The effect of NK3-Saporin injection within the arcuate nucleus on puberty, the LH surge, and the response to Senktide in female sheep†.

The timing of puberty onset is reliant on increased gonadotropin-releasing hormone (GnRH). This elicits a corresponding increase in luteinizing hormone (LH) due to a lessening of sensitivity to the inhibitory actions of estradiol (E2). The mechanisms underlying the increase in GnRH release likely involve a subset of neurons within the arcuate (ARC) nucleus of the hypothalamus that contain kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons). We aimed to determine if KNDy neurons in female sheep are critical for: timely puberty onset; the LH surge; and the response to an intravenous injection of the neurokinin-3 receptor (NK3R) agonist, senktide. Prepubertal ewes received injections aimed at the ARC containing blank-saporin (control, n = 5) or NK3-saporin (NK3-SAP, n = 6) to ablate neurons expressing NK3R. Blood samples taken 3/week for 65 days following surgery were assessed for progesterone to determine onset of puberty. Control ewes exhibited onset of puberty at 33.2 ± 3.9 days post sampling initiation, whereas 5/6 NK3-SAP treated ewes didn't display an increase in progesterone. After an artificial LH surge protocol, surge amplitude was lower in NK3-SAP ewes. Finally, ewes were treated with senktide to determine if an LH response was elicited. LH pulses were evident in both groups in the absence of injections, but the response to senktide vs saline was similar between groups. These results show that KNDy cells are necessary for timely puberty onset and for full expresson of the LH surge. The occurrence of LH pulses in NK3-SAP treated ewes may indicate a recovery from an apulsatile state.

Probing electrophysiological activity of amphiphilic Dynorphin A in planar neutral membranes reveals both ion channel-like activity and neuropeptide translocation.

Dynorphin A (DynA) is an endogenous neuropeptide that besides acting as a ligand of the κ-opioid receptor, presents some non-opioid pathophysiological properties associated to its ability to induce cell permeability similarly to cell-penetrating peptides (CPPs). Here, we use electrophysiology experiments to show that amphiphilic DynA generates aqueous pores in neutral membranes similar to those reported previously in charged membranes, but we also find other events thermodynamically incompatible with voltage-driven ion channel activity (i.e. non-zero currents with no applied voltage in symmetric salt conditions, reversal potentials that exceed the theoretical limit for a given salt concentration gradient). By comparison with current traces generated by other amphiphilic molecule known to spontaneously cross membranes, we hypothesize that DynA could directly translocate across neutral bilayers, a feature never observed in charged membranes following the same electrophysiological protocol. Our findings suggest that DynA interaction with the cellular membrane is modulated by the lipid charge distribution, enabling either passive ionic transport via membrane remodeling and pore formation or by peptide direct internalization independent of cellular transduction pathways.

Dynorphin 1-17 biotransformation peptides: properties, challenges and solutions for future therapeutics development.

It is well established that endogenously produced dynorphin 1-17 (DYN 1-17) is susceptible to enzymatic degradation, producing a variety of unique fragments in different tissue matrices and disease pathologies. DYN 1-17 and its major biotransformation fragments have significant roles in neurological and inflammatory disorders upon interacting with opioid and non-opioid receptors at both central and peripheral levels, thus highlighting their potential as drug candidates. Nevertheless, their development as promising therapeutics is challenged by several issues. This review aims to provide the latest and comprehensive updates on DYN 1-17 biotransformed peptides, including their pharmacological roles, pharmacokinetic studies and relevant clinical trials. Challenges in their development as potential therapeutics and proposed solutions to overcome these limitations are also discussed.

This is a summary of published articles on the important roles of dynorphin 1-17 and its fragments in several disease pathologies, including neurological and inflammatory disorders. Dynorphin 1-17, which consists of 17 amino acids, is a substance produced in the human body that is easily degraded by the body's enzymes, producing a shorter chain of amino acids. For the past few decades, researchers have attempted to utilize these substances to treat the above-mentioned conditions. However, upon introduction, these substances are rapidly degraded by the enzymes, which hinder the molecules from reaching the site of action. Therefore, many studies have focused on addressing the degradation issue in order to benefit from the important role of dynorphin 1-17 and its fragments in treating respective diseases. Previous researchers have attempted structural modification of these substances by either changing the terminals of the amino acid chains or attaching them to other agents to increase the resistance of dynorphin 1-17 and its fragments toward enzymatic breakage. These substances were also incorporated into nano-sized delivery systems, which have been shown to protect the molecules while improving their delivery to different parts of the body. These results showed that the structurally modified dynorphin 1-17 and its fragments and their nano-sized delivery system could improve the stability of the molecules and allow them to be used to treat many conditions.

