IL1RN coding variant is associated with lower risk of acute respiratory distress syndrome and increased plasma IL-1 receptor antagonist

Interleukin-1 Receptor Antagonist Gene (IL1RN) Variants Modulate the Cytokine Release Syndrome and Mortality of COVID-19

BACKGROUND

We examined effects of single-nucleotide variants (SNVs) of IL1RN, the gene encoding the anti-inflammatory interleukin 1 receptor antagonist (IL-1Ra), on the cytokine release syndrome (CRS) and mortality in patients with acute severe respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

METHODS

IL1RN CTA haplotypes formed from 3 SNVs (rs419598, rs315952, rs9005) and the individual SNVs were assessed for association with laboratory markers of inflammation and mortality. We studied 2589 patients hospitalized with SARS-CoV-2 between March 2020 and March 2021.

RESULTS

Mortality was 15.3% and lower in women than men (13.1% vs 17.3%, P = .0003). Carriers of the CTA-1/2 IL1RN haplotypes exhibited decreased inflammatory markers and increased plasma IL-1Ra. Evaluation of the individual SNVs of the IL1RN, carriers of the rs419598 C/C SNV exhibited significantly reduced inflammatory biomarker levels and numerically lower mortality compared to the C/T-T/T genotype (10.0% vs 17.8%, P = .052) in men, with the most pronounced association observed in male patients ≤74 years old, whose mortality was reduced by 80% (3.1% vs 14.0%, P = .030).

CONCLUSIONS

The IL1RN haplotype CTA and C/C variant of rs419598 are associated with attenuation of the CRS and decreased mortality in men with acute SARS-CoV-2 infection. The data suggest that the IL1RN pathway modulates the severity of coronavirus disease 2019 (COVID-19) via endogenous anti-inflammatory mechanisms.

NLRP6 negatively regulates host defense against polymicrobial sepsis

Introduction

Sepsis remains a major cause of death in Intensive Care Units. Sepsis is a life-threatening multi-organ dysfunction caused by a dysregulated systemic inflammatory response. Pattern recognition receptors, such as TLRs and NLRs contribute to innate immune responses. Upon activation, some NLRs form multimeric protein complexes in the cytoplasm termed "inflammasomes" which induce gasdermin d-mediated pyroptotic cell death and the release of mature forms of IL-1β and IL-18. The NLRP6 inflammasome is documented to be both a positive and a negative regulator of host defense in distinct infectious diseases. However, the role of NLRP6 in polymicrobial sepsis remains elusive.

Methods

We have used NLRP6 KO mice and human septic spleen samples to examine the role of NLRP6 in host defense in sepsis.

Results

NLRP6 KO mice display enhanced survival, reduced bacterial burden in the organs, and reduced cytokine/chemokine production. Co-housed WT and KO mice following sepsis show decreased bacterial burden in the KO mice as observed in singly housed groups. NLRP6 is upregulated in CD3, CD4, and CD8 cells of septic patients and septic mice. The KO mice showed a higher number of CD3, CD4, and CD8 positive T cell subsets and reduced T cell death in the spleen following sepsis. Furthermore, administration of recombinant IL-18, but not IL-1β, elicited excessive inflammation and reversed the survival advantages observed in NLRP6 KO mice.

Conclusion

These results unveil NLRP6 as a negative regulator of host defense during sepsis and offer novel insights for the development of new treatment strategies for sepsis.

Acute respiratory distress syndrome heterogeneity and the septic ARDS subgroup

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

Interesting effects of interleukins and immune cells on acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a medical condition characterized by widespread inflammation in the lungs with consequent proportional loss of gas exchange function. ARDS is linked with severe pulmonary or systemic infection. Several factors, including secretory cytokines, immune cells, and lung epithelial and endothelial cells, play a role in the development and progression of this disease. The present study is based on Pubmed database information (1987-2022) using the words "Acute respiratory distress syndrome", "Interleukin", "Cytokines" and "Immune cells". Cytokines and immune cells play an important role in this disease, with particular emphasis on the balance between pro-inflammatory and anti-inflammatory factors. Neutrophils are one of several important mediators of Inflammation, lung tissue destruction, and malfunction during ARDS. Some immune cells, such as macrophages and eosinophils, play a dual role in releasing inflammatory mediators, recruitment inflammatory cells and the progression of ARDS, or releasing anti-inflammatory mediators, clearing the lung of inflammatory cells, and helping to improve the disease. Different interleukins play a role in the development or inhibition of ARDS by helping to activate various signaling pathways, helping to secrete other inflammatory or anti-inflammatory interleukins, and playing a role in the production and balance between immune cells involved in ARDS. As a result, immune cells and, inflammatory cytokines, especially interleukins play an important role in the pathogenesis of this disease Therefore, understanding the relevant mechanisms will help in the proper diagnosis and treatment of this disease.

The emerging role of IL-38 in diseases: A comprehensive review

INTRODUCTION

Interleukin-38 (IL-38) is a new type of anti-inflammatory cytokine, which is mainly expressed in the immunity-related organs and is involved in various diseases including cardiovascular and cerebrovascular diseases, lung diseases, viral infectious diseases and autoimmune diseases.

AIM

This review aims to detail the biological function, receptors and signaling of IL-38, which highlights its therapeutic potential in related diseases.

CONCLUSION

This article provides a comprehensive review of the association between interleukin-38 and related diseases, using interleukin-38 as a keyword and searching the relevant literature through Pubmed and Web of science up to July 2023.

Interleukin-1 receptor antagonist gene ( IL1RN ) variants modulate the cytokine release syndrome and mortality of SARS-CoV-2

Objective

To explore the regulation of the inflammatory response in acute SARS-CoV-2 infection, we examined effects of single nucleotide variants (SNVs) of IL1RN , the gene encoding the anti-inflammatory IL-1 receptor antagonist (IL-1Ra), on the cytokine release syndrome and mortality.

Methods

We studied 2589 patients hospitalized with SARS-CoV-2 between March 2020 and March 2021 at NYU Langone's Tisch Hospital. CTA and TTG haplotypes formed from three SNVs (rs419598, rs315952, rs9005) and the individual SNVs of the IL1RN gene were assessed for association with laboratory markers of the cytokine release syndrome (CRS) and mortality.

Results

Mortality in the population was 15.3%, and was lower in women than men (13.1% vs.17.3%, p<0.0003). Carriers of the CTA-1/2 IL1RN haplotypes exhibited decreased inflammatory markers and increased plasma IL-1Ra relative to TTG carriers. Decreased mortality among CTA-1/2 carriers was observed in male patients between the ages of 55-74 [9.2% vs. 17.9%, p=0.001]. Evaluation of individual SNVs of the IL1RN gene (rs419598, rs315952, rs9005) indicated that carriers of the IL1RN rs419598 CC SNV exhibited lower inflammatory biomarker levels, and was associated with reduced mortality compared to the CT/TT genotype in men (OR 0.49 (0.23 - 1.00); 0.052), with the most pronounced effect observed between the ages of 55-74 [5.5% vs. 18.4%, p<0.001].

