Endothelin production in sepsis and the adult respiratory distress syndrome

Transpulmonary Plasma Endothelin-1 Arterial:Venous Ratio Differentiates Survivors from Non-Survivors in Critically Ill Patients with COVID-19-Induced Acute Respiratory Distress Syndrome

Endothelin-1 (ET-1) is a potent vasoconstrictor produced by endothelial cells and cleared from circulating blood mainly in the pulmonary vasculature. In a healthy pulmonary circulation, the rate of local production of ET-1 is less than its rate of clearance. In the present study, we aimed to investigate whether the abnormal pulmonary circulatory handling of ET-1 relates to poor clinical outcomes in patients with coronavirus disease 2019 (COVID-19)-induced acute respiratory distress syndrome (ARDS). To this end, central venous and systemic arterial ET-1 plasma levels were simultaneously measured on Days 1 and 3 following ICU admission in mechanically ventilated COVID-19 patients with ARDS (COVID-19 ARDS, N = 18). Central venous and systemic arterial ET-1 plasma levels were also measured in two distinct SARS-CoV-2-negative mechanically ventilated critically ill patient groups, matched for age, sex, and critical illness severity, with ARDS (non-COVID-19 ARDS, N = 14) or without ARDS (non-COVID-19 non-ARDS, N = 20). Upon ICU admission, COVID-19-induced ARDS patients had higher systemic arterial and central venous ET-1 levels compared to the non-COVID-19 ARDS and non-COVID-19 non-ARDS patients (p < 0.05), yet a normal systemic arterial:central venous (A:V) ET-1 ratio [0.63 (0.49-1.02)], suggesting that pulmonary ET-1 clearance is intact in these patients. On the other hand, the non-COVID-19 ARDS patients demonstrated abnormal ET-1 handling [A:V ET-1 ratio 1.06 (0.93-1.20)], while the non-COVID-19 non-ARDS group showed normal ET-1 handling [0.79 (0.52-1.11)]. On Day 3, the A:V ratio in all three groups was <1. When the COVID-19 ARDS patients were divided based on 28-day ICU mortality, while their systemic arterial and central venous levels did not differ, the A:V ET-1 ratio was statistically significantly higher upon ICU admission in the non-survivors [0.95 (0.78-1.34)] compared to the survivors [0.57 (0.48-0.92), p = 0.027]. Our results highlight the potential importance of ET-1 as both a biomarker and a therapeutic target in critically ill COVID-19 patients. The elevated A:V ET-1 ratio in non-survivors suggests that the early disruption of pulmonary ET-1 handling may be a key marker of poor prognosis.

Improvement in idiopathic interstitial pneumonia by adding macitentan to a patient unresponsive to nintedanib

A 69-year-old woman was diagnosed with idiopathic interstitial pneumonia (IIP). The patient underwent a combination therapy of steroid therapy and intravenous cyclophosphamide, long-term oxygen therapy, and the initiation of Nintedanib. However, there was no improvement in IIP, and as a result, the activities of daily living also declined. As one of the various examinations conducted, the results of the right heart catheterization diagnosed the patient with mild pulmonary hypertension, and Macitentan therapy was initiated. The subsequent clinical course appeared to show an improvement in Idiopathic Interstitial Pneumonia (IIP) by adding Macitentan therapy to Nintedanib therapy.

Acute respiratory distress syndrome heterogeneity and the septic ARDS subgroup

Acute respiratory distress syndrome (ARDS) is an acute diffuse inflammatory lung injury characterized by the damage of alveolar epithelial cells and pulmonary capillary endothelial cells. It is mainly manifested by non-cardiogenic pulmonary edema, resulting from intrapulmonary and extrapulmonary risk factors. ARDS is often accompanied by immune system disturbance, both locally in the lungs and systemically. As a common heterogeneous disease in critical care medicine, researchers are often faced with the failure of clinical trials. Latent class analysis had been used to compensate for poor outcomes and found that targeted treatment after subgrouping contribute to ARDS therapy. The subphenotype of ARDS caused by sepsis has garnered attention due to its refractory nature and detrimental consequences. Sepsis stands as the most predominant extrapulmonary cause of ARDS, accounting for approximately 32% of ARDS cases. Studies indicate that sepsis-induced ARDS tends to be more severe than ARDS caused by other factors, leading to poorer prognosis and higher mortality rate. This comprehensive review delves into the immunological mechanisms of sepsis-ARDS, the heterogeneity of ARDS and existing research on targeted treatments, aiming to providing mechanism understanding and exploring ideas for accurate treatment of ARDS or sepsis-ARDS.

Endothelin antagonism and sodium glucose Co-transporter 2 inhibition. A potential combination therapeutic strategy for COVID-19

The novel coronavirus 2019 (COVID-19) infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global pandemic that requires a multi-faceted approach to tackle this unprecedent health crisis. Therapeutics to treat COVID-19 are an integral part of any such management strategy and there is a substantial unmet need for treatments for individuals most at risk of severe disease. This perspective review provides rationale of a combined therapeutic regimen of selective endothelin-A (ET-A) receptor antagonism and sodium glucose co-transporter-2 (SGLT-2) inhibition to treat COVID-19. Endothelin is a potent vasoconstrictor with pro-inflammatory and atherosclerotic effects. It is upregulated in a number of conditions including acute respiratory distress syndrome and cardiovascular disease. Endothelin mediates vasocontractility via endothelin (ET-A and ET-B) receptors on vascular smooth muscle cells (VSMCs). ET-B receptors regulate endothelin clearance and are present on endothelial cells, where in contrast to their role on VSMCs, mediate vasodilation. Therefore, selective endothelin-A (ET-A) receptor inhibition is likely the optimal approach to attenuate the injurious effects of endothelin and may reduce ventilation-perfusion mismatch and pulmonary inflammation, whilst improving pulmonary haemodynamics and oxygenation. SGLT-2 inhibition may dampen inflammatory cytokines, reduce hyperglycaemia if present, improve endothelial function, cardiovascular haemodynamics and cellular bioenergetics. This combination therapeutic approach may therefore have beneficial effects to mitigate both the pulmonary, metabolic and cardiorenal manifestations of COVID-19. Given these drug classes include medicines licensed to treat heart failure, diabetes and pulmonary hypertension respectively, information regarding their safety profile is established. Randomised controlled clinical trials are the best way to determine efficacy and safety of these medicines in COVID-19.

