Stylianos E. Orfanos

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

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

Angiopoietin-2 is increased in severe sepsis: correlation with inflammatory mediators.

Objective: Angiopoietin (Ang)‐2 is an endothelium‐specific growth factor, regulated by proinflammatory stimuli, that destabilizes vascular endothelium and increases vascular leakage; consequently, Ang‐2 may contribute to sepsis pathophysiology. We have studied 1) serum Ang‐2 levels in critically‐ill patients and investigated potential relationships with inflammatory mediators and indices of disease severity and 2) the effect of sepsis‐related inflammatory mediators on Ang‐2 production by lung endothelium in vitro. Design: Prospective clinical study followed by cell culture studies. Setting: General intensive care unit and research laboratory of a university hospital. Subjects: Human and bovine lung microvascular endothelial cells and 61 patients (32 men). Patients were grouped according to their septic stage as having: no systemic inflammatory response syndrome (n = 6), systemic inflammatory response syndrome (n = 8), sepsis (n = 16), severe sepsis (n = 18), and septic shock (n = 13). Interventions: Cells were exposed to lipopolysaccharide, tumor necrosis factor‐&agr;, and interleukin‐6. Measurements and Main Results: Patients’ serum Ang‐2 levels were significantly increased in severe sepsis as compared with patients with no systemic inflammatory response syndrome or sepsis (p < .05 by analysis of variance). Positive linear relationships were observed with: serum tumor necrosis factor‐&agr; (rs = 0.654, p < .001), serum interleukin‐6 (rs = 0.464, p < .001), Acute Physiology and Chronic Health Evaluation II score (rs = 0.387, p < .001), and Sequential Organ Failure Assessment score (rs = 0.428, p < .001). Multiple regression analysis revealed that serum Ang‐2 is mostly related to serum tumor necrosis factor‐&agr; and severe sepsis. Treatment of human lung microvascular endothelial cells with all mediators resulted in a concentration‐dependent Ang‐2 reduction. Treatment of bovine lung microvascular endothelial cells with lipopolysaccharide and tumor necrosis factor‐&agr; increased Ang‐2 release, and interleukin‐6 reduced basal Ang‐2 levels. Conclusions: First, patients’ serum Ang‐2 levels are increased during severe sepsis and associated with disease severity. The strong relationship of serum Ang‐2 with serum tumor necrosis factor‐&agr; suggests that the latter may participate in the regulation of Ang‐2 production in sepsis. Second, inflammatory mediators reduce Ang‐2 release from human lung microvascular endothelial cells, implying that this vascular bed may not be the source of increased Ang‐2 in human sepsis.

Endothelial pathomechanisms in acute lung injury

Abstract Acute lung injury (ALI) and its most severe extreme the acute respiratory distress syndrome (ARDS) refer to increased-permeability pulmonary edema caused by a variety of pulmonary or systemic insults. ALI and in particular ARDS, are usually accompanied by refractory hypoxemia and the need for mechanical ventilation. In most cases, an exaggerated inflammatory and pro-thrombotic reaction to an initial stimulus, such as systemic infection, elicits disruption of the alveolo-capillary membrane and vascular fluid leak. The pulmonary endothelium is a major metabolic organ promoting adequate pulmonary and systemic vascular homeostasis, and a main target of circulating cells and humoral mediators under injury; pulmonary endothelium is therefore critically involved in the pathogenesis of ALI. In this review we will discuss mechanisms of pulmonary endothelial dysfunction and edema generation in the lung with special emphasis on the interplay between the endothelium, the immune and hemostatic systems, and highlight how these principles apply in the context of defined disorders and specific insults implicated in ALI pathogenesis.

