Isolation and amino acid sequence analysis of a 4,000-dalton dynorphin from porcine pituitary

Neuropeptide System Regulation of Prefrontal Cortex Circuitry: Implications for Neuropsychiatric Disorders

Neuropeptides, a diverse class of signaling molecules in the nervous system, modulate various biological effects including membrane excitability, synaptic transmission and synaptogenesis, gene expression, and glial cell architecture and function. To date, most of what is known about neuropeptide action is limited to subcortical brain structures and tissue outside of the central nervous system. Thus, there is a knowledge gap in our understanding of neuropeptide function within cortical circuits. In this review, we provide a comprehensive overview of various families of neuropeptides and their cognate receptors that are expressed in the prefrontal cortex (PFC). Specifically, we highlight dynorphin, enkephalin, corticotropin-releasing factor, cholecystokinin, somatostatin, neuropeptide Y, and vasoactive intestinal peptide. Further, we review the implication of neuropeptide signaling in prefrontal cortical circuit function and use as potential therapeutic targets. Together, this review summarizes established knowledge and highlights unknowns of neuropeptide modulation of neural function underlying various biological effects while offering insights for future research. An increased emphasis in this area of study is necessary to elucidate basic principles of the diverse signaling molecules used in cortical circuits beyond fast excitatory and inhibitory transmitters as well as consider components of neuropeptide action in the PFC as a potential therapeutic target for neurological disorders. Therefore, this review not only sheds light on the importance of cortical neuropeptide studies, but also provides a comprehensive overview of neuropeptide action in the PFC to serve as a roadmap for future studies in this field.

Pituitary neuropeptides and B lymphocyte function

This review discusses the accumulated evidence that pro-opiomelanocortin (POMC) gene products as well as other pituitary neuropeptides derived from related genes (Proenkephalin, PENK; Prodynorphin, PDYN, and Pronociceptin, PNOC) can exert direct effects on B lymphocytes to modulate their functions. We also review the available data on receptor systems that might be involved in the transmission of such hormonal signals to B cells.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

Opioid Peptides and Their Receptors in Chickens: Structure, Functionality, and Tissue Distribution

Opioid peptides, derived from PENK, POMC, PDYN and PNOC precursors, together with their receptors (DOR, MOR, KOR and ORL1), constitute the opioid system and are suggested to participate in multiple physiological/pathological processes in vertebrates. However, the question whether an opioid system exists and functions in non-mammalian vertebrates including birds remains largely unknown. Here, we cloned genes encoding opioid system from the chicken brain and examined their functionality and tissue expression. As in mammals, 6 opioid peptides encoded by PENK (Met-enkephalin and Leu-enkephalin), POMC (β-endorphin), PDYN (dynorphin-A and dynorphin-B) and PNOC (nociceptin) precursors and four opioid receptors were found to be highly conserved in chickens. Using pGL3-CRE-luciferase and pGL4-SRE-luciferase reporter systems, we demonstrated that chicken opioid receptors (cDOR, cMOR, cKOR and cORL1) expressed in CHO cells, could be differentially activated by chicken opioid peptides, and resulted in the inhibition of cAMP/PKA and activation of MAPK/ERK signaling pathways. cDOR is potently activated by Met-enkephalin and Leu-enkephalin, and cKOR is potently activated by dynorphin-A, dynorphin-B and nociceptin, whereas cORL1 is specifically activated by nociceptin. Unlike cDOR, cKOR and cORL1, cMOR is moderately/weakly activated by enkephalins and other opioid peptides. These findings suggest the ligand-receptor pair in chicken opioid system is similar, but not identical to, that in mammals. Quantitative real-time PCR revealed that the opioid system is mainly expressed in chicken central nervous system including the hypothalamus. Collectively, our data will help to facilitate the better understanding of the conserved roles of opioid system across vertebrates.

Dynorphin and its role in alcohol use disorder

The dynorphin / kappa opioid receptor (KOR) system has been implicated in many aspects that influence neuropsychiatric disorders. Namely, this system modulates neural circuits that primarily regulate reward seeking, motivation processing, stress responsivity, and pain sensitivity, thus affecting the development of substance and alcohol use disorder (AUD). The effects of this system are often bidirectional and depend on projection targets. To date, a majority of the studies focusing on this system have examined the KOR function using agonists and antagonists. Indeed, there are studies that have examined prodynorphin and dynorphin levels by measuring mRNA and tissue content levels; however, static levels of the neuropeptide and its precursor do not explain complete and online function of the peptide as would be explained by measuring dynorphin transmission in real time. New and exciting methods using optogenetics, chemogenetics, genetic sensors, fast scan cyclic voltammetry are now being developed to detect various neuropeptides with a focus on opioid peptides, including dynorphin. In this review we discuss studies that examine dynorphin projections in areas involved in AUD, its functional involvement in AUD and vulnerability to develop AUD at various ages. Moreover, we discuss dynorphin's role in promoting AUD by dysregulation motivation circuits and how advancements in opioid peptide detection will further our understanding.

Alanine scan of the opioid peptide dynorphin B amide

To date structure-activity relationship (SAR) studies of the dynorphins (Dyn), endogenous peptides for kappa opioid receptors (KOR), have focused almost exclusively on Dyn A with minimal studies on Dyn B. While both Dyn A and Dyn B have identical N-terminal sequences, their C-terminal sequences differ, which could result in differences in pharmacological activity. We performed an alanine scan of the non-glycine residues up through residue 11 of Dyn B amide to explore the roles of these side chains in the activity of Dyn B. The analogs were synthesized by fluorenylmethyloxycarbonyl (Fmoc)-based solid phase peptide synthesis and evaluated for their opioid receptor affinities and opioid potency and efficacy at KOR. Similar to Dyn A the N-terminal Tyr¹ and Phe⁴ residues of Dyn B amide are critical for opioid receptor affinity and KOR agonist potency. The basic residues Arg⁶ and Arg⁷ contribute to the KOR affinity and agonist potency of Dyn B amide, while Lys¹⁰ contributes to the opioid receptor affinity, but not KOR agonist potency, of this peptide. Comparison to the Ala analogs of Dyn A (1-13) suggests that the basic residues in the C-terminus of both peptides contribute to KOR binding, but differences in their relative positions may contribute to the different pharmacological profiles of Dyn A and Dyn B. The other unique C-terminal residues in Dyn B amide also appear to influence the relative affinity of this peptide for KOR versus mu and delta opioid receptors. This SAR information may be applied in the design of new Dyn B analogs that could be useful pharmacological tools.

