A Novel Peptide, Vasoactive Intestinal Contractor, of a New (Endothelin) Peptide Family

Determination of the structure of [Nle7]-endothelin by 1H NMR

[Nle7]-endothelin was synthesized and studied by 1H NMR and distance geometry calculations. The NMR study was performed first in DMSO-d6 and then in 50% acetonitrile/water since this peptide aggregates in pure water. In both cases, all spin systems were identified and assigned with the aid of two-dimensional spectroscopy (2D): COSY (for scalar couplings) and NOESY (for dipolar couplings). On the basis of the acetonitrile/water NMR parameters, and using the DISGEO program, a three-dimensional structure of [Nle7]-endothelin is proposed and discussed.

Expression of human preproendothelin-1 cDNA in COS cells results in the production of mature vasoactive endothelin-1

Transient transfection of simian kidney (COS) cells with a recombinant plasmid encoding human preproendothelin-1 resulted in the production of biologically active endothelin-1. Conditioned medium from human preproendothelin-1 transfected cells demonstrated a significant increase in immunoreactive endothelin and big endothelin which co-eluted, when analyzed by reverse phase HPLC, with synthetic endothelin-1 and big endothelin-1, respectively. In addition, biological activity was confirmed by both inhibition of [125I]endothelin-1 binding to rat cerebellar and renal medullary membrane endothelin receptors and in vitro vasoconstriction of rabbit aorta. This is the first demonstration that human preproendothelin-1 is capable of being processed to a vasoactive form in a heterologous system and suggests that human preproendothelin-1 transfected COS cells may provide a useful model system for the study of endothelin biosynthesis.

Effect of endothelin-1 and vasoactive intestinal contractor on blood flow and output of vasoactive intestinal polypeptide in the feline colon

Injection of the structurally related peptides, endothelin-1 and vasoactive intestinal contractor (VIC), into a branch of the superior mesenteric artery in anesthetized cats caused dose-dependent reductions in blood flow in the portal vein and inferior mesenteric artery. The maximum effect occurred after 1 minute and was more prolonged in the portal vein. The effects of the two peptides were not significantly different. The colonic output of vasoactive intestinal polypeptide (VIP) into portal venous blood was decreased significantly by endothelin-1 and VIC, returning to baseline more rapidly than blood flow. When norepinephrine was injected to produce comparable reductions in blood flow, the output of VIP into portal venous blood was not altered significantly. These results suggest that inhibition of output of the vasodilator VIP contributes to the vasoconstrictor effects of endothelin-1 and VIC in the feline colonic vascular bed.

Ca2+ signaling by distinct endothelin peptides in glomerular mesangial cells

Ca2+ signaling by peptides of the endothelin (ET) gene family was studied in cultured glomerular mesangial cells. In addition to the increase in cytosolic free [Ca2+] ([Ca2+]i) previously described for ET-1, we also observed that ET-2, ET-3, and sarafotoxin S6b generate similar [Ca2+]i waveforms but with dissimilar potencies and kinetics. The prepro form of ET-1 was inactive, suggesting that mature ET peptides are constrained in an inactive conformation within the preproET species. ET isopeptides caused both release of Ca2+ from intracellular stores and Ca2+ influx via a voltage- and dihydropyridine-insensitive pathway. ET-mediated Ca2+ influx was independent of the increase in [Ca2+]i. Activation of protein kinase C inhibited ET-induced Ca2+ signaling, whereas addition of ET to protein kinase C-depleted cells resulted in enhanced [Ca2+]i waveforms. Mesangial cells also demonstrated a marked adaptive desensitization response to ET. These data demonstrate that Ca2+ signaling is a common response to different ET peptides in glomerular mesangial cells and that activation of protein kinase C down-regulates these Ca2+ signals.

