Endothelin-1 and -3 induce the release of tissue-type plasminogen activator and von Willebrand factor from endothelial cells

In vitro endothelial cell susceptibility to xenobiotics: Comparison of three cell types

In three different endothelial cell (EC) cultures (primary human umbilical cord vein, so-called HUVEC; and immortalized cell lines HBMEC and EA-hy-926), the effects of different xenobiotics were studied in order to standardize vascular EC models for in vitro pharmacotoxicological studies. Cell characteristics were first investigated by the production and the mRNA levels of known endothelial markers in the three EC culture models. EC secretory products, tissue plasminogen activator (tPA) and von Willebrand factor (vWF), were present in the supernatant of the immortalized cell lines. The mRNA levels of vWF, tPA, platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), and beta -integrin subunit, which are involved in the control of platelet function, coagulation, and fibrinolysis as well as in cell-matrix interactions, were investigated in all EC types. For at least three parameters, cultured cells provided marked characteristics of EC phenotype, in HUVEC and in immortalized cell lines, regardless of their origin from the macro- or microcirculation. Toxicity experiments were assessed after 24 h exposure to cadmium, cyclosporin A and cisplatin by MTT assay. These experiments show nonsignificant difference in susceptibility to cyclosporin A and cadmium on HUVEC, HBMEC, and EA-hy-926. However, HBMEC, seems to be highly susceptible to cisplatin compared to HUVEC, the latter being more sensitive than EA-hy-926. For experiments conducted with cyclosporin and cadmium, cell lines could constitute an alternative material for routine cytotoxicity studies.

Augmented expression of endothelin-1, endothelin-3 and the endothelin-B receptor in breast carcinoma

AIMS

Endothelins (ETs) are peptides expressed in many tumours which may stimulate angiogenesis and desmoplasia. Because ETs have not been extensively studied mammary neoplasia, we assessed ET protein and mRNA expression and receptor mRNA expression in normal and neoplastic breast tissues.

METHODS AND RESULTS

Tissues from five normal breasts, six fibroadenomas, seven ductal carcinomas in situ (DCIS) and 25 invasive carcinomas were stained with anti-ET-1 and anti-ET-3 antibodies and analysed using a grading system. ET-1, ET-3, ETA and ETB mRNA expression was assessed by quantitative RT-PCR from eight carcinomas and five normals. Weak staining for ET-1 and ET-3 was detected in all normals. Moderate to strong staining was seen in 72% and 64% of carcinomas for ET-1 and ET-3, respectively. Most fibroadenomas showed weak positivity for ET-1 (83%) and ET-3 (67%). ET-1 and ET-3 mRNA levels were upregulated in carcinomas compared with normal breast. No ETA mRNA was not detected in any tissue. ETB mRNA was detected in normal breast and was increased in carcinomas.

CONCLUSION

These results suggest that the ET system is altered in breast carcinomas and this may be of importance in the progression from in-situ to invasive carcinoma.

Hematologic evaluation of cardiopulmonary bypass circuits prepared with a novel block copolymer

BACKGROUND

To decrease the complications associated with cardiopulmonary bypass, novel biomaterials have been introduced that may be less thrombogenic than standard synthetic surfaces.

METHODS

Thirty-four patients undergoing coronary artery bypass grafting were randomized to bypass using either a control circuit or a circuit prepared "tip-to-tip" with a triblock-copolymer (polycaprolactone-polydimethylsiloxane-polycaprolactone).

RESULTS

There was a progressive increase in thrombin generation in the control group during bypass, which was not seen in the test group. The test surface decreased the release of tissue plasminogen activator and plasmin-alpha2-antiplasmin complex formation (p<0.005). There was also an increased platelet count and a decreased platelet activation in the test group, as detected by GMP-140 expression and beta-thromboglobulin release (p = 0.017). There was also significantly more debris that accumulated on the arterial filter in the control group, as confirmed by scanning electron microscopy.

CONCLUSIONS

This clinical trial has demonstrated a significant difference in the hematologic effects of the test circuits, with evidence of platelet preservation, decreased fibrinolysis, and decreased thrombin generation. A larger trial would be necessary to establish the clinical relevance of these differences.

High capacity for tissue-type plasminogen activator release from vascular endothelium in vivo

BACKGROUND

Tissue-type plasminogen activator (t-PA) is the key mediator of intravascular fibrinolysis. We showed recently that local administrations both of methacholine (MCH) and of desmopressin (1-desamino-8-D-arginine vasopressin, DDAVP) induced a massive local release of t-PA in the human forearm vasculature.

OBJECTIVE

To determine whether the human vascular endothelium could respond to repeated stimulation with the same agonist, and, if so, to further evaluate the releasable endothelial pool of t-PA.