AGH is a new hemoglobin alpha-chain fragment with antinociceptive activity

Limited proteolysis of certain proteins leads to the release of endogenous bioactive peptides. Hemoglobin-derived peptides such as hemorphins and hemopressins are examples of intracellular protein-derived peptides that have antinociceptive effects by modulating G-protein coupled receptors activities. In the present study, a previously characterized substrate capture assay that uses a catalytically inactive form of the thimet oligopeptidase was combined with isotopic labeling and mass spectrometry in order to identify new bioactive peptides. Indeed, we have identified the peptide AGHLDDLPGALSAL (AGH), a fragment of the hemoglobin alpha-chain, which specifically bind to the inactive thimet oligopeptidase in the substrate capture assay. Previous peptidomics studies have identified the AGH as well as many other natural peptides derived from hemoglobin alpha-chain containing this sequence, further suggesting that AGH is a natural endogenous peptide. Pharmacological assays suggest that AGH inhibits peripheral inflammatory hyperalgesic responses through indirect activation of mu opioid receptors, without having a central nervous system activity. Therefore, we have successfully used the substrate capture assay to identify a new endogenous bioactive peptide derived from hemoglobin alpha-chain.

Dynorphin--still an extraordinarily potent opioid peptide

This issue of Molecular Pharmacology is dedicated to Dr. Avram Goldstein, the journal's founding editor and one of the leaders in the development of modern pharmacology. This article focuses on his contributions to the discovery of the dynorphins and evidence that members of this family of opioid peptides are endogenous agonists for the kappa opioid receptor. In his original publication describing the purification and sequencing of dynorphin A, Avram described this peptide as "extraordinarily potent" ("dyn" from the Greek, dynamis = power and "orphin" for endogenous morphine peptide). The name originally referred to its high affinity and great potency in the bioassay that was used to follow its activity during purification, but the name has come to have a second meaning: studies of its physiologic function in brain continue to provide powerful insights to the molecular mechanisms controlling mood disorders and drug addiction. During the 30 years since its discovery, we have learned that the dynorphin peptides are released in brain during stress exposure. After they are released, they activate kappa opioid receptors distributed throughout the brain and spinal cord, where they trigger cellular responses resulting in different stress responses: analgesia, dysphoria-like behaviors, anxiety-like responses, and increased addiction behaviors in experimental animals. Avram predicted that a detailed molecular analysis of opiate drug actions would someday lead to better treatments for drug addiction, and he would be gratified to know that subsequent studies enabled by his discovery of the dynorphins resulted in insights that hold great promise for new treatments for addiction and depressive disorders.

The dynorphin/κ-opioid receptor system and its role in psychiatric disorders

The dynorphin/κ-opioid receptor system has been implicated in the pathogenesis and pathophysiology of several psychiatric disorders. In the present review, we present evidence indicating a key role for this system in modulating neurotransmission in brain circuits that subserve mood, motivation, and cognitive function. We overview the pharmacology, signaling, post-translational, post-transcriptional, transcriptional, epigenetic and cis regulation of the dynorphin/κ-opioid receptor system, and critically review functional neuroanatomical, neurochemical, and pharmacological evidence, suggesting that alterations in this system may contribute to affective disorders, drug addiction, and schizophrenia. We also overview the dynorphin/κ-opioid receptor system in the genetics of psychiatric disorders and discuss implications of the reviewed material for therapeutics development.

Activation of κ opioid receptors increases intrinsic excitability of dentate gyrus granule cells

The dentate gyrus of the hippocampus is thought to control information flow into the rest of the hippocampus. Under pathological conditions, such as epilepsy, this protective feature is circumvented and uninhibited activity flows throughout the hippocampus. Many factors can modulate excitability of the dentate gyrus and ultimately, the hippocampus. It is therefore of critical importance to understand the mechanisms involved in regulating excitability in the dentate gyrus. Dynorphin, the endogenous ligand for the kappa (κ) opioid receptor (KOR), is thought to be involved in neuromodulation in the dentate gyrus. Both dynorphin and its receptor are widely expressed in the dentate gyrus and have been implicated in epilepsy and other complex behaviours such as stress-induced deficits in learning and stress-induced depression-like behaviours. Administration of KOR agonists can prevent both the behavioural and electroencephalographic measures of seizures in several different models of epilepsy. Antagonism of the KORs also prevents stress-induced behaviours. This evidence suggests the KORs as possible therapeutic targets for various pathological conditions. In addition, KOR agonists prevent the induction of LTP. Although there are several mechanisms through which dynorphin could mediate these effects, no studies to date investigated the effects of KOR activation on intrinsic membrane properties and cell excitability. We used whole-cell, patch-clamp recordings from acute mouse hippocampus slices to investigate the effect of KOR activation on dentate gyrus granule cell excitability. The agonist U69,593 (U6, 1 μM) resulted in a lower spike threshold, a decreased latency to first spike, an increased spike half-width, and an overall increase in spike number with current injections ranging from 15 to 45 pA. There was also a reduction in the interspike interval (ISI) both early and late in the spike train, with no change in membrane potential or input resistance. Preincubation of the slice with the selective KOR antagonist, nor-binalthorphimine (BNI, 1 μM) inhibited the effect of U6 on the latency to first spike and spike half-width suggesting that these effects are mediated through KORs. The inclusion of GDP-βS (1 mM) in the recording pipette prevented all of the U6 effects, suggesting that all effects are mediated via a G-protein-dependent mechanism. Inclusion of the A-type K+ current blocker, 4-aminopyridine (4-AP, 5 mM) in the pipette also antagonised the effects of U6. Kv4.2 is one of the channel α subunits thought to be responsible for carrying the A-type K+ current. Incubation of hippocampus slices with U6 resulted in a decrease in the Kv4.2 subunit protein at the cell surface. These results are consistent with an increase in cell excitability in response to KOR activation and may reflect new possibilities for additional opioid functions.

