Antinociceptive and other opioid effects of a new series of dermorphin analogues after subcutaneous administration in the rat

Synthesis and opioid activity of novel tetrapeptides analogous to sequence (1-4) of dermorphin

Seven new tetrapeptides analogous to (1-4) sequence of dermorphin were synthesized and evaluated for their opioid activity. The peptides were synthesized by the solution phase method. Their opioid activity revealed that peptides II and V were the most potent in the analgesia test as well as in the peripheral assays. Peptide II was most active in the guinea pig ileum assay, whereas peptide VI was 2763 times more selective for mu-receptors.

Synthesis and receptor binding analysis of dermorphin hepta-, hexa- and pentapeptide analogues. Evidence for one- and two-side binding models for the mu-opioid receptor

Sixteen dermorphin analogues were synthesized and characterized for mu- and delta-opioid receptor binding properties using [3H]DAGO and [3H]DPDPE, respectively. The analogues included the following: substitutions at position 4 and/or the C-terminal residue; deletions of Gly4 or Pro6-Ser7; inclusion of Z or an acetyl group on the epsilon-amino group of Lys7; and the presence of either a C-terminal amide or free acid group. Two peptides, [Lys7-OH]- and [Lys7-NH2]dermorphin, had mu-affinities (Ki mu = 0.15-0.13 nM) and mu-selectivities (Ki delta/Ki mu = 1158-1482) higher than dermorphin (Ki mu = 0.28 nM; Ki delta/Ki mu = 295) and best fitted a one-site binding model similar to dermorphin. Significantly better (P < 0.0001) fits to a two-site binding model vs. a one-site model were observed with four dermorphin analogues: [Lys(Z)7-OH]heptapeptide, [des-Gly4(Tyr4,Pro5,Asn6-OH)]hexapeptide and two pentapeptides, [Tyr5-NH2] and [Trp4,Asn5-OH]. Our data revealed a complex binding pattern for dermorphin analogues to brain mu-receptors in which Hill coefficients less than 0.85 generally suggest heterogeneity of mu-receptors; however, only detailed analyses of the data derived from the non-linear regression fits for one- or two-components gave evidence for the possible existence of two separate [3H]DAGO binding sites. Eight of our dermorphin analogues had significantly better fits for a two-site model (P < 0.05), but only four seemed to have two distinct Ki values (P < 0.0001).

Effect of dermorphin on behavior and hippocampal electrical activity in rabbits

Dermorphin, a naturally occurring heptapeptide that selectively binds to mu-opioid receptors, was injected intravenously 0.4 mg/kg in male rabbits. Eight days before injection the spontaneous behavior of the animals was observed in a neutral environment in the absence of external stimuli. At the same time, hippocampal EEG was recorded by telemetry. After dermorphin injection, the same experimental procedure was repeated. Behavior showed a strong increase in quiet immobility and a concomitant reduction in voluntary activities as compared to control periods. Treatment did not affect either the pattern or the frequency of hippocampal electrical activity.

Characterisation and visualisation of [3H]dermorphin binding to mu opioid receptors in the rat brain. Combined high selectivity and affinity in a natural peptide agonist for the morphine (mu) receptor