METHOD

Seven young, healthy men participated. MCH and DDAVP were administered as local infusions into the brachial artery. In protocol 1 (n = 3) 2 microg/min MCH was infused for 2 (30 min with a free interval of 20 min). In protocol 2 (n = 4) 70 ng/min DDAVP was infused for 2 (20 min with an interval of 75 min). Dosages and time intervals were based on the different release profiles of the two drugs observed in previous studies. Brachial arterial and venous blood samples were obtained at baseline and throughout infusions. Net release of t-PA was calculated as the product of the arteriovenous concentration gradient and forearm plasma flow.

RESULTS

Forearm blood flow was increased 3-4-fold by MCH and 2-3-fold by DDAVP infusions. During the first and second infusions of MCH, the average amounts of t-PA released were 1600 and 1000 ng/l forearm tissue, respectively. In contrast, DDAVP induced similar t-PA responses during both infusions; the average total releases of t-PA were 2300 and 2400 ng/l tissue, respectively.

CONCLUSION

The results show that the vascular endothelium is responsive to repeated stimulation both with MCH and with DDAVP. The diminished t-PA response to the second MCH infusion can not be explained in terms of depletion of intracellular pools, in view of the large amount of t-PA released by a single infusion of DDAVP. The dynamic pool of t-PA available for release is very large, but further studies are required in order to quantify the releasable endothelial stores.

Evidence against an effect of endothelin-1 on blood coagulation, fibrinolysis, and endothelial cell integrity in healthy men

On the basis of an array of preclinical experimental results, it has been widely assumed that endothelin-1 (ET-1) may affect blood coagulation, fibrinolysis, and endothelial cell function, thereby playing a pathophysiological role in various cardiovascular diseases in humans. However, confirmation of this assumption is still lacking. ET-1 or placebo was administered intravenously to 12 healthy volunteers in a prospective, randomized, double-blind, crossover trial. Pathophysiologically relevant concentrations of ET-1 (an approximate threefold increase of normal blood levels) causing hemodynamic effects were reached by continuous intravenous infusion for 6 hours. Components of the coagulation (thrombin-antithrombin complexes, prothrombin fragment F1 + 2, activated factor VII, and factor VII antigen) and fibrinolytic (fibrin split product D-dimer, plasmin-plasmin inhibitor complex, tissue-type plasminogen activator, urokinase-type plasminogen activator, and plasminogen activator inhibitor-1) systems and markers of endothelial cell perturbation/dysfunction (von Willebrand factor and thrombomodulin) were measured before the start of infusion and after 2, 6, 12, and 24 hours. Comparing changes in the plasma concentrations of these parameters during and after infusion of ET-1 and placebo, we found no specific effects of ET-1. In contrast to previous reports from preclinical experiments, ET-1 does not appear to affect coagulation or fibrinolysis, nor does this peptide induce relevant endothelial cell perturbations in humans.

Involvement of calcium and G proteins in the acute release of tissue-type plasminogen activator and von Willebrand factor from cultured human endothelial cells

In this study, we investigated the role of Ca2+ and G proteins in thrombin-induced acute release (regulated secretion) of tissue-type plasminogen activator (TPA) and von Willebrand factor (vWF), using a previously described system of primary human umbilical vein endothelial cells (HUVECs). The acute release of TPA and vWF, as induced by alpha-thrombin, was almost zero after chelation of Ca2+i, showing that an increase in [Ca2+]i was required. It did not matter whether the increase in [Ca2+]i came from an intracellular or extracellular Ca2+ source. Thrombin-induced release of TPA and vWF already started at low [Ca2+]i, around 100 nmol/L. Half-maximal release was found at a [Ca2+]i, of 261 nmol/L for TPA and at 222 nmol/L for vWF. The Ca2+ signal was transduced to calmodulin, as calmodulin inhibitors inhibited TPA and vWF release. The Ca2+ ionophore ionomycin dose dependently released vWF; half-maximal vWF release occurred at a [Ca2+]i of 311 nmol/L. In contrast, no TPA release was found at all below a [Ca2+]i of 500 nmol/L. Thus, below 500 nmol/L [Ca2+]i, an increase in [Ca2+]i alone was sufficient to induce vWF release but not sufficient to induce TPA release. Protein kinase C did not appear to be involved in TPA or vWF release, as neither an activator nor an inhibitor of protein kinase C significantly influenced release. Inhibition of phospholipase A2 also did not reduce thrombin-induced TPA and vWF release. The involvement of G proteins was studied by using both saponin-permeabilized and intact cells. GDP-beta-S, which inhibits heterotrimeric and small G proteins, significantly inhibited thrombin-induced vWF and TPA release from permeabilized cells. AlF-4, which activates heterotrimeric G proteins, induced TPA and vWF release in both intact and permeabilized HUVECs. Preincubation of HUVECs with pertussis toxin significantly inhibited thrombin-induced vWF release, due to inhibition of thrombin-induced Ca2+ influx. Pertussis toxin did not affect ionomycin-induced release. The inhibitory effect of pertussis toxin was less obvious in thrombin-induced TPA release, because it was counterbalanced by a positive effect of the toxin on TPA release. Thus, both inhibitory and stimulatory (pertussis toxin-sensitive) G proteins were involved in TPA release. Therefore, thrombin-induced acute release of TPA and vWF differed in two respects. First, below a [Ca2+]i of 500 nmol/L, an increase in Ca2+ was sufficient for vWF release but not for TPA release. Second, pertussis toxin-sensitive G proteins were differentially involved in acute TPA and vWF release.

