The opioid receptor triple agonist DPI-125 produces analgesia with less respiratory depression and reduced abuse liability.

Opioid analgesics remain the first choice for the treatment of moderate to severe pain, but they are also notorious for their respiratory depression and addictive effects. This study focused on the pharmacology of a novel opioid receptor mixed agonist DPI-125 and attempted to elucidate the relationship between the δ-, µ- and κ-receptor potency ratio and respiratory depression and abuse liability. Five diarylmethylpiperazine compounds (DPI-125, DPI-3290, DPI-130, KUST202 and KUST13T02) were selected for this study. PKA fluorescence redistribution assays in CHO cells individually expressing δ-, µ- or κ-receptors were used to measure the agonist potency. The respiratory safety profiles were estimated in rats by the ratio of ED50 (pCO2 increase)/ED50 (antinociception). The abuse liability of DPI-125 was evaluated with a self-administration model in rhesus monkeys. The observed agonist potencies of DPI-125 for δ-, µ- and κ-opioid receptors were 4.29±0.36, 11.10±3.04, and 16.57±4.14 nmol/L, respectively. The other four compounds were also mixed agonists with varying potencies. DPI-125 exhibited a high respiratory safety profile, clearly related to its high δ-receptor potency. The ratio of the EC50 potencies for the µ- and δ-receptors was found to be positively correlated with the respiratory safety ratio. DPI-125 has similar potencies for µ- and κ-receptors, which is likely the reason for its reduced abuse potential. Our results demonstrate that the opioid receptor mixed agonist DPI-125 is safer and less addictive than traditional µ-agonist analgesics. These findings suggest that the development of δ>µâˆ¼κ opioid receptor mixed agonists is feasible, and such compounds could represent a promising class of potent analgesics with wider therapeutic windows.

Mas-related G protein-coupled receptor D is coupled to endogenous calcium-activated chloride channel in Xenopusoocytes

Mas-related G protein-coupled receptor D (MrgD) is expressed almost exclusively in nociceptive primary sensory neurons and the neurons located in stratum granulosum of skin. More and more evidence suggest that MrgD plays an important role in pain sensation and/or transduction. Recent studies have demonstrated that the receptor is also involved in itch sensation in both mouse and human. In the present study, we identified a robust inward current in MrgD-expressing Xenopusoocytes by using â-alanine, a putative ligand of MrgD. The currents were sensitive to inhibitor of Ca2+-activated chloride channels (CaCCs) and intracellular Ca2+ chelator, suggesting they were produced by endogenous CaCCs. Furthermore, it was demonstrated that upon the application of phospholipase C (PLC) inhibitor, or antisense oligonucleotides of inositol trisphosphate receptor (IP3R), the â-alanine-induced currents were dramatically depressed. However, protein kinase C inhibitor did not display any visible effect on CaCC currents. In summary, our data suggest that the activation of MrgD promotes the open of endogenous CaCCs via Gq-PLC-IP3-Ca2+ pathway. The current findings reveal the functional coupling between MrgD and CaCCs in Xenopus oocytes and also provide a facile model to assay the activity of MrgD

Multiple mechanisms underlying the long duration of action of thienorphine, a novel partial opioid agonist for the treatment of addiction.

AIMS: It is considered that a long-acting therapy would be advantageous in the treatment of addiction. In a search for novel buprenorphine analogues, thienorphine was demonstrated to be an extremely long-acting orally active partial opioid agonist. This study explored the mechanisms underlying the long-lasting effects of thienorphine. METHODS: The binding kinetics of [(3) H]thienorphine were measured in membrane preparations expressing cloned rat opioid receptors. Flow cytometric analysis was used to determine the effect of thienorphine on the surface opioid receptor number. The long-lasting effects of thienorphine were also confirmed at the tissue level and in vivo. RESULTS: At 37°C, [(3) H]thienorphine showed rapid association with µ- and κ-opioid receptors, while its dissociation was sluggish and biphasic (K-1 = 0.21 min(-1) , K-2 = 0.0078 min(-1) for the µ-receptor; K-1 = 0.17 min(-1) , K-2 = 0.0042 min(-1) for the κ-receptor). Treatment with thienorphine for 24, 48, and 72 h downregulated surface µ-receptor in a dose- and time-dependent manner. The inhibitory effect of thienorphine on guinea pig ileum persisted for more than 120 min after prolonged washing. In vivo, thienorphine exhibited significant antagonism of morphine-induced antinociception for more than 7 days. CONCLUSIONS: These results indicate that multiple factors, including persistent receptor occupation and enhanced receptor downregulation, may contribute to the long-lasting effects of thienorphine that would be beneficial for its application in addiction treatment.

