Biomedical subjects
Publications and source records attributed to R Tomatis.
We studied the effect of partial retro-inverso modification of a selected peptide bond of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) related peptides. The drastic loss of mu-receptor affinity following introduction of retro-inverso peptide bond between Phe1-D-Ala2 in the new peptide analogues, emphasized the importance of this backbone in the dermorphin peptides.
The cyclo [Thr-Thr-Thr-Tyr-Asn-Thr] hexapeptide related to peptide T, H-Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr-OH, competitor of the Human Immunodeficiency Virus in the binding to human T cells, was synthesized and tested for its ability to stimulate monocyte migration (chemotaxis). The new cyclic derivative showed negligible biological activity.
Fifteen pentapeptide analogs of C-terminal fragment of peptide T, H-Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr-OH, were prepared and tested for human monocyte chemotaxis. Structure-activity studies suggest that the potent chemotactic activity of H-Thr-Thr-Asn-Tyr-Thr-OH is mediated through the polar properties of the C-terminal carboxyl group and Thr side chains at the critical positions 5 and 8, while the hydroxyl group of N-terminal Thr and its free amino function are not essential requirements for CD4 receptor interactions.
Peptide T, an octapeptide of sequence ASTTTNYT that binds to human T cells, was studied as a zwitterion in DMSOd6 solution by means of proton NMR spectroscopy at 500 MHz. The unusual dispersion of the resonances of residues of the same type (T) makes it possible to assign all resonances to specific residues by means of several 2D techniques. The non-random nature of the conformation is substantiated by the observation of sequential nuclear Overhauser enhancements (NOEs). The low value of the temperature coefficient of the chemical shift of the NH of T8 and a diagnostic NOE between the NHs of T7 and T8 hint that a beta-turn including T5, N6, Y7 and T8 is a prominent conformational feature in solution. The ring current high field shifts of the methyl group and of the NH of T8 are consistent with an interaction with the side-chain of Y7, favoured by the beta-turn.
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A new series of 12 dermorphin tetrapeptides, W-Tyr-D-MetO-Phe-Xaa-Y (W = H, H2NC = (NH); Xaa = Gly, Sar, D-Ala; Y = OH, OCH3, NH2) were prepared by traditional methods in solution and tested for opioid activity. In binding studies based on displacement of mu, delta, and kappa opioid receptor selective radiolabels from guinea pig brain membranes, the new analogues showed a negligible affinity for the kappa binding site and a preference for mu- over delta-receptors with an evident dependence on N- and/or C-terminal modifications; H-Tyr-D-MetO-Phe-Gly-OCH3 was shown to be one of the most selective mu-receptor ligands reported to date. All these tetrapeptides display dose-related naloxone-reversible antinociceptive effects following intracerebroventricular (icv) or subcutaneous (sc) administrations in mice. In comparison to morphine, H-Tyr-D-MetO-Phe-Sar-NH2 and the guanidino derivative H2NC = (NH)-Tyr-D-MetO-Phe-Gly-NH2 showed lower affinity for mu, delta, and kappa sites but exceptionally stronger analgesia: respectively they are 560 and 1550 times as potent an analgesic as morphine. Among analogues tested after sc administration, H-Tyr-D-MetO-Phe-Sar-NH2 and H-Tyr-D-MetO-Phe-D-Ala-OH displayed the highest activities; they were respectively 22 and 30 times more potent than morphine on a molar basis. These results indicate that N- or C-terminal modifications and substitution at position 2 or 4 of dermorphin-(1-4) peptide do not only influence the affinity of the resulting analogues to opioid receptors but also may favorably alter their pharmacokinetic properties.
The structure-activity relationship of several mu selective opioid peptides has been evaluated on the basis of both experimental and theoretical approaches. The conformations of Tyr-D-Ala-Phe-Gly-NH2, the tetrapeptide N-fragment of dermorphin, and two analogues have been studied in solution by 1H NMR spectroscopy. The physicochemical environment inside the receptor has been simulated by complexing the peptides with a crown ether and dissolving the complexes in chloroform. The family of conformations derived from the NMR data possesses most of the features previously proposed for mu agonists and is fully consistent with an original model of the mu receptor based on the structures of many rigid opiates. As a simple test of this model, the synthesis of a linear peptide with significant mu activity in spite of the absence of Tyr1 is reported.
Eight new dermorphin peptides, X-C6H4-CH2CH2CO-D-Ala-Phe-(L or D)-Yaa-NH2 [X = H, OH; Y = lysine, homoarginine (Har)], were prepared and tested by binding assays. They show negligible affinity for mu-, delta- and K-receptor sites. These findings indicate that the N-terminal ammonium group can not be replaced by the ammonium or guanidinium function located at the side-chain in Lys or Har derivatives.
The opioid activity pattern of 8 dermorphin tetrapeptides, W-Tyr-D-MetO-Phe-Xaa-Y (W = H, H2N-C = (NH); Xaa = Gly, 2-aminoethanol, sarcosine; Y = NH2, NH-alkyl), was determined in guinea-pig ileum (GPI) preparations and in brain binding assays and compared with their antinociceptive potency in mice. Almost all modifications increased potency on the GPI test as well as the antinociceptive action of the parent H-Tyr-D-Ala-Phe-Gly-NH2. Dermorphin, H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2, and related tetrapeptide analogues show negligible K-binding activity and, like morphine, possess a higher affinity to mu- than delta-receptors. Nevertheless the correlation of analgesia with the effects on GPI and binding data separate the peptides from morphine. For example, in comparison with the opiate alkaloid H-Tyr-D-MetO-Phe-Gly-ol and H-Tyr-D-MetO-Phe-Gly-NH2 displayed a lower affinity for mu sites, a moderately higher potency on GPI but an exceptionally stronger analgesia, being respectively 350 and 1500 times as potent an analgesic as morphine. This may involve different subpopulations of opioid mu-receptors.