Conclusion

The IL1RN haplotype CTA, and sequence variant of rs419598 are associated with attenuation of the cytokine release syndrome and decreased mortality in males with acute SARS-CoV2 infection. The data suggest that IL1RN modulates the COVID-19 cytokine release syndrome via endogenous " anti-inflammatory" mechanisms.

Significance statement

We provide evidence that variants of IL1RN modulate the severity of SARS-CoV-2 infection. The IL1RN CTA haplotype and rs419598 CC single nucleotide variant are associated with decreased plasma levels of inflammatory markers, interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interleukin-2 (IL-2), C-reactive protein (CRP), D-dimer, ferritin, and procalcitonin, in association with higher levels of IL-1Ra and IL-10, anti-inflammatory proteins. Both haplotype CTA and rs419598 CC genotype are associated with a significant reduction in the mortality of men. These data provide genetic evidence that inflammasome activation and the IL-1 pathway plays an important role in the mortality and morbidity associated with severe SARS-CoV-2 infection, and that genetic regulation of inflammatory pathways by variants of IL1RN merits further evaluation in severe SARS-CoV-2 infection.

Biomarkers for the Prediction and Judgement of Sepsis and Sepsis Complications: A Step towards precision medicine?

Sepsis and septic shock are a major public health concern and are still associated with high rates of morbidity and mortality. Whilst there is growing understanding of different phenotypes and endotypes of sepsis, all too often treatment strategies still only employ a “one-size-fits-all” approach. Biomarkers offer a unique opportunity to close this gap to more precise treatment approaches by providing insight into clinically hidden, yet complex, pathophysiology, or by individualizing treatment pathways. Predicting and evaluating systemic inflammation, sepsis or septic shock are essential to improve outcomes for these patients. Besides opportunities to improve patient care, employing biomarkers offers a unique opportunity to improve clinical research in patients with sepsis. The high rate of negative clinical trials in this field may partly be explained by a high degree of heterogeneity in patient cohorts and a lack of understanding of specific endotypes or phenotypes. Moving forward, biomarkers can support the selection of more homogeneous cohorts, thereby potentially improving study conditions of clinical trials. This may finally pave the way to a precision medicine approach to sepsis, septic shock and complication of sepsis in the future.

New Insights into Clinical and Mechanistic Heterogeneity of the Acute Respiratory Distress Syndrome: Summary of the Aspen Lung Conference 2021

Clinical and molecular heterogeneity are common features of human disease. Understanding the basis for heterogeneity has led to major advances in therapy for many cancers and pulmonary diseases such as cystic fibrosis and asthma. Although heterogeneity of risk factors, disease severity, and outcomes in survivors are common features of the acute respiratory distress syndrome (ARDS), many challenges exist in understanding the clinical and molecular basis for disease heterogeneity and using heterogeneity to tailor therapy for individual patients. This report summarizes the proceedings of the 2021 Aspen Lung Conference, which was organized to review key issues related to understanding clinical and molecular heterogeneity in ARDS. The goals were to review new information about ARDS phenotypes, to explore multicellular and multisystem mechanisms responsible for heterogeneity, and to review how best to account for clinical and molecular heterogeneity in clinical trial design and assessment of outcomes. The report concludes with recommendations for future research to understand the clinical and basic mechanisms underlying heterogeneity in ARDS to advance the development of new treatments for this life-threatening critical illness.

Novel biomarkers for acute respiratory distress syndrome: genetics, epigenetics and transcriptomics

Acute respiratory distress syndrome (ARDS) can be induced by multiple clinical factors, including sepsis, acute pancreatitis, trauma, intestinal ischemia/reperfusion and burns. However, these factors alone may poorly explain the risk and outcomes of ARDS. Emerging evidence suggests that genomic-based or transcriptomic-based biomarkers may hold the promise to establish predictive or prognostic stratification methods for ARDS, and also to help in developing novel therapeutic targets for ARDS. Notably, genetic/epigenetic variations correlated with susceptibility and prognosis of ARDS and circulating microRNAs have emerged as potential biomarkers for diagnosis or prognosis of ARDS. Although limited by sample size, ethnicity and phenotypic heterogeneity, ongoing genetic/transcriptomic research contributes to the characterization of novel biomarkers and ultimately helps to develop innovative therapeutics for ARDS patients.

Genetics of Acute Respiratory Distress Syndrome: Pathways to Precision

Clinical risk factors alone fail to fully explain acute respiratory distress syndrome (ARDS) risk or ARDS death, suggesting that individual risk factors contribute. The goals of genomic ARDS studies include better mechanistic understanding, identifying dysregulated pathways that may be amenable to pharmacologic targeting, using genomic causal inference techniques to find measurable traits with meaning, and deconvoluting ARDS heterogeneity by proving reproducible subpopulations that may share a unique biology. This article discusses the latest advances in ARDS genomics, provides historical perspective, and highlights some of the ways that the coronavirus disease 2019 (COVID-19) pandemic is accelerating genomic ARDS research.

Will a little change do you good? A putative role of polymorphisms in COVID-19

An alarming disease caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) named COVID-19 has emerged as an unprecedented public health problem and ignited a world health crisis. As opposed to what was believed at the beginning of the pandemic, the virus has not only spread but persevere causing secondary waves and challenging the concept of herd immunity against viral infections. While the majority of SARS-CoV-2-infected individuals may remain asymptomatic, a fraction of individuals may develop low to high-grade severity signs and symptoms of COVID-19. The disease is multifactorial and can progress quickly, leading to severe complications and even death in a few days. Therefore, understanding the pre-existing factors for disease development has never been so pressing. In this scenario, the insights on the mechanisms underlying disease allied to the immune response developed during the viral invasion could shed light on novel predictive factors and prognostic tools for COVID-19 management and interventions. A recent genome-wide association study (GWAS) revealed several molecules that significantly impacted critically ill COVID-19 patients, leading to the core mechanisms of COVID-19 pathogenesis. Considering these findings and the fact that ACE-2 polymorphisms alone cannot explain disease progress and severity, this review aims at summarizing the most important and recent findings of the research and expert consensus of possible cytokine-related polymorphisms existing in the differential expression of paramount immune molecules that could be crucial for providing guidelines for decision-making and appropriate clinical management of COVID-19.

Photobiomodulation and Antiviral Photodynamic Therapy in COVID-19 Management

Coronavirus disease 2019 (COVID-19) has shocked the world by its spread and contagiousness. There is no approved vaccine and no proven treatment for this infection. Some potential treatments that have already been associated with antiviral and anti-inflammatory effects are under investigation. Photobiomodulation therapy (PBMT) is a photon-based therapy that uses light to mediate a variety of metabolic, analgesic, anti-inflammatory, and immunomodulatory effects. Antiviral photodynamic therapy (aPDT) is a branch of photodynamic therapy based on the reaction between a photosensitizing agent and a light source in the presence of oxygen, which can produce oxidative and free radical agents to damage the viral structures such as proteins and nucleic acids. This chapter aims to discuss the potential therapeutic benefit of PBMT and aPDT in the context of the novel coronavirus. Studies indicate that PBMT and aPDT could be useful in many viral and bacterial pulmonary complications like influenza, SARS-CoV, and MERS, but we found no direct study on SARS-CoV-2. With a combination of PBMT and aPDT, we may be able to combat COVID-19 with minimal interference with pharmaceutical agents. It might improve the efficacy of PBMT and aPDT by using monoclonal antibodies and preparing new photosensitizers at the nanoscale that target the lung tissue specifically. More animal and human studies would need to take place to reach an effective protocol. This chapter would encourage other scientists to work on this new platform.