kappa-Opioid receptor signaling and brain reward function

The dynorphin-like peptides have profound effects on the state of the brain reward system and human and animal behavior. The dynorphin-like peptides affect locomotor activity, food intake, sexual behavior, anxiety-like behavior, and drug intake. Stimulation of kappa-opioid receptors, the endogenous receptor for the dynorphin-like peptides, inhibits dopamine release in the striatum (nucleus accumbens and caudate putamen) and induces a negative mood state in humans and animals. The administration of drugs of abuse increases the release of dopamine in the striatum and mediates the concomitant release of dynorphin-like peptides in this brain region. The reviewed studies suggest that chronic drug intake leads to an upregulation of the brain dynorphin system in the striatum and in particular in the dorsal part of the striatum/caudate putamen. This might inhibit drug-induced dopamine release and provide protection against the neurotoxic effects of high dopamine levels. After the discontinuation of chronic drug intake these neuroadaptations remain unopposed which has been suggested to contribute to the negative emotional state associated with drug withdrawal and increased drug intake. kappa-Opioid receptor agonists have also been shown to inhibit calcium channels. Calcium channel inhibitors have antidepressant-like effects and inhibit the release of norepinephrine. This might explain that in some studies kappa-opioid receptor agonists attenuate nicotine and opioid withdrawal symptomatology. A better understanding of the role of dynorphins in the regulation of brain reward function might contribute to the development of novel treatments for mood disorders and other disorders that stem from a dysregulation of the brain reward system.

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.

30 years of dynorphins--new insights on their functions in neuropsychiatric diseases

Since the first description of their opioid properties three decades ago, dynorphins have increasingly been thought to play a regulatory role in numerous functional pathways of the brain. Dynorphins are members of the opioid peptide family and preferentially bind to kappa opioid receptors. In line with their localization in the hippocampus, amygdala, hypothalamus, striatum and spinal cord, their functions are related to learning and memory, emotional control, stress response and pain. Pathophysiological mechanisms that may involve dynorphins/kappa opioid receptors include epilepsy, addiction, depression and schizophrenia. Most of these functions were proposed in the 1980s and 1990s following histochemical, pharmacological and electrophysiological experiments using kappa receptor-specific or general opioid receptor agonists and antagonists in animal models. However, at that time, we had little information on the functional relevance of endogenous dynorphins. This was mainly due to the complexity of the opioid system. Besides actions of peptides from all three classical opioid precursors (proenkephalin, prodynorphin, proopiomelanocortin) on the three classical opioid receptors (delta, mu and kappa), dynorphins were also shown to exert non-opioid effects mainly through direct effects on NMDA receptors. Moreover, discrepancies between the distribution of opioid receptor binding sites and dynorphin immunoreactivity contributed to the difficulties in interpretation. In recent years, the generation of prodynorphin- and opioid receptor-deficient mice has provided the tools to investigate open questions on network effects of endogenous dynorphins. This article examines the physiological, pathophysiological and pharmacological implications of dynorphins in the light of new insights in part obtained from genetically modified animals.

Nociceptive behavior induced by the endogenous opioid peptides dynorphins in uninjured mice: evidence with intrathecal N-ethylmaleimide inhibiting dynorphin degradation

Dynorphins, the endogenous opioid peptides derived from prodynorphin may participate not only in the inhibition, but also in facilitation of spinal nociceptive transmission. However, the mechanism of pronociceptive dynorphin actions, and the comparative potential of prodynorphin processing products to induce these actions were not fully elucidated. In our studies, we examined pronociceptive effects of prodynorphin fragments dynorphins A and B and big dynorphin consisting of dynorphins A and B, and focused on the mechanisms underlying these effects. Our principal finding was that big dynorphin was the most potent pronociceptive dynorphin; when administered intrathecally into mice at extremely low doses (1-10fmol), big dynorphin produced nociceptive behavior through the activation of the NMDA receptor ion-channel complex by acting on the polyamine recognition site. We next examined whether the endogenous dynorphins participate in the spinal nociceptive transmission using N-ethylmaleimide (NEM) that blocks dynorphin degradation by inhibiting cysteine proteases. Similar to big dynorphin and dynorphin A, NEM produced nociceptive behavior mediated through inhibition of the degradation of endogenous dynorphins, presumably big dynorphin that in turn activates the NMDA receptor ion-channel complex by acting on the polyamine recognition site. Our findings support the notion that endogenous dynorphins are critical neurochemical mediators of spinal nociceptive transmission in uninjured animals. This chapter will review above-described phenomena and their mechanism.

Calcium influx into phospholipid vesicles caused by dynorphin neuropeptides

Dynorphins, endogeneous opioid peptides, function as ligands to the opioid kappa receptors but also induce non-opioid excitotoxic effects. Dynorphin A can increase the intra-neuronal calcium concentration through a non-opioid and non-NMDA mechanism. In this investigation, we show that big dynorphin, dynorphin A and to some extent dynorphin A (1-13), but not dynorphin B, allow calcium to enter into large unilamellar phospholipid vesicles with partly negative headgroups. The effects parallel the previously studied potency of dynorphins to translocate through biological membranes and to cause calcein leakage from large unilamellar phospholipid vesicles. There is no calcium ion influx into vesicles with zwitterionic headgroups. We have also investigated if the dynorphins can translocate through the vesicle membranes and estimated the relative strength of interaction of the peptides with the vesicles by fluorescence resonance energy transfer. The results show that dynorphins do not translocate in this membrane model system. There is a strong electrostatic contribution to the interaction of the peptides with the membrane model system.

