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Cell Reports Sep 2022Low dopamine D2 receptor (D2R) availability in the striatum can predispose for cocaine abuse; though how low striatal D2Rs facilitate cocaine reward is unclear....
Low dopamine D2 receptor (D2R) availability in the striatum can predispose for cocaine abuse; though how low striatal D2Rs facilitate cocaine reward is unclear. Overexpression of D2Rs in striatal neurons or activation of D2Rs by acute cocaine suppresses striatal Penk mRNA. Conversely, low D2Rs in D2-striatal neurons increases striatal Penk mRNA and enkephalin peptide tone, an endogenous mu-opioid agonist. In brain slices, met-enkephalin and inhibition of enkephalin catabolism suppresses intra-striatal GABA transmission. Pairing cocaine with intra-accumbens met-enkephalin during place conditioning facilitates acquisition of preference, while mu-opioid receptor antagonist blocks preference in wild-type mice. We propose that heightened striatal enkephalin potentiates cocaine reward by suppressing intra-striatal GABA to enhance striatal output. Surprisingly, a mu-opioid receptor antagonist does not block cocaine preference in mice with low striatal D2Rs, implicating other opioid receptors. The bidirectional regulation of enkephalin by D2R activity and cocaine offers insights into mechanisms underlying the vulnerability for cocaine abuse.
Topics: Analgesics, Opioid; Animals; Cocaine; Cocaine-Related Disorders; Corpus Striatum; Enkephalin, Methionine; Enkephalins; Mice; Narcotic Antagonists; RNA, Messenger; Receptors, Dopamine D1; Receptors, Dopamine D2; Reward; gamma-Aminobutyric Acid
PubMed: 36170833
DOI: 10.1016/j.celrep.2022.111440 -
Organic & Biomolecular Chemistry Jul 2013Although peptide-oligonucleotide conjugates (POCs) are well-known for nucleic acids delivery and therapy, reports on internal attachment of peptides to oligonucleotides...
Although peptide-oligonucleotide conjugates (POCs) are well-known for nucleic acids delivery and therapy, reports on internal attachment of peptides to oligonucleotides are limited in number. To develop a convenient route for preparation of internally labeled POCs with improved biomedical properties, peptides were introduced into oligonucleotides via a 2'-alkyne-2'-amino-LNA scaffold. Derivatives of methionine- and leucine-enkephalins were chosen as model peptides of mixed amino acid content, which were singly and doubly incorporated into LNA/DNA strands using highly efficient copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry. DNA/RNA target binding affinity and selectivity of the resulting POCs were improved in comparison to LNA/DNA mixmers and unmodified DNA controls. This clearly demonstrates that internal attachment of peptides to oligonucleotides can significantly improve biomolecular recognition by synthetic nucleic acid analogues. Circular dichroism (CD) measurements showed no distortion of the duplex structure by the incorporated peptide chains while studies in human serum indicated superior stability of the POCs compared to LNA/DNA mixmers and unmodified DNA references. Molecular modeling suggests strong interactions between positively charged regions of the peptides and the negative oligonucleotide backbones which leads to clamping of the peptides in a fixed orientation along the duplexes.
Topics: Amino Acid Sequence; Base Sequence; Click Chemistry; Enkephalins; Humans; Models, Molecular; Oligonucleotides; Serum
PubMed: 23681061
DOI: 10.1039/c3ob40786a -
The Journal of Pain 2020Understanding molecular alterations associated with peripheral inflammation is a critical factor in selectively controlling acute and persistent pain. The present report...
Understanding molecular alterations associated with peripheral inflammation is a critical factor in selectively controlling acute and persistent pain. The present report employs in situ hybridization of the 2 opioid precursor mRNAs coupled with quantitative measurements of 2 peptides derived from the prodynorphin and proenkephalin precursor proteins: dynorphin A 1-8 and [Met]-enkephalin-Arg-Gly-Leu. In dorsal spinal cord ipsilateral to the inflammation, dynorphin A 1-8 was elevated after inflammation, and persisted as long as the inflammation was sustained. Qualitative identification by high performance liquid chromatography and gel permeation chromatography revealed the major immunoreactive species in control and inflamed extracts to be dynorphin A 1-8. In situ hybridization in spinal cord after administration of the inflammatory agent, carrageenan, showed increased expression of prodynorphin (Pdyn) mRNA somatotopically in medial superficial dorsal horn neurons. The fold increase in preproenkephalin mRNA (Penk) was comparatively lower, although the basal expression is substantially higher than Pdyn. While Pdyn is not expressed in the dorsal root ganglion (DRG) in basal conditions, it can be induced by nerve injury, but not by inflammation alone. A bioinformatic meta-analysis of multiple nerve injury datasets confirmed Pdyn upregulation in DRG across different nerve injury models. These data support the idea that activation of endogenous opioids, notably dynorphin, is a dynamic indicator of persistent pain states in spinal cord and of nerve injury in DRG. PERSPECTIVE: This is a systematic, quantitative assessment of dynorphin and enkephalin peptides and mRNA in dorsal spinal cord and DRG neurons in response to peripheral inflammation and axotomy. These studies form the foundational framework for understanding how endogenous spinal opioid peptides are involved in nociceptive circuit modulation.
