Delta-opioid Agonist Research Articles

Maternal treatment with a selective delta-opioid receptor agonist during gestation has a sex-specific pro-cognitive action in offspring: mechanisms involved.

Background: There is growing evidence that the treatment of several mental disorders can potentially benefit from activation of delta-opioid receptors. In the future, delta-agonists with a safe pharmacological profile can be used for the treatment of mood disorders in pregnant women. However, the data on prenatal exposure to delta-opioid agonists are missing. The present study is aimed to test the hypothesis that the activation of delta-opioid receptors during gravidity has positive effects on the behaviour accompanied by changes in glutamate and monoamine neurotransmission. Methods: Gestating Wistar rats were chronically treated with a selective delta-agonist SNC80 or vehicle. Adult male and female offspring underwent novel object recognition (for the assessment of cognition) and open field (for the assessment of anxiety and habituation) tests, followed by in vivo electrophysiological examination of the activity of hippocampal glutamate and midbrain serotonin (5-HT) and dopamine neurons. Results: We found that the maternal treatment with SNC80 did not affect the offspring's anxiety, habituation, and 5-HT neuronal firing activity. Female offspring of SNC80-treated dams exhibited improved novelty recognition associated with decreased firing rate and burst activity of glutamate and dopamine neurons. Conclusion: Maternal treatment with delta-opioid agonists during gestation may have a pro-cognitive effect on offspring without any negative effects on anxiety and habituation. The putative pro-cognitive effect might be mediated via mechanism(s) involving the firing activity of hippocampal glutamate and mesolimbic dopamine neurons.

Identification of 1,3,8-Triazaspiro[4.5]Decane-2,4-Dione Derivatives as a Novel δ Opioid Receptor-Selective Agonist Chemotype.

δ opioid receptors (DORs) hold potential as a target for neurologic and psychiatric disorders, yet no DOR agonist has proven efficacious in critical phase II clinical trials. The exact reasons for the failure to produce quality drug candidates for the DOR are unclear. However, it is known that certain DOR agonists can induce seizures and exhibit tachyphylaxis. Several studies have suggested that those adverse effects are more prevalent in delta agonists that share the (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80)/4-[(αR*)-α-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl]-N,N-diethylbenzamide chemotype. There is a need to find novel lead candidates for drug development that have improved pharmacological properties to differentiate them from the current failed delta agonists. Our objective in this study was to identify novel DOR agonists. We used a β-arrestin assay to screen a small G-protein coupled receptors (GPCR)-focused chemical library. We identified a novel chemotype of DOR agonists that appears to bind to the orthosteric site based of docking and molecular dynamic simulation. The most potent agonist hit compound is selective for the DOR over a panel of 167 other GPCRs, is slightly biased toward G-protein signaling and has anti-allodynic efficacy in a complete Freund's adjuvant model of inflammatory pain in C57BL/6 male and female mice. The newly discovered chemotype contrasts with molecules like SNC80 that are highly efficacious β-arrestin recruiters and may suggest this novel class of DOR agonists could be expanded on to develop a clinical candidate drug. SIGNIFICANCE STATEMENT: δ opioid receptors are a clinical target for various neurological disorders, including migraine and chronic pain. Many of the clinically tested delta opioid agonists share a single chemotype, which carries risks during drug development. Through a small-scale high-throughput screening assay, this study identified a novel δ opioid receptor agonist chemotype, which may serve as alternative for the current analgesic clinical candidates.

P-209 Implication of delta opioid receptor in the in vitro maturation of oocytes and its effects on subsequent fertilization and embryo development in mice

