Delta-opioid Research Articles

A Small-molecule Antagonist Radiotracer for Positron Emission Tomography Imaging of the Mu Opioid Receptor.

The opioid crisis is a catastrophic health emergency catalyzed by the misuse of opioids that target and activate the mu opioid receptor. Traditional radioligands used to study the mu opioid receptor are often tightly regulated owing to their abuse and respiratory depression potential. In the present study, we sought to design and characterize a library of 24 non-agonist ligands for the mu opioid receptor. Ligands were evaluated for the binding affinity, intrinsic activity, and predicted blood-brain barrier permeability. Several ligands demonstrated single-digit nM binding affinity for the mu opioid receptor while also demonstrating selectivity over the delta and kappa opioid receptors. The antagonist behavior of 1A and 3A at the mu opioid receptor indicate that these ligands would likely not induce opioid-dependent respiratory depression. Therefore, these ligands can enable a safer means to interrogate the endogenous opioid system. Based on binding affinity, selectivity, and potential off-target binding, [ 11 C] 1A was prepared via metallophotoredox of the aryl-bromide functional group to [ 11 C]methyl iodide. The nascent radiotracer demonstrated brain uptake in a rhesus macaque model and accumulation in the caudate and putamen. Naloxone was able to reduce [ 11 C] 1A binding, though the interactions were not as pronounced as naloxone's ability to displace [ 11 C]carfentanil. These results suggest that GSK1521498 and related congeners are amenable to radioligand design and can offer a safer way to query opioid neurobiology.

Classics in Chemical Neuroscience: Tianeptine.

Tianeptine (1) is an unusual antidepressant in that its mechanism of action appears to be independent from any activity at serotonin receptors or monoamine transporters. In fact, tianeptine has been shown to be a moderately potent agonist for the mu opioid receptor (MOR) and to a lesser extent the delta opioid receptor (DOR). Additionally, tianeptine's efficacy may be related to its action on glutamate-mediated pathways of neuroplasticity. Regardless of which neurotransmitter system is primarily responsible for the observed efficacy, the MOR agonist activity is problematic with respect to abuse liability. Increasing numbers of case reports have demonstrated that tianeptine is indeed being used recreationally at doses far beyond what are considered therapeutically relevant or safe, and scheduling reclassifications or outright bans on tianeptine products are ongoing around the world. It is the aim of this review to discuss the medicinal chemistry and pharmacology of tianeptine and to summarize this intriguing discrepancy between tianeptine's historical use as a safe and effective antidepressant and its emerging potential for abuse.

Chronic olanzapine treatment leads to increased opioid receptor expression and changes in feeding regulating neurons in the female rat hypothalamus

Opioid receptor antagonists have shown increasing promise as an adjunct therapy to psychotropic medication. The goal is to reduce the weight gain and metabolic adverse effects that are associated with certain second-generation antipsychotics, such as olanzapine and clozapine. In this study, female rats were treated for 4 weeks with a long-acting injectable formulation of olanzapine to assess effects on hypothalamic feeding regulation. Using quantitative spatial in situ hybridization and receptor autoradiography, expression levels of the mu, kappa and delta opioid receptors were defined in the five hypothalamic areas: paraventricular nucleus (PVN), arcuate nucleus (ARC), ventromedial nucleus (VMN), dorsomedial nucleus (DMN) and lateral hypothalamus (LH). In addition, hypothalamic neuron number and size were estimated using the unbiased optical fractionator and spatial rotator methods. Hyperphagia was observed after only 24hours of olanzapine treatment, with continued weight gain throughout the duration of the study. In contrast, the observed food intake reversed to control levels after 2 weeks of olanzapine treatment. Chronic olanzapine treatment increased expression of kappa opioid receptor mRNA and receptor availability in the PVN, as well as increased mu opioid receptor availability in the PVN, ARC and VMN. These changes were accompanied by fewer anorexigenic proopiomelanocortin-expressing neurons of the ARC and corticotropin-releasing hormone expressing neurons of the PVN. This study links olanzapine-driven metabolic effects to increased opioid receptor expression in the hypothalamus, thus providing a rationale for the positive effects of using opioid receptor antagonists to relieve olanzapine adverse effects.

