The control of endothelin-1 secretion

Role of Endothelin 1 on Proliferation and Migration of Human MCF-7 Cells

Objective

The aim of this study was to explore the role of endothelin 1 (ET-1) in human breast cancer proliferation and migration and antagonism of endothelin receptor A (ETAR) and endothelin receptor B (ETBR) by using the non-selective dual ETA/ETB receptor antagonist bosentan and determine its anti-proliferative, anti-metastatic, and apoptotic effects demonstrated by nuclear factor kappa B (NF-kB), vascular endothelial growth factor (VEGF), Caspase 3 and Caspase 9 expression on endothelin-induced proliferation of MCF-7 cell line in vitro.

Materials and Methods

A total of 8,000 cells were seeded into e-plates 24 hours after the cells were incubated with or without 10-4 M BOS (1 hour before ET-1 treatment); 10-7, 10-8, and 10-9 M ET-1 for 1-4 days.

Results

Whether ET-1 is present or not in the tumor area, bosentan exerts anti-proliferative effect on breast cancer. However, ET-1 and bosentan group showed important inhibitory effect on tumor migration compared to bosentan alone, which can be attributed to increased activity of ET-1 axis in the presence of ET-1. The imbalance among the NF-kB, caspases, and VEGF, which are predictive factors of carcinogenesis significantly improved after bosentan administration.

Conclusion

Our study definitely demonstrated ET-1 and its critical role in cancer progression with apoptotic and anti-apoptotic pathways (NF-κB) and VEGF expression, and migration analyses were also performed. The second major finding was that bosentan inhibited ET-1-mediated effects on tumor proliferation and migration.

Expression patterns of endothelin-1 and its receptors in colorectal cancer

BACKGROUND AND OBJECTIVES

Endothelin-1 (ET-1), a potent vasoconstricting peptide, plays an important role in carcinogenesis. Previous in vitro studies have shown that colorectal cancer cells produce ET-1.

METHODS

ET-1 and its receptors ET-A (ET(A) R) and ET-B (ET(B) R) were analyzed in colorectal cancer cell lines and tumors by Western blot and immunohistochemistry. Also, ET-1 levels were measured by ELISA in blood samples collected before and after tumor resection.

RESULTS

ET-1 was immunohistochemically expressed by tumor cells at a variable level in 39 cases tested. The adjacent normal mucosa was negative for ET-1 expression. Strong ET(A) R expression observed in the deeper infiltrating areas at the periphery of neoplastic tissue correlated significantly with tumor stage. ET(B) R levels were very low or undetectable. Western blot analysis in paired (normal, tumor) fresh-frozen samples of colorectal cancers and in four colon carcinoma cell lines confirmed these findings. In addition, lower levels of ET-1 in the peripheral circulation after the tumor resection were found by ELISA as compared to those observed before surgery.

CONCLUSIONS

ET-1 and ET(A) R, but not ET(B) R, are expressed at a higher level in primary and cultured colon carcinoma cells as compared to normal colon mucosa cells. Further functional studies are needed to explore the role of ET-1/ET(A) R axis in colon carcinogenesis.

Thrombin-induced endothelin-1 synthesis and secretion in retinal pigment epithelial cells is rho kinase dependent

PURPOSE

The retinal pigment epithelium (RPE) is a major source for endothelin-1 (ET-1), a potent vasoactive peptide, at the outer blood–retinal barrier. Factors that regulate ET-1 synthesis at this site may help identify its normal function and its role in pathologic states accompanying retinal injury. Thrombin is one such factor that might act on the RPE after injury and breakdown of the blood–retinal barrier. The present study was conducted to identify signaling intermediates in thrombin-induced ET-1 synthesis and secretion in primary human RPE (hRPE) and transformed RPE cells (ARPE-19) and a possible pharmacological strategy to block excess release of ET-1.

METHODS

Cultured hRPE cells were treated with different concentrations of thrombin and thrombin receptor agonists, and a time course to measure levels of preproET-1 (ppET-1) mRNA and secreted mature ET-1 was performed. Levels of secondary messengers [Ca²+]i and RhoA were measured and pharmacologically inhibited to determine how receptor-mediated thrombin activity lead to changes in ET-1 levels.

RESULTS

Thrombin primarily acts via the protease-activated receptor-1 (PAR-1) subtype in RPE to induce ET-1 synthesis. Thrombin and other receptor agonists increased both [Ca²+]<]i and active RhoA. PAR-1-dependent rho/Rho kinase activation led to increase in ppET-1 mRNA and mature ET-1 secretion.

CONCLUSIONS

Transient intracellular calcium mobilization and protein kinase C activation by thrombin play a minor role, if any, in ET-1 synthesis in RPE. Instead, rho/Rho kinase activation after PAR-1 stimulation strongly increased ppET-1 mRNA and ET-1 secretion in hRPE cells.

Identification of two nuclear factor of activated T-cells (NFAT)-response elements in the 5'-upstream regulatory region of the ET-1 promoter

Collecting duct-derived ET-1 regulates salt excretion and blood pressure. We have reported the presence of an inner medullary collecting duct (IMCD)-specific enhancer region in the 5'-upstream ET-1 promoter (Strait, K. A., Stricklett, P. K., Kohan, J. L., Miller, M. B., and Kohan, D. E. (2007) Am. J. Physiol. Renal Physiol. 293, F601-F606). The current studies provide further characterization of the ET-1 5'-upstream distal promoter to identify the IMCD-specific enhancer elements. Deletion studies identified two regions of the 5'-upstream ET-1 promoter, -1725 to -1319 bp and -1319 to -1026 bp, which were required for maximal promoter activity in transfected rat IMCD cells. Transcription factor binding site analysis of these regions identified two consensus nuclear factor of activated T-cells (NFAT) binding sites at -1263 and -1563. EMSA analysis using nuclear extracts from IMCD cells showed that both the -1263 and the -1563 NFAT sites in the ET-1 distal promoter competed for NFAT binding to previously identified NFAT sites in the IL-2 and TNF genes. Gel supershift analysis showed that each of the NFAT binding sites in the ET-1 promoter bound NFAT proteins derived from IMCD nuclear extracts, but they selectively bound different NFAT isoforms; ET-1263 bound NFATc1, whereas ET-1563 bound NFATc3. Site-directed mutagenesis of either the ET-1263 or the ET-1563 sites prevented NFAT binding and reduced ET-1 promoter activity. Thus, NFAT appears to be an important regulator of ET-1 transcription in IMCD cells, and thus, it may play a role in controlling blood pressure through ET-1 regulation of renal salt excretion.