Mechanisms of Pulmonary Hypertension in Acute Respiratory Distress Syndrome (ARDS)

Background: Acute respiratory distress syndrome (ARDS) is a severe and often fatal disease. The causes that lead to ARDS are multiple and include inhalation of salt water, smoke particles, or as a result of damage caused by respiratory viruses. ARDS can also arise due to systemic complications such as blood transfusions, sepsis, or pancreatitis. Unfortunately, despite a high mortality rate of 40%, there are limited treatment options available for ARDS outside of last resort options such as mechanical ventilation and extracorporeal support strategies. Aim of review: A complication of ARDS is the development of pulmonary hypertension (PH); however, the mechanisms that lead to PH in ARDS are not fully understood. In this review, we summarize the known mechanisms that promote PH in ARDS. Key scientific concepts of review: (1) Provide an overview of acute respiratory distress syndrome; (2) delineate the mechanisms that contribute to the development of PH in ARDS; (3) address the implications of PH in the setting of coronavirus disease 2019 (COVID-19).

Endothelial Damage in Acute Respiratory Distress Syndrome

The pulmonary endothelium is a metabolically active continuous monolayer of squamous endothelial cells that internally lines blood vessels and mediates key processes involved in lung homoeostasis. Many of these processes are disrupted in acute respiratory distress syndrome (ARDS), which is marked among others by diffuse endothelial injury, intense activation of the coagulation system and increased capillary permeability. Most commonly occurring in the setting of sepsis, ARDS is a devastating illness, associated with increased morbidity and mortality and no effective pharmacological treatment. Endothelial cell damage has an important role in the pathogenesis of ARDS and several biomarkers of endothelial damage have been tested in determining prognosis. By further understanding the endothelial pathobiology, development of endothelial-specific therapeutics might arise. In this review, we will discuss the underlying pathology of endothelial dysfunction leading to ARDS and emerging therapies. Furthermore, we will present a brief overview demonstrating that endotheliopathy is an important feature of hospitalised patients with coronavirus disease-19 (COVID-19).

mTOR/STAT-3 pathway mediates mesenchymal stem cell-secreted hepatocyte growth factor protective effects against lipopolysaccharide-induced vascular endothelial barrier dysfunction and apoptosis

Mesenchymal stem cells (MSCs) protect the endothelial barrier complex and survival, implicated in the pathogenesis of acute lung injury (ALI) via paracrine hepatocyte growth factor (HGF). However, the mechanism of HGF in endothelial regulation remains unclear. Here, we introduced a coculture protocol of pulmonary microvascular endothelial cells (PMVECs) and overexpression of the HGF gene of MSCs (MSC-HGF). Immunofluorescence and endothelial permeability analysis revealed that MSC-HGF protected endothelial tight junction protein occludin expression and attenuated cellular permeability as well as endothelial apoptosis. To investigate the novel mechanism mammalian TOR (mTOR)/ signal transducer and activator of transcription 3 (STAT-3) signaling in HGF protective effects against endothelial barrier and apoptosis, we used recombinant mouse HGF in endothelial cells. In addition, we used mTOR inhibitor rapamycin to inhibit the mTOR pathway. Our study demonstrated that rapamycin decreased the protective effects of HGF on the endothelium by decreasing tight junction protein occludin expression and cell proliferation, and raising lipopolysaccharide (LPS)-induced endothelial permeability, endothelial cell injury factors ET-1 and vWF. Similarly, the protective effects of HGF on reducing endothelial barrier and apoptosis were weakened when PMVECs were treated with the STAT-3 inhibitor S3I-201. Moreover, mTOR/STAT-3 were activated by HGF demonstrated as raising mTOR (Ser2448) and STAT3 (Ser727) phosphorylation proteins, leading to endothelial barrier improvement and survival. Reversely, rapamycin or S3I-201 inhibited mTOR/STAT-3 activation. Taken together, our findings highlight that the activation of the mTOR/STAT-3 pathway provides novel mechanistic insights into MSC-secreted HGF protection against LPS-induced vascular endothelial permeability dysfunction and apoptosis, which contributes to decreasing microvascular loss and lung injury.

Endotoxemia Induces IκBβ/NF-κB-Dependent Endothelin-1 Expression in Hepatic Macrophages

Elevated serum concentrations of the vasoactive protein endothelin-1 (ET-1) occur in the setting of systemic inflammatory response syndrome and contribute to distal organ hypoperfusion and pulmonary hypertension. Thus, understanding the cellular source and transcriptional regulation of systemic inflammatory stress-induced ET-1 expression may reveal therapeutic targets. Using a murine model of LPS-induced septic shock, we demonstrate that the hepatic macrophage is the primary source of elevated circulating ET-1, rather than the endothelium as previously proposed. Using pharmacologic inhibitors, ET-1 promoter luciferase assays, and by silencing and overexpressing NF-κB inhibitory protein IκB expression, we demonstrate that LPS-induced ET-1 expression occurs via an NF-κB-dependent pathway. Finally, the specific role of the cRel/p65 inhibitory protein IκBβ was evaluated. Although cytoplasmic IκBβ inhibits activity of cRel-containing NF-κB dimers, nuclear IκBβ stabilizes NF-κB/DNA binding and enhances gene expression. Using targeted pharmacologic therapies to specifically prevent IκBβ/NF-κB signaling, as well as mice genetically modified to overexpress IκBβ, we show that nuclear IκBβ is both necessary and sufficient to drive LPS-induced ET-1 expression. Together, these results mechanistically link the innate immune response mediated by IκBβ/NF-κB to ET-1 expression and potentially reveal therapeutic targets for patients with Gram-negative septic shock.

Selective endothelin-A receptor blockade attenuates endotoxin-induced pulmonary hypertension and pulmonary vascular dysfunction

Endothelin-1 is a potent mediator of sepsis-induced pulmonary hypertension (PH). The pulmonary vascular effects of selective blockade of endothelin receptor subtype A (ETAR) during endotoxemia remain unknown. We hypothesized that selective ETAR antagonism attenuates endotoxin-induced PH and improves pulmonary artery (PA) vasoreactivity. Adult male Sprague-Dawley rats (250-450 g) received lipopolysaccharide (LPS; Salmonella typhimurium; 20 mg/kg intraperitoneally) or vehicle 6 hours before hemodynamic assessment and tissue harvest. The selective ETAR antagonist sitaxsentan (10 or 20 mg/kg) or vehicle was injected intravenously 3 hours after receipt of LPS. Right ventricular systolic pressure, mean arterial pressure (MAP), cardiac output (CO), oxygenation (P/F ratio), and serum bicarbonate were measured. Bronchoalveolar lavage (BAL) cell differential and lung wet-to-dry ratios were obtained. Endothelium-dependent and endothelium-independent vasorelaxations were determined in isolated PA rings. PA interleukin (IL)-1β, IL-6, tumor necrosis factor α (TNF-α), and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) were measured. LPS caused PH, decreased MAP, CO, and serum bicarbonate, and increased PA IL-1β, IL-6, TNF-α, and iNOS mRNA. Sitaxsentan attenuated sepsis-induced PH and increased MAP. The P/F ratio, CO, serum bicarbonate, and BAL neutrophilia were not affected by sitaxsentan. In isolated PA rings, while not affecting phenylephrine-induced vasocontraction or endothelium-dependent relaxation, sitaxsentan dose-dependently attenuated LPS-induced alterations in endothelium-independent relaxation. PA cytokine mRNA levels were not significantly attenuated by ETAR blockade. We conclude that ETAR blockade attenuates endotoxin-induced alterations in systemic and PA pressures without negatively affecting oxygenation. This protective effect appears to be mediated not by attenuation of sepsis-induced cardiac dysfunction, acidosis, or alveolar inflammation but rather by improved endothelium-independent vasorelaxation.