Mas-related G protein-coupled receptor D is coupled to endogenous calcium-activated chloride channel in Xenopus oocytes.

Mas-related G protein-coupled receptor D (MrgD) is expressed almost exclusively in nociceptive primary sensory neurons and the neurons located in stratum granulosum of skin. More and more evidence suggest that MrgD plays an important role in pain sensation and/or transduction. Recent studies have demonstrated that the receptor is also involved in itch sensation in both mouse and human. In the present study, we identified a robust inward current in MrgD-expressing Xenopus oocytes by using ß-alanine, a putative ligand of MrgD. The currents were sensitive to inhibitor of Ca(2+)-activated chloride channels (CaCCs) and intracellular Ca(2+) chelator, suggesting they were produced by endogenous CaCCs. Furthermore, it was demonstrated that upon the application of phospholipase C (PLC) inhibitor, or antisense oligonucleotides of inositol trisphosphate receptor (IP3R), the ß-alanine-induced currents were dramatically depressed. However, protein kinase C inhibitor did not display any visible effect on CaCC currents. In summary, our data suggest that the activation of MrgD promotes the open of endogenous CaCCs via G(q)-PLC-IP3-Ca(2+) pathway. The current findings reveal the functional coupling between MrgD and CaCCs in Xenopus oocytes and also provide a facile model to assay the activity of MrgD.

Effect of thienorphine on intestinal transit and isolated guinea-pig ileum contraction.

AIM: To evaluate the effect of thienorphine on small intestinal transit in vivo and on guinea-pig ileum (GPI) contraction in vitro. METHODS: The effects of thienorphine on intestinal transit were examined in mice and in isolated GPI. Buprenorphine and morphine served as controls. The distance traveled by the head of the charchol and the total length of the intestine were measured in vivo. Gastrointestinal transit was expressed as a percentage of the distance traveled by the head of the marker relative to the total length of the small intestine. The isolated GPI preparations were connected to an isotonic force transducer and equilibrated for at least 1 h before exposure to drugs. Acetylcholine was used for muscle stimulation. RESULTS: Thienorphine (0.005-1.0 mg/kg, ig) or buprenorphine (0.005-1.0 mg/kg, sc) dose-dependently significantly inhibited gut transit compared with saline. Thienorphine inhibited gut transit less than buprenorphine. The maximum inhibition by thienorphine on the intestinal transit was 50%-60%, whereas the maximum inhibition by morphine on gut transit was about 100%. Thienorphine also exhibited less inhibition on acetylcholine-induced contraction of GPI, with a maximum inhibition of 65%, compared with 93% inhibition by buprenorphine and 100% inhibition by morphine. Thienorphine induced a concentration-dependent decrease in the basal tonus of spontaneous movement of the GPI, the effect of which was weaker than that with buprenorphine. The duration of the effect of thienorphine on the GPI was longer than that with buprenorphine. CONCLUSION: Thienorphine had less influence, but a longer duration of action on GPI contraction and moderately inhibited intestinal transit.

[Construction of the recombinant plasmid of pcDNA3.0-RKIP and expression in PC12 cells].

AIM: To construct the eukaryotic expression vectors of RKIP plasmid and detect its expression in PC12 cells. METHODS: The coding sequence of RKIP was generated by nested-PCR using total RNA extracted from the root ganglion neurons of rats. RKIP gene was cloned into the eukaryotic expression vector pcDNA3.0. After restriction enzyme analysis and sequence identification, the recombinant plasmid was transfected into PC12 cells with non-liposome mediated method by Vigofect. The expression of RKIP was detected by Western blot. RESULTS: The results of enzyme analysis and sequencing both identified DNA sequence of recombinant plasmid pcDNA3.0-RKIP correctly. The expression of RKIP increased obviously after transfection into PC12 cells. CONCLUSION: The eukaryotic expression plasmid of pcDNA3.0-RKIP was constructed successfully and it can be sustainly expressed in PC12 cells. This provides experimental basis for further study on the neurological function of RKIP.

