Outcome value of Clara cell protein in serum of patients with acute respiratory distress syndrome

Airway epithelium damage in acute respiratory distress syndrome

BACKGROUND

The airway epithelium (AE) fulfils multiple functions to maintain pulmonary homeostasis, among which ensuring adequate barrier function, cell differentiation and polarization, and actively transporting immunoglobulin A (IgA), the predominant mucosal immunoglobulin in the airway lumen, via the polymeric immunoglobulin receptor (pIgR). Morphological changes of the airways have been reported in ARDS, while their detailed features, impact for mucosal immunity, and causative mechanisms remain unclear. Therefore, this study aimed to assess epithelial alterations in the distal airways of patients with ARDS.

METHODS

We retrospectively analyzed lung tissue samples from ARDS patients and controls to investigate and quantify structural and functional changes in the small airways, using multiplex fluorescence immunostaining and computer-assisted quantification on whole tissue sections. Additionally, we measured markers of mucosal immunity, IgA and pIgR, alongside with other epithelial markers, in the serum and the broncho-alveolar lavage fluid (BALF) prospectively collected from ARDS patients and controls.

RESULTS

Compared to controls, airways of ARDS were characterized by increased epithelial denudation (p = 0.0003) and diffuse epithelial infiltration by neutrophils (p = 0.0005). Quantitative evaluation of multiplex fluorescence immunostaining revealed a loss of ciliated cells (p = 0.0317) a trend towards decreased goblet cells (p = 0.056), and no change regarding cell progenitors (basal and club cells), indicating altered mucociliary differentiation. Increased epithelial permeability was also shown in ARDS with a significant decrease of tight (p < 0.0001) and adherens (p = 0.025) junctional proteins. Additionally, we observed a significant decrease of the expression of pIgR, (p < 0.0001), indicating impaired mucosal IgA immunity. Serum concentrations of secretory component (SC) and S-IgA were increased in ARDS (both p < 0.0001), along other lung-derived proteins (CC16, SP-D, sRAGE). However, their BALF concentrations remained unchanged, suggesting a spillover of airway and alveolar proteins through a damaged AE.

CONCLUSION

The airway epithelium from patients with ARDS exhibits multifaceted alterations leading to altered mucociliary differentiation, compromised defense functions and increased permeability with pneumoproteinemia.

Botanical formulation HX110B ameliorates PPE-induced emphysema in mice via regulation of PPAR/RXR signaling pathway

Chronic obstructive pulmonary disease (COPD), an inflammatory lung disease, causes approximately 3 million deaths each year; however, its pathological mechanisms are not fully understood. In this study, we examined whether HX110B, a mixture of Taraxacum officinale, Dioscorea batatas, and Schizonepeta tenuifolia extracts, could suppress porcine pancreatic elastase (PPE)-induced emphysema in mice and its mechanism of action. The therapeutic efficacy of HX110B was tested using a PPE-induced emphysema mouse model and human bronchial epithelial cell line BEAS-2B. In vivo data showed that the alveolar wall and air space expansion damaged by PPE were improved by HX110B administration. HX110B also effectively suppresses the expression levels of pro-inflammatory mediators including IL-6, IL-1β, MIP-2, and iNOS, while stimulating the expression of lung protective factors such as IL-10, CC16, SP-D, and sRAGE. Moreover, HX110B improved the impaired OXPHOS subunit gene expression. In vitro analysis revealed that HX110B exerted its effects by activating the PPAR-RXR signaling pathways. Overall, our data demonstrated that HX110B could be a promising therapeutic option for COPD treatment.

Endothelial cell dynamics in sepsis-induced acute lung injury and acute respiratory distress syndrome: pathogenesis and therapeutic implications

Sepsis, a prevalent critical condition in clinics, continues to be the leading cause of death from infections and a global healthcare issue. Among the organs susceptible to the harmful effects of sepsis, the lungs are notably the most frequently affected. Consequently, patients with sepsis are predisposed to developing acute lung injury (ALI), and in severe cases, acute respiratory distress syndrome (ARDS). Nevertheless, the precise mechanisms associated with the onset of ALI/ARDS remain elusive. In recent years, there has been a growing emphasis on the role of endothelial cells (ECs), a cell type integral to lung barrier function, and their interactions with various stromal cells in sepsis-induced ALI/ARDS. In this comprehensive review, we summarize the involvement of endothelial cells and their intricate interplay with immune cells and stromal cells, including pulmonary epithelial cells and fibroblasts, in the pathogenesis of sepsis-induced ALI/ARDS, with particular emphasis placed on discussing the several pivotal pathways implicated in this process. Furthermore, we discuss the potential therapeutic interventions for modulating the functions of endothelial cells, their interactions with immune cells and stromal cells, and relevant pathways associated with ALI/ARDS to present a potential therapeutic strategy for managing sepsis and sepsis-induced ALI/ARDS.

Circulating Pulmonary-Originated Epithelial Biomarkers for Acute Respiratory Distress Syndrome: A Systematic Review and Meta-Analysis

Previous studies have found several biomarkers for acute respiratory distress syndrome (ARDS), but the accuracy of most biomarkers is still in doubt due to the occurrence of other comorbidities. In this systematic review and meta-analysis, we aimed to explore ideal ARDS biomarkers which can reflect pathophysiology features precisely and better identify at-risk patients and predict mortality. Web of Science, PubMed, Embase, OVID, and the Cochrane Library were systematically searched for studies assessing the reliability of pulmonary-originated epithelial proteins in ARDS. A total of 32 studies appeared eligible for meta-analysis, including 2654 ARDS/ALI patients in this study. In the at-risk patients' identification group, the highest pooled effect size was observed in Krebs von den Lungren-6 (KL-6) (SMD: 1.17 [95% CI: 0.55, 1.79]), followed by club cell proteins 16 (CC16) (SMD: 0.74 [95% CI: 0.01, 1.46]), and surfactant proteins-D (SP-D) (SMD: 0.71 [95% CI: 0.57, 0.84]). For the mortality prediction group, CC16 exhibited the largest effect size with SMD of 0.92 (95% CI: 0.42, 1.43). Meanwhile, the summary receiver operating characteristic (SROC) of CC16 for ARDS diagnosis reached an AUC of 0.80 (95% CI: 0.76, 0.83). In conclusion, this study provides a ranking system for pulmonary-originated epithelial biomarkers according to their association with distinguishing at-risk patients and predicting mortality. In addition, the study provides evidence for the advantage of biomarkers over traditional diagnostic criteria. The performance of biomarkers may help to clinically improve the ARDS diagnosis and mortality prediction.

Danger signals in traumatic hemorrhagic shock and new lines for clinical applications

Hemorrhage is the leading cause of death in severe trauma injuries. When organs or tissues are subjected to prolonged hypoxia, danger signals-known as damage-associated molecular patterns (DAMPs)-are released into the intercellular environment. The endothelium is both the target and a major provider of damage-associated molecular patterns, which are directly involved in immuno-inflammatory dysregulation and the associated tissue suffering. Although damage-associated molecular patterns release begins very early after trauma, this release and its consequences continue beyond the initial treatment. Here we review a few examples of damage-associated molecular patterns to illustrate their pathophysiological roles, with emphasis on emerging therapeutic interventions in the context of severe trauma. Therapeutic intervention administered at precise points during damage-associated molecular patterns release may have beneficial effects by calming the inflammatory storm triggered by traumatic hemorrhagic shock.

Validation of Prognostic Club Cell Secretory Protein (CC16) Cut-point in an Independent ALTA Cohort

Background

Club cell secretory protein (CC16) has demonstrated utility as a lung-specific biomarker in predicting mortality in acute respiratory distress syndrome (ARDS). These findings have been observed in pre-clinical trials and a re-analysis of a large, randomized controlled trial of ARDS (Fluid and Catheter Treatment Trial (FACTT)).

Objectives

The purpose of this study was to validate previous findings by evaluating CC16 level as a mortality predictor in patients from the albuterol to treat acute lung injury (ALTA) trial.

Design and Method

In this secondary biomarker analysis, plasma CC16 level was measured from 100 ALTA subjects using enzyme-linked immunosorbent assay (ELISA). The rate of mortality was assessed in patients with high (⩾45 ng/mL) versus low CC16 (<45 ng/mL) levels. This cut-off level was applied based on our previous analysis from FACTT trial. Significance was assessed using Kaplan-Meier curves and a log-rank test.

Results

Subjects were an average of 50 years old and 46% of them were females. Patients with high CC16 levels had higher 90-day mortality compared to those with low CC16 levels, (37.73% vs 8.95%, P < .001). Other clinical outcomes including ICU-free days, ventilator-free days, and organ failure free days were significantly different between the groups (All P < .05).

