Tezosentan-induced attenuation of lung injury in endotoxemic sheep is associated with reduced activation of protein kinase C

Tobacco smoking and vascular biology and function: evidence from human studies

Tobacco cigarette smoking is among the most complex and least understood health risk factors. A deeper insight into the pathophysiological actions of smoking exposure is of special importance as smoking is a major cause of chronic non-communicable diseases, in particular of cardiovascular disease as well as risk factors such as atherosclerosis and arterial hypertension. It is well known that smoking exerts its negative effects on cardiovascular health through various interdependent pathophysiological actions including hemodynamic and autonomic alterations, oxidative stress, inflammation, endothelial dysfunction, thrombosis, and hyperlipidemia. Importantly, impaired vascular endothelial function is acknowledged as an early key event in the initiation and progression of smoking-induced atherosclerosis. Increasing evidence from human studies indicates that cigarette smoke exposure associates with a pathological state of the vascular endothelium mainly characterized by reduced vascular nitric oxide bioavailability due to increased vascular superoxide production. In the present overview, we provide compact evidence on the effects of tobacco cigarette smoke exposure on vascular biology and function in humans centered on main drivers of adverse cardiovascular effects including endothelial dysfunction, inflammation, and oxidative stress.

Therapeutic regimens of endotoxaemia in sheep

Endotoxaemia is an inflammatory condition which happens due to the presence of outer cell wall layer of Gram-negative bacteria in blood circulation, containing lipopolysaccharide commonly known as endotoxin. This condition causes high mortality in affected animals and sheep are highly susceptible in this regard. Several researchers have emphasised the therapeutic regimens of endotoxaemia and its sequels in sheep. Furthermore, sheep are among the most commonly used animal species in experimental studies on endotoxaemia, and for the past five decades, ovine models have been employed to evaluate different aspects of endotoxaemia. Currently, there are several studies on experimentally induced endotoxaemia in sheep, and information regarding novel therapeutic protocols in this species contributes to better understanding and treating the condition. This review aims to specifically introduce various treatment methods of endotoxaemia in sheep.

EGCG promotes PRKCA expression to alleviate LPS-induced acute lung injury and inflammatory response

Acute lung injury (ALI), which could be induced by multiple factors such as lipopolysaccharide (LPS), refer to clinical symptoms of acute respiratory failure, commonly with high morbidity and mortality. Reportedly, active ingredients from green tea have anti-inflammatory and anticancer properties, including epigallocatechin-3-gallate (EGCG). In the present study, protein kinase C alpha (PRKCA) is involved in EGCG protection against LPS-induced inflammation and ALI. EGCG treatment attenuated LPS-stimulated ALI in mice as manifested as improved lung injury scores, decreased total cell amounts, neutrophil amounts and macrophage amounts, inhibited the activity of MPO, decreased wet-to-dry weight ratio of lung tissues, and inhibited release of inflammatory cytokines TNF-α, IL-1β, and IL-6. PRKCA mRNA and protein expression showed to be dramatically decreased by LPS treatment while reversed by EGCG treatment. Within LPS-stimulated ALI mice, PRKCA silencing further aggravated, while PRKCA overexpression attenuated LPS-stimulated inflammation and ALI through MAPK signaling pathway. PRKCA silencing attenuated EGCG protection. Within LPS-induced RAW 264.7 macrophages, EGCG could induce PRKCA expression. Single EGCG treatment or Lv-PRKCA infection attenuated LPS-induced increases in inflammatory factors; PRKCA silencing could reverse the suppressive effects of EGCG upon LPS-stimulated inflammatory factor release. In conclusion, EGCG pretreatment inhibits LPS-induced ALI in mice. The protective mechanism might be associated with the inhibitory effects of PRKCA on proinflammatory cytokine release via macrophages and MAPK signaling pathway.

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.

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).

