Neutrophilia and NETopathy as Key Pathologic Drivers of Progressive Lung Impairment in Patients With COVID-19.

There is an urgent need for new therapeutic strategies to contain the spread of the novel coronavirus disease 2019 (COVID-19) and to curtail its most severe complications. Severely ill patients experience pathologic manifestations of acute respiratory distress syndrome (ARDS), and clinical reports demonstrate striking neutrophilia, elevated levels of multiple cytokines, and an exaggerated inflammatory response in fatal COVID-19. Mechanical respirator devices are the most widely applied therapy for ARDS in COVID-19, yet mechanical ventilation achieves strikingly poor survival. Many patients, who recover, experience impaired cognition or physical disability. In this review, we argue the need to