Differential biotransformation of dynorphin A (1-17) and dynorphin A (1-13) peptides in human blood, ex vivo

Design and development of novel, short, stable dynorphin-based opioid agonists for safer analgesic therapy

Kappa opioid receptors have exceptional potential as an analgesic target, seemingly devoid of many problematic Mu receptor side-effects. Kappa-selective, small molecule pharmaceutical agents have been developed, but centrally mediated side-effects limit clinical translation. We modify endogenous dynorphin peptides to improve drug-likeness and develop safer KOP receptor agonists for clinical use. Using rational, iterative design, we developed a series of potent, selective, and metabolically stable peptides from dynorphin 1-7. Peptides were assessed for in vitro cAMP-modulation against three opioid receptors, metabolic stability, KOP receptor selectivity, desensitisation and pERK-signalling capability. Lead peptides were evaluated for in vivo efficacy in a rat model of inflammatory nociception. A library of peptides was synthesised and assessed for pharmacological and metabolic stability. Promising peptide candidates showed low nanomolar KOP receptor selectivity in cAMP assay, and improved plasma and trypsin stability. Selected peptides showed bias towards cAMP signalling over pERK activity, also demonstrating reduced desensitisation. In vivo, two peptides showed significant opioid-like antinociception comparable to morphine and U50844H. These highly potent and metabolically stable peptides are promising opioid analgesic leads for clinical translation. Since they are somewhat biased peptide Kappa agonists they may lack many significant side-effects, such as tolerance, addiction, sedation, and euphoria/dysphoria, common to opioid analgesics.

Induced dysregulation of ACE2 by SARS-CoV-2 plays a key role in COVID-19 severity

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, is reported to increase the rate of mortality worldwide. COVID-19 is associated with acute respiratory symptoms as well as blood coagulation in the vessels (thrombosis), heart attack and stroke. Given the requirement of angiotensin converting enzyme 2 (ACE2) receptor for SARS-CoV-2 entry into host cells, here we discuss how the downregulation of ACE2 in the COVID-19 patients and virus-induced shift in ACE2 catalytic equilibrium, change the concentrations of substrates such as angiotensin II, apelin-13, dynorphin-13, and products such as angiotensin (1-7), angiotensin (1-9), apelin-12, dynorphin-12 in the human body. Substrates accumulation ultimately induces inflammation, angiogenesis, thrombosis, neuronal and tissue damage while diminished products lead to the loss of the anti-inflammatory, anti-thrombotic and anti-angiogenic responses. In this review, we focus on the viral-induced imbalance between ACE2 substrates and products which exacerbates the severity of COVID-19. Considering the roadmap, we propose multiple therapeutic strategies aiming to rebalance the products of ACE2 and to ameliorate the symptoms of the disease.

Strategies for Developing κ Opioid Receptor Agonists for the Treatment of Pain with Fewer Side Effects

There is significant need to find effective, nonaddictive pain medications. κ Opioid receptor (KOPr) agonists have been studied for decades but have recently received increased attention because of their analgesic effects and lack of abuse potential. However, a range of side effects have limited the clinical development of these drugs. There are several strategies currently used to develop safer and more effective KOPr agonists. These strategies include identifying G-protein-biased agonists, developing peripherally restricted KOPr agonists without centrally mediated side effects, and developing mixed opioid agonists, which target multiple receptors at specific ratios to balance side-effect profiles and reduce tolerance. Here, we review the latest developments in research related to KOPr agonists for the treatment of pain. SIGNIFICANCE STATEMENT: This review discusses strategies for developing safer κ opioid receptor (KOPr) agonists with therapeutic potential for the treatment of pain. Although one strategy is to modify selective KOPr agonists to create peripherally restricted or G-protein-biased structures, another approach is to combine KOPr agonists with μ, δ, or nociceptin opioid receptor activation to obtain mixed opioid receptor agonists, therefore negating the adverse effects and retaining the therapeutic effect.