Ginsenoside Rb1, a principal effective ingredient of Panax notoginseng, produces pain antihypersensitivity by spinal microglial dynorphin A expression.

Panax notoginseng (Chinese ginseng, Sanqi), one of the major ginseng species, has been traditionally used to alleviate different types of chronic pain. The raw P. notoginseng powder is commonly available in China as a non-prescription drug to treat various aliments including arthritic pain. However, strong scientific evidence is needed to illustrate its pain antihypersensitive effects, effective ingredients and mechanism of action. The oral P. notoginseng powder dose-dependently alleviated formalin-induced tonic hyperalgesia, and its total ginsenosides remarkably inhibited neuropathic pain hypersensitivity. Ginsenoside Rb1, the most abundant ginsenoside of P. notoginseng, dose-dependently produced neuropathic pain antihypersensitivity. Conversely, ginsenosides Rg1, Re and notoginseng R1, the other major saponins from P. notoginseng, failed to inhibit formalin-induced tonic pain or mechanical allodynia in neuropathic pain. Ginsenoside Rb1 metabolites ginsenosides Rg3, Compound-K and protopanaxadiol also had similar antineuropathic pain efficacy to ginsenoside Rb1. Additionally, intrathecal ginsenoside Rb1 specifically stimulated dynorphin A expression which was colocalized with microglia but not neurons or astrocytes in the spinal dorsal horn and primary cultured cells. Pretreatment with microglial metabolic inhibitor minocycline, dynorphin A antiserum and specific κ-opioid receptor antagonist GNTI completely blocked Rb1-induced mechanical antiallodynia in neuropathic pain. Furthermore, the specific glucocorticoid receptor (GR) antagonist Dex-21-mesylate (but not GPR30 estrogen receptor antagonist G15) also entirely attenuated ginsenoside Rb1-related antineuropathic pain effects. All these results, for the first time, show that P. notoginseng alleviates neuropathic pain and ginsenoside Rb1 is its principal effective ingredient. Furthermore, ginsenoside Rb1 inhibits neuropathic pain by stimulation of spinal microglial dynorphin A expression following GR activation.

Morphine-induced changes in the function of microglia and macrophages after acute spinal cord injury.

BACKGROUND: Opioids are among the most effective and commonly prescribed analgesics for the treatment of acute pain after spinal cord injury (SCI). However, morphine administration in the early phase of SCI undermines locomotor recovery, increases cell death, and decreases overall health in a rodent contusion model. Based on our previous studies we hypothesize that morphine acts on classic opioid receptors to alter the immune response. Indeed, we found that a single dose of intrathecal morphine increases the expression of activated microglia and macrophages at the injury site. Whether similar effects of morphine would be seen with repeated intravenous administration, more closely simulating clinical treatment, is not known. METHODS: To address this, we used flow cytometry to examine changes in the temporal expression of microglia and macrophages after SCI and intravenous morphine. Next, we explored whether morphine changed the function of these cells through the engagement of cell-signaling pathways linked to neurotoxicity using Western blot analysis. RESULTS: Our flow cytometry studies showed that 3 consecutive days of morphine administration after an SCI significantly increased the number of microglia and macrophages around the lesion. Using Western blot analysis, we also found that repeated administration of morphine increases ß-arrestin, ERK-1 and dynorphin (an endogenous kappa opioid receptor agonist) production by microglia and macrophages. CONCLUSIONS: These results suggest that morphine administered immediately after an SCI changes the innate immune response by increasing the number of immune cells and altering neuropeptide synthesis by these cells.

Properties and modulation of excitatory inputs to the locus coeruleus.

