endomorphin-1 and Inflammation

Although endomorphins-1 (EM-1; H-Tyr-Pro-Phe-Trp-NH(2)) and -2 (EM-2; H-Tyr-Pro-Phe-Phe-NH(2)) are primarily considered agonists for the μ-opioid receptor (MOR), systematic alterations to specific residues provided antagonists and ligands with mixed μ/δ-opioid properties, suitable for application to health-related topics. While the application of endomorphins as antinociceptive agents and numerous biological endpoints were experimentally delineated in laboratory animals and in vitro, clinical use is currently absent. However, structural alterations provide enhanced stability; formation of MOR antagonists or mixed and dual μ/δ-acting ligands could find considerable therapeutic potential.. This review attempts to succinctly provide insight on the development and bioactivity of endomorphin analogues during the past decade. Rational design approaches will focus on the engineering of endomorphin agonists, antagonists and mixed ligands for their application as a multi-target ligand.. Aside from alleviating pain, EM analogues open new horizons in the treatment of medical syndromes involving neural reward mechanisms and extraneural regulation effects on homeostasis. Highly selective MOR antagonists may be promising to reduce inflammation, attenuate addiction to drugs and excess consumption of high-caloric food, ameliorate alcoholism, affect the immune system and combat opioid bowel dysfunction.

Topics: Animals; Drug Design; Humans; Inflammation; Ligands; Oligopeptides; Patents as Topic; Receptors, Opioid, mu; Substance-Related Disorders

Endomorphin (EM)-1 and EM-2 are tetrapeptides located within the mammalian central nervous system and immune tissues, with high affinity and specificity for micro-opioid receptors. Most of the literature has focused on the analgesic properties of EM-1 and EM-2 in animal models of neuropathic or neurogenic pain, but there is persuasive evidence emerging that EMs can also exert potent anti-inflammatory effects in both acute and chronic peripheral inflammation. The purpose of this review is to present and evaluate the evidence for anti-inflammatory properties of EM-1 and EM-2 with a view to their potential for use in chronic human inflammatory disease. Distribution of EMs within the immune system and functional roles as immunomodulatory agents are summarized and discussed. Possible milestones to be met revolve around issues of peptide stability, biodegradability problems and optimal route and method of delivery. The potential for delivery of a low-cost drug with both peripheral anti-inflammatory and analgesic properties, effective in low doses, and targeted to the site of inflammation, should focus our attention on further development of EMs as potent therapeutic agents in chronic inflammation.

Topics: Animals; Chronic Disease; Humans; Inflammation; Oligopeptides; Receptors, Opioid, mu

Changes in airway innervation are believed to play a key role in the pathophysiology of asthma. A group of regulatory peptides which act as neuroregulators is resembled by the opioids. Their localization to neurons projecting into airways suggested a possible role as regulators of neurogenic inflammation, bronchoconstriction and mucus secretion. They mainly act through modification of tachykinergic and cholinergic impulses and their ability to inhibit bronchoconstriction prompted discussion of their potential value in asthma therapy. Apart from the presence of the classical opioids and their receptors in the lung and their functional role, a new group of peptides such as nociceptin and endomorphins have been characterized in the airways. Whereas at least endomorphin-1 acts via the classical OP(3) (mu) receptor, nociceptin binds to a new receptor termed opioid receptor-like-receptor (ORL(1)) and inhibits tachykinergic constriction. Contrary to these promising modulatory effects on airway smooth muscle tone, effective therapeutic strategies have not been developed yet. In conclusion, opioids resemble a group of regulatory peptides which are present within airway-innervating nerve fibres and influence a multitude of airway functions via modification of neural transmission.

