Deltorphin I

N-terminal guanidinylation of the cyclic 1,4-ureido-deltorphin analogues: the synthesis, receptor binding studies, and resistance to proteolytic digestion.[Pubmed:25755050]

J Pept Sci. 2015 Jun;21(6):467-75.

The synthesis of a series of N-guanidinylated cyclic ureidopeptides, analogues of 1,4-ureido-deltorphin/dermorphine tetrapeptide is described. The delta- and mu-opioid receptor affinity of new guanidinylated analogues and their non-guanidinylated precursors was determined by the displacement radioligand binding experiments. Our results indicate that the guanidinylation of cyclic 1,4-ureidodeltorphin peptide analogues does not exhibit a uniform influence on the opioid receptor binding properties, similarly as reported earlier for some linear peptides. All analogues were also tested for their in vitro resistance to proteolysis during incubation with large excess of chymotrypsin, pepsin, and papain by means of mass spectroscopy. Guanidinylated ureidopeptides 1G-4G showed mixed mu agonist/delta agonist properties and high enzymatic stability indicating their potential as therapeutic agents for treatment of pain.

Effects of Deltorphin II and Its Retroenantio Analog on Cardiac Tolerance to Ischemia and Reperfusion.[Pubmed:28091919]

Bull Exp Biol Med. 2017 Jan;162(3):306-309.

Selective agonist of delta2-opioid receptors Deltorphin II and its retroenantio analog (0.12 mg/kg intravenously) were preventively injected to male Wistar rats 15 min prior to 45-min coronary occlusion or 5 min before 120-min reperfusion. Administration of Deltorphin II before artery occlusion and before reperfusion decreased the infarct size/area at risk ratio. Deltorphin II prevented the appearance of ischemia-provoked ventricular arrhythmias and exerted no effect on HR and BP (systolic and diastolic). The retroenantio analog of Deltorphin II produced no antiarrhythmic or infarct-limiting effects, but reduced HR without affecting BP. Deltorphin II can be viewed as a promising prototype for a medicinal remedy to treat acute myocardial infarction.

Synthesis and pharmacology of halogenated delta-opioid-selective [d-Ala(2)]deltorphin II peptide analogues.[Pubmed:25844930]

ACS Chem Neurosci. 2015 Jun 17;6(6):905-10.

Deltorphins are naturally occurring peptides produced by the skin of the giant monkey frog (Phyllomedusa bicolor). They are delta-opioid receptor-selective agonists. Herein, we report the design and synthesis of a peptide, Tyr-d-Ala-(pI)Phe-Glu-Ile-Ile-Gly-NH2 3 (GATE3-8), based on the [d-Ala(2)]Deltorphin II template, which is delta-selective in in vitro radioligand binding assays over the mu- and kappa-opioid receptors. It is a full agonist in [(35)S]GTPgammaS functional assays and analgesic when administered supraspinally to mice. Analgesia of 3 (GATE3-8) is blocked by the selective delta receptor antagonist naltrindole, indicating that the analgesic action of 3 is mediated by the delta-opioid receptor. We have established a radioligand in which (125)I is incorporated into 3 (GATE3-8). The radioligand has a KD of 0.1 nM in Chinese hamster ovary (CHO) cells expressing the delta receptor. Additionally, a series of peptides based on 3 (GATE3-8) was synthesized by incorporating various halogens in the para position on the aromatic ring of Phe(3). The peptides were characterized for binding affinity at the mu-, delta-, and kappa-opioid receptors, which showed a linear correlation between binding affinity and the size of the halogen substituent. These peptides may be interesting tools for probing delta-opioid receptor pharmacology.

Synthesis, Biological Activity, and NMR-Based Structural Studies of Deltorphin I Analogs Modified in Message Domain with a New alpha,alpha-Disubstituted Glycines.[Pubmed:26808639]

Chem Biol Drug Des. 2016 Jun;87(6):824-32.

This article describes new Deltorphin I analogs in which phenylalanine residues were replaced by the corresponding (R) or (S)-alpha-benzyl-beta-azidoalanine, alpha-benzyl-beta-(1-pyrrolidinyl)alanine, alpha-benzyl-beta-(1-piperidinyl)alanine, and alpha-benzyl-beta-(4-morpholinyl)-alanine residues. The potency and selectivity of the new analogs were evaluated by a competitive receptor binding assay in the rat brain using [(3) H]DAMGO (a mu ligand) and [(3) H]DELT (a delta ligand). The affinity of analogs containing (R) or (S)-alpha-benzyl-beta-azidoalanine in position 3 to delta-receptors strongly depended on the chirality of the alpha,alpha-disubstituted residue. The conformational behavior of peptides modified with (R) or (S)-alpha-benzyl-beta-(1-piperidinyl)Ala, which displays the opposite selectivity, was analyzed by (1) H and (13) C NMR. The mu-selective Tyr-d-Ala-(R)-alpha-benzyl-beta-(1-piperidinyl)Ala-Asp-Val-Val-Gly-NH2 lacks the helical conformation observed in the delta-selective Tyr-d-Ala-(S)-alpha-benzyl-beta-(1-piperidinyl)Ala-Asp-Val-Val-Gly-NH2 . Our results support the proposal that differences between delta- and mu-selective opioid peptides are attributable to the presence or absence of a spatial overlap between the N-terminal message domain and the C-terminal address domain.