Unique inflammatory profile is associated with higher SARS-CoV-2 acute respiratory distress syndrome (ARDS) mortality

The COVID19 pandemic has caused more than a million of deaths worldwide, primarily due to complications from COVID19-associated acute respiratory distress syndrome (ARDS). Controversy surrounds the circulating cytokine/chemokine profile of COVID19-associated ARDS, with some groups suggesting that it is similar to patients without COVID19 ARDS and others observing substantial differences. Moreover, although a hyperinflammatory phenotype associates with higher mortality in non-COVID19 ARDS, there is little information on the inflammatory landscape's association with mortality in patients with COVID19 ARDS. Even though the circulating leukocytes' transcriptomic signature has been associated with distinct phenotypes and outcomes in critical illness including ARDS, it is unclear whether the mortality-associated inflammatory mediators from patients with COVID19 are transcriptionally regulated in the leukocyte compartment. Here, we conducted a prospective cohort study of 41 mechanically ventilated patients with COVID19 infection using highly calibrated methods to define the levels of plasma cytokines/chemokines and their gene expressions in circulating leukocytes. Plasma IL1RA and IL8 were found positively associated with mortality, whereas RANTES and EGF negatively associated with that outcome. However, the leukocyte gene expression of these proteins had no statistically significant correlation with mortality. These data suggest a unique inflammatory signature associated with severe COVID19.

Unique inflammatory profile is associated with higher SARS-CoV-2 acute respiratory distress syndrome (ARDS) mortality

The COVID19 pandemic is likely to cause more than a million of deaths worldwide, primarily due to complications from COVID19-associated acute respiratory distress syndrome (ARDS). Controversy surrounds the circulating cytokine/chemokine profile of COVID19-associated ARDS, with some groups suggesting that it is similar to non-COVID19 ARDS patients and others observing substantial differences. Moreover, while a hyperinflammatory phenotype associates with higher mortality in non-COVID19 ARDS, there is little information on the inflammatory landscape's association with mortality in COVID19 ARDS patients. Even though the circulating leukocytes' transcriptomic signature has been associated with distinct phenotypes and outcomes in critical illness including ARDS, it is unclear whether the mortality-associated inflammatory mediators from COVID19 patients are transcriptionally regulated in the leukocyte compartment. Here, we conducted a prospective cohort study of 41 mechanically ventilated patients with COVID19 infection using highly calibrated methods to define the levels of plasma cytokines/chemokines and their gene expressions in circulating leukocytes. Plasma IL1RA and IL8 were found positively associated with mortality while RANTES and EGF negatively associated with that outcome. However, the leukocyte gene expression of these proteins had no statistically significant correlation with mortality. These data suggest a unique inflammatory signature associated with severe COVID19.

Effects of host genetic variations on response to, susceptibility and severity of respiratory infections

The recent outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a global crisis, necessitating the identification of genetic factors that modulate the risk of disorder or its severity. The current data about the role of genetic risk factors in determination of rate of SARS-CoV-2 infection in each ethnic group and the severity of disorder is limited. Moreover, several confounding parameters such as the number of tests performed in each country, the structure of the population especially the age distribution, the presence of risk factors for respiratory disorders such as smoking and other environmental factors might be involved in the variability in disease course or prevalence of infection among different ethnic groups. However, assessment of the role of genetic variants in determination of the course of other respiratory infections might help in recognition of possible candidate for further analysis in patients affected with SARS-CoV-2. In the current review, we summarize the data showing the association between genomic variants and risk of acute respiratory distress syndrome, respiratory infections or severity of these conditions with an especial focus on the SARS-CoV-2.

IL-1β suppression of VE-cadherin transcription underlies sepsis-induced inflammatory lung injury

Unchecked inflammation is a hallmark of inflammatory tissue injury in diseases such as acute respiratory distress syndrome (ARDS). Yet the mechanisms of inflammatory lung injury remain largely unknown. Here we showed that bacterial endotoxin lipopolysaccharide (LPS) and cecal ligation and puncture-induced (CLP-induced) polymicrobial sepsis decreased the expression of transcription factor cAMP response element binding (CREB) in lung endothelial cells. We demonstrated that endothelial CREB was crucial for VE-cadherin transcription and the formation of the normal restrictive endothelial adherens junctions. The inflammatory cytokine IL-1β reduced cAMP generation and CREB-mediated transcription of VE-cadherin. Furthermore, endothelial cell-specific deletion of CREB induced lung vascular injury whereas ectopic expression of CREB in the endothelium prevented the injury. We also observed that rolipram, which inhibits type 4 cyclic nucleotide phosphodiesterase-mediated (PDE4-mediated) hydrolysis of cAMP, prevented endotoxemia-induced lung vascular injury since it preserved CREB-mediated VE-cadherin expression. These data demonstrate the fundamental role of the endothelial cAMP-CREB axis in promoting lung vascular integrity and suppressing inflammatory injury. Therefore, strategies aimed at enhancing endothelial CREB-mediated VE-cadherin transcription are potentially useful in preventing sepsis-induced lung vascular injury in ARDS.

Impact of Bilateral Infiltrates on Inflammatory Biomarker Levels and Clinical Outcomes of Children With Oxygenation Defect

OBJECTIVES

The 2015 definition for pediatric acute respiratory distress syndrome did not require the presence of bilateral infiltrates. We tested the hypothesis that pediatric patients meeting oxygenation criteria for pediatric acute respiratory distress syndrome but without bilateral infiltrates would have different inflammatory biomarker levels and clinical outcomes than those with bilateral infiltrates.

DESIGN

Secondary analysis of a prospective cohort study.

SETTING

Twenty-two PICUs.

PATIENTS

Four-hundred forty-six patients age 2 weeks to 17 years intubated for respiratory failure with oxygenation index greater than or equal to 4 or oxygenation saturation index greater than or equal to 5 on the day of intubation or the day after.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients with bilateral infiltrates, either on the day of intubation or within the following 2 days, were compared with children who never developed bilateral infiltrates. Two analyses were performed to test 1) whether bilateral infiltrates are associated with elevated interleukin-1 receptor antagonist or interleukin-8 and 2) whether bilateral infiltrates are associated with worse clinical outcomes. Patients with bilateral infiltrates more often had a primary diagnosis of pneumonia (41% vs 28%; p = 0.02) and less often asthma (8% vs 23%; p < 0.01). After controlling for age, gender, and primary diagnosis, interleukin-1 receptor antagonist was higher on study days 1 and 2 in patients with bilateral infiltrates. There was no difference in interleukin-8 levels. After adjusting for age, gender, Pediatric Risk of Mortality score, and severity of oxygenation defect, presence of bilateral infiltrates was associated with longer duration of mechanical ventilation in survivors (hazard ratio, 0.64; 95% CI, 0.49-0.82; p < 0.01); this association was independent of primary diagnosis. Overall mortality was 9%; mortality was higher in those without bilateral infiltrates (14% vs 8%; p = 0.04).