Conclusion

In this validation study, we demonstrated that ARDS patients with high plasma CC16 concentration had a higher mortality rate than those with low CC16 levels, confirming previous findings that CC16 levels are associated with ARDS mortality.

Brief Research Report: Serum clara cell 16 kDa protein levels are increased in patients hospitalized for severe SARS-CoV-2 or sepsis infection

Background

Clara cell 16 kDa protein (CC16) is a secretory protein primarily expressed in epithelial cells in the lungs. Previous studies show that CC16 exerts anti-inflammatory and immune-modulatory properties in both acute and chronic pulmonary diseases. However, despite the evidence of CC16’s high biomarker potential, evaluation of its role in infectious diseases is yet very limited.

Methods

Serum CC16 concentrations were measured by ELISA and assessed in two different types of severe infections. Using a case-control study design, patients treated for either severe SARS-CoV-2 or severe non-pulmonary sepsis infection were compared to age- and sex-matched healthy human subjects.

Results

Serum CC16 was significantly increased in both types of infection (SARS-CoV-2: 96.22 ± 129.01 ng/ml vs. healthy controls: 14.05 ± 7.48 ng/ml, p = 0.022; sepsis: 35.37 ± 28.10 ng/ml vs. healthy controls: 15.25 ± 7.51 ng/ml, p = 0.032) but there were no distinct differences between infections with and without pulmonary focus (p = 0.089). Furthermore, CC16 serum levels were positively correlated to disease duration and inversely to the platelet count in severe SARS-CoV-2 infection.

Conclusions

Increased CC16 serum levels in both SARS-CoV-2 and sepsis reinforce the high potential as a biomarker for epithelial cell damage and bronchoalveolar−blood barrier leakage in pulmonary as well as non-pulmonary infectious diseases.

SP-D and CC-16 Pneumoproteins' Kinetics and Their Predictive Role During SARS-CoV-2 Infection

Background

Surfactant protein D (SP-D) and pulmonary club cell protein 16 (CC-16) are called “pneumoproteins” and are involved in host defense against oxidative stress, inflammation, and viral outbreak. This study aimed to determine the predictive value of these pneumoproteins on the incidence of acute respiratory distress syndrome (ARDS) or death in patients with coronavirus disease-2019 (COVID-19).

Methods

This retrospective study included 87 patients admitted to an emergency department. Blood samples were collected on three time points (days 1, 5, and 14 from hospital admission). SP-D and CC-16 serum levels were determined, and univariate and multivariate analyses considering confounding variables (age, body mass index, tobacco use, dyspnea, hypertension, diabetes mellitus, neutrophil-to-lymphocyte ratio) were performed.

Results

Based on the multivariate analysis, SP-D level on D1 was positively and slightly correlated with subsequent development of ARDS, independent of body mass index, dyspnea, and diabetes mellitus. CC-16 level on D1 was modestly and positively correlated with fatal outcome. A rise in SP-D between D1 and D5 and D1 and D14 had a strong negative association with incidence of ARDS. These associations were independent of tobacco use and neutrophil-to-lymphocyte ratio.

Conclusions

Overall, our data reveal that increase in SP-D levels is a good prognostic factor for patients with COVID-19, and that initial CC-16 levels correlated with slightly higher risk of death. SP-D and CC-16 may prove useful to predict outcomes in patients with COVID-19.

Surfactant protein D is a biomarker of influenza-related pediatric lung injury

BACKGROUND

Biomarkers that can risk-stratify children with influenza virus lower respiratory infection may identify patients for targeted intervention. Early elevation of alveolar-related proteins in the bloodstream in these patients could indicate more severe lung damage portending worse outcomes.

METHODS

We used a mouse model of human influenza infection and evaluated relationships between lung pathophysiology and surfactant protein D (SP-D), SP-A, and Club cell protein 16 (CC16). We then measured SP-A, SP-D, and CC16 levels in plasma samples from 94 children with influenza-associated acute respiratory failure (PICFLU cohort), excluding children with underlying conditions explaining disease severity. We tested for associations between levels of circulating proteins and disease severity including the diagnosis of acute respiratory distress syndrome (ARDS), mechanical ventilator, intensive care unit and hospital days, and hospital mortality.

RESULTS

Circulating SP-D showed a greater increase than SP-A and CC16 in mice with increased alveolar-vascular permeability following influenza infection. In the PICFLU cohort, SP-D was associated with moderate-severe ARDS diagnosis (p = 0.01) and with mechanical ventilator (r = 0.45, p = 0.002), ICU (r = 0.44, p = 0.002), and hospital days (r = 0.37, p = 0.001) in influenza-infected children without bacterial coinfection. Levels of SP-D were lower in children with secondary bacterial pneumonia (p = 0.01) and not associated with outcomes. CC16 and SP-A levels did not differ with bacterial coinfection and were not consistently associated with severe outcomes.

CONCLUSIONS

SP-D has potential as an early circulating biomarker reflecting a degree of lung damage caused directly by influenza virus infection in children. Secondary bacterial pneumonia alters SP-D biomarker performance.

CC16 Regulates Inflammation, ROS Generation and Apoptosis in Bronchial Epithelial Cells during Klebsiella pneumoniae Infection

Gram-negative (G-) bacteria are the leading cause of hospital-acquired pneumonia in the United States. The devastating damage caused by G- bacteria results from the imbalance of bactericidal effects and overwhelming inflammation. Despite decades of research, the underlying mechanisms by which runaway inflammation is developed remain incompletely understood. Clara Cell Protein 16 (CC16), also known as uteroglobin, is the major protein secreted by Clara cells and the most abundant protein in bronchoalveolar lavage fluid (BALF). However, the regulation and functions of CC16 during G- bacterial infection are unknown. In this study, we aimed to assess the regulation of CC16 in response to Klebsiella pneumoniae (K. pneu) and to investigate the role of CC16 in bronchial epithelial cells. After K. pneu infection, we found that CC16 mRNA expression was significantly decreased in bronchial epithelial cells. Our data also showed that K. pneu infection upregulated cytokine and chemokine genes, including IL-1β, IL-6, and IL-8 in BEAS-2B cells. Endogenously overexpressed CC16 in BEAS-2B cells provided an anti-inflammatory effect by reducing these markers. We also observed that endogenous CC16 can repress NF-κB reporter activity. In contrast, the recombinant CC16 (rCC16) did not show an anti-inflammatory effect in K. pneu-infected cells or suppression of NF-κB promoter activity. Moreover, the overexpression of CC16 reduced reactive oxygen species (ROS) levels and protected BEAS-2B cells from K. pneu-induced apoptosis.

The Potential of Lung Epithelium Specific Proteins as Biomarkers for COVID-19-Associated Lung Injury

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection was first reported in Wuhan, China, and was declared a pandemic by the World Health Organization (WHO) on 20 March 2020. The respiratory system is the major organ system affected by COVID-19. Numerous studies have found lung abnormalities in patients with COVID-19, including shortness of breath, respiratory failure, and acute respiratory distress syndrome. The identification of lung-specific biomarkers that are easily measurable in serum would be valuable for both clinicians and patients with such conditions. This review is focused on the pneumoproteins and their potential to serve as biomarkers for COVID-19-associated lung injury, including Krebs von den Lungen-6 (KL-6), surfactant proteins (SP-A, SP-B, SP-C, SP-D), and Clara cell secretory protein (CC16). The current findings indicate the aforementioned pneumoproteins may reflect the severity of pulmonary manifestations and could serve as potential biomarkers in COVID-19-related lung injury.

Strategies to protect surfactant and enhance its activity

The knowledge about surfactant biology is now deeper and recent research has allowed to clarify its role in several human lung disorders. The balance between surfactant production and consumption is better known and the same applies to their regulatory mechanisms. This has allowed to hypothesize and investigate several new and original strategies to protect surfactant and enhance its activity. These interventions are potentially useful for several disorders and particularly for acute respiratory distress syndrome. We here highlight the mechanisms regulating surfactant consumption, encompassing surfactant catabolism but also surfactant injury due to other mechanisms, in a physiopathology-driven fashion. We then analyze each corresponding strategy to protect surfactant and enhance its activity. Some of these strategies are more advanced in terms of research & development pathway, some others are still investigational, but all are promising and deserve a joint effort from clinical-academic researchers and the industry.

A Simple-to-Use Web-Based Calculator for Survival Prediction in Acute Respiratory Distress Syndrome

Background: The aim of this study was to construct and validate a simple-to-use model to predict the survival of patients with acute respiratory distress syndrome.