Effect of the endothelin receptor antagonist tezosentan on alpha-naphthylthiourea-induced lung injury in rats

Acute lung injury is an inflammatory syndrome that increases the permeability of the blood-gas barrier, resulting in high morbidity and mortality. Despite intensive research, treatment options remain limited. We investigated the protective efficacy of tezosentan, a novel, dual endothelin receptor antagonist, in an experimental model of alpha-naphthylthiourea (ANTU)-induced acute lung injury in rats. ANTU was intraperitoneally (i.p.) injected into rats at a dose of 10 mg/kg. Tezosentan was injected 30 minutes before ANTU was subcutaneously (s.c.) injected at doses of 2, 10, or 30 mg/kg, 60 minutes before ANTU was injected at doses of 2, 10, or 30 mg/kg (i.p.), and 90 minutes before ANTU at a dose of 10 mg/kg (i.p.). Four hours later, the lung weight/body weight (LW/BW) ratio and pleural effusion (PE) were measured. When injected 30 minutes before ANTU at doses of 2, 10, or 30 mg/kg (s.c.), tezosentan had no effect on lung pathology. When injected 60 minutes before ANTU at doses of 2, 10, or 30 mg/kg (i.p.) or 90 minutes before ANTU (10 mg/kg, i.p.), tezosentan significantly decreased the PE/BW ratio and had a prophylactic effect on PE formation at all doses. Therefore, tezosentan may attenuate lung injury. Furthermore, its acute and inhibitory effects on fluid accumulation were more effective in the pleural cavity than in the interstitial compartment in this experimental model.

Mechanisms, detection, and potential management of microcirculatory disturbances in sepsis

Despite improvements in resuscitation and treatment of sepsis, the morbidity and mortality remain unacceptably high. Microvascular dysfunction has been shown to play a significant role in the pathogenesis of sepsis and is a potential new target in the management of sepsis. Clinical studies, aided by new techniques that allow for real-time assessment of the microcirculation, have shown that disturbances in microcirculatory flow are common in sepsis and correlate with worse outcomes. Bedside measurement of microcirculatory perfusion has become simpler and more accessible, and may provide key insights into prognosis in sepsis and guide future therapeutics, much like mean arterial pressure (MAP), lactate, and mixed central oxygen saturation (SvO(2)) do now. The authors review here the role of microcirculatory dysfunction in sepsis and its potential role as a therapeutic target in sepsis.

Inhalation of an endothelin receptor A antagonist attenuates pulmonary inflammation in experimental acute lung injury

We recently demonstrated that inhalation of the endothelin receptor A (ETA) antagonist LU 135252 improved arterial oxygenation and reduced pulmonary artery pressure in experimental acute lung injury (ALI). In this study we analyzed potential immune modulatory effects of inhaled LU 135252 in experimental ALI. ALI was induced by repeated lung lavage in intubated (100% O2) and anesthetized piglets. Animals were randomly assigned to inhale either nebulized LU 135252 (0.3 mg.kg(-1), ALI + LU group, n = 8) or saline buffer (ALI control group, n = 16), both for 30 min. Surviving animals were sacrificed 6 h after induction of ALI, and lung tissue specimens were obtained from all animals for histology and immunhistochemistry. Induction of ALI significantly decreased arterial oxygenation in all animals. Inhalation of LU 135252 significantly reduced mortality and induced significant and sustained increase in PaO2 (316 +/- 47 mm Hg vs. control 53 +/- 3 mm Hg, p < 0.001). We measured a significant reduction in the number of pulmonary leukocyte L1 antigen-positive cells in ALI + LU animals (8% +/- 1% positive cells vs. control 12% +/- 2% positive cells, p < 0.05). The number of CD3-positive cells was not altered by treatment with LU 135252. Pulmonary tissue concentration of IL-6 was significantly suppressed by LU 135252 inhalation (4 +/- 1 pg.100 mg-1 wet weight vs. control 7 +/- 1 pg.100 mg(-1) wet weight, p < 0.05). Concentrations of TNF-alpha, IL-1beta, and ET-1 in pulmonary tissue were not influenced by inhalation of LU 135252. In conclusion, we demonstrated that inhalation of LU 135252 not only improves mortality and gas exchange, but also blunts the local immune response in experimental ALI.

Endothelin-1 precursor peptides correlate with severity of disease and outcome in patients with community acquired pneumonia

Background

Circulating levels of endothelin-1 are increased in sepsis and correlate with severity of disease. A rapid and easy immunoassay has been developed to measure the more stable ET-1 precursor peptides proET-1. The objective of this study was to assess the diagnostic and prognostic value of proET-1 in a prospective cohort of mainly septic patients with community-acquired pneumonia.

Methods

We evaluated 281 consecutive patients with community acquired pneumonia. Serum proET-1 plasma levels were measured using a new sandwich immunoassay.

Results

ProET-1 levels exhibited a gradual increase depending on the clinical severity of pneumonia as assessed by the pneumonia severity index (PSI) and the CURB65 scores (p < 0.001 and p < 0.01). The diagnostic accuracy to predict bacteraemia of procalcitonin (AUC 0.84 [95% 0.74–0.93]) was superior than C-reactive protein (AUC 0.67 [95%CI 0.56–0.78]) and leukocyte count (AUC 0.66 [95%CI 0.55–0.78]) and in the range of proET-1(AUC of 0.77 [95%CI 0.67–0.86]). ProET-1 levels on admission were increased in patients with adverse medical outcomes including death and need for ICU admission. ROC curve analysis to predict the risk for mortality showed a prognostic accuracy of proET-1 (AUC 0.64 [95%CI 0.53–0.74]), which was higher than C-reactive protein (AUC 0.51 [95%CI 0.41–0.61]) and leukocyte count (AUC 0.55 [95%CI 0.44–0.65]) and within the range of the clinical severity scores (PSI AUC 0.69 [95%CI 0.61–0.76] and CURB65 0.67 [95%CI 0.57–0.77]) and procalcitonin (AUC 0.59 [95% 0.51–0.67]). ProET-1 determination improved significantly the prognostic accuracy of the CURB65 score (AUC of the combined model 0.69 [95%CI 0.59–0.79]). In a multivariate logistic regression model, only proET1 and the clinical severity scores were independent predictors for death and for the need for ICU admission.