Endothelin receptor antagonist improves donor lung function in an ex vivo perfusion system

BACKGROUND

A lung transplant is the last resort treatment for many patients with advanced lung disease. The majority of donated lungs come from donors following brain death (BD). The endothelin axis is upregulated in the blood and lung of the donor after BD resulting in systemic inflammation, lung damage and poor lung graft outcomes in the recipient. Tezosentan (endothelin receptor blocker) improves the pulmonary haemodynamic profile; however, it induces adverse effects on other organs at high doses. Application of ex vivo lung perfusion (EVLP) allows the development of organ-specific hormone resuscitation, to maximise and optimise the donor pool. Therefore, we investigate whether the combination of EVLP and tezosentan administration could improve the quality of donor lungs in a clinically relevant 6-h ovine model of brain stem death (BSD).

METHODS

After 6 h of BSD, lungs obtained from 12 sheep were divided into two groups, control and tezosentan-treated group, and cannulated for EVLP. The lungs were monitored for 6 h and lung perfusate and tissue samples were processed and analysed. Blood gas variables were measured in perfusate samples as well as total proteins and pro-inflammatory biomarkers, IL-6 and IL-8. Lung tissues were collected at the end of EVLP experiments for histology analysis and wet-dry weight ratio (a measure of oedema).

RESULTS

Our results showed a significant improvement in gas exchange [elevated partial pressure of oxygen (P = 0.02) and reduced partial pressure of carbon dioxide (P = 0.03)] in tezosentan-treated lungs compared to controls. However, the lungs hematoxylin-eosin staining histology results showed minimum lung injuries and there was no difference between both control and tezosentan-treated lungs. Similarly, IL-6 and IL-8 levels in lung perfusate showed no difference between control and tezosentan-treated lungs throughout the EVLP. Histological and tissue analysis showed a non-significant reduction in wet/dry weight ratio in tezosentan-treated lung tissues (P = 0.09) when compared to control.

CONCLUSIONS

These data indicate that administration of tezosentan could improve pulmonary gas exchange during EVLP.

B-type natriuretic peptide is upregulated by c-Jun N-terminal kinase and contributes to septic hypotension

B-type natriuretic peptide (BNP) is secreted by ventricular cardiomyocytes in response to various types of cardiac stress and has been used as a heart failure marker. In septic patients, increased BNP suggests poor prognosis; however, no causal link has been established. Among various effects, BNP decreases systemic vascular resistance and increases natriuresis that leads to lower blood pressure. We previously observed that JNK inhibition corrects cardiac dysfunction and suppresses cardiac BNP mRNA in endotoxemia. In this study, we investigated the transcriptional mechanism that regulates BNP expression and the involvement of plasma BNP in causing septic hypotension. Our in vitro and in vivo findings confirmed that activation of JNK signaling increases BNP expression in sepsis via direct binding of c-Jun in activating protein–1 (AP-1) regulatory elements of the Nppb promoter. Accordingly, genetic ablation of BNP, as well as treatment with a potentially novel neutralizing anti-BNP monoclonal antibody (19B3) or suppression of its expression via administration of JNK inhibitor SP600125 improved cardiac output, stabilized blood pressure, and improved survival in mice with polymicrobial sepsis. Therefore, inhibition of JNK signaling or BNP in sepsis appears to stabilize blood pressure and improve survival.

Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 Regulates LPS-Induced Inflammation and Alveolar Remodeling in the Developing Lung

In premature infants, sepsis is associated with alveolar simplification manifesting as bronchopulmonary dysplasia. The redox-dependent mechanisms underlying sepsis-induced inflammation and alveolar remodeling in the immature lung remain unclear. We developed a neonatal mouse model of sepsis-induced lung injury to investigate whether nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) regulates Toll-like receptor (TLR)-mediated inflammation and alveolar remodeling. Six-day-old NOX2^+/+ and NOX2^-/- mice were injected with intraperitoneal LPS to induce sepsis. Lung inflammation and canonical TLR signaling were assessed 24 hours after LPS. Alveolar development was examined in 15-day-old mice after LPS on Day 6. The in vivo efficacy of a NOX2 inhibitor (NOX2-I) on NOX2 complex assembly and sepsis-induced lung inflammation were examined. Lung cytokine expression and neutrophil influx induced with sepsis in NOX2^+/+ mice was decreased by >50% in NOX2^-/- mice. LPS-induced TLR4 signaling evident by inhibitor of NF-κB kinase-β and mitogen-activated protein kinase phosphorylation, and nuclear factor-κB/AP-1 translocation were attenuated in NOX2^-/- mice. LPS increased matrix metalloproteinase 9 while decreasing elastin and keratinocyte growth factor levels in NOX2^+/+ mice. An LPS-induced increase in matrix metalloproteinase 9 and decrease in fibroblast growth factor 7 and elastin were not evident in NOX2^-/- mice. An LPS-induced reduction in radial alveolar counts and increased mean linear intercepts were attenuated in NOX2^-/- mice. LPS-induced NOX2 assembly evident by p67phox/gp91phox coimmunoprecipitation was disrupted with NOX2-I. NOX2-I also mitigated LPS-induced cytokine expression, TLR pathway signaling, and alveolar simplification. In a mouse model of neonatal sepsis, NOX2 regulates proinflammatory TLR signaling and alveolar remodeling induced by a single dose of LPS. Our results provide mechanistic insight into the regulation of sepsis-induced alveolar remodeling in the developing lung.

