Giuliana Falconieri Erspamer

Deltorphin, a novel amphibian skin peptide with high selectivity and affinity for δ opioid receptors

With a cDNA library prepared from skin of Phyllomedusa sauvagei, the sequence of the precursor of dermorphin was elucidated recently. The sequence suggested the existence of another peptide, distantly related to dermorphin. Two variants of this peptide have now been synthesized containing either L- or D-methionine as the second amino acid. The peptide containing the D-methionine exhibited high-affinity and selectivity for delta opioid receptors in the mouse vas deferens and in rat brain homogenates. Moreover, using the synthetic peptide as marker, we could isolate small quantities of the corresponding natural peptide containing D-methionine as the second amino acid from skin extracts of Phyllomedusa sauvagei. The name deltorphin is proposed for this new peptide and its sequence is Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2.

The brain-gut-skin triangle: New peptides

New data on tachykinins and bombesins are displayed and the present situation of research on the novel amphibian skin peptides sauvagine and dermorphin is illustrated. The potent stimulant effect of sauvagine on ACTH and beta-endorphin release has been confirmed both in vivo and on columns of isolated and dispersed rat pituitary cells, and similarly the potent inhibitory effect on PRL and GH release, both in the rat and man. Particular emphasis is laid on the occurrence of sauvagine-like immunoreactivity in fish urophysis and in amphibian nervous structures, including the retina. It is suggested that the long-searched corticotropin releasing factor and PRL release-inhibiting factor may be a sauvagine-like peptide. Dermorphin, in its turn, has been found to cause, by intracerebroventricular injection, not only analgesia and catalepsy, but also conspicuous EEG and behavioral changes in the rabbit and chick, as well as a sharp reduction in gastric emptying time and gastric acid output in the rat, together with marked stimulation of PRL release.

Parallel bioassay of 27 bombesin-like peptides on 9 smooth muscle preparations. Structure-activity relationships and bombesin receptor subtypes.

Thirteen natural bombesin-like peptides and 14 synthetic analogues were submitted to parallel bioassay on 9 smooth muscle preparations in order to determine their relative potency, in comparison to bombesin and litorin. The natural peptides of the bombesin subfamily showed a uniformly high or moderate potency on all preparations. However, synthetic bombesins of shorter chain length (hepta- and octapeptides) manifested a good potency only on the rat uterus preparation. Among the peptides of the litorin and phyllolitorin subfamilies, only litorin and ranatensin presented a full spectrum of potency, equalling or even surpassing that of bombesin. All other natural and synthetic members of the two subfamilies showed a sharply dissociated spectrum of potency on the different smooth muscle preparations. The only exception was the rat urinary bladder and, in part, the chicken intestine, on which the peptides displayed a uniformly high potency, comparable to, or even greater than that of bombesin. The present results help to explain structure/activity relationships and suggest the probable existence, in the periphery, of multiple bombesin receptor subtypes.

Purification and characterization of bioactive peptides from skin extracts of Rana esculenta

The peptide fraction extracted by methanol from the skin of Rana esculenta, a species widely distributed in Western Europe, was investigated. The pharmacological activity found in the extract is attributable to the presence of authentic bradykinin, together with a shorter, partially active version of this molecule, des-Arg9-bradykinin. Also the bradykinin fragment 1-7 has been isolated, but it was inactive in our bioassay system. Moreover, a family of hydrophobic peptides has been purified and characterized, which appeared devoid of pharmacological activities when tested on smooth muscle preparations, but were provided with hemolytic activities.