Cryo-EM structure of small-molecule agonist bound delta opioid receptor-Gi complex enables discovery of biased compound

Delta opioid receptor (δOR) plays a pivotal role in modulating human sensation and emotion. It is an attractive target for drug discovery since, unlike Mu opioid receptor, it is associated with low risk of drug dependence. Despite its potential applications, the pharmacological properties of δOR, including the mechanisms of activation by small-molecule agonists and the complex signaling pathways it engages, as well as their relation to the potential side effects, remain poorly understood. In this study, we use cryo-electron microscopy (cryo-EM) to determine the structure of the δOR-Gi complex when bound to a small-molecule agonist (ADL5859). Moreover, we design a series of probes to examine the key receptor-ligand interaction site and identify a region involved in signaling bias. Using ADL06 as a chemical tool, we elucidate the relationship between the β-arrestin pathway of the δOR and its biological functions, such as analgesic tolerance and convulsion activities. Notably, we discover that the β-arrestin recruitment of δOR might be linked to reduced gastrointestinal motility. These insights enhance our understanding of δOR’s structure, signaling pathways, and biological functions, paving the way for the structure-based drug discovery.

Preparation, Evaluation and Optimization of Polymeric Nanoparticles of Eluxadoline for the Treatment of Irritable Bowel Syndrome

ABSTRACT Eluxadoline, exhibits potential as an irritable bowel syndrome treatment and management strategy. Eluxadoline, a muopioid receptor agonist and delta-opioid receptor antagonist, has shown efficacy in relieving IBS symptoms. However, its applications have been limited due to low water solubility, which causes a low dissolution rate and oral bioavailability. In this study, we aimed to enhance the therapeutic efficacy of eluxadoline by formulating polymeric nanoparticles of eluxadoline. Polymeric nanoparticles of chitosan loaded with eluxadoline were prepared using the ionic gelation method. The formulation parameters including concentration of chitosan, concentration of tripolyphosphate and volume of tripolyphosphate were systematically optimized using a Box-Behnken design to achieve nanoparticles (CNP1-CNP17) with optimal physicochemical properties. The optimized formulation based on particle size of (300.4 nm) with a low PDI value (0.305), zeta potential (41.2mV) and % entrapment efficacy (76.89%). The efficiency of the drug release from optimised formulation was studied in vitro by using a dialysis bag diffusion technique in buffer condition pH 6.8 intestinal condition and showed a sustained release behaviour with maximum drug release 80.23%. Thus, the findings demonstrated that the formulated chitosan-based polymeric nanoparticles present a promising strategy for efficiently delivering eluxadoline via oral administration, offering a potential solution for treating irritable bowel syndrome.

Identification of pharmacological inducers of a reversible hypometabolic state for whole organ preservation

Drugs that induce reversible slowing of metabolic and physiological processes would have great value for organ preservation, especially for organs with high susceptibility to hypoxia-reperfusion injury, such as the heart. Using whole-organism screening of metabolism, mobility, and development in Xenopus, we identified an existing drug, SNC80, that rapidly and reversibly slows biochemical and metabolic activities while preserving cell and tissue viability. Although SNC80 was developed as a delta opioid receptor activator, we discovered that its ability to slow metabolism is independent of its opioid modulating activity as a novel SNC80 analog (WB3) with almost 1000 times less delta opioid receptor binding activity is equally active. Metabolic suppression was also achieved using SNC80 in microfluidic human organs-on-chips, as well as in explanted whole porcine hearts and limbs, demonstrating the cross-species relevance of this approach and potential clinical relevance for surgical transplantation. Pharmacological induction of physiological slowing in combination with organ perfusion transport systems may offer a new therapeutic approach for tissue and organ preservation for transplantation, trauma management, and enhancing patient survival in remote and low-resource locations.