Endothelin role in kidney acidification

Endothelin is a potent vasoconstrictor that recent studies show modulates transport in kidney tubules, including that related to acidification. The data support a physiologic role for endothelin in mediating enhanced kidney tubule acidification in response to an acid challenge to systemic acid-base balance status. The data to date do not support an endothelin role in maintaining kidney tubule acidification in control, nonacid-challenged states. Endothelin also contributes to the enhanced acidification of some pathophysiologic states and might have a role in some of the untoward outcomes associated with these conditions. This reviews supports continuation of studies into the physiologic and possibly pathophysiologic role of endothelin in settings of increased tubule acidification.

HLA-B35 upregulates the production of endothelin-1 in HLA-transfected cells: a possible pathogenetic role in pulmonary hypertension

HLA-B35 is associated with an increased risk for developing isolated pulmonary hypertension (iPHT) in systemic sclerosis, but the mechanisms underlying this association have not been fully elucidated yet. Endothelin-1 (ET-1) is the main pathogenetic molecule implied in the development of iPHT; therefore, we sought to determine if ECV304 cells transfected with the HLA-B35 allele produce increased amounts of ET-1 after incubation with physiological concentrations of interleukin-1 beta (IL-1beta). ECV304 cells transfected with HLA-B*3501 and HLA-B*0801 polymorphic alpha chain or with pIRESneo2 were incubated with 100 U/ml of IL-1beta for 6, 12, 24, 36 and 48 h. ET-1 levels were determined using EIA kit (CAYMAN Chemical, Ann Arbor, MI) in supernatants from different cell cultures; the relative expression of the preproendothelin-1 (PPET-1) gene was also determined by reverse transcription-polymerase chain reaction. Cells expressing the HLA-B35 allele showed significantly increased levels of ET-1 at all the selected times compared with controls or HLA-B8-transfected cells. The relative expression of the PPET-1 gene was also increased in a proportionally direct manner. The HLA-B35 allele influences the production of ET-1 in HLA-B35-transfected ECV304 cells by promoting the expression of its precursor, PPET-1. Our results provide an explanation for the epidemiological association existing between iPHT and HLA-B35.

Peripheral endothelin A receptor antagonism attenuates carcinoma-induced pain

In this study we investigated the role of endothelin-1 (ET-1) and its peripheral receptor (ET-A) in carcinoma-induced pain in a mouse cancer pain model. Tumors were induced in the hind paw of female mice by local injection of cells derived from a human oral squamous cell carcinoma (SCC). Significant pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, began at four days after SCC inoculation and lasted to 28 days, the last day of measurement. Intra-tumor expression of both ET-1 mRNA and ET-1 protein were significantly upregulated compared to normal tissue, and local administration of the ET-A receptor selective antagonist, BQ-123 (100 microM) significantly elevated withdrawal thresholds, indicating the induction of an antinociceptive effect. These findings support the suggestion that ET-1 and ET-A receptors contribute to the severity of carcinoma-induced soft tissue cancer pain.

Elevated salivary endothelin levels in oral cancer patients--a pilot study

The analysis of saliva has been proposed as a potentially rapid, non-invasive method to monitor and diagnose patients with oral disease. In this study we measured salivary endothelin-1 (ET-1) levels in patients diagnosed with oral squamous cell carcinoma (SCC) prior to treatment. We demonstrate significantly elevated salivary ET-1 levels in the oral SCC group (4.37+/-1.35pg/ml), relative to the control group (1.16+/-0.29pg/ml). ET-1 and ET-1 mRNA were also measured in oral SCC tissue specimens and compared to normal oral epithelial controls. The concentration of ET-1 in the oral SCC specimens was 17.87+/-4.0pg/ml and in the normal epithelial controls the concentration of ET-1 was 5.43+/-2.5pg/ml. ET-1 mRNA was significantly overexpressed in 80% (8/10) of the oral SCC specimens. Our results demonstrate the potential utility of salivary analysis for ET-1 levels to monitor patients at risk for oral SCC.

Selective Suppression of an Endothelin and Platelet-Derived Growth Factor Containing Vesicular System in Endothelium of Rat Saphenous Vein by Long-Term Orthostasis

Electron-dense vesicles were observed in rat vascular endothelium. The purpose of this study was to characterize their content(s), venous-arterial distribution and response to chronic orthostatic stress in extremity vessels. Saphenous and brachial vessels - saphenous vein (SV), saphenous artery (SA), brachial vein, brachial artery - were prepared for electron microscopy to quantitate the vesicle area within the endothelium following immunohistochemical and immunocytochemical identification. The effect of long-term orthostasis was assessed by exposure to head-up tilt for 2 weeks. The vesicular area in relation to the total cross-sectional area of the endothelial cells in the SV and SA of normal and confined control groups was 3.88 +/- 0.38 versus 0.89 +/- 0.06% (p < 0.05) and 4.92 +/- 0.25 versus 1.09 +/- 0.47% (p < 0.05), respectively. Head-up tilt suppressed the vesicle content of the SV to 2.26 +/- 0.39% (p < 0.05), but it remained low in the SA (1.29 +/- 0.45%), brachial vein (0.45 +/- 0.12%) and brachial artery (0.59 +/- 0.17%). Endothelin and platelet-derived growth factor, but not acidic phosphatase activity or lipid content, could be identified in the vesicles. Plasma endothelin levels were unchanged. We conclude that dense vesicles in the endothelium of extremity vessels are not cell degradation products. They may represent a vesicular secretory or storage system for endothelin and platelet-derived growth factor which participates in regional vascular adaptation to long-term orthostatic load.