Stimulation or endothelin-1 secretion by human breast cancer cells through protein kinase A activation: a possible novel paracrine loop involving breast fibroblast-derived prostaglandin E2

Breast cancer cells secrete endothelin-1 (ET-1), which may act as a paracrine mitogen in breast tumours. The paracrine factors and signal transduction pathways responsible for regulating ET-1 production in breast cancer are unknown. In this study we have examined the involvement of the protein kinase A (PKA) signalling pathway in the control of ET-1 secretion in the human breast cancer cell line MCF-7. Treatment of MCF-7 cells with various agents that activate protein kinase A (PKA) through increases in intracellular cAMP levels including forskolin, cholera toxin (ChT), the cAMP analogue 8-Br-cAMP, or the cAMP phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthine (IBMX) all markedly increased ET-1 release. Prostaglandin E2 (PGE2) while stimulating cAMP production, but not inositol lipid hydrolysis also significantly stimulated ET-1 release. Activation of PKC by 2-O-tetradecanoyl phorbol 13-acetate (TPA) also stimulated ET-1 secretion in MCF-7 cells. The PKA inhibitor H-89 attenuated the ET-1 response to PGE2, forskolin and ChT, but not that due to the PKC agonist TPA. The possibility that human breast fibroblasts (HBFs) are a target for ET-1 action with regard to PGE2 production was also investigated, and revealed that while HBFs were unresponsive to ET-1 alone, pretreatment with the cytokine IL-beta greatly potentiated PGE2 release in response to ET-1. In conclusion our results show that activation of either the PKA or PKC signalling pathways in human breast cancer cells increases ET-1 secretion. We also found that HBFs release PGE2 after treatment with ET-1 and that PGE2 itself stimulates ET-1 production in MCF-7 cells. The implication of this potential novel paracrine loop may be significant in view of the high levels of PGE2 and ET-1 found in malignant breast tissues.

The control of production and release of haemostatic factors in the endothelial cell

Endothelial cell products contribute to many aspects of the regulation of haemostasis. They include potent inhibitors of platelet aggregation (prostacyclin and nitric oxide) rapidly released in response to agonists such as thrombin. Similar agonists also induce the formation of platelet-activating factor by endothelium. Endothelial cell surface ectonucleotidase enzymes control the catabolism of platelet-active adenine nucleotides. The main source of the circulating coagulant cofactor von Willebrand factor is the endothelium, where it is stored in granules for agonist-triggered exocytosis and also secreted constitutively. Surface anticoagulant activities are due to the presence of antithrombin and thrombomodulin. Endothelial cells also secrete plasminogen activator and its inhibitor. Many of these reactions are significantly modulated by exposure of endothelium to cytokines or bacterial endotoxin, the most striking example being the new synthesis and surface expression of the procoagulant tissue factor (thromboplastin).

Two preproendothelin 1 mRNAs transcribed by alternative promoters

Endothelin-1, initially identified as potent vasoconstrictor secreted by vascular endothelial cells, was subsequently found to have many effects on both vascular and nonvascular tissues. We have identified from a human placenta cDNA library a clone (cDNA-2) which corresponds to a novel 5'-extended preproendothelin 1 (preproET-1) mRNA. Comparison with the known preproET-1 mRNA (cDNA-1), showed that the two molecules share the same coding sequence but differ in the 5'-untranslated region. Interestingly, cDNA-2 extends upstream of promoter regions previously shown to be essential for full preproET-1 expression. Primer extension and PCR analysis of human placenta RNA demonstrated the presence of additional transcription initiation sites located upstream of the previously identified preproET-1 CAP site. Moreover, the two mRNAs show different pattern of expression. To elucidate the mechanisms controlling the production of alternative transcripts we transfected COS-1 cells with a series of preproET-1 promoter deletion mutants. This analysis revealed that the human preproET-1 gene can be transcribed from a proximal and a distal promoter element which has hitherto been undetected. In addition, we demonstrate the presence of a region in the down-epithelial specific expression.