Identification of pharmacological inducers of a reversible hypometabolic state for whole organ preservation.

Drugs that induce reversible slowing of metabolic and physiological processes would have great value for organ preservation, especially for organs with high susceptibility to hypoxia-reperfusion injury, such as the heart. Using whole-organism screening of metabolism, mobility, and development in Xenopus, we identified an existing drug, SNC80, that rapidly and reversibly slows biochemical and metabolic activities while preserving cell and tissue viability. Although SNC80 was developed as a delta opioid receptor activator, we discovered that its ability to slow metabolism is independent of its opioid modulating activity as a novel SNC80 analog (WB3) with almost 1000 times less delta opioid receptor binding activity is equally active. Metabolic suppression was also achieved using SNC80 in microfluidic human organs-on-chips, as well as in explanted whole porcine hearts and limbs, demonstrating the cross-species relevance of this approach and potential clinical relevance for surgical transplantation. Pharmacological induction of physiological slowing in combination with organ perfusion transport systems may offer a new therapeutic approach for tissue and organ preservation for transplantation, trauma management, and enhancing patient survival in remote and low-resource locations.

Opioid drug seeking after early-life adversity: a role for delta opioid receptors

Opioid use disorder (OUD) is associated with a history of early-life adversity (ELA), an association that is particularly strong in women. In a rodent model, we previously found that ELA enhances risk for opioid addiction selectively in females, but the mechanisms for this effect are unclear. Here, we show that ELA robustly alters cFos responses to opioid drugs in females’ nucleus accumbens (NAc) and basolateral amygdala (BLA), but not elsewhere. We further identify delta opioid receptors (DOR), which mature in the first week of life and thus later than kappa or mu opioid receptors, as a potential mediator of ELA's impacts on reward circuit functions. Accordingly, DOR mRNA in NAc was persistently reduced in adult females with ELA history. Moreover, pharmacological stimulation of NAc DORs increased opioid demand in control females (recapitulating the ELA phenotype), while blocking DORs in ELA females conversely reduced high-effort drug consumption, simulating the control rearing phenotype. These findings support a role for NAc DORs in mediating ELA-induced opioid vulnerability. In contrast, BLA neurons expressing DOR protein do not overlap heroin- responsive cells in ELA rats, arguing against a direct relationship of BLA DORs to heroin's addiction-relevant actions in the brain. Together, these results suggest a novel and selective role for NAc DORs in contributing to enduring, ELA-provoked vulnerability to OUD.

Pregnancy ameliorates neuropathic pain through suppression of microglia and upregulation of the δ-opioid receptor in the anterior cingulate cortex in late-pregnant mice.

Pregnancy-induced analgesia develops in late pregnancy, but its mechanisms are unclear. The anterior cingulate cortex (ACC) plays a key role in the pathogenesis of neuropathic pain. The authors hypothesized that pregnancy-induced analgesia ameliorates neuropathic pain by suppressing activation of microglia and the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and by upregulating opioid receptors in the ACC in late-pregnant mice. Neuropathic pain was induced in non-pregnant (NP) or pregnant (P) C57BL/6JJmsSlc female mice by partial sciatic nerve ligation (PSNL). The nociceptive response was evaluated by mechanical allodynia and activation of microglia in the ACC was evaluated by immunohistochemistry. The expressions of phosphorylated AMPA receptors and opioid receptors in the ACC were evaluated by immunoblotting. In von Frey reflex tests, NP-PSNL-treated mice showed a lower 50% paw-withdrawal threshold than NP-Naïve mice on experimental day 9. No difference in 50% paw-withdrawal threshold was found among the NP-Naïve, NP-Sham, P-Sham, and P-PSNL-treated mice. The number of microglia in the ACC was significantly increased in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting showed significantly increased expression of phosphorylated AMPA receptor subunit GluR1 at Ser831 in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting also showed significantly increased δ-opioid receptor in the ACC in P-Sham and P-PSNL-treated mice compared to NP-Sham mice. Pregnancy-induced analgesia ameliorated neuropathic pain by suppressing activation of microglia and the expression of phosphorylated AMPA receptor subunit GluR1 at Ser831, and by upregulation of the δ-opioid receptor in the ACC in late-pregnant mice.

