Involvement of endothelin in mononuclear phagocyte inflammation in asthma

Tobacco smoking aggravates airway inflammation by upregulating endothelin-2 and activating the c-Jun amino terminal kinase pathway in asthma

BACKGROUND

Asthma is closely associated with tobacco smoking (TS) and is more difficult to effectively treat after exposure to TS.

OBJECTIVE

To observe the effects of TS on the expression of endothelin-2 (ET-2) and airway inflammation in asthmatic rats and to explore the related mechanisms.

METHODS

We established an animal model of asthma with ovalbumin (OVA)/Al(OH)₃ and subjected different animal groups to TS and/or dexamethasone/bosentan. The differences in the inflammatory cell infiltration, the pathological changes to the bronchial wall and the bronchial smooth muscle thickness, and the expression of ET-2, c-Jun amino terminal kinase (JNK1/2), malondialdehyde (MDA), and glutathione peroxidase (GSH) in the lung tissue and of interleukin (IL)-7 in bronchoalveolar lavage fluid (BALF) were assessed.

RESULTS

Exposure to TS or OVA caused an obvious increase in the inflammatory cells in the BALF over what was observed in the control group. In asthma models, the expression of ET-1, JNK1/2, MDA, and GSH in the lung tissues, as well as that of IL-17 in the BALF, was increased. After treatment with dexamethasone/bosentan, the expression of IL-17, JNK1/2, MDA, and GSH decreased compared to the smoking group; airway inflammation and the staining intensity in the lung tissue were also reduced.

CONCLUSION

TS exposure can clearly exacerbate airway inflammation in asthmatic rats, while bosentan can alleviate airway inflammation through regulation of the ET-2/JNK1/2 signalling pathway.

Experimental investigation of the role of endothelin-1 in idiopathic portal hypertension

BACKGROUND AND AIM

The authors' previous report revealed that endothelin-1 might be released from B lymphocytes in cirrhotic patients with hypersplenism. Other investigators have shown that persistent exposure to environmental contaminants including arsenic might induce idiopathic portal hypertension. The aim of this study was to experimentally identify how endothelin-1 is involved in the development of idiopathic portal hypertension and which cells produce endothelin-1 in the spleen.

METHODS

Portal pressure and venous endothelin-1 concentrations were measured in rats that were given sodium arsenate orally for long periods, and endothelin-1 expression levels in the spleen were assessed by staining. In a second experiment, B and T lymphocytes and monocyte-derived macrophages cultured from healthy human peripheral blood were stimulated with sodium arsenite, sodium arsenate, lipopolysaccharide and interferon-gamma. Endothelin-1 concentrations in the supernatants were measured by ELISA.

RESULTS

Arsenic exposure gradually increased portal pressure and venous endothelin-1 levels in rats. Endothelin-1 concentration in the supernatant did not change in every cell type stimulated with arsenic, but it increased in B lymphocytes and monocyte-derived macrophages treated with lipopolysaccharide and interferon-gamma.

CONCLUSIONS

The in vivo study indicated that arsenic might elevate portal pressure through mechanisms involving endothelin-1. In the in vitro study, lipopolysaccharide and interferon-gamma clearly induced endothelin-1 synthesis not only in monocyte-derived macrophages but also in B lymphocytes, although arsenic treatment did not affect those cells. This study partially supports the hypothesis that idiopathic portal hypertension might be promoted by endothelin-1 overproduction from splenic B lymphocytes in response to certain substances.

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.