Synthesis and biological activity of homoarginine-containing opioid peptides

Two tris-alkoxycarbonyl homoarginine derivatives, Boc-Har{omega,omega'-[Z(2Br)]2}-OH and Boc-Har{omega,omega'-[Z(2Cl)]2}-OH, were prepared by guanidinylation of Boc-Lys-OH, and used for the synthesis of neo-endorphins and dynorphins. The results were compared with that obtained in the synthesis in which Boc-Lys(Fmoc)-OH was incorporated into the peptide chain, and after removing Fmoc protection, the resulting peptide-resin was guanidinylated with N,N'-[Z(2Br)]2- or N,N'-[Z(2Cl)]2-S-methylisourea. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. The results indicated that replacement of Arg by Har may be a good avenue for the design of biologically active peptides with increased resistance to degradation by trypsin-like enzymes.

Big dynorphin, a prodynorphin-derived peptide produces NMDA receptor-mediated effects on memory, anxiolytic-like and locomotor behavior in mice

Effects of big dynorphin (Big Dyn), a prodynorphin-derived peptide consisting of dynorphin A (Dyn A) and dynorphin B (Dyn B) on memory function, anxiety, and locomotor activity were studied in mice and compared to those of Dyn A and Dyn B. All peptides administered i.c.v. increased step-through latency in the passive avoidance test with the maximum effective doses of 2.5, 0.005, and 0.7 nmol/animal, respectively. Effects of Big Dyn were inhibited by MK 801 (0.1 mg/kg), an NMDA ion-channel blocker whereas those of dynorphins A and B were blocked by the kappa-opioid antagonist nor-binaltorphimine (6 mg/kg). Big Dyn (2.5 nmol) enhanced locomotor activity in the open field test and induced anxiolytic-like behavior both effects blocked by MK 801. No changes in locomotor activity and no signs of anxiolytic-like behavior were produced by dynorphins A and B. Big Dyn (2.5 nmol) increased time spent in the open branches of the elevated plus maze apparatus with no changes in general locomotion. Whereas dynorphins A and B (i.c.v., 0.05 and 7 nmol/animal, respectively) produced analgesia in the hot-plate test Big Dyn did not. Thus, Big Dyn differs from its fragments dynorphins A and B in its unique pattern of memory enhancing, locomotor- and anxiolytic-like effects that are sensitive to the NMDA receptor blockade. The findings suggest that Big Dyn has its own function in the brain different from those of the prodynorphin-derived peptides acting through kappa-opioid receptors.

Membrane leakage induced by dynorphins

Dynorphins, endogeneous opioid peptides, function as ligands to the opioid kappa receptors and induce non-opioid excitotoxic effects. Here we show that big dynorphin and dynorphin A, but not dynorphin B, cause leakage effects in large unilamellar phospholipid vesicles (LUVs). The effects parallel the previously studied potency of dynorphins to translocate through biological membranes. Calcein leakage caused by dynorphin A from LUVs with varying POPG/POPC molar ratios was promoted by higher phospholipid headgroup charges, suggesting that electrostatic interactions are important for the effects. A possibility that dynorphins generate non-opioid excitatory effects by inducing perturbations in the lipid bilayer of the plasma membrane is discussed.

Big dynorphin as a putative endogenous ligand for the kappa-opioid receptor

The diversity of peptide ligands for a particular receptor may provide a greater dynamic range of functional responses, while maintaining selectivity in receptor activation. Dynorphin A (Dyn A), and dynorphin B (Dyn B) are endogenous opioid peptides that activate the kappa-opioid receptor (KOR). Here, we characterized interactions of big dynorphin (Big Dyn), a 32-amino acid prodynorphin-derived peptide consisting of Dyn A and Dyn B, with human KOR, mu- (hMOR) and delta- (hDOR) opioid receptors and opioid receptor-like receptor 1 (hORL1) expressed in cells transfected with respective cDNA. Big Dyn and Dyn A demonstrated roughly similar affinity for binding to hKOR that was higher than that of Dyn B. Dyn A was more selective for hKOR over hMOR, hDOR and hORL1 than Big Dyn, while Dyn B demonstrated low selectivity. In contrast, Big Dyn activated G proteins through KOR with much greater potency, efficacy and selectivity than other dynorphins. There was no correlation between the rank order of the potency for the KOR-mediated activation of G proteins and the binding affinity of dynorphins for KOR. The rank of the selectivity for the activation of G proteins through hKOR and of the binding to this receptor also differed. Immunoreactive Big Dyn was detected using the combination of radioimmunoassay (RIA) and HPLC in the human nucleus accumbens, caudate nucleus, hippocampus and cerebrospinal fluid (CSF) with the ratio of Big Dyn and Dyn B being approximately 1:3. The presence in the brain implies that Big Dyn, along with other dynorphins, is processed from prodynorphin and secreted from neurons. Collectively, the high potency and efficacy and the relative abundance suggest that Big Dyn may play a role in the KOR-mediated activation of G proteins.