Conclusion

In community-acquired pneumonia, ET-1 precursor peptides correlate with disease severity and are independent predictors for mortality and ICU admission. If confirmed in future studies, proET-1 levels may become another helpful tool for risk stratification and management of patients with community-acquired pneumonia.

Trial registration

ISRCTN04176397

Endothelin-1 level in epithelial lining fluid of patients with acute respiratory distress syndrome

BACKGROUND AND OBJECTIVES

Endothelin-1 (ET-1), a potent vasoconstrictor peptide produced by endothelial cells, has been implicated in the dysfunction of various organs. To determine the role of ET-1 in acute lung injury (ALI) and ARDS, ET-1 levels were measured in epithelial lining fluid (ELF) and plasma obtained from patients with ALI/ARDS.

METHODS

A cross-sectional study of patients with ALI/ARDS in the intensive care unit of two university hospitals was performed. Patients with ALI/ARDS underwent bronchoscopic microsampling to collect ELF on the day of onset of the disease. Patients who underwent bronchoscopy to examine a small peripheral pulmonary nodule served as controls.

RESULTS

In the 23 patients with ALI/ARDS, the ET-1 level in ELF was significantly greater than that in plasma (P < 0.001). In contrast, ET-1 was not detectable in the ELF from six of the seven control subjects. The albumin concentration of ELF, used as a marker of endothelial and epithelial permeability, correlated with the ET-1 level in ELF (P < 0.001). The oxygenation index (PaO(2)/FiO(2)) was also correlated with ET-1 concentration in ELF (P < 0.001).

CONCLUSION

In patients with ALI/ARDS, ET-1 is produced mainly in the lung and is associated not only with pulmonary vasoconstriction but also the development of permeability oedema, leading to the impairment of oxygenation.

Endothelins in health and disease

Endothelins are powerful vasoconstrictor peptides that also play numerous other roles. The endothelin (ET) family consists of three peptides produced by a variety of tissues. Endothelin-1 (ET-1) is the principal isoform produced by the endothelium in the human cardiovascular system, and it exerts its actions through binding to specific receptors, the so-called type A (ET(A)) and type B (ET(B)) receptors. ET-1 is primarily a locally acting paracrine substance that appears to contribute to the maintenance of basal vascular tone. It is also activated in several diseases, including congestive heart failure, arterial hypertension, atherosclerosis, endothelial dysfunction, coronary artery diseases, renal failure, cerebrovascular disease, pulmonary arterial hypertension, and sepsis. Thus, ET-1 antagonists are promising new agents. They have been shown to be effective in the management of primary pulmonary hypertension, but disappointing in heart failure. Clinical trials are needed to determine whether manipulation of the ET system will be beneficial in other diseases.

Biologic markers of mortality in acute lung injury

Acute lung injury (ALI) is a clinical syndrome in which patients develop severe and progressive pulmonary gas exchange defects and pulmonary mechanical dysfunction. The high morbidity and mortality (40%) associated with ALI provide a compelling need to identify clinical and/or biochemical parameters that robustly risk stratify patients for both accurate prognostication and clinical trial purposes. In this review, we will examine and critically evaluate studies pertaining to biochemical markers of mortality in ALI. These markers may not only serve as prognostic measures of disease, but in some cases, add to our overall understanding of the pathophysiology of ALI.

Extravascular lung water determined with single transpulmonary thermodilution correlates with the severity of sepsis-induced acute lung injury

OBJECTIVE

To find out if the extravascular lung water index (EVLWI) and the derived permeability indexes determined by the single transpulmonary thermodilution technique are associated with markers of acute lung injury in human septic shock.

DESIGN

Prospective, observational study.

SETTING

Mixed intensive care unit of a 900-bed university hospital.

PATIENTS

Thirty-eight consecutive adult patients with septic shock and acute lung injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The variables were assessed over a 72-hr period and included hemodynamics, EVLWI, and pulmonary vascular permeability indexes determined with the single indicator transpulmonary thermodilution technique, lung compliance, oxygenation ratio (Pao2/Fio2), lung injury score, cell counts, and the plasma concentration of endothelin-1. At day 1, EVLWI was elevated (>or=7 mL/kg) in 28 (74%) patients and correlated with lung compliance (r=-.48, p=.002), Pao2/Fio2 (r=-.50, p=.001), lung injury score (r=.46, p=.004), roentgenogram quadrants (r=.39, p=.02), and platelet count (r=-.43, p=.007). At day 3, EVLWI correlated with compliance (r=-.51, p=.002), Pao2/Fio2 (r=-.49, p = .006), and lung injury score (r=.53, p=.003). At day 3, EVLWI and pulmonary vascular permeability indexes were higher in nonsurvivors (p<.05). The plasma concentration of endothelin-1 (mean+/-sd) was significantly higher in patients with elevated EVLWI (>or=7 mL/kg) (3.85+/-1.40 vs. 2.07+/-0.38 pg/mL, respectively). Twenty-two (59%) patients died before day 28.

CONCLUSIONS

In human septic shock, EVLWI demonstrated moderate correlation with markers of acute lung injury, such as lung compliance, oxygenation ratio, roentgenogram quadrants, and lung injury score. In nonsurvivors, EVLWI and permeability indexes were significantly increased at day 3. Thus, EVLWI might be of value as an indicator of prognosis and severity of sepsis-induced acute lung injury.

Tezosentan reduces the microvascular filtration coefficient in isolated lungs from rats subjected to cecum ligation and puncture

INTRODUCTION

We recently demonstrated that the non-selective endothelin-1 (ET-1) receptor blocker tezosentan antagonizes ovine acute lung injury (ALI) following infusion of endotoxin or ET-1 by reducing the enhanced lung microvascular pressure, although we could not exclude the possibility of a simultaneous decline in microvascular permeability. In the present study, our aim was to find out if tezosentan reverses the rise in microvascular filtration coefficient (Kfc) in rat lungs that have been isolated and perfused 12 h after cecum ligation and puncture (CLP) or infusion of ET-1.