The permeation of dynorphin A 1-6 across the blood brain barrier and its effect on bovine brain microvessel endothelial cell monolayer permeability

Dynorphin A 1-17 (Dyn A 1-17) is an endogenous neuropeptide known to act at the kappa opioid receptor; it has been implicated in a number of neurological disorders, including neuropathic pain, stress, depression, and Alzheimer's and Parkinson's diseases. The investigation of Dyn A 1-17 metabolism at the blood-brain barrier (BBB) is important since the metabolites exhibit unique biological functions compared to the parent compound. In this work, Dyn A 1-6 is identified as a metabolite of Dyn A 1-17 in the presence of bovine brain microvessel endhothelial cells (BBMECs), using LC-MS/MS. The transport of Dyn A 1-6 at the BBB was examined using this in vitro cell culture model of the BBB. Furthermore, the permeation of the BBB by the low molecular weight permeability marker fluorescein was characterized in the presence and absences of Dyn A 1-6.

2',6'-dimethylphenylalanine: a useful aromatic amino Acid surrogate for tyr or phe residue in opioid peptides

Two aromatic amino acids, Tyr(1) and Phe(3) or Phe(4), are important structural elements in opioid peptides because they interact with opioid receptors. The usefulness of an artificial amino acid residue 2',6'-dimethylphenylalanine (Dmp) was investigated as an aromatic amino acid surrogate for several opioid peptides, including enkephalin, dermorphin, deltorphin, endomorphin, dynorphin A, and nociceptin peptides. In most peptides, substitutions of Phe(3) by a Dmp residue produced analogs with improved receptor-binding affinity and selectivity, while the same substitution of Phe(4) induced markedly reduced receptor affinity and selectivity. Interestingly, replacement of Tyr(1) by Dmp produced analogs with unexpectedly high affinity or produced only a slight drop in receptor affinity and bioactivity for most peptides. Thus, Dmp is also a useful surrogate for the N-terminal Tyr residue in opioid peptides despite the lack of a phenolic hydroxyl group, which is considered necessary for opioid activity. The Dmp(1)-substituted analogs are superior to 2',6'-dimethyltyrosine (Dmt)(1)-substituted analogs for high receptor selectivity since the latter generally have poor receptor selectivity. Thus, Dmp is very useful as an aromatic amino acid surrogate in opioid peptides and may be useful for developing other novel peptide mimetics with high receptor specificity.

Evaluation of an on-capillary copper complexation methodology for the investigation of in vitro metabolism of dynorphin A 1-17

Dynorphin A 1-17 is an endogenous neuropeptide implicated in a variety of neurological disorders including Alzheimer's and Parkinson's diseases and neuropathic pain. Metabolites of this peptide can exhibit their own unique effects in vivo, and it is possible that one of these metabolites is responsible for the neurotoxicity. In this article, the use of CE for the separation of dynorphin A 1-17 from four of its metabolites is described. Buffer additives were investigated to eliminate peptide adsorption to the capillary wall and to improve resolution between closely related metabolites. On-capillary copper complexation was employed and was shown to improve separation efficiency as compared with the separation of native peptides. The method was then applied to in vitro dynorphin metabolism in human plasma as well as rat brain and rat spinal cord slices.

Peptide kappa opioid receptor ligands: potential for drug development

While narcotic analgesics such as morphine, which act preferentially through mu opioid receptors, remain the gold standard in the treatment of severe pain, their use is limited by detrimental liabilities such as respiratory depression and drug dependence. Thus, there has been considerable interest in developing ligands for kappa opioid receptors (KOR) as potential analgesics and for the treatment of a variety of other disorders. These include effects mediated both by central receptors, such as antidepressant activity and a reduction in cocaine-seeking behavior, and activity resulting from the activation of peripheral receptors, such as analgesic and anti-inflammatory effects. While the vast majority of opioid receptor ligands that have progressed in preclinical development have been small molecules, significant advances have been made in recent years in identifying opioid peptide analogs that exhibit promising in vivo activity. This review will focus on possible therapeutic applications of ligands for KOR and specifically on the potential development of peptide ligands for these receptors.

Opioids, dopamine, stress, and the addictions

The articulated goals of Dialogues in Clinical Neuroscience are to serve as "an interface between clinical neuropsychiatry and the neurosciences by providing state-of-the-art information and original insights into relevant clinical, biological, and therapeutic aspects." My laboratory the Laboratory of the Biology of Addictive Diseases at The Rockefeller University, has for years been focused on "bidirectional translational research," that is, learning by careful observations and study in patient populations with the disorders under study, in this case primarily specific addictive diseases, and then using that knowledge to create improved animal models or other laboratory-based research paradigms, while, at the same time, taking research findings made at the bench into the clinic as promptly as that is appropriate and feasible. In this invited review, therefore, the focus will be on perspectives of our Laboratory of the Biology of Addictive Diseases and related National Institutes of Health/National Institute on Drug Abuse research Center, including laboratory-based molecular neurobiological research, research using several animal models designed to mimic human patterns of drug abuse and addiction, as well as basic clinical research, intertwined with treatment-related research.