Endothelin-1 is secreted after total knee arthroplasty regardless of the use of a tourniquet

Early infections and wound healing disorders after implantation of a total knee replacement occur regardless of the intraoperative use of a tourniquet. The biochemical regulatory processes responsible for the disturbances in microcirculation and thus the potential therapeutic options have yet to be elucidated. The hypothesis of the present paper was that endothelin-1 (ET-1), a mediator of microcirculation disturbances in parenchymatous organs, also is released after major operations on peripheral joints. The concentration of ET-1 in the plasma was determined preoperatively and at 10 postoperative time points (5 min-48 h) with (group A, n=10) and without the use of a tourniquet (group B, n=10). The ET-1 concentration achieved its maximum 6h after opening the tourniquet, which corresponded to 3.3 times the preoperative value. Without a tourniquet, the concentration maximum (2.9 times the baseline value) was achieved already 1.5 h after the end of the operation. However, the total amount of ET-1 secreted over 24 h was identical in both groups (p>0.5). We conclude that the tissue hypoxia resulting from the use of a tourniquet modulates ET-1 secretion, but that traumatization during the operation has a much stronger influence on the total amount secreted. ET-1 antagonists thus should be discussed for the drug prophylaxis of wound healing disorders, regardless of the use of a tourniquet.

Mechanosensation and endothelin in astrocytes--hypothetical roles in CNS pathophysiology

Endothelin (ET) is a potent autocrine mitogen produced by reactive and neoplastic astrocytes. ET has been implicated in the induction of astrocyte proliferation and other transformations engendered by brain pathology, and in promoting the malignant behavior of astrocytomas. Reactive astrocytes containing ET are found in the periphery/penumbra of a wide array of CNS pathologies. Virtually all brain pathology deforms the surrounding parenchyma, either by direct mass effect or edema. Mechanical stress is a well established stimulus for ET production and release by other cell types, but has not been well studied in the brain. However, numerous studies have illustrated that astrocytes can sense mechanical stress and translate it into chemical messages. Furthermore, the ubiquitous reticular meshwork formed by interconnected astrocytes provides an ideal morphology for sensing and responding to mechanical disturbances. We have recently demonstrated stretch-induced ET production by astrocytes in vitro. Inspired by this finding, the purpose of this article is to review the literature on (1) astrocyte mechanosensation, and (2) the endothelin system in astrocytes, and to consider the hypothesis that mechanical induction of the ET system may influence astrocyte functioning in CNS pathophysiology. We conclude by discussing evidence supporting future investigations to determine whether specific inhibition of stretch-activated ion channels may represent a novel strategy for treating or preventing CNS disturbances, as well as the relevance to astrocyte-derived tumors.

Endothelin-1 distribution and basolateral secretion in the retinal pigment epithelium

Endothelins are a family of conserved vasoactive peptides that are widely expressed in different biological systems including the eye. In the cell culture model of retinal pigment epithelium, ARPE-19, the synthesis and secretion of endothelin-1 (ET-1) is regulated by cholinergics and TNF-alpha. In the present study we investigated the expression of ET-1 in RPE in situ, in rat and human eyes. Additionally, we have employed the human retinal pigment epithelial (ARPE-19) cells to delineate the apical and basolateral ET-1 expression and secretion by confocal microscopy and radioimmunoassay, respectively. Our results suggest a possible conservation of ET-1 expression predominantly in the mammalian RPE underlining its importance at this site. Additionally, our results suggest that constitutive ET-1 secretion is predominantly towards the basolateral side in cultured RPE possibly allowing ET-1 to activate its receptors located in the choroidal blood vessels and regulate retinal and choroidal blood flow.

Attenuation of renal vasopressin V2 receptor upregulation by bosentan, an ETA/ETB receptor antagonist

Circulating endothelin (ET) levels are elevated in heart failure and positively correlated with severity of heart failure. Recent studies demonstrated arginine vasopressin (AVP) V2 mRNA expression was upregulated in the inner medullary collecting duct (IMCD) of cardiomyopathic hamsters (CM). The goal of the present studies was to determine if ET-1 is involved in upregulating the expression of AVP V2 mRNA in the IMCD of CM by using a mixed ETA/ETB receptor antagonist bosentan. Our results showed plasma ET-1 levels increased in CM hamsters and related with the severity of heart failure. The competitive reverse-transcriptase polymerase chain reaction (RT-PCR) method was used to quantify the expression of AVP V2 and aquaporin 2 (AQP2) mRNA in the IMCD. AVP V2 mRNA expression was elevated in placebo-treated CM hamsters and decreased significantly with 14 days of bosentan treatment. Similar results were seen with AQP2 mRNA. The effect of bosentan in normalizing the expression of AVP V2 and AQP2 mRNA in the IMCD of CM was confirmed by in situ hybridization studies. Bosentan treatments reduced the intensitites of the signals in the IMCD of CM hamsters to that seen in normal hamsters. This study demonstrated that AVP V2 and AQP2 mRNA are upregulated in CM hamsters and these upregulations are attenuated by bosentan treatment, suggesting that ET-1 plays a role in upregulating the expression of AVP V2 mRNA in CM hamsters.

Vasopressin induces vascular superoxide via endothelin-1 in mineralocorticoid hypertension

We have recently reported that endothelin-1 (ET-1), which is increased in the arteries of deoxycorticosterone acetate (DOCA)-salt hypertensive rats, stimulates superoxide production. However, the humoral mechanisms responsible for ET-1-induced superoxide formation in low-renin models of hypertension, such as DOCA-salt hypertension, remain undefined. Vasopressin is known to upregulate vascular preproET-1 gene expression in DOCA-salt rats, an effect that is absent in vasopressin-deficient Brattleboro rats treated with DOCA-salt. The present study tested the hypothesis that vasopressin contributes to ET-1-induced vascular superoxide production in DOCA-salt hypertensive rats. Carotid arterial segments of DOCA, sham (uninephrectomized), or normal (untreated) rats were used for the study. In vitro vasopressin treatment of carotid arteries from normal rats for 24 hours, but not 4 hours, increased both ET-1 and superoxide levels. The increase of vasopressin-induced superoxide was reduced by pretreatment of the vessels with ABT627, a selective ETA receptor antagonist ABT627. Vasopressin, ET-1, and superoxide levels were significant elevated in carotid arteries of DOCA-salt rats compared with sham controls. The selective V1-vasopressin receptor antagonist (beta-Mercapto-beta, beta-cyclopentamethylenepropiony1, O-Me-Tyr2, Arg8 vasopressin, ME-AVP), decreased superoxide both in vasopressin-treated vessels of normal rats and in vessels of DOCA-salt rats, with a concomitant reduction of ET-1 content. These results suggest that vasopressin increases vascular superoxide levels by stimulating ET-1 formation in mineralocorticoid hypertension, and that V1-vasopressin receptors play an important role in this process.