Abstract Study question Could opiods modulate in vitro maturation of oocyte and improve fertilization rates? Summary answer Delta opioid receptor was present in mice oocytes, changing its expression pattern depending on the maturation stage and helping oocytes to reach blastocyst stage. What is known already The molecular mechanisms responsible for oocyte maturation are not completely understood and different molecules have been reported to be implicated as modulators of this process. The endogenous opioid peptides could be interesting candidates because they are involved in the regulation of reproductive physiology at multiple sites. When those receptors are activated, the adenylyl cyclase is inhibited, thus reducing cyclic AMP and blocking PKA. Moreover, opioids are also able to activate proteins involved in maturation. There is evidence suggesting a role for opioids during oocyte maturation because the signaling exerted by opioids is similar to that necessary for the meiosis resumption. Study design, size, duration Immature cumulus–oocyte complexes (COCs) from female 8 to 10 week old WT (C57BL/6xCBA) were retrieved after EGF stimulation. Mouse in vitro maturation culture was performed. In vitro grown oocytes, their corresponding cumulus (CC) and granulosa cells (GC) were classified at germinal vesicle stage (GV), at metaphase 1 (MI) and at metaphase 2 (MII). Participants/materials, setting, methods The presence of DOR was analysed in granulosa cells and oocytes at each stage of maturation by qRT-PCR and immunocytochemistry. AKT and MAPK signalling pathway (ERK 1/2) was studied by immunocytochemistry. Similarly, COCs were matured in vitro in the absence and presence of DPDPE and naltrindole at various concentrations. After IVM, in vitro fertilisation (IVF) was performed and development was observed until the blastocyst stage was reached, analysing fertilisation and embryo production percentages (p < 0.05). Main results and the role of chance Our findings showed that OPRD1 was present in mice oocytes and granulosa cells, changing its expression pattern depending on the maturation stage. The evaluation of RT-PCR examination and immunohistochemical (IHC) staining revealed the presence of the transcript for Oprd1 gene in the different stages of the mouse oocyte's maturation, as well as in the granulosa cells at the moment of the extraction from the ovary. The obtained transcript was compared with the transcript for Oprd1 of mouse cerebral cortex as a positive control. The expected 482 bp fragment was detected in the germinal vesicle stage and in granulosa cells, whereas in MI and MII stage the signal was lower. Immunofluorescence analysis revealed that OPRD1 protein was present in mouse oocytes but, its localization differed at the different stages of the maturation process. Furthermore, the selective delta opioid agonist DPDPE, modulating PI3K/Akt and MAPK pathways, helped oocytes to reach blastocyst stage. Finally, we examined that the observed effect of DPDPE during oocyte maturation in the in vitro fertilization and subsequent embryo development could be blocked by the opioid antagonist naltrindole. Limitations, reasons for caution Although we have obtained higher rates of blastocysts, the quality of these embryos still needs to be analysed and transferred to recipient females to evaluate the offspring. Wider implications of the findings Our study has clinical implications for the improvement of oocyte in vitro maturation techniques (IVM). OPRD1 could be a possible therapeutic target for in vitro maturation culture medium, as it could improve the blastocyst rates obtained in the actual reproduction assisted techniques. Trial registration number not applicable

Antinociceptive Effects of Aaptamine, a Sponge Component, on Peripheral Neuropathy in Rats

Aaptamine, a natural marine compound isolated from the sea sponge, has various biological activities, including delta-opioid agonist properties. However, the effects of aaptamine in neuropathic pain remain unclear. In the present study, we used a chronic constriction injury (CCI)-induced peripheral neuropathic rat model to explore the analgesic effects of intrathecal aaptamine administration. We also investigated cellular angiogenesis and lactate dehydrogenase A (LDHA) expression in the ipsilateral lumbar spinal cord after aaptamine administration in CCI rats by immunohistofluorescence. The results showed that aaptamine alleviates CCI-induced nociceptive sensitization, allodynia, and hyperalgesia. Moreover, aaptamine significantly downregulated CCI-induced vascular endothelial growth factor (VEGF), cluster of differentiation 31 (CD31), and LDHA expression in the spinal cord. Double immunofluorescent staining showed that the spinal VEGF and LDHA majorly expressed on astrocytes and neurons, respectively, in CCI rats and inhibited by aaptamine. Collectively, our results indicate aaptamine's potential as an analgesic agent for neuropathic pain. Furthermore, inhibition of astrocyte-derived angiogenesis and neuronal LDHA expression might be beneficial in neuropathy.

Delta Opioid Receptor-Mediated Antidepressant-Like Effects of Diprenorphine in Mice.