Caspase-3 activity is reduced after spinal cord injury in mice lacking dynorphin: differential effects on glia and neurons

Dynorphins are endogenous opioid peptide products of the prodynorphin gene. An extensive literature suggests that dynorphins have deleterious effects on CNS injury outcome. We thus examined whether a deficiency of dynorphin would protect against tissue damage after spinal cord injury (SCI), and if individual cell types would be specifically affected. Wild-type and prodynorphin(-/-) mice received a moderate contusion injury at 10th thoracic vertebrae (T10). Caspase-3 activity at the injury site was significantly decreased in tissue homogenates from prodynorphin(-/-) mice after 4 h. We examined frozen sections at 4 h post-injury by immunostaining for active caspase-3. At 3-4 mm rostral or caudal to the injury, >90% of all neurons, astrocytes and oligodendrocytes expressed active caspase-3 in both wild-type and knockout mice. At 6-7 mm, there were fewer caspase-3(+) oligodendrocytes and astrocytes than at 3-4 mm. Importantly, caspase-3 activation was significantly lower in prodynorphin(-/-) oligodendrocytes and astrocytes, as compared with wild-type mice. In contrast, while caspase-3 expression in neurons also declined with further distance from the injury, there was no effect of genotype. Radioimmunoassay showed that dynorphin A(1-17) was regionally increased in wild-type injured versus sham-injured tissues, although levels of the prodynorphin processing product Arg(6)-Leu-enkephalin were unchanged. Our results indicate that dynorphin peptides affect the extent of post-injury caspase-3 activation, and that glia are especially sensitive to these effects. By promoting caspase-3 activation, dynorphin peptides likely increase the probability of glial apoptosis after SCI. While normally beneficial, our findings suggest that prodynorphin or its peptide products become maladaptive following SCI and contribute to secondary injury.

Dynorphin peptides differentially regulate the human kappa opioid receptor

Dynorphins, endogenous peptides for the kappa opioid receptor, play important roles in many physiological and pathological functions. Here, we examined how prolonged treatment with three major prodynorphin peptides, dynorphin A (1-17) (Dyn A), dynorphin B (1-13) (Dyn B) and alpha-neoendorphin (alpha-Neo), regulated the human kappa opioid receptor (hKOR) stably expressed in Chinese hamster ovary (CHO) cells. Results from receptor binding and [(35)S]GTPgammaS binding assays showed that these peptides were potent full agonists of the hKOR with comparable receptor reserve and intrinsic efficacy to stimulate G proteins. A 4-h incubation with alpha-Neo at a concentration of approximately 600xEC(50) value (from [(35)S]GTPgammaS binding) resulted in receptor down-regulation to a much lower extent than the incubation with Dyn A and Dyn B at comparable concentrations ( approximately 10% vs. approximately 65%). Extending incubation period and increasing concentrations did not significantly affect the difference. The plateau level of alpha-Neo-mediated receptor internalization (30 min) was significantly less than those of Dyn A and Dyn B. Omission of the serum from the incubation medium or addition of peptidase inhibitors into the serum-containing medium enhanced alpha-Neo-, but not Dyn A- or Dyn B-, mediated receptor down-regulation and internalization; however, the degrees of alpha-Neo-induced adaptations were still significantly less than those of Dyn A and Dyn B. Thus, these endogenous peptides differentially regulate KOR after activating the receptor with similar receptor occupancy and intrinsic efficacy. Both stability in the presence of serum and intrinsic capacity to promote receptor adaptation play roles in the observed discrepancy among the dynorphin peptides.