Signalling and regulation of collagen I synthesis by ET-1 and TGF-beta1

Endothelin-1 (ET-1) plays an important role in tissue remodelling and fibrogenesis by inducing synthesis of collagen I via protein kinase C (PKC). ET-1 signals are transduced by two receptor subtypes, the ETA- and ETB-receptors which activate different Galpha proteins. Here, we investigated the expression of both ET-receptor subtypes in human primary dermal fibroblasts and demonstrated that the ETA-receptor is the major ET-receptor subtype expressed. To determine further signalling intermediates, we inhibited Galphai and three phospholipases. Pharmacologic inhibition of Galphai, phosphatidylcholine-phospholipase C (PC-PLC) and phospholipase D (PLD), but not of phospholipase Cbeta, abolished the increase in collagen I by ET-1. Inhibition of all phospholipases revealed similar effects on TGF-beta1 induced collagen I synthesis, demonstrating involvement of PC-PLC and PLD in the signalling pathways elicited by ET-1 and TGF-beta1. ET-1 and TGF-beta1 each stimulated collagen I production and in an additive manner. ET-1 further induced connective tissue growth factor (CTGF), as did TGF-beta1, however, to lower levels. While rapid and sustained CTGF induction was seen following TGF-beta1 treatment, ET-1 increased CTGF in a biphasic manner with lower induction at 3 h and a delayed and higher induction after 5 days of permanent ET-1 treatment. Coincidentally at 5 days of permanent ET-1 stimulation, a switch in ET-receptor subtype expression to the ETB-receptor was observed. We conclude that the signalling pathways induced by ET-1 and TGF-beta1 leading to augmented collagen I production by fibroblasts converge on a similar signalling pathway. Thereby, long-time stimulation by ET-1 resulted in a changed ET-receptor subtype ratio and in a biphasic CTGF induction.

Attenuation of proinflammatory gene expression and microcirculatory disturbances by endothelin A receptor blockade after orthotopic liver transplantation in pigs

BACKGROUND

Endothelin-1 (ET-1), a very potent mediator of vasoconstriction, leads to microcirculatory disturbances and release of proinflammatory cytokines under pathophysiologic conditions. Our aim was to evaluate the effect of a selective ET(A)-receptor antagonist (ET(A)-RA) on cold ischemia/reperfusion (I/R) injury in a pig model.

METHODS

Twenty pigs revealed orthotopic liver transplantation. The animals were randomized into 2 groups: control pigs received isotonic saline; the treated group received the selective ET(A)-RA BSF 208075 at the beginning of reperfusion. On postoperative days 4 and 7, animals were re-laparotomized to obtain tissue specimens. Liver tissue samples were collected and quantitative mRNA expression for prepro-ET-1, ET(A) receptor, pro-IL-1beta, pro-IL-6, pro-TNF-alpha, and endothelial nitric oxide synthase was analyzed using the TaqMan system. Additionally, immunohistochemical analysis for ET-1 was performed. Hepatic microcirculation was evaluated by laser Doppler flow measurement and partial pressure of oxygen and carbon dioxide measurements with the Paratrend sensor. Postischemic liver damage was monitored by measurement of liver enzymes and by histologic analysis using a semiquantitative scoring classification.

RESULTS

Treatment with the ET(A)-RA significantly reduced the severity of I/R injury evidenced by lower serum AST, ALT and GLDH. Analysis of partial pressure of oxygen and blood flow revealed a significant improvement of capillary perfusion and blood flow in the treated group and was associated with a relevant reduction of tissue injury. One hour after reperfusion, quantitative RT-PCR revealed significantly lower expression of prepro-ET-1, ET(A) receptor, endothelial nitric oxide synthase, pro-TNF-alpha, pro-IL-1beta and pro-IL-6 in the therapy group. Immunohistochemical analysis demonstrated significantly reduced ET-1 immunostaining after therapy. Histologic investigation suggested less tissue damage in treated animals.

CONCLUSIONS

Treatment with the selective ET(A)-RA BSF 208075 has protective effects on microcirculation after liver transplantation. ET(A)-RA not only affects the expression of vasoactive genes, but also decreases gene expression of proinflammatory cytokines such as TNF-alpha, IL-1beta and IL-6.

Effects of ET(A) receptor antagonism on proinflammatory gene expression and microcirculation following hepatic ischemia/reperfusion

BACKGROUND

The objective of this study was to investigate the effect of a specific endothelin(A) receptor antagonist (ET(A)-RA) on mRNA expression of genes encoding vasoactive mediators and proinflammatory cytokines and on the microhemodynamics (assessed by measurement of laser Doppler flow and tissue blood gases) following complete vascular exclusion of the porcine liver.

STUDY DESIGN

Sixteen adult German landrace pigs were subjected to 120 min of warm hepatic ischemia by total vascular exclusion. To avoid portal congestion, a passive porto-femoro/jugular bypass was implanted. The animals were divided into 2 groups: the control group received saline solution and the therapy group was given the selective ET(A)-RA BSF 208075. Hepatic microcirculation was evaluated by p(O(2)) and p(CO(2)) measurement with the Paratrend sensor and by laser Doppler flow measurement. Liver tissue samples were collected 1 h after reperfusion and quantitative mRNA expression for prepro-ET-1, pro-IL-1beta, pro-IL-6, pro-TNF-alpha, eNOS was analyzed using the TaqMan system. Additionally, immunohistochemical analysis using a semiquantitative score for ET-1 was performed. Postischemic liver damage was monitored by measurement of liver enzymes and assessed by histological analysis using a semiquantitative scoring classification.