Major depressive disorder is a highly common disorder, with a lifetime prevalence in the United States of approximately 21%. Traditional antidepressant treatments are limited by a delayed onset of action and minimal efficacy in some patients. Ketamine is effective and fast-acting, but there are concerns over its abuse liability. Thus, there is a need for safe, fast-acting antidepressant drugs. The opioid buprenorphine shows promise but also has abuse liability due to its mu-agonist component. Preclinical evidence indicates that the delta-opioid system contributes to mood disorders, and delta-opioid agonists are effective in preclinical models of depression- and anxiety-like states. In this study, we test the hypothesis that the mu-opioid antagonist diprenorphine by virtue of its partial delta opioid agonist activity may offer a beneficial profile for an antidepressant medication without abuse liability. Diprenorphine was confirmed to bind with high affinity to all three opioid receptors, and functional experiments for G protein activation verified diprenorphine to be a partial agonist at delta- and kappa-opioid receptors and a mu-antagonist. Studies in C57BL/6 mice demonstrated that an acute dose of diprenorphine produced antidepressant-like effects in the tail suspension test and the novelty-induced hypophagia test that were inhibited in the presence of the delta-selective antagonist, naltrindole. Diprenorphine did not produce convulsions, a side effect of many delta agonists but rather inhibited convulsions caused by the full delta agonist SNC80; however, diprenorphine did potentiate pentylenetetrazole-induced convulsions. Diprenorphine, and compounds with a similar pharmacological profile, may provide efficient and safe rapidly acting antidepressants. SIGNIFICANCE STATEMENT: The management of major depressive disorder, particularly treatment-resistant depression, is a significant unmet medical need. Here we show that the opioid diprenorphine, a compound with mu-opioid receptor antagonist activity and delta- and kappa-opioid receptor partial agonist activities, has rapid onset antidepressant-like activity in animal models. Diprenorphine and compounds with a similar pharmacological profile to diprenorphine should be explored as novel antidepressant drugs.

Peripheral signaling mechanisms underlying mu‐delta opioid synergy

In response to the ongoing opioid epidemic, and in an effort to develop new analgesics with improved safety profiles, researchers have invested significant energy into further understanding the various downstream signaling cascades initiated by opioid receptor activation. Recent studies have demonstrated that G protein-biased ligands demonstrate reduced side effects such as respiratory depression and tolerance. Further research has shown that bivalent or bifunctional opioid compounds can also result in differential signal transduction. We hypothesized that a combination of mu and delta opioid agonists would engage different signaling pathways than drugs that target only one opioid receptor. Therefore, we probed the signaling mechanisms underlying the behavioral analgesic synergy previously demonstrated by a 1:1 combination of loperamide, a peripherally-restricted mu-opioid agonist, and oxymorphindole, a delta-opioid agonist. Using the complete Freund's adjuvant model of inflammatory pain and the Hargreaves assay for thermal nociception, the anti-hyperalgesic effect of loperamide-oxymorphindole in male and female mice was challenged by co-administration of a recently developed antagonist against MOR-DOR heteromers, D24M. Then, mice were given an injection of loperamide, oxymorphindole, or their combination with and without pertussis toxin in order to assess the involvement of Gai/o signaling on the behavioral anti-hyperalgesia. Finally, in naïve mice, the role of G protein-coupled inwardly-rectifying potassium (GIRK) channels, a downstream target of G proteins, was investigated using the peptide inhibitor tertiapin-Q, as well as GIRK KO mice. The data demonstrate that D24M was significantly more potent in antagonizing the loperamide-oxymorphindole combination (p<0.01) than either drug alone, and that pertussis toxin significantly reduces the anti-hyperalgesic effect of the combination (p<0.05). Finally, both pharmacologic and genomic inhibition of GIRK2 function results in a significant reduction of the combination's anti-nociceptive effect (p<0.0001). From these data we conclude that the loperamide-oxymorphindole combination binds to heterodimeric opioid receptors, activates a G protein signaling pathway, and opens GIRK channels.

494 Mechanisms underlying MOR-DOR analgesic synergy in epidermal nerve fibers

We recently published electrophysiological data showing that the combination of the mu-opioid (MOR) agonist loperamide and the delta-opioid (DOR) agonist oxymorphindole (Lo-OMI), applied topically to mouse toe pads, prevents activation of nociceptive epidermal nerve fibers with high potency and efficacy (Uhelski et al., 2020). The present study tested the hypotheeis that i) heterodimeric opioid receptors mediate this analgesic action, and ii) inhibitory G proteins mediate this action via activation of G protein-coupled inwardly rectifying potassium (GIRK) channels. Recent studies have demonstrated that G protein-biased ligands demonstrate reduced side effects such as respiratory depression and tolerance. Using the complete Freund’s adjuvant model of inflammatory pain and the Hargreaves assay for thermal nociception, the anti-hyperalgesic effect of Lo-OMI in male and female mice was challenged by co-administration of a recently developed antagonist against MOR-DOR heteromers, D24M (Olson, Streicher et al., 2018). Then, mice were given an injection of Lo, OMI, or their combination with and without pertussis toxin in order to assess the involvement of Gai/o signaling on the behavioral anti-hyperalgesia. Finally, in naïve mice, the role of GIRK channels, a downstream target of G proteins, was investigated using the peptide inhibitor tertiapin-Q, as well as GIRK KO mice. The data demonstrate that D24M was significantly more potent in antagonizing the Lo-OMI combination (p<0.01) than either drug alone, supporting the heterodimeric opioid receptor hypothesis, and that pertussis toxin significantly reduces the anti-hyperalgesic effect of the combination (p<0.05), supporting the Gai/o signaling hypothesis. Finally, both pharmacologic and genomic inhibition of GIRK2 function results in a significant reduction of the combination’s anti-nociceptive effect (p<0.0001), supporting the requirement for GIRK channels.