Methods: A total of 197 patients with acute respiratory distress syndrome were selected from the Dryad Digital Repository. All eligible individuals were randomly stratified into the training set (n=133) and the validation set (n=64) as 2: 1 ratio. LASSO regression analysis was used to select the optimal predictors, and receiver operating characteristic and calibration curves were used to evaluate accuracy and discrimination of the model. Clinical usefulness of the model was also assessed using decision curve analysis and Kaplan-Meier analysis.

Results: Age, albumin, platelet count, PaO₂/FiO₂, lactate dehydrogenase, high-resolution computed tomography score, and etiology were identified as independent prognostic factors based on LASSO regression analysis; these factors were integrated for the construction of the nomogram. Results of calibration plots, decision curve analysis, and receiver operating characteristic analysis showed that this model has good predictive ability of patient survival in acute respiratory distress syndrome. Moreover, a significant difference in the 28-day survival was shown between the patients stratified into different risk groups (P < 0.001). For convenient application, we also established a web-based calculator (https://huangl.shinyapps.io/ARDSprognosis/).

Conclusions: We satisfactorily constructed a simple-to-use model based on seven relevant factors to predict survival and prognosis of patients with acute respiratory distress syndrome. This model can aid personalized treatment and clinical decision-making.

Club Cell Secreted Protein CC16: Potential Applications in Prognosis and Therapy for Pulmonary Diseases

Club cell secretory protein (CC16) is encoded by the SCGB1A1 gene. It is also known as CC10, secretoglobin, or uteroglobin. CC16 is a 16 kDa homodimeric protein secreted primarily by the non-ciliated bronchial epithelial cells, which can be detected in the airways, circulation, sputum, nasal fluid, and urine. The biological activities of CC16 and its pathways have not been completely understood, but many studies suggest that CC16 has anti-inflammatory and anti-oxidative effects. The human CC16 gene is located on chromosome 11, p12-q13, where several regulatory genes of allergy and inflammation exist. Studies reveal that factors such as gender, age, obesity, renal function, diurnal variation, and exercise regulate CC16 levels in circulation. Current findings indicate CC16 not only may reflect the pathogenesis of pulmonary diseases, but also could serve as a potential biomarker in several lung diseases and a promising treatment for chronic obstructive pulmonary disease (COPD). In this review, we summarize our current understanding of CC16 in pulmonary diseases.

Renal dysfunction reduces the diagnostic and prognostic value of serum CC16 for acute respiratory distress syndrome in intensive care patients

BACKGROUND

Contradictory results regarding changes in serum club cell protein 16 (CC16) levels in patients with acute respiratory distress syndrome (ARDS) have been reported, challenging the value of CC16 as a diagnostic and prognostic marker for ARDS. We have also observed increased serum CC16 levels in patients with renal dysfunction (RD). Therefore, the present study aimed to determine whether RD affects the diagnostic performance of CC16 for ARDS in intensive care unit (ICU) patients.

METHODS

We measured serum CC16 concentrations in 479 ICU patients, who were categorized into six groups according to their diagnoses: control, acute kidney injury (AKI), chronic kidney disease (CKD), ARDS, ARDS+AKI, and ARDS+CKD. The sensitivity, specificity, and cutoff values for serum CC16 were assessed by receiver operating characteristic curve analysis.

RESULTS

Serum CC16 concentrations were higher in the ARDS group than in the control group, and in ARDS patients with normal renal function, serum CC16 could identify ARDS and predict survival outcomes at 7 and 28 days. However, serum CC16 levels were similar among the ARDS+AKI, ARDS+CKD, AIK, and CKD groups. Consequently, in patients with AKI and/or CKD, the specificity of CC16 for diagnosing ARDS or ARDS+RD decreased from 86.62 to 2.82% or 81.70 to 2.12%, respectively. Consistently, the CC16 cutoff value of 11.57 ng/ml in patients with RD differed from the established values of 32.77-33.72 ng/ml with normal renal function. Moreover, the predictive value of CC16 for mortality in ARDS+RD patients was lost before 7 days but regained by 28 days.

CONCLUSION

RD reduces the diagnostic specificity, diagnostic cutoff value, and predictive value for 7-day mortality of serum CC16 for ARDS among ICU patients.

A systematic review of biomarkers multivariately associated with acute respiratory distress syndrome development and mortality

Background

Heterogeneity of acute respiratory distress syndrome (ARDS) could be reduced by identification of biomarker-based phenotypes. The set of ARDS biomarkers to prospectively define these phenotypes remains to be established.

Objective

To provide an overview of the biomarkers that were multivariately associated with ARDS development or mortality.

Data sources

We performed a systematic search in Embase, MEDLINE, Web of Science, Cochrane CENTRAL, and Google Scholar from inception until 6 March 2020.

Study selection

Studies assessing biomarkers for ARDS development in critically ill patients at risk for ARDS and mortality due to ARDS adjusted in multivariate analyses were included.

Data extraction and synthesis

We included 35 studies for ARDS development (10,667 patients at risk for ARDS) and 53 for ARDS mortality (15,344 patients with ARDS). These studies were too heterogeneous to be used in a meta-analysis, as time until outcome and the variables used in the multivariate analyses varied widely between studies. After qualitative inspection, high plasma levels of angiopoeitin-2 and receptor for advanced glycation end products (RAGE) were associated with an increased risk of ARDS development. None of the biomarkers (plasma angiopoeitin-2, C-reactive protein, interleukin-8, RAGE, surfactant protein D, and Von Willebrand factor) was clearly associated with mortality.

Conclusions

Biomarker data reporting and variables used in multivariate analyses differed greatly between studies. Angiopoeitin-2 and RAGE in plasma were positively associated with increased risk of ARDS development. None of the biomarkers independently predicted mortality. Therefore, we suggested to structurally investigate a combination of biomarkers and clinical parameters in order to find more homogeneous ARDS phenotypes.

PROSPERO identifier

PROSPERO, CRD42017078957

Validation of age, PaO2/FlO2 and plateau pressure score in Korean patients with acute respiratory distress syndrome: a retrospective cohort study

Background

A predictive scoring system for acute respiratory distress syndrome (ARDS) patients, which incorporates age, PaO₂/FlO₂, and plateau pressure, APPS, was developed recently. It was validated externally in a Caucasian population but has not been studied in Asian populations. The aim of this study was to validate APPS in Korean ARDS patients.

Methods

We retrospectively reviewed the medical records of patients who were diagnosed with ARDS using the Berlin criteria and admitted to the medical ICU at Seoul National University Hospital from January 2015 to December 2016. The validation of the APPS was performed by evaluating its calibration and predictive accuracy. Its calibration was plotted and quantified using the Hosmer–Lemeshow test. Its predictive accuracy was assessed by calculating the area under the receiver operating characteristics (AUC–ROC) curve.

Results

A total of 116 patients were analyzed, 32 of whom survived. Of the 116 patients, 11 (9.5%) were classified as APPS grade 1 (score 3–4), 88 (75.9%) as grade 2 (score 5–7) and 17 (14.6%) as grade 3 (score 8–9). In-hospital mortality was 27.3% for grade 1, 73.9% for grade 2 and 94.1% for grade 3 (P for trend < 0.001). The APPS was well calibrated (Hosmer–Lemeshow test, P = 0.578) and its predictive accuracy was acceptable (AUC–ROC 0.704, 95% confidence interval 0.599–0.809).

Conclusions

The APPS predicted in-hospital mortality in Korean patients with ARDS with similar power to its application in a Western population and with acceptable predictive accuracy.

Trial registration

Retrospectively registered.

Association between Early Acute Respiratory Distress Syndrome after Living-Donor Liver Transplantation and Perioperative Serum Biomarkers: The Role of Club Cell Protein 16

Background

Acute respiratory distress syndrome (ARDS) after living-donor liver transplantation (LDLT) is not uncommon, but it lacks the biomarkers for early detection. Club cell protein 16 (CC16), high-motility group box 1 protein (HMGB1), interleukin-1β (IL-1β), and IL-10 have been reported as relevant to the development of ARDS. However, they have not been investigated during LDLT.

Methods

Seventy-three consecutive recipients undergoing LDLT were enrolled and received the same perioperative care plan. Perioperative serum CC16, HMGB1, IL-1β, and IL-10 levels were measured at the pretransplant state, 30 minutes after reperfusion, postoperative day 1 (POD1), and POD3. ARDS was diagnosed according to the 2012 Berlin definition.

Results

Of the 73 recipients, 13 developed ARDS with significantly longer durations of mechanical ventilation and intensive care unit stay. Serum CC16 levels on POD1 increased significantly from the pretransplant state in the ARDS group but not in the non-ARDS group. Pretransplant serum CC16 levels were also higher in the ARDS group. The area under the receiver operating characteristic curves for POD1 serum CC16 levels used to discriminate ARDS was 0.803 (95% confidence interval: 0.679 to 0.895; p < 0.001). By comparison, HMGB1, IL-1β, and IL-10 were not associated with ARDS after LDLT.