Tachykinins and other biologically active peptides from the skin of the Costa Rican phyllomedusid frog Agalychnis callidryas

Peptides present in a methanol extract prepared from skin of the Costa Rican frog Agalychnis callidryas of the Phyllomedusinae subfamily were studied by sequence analysis and pharmacological tests. Members of five different peptide families-tachykinins, bradykinins, caerulein, opioid peptides and sauvagine-were found. In particular, the extract contained a number of tachykinins with the following sequences: Gly-Pro-Pro-Asp-Pro-Asn-Lys-Phe-Ile-Gly-Leu-Met-NH2, Gly-Pro-Pro-Asp-Pro-Asp-Arg(Lys)-Phe-Tyr-Pro-Gly-Met-NH2, pGlu-Pro-Asp-Pro-Asp-Arg-Phe-Tyr-Pro-Gly-Met-NH2, Gly-Pro-Pro-Asp-Pro-Asn-Lys-Phe-Tyr-Pro-Val-Met. The latter three peptides have the unusual C-terminal sequence Pro-Gly(or Val)-Met-NH2 rather than Gly-Leu-Met-NH2 found in many other members of the tachykinin family. The observed amino acid substitutions may be the reason for the marked decrease in the biological activity observed in all in vitro and in vivo tests, even through the spectrum of tachykinin activities was retained. A kassinin-like peptide, with the sequence Gly-Pro-Pro-Asp-Pro-Asn-Lys-Phe-Ile-Gly-Leu-Met-NH2, was also found in the A. callidryas skin. While kassinin has a much higher affinity for NK-3 than for NK-1 receptors, the opposite is true for this A. callidryas peptide. The extract from A. callidryas skin also contained a new caerulein (pGlu-Asp-Tyr(HSO3)-Lys-Gly-Trp-Met-Asp-Phe-NH2) and a phyllokinin (Arg-Pro-Hyp-Gly-Phe-Ser-Pro-Phe-Arg-Ile-Tyr), as well as the opioid peptides dermorphin and [Hyp6]dermorphin, both previously isolated from different Phyllomedusa species.

Identification and characterization of two dermorphins from skin extracts of the Amazonian frog Phyllomedusa bicolor

Skin extracts of South American hylid frogs of the subfamily Phyllomedusinae contain dermorphins and deltorphins, opioid heptapeptides highly selective for either μ or δ receptors. In all these peptides, a d‐amino acid is present in the second position. The structure of the precursors for Ala‐deltorphins was recently deduced from cloned cDNAs derived from skin of Phyllomedusa bicolor (Richter et al. (1990) Proc. Natl. Acad. Sci. USA 87, 4836–4839). From the amino acid sequence of these precursors, the existence of three peptides related to dermorphin could be predicted. From methanol extracts of skin of Ph. bicolor we have isolated two of these peptides. [Lys7]dermorphin‐OH and [Trp4,Asn7]dermorphin‐OH. The biological activity of these new dermorphins and their amidated counterparts is presented.

Guinea-pig ileum (GPI) and mouse vas deferens (MVD) preparations in the discovery, discrimination and parallel bioassay of opioid peptides

As many as 47 amphibian and mammalian, natural and non-natural opioid peptides have been examined in guinea-pig ileum (GPI) and mouse vas deferens (MVD) preparations. The great value of these extremely simple and accessible tissue models in the identification, isolation and purification of endogenous opioid peptides, in studying structure/activity relationships, and in determining selectivity of the peptide molecules for the various opioid receptors, especially delta- and mu-receptors, is emphasized.

Neuropeptide Y release by pumiliotoxin-B in the electrically-stimulated mouse vas deferens: an immunohistochemical study.

Morphologic and immunohistochemical studies were conducted to ascertain whether pumiliotoxin-B (PTX-B), an indolizine alkaloid from the skin of the Neotropical dendrobatid frog, Dendrobates pumilio, affects the anatomic and immunohistochemical features of the electrically stimulated mouse vas deferens preparations. PTX-B, at a concentration of 1 microM, consistently decreased the density pattern of neuropeptide Y (NPY)-immunoreactive nerve fibers contained within the circular muscular layer. The alkaloid also induced striking morphologic changes. It enlarged the lumen of the vasa and relaxed the muscular wall. Pretreatment with prazosin or haloperidol affected neither the release of NPY nor the morphologic changes; pretreatment with tetrodotoxin and guanethidine abolished NPY release and prevented the PTX-B-induced morphologic changes. PTX-B had no appreciable effect on the density and distribution pattern of nerve fibers immunostained for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, enkephalin, pancreatic polypeptide, 5-hydroxy-tryptamine and tyrosine hydroxylase.