enkephalin--ala(2)-mephe(4)-gly(5)- and tyrosyl-prolyl-tryptophyl-glycinamide

The antagonism by Tyr-D-Pro-Trp-Gly-NH2 (D-Pro2-Tyr-W-MIF-1), a Tyr-Pro-Trp-Gly-NH2 (Tyr-W-MIF-1) analog, of the antinociception induced by the mu-opioid receptor agonists Tyr-W-MIF-1, [D-Ala2,NMePhe4,Gly(ol)5]-enkephalin (DAMGO), Tyr-Pro-Trp-Phe-NH2 (endomorphin-1), and Tyr-Pro-Phe-Phe-NH2 (endomorphin-2) was studied with the mouse tail-flick test. D-Pro2-Tyr-W-MIF-1 (0.5-3 nmol) given intracerebroventricularly (i.c.v.) had no effect on the thermal nociceptive threshold. High doses of D-Pro2-Tyr-W-MIF-1 (4-16 nmol) administered i.c.v. produced antinociception with a low intrinsic activity of about 30% of the maximal possible effect. D-Pro2-Tyr-W-MIF-1 (0.25-2 nmol) co-administered i.c.v. showed a dose-dependent attenuation of the antinociception induced by Tyr-W-MIF-1 or DAMGO without affecting endomorphin-2-induced antinociception. A 0.5 nmol dose of D-Pro2-Tyr-W-MIF-1 significantly attenuated Tyr-W-MIF-1-induced antinociception but not DAMGO- or endomorphin-1-induced antinociception. The highest dose (2 nmol) of D-Pro2-Tyr-W-MIF-1 almost completely attenuated Tyr-W-MIF-1-induced antinociception. However, that dose of D-Pro2-Tyr-W-MIF-1 significantly but not completely attenuated endomorphin-1 or DAMGO-induced antinociception, whereas the antinociception induced by endomorphin-2 was still not affected by D-Pro2-Tyr-W-MIF-1. Pretreatment i.c.v. with various doses of naloxonazine, a mu1-opioid receptor antagonist, attenuated the antinociception induced by Tyr-W-MIF-1, endomorphin-1, endomorphin-2, or DAMGO. Judging from the ID50 values for naloxonazine against the antinociception induced by the mu-opioid receptor agonists, the antinociceptive effect of Tyr-W-MIF-1 is extremely less sensitive to naloxonazine than that of endomorphin-1 or DAMGO. In contrast, endomorphin-2-induced antinociception is extremely sensitive to naloxonazine. The present results clearly suggest that D-Pro2-Tyr-W-MIF-1 is a selective antagonist for the mu2-opioid receptor in the mouse brain. D-Pro2-Tyr-W-MIF-1 may also discriminate between Tyr-W-MIF-1-induced antinociception and the antinociception induced by endomorphin-1 or DAMGO, which both show a preference for the mu2-opioid receptor in the brain.

Topics: Analgesics, Opioid; Animals; Brain; Disease Models, Animal; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Hot Temperature; Injections, Intraventricular; Male; Mice; MSH Release-Inhibiting Hormone; Naloxone; Narcotic Antagonists; Oligopeptides; Pain; Pain Measurement; Pain Threshold; Reaction Time; Receptors, Opioid, mu; Somatostatin; Time Factors

The involvement of spinal mu-opioid receptor subtypes on the antinociception induced by i.t.-administered Tyr-D-Arg-Phe-sarcosine (TAPS), a N-terminal tetrapeptide analog of dermorphin, was determined in mice tail-flick test. Intrathecal administration of TAPS produced the marked inhibition of the tail-flick response in a dose-dependent manner. The antinociception induced by TAPS was completely eliminated by i.t.-co-administration of Tyr-D-Pro-Phe-Phe-NH2 (D-Pro2-endomorphin-2), the mu1-opioid receptor antagonist, whereas i.t. co-treatment with Tyr-D-Pro-Trp-Phe-NH2 (D-Pro2-endomorphin-1) or Tyr-D-Pro-Trp-Gly-NH2 (D-Pro2-Tyr-W-MIF-1), the mu2-opioid receptor antagonists, did not affect the TAPS-induced antinociception. In contrast, the antinociception induced by i.t.-administered [D-Ala2,N-MePhe4,Gly-ol5]enkephalin was significantly attenuated by i.t.-co-administration of D-Pro2-endomorphin-1 or D-Pro2-Tyr-W-MIF-1, but not D-Pro2-endomorphin-2. These results suggest that TAPS may stimulate spinal mu1-opioid receptors to produce the antinociception.