Excitatory inputs drive burst firing of locus coeruleus (LC) noradrenaline (NA) neurons in response to a variety of stimuli. Though a small number of glutamatergic LC afferents have been investigated, the overall landscape of these excitatory inputs is largely unknown. The current study used an optogenetic approach to isolate three glutamatergic afferents: the prefrontal cortex (PFC), lateral hypothalamus (LH) and periaqueductal grey (PAG). AAV5-DIO-ChR2 was injected into each region in male and female CaMKII-Cre mice and the properties of excitatory inputs on LC-NA cells were measured. Notably we found differences among these inputs. First, the pattern of axonal innervation differed between inputs such that LH afferents were concentrated in the posterior portion of the LC-NA somatic region while PFC afferents were denser in the medial dendritic region. Second, basal intrinsic properties varied for afferents, with LH inputs having the highest connectivity and the largest amplitude excitatory postsynaptic currents while PAG inputs had the lowest initial release probability. Third, while orexin and oxytocin had minimal effects on any input, dynorphin strongly inhibited excitatory inputs originating from the LH and PAG, and corticotrophin releasing factor (CRF) selectively inhibited inputs from the PAG. Overall, these results demonstrate that individual afferents to the LC have differing properties, which may contribute to the modularity of the LC and its ability to mediate various behavioural outcomes. KEY POINTS: Excitatory inputs to the locus coeruleus (LC) are important for driving noradrenaline neuron activity and downstream behaviours in response to salient stimuli, but little is known about the functional properties of different glutamate inputs that innervate these neurons We used a virus-mediated optogenetic approach to compare glutamate afferents from the prefrontal cortex (PFC), the lateral hypothalamus (LH) and the periaqueductal grey (PAG). While PFC was predicted to make synaptic inputs, we found that the LH and PAG also drove robust excitatory events in LC noradrenaline neurons. The strength, kinetics, and short-term plasticity of each input differed as did the extent of neuromodulation by both dynorphin and corticotrophin releasing factor. Thus each input displayed a unique set of basal properties and modulation by peptides. This characterization is an important step in deciphering the heterogeneity of the LC.

Dynorphin promotes stress-induced depressive behaviors by inhibiting ventral pallidal neurons in rats.

AIM: Endogenous dynorphin signaling via kappa opioid receptors (KORs) plays a key role in producing the depressive and aversive consequences of stress. We investigated the behavioral effects of the dynorphin/KOR system in the ventral pallidum (VP) and studied the underlying mechanisms. METHODS: To investigate the effects of dynorphin on the VP, we conducted behavioral experiments after microinjection of drugs or shRNA and brain-slice electrophysiological recordings. Histological tracing and molecular biological experiments were used to identify the distribution of KORs and the possible sources of dynorphin projections to the VP. RESULTS: An elevated dynorphin concentration and increased KOR activity were observed in the VP after acute stress. Infusion of dynorphin-A into the VP produced depressive-like phenotypes including anhedonia and despair and anxiety behaviors, but did not alter locomotor behavior. Mechanistically, dynorphin had an inhibitory effect on VP neurons-reducing their firing rate and inhibiting excitatory transmission-through direct activation of KORs and modulation of downstream G-protein-gated inwardly rectifying potassium (GIRK) channels and high-voltage gated calcium channels (VGCCs). Tracing revealed direct innervation of VP neurons by dynorphin-positive projections; potential sources of these dynorphinergic projections include the nucleus accumbens, amygdala, and hypothalamus. Blockade of dynorphin/KOR signaling in the VP by drugs or viral knock-down of KORs significantly reduced despair behavior in rats. CONCLUSIONS: Endogenous dynorphinergic modulation of the VP plays a critical role in mediating depressive reactions to stress.

Hyperandrogenism induces proportional changes in the expression of Kiss-1, Tac2, and DynA in hypothalamic KNDy neurons.