Dermorphin, Tyr-DAla-Phe-Gly-Tyr-Pro-Ser-NH2, a potent opioid peptide isolated from amphibian skin, is endowed with outstanding structural and biological features. It has no common structure with mammalian opioid peptides and is a unique example of a peptide, synthesized by an animal cell, which contains a D-amino acid in its native sequence. We have undertaken a complete evaluation of the receptor selectivity of dermorphin, together with the binding characteristics and receptor distribution of [3H]dermorphin in the rat brain. 1. Dermorphin was tested for its relative affinity to mu-, delta- and chi-opioid receptors by determining its potency in displacing the selective mu-receptor ligand [3H]Tyr-DAla-Gly-MePhe-Gly-ol (where Gly-ol = glycinol), the prototypic delta-receptor ligand [3H]Tyr-DPen-Gly-Phe-DPen (where DPen = beta, beta-dimethylcysteine) and the chi ligand [3H]ethylketocyclazocine from rat brain and/or guinea pig cerebellum membrane preparations. Inhibitory constant (Ki) values of dermorphin were 0.7 nM, 62 nM and greater than 5000 nM respectively for mu, delta and chi sites, indicating a selectivity ratio Ki(delta)/Ki(mu) = 88. Under similar conditions, Tyr-DAla-Gly-MePhe-Gly-ol, which is regarded as one of the most selective high-affinity mu-agonist available, exhibited a selectivity ratio of 84. 2. Specific binding properties of tritium-labeled dermorphin (52 Ci/mmol) were characterized in the rat brain. Equilibrium measurements performed over a large range of concentrations revealed a single homogeneous population of high-affinity binding sites (Kd = 0.46 nM; Bmax = 92 fmol/mg membrane protein). 3. Profound differences were observed in the potencies displayed by various selective opiates and opioids ligands in inhibiting the specific binding of [3H]dermorphin. The rank order of potency was in good agreement with that obtained with other mu-selective radiolabeled ligands. 4. Receptor autoradiography in vitro was used to visualize the distribution of [3H]dermorphin binding sites in rat brain. The labeling pattern paralleled that observed using other mu probes. Binding parameters and selectivity profile of [3H]dermorphin on slide-mounted sections were similar to those obtained with membrane homogenates. 5. Finally, intracerebroventricular administration of synthetic dermorphin into mice showed that this peptide is the most potent analgesic known to date, being up to 5 and 670 times more active than beta-endorphin and morphine, respectively. Higher doses induced catalepsy. The overall data collected demonstrate that dermorphin is the first among the naturally occurring peptides to be highly potent and nearly specific super-agonist towards the morphine (mu) receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural requirements for dermorphin opioid receptor binding

Structural features influencing binding activity of dermorphin to opioid receptors have been investigated in the rat brain through the synthesis and evaluation of binding affinity of a series of synthetic dermorphin analogs. Tritiated dermorphin was used as primary ligand. The single population of high affinity dermorphin binding sites present in the rat brain is clearly of an opioid nature since bound radiolabeled dermorphin was fully displaced with high affinity either by morphine or naloxone. Displacement of tritiated dermorphin by all alkaloid opiates or dermorphin related peptides tested was monophasic, consistent with simple competitive inhibition at a single population of binding sites. Dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) was the most potent competitor in all experiments. The D-configuration of the amino acid residue in position 2 was found to be of crucial importance for binding. Replacement of D-Ala2 with L-Ala led to a deleterious effect, this analog being 1/5000th as potent as dermorphin in displacing bound tritiated dermorphin from its receptor. Shorter dermorphin homologs, dermorphin-(1-4)-NH2 and dermorphin-(1-3)-NH2, were found to be 20 and 40-fold less potent, respectively, than dermorphin. The C-terminal carboxamide function is of significant importance for manifestation of the full intrinsic binding potency of dermorphin. Deamidated dermorphin had 1/5th the potency of the parent peptide. This suggests that while the whole dermorphin sequence is required for the expression of the full intrinsic binding activity of the molecule, the N-terminal tripeptide is a key structure as it contains the features which allow receptor recognition.

Opioid receptor binding profile of selected dermorphin-like peptides

The receptor binding profile of a selected group of dermorphin-like peptides was determined and correlated with the results of the guinea pig ileum (GPI) and mouse vas deferens (MVD) bioassays and with the currently used antinociception tests in the rat. For the peptides with the characteristic dermorphin D-Ala2-Phe3-Gly4 sequence, a linear negative correlation was found between the reciprocal of sodium shift and relative affinity for the mu-type opioid receptor. For the same peptides, a positive correlation was evidenced between relative potency on GPI and MVD and relative affinity for mu- and delta-type receptors, respectively.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

Structure-activity relationships of dermorphin synthetic analogues

A number of dermorphin analogues have been reviewed for antinociceptive activity after systemic administration. Analgesic peptides as potent as or more potent than dermorphin are found among the hepta- and tetrapeptide analogues, probably because of enhanced stability towards carboxyldipeptidases imparted by the Pro6 and D-Ala2 residues lying on the right and left side, respectively, of the point of cleavage. Hexapeptide analogues are practically inactive. [D-Arg2]derivatives are very potent, particularly in the tetrapeptide series. In binding studies dermorphin behaves as a pure opioid agonist, with a marked affinity and selectivity for the mu-type opioid receptors. In the heptapeptide analogues a direct correlation seems to exist between mu-selectivity and "sodium shift," and between lipophilicity and MVD/GPI potency ratio.