Translocation of Dynorphin Neuropeptides across the Plasma Membrane

Several peptides, including penetratin and Tat, are known to translocate across the plasma membrane. Dynorphin opioid peptides are similar to cell-penetrating peptides in a high content of basic and hydrophobic amino acid residues. We demonstrate that dynorphin A and big dynorphin, consisting of dynorphins A and B, can penetrate into neurons and non-neuronal cells using confocal fluorescence microscopy/immunolabeling. The peptide distribution was characterized by cytoplasmic labeling with minimal signal in the cell nucleus and on the plasma membrane. Translocated peptides were associated with the endoplasmic reticulum but not with the Golgi apparatus or clathrin-coated endocytotic vesicles. Rapid entry of dynorphin A into the cytoplasm of live cells was revealed by fluorescence correlation spectroscopy. The translocation potential of dynorphin A was comparable with that of transportan-10, a prototypical cell-penetrating peptide. A central big dynorphin fragment, which retains all basic amino acids, and dynorphin B did not enter the cells. The latter two peptides interacted with negatively charged phospholipid vesicles similarly to big dynorphin and dynorphin A, suggesting that interactions of these peptides with phospholipids in the plasma membrane are not impaired. Translocation was not mediated via opioid receptors. The potential of dynorphins to penetrate into cells correlates with their ability to induce non-opioid effects in animals. Translocation across the plasma membrane may represent a previously unknown mechanism by which dynorphins can signal information to the cell interior.

Conversion of delta-, kappa- and mu-receptor selective opioid peptide agonists into delta-, kappa- and mu-selective antagonists

2',6'-Dimethyl substitution of the Tyr(1) residue of opioid agonist peptides and deletion of the positively charged N-terminal amino group or its replacement with a methyl group has recently been shown to represent a general structural modification to convert opioid peptide agonists into antagonists. This conversion requires the syntheses of opioid peptide analogues containing either 3-(2,6-dimethyl-4-hydroxyphenyl)propanoic acid (Dhp) or (2S)-2-methyl-3-(2,6-dimethyl-4-hydroxyphenyl)propanoic acid [(2S)-Mdp] in place of Tyr(1). Using this approach, delta-, kappa- and mu-selective opioid peptide agonist peptides were successfully converted into corresponding delta-, kappa- and mu-selective antagonists, whereby receptor selectivity was often maintained or even improved. Thus, two (2S)-Mdp(1)-analogues of the delta-selective cyclic enkephalin analogue H-Tyr-c[D-Pen-Gly-Phe(pF)-Pen]-Phe-OH turned out to be potent and selective delta antagonists. Most successful was the development of kappa antagonists derived from dynorphin A (Dyn A), including the highly potent and selective kappa-antagonist [(2S)-Mdp(1)]Dyn A(1-11)-NH(2) (dynantin) and the enzymatically stable octapeptide analogue [(2S)-Mdp(1),MeArg(7),D-Leu(8)]Dyn A(1-8)-NH(2). The (2S)-Mdp(1)-analogues of dynorphin B and alpha-neoendorphin also were kappa antagonists and may be useful as pharmacological tools in studies of kappa receptor subtypes. Finally, the Dhp(1)-analogues of the mu-selective cyclic enkephalin analogue H-Tyr-c[N(epsilon ),N(beta)-carbonyl-D-Lys(2),Dap(5)]enkephalinamide and of endomorphin-2 were moderately potent mu opioid antagonists.

Intrathecally administered big dynorphin, a prodynorphin-derived peptide, produces nociceptive behavior through an N-methyl-D-aspartate receptor mechanism

Intrathecal (i.t.) administration of big dynorphin (1-10 fmol), a prodynorphin-derived peptide consisting of dynorphin A and dynorphin B, to mice produced a characteristic behavioral response, the biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank, which peaked at 5-15 min after an injection. Dynorphin A produced a similar response, though the doses required were higher (0.1-30 pmol) whereas dynorphin B was practically inactive even at 1000 pmol. The behavior induced by big dynorphin (3 fmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.125-2 mg/kg) and also dose-dependently, by i.t. co-administration of D(-)-2-amino-5-phosphonovaleric acid (D-APV) (1-4 nmol), a competitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (0.25-4 nmol), an NMDA ion-channel blocker, and ifenprodil (2-8 pmol), an inhibitor of the NMDA receptor ion-channel complex interacting with the NR2B subunit and the polyamine recognition site. On the other hand, naloxone, an opioid receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA glutamate receptor antagonist, 7-chlorokynurenic acid, a competitive antagonist of the glycine recognition site on the NMDA receptor ion-channel complex, [D-Phe(7),D-His(9)]-substance P(6-11), a specific antagonist for substance P (NK1) receptors, and MEN-10376, a tachykinin NK2 receptor antagonist, had no effect. These results suggest that big dynorphin-induced nociceptive behavior is mediated through the activation of the NMDA receptor ion-channel complex by acting on the NR2B subunit and/or the polyamine recognition site but not on the glycine recognition site, and does not involve opioid, non-NMDA glutamate receptor mechanisms or tachykinin receptors in the mouse spinal cord.

The hemorphins: a new class of opioid peptides derived from the blood protein hemoglobin

Hemorphins are endogenous peptides belonging to the family of "nonclassical" or "atypical" opioid peptides. They are generated by enzymatic hydrolysis of the beta-, kappa-, delta-, or epsilon-chain of the blood protein hemoglobin. Originally, the hemorphins were isolated from enzymatically treated bovine blood. In recent years hemorphin structures have been identified as naturally occurring peptides in brain, plasma, and cerebrospinal fluid. This article will review recent studies of the hemorphins regarding their structures, mechanisms for their release, and their biological actions. A particular emphasis will be directed to their role in exercising human and their clinical relevance.