BACKGROUND: Kisspeptin released from Kiss-1 neurons in the hypothalamus plays an essential role in the control of the hypothalamic-pituitary-gonadal axis by regulating the release of gonadotropin-releasing hormone (GnRH). In this study, we examined how androgen supplementation affects the characteristics of Kiss-1 neurons. METHODS: We used a Kiss-1-expressing mHypoA-55 cell model that originated from the arcuate nucleus (ARC) of the mouse hypothalamus. These cells are KNDy neurons that co-express neurokinin B (NKB) and dynorphin A (DynA). We stimulated these cells with androgens and examined them. We also examined the ARC region of the hypothalamus in ovary-intact female rats after supplementation with androgens. RESULTS: Stimulation of mHypoA-55 cells with 100 nM testosterone significantly increased Kiss-1 gene expression by 3.20 ± 0.44-fold; testosterone also increased kisspeptin protein expression. The expression of Tac3, the gene encoding NKB, was also increased by 2.69 ± 0.64-fold following stimulation of mHypoA-55 cells with 100 nM testosterone. DynA gene expression in these cells was unchanged by testosterone stimulation, but it was significantly reduced at the protein level. Dihydrotestosterone (DHT) had a similar effect to testosterone in mHypoA-55 cells; kisspeptin and NKB protein expression was significantly increased by DHT, whereas it significantly reduced DynA expression. In ovary-intact female rats, DTH administration significantly increased the gene expression of Kiss-1 and Tac3, but not DynA, in the arcuate nucleus. Exogenous NKB and DynA stimulation failed to modulate Kiss-1 gene expression in mHypoA-55 cells. Unlike androgen stimulation, prolactin stimulation did not modulate kisspeptin, NKB, or DynA protein expression in these cells. CONCLUSIONS: Our observations imply that hyperandrogenemia affects KNDy neurons and changes their neuronal characteristics by increasing kisspeptin and NKB levels and decreasing DynA levels. These changes might cause dysfunction of the hypothalamic-pituitary-gonadal axis.

Optogenetic stimulation of lateral hypothalamic orexin/dynorphin inputs in the ventral tegmental area potentiates mesolimbic dopamine neurotransmission and promotes reward-seeking behaviours.

Reward and reinforcement processes are critical for survival and propagation of genes. While numerous brain systems underlie these processes, a cardinal role is ascribed to mesolimbic dopamine. However, ventral tegmental area (VTA) dopamine neurons receive complex innervation and various neuromodulatory factors, including input from lateral hypothalamic (LH) orexin/hypocretin neurons which also express and co-release the neuropeptide, dynorphin. Dynorphin in the VTA induces aversive conditioning through the Kappa opioid receptor (KOR) and decreases dopamine when administered intra-VTA. Exogenous application of orexin or orexin 1 receptor (oxR1) antagonists in the VTA bidirectionally modulates dopamine-driven motivation and reward-seeking behaviours, including the attribution of motivational value to primary rewards and associated conditioned stimuli. However, the effect of endogenous stimulation of LH orexin/dynorphin-containing projections to the VTA and the potential contribution of co-released dynorphin on mesolimbic dopamine and reward related processes remains uncharacterised. We combined optogenetic, electrochemical, and behavioural approaches to examine this. We found that optical stimulation of LH orexin/dynorphin inputs in the VTA potentiates mesolimbic dopamine neurotransmission in the nucleus accumbens (NAc) core, produces real time and conditioned place preference, and increases the food cue-directed orientation in a Pavlovian conditioning procedure. LH orexin/dynorphin potentiation of NAc dopamine release and real time place preference was blocked by an oxR1, but not KOR antagonist. Thus, rewarding effects associated with optical stimulation of LH orexin/dynorphin inputs in the VTA are predominantly driven by orexin rather than dynorphin.

Brain site-specific regulation of hedonic intake by orexin and DYN peptides: role of the PVN and obesity.

The orexin peptides promote hedonic intake and other reward behaviors through different brain sites. The opioid dynorphin peptides are co-released with orexin peptides but block their effects on reward in the ventral tegmental area (VTA). We previously showed that in the paraventricular hypothalamic nucleus (PVN), dynorphin and not orexin peptides enhance hedonic intake, suggesting they have brain-site-specific effects. Obesity alters the expression of orexin and dynorphin receptors, but whether their expression across different brain sites is important to hedonic intake is unclear. We hypothesized that hedonic intake is regulated by orexin and dynorphin peptides in PVN and that hedonic intake in obesity correlates with expression of their receptors. Here we show that in mice, injection of DYN-A1-13 (an opioid dynorphin peptide) in the PVN enhanced hedonic intake, whereas in the VTA, injection of OXA (orexin-A, an orexin peptide) enhanced hedonic intake. In PVN, OXA blunted the increase in hedonic intake caused by DYN-A1-13. In PVN, injection of norBNI (opioid receptor antagonist) reduced hedonic intake but a subsequent OXA injection failed to increase hedonic intake, suggesting that OXA activity in PVN is not influenced by endogenous opioid activity. In the PVN, DYN-A1-13 increased the intake of the less-preferred food in a two-food choice task. In obese mice fed a cafeteria diet, orexin 1 receptor mRNA across brain sites involved in hedonic intake correlated with fat preference but not caloric intake. Together, these data support that orexin and dynorphin peptides regulate hedonic intake in an opposing manner with brain-site-specific effects.

