The use of opioid analgesics has a long history in clinical settings, although the functions of opioid receptors, especially their role in the brain, are not well understood yet. Recent studies have generated abundant new data on opioid receptor-mediated functions and the underlying mechanisms. The most exciting finding in the past decade is probably the neuroprotection against hypoxic/ischemic stress mediated by delta-opioid receptors (DOR). An up-regulation of DOR expression and the release of endogenous opioids may increase neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers, depending on stress duration and severity, different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of ionic homeostasis, an increase in pro-survival signaling (e.g., PKC-ERK-Bcl 2) and the enhanced anti-oxidative capacity. Recent data on DOR-mediated neuroprotection provide us a new concept of neuroprotection against neurological disorders and have a potentially significant impact on the prevention and treatment of some serious neurological conditions, such as stroke.
Analgesics, Opioid ; pharmacology ; Humans ; Hypoxia ; metabolism ; Neurons ; metabolism ; Neuroprotective Agents ; pharmacology ; Receptors, Opioid, delta ; metabolism ; Signal Transduction

A series of aralkyl-ketone-4-piperidol derivatives were synthesized and tested for their analgesic activities. All of the novel 30 compounds were prepared from 4-piperidone and alpha-halo-aralkyl-ketone through five steps, including Boc protection, nucleophilic addition in presence of CeCl3/NaI catalyst, deprotection, condensation and salification. Their structures were confirmed by 1H NMR and HRMS. Preliminary in vivo pharmacological trials showed that most of the synthesized compounds revealed analgesic effects. Among the tested compounds, 8, 13 and 22 exhibited potent analgesic activities in both mice writhing and mice hot plate model. The three compounds have low affinity for mu, delta, kappa receptors, which is a chance to find a better precursor of non-opioid analgesic for further optimization.
Analgesics, Non-Narcotic ; chemical synthesis ; chemistry ; pharmacology ; Animals ; Mice ; Molecular Structure ; Pain Measurement ; Pain Threshold ; drug effects ; Piperidones ; chemical synthesis ; chemistry ; pharmacology ; Receptors, Opioid, delta ; metabolism ; Receptors, Opioid, kappa ; metabolism ; Receptors, Opioid, mu ; metabolism ; Structure-Activity Relationship

BACKGROUND: WIN55212-2 is a synthetic cannabinoid agonist and selective to cannabinoid 1 (CB1) receptors, which are distributed mainly in the central nervous system. Opioid receptors and CB1 receptors have several similarities in terms of their intracellular signal transduction mechanisms, distributions, and pharmacological action. Several studies have therefore sought to describe the functional interactions between opioids and cannabinoids at the cellular and behavioral levels. The present study investigated agonist-stimulated [35S]GTPgammaS binding by WIN55212-2 in rat brain membranes and determined the antagonism by selective opioid antagonists at the level of receptor-ligand interaction and intracellular signal transduction. METHODS: Sprague-Dawley rats (male, n = 20) were euthanized for the preparation of brain membranes. In agonist-stimulated [35S]GTPgammaS binding by WIN55212-2, the values of EC50 and maximum stimulation (% over basal) were determined in the absence or presence of the micro, kappa and delta opioid receptor antagonists naloxone (20 nM), norbinaltorphimine (3 nM), and naltrindole (3 nM), respectively. Ke values for opioid antagonist inhibition in the absence or presence of each opioid receptor antagonist were calculated using the following equation: [nanomolar antagonist] / (dose ratio of EC50 - 1). RESULTS: In WIN55212-2-stimulated [35S]GTPgammaS binding in the rat brain membranes, the values of EC50 and maximum stimulation (% over basal) were 154 +/- 39.5 nM and 27.6 +/- 5.3% over basal, respectively. Addition of selective opioid antagonists did not produce a significant rightward shift in the WIN55212-2 concentration-response curve, and Ke values were not applicable. CONCLUSIONS: Our results suggest that the functional activity of WIN55212-2-stimulated [35S]GTPgammaS binding was not affected by opioid antagonists in the rat brain membranes. Although the exact mechanism remains unclear, our results may partially elucidate their actions.
Analgesics, Opioid ; Animals ; Benzoxazines ; Brain ; Cannabinoids ; Central Nervous System ; Membranes ; Morpholines ; Naloxone ; Naltrexone ; Naphthalenes ; Narcotic Antagonists ; Rats ; Rats, Sprague-Dawley ; Receptor, Cannabinoid, CB1 ; Receptors, Opioid ; Receptors, Opioid, delta ; Signal Transduction