ORL1 and opioid receptor preferences of nociceptin and dynorphin A analogues with Dmp substituted for N-terminal aromatic residues

Nociceptin (NOC) and dynorphin A (DYN) analogues containing 2',6'-dimethylphenylalanine (Dmp) in place of Phe or Tyr in position 1 and/or 4 were synthesized and their metabolic stability and receptor-binding properties were investigated. [Dmp1]NOC(1-13)-NH2 (1) possessed high ORL1 receptor affinity comparable to that of the parent peptide with substantially improved affinities for kappa-, mu-, and delta-opioid receptors. However, Dmp4 substitution of NOC peptide (2) reduced ORL1 receptor affinity. [Dmp1]DYN(1-13)-NH2 (4) and its Dmp4 analogue (5) possessed a 3-fold greater kappa-opioid receptor affinity and improved kappa-receptor selectivity compared to the parent peptide. Analogue 4 however exhibited an unexpectedly low in vitro bioactivity (GPI assay), suggesting, the phenolic hydroxyl group at the N-terminal residue in DYN peptide is extremely important for activation of the kappa-opioid receptor. Analogue 5 possessed an improved kappa-opioid receptor selectivity with an IC50 ratio of 1(kappa)/509(mu)/211598(delta); thus, this peptide may serve as a highly selective kappa-receptor agonist for pharmacological study. Dmp1 substitution in both the NOC and DYN peptides improved metabolic stability toward these peptides, while Dmp4 substitution provided no additional metabolic stability.

Altered extracellular striatal in vivo biotransformation of the opioid neuropeptide dynorphin A(1-17) in the unilateral 6-OHDA rat model of Parkinson's disease

The in vivo biotransformation of dynorphin A(1-17) (Dyn A) was studied in the striatum of hemiparkinsonian rats by using microdialysis in combination with nanoflow reversed-phase liquid chromatography/electrospray time-of-flight mass spectrometry. The microdialysis probes were implanted into both hemispheres of unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats. Dyn A (10 pmol microl(-1)) was infused through the probes at 0.4 microl min(-1) for 2 h. Samples were collected every 30 min and analyzed by mass spectrometry. The results showed for the first time that there was a difference in the Dyn A biotransformation when comparing the two corresponding sides of the brain. Dyn A metabolites 1-8, 1-16, 5-17, 10-17, 7-10 and 8-10 were detected in the dopamine-depleted striatum but not in the untreated striatum. Dyn A biotransformed fragments found in both hemispheres were N-terminal fragments 1-4, 1-5, 1-6, 1-11, 1-12 and 1-13, C-terminal fragments 2-17, 3-17, 4-17, 7-17 and 8-17 and internal fragments 2-5, 2-10, 2-11, 2-12, and 8-15. The relative levels of these fragments were lower in the dopamine-depleted striatum. The results imply that the extracellular in vivo processing of the dynorphin system is being disturbed in the 6-OHDA-lesion animal model of Parkinson's disease.

Evolving perspectives on neurobiological research on the addictions: celebration of the 30th anniversary of NIDA

The roots of the Laboratory of the Biology of the Addictive Diseases are in the development of methadone maintenance for the treatment of opiate addiction. Methadone maintenance therapy continues to be one of the major effective forms of addiction pharmacotherapy and underscores the importance of biological factors in the physiology and treatment of the addictive diseases. Recent work in the Laboratory has focused on the neurobiological, neurochemical, neuroendocrine and behavioral aspects of addictive diseases (principally cocaine and the opiate addictions), using an interdisciplinary approach. The models we have focused on range from in vitro molecular biology and neuroscience, to in vivo animal models, to experiments in normal human populations and patients with specific addictive diseases, and most recently to the human molecular genetics of different addictive diseases. Two long-term corollary hypotheses have guided the Laboratory's work: (1) That the endogenous opioid peptide/receptor systems play a central role in the addictive states and therefore in their treatment. (2) That atypical responsivity to stressors (e.g., in the hypothalamic-pituitary-adrenal axis) plays a role in vulnerability and relapse to specific addictive diseases. This atypical responsivity may be drug-induced, environmentally acquired, and/or due to genetic variation.

Dynorphin-A(1–17) decreases nitric oxide release and cytotoxicity induced with lipopolysaccharide plus interferon-γ in murine macrophage cell line J774