Co-localisation of nitric oxide synthase and endothelin in the rat supraoptic nucleus

The co-localisation of neuronal nitric oxide synthase and endothelin-1 was studied in the rat supraoptic nucleus at the electron microscopy level. Double pre-embedding immunocytochemistry was performed using ExtrAvidin-horseradish peroxidase and immunogold-silver techniques. Immunoreactivities to neuronal nitric oxide synthase and endothelin-1 were co-localised in sub-populations of endocrine neurones (cell bodies) and dendrites. Double-labelled axon terminals making asymmetrical synapses on unlabelled dendrites were also observed. The findings are discussed in terms of the possible role and significance of nitric oxide and endothlin-1 in the hypothalamo-neurohypophysial system.

Biology of kidney cells: ontogeny-recapitulating phylogeny

Biology of kidney cells can be used as a model for further understanding of ontogeny-recapitulating phylogeny. The common and species-specific structural and functional relationship between blood capillaries and the environment via a filtration barrier of nephrons is a biological phenomenon resulting from renal cell memory acquired through evolution. Genetically programmed development, a subsequent series of gene expression, and inductive interactions played a key role in differentiation and maintenance of specific activities of kidneys in birds and mammals. Various environmental factors may alter kidney development and specific activities at the levels of gene expression, repression, or derepression, and defensive mechanisms involved in reaction to risk factors are developed. Autoimmunity and cancerogenesis are closely dependent on a variety of environmental agents, such as antigens originating from infections with some viruses and toxins, or irradiation, advanced industrialization, and progress of civilization. As a result of gene mutation, delation, rearrangement, and/or susceptibility to different agents, renal cell memory is altered. Instead of cell-specific activities, the abilities for regeneration, and other genetically programmed activities, the genesis of kidney diseases are common. Balkan endemic nephropathy, as regional disease, is an important example of the role, of environmental agents, at the level of genes. Research programs on molecular genetics will contribute to our efforts both to prevent infections and to elucidate the genesis, diagnosis, prognosis, prevention, and therapy of kidney diseases.

Cigarette smoke extract induces endothelin-1 via protein kinase C in pulmonary artery endothelial cells

We examined the mechanism of endothelin (ET)-1 regulation by cigarette smoke extract (CSE) and the effect of platelets on CSE-induced stimulation of ET-1 gene expression in human and bovine pulmonary artery endothelial cells (PAECs). Our data show that CSE (1%) induces ET-1 gene expression (after 1 h) and ET-1 peptide synthesis (after 4 h) in bovine PAECs. The induction of preproET-1 mRNA level was due to de novo transcription, and new protein synthesis was not required for this induction. The protein kinase C inhibitors staurosporine (10(-8) mol/l) and calphostin C (10(-7) mol/l) abolished the induction of ET-1 gene expression by CSE in bovine and human PAECs. Although a lower concentration of platelets (10(6) cells/ml in bovine PAECs; 10(7) cells/ml in human PAECs) did not significantly alter ET-1 gene expression in PAECs, incubation of platelets with CSE (1%) and PAECs produced a significant increase in preproET-1 mRNA and ET-1 peptide compared with the values in the presence of CSE (1%) alone. CSE (1%) induced platelet aggregation and increased the expression of platelet membrane glycoproteins ex vivo. Thus our data suggest that CSE stimulates ET-1 gene expression via PKC in PAECs. CSE and platelets showed a synergistic effect on ET-1 gene expression, possibly through the activation of platelets by CSE.

Adrenomedullin increases fluid extravasation from the splenic circulation of the rat

1. We studied the effect of adrenomedullin (ADM) on fluid efflux from the splenic vasculature into extravascular spaces. 2. Splenic arterial infusion of ADM (1, 3 and 9 ng min(-1); n = 9, 11 and 10, respectively) caused a dose-dependent increase in intrasplenic fluid efflux (+0.6 +/- 0.3 (saline) vs. +2.0 +/- 0.3 ml min(-1) (9 ng min(-1) ADM), P < 0.05), and in splenic (venous minus arterial) haematocrit (+0.8 +/- 0.1 (saline, n = 6) vs. +3.1 +/- 0.3 % (9 ng min(-1) ADM, n = 7), P < 0.05). There was no change in splenic weight (0.99 +/- 0.02 (saline, n = 6) vs. 0.99 +/- 0.02 g (9 ng min(-1) ADM, n = 7), P > 0.05). 3. There was no change in MAP before (97.5 +/- 2.2 mmHg), during (98.4 +/- 3.4 mmHg), or after (100.2 +/- 2.2 mmHg) intrasplenic infusion of ADM (9 ng min(-1)) (n = 11, P < 0.05). 4. ADM (9 ng min(-1)) caused an increase in intrasplenic microvascular pressure (11.3 +/- 0.3 (saline, n = 5) vs. 13.0 +/- 0.3 mmHg (9 ng min(-1) ADM, n = 6), P < 0.05). 5. ADM (1 x 10(-11) to 1 x 10(-6) M) induced greater vasorelaxation of isolated preconstricted splenic resistance arteries than veins (maximal relaxation: 60 +/- 0.9 (artery, n = 9) vs. 43 +/- 1.7 % (vein, n = 8), P < 0.05). L-NMMA (10(-4) M) partially inhibited the ADM-induced relaxation in splenic arteries (maximal relaxation: 38 +/- 3 (ADM + L-NMMA, n = 5) vs. 60 +/- 3 % (ADM + D-NMMA, n = 5), P < 0.05). 6. It is concluded that ADM increases fluid efflux from the splenic vasculature by differentially reducing pre- vs. post-capillary resistance, thus increasing intrasplenic microvascular pressure.