Loss of mu and delta opioid receptors on neurons expressing dopamine receptor D1 has no effect on reward sensitivity

Opioid signaling controls the activity of the brain's reward system. It is involved in signaling the hedonic effects of rewards and has essential roles in reinforcement and motivational processes. Here, we focused on opioid signaling through mu and delta receptors on dopaminoceptive neurons and evaluated the role these receptors play in reward-driven behaviors. We generated a genetically modified mouse with selective double knockdown of mu and delta opioid receptors in neurons expressing dopamine receptor D1. Selective expression of the transgene was confirmed using immunostaining. Knockdown was validated by measuring the effects of selective opioid receptor agonists on neuronal membrane currents using whole-cell patch clamp recordings. We found that in the nucleus accumbens of control mice, the majority of dopamine receptor D1-expressing neurons were sensitive to a mu or delta opioid agonist. In mutant mice, the response to the delta receptor agonist was blocked, while the effects of the mu agonist were strongly attenuated. Behaviorally, the mice had no obvious impairments. The mutation did not affect the sensitivity to the rewarding effects of morphine injections or social contact and had no effect on preference for sweet taste. Knockdown had a moderate effect on motor activity in some of the tests performed, but this effect did not reach statistical significance. Thus, we found that knocking down mu and delta receptors on dopamine receptor D1-expressing cells does not appreciably affect some of the reward-driven behaviors previously attributed to opioid signaling.

Activation of Kappa Opioid Receptor Regulates the Hypothermic Response to Calorie Restriction and Limits Body Weight Loss.

Mammals maintain a nearly constant core body temperature (Tb) by balancing heat production and heat dissipation. This comes at a high metabolic cost that is sustainable if adequate calorie intake is maintained. When nutrients are scarce or experimentally reduced such as during calorie restriction (CR), endotherms can reduce energy expenditure by lowering Tb [1-6]. This adaptive response conserves energy, limiting the loss of body weight due to low calorie intake [7-10]. Here we show that this response is regulated by the kappa opioid receptor (KOR). CR is associated with increased hypothalamic levels of the endogenous opioid Leu-enkephalin, which is derived from the KOR agonist precursor dynorphin [11]. Pharmacological inhibition of KOR, but not of the delta or the mu opioid receptor subtypes, fully blocked CR-induced hypothermia and increased weight loss during CR independent of calorie intake. Similar results were seen with DIO mice subjected to CR. In contrast, inhibiting KOR did not change Tb in animals fed ad libitum (AL). Chemogenetic inhibition of KOR neurons in the hypothalamic preoptic area reduced the CR-induced hypothermia, whereas chemogenetic activation of prodynorphin-expressing neurons in the arcuate or the parabrachial nucleus lowered Tb. These data indicate that KOR signaling is a pivotal regulator of energy homeostasis and can affect body weight during dieting by modulating Tb and energy expenditure.

D-Ala2, D-Leu5] Enkephalin Improves Liver Preservation During Normothermic Ex Vivo Perfusion

BackgroundMeeting the metabolic demands of donor livers using normothermic ex vivo liver perfusion (NEVLP) preservation technology is challenging. The delta opioid agonist [D-Ala2, D-Leu5] enkephalin (DADLE) has been reported to decrease the metabolic demand in models of ischemia and cold preservation. We evaluated the therapeutic potential of DADLE by investigating its ability to protect against oxidative stress and hepatic injury during normothermic perfusion. Materials and methodsPrimary rat hepatocytes were used in an in vitro model of oxidative stress to determine the minimum dose of DADLE needed to induce protection and the mechanisms associated with protection. NEVLP was then used to induce injury in rat livers and determine the effectiveness of DADLE in preventing liver injury. ResultsIn hepatocytes, DADLE was protective against oxidative stress and led to a decrease in phosphorylation of JNK and p38. Naltrindole, a δ-opioid receptor antagonist, blocked this effect. DADLE also activated the PI3K/Akt signaling pathway, and PI3K/Akt inhibition decreased the protective effects of DADLE treatment. In addition, DADLE treatment during NEVLP resulted in lower perfusate alanine aminotransferase and tissue malondialdehyde and better tissue adenosine triphosphate and glutathione. Furthermore, perfusion with DADLE compared with perfusate alone preserved tissue architecture. ConclusionsDADLE confers protection against oxidative stress in hepatocytes and during NEVLP. These data suggest that the mechanism of protection involved the prevention of mitochondrial dysfunction by opioid receptor signaling and subsequent increased expression of prosurvival/antiapoptotic signaling pathways. Altogether, data suggest that opioid receptor agonism may serve as therapeutic target for improved liver protection during NEVLP.