Dermorphin (D) is a potent opiate-like peptide isolated from the skin of some species of frogs. Experimental studies in animals indicate that D has a potent antinociceptive effect, while no investigation exists about its analgesic properties in humans. Our study shows that i.v. infusion of 0.16 mg/kg D induces a marked and long-lasting increase in the threshold of nociceptive flexion reflex in healthy volunteers. This effect is also evident in a complete chronic spinal subject, showing that D depresses the nociceptive transmission mainly acting at spinal level. Naloxone, while fully antagonizing the effects of morphine and enkephalin analogue, is able to reverse only partly (ca. 50%) the depressive effect of D on nociceptive spinal reflex. This fact may suggest that D interacts with different spinal opiate receptor populations in inducing analgesia.
Eight new dermorphin tetrapeptides, X-Tyr-D-MetO-Phe-aa-Y (X = H, H2N = C(NH); aa = Gly, 2-aminoethanol, sarcosine; Y = NH2, NH-alkyl), were prepared and tested for opioid activity. They show dose-related naloxone-reversible opioid effects in vitro and in vivo. H-Tyr-D-MetO-Phe-Gly-NH2 (I) (guinea pig ileum IC50 = 13.6 nM; tail-flick ED50 = 1.97 pmol/mouse, icv, and 0.65 mumol/kg, sc), though less effective in the periphery, has central activities higher than those of dermorphin H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2. Following intracerebroventricular or subcutaneous administrations in mice, I is about respectively 1500 and 17 times as potent an analgesic as morphine.
Dermorphinoyl(DMR)-glycine, DMR-sarcosine and DMR-glycyl-arginine have been prepared in order to examine the effect of C-terminal extension of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) on opioid activity. On GPI preparation the addition of Gly, Sar, or Gly-Arg to the carboxyl terminus of dermorphinoic acid was detrimental to mu activity: dermorphinoyl-derivatives, in fact, retain only 5-20% of dermorphin potency. Following intracerebroventricular administration (tail-flick test), whereas the analgesic activities of compounds showed the trend dermorphin greater than DMR-Sar greater than DMR-Gly-Arg greater than DMR-Gly greater than morphine, the nonapeptide displayed highest activity after subcutaneous injection in mice: DMR-Gly-Arg was 2.5 and 10 times more potent than dermorphin and morphine, respectively.
We have studied the effect of the intravenous administration of somatostatin (SRIF) on the thyrotropin (TSH) response to intravenous dermorphin (D), a new potent opioid peptide, in 7 healthy men. D significantly increased the serum TSH concentration. SRIF administration prior to, during and after D completely prevented the D-induced rise in serum TSH. These results confirm that D stimulates TSH release in man and that this stimulatory effect can be prevented by SRIF.
The effects of pirenzepine (P), a cholinergic muscarinic antagonist, on growth hormone (GH) and prolactin (PRL) response to dermorphin (D) were studied in a group of 7 healthy men. D produced clear elevations in GH and PRL levels. P completely blocked the GH-releasing activity of D, whereas it did not alter the PRL-releasing activity. These results indicate that GH-releasing action of D is mediated via the central cholinergic nervous system in man.
We describe the synthesis and preliminary in vitro and in vivo pharmacological tests of four [OGly4] tetrapeptide analogues of the opioid heptapeptide dermorphin H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2. The modification obtained by substituting aminoxy-acetic acid (OGly) for Gly4 provided analogues with substantial reduction of activity.
Dehydropeptide analogs of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) and N-terminal fragments containing one or two dehydrophenylalanine residues in the 3rd and/or 5th position, have been investigated by means of CD spectroscopy. The results indicate that the above dehydropeptides can adopt different conformations in alcohol and water solutions. In methanol and trifluoroethanol, the CD spectra are mainly consistent with the presence of folded structures, probably stabilized by intramolecular hydrogen bonds. In water, conversely, CD data indicate disruption of ordered structures and formation of preferentially extended flexible conformations. Models of the involved folded structures are tentatively proposed, taking into account the geometric features of dehydro residues and their tendency to favor hydrogen-bonded 10-membered rings.
Dehydrophenylalanine having the Z-configuration (delta Phe) and D-Phe were incorporated in positions 3 and/or 5 into dermorphin-(1-5)-peptide amide (H-Tyr-D-Ala-Phe-Gly-Tyr-NH2) in order to study the effect of structure or configurational changes. On GPI preparation, whereas the activity of [L-Phe5]-pentapeptide was fourfold higher than parent peptide and comparable to that of dermorphin, the substitution of Phe3 by its D-enantiomer was barely tolerated. The pentapeptides containing delta Phe in positions 3 and/or 5 displayed even lower potency: particularly the unsaturation at position 3 alone or at position 3 and 5 was very detrimental to mu activity.
The Phe3 and/or Tyr5 residues in dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) and its N-terminal hexapeptide-amide were replaced by delta-Phe or by Phe5 in order to examine the effect on opioid activity. On GPI preparation, the substitution of Phe5 for Tyr5 was well tolerated, whereas the hexa and heptapeptides containing delta Phe in position 3 and/or 5 displayed low potency. The unsaturation at position 3 alone or at positions 3 and 5 was particularly detrimental to mu activity. In the tail flick test, the influence of unsaturation or substitution at positions 3 and 5 generally matched the results of the in vitro assay. Dehydropeptides showed comparatively low antinociceptive effects and [Phe5] analogues displayed about 50% of the analgesic potency of the original peptides.