Vascular activities of the endothelins

The endothelins are a family of novel 21 amino-acid peptides and are the most potent vasoconstrictor substances yet discovered. The endothelins not only produce prolonged pressor responses in intact animals but they also constrict large and small arterial and venous vessels studied as isolated vascular preparations, influence autonomic transmission, exert positive inotropic effects on the heart and have been shown to be capable of releasing EDRF, prostanoids and atrial natriuretic factor. Release of endothelins occurs after de novo synthesis which may be stimulated by various agonists, fluid-flow and possibly hypoxia. The endothelins have been implicated in the pathophysiology of a variety of cardiovascular disorders but their precise role remains to be elucidated.

Evolution of the sarafotoxin/endothelin superfamily of proteins

Sixteen protein and nucleic acid sequences from the vasoconstrictor sarafotoxin/endothelin/endothelin-like superfamily of peptides were studied, and the evolutionary relationships between the sarafotoxin and endothelin gene families as well as the phylogenetic topology within each gene family and the three endothelin subfamilies was reconstructed. The endothelin gene family has diverged from an ancestral gene that has experienced an exon duplication event followed by two gene duplication events. The sarafotoxins' lineage diverged from the ancestral gene prior to the first endothelin gene duplication event. Analysis of the resulting phylogenetic trees revealed that in several lineages, the peptides have independently accumulated identical replacements in position 2, therefore supporting the hypothesis that residue 2 is crucial to their activity.

Autoradiographic localization of endothelin-1 binding sites in porcine skin

Autoradiographic techniques and 125I-labeled endothelin-1 were used to study the distribution of endothelin-1 binding sites in porcine skin. Specific endothelin-1 binding sites were localized to blood vessels (capillaries, deep cutaneous vascular plexus, arteries, and arterioles), the deep dermal and connective tissue sheath of hair follicles, sebaceous and sweat glands, and arrector pili muscle. Specific binding was inhibited by endothelin-2 and endothelin-3 as well as endothelin-1. Non-specific binding was found in the epidermis and the medulla of hair follicles. No binding was found in connective tissue or fat. These vascular binding sites may represent endothelin receptors, in keeping with the known cutaneous vasoconstrictor actions of the peptide. If all binding sites are receptors, the results suggest that endothelin could also regulate the function of sweat glands and may have trophic effects in the skin.

Effects of endothelin-1 on the isolated guinea-pig ileum: role of Na+ ions

Endothelin-1 induced a unusual transient biphasic effect (relaxation followed by contraction) in the isolated guinea-pig ileum. The contractile component of the response was concentration-dependent in the dose range studied, but the relaxant component was not. Neuronal mechanisms and cyclic GMP do not seem to be involved in the relaxing effect since this component was not affected by either tetrodotoxin, atropine or methylene blue. Endothelin-1 induced desensitization which was well characterized for the contractile component of the response, and was only partially reversed after a 3-h resting period. The effects of endothelin-1 were particularly sensitive to decreases in the Na+ gradient induced either by lowering the Na+ concentration in the medium or by treating the tissue with ouabain or by a previous treatment with acetylcholine. Amiloride partially inhibited the response induced by endothelin-1 indicating that Na+ channels and/or Na+/H+ exchange are probably involved in its action. Our results suggest that the contractile response induced by endothelin-1 in the isolated guinea-pig ileum depends greatly on Na+ ions, in contrast to the responses observed in vascular smooth muscle.

Isolation of anti-endothelin receptor monoclonal antibodies for use in receptor characterization

Monoclonal antibodies reactive with endothelin (ET) receptors have been prepared by immunization of mice with rat lung membranes. Of four clones isolated, three clones preferentially recognized 32,000-dalton ET receptor and the other has a higher affinity for the 45,000-dalton receptor. The binding of 125I-ET-1 to detergent-solubilized ET receptors which were adsorbed to the antibodies was displaced by increasing concentrations of unlabeled ET isopeptides. These results demonstrate that the four clones specific for the receptor have the potential to be a useful tool in the characterization of ET receptors.