Conclusion

The higher pretransplant serum CC16 level and its increased level on POD1 were associated with the development of early ARDS after LDLT. This trial is registered with NCT01936545, 27 August 2013.

Relation between Red Cell Distribution Width and Mortality in Critically Ill Patients with Acute Respiratory Distress Syndrome

Background

Currently, evidence regarding the predictive significance of red blood cell distribution width (RDW) among patients with acute respiratory distress syndrome (ARDS) remains scarce. The aim of this study was to determine the prognostic value of RDW for critically ill patients with ARDS.

Methods

We studied all patients with ARDS from the Multiparameter Intelligent Monitoring in Intensive Care Database III (MIMIC-III) for whom RDW was available. The clinical outcomes were 30-day and 90-day mortality. Analyses included logistic multivariate regression model, Receiver Operating Characteristic (ROC) analysis, and subgroup analysis.

Results

A total of 404 eligible ARDS patients were included. After adjustment for several clinical characteristics related to 30-day mortality, the adjusted OR (95% CIs) for RDW levels ≥14.5% was 1.91 (1.08, 3.39). A similar trend was observed for 90-day mortality. The RDW levels ≥14.5% were also an independent predictor of 90-day mortality (OR, 2.56; 95% CI, 1.50 to 4.37; P = 0.0006) compared with the low RDW levels (<14.5%). In subgroup analyses, RDW showed no significant interactions with other relevant risk factors for 30-day mortality.

Conclusions

RDW appeared to be a novel, independent predictor of mortality in critically ill patients with ARDS.

Kinetics of plasma biomarkers of inflammation and lung injury in surgical patients with or without postoperative pulmonary complications

BACKGROUND

Postoperative pulmonary complications (PPCs) are common after major abdominal surgery. The kinetics of plasma biomarkers could improve identification of patients developing PPCs, but the kinetics may depend on intraoperative ventilator settings.

OBJECTIVE

To test whether the kinetics of plasma biomarkers are capable of identifying patients who will develop PPCs, and whether the kinetics depend on the intraoperative level of positive end-expiratory pressure (PEEP).

DESIGN

A preplanned substudy of a randomised controlled trial.

SETTING

Operation room of five centres.

PATIENTS

Two hundred and forty-two adult patients scheduled for abdominal surgery at risk of developing PPCs.

INTERVENTIONS

High (12 cmH2O) versus low (≤2 cmH2O) levels of PEEP.

MAIN OUTCOME MEASURES

Individual PPCs were combined as a composite endpoint. Plasma samples were collected before surgery, directly after surgery and on the fifth postoperative day. The levels of the following were measured: tumour necrosis factor (TNF)-α, interleukin (IL)-6 and IL-8, the soluble form of the Receptor for Advanced Glycation End-products (sRAGE), Surfactant Protein (SP)-D, Clara Cell protein (CC)-16 and Krebs von den Lungen 6 (KL6).

RESULTS

Blood sampling was complete in 242 patients: 120 patients in the high PEEP group and 122 patients in the low PEEP group. Increases in plasma levels of TNF- IL-6, IL-8 and CC-16, and a decrease in plasma levels of SP-D were greater in patients who developed PPCs; however, the area under the receiver operating characteristic curve was low for all biomarkers. CC-16 was the only biomarker whose level increased more in patients who had received high levels of PEEP.

CONCLUSION

In patients undergoing abdominal surgery and at risk of developing PPCs, plasma levels of biomarkers for inflammation or lung injury showed distinct kinetics with development of PPCs, but none of the biomarkers showed sufficient prognostic value. The use of high levels of PEEP was associated with increased levels of CC-16, suggesting lung overdistension.

TRIAL REGISTRATION

The PROVHILO trial, including this substudy, was registered at clinicaltrials.gov (NCT01441791).

Diagnostic and prognostic values of Club cell protein 16 (CC16) in critical care patients with acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS) is a critical condition characterized by bilateral pulmonary infiltrates and severe hypoxemia. This study aimed to evaluate the diagnostic and prognostic values of Club cell protein 16 (CC16) in critical care patients with ARDS.

Methods

In this retrospective observational study, 83 patients with ARDS and 129 non‐ARDS patients on ICU admission were enrolled. The differences in serum CC16 and other laboratory indicators between two groups were analyzed. The sensitivity, specificity, positive and negative predictive values, and accuracy of CC16 as a diagnostic marker on ICU admission were determined by receiver operating characteristic (ROC) curve analysis. The correlation between serum CC16 levels and the severity of ARDS as quantified by PaO₂/FiO₂ ratio were further assessed. CC16 levels were compared between survivors and non‐survivors. The relationships between CC16 levels and duration of ICU and hospitalization were evaluated.

Results

The serum CC16 levels in ARDS patients were significantly higher than that in non‐ARDS patients (54.44±19.62 vs 24.13±12.32 ng/mL, P=.001). ROC analysis showed that the sensitivity, specificity, positive predictive value, and negative predictive value were 90.4%, 79.8%, 74.2%, and 92.8%, respectively, when the cut‐off value was set at 33.3 ng/mL. CC16 levels were correlated with the severity of ARDS. The serum CC16 levels were significantly greater in non‐survivors than in survivors from the ARDS group. CC16 levels were associated with ICU stay but not hospital stay.

Conclusions

CC16 may serve as a diagnostic and stratification marker for ARDS. However, it provided limited prognostic information for ARDS.

Biomarkers in Pediatric ARDS: Future Directions

Acute respiratory distress syndrome (ARDS) is common among mechanically ventilated children and accompanies up to 30% of all pediatric intensive care unit deaths. Though ARDS diagnosis is based on clinical criteria, biological markers of acute lung damage have been extensively studied in adults and children. Biomarkers of inflammation, alveolar epithelial and capillary endothelial disruption, disordered coagulation, and associated derangements measured in the circulation and other body fluids, such as bronchoalveolar lavage, have improved our understanding of pathobiology of ARDS. The biochemical signature of ARDS has been increasingly well described in adult populations, and this has led to the identification of molecular phenotypes to augment clinical classifications. However, there is a paucity of data from pediatric ARDS (pARDS) patients. Biomarkers and molecular phenotypes have the potential to identify patients at high risk of poor outcomes, and perhaps inform the development of targeted therapies for specific groups of patients. Additionally, because of the lower incidence of and mortality from ARDS in pediatric patients relative to adults and lack of robust clinical predictors of outcome, there is an ongoing interest in biological markers as surrogate outcome measures. The recent definition of pARDS provides additional impetus for the measurement of established and novel biomarkers in future pediatric studies in order to further characterize this disease process. This chapter will review the currently available literature and discuss potential future directions for investigation into biomarkers in ARDS among children.

Urine Club Cell 16-kDa Secretory Protein and Childhood Wheezing Illnesses After Lower Respiratory Tract Infections in Infancy

Background: Infants with lower respiratory tract infections (LRTIs) are at an increased risk of developing childhood wheezing illnesses (including asthma), but it is not currently possible to predict those at risk for these long-term outcomes. The current objective was to examine whether urine levels of club cell 16-kDa secretory protein (CC16) at the time of an infant LRTI are associated with the development of childhood wheezing illnesses. Methods: Prospective study of 133 previously healthy infants enrolled during a healthcare visit for a LRTI and followed longitudinally for childhood wheezing illnesses. Urine levels of CC16 at the time of enrollment were measured after validating a commercially available enzyme-linked immunosorbent assay kit for serum. The outcome of interest was parental report of subsequent childhood wheeze (defined as ≥1 episode of wheezing following the initial LRTI) at the 1-year follow-up visit. Logistic regression was used for the main analysis. Results: The median (interquartile range) urine levels of CC16 (ng/mg of creatinine) at the time of an infant LRTI were 11.1 (7.7-20.1) for infants with subsequent childhood wheeze and 13.4 (8.3-61.1) for those without (p = 0.11). In the main multivariate analysis using a logarithmic transformation of the urine levels of CC16, a twofold increase in urine levels of CC16 was associated with ∼30% decreased odds (OR = 0.74 [95% confidence interval (CI) 0.56-0.98], p = 0.04) of subsequent childhood wheeze after adjustment for potential confounders. Conclusions: An inverse association was found between urine levels of CC16 at the time of an infant LRTI and the odds of subsequent childhood wheeze. Urine CC16 may be a useful biomarker of the development of childhood wheezing illnesses after LRTIs in infancy.