The role of endothelin-1 and endothelin receptor antagonists in inflammatory response and sepsis

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor, mainly secreted by endothelial cells. It acts through two types of receptors: ETA and ETB. Apart from a vasoconstrictive action, ET-1 causes fibrosis of the vascular cells and stimulates production of reactive oxygen species. It is claimed that ET-1 induces proinflammatory mechanisms, increasing superoxide anion production and cytokine secretion. A recent study has shown that ET-1 is involved in the activation of transcription factors such as NF-κB and expression of proinflammatory cytokines including TNF-α, IL-1, and IL-6. It has been also indicated that during endotoxaemia, the plasma level of ET-1 is increased in various animal species. Some authors indicate a clear correlation between endothelin plasma level and morbidity/mortality rate in septic patients. These pathological effects of ET-1 may be abrogated at least partly by endothelin receptor blockade. ET-1 receptor antagonists may be useful for prevention of various vascular diseases. This review summarises the current knowledge regarding endothelin receptor antagonists and the role of ET-1 in sepsis and inflammation.

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.

Endothelin receptor A antagonism attenuates renal medullary blood flow impairment in endotoxemic pigs

Background

Endothelin-1 is a potent endogenous vasoconstrictor that contributes to renal microcirculatory impairment during endotoxemia and sepsis. Here we investigated if the renal circulatory and metabolic effects of endothelin during endotoxemia are mediated through activation of endothelin-A receptors.

Methods and Findings

A randomized experimental study was performed with anesthetized and mechanically ventilated pigs subjected to Escherichia coli endotoxin infusion for five hours. After two hours the animals were treated with the selective endothelin receptor type A antagonist TBC 3711 (2 mg⋅kg⁻¹, n = 8) or served as endotoxin-treated controls (n = 8). Renal artery blood flow, diuresis and creatinine clearance decreased in response to endotoxemia. Perfusion in the cortex, as measured by laser doppler flowmetry, was reduced in both groups, but TBC 3711 attenuated the decrease in the medulla (p = 0.002). Compared to control, TBC 3711 reduced renal oxygen extraction as well as cortical and medullary lactate/pyruvate ratios (p<0.05) measured by microdialysis. Furthermore, TBC 3711 attenuated the decline in renal cortical interstitial glucose levels (p = 0.02) and increased medullary pyruvate levels (p = 0.03). Decreased creatinine clearance and oliguria were present in both groups without any significant difference.

Conclusions

These results suggest that endothelin released during endotoxemia acts via endothelin A receptors to impair renal medullary blood flow causing ischemia. Reduced renal oxygen extraction and cortical levels of lactate by TBC 3711, without effects on cortical blood flow, further suggest additional metabolic effects of endothelin type A receptor activation in this model of endotoxin induced acute kidney injury.

Radiographic lung density assessed by computed tomography is associated with extravascular lung water content

BACKGROUND

We hypothesized that in acute lung injury (ALI), the volume of pulmonary tissue with aqueous density, as determined by spiral computed tomography (CT), is associated with extravascular lung water content. Our aim was to compare tissue volume index, as assessed by CT, before and after oleic acid-induced ALI, with extravascular lung water indexes (EVLWI), determined with single transpulmonary thermodilution (EVLWI(STD)), thermal-dye dilution (EVLWI(TDD)), and postmortem gravimetry (EVLWI(G)).