Topics: Asthma; Bronchoconstriction; Humans; Inflammation; Lung; Neurons; Nociceptin; Nociceptin Receptor; Oligopeptides; Opioid Peptides; Receptors, Opioid; Signal Transduction

The recently discovered endogenous opioid peptides, endomorphins-1 and -2, appear to have properties consistent with neurotransmitter/neuromodulator actions in mammals. This review surveys the information gained so far from studies of different aspects of the endomorphins. Thus, the endomorphins have been found unequally in the brain; they are stored in neurons and axon terminals, with a heterogeneous distribution; they are released from synaptosomes by depolarization; they are enzymatically converted by endopeptidases; and they interact specifically and with high affinity with mu-opioid receptors. The most outstanding effect of the endomorphins is their antinociceptive action. This depends on both central and peripheral neurons. Additionally, the endomorphins cause vasodilatation by stimulating nitric oxide release from the endothelium. Their roles in different central and peripheral functions, however, have not been fully clarified yet. From a therapeutic perspective, therefore, they may be conceived at present as potent antinociceptive and vasodilator agents.

Topics: Analgesics, Opioid; Animals; Cardiovascular Physiological Phenomena; Digestive System Physiological Phenomena; Endothelium; Humans; Immune System; Inflammation; Mammals; Nitric Oxide; Oligopeptides; Receptors, Opioid, mu; Respiratory Physiological Phenomena; Signal Transduction; Vasodilation

Spinal analgesic effects of endomorphin-1 and endomorphin-2 were studied during acute, inflammatory, and neuropathic pain in rats chronically implanted with intrathecal cannulas. Endomorphin-1 and endomorphin-2 (2.5-10 micrograms i.t.), as well as their analogues, increased the tail-flick and the paw pressure latencies. In a model of inflammatory pain, the formalin-induced behavior was attenuated by endomorphins; however, the effect studied was not dose-dependent and was less pronounced in comparison with that evoked by morphine. On the other hand, in rats with a sciatic nerve injury (crush), endomorphins antagonized allodynia in a dose-dependent manner, whereas morphine was found to be ineffective in a similar dose range. Endomorphins also exhibited an antinociceptive potency in rats tolerant to morphine. In conclusion, our results show a powerful analgesic action of endomorphins at the spinal level. The most interesting finding is a strong effect of endomorphins in neuropathic pain, which opens up a possibility of using these compounds in pain therapy.

Topics: Analgesics, Opioid; Animals; Inflammation; Neuralgia; Oligopeptides; Pain; Pain Threshold; Rats; Spinal Cord

Preemptive administration of analgesic drugs reduces perceived pain and prolongs duration of antinociceptive action. Whereas several lines of evidence suggest that endomorphins, the endogenous mu-opioid agonists, attenuate acute and chronic pain at the spinal level, their preemptive analgesic effects remain to be determined. In this study, we evaluated the anti-allodynic activities of endomorphins and explored their mechanisms of action after preemptive administration in a mouse model of inflammatory pain.. The anti-allodynic activities of preemptive intrathecal administration of endomorphin-1 and endomorphin-2 were investigated in complete Freund's adjuvant (CFA)-induced inflammatory pain model and paw incision-induced postoperative pain model. The modulating effects of endomorphins on the expression of p38 mitogen-activated protein kinase (p38 MAPK) and inflammatory mediators in dorsal root ganglion (DRG) of CFA-treated mice were assayed by real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, or immunofluorescence staining.. Preemptive intrathecal injection of endomorphins dose-dependently attenuated CFA-induced mechanical allodynia via the mu-opioid receptor and significantly reversed paw incision-induced allodynia. In addition, CFA-caused increase of phosphorylated p38 MAPK in DRG was dramatically reduced by preemptive administration of endomorphins. Repeated intrathecal application of the specific p38 MAPK inhibitor SB203580 reduced CFA-induced mechanical allodynia as well. Further RT-PCR assay showed that endomorphins regulated the mRNA expression of inflammatory cytokines in DRGs induced by peripheral inflammation.. Our findings reveal a novel mechanism by which preemptive treatment of endomorphins attenuates inflammatory pain through regulating the production of inflammatory cytokines in DRG neurons via inhibition of p38 MAPK phosphorylation.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Freund's Adjuvant; Ganglia, Spinal; Gene Expression Regulation; Inflammation; Injections, Spinal; Male; Mice; Neurons; Oligopeptides; Opioid Peptides; p38 Mitogen-Activated Protein Kinases; Pain; Pain Threshold; Signal Transduction; Time Factors