Spinal antinociception of synthetic omega-conotoxin SO-3, a selective N-type neuronal voltage-sensitive calcium channel blocker, and its effects on morphine analgesia in chemical stimulus tests in rodent.

SO-3, a novel Omega-superfamily conotoxin derived from Conus striatus, selectively inhibits N-type neuronal voltage-sensitive calcium channels. In current study, antinociception of SO-3 compared with MVIIA or morphine and its effects on morphine analgesia were investigated in rodent chemical stimulus tests after acute or repeated intrathecal administration. In mice acetic acid writhing test, similar to MVIIA, SO-3 caused dose- and time-dependent spinal antinociception with ED(50) of 0.25 microg/kg and t(1/2) of 4h, which was more potent and longer-acting than morphine. In rat formalin test after intrathecal bolus injection, SO-3 produced dose- and time-dependent antinociception by suppressing acute (ED(50), 1.79 microg/kg) and tonic phases (ED(50), 0.41 microg/kg), which was similar to MVIIA and approximately 10-fold potency and twice longer-acting of morphine in blocking tonic phase responses. After repeated intrathecal injections twice daily for 5 consecutive days, SO-3 produced analgesia without loss of potency whereas morphine produced analgesia tolerance in rat formalin test; further, SO-3 still produced potent analgesia in morphine-tolerant rats. SO-3 co-administered with morphine left-shift the dose-response curve of morphine in mice acetic acid writhing test and significantly potentiated morphine analgesia in rat formalin test. No changes in motor function were seen in mice or rats receiving antinociceptive doses of SO-3 whereas MVIIA caused motor dysfunction at doses of 1.0-2.0 microg/kg in rats. This study showed that (1) novel SO-3 produced potent and long-acting spinal antinociception without observable motor dysfunction, (2) SO-3 significantly potentiated morphine analgesia, (3) After repeated intrathecal administration, SO-3 produced neither tolerance nor cross-tolerance to morphine analgesia.

Levo-tetrahydropalmatine attenuates oxycodone-induced conditioned place preference in rats.

Levo-tetrahydropalmatine (l-THP) is an alkaloid purified from the Chinese herb corydalis and stephania and is contained in many traditional Chinese herbal preparations. Our previous studies demonstrated the ability of l-THP to inhibit locomotor stimulation and physical dependence induced by oxycodone in mice and rats. The present study was designed to evaluate effects of l-THP on reward of oxycodone using conditioned place preference assay. Oxycodone (0.32-5.0 mg/kg) induced the development of conditioned place preference in rats. Furthermore, oxycodone (2.5 mg/kg) induced the increased phosphorylation of CREB and ERK in nucleus accumbens and hippocampus, but not in prefrontal cortex. l-THP (6.25-18.50 mg/kg) per se was not able to induce conditioned place preference or conditioned place aversion. l-THP co-administered with oxycodone during the conditioning sessions partly abolished the development of oxycodone-induced conditioned place preference in rats. Furthermore, l-THP inhibited the increased phosphorylation of ERK and CREB in nucleus accumbens and hippocampus of rats. All these results suggest that l-THP can inhibit oxycodone-induced psychological dependence by affecting phosphorylation of CREB and ERK in nucleus accumbens and hippocampus of rats. Together, the present data, combined with previous finding, support the potential use of l-THP for treatment of oxycodone addiction.

[Synthesis and antinociceptive activity of seselin derivatives].

Natural product seselin and related derivatives with an angular pyranocoumarin skeleton were synthesized from 8-acetyl-7-hydroxycoumarins by condensation with acetone, reduction, and dehydration successively under mild conditions with total yield of > 50%. Twelve seselin derivatives were tested by the writhing response assay induced by acetic acid at a dose of 40 mg x kg(-1). Seselin (4a) and 4,8,8-trimethyl-9,9-dihydro-pyran[2,3-f] chromene-2,10-dione (2b) showed obviously antinociceptive activity with inhibitory effect of 85% and 50%, respectively, more or quite potent than aspirin in the same assay, suggesting that seselin derivatives could be a novel kind of potential antinociceptive agents.