METHODS

Seven instrumented sheep received an intravenous infusion of oleic acid 0.08 ml/kg (OA group) and four animals had vehicle only (Control group). The day before, and immediately after the experiment, sheep were anesthetized to undergo quantitative CT examinations during a short breath hold. Hemodynamics, oxygenation, EVLWI(STD), and EVLW(TDD) were registered. Linear regression analysis was used to assess the relationships between EVLWI(STD), EVLW(TDD), EVLWI(G), and lung tissue volume index (TVI(CT)) determined with CT.

RESULTS

In the OA group, total lung volume increased compared with Controls. Poorly and non-aerated lung volumes increased a 3.6- and 4.9-fold, respectively, and TVI(CT) almost doubled. EVLWI(STD), EVLWI(TDD), and TVI(CT) were associated significantly with EVLWI(G) (r=0.85, 0.90, and 0.88, respectively; P<0.001). TVI(CT) deviated from the reference EVLWI(G) values to the greatest extent with a mean bias +/- 2SD of 4.0 +/- 6.0 ml/kg.

CONCLUSIONS

In ovine oleic acid-induced ALI, lung tissue volume, as assessed by quantitative CT, is in close agreement with EVLWI, as determined by indicator dilution methods and postmortem gravimetry, but overestimates lung fluid content.

Sildenafil attenuates pulmonary arterial pressure but does not improve oxygenation during ARDS

Objective

Pulmonary hypertension is a characteristic feature of acute respiratory distress syndrome (ARDS) and contributes to mortality. Administration of sildenafil in ambulatory patients with pulmonary hypertension improves oxygenation and ameliorates pulmonary hypertension. Our aim was to determine whether sildenafil is beneficial for patients with ARDS.

Design

Prospective, open-label, multicenter, interventional cohort study.

Setting

Medical-surgical ICU of two university hospitals.

Patients

Ten consecutive patients meeting the NAECC criteria for ARDS.

Interventions

A single dose of 50 mg sildenafil citrate administered via a nasogastric tube.

Main results

Administration of sildenafil in patients with ARDS decreased mean pulmonary arterial pressure from 25 to 22 mmHg (P = 0.022) and pulmonary artery occlusion pressure from 16 to 13 mmHg (P = 0.049). Systemic mean arterial pressures were markedly decreased from 81 to 75 mmHg (P = 0.005). Sildenafil did not improve pulmonary arterial oxygen tension, but resulted in a further increase in the shunt fraction.

Conclusion

Although sildenafil reduced pulmonary arterial pressures during ARDS, the increased shunt fraction and decreased arterial oxygenation render it unsuitable for the treatment of patients with ARDS.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-1754-3) contains supplementary material, which is available to authorized users.

Role of endothelin-1 in acute lung injury

The alveolar-capillary membrane serves as a barrier that prevents the accumulation of fluid in the alveolar space and restricts the diffusion of large solutes while facilitating an efficient gas exchange. When this barrier becomes dysfunctional, patients develop acute lung injury (ALI), which is characterized by pulmonary edema and increased lung inflammation that leads to a life-threatening impairment of gas exchange. In addition to the increase of inflammatory cytokines, plasma levels of endothelin-1 (ET-1), which is a primarily endothelium-derived vasoconstrictor, are increased in patients with ALI. As patients recover, ET-1 levels decrease, which suggests that ET-1 may not only be a marker of endothelial dysfunction but may have a role in the pathogenesis of ALI. While pulmonary edema accumulates, alveolar fluid clearance (AFC) is of critical importance, as failure to return to normal clearance is associated with poor prognosis in patients with pulmonary edema. AFC involves active transport mechanisms where sodium (Na(+)) is actively transported from the alveolar airspaces, across the alveolar epithelium, and into the pulmonary circulation, which creates an osmotic gradient that is responsible for the clearance of lung edema. In this article, we review the relevance of ET-1 in the development of ALI, not only as a vasoconstrictor molecule but also by inhibiting AFC via the activation of endothelial ET-B receptors and generation. Furthermore, this review highlights the therapeutic role of drugs such as beta-adrenergic agonists and, in particular, of endothelin receptor antagonists in patients with ALI.