BACKGROUNDPreconditioning with repeated electroacupuncture (EA) could mimic ischemic preconditioning to induce cerebral ischemic tolerance in rats. The present study was designed to investigate whether mu (micro)-, delta (delta)- or kappa (kappa)-opioid receptors are involved in the neuroprotection induced by repeated EA preconditioning.

METHODSThe rats were pretreated with naltrindole (NTI), nor-binaltorphimine (nor-BNI) or D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), which is a highly selective delta-, kappa- or micro-opioid receptor antagonist respectively, before each EA preconditioning (30 minutes per day, 5 days). Twenty-four hours after the last EA treatment, the middle cerebral artery occlusion (MCAO) was induced for 120 minutes. The brain infarct volume was determined with 2, 3, 5-triphenyltetrazolium chloride staining at 24 hours after MCAO and compared with that in rats which only received EA preconditioning. In another experiment, the met-enkephalin-like immunoreactivity in rat brain was investigated by immunohistochemistry in both EA preconditioning and control rats.

RESULTSThe EA preconditioning reduced brain infarct volume compared with the control rats (P = 0.000). Administration of both NTI and CTOP attenuated the brain infarct volume reduction induced by EA preconditioning, presenting with larger infarct volume than that in the EA preconditioning rats (P < 0.001). But nor-BNI administration did not block the infarct volume reduction induced by EA preconditioning, presenting with smaller infarct volume than the control group rats (P = 0.000). The number of met-enkephalin-like immunoreactivity positive neurons in the EA preconditioning rats was more than that of the control rats (P = 0.000).

CONCLUSIONRepeated EA preconditioning stimulates the release of enkephalins, which may bind delta- and micro-opioid receptors to induce the tolerance against focal cerebral ischemia.

Animals ; Brain Ischemia ; prevention & control ; Electroacupuncture ; Enkephalin, Methionine ; analysis ; Immunohistochemistry ; Ischemic Preconditioning ; Male ; Naltrexone ; analogs & derivatives ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; physiology ; Receptors, Opioid, mu ; physiology ; Somatostatin ; analogs & derivatives ; pharmacology

AIMTo design and synthesize new chiral 8-(substituted) amino-analogues of 3-[(tetrahydro-2-furanyl)methyl] benzomorphans, to expand knowledge of the structure-activity relationship (SAR) for 8-aminobenzomorphan.

METHODSTarget compounds were synthesized from the 8-triflate of the optically active 3-[(tetrahydro-2-furanyl)methyl]-2,6-methano-benzomorphans using Pd-catalyzed aminations. Opioid receptor binding experiments were performed to evaluate their biological activities.

RESULTSBoth 8-amino and 8-phenylamino analogues showed lower binding affinity for mu, delta and kappa receptors than corresponding 8-hydroxy-3-[(tetrahydro-2-furanyl)methyl]-2,6-methano-benzomorphan in vitro.

CONCLUSIONThe relative poor binding affinity of the target compounds did not warrant conducting the in vivo studies to determine if they have the profile(kappa agonist/mu antagonist) that will be potentially useful in the treatment of drug addiction. Further study is in progress.

Animals ; Benzomorphans ; chemical synthesis ; chemistry ; pharmacology ; Brain ; metabolism ; Furans ; chemical synthesis ; chemistry ; pharmacology ; Guinea Pigs ; Molecular Structure ; Narcotic Antagonists ; chemical synthesis ; chemistry ; pharmacology ; Radioligand Assay ; Receptors, Opioid ; metabolism ; Receptors, Opioid, delta ; metabolism ; Receptors, Opioid, kappa ; metabolism ; Receptors, Opioid, mu ; metabolism ; Structure-Activity Relationship

AIMTo investigate the effect of 8-opioid receptors in the cardioprotection elicited by ischemic postconditioning and the underlying mechanism.