Topics: Animals; Dynorphins; Enkephalins; Ganglia, Spinal; Hyperalgesia; Inflammation Mediators; Male; Opioid Peptides; Peptide Fragments; RNA, Messenger; Rats; Rats, Sprague-Dawley; Spinal Cord
PubMed: 31931229
DOI: 10.1016/j.jpain.2020.01.001 -
The Journal of Clinical Investigation Mar 1982To elucidate the physiological and pathophysiological significance of methionine- and leucine-enkephalin (Met-and Leu-enkephalin, respectively) in human sympathoadrenal...
To elucidate the physiological and pathophysiological significance of methionine- and leucine-enkephalin (Met-and Leu-enkephalin, respectively) in human sympathoadrenal system, the contents of these peptides in normal human sympathetic nervous system, adrenal medulla, and pheochromocytomas were determined by specific radioimmunoassays combined with reverse-phase high-performance liquid chromatography. Met-enkephalin-LI and Leu-enkephalin-LI, respectively) were detected by radioimmunoassay in adrenal glands, adrenal medulla, stellate ganglia, sympathetic trunks, and celiac ganglia, and their contents in adrenal medulla were highest. Existence of authentic Met- and Leu-enkephalin was confirmed by reverse-phase high-performance liquid chromatography. Met-enkephalin was approximately 74% of Met-enkephalin-LI, whereas Leu-enkephalin was approximately 30% of Leu-enkephalin-LI in human adrenal medulla. The ratio of Met- to Leu-enkephalin was 2.6 in human adrenal medulla, whereas it was higher in sympathetic ganglia or trunks. In four cases of pheochromocytoma marked difference in Met- and Leu-enkephalin contents was found between medullary and extramedullary tumors. The contents were about three orders higher and the Met- to Leu-enkephalin ratio was lower in medullary than in extramedullary pheochromocytomas, reflecting the tissues where the tumors arose. These results suggest the physiological roles of Met- and Leu-enkephalin in sympathetic nervous system and adrenal glands and their pathophysiological significances in pheochromocytomas.
Topics: Adrenal Gland Neoplasms; Adrenal Medulla; Chromatography, High Pressure Liquid; Endorphins; Enkephalin, Leucine; Enkephalin, Methionine; Enkephalins; Humans; Pheochromocytoma; Radioimmunoassay; Sympathetic Nervous System
PubMed: 7061706
DOI: 10.1172/jci110491 -
British Journal of Pharmacology Feb 19971. A method is described for the rapid extraction of opioid peptides from the brain and other tissues. The method is based on acid extraction of tissues followed by...
1. A method is described for the rapid extraction of opioid peptides from the brain and other tissues. The method is based on acid extraction of tissues followed by adsorption of the extract onto Amberlite XAD-2 resin. Elution with methanol separates the enkephalins and α-endorphin from β-endorphin. 2. Over 90% of the opioid peptide activity isolated from brain and gut of several species by our method was due to methionine- and leucine-enkephalin. In contrast, the major opioid peptide activity recovered from the pituitary was due to peptides of much greater mol. wt. than the enkephalins. 3. An opioid peptide with properties unlike those of the known endorphins or enkephalins was present in brain extracts. This peptide, termed ∈-endorphin, has an apparent mol. wt. of 700 to 1200; it constituted between 5 to 10% of the total opioid activity in our extracts. 4. A differential assay of methionine- and leucine-enkephalin was made either by destroying methionine-enkephalin activity with cyanogen bromide or by separating the peptides by thin layer chromatography. 5. The ratio of methionine-enkephalin to leucine-enkephalin varied greatly in different brain regions. The highest proportions of leucine-enkephalin were found in the cerebral cortex and hippocampus. 6. Formaldehyde perfusion and fixation of the brain had no significant effect on the brain content of enkephalin, indicating that proteolytic breakdown is not a major problem in the extraction of these peptides. 7. It is suggested that the enkephalins may have a neurotransmitter role in both brain and peripheral tissues and that methionine- and leucine-enkephalin may subserve separate neuronal functions.