Activation of the mu-opioid receptor provides the gold standard for pain relief, but most opioids used clinically have adverse effects that have contributed to an epidemic of overdose deaths. We recently characterized mu-opioid receptor selective endomorphin (EM) analogs that provide potent antinociception with reduction or absence of a number of side effects of traditionally prescribed opioids including abuse liability, respiratory depression, motor impairment, tolerance, and inflammation. The current study explores the effectiveness of these EM analogs relative to morphine in four major pain models by intrathecal as well as intravenous administration in male Sprague Dawley rats and subcutaneous administration in male CD-1 mice. In the spared nerve injury model of neuropathic pain, mechanical allodynia and mechanical hyperalgesia were assessed with von Frey and Randall-Selitto tests, respectively. In the paw incision model of postoperative pain, von Frey testing was used to assess mechanical allodynia and thermal hyperalgesia was evaluated with Hargreaves testing. In the Complete Freund's Adjuvant model of inflammatory pain, thermal hyperalgesia was assessed using Hargreaves testing. In CD-1 mice, visceral pain was assessed with the acetic acid writhing test. In all cases, EM analogs had equal or greater potency and longer duration of action relative to morphine. The data suggest that EM analogs, particularly analog 4 (ZH853), could provide effective therapy for a diverse spectrum of pain conditions with low risk of adverse side effects compared with currently used opioids such as morphine.. Novel EM analogs show equal or greater potency and effectiveness relative to morphine in multiple pain models. Together with substantially reduced side effects, including abuse liability, the compounds show promise for addressing the critical need for effective pain relief as well as reducing the opioid overdose epidemic.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Hyperalgesia; Inflammation; Injections, Intravenous; Injections, Spinal; Male; Mice; Morphine; Neuralgia; Nociceptive Pain; Oligopeptides; Pain, Postoperative; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Visceral Pain

Long-lasting pain may partly be a consequence of ongoing neuroinflammation, in which astrocytes play a significant role. Following noxious stimuli, increased inflammatory receptor activity, influences in Na(+)/K(+)-ATPase activity and actin filament organization occur within the central nervous system. In astrocytes, the Ca(2+) signaling system, Na(+) transporters, cytoskeleton, and release of pro-inflammatory cytokines change during inflammation. The aim of this study was to restore these cell parameters in inflammation-reactive astrocytes. We found that the combination of (1) endomorphin-1, an opioid agonist that stimulates the Gi/o protein of the μ-opioid receptor; (2) naloxone, an opioid antagonist that inhibits the Gs protein of the μ-opioid receptor at ultralow concentrations; and (3) levetiracetam, an anti-epileptic agent that counteracts the release of IL-1β, managed to activate the Gi/o protein and Na(+)/K(+)-ATPase activity, inhibit the Gs protein, and decrease the release of IL-1β. The cell functions of astrocytes in an inflammatory state were virtually restored to their normal non-inflammatory state and it could be of clinical significance and may be useful for the treatment of long-term pain.

Topics: Actins; Analgesics, Opioid; Animals; Astrocytes; Calcium Signaling; Capillaries; Coculture Techniques; Cytokines; Cytoskeleton; Endothelial Cells; Glutamic Acid; Inflammation; Interleukin-1beta; Levetiracetam; Lipopolysaccharides; Male; Naloxone; Narcotic Antagonists; Nootropic Agents; Oligopeptides; Piracetam; Primary Cell Culture; Rats; Rats, Sprague-Dawley; Sodium-Potassium-Exchanging ATPase