METHODSThe isolated perfused hearts of male Sprague-Dawley rats were subjected to 30 min of global ischemia followed by 120 min of reperfusion. Formazan content of myocardium was measured spectrophotometrically, and the activity of lactate dehydrogenase (LDH) in the coronary effluent was measured. In isolated ventricular myocytes hypoxic postconditioning was achieved by 3 cycles of 5 min reoxygenation/5 min hypoxia starting at the beginning of reoxygenation, and cell viability was measured.

RESULTSIn the Langendorff perfused rat heart model, ischemic postconditioning (6 cycles of 10 s reperfusion/10 s global ischemia starting at the beginning of reperfusion) increased formazan content, reduced LDH release, improved the recovery of the left ventricular developed pressure, maximal rise/fall rate of left ventricular pressure and rate pressure product (left ventricular developed pressure multiplied by heart rate), attenuated the decrease of coronary flow during reperfusion and increased the isolated cell viability. Pretreatment with naltrindole, an antagonist of delta-opioid receptors and calcium-activated potassium channel (KCa) blocker paxilline attenuated the effect of ischemic/hypoxic postconditioning.

CONCLUSIONThe findings indicate that ischemic postconditioning protects myocardium against ischemia/reperfusion injury via activating delta-opioid receptors and opening KCa.

Animals ; Cell Survival ; In Vitro Techniques ; Ischemic Postconditioning ; Male ; Myocardium ; metabolism ; Myocytes, Cardiac ; cytology ; metabolism ; Potassium Channels, Calcium-Activated ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; antagonists & inhibitors

OBJECTIVETo construct the delta-pIRES2-EGFP plasmid and investigate its expression in HEK293 cells.

METHODSFull length cDNA of rat delta opioid receptor gene amplified from rat brain tissues using reverse transcription and nested PCR was cloned into pMD20 T vector. The delta cDNA was inserted into pIRES2-EGFP plasmid to construct the recombinant eukaryotic plasmid delta-pIRES2-EGFP, which was transfected into HEK293 cells via Lipofectamine2000. The expression of delta was examined under fluorescence microscope.

RESULTSThe recombinant delta-pIRES2-EGFP plasmid was successfully constructed, and high expression of delta was detected in HEK293 cells transfected by the plasmid.

CONCLUSIONdelta-pIRES2-EGFP has been successfully cloned, which shows high expression of delta in HEK293 cells.

Animals ; DNA, Complementary ; genetics ; Gene Expression ; Genetic Vectors ; Green Fluorescent Proteins ; biosynthesis ; genetics ; HEK293 Cells ; Humans ; Plasmids ; Polymerase Chain Reaction ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; genetics ; Recombinant Fusion Proteins ; biosynthesis ; genetics ; Transfection

This study was aimed to investigate the role of the delta-opioid receptor (DOR)-β-arrestin1-Bcl-2 signal transduction pathway in the pathogenesis of ulcerative colitis (UC) and the intervention effects of oxymatrine on UC. Forty Sprague-Dawley rats were divided into normal group, model group, oxymatrine-treated group and mesalazine-treated group (n=10 each) at random. The rat UC model was established by intra-colonic injection of trinitrobenzene sulfonic acid in the model group and two treatment groups. The rats in oxymatrine-treated group were subjected to intramuscular injection of oxymatrine [63 mg/(kg·day)] for 15 days, and those in mesalazine-treated group given mesalazine solution [0.5 g/(kg·day)] by gastric lavage for the same days. Animals in normal group and model group were administered 3 mL water by gastric lavage for 15 days. On the 16th day, after fasting for 24 h, the rats were sacrificed for the removal of colon tissues. The expression levels of DOR, β-arrestin1 and Bcl-2 were determined in colon tissues by immunohistochemistry and real-time quantitative polymerase chain reaction (RT-PCR), respectively. It was found that the expression levels of DOR, β-arrestin1 and Bcl-2 protein and mRNA were significantly increased in the model group as compared with the other groups (P<0.05). They were conspicuously decreased in both mesalazine-treated and oxymatrine-treated groups in contrast to the model group (P<0.05). No statistically significant difference was noted in these indices between mesalazine- and oxymatrinetreated groups (P>0.05). This study indicated that the DOR-β-arrestin1-Bcl-2 signal transduction pathway may participate in the pathogenesis of UC. Moreover, oxymatrine can attenuate the development of UC by regulating the DOR-β-arrestin1-Bcl-2 signal transduction pathway.
Alkaloids ; pharmacology ; Animals ; Anti-Arrhythmia Agents ; pharmacology ; Arrestins ; metabolism ; Colitis, Ulcerative ; metabolism ; pathology ; prevention & control ; Male ; Proto-Oncogene Proteins c-bcl-2 ; metabolism ; Quinolizines ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; metabolism ; Signal Transduction ; drug effects ; beta-Arrestins