RESULTS

Partial oxygen pressure in the hepatic tissue and laser Doppler flow were significantly improved in the therapy group. One hour after reperfusion, quantitative RT-PCR revealed significantly lower expression of prepro-ET-1, eNOS, pro-TNF-alpha, and pro-IL-6 in the therapy group compared to controls. Immunohistochemical analysis demonstrated significantly reduced ET-1 immunostaining after therapy. Furthermore, blockade of ET(A) receptors prevents tissue damage.

CONCLUSIONS

Treatment with the selective ET(A)-RA BSF 208075 has protective effects on microcirculation after 120 min liver ischemia and reperfusion. The authors were able to show that ET(A)-RA not only affects the expression of vasoactive genes, but also decreases gene expression of proinflammatory cytokines such as TNF-alpha and IL-6.

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.

Localization of endothelin receptors in bleomycin-induced pulmonary fibrosis in the rat

Pulmonary fibrosis is characterized by excessive extracellular matrix deposition with concomitant loss of gas exchange units, and endothelin-1 (ET-1) has been implicated in its pathogenesis. Increased levels of ET-1 from tissues and bronchoalveolar lavage have been reported in patients with pulmonary fibrosis and in animal models after intratracheal bleomycin. We characterized the cellular distribution of alveolar ET receptors by immunohistochemistry in bleomycin-induced pulmonary fibrosis in the rat and determined the regulation by bleomycin of ET receptor mRNA expression in isolated alveolar macrophages and rat lung fibroblasts. We found significant increases in the numbers of fibroblasts and macrophages at day 7 compared to day 28 and control animals. ET(B) receptor immunoreactivity was observed on fibroblasts and invading monocytes. Isolated fibroblasts expressed both ET(A) and ET(B) receptor mRNA, and ET(A) receptor mRNA was upregulated by bleomycin. Isolated resident alveolar macrophages expressed neither ET(A) nor ET(B) receptor mRNA which were also not induced by bleomycin. We conclude that, while ET(B) receptor stimulation of fibroblasts and monocytes recruited during bleomycin-induced lung injury exerts antagonistic effects on fibroblast collagen synthesis, the observed increase in the number of fibroblasts in vivo and upregulation of fibroblast ET(A) receptor mRNA by bleomycin in vitro point to a predominance of the profibrotic effects of ET receptor engagement.

Plasma endothelin-1 immunoreactivity in asthmatic children

BACKGROUND

Endothelin-1 (ET-1) has been formerly demonstrated to have potent vasocontractile as well as bronchoconstrictor effects in vitro. This followup study was aimed to evaluate the possible changes in ET-1 levels in the plasma of asthmatic children, according to disease activity and severity.

METHODS

Plasma ET-1 was estimated by enzyme-linked immunoadsorbent assay in 30 asthmatic patients (6 to 12 years old) during and after remission of an acute attack. Thirty age- and sex-matched healthy children were included as a control group.

RESULTS

Plasma ET-1 immunoreactivity was significantly increased in the asthmatic children during the attacks (17.2+/-6.9 pg/mL) in comparison to the levels during quiescence of symptoms (0.9+/-1.13 pg/mL). Further, both values were significantly higher than the control value (0.22+/-0.29 pg/mL). The severity of attacks as judged clinically and by peak expiratory flow rate measurement did not influence the plasma endothelin status; neither did the family history of atopy nor the absolute eosinophil count. However, serum total IgE levels could be positively correlated to the plasma endothelin concentrations measured after remission of the asthmatic attacks (P < 0.05).

CONCLUSIONS

Our findings reinforce the concept that ET-1 may be implicated in the pathogenesis of bronchoconstriction. This may encourage further studies on the value of ET-1 antagonism among alternative therapeutic modalities of childhood asthma.