Dynorphin A(6-12) analogs suppress thermal edema

Dynorphin A (Dyn A) is a 17-residue opioid peptide derived from prodynorphin precursors found in mammalian tissues. Removal of Tyr1 from Dyn A produces a peptide that is more potent than Dyn A in attenuating the acute phase of the inflammatory response, as measured by inhibition of heat-induced edema in the anesthetized rat's paw (exposure to 58 degrees C water for 1 min). Dyn A(2-17), however, no longer interacts with opioid receptors. It was postulated that the non-opioid anti-inflammatory actions of Dyn A(2-17) may reside in Dyn A(6-12); that is, Arg-Arg-Ile-Arg-Pro-Lys-Leu. here we report on the activities of Dyn A(6-12) analogs modified by substitutions on the N terminus, by single N-methyl substitution and by single replacement of residues by alanine. The results indicated that the minimal sequence required for an anti-edema ED50 of <1.0 micromol/kg i.v. was anisoyl-Arg6-Arg7-Xaa8-Arg9-Pro10)-Xaa11-+ ++Xaa12-NH2. A prototype, p-anisoyl-[D-Leu12] Dyn A(6-12)-NH2, with an ED50 of 0.20 micromol/kg i.v. compared to an ED50 of 0.08 micromol/kg i.v. for Dyn A(2-17), was selected for further tests of biological activity. This analog, like Dyn A(2-17), lowered blood pressure in anesthetized rats. In a model of neurogenic inflammation, produced by antidromic stimulation of the vagus in the anesthetized rat, p-anisoyl-[D-Leu12] Dyn A(6-12)-NH2, 0.23 micromol/kg i.v., attenuated the negativity of tracheal tissue interstitial pressure (Pif), which normally develops after nerve stimulation. Modulation of interstitial pressure may be the mechanistic basis for the anti-edema properties of these Dyn A(6-12) analogs.

Structure-activity relationship studies of dynorphin A and related peptides

An up-to-date review is presented covering all the available information concerning the isolation, discovery, synthesis, conformation, receptor binding characteristics, pharmacological properties and SAR studies of dynorphin A and related peptides. The potential of dynorphin A and its analogs has yet to be fully realized.

Dynorphin and epilepsy

Studies on dynorphin involvement in epilepsy are summarised in this review. Electrophysiological, biochemical and pharmacological data support the hypothesis that dynorphin is implicated in specific types of seizures. There is clear evidence that this is true for complex partial (limbic) seizures, i.e. those characteristic of temporal lobe epilepsy, because; (1) dynorphin is highly expressed in various parts of the limbic system, and particularly in the granule cells of the hippocampus; (2) dynorphin appears to be released in the hippocampus (and in other brain areas) during complex partial seizures; (3) released dynorphin inhibits excitatory neurotransmission at multiple synapses in the hippocampus via activation of kappa opioid receptors; (4) kappa opioid receptor agonists are highly effective against limbic seizures. Data on generalised tonic-clonic seizures are less straightforward. Dynorphin release appears to occur after ECS seizures and kappa agonists exert a clear anticonvulsant effect in this model. However, more uncertain biochemical data and lack of efficacy of kappa agonists in other generalised tonic-clonic seizure models argue that the involvement of dynorphin in this seizure type may not be paramount. Finally, an involvement of dynorphin in generalised absence seizures appears unlikely on the basis of available data. This may not be surprising, given the presumed origin of absence seizures in alterations of the thalamo-cortical circuit and the low representation of dynorphin in the thalamus. In conclusion, it may be suggested that dynorphin plays a role as an endogenous anticonvulsant in complex partial seizures and in some cases of tonic-clonic seizures, but most likely not in generalised absence. This pattern of effects may coincide with the antiseizure spectrum of selective kappa agonists.

The opioid peptide dynorphin directly blocks NMDA receptor channels in the rat

1. The actions of dynorphin on N-methyl-D-aspartate (NMDA) responses were examined in acutely dissociated trigeminal neurons in rat. Whole-cell and single-channel currents were recorded using the patch clamp technique. 2. Dynorphins reduced NMDA-activated currents (INMDA). The IC50 was 0.25 microM for dynorphin (1-32), 1.65 microM for dynorphin (1-17) and 1.8 microM for dynorphin (1-13). 3. The blocking action of dynorphin is voltage independent. 4. The inhibitory action of dynorphin cannot be blocked by high concentration of the non-selective opioid receptor antagonist naloxone, nor by the specific kappa-opioid receptor antagonist nor-Binaltorphimine (nor-BNI). 5. Single-channel analyses indicate that dynorphin reduces the fraction of time the channel is open without altering the channel conductance. 6. We propose that dynorphin acts directly on NMDA receptors.

Guinea-pig ileum (GPI) and mouse vas deferens (MVD) preparations in the discovery, discrimination and parallel bioassay of opioid peptides

As many as 47 amphibian and mammalian, natural and non-natural opioid peptides have been examined in guinea-pig ileum (GPI) and mouse vas deferens (MVD) preparations. The great value of these extremely simple and accessible tissue models in the identification, isolation and purification of endogenous opioid peptides, in studying structure/activity relationships, and in determining selectivity of the peptide molecules for the various opioid receptors, especially delta- and mu-receptors, is emphasized.

Subcellular localization, partial purification, and characterization of a dynorphin processing endopeptidase from bovine pituitary

An enzyme capable of cleaving dynorphin B-29 to dynorphin B-13 is present in bovine pituitary, with 40- to 50-fold higher specific activity in the posterior and intermediate lobes than in the anterior lobe. Subcellular fractionation of bovine neurointermediate pituitary shows that this enzyme is present in the peptide-containing secretory vesicles. The enzyme has been purified 2,800-fold from whole bovine pituitaries using ion-exchange and gel filtration chromatography. Purified dynorphin-converting enzyme has a neutral pH optimum, and is subsantially inhibited by the thiol-protease inhibitor p-chloromercuriphenylsulfonic acid, but not by serine or metalloprotease inhibitors. The purified enzyme processes dynorphin B-29 at Arg14, producing both dynorphin B-14 and dynorphin B-13 in a 5:1 ratio. No other cleavages are observed, suggesting that the activity is free from other proteases and is specific for single Arg sequences. Purified enzyme also processes dynorphin A-17 at the single Arg cleavage site, generating both dynorphin A-8 and A-9 in a 7:1 ratio. The tissue distribution, subcellular localization, and substrate specificity of this enzyme are consistent with a physiological role in the processing of dynorphin B-29 and dynorphin A-17, and possibly other peptides, at single Arg residues.