[D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P, a neuropeptide antagonist, blocks binding, Ca2(+)-mobilizing, and mitogenic effects of endothelin and vasoactive intestinal contractor in mouse 3T3 cells

Endothelin (ET1) and vasoactive intestinal contractor (VIC) stimulate quiescent Swiss 3T3 cells to resume DNA synthesis acting synergistically with epidermal growth factors (EGF) and other mitogens. The peptide [D-Arg1,D-Phe5,D-Trp7,9,Leu11] substance P has been identified as a broad spectrum neuropeptide antagonist which blocks the binding and biological effects of the Ca2(+)-mobilizing neuropeptides bombesin, vasopressin, and bradykinin. In the present study we show that [D-Arg1,D-Phe5,D-Trp7,9,Leu11] substance P also acts as an ET1/VIC antagonist as judged by the following criteria: a) inhibition of specific 125I-labelled ET1 binding to a ET1/VIC receptor in a competitive and dose-dependent manner; b) blocking of the rapid increase in the cytosolic Ca2+ concentration promoted by ET1 or VIC; and c) inhibition of DNA synthesis stimulated by VIC in the presence of EGF. The inhibitory effects of [D-Arg1,D-Phe5,D-Trp7,9,Leu 11] substance P on Ca2+ mobilization and DNA synthesis were reversed by increasing the concentration of VIC. This is the first time that a peptide structurally unrelated to ET1 or VIC is shown to block the binding and mitogenic effects of peptides of the endothelin family.

Binding of [125I]-endothelin-1 to rat cerebellar homogenates and its interactions with some analogues

1. [125I]-endothelin-1, over the concentration range 6 pM-10 nM, bound to a single site in homogenates of rat cerebellum with high affinity (Kd = 2.8 +/- 0.6 x 10(-10) M). The site was present in a concentration of 321 +/- 58 fmol mg-1 protein. 2. The rates of association and dissociation of [125I]-endothelin-1 with the binding site were slow (at 25 degrees C, k+1 = 8.0 +/- 1.3 x 10(5) M-1s-1; k-1 = 2.6 x 10(-4)s-1) and, on addition of a maximally displacing concentration of endothelin-1 (100 nM), 94.0 +/- 8.4% of the [125I]-endothelin-1 was still bound after 14 h. 3. [125I]-endothelin-1 binding was inhibited by a number of naturally occurring or genetically encoded members of the endothelin/sarafotoxin family of peptides. The order of potency was endothelin-3 = sarafotoxin S6b greater than endothelin-2 = endothelin-1 much greater than porcine proendothelin1-39. 4. Binding was also inhibited by analogues in which either one or both of the cystine disulphide bridges had been replaced by substitution with 2 or 4 alanine residues. The tetra-alanyl substituted analogue, [Ala1,3,11,15]endothelin-1, was equipotent with endothelin-1 at inhibiting the binding of [125I]-endothelin-1. [Ala3,11]endothelin-1 and [Ala1,15]endothelin-1, analogues which each contained one of the disulphide bridges from the parent peptide, were respectively 3 and 14 times less potent than the parent peptide. An analogue in which the Glu10 residue had been anisylated was 25 fold less potent than endothelin-1. 5. It is concluded that the structural requirements for binding to the cerebellar sites for [1251]_ endothelin-1 do not require the presence of the disulphide bridges characteristic of the endothelin/ sarafotoxin family. Rather, the binding may be more sensitive to the presence of bulky side chain substituents, at least in the smaller intramolecular loop.

Endothelium-dependent vascular activities of endothelin-like peptides in the isolated superior mesenteric arterial bed of the rat