METHODS

Wistar rats (n = 42) were subjected to CLP. Postoperatively, rats were randomized to a CLP group (n = 7) and a CLP + tezosentan group (n = 7); the latter received tezosentan 30 mg/kg. A sham-operated group (n = 5) underwent laparotomy without CLP. Twelve hours postoperatively, the lungs were isolated and perfused with blood from similarly treated rats that also were used to assess plasma concentration of ET-1 and protein kinase Calpha (PKCalpha) in lung tissue. Additionally, isolated blood perfused lungs from healthy rats were randomized to a control group (n = 8), an ET-1 group (n = 7) subjected to pulmonary arterial injection of ET-1 10 nM, and an ET-1 + tezosentan group (n = 7) that received tezosentan 30 mg/kg. All lung preparations received papaverine 0.1 microg/kg added to the perfusate for vasoplegia. Pulmonary hemodynamic variables, Kfc and lung compliance (CL) were assessed.

RESULTS

After CLP, the plasma concentration of ET-1 increased. Papaverine abolished the vasoconstrictor response to ET-1 and the pulmonary vascular pressures remained close to baseline throughout the experiments. Both CLP and injection of ET-1 caused significant changes in Kfc and CL that were prevented in tezosentan-treated rats. Compared to sham-operated animals, CLP increased the content of PKCalpha by 50% and 70% in the cytosolic and the membrane fractions of lung tissue homogenates, respectively. Tezosentan prevented the upregulation of PKCalpha in the membrane fraction.

CONCLUSION

In rat lungs isolated and perfused after CLP, tezosentan precludes both the increase in Kfc and the upregulation of PKCalpha in the membrane fraction of lung tissue.

Circulating cardiovascular markers and mediators in acute illness: an update

An update is given of the circulating markers and mediators of cardiovascular dysfunction in acute illness. Some of these circulating markers reflect mediator action on the peripheral vasculature, such as endothelium-derived endothelin and nitrite/nitritate, the stable end products of nitric oxide. Other markers mainly reflect actions on the heart, such as the natriuretic peptide family, released from the heart upon dilatation, serving as a marker of congestive heart failure and potentially having negative inotropic effects. Indeed, some factors may be both markers as well as mediators of cardiovascular dysfunction of the acutely ill and bear prognostic significance. Assessing circulating levels may help refine clinical judgment of the cardiovascular derangements encountered at the bedside, together with clinical signs and hemodynamic variables. For instance, assessing natriuretic peptides in patients with pulmonary edema of unclear origin may help to diagnose congestive heart failure and cardiogenic pulmonary edema, when the pulmonary capillary wedge pressure is not measured or inconclusive. Future aligning of hemodynamic abnormalities with patterns of circulating cardiovascular markers/mediators may help to stratify patients for inclusion in studies to assess the causes, response to therapy and prognosis of cardiovascular derangements in the acutely ill.

A new therapeutic approach for the treatment of sepsis

Despite important advances in understanding its pathophysiology, therapy for septic shock remains largely symptomatic and supportive. Aiming to elevate the systemic arterial blood pressure by using vasoconstrictor manoeuvers are preferred without paying much attention to the ischaemia produced at the peripheral tissues. Since, these maneuvers proved no remarkable success in reducing the mortality up to date, we now propose a different perspective in this manuscript. Although it is not always easy to distinguish the different phases of septic shock, at least two fundamentally different phases can be distinguished, i.e. (i) hyperdynamic phase and (ii) hypodynamic phase mandating the adoption of vasodilative and vasoconstrictive interventions, consequently. Additionally, endothelium-derived vasodilator and vasoconstrictor substances such as nitric oxide and endothelin play key roles in systemic inflammatory response syndrome that lead to fatal multiple organ dysfunction. Therefore, we hypothesize that the inhibition of nitric oxide production during earlier phases of septic shock combined with the blockade of endothelin receptors at later stages appear feasible and a novel strategy for the therapy of septic shock.

[Pathophysiological role of endotoxins, a common denominator to various diseases]

A growing number of investigations point to endotoxin or lipopolysaccharide as a central player in many pathophysiological states and diseases. Endotoxins are one of the most toxic biological contaminants continuously shed by both dead and live Gram negative bacteria. Endotoxins induce the primitive form of defense called innate immunity. Endotoxins have been related to inflammatory reactions observed in patients suffering from respiratory distress syndrome, multiorgan failure and septic shock, hepatic diseases, or in subjects affected by graft versus host disease after allogeneic transplantation. As our understanding of the molecular mechanisms underlying pathologies progresses, more diseases involving endotoxins emerge. Although these illnesses are multifactorial, the objective of this article is to review some of the common and distinct processes involving endotoxins in various disease states.

Pulmonary endothelium in acute lung injury: from basic science to the critically ill

BACKGROUND

Pulmonary endothelium is an active organ possessing numerous physiological, immunological, and metabolic functions. These functions may be altered early in acute lung injury (ALI) and further contribute to the development of acute respiratory distress syndrome (ARDS). Pulmonary endothelium is strategically located to filter the entire blood before it enters the systemic circulation; consequently its integrity is essential for the maintenance of adequate homeostasis in both the pulmonary and systemic circulations. Noxious agents that affect pulmonary endothelium induce alterations in hemodynamics and hemofluidity, promote interactions with circulating blood cells, and lead to increased vascular permeability and pulmonary edema formation.

OBJECTIVE

We highlight pathogenic mechanisms of pulmonary endothelial injury and their clinical implications in ALI/ARDS patients.

Endothelin A but not endothelin B receptor blockade reduces capillary permeability in severe experimental pancreatitis

INTRODUCTION

Microcirculatory disorders, in particular increased capillary permeability (CapPerm), contribute to the multiple organ dysfunction syndrome in severe acute pancreatitis (AP). Endothelin receptor antagonists (ET-RA) have been shown to stabilize capillary leakage and improve organ function in AP.

AIM

To find out which endothelin receptor subtype (ET-A or ET-B) mediates the changes in CapPerm.

METHODOLOGY

Severe AP was induced in rats by intraductal bile salt infusion and i.v. cerulein. Animals were randomized to receive (1) saline; (2) selective ET-A-RA (LU-135252; 30 mg/kg); (3) selective ET-B-RA (A-192621); (4) nonselective ET-RA (LU-135252; 120 mg/kg); or (5) combined ET-A/B-RA (30 mg/kg LU-135252 + A-192621). Capillary blood flow (CBF) and CapPerm in the pancreas and colon and leukocyte rolling in mesenteric venules were determined.