An engineered trafficking biosensor reveals a role for DNAJC13 in DOR downregulation.

Trafficking of G protein-coupled receptors (GPCRs) through the endosomal-lysosomal pathway is critical to homeostatic regulation of GPCRs following activation with agonist. Identifying the genes involved in GPCR trafficking is challenging due to the complexity of sorting operations and the large number of cellular proteins involved in the process. Here, we developed a high-sensitivity biosensor for GPCR expression and agonist-induced trafficking to the lysosome by leveraging the ability of the engineered peroxidase APEX2 to activate the fluorogenic substrate Amplex UltraRed (AUR). We used the GPCR-APEX2/AUR assay to perform a genome-wide CRISPR interference screen focused on identifying genes regulating expression and trafficking of the δ-opioid receptor (DOR). We identified 492 genes consisting of both known and new regulators of DOR function. We demonstrate that one new regulator, DNAJC13, controls trafficking of multiple GPCRs, including DOR, through the endosomal-lysosomal pathway by regulating the composition of the endosomal proteome and endosomal homeostasis.

Effect of bovine beta-casomorphins on rat pancreatic beta cells (RIN-5F) under glucotoxic stress

Beta-casomorphins (BCMs) are the bio-active peptides having opioid properties which are formed by the proteolytic digestion of β-caseins in milk. BCM-7 forms when A1 milk is digested in the small intestine due to a histidine at the 67th position in β-casein, unlike A2 milk, which has proline at this position and produces BCM-9. BCM-7 has further degraded into BCM-5 by the dipeptidyl peptidase-IV (DPP-IV) enzyme in the intestine. The opioid-like activity of BCM-7 is responsible for eliciting signaling pathways which enable a wide range of physiological effects. The aim of our study was to find out the differential role of BCMs (BCM-7, BCM-9 and BCM-5) on pancreatic β-cell proliferation, insulin secretion, and opioid peptide binding receptors from β-cells (RIN-5F cell line) in normal (5.5 mM) and high glucose (27.5 mM) concentrations. Our results showed that BCM-7/9/5 did not affect β-cell viability, proliferation, and insulin secretion at normal glucose level. However, at higher glucose concentration, BCMs significantly protected β-cells from glucotoxicity but did not affect the insulin secretion. Interestingly, in the presence of Mu-opioid peptide receptor antagonist CTOP, BCMs did not protect β-cells from glucotoxicity. The results suggest that BCMs protect β-cells from glucotoxicity via non-opioid mediated pathways because BCMs did not modulate the gene expression of the mu, kappa and delta opioid peptide receptors.

Identification of Cytisine Derivatives as Agonists of the Human Delta Opioid Receptor by Supercomputer-Based Virtual Drug Screening and Transcriptomics.

Delta opioid receptors (DORs) are rising as therapeutic targets, not only for the treatment of pain but also other neurological disorders (e.g., Parkinson's disease). The advantage of DOR agonists compared to μ-opioid receptor agonists is that they have fewer side effects and a lower potential to induce tolerance. However, although multiple candidates have been tested in the past few decades, none have been approved for clinical use. The current study focused on searching for new DOR agonists by screening a chemical library containing 40,000 natural and natural-derived products. The functional activity of the top molecules was evaluated in vitro through the cyclic adenosine monophosphate accumulation assay. Compound 3 showed promising results, and its activity was further investigated through transcriptomic methods. Compound 3 inhibited the expression of TNF-α, prevented NF-κB translocation to the nucleus, and activated the G-protein-mediated ERK1/2 pathway. Additionally, compound 3 is structurally different from known DOR agonists, making it a valuable candidate for further investigation for its anti-inflammatory and analgesic potential.

Opiorphin: an endogenous human peptide with intriguing application in diverse range of pathologies.