Nitric oxide (NO) is an important mediator of cytotoxicity caused by macrophages or by their resident counterpart in brain-glial cells. Modulation of NO release by both activated macrophages and glial cells has been reported in the presence of endogenous (peptide) and synthetic (non-peptide) agonists with kappa opioid-receptors (KOR) selectivity. The data obtained with macrophages and glial cells are contradictory: enhanced NO release by mouse macrophages was reported in the presence of synthetic agonist of KOR selectivity (Neuropeptides 32 (1998) 287), and decreased NO release by glial cells, in the presence of dynorphin-A((1-8)), endogenous opioid peptide with KOR selectivity (J. Biomed. Sci. 7 (2000) 241). In this study, we used a murine cell line J774 of macrophage origin and examined the effect of dynorphin-A((1-17)), endogenous opioid peptide with selectivity for KOR, on NO release induced with lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). Dynorphin-A((1-17)) was chosen since in comparison to dynorphin-A((1-13)), it is more resistant to biodegradation (Peptides 17 (1996) 983), and its effects during prolonged treatment of cells could be more pronounced. The effect of dynorphin-A((1-17)) on NO release was compared to its effect on cytotoxicity, induced with LPS plus IFN-gamma. The data obtained have shown that activation-induced NO release by J774 cells is decreased in the presence of dynorphin-A((1-17)). This was associated with deceased LPS and IFN-gamma-induced cytotoxicity of J774 cells, suggesting their causal relationship. Neither of the observed effects of dynorphin-A((1-17)) could be prevented with the KOR selective antagonist, norbinaltorphimine, suggesting that they are mediated via non-opioid mechanism. By diminishing NO release dynorphin-A((1-17)) may affect cytotoxic ability of macrophages, but may also beneficially influence inflammation-induced damage of local tissue.

Metabolism of dynorphins by peptidases of pulmonary artery endothelial cells

Degradation of several dynorphins by peptidases expressed in cultured porcine pulmonary artery endothelial cells was studied by incubation of the peptide in cell suspensions followed by electrospray ionization and tandem mass spectrometric analyses. Under the in vitro conditions applied, only the metabolism of dynorphin A1-8 occurred in a significant extent. Studies involving specific peptidase inhibitors indicated that mainly bestatin-sensitive aminopeptidases, thiorphan-sensitive endopeptidases, and cFPAAF-pAB-sensitive endopeptidases expressed by the endothelial cells were involved in the process that converted dynorphin A1-8 to dynorphin A2-8, dynorphin A1-6, and leucine enkephalin (dynorphin A1-5), respectively. These peptidases may form a metabolic barrier for the cellular penetration of intact dynorphin A1-8 and/or control effects of the circulating peptide on endothelial opioid receptors of the cells.

Suppressed prolactin response to dynorphin A1-13 in methadone-maintained versus control subjects

Dynorphin A1-13, a shortened sequence of the natural peptide dynorphin A1-17, is a primarily kappa-opioid receptor-preferring peptide. Previously, we showed that dynorphin A1-13 administered to normal volunteers causes a prompt dose-dependent elevation in serum prolactin that may reflect a reduction in tuberoinfundibular dopaminergic tone. This study was conducted to determine whether tuberoinfundibular dopaminergic tone is reduced in methadone-maintained patients. Eight former heroin addicts on stable-dose methadone maintenance with no ongoing drug or alcohol abuse or dependence and 15 normal volunteer controls with no history of drug or alcohol dependence received dynorphin A1-13 intravenously at doses of 120 microg/kg and 500 microg/kg. Studies began one hour before methadone dosing to avoid the expected increase in prolactin that coincides with peak plasma levels of methadone. After intravenous dynorphin A1-13, a dose-response increase in serum prolactin, which peaked within 20 min, was observed in both groups. There was no difference in prolactin between the two groups at baseline or following a placebo. The prolactin response to each dose of dynorphin A1-13 was significantly lower in the methadone-maintained volunteers compared with the controls. These results suggest that tuberoinfundibular dopaminergic tone is altered in methadone-maintained subjects. It is unknown whether altered dopaminergic tone existed before opiate addiction, is a result of heroin addiction, or is reflective of methadone maintenance. Whether methadone-maintained subjects also have decreased dopaminergic response to dynorphin and other kappa-opioid receptor ligands in mesolimbic-mesocortical and nigrostriatal dopaminergic systems cannot be determined from this study.