This work was performed to determine the role of delta-opioid receptor (DOR) in protection against acute ischemia/reperfusion injury. Transient (1 h) focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). DOR agonist TAN-67 (30 nmol, 60 nmol, 200 nmol), DOR antagonist naltrindole (20 nmol, 50 nmol, 100 nmol) or artificial cerebral spinal fluid (aCSF) was injected respectively into the lateral cerebroventricle of the rat 30 min before the induction of brain ischemia. Neurological deficits were assessed by the five-grade system (Longa's methods). The brain infarct was measured by cresyl violet (CV) staining and infarct volume was analyzed by an image processing and analysis system. The expression of DOR was detected by Western blot. The results showed that 60 nmol TAN-67 significantly reduced the infarct volume (P<0.05), attenuated neurological deficits (P<0.05) and tended to increase the expression of about 60 kDa DOR protein (P>0.05), while 100 nmol naltrindole aggravated ischemic damage and decreased about 60 kDa DOR protein expression (P<0.05). These results suggest that DOR activation protects the brain against acute ischemia/reperfusion injury in rat.
Animals ; Brain ; pathology ; Brain Ischemia ; drug therapy ; Infarction, Middle Cerebral Artery ; Injections, Intraventricular ; Naltrexone ; analogs & derivatives ; pharmacology ; Quinolines ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Opioid, delta ; agonists ; Reperfusion Injury

In the present study, whole-cell patch-clamp technique was used to observe the effects of SNC162, a selective agonist of &delta;-opioid receptors, on L-type Ca(2+) current (I(Ca-L)) and transient outward K(+) current (I(to)) in rat ventricular myocytes. The results showed that SNC162 significantly inhibited I(Ca-L) and I(to) in rat ventricular myocytes. The maximal inhibition rate of I(Ca-L) and I(to) reached (46.13±4.12)% and (36.53±10.57)%, respectively. SNC162 at 1×10(-4) mol/L inhibited the current density of I(Ca-L) from (8.98±0.40) pA/pF to (4.84±0.44) pA/pF (P<0.01, n=5) and inhibited that of I(to) from (18.69±2.42) pA/pF to (11.73±1.67) pA/pF (P<0.01, n=5). Furthermore, the effects of naltrindole, a highly selective antagonist of &delta;-opioid receptors, on I(Ca-L) and I(to) were also observed. The results showed that naltrindole alone had no effects on I(Ca-L) and I(to), while it abolished the inhibitory effects of SNC162 on I(Ca-L) and I(to). In conclusion, SNC162 concentration-dependently inhibited I(Ca-L) and I(to) in rat ventricular myocytes via activation of the &delta;-opioid receptors, which may be a fundamental mechanism underlying the antiarrhythmic effect of activating &delta;-opioid receptors.
Animals ; Anti-Arrhythmia Agents ; Benzamides ; pharmacology ; Calcium Channels, L-Type ; metabolism ; Cells, Cultured ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; drug effects ; metabolism ; Naltrexone ; analogs & derivatives ; pharmacology ; Patch-Clamp Techniques ; Piperazines ; pharmacology ; Potassium Channels ; metabolism ; Rats ; Receptors, Opioid, delta ; agonists