Prognostic factors in the acute respiratory distress syndrome

Despite improvements in critical care, acute respiratory distress syndrome (ARDS) remains a devastating clinical problem with high rates of morbidity and mortality. A better understanding of the prognostic factors associated with ARDS is crucial for facilitating risk stratification and developing new therapeutic interventions that aim to improve clinical outcomes. In this article, we present an up-to-date summary of factors that predict mortality in ARDS in four categories: (1) clinical characteristics; (2) physiological parameters and oxygenation; (3) genetic polymorphisms and biomarkers; and (4) scoring systems. In addition, we discuss how a better understanding of clinical and basic pathogenic mechanisms can help to inform prognostication, decision-making, risk stratification, treatment selection, and improve study design for clinical trials.

Early effect of tidal volume on lung injury biomarkers in surgical patients with healthy lungs

BACKGROUND

The early biological impact of short-term mechanical ventilation on healthy lungs is unknown. The authors aimed to characterize the immediate tidal volume (VT)-related changes on lung injury biomarkers in patients with healthy lungs and low risk of pulmonary complications.

METHODS

Twenty-eight healthy patients for knee replacement surgery were prospectively randomized to volume-controlled ventilation with VT 6 (VT6) or 10 (VT10) ml/kg predicted body weight. General anesthesia and other ventilatory parameters (positive end-expiratory pressure, 5 cm H2O, FIO2, 0.5, respiratory rate titrated for normocapnia) were managed similarly in the two groups. Exhaled breath condensate and blood samples were collected for nitrite, nitrate, tumor necrosis factor-α, interleukins-1β, -6, -8, -10, -11, neutrophil elastase, and Clara Cell protein 16 measurements, at the onset of ventilation and 60 min later.

RESULTS

No significant differences in biomarkers were detected between the VT groups at any time. The coefficient of variation of exhaled breath condensate nitrite and nitrate decreased in the VT6 but increased in the VT10 group after 60-min ventilation. Sixty-minute ventilation significantly increased plasma neutrophil elastase levels in the VT6 (35.2 ± 30.4 vs. 56.4 ± 51.7 ng/ml, P = 0.008) and Clara Cell protein 16 levels in the VT10 group (16.4 ± 8.8 vs. 18.7 ± 9.5 ng/ml, P = 0.015). Exhaled breath condensate nitrite correlated with plateau pressure (r = 0.27, P = 0.042) and plasma neutrophil elastase (r = 0.44, P = 0.001). Plasma Clara Cell protein 16 correlated with compliance (r = 0.34, P = 0.014).

CONCLUSIONS

No tidal volume-related changes were observed in the selected lung injury biomarkers of patients with healthy lungs after 60-min ventilation. Plasma neutrophil elastase and plasma Clara Cell protein 16 might indicate atelectrauma and lung distention, respectively.

Tidal volume and plateau pressure use for acute lung injury from 2000 to present: a systematic literature review

OBJECTIVE

Since publication of the Respiratory Management of Acute Lung Injury and Acute Respiratory Distress Syndrome (ARMA) trial in 2000, use of tidal volume (VT) less than or equal to 6 mL/kg predicted body weight with corresponding plateau airway pressures (PPlat) less than or equal to 30 cm H2O has been advocated for acute lung injury. However, compliance with these recommendations is unknown. We therefore investigated VT (mL/kg predicted body weight) and PPlat (cm H2O) practices reported in studies of acute lung injury since ARMA using a systematic literature review (i.e., not a meta-analysis).

DATA SOURCES

PubMed, Scopus, and EMBASE.

STUDY SELECTION

Randomized controlled trials and nonrandomized studies enrolling patients with acute lung injury from May 2000 to June 2013 and reporting VT.

DATA EXTRACTION

Whether the study was a randomized controlled trial or a nonrandomized study and performed or not at an Acute Respiratory Distress Syndrome Network center; in randomized controlled trials, the pre- and postrandomization VT (mL/kg predicted body weight) and PPlat (cm H2O) and whether a VT protocol was used postrandomization; in nonrandomized studies, baseline VT and PPlat.

DATA SYNTHESIS

Twenty-two randomized controlled trials and 71 nonrandomized studies were included. Since 2000 at acute respiratory distress syndrome Network centers, routine VT was similar comparing randomized controlled trials and nonrandomized studies (p = 0.25) and unchanged over time (p = 0.75) with a mean value of 6.81 (95% CI, 6.45, 7.18). At non-acute respiratory distress syndrome Network centers, routine VT was also similar when comparing randomized controlled trials and nonrandomized studies (p = 0.71), but decreased (p = 0.001); the most recent estimate for it was 6.77 (6.22, 7.32). All VT estimates were significantly greater than 6 (p ≤ 0.02). In randomized controlled trials employing VT protocols, routine VT was reduced in both acute respiratory distress syndrome Network (n = 4) and non-acute respiratory distress syndrome Network (n = 11) trials (p ≤ 0.01 for both), but even postrandomization was greater than 6 (6.47 [6.29, 6.65] and 6.80 [6.42, 7.17], respectively; p ≤ 0.0001 for both). In 59 studies providing data, routine PPlat, averaged across acute respiratory distress syndrome Network or non-acute respiratory distress syndrome Network centers, was significantly less than 30 (p ≤ 0.02).

CONCLUSIONS

For clinicians treating acute lung injury since 2000, achieving VT less than or equal to 6 mL/kg predicted body weight may not have been as attainable or important as PPlat less than or equal to 30 cm H2O. If so, there may be equipoise to test if VT less than or equal to 6 mL/kg predicted body weight are necessary to improve acute lung injury outcome.

Biomarkers in acute respiratory distress syndrome

PURPOSE OF REVIEW

The article provides an overview of efforts to identify and validate biomarkers in acute respiratory distress syndrome (ARDS) and a discussion of the challenges confronting researchers in this area.

RECENT FINDINGS

Although various putative biomarkers have been investigated in ARDS, the data have been largely disappointing and the 'troponin' of ARDS remains elusive. Establishing a relationship between measurable biological processes and clinical outcomes is vital to advancing clinical trials in ARDS and expanding our arsenal of treatments for this complex syndrome.

SUMMARY

This article summarizes the current status of ARDS biomarker research and provides a framework for future investigation.

Proteomic profiles in acute respiratory distress syndrome differentiates survivors from non-survivors

Acute Respiratory Distress Syndrome (ARDS) continues to have a high mortality. Currently, there are no biomarkers that provide reliable prognostic information to guide clinical management or stratify risk among clinical trial participants. The objective of this study was to probe the bronchoalveolar lavage fluid (BALF) proteome to identify proteins that differentiate survivors from non-survivors of ARDS. Patients were divided into early-phase (1 to 7 days) and late-phase (8 to 35 days) groups based on time after initiation of mechanical ventilation for ARDS (Day 1). Isobaric tags for absolute and relative quantitation (iTRAQ) with LC MS/MS was performed on pooled BALF enriched for medium and low abundance proteins from early-phase survivors (n = 7), early-phase non-survivors (n = 8), and late-phase survivors (n = 7). Of the 724 proteins identified at a global false discovery rate of 1%, quantitative information was available for 499. In early-phase ARDS, proteins more abundant in survivors mapped to ontologies indicating a coordinated compensatory response to injury and stress. These included coagulation and fibrinolysis; immune system activation; and cation and iron homeostasis. Proteins more abundant in early-phase non-survivors participate in carbohydrate catabolism and collagen synthesis, with no activation of compensatory responses. The compensatory immune activation and ion homeostatic response seen in early-phase survivors transitioned to cell migration and actin filament based processes in late-phase survivors, revealing dynamic changes in the BALF proteome as the lung heals. Early phase proteins differentiating survivors from non-survivors are candidate biomarkers for predicting survival in ARDS.

Predictive value of plasma biomarkers for mortality and organ failure development in patients with acute respiratory distress syndrome

PURPOSE

To evaluate the predictive value of 6 different biomarkers in the development of multiple-organ failure (MOF) and mortality in a contemporary prospective cohort of acute respiratory distress syndrome (ARDS).

METHODS

Patients with ARDS admitted to a tertiary referral center during an 8-month period were included. Plasma sample collection of 6 different biomarkers on days 1, 3, and 5 after ARDS onset was performed (von Willebrand factor, thrombin-antithrombin III complex, plasminogen activator inhibitor 1, interleukin 8, receptor for advanced glycation end-products, and club cell secretory protein). Main outcomes included hospital mortality and development of MOF. Logistic regression models for MOF and mortality prediction were created including biomarkers levels and clinical predictors.

RESULTS

One hundred patients were included in the study. Do-not-resuscitate status and McCabe score were independently associated with increased mortality. None of the 6 biomarkers measured at the time of ARDS diagnosis predicted hospital mortality. After adjustment for important clinical characteristics, elevated day-1 interleukin 8 levels were associated with the development of MOF.