CONCLUSIONS

Children meeting pediatric acute respiratory distress syndrome oxygenation criteria with bilateral infiltrates on chest radiograph experience a more intense early inflammatory response. Bilateral infiltrates are associated with longer time on the ventilator independent of oxygenation defect severity.

ARDS Subphenotypes: Understanding a Heterogeneous Syndrome

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Neutrophil extracellular traps activate IL-8 and IL-1 expression in human bronchial epithelia

Neutrophil extracellular traps (NETs) provide host defense but can contribute to the pathobiology of diverse human diseases. We sought to determine the extent and mechanism by which NETs contribute to human airway cell inflammation. Primary normal human bronchial epithelial cells (HBEs) grown at air-liquid interface and wild-type (wt)CFBE41o- cells (expressing wtCFTR) were exposed to cell-free NETs from unrelated healthy volunteers for 18 h in vitro. Cytokines were measured in the apical supernatant by Luminex, and the effect on the HBE transcriptome was assessed by RNA sequencing. NETs consistently stimulated IL-8, TNF-α, and IL-1α secretion by HBEs from multiple donors, with variable effects on other cytokines (IL-6, G-CSF, and GM-CSF). Expression of HBE RNAs encoding IL-1 family cytokines, particularly IL-36 subfamily members, was increased in response to NETs. NET exposure in the presence of anakinra [recombinant human IL-1 receptor antagonist (rhIL-1RA)] dampened NET-induced changes in IL-8 and TNF-α proteins as well as IL-36α RNA. rhIL-36RA limited the increase in expression of proinflammatory cytokine RNAs in HBEs exposed to NETs. NETs selectively upregulate an IL-1 family cytokine response in HBEs, which enhances IL-8 production and is limited by rhIL-1RA. The present findings describe a unique mechanism by which NETs may contribute to inflammation in human lung disease in vivo. NET-driven IL-1 signaling may represent a novel target for modulating inflammation in diseases characterized by a substantial NET burden.

Phenotypes in acute respiratory distress syndrome: moving towards precision medicine

PURPOSE OF REVIEW

To provide an overview of the current research in identifying homogeneous subgroups and phenotypes in ARDS.

RECENT FINDINGS

In recent years, investigations have used either physiology, clinical data, biomarkers or a combination of these to stratify patients with ARDS into distinct subgroups with divergent clinical outcomes. In some studies, there has also been evidence of differential treatment response within subgroups. Physiologic approaches include stratification based on P/F ratio and ventilatory parameters; stratification based on P/F ratio is already being employed in clinical trials. Clinical approaches include stratification based on ARDS risk factor or direct vs. indirect ARDS. Combined clinical and biological data has been used to identify two phenotypes across five cohorts of ARDS, termed hyperinflammatory and hypoinflammatory. These phenotypes have widely divergent clinical outcomes and differential response to mechanical ventilation, fluid therapy, and simvastatin in secondary analysis of completed trials. Next steps in the field include prospective validation of inflammatory phenotypes and integration of high-dimensional 'omics' data into our understanding of ARDS heterogeneity.

SUMMARY

Identification of distinct subgroups or phenotypes in ARDS may impact future conduct of clinical trials and can enhance our understanding of the disorder, with potential future clinical implications.

Risk Factors and Etiologies of Pediatric Acute Respiratory Distress Syndrome

The risk factors for acute respiratory distress syndrome (ARDS) have been a focus for clinicians and researchers from the original description in 1967 to the most recent Pediatric Acute Lung Injury Consensus Conference (PALICC). Indeed, there are many comorbidities and risk factors that predispose a patient to develop pediatric ARDS (PARDS) including, but not limited to, immunodeficiency, weight extremes, genetics, and environmental factors. These are particularly important to investigators because accurate prediction of which patients are at greatest risk of PARDS – both the development of PARDS and worse clinical outcomes after PARDS has been established – is key to identifying the next generation of diagnostic techniques and preventative strategies. In addition to those risk factors, there are specific disease processes that lead to the development of PARDS, often divided into direct or pulmonary insults and indirect or extrapulmonary insults. Finally, beyond the clinically visible risk factors, researchers are attempting to identify novel biomarkers to uncover hidden phenotypes of PARDS and enrich the prognostication and prediction of patient outcomes. This chapter delves into each of these concepts.

Genomic and Genetic Approaches to Deciphering Acute Respiratory Distress Syndrome Risk and Mortality

Significance: Acute respiratory distress syndrome (ARDS) is a severe, highly heterogeneous critical illness with staggering mortality that is influenced by environmental factors, such as mechanical ventilation, and genetic factors. Significant unmet needs in ARDS are addressing the paucity of validated predictive biomarkers for ARDS risk and susceptibility that hamper the conduct of successful clinical trials in ARDS and the complete absence of novel disease-modifying therapeutic strategies. Recent Advances: The current ARDS definition relies on clinical characteristics that fail to capture the diversity of disease pathology, severity, and mortality risk. We undertook a comprehensive survey of the available ARDS literature to identify genes and genetic variants (candidate gene and limited genome-wide association study approaches) implicated in susceptibility to developing ARDS in hopes of uncovering novel biomarkers for ARDS risk and mortality and potentially novel therapeutic targets in ARDS. We further attempted to address the well-known health disparities that exist in susceptibility to and mortality from ARDS. Critical Issues: Bioinformatic analyses identified 201 ARDS candidate genes with pathway analysis indicating a strong predominance in key evolutionarily conserved inflammatory pathways, including reactive oxygen species, innate immunity-related inflammation, and endothelial vascular signaling pathways. Future Directions: Future studies employing a system biology approach that combines clinical characteristics, genomics, transcriptomics, and proteomics may allow for a better definition of biologically relevant pathways and genotype-phenotype connections and result in improved strategies for the sub-phenotyping of diverse ARDS patients via molecular signatures. These efforts should facilitate the potential for successful clinical trials in ARDS and yield a better fundamental understanding of ARDS pathobiology.

Precision Medicine in Critical Illness: Sepsis and Acute Respiratory Distress Syndrome

Sepsis and the acute respiratory distress syndrome (ARDS) each cause substantial morbidity and mortality. In contrast to other lung diseases, the entire course of disease in these syndromes is measured in days to weeks rather than months to years, which raises unique challenges in achieving precision medicine. We review advances in sepsis and ARDS resulting from omics studies, including those involving genome-wide association, gene expression, targeted proteomics, and metabolomics approaches. We focus on promising evidence of biological subtypes in both sepsis and ARDS that consistently display high risk for death. In sepsis, a gene expression signature with dysregulated adaptive immune signaling has evidence for a differential response to systemic steroid therapy, whereas in ARDS, a hyperinflammatory pattern identified in plasma using targeted proteomics responded more favorably to randomized interventions including high positive end-expiratory pressure, volume conservative fluid therapy, and simvastatin therapy. These early examples suggest heterogeneous biology that may be challenging to detect by clinical factors alone and speak to the promise of a precision approach that targets the right treatment at the right time to the right patient.