Respiratory burst function of ovine neutrophils

BACKGROUND

Respiratory burst function resulting in the release of reactive oxygen species such as superoxide anion (O2-) from neutrophils is one of the key mechanisms of the innate immune system, and maladaptive control of this mechanism is thought to play a pivotal role in the development of pathologies such as acute lung injury and sepsis. Ovine models of these pathologies are limited by the poor understanding of ovine neutrophil respiratory burst function.

RESULTS

Aspects of ovine neutrophil respiratory burst function to be characterised were: i) the maximum rate of O2- generated (Vmax); ii) the time taken to reach Vmax; iii) the total amount of O2- generated during the reaction; and iv) the duration of the reaction. As well as for unstimulated neutrophils, these aspects were also characterised after incubation with a priming agonist (platelet activating factor [PAF], tumour necrosis factor alpha [TNF-alpha] and lipopolysaccharides [LPS]) activating agonists (N-formylmethionyl-leucyl-phenylalanine [fMLP] and phorbol 12-myristate 13-acetate [PMA]) or a combination of a priming and an activating agonist. In the absence of priming or activating agonists, ovine neutrophils displayed a low level of respiratory burst function which was not enhanced by either PAF, TNF-alpha, LPS or fMLP, but was significantly enhanced by PMA. The PMA-induced respiratory burst function was further enhanced by pre-incubation with PAF, but not with TNF-alpha or LPS. By varying the length of pre-incubation with PAF it was demonstrated that this effect decreased as the duration of pre-incubation with PAF increased, and that PAF was enhancing PMA's effects rather than PMA enhancing PAF's effects.

CONCLUSION

This study successfully adapted a commonly used method of measuring human neutrophil respiratory burst function to characterise different aspects of ovine neutrophil respiratory burst function. This improved understanding of ovine neutrophils will facilitate the validitation of ovine biomedical models of human pathologies in which neutrophils have been implicated.

Calpain-1 induces apoptosis in pulmonary microvascular endothelial cells under septic conditions

This study was to investigate the role of calpain in the apoptosis of pulmonary microvascular endothelial cells (PMEC) during septic plasma stimulation. Septic plasma was collected from endotoxemic mice. In cultured PMEC, incubation with septic plasma stimulated calpain activation, increased caspase-3 activity and induced apoptotic cell death. These effects of septic plasma were abrogated by knockdown of calpain-1 but not calpain-2 using specific siRNA. Consistently, treatment with calpain inhibitor-III, or over-expression of calpastatin, an endogenous calpain inhibitor significantly decreased apoptosis induced by septic plasma. Septic plasma also induced NADPH oxidase activation and reactive oxygen species (ROS) production. Inhibiting NADPH oxidase or scavenging ROS attenuated calpain activity and decreased apoptosis in PMEC during septic plasma stimulation. In summary, our study demonstrates that ROS produced from NADPH oxidase stimulates calpain-1 activation, which induces apoptosis under septic conditions. Thus, targeting calpain-1/calpastatin may represent a potential strategy to protect against endothelial injury in sepsis.

Endothelin receptor antagonism by tezosentan attenuates lung injury induced by aortic ischemia-reperfusion

Tezosentan is a novel dual endothelin receptor antagonist. The purpose of this study was to examine the effect of tezosentan on lung injury induced by abdominal aortic ischemia-reperfusion (IR) in rats. Thirty-two Wistar-albino rats were randomized into four groups (eight per group) as follows: control group (sham laparotomy), aortic IR group (120 min ischemia and 120 min reperfusion), aortic IR + tezosentan group (a bolus intravenous injection of 10 mg/kg tezosentan before ischemia plus continuous intravenous infusion of 1 mg/kg/hr tezosentan during 120 min ischemia and 120 min reperfusion), and control + tezosentan. Blood and lung tissue samples were obtained for biochemical analysis. Protein concentrations in bronchoalveolar lavage fluid and lung wet/dry weight ratios were measured. A histological evaluation was also done. Aortic IR significantly increased (p < 0.05 vs. control group) and tezosentan significantly decreased (p < 0.05 vs. aortic IR group) the plasma level of tumor necrosis factor-alpha; lung tissue levels of malondialdehyde, catalase, and myleperoxidase; and protein concentration in bronchoalveolar lavage fluid and lung wet/dry weight ratio. Histological evaluation showed that tezosentan attenuated the morphological changes associated with lung injury. The results of this study indicate that tezosentan attenuates lung injury induced by aortic IR in rats. We propose that this protective effect of tezosentan is due to (1) reduced systemic inflammatory response, (2) reduced oxidative stress and lipid peroxidation in lung tissue, (3) reduced pulmonary microvascular leakage, and (4) inhibition of leukocyte infiltration into lung tissue.