Mammalian zinc ectopeptidases have significant functions in deactivating neurological and hormonal peptide signals on the cell surface. The identification of Opiorphin, a physiological inhibitor of zinc ectopeptidases that inactivate enkephalin, has revealed its strong analgesic effects in both chemical and mechanical pain models. Opiorphin achieves this by increasing the transmission of endogenous opioids, which are dependent on the body's own opioid system. The function of opiorphin is closely linked to the rat sialorphin peptide, which inhibits pain perception by enhancing the activity of naturally occurring enkephalinergic pathways that depend on μ- and δ-opioid receptors. Opiorphin is highly intriguing in terms of its physiological implications within the endogenous opioidergic pathways, particularly in its ability to regulate mood-related states and pain perception. Opiorphin can induce antidepressant-like effects by influencing the levels of naturally occurring enkephalin, which are released in response to specific physical and/or psychological stimuli. This effect is achieved through the modulation of delta-opioid receptor-dependent pathways. Furthermore, research has demonstrated that opiorphin's impact on the cardiovascular system is facilitated by the renin-angiotensin system (RAS), sympathetic ganglia, and adrenal medulla, rather than the opioid system. Hence, opiorphin shows great potential as a solitary candidate for the treatment of several illnesses such as neurodegeneration, pain, and mood disorders.

Modulatory Effects of Morphine and Xylopia aethioica Extract on Kappa Opiod Receptors (KOR), Delta Opioid Receptor (DOR), Pain Hypersensitivity and Motor Functions in Wistar Rats

This study investigates the modulatory effects of morphine and Xylopia aethiopica extract on kappa opioid receptors (KOR), delta opioid receptors (DOR), pain hypersensitivity, and motor functions in Wistar rats. We utilized three experimental groups: a control group receiving distilled water, a morphine group receiving either low (5 mg/kg) or high (10 mg/kg) doses after inducing pain, Xylopia aethiopica group received either 25 mg/kg or 50 mg/kg of hydromethanolic extract following similar pain induction. Pain perception was quantified using the tail flick test and Analgesy-Meter while motor functions were assessed through the Rotarod and Climbing/Beam Walk tests. Additionally, molecular docking studies were performed on selected compounds from Xylopia aethiopica to determine their binding affinities to opioid receptors using Vina. Results demonstrated that morphine and Xylopia aethiopica significantly increased tail flick response times, indicating notable analgesic effects, while improving motor functions particularly in animals treated with higher doses of Xylopia aethiopica. Molecular analysis revealed potential interactions between bioactive compounds and opioid receptors, suggesting further therapeutic applications. These findings highlight the potential of Xylopia aethiopica as a natural analgesic and its implications in managing pain and associated motor deficits, the findings further revealed that Morphine and not Xylopia aethiopica is implicated in pain hypersensitivity after long term exposure. Further research should pay attention on improving the pharmacological profiles of the identified compounds for clinical use.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity.

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without a liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels, but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Regulation of Cannabinoid and Opioid Receptor Levels by Endogenous and Pharmacological Chaperones.

Cannabinoid and opioid receptor activities can be modulated by a variety of post-translational mechanisms including the formation of interacting complexes. This study examines the involvement of endogenous and exogenous chaperones in modulating the abundance and activity of cannabinoid CB1 receptor (CB1R), δ opioid receptor (DOR), and CB1R-DOR interacting complexes. Focusing on endogenous protein chaperones, namely receptor transporter proteins (RTPs), we examined relative mRNA expression in the mouse spinal cord and found RTP4 to be expressed at higher levels compared with other RTPs. Next, we assessed the effect of RTP4 on receptor abundance by manipulating RTP4 expression in cell lines. Overexpression of RTP4 causes an increase and knock-down causes a decrease in the levels of CB1R, DOR, and CB1R-DOR interacting complexes; this is accompanied by parallel changes in signaling. The ability of small molecule lipophilic ligands to function as exogenous chaperones was examined using receptor-selective antagonists. Long-term treatment leads to increases in receptor abundance and activity with no changes in mRNA supporting a role as pharmacological chaperones. Finally, the effect of cannabidiol (CBD), a small molecule ligand and a major active component of cannabis, on receptor abundance and activity in mice was examined. We find that CBD administration leads to increases in receptor abundance and activity in mouse spinal cord. Together, these results highlight a role for chaperones (proteins and small molecules) in modulating levels and activity of CB1R, DOR, and their interacting complexes potentially through mechanisms including receptor maturation and trafficking. SIGNIFICANCE STATEMENT: This study highlights a role for chaperones (endogenous and small membrane-permeable molecules) in modulating levels of cannabinoid CB1 receptor, delta opioid receptor, and their interacting complexes. These chaperones could be developed as therapeutics for pathologies involving these receptors.