The endothelium in acute lung injury/acute respiratory distress syndrome

Purpose of reviewSince pulmonary edema from increased endothelial permeability is the hallmark of acute lung injury, a frequently encountered entity in critical care medicine, the study of endothelial responses in this setting is crucial to the development of effective endothelial-targeted treatments. Recent findingsFrom the enormous amount of research in the field of endothelial pathophysiology, we have focused on work delineating endothelial alterations elicited by noxious stimuli implicated in acute lung injury. The bulk of the material covered deals with molecular and cellular aspects of the pathogenesis, reflecting current trends in the published literature. We initially discuss pathways of endothelial dysfunction in acute lung injury and then cover the mechanisms of endothelial protection. Several experimental treatments in animal models are presented, which aid in the understanding of the disease pathogenesis and provide evidence for potentially useful therapies. SummaryMechanistic studies have delivered several interventions, which are effective in preventing and treating experimental acute lung injury and have thus provided objectives for translational studies. Some of these modalities may evolve into clinically useful tools in the treatment of this devastating illness.

Pulmonary Capillary Endothelium-Bound Angiotensin-Converting Enzyme Activity in Acute Lung Injury

BackgroundPulmonary capillary endothelium-bound (PCEB) angiotensin-converting ectoenzyme (ACE) activity alteration is an early, sensitive, and quantifiable lung injury index in animal models. We hypothesized that (1) PCEB-ACE alterations can be found in patients with acute lung injury (ALI) and (2) PCEB-ACE activity correlates with the severity of lung injury and may be used as a quantifiable marker of the underlying pulmonary capillary endothelial dysfunction. Methods and ResultsApplying indicator-dilution techniques, we measured single-pass transpulmonary hydrolysis of the synthetic ACE substrate 3H-benzoyl-Phe-Ala-Pro (BPAP) in 33 mechanically ventilated, critically ill patients with a lung injury score (LIS) ranging from 0 (no lung injury) to 3.7 (severe lung injury) and calculated the kinetic parameter Amax/Km. Both parameters decreased early during the ALI continuum and were inversely related to APACHE II score and LIS. Hydrolysis decreased with increasing cardiac output (CO), whereas 2 different patterns were observed between CO and Amax/Km. ConclusionsPCEB-ACE activity decreases early during ALI, correlates with the clinical severity of both the lung injury and the underlying disease, and may be used as a quantifiable marker of underlying pulmonary capillary endothelial dysfunction.

High prevalence of decreased cortisol reserve in brain-dead potential organ donors.

ObjectiveTo investigate the adrenocortical function in brain-dead patients, potential organ donors. DesignProspective study. SettingIntensive care units in two teaching hospitals. PatientsA total of 37 patients (28 men, nine women) with severe brain injury, having a mean age of 42 ± 18 yrs, were included in the study. Group A consisted of 20 brain-injured patients who did not deteriorate to brain death. Group B included 17 brain-injured patients who were brain dead; of these, ten patients developed brain death during ICU stay and seven patients were admitted to the ICU after clinical brain death. InterventionsIn all patients (group A and group B), a morning blood sample was obtained at admission to the ICU to determine baseline plasma cortisol. Subsequently, 1 &mgr;g of corticotropin (adrenocorticotropic hormone, Synacthen) was administered intravenously, and a blood sample was taken 30 mins after the injection. In group B patients who became brain dead while being treated in the ICU (n = 10), the same procedure was repeated the morning after the confirmation of brain death. Patients having a cortisol level of at least 18 &mgr;g/dL after the administration of adrenocorticotropic hormone were defined as responders. Measurements and Main ResultsAfter the occurrence of brain death, group B patients had significantly lower values for baseline (8.5 ± 6.2 vs. 17.0 ± 6.6 &mgr;g/dL, p < .001) and stimulated (16.9 ± 6.3 vs. 23.9 ± 5.7 &mgr;g/dL, p = .001) plasma cortisol compared with group A patients. Thirteen group B patients (76%) and two group A patients (10%) were nonresponders to adrenocorticotropic hormone (p < .001). In group B patients, baseline and stimulated cortisol concentrations were significantly related (r = .71, p = .001), whereas there was no correlation between baseline cortisol and the increment in cortisol (r = −.37, p = .15). Mean hormonal data of the ten brain-dead patients studied at admission in the ICU and after the occurrence of brain death were the following: baseline plasma cortisol (23.5 ± 11.4 vs. 6.8 ± 4.2 &mgr;g/dL, p = .003) and stimulated serum cortisol (28.8 ± 9.9 vs. 16.3 ± 4.3 &mgr;g/dL, p = .008). ConclusionsAdrenal cortisol secretion after dynamic stimulation is deficient in a substantial proportion of brain-dead potential organ donors.