Dynorphin A(1-17) biotransformation in striatum of freely moving rats using microdialysis and matrix-assisted laser desorption/ionization mass spectrometry

The biotransformation of the opioid peptide dynorphin A(1-17) was investigated in striatum of freely moving Fischer rats, by direct infusion of this peptide, followed by recovery of the resulting biotransformation products via microdialysis and identification using matrix-assisted laser desorption/ionization mass spectrometry. The observed peptides are consistent with enzymatic cleavage at the Arg7-Ile8 position of dynorphin A(1-17), followed by terminal degradation of the resulting dynorphin A(1-7) and dynorphin A(8-17) peptides. Unexpectedly, novel post-translational modifications were found on C-terminal fragments of dynorphin A(1-17). Using tandem mass spectrometry, a covalent modification of mass 172 Da, the nature of which is not understood, was found on the tryptophan residue of C-terminal fragments (Trp14). Additional modifications, of mass 42 and 113 Da, were also found on the N-terminus (Ile8 or Pro10) of these same C-terminal fragments. The role of these modifications of C-terminal fragments has not yet been characterized.

Dipeptidyl peptidase IV (DPPIV) enzyme activity on immature T-cell line R1.1 is down-regulated by dynorphin-A(1-17) as a non-substrate inhibitor

In this study we examined surface expression of CD26 and the corresponding enzyme activity of dipeptidyl peptidase IV (DPPIV) on the cells of immature murine T-cell line, R1.1. The data obtained have shown that R1.1 cells express high density of surface CD26 as compared to normal thymus cells. This was associated with strong enzyme activity, which, based on substrates and inhibitor specificity, corresponded to DPPIV. The DPPIV enzyme activity of R1.1 cells was 10 times stronger than that found on normal murine thymus cells (V(max) = 39 micromol/min/10(6) cells, vs 3.7 micromol/min/10(6) cells, respectively). Upon activation with anti-CD3, up-regulation of both membrane CD26, as well as of DPPIV enzyme activity on R1.1 cells were observed. The finding of strong DPPIV on R1.1 cells makes them suitable model for testing putative substrates/inhibitors of the enzyme in its natural microenvironment. Since in addition to strong DPPIV, R1.1 cells also express kappa opioid receptors (KOR) [European Journal of Pharmacology 227 (1992) 257], we tested the effect of dynorphin-A(1-17), an endogenous opioid peptide with KOR selectivity, on DPPIV of R1.1 cells. Dynorphin-A(1-17) down-regulated DPPIV in a dose-dependent manner, with the potency similar to that of substance P, a known natural DPPIV substrate [Journal of Pharmacology and Experimental Therapeutics 260 (1992) 1257]. DPPIV down-regulation was resistant to bestatin and thiorphan, the inhibitors of two cell surface peptidases (APN and NEP, respectively) with potential of dynorphin-A(1-17) degradation, suggesting that the mechanism underlying the observed effect does not involve degradative products of dynorphin-A(1-17). DPPIV down-regulation was also resistent to KOR antagonist, NBI, suggesting that the mechanism underlying the observed phenomenon involves neither cointernalization of KOR and DPPIV. Collectively, cells of immature T cell line, R1.1 exert strong DPPIV enzyme activity, which could be down-regulated in the presence of dynorphin-A(1-17) by mechanism that presumably includes non-substrate inhibition. By down-regulating DPPIV, dynorphin-A(1-17) may indirectly affect activity and/or specificity of natural substrates of DPPIV, such as substance P, RANTES, and endomorphins.

Site and mechanism of action of dynorphin A-(1-13) and N-methyl-D-aspartate on ACTH release in fetal sheep

Dynorphin A (Dyn A) stimulates the release of ACTH in fetal sheep, a response that involves N-methyl-D-aspartate (NMDA) receptors but not the secretogogues corticotropin-releasing hormone or arginine vasopressin. We now find that neither Dyn A-(1-13) (0.5 mg/kg, i.v.) nor NMDA (4 mg/kg, i.v.) elicits ACTH release in postnatal lambs. This led us to hypothesize that Dyn A-(1-13) and NMDA might act to release placental ACTH. However, the ability of Dyn A-(1-13), NMDA, and the kappa-opioid receptor agonist U-50488H (1 mg/kg, i.v.) to release ACTH was lost after either fetal hypophysectomy (n = 4) or hypothalamo-pituitary disconnection (n = 4). These results indicate that neither the placenta nor the fetal pituitary is the site of action for these agonists and suggest a hypothalamic or suprahypothalamic site of action. Furthermore, the release of ACTH by Dyn A-(1-13) and NMDA was abolished after pretreatment with indomethacin, suggesting that they might cause the release of a prostanoid, possibly from the placenta, that subsequently acts at the hypothalamus or serves as a permissive factor in the action of Dyn A-(1-13) and NMDA at the hypothalamus.

