dynorphins and deltorphin

This review gives a historical perspective, summarizing approximately 25 years of research on opioids. The "typical" opioid peptides produced in the brain, "atypical" opioids encrypted in milk protein or hemoglobin sequences, and extremely potent and selective opioids of amphibian origin are described. The main focus is on the structure-activity relationship studies of peptide ligands for three main opioid receptor types (micro, delta, kappa), their selectivities and pharmacological activities in vitro. Chemical modifications that led to obtaining potent and selective agonists and antagonists for these receptors are discussed.

Topics: Amino Acid Sequence; Animals; Brain; Dynorphins; Enkephalins; Humans; Ligands; Molecular Sequence Data; Narcotic Antagonists; Oligopeptides; Opioid Peptides; Protein Binding; Receptors, Opioid; Recombinant Fusion Proteins; Structure-Activity Relationship

The peptide nociceptin/orphanin FQ (N/OFQ) and its receptor ORL-1, also designated opioid receptor 4 (OP(4)) are involved in the modulation of nociception. Using OP(4)-knockout mice, we have studied their response following opioid receptor stimulation and under neuropathic conditions.In vas deferens from wild-type and OP(4)-knockout mice, DAMGO (mu/OP(3) agonist), deltorphine II (delta/OP(1) agonist) and (-)-U-50488 (kappa/OP(2) agonist) induced similar concentration-dependent inhibition of electrically-evoked contractions. Naloxone and naltrindole (delta/OP(1) antagonists) shifted the curves of DAMGO (pA(2)=8.6) and deltorphine II (pA(2)=10.2) to the right, in each group. In the hot-plate assay, N/OFQ (10 nmol per mouse, i.t.) increased baseline latencies two-fold in wild-type mice while morphine (10mg/kg, s.c.), deltorphine II (10 nmol per mouse, i.c.v.) and dynorphin A (20 nmol per mouse, i.c.v.) increased hot-plate latencies by about four- to five-fold with no difference observed between wild-type and knockout mice. Furthermore, no change was evident in the development of the neuropathic condition due to chronic constriction injury (CCI) of the sciatic nerve, after both thermal and mechanical stimulation. Altogether these results suggest that the presence of OP(4) receptor is not crucial for (1) the development of either acute or neuropathic nociceptive responses, and for (2) the regulation of full receptor-mediated responses to opioid agonists, even though compensatory mechanisms could not be excluded.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Female; Male; Mice; Mice, Knockout; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Nociceptin; Nociceptin Receptor; Oligopeptides; Opioid Peptides; Pain; Receptors, Opioid; Time Factors; Vas Deferens

Most electrophysiological studies of opioids on hippocampal principal neurons have found indirect actions, usually through interneurons. However, our laboratory recently found reciprocal alteration of the voltage-dependent K(+) current, known as the M-current (I(M)), by kappa and delta opioid agonists in CA3 pyramidal neurons. Recent ultrastructural studies have revealed postsynaptic delta opiate receptors on dendrites and cell bodies of CA1 and CA3 hippocampal pyramidal neurons (HPNs). Reasoning that previous electrophysiological studies may have overlooked voltage-dependent postsynaptic effects of the opioids in CA1, we reevaluated their role in CA1 HPNs using the rat hippocampal slice preparation for intracellular current- and voltage-clamp recording. None of the delta and mu; receptor-selective opioids tested, including [D-Pen(2,5)]-enkephalin (DPDPE), [D-Ala(2)]-deltorphin II (deltorphin), [D-Ala(2), NMe-Phe(4), Gly-ol]-enkephalin (DAMGO), and [D-Ala(2), D-Leu(5)] enkephalin (DADLE), altered membrane properties such as I(M) or Ca(2+)-dependent spikes in CA1 HPNs. The nonopioid, Des-Tyr-dynorphin (D-T-dyn), also had no effect. By contrast, dynorphin A (1-17) markedly increased I(M) at low concentrations and caused an outward current at depolarized membrane potentials. The opioid antagonist naloxone and the kappa receptor antagonist nor-binaltorphimine (nBNI) blocked the I(M) effect. However, the kappa-selective agonists U69,593 and U50,488h did not significantly alter I(M) amplitudes when averaged over all cells tested, although occasional cells showed an I(M) increase with U50,488h. Our results suggest that dynorphin A postsynaptically modulates the excitability of CA1 HPNs through opiate receptors linked to voltage-dependent K(+) channels. These findings also provide pharmacological evidence for a functional kappa opiate receptor subtype in rat CA1 HPNs but leave unanswered questions on the role of delta receptors in CA1 HPNs.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Benzeneacetamides; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine-2-Alanine; Hippocampus; In Vitro Techniques; Oligopeptides; Peptide Fragments; Potassium Channels; Pyramidal Cells; Pyrrolidines; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa

Substitution of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) in place of Gly2 in dynorphin A-(1-13)-NH2 and -(1-11)-NH2 (DYN) analogues (1 and 2) decreased the affinity to the kappa, delta, and mu receptors, and kappa selectivity. The analogue [D-Ala2, des-Gly3]DYN (4), a chimera between deltorphin/dermorphin N-terminal tripeptide and DYN, was virtually inactive for kappa-sites while the affinities for delta- and mu-receptors remained essentially unchanged. The doubly substituted analogue [2',6'-dimethyl-L-tyrosine (Dmt1)-Tic2]DYN (3) exhibited high delta-affinity (Ki=0.39 nM) while mu- and kappa-affinities were only an order of magnitude less (4-5 nM). Bioactivity of [Tic2]DYN peptides (1-3) on guinea-pig ileum and rabbit jejunum revealed potent delta- and kappa-antagonism, while the delta agonist potency of 4 was comparable to DYN. Thus, conversion from a kappa-agonist to antagonist occurred with the inclusion of Tic into DYN analogues, similar to the appearance of antagonist properties with delta- and mu-opioid agonists containing a Tic2 residue.

Topics: Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Drug Design; Dynorphins; Electrophysiology; Guinea Pigs; Ileum; Isoquinolines; Muscle Contraction; Muscle, Smooth; Oligopeptides; Peptide Fragments; Rabbits; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Structure-Activity Relationship; Tetrahydroisoquinolines