Topics: Animals; Biological Assay; Brain; Enkephalin, Leucine; Enkephalin, Methionine; Guinea Pigs; History, 20th Century; Ileum; Mice; Pituitary Gland; Rabbits; Rats; Tissue Distribution
PubMed: 9142421
DOI: 10.1111/j.1476-5381.1997.tb06829.x -
Proceedings of the National Academy of... Feb 1982The biosynthesis of the protein precursor of [Met]enkephalin (Tyr-Gly-Gly-Phe-Met) was studied using cell-free translation systems to characterize the...
The biosynthesis of the protein precursor of [Met]enkephalin (Tyr-Gly-Gly-Phe-Met) was studied using cell-free translation systems to characterize the enkephalin-precursor gene product and mRNA. Proteins obtained by translation of bovine adrenal medullary mRNA in the presence of [35S]methionine were digested with trypsin and carboxypeptidase B. The resultant peptides were immunoprecipitated with anti[Met]enkephalin serum and subsequently analyzed by reverse phase HPLC. [35S][Met]Enkephalin (up to 0.2 fmol/micrograms mRNA, identified by antigenic specificity and chromatographic mobility, was isolated from peptides obtained from proteins whose synthesis was dependent upon adrenal medullary mRNA. Both trypsin and carboxy-peptidase B were required to generate [35S][Met]enkephalin from translation products. The largest protein containing the [35S]-[Met]enkephalin sequence synthesized in the wheat germ system has a Mr, of 31,000 +/- 1000, determined by NaDodSO4/polyacrylamide gel electrophoresis. Adrenal medullary mRNA coding for protein containing the [35S][Met]enkephalin sequence was resolved into a major fraction of 1450 +/- 150 nucleotides and a minor fraction of 47000 +/- 450 nucleotides, as determined by agarose gel electrophoresis in the presence of methylmercuric hydroxide. It is proposed that the major enkephalin-precursor gene product of adrenal medulla is a protein of Mr approximately 31,000.U
Topics: Adrenal Medulla; Animals; Base Sequence; Carboxypeptidase B; Carboxypeptidases; Cattle; Cell-Free System; Endorphins; Enkephalin, Methionine; Enkephalins; Molecular Weight; Protein Biosynthesis; Protein Precursors; RNA, Messenger; Trypsin
PubMed: 6951159
DOI: 10.1073/pnas.79.4.1017 -
International Journal of Molecular... Oct 2021Biphalin, one of the opioid agonists, is a dimeric analog of enkephalin with a high affinity for opioid receptors. Opioid receptors are widespread in the central nervous... (Review)
Review
Biphalin, one of the opioid agonists, is a dimeric analog of enkephalin with a high affinity for opioid receptors. Opioid receptors are widespread in the central nervous system and in peripheral neuronal and non-neuronal tissues. Hence, these receptors and their agonists, which play an important role in pain blocking, may also be involved in the regulation of other physiological functions. Biphalin was designed and synthesized in 1982 by Lipkowski as an analgesic peptide. Extensive further research in various laboratories on the antinociceptive effects of biphalin has shown its excellent properties. It has been demonstrated that biphalin exhibits an analgesic effect in acute, neuropathic, and chronic animal pain models, and is 1000 times more potent than morphine when administered intrathecally. In the course of the broad conducted research devoted primarily to the antinociceptive effect of this compound, it has been found that biphalin may also potentially participate in the regulation of other opioid system-dependent functions. Nearly 40 years of research on the properties of biphalin have shown that it may play a beneficial role as an antiviral, antiproliferative, anti-inflammatory, and neuroprotective agent, and may also affect many physiological functions. This integral review analyzes the literature on the multidirectional biological effects of biphalin and its potential in the treatment of many opioid system-dependent pathophysiological diseases.