Early apoptosis of blood monocytes in the septic host: is it a mechanism of protection in the event of septic shock?

IntroductionBased on the central role of the triggering of monocytes for the initiation of the septic cascade, it was investigated whether apoptosis of blood monocytes in septic patients is connected to their final outcome.MethodsBlood monocytes were isolated from 90 patients with septic syndrome due to ventilator-associated pneumonia on days 1, 3, 5 and 7 from the initiation of symptoms. Apoptosis was defined after incubation with annexin-V-fluorescein isothiocyanate and propidium iodine and reading by a flow cytometer. The function of first-day monocytes was evaluated from the concentrations of tumour necrosis factor alpha (TNFα) and IL-6 in supernatants of cell cultures after triggering with endotoxins. TNFα, IL-6 and IL-8 were estimated in serum by an enzyme immunoassay.ResultsMortality rates of patients with apoptosis ≤50% compared with patients with apoptosis >50% were 49.12% and 15.15%, respectively (P < 0.0001). Kaplan-Meier analysis showed a 28-day survival benefit in patients with septic shock and monocyte apoptosis >50% compared with those patients with apoptosis ≤50% (P = 0.0032). Production of IL-6 by monocytes on the first day by patients with apoptosis ≤50% was similar compared with monocytes isolated from healthy controls. Serum concentrations of TNFα were higher in patients with monocyte apoptosis ≤50% and septic shock compared with patients with apoptosis >50% on day 7; similar findings occurred for serum IL-6 on days 1 and 7 and for serum IL-8 on days 1 and 5.ConclusionEarly apoptosis of monocytes upon presentation of clinical signs of sepsis is connected to a favourable outcome. These findings are of particular importance for the patient with septic shock, where they might constitute a mechanism of pathogenesis.

Pulmonary Capillary Endothelium-Bound Angiotensin-Converting Enzyme Activity in Humans

BACKGROUND Pulmonary endothelium has metabolic functions including the conversion of angiotensin I to angiotensin II by angiotensin-converting ectoenzyme (ACE). In this study, we have validated an indicator-dilution technique that provides estimations of dynamically perfused capillary surface area (DPCSA) in humans, and we have characterized pulmonary endothelial ACE in vivo. METHODS AND RESULTS In 12 adults, single-pass transpulmonary (one or both lungs) hydrolysis of the specific ACE substrate 3H-benzoyl-Phe-Ala-Pro (3H-BPAP) was measured and expressed as % metabolism (%M) and v=-ln(1-M). We also calculated Amax/Km, an index of DPCSA. %M (70.1+/-3.2 vs 67.9+/-3.1) and v (1.29+/-0.14 vs 1. 20+/-0.12) were similar in both lungs and the right lung, respectively, whereas Amax/Km//body surface area decreased from 2460+/-193 to 1318+/-115 mL/min per square meter. CONCLUSIONS Pulmonary endothelial ACE activity can be assessed in humans at the bedside by means of indicator-dilution techniques. Our data suggest homogeneous pulmonary capillary ACE concentrations and capillary transit times (tc) in both human lungs, and similar tc within the normal range of cardiac index. Amax/Km in the right lung is 54% of total Amax/Km in both lungs, suggesting that Amax/Km is a reliable and quantifiable index of DPCSA in humans.