Recombinant human activated protein C attenuates endotoxin-induced lung injury in awake sheep

Introduction

Acute lung injury often complicates severe sepsis. In Gram-negative sepsis, bacterial endotoxin activates both coagulation and inflammation. Enhanced lung vascular pressures and permeability, increased extravascular lung water content and deteriorated gas exchange characterize ovine endotoxin-induced lung injury, a frequently used model of acute lung injury. Recombinant human activated protein C (rhAPC), with its anticoagulant, anti-inflammatory, fibrinolytic and antiapoptotic effects, reportedly reduces the respirator-dependent days and the mortality of patients with severe sepsis. We speculate whether rhAPC antagonizes endotoxin-induced lung injury in sheep.

Methods

Two groups of sheep were exposed to Escherichia coli endotoxin (lipopolysaccharide) 15 ng/kg/minute intravenously from 0 to 24 hours; one group received only lipopolysaccharide throughout (n = 8), and the other group received lipopolysaccharide in combination with rhAPC 24 μg/kg/hour from 4 to 24 hours (n = 9). In addition, one group received rhAPC as above as the only intervention (n = 4), and four sham-operated sheep were used for determination of the α and ε isoforms of protein kinase C in pulmonary tissue. Data were assessed by one-way analysis of variance for repeated measurements. Biochemical data were analyzed using Student's t test, or using the Mann–Whitney U test when appropriate.

Results

Infusion of endotoxin caused lung injury, manifested by increments in pulmonary artery pressure, in pulmonary micro-occlusion pressure, in pulmonary vascular downstream resistance, in pulmonary vascular permeability index, in extravascular lung water index and in deterioration of oxygenation that were all attenuated by infusion of rhAPC. Endotoxemia led to changes in inflammation and coagulation, including pulmonary neutrophil accumulation paralleled by increased TNFα and decreased protein C and fibrinogen in animal plasma, which all improved following infusion of rhAPC. Moreover, rhAPC prevented the translocation of protein kinase C α and ε isoforms from the cytosolic fraction of lung tissue extracts.

Conclusion

In awake sheep, rhAPC alleviates endotoxin-induced lung injury – as characterized by improvements of oxygenation, coagulation and inflammation, as well as by reversal of pulmonary hemodynamic and volumetric changes.

Mixed endothelin receptor antagonism with tezosentan improves intestinal microcirculation in endotoxemic shock

BACKGROUND

Microcirculatory dysfunction is a common feature of sepsis. The potent vasoconstrictor endothelin (ET) is released in sepsis and endotoxemia, potentially contributing to sepsis-induced microcirculatory failure. In this study we tested the hypothesis that mixed ET receptor antagonism with tezosentan would improve splanchnic microcirculatory blood flow in acute porcine endotoxemia.

MATERIALS AND METHODS

Sixteen anesthetized and mechanically ventilated pigs received an infusion of endotoxin for 300 min. After 120 min eight pigs received a bolus dose of tezosentan 1 mg/kg followed by an infusion of tezosentan of 1 mg/kg/h throughout the experiment. Eight pigs served as endotoxin controls. Laser Doppler flowmetry was used to measure microcirculatory blood flow in the liver and in the ileal and colon mucosa. PCO(2) in the ileal mucosa was measured by air tonometry and portal vein flow by an ultrasonic flow probe.