Treatment With the Delta Opioid Agonist UFP-512 Alleviates Chronic Inflammatory and Neuropathic Pain: Mechanisms Implicated.

We investigated whether administration of the δ-opioid receptor (DOR) agonist H-Dmt-Tic-NH-CH(CH2-COOH)-Bid (UFP-512), which also activates nuclear factor erythroid 2-related factor 2 (Nrf2), alleviated chronic inflammatory and/or neuropathic pain and inhibited the depressive-like behaviors associated with persistent neuropathic pain. The possible mechanisms implicated were also assessed. We evaluated the following effects in male C57BL/6J mice with inflammatory pain induced by complete Freund’s adjuvant or neuropathic pain caused by the chronic constriction of sciatic nerve: (1) the antinociceptive effects of UFP-512; (2) the effects of UFP-512 on the expression of Nrf2, heme oxygenase 1 (HO-1), NAD(P)H quinone oxidoreductase 1, phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), inducible nitric oxide synthase, DOR, and mitogen-activated protein kinases (MAPK) in the spinal cord of animals with inflammatory or neuropathic pain; (3) the antinociceptive effects of the coadministration of UFP-512 with the Nrf2 activator sulforaphane (SFN); and (4) the antidepressant effects of UFP-512 in animals with depressive-like behaviors associated with neuropathic pain. Our results demonstrated that the intraperitoneal administration of UFP-512 inhibited chronic inflammatory and neuropathic pain and reduced the depressive-like behaviors associated with persistent neuropathic pain. The antiallodynic effects of UFP-512 were significantly augmented when it was coadministered with SFN in both types of chronic pain. The administration of UFP-512 increased/reestablished the spinal cord protein levels of Nrf2 and HO-1 in mice with inflammatory or neuropathic pain. However, while during inflammatory pain UFP-512 inhibited spinal c-Jun N-terminal kinase (JNK) and extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation induced by peripheral inflammation. This DOR agonist blocked the spinal activated PI3K/Akt signaling pathway under chronic neuropathic pain conditions, but it did not alter the enhanced protein levels of p-JNK or p-ERK1/2 induced by sciatic nerve injury. These results revealed the antinociceptive and antidepressant effects of UFP-512 in animals with chronic pain and the different mechanism of action of this DOR agonist in the presence of inflammatory or neuropathic pain. Our data also suggest the administration of UFP-512 as an alternative for the treatment of chronic pain and the depressive-like behaviors associated with neuropathic pain.

(257) The Efficacy of a Dual-Acting, Peripherally-Restricted Kappa/Delta Opioid Agonist (CA1001) in Neuropathic Pain in the Rat

Nerve injury can precipitate a neuroimmune inflammatory response. This response might lead to the activation of peripheral delta-opioid receptors, allowing delta-opioid agonists in the periphery to become analgesic directly and through allosteric modulation of peripheral kappa-opioid receptors. This study evaluated the efficacy of a single intraperitoneal injection of CA1001 (a novel peripherally-restricted dual-acting kappa/delta-opioid agonist) and the comparator, gabapentin, in the spinal nerve ligation (SNL) model for neuropathic pain in the rat. Following IACUC approval, neuropathy was induced by surgically ligating the 5th and 6th lumbar spinal nerves (L5 and L6). Mechanical sensitivity was assessed via paw compression thresholds (PCTs) using a digital Randall-Selitto device. 50 animals that met the inclusion criteria were randomly assigned to 5 groups with 10 animals per group (Power: 80%). Animals were administered a single dose of vehicle, CA1001 (1 mg/kg, 5 mg/kg, or 10 mg/kg IP), or control compound (gabapentin 100 mg/kg PO; active control: internal validity) on day 0 (15 days after SNL) and PCTs were determined 1, 2, and 4 hours after compound administration. All behavioral evaluations were performed by a blinded observer. CA1001 at the 1 mg/kg dose did not significantly reverse mechanical hyperalgesia at any of the time points tested. The 5 mg/kg and 10 mg/kg doses of CA1001 did not significantly reverse mechanical hyperalgesia at the 1-hour post-dosing time point but did significantly reverse mechanical hyperalgesia at the 2-hour (p