Nephrotoxicants Induce Endothelin Release and Signaling in Renal Proximal Tubules: Effect on Drug Efflux

We previously used killifish proximal tubules, fluorescent substrates, and confocal microscopy to demonstrate that transport mediated by the multidrug resistance protein (Mrp2) and by P-glycoprotein was reduced by nanomolar concentrations of endothelin-1 (ET), acting through a basolateral B-type ET receptor and protein kinase C (PKC). Here we show that representatives of two classes of nephrotoxicants decrease transport by activating the endothelin-PKC signaling pathway. Exposing tubules to radiocontrast agents (iohexol, diatrizoate) or aminoglycoside antibiotics (gentamicin, amikacin) reduced Mrp2-mediated fluorescein methotrexate (FL-MTX) transport from cell to tubular lumen. Pretreating the tubules with an ET(B)-receptor antagonist or with PKC-selective inhibitors abolished these effects. The nephrotoxicants activated signaling by inducing release of ET from the tubules, because adding of an antibody against ET to the medium abolished the effects. Elevating medium Ca(2+) also reduced FL-MTX transport; this reduction was abolished when tubules were pretreated with an ET antibody, an ET(B)-receptor antagonist, PKC-selective inhibitors, or the Ca(2+) channel blocker, nifedipine. None of these drugs by themselves affected FL-MTX transport. Importantly, nifedipine also blocked the ET(B)-receptor/PKC-dependent reduction in FL-MTX transport caused by gentamicin and diatrizoate. These results for two classes of structurally unrelated nephrotoxicants suggest that Ca(2+)-dependent ET release and subsequent action through an autocrine mechanism may be an early response to tubular injury.

Transforming growth factor-beta1 induces endothelin-1 in a bovine pulmonary artery endothelial cell line and rat lungs via cAMP

We investigated the mechanism of Endothelin-1 regulation by transforming growth factor-beta1 (TGF-beta1) in bovine pulmonary artery endothelial cells (BPAECs) and in isolated perfused rat lungs. Our data show that TGF-beta1 induces ET-1 gene expression and ET-1 peptide synthesis in BPAECs. The induction of preproET-1 mRNA level was due to de novo transcription, as well as mRNA stabilization, and new protein synthesis was not required for this induction. To investigate the role of cAMP-protein kinase A pathway in TGF-beta1-stimulated-ET-1 induction, we exposed BPAECs to various compounds which modulate this pathway. Dibutyryl-cAMP led to an increase in preproET-1 mRNA and Rp-cAMP abolished the induction of preproET-1 mRNA and ET-1 peptide by TGF-beta1. TGF-beta1 increased cAMP in BPAECs. Dexamethasone up-regulated preproET-1 mRNA expression and ET-1 peptide synthesis under basal and TGF-beta1-stimulated conditions. In isolated perfused rat lungs, TGF-beta1 increased preproET-1 mRNA abundance whereas Rp-cAMP inhibited the TGF-beta1-induced ET-1 gene activation. Thus our data suggest that TGF-beta1 stimulates ET-1 gene expression in BPAECs and in rat lungs via a cAMP dependent mechanism.

Studies on the effect of diadenlyated nucleotides on calcium mobilization and prostacyclin synthesis in bovine aortic endothelial cells

Extracellular adenine dinucleotides are modulators of blood vessel tone. We have previously demonstrated that Ap(2)A and Ap(4)A induce the synthesis of nitric oxide (NO) from bovine aortic endothelial cells (BAEC) while Ap(3)A and Ap(5)A do not [FEBS Lett. 427 (1998) 320; Arch. Biochem. Biophys. 364 (1999) 280.]. In this communication we determine the effect of Ap(x)As (x=2-5) on prostacyclin (PGI(2)) synthesis and Ca(2+) mobilization in BAEC. Ap(2)A and Ap(4)A significantly enhanced the synthesis of PGI(2) while Ap(3)A and Ap(5)A do not. These data support the notion that Ap(2)A and Ap(4)A are vasodilators. All four dinucleotides significantly enhanced Ca(2+) mobilization over basal levels. Ap(5)A and Ap(3)A enhanced 2.0 and 1.6 times more Ca(2+) release than Ap(4)A, respectively. Since neither Ap(5)A nor Ap(3)A enhanced the synthesis of either PGI(2) or NO but did mobilize Ca(2+), these data support the hypothesis that in BAEC Ca(2+) release is localized or compartmentalized.

Endothelin immunoreactivity and mRNA expression in sensory and sympathetic neurones following selective denervation

The localization of endothelin (ET) in perivascular nerve varicosities supports pharmacological evidence that ET is a neurotransmitter in the autonomic nervous system. To examine the potential source of ET previously localized in cerebrovascular nerves, ganglia which send projections to these vessels were immunolabelled for ET and examined at the ultrastructural level. The trigeminal (TG) and superior cervical ganglia (SCG) were examined in control rats and following either sensory denervation or sympathectomy. In control TG, ET immunolabelling was detected throughout the cytoplasm of a subpopulation of neurones whereas in the SCG only the occasional ET-positive neurone was seen. Following sensory denervation with capsaicin, very few ET-immunoreactive nerve cell bodies or nerve fibres were detected in the TG compared with control ganglia, suggesting that ET is predominantly localized in primary afferent neurones, although some remaining myelinated nerve fibres stained positively. ET labelling of neurones in the SCG was unaffected by sensory denervation. Following selective damage to sympathetic nerves with 6-hydroxydopamine, there was a marked increase in intensity of ET-labelling of nerve fibres in the TG, probably due to increased availability of nerve growth factor for sensory nerves. There was no effect on ET immunoreactivity in the nerve cell bodies and nerve fibres within the SCG. However, in situ hybridization techniques demonstrated that 6-hydroxydopamine sympathectomy resulted in a marked increase in ET-1 mRNA expression in the SCG neurones. In conclusion, sensory nerves projecting from the TG are a more likely source of ET-positive perivascular nerves in cerebral arteries than sympathetic nerves from the SCG. Damaged sympathetic neurones markedly increase ET mRNA expression. In view of the neuroprotective properties of ET, this may represent a compensatory mechanism to promote repair.