Oxytocin Is a Positive Allosteric Modulator of κ-Opioid Receptors but Not δ-Opioid Receptors in the G Protein Signaling Pathway.

Oxytocin (OT) influences various physiological functions such as uterine contractions, maternal/social behavior, and analgesia. Opioid signaling pathways are involved in one of the analgesic mechanisms of OT. We previously showed that OT acts as a positive allosteric modulator (PAM) and enhances µ-opioid receptor (MOR) activity. In this study, which focused on other opioid receptor (OR) subtypes, we investigated whether OT influences opioid signaling pathways as a PAM for δ-OR (DOR) or κ-OR (KOR) using human embryonic kidney-293 cells expressing human DOR or KOR, respectively. The CellKeyTM results showed that OT enhanced impedance induced by endogenous/exogenous KOR agonists on KOR-expressing cells. OT did not affect DOR activity induced by endogenous/exogenous DOR agonists. OT potentiated the KOR agonist-induced Gi/o protein-mediated decrease in intracellular cAMP, but did not affect the increase in KOR internalization caused by the KOR agonists dynorphin A and (-)-U-50488 hydrochloride (U50488). OT did not bind to KOR orthosteric binding sites and did not affect the binding affinities of dynorphin A and U50488 for KOR. These results suggest that OT is a PAM of KOR and MOR and enhances G protein signaling without affecting ß-arrestin signaling. Thus, OT has potential as a specific signaling-biased PAM of KOR.

Inhaled [D-Ala2]-Dynorphin 1-6 Prevents Hyperacetylation and Release of High Mobility Group Box 1 in a Mouse Model of Acute Lung Injury.

COVID-19 is a respiratory infection caused by the SARS-CoV-2 virus that can rapidly escalate to life-threatening pneumonia and acute respiratory distress syndrome (ARDS). Recently, extracellular high mobility group box 1 (HMGB1) has been identified as an essential component of cytokine storms that occur with COVID-19; HMGB1 levels correlate significantly with disease severity. Thus, the modulation of HMGB1 release may be vital for treating COVID-19. HMGB1 is a ubiquitous nuclear DNA-binding protein whose biological function depends on posttranslational modifications, its redox state, and its cellular localization. The acetylation of HMGB1 is a prerequisite for its translocation from the nucleus to the cytoplasm and then to the extracellular milieu. When released, HMGB1 acts as a proinflammatory cytokine that binds primarily to toll-like receptor 4 (TLR4) and RAGE, thereby stimulating immune cells, endothelial cells, and airway epithelial cells to produce cytokines, chemokines, and other inflammatory mediators. In this study, we demonstrate that inhaled [D-Ala2]-dynorphin 1-6 (leytragin), a peptide agonist of δ-opioid receptors, significantly inhibits HMGB1 secretion in mice with lipopolysaccharide- (LPS-) induced acute lung injury. The mechanism of action involves preventing HMGB1's hyperacetylation at critical lysine residues within nuclear localization sites, as well as promoting the expression of sirtuin 1 (SIRT1), an enzyme known to deacetylate HMGB1. Leytragin's effects are mediated by opioid receptors, since naloxone, an antagonist of opioid receptors, abrogates the leytragin effect on SIRT1 expression. Overall, our results identify leytragin as a promising therapeutic agent for the treatment of pulmonary inflammation associated with HMGB1 release. In a broader context, we demonstrate that the opioidergic system in the lungs may represent a promising target for the treatment of inflammatory lung diseases.

Quantification of kappa opioid receptor ligand potency, efficacy and desensitization using a real-time membrane potential assay.