Acute Respiratory Distress Syndrome Phenotypes

The acute respiratory distress syndrome (ARDS) phenotype was first described over 50 years ago and since that time significant progress has been made in understanding the biologic processes underlying the syndrome. Despite this improved understanding, no pharmacologic therapies aimed at the underlying biology have been proven effective in ARDS. Increasingly, ARDS has been recognized as a heterogeneous syndrome characterized by subphenotypes with distinct clinical, radiographic, and biologic differences, distinct outcomes, and potentially distinct responses to therapy. The Berlin Definition of ARDS specifies three severity classifications: mild, moderate, and severe based on the PaO₂ to FiO₂ ratio. Two randomized controlled trials have demonstrated a potential benefit to prone positioning and neuromuscular blockade in moderate to severe phenotypes of ARDS only. Precipitating risk factor, direct versus indirect lung injury, and timing of ARDS onset can determine other clinical phenotypes of ARDS after admission. Radiographic phenotypes of ARDS have been described based on a diffuse versus focal pattern of infiltrates on chest imaging. Finally and most promisingly, biologic subphenotypes or endotypes have increasingly been identified using plasma biomarkers, genetics, and unbiased approaches such as latent class analysis. The potential of precision medicine lies in identifying novel therapeutics aimed at ARDS biology and the subpopulation within ARDS most likely to respond. In this review, we discuss the challenges and approaches to subphenotype ARDS into clinical, radiologic, severity, and biologic phenotypes with an eye toward the future of precision medicine in critical care.

Plasma angiopoietin-2 as a potential causal marker in sepsis-associated ARDS development: evidence from Mendelian randomization and mediation analysis

PURPOSE

A causal biomarker for acute respiratory distress syndrome (ARDS) could fuel precision therapy options. Plasma angiopoietin-2 (ANG2), a vascular permeability marker, is a strong candidate on the basis of experimental and observational evidence. We used genetic causal inference methods-Mendelian randomization and mediation-to infer potential effects of plasma ANG2.

METHODS

We genotyped 703 septic subjects, measured ICU admission plasma ANG2, and performed a quantitative trait loci (QTL) analysis to determine variants in the ANGPT2 gene associated with plasma ANG2 (p < 0.005). We then used linear regression and post-estimation analysis to genetically predict plasma ANG2 and tested genetically predicted ANG2 for ARDS association using logistic regression. We estimated the proportion of the genetic effect explained by plasma ANG2 using mediation analysis.

RESULTS

Plasma ANG2 was strongly associated with ARDS (OR 1.59 (95% CI 1.35, 1.88) per log). Five ANGPT2 variants were associated with ANG2 in European ancestry subjects (n = 404). Rs2442608C, the most extreme cis QTL (coefficient 0.22, 95% CI 0.09-0.36, p = 0.001), was associated with higher ARDS risk: adjusted OR 1.38 (95% CI 1.01, 1.87), p = 0.042. No significant QTL were identified in African ancestry subjects. Genetically predicted plasma ANG2 was associated with ARDS risk: adjusted OR 2.25 (95% CI 1.06-4.78), p = 0.035. Plasma ANG2 mediated 34% of the rs2442608C-related ARDS risk.

CONCLUSIONS

In septic European ancestry subjects, the strongest ANG2-determining ANGPT2 genetic variant is associated with higher ARDS risk. Plasma ANG2 may be a causal factor in ARDS development. Strategies to reduce plasma ANG2 warrant testing to prevent or treat sepsis-associated ARDS.

Interleukin-1 Receptor Antagonist Is Associated With Pediatric Acute Respiratory Distress Syndrome and Worse Outcomes in Children With Acute Respiratory Failure

OBJECTIVES

To test whether plasma interleukin-1 receptor antagonist or variants within the gene encoding for interleukin-1ra (IL1RN), or proteins involved in regulating interleukin-1β levels or interleukin-1β response, are associated with pediatric acute respiratory distress syndrome or outcomes in mechanically ventilated children with parenchymal lung disease.

DESIGN

Prospective cohort study.

SETTING

Twenty-two PICUs participating in the multisite clinical trial, Randomized Evaluation of Sedation Titration for Respiratory Failure (U01 HL086622).

SUBJECTS

Children 2 weeks to 17 years old treated with invasive mechanical ventilation for acute airways and/or parenchymal lung disease.

MEASUREMENTS AND MAIN RESULTS

Three-hundred seventy-eight of 549 patients had pediatric acute respiratory distress syndrome; DNA and plasma were obtained from 523 of 549 and 480 of 549 patients, respectively. Plasma interleukin-1ra was highest on the day of intubation (day 0) and decreased over the subsequent 3 days (p < 0.0001). Interleukin-1ra level was higher in patients with pediatric acute respiratory distress syndrome than those without pediatric acute respiratory distress syndrome (p < 0.0001). Multivariable regression analysis of data across all days demonstrated a significant association of interleukin-1ra (odds ratio, 1.30; 95% CI, 1.10-1.52; p = 0.002) and day (p < 0.05) with pediatric acute respiratory distress syndrome, independent of age and Pediatric Risk of Mortality-III score. Analysis on individual days indicated that plasma interleukin-1ra levels were associated with pediatric acute respiratory distress syndrome on days 0 and 2, independent of age and Pediatric Risk of Mortality-III score (p = 0.04 and 0.003, respectively), however did not quite reach significance on days 1 and 3 (p = 0.06 and 0.07, respectively). Interleukin-1ra was independently associated with mortality on day 1 (p = 0.02). Interleukin-1ra also correlated with length of mechanical ventilation, measures of oxygenation, and PICU length of stay. No genetic variants were associated with pediatric acute respiratory distress syndrome.

CONCLUSIONS

Plasma interleukin-1ra is associated with pediatric acute respiratory distress syndrome, PICU length of stay, length of mechanical ventilation, and mortality in children with acute respiratory failure requiring mechanical ventilation.

Genome-Wide Association Study in African Americans with Acute Respiratory Distress Syndrome Identifies the Selectin P Ligand Gene as a Risk Factor

RATIONALE

Genetic factors are involved in acute respiratory distress syndrome (ARDS) susceptibility. Identification of novel candidate genes associated with increased risk and severity will improve our understanding of ARDS pathophysiology and enhance efforts to develop novel preventive and therapeutic approaches.

OBJECTIVES

To identify genetic susceptibility targets for ARDS.

METHODS

A genome-wide association study was performed on 232 African American patients with ARDS and 162 at-risk control subjects. The Identify Candidate Causal SNPs and Pathways platform was used to infer the association of known gene sets with the top prioritized intragenic SNPs. Preclinical validation of SELPLG (selectin P ligand gene) was performed using mouse models of LPS- and ventilator-induced lung injury. Exonic variation within SELPLG distinguishing patients with ARDS from sepsis control subjects was confirmed in an independent cohort.