1. The vasoconstrictor activities of endothelin-2, endothelin-3, sarafotoxin S6b, human proendothelin1-38 and mouse vasoactive intestinal contractor (VIC) were studied in the isolated Krebs-Henseleit perfused mesenteric arterial bed of the rat in the presence and absence of the endothelium. The vasoconstrictor properties of endothelin-1 were studied in control preparations and in preparations treated with methylene blue or N omega-nitro-L-arginine methyl ester (NAME). Finally, the direct vasodilator properties of endothelin-2, endothelin-3 and sarafotoxin S6b were studied in preparations preconstricted with methoxamine. 2. In the presence of an intact endothelium, all of the peptides caused dose-dependent increases in perfusion pressure and sarafotoxin S6b was a full agonist relative to the other peptides studied (maximum increase in perfusion pressure, Rmax = 106 +/- 11 mmHg). Endothelin-1, endothelin-2 and VIC were more potent vasoconstrictors (ED50 93.0 +/- 40.0, 90.8 +/- 20.5 and 106 +/- 63 pmol, respectively) than endothelin-3 and sarafotoxin S6b, which were found to be equipotent (ED50 values 411 +/- 195 and 345 +/- 86 pmol, respectively). A full dose-response relationship could not be constructed for proendothelin, but the highest dose used (4 nmol) increased the perfusion pressure by 15.4 +/- 1.6 mmHg. 3. Destruction of the endothelium with the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate (CHAPS) significantly enhanced the pressor activity of all 5 peptides. The Rmax for sarafotoxin S6b was not significantly altered by removal of the endothelium but its potency was significantly increased (ED50 = 115 +/- 15 pmol). Although their R,,, values were significantly increased, endothelin-2 and VIC were still partial agonists relative to sarafotoxin S6b in CHAPSpretreated preparations; their potencies were unchanged (ED5o values 118 + 53 and 416 + 196pmol, respectively). Removal of the endothelium significantly reduced the potency of endothelin-3 (ED5o, 6.3 + 2.2 nmol) but this peptide then exhibited full agonist activity (R..x = 106 + 14 mmHg). After endothelial cell destruction, the pressor responses to proendothelin were increased; 4 nmol gave a response of 38.8 + 5.5 mmHg. 4. Exposure of preparations to either 100 microM NAME (R,,,X = 42.6 + 2.4mmHg and EDSo = 57.5 + 13.7 pmol) or 10 microM methylene blue (R,,,. = 36.0 + 5.1 mmHg and ED50 = 81.5 + 26.1 pmol) significantly enhanced the maximum pressor responses to endothelin-l (control: R.,=X = 22.5 + 2.6 mmHg; ED5o = 93.0 + 40.Opmol). The values in the presence of NAME or methylene blue were not significantly different from those found previously for endothelin-1 after removal of the endothelium with CHAPS. 5. Endothelin-2, endothelin-3 and sarafotoxin S6b all caused vasorelaxation in preparations which had been precontracted with 100 microM methoxamine. This action was endothelium-dependent as it was abolished by perfusing the mesentery with CHAPS. Endothelin-3 and sarafotoxin S6b caused relaxation at much lower doses than were needed with endothelin-1 and endothelin-2. 6. The endothelium significantly modulates the vasoconstrictor activity of all the endothelin-like peptides studied, including the precursor peptide proendothelin (which was the least potent of the peptides). This modulation is likely to be due to the release of endothelium-derived relaxing factor, since similar results to destruction of the endothelium were obtained when endothelin-l was investigated in the presence of either methylene blue or NAME (an inhibitor of nitric oxide formation) in the perfusion fluid. The vasodilator effects of the peptides were also endothelium-dependent. There was a different order of potency for vasoconstriction and vasodilatation supporting the suggestion that there are sub-types of receptor for the endothelin-like peptides in the vasculature; one type on the vascular smooth muscle and a second type on the endothelium.

Endothelin receptor subtypes and stimulation of aldosterone secretion

Endothelins (ETs) are 21-amino acid peptides with two disulfide bonds that have powerful vasoactive properties. We have previously shown the presence of a specific, high-affinity, saturable receptor for porcine or human endothelin (ET-1) in cultured calf zona glomerulosa cells. ET-1 was a stimulator of aldosterone secretion although not as powerful as angiotensin II. Incubations of cultured calf zona glomerulosa cells with Sarafotoxin S6b (S6b), a snake venom that has a structure highly homologous to ET-1, stimulated aldosterone secretion with a potency similar to that of ET-1. Binding of [125I]ET-1 to the adrenal receptor gave a Kd of 0.17 +/- 0.05 nM and a Bmax of 36 +/- 8.5 fmol/well (n = 4). Displacement of [125I]ET-1 by unlabeled ETs and S6b showed that the concentrations needed to displace 50% of the tracer were 0.3 nM for ET-1, 0.3 nM for ET-2, 10 nM for S6b, and 100 nM for ET-3. Binding of [125I]S6b to cultured adrenal cells revealed a receptor with a Kd of 0.05 +/- 0.01 nM and a Bmax of 8 +/- 2 fmol/well (n = 4). Displacement of [125I]S6b by unlabeled ETs and S6b showed that the concentrations needed to displace 50% of the tracer were 0.03 nM for S6b, 0.06 nM for ET-1, 0.04 nM for ET-2, and 0.05 nM for ET-3. Unlabeled ET-1 and ET-2 preferentially down-regulated the binding of [125I]ET-1, and S6b preferentially down-regulated the binding of [125I]S6b.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of putative endothelin converting enzyme in bovine adrenal medulla: evidence for a cathepsin D-like enzyme