We explored the utility of the real-time FLIPR Membrane Potential (FMP) assay as a method to assess kappa opioid receptor (KOR)-induced hyperpolarization. The FMP Blue dye was used to measure fluorescent signals reflecting changes in membrane potential in KOR expressing CHO (CHO-KOR) cells. Treatment of CHO-KOR cells with kappa agonists U50,488 or dynorphin [Dyn (1-13)NH2] produced rapid and concentration-dependent decreases in FMP Blue fluorescence reflecting membrane hyperpolarization. Both the nonselective opioid antagonist naloxone and the κ-selective antagonists nor-binaltorphimine (nor-BNI) and zyklophin produced rightward shifts in the U50,488 concentration-response curves, consistent with competitive antagonism of the KOR mediated response. The decrease in fluorescent emission produced by U50,488 was blocked by overnight pertussis toxin pretreatment, indicating the requirement for PTX-sensitive G proteins in the KOR mediated response. We directly compared the potency of U50,488 and Dyn (1-13)NH2 in the FMP and [35S]GTPγS binding assays, and found that both were approximately 10 times more potent in the cellular fluorescence assay. The maximum responses of both U50,488 and Dyn (1-13)NH2 declined following repeated additions, reflecting receptor desensitization. We assessed the efficacy and potency of structurally distinct KOR small molecule and peptide ligands. The FMP assay reliably detected both partial agonists and stereoselectivity. Using KOR-selective peptides with varying efficacies, we found that the FMP assay allowed high throughput quantification of peptide efficacy. These data demonstrate that the FMP assay is a sensitive method for assessing κ-opioid receptor induced hyperpolarization, and represents a useful approach for quantification of potency, efficacy and desensitization of KOR ligands.

Improving the Utility of a Dynorphin Peptide Analogue Using Mannosylated Glycoliposomes.

Peptide therapeutics offer numerous advantages in the treatment of diseases and disorders of the central nervous system (CNS). However, they are not without limitations, especially in terms of their pharmacokinetics where their metabolic lability and low blood-brain barrier penetration hinder their application. Targeted nanoparticle delivery systems are being tapped for their ability to improve the delivery of therapeutics into the brain non-invasively. We have developed a family of mannosylated glycoliposome delivery systems for targeted drug delivery applications. Herein, we demonstrate via in vivo distribution studies the potential of these glycoliposomes to improve the utility of CNS active therapeutics using dynantin, a potent and selective dynorphin peptide analogue antagonist of the kappa opioid receptor (KOR). Glycoliposomal entrapment protected dynantin against known rapid metabolic degradation and ultimately improved brain levels of the peptide by approximately 3-3.5-fold. Moreover, we linked this improved brain delivery with improved KOR antagonist activity by way of an approximately 30-40% positive modulation of striatal dopamine levels 20 min after intranasal administration. Overall, the results clearly highlight the potential of our glycoliposomes as a targeted delivery system for therapeutic agents of the CNS.

Dynorphin A (1-8) inhibits oxidative stress and apoptosis in MCAO rats, affording neuroprotection through NMDA receptor and κ-opioid receptor channels.

The contents of Dynorphin A(1-8) decreased gradually in ischemic cortices in rats and an intracerebroventricular administration of synthetic Dynorphin A(1-8) reduced the volume of cerebral infarction in our previous research. However, the specific protective mechanism is unclear and Dynorphin A(1-8) is unlikely to cross the blood-brain barrier (BBB) by noninvasive oral or intravenous administration as a macromolecule neuropeptide. In this study, intranasal administration was used to middle cerebral artery occlusion(MCAO) rats to assessed the therapeutic effects of Dynorphin A(1-8) by evaluating behavior, volume of cerebral infarct, cerebral edema ratio, histological observation. Then apoptosis neuron rate was detected by TUNEL staining. Immunohistochemical staining was carried out to explore the alteration of Bcl-2, Bax and Caspase-3. Finally, κ-opioid receptor antagonist and N-methyl-d-aspartate(NMDA) receptor antagonist were used to explore its possible mechanism. We found that MCAO rats under intranasal administration of Dynorphin A(1-8) showed better behavioral improvement, higher extent of Bcl-2, activity of SOD along with much lower level of infarction volume, brain water content, number of cell apoptosis, extent of Bax and Caspase-3, and concentration of MDA compared with those in MCAO model group and intravenous Dynorphin A(1-8) group. Administration of nor-BNI or MK-801 reversed these neuroprotective effects of intranasal Dynorphin A(1-8). In summary, Dynorphin A(1-8), with advantages of intranasal administration, could be effectively delivered to central nervous system(CNS). Dynorphin A(1-8) inhibited oxidative stress and apoptosis against cerebral ischemia/reperfusion injury, affording neuroprotection through NMDA receptor and κ-opioid receptor channels.

Dysregulation of Nociceptin/Orphanin FQ and Dynorphin Systems in the Extended Amygdala of Alcohol Preferring Marchigian Sardinian (msP) Rats.