Pulmonary capillary endothelial dysfunction in early systemic sclerosis

OBJECTIVE Pulmonary capillary endothelium-bound angiotensin-converting enzyme (PCEB-ACE) activity is a sensitive and quantifiable index of endothelial function in vivo. Systemic sclerosis (SSc) is characterized by endothelial damage and excess collagen formation, causing mainly pulmonary hypertension (PH) in the limited cutaneous SSc (lcSSc) subset and interstitial lung disease with pulmonary interstitial fibrosis (PIF) in the diffuse cutaneous SSc (dcSSc) subset. This study was undertaken to investigate the hypothesis that PCEB-ACE activity is reduced early in SSc, in the absence of PH or PIF. METHODS Applying indicator-dilution techniques, we measured single-pass transpulmonary hydrolysis and percent metabolism (%M) of a synthetic ACE substrate and calculated functional capillary surface area (FCSA) in 25 SSc patients and 11 controls. Substrate hydrolysis and %M reflect ACE activity per capillary; FCSA reflects ACE activity per vascular bed. RESULTS PCEB-ACE activity was decreased in both SSc subsets. Among patients without PH, substrate hydrolysis and %M were decreased in patients with lcSSc and more profoundly in those with dcSSc; loss of FCSA normalized to body surface area (FCSA/BSA) was observed in dcSSc, but not in lcSSc. High-resolution computed tomography of the lung, performed in all SSc patients, revealed no correlation between substrate %M, hydrolysis, or FCSA/BSA and the degree of PIF; 5 dcSSc and 5 lcSSc patients with no detectable PIF exhibited decreases in hydrolysis and %M, while FCSA/BSA was decreased only in dcSSc. CONCLUSION Depression of PCEB-ACE activity, indicating pulmonary endothelial dysfunction, occurs early in SSc, in the absence of PH or PIF, and is more pronounced, at this early pulmonary disease stage, in dcSSc than in lcSSc.

Prognostic importance of increased plasma amino-terminal pro-brain natriuretic peptide levels in a large noncardiac, general intensive care unit population.

The present study aimed to determine whether amino-terminal pro-brain natriuretic peptide (NT-pro-BNP) predicts intensive care unit (ICU) mortality in a cohort of general, noncardiac, critically ill patients. To this end, a total of 233 consecutive mechanically ventilated patients (109 men) having a median age of 60 years and a wide range in admitting diagnoses, including medical (n = 118), surgical (n = 83), and multiple trauma (n = 32) cases were prospectively studied. Median Acute Physiology and Chronic Health Evaluation (APACHE) II and Sequential Organ Failure Assessment scores on ICU admission were 16 and 9, respectively. The study end point was ICU outcome. Blood samples were drawn on admission in the ICU and on postadmission days 1 and 2 to determine NT-pro-BNP levels. In a subgroup (n = 77), admission proinflammatory and anti-inflammatory cytokine levels, including TNF-&agr;, IL-6, and IL-10, were also measured. Nonsurvivors (n = 98) had significantly higher NT-pro-BNP levels than survivors (n = 135) on admission in the ICU (2,074 vs. 283 pg/mL; P < 0.001), on day 1 (2,197 vs. 221 pg/mL; P < 0.001), and on day 2 (2,726 vs. 139 pg/mL; P < 0.001). Median values for TNF-&agr;, IL-6, and IL-10 were 3.70, 131.57, and 111.88 pg/mL, respectively. Receiver operating characteristic analysis showed that the area under the receiver operating characteristic curve in predicting ICU mortality was 0.70 for APACHE II and 0.77 for admission NT-pro-BNP (P = 0.08). The cutoff in admission NT-pro-BNP that best predicted outcome was 941 pg/mL. Multiple logistic regression analysis revealed that APACHE II score (odds ratio, 1.06; P = 0.007) and the best cutoff point in admission NT-pro-BNP (odds ratio, 7.74; P < 0.001) independently predicted ICU mortality, even if cytokines were entered in the analysis. In conclusion, plasma NT-pro-BNP is frequently raised in noncardiac, mixed, critically ill patients, and nonsurvivors have consistently higher levels than survivors. Elevated admission NT-pro-BNP represents an independent predictor for poor ICU outcome in the presence of clinical severity scores.