RESULTS

Endotoxin administration induced a state of shock with impaired splanchnic microcirculatory blood flow. Microcirculation in the mucosa of the colon and ileum and mucosal-arterial PCO(2) gap were improved by tezosentan. Portal vein flow was increased, but hepatic microcirculatory blood flow was not significantly improved. Tezosentan preserved cardiac index and decreased pulmonary capillary wedge pressure compared to controls, without causing any differences in the heart rate or mean arterial blood pressure response. Tezosentan also distinctly improved pH and arterial lactate values.

CONCLUSIONS

The findings of this study indicate that ET is involved in the microcirculatory dysfunction seen in the ileal and colon mucosa in early endotoxemia. Moreover, this detrimental effect was counteracted by i.v. administration of the mixed ET receptor antagonist tezosentan.

Role of oxidants in lung injury during sepsis

The role of oxidative stress has been well appreciated in the development of sepsis-induced acute lung injury (ALI). Oxidative stress in sepsis-induced ALI is believed to be initiated by products of activated lung macrophages and infiltrated neutrophils, promptly propagating to lung epithelial and endothelial cells. This leads to tissue damage and organ dysfunction. On stimulation, neutrophils (PMNs) enable their migration machinery. The lung undergoes changes favoring adhesion and transmigration of PMNs, resulting in PMN accumulation in lung, which is a characteristic of sepsis-induced ALI. Oxidative stress turns on the redox-sensitive transcription factors (NF-kappaB, AP-1), resulting in a large output of proinflammatory cytokines and chemokines, which further aggravate inflammation and oxidative stress. During the process, transcription factor nuclear factor-erythroid 2-p45-related factor 2 (Nrf2) and heme oxygenase (HO) appear to play the counterbalancing roles to limit the propagation of oxidative stress and inflammatory responses in lung. Many antioxidants have been tested to treat sepsis-induced ALI in animal models and in patients with sepsis. However, the results are inconclusive. In this article, we focus on the current understanding of the pathogenesis of sepsis-induced ALI and novel antioxidant strategies for therapeutic purposes.

Effects of the dual endothelin receptor antagonist tezosentan and hypertonic saline/dextran on porcine endotoxin shock

AIM

To evaluate the haemodynamic effects of the dual endothelin receptor antagonist tezosentan, both alone and combined with hypertonic saline/dextran (HSD), on porcine endotoxin shock, with focus on cardiopulmonary circulation. The effects on gas exchange and short-term survival were also studied.

METHODS

A prospective, randomized experimental study was carried out. Thirty-two anaesthetized pigs underwent pulmonary and carotid artery catheterization. Following haemodynamic stabilization and baseline measurements, endotoxaemia was induced by an Escherichia coli-endotoxin infusion over 180 min and the animals observed another 120 min. After 60 min of endotoxaemia, directly before intervention, animals were randomized into four groups: a tezosentan group, an HSD group, a combined tezosentan/HSD group and a control group. The consequent haemodynamic effects and blood gas results were recorded.

RESULTS

The endotoxin infusion reduced mean arterial blood pressure from 111 +/- 14 (mean +/- standard deviation) to 77 +/- 27 mmHg and cardiac index from 126.9 +/- 27.2 to 109.3 +/- 22.6 mL min(-1) kg(-1) within 90 min in the control group. In addition, endotoxin simultaneously increased mean pulmonary artery pressure from 24 +/- 17 to 38 +/- 19 mmHg and reduced arterial oxygenation from 18.9 +/- 2.0 to 12.2 +/- 5.3 kPa. Tezosentan, alone and combined with HSD, reversed the pulmonary hypertension and prevented the reduction in cardiac index and arterial oxygenation, resulting in reduced metabolic acidosis. Additionally, in the tezosentan group, the mean arterial blood pressure was reduced to the same level as in controls, an effect not prevented by the addition of HSD. It was found that all three interventions improved survival rates.

CONCLUSION

Tezosentan, alone and in combination with HSD, improved cardiac index and arterial oxygenation. The addition of HSD to tezosentan treatment did not improve the endotoxin-induced hypotension, but beneficial effects on microcirculation and systemic oxygenation were seen despite low perfusion pressure, as indicated by increased SvO(2) and reduced metabolic acidosis.