Previous studies have shown that genetically selected Marchigian Sardinian alcohol-preferring (msP) rats consume excessive amounts of ethanol to self-medicate from negative moods and to relieve innate hypersensitivity to stress. This phenotype resembling a subset of alcohol use disorder (AUD) patients, appears to be linked to a dysregulation of the equilibrium between stress and antistress mechanisms in the extended amygdala. Here, comparing water and alcohol exposed msP and Wistar rats we evaluate the transcript expression of the anti-stress opioid-like peptide nociceptin/orphanin FQ (N/OFQ) and its receptor NOP as well as of dynorphin (DYN) and its cognate κ-opioid receptor (KOP). In addition, we measured the transcript levels of corticotropin-releasing factor (CRF), CRF receptor 1 (CRF1R), brain-derived neurotrophic factor (BDNF) and of the tropomyosin receptor kinase B receptor (Trk-B). Results showed an innately up-regulation of the CRFergic system, mediating negative mood and stress responses, as well as an inherent up-regulation of the anti-stress N/OFQ system, both in the amygdala (AMY) and bed nucleus of the stria terminalis (BNST) of msP rats. The up-regulation of this latter system may reflect an attempt to buffer the negative condition elicited by the hyperactivity of pro-stress mechanisms since results showed that voluntary alcohol consumption dampened N/OFQ. Alcohol exposure also reduced the expression of dynorphin and CRF transmissions in the AMY of msP rats. In the BNST, alcohol intake led to a more complex reorganization of these systems increasing receptor transcripts in msP rats, along with an increase of CRF and a decrease of N/OFQ transcripts, respectively. Moreover, mimicking the effects of alcohol in the AMY we observed that the activation of NOP receptor by intracerebroventricular administration of N/OFQ in msP rats caused an increase of BDNF and a decrease of CRF transcripts. Our study indicates that both stress and anti-stress mechanisms are dysregulated in the extended AMY of msP rats. The voluntary alcohol drinking, as well as NOP agonism, have a significant impact on neuropeptidergic systems arrangement, bringing the systems back to normalization.

Conformational Constraint between Aromatic Residue Side Chains in the "Message" Sequence of the Peptide Arodyn Using Ring Closing Metathesis Results in a Potent and Selective Kappa Opioid Receptor Antagonist.

Kappa opioid receptor (KOR) antagonists have recently shown potential for treating drug addiction and mood disorders. The linear acetylated dynorphin A analog arodyn (Ac[Phe1,2,3,Arg4,d-Ala8]dynorphin A-(1-11)NH2), synthesized in our laboratory, demonstrated potent and selective KOR antagonism. Cyclization of arodyn could potentially stabilize the bioactive conformation and enhance its metabolic stability. The cyclization strategy employed involved ring closing metathesis between adjacent meta- or para-substituted Tyr(allyl) residues in the "message" sequence that were predicted in a docking study to yield analogs that would bind to the KOR with binding poses similar to arodyn. Consistent with the modeling, the resulting analogs retained KOR affinity similar to arodyn; the peptides involving cyclization between para O-allyl groups also retained high KOR selectivity, with one analog exhibiting KOR antagonist potency (KB = 15 nM) similar to arodyn. These promising cyclized analogs with constrained aromatic residues represent novel leads for further exploration of KOR pharmacology.

Kappa opioid receptor controls neural stem cell differentiation via a miR-7a/Pax6 dependent pathway.

Although the roles of opioid receptors in neurogenesis have been implicated in previous studies, the mechanism by which κ-opioid receptor (OPRK1) regulates adult neurogenesis remains elusive. We now demonstrate that two agonists of OPRK1, U50,488H and dynorphin A, inhibit adult neurogenesis by hindering neuronal differentiation of mouse hippocampal neural stem cells (NSCs), both in vitro and in vivo. This effect was blocked by nor-binaltorphimine (nor-BNI), a specific antagonist of OPRK1. By examining neurogenesis-related genes, we found that OPRK1 agonists were able to downregulate the expression of Pax6, Neurog2, and NeuroD1 in mouse hippocampal NSCs, in a way that Pax6 regulates the transcription of Neurog2 and Neurod1 by directly interacting with their promoters. Moreover, this effect of OPRK1 was accomplished by inducing expression of miR-7a, a miRNA that specifically targeted Pax6 by direct interaction with its 3'-UTR sequence, and thereby decreased the levels of Pax6, Neurog2, and NeuroD1, thus resulted in hindrance of neuronal differentiation of NSCs. Thus, by modulating Pax6/Neurog2/NeuroD1 activities via upregulation of miR-7a expression, OPRK1 agonists hinder the neuronal differentiation of NSCs and hence inhibit adult neurogenesis in mouse hippocampus.

