKA/ERK1/2/AKT cascade. In contrast, muOR activation stimulates the cAMP/PKA/ERK1/2/AKT cascade but does not affect the IP3/CamKIIalpha/PKCalpha pathway. The blockage of endogenous opioid peptides by naloxone further enhanced cholangiocyte growth both in vivo and in vitro.

CONCLUSIONS

The increase in opioid peptide synthesis in the course of cholestasis aims to limit the excessive growth of the biliary tree in the course of cholestasis by the interaction with the deltaOR expressed by cholangiocytes.

Endomorphin-2 and endomorphin-1 promote the extracellular amount of accumbal dopamine via nonopioid and mu-opioid receptors, respectively

Activation of mu-opioid receptors in the nucleus accumbens (NAc) is known to increase accumbal dopamine efflux in rats. Endomorphin-2 (Tyr-Pro-Phe-Phe-NH(2); EM-2) and endomorphin-1 (Tyr-Pro-Trp-Phe-NH(2); EM-1) are suggested to be the endogenous ligands for the mu-opioid receptor. As the ability of EM-2 and EM-1 to alter the accumbal extracellular dopamine level has not yet been studied in freely moving rats, the present study was performed, using a microdialysis technique that allows on-line monitoring of the extracellular dopamine with a temporal resolution of 5 min. A 25 min infusion of either EM-2 or EM-1 into the NAc (5, 25, and 50 nmol) produced a dose-dependent increase of the accumbal dopamine level. The EM-2 (50 nmol)- and EM-1 (25 and 50 nmol)-induced dopamine efflux were abolished by intra-accumbal perfusion of tetrodotoxin (2 muM). Intra-accumbal perfusion of the mu-opioid receptor antagonist CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH(2); 3 nmol) failed to affect the EM-2 (50 nmol)-induced dopamine release, whereas it significantly inhibited the EM-1 (25 and 50 nmol)-induced dopamine release. The EM-1 (50 nmol)-induced accumbal dopamine efflux was significantly reduced by the systemic administration of the putative mu1-opioid receptor antagonist naloxonazine (15 mg/kg, intraperitoneally (i.p.), given 24 h before starting the perfusion). Systemic administration of the aspecific opioid receptor antagonist naloxone (1 mg/kg, i.p., given 10 or 20 min before starting the perfusion) also failed to affect the EM-2 (50 nmol)-induced dopamine efflux, whereas it significantly inhibited the EM-1 (25 and 50 nmol)-induced dopamine efflux. The present study shows that the intra-accumbal infusion of EM-2 and EM-1 increases accumbal dopamine efflux by mechanisms that fully differ. It is concluded that the effects of EM-2 are not mediated via opioid receptors in contrast to the effects of EM-1 that are mediated via mu1-opioid receptors in the NAc.

Dynorphin A (2-13) improves mecamylamine-induced learning impairment accompanied by reversal of reductions in acetylcholine release in rats

Accumulating evidence indicates that the endogenous opioid peptides dynorphin A (1-17) and synthetic dynorphin A (1-13) interact not only with opioid receptors but also with as yet poorly characterized non-opioid binding sites. Dynorphin A (1-13) improved impairments of learning and memory via not only kappa-opioid receptor-mediated, but also 'non-opioid' mechanisms. In the present study, the effects of des-tyrosine(1) dynorphin A (2-13) as a non-opioid metabolite of dynorphin A, and dynorphin A (1-13) on mecamylamine-induced impairment of the acquisition of learning in rats were investigated using a step-through type passive avoidance task. Further, hippocampal acetylcholine release was examined using in vivo microdialysis. Mecamylamine significantly shortened the step-through latency when given 30 min before the acquisition trial. Not only dynorphin A (1-13) but also dynorphin A (2-13) attenuated the mecamylamine-induced impairment of the acquisition of learning. The effect of dynorphin A (2-13) was not blocked by pre-treatment with nor-binaltorphimine (nor-BNI), a selective kappa-opioid receptor antagonist. Dynorphin A (2-13) completely abolished the decrease in the extracellular acetylcholine concentration induced by mecamylamine and this effect was not blocked by nor-BNI. Taken together with our previous findings, the present results may indicate that dynorphin A (2-13) improves impairment of learning and/or memory in 'non-opioid' mechanisms and dynorphin A (1-13) ameliorates impairment of the acquisition of learning via not only kappa-opioid receptor-mediated mechanisms but also 'non-opioid' mechanisms, by regulating the release of extracellular acetylcholine.

Transduction peptides within naturally occurring proteins

First identified as peptides derived from the human immunodeficiency virus (HIV) transcriptional regulator Tat and the Drosophila transcription factor Antennapedia, transduction (or cell-penetrating) peptide sequences enable soluble proteins to cross biological membranes and interact with cytosolic and nuclear targets. Proteins containing such sequences have been found to function as transcription factors, to inhibit apoptosis, to play roles in axon guidance, or to transport viral mRNA between cells. The recent demonstration that dynorphins are able to act as transduction peptides suggests that these neuropeptides may have roles independent of opiate receptor activation.