Long-lasting antinociceptive effects of a novel dynorphin analogue, Tyr-D-Ala-Phe-Leu-Arg psi (CH(2)NH) Arg-NH(2), in mice

Tyr-D-Ala-Phe-Leu-Arg psi (CH(2)NH) Arg-NH(2) (SK-9709) is a dynorphin derivative in which the peptide bond was replaced with a psi (CH(2)NH) bond. In the present study, the antinociceptive effects of SK-9709 were determined in an acetic acid-induced writhing test and a hot-plate test. In the acetic acid-induced writhing test, significant antinociceptive effects were observed after subcutaneous (s.c.), intracerebroventricular (i.c.v.) and intrathecal (i.t.) injection of SK-9709, with maximal effects at 120, 30 and 15 min, respectively. The antinociceptive effects were dose-dependent and ED(50) values (range of 95% confidence limits) after s.c., i.c.v. and i.t. injection were 1.36 (0.61 - 3.02) micromol kg(-1), 2.11 (1.18 - 3.79) and 0.79 (0.61 - 1.03) nmol per mouse, respectively. The effects of SK-9709 (s.c., i.c.v. and i.t.) were reversed by the opioid receptor antagonist naloxone (1.36 micromol kg(-1), s.c.). The effects of SK-9709 (s.c.) were also reversed by the selective mu-opioid receptor antagonist beta-funaltrexamine (4.7 nmol per mouse, i.c.v.), and kappa-opioid receptor antagonist nor-binaltorphimine (4.9 nmol per mouse, i.t.). In the hot-plate test, the antinociceptive effect of SK-9709 (s.c., i.c.v. and i.t.) was also dose-dependent with the maximal peak effect at 120, 15 and 15 min similarly to the acetic acid-induced writhing test. The antinociceptive effects were dose-dependent and ED(50) values (range of 95% confidence limits) after s.c., i.c.v. and i.t. injection were 39.1 (5.4 - 283.0) micromol kg(-1), 6.5 (4.0 - 10.7) and 7.4 (5.0 - 11.0) nmol per mouse, respectively. These findings indicated that systemically administered SK-9709 produced long-lasting antinociceptive effects and these effects were mediated by both supra-spinal mu- and spinal kappa-opioid receptors.

Cannabinoid modulation of dynorphin A: correlation to cannabinoid-induced antinociception

Intrathecal administration of anandamide, delta9-tetrahydrocannabinol (THC) and (-)-3-[2-hydroxy-4-(1,1-dimethyheptyl)ptyl)phenyl]-4-(3-hydr oxypropyl)-cicloexan-1-ol (CP55,940) induced spinal antinociception accompanied by differential kappa-opioid receptor involvement and dynorphin A peptide release. Antinociception using the tail-flick test was induced by the classical cannabinoid THC and was blocked totally by 17,17'-bis(cyclopropylmethyl)-6',6,7,7'-tetrahydro-4,5,4'5'-diepoxy++ +-6,6'-(imino)[7,7'-bimorphinan]-3,3',14,14'-tetrol (norbinaltorphimine) indicating a significant and critical kappa-opioid receptor component. The endogenous cannabinoid, anandamide and the non-classical bicyclic cannabinoid, CP55,940, induced non-nor-BNI-sensitive effects. The N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazo le-carboxamide (SR141716A)-mediated attenuation of spinal antinociception imparted by the various cannabinoids indicates cannabinoid CB1 receptor involvement. THC-induced an enhancement of immunoreactive dynorphin A release which coincided with the onset, but not duration antinociception. The release of dynorphin A was also attenuated by SR141716A suggesting it is cannabinoid CB1 receptor-mediated. These data indicate a critical role for dynorphin A release in the initiation of the antinociceptive effects of the cannabinoids at the spinal level.

Acute subjective effects of dynorphin A(1-13) infusion in normal healthy subjects

Twelve healthy subjects with no history of substance abuse participated in a placebo-controlled single-blinded study of subjective response to acute i.v. administration of placebo and two doses of the natural shortened peptide sequence of the kappa-opioid agonist, dynorphin A(1-13) (low dose 120 micrograms/kg, high dose 500 micrograms/kg). Visual analog scales showed small but significant negative mood and positive drug effect 10 min post infusion in the high dose dynorphin compared to placebo infusion. The differences were no longer apparent at 30 min. These results show that dynorphin A(1-13), shown previously to have both neuroendocrine and modest analgesic effects, was well tolerated and produced modest transient subjective responses.