Topics: Analgesics; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Mice; MSH Release-Inhibiting Hormone; Oligopeptides; Pain Measurement; Protein Isoforms; Receptors, Opioid, mu; Spinal Cord

The antagonistic properties of Tyr-d-Pro-Trp-Gly-NH(2) (d-Pro(2)-Tyr-W-MIF-1), a Tyr-Pro-Trp-Gly-NH(2)(Tyr-W-MIF-1) analog, on the antinociception induced by the mu-opioid receptor agonists Tyr-W-MIF-1, [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO), Tyr-Pro-Trp-Phe-NH(2) (endomorphin-1), and Tyr-Pro-Phe-Phe-NH(2) (endomorphin-2) were studied in the mouse paw-withdrawal test. d-Pro(2)-Tyr-W-MIF-1 injected intrathecally (i.t.) had no apparent effect on the thermal nociceptive threshold. d-Pro(2)-Tyr-W-MIF-1 (0.1-0.4 nmol) coadministered i.t. showed a dose-dependent attenuation of the antinociception induced by Tyr-W-MIF-1 without affecting endomorphin- or DAMGO-induced antinociception. However, higher doses of d-Pro(2)-Tyr-W-MIF-1 (0.8-1.2 nmol) significantly attenuated endomorphin-1- or DAMGO-induced antinociception, whereas the antinociception induced by endomorphin-2 was still not affected by d-Pro(2)-Tyr-W-MIF-1. Pretreatment i.t. with various doses of naloxonazine, a mu(1)-opioid receptor antagonist, attenuated the antinociception induced by Tyr-W-MIF-1, endomorphin-1, endomorphin-2, or DAMGO. Judging from the ID(50) values for naloxonazine against the antinociception induced by the mu-opioid receptor agonists, the antinociceptive effect of Tyr-W-MIF-1 is extremely less sensitive to naloxonazine than those of endomorphin-1 or DAMGO. In contrast, endomorphin-2-induced antinociception is extremely sensitive to naloxonazine. The present results clearly suggest that d-Pro(2)-Tyr-W-MIF-1 is the selective antagonist to be identified for the mu(2)-opioid receptor in the mouse spinal cord. d-Pro(2)-Tyr-W-MIF-1 may also discriminate between Tyr-W-MIF-1-induced antinociception and the antinociception induced by endomorphin-1 or DAMGO, all of which show a preference for the mu(2)-opioid receptor in the spinal cord.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Animals; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Male; Mice; MSH Release-Inhibiting Hormone; Naloxone; Naltrexone; Narcotic Antagonists; Oligopeptides; Receptors, Opioid, mu

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2), peptides recently isolated from bovine and human brain, have high affinity and selectivity for mu opiate receptors. They share sequence similarity with the endogenous opiate-modulating peptide Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2). The efficacies of these endogenous peptides and of the enkephalin analog DAMGO were compared by measuring their effects on the binding of guanosine-5'-O-(-gamma-[35S]thio)triphosphate ([35S]GTPgammaS) to G-proteins in membranes from SH-SYSY human neuroblastoma cells. DAMGO, endomorphin-1, and endomorphin-2 stimulated [35S]GTPgammaS binding dose dependently, with maximal effects of 60 +/- 9%, 47 +/- 9%, and 43 +/- 6% stimulation above basal and ED50 of 49 +/- 8 nM, 38 +/- 8 nM, and 64 +/- 13 nM, respectively. Tyr-W-MIF-1 showed only a small stimulation of binding (5% stimulation above basal, ED50 = 2 microM). When given in combination with the other opioids, however, Tyr-W-MIF-1 attenuated their ability to activate G-proteins. Thus, the endogenous opioids endomorphin-1 and endomorphin-2 activate G-proteins similarly to the synthetic agonist DAMGO, but the structurally similar peptide Tyr-W-MIF-1 produces only minimal stimulation of G-proteins.

