endomorphin-2 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

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

We examined the analgesic properties of endomorphin-2 expressed in DRG neurons transduced with a non-replicating herpes simplex virus (HSV)-based vector containing a synthetic endomorphin-2 gene construct. HSV-mediated endomorphin-2 expression reduced nocisponsive behaviors in response to mechanical and thermal stimuli after injection of complete Freund's adjuvant (CFA) into the paw, and reduced peripheral inflammation measured by paw swelling after injection of CFA. The analgesic effect of the vector was blocked by either intraperitoneal or intrathecal administration of naloxone methiodide, blocking peripheral and central mu opioid receptors, respectively. Endomorphin-2 vector injection also reduced spontaneous pain-related behaviors in the delayed phase of the formalin test and in both CFA and formalin models suppressed spinal c-fos expression. The magnitude of the vector-mediated analgesic effect on the delayed phase of the formalin test was similar in naïve animals and in animals with opiate tolerance induced by twice daily treatment with morphine, suggesting that there was no cross-tolerance between vector-mediated endomorphin-2 and morphine. These results suggest that transgene-mediated expression of endomorphin-2 in transduced DRG neurons in vivo acts both peripherally and centrally through mu opioid receptors to reduce pain perception.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Drug Tolerance; Ganglia, Spinal; Genetic Therapy; Genetic Vectors; Inflammation; Inflammation Mediators; Male; Narcotic Antagonists; Nociceptors; Oligopeptides; Pain; Pain Management; Pain Measurement; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Sensory Receptor Cells; Transgenes

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

In this study, we evaluated the effects of intrathecally administered agonists of mu- and delta-opioid receptor and their analogs on the pain-induced behavior and expression of c-Fos immunoreactivity in the spinal cord, elicited by intraplantar injection of 12% formalin to the hindpaw of the rat. Previous report from our laboratory and other author's study indicated that intrathecal administration of mu agonists morphine and endomorphin-2 and delta-opioid agonist deltorphin II produced a dose-dependent antinociceptive effects in acute and inflammatory pain. In this study, intrathecal injection of morphine (10 microg), endomorphin-2 (5 microg) and its analog Dmt-endomorphin-2 (10 microg) significantly decreased the formalin-induced pain behavior, and lowered a number of c-Fos positive neurons in the laminae I, II and III of the spinal cord by about 40%, 30% and 40%, respectively. Significant reduction of formalin-induced behavioral responses was also observed after i.th. administration of deltorphin II (15 microg) and its analog ile-deltorphin II (15 microg). Agonists of delta-opioid receptor significantly reduced a number of c-Fos positive neurons by about 28% and 40%, respectively. Analog of endomorphin-2 and analog of deltorphin II suppressed more potently expression of c-Fos in the dorsal horn of the spinal cord than the parent peptides. Our study indicates that new analogs of mu- and delta-opioid receptor exhibit strong antinociceptive potency similar or even higher than the parent peptides, and that their effect is positively correlated with the inhibition of c-Fos expression.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Dose-Response Relationship, Drug; Formaldehyde; Inflammation; Male; Morphine; Nociceptors; Oligopeptides; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Receptors, Opioid, delta; Receptors, Opioid, mu; Spinal Cord; Time Factors

Endomorphin-2, a newly discovered endogenous opioid peptide and agonist at the mu-opioid receptor, was injected intrathecally in normal rats and animals with unilateral peripheral inflammation or sciatic nerve section and its effect on the nociceptive flexor reflex was analysed. In normal rats, intrathecal endomorphin-2 induced a strong and dose-dependent depression of the reflex, which was naloxone-reversible. The effect of intrathecal endomorphin-2 was fairly brief, lasting for about 20-30 min at the highest dose, 4 microg. The effect of endomorphin-2 in inflamed rats was not significantly different from that in normals. After nerve section some rats developed autotomy behavior. In these rats endomorphin-2 had significantly reduced effect. However, the reflex depressive effect of intrathecal endomorphin-2 was unchanged in axotomized rats without autotomy. It is suggested that intrathecal endomorphin-2 has antinociceptive effect in the rat spinal cord under normal and inflammatory conditions. After peripheral nerve injury the sensitivity to endmorphin-2 may be reduced in rats that exhibit ongoing neuropathic pain-like behaviors.

Topics: Analgesics, Opioid; Animals; Axotomy; Carrageenan; Female; Inflammation; Injections, Spinal; Nociceptors; Oligopeptides; Pain; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley; Reflex; Sciatic Nerve; Self Mutilation; Spinal Cord