Deltorphin transport across the blood-brain barrier.[Pubmed:9256506]

Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):9469-74.

In vivo antinociception studies demonstrate that deltorphins are opioid peptides with an unusually high blood-brain barrier penetration rate. In vitro, isolated bovine brain microvessels can take up deltorphins through a saturable nonconcentrative permeation system, which is apparently distinct from previously described systems involved in the transport of neutral amino acids or of enkephalins. Removing Na+ ions from the incubation medium decreases the carrier affinity for deltorphins (-25%), but does not affect the Vmax value of the transport. The nonselective opiate antagonist naloxone inhibits deltorphin uptake by brain microvessels, but neither the selective delta-opioid antagonist naltrindole nor a number of opioid peptides with different affinities for delta- or mu-opioid receptors compete with deltorphins for the transport. Binding studies demonstrate that mu-, delta-, and kappa-opioid receptors are undetectable in the microvessel preparation. Preloading of the microvessels with L-glutamine results in a transient stimulation of deltorphin uptake. Glutamine-accelerated deltorphin uptake correlates to the rate of glutamine efflux from the microvessels and is abolished by naloxone.

[D-Ala2]deltorphin I binding and pharmacological evidence for a special subtype of delta opioid receptor on human and invertebrate immune cells.[Pubmed:1329092]

Proc Natl Acad Sci U S A. 1992 Oct 1;89(19):9316-20.

The effects of the opioid neuropeptide [D-Ala2]Deltorphin I, isolated from amphibian skin, on immunoregulatory activities were studied in representatives of vertebrates and invertebrates. The high potency of this compound parallels that of [Met]enkephalin, which was previously demonstrated in vertebrate plasma and invertebrate hemolymph. The addition of [D-Ala2]Deltorphin I at 10(-11) M to human granulocytes or immunocytes of the mollusc Mytilus edulis resulted in cellular adherence and conformational changes indicative of cellular activation. This value is in line with the concentrations obtained with [Met]enkephalin, tested in the presence of the specific neutral endopeptidase 24.11 inhibitor phosphoramidon, and this opioid's synthetic analog [D-Ala2, Met5]enkephalin which, like [D-Ala2]Deltorphin I, is resistant to proteolytic degradation. Both ligands appear to be acting on the same population of immunocytes. The same relationship was estimated to exist in the insect Leucophaea maderae, in which the high viscosity of the hemolymph makes the quantification of reactive cells more difficult than in Mytilus. In addition, [D-Ala2]Deltorphin I is as potent as beta-endorphin in affecting the proliferation of lymphocytes in response to mitogen. Saturation experiments with unlabeled ligands and the radioligands [3H][D-Ala2]Deltorphin I and [3H][D-Ala2,Met5]enkephalinamide revealed the presence of two high-affinity binding sites on human granulocytes, one sensitive to the nonequilibrium delta opioid antagonist [D-Ala2,Leu5,Cys6]enkephalinamide and the other relatively insensitive. The results obtained with [D-Ala2]Deltorphin I support the view that the special role played by endogenous [Met]enkephalin in immunobiological activities of vertebrates and invertebrates is mediated by a special subtype of delta opioid receptor.

Deltorphins: a family of naturally occurring peptides with high affinity and selectivity for delta opioid binding sites.[Pubmed:2544892]

Proc Natl Acad Sci U S A. 1989 Jul;86(13):5188-92.

Deltorphins are endogenous linear heptapeptides, isolated from skin extracts of frogs belonging to the genus Phyllomedusa, that have a higher affinity and selectivity for delta opioid binding sites than any other natural compound known. Two deltorphins with the sequence Tyr-Ala-Phe-Asp(or Glu)-Val-Val-Gly-NH2 have been isolated from skin extracts of Phyllomedusa bicolor. The alanine in position 2 is in the D configuration. These peptides, [D-Ala2]deltorphins I and II, show an even higher affinity for delta receptors than the previously characterized deltorphin, which contains D-methionine as the second amino acid. These peptides show some similarity to another constituent of Phyllomedusa skin, dermorphin, which is highly selective for mu-opioid receptors. These peptides all have the N-terminal sequence Tyr-D-Xaa-Phe, where D-Xaa is either D-alanine or D-methionine. While this structure seems to be capable of activating both mu and delta opioid receptors, differences in the C-terminal regions of these peptides are probably responsible for the observed high receptor selectivity of dermorphin and deltorphin.