Role of P-Selectin in Platelet Sequestration in Pulmonary Capillaries during Endotoxemia

BACKGROUND

There is growing evidence that platelets accumulate in the lung and contribute to the pathogenesis of acute lung injury during endotoxemia. The aims of the present study were to localize platelet sequestration in the pulmonary microcirculation and to investigate the role of P-selectin as a molecular mechanism of platelet endothelial cell interaction.

METHODS

We used in vivo fluorescence microscopy to quantify the kinetics of fluorescently labeled erythrocytes and platelets in alveolar capillary networks in rabbit lungs.

RESULTS

Six hours after onset of endotoxin infusion we observed a massive rolling along and firm adherence of platelets to lung capillary endothelial cells whereas under control conditions no platelet sequestration was detected. P-selectin was expressed on the surface of separated platelets which were incubated with endotoxin and in lung tissue. Pretreatment of platelets with fucoidin, a P-selectin antagonist, significantly attenuated the endotoxin-induced platelet rolling and adherence. In contrast, intravenous infusion of fucoidin in endotoxin-treated rabbits did not inhibit platelet sequestration in pulmonary capillaries.

CONCLUSION

We conclude that platelets accumulate in alveolar capillaries following endotoxemia. P-selectin expressed on the surface of platelets seems to play an important role in mediating this platelet-endothelial cell interaction.

The last 10 amino acid residues beyond the hydrophobic motif are critical for the catalytic competence and function of protein kinase Calpha

The segment C-terminal to the hydrophobic motif at the V5 domain of protein kinase C (PKC) is the least conserved both in length and in amino acid identity among all PKC isozymes. By generating serial truncation mutants followed by biochemical and functional analyses, we show here that the very C terminus of PKCalpha is critical in conferring the full catalytic competence to the kinase and for transducing signals in cells. Deletion of one C-terminal amino acid residue caused the loss of approximately 60% of the catalytic activity of the mutant PKCalpha, whereas deletion of 10 C-terminal amino acid residues abrogated the catalytic activity of PKCalpha in immune complex kinase assays. The PKCalpha C-terminal truncation mutants were found to lose their ability to activate mitogen-activated protein kinase, to rescue apoptosis induced by the inhibition of endogenous PKC in COS cells, and to augment melatonin-stimulated neurite outgrowth. Furthermore, molecular dynamics simulations revealed that the deletion of 1 or 10 C-terminal residues results in the deformation of the V5 domain and the ATP-binding pocket, respectively. Finally, PKCalpha immunoprecipitated using an antibody against its C terminus had only marginal catalytic activity compared with that of the PKCalpha immunoprecipitated by an antibody against its N terminus. Therefore, the very C-terminal tail of PKCalpha is a novel determinant of the catalytic activity of PKC and a promising target for selective modulation of PKCalpha function. Molecules that bind preferentially to the very C terminus of distinct PKC isozymes and suppress their catalytic activity may constitute a new class of selective inhibitors of PKC.

Year in review 2005: Critical Care--respirology: mechanical ventilation, infection, monitoring, and education

We summarize all original research in the field of respiratory intensive care medicine published in 2005 in Critical Care. Twenty-seven articles were grouped into the following categories and subcategories to facilitate rapid overview: mechanical ventilation (physiology, spontaneous breathing during mechanical ventilation, high frequency oscillatory ventilation, side effects of mechanical ventilation, sedation, and prone positioning); infection (pneumonia and sepsis); monitoring (ventilatory monitoring, pulmonary artery catheter and pulse oxymeter); and education (training and health outcome).

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.

Endothelin antagonists: new bullets against lung injury?

Acute lung injury is a syndrome of inflammation and of increased permeability of the blood–gas barrier. Endothelins are thought to exert proinflammatory effects. Kuklin and colleagues show that the endothelin receptor antagonist tezosentan reduces pulmonary edema in endotoxemic sheep, in parallel with a prevention of protein kinase C-α activation. In turn, the level of some cytokines increased after tezosentan treatment. Whether these contrasting effects of endothelin blockade on inflammatory mechanisms have clinical relevance and whether these agents might benefit patients with acute lung injury is unknown.