1. Although it is well known that the combined administration of synthetic or plant-originated opioids with cannabinoids (CB) results in synergistic antinociception, the effects of combined administration of endogenous ligands acting at micro-opioid and CB receptors are not known. The aim of the present study was to determine the interaction between anandamide (AEA; a CB(1) receptor agonist) and endomorphin-1 (EM-1; a micro-opioid receptor agonist) after intrathecal administration. 2. Nociception was assessed by the paw-withdrawal test after carrageenan-induced inflammation in male Wistar rats. 3. Endomorphin-1 (16.4 pmol to 16.4 nmol) and AEA (4.3-288 nmol) alone dose-dependently decreased carrageenan-induced thermal hyperalgesia, although the highest dose of AEA also exhibited pain-inducing potential. The potency of AEA was approximately 59-fold lower than that of EM-1 (35% effective dose (ED(35)) 194.4 vs 3.3 nmol, respectively). Coadministration of these ligands revealed that combinations of 16.4 pmol EM-1 plus 28.8 or 86.5 nmol AEA were more effective than either drug alone, but other combinations were no more effective than the administration of EM-1 itself. Therefore, coadministration of AEA did not significantly shift the dose-response curve to EM-1. 4. The results of the present study indicate that the coadministration of AEA and EM-1 results in potentiated antihyperalgesia only for a combination of specific doses. Because AEA activates other receptor types (e.g. TRPV1) in addition to CB(1) receptors, the results of the present suggest that, after the coadministration of EM-1 and AEA, complex interactions ensue that may lead to different outcomes compared with those seen following the injection of exogenous ligands.

Topics: Analgesics; Animals; Arachidonic Acids; Carrageenan; Drug Combinations; Drug Evaluation, Preclinical; Drug Interactions; Endocannabinoids; Hyperalgesia; Inflammation; Injections, Spinal; Male; Oligopeptides; Pain; Polyunsaturated Alkamides; Rats; Rats, Wistar; Spine; Time Factors

Endomorphins (EMs) are endogenous selective mu-opioid receptor agonists. Their role in inflammatory pain has not been fully elucidated. Here we examine peripheral antinociception elicited by exogenously applied EM-1 and EM-2 and the contribution of EM-containing leukocytes to stress- and corticotropin-releasing factor (CRF)-induced antinociception. To this end, we applied behavioral (paw pressure) testing, radioligand binding, immunohistochemistry, and flow cytometry in rats with unilateral hindpaw inflammation induced with Freund's adjuvant. EMs injected directly into both hindpaws produced antinociception exclusively in inflamed paws. This was blocked by locally applied mu-receptor-selective (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2) but not kappa-receptor-selective (nor-binaltorphimine) antagonists. Delta-receptor antagonists (naltrindole and N,N-diallyl-Tyr-Aib-Aib-Phe-Leu) did not influence EM-1-induced but dose-dependently decreased EM-2-induced antinociception. Antibodies against beta-endorphin, methionine-enkephalin, or leucine-enkephalin did not significantly change EM-2-induced antinociception. Both EMs displaced binding of [3H]-[D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin to mu-receptors in dorsal root ganglia (DRG). Using [3H]-naltrindole or [(125)I]-[D-Pen2,5]-enkephalin, no detectable delta-binding was found in DRG of inflamed hindlimbs. Numerous beta-endorphin-containing and fewer EM-1- and EM-2-containing leukocytes were detected in subcutaneous tissue of inflamed paws. Leukocyte-depleting serum decreased the number of immigrating opioid-containing immune cells and attenuated swim stress- and CRF-induced antinociception in inflamed paws. Both forms of antinociception were strongly attenuated by anti-beta-endorphin and to a lesser degree by anti-EM-1 and anti-EM-2 antibodies injected into inflamed paws. Together, exogenously applied and immune cell-derived EMs alleviate prolonged inflammatory pain through selective activation of peripheral opioid receptors. Exogenous EM-2 in addition to mu-receptors also activates peripheral delta-receptors, which does not involve actions via other opioid peptides.