An inhibitor of endopeptidase-24.15 blocks the degradation of intraventricularly administered dynorphins

Conversion of the octapeptide dynorphin (Dyn) A-(1-8) to Leu5-enkephalin (LE) by endopeptidase EC 3.4.24.15 (EP-24.15) in vivo was examined using the technique of ventriculocisternal perfusion. Peptides were administered intracerebroventricularly in the presence or absence of the EP-24.15 inhibitor N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate (cFPAAF-pAB) via cannulae placed into the lateral ventricle of urethane-anesthetized rats. The concentration of Dyn-like peptides and LE within the CSF was monitored by radioimmunoassay in samples of CSF taken from a second cannula placed in the cisterna magna. In the absence of inhibitor, less than 5% of the Dyn A-(1-8) administered was recovered in CSF. Immunoreactive LE, which is normally not found in CSF, increased rapidly in content following Dyn A-(1-8) infusion, an observation suggesting that the larger peptide is converted to LE. When the inhibitor cFPAAF-pAB was coadministered with Dyn A-(1-8), the concentration of immunoreactive Dyn A-(1-8) after 5 min was 40 times higher than that found in the absence of inhibitor. The angiotensin converting enzyme inhibitor captopril reduced the degradation of Dyn A-(1-8) to a much lesser degree. The inhibitor of EP-24.15 also afforded some protection of other Dyn-like peptides. No EP-24.15 activity was found in rat CSF, whereas high activity was found in the choroid plexus. Taken together, these data clearly indicate that an ectoenzyme form of EP-24.15 rapidly converts intracerebroventricularly administered Dyn-like peptides to LE.

Formation of [Leu5]enkephalin from dynorphin A(1-8) by rat central nervous tissue in vitro

[3H]Dynorphin A(1-8) is readily metabolised by rat lumbosacral spinal cord tissue in vitro, affording a variety of products including a significant amount (20% recovered activity) of [3H][Leu5]enkephalin. In the presence of the peptidase inhibitors bestatin, captopril, thiorphan, and leucyl-leucine, [3H][Leu5]enkephalin was the major metabolic product, accounting for 60% of recovered activity. Production of [3H][Leu5]enkephalin was seen across all gross brain regions. The enzyme responsible for the cleavage has an optimal substrate length of 8-13 amino acids and is inhibited by N-[1-(RS)-carboxy-2-phenylethyl]-Ala-Ala-Phe-p-aminobenzoate, a site-directed inhibitor of the metalloendopeptidase EC 3.4.24.15. However the enzymic breakdown also has properties in common with involvement of endo-oligopeptidase A. Possible consequences of the formation of [Leu5]-enkephalin from the smaller dynorphins are discussed.

Chimeric opioid peptides: tools for identifying opioid receptor types

We synthesized several chimeric peptides in which the N-terminal nine residues of dynorphin-32, a peptide selective for the kappa opioid receptor, were replaced by opioid peptides selective for other opioid receptor types. Each chimeric peptide retained the high affinity and type selectivity characteristic of its N-terminal sequence. The common C-terminal two-thirds of the chimeric peptides served as an epitope recognized by the same monoclonal antibody. When bound to receptors on a cell surface or membrane preparation, these peptides could still bind specifically to the monoclonal antibody. These chimeric peptides should be useful for isolating mu, delta, and kappa opioid receptors and for identifying opioid receptors on transfected cells in expression cloning procedures. The general approach using chimeric peptides should be applicable to other peptide receptors.

Opioid and tachykinin peptides, and their precursors and precursor-processing enzymes, in human cerebrospinal fluid

Opioid and tachykinin neuropeptides, which were derived from two biological sources (intact, and released from their corresponding precursors by the action of human cerebrospinal fluid (CSF) neuropeptidases), were characterized in human CSF by using a combination of post-high-performance liquid chromatographic (HPLC) detection techniques. Peptides were separated using gradient and isocratic reversed-phase HPLC. Radioimmunoassay measured immunoreactivity corresponding to several different individual neuropeptides including methionine enkephalin, leucine enkephalin, substance P and beta-endorphin. Commercial enzymes (trypsin, carboxypeptidase B) were used to release methionine- and leucine-enkephalin from precursors. Human CSF also served as a source of endogenous neuropeptidases. Mass spectrometry produced fragment ions that corroborated the amino acid sequence of methionine enkephalin and of substance P derived from both sources (intact, from precursors). These results demonstrated the presence of endogenous intact neuropeptides, several different neuropeptide-containing precursors and appropriate precursor-processing enzymes in human CSF for precursors of methionine enkephalin, leucine enkephalin, beta-endorphin1-31 and substance P.

Membrane receptors in the gastrointestinal tract

This review focusses on the roles that membrane receptors and their transducers play in the physiology and pathology of the gastrointestinal tract. The multifactorial regulation of [correction] mucosal growth and function is discussed in relation to the heterogeneity of exocrine and endocrine populations that originate from progenitor cells in stomach and intestine.

Precursors to regulatory peptides: their proteolytic processing

Precursors to regulatory peptides undergo maturation processes which include proteolytic processing. The enzymes involved in this process remove the hydrophobic peptide located at the amino-terminus of the precursor. Endoprotease cleavage also occurs at single and two adjacent basic residues, this is followed by a removal of basic residues located at the C-terminus of the peptides by a carboxypeptidase-like enzyme.