Functional genetics reveals the contribution of delta opioid receptor to type 2 diabetes and beta-cell function

Functional genetics has identified drug targets for metabolic disorders. Opioid use impacts metabolic homeostasis, although mechanisms remain elusive. Here, we explore the OPRD1 gene (encoding delta opioid receptor, DOP) to understand its impact on type 2 diabetes. Large-scale sequencing of OPRD1 and in vitro analysis reveal that loss-of-function variants are associated with higher adiposity and lower hyperglycemia risk, whereas gain-of-function variants are associated with lower adiposity and higher type 2 diabetes risk. These findings align with studies of opium addicts. OPRD1 is expressed in human islets and beta cells, with decreased expression under type 2 diabetes conditions. DOP inhibition by an antagonist enhances insulin secretion from human beta cells and islets. RNA-sequencing identifies pathways regulated by DOP antagonism, including nerve growth factor, circadian clock, and nuclear receptor pathways. Our study highlights DOP as a key player between opioids and metabolic homeostasis, suggesting its potential as a therapeutic target for type 2 diabetes.

Age- and sex-driven alterations in alcohol consumption patterns: Role of brain ethanol metabolism and the opioidergic system in the nucleus accumbens

Alcohol consumption leads to significant neurochemical and neurobiological changes, contributing to the development of alcohol use disorders (AUDs), which exhibit sex- and age-dependent variations according to clinical data. However, preclinical studies often neglect these factors when investigating alcohol consumption patterns. In this study, we present data on male and female rats continuously exposed to a 20 % ethanol solution for one month. The animals were divided into two groups based on their age at the onset of drinking (8 and 12 weeks old). Interestingly, 12-week-old males consumed significantly less alcohol than both 12-week-old females and 8-week-old animals, indicating that alcohol consumption patterns vary with sex and age in our model. Additionally, to advance in the study of the neurobiological alterations induced by ethanol intake in the mesocorticolimbic system (MCLS) that may participate in its reinforcing properties and the maintenance of alcohol drinking behavior, we measured catalase activity—an enzyme involved in alcohol metabolism and related to ethanol reinforcement—in the nucleus accumbens (NAc) of these animals. Furthermore, we measured the levels of mu (MOR), kappa (KOR), delta (DOR), and nociceptin (NOP) opioid receptors in the NAc, as the endogenous opioidergic system plays a pivotal role in regulating the MCLS and alcohol reinforcement. MOR levels were lower in high alcohol-consuming groups (8-week-old males and all females). Both DOR and NOP levels decreased with age, whereas KOR levels remained unchanged. Our findings suggest that the age at onset of alcohol consumption critically influences alcohol intake, particularly in males. Additionally, females consistently showed higher alcohol intake regardless of age, highlighting inherent sex-specific differences. The dynamic changes in catalase activity and opioid receptor expression suggest the involvement of these factors in modulating alcohol consumption.