Topics: Cell Membrane; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Humans; MSH Release-Inhibiting Hormone; Narcotic Antagonists; Neuroblastoma; Oligopeptides; Receptors, Opioid; Tumor Cells, Cultured

Peptides have been identified in mammalian brain that are considered to be endogenous agonists for the delta (enkephalins) and kappa (dynorphins) opiate receptors, but none has been found to have any preference for the mu receptor. Because morphine and other compounds that are clinically useful and open to abuse act primarily at the mu receptor, it could be important to identify endogenous peptides specific for this site. Here we report the discovery and isolation from brain of such a peptide, endomorphin-1 (Tyr-Pro-Trp-Phe-NH2), which has a high affinity (Ki = 360 pM) and selectivity (4,000- and 15,000-fold preference over the delta and kappa receptors) for the mu receptor. This peptide is more effective than the mu-selective analogue DAMGO in vitro and it produces potent and prolonged analgesia in mice. A second peptide, endomorphin-2 (Tyr-Pro-Phe-Phe-NH2), which differs by one amino acid, was also isolated. The new peptides have the highest specificity and affinity for the mu receptor of any endogenous substance so far described and they may be natural ligands for this receptor.

Topics: Amino Acid Sequence; Analgesics, Opioid; Animals; Brain Chemistry; Cattle; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Mice; MSH Release-Inhibiting Hormone; Oligopeptides; Radioimmunoassay; Receptors, Opioid, mu

Two cyclic analogues of the brain peptide Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2) were synthesized and tested for analgesic activity in the rat tail flick test after intracerebroventricular (ICV) injection. The analogues were about 200-fold more potent than the parent peptide. Analgesia was dose dependent, and at 1 microgram the two analogues, the mu-selective enkephalin analogue DAMGO (Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol), and morphine, all produced analgesia lasting between 40 and 60 min. Analgesia of longer duration was evident at higher doses of the analogues and lasted more than 6 h after 100 micrograms, the highest dose tested. The results show that peptide analogues based on the structure of the endogenously occurring Tyr-W-MIF-1 can produce potent and long-lasting effects on nociception.

Topics: Analgesia; Analgesics; Animals; Cerebral Ventricles; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Injections, Intraventricular; Male; Morphine; MSH Release-Inhibiting Hormone; Narcotic Antagonists; Pain; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Time Factors

The relative binding to mu, delta, and kappa opiate receptors was characterized for the brain peptides Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2), and two fragments of Tyr-W-MIF-1 (Tyr-Pro-Trp and Tyr-Pro-Trp-Gly) previously shown to have antagonist as well as agonist activity in the guinea pig ileum. Tyr-MIF-1 had relatively low affinity (Ki = 1 microM at the mu site) but high selectivity (400- and 700-fold greater affinity for mu over delta and mu over kappa binding). Tyr-W-MIF-1 (Ki = 71 nM at the mu site) showed higher affinity binding to all three sites than Tyr-MIF-1 while retaining 200-fold selectivity for mu over delta and kappa receptors. The affinity of the fragments of Tyr-W-MIF-1 was lower for mu but higher for delta receptors. We also tested two cyclized analogs of Tyr-W-MIF-1 that were about 200-fold more active than the parent compound in producing analgesia. These analogs showed higher affinity binding to all three opiate receptors. One of the analogs showed binding affinity to mu sites (Ki = 1.3 nM) that was within 3-fold of that of the potent analog of enkephalin, DAMGO. Thus, brain peptides with an N-terminal Tyr-Pro, rather than the Tyr-Gly-Gly-Phe sequence typical of other endogenous opiates, can provide high selectivity for mu opiate receptors. Analogs based on one of them, Tyr-Pro-Trp-Gly-NH2, show high affinity as well as potent analgesic activity.

Topics: Amino Acid Sequence; Animals; Brain; Cerebellum; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Guinea Pigs; Molecular Sequence Data; MSH Release-Inhibiting Hormone; Peptide Fragments; Peptides, Cyclic; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Structure-Activity Relationship; Synaptic Membranes