Comparison of met-enkephalin-, dynorphin A-, and neurotensin-immunoreactive neurons in the cat and rat spinal cords: I. Lumbar cord

This study compared the distribution of methionine enkephalin-, dynorphin A 1-8-, and neurotensin-immunoreactive (IR) perikarya in laminae I and IV-VII of selected segments of lumbar spinal cord of cat(L5) and rat(4). Immunoreactive neurons for each peptide were found throughout the dorsal horn and dorsal lamina VII but were quantified only within laminae I and IV-VII. In lamina I, both large (greater than 20 micron) and small (less than 20 micron) IR neurons were identified. Large IR neurons for each peptide in both species resembled Waldeyer neurons studied by Golgi stain and were outnumbered by small IR neurons. Comparison among the laminae of the distribution of met-enkephalin IR neurons showed a similar pattern in the two species with the majority of IR neurons (greater than 65%) in laminae V and VI. Differences in laminar distribution occurred between species for the other peptides. Dynorphin IR neurons were greatest in number in lamina V in rat but greatest in number in laminae I and V in cat. Neurotensin IR neurons occurred predominantly in cat lamina I but were nearly equal in density in rat laminae I and VI. The topographic distribution of each peptide in laminae V and VI was similar between the two species with IR neurons occurring laterally in lamina V and more medially in lamina VI. Comparisons between species of the numbers of IR neurons/segment indicated distinct relationships for each peptide. The number of met-enkephalin IR neurons in laminae of cat L5 was generally two times greater than the number of IR neurons in the same laminae of rat L4, except in laminae I and IV, where the numbers were nearly equal. In contrast, the number of dynorphin IR neurons in cat laminae was generally one-half the number in rat, except in lamina I, where the number in cat was two times greater than rat. A high degree of variability occurred in laminar comparisons of neurotensin IR neurons. Neurotensin IR neurons in lamina I of cat outnumbered those of rat 2:1, but in laminae IV-VII, the ratio of cat to rat IR neurons varied from 1:1 to 1:20. The met-enkephalin, dynorphin, and neurotensin IR neurons quantified in this study may be interneurons or may serve as projection neurons to brainstem and/or thalamic nuclei. The observed differences in distribution may be relevant to differences in spinal cord physiology in the two species.

Opioids and opioid receptors in peripheral tissues

Opioid peptides belonging to the enkephalin, beta-endorphin or dynorphin family, acting on specific opiate receptors may be found in peripheral tissues. Enkephalins have a widespread peripheral distribution, while beta-endorphin and dynorphin may be found locally in the enteric nervous system. The peptides of the various families are formed from specific precursor molecules. Apart from the enteric nervous system, opioids are also found in the adrenal medulla as well as in several autonomic ganglia. There is some evidence of three different classes of opioid receptors in peripheral tissues, i.e. mu-, delta- and kappa-receptors. These receptors are not only found on enteric nervous and mucosa cells but also on various cells in the immune system where opioid peptides seem to have important actions and appear to link the neuroendocrine and immune systems to control immunological functions. The physiological as well as the pathophysiological role of opioid peptides in the periphery is gradually being elucidated and, based on such knowledge, new therapeutic implications in gastrointestinal or immune diseases may be developed.

Synthesis and biological activity of carboxyl terminally extended dermorphins

Dermorphinoyl(DMR)-glycine, DMR-sarcosine and DMR-glycyl-arginine have been prepared in order to examine the effect of C-terminal extension of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) on opioid activity. On GPI preparation the addition of Gly, Sar, or Gly-Arg to the carboxyl terminus of dermorphinoic acid was detrimental to mu activity: dermorphinoyl-derivatives, in fact, retain only 5-20% of dermorphin potency. Following intracerebroventricular administration (tail-flick test), whereas the analgesic activities of compounds showed the trend dermorphin greater than DMR-Sar greater than DMR-Gly-Arg greater than DMR-Gly greater than morphine, the nonapeptide displayed highest activity after subcutaneous injection in mice: DMR-Gly-Arg was 2.5 and 10 times more potent than dermorphin and morphine, respectively.

Distribution of dynorphin and enkephalin peptides in the rat brain

The neuroanatomical distribution of dynorphin B-like immunoreactivity (DYN-B) was studied in the adult male and female albino rat. The distribution of DYN B in colchicine- and noncolchicine-treated animals was also compared to that of another opioid peptide derived from the prodynorphin precursor dynorphin A (1-8) (DYN 1-8), and an opioid peptide derived from the proenkephalin precursor met-enkephalin-arg-gly-leu (MERGL). DYN B cell bodies were present in nonpyramidal cells of neo- and allocortices, medium-sized cells of the caudate-putamen, nucleus accumbens, lateral part of the central nucleus of the amygdala, bed nucleus of the stria terminalis, preoptic area, and in sectors of nearly every hypothalamic nucleus and area, medial pretectal area, and nucleus of the optic tract, periaqueductal gray, raphe nuclei, cuneiform nucleus, sagulum, retrorubral nucleus, peripeduncular nucleus, lateral terminal nucleus, pedunculopontine nucleus, mesencephalic trigeminal nucleus, parabigeminal nucleus, dorsal nucleus of the lateral lemniscus, lateral superior olivary nucleus, superior paraolivary nucleus, medial superior olivary nucleus, ventral nucleus of the trapezoid body, lateral dorsal tegmental nucleus, accessory trigeminal nucleus, solitary nucleus, nucleus ambiguus, paratrigeminal nucleus, area postrema, lateral reticular nucleus, and ventrolateral region of the reticular formation. Fiber systems are present that conform to many of the known output systems of these nuclei, including major descending pathways (e.g., striatonigral, striatopallidal, reticulospinal, hypothalamospinal pathways), short projection systems (e.g., mossy fibers in hippocampus, hypothalamo-hypophyseal pathways), and local circuit pathways (e.g., in cortex, hypothalamus). The distribution of MERGL was, with a few notable exceptions, in the same nuclei as DYN B. From these neuroanatomical data, it appears that the dynorphin and enkephalin peptides are strategically located in brain regions that regulate extrapyramidal motor function, cardiovascular and water balance systems, eating, sensory processing, and pain perception.