RESULTS

Selective ET-A-RA increased CBF and decreased CapPerm in the pancreas and colon by 90-147% and reduced leukocyte rolling in AP but had no effect in healthy controls. Selective ET-B-RA increased pancreatic CBF (2.3 +/- 0.03 versus 2.1 +/- 0.04 nL/min) and enhanced CapPerm in the pancreas and colon by 24-35% in healthy controls but had no effect in AP. Blockade of both receptors produced effects similar to but less pronounced than those of selective ET-A-RA.

CONCLUSIONS

Blockade of ET-A and ET-B receptors has different effects on CapPerm in healthy animals and those with AP. This may explain the inconclusive results reported with nonselective ET-RA. In severe AP, blockade of ET-A but not ET-B receptors reduces CapPerm.

Role of endothelin-1 in lung disease

Endothelin-1 (ET-1) is a 21 amino acid peptide with diverse biological activity that has been implicated in numerous diseases. ET-1 is a potent mitogen regulator of smooth muscle tone, and inflammatory mediator that may play a key role in diseases of the airways, pulmonary circulation, and inflammatory lung diseases, both acute and chronic. This review will focus on the biology of ET-1 and its role in lung disease.

A study of mechanisms underlying amitriptyline-induced acute lung function impairment

In this study possible mechanisms underlying the vaso- and bronchoconstriction caused by the tricyclic antidepressant drug amitriptyline in isolated rat lungs were investigated. Some features here are similar to those apparent in adult respiratory distress syndrome and acute lung injury. Amitriptyline exposure (50 and 100 microM) caused a dose-related, pronounced, and rapid vaso- (50 microM, 30 min, p < 0.001 and 100 microM, 30 min, p < 0.001) and bronchoconstriction (50 microM, 30 min, p = 0.01 and 100 microM, 30 min, p < 0.001). The maximal noted decrease in perfusion flow was 28 +/- 2.9% at 25 min and 80 +/- 4.5% at 30 min for 50 and 100 microM amitriptyline, respectively. The maximal noted decrease in airway conductance was 29 +/- 4.7% at 25 min and 68 +/- 5.0% at 30 min. To investigate mechanisms thought to be involved in amitriptyline-induced lung function impairment, lungs were treated with several different substances including antiinflammatory agents, antioxidants, inhibitors of enzymes involved in the arachidonic acid cascade, physiological antagonists, and neurogenic antagonists. A significant reduction of amitriptyline-induced vasoconstriction was observed when lungs were treated with the protein kinase inhibitor staurosporine (3 microM, 30 min, p < 0.001), the NO-donor S-nitrosoglutathione (100 microM, 30 min, p < 0.001) and the combined endothelin A/endothelin B receptor antagonist PD 145065. This latter inhibitor caused a significant attenuation of late vasoconstriction (1 microM, 60 min, p = 0.03). The amitriptyline-induced bronchoconstriction was attenuated by the beta(2)-agonist salbutamol (1 microM, 30 min, p = 0.03) and the platelet-activating factor antagonist WEB2086 (10 microM, 30 min, p = 0.03). Staurosporine had an initial protective effect on bronchoconstriction (3 microM, 5 min, p = 0.003), while PD145065 significantly decreased bronchoconstriction 60 min after start of amitriptyline exposure (1 microM, 30 min, p = 0.003). This indicates that endothelin as well as platelet activating factor and protein kinase activation are important in mediating amitriptyline-induced lung function impairment in our experimental model and perhaps also in acute lung injury.

Plasma endothelin levels and outcome in patients undergoing repair of ruptured infrarenal abdominal aortic aneurysm

BACKGROUND

Endothelin-1 (ET-1) is the most potent known vasoconstrictor. Elevated plasma levels have been demonstrated in patients with myocardial infarction, cardiogenic and septic shock, and respiratory, heart, and kidney failure, as well as in those undergoing elective abdominal aortic aneurysm (AAA) repair. However, endothelin levels have not previously been examined in patients undergoing repair of ruptured AAA. We hypothesized that hemorrhagic shock, lower torso ischemia, and reperfusion associated with ruptured AAA repair lead to increased synthesis and secretion of ET-1, which, in turn, predispose to organ failure, one of the principal causes of death in this condition.

METHODS

Fourteen patients were studied. Plasma levels of big ET-1 and ET-1 were measured immediately before operation and immediately before, 5 minutes, and 6 hours after aortic clamp release.

RESULTS

All patients survived for at least 24 hours after operation. Big ET-1 levels were above the normal range at one or more sample points in all patients, and the ET-1 levels were above the normal range in all survivors and four of five nonsurvivors. Five patients who died of organ failure had significantly lower big ET-1 levels at all sample points and significantly lower ET-1 levels after 5 minutes of reperfusion when compared with survivors. Preoperative ET-1 levels were significantly lower in eight patients who subsequently developed kidney failure than in six patients who did not.

CONCLUSION

Contrary to our original hypothesis, these novel data demonstrate that patients with ruptured AAA in whom fatal postoperative organ failure develops have significantly lower perioperative endothelin levels than survivors.

Effect of endothelin antagonists, including the novel ET(A) receptor antagonist LBL 031, on endothelin-1 and lipopolysaccharide-induced microvascular leakage in rat airways

1. The effect of the novel ET(A) receptor antagonist LBL 031 and other selective and mixed endothelin receptor antagonists on endothelin-1 (ET-1)-induced and lipopolysaccharide (LPS)-induced microvascular leakage was assessed in rat airways. 2. Intravenously administered ET-1 (1 nmole kg(-1)) or LPS (30 mg kg(-1)) caused a significant increase in microvascular leakage in rat airways when compared to vehicle treated animals. 3. Pre-treatment with the selective ET(A) receptor antagonists, LBL 031 or PD 156707, or the mixed ET(A/B) receptor antagonist, bosentan (each at 30 mg kg(-1)), reduced ET-1-induced leakage to baseline levels. ET-1-induced leakage was not reduced by pre-treatment with the ET(B) selective antagonist BQ 788 (3 mg kg(-1)). 4. Pre-treatment with the selective ET(A) receptor antagonist, LBL 031 (0.1 mg kg(-1)) or PD 156707 (10 mg kg(-1)), or the mixed ET(A/B) receptor antagonist, bosentan (30 mg kg(-1)), reduced LPS-induced leakage by 54, 48 and 59% respectively. LPS-induced leakage was not affected by pre-treatment with the ET(B) selective antagonist BQ 788 (3 mg kg(-1)). 5. The data suggests that ET-1-induced microvascular leakage in the rat airway is ET(A) receptor mediated and that part of the increase induced by LPS may be due to the actions of ET-1. Therefore, a potent ET(A) receptor selective antagonist, such as LBL 031, may provide a suitable treatment for inflammatory diseases of the airways, especially those involving LPS and having an exudative phase, such as the septic shock-induced adult respiratory distress syndrome.