Topics: Analgesics; Animals; Dose-Response Relationship, Drug; Inflammation; Male; Neutrophils; Oligopeptides; Pain; Pain Measurement; Rats; Rats, Wistar; Time Factors

Endomorphin 1 (EM1) and endomorphin 2 (EM2) are highly potent and selective mu-opioid receptor agonists and have significant antinociceptive action. In the mu-selective pocket of endomorphins (EMs), Pro2 residue is a spacer and directs the Tyr1 and Trp3/Phe3 side chains into the required orientation. The present work was designed to substitute the peptide bond between Tyr1 and Pro2 of EMs with a reduced (CH2NH) bond and study the agonist potency and antinociception of EM1[psi] (Tyr[psi(CH2NH)]Pro-Trp-Phe-NH2) and EM2[psi] (Tyr[psi(CH2NH)]Pro-Phe-Phe-NH2). Both EM1[psi] and EM2[psi] are partial mu opioid receptor agonists showing significant loss of agonist potency in GPI assay. However, EMs[psi] exhibited potent supraspinal antinociceptive action in vivo. In the mice tail-flick test, EMs[psi] (1, 5, 10 nmol/mouse, i.c.v.) produced potent and short-lasting antinociception in a dose-dependent and naloxone (1 mg/kg) reversed manner. At the highest dose of 10 nmol, the effect of EM2[psi] was prolonged and more significant than that of EM2. In the rat model of formalin injection induced inflammatory pain, EMs[psi] (0.1, 1, 10 nmol/rat, i.c.v.), like EMs, exerted transient but not dose-dependent antinociception. These results suggested that in the mu-selective pocket of EMs, the rigid conformation induced by the peptide bond between Tyr1 and Pro2 is essential to regulate their agonist properties at the mu opioid receptors. However, the increased conformational flexibility induced by the reduced (CH2NH) bond made less influence on their antinociception.

Topics: Amides; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Formaldehyde; Guinea Pigs; Inflammation; Injections, Intraventricular; Male; Mice; Oligopeptides; Oxidation-Reduction; Pain; Pain Measurement; Protein Conformation; Rats; Rats, Wistar; Reaction Time; Receptors, Opioid; Structure-Activity Relationship

Although both pre- and postsynaptic mechanisms have been implicated in the analgesia produced by mu-opioids at the spinal cord, it is not known under what conditions these different controls come into play. Because the mu-opioid receptor (MOR) can be visualized in individual lamina II excitatory interneurons and internalizes into endosomes on ligand binding, we tested whether MOR internalization could be monitored and used to measure postsynaptic MOR signaling. To test whether endogenous opioids modulate these lamina II interneurons during noxious stimulation, we next assessed the magnitude of postsynaptic MOR internalization under a variety of nociceptive conditions. As observed in other systems, we show that MOR internalization in dorsal horn interneurons is demonstrated readily in response to opioid ligands. The MOR internalization is dose-dependent, with a similar dose-response to that observed for opioid-induced increases in potassium conductance. We demonstrate that MOR internalization in lamina II neurons correlates precisely with the extent of analgesia produced by intrathecal DAMGO. These results suggest that MOR internalization provides a good marker of MOR signaling in the spinal cord and that postsynaptic MORs on lamina II interneurons likely participate in the analgesia that is produced by exogenous opioids. We found, however, that noxious stimuli, under normal or inflammatory conditions, did not induce MOR internalization. Thus, endogenous enkephalins and endomorphins, thought to be released during noxious peripheral stimuli, do not modulate nociceptive messages via postsynaptic MORs on lamina II interneurons. We suggest that any endogenous opioids that are released by noxious stimuli target presynaptic MORs or delta-opioid receptors.

Topics: Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Drug Implants; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; In Vitro Techniques; Inflammation; Injections, Spinal; Injections, Subcutaneous; Interneurons; Ligands; Morphine; Narcotics; Oligopeptides; Pain Measurement; Piperidines; Posterior Horn Cells; Potassium; Rats; Receptors, Opioid, mu; Remifentanil; Signal Transduction; Substantia Gelatinosa; Synapses