CONCLUSIONS

Addition of biomarkers did not improve mortality prediction in this cohort of ARDS. Association between elevated interleukin 8 levels and progression of organ failures suggests an important role of exaggerated inflammatory response in the development of MOF.

Pathophysiology and biomarkers of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is defined as an acute-onset, progressive, hypoxic condition with radiographic bilateral lung infiltration, which develops after several diseases or injuries, and is not derived from hydrostatic pulmonary edema. One specific pathological finding of ARDS is diffuse alveolar damage. In 2012, in an effort to increase diagnostic specificity, a revised definition of ARDS was published in JAMA. However, no new parameters or biomarkers were adopted by the revised definition. Discriminating between ARDS and other similar diseases is critically important; however, only a few biomarkers are currently available for diagnostic purposes. Furthermore, predicting the severity, response to therapy, or outcome of the illness is also important for developing treatment strategies for each patient. However, the PaO₂/FIO₂ ratio is currently the sole clinical parameter used for this purpose. In parallel with progress in understanding the pathophysiology of ARDS, various humoral factors induced by inflammation and molecules derived from activated cells or injured tissues have been shown as potential biomarkers that may be applied in clinical practice. In this review, the current understanding of the basic pathophysiology of ARDS and associated candidate biomarkers will be discussed.

Plasma biomarkers for acute respiratory distress syndrome: a systematic review and meta-analysis*

OBJECTIVE

Numerous studies have focused on biomarkers for acute lung injury and acute respiratory distress syndrome. Although several biomarkers have been identified, their relative performance is unclear. We aim to provide a quantitative overview of plasma-derived biomarkers associated with acute respiratory distress syndrome diagnosis or mortality.

DATA SOURCES

MEDLINE (inception to January 2012) and personal databases.

STUDY SELECTION

English-language studies on plasma biomarkers associated with acute respiratory distress syndrome diagnosis or mortality.

DATA EXTRACTION

Demographic variables, plasma levels of biomarker, statistical data, acute respiratory distress syndrome occurrence, and mortality rates were retrieved. The methodological quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies score. Clinical outcomes included 1) diagnosis of acute respiratory distress syndrome in the at-risk population and 2) mortality in acute respiratory distress syndrome patients. For each biomarker, pooled odds ratios for clinical outcome were calculated by meta-analysis, and biomarkers were ranked according to pooled odds ratio.

DATA SYNTHESIS

Fifty-four studies appeared eligible for meta-analysis, together including 3,753 patients. We identified 20 biomarkers for diagnosis of acute respiratory distress syndrome in the at-risk population and 19 biomarkers for mortality of acute respiratory distress syndrome patients. The biomarkers most strongly associated with acute respiratory distress syndrome diagnosis in the at-risk population, when increased, were Krebs von den Lungen-6 (odds ratio [95% CI], 6.1 [3.0-12.1]), lactate dehydrogenase (5.7 [1.7-19.1]), soluble receptor for advanced glycation end products (3.5 [1.7-7.2]), and von Willebrand Factor (3.1 [2.0-5.2]). The biomarkers most strongly associated with acute respiratory distress syndrome mortality, when increased, were interleukin-4 (18.0 [6.0-54.2]), interleukin-2 (11.8 [4.3-32.2]), angiopoietin-2 (6.4 [1.3-30.4]), and Krebs von den Lungen-6 (5.1 [3.0-12.2]). Decreased levels of Protein C were associated with increased odds for acute respiratory distress syndrome diagnosis and mortality.

CONCLUSIONS

This meta-analysis provides a unique ranking of plasma biomarkers according to their strength of association with acute respiratory distress syndrome diagnosis or acute respiratory distress syndrome mortality. The relative performance of biomarkers among studies shown in this ranking may help to improve acute respiratory distress syndrome diagnosis and outcome prediction.

Preoperative plasma club (clara) cell secretory protein levels are associated with primary graft dysfunction after lung transplantation

Inherent recipient factors, including pretransplant diagnosis, obesity and elevated pulmonary pressures, are established primary graft dysfunction (PGD) risks. We evaluated the relationship between preoperative lung injury biomarkers and PGD to gain further mechanistic insight in recipients. We performed a prospective cohort study of recipients in the Lung Transplant Outcomes Group enrolled between 2002 and 2010. Our primary outcome was Grade 3 PGD on Day 2 or 3. We measured preoperative plasma levels of five biomarkers (CC-16, sRAGE, ICAM-1, IL-8 and Protein C) that were previously associated with PGD when measured at the postoperative time point. We used multivariable logistic regression to adjust for potential confounders. Of 714 subjects, 130 (18%) developed PGD. Median CC-16 levels were elevated in subjects with PGD (10.1 vs. 6.0, p<0.001). CC-16 was associated with PGD in nonidiopathic pulmonary fibrosis (non-IPF) subjects (OR for highest quartile of CC-16: 2.87, 95% CI: 1.37, 6.00, p=0.005) but not in subjects with IPF (OR 1.38, 95% CI: 0.43, 4.45, p=0.59). After adjustment, preoperative CC-16 levels remained associated with PGD (OR: 3.03, 95% CI: 1.26, 7.30, p=0.013) in non-IPF subjects. Our study suggests the importance of preexisting airway epithelial injury in PGD. Markers of airway epithelial injury may be helpful in pretransplant risk stratification in specific recipients.

Biomarkers and bacterial pneumonia risk in patients with treated HIV infection: a case-control study

Background

Despite advances in HIV treatment, bacterial pneumonia continues to cause considerable morbidity and mortality in patients with HIV infection. Studies of biomarker associations with bacterial pneumonia risk in treated HIV-infected patients do not currently exist.

Methods

We performed a nested, matched, case-control study among participants randomized to continuous combination antiretroviral therapy (cART) in the Strategies for Management of Antiretroviral Therapy trial. Patients who developed bacterial pneumonia (cases) and patients without bacterial pneumonia (controls) were matched 1∶1 on clinical center, smoking status, age, and baseline cART use. Baseline levels of Club Cell Secretory Protein 16 (CC16), Surfactant Protein D (SP-D), C-reactive protein (hsCRP), interleukin-6 (IL-6), and d-dimer were compared between cases and controls.

Results

Cases (n = 72) and controls (n = 72) were 25.7% female, 51.4% black, 65.3% current smokers, 9.7% diabetic, 36.1% co-infected with Hepatitis B/C, and 75.0% were on cART at baseline. Median (IQR) age was 45 (41, 51) years with CD4+ count of 553 (436, 690) cells/mm³. Baseline CC16 and SP-D were similar between cases and controls, but hsCRP was significantly higher in cases than controls (2.94 µg/mL in cases vs. 1.93 µg/mL in controls; p = 0.02). IL-6 and d-dimer levels were also higher in cases compared to controls, though differences were not statistically significant (p-value 0.06 and 0.10, respectively).

Conclusions

In patients with cART-treated HIV infection, higher levels of systemic inflammatory markers were associated with increased bacterial pneumonia risk, while two pulmonary-specific inflammatory biomarkers, CC16 and SP-D, were not associated with bacterial pneumonia risk.

Biomarkers in acute lung injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) result in high permeability pulmonary edema causing hypoxic respiratory failure with high morbidity and mortality. As the population ages, the incidence of ALI is expected to rise. Over the last decade, several studies have identified biomarkers in plasma and bronchoalveolar lavage fluid providing important insights into the mechanisms involved in the pathophysiology of ALI. Several biomarkers have been validated in subjects from the large, multicenter ARDS clinical trials network. Despite these studies, no single or group of biomarkers has made it into routine clinical practice. New high throughput "omics" techniques promise improved understanding of the biologic processes in the pathogenesis in ALI and possibly new biomarkers that predict disease and outcomes. In this article, we review the current knowledge on biomarkers in ALI.

Biomarkers in acute lung injury: insights into the pathogenesis of acute lung injury

Studies of potential biomarkers of acute lung injury (ALI) have provided information relating to the pathophysiology of the mechanisms of lung injury and repair. The utility of biomarkers remains solely among research tools to investigate lung injury and repair mechanisms. Because of lack of sensitivity and specificity, they cannot be used in decision making in patients with ALI or acute respiratory distress syndrome. The authors reviewed known biomarkers in context of their major biologic activity. The continued interest in identifying and studying biomarkers is relevant, as it provides information regarding the mechanisms involved in lung injury and repair and how this may be helpful in identifying and designing future therapeutic targets and strategies and possibly identifying a sensitive and specific biomarker.