Hemodynamic and cardiovascular effects of nitric oxide modulation in the therapy of septic shock

Nitric oxide synthase (NOS) of the inducible subtype (iNOS) plays a pivotal role in vasodilation associated with sepsis. Various biochemical pathways are involved, revealing targets for inhibiting the consequence of iNOS activation. Interactions of transcription factors, inducers, cofactors, and regulators of iNOS are important in understanding the development of iNOS inhibitors. Inhibition through L-arginine analogs, depletion of arginine, inhibition of cofactors, modulating gene transcription, and scavenging nitric oxide have been studied. Human studies were conducted only with nonselective L-arginine analogs. Reduction of mortality from sepsis was not reported. It is anticipated that iNOS-specific compounds will be clinically useful. The focus of future human trials will be on these agents. Although ideal therapy for treating vasodilation from sepsis is not available, research into the pathophysiology of NOS in sepsis clarified the complexities surrounding this therapeutic dilemma.

Endothelin in septic patients: effects on cardiovascular and renal function and its relationship to proinflammatory cytokines

OBJECTIVE

To determine the time course of big-endothelin (big-ET) and its relationship to proinflammatory cytokines and organ function in sepsis.

DESIGN

Prospective analysis in patients meeting criteria of severe sepsis as part of a multicenter study (RAMSES) with an anti-tumor necrosis factor monoclonal antibody F(ab')2 fragment (afelimomab).

SETTING

University hospital intensive care unit.

PATIENTS

A total of 23 nontrauma patients with severe sepsis or septic shock and ten multiple trauma patients. Septic patients were randomized for additional experimental treatment when initial interleukin (IL)-6 serum level was above 1000 pg/mL.

INTERVENTIONS

Randomized patients received 1.0 mg/kg afelimomab or placebo three times daily over 3 days in addition to standard treatment. In each patient, serial blood samples for plasma big-ET and cytokine determination as well as clinical data were collected over 28 days.

MEASUREMENTS AND MAIN RESULTS

Significantly increased concentrations of circulating big-ET were found in patients with severe sepsis as compared with healthy subjects. In septic patients, big-ET plasma levels were higher than in multiple trauma patients, and were more elevated in randomized than in nonrandomized patients. At study entry (day 0), big-ET reached a peak concentration and significantly correlated with IL-6 (r2 = .43) and IL-8 (r2 = .44) in patients with severe sepsis. Moreover, big-ET levels in septic patients, pooled over all observation days, correlated positively with pressure-adjusted heart rate, central venous pressure, pulmonary artery pressure, and pulmonary vascular resistance and correlated inversely with creatinine clearance (r2 = .54, .54, .59, .40, and .51, respectively, p = .0001). In all randomized septic patients, pressure-adjusted heart rate decreased from day 0 to day 2 in parallel with big-ET; however, a significant decrease in big-ET (day 0 to day 2) was only found in patients additionally treated with afelimomab.

CONCLUSIONS

In patients with severe sepsis, big-ET plasma levels are markedly increased, even above those of multiple trauma patients, in close relationship to IL-6 and IL-8, and with significant correlation to renal function and pulmonary vascular tone.

Endothelins and the lung

Since endothelins were discovered by Yanasigawa in 1988 it has been recognised that they may have an important role in lung pathophysiology. Despite their biological importance as vasoconstrictors the physiological role of endothelin has not yet been defined within the lungs. This review explores their role in acute and chronic disease. During acute inflammation and ischaemia-reperfusion injury cytokines may induce release of endothelin. This is important in the realm of acute lung injury and during surgical procedures such as cardiopulmonary operations including lung resections and transplantation. Complications of surgery including primary organ failure resulting in poor gas exchange as well as increased pulmonary vascular resistance have been linked to the presence of excessive endothelin. Endothelin may have an important role in transplantation biology. The complex process leading to successful lung transplantation includes optimising the donor with brain death, harvesting the lungs, managing acute and chronic rejection, and protecting the vital organs from toxic effects of immunosuppressants. During chronic disease processes, the mitotic action of endothelin may be important in vascular and airway remodelling by means of smooth muscle cell proliferation. We also explore recent advances in drug development, animal models and future directions for research.

ET-1-induced pulmonary vasoconstriction shifts from ET(A)- to ET(B)-receptor-mediated reaction after preconstriction

Endothelin-1 (ET-1) has been reported to induce pulmonary vasoconstriction via either ET(A) or ET(B) receptors, and vasorelaxation after ET-1 injection has been observed. Our study investigated the effects of ET-1 in isolated rabbit lungs, which were studied at basal tone (part I) and after preconstriction (U-46619; part II). Pulmonary arterial pressure (PAP) and lung weight gain were monitored continuously. In part I, ET-1 (10(-8) M; n = 6; control) was injected after pretreatment with the ET(A)-receptor antagonist BQ-123 (10(-6) M; n = 6) or the ET(B)-receptor antagonist BQ-788 (10(-6) M; n = 6). The same protocol was carried out in part II after elevation of pulmonary vascular tone. ET-1 induced an immediate PAP increase (DeltaPAP 4.3 +/- 0.4 mmHg at 10 min) that was attenuated by pretreatment with BQ-123 (P < 0.05 at 10 min and P < 0.01 thereafter) and that was more pronounced after BQ-788 (P < 0.01 at 10 min and P < 0.001 thereafter). In part II, ET-1 induced an immediate rise in PAP with a maximum after 5 min (DeltaPAP 6.3 +/- 1.4 mmHg), leveling off at DeltaPAP 3.2 +/- 0.2 mmHg after 15 min. Pretreatment with BQ-123 failed to attenuate the increase. BQ-788 significantly reduced the peak pressure at 5 min (0.75 +/- 0.4 mmHg; P < 0.001) as well as the plateau pressure thereafter (P < 0.01). We conclude that ET-1 administration causes pulmonary vasoconstriction independent of basal vascular tone, and, at normal vascular tone, the vasoconstriction seems to be mediated via ET(A) receptors. BQ-788 treatment resulted in even more pronounced vasoconstriction. After pulmonary preconstriction, ET(A) antagonism exerted no effects on PAP, whereas ET(B) antagonism blocked the PAP increase. Therefore, ET-1-induced pulmonary vasoconstriction is shifted from an ET(A)-related to an ET(B)-mediated mechanism after pulmonary vascular preconstriction.