MEASUREMENTS AND MAIN RESULTS

Pathway prioritization analysis identified a nonsynonymous coding SNP (rs2228315) within SELPLG, encoding P-selectin glycoprotein ligand 1, to be associated with increased susceptibility. In an independent cohort, two exonic SELPLG SNPs were significantly associated with ARDS susceptibility. Additional support for SELPLG as an ARDS candidate gene was derived from preclinical ARDS models where SELPLG gene expression in lung tissues was significantly increased in both ventilator-induced (twofold increase) and LPS-induced (5.7-fold increase) murine lung injury models compared with controls. Furthermore, Selplg-/- mice exhibited significantly reduced LPS-induced inflammatory lung injury compared with wild-type C57/B6 mice. Finally, an antibody that neutralizes P-selectin glycoprotein ligand 1 significantly attenuated LPS-induced lung inflammation.

CONCLUSIONS

These findings identify SELPLG as a novel ARDS susceptibility gene among individuals of European and African descent.

Mortality Benefit of Recombinant Human Interleukin-1 Receptor Antagonist for Sepsis Varies by Initial Interleukin-1 Receptor Antagonist Plasma Concentration

OBJECTIVE

Plasma interleukin-1 beta may influence sepsis mortality, yet recombinant human interleukin-1 receptor antagonist did not reduce mortality in randomized trials. We tested for heterogeneity in the treatment effect of recombinant human interleukin-1 receptor antagonist by baseline plasma interleukin-1 beta or interleukin-1 receptor antagonist concentration.

DESIGN

Retrospective subgroup analysis of randomized controlled trial.

SETTING

Multicenter North American and European clinical trial.

PATIENTS

Five hundred twenty-nine subjects with sepsis and hypotension or hypoperfusion, representing 59% of the original trial population.

INTERVENTIONS

Random assignment of placebo or recombinant human interleukin-1 receptor antagonist × 72 hours.

MEASUREMENTS AND MAIN RESULTS

We measured prerandomization plasma interleukin-1 beta and interleukin-1 receptor antagonist and tested for statistical interaction between recombinant human interleukin-1 receptor antagonist treatment and baseline plasma interleukin-1 receptor antagonist or interleukin-1 beta concentration on 28-day mortality. There was significant heterogeneity in the effect of recombinant human interleukin-1 receptor antagonist treatment by plasma interleukin-1 receptor antagonist concentration whether plasma interleukin-1 receptor antagonist was divided into deciles (interaction p = 0.046) or dichotomized (interaction p = 0.028). Interaction remained present across different predicted mortality levels. Among subjects with baseline plasma interleukin-1 receptor antagonist above 2,071 pg/mL (n = 283), recombinant human interleukin-1 receptor antagonist therapy reduced adjusted mortality from 45.4% to 34.3% (adjusted risk difference, -0.12; 95% CI, -0.23 to -0.01), p = 0.044. Mortality in subjects with plasma interleukin-1 receptor antagonist below 2,071 pg/mL was not reduced by recombinant human interleukin-1 receptor antagonist (adjusted risk difference, +0.07; 95% CI, -0.04 to +0.17), p = 0.230. Interaction between plasma interleukin-1 beta concentration and recombinant human interleukin-1 receptor antagonist treatment was not statistically significant.

CONCLUSIONS

We report a heterogeneous effect of recombinant human interleukin-1 receptor antagonist on 28-day sepsis mortality that is potentially predictable by plasma interleukin-1 receptor antagonist in one trial. A precision clinical trial of recombinant human interleukin-1 receptor antagonist targeted to septic patients with high plasma interleukin-1 receptor antagonist may be worthy of consideration.

Fifty Years of Research in ARDS. Genomic Contributions and Opportunities

Clinical factors alone poorly explain acute respiratory distress syndrome (ARDS) risk and ARDS outcome. In the search for individual factors that may influence ARDS risk, the past 20 years have witnessed the identification of numerous genes and genetic variants that are associated with ARDS. The field of ARDS genomics has cycled from candidate gene association studies to bias-free approaches that identify new candidates, and increasing effort is made to understand the functional consequences that may underlie significant associations. More recently, methodologies of causal inference are being applied to maximize the information gained from genetic associations. Although challenges of sample size, both recognized and unrecognized phenotypic heterogeneity, and the paucity of early ARDS lung tissue limit some applications of the rapidly evolving field of genomic investigation, ongoing genetic research offers unique contributions to elucidating ARDS pathogenesis and the paradigm of precision ARDS medicine.

A Missense Genetic Variant in LRRC16A/CARMIL1 Improves Acute Respiratory Distress Syndrome Survival by Attenuating Platelet Count Decline

RATIONALE

Platelets are believed to contribute to acute respiratory distress syndrome (ARDS) pathogenesis through inflammatory coagulation pathways. We recently reported that leucine-rich repeat-containing 16A (LRRC16A) modulates baseline platelet counts to mediate ARDS risk.

OBJECTIVES

To examine the role of LRRC16A in ARDS survival and its mediating effect through platelets.

METHODS

A total of 414 cases with ARDS from intensive care units (ICUs) were recruited who had exome-wide genotyping data, detailed platelet counts, and follow-up data during ICU hospitalization. Association of LRRC16A single-nucleotide polymorphisms (SNPs) and ARDS prognosis, and the mediating effect of SNPs through platelet counts were analyzed. LRRC16A mRNA expression levels for 39 cases with ARDS were also evaluated.

MEASUREMENTS AND MAIN RESULTS

Missense SNP rs9358856G>A within LRRC16A was associated with favorable survival within 28 days (hazard ratio [HR], 0.57; 95% confidence interval [CI], 0.38-0.87; P = 0.0084) and 60 days (P = 0.0021) after ICU admission. Patients with ARDS who carried the variant genotype versus the wild-type genotype showed an attenuated platelet count decline (∆PLT) within 28 days (difference of ∆PLT, -27.8; P = 0.025) after ICU admission. Patients with ∆PLT were associated with favorable ARDS outcomes. Mediation analysis indicated that the SNP prognostic effect was mediated through ∆PLT within 28 days (28-day survival: HR_Indirect, 0.937; 95% CI, 0.918-0.957; P = 0.0009, 11.53% effects mediated; 60-day survival: HR_Indirect, 0.919; 95% CI, 0.901-0.936; P = 0.0001, 14.35% effects mediated). Functional exploration suggested that this SNP reduced LRRC16A expression at ICU admission, which was associated with a lesser ∆PLT during ICU hospitalization.

CONCLUSIONS

LRRC16A appears to mediate ∆PLT after ICU admission to affect the prognosis in patients with ARDS.

Pediatric Multiple Organ Dysfunction Syndrome: Promising Therapies

OBJECTIVE

To describe the state of the science, identify knowledge gaps, and offer potential future research questions regarding promising therapies for children with multiple organ dysfunction syndrome presented during the Eunice Kennedy Shriver National Institute of Child Health and Human Development Workshop on Pediatric Multiple Organ Dysfunction Syndrome (March 26-27, 2015).

DATA SOURCES

Literature review, research data, and expert opinion.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Moderated by an expert from the field, issues relevant to the association of multiple organ dysfunction syndrome with a variety of conditions were presented, discussed, and debated with a focus on identifying knowledge gaps and research priorities.

DATA SYNTHESIS

Summary of presentations and discussion supported and supplemented by relevant literature.