Vasocontractions of the in-vitro toad aortas induced by endothelin-1 and sarafotoxin-S6b

Dose-dependent tension curves were recorded from the in vitro toad aortas by administration of endothelin-1 and sarafotoxin-S6b. The maximal contractile tensions by both drugs were evoked at a 10(-8) M concentration. By a single dose application (10(-8) M) of endothelin-1 and sarafotoxin-S6b to both endothelium-preserved and denuded vessels, the induction of the endothelium-dependent vasocontraction occurs after 2 min of administration. Ultrastructural changes of Weibel-Palade bodies such as decrease in electron density, swelling with a wide peripheral halo, and expulsion of their contents in a manner of exocytosis become evident within 2 min after administration of these drugs. These findings indicate that some vasocontractile substances in Weibel-Palade bodies are extracellularly discharged by endothelin-1 and sarafotoxin-S6b.

Type IIB von Willebrand's disease: gene mutations and clinical presentation in nine families from Denmark, Germany and Sweden

Type IIB of von Willebrand's disease (vWD) is a variant in which the structurally abnormal von Willebrand factor (vWF) shows an increased affinity for the platelet vWF receptor, glycoprotein Ib (GPIb). This may sometimes give rise to platelet aggregation and thrombocytopenia in vivo. In 20 patients from nine unrelated families with type IIB vWD from Denmark, Germany and Sweden we studied the molecular defect by amplification and direct sequencing of parts of exon 28 which encode for the vWF domain that interacts with platelet GPIb. Three different point mutations were identified one of which has not previously been reported. Fifteen patients from five families were heterozygous for the Arg543-->Trp substitution. The mutation had occurred independently in all five families and in two of them represented a de novo mutation. In one of these families the father, though asymptomatic and with normal laboratory test results, carried the mutation in heterozygous form. In three families, four affected members were found to be heterozygous for the Arg543-->Cys substitution. The mutations were of different origin at least in two of the families. The third substitution, Val551-->Leu, which has not previously been described, was found in one patient and was due to a de novo mutation. In most of the patients spontaneous thrombocytopenia had been recorded on at least one occasion. Five of the patients with the Arg543-->Trp substitution and the one with the Val555-->Leu substitution had all had bleeding associated with thrombocytopenia in the neonatal period of early infancy.

Role of platelet activating factor on the fibrinolytic activation in the pathogenesis of gastric mucosal damage induced by endothelin-1

We have examined the hypothesis that the release of tissue type plasminogen activator may play a prominent role in endothelin induced gastric mucosal injury. We determined tissue type plasminogen activator activity in the regional blood sample and the concentration of platelet activating factor in the gastric mucosa after the administration of endothelin-1 in a range of 50-500 pmol/kg into the left gastric artery of male Wistar rats. Endothelin-1 increased the tissue type plasminogen activator release and platelet activating factor formation, and induced subsequent gastric mucosal haemorrhagic change in a dose dependent manner. In addition CV-6209, a selective platelet activating factor blocker, attenuated the activation of regional tissue type plasminogen activator and the development of mucosal damage induced by endothelin-1. The results of this study showed that tissue type plasminogen activator activation may play an important role in the pathogenesis of endothelin induced mucosal injury of rat stomach, and suggest that the platelet activating factor may be involved in the process of regional fibrinolytic activation induced by endothelin-1.

The involvement of products of the phospholipase pathway in the acute release of tissue-type plasminogen activator from perfused rat hindlegs

Using a perfused rat hindleg system, release of tissue-type plasminogen activator (t-PA) from endothelial cells could be induced by platelet-activating factor (PAF), bradykinin, substance P, thrombin, carbachol and A23187, while this release was inhibited by mepacrine and by nor-dihydroguaiaretic acid. The PAF-induced release of t-PA was inhibited by the cytochrome P-450 mono-oxygenase inhibitors, metyrapone, ketoconazole and SKF 525A and by eicosatetraynoic acid but not by indomethacin or BW 755C, suggesting the involvement of epoxygenase products. The PAF-induced release of von Willebrand factor (vWF) was also similarly inhibited by the cytochrome P-450 monooxygenase inhibitor, ketoconazole. Phorbol ester and phospholipase C induced the release of both t-PA and vWF, while phospholipase A2 did not. The release induced by PAF and bradykinin was not influenced by pretreatment with pertussis toxin.