Amitriptyline-induced release of endothelin-1 in isolated perfused and ventilated rat lungs

We have previously shown that tricyclic antidepressants can induce vaso- and bronchoconstriction as well as oedema formation in isolated perfused lungs. This is an effect similar to that seen clinically in adult respiratory distress syndrome. In order to investigate whether endothelin can be a mediator of this reaction, isolated perfused rat lungs were exposed to 0.1 mM amitriptyline via the pulmonary circulation, perfusate was collected and endothelin-1 present in the perfusate and lavage fluids was determined by radioimmunoassay. A significant increase in perfusate concentration of endothelin-1 was noted, with the highest release seen within the first 10 min. of exposure. Histamine and thromboxane have also been proposed as mediators in induction of adult respiratory distress syndrome. However, no increased amounts of these mediators were detected in the perfusate. Experiments where lungs were exposed to exogenous endothelin-1(0.1-1 nmol), both via the perfusate and via intratracheal instillation were conducted. Similar effects as observed with amitriptyline (0.1 mM) on lung function and perfusion flow were detected. In conclusion, the detection of endothelin-1 release in our lung model proposes a role for endothelin-1 in amitriptyline-induced vaso- and bronchoconstriction and possibly in adult respiratory distress syndrome type reaction. Further studies with this model are interesting in order to elucidate mechanisms behind the complex issue of adult respiratory distress syndrome-induction.

Differentiation of the peptidergic vasoregulatory response to standardized splanchnic hypoperfusion by acute hypovolaemia or sepsis in anaesthetized pigs

This study was performed to integratively investigate the vasoregulatory response during standardized splanchnic hypoperfusion in pigs. Splanchnic perfusion was reduced to 50% of baseline by: haemorrhage by 20 and 40% of the estimated total blood volume; femoral venous infusion of live E. coli to establish sepsis of systemic origin; portal venous infusion of live E. coli to establish sepsis of splanchnic origin. Invasive haemodynamic monitoring and radioimmunoassay analyses of arterial plasma concentrations of angiotensin II, endothelin-1 and atrial natriuretic peptide were carried out. Acute hypovolaemia reduced systemic and splanchnic vascular resistances following transient increases and increased angiotensin II levels (+587%), whereas endothelin-1 and atrial natriuretic peptide levels did not change significantly. Systemic sepsis following femoral venous infusion of E. coli resulted in increased splanchnic vascular resistance and increased levels of angiotensin II (+274%), endothelin-1 (+134%) and atrial natriuretic peptide (+185%). Infusion of E. coli via the portal venous route induced an increase in splanchnic vascular resistance associated with particularly elevated levels of angiotensin II (+1770%) as well as increased endothelin-1 (+201%) and atrial natriuretic peptide (+229%) concentrations. Hypovolaemia and sepsis, although standardized with a predefined level of splanchnic hypoperfusion, elicited differentiated cardiovascular and vasopeptidergic responses. Sepsis, particularly of portal origin, notably increased splanchnic vascular resistance related to increased production of the vasoconstrictors angiotensin II and endothelin-1. The role of atrial natriuretic peptide as a vasodilator seems to be of subordinate importance in hypovolaemia and sepsis.

Endothelin-1 and blood pressure after inhibition of nitric oxide synthesis in human septic shock

BACKGROUND

The systemic hypotension during human sepsis has been ascribed to increased production of nitric oxide (NO). Therefore, inhibitors of NO synthesis have been used in the treatment of hypotension in patients with septic shock. In addition, NO production may inhibit the synthesis and vasoconstrictor effects of endothelin-1 (ET-1). In this study, we tested whether ET-1 contributed to the vasopressor action of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in patients with severe septic shock.

METHODS AND RESULTS

Compared with healthy volunteers, patients with septic shock had increased plasma levels of nitrite/nitrate (37+/-5 [SEM] versus 12+/-5 mmol/L, P<0.01), the stable end products of NO metabolism, and ET-1 (45+/-7 versus 3+/-2 pg/mL, P<0.001). Plasma ET-1 concentration was not related to plasma nitrite/nitrate concentration or blood pressure. Continuous infusion of L-NAME (1 mg. kg-1. h-1 IV) for 12 hours increased mean arterial pressure by 43+/-5% and systemic vascular resistance by 64+/-10% (both P<0.01). The increase in blood pressure and systemic vascular resistance correlated positively with the level of ET-1 (both P<0. 005) but not with plasma nitrite/nitrate level. L-NAME infusion did not result in significant changes in the plasma concentrations of ET-1 or nitrite/nitrate.

CONCLUSIONS

NO and ET-1 may both play a role in the cardiovascular derangements of human sepsis. Although L-NAME does not increase ET-1 concentration in patients with septic shock, the vasopressor response induced by L-NAME depends on the plasma level of ET-1. These findings may indicate that inhibitors of NO synthesis unmask a tonic pressor response of ET-1 in human septic shock.

Different endothelins stimulate cytokine production by peritoneal macrophages and microglial cell line

Endothelins (ETs), potent vasoconstricting peptides, are produced by macrophages upon stimulation and may participate in the amplification or regulation of the inflammatory response. However, it is not clear whether ETs can act in an autocrine manner on macrophages and which role they play in relationship with other cytokines. To address these issues, we studied the effects of ETs on the production of inflammatory cytokines by mouse peritoneal macrophages or by a retrovirus-transformed microglial cell line. Here, we report that ET-2, but not ET-1 or ET-3, is able to stimulate the production of interleukin-1 (IL-1) and interleukin-6 (IL-6) by peptone-elicited mouse macrophages (pMO). In contrast, ET-3 and ET-1, but not ET-2, are active on microglial cells. No tumour necrosis factor-alpha (TNF-alpha) or nitric oxide (NO) were detected in the supernatants of ET-stimulated cultures. The activity of ET-2 on pMO was time and dose dependent and was inhibited by the addition of ETA and ETB receptor antagonists, BQ123 and IRL1038, respectively. In addition, when pMO were stimulated by interferon-gamma (IFN-gamma) in the presence of ET-2, a significant inhibition of IL-6 and IL-1 production was observed compared with the effects of the same doses of IFN-gamma or ET-2 used separately. The inhibition was specifically due to the activity of ET-2, since it was reversed by the addition of BQ123 or IRL1038. Similar results were seen when the content of NO in the supernatants of pMO stimulated by IFN-gamma plus ET-2 was evaluated. These results suggest that ETs may possess both a pro-inflammatory action on macrophages from different tissues and a regulatory activity on IFN-gamma.