CONCLUSIONS

Among critically ill children, multiple organ dysfunction syndrome is relatively common and associated with significant morbidity and mortality. For outcomes to improve, effective therapies aimed at preventing and treating this condition must be discovered and rigorously evaluated. In this article, a number of potential opportunities to enhance current care are highlighted including the need for a better understanding of the pharmacokinetics and pharmacodynamics of medications, the effect of early and optimized nutrition, and the impact of effective glucose control in the setting of multiple organ dysfunction syndrome. Additionally, a handful of the promising therapies either currently being implemented or developed are described. These include extracorporeal therapies, anticytokine therapies, antitoxin treatments, antioxidant approaches, and multiple forms of exogenous steroids. For the field to advance, promising therapies and other therapies must be assessed in rigorous manner and implemented accordingly.

Neutropenic sepsis is associated with distinct clinical and biological characteristics: a cohort study of severe sepsis

Background

Immunocompromised patients who develop sepsis while neutropenic are at high risk for morbidity and mortality; however, it is unknown if neutropenic sepsis is associated with distinct clinical and biological characteristics.

Methods

We conducted a prospective cohort study of patients admitted to the medical intensive care unit of an academic medical center with severe sepsis. Patients were followed for the development of acute respiratory distress syndrome (ARDS), acute kidney injury (AKI), and mortality. Plasma proteins, representing the host inflammatory response, anti-inflammatory response, and endothelial leak were measured in 30 % of subjects. Clinical characteristics and plasma protein concentrations of patients with neutropenia at enrollment were compared to patients without neutropenia.

Results

Of 797 subjects enrolled, 103 (13 %) were neutropenic at ICU admission. The neutropenic subjects were more often in shock, admitted from the hospital ward, had higher APACHE III scores, and more likely bacteremic. Neutropenia was an independent risk factor for AKI (RR 1.28; 95 % CI 1.04, 1.57; p = 0.03), but not ARDS (RR 0.90; 95 % CI 0.70, 1.17; p = 0.42) or 30-day mortality (RR 1.05; 95 % CI 0.85, 1.31; p = 0.65). Neutropenic subjects had higher plasma interleukin (IL)-6 (457 vs. 249 pg/ml; p = 0.03), IL-8 (581 vs. 94 pg/ml; p <0.001), and granulocyte colony-stimulating factor (G-CSF) (3624 vs. 99 pg/ml; p <0.001). Angiopoietin-2 and IL-1 receptor antagonist concentrations did not differ between groups.

Conclusions

Neutropenic sepsis is associated with a higher AKI risk and concentrations of inflammatory mediators IL-6, IL-8, and G-CSF relative to non-neutropenic patients. These differences may have implications for future therapies targeting neutropenic sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1398-y) contains supplementary material, which is available to authorized users.

Genetic and epigenetic factors in the regulation of the immune response

PURPOSE OF REVIEW

The review will update readers on research examining the influence of genetic variation and epigenetics on the immune system and whether genetic variation influences the outcome of critically ill children.

RECENT FINDINGS

Although there have been few recent studies examining the role of genetic variation in the severity of disease or outcome in critically ill children, studies in critically ill adults have been informative. For example, genetic variations in the genes coding for various components of the immune response, such as the Toll-like receptor 1, interleukin-1RA, proprotein convertase subtilisin/kexin type 9, adoponectin, nuclear factor erythroid 2-related factor 2, elafin, sphingosine 1-phosphate receptor 3, and sushi, von Willebrand factor type A, EGF and pentraxin domain containing 1 have been associated with various outcomes in critically ill adult populations. Many of the variants demonstrate functional consequences in the protein levels or activities. In critically ill children, there is an association with increased ICU length of stay in children with septic shock with one of the Toll-like receptor 1 variants.

SUMMARY

The degree of influence of host genetic variation in the outcome in critically ill children remains a much understudied area of research. However, it remains important because it may not only help identify children at risk for worse outcomes but it may provide insight into mechanisms of critical illnesses and novel therapies.

Protein Quantitative Trait Loci Analysis Identifies Genetic Variation in the Innate Immune Regulator TOLLIP in Post-Lung Transplant Primary Graft Dysfunction Risk

The authors previously identified plasma plasminogen activator inhibitor-1 (PAI-1) level as a quantitative lung injury biomarker in primary graft dysfunction (PGD). They hypothesized that plasma levels of PAI-1 used as a quantitative trait could facilitate discovery of genetic loci important in PGD pathogenesis. A two-stage cohort study was performed. In stage 1, they tested associations of loci with PAI-1 plasma level using linear modeling. Genotyping was performed using the Illumina CVD Bead Chip v2. Loci meeting a p < 5 × 10(-4) cutoff were carried forward and tested in stage 2 for association with PGD. Two hundred ninety-seven enrollees were evaluated in stage 1. Six loci, associated with PAI-1, were carried forward to stage 2 and evaluated in 728 patients. rs3168046 (Toll interacting protein [TOLLIP]) was significantly associated with PGD (p = 0.006). The increased risk of PGD for carrying at least one copy of this variant was 11.7% (95% confidence interval 4.9-18.5%). The false-positive rate for individuals with this genotype who did not have PGD was 6.1%. Variants in the TOLLIP gene are associated with higher circulating PAI-1 plasma levels and validate for association with clinical PGD. A protein quantitative trait analysis for PGD risk prioritizes genetic variations in TOLLIP and supports a role for Toll-like receptors in PGD pathogenesis.

Platelets in the pathogenesis of acute respiratory distress syndrome

Platelets have an emerging and incompletely understood role in a myriad of host immune responses, extending their role well beyond regulating thrombosis. Acute respiratory distress syndrome is a complex disease process characterized by a range of pathophysiologic processes including oxidative stress, lung deformation, inflammation, and intravascular coagulation. The objective of this review is to summarize existing knowledge on platelets and their putative role in the development and resolution of lung injury.

Distinct molecular phenotypes of direct vs indirect ARDS in single-center and multicenter studies

BACKGROUND

ARDS is a heterogeneous syndrome that encompasses lung injury from both direct and indirect sources. Direct ARDS (pneumonia, aspiration) has been hypothesized to cause more severe lung epithelial injury than indirect ARDS (eg, nonpulmonary sepsis); however, this hypothesis has not been well studied in humans.

METHODS

We measured plasma biomarkers of lung epithelial and endothelial injury and inflammation in a single-center study of 100 patients with ARDS and severe sepsis and in a secondary analysis of 853 patients with ARDS drawn from a multicenter randomized controlled trial. Biomarker levels in patients with direct vs indirect ARDS were compared in both cohorts.

RESULTS

In both studies, patients with direct ARDS had significantly higher levels of a biomarker of lung epithelial injury (surfactant protein D) and significantly lower levels of a biomarker of endothelial injury (angiopoietin-2) than those with indirect ARDS. These associations were robust to adjustment for severity of illness and ARDS severity. In the multicenter study, patients with direct ARDS also had lower levels of von Willebrand factor antigen and IL-6 and IL-8, markers of endothelial injury and inflammation, respectively. The prognostic value of the biomarkers was similar in direct and indirect ARDS.