Comparable effect of conventional ventilation versus early high-frequency oscillation on serum CC16 and IL-6 levels in preterm neonates

OBJECTIVE

Clara cell 16 kD protein (CC16) and interleukin (IL)-6 have been used as peripheral blood biomarkers of alveolar leakage and inflammation, respectively. Thus, their measurement in the bloodstream could be used to assess ventilator-induced lung injury. The objective of this study was to evaluate the effect of optimized synchronized intermittent mandatory ventilation (SIMV) and high-frequency oscillatory ventilation (HFOV) on circulating CC16 and IL-6 levels when used as the initial ventilation modes in preterm neonates.

STUDY DESIGN

Single center, prospective, randomized clinical study in preterm neonates (gestational age 30 weeks) requiring mechanical ventilation within the first 2 h of life. Serum CC16 and IL-6 were measured on establishment of the assigned ventilation mode after admission, at days 3 and 14 of life as well as at 36 weeks postmenstrual age. Demographic-perinatal data and clinical parameters were also recorded.

RESULT

Of the 30 neonates studied, 24 (gestational age 27.1±1.7 weeks, birth weight 942±214 g) were finally analyzed, equally assigned into the SIMV and HFOV groups. Both groups had comparable demographic-perinatal characteristics and clinical parameters. Serum CC16 and IL-6 altered significantly over time (repeated-measures analysis of variance, both P<0.001). However, changes were not affected by the ventilation mode. Post hoc analysis showed a significant decrease in CC16 and IL-6 from birth up to 36 weeks postmenstrual age in both groups.

CONCLUSION

In preterm neonates, SIMV and HFOV are associated with comparable circulating CC16 and IL-6 levels. These findings suggest a similar alveolar leakage and systemic inflammation with any of the ventilation modes evaluated when their usage is optimized.

Human immunodeficiency virus infection and hospital mortality in acute lung injury patients

OBJECTIVE

To evaluate the impact of human immunodeficiency virus infection on hospital mortality in patients with acute lung injury and to evaluate predictors of mortality among acute lung injury patients with human immunodeficiency virus.

DESIGN, SETTING, AND PATIENTS

Retrospective study of human immunodeficiency virus-infected patients enrolled in an ongoing prospective cohort study of acute lung injury patients conducted at 13 intensive care units in four teaching hospitals in Baltimore, Maryland.

MEASUREMENTS AND MAIN RESULTS

Of 520 consecutive acute lung injury patients, 66 (13%) were human immunodeficiency virus-positive. In human immunodeficiency virus-positive vs. human immunodeficiency virus-negative patients, pneumonia was the most common acute lung injury risk factor (43 [65%] vs. 184 [41%]; p=.001), and the median (interquartile range) Acute Physiology and Chronic Health Evaluation II score was modestly higher (27 [22-33] vs. 26 [20-33]; p=.06). There was no difference in crude hospital mortality (44% vs. 46%; p=.78) between human immunodeficiency virus-positive and human immunodeficiency virus-negative acute lung injury patients. After adjustment for potential confounders, human immunodeficiency virus infection was not an independent predictor of hospital mortality (odds ratio, 1.39; 95% confidence interval, 0.69-2.78; p=.35). In the human immunodeficiency virus-infected acute lung injury patients, among 23 relevant measures of intensive care unit and human immunodeficiency virus severity of illness, only the presence of an opportunistic infection before hospital admission was independently associated with hospital mortality (odds ratio, 6.4; 95% confidence interval, 1.27-32.3; p=.025).

CONCLUSIONS

In patients with acute lung injury, human immunodeficiency virus-positive patients had similar hospital mortality as human immunodeficiency virus-negative patients; hence, human immunodeficiency virus status should not influence estimates of short-term prognosis for acute lung injury patients in the intensive care unit. Among human immunodeficiency virus-positive patients with acute lung injury, the presence of a previous opportunistic infection, rather than traditional measures of severity of illness, may be most strongly predictive of hospital mortality.

Non-invasive assessment of small airway remodelling in smokers

Smoking associated COPD progression is likely to be directly linked to differential injury and repair dynamics in small airways (SA). Although IL8 is a well-accepted marker for injured airway epithelium, Clara cells [the predominant proliferating cells in SA] and SCGB1A1 protein [their major secretory product] have only recently emerged as potential SA repair markers. We therefore postulate that the SCGB1A1/IL8 ratio in the airways of smokers would be inversely associated with physiological, radiological and clinical measures of COPD. A cross-sectional cohort of 28 smokers undergoing surgery for peripheral nodule was recruited (24M/4F, age 61 +/- 11 y, FEV1s 76 +/- 20%, smoking 40 +/- 12 p.y). SCGB1A1 and IL8 were measured by ELISA in the induced sputum (IS) 3 to 5 days prior to surgery as well as by immunohistochemistry from lung tissue (also assessed morphometrically) obtained distant to the cancer surgery site. COPD was assessed using standard clinical, functional and radiological parameters. Log-transformed IS-SCGB1A1 was linearly correlated with SCGB1A1-positive epithelial cells detected via immunohistochemistry (r = .533, p = .001), while IS-IL8 was positively related to SA infiltrating neutrophils (Elastase-positive cells). There was a striking negative correlation between IS-SCGB1A1/IL8 levels and whole airway thickness [SA < 2 mm] at morphometry (r = -0.83, p < 0.0001). IS-SCGB1A1/IL8 levels were also inversely associated with nitrogen slope [r = -0.52, p < 0.001] and HRCT SA score [r = -0.51, p < 0.001]. In a multivariate analysis the IS-SCGB1A1/IL8 ratio was a stronger predictor than both the physiological and radiological measures of SA disease assessed. The SCGB1A1/IL8 ratio measured in sputum is a potentially valuable biomarker for non-invasive assessment of SA remodelling in smokers.

Effects of ultrafine particles-induced oxidative stress on Clara cells in allergic lung inflammation

Background

Clara cell protein (CC16), the main secretory product of bronchiolar Clara cells, plays an important protective role in the respiratory tract against oxidative stress and inflammation. The purpose of the study was to investigate the role of elemental carbon ultrafine particles (EC-UFP)-induced oxidative stress on Clara cells and CC16 in a mouse model of allergic lung inflammation.

Methods

Ovalbumin (OVA)-sensitized mice were exposed to EC-UFP (507 μg/m³ for 24 h) or filtered air immediately prior to allergen challenge and systemically treated with N-acetylcysteine (NAC) or vehicle prior and during EC-UFP inhalation. CC16 was measured up to one week after allergen challenge in bronchoalveolar lavage fluid (BALF) and in serum. The relative expression of CC16 and TNF-α mRNA were measured in lung homogenates. A morphometrical analysis of mucus hypersecretion and electron microscopy served to investigate goblet cell metaplasia and Clara cell morphological alterations.

Results

In non sensitized mice EC-UFP inhalation caused alterations in CC16 concentration, both at protein and mRNA level, and induced Clara cell hyperplasia. In sensitized mice, inhalation of EC-UFP prior to OVA challenge caused most significant alterations of BALF and serum CC16 concentration, BALF total protein and TNF-α relative expression compared to relevant controls; their Clara cells displayed the strongest morphological alterations and strongest goblet cell metaplasia occurred in the small airways. NAC strongly reduced both functional and morphological alterations of Clara cells.

Conclusion

Our findings demonstrate that oxidative stress plays an important role in EC-UFP-induced augmentation of functional and morphological alterations of Clara cells in allergic lung inflammation.

Plasma levels of surfactant protein D and KL-6 for evaluation of lung injury in critically ill mechanically ventilated patients

Background

Preventing ventilator-associated lung injury (VALI) has become pivotal in mechanical ventilation of patients with acute lung injury (ALI) or its more severe form, acute respiratory distress syndrome (ARDS). In the present study we investigated whether plasma levels of lung-specific biological markers can be used to evaluate lung injury in patients with ALI/ARDS and patients without lung injury at onset of mechanical ventilation.

Methods

Plasma levels of surfactant protein D (SP-D), Clara Cell protein (CC16), KL-6 and soluble receptor for advanced glycation end-products (sRAGE) were measured in plasma samples obtained from 36 patients - 16 patients who were intubated and mechanically ventilated because of ALI/ARDS and 20 patients without lung injury at the onset of mechanical ventilation and during conduct of the study. Patients were ventilated with either a lung-protective strategy using lower tidal volumes or a potentially injurious strategy using conventional tidal volumes. Levels of biological markers were measured retrospectively at baseline and after 2 days of mechanical ventilation.

Results

Plasma levels of CC16 and KL-6 were higher in ALI/ARDS patients at baseline as compared to patients without lung injury. SP-D and sRAGE levels were not significantly different between these patients. In ALI/ARDS patients, SP-D and KL-6 levels increased over time, which was attenuated by lung-protective mechanical ventilation using lower tidal volumes (P = 0.02 for both biological markers). In these patients, with either ventilation strategy no changes over time were observed for plasma levels of CC16 and sRAGE. In patients without lung injury, no changes of plasma levels of any of the measured biological markers were observed.