Topics: Analgesics; Analgesics, Opioid; Enkephalins; Morphine; Opioid-Related Disorders; Pain; Receptors, Opioid
PubMed: 34768778
DOI: 10.3390/ijms222111347 -
CNS Drug Reviews 2007The endogenous opioids met- and leu-enkephalin are inactivated by peptidases preventing the activation of opioid receptors. Inhibition of enkephalin-degrading enzymes... (Review)
Review
The endogenous opioids met- and leu-enkephalin are inactivated by peptidases preventing the activation of opioid receptors. Inhibition of enkephalin-degrading enzymes increases endogenous enkephalin levels and stimulates robust behavioral effects. RB101, an inhibitor of enkephalin-degrading enzymes, produces antinociceptive, antidepressant, and anxiolytic effects in rodents, without typical opioid-related negative side effects. Although enkephalins are not selective endogenous ligands, RB101 induces these behaviors through receptor-selective activity. The antinociceptive effects of RB101 are produced through either the mu-opioid receptor alone or through activation of both mu- and delta-opioid receptors; the antidepressant-like and anxiolytic effects of RB101 are mediated only through the delta-opioid receptor. Although little is known about the effects of RB101 on other physiologically and behaviorally relevant peptides, these findings suggest that RB101 and other inhibitors of enkephalin-degrading enzymes may have potential as novel therapeutic compounds for the treatment of pain, depression, and anxiety.
Topics: Aminopeptidases; Animals; Cholecystokinin; Disulfides; Enkephalin, Leucine; Enkephalin, Methionine; Enzyme Inhibitors; Mice; Phenylalanine; Prodrugs; Rats
PubMed: 17627672
DOI: 10.1111/j.1527-3458.2007.00011.x -
Proceedings of the National Academy of... Jun 1980Leu[Enkephalin (400.0 micrograms/kg) and the enkephalin analog [DAla,DLeu]enkephalin (0.4, 4.0, and 40.0 micrograms/kg) were intraperitoneally administered to rats 5 min...
Leu[Enkephalin (400.0 micrograms/kg) and the enkephalin analog [DAla,DLeu]enkephalin (0.4, 4.0, and 40.0 micrograms/kg) were intraperitoneally administered to rats 5 min before they were trained on aversively motivated tasks. The peptides impaired acquisition of a one-way active avoidance response, facilitated acquisition of an inhibitory avoidance response, and had no effect on acquisition of a swim-escape response. The data indicate that the enkephalin effects are not mediated through actions on locomotor activity, pain perception or reactivity, or light sensitivity. Rather, we suggest that [Leu]enkephalin and its analog strengthen the tendency of rats to suppress behavior in the presence of cues previously associated with aversive stimulation. This effect may be due to an enkephalin-induced increase in fear or arousal. The enkephalin effect on behavior was obtained at low doses and was observed within a few minutes after administration. These findings are consistent with the interpretation that enkephalin effects may be initiated at a peripheral site.
Topics: Animals; Avoidance Learning; Behavior, Animal; Electroshock; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Escape Reaction; Fear; Light; Male; Pain; Perception; Rats; Sensory Thresholds; Visual Perception; Water
PubMed: 6997883
DOI: 10.1073/pnas.77.6.3729 -
British Journal of Pharmacology May 19781 The actions of morphine, methionine and leucine enkephalin, administered electrophoretically, were studied on supraspinal neurones in the cortex and brainstem of the...
1 The actions of morphine, methionine and leucine enkephalin, administered electrophoretically, were studied on supraspinal neurones in the cortex and brainstem of the rat anaesthetized with urethane and on spinal Renshaw cells and dorsal horn interneurones in the cat anaesthetized with pentobarbitone.2 The majority of Renshaw cells and cortical and brainstem neurones were excited by all three compounds although some supraspinal neurones were depressed.3 Naloxone reversibly antagonized both excitatory and depressant actions of morphine and enkephalin. Acetylcholine-induced excitation but not amino acid-induced excitation was also antagonized by naloxone.4 Neither morphine nor the enkephalins had any naloxone-reversible action on dorsal horn neurones when ejected from conventional multibarrelled electrodes. However, morphine but not enkephalin, administered into the substantia gelatinosa region of the spinal cord selectively reduced responses to noxious stimuli of neurones in deeper laminae. Naloxone administered into the same region antagonized this action of morphine.5 Intravenous morphine also antagonized responses of dorsal horn neurones to noxious stimuli and subsequent intravenous naloxone reversed this effect.6 It was concluded that the excitatory and inhibitory effects of morphine and enkephalin on central neurones may be mediated by actions on different opiate receptors and that depression of noxious responses of dorsal horn neurones may be relevant to the analgesic action of morphine.
Topics: Animals; Brain Stem; Cats; Cerebral Cortex; Electrophysiology; Endorphins; Enkephalins; Female; Male; Morphine; Neurons; Rats; Spinal Cord; Synaptic Transmission
PubMed: 206309
DOI: 10.1111/j.1476-5381.1978.tb07778.x