Arterial and bronchoalveolar lavage fluid endothelin-1 concentration in asthma

Endothelins are a family of peptide mediators that have a number of biological properties, including the ability to act as bronchoconstrictors and vasoconstrictors of isolated airways and vessels. Endothelin-1 (ET-1) is the more potent peptide compared with the other two peptides of the family. To examine a possible involvement of ET- 1 in the pathogenesis of asthma, we measured arterial ET-1 levels in 11 patients with atopic asthma during attack and during remission, and in 11 healthy control subjects. We also performed fiberoptic bonchoscopy and bronchoalveolar lavage (BAL) to measure ET-1 levels in the 11 asthmatic patients during remission, and in the 11 healthy control subjects. ET-1 concentrations in arterial blood and in BAL were measured by a radioimmunoassay method. Arterial ET-1 levels were very significantly higher in asthma attack (3.67 +/- 0.51 pg ml(-1)) and in asthma remission (2.65 +/- 10.62 pg ml(-1)) compared with those of the healthy controls (1.37 +/- 0.14 pg ml(-1)) (P < 0.001). Arterial ET-1 levels were also very significantly higher during asthma attack compared with those in asthma remission (P < 0.001). BAL ET-1 levels were significantly higher in asthma remission (0.73 +/- 0.53 pmol g(-1)) compared with those of the healthy controls (0.16 +/- 0.02 pmol g(-1)) (P < 0.05). No correlation was observed between arterial and BAL ET-1 levels, PaO2 and peak expiratory flow rate (PEFR). These data are consistent with the hypothesis that ET-1 contributes to the pathophysiology of asthma. However, it is likely that the true importance of this vasoconstrictor peptide will only be revealed by pharmacological studies with specific receptor antagonists.

The effect of endothelin-1 on lipopolysaccharide-induced cyclooxygenase 2 expression in association with prostaglandin E(2)

We demonstrated previously that endothelin-1 (10(-14) to 10(-8) M) promotes lipopolysaccharide-induced cyclooxygenase 2 expression and prostaglandin E(2) production through endothelin ET(B) receptors effects which are up-regulated by lipopolysaccharide. In the present study, we confirmed these findings and showed that prostaglandin E(2) (10(-6) to 10(-5) M) inhibited the lipopolysaccharide plus endothelin-1-induced cyclooxygenase 2 expression more profoundly as compared to its inhibition of the lipopolysaccharide-induced cyclooxygenase 2 expression. The endothelin ET(B) receptor selective antagonist, N-cis-2, 6-dimethylpiperidino-carbonyl-L-gamma-methyl-leucyl-D-L-methoxy carbon yl-tryptophanyl-D-norleucine (BQ788), partly inhibited this suppression. Interestingly, the expression of endothelin ET(B) receptors in macrophages was increased by lipopolysaccharide plus prostaglandin E(2) (10(-8) to 10(-5) M) about 1.6-fold compared with that evoked by lipopolysaccharide stimulation alone. We also showed that treatment with endothelin-1 at 10(-14) M (15 min) elevated an intracellular cyclic AMP concentration in macrophages stimulated by lipopolysaccharide or lipopolysaccharide plus prostaglandin E(2) (10(-6) M) for 6 h, and the elevation in the latter cells was more pronounced. These results suggested that endothelin-1 shows an opposite modulation of lipopolysaccharide-induced cyclooxygenase 2 expression in macrophages through endothelin ET(B) receptors, depending on the level of extracellular prostaglandin E(2), and the changes of intracellular cyclic AMP by endothelin-1 may be involved in this mechanism.

Sputum cellular and cytokine responses to inhaled endothelin-1 in asthma

BACKGROUND

Endothelin (ET)-1 is a 21-amino acid peptide which has potent bronchoconstrictor activity. Animal studies show elevation of ET-1 during experimental airway inflammation, and inhibition of inflammation by endothelin-antagonists, suggesting pro-inflammatory activity for ET-1.

OBJECTIVE

We wanted to assess any acute influence that bronchoconstrictor doses of inhaled ET-1 might have on cells, tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, nitrite (NO2) and albumin in induced sputum in asthma.

METHODS

Bronchial challenge was performed using nebulized ET-1 (nebulized dose range 0.96-15.36 nmol) and placebo in 10 adult asthmatic subjects in a randomized double-blind placebo-controlled cross-over study. Sputum induction was performed 30 min and 4 h after placebo or ET-1 bronchial challenge.