Cell-specific differences in ET-1 system in adjacent layers of main pulmonary artery. A new source of ET-1

Endothelin-1 (ET-1) is a potent vasoconstrictor that causes sustained constriction of the pulmonary artery and modulates normal vascular tone. Endothelial cells were thought to be the major source of ET-1, but recent studies show that vascular smooth muscle cells (SMCs) are also capable of its synthesis. We examined the ET-1 and endothelin-converting enzyme-1 (ECE-1) system in cells cultured from two adjacent layers, subendothelial (L1) and inner medial (L2), of normal sheep main pulmonary artery and the response of this system to exogenous ET-1 and transforming growth factor-beta1 (TGF-beta1). End points include assessment of preproET-1 (ppET-1) and ECE-1 gene coexpression, measurement of intracellular and released ET-1, and ECE-1 activity. RT-PCR analysis revealed that ppET-1 and ECE-1 transcripts were greater in L1 than in L2 cells. The L1 cells also synthesized (L1, 3.2 +/- 0.1; L2, 1.2 +/- 0.1 fmol/10(6) cells) and released (L1, 9.2 +/- 0.5; L2, 2.3 +/-0.1 fmol/ml) greater amounts of ET-1 than L2 cells. The L2 cells internalized exogenous ET-1 in a dose-dependent manner (EC(50) 8 nmol/l) and were more responsive to exogenous ET-1 than L1 cells, showing upregulation of both the ppET-1 and ECE genes. TGF-beta1 downregulated ET-1-stimulated ppET-1 and ECE-1 transcripts but only in L2 cells. In addition, L1 cells showed greater ECE-1 activity than L2 cells, and in both, the activity was sensitive to the metalloprotease inhibitor phosphoramidon. We conclude that the ET-1 system in L1 and L2 cells is distinct. The data suggest that the two cell types have diverse functions in the arterial wall; the L1 cells, like endothelial cells, provide a local source of ET-1; and since the L2 cells are more responsive to exogenous ET-1, they are likely to affect normal pulmonary vascular tone.

Neural endothelin in hypertension: increased expression in ganglia and nerves to cerebral arteries of the spontaneously hypertensive rat

Endothelin has previously been localised in perivascular nerves of the rat basilar artery. Considering its potent vasoconstrictor and mitogenic properties on vascular smooth muscle, the potential role of a neural source of this peptide in hypertension has been investigated. The trigeminal, superior cervical and sphenopalatine ganglia of Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) at 16 weeks of age have been examined for immunolocalisation of endothelin at the light and electron microscope level. At the light microscope level, neurones immunopositive for endothelin were detected in these ganglia of the SHR but were not seen in ganglia from WKY rats. This difference was particularly marked in the trigeminal ganglia where endothelin-positive neurones colocalised with substance P immunoreactivity. Using in situ hybridisation techniques, endothelin-1 mRNA was localised to the cytoplasm of neurones in the ganglia and was more prominent in the SHR. At the electron microscope level, endothelin-immunoreactivity was localised at the peripheral perikarya of some neuronal cell bodies of the trigeminal, superior cervical and sphenopalatine ganglia of WKY rats but was more prominent with heavy labelling throughout the cytoplasm of neurones in the SHR. Notably, in the trigeminal ganglia of the SHR only, some endothelin-immunopositive nerve fibres appeared to be damaged and contained vacuoles with granular material. Ultrastructural examination of the basilar artery revealed an increased number of endothelin-positive axons in the SHR, but these axons usually showed selective damage. In summary, in the SHR, there was a marked increase in endothelin particularly in sensory neurones projecting to the basilar artery which also appear to be undergoing degenerative changes. An increased neural source of endothelin in the SHR may contribute to the development of hypertension or may be a consequence of selective degenerative change.

Cytokines induce increased endothelin ET(B) receptor-mediated contraction

The effect of cytokines on the induction of contractile endothelin ET(B) receptors during organ culture was examined. Ring segments of rat superior mesenteric artery were used fresh or incubated for 24 h in Dulbecco's modified Eagle's medium alone, or with either interleukin-1beta, tumor necrosis factor-alpha (TNF-alpha) or interleukin-2. In fresh arterial segments there was no endothelin ET(B) receptor-induced contraction. After incubation, the selective endothelin ET(B) receptor agonist sarafotoxin 6c evoked a contraction of 22 +/- 6% relative to that induced by 60 mM K+. The endothelin ET(B) receptor-induced contraction was further increased to 125 +/- 25% and 157 +/- 29% by interleukin-1beta and TNF-alpha, respectively, while interleukin-2 did not alter the endothelin ET(B) receptor-induced contraction. The identity of the contractile receptor was confirmed as the endothelin ET(B) receptor by the use of an additional specific endothelin ET(B) receptor agonist, IRL 1620, and by antagonist experiments with FR 139317 and IRL 2500. The endothelin-1-induced contraction was not altered by either of the cytokines. Reverse transcriptase-polymerase chain reaction revealed increased levels of endothelin ET(B) mRNA, relative to endothelin ET(A) mRNA following organ culture, suggesting that contractile endothelin ET(B) receptors appear via de novo transcription. None of the cytokines changed the ratio of endothelin ET(A) and endothelin ET(B) receptor mRNA, indicating that the further increased sarafotoxin 6c-induced contraction is mediated through an enhancement of intracellular signalling mechanisms.

Effect of verapamil on responses to endothelin-1 in aortic rings from streptozotocin-induced diabetic rats

In this study, we investigated the constrictor responsiveness to endothelin-1 (ET-1, 10-30 n m) of aortic rings (under 1 g resting tension in Krebs-Bicarbonate solution) from 8-weeks streptozotocin (STZ, 65 mg kg-1, i.p)-induced diabetic rats and vehicle-treated control rats. The maximum ET-1-induced contraction of the aorta in diabetic rats was increased by 150%, but the EC50 of ET-1 remained unchanged. Although in both groups, verapamil reduced the constrictor responses to ET-1 (diabetic group P<0.001, control group P<0.05), there were not any significant differences between PD2 values. These results suggest that verapamil inhibits ET-1-induced Ca2+ entry through the L-type channel and this effect did not change in diabetes mellitus.