CONCLUSIONS

Direct lung injury in humans is characterized by a molecular phenotype consistent with more severe lung epithelial injury and less severe endothelial injury. The opposite pattern was identified in indirect lung injury. Clinical trials of novel therapies targeted specifically at the lung epithelium or endothelium may benefit from preferentially enrolling patients with direct and indirect ARDS, respectively.

Phagocytosed Clofazimine Biocrystals Can Modulate Innate Immune Signaling by Inhibiting TNFα and Boosting IL-1RA Secretion

Clofazimine (CFZ) is an FDA-approved leprostatic and anti-inflammatory drug that massively accumulates in macrophages, forming insoluble, intracellular crystal-like drug inclusions (CLDIs) during long-term oral dosing. Interestingly, when added to cells in vitro, soluble CFZ is cytotoxic because it depolarizes mitochondria and induces apoptosis. Accordingly, we hypothesized that, in vivo, macrophages detoxify CFZ by sequestering it in CLDIs. To test this hypothesis, CLDIs of CFZ-treated mice were biochemically isolated and then incubated with macrophages in vitro. The cell biological effects of phagocytosed CLDIs were compared to those of soluble CFZ. Unlike soluble CFZ, phagocytosis of CLDIs did not lead to mitochondrial destabilization or apoptosis. Rather, CLDIs altered immune signaling response pathways downstream of Toll-like receptor (TLR) ligation, leading to enhanced interleukin-1 receptor antagonist (IL-1RA) production, dampened NF-κB activation and tissue necrosis factor alpha (TNFα) production, and ultimately decreased TLR expression levels. In aggregate, our results constitute evidence that macrophages detoxify soluble CFZ by sequestering it in a biocompatible, insoluble form. The altered cellular response to TLR ligation suggests that CLDI formation may also underlie CFZ's anti-inflammatory activity.

Pathobiology of acute respiratory distress syndrome

The unique characteristics of pulmonary circulation and alveolar-epithelial capillary-endothelial barrier allow for maintenance of the air-filled, fluid-free status of the alveoli essential for facilitating gas exchange, maintaining alveolar stability, and defending the lung against inhaled pathogens. The hallmark of pathophysiology in acute respiratory distress syndrome is the loss of the alveolar capillary permeability barrier and the presence of protein-rich edema fluid in the alveoli. This alteration in permeability and accumulation of fluid in the alveoli accompanies damage to the lung epithelium and vascular endothelium along with dysregulated inflammation and inappropriate activity of leukocytes and platelets. In addition, there is uncontrolled activation of coagulation along with suppression of fibrinolysis and loss of surfactant. These pathophysiological changes result in the clinical manifestations of acute respiratory distress syndrome, which include hypoxemia, radiographic opacities, decreased functional residual capacity, increased physiologic deadspace, and decreased lung compliance. Resolution of acute respiratory distress syndrome involves the migration of cells to the site of injury and re-establishment of the epithelium and endothelium with or without the development of fibrosis. Most of the data related to acute respiratory distress syndrome, however, originate from studies in adults or in mature animals with very few studies performed in children or juvenile animals. The lack of studies in children is particularly problematic because the lungs and immune system are still developing during childhood and consequently the pathophysiology of pediatric acute respiratory distress syndrome may differ in significant ways from that seen in acute respiratory distress syndrome in adults. This article describes what is known of the pathophysiologic processes of pediatric acute respiratory distress syndrome as we know it today while also presenting the much greater body of evidence on these processes as elucidated by adult and animal studies. It is also our expressed intent to generate enthusiasm for larger and more in-depth investigations of the mechanisms of disease and repair specific to children in the years to come.

Platelet count mediates the contribution of a genetic variant in LRRC16A to ARDS risk

BACKGROUND

Platelets are believed to be critical in pulmonary-origin ARDS as mediators of endothelial damage through their interactions with fibrinogen and multiple signal transduction pathways. A prior meta-analysis identified five loci for platelet count (PLT): BAD, LRRC16A, CD36, JMJD1C, and SLMO2. This study aims to validate the quantitative trait loci (QTLs) of PLT within BAD, LRRC16A, CD36, JMJD1C, and SLMO2 among critically ill patients and to investigate the associations of these QTLs with ARDS risk that may be mediated through PLT.

METHODS

ARDS cases and at-risk control subjects were recruited from the intensive care unit of the Massachusetts General Hospital. Exome-wide genotyping data of 629 ARDS cases and 1,026 at-risk control subjects and genome-wide gene expression profiles of 18 at-risk control subjects were generated for analysis.

RESULTS

Single-nucleotide polymorphism (SNP) rs7766874 within LRRC16A was a significant locus for PLT among at-risk control subjects (β = -13.00; 95% CI, -23.22 to -2.77; P = .013). This association was validated using LRRC16A gene expression data from at-risk control subjects (β = 77.03 per 1 SD increase of log2-transformed expression; 95% CI, 27.26-126.80; P = .005). Further, rs7766874 was associated with ARDS risk conditioned on PLT (OR = 0.68; 95% CI, 0.51-0.90; P = .007), interacting with PLT (OR = 1.15 per effect allele per 100 × 103/μL of PLT; 95% CI, 1.03-1.30; P = .015), and mediated through PLT (indirect OR = 1.045; 95% CI, 1.007-1.085; P = .021).

CONCLUSIONS

Our findings support the role of LRRC16A in platelet formation and suggest the importance of LRRC16A in ARDS pathophysiology by interacting with, and being mediated through, platelets.

A functional synonymous coding variant in the IL1RN gene is associated with survival in septic shock

RATIONALE

Death from infection is a highly heritable trait, yet there are few genetic variants with known mechanism influencing survival during septic shock.

OBJECTIVES

We hypothesized that a synonymous coding variant in the IL-1 receptor antagonist gene (IL1RN), rs315952, previously associated with reduced risk for acute respiratory distress syndrome, would be functional and associate with improved survival in septic shock.

METHODS

We used a human endotoxin (LPS) model of evoked inflammatory stress to measure plasma IL-1 receptor antagonist (IL1RA) following low-dose Food and Drug Administration-grade LPS injection (1 ng/kg) in 294 human volunteers. RNA sequencing of adipose tissue pre- and post-LPS was used to test for allelic imbalance at rs315952. In the Vasopressin and Septic Shock Trial cohort, we performed a genetic association study for survival, mortality, and organ failure-free days.

MEASUREMENTS AND MAIN RESULTS

Adipose tissue displayed significant allelic imbalance favoring the rs315952C allele in subjects of European ancestry. Consistent with this, carriers of rs315952C had slightly higher plasma IL1RA at baseline (0.039) and higher evoked IL1RA post-LPS (0.011). In the Vasopressin and Septic Shock Trial cohort, rs315952C associated with improved survival (P = 0.028), decreased adjusted 90-day mortality (P = 0.044), and faster resolution of shock (P = 0.029).

CONCLUSIONS

In European ancestry subjects, the IL1RN variant rs315952C is preferentially transcribed and associated with increased evoked plasma IL1RA and with improved survival from septic shock. It may be that genetically determined IL1RA levels influence survival from septic shock.