RESULTS

All subjects experienced dose-dependent bronchoconstriction to inhaled ET-1 with a mean (range) PC15 forced expiratory volume in 1 s (FEV1) to ET-1 of 9.45 (1.2-21.7) nmol. Comparing ET-1 with placebo inhalation, there was no change in sputum differential cell counts, TNFalpha, IL-1beta, NO2 or albumin at 30 min or 4 h after inhalation, nor was there a difference in these parameters at 4 h compared with 30 min after ET-1 inhalation. There was no fall in FEV1 at 4 h after ET-1 inhalation, suggesting that ET-1 inhalation is not associated with a late bronchoconstrictor response.

CONCLUSIONS

We conclude that inhaled ET-1 does not appear to stimulate an acute inflammatory response in asthma as assessed by differential cell count, TNFalpha, IL-1beta, NO2 and albumin concentrations in induced sputum.

Modulation by endothelin-1 of lipopolysaccharide-induced cyclooxygenase 2 expression in mouse peritoneal macrophages

We investigated the modulation by endothelin-1 of lipopolysaccharide-induced cyclooxygenase 2 expression and prostaglandin E2 production by mouse peritoneal macrophages. Our previous report showed that endothelin-1 at concentrations above 10(-11) M induced cyclooxygenase 2 expression through mainly endothelin ET(B) receptors and that an endothelin ET(B) receptor-mediated process was not involved in cyclooxygenase 2 activation in macrophages stimulated by lipopolysaccharide for 4 h. In the present study, when macrophages were stimulated by lipopolysaccharide for 12 h in the presence of endothelin-1 (10(-15) to 10(-8) M), cyclooxygenase 2 expression and prostaglandin E2 production were enhanced by 1.2- to 1.6-fold. The endothelin ET(B) receptor selective antagonist, BQ788 (N-cis-2,6-dimethylpiperidino-carbonyl-L-gamma-methyl-leucyl-D-L-m ethoxycarbonyl-tryptophanyl-norleucine), significantly inhibited this synergistic effect of endothelin-1. In addition, the cyclooxygenase 2-selective inhibitor, NS398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide), also suppressed this effect. Western blot analysis showed that the endothelin ET(B) receptor was up-regulated by lipopolysaccharide in a time- and concentration-dependent manner, and that this up-regulation was inhibited by NS398. From these results, we conclude that endothelin-1 promotes lipopolysaccharide-induced cyclooxygenase 2 activation in the delayed phase through endothelin ET(B) receptors up-regulated by lipopolysaccharide.

Endothelin receptor distribution and function in the airways

1. Within the lung, endothelin (ET)-1 is synthesized and released by airway epithelial and vascular endothelial cells, as well as by inflammatory cells, such as macrophages. Following release, ET-1 can modulate the activities of a wide range of different cell types within the lung through the stimulation of specific endothelin ETA and ETB receptors. The present review focuses on recent advances in our understanding of the distribution and function of endothelin receptors within the airway wall and peripheral lung and, where possible, particular attention is given to studies using human cells, tissues and subjects. 2. The highest densities of endothelin receptors within the lung appear to be associated with airway smooth muscle and the alveolar septae. The relative proportions of ETA and ETB receptors present within these tissues display marked interspecies differences, although ETB receptors predominate at both sites in human lung. 3. The effects induced by ET-1 within the lung include contraction and proliferation of airway smooth muscle, facilitation of cholinergic neurotransmission, mucous gland hypersecretion, microvascular leakage and inflammatory cell influx and activation. There is also evidence that a proportion of ETB receptors in the pulmonary microvasculature act as clearance receptors for endothelin-1. 4. Evidence to date suggests that changes in the endothelin content within the airway wall, conceivably associated with lung pathology, are likely to have profound effects on the function of many cells within the lung.