A specific and sensitive assay has been established for measurement of endothelin converting activity in a tissue extract. This assay is based on measuring endothelin-1 generated from big endothelin-1 by endothelin converting enzyme (ECE) with radioimmunoassay using an endothelin C-terminal specific antibody. By using this assay, we purified and characterized ECE in bovine adrenomedullary chromaffin granules ECE was purified over 3,000 times by a combination of DEAE, hydrophobic and gel filtration chromatography. A molecular weight of ECE was estimated to be approximately 30,000 by gel filtration. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that ECE had three major components with estimated molecular weights of 45,000, 30,000 and 15,000 like bovine spleen cathepsin D. ECE had a pH optimum at 3.5 and was inhibited by pepstatin. These results strongly suggest that ECE is a cathepsin D-like aspartic protease.

Vasoactive intestinal contractor, a novel peptide, shares a common receptor with endothelin-1 and stimulates Ca2+ mobilization and DNA synthesis in Swiss 3T3 cells

Vasoactive intestinal contractor peptide (VIC), a novel member of the endothelin family, stimulated a rapid increase in the intracellular Ca2+ concentration in fura-2-loaded Swiss 3T3 cells. Sequential addition of VIC and endothelin-1 (ET1) demonstrated the induction of both homologous and heterologous desensitization. VIC was as potent as ET1 in displacing the binding of 125I-ET1 and in stimulating mitogenesis in Swiss 3T3 cells. These findings suggest that VIC and ET1 share a common receptor in Swiss 3T3 cells.

Rat mesenteric artery endothelial cells in culture secrete ET-1

Endothelial cells were harvested by the collagenase perfusion of isolated mesenteric arteries of rats and cultured. An endothelin peptide was detected in the supernatant of these cells by an antibody which recognizes ET-1 but not "rat" endothelin (ET-3). Culture media was extracted using a C-8 solid phase column and subjected to reverse phase HPLC using a system that separates all known endothelins and immunoreactive endothelins measured using another antibody which recognizes all endothelins. The main immunoreactive peak co-eluted with ET-1. We could not detect any ET-2, ET-3 or Vasoactive Intestinal Contractor. A smaller immunoreactive peak of unknown structure that eluted earlier than ET-1 was also detected. In conclusion, rat endothelial cells secrete a peptide of similar chromatographic and immunoreactive properties as ET-1.

Endothelium-derived contractile factors

1. Vascular endothelium releases different substances (endothelium-derived contractile factors, EDCFs), which mediate vasoconstrictor responses induced by several agents. 2. Clear differences have been reported in endothelium-dependent contractions, which suggest at least three distinct EDCFs, named EDCF1, EDCF2 and EDCF3, respectively. 3. EDCF1 is a cyclooxygenase metabolite(s) of arachidonic acid. EDCF2 is a polypeptide released from cultured endothelial cells. It has been isolated and identified as a 21-amino acid peptide called endothelin, which is described as the most potent vasoconstrictor agent known to date. EDCF3 is an unidentified contractile factor(s), which is neither EDCF1 nor EDCF2. 4. The physiological role of these endothelial contractile factors is not yet clear. However, they have been implicated in the local mechanisms involved in blood flow regulation, as well as in some pathological conditions, such as hypertension or cerebral vasospasm.