Altered gene expression during hypoxia and reoxygenation of the heart

The heart is exposed to alterations in oxygen tension under different pathophysiological conditions. In order to maintain function, changes in the pattern of cardiac gene expression arise. Through the activity of multiple transcription factors, which include activating protein-1, hypoxia-inducible factor-1, and nuclear factor kappaB, there is up-regulation of mRNA encoding factors that enable the cardiomyocyte to adapt to the new environment. In the case of hypoxia or anoxia, there is an increased expression of growth factors, glucose transporters, enzymes associated with anaerobic glycolysis, and stress proteins. When the cardiomyocyte is reoxygenated after hypoxia, there is a rapid increase in antioxidants, pro-inflammatory cytokines, and stress proteins.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.

Endothelin in perivascular nerves. An electron-immunocytochemical study of rat basilar artery

The endothelium is recognized as a major source of endothelin in the vasculature. In this report we show for the first time that endothelin can be demonstrated with immunoelectronmicroscopy in perivascular nerves. About 36% of the axon profiles (varicosity/intervaricosity) examined in the rat basilar artery showed immunolabelling with a polyclonal antibody to endothelin-1. Endothelin-labelled axon varicosities were characterized by the presence of small spherical agranular vesicles (42 +/- 1 nm); some varicosities also contained large granular vesicles (92 +/- 5 nm) with labelled cores. Immunolabelling was mostly distributed in the axoplasm and in association with the membrane of synaptic vesicles (the lumen of the small agranular vesicles was immuno-negative). The presence of endothelin in perivascular nerves of the basilar artery suggests a neuronal as well as endothelial role in the physiological control of the vessel wall.

Thrombin Receptor Activation Inhibits Monocyte Spreading by Induction of ETB Receptor-Coupled Nitric Oxide Release

The effect of thrombin receptor activation on monocyte conformation was evaluated using the human monocyte cell line, THP-1, and the thrombin mimetic peptide, Trap-14. Treatment of THP-1 cells with Trap-14 induced rapid rounding of ameboid cells adherent to fibronectin-coated slides, whereas cell rounding was abrogated in the presence of the nitric oxide synthase inhibitor, NG-nitro-l-arginine or the endothelin B receptor antagonist, BQ-788. Endothelin-1 (ET-1) levels in the culture supernatant increased markedly within minutes of Trap-14 exposure with a concomitant loss in cellular ET-1 immunoreactivity. Importantly, loss of ET-1 immunoreactivity was blocked by pretreatment with the vesicle translocation inhibitor, nocodazole. Trap-14 potently induced the release of NO from THP-1 cells, whereas NO release was ablated by preincubation with BQ-788. These data demonstrate that thrombin receptor activation may inhibit cellular spreading as a result of autocrine ET-1 release and subsequent endothelin B receptor-dependent NO production, and suggest that initial exposure of inflammatory cells to thrombin may limit cellular activation and recruitment.

Regulation of intrarenal blood flow in experimental heart failure: role of endothelin and nitric oxide

Congestive heart failure(CHF) is associated with a marked decrease in cortical blood flow and preservation of medullary blood flow. In the present study we tested the hypothesis that changes in the endothelin (ET) and nitric oxide (NO) systems in the kidney may contribute to the altered intrarenal hemodynamics in rats with aortocaval fistula, an experimental model of CHF. Cortical and medullary blood flow were measured simultaneously by laser-Doppler flowmetry in controls and rats with compensated and decompensated CHF. As previously reported [K. Gurbanov, I. Rubinstein, A. Hoffman, Z. Abassi, O. S. Better, and J. Winaver. Am. J Physiol. 271 (Renal Fluid Electrolyte Physiol. 40): F1166-F1172, 1996], administration of ET-1 in control rats produced a sustained cortical vasoconstriction and a transient medullary vasodilatory response. In rats with decompensated CHF, cortical vasoconstriction was severely blunted, whereas ET-1-induced medullary vasodilation was significantly prolonged. This prolonged response was mimicked by IRL-1620, a specific ETB agonist, and partially abolished by NO synthase (NOS) blockade. In line with these findings, expression of ET-1, ETA and ETB receptors, and endothelial NOS (eNOS), assessed by RT-PCR, and eNOS immunoreactivity, assessed by Western blotting, was significantly higher in the medulla than in the cortex. Moreover, expression of ET-1 mRNA in the cortex and eNOS mRNA in the cortex and the medulla increased in proportion to the severity of heart failure. These findings indicate that CHF is associated with altered regulation of intrarenal blood flow, which reflects alterations in expression and activity of the ET and NO systems. It is further suggested that exaggerated NO activity in the medulla contributes to preservation of medullary blood flow in the face of cortical vasoconstriction in CHF.

Control of vascular tone by endogenous endothelin-1 in human pial arteries

BACKGROUND AND PURPOSE

Endothelin-1 (ET) has been shown to be involved in human pathological conditions, but its physiological function remains to be elucidated. The aim of this work was to assess whether endothelium-derived ET was involved in the overall responsiveness of freshly isolated human pial arteries.

METHODS

Samples of cerebral cortex, otherwise discarded, were obtained during tumor or epileptic lesion resections (n = 10 donors). Arterial segments were isolated and mounted on a microvessel myograph.