(258) Reversal of Mechanical Hyperalgesia by a Dual-Acting, Peripherally-Restricted Kappa/Delta Opioid Agonist (CA1001) in a Rat Model of Inflammatory Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory pain condition. In RA and other inflammatory states, normally sequestersed peripheral delta-opioid receptors may become active, allowing delta-opioid agonists to participate in the pain pathway directly and through allosteric modulation of peripheral kappa-opioid receptors. This study evaluated the efficacy of a single intraperitoneal injection of CA1001 (a novel dual-acting, peripherally restricted kappa/delta opioid agonist) on hyperalgesic nociceptive behaviors in the CFA (Complete Freund's Adjuvant) Model of Inflammatory Arthritis Pain in Rats. Following IACUC approval, inflammatory arthritis pain was induced with injection of 50 μL CFA into the tibio-tarsal joint. Mechanical hyperalgesia was assessed via joint compression thresholds (JCTs). 50 animals were randomly assigned to 5 groups (Power: 80%). Ipsilateral and contralateral joint compression thresholds (JCTs) were assessed prior to CFA injection, pre-dosing on Day 0, and 1, 2, and 4 hours post-dosing. Animals were administered a single dose of vehicle, CA1001 (1, 5, or 10 mg/kg IP), or celecoxib (30 mg/kg PO: active control; internal validity) on day 0 (14 days after CFA). All behavioral evaluations were performed by a blinded observer. Mechanical hyperalgesia was measured using a digital Randall-Selitto device. CA1001 (10 mg/kg) significantly increased paw compression thresholds compared to vehicle at all time points, (p

Opioid-mediated Sertoli cells apoptosis is involved in testicular homeostasis and/or reproductive dysfunction.

The opioid system may exert positive direct and/or indirect effects on spermatogenesis at multiple levels including the levels of the central nervous system and at the testes/sperm levels. However, long term opioid use could be associatedwith several reproductive complications that place the users at risk of hypogonadism and even infertility. There is little available information regarding the contribution of opioids and their apoptotic effects on testis Sertoli cells. Here, the effects of DAMGO (mu opioid receptor's agonist), DPDPE (delta opioid receptor's agonist) and DYN 1-9 (kappa opioid receptor's agonist) on Sertoli cell viability and apoptosis were investigated. Cultured Sertoli cells were exposed to each agonist (0.1-100 µM, for 24 or 48 hours) and their apoptotic effects were investigated. Cell viability was decreased and apoptosis was increased in the cells exposed to DAMGO in a concentration-dependent manner, while in the cells exposed to DPDPE, no significant changes were observed. In cells exposed to DYN 1-9, the viability did not significantly change, however apoptosis increased significantly, following the exposure to the high concentration of DYN 1-9. These data suggest that mu and Kappa, but not delta receptors mediated apoptosis in Sertoli cells may be involved, at leastin part, in testicular homeostasis and/or reproductive dysfunction (Tab. 1, Fig. 3, Ref. 52).

DPI-289, a novel mixed delta opioid agonist / mu opioid antagonist (DAMA), has L-DOPA-sparing potential in Parkinson's disease.

L-DOPA-induced dyskinesia (LID) remains a significant problem in the management of Parkinson's disease (PD). In rodent and macaque models of PD, delta opioid receptor agonists have anti-parkinsonian actions while mu opioid antagonists can reduce the expression of LID. DPI-289 is a novel molecule with a unique combination of opioid receptor DAMA actions: delta agonist (Ki: 0.73 nM); mu antagonist (Ki: 12 nM). We demonstrated that DPI-289 has oral bioavailability and established its pharmacokinetic profile in both rat and primate. We hypothesised that these combined DAMA actions would provide an enhancement of L-DOPA effect without an associated increase in dyskinesia. In parkinsonian 6-OHDA lesioned rats and MPTP-lesioned macaques, DPI-289 provided anti-parkinsonian actions as monotherapy and an enhancement of L-DOPA benefit. Thus, acute administration of DPI-289 (3 mg/kg, p.o.) to 6-OHDA-lesioned rats produced a significant reduction in forelimb asymmetry (by 48%) that was maintained throughout the fifteen-day repeat-treatment period. Importantly, and in contrast to L-DOPA administration (6 mg/kg, i.p.), these benefits were not compromised by the development of abnormal involuntary movements. In the macaque, as monotherapy, DPI-289 (10 and 20 mg/kg) had significant, though incomplete, anti-parkinsonian actions lasting approximately 4 h. These benefits were not associated with dyskinesia. In fact, over the 6 h period of observation, DPI-289 (20 mg/kg) decreased parkinsonism by 19% and increased activity by 67% compared to vehicle treatment. By contrast, while high-dose L-DOPA (LDh) alone alleviated parkinsonism (for 3 h) this benefit was accompanied by significant dyskinesia that was disabling in nature. LDh provided a 50% reduction in parkinsonism over 6 h and 151% increase in activity. The combination of DPI-289 (20 mg/kg) and a low-dose of L-DOPA (LDl) provided anti-parkinsonian benefits greater than LDl alone without eliciting any significant dyskinesia. Treatment with LDl alone provided only transient statistically significant anti-parkinsonian benefit. However, the combination of LDl and DPI-289 reduced parkinsonism for 6 h (duration of monitoring), with parkinsonism being reduced by 35% and activity increased by 90% but with no increase in dyskinesia over that observed with LDl alone. Thus, DPI-289 has potential to improve the benefits of dopaminergic therapy in Parkinson's disease.