Unique Pharmacological Properties of the Kappa Opioid Receptor Signaling Through Gαz as Shown with Bioluminescence Resonance Energy Tranfer.

Opioid receptors (ORs) convert extracellular messages to signaling events by coupling to the heterotrimeric G proteins, Gα•ßγ Classic pharmacological methods, such as [35S]GTPγS binding and inhibition of cyclic AMP production, allow for general opioid characterization, but they are subject to the varying endogenous Gα proteins in a given cell type. Bioluminescence resonance energy transfer (BRET) technology offers new insight by allowing the direct observation of Gα subunit-specific effects on opioid pharmacology. Using a Venus-tagged Gßγ and nanoluciferase-tagged truncated G protein receptor kinase 3, an increase in BRET signal correlated with OR activation mediated by a specific Gα protein. The magnitude of the BRET signal was normalized to the maximum response obtained with 10 µM 2-(3,4-dichlorophenyl)-N-methyl-N-[(1R,2R)-2-pyrrolidin-1-ylcyclohexyl]acetamide (U50,488) for the kappa OR (KOR). Opioids reached equilibrium with the KOR, and concentration-response curves were generated. Although the full agonists U50,488, salvinorin A, nalfurafine, and dynorphin peptides were equally efficacious regardless of the Gα subunit present, the concentration-response curves were leftward shifted when the KOR was signaling through Gαz compared with other Gαi/o subunits. In contrast, the Gα subunit distinctly affected both the efficacy and potency of partial kappa agonists, such as the benzomorphans, and the classic mu opioid antagonists, naloxone, naltrexone, and nalmefene. For example, (-)pentazocine had EC50 values of 7.3 and 110 nM and maximal stimulation values of 79% and 35% when the KOR signaled through Gαz and Gαi1, respectively. Together, these observations suggest KOR pharmacology varies based on the specific Gα subunit coupled to the KOR. SIGNIFICANCE STATEMENT: Opioid receptors couple to various heterotrimeric Gαßγ proteins to convert extracellular cues to precise intracellular events. This paper focuses on how the various inhibitory Gα subunits influence the pharmacology of full and partial agonists at the kappa opioid receptor. Using a bioluminescent assay, the efficacy and potency of kappa opioids was determined. Opioid signaling was more potent through Gαz compared with other Gα proteins. These observations suggest that Gαz may impact opioid pharmacology and cellular physiology more than previously thought.

The endomorphin-1/2 and dynorphin-B peptides display biased agonism at the mu opioid receptor.

BACKGROUND: Opioid agonist activation at the mu opioid receptor (MOR) can lead to a wide variety of physiological responses. Many opioid agonists share the ability to selectively and preferentially activate specific signaling pathways, a term called biased agonism. Biased opioid ligands can theoretically induce specific physiological responses and might enable the generation of drugs with improved side effect profiles. METHODS: Dynorphins, enkephalins, and endomorphins are endogenous opioid agonist peptides that may possess distinct bias profiles; biased agonism of endogenous peptides could explain the selective roles of these ligands in vivo. Our purpose in the present study was to investigate biased signaling and potential underlying molecular mechanisms of bias using 35S-GTPγS and cAMP assays, specifically focusing on the role of adenylyl cyclases (ACs) and regulators of G-protein signaling proteins (RGSs) in CHO, N2a, and SH-SY5Y cell lines, all expressing the human MOR. RESULTS: We found that endomorphin-1/2 preferentially activated cAMP signaling, while dynorphin-B preferentially activated 35S-GTPγS signaling in most cell lines. Experiments carried out in the presence of an isoform selective RGS-4 inhibitor, and siRNA knockdown of AC6 in N2a cells did not significantly affect the bias properties of endomorphins, suggesting that these proteins may not play a role in endomorphin bias. CONCLUSION: We found that endomorphin-1/2 and dynorphin-B displayed contrasting bias profiles at the MOR, and ruled out potential AC6 and RGS4 mechanisms in this bias. This identified signaling bias could be involved in specifying endogenous peptide roles in vivo, where these peptides have low selectivity between opioid receptor family members.