Conclusion

Plasma levels of SP-D and KL-6 rise with potentially injurious ventilator settings, and thus may serve as biological markers of VALI in patients with ALI/ARDS.

Plasma CC16 levels are associated with development of ALI/ARDS in patients with ventilator-associated pneumonia: a retrospective observational study

BACKGROUND

Despite consensus criteria, diagnosing acute lung injury, or its more severe form acute respiratory distress syndrome (ALI/ARDS) remains challenging. Adding objective measures, such as plasma levels of biological markers could facilitate recognition of ALI/ARDS. This study was designed to assess and compare the diagnostic accuracy of biological markers for ALI/ARDS with ventilator-associated pneumonia (VAP).

METHODS

We performed serial measurements of Clara cell protein (CC16), soluble receptor for advanced glycation end products (sRAGE), surfactant protein D (SP-D) and Krebs von den Lungen (KL-6) in plasma of patients with VAP and mechanically ventilated control patients without VAP. ALI/ARDS was diagnosed using the criteria of the North-American European consensus conference.

RESULTS

Thirty-seven patients were enrolled - 22 patients with VAP and 15 control patients. Ten patients with pneumonia met the ALI/ARDS consensus criteria. Control patients never met these criteria. Plasma CC16 had a good diagnostic capacity for ALI/ARDS as shown by the receiver operating characteristic curve with an area under the curve of 0.91 (95% confidence interval (CI) 0.79 - 1.00; p < 0.001). Identification of ALI/ARDS patients by sudden increases in plasma CC16 of 30% or more yielded a sensitivity of 90% and a specificity of 92%. Of note, levels of CC16 increased 2 days before ALI/ARDS diagnosis. A cut-off level of 50 ng/ml SP-D yielded a specificity of 100% while the sensitivity was 70%. The area under the curve for SP-D was 0.80 (95% CI 0.58 - 1.00; p = 0.02). The diagnostic accuracies of KL-6 and sRAGE were low.

CONCLUSION

Plasma CC16 seems a potential biological marker for ALI/ARDS in patients with VAP. Plasma levels of sRAGE, SP-D and KL-6 have limited discriminative power for diagnosing ALI/ARDS in VAP.

Clara cell protein (CC16), a marker of lung epithelial injury, is decreased in plasma and pulmonary edema fluid from patients with acute lung injury

BACKGROUND

Acute lung injury (ALI) and ARDS are common clinical syndromes that are underdiagnosed. Clara cell secretory protein (CC16) is an antiinflammatory protein secreted by the Clara cells of the distal respiratory epithelium that has been proposed as a biomarker of lung epithelial injury. We tested the diagnostic and prognostic utility of CC16 in patients with non-trauma-related ALI/ARDS compared to a control group of patients with acute cardiogenic pulmonary edema (CPE).

METHODS

Plasma and pulmonary edema fluid samples were obtained from medical and surgical patients with ALI/ARDS or CPE requiring intubation for mechanical ventilation. The etiology of pulmonary edema was determined using consensus clinical criteria for ALI/ARDS and CPE and the edema fluid-to-plasma protein ratio. Plasma and edema fluid CC16 levels were measured by sandwich enzyme-linked immunosorbent assay. CC16 levels were log transformed for analysis, and comparisons were made by the Student t test or Chi(2) as appropriate.

RESULTS

Compared to patients with CPE (n = 9), patients with ALI/ARDS (n = 23) had lower median CC16 levels in plasma (22 ng/mL [interquartile range (IQR), 9 to 44 ng/mL] vs 55 ng/mL [IQR, 18 to 123 ng/mL], respectively; p = 0.053) and pulmonary edema fluid (1,950 ng/mL [IQR, 1,780 to 4,024 ng/mL] vs 4,835 ng/mL [IQR, 2,006 to 6,350 ng/mL], respectively; p = 0.044). Relative to total pulmonary edema fluid protein concentration, the median CC16 level was significantly lower in patients with ALI/ARDS (45 ng CC16/mg total protein [IQR, 4 to 64 ng CC16/mg total protein] vs 120 ng CC16/mg total protein [IQR, 87 to 257 ng CC16/mg total protein], respectively; p = 0.005). Neither plasma nor edema fluid CC16 levels predicted mortality, the number of days of unassisted ventilation, or ICU length of stay.

CONCLUSION

CC16 is a promising diagnostic biomarker for helping to discriminate ALI from CPE. Larger scale validation is warranted to better characterize the utility of CC16 in the diagnosis of this underrecognized syndrome.

Clara cell secretory protein (CC16) as a peripheral blood biomarker of lung injury in ventilated preterm neonates

The aim of this study was to assess the serum concentrations of Clara cell secretory protein (CC16) in association with acute and chronic lung injury in mechanically ventilated preterm neonates. Thirty-five preterm neonates (gestational age [GA] <or=31 weeks) with acute respiratory failure were enrolled. Of these, 23 neonates requiring ventilatory support within 2 h after birth comprised the mechanically ventilated group (MV group), and 12 neonates who were not ventilated made up the nonventilated group (NV group). Serum CC16 was measured (using enzyme-linked immunosorbent assay [ELISA]) within 2 h (T0) and at 72 h (T1) after birth, at day 14 of life (T2) and at 36 weeks postmenstrual age (T3). The median CC16 concentrations were significantly higher in the MV group compared to the NV group at all times. Analysis with respect to differences observed in the group characteristics showed that GA, Apgar score at 5 min and mechanical ventilation were significant covariates of serum CC16 at T0. All neonates in the NV group and 18 cases in the MV group, respectively, survived discharge. Ventilated survivors with later bronchopulmonary dysplasia (BPD; oxygen requirement at T3, n = 7) had significantly higher CC16 at all times compared to nonventilated neonates. Elevated serum CC16 levels at T2 were predictive of BPD development. In conclusion, our results show that serum CC16 increases significantly in preterm neonates ventilated early after birth and remains high in those with later BPD. Further research is needed to validate the usefulness of CC16 as a peripheral blood biomarker of acute and chronic lung injury.

Acute respiratory distress syndrome 40 years later: time to revisit its definition

OBJECTIVE

Acute respiratory distress syndrome is a common disorder associated with significant mortality and morbidity. The aim of this article is to critically evaluate the definition of acute respiratory distress syndrome and examine the impact the definition has on clinical practice and research.

DATA SOURCES

Articles from a MEDLINE search (1950 to August 2007) using the Medical Subject Heading respiratory distress syndrome, adult, diagnosis, limited to the English language and human subjects, their relevant bibliographies, and personal collections, were reviewed.

DATA SYNTHESIS

The definition of acute respiratory distress syndrome is important to researchers, clinicians, and administrators alike. It has evolved significantly over the last 40 years, culminating in the American-European Consensus Conference definition, which was published in 1994. Although the American-European Consensus Conference definition is widely used, it has some important limitations that may impact on the conduct of clinical research, on resource allocation, and ultimately on the bedside management of such patients. These limitations stem partially from the fact that as defined, acute respiratory distress syndrome is a heterogeneous entity and also involve the reliability and validity of the criteria used in the definition. This article critically evaluates the American-European Consensus Conference definition and its limitations. Importantly, it highlights how these limitations may contribute to clinical trials that have failed to detect a potential true treatment effect. Finally, recommendations are made that could be considered in future definition modifications with an emphasis on the significance of accurately identifying the target population in future trials and subsequently in clinical care.

CONCLUSION

How acute respiratory distress syndrome is defined has a significant impact on the results of randomized, controlled trials and epidemiologic studies. Changes to the current American-European Consensus Conference definition are likely to have an important role in advancing the understanding and management of acute respiratory distress syndrome.

Kinetics and determinants of the changes of CC16, a lung secretory protein in a rat model of toxic lung injury

PURPOSE

To investigate the kinetics and the determinants of the changes of the Clara cell 16 kDa protein (CC16) as a marker of lung injury following exposure to different toxicants.

METHODS

Rats were treated with 4-Ipomeanol (IPO), alpha-naphtylthiourea (ANTU), sodium chromate (Na(2)CrO(4)) or paraquat-(PQ). The changes of CC16, total protein, albumin, and cystatin-C were determined on BALF supernatan, and CC16, cystatin-C and creatinine levels were also determined in serum.

RESULTS

Bronchiolar insult due to IPO or ANTU resulted in an initial transient increase of serum CC16, parallel to that of albumin in BALF, and a subsequent reduction in both BALF and serum. A slight reduction of CC16 in BALF was already apparent one hour following treatment with PQ. In the serum, CC16 increased to 400% of basal value. With PQ and Na(2)CrO(4), the elevation of CC16 was mainly determined by the degree of renal impairment.