Interactions between Delta and Mu Opioid Agonists in Assays of Pain‐Depressed Operant Responding and Schedule‐Controlled Rate Suppression

Interactions between delta and mu opioid agonists in rodents vary as a function of behavioral endpoint. Previous literature includes assessment of interactions across therapeutic (eg: antinociceptive) and side effect (eg: sedation, respiratory depression) endpoints. The present study is the first to characterize these receptor interactions using a mult‐cycle operant assay of pain‐depressed behavior as the antinociceptive measure. The selective delta agonist SNC80 (ED50 = 4.11mg/kg) and the selective mu agonist methadone (ED50 = 0.35mg/kg) both produced dose‐dependent restoration of lactic acid pain‐depressed operant responding. SNC80 (ED50 = 56.0mg/kg) and methadone (ED50 = 1.55mg/kg) also produced a dose‐dependent suppression of response rates in the operant assay in the absence of the pain‐like stimulus. Based on relative potencies in the nociceptive assay, fixed‐ratio mixtures of SNC80 and methadone (35.1:1, 11.7:1, 3.9:1) are currently being characterized in both assays. Preliminary data indicate that the 11.7:1 mixture produced additive effects in the antinociceptive assay and sub‐additive effects in the rate suppression assay, thus yielding a higher therapeutic index (TI or dose ratio) for the mixture relative to the TI of either drug alone. These results provide further evidence that delta/mu interactions depend on experimental endpoint and that assessment of these interactions utilizing an assay of pain‐depressed behavior is possible.Support or Funding InformationAR0554975‐02A1 (NIAMS) to G.W.S.

Delta Opioid Receptor and Peptide: A Dynamic Therapy for Stroke and Other Neurological Disorders.

Research of the opioid system and its composite receptors and ligands has revealed its promise as a potential therapy for neurodegenerative diseases such as stroke and Parkinson's Disease. In particular, delta opioid receptors (DORs) have been elucidated as a therapeutically distinguished subset of opioid receptors and a compelling target for novel intervention techniques. Research is progressively shedding light on the underlying mechanism of DORs and has revealed two mechanisms of DOR neuroprotection; DORs function to maintain ionic homeostasis and also to trigger endogenous neuroprotective pathways. Delta opioid agonists such as (D-Ala2, D-Leu5) enkephalin (DADLE) have been shown to promote neuronal survival and decrease apoptosis, resulting in a substantial amount of research for its application as a neurological therapeutic. Most notably, DADLE has demonstrated significant potential to reduce cell death following ischemic events. Current research is working to reveal the complex mechanisms of DADLE's neuroprotective properties. Ultimately, our knowledge of the DOR receptors and agonists has made the opioid system a promising target for therapeutic intervention in many neurological disorders.

Featured Article: Pharmacological postconditioning with delta opioid attenuates myocardial reperfusion injury in isolated porcine hearts.