Granulocyte-macrophage colony-stimulating factor and interleukin-3 potentiate interferon-gamma-mediated endothelin production by human monocytes: role of protein kinase C

Monocytic cells have been shown to produce endothelin, a potent vasoconstrictor molecule with immune modulating properties. The signalling mechanisms involved in this response are presently unclear. Monocytes are also believed to play an important role in inflammatory bowel disease (IBD). The objective of this study was to characterize the role of various cytokines, bacterial lipopolysaccharide (LPS) and colony-stimulating factors on the production of endothelin (ET) by freshly isolated human monocytes. Compelling circumstantial evidence exists for the conditions being investigated occurring in inflamed bowel mucosa to where monocytes migrate. Whereas LPS stimulated the release of 7 pg ET/2x106 cells in 40 hr, interferon-gamma (IFN-gamma) stimulated 45 pg ET/2x106 cells in 40 hr. There was an additive response when the two stimuli were employed together. Significantly the addition of either granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) effected a two- to threefold, dose-dependent increase in the production of ET. Production of endothelin was reproducibly blocked by the addition of the protein kinase C (PKC) inhibitors staurosporine and H7, as well as by the protein synthesis inhibitor cycloheximide. Assessment of the activities of the alpha and beta isoforms of conventional protein kinase C (PKC), as determined by MonoQ column fractionated calcium and lipid activatible phosphotransferase activity towards myelin basic protein (MBP) revealed an additive effect of using LPS, IFN-gamma and GM-CSF, which was even greater than that demonstrated for phorbol myristate acetate (PMA). Additionally the secretion of ET by monocytes from Crohn's disease patients (in remission) was analysed and compared with an age-matched control group. There was no significant difference between the two. These results: (1) demonstrate an important synergistic role for GM-CSF and IL-3 in the predominantly IFN-gamma-mediated ET production by normal human monocytes; (2) indicate a possible role for the protein kinase C signalling pathway in this response; and (3) argue against a primary abnormality of ET production in peripheral monocytes from patients with Crohn's disease.

Increased synthesis and release of endothelin-1 during the initial phase of airway inflammation

Recently, we have shown a substantial increase in the endothelin-1 (ET-1) concentration in bronchoalveolar fluid (BALF) during an experimental eosinophilic airway inflammation. Moreover, we observed a significant inhibition of the inflammatory response after treatment with an endothelin receptor antagonist. This indicates that ET-1 may have proinflammatory properties and play a key role in eosinophilic inflammations, such as bronchial asthma. Accordingly, we hypothesized that the synthesis and release of ET-1 precedes the inflammatory response, and that the bronchial epithelium is the site of ET-1 synthesis in the lungs. An eosinophilic airway inflammation was induced by intratracheal Sephadex instillation in rats, and the animals were evaluated after 15 min, 30 min, 1, 2, 3, 6, 12, and 48 h. The ET-1 mRNA synthesis, assessed by Northern and slot blot analyses, was significantly increased 15 min after Sephadex challenge, peaking at 30 min with a 4.7-fold increase, before any signs of inflammation in the BALF could be observed. The increased synthesis was mainly located to the bronchial epithelium and macrophages at sites of inflammation as determined by in situ hybridization. A significant increase in tissue ET-1 was observed 3 h after provocation, and the recruitment of eosinophils followed a substantial release of ET-1 peptide in BALF peaking at 24 h with a 13-fold increase. Therefore, the rapid ET-1 mRNA synthesis and the considerable increase in the level of ET-1 indicate that this peptide plays an important role in the initiation of an eosinophilic airway inflammation.

Endothelin-1 secretion by alveolar macrophages in systemic sclerosis

Endothelin-1 (ET-1), a potent fibroblast/smooth muscle cells mitogen, has been implicated in the pathogenesis of systemic sclerosis lung disease (SSc). Since monocytes and macrophages are thought to be activated in SSc, we hypothesized that alveolar macrophages (AM) and their precursors blood monocytes from patients with SSc produced more ET-1 than cells from healthy subjects. ET-1 and big ET-1 concentrations were measured in plasma, in bronchoalveolar lavage (BAL) fluids and in cell culture supernatants from monocytes and alveolar macrophages derived from 13 patients with definite SSc with lung involvement and from 10 control subjects. Plasma and BAL fluid ET-1 and big ET-1 levels were similar in both controls and patients with SSc. ET-1 and big ET-1 concentrations in unstimulated alveolar macrophage supernatants were similar in both groups. In contrast, LPS-stimulated alveolar macrophages from patients with SSc secreted higher amounts of ET-1 and big ET-1 than control subjects. ET-1 and big ET-1 concentrations in monocyte supernatants (either LPS-stimulated or not) were not different in patients and controls. These results show that AM from patients with SSc are hyperresponsive to LPS in vitro in terms of ET-1 and big ET-1 production and suggest that AM could participate in vivo in the overproduction of this potentially profibrotic mediator in patients with SSc.