Abstract We092: Naltrindole Attenuates Superoxide Release in Polymorphonuclear Leukocytes by a Novel Mechanism devoid of Delta opioid receptor antagonism Related to Reduced Intracellular Calcium Levels

Introduction: Naltrindole (NTI), known as a delta opioid receptor antagonist, inhibited phorbol 12-myristate 13-acetate (PMA) induced superoxide (SO) release in polymorphonuclear leukocytes (PMNs). PMNs do not express opioid receptors. We propose NTI reduces PMN SO by reducing intracellular calcium (Ca 2+ ). To test this hypothesis, we did experiments using KB-R7943 (KB) as a positive control, known to reduce intracellular Ca 2+ via inhibition of the reverse mode Na + /Ca 2+ exchanger. Naloxone (NX), a broad-spectrum opioid receptor antagonist, was used as a negative control. We predict that NTI will diminish PMA-induced PMN SO release similar to KB, while NX will have no effect, and that there will be no difference in cell viability compared to vehicle controls. Methods: Male Sprague Dawley (SD) rat PMNs (5x10 6 ) were incubated for 15 min at 37 o C in the presence or absence (dH 2 O vehicle control) of NTI (10 - 200 µM), KB (5-20 µM), and NX (100-200 µM). PMN SO release was measured by the change in absorbance at 550 nm over 420 sec via ferricytochrome c reduction after PMA stimulation (100 nM). The cell viability was determined microscopically by 0.2% trypan blue exclusion at the end of PMN SO release assay. Data were analyzed using ANOVA Fisher’s PLSD post-hoc test. Results: NTI significantly decreased PMN SO release at 200 μM (n=10, 0.196±0.06, p<0.05) compared to vehicle control (n=22, 0.731±0.07) or NX 100/200 μM (n=3, 0.593±0.06), and NTI at 100 μM (n=7, 0.461±0.08, p<0.05) versus vehicle control. Likewise, KB significantly decreased PMN SO release at 20 μM (n=7, 0.507±0.07), 10 μM (n=7, 0.552±0.07), and 5 μM (n=5, 0.615±0.11) compared to vehicle control (n=10, 0.908±0.07). Cell viability was statistically similar (80-90±5%) among all study groups. Conclusion: NTI (10-200 μM) and KB (5-20 µM) exhibited concentration-dependent effects in reducing PMN SO release without compromising cell viability. The results suggest that the novel effect of NTI maybe mediated through a reduction in intracellular Ca 2+ and independent of delta opioid receptor antagonism. These results are consistent with the effects of NTI, KB and NX in myocardial ischemia/reperfusion injuries. Future studies will assess the effects of NTI on ROS attenuation in human umbilical vein endothelial cells.

Lack of evidence for direct ligand-gated ion channel activity of GluD receptors

Delta receptors (GluD1 and GluD2), members of the large ionotropic glutamate receptor (iGluR) family, play a central role in numerous neurodevelopmental and psychiatric disorders. The amino-terminal domain (ATD) of GluD orchestrates synapse formation and maturation processes through its interaction with the Cbln family of synaptic organizers and neurexin (Nrxn). The transsynaptic triad of Nrxn-Cbln-GluD also serves as a potent regulator of synaptic plasticity, at both excitatory and inhibitory synapses. Despite these recognized functions, there is still debate as to whether GluD functions as a "canonical" ion channel, similar to other iGluRs. A recent report proposes that the ATD of GluD2 imposes conformational constraints on channel activity; removal of this constraint by binding to Cbln1 and Nrxn, or removal of the ATD, reveals channel activity in GluD2 upon administration of glycine (Gly) and d-serine (d-Ser), two GluD ligands. We were able to reproduce currents when Gly or d-Ser was administered to clusters of heterologous human embryonic kidney 293 (HEK293) cells expressing Cbln1, GluD2 (or GluD1), and Nrxn. However, Gly or d-Ser, but also l-glutamate (l-Glu), evoked similar currents in naive (i.e., untransfected) HEK293 cells and in GluD2-null Purkinje neurons. Furthermore, no current was detected in isolated HEK293 cells expressing GluD2 lacking the ATD upon administration of Gly. Taken together, these results cast doubt on the previously proposed hypothesis that extracellular ligands directly gate wild-type GluD channels.