RESULTS

Inhibition of nitric oxide (NO) formation with N omega-nitro-L-arginine (L-NA, 100 micromol/L) increased basal tone by 7+/-1% Emax (n=5). This increase in tone was fully abolished in the presence of BQ123 (1 micromol/L; ET(A) receptor antagonist, P<.05) but potentiated by a subthreshold concentration of exogenous ET (1 nmol/L; 33+/-8% Emax; P<.05). In the presence of L-NA, serotonin (10 micromol/L)-induced tone was doubled compared with the control response (P<.05) but reduced by 90% in the presence of BQ123 (P<.05). In the absence of L-NA, BQ123 prevented serotonin-induced tone (n=3). Oxymetazoline, a selective alpha2-adrenergic receptor agonist, induced an endothelium-dependent relaxation of preconstricted human pial arteries. The relaxation was partially sensitive to NO synthase inhibition and fully prevented by the addition of ET, whereas substance P-induced relaxation was preserved. Glibenclamide (1 micromol/L), an inhibitor of ATP-sensitive K+ channels and tetraethylammonium (1 mmol/L), an inhibitor of Ca2+-activated K+ channels had no effect on oxymetazoline-induced relaxation.

CONCLUSIONS

The results of this study suggest first that ET is involved in the tonic response induced by NO synthase inhibition; second, part of the contractile response induced by serotonin is endothelium-dependent and sensitive to BQ123; and third, the data suggest that activation of alpha2-adrenergic receptors generated an endothelium-dependent relaxation that was selectively inhibited by exogenous ET.

Reversal of endothelin-1 release by stimulation of endothelial alpha2-adrenoceptor contributes to cerebral vasorelaxation

Agonists acting on the vascular endothelium can modulate the release of a number of factors that interact with the surrounding smooth muscle cells and influence their tone. One such factor is the vasoconstricting agent endothelin-1 (ET-1), which has been implicated in several disease states, including stroke. However, very little is known about the physiological role of ET-1 in the cerebral circulation. We demonstrate that activation of alpha2-adrenoceptors in human pial artery endothelial cells reduces both constitutive and agonist-stimulated release of immunoreactive ET-1. That this has physiological relevance is supported by our demonstration that in segments of rabbit middle cerebral arteries, alpha2-adrenoceptor activation reduces the release of endothelium-derived ET-1 and causes an endothelium-dependent relaxation. The adrenoceptor-dependent relaxation was not blocked by combined addition of indomethacin and N omega-nitro-L-arginine in 25 mmol/L KCl-depolarizing physiological solution but was selectively antagonized by a subthreshold concentration of exogenous ET-1. Our data suggest that activation of endothelial alpha2-adrenoceptor would favor a decrease in ET-1 production and possibly promote vascular relaxation.

Endothelins in the normal and diseased kidney

Endothelin-1 (ET-1) is a 21-amino acid peptide that potently modulates renal function. ET-1 is produced by, and binds to, most renal cell types. ET-1 exerts a wide range of biologic effects in the kidney, including constriction of most renal vessels, mesangial cell contraction, inhibition of sodium and water reabsorption by the nephron, enhancement of glomerular cell proliferation, and stimulation of extracellular matrix accumulation. ET-1 functions primarily as an autocrine or paracrine factor; its renal effects must be viewed in the context of its local production and actions. This is particularly important when comparing ET-1 biology in the nephron, where it promotes relative hypotension through increased salt and water excretion, with ET-1 effects in the vasculature, where it promotes relative hypertension through vasoconstriction. Numerous studies indicate that ET-1 is involved in the pathogenesis of a broad spectrum of renal diseases. These include those characterized by excessive renal vascular resistance, such as ischemic renal failure, cyclosporine (CyA) nephrotoxicity, radiocontrast nephropathy, endotoxemia, rhabdomyolysis, acute liver rejection, and others. ET-1 appears to play a role in cell proliferation in the setting of inflammatory glomerulonephritides. The peptide also may mediate, at least in part, excessive extracellular matrix accumulation and fibrosis occurring in chronic renal failure, diabetes mellitus, and other disorders. Deranged ET-1 production in the nephron may cause inappropriate sodium and water retention, thereby contributing to the development and/or maintenance of hypertension. Finally, impaired renal clearance of ET-1 may cause hypertension in patients with end-stage renal disease. Many ET-1 antagonists have been developed; however, their clinical usefulness has not yet been determined. Despite this, these agents hold great promise for the treatment of renal diseases; it is hoped that the next decade will witness their introduction into clinical practice.

Multiple roles for endothelin in melanocyte development: regulation of progenitor number and stimulation of differentiation

Melanocytes in the skin are derived from the embryonic neural crest. Recently, mutations in endothelin 3 and the endothelin receptor B genes have been shown to result in gross pigment defects, indicating that this signalling pathway is required for melanocyte development. We have examined the effects of endothelins on melanocyte progenitors in cultures of mouse neural crest. Firstly, they stimulate an increase in progenitor number and act synergistically with another factor, Steel factor, in the survival and proliferation of the progenitors. These findings are consistent with findings from mice with natural mutations in the endothelin receptor B gene, which show an early loss of melanocyte progenitors. Secondly, endothelins induce differentiation of the progenitors into fully mature pigmented melanocytes. This finding is consistent with the expression of endothelins in the skin of mice at the initiation of pigmentation. The melanocytes generated in endothelin-treated cultures also become responsive to alpha melanocyte-stimulating hormone, which then acts to regulate the activity of the pigmentation pathway. These findings indicate two key roles for endothelin in melanocyte development: regulation of expansion of the progenitor pool and differentiation of progenitors into mature melanocytes.

Chronic sensory denervation reduces thrombin-stimulated endothelin release from aortic endothelial cells

The long-term (trophic) influence of perivascular nerves on the endothelium was investigated by measuring changes in thrombin-stimulated release of the potent vasoconstrictor, endothelin, after selective chronic denervation. Rat pups were treated with either guanethidine or capsaicin to destroy sympathetic or sensory nerves, respectively. The abdominal aortas from the rats at three months of age (5 pooled per experiment) were incubated with 4U thrombin/ml in medium for 24 h at 37 degrees C, and the amount of endothelin released from the preparation determined by immunoassay. After neonatal sensory denervation there was a significant reduction in the thrombin-stimulated release of endothelin compared to the controls (0.012 +/ -0.012 (4) compared to 0.063 +/- 0.012 (6), pmol/cm2/24 h, p < 0.02). There was no change in endothelin release after sympathetic denervation. In summary, sensory nerves play a trophic role in the expression of endothelin in endothelial cells of the intima.