Regional quantitation of preprodynorphin mRNA in guinea pig gastrointestinal tract

The endogenous opioid peptide dynorphin has been shown by immunochemical studies to be widely distributed in the gastrointestinal tract. The aim of this study was to determine basal levels of preprodynorphin (ppDyn) mRNA in different regions of the gastrointestinal tract of the guinea pig. A modified sensitive and specific solution hybridization RNase protection assay was used to quantitate ppDyn mRNA, with confirmation by gel analysis of the RNase protected hybrids and PCR amplified cDNA. This method combines high sensitivity and sufficient throughput to analyze large number of samples in a single assay. Low but measurable amounts of ppDyn mRNA were detected in fundus, duodenum, jejunum, ileum, cecum, and rectum. The rectum contained significantly more ppDyn mRNA than the stomach, small bowel, and cecum. The muscularis/myenteric plexus layer of both ileum and rectum contained a higher concentration of ppDyn mRNA per microg total RNA compared to the mucosa/submucosa/submucosal plexus. However, a greater absolute amount of ppDyn mRNA (80-85%) localized to the mucosal layer. The greater absolute amount of ppDyn mRNA in the mucosal layer may indicate the presence of dynorphin in the endocrine cells of the mucosa.

Potentiation of NMDA receptor-mediated responses by dynorphin at low extracellular glycine concentrations

The effect of dynorphin A(1-13) on N-methyl-D-aspartate (NMDA)-activated currents was investigated in the presence of low extracellular glycine concentrations in Xenopus oocytes expressing recombinant heteromeric NMDA receptors and in cultured hippocampal neurons with the use of voltage-clamp techniques. At an extracellular added glycine concentration of 100 nM, dynorphin A(1-13) (10 microM) greatly increased the amplitude of NMDA-activated currents for all heteromeric subunit combinations tested; on average, the potentiation was: epsilon1/zeta1, 3,377 +/- 1,416% (mean +/- SE); epsilon2/zeta1, 1,897 +/- 893%; epsilon3/zeta1, 4,356 +/- 846%; and epsilon4/zeta1, 1,783 +/- 503%. Potentiation of NMDA-activated current by dynorphin A(1-13) was concentration dependent between 0.1 and 10 microM dynorphin A(1-13), with a half-maximal concentration value of 2.77 microM and an apparent Hill coefficient of 2.53, for epsilon2/zeta1 subunits at 100 nM added extracellular glycine. Percentage potentiation by dynorphin A(1-13) was maximal at the lowest glycine concentrations tested (0.01 and 0.1 microM), and decreased with increasing glycine concentration. No significant potentiation was observed at glycine concentrations > 0.1 microM for epsilon1/zeta1, epsilon2/zeta1, and epsilon4/zeta1 subunits, or at > 1 microM for epsilon3/zeta1 subunits. Potentiation of NMDA-activated currents by dynorphin A(1-13) was not inhibited by 1 microM of the kappa-opioid receptor antagonist nor-binaltorphimine, and potentiation was not observed with 10 microM of the kappa-opioid receptor agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzene-acetamide. Potentiation of NMDA-activated current by dynorphin A(1-13) was inhibited by the glycine antagonist kynurenic acid (50 microM). NMDA-activated current was also potentiated at low glycine concentrations by 10 microM dynorphin A(2-13) or (3-13), both of which have a glycine as the first amino acid, but not by 10 microM dynorphin A(4-13), which does not have glycine as an amino acid. In hippocampal neurons, 10 microM dynorphin A(1-13) or (2-13) potentiated steady-state NMDA-activated current in the absence of added extracellular glycine. The extracellular free glycine concentration, determined by high-performance liquid chromatography, was between 26 and 36 nM for the bathing solution in presence or absence of 10 microM dynorphin A(1-13), (2-13), (3-13), or (4-13), and did not differ significantly among these solutions. The observations are consistent with the potentiation of NMDA-activated current at low extracellular glycine concentrations resulting from an interaction of the glycine amino acids in dynorphin A(1-13) with the glycine coagonist site on the NMDA receptor. Because dynorphin A is an endogenous peptide that can be coreleased with glutamate at glutamatergic synapses, the potentiation of NMDA receptor-mediated responses could be an important physiological regulator of NMDA receptor function at these synapses.