Ischemic preconditioning has been utilized to protect the heart from ischemia prior to ischemia onset, whereas postconditioning is employed to minimize the consequences of ischemia at the onset of reperfusion. The underlying mechanisms and pathways of ischemic pre- and postconditioning continue to be investigated as therapeutic targets. We evaluated the administration of a delta opioid agonist or cariporide on various parameters associated with myocardial reperfusion injury upon reperfusion of isolated porcine hearts. The hearts were reperfused invitro with a Krebs buffer containing either: (1) 1 µM Deltorphin D (delta opioid specific agonist, n = 6); (2) 3 µM cariporide (sodium-hydrogen exchange inhibitor, n = 4); or (3) no treatment (control, n = 6). Subsequently, postischemic hemodynamic performance, arrhythmia burden, relative tissue perfusion, and development of necrosis were assessed over a 2 h reperfusion period. Postconditioning with Deltorphin D significantly improved diastolic relaxation (Tau, P < 0.05 versus controls) and decreased the incidence of ventricular arrhythmias during early reperfusion. Additionally, these treated hearts demonstrated increased tissue perfusion after 2 h ( P < 0.05 versus controls), suggesting improved microvascular function. Delta opioid agonists elicited the potential to attenuate reperfusion injury, suggesting a postconditioning effect of these agents. We hypothesize that the induced benefits of delta opioids, in part, are associated with decreased calcium influx on reperfusion, independent of sodium-hydrogen exchange inhibition. Such agents may have a potential role in minimizing reperfusion injury associated with coronary stenting, bypass surgery, myocardial infarction, cardiac transplantation, or with the utilization of heart preservation systems. Impact statement In this study, we found that postconditioning with Deltorphin D significantly improved diastolic relaxation and decreased the incidence of ventricular arrhythmias during early reperfusion. Furthermore, these treated hearts demonstrated increased tissue perfusion after 2 h, suggesting improved microvascular function. Delta opioid agonists attenuated reperfusion injury, suggestive of a postconditioning effect. Such agents may have a potential role in minimizing reperfusion injury associated with coronary stenting, bypass surgery, myocardial infarction, cardiac transplantation, or with the utilization of heart preservation systems.

Synergistic antidepressant-like effects between a kappa opioid antagonist (LY2444296) and a delta opioid agonist (ADL5859) in the mouse forced swim test

Kappa opioid (KOP) receptor antagonists and delta opioid (DOP) receptor agonists have antidepressant-like effects in animal tests and may be useful for treatment-resistant depression in humans. In this study, we examined whether the combination of a KOP receptor antagonist and a DOP receptor agonist would produce a better than additive effect (i.e. synergy). LY2444296 is a short-acting selective nonpeptide KOP receptor antagonist. ADL5859 is a selective nonpeptide DOP receptor agonist which does not produce seizures and EEG disturbances. Each compound and combinations of the two were examined in the forced swim test (FST) one h post injection, a screening test for antidepressant-like effect, in male adult C57BL/6J mice (Jackson Lab). LY2444296 [subcutaneous (s.c.) injection] at 10 and 30mg/kg, but not 3mg/kg, significantly decreased immobility time in a dose-dependent manner. Intraperitoneal (i.p.) injections of ADL5859 also reduced immobility time dose-dependently at doses of 3 and 10mg/kg, but not at 1mg/kg. An analysis was conducted using the method of Tallarida and Raffa (2010), which employed dose equivalence. The relative potency of the drugs was determined to be LY2444296: ADL5859=1:0.28, which was the dose ratio for combination studies. Six combinations of the two compounds were tested in mice at a fixed dose ratio. We found that LY2444296 and ADL5859 yielded significant synergistic effects for the antidepressant-like effect at the combined dose ranging from 3.84mg/kg to 9.0mg/kg. ADL5859 (10mg/kg), LY2444296 (30mg/kg) and their combined dose (3.84mg/kg) had no effects on locomotor activities. Since the two drugs have distinct pharmacological profiles, such a synergism will allow use of lower doses of both drugs to achieve desired antidepressant effects with fewer side effects.

Novel diazabicycloalkane delta opioid agonists

Here we report the investigation of diazabicycloalkane cores as potential new scaffolds for the development of novel analogues of the previously reported diazatricyclodecane selective delta (δ) opioid agonists, as conformationally constrained homologues of the reference δ agonist (+)-4-[(αR)-α((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80).In particular, we have simplified the diazatricyclodecane motif of δ opioid agonist prototype 1a with bridged bicyclic cores. 3,6-diazabicyclo[3.1.1]heptane, 3,8-diazabicyclo[3.2.1]octane, 3,9-diazabicyclo[3.3.1]nonane, 3,9-diazabicyclo[4.2.1]nonane, and 3,10-diazabicyclo[4.3.1]decane were adopted as core motifs of the novel derivatives. The compounds were synthesized and biologically assayed as racemic (3–5) or diastereoisomeric (6,7) mixtures.All the novel compounds 3–7 showed δ agonism behaviour and remarkable affinity to δ receptors. Amongst the novel derivatives, 3,8-diazabicyclo[3.2.1]octane based compound 4 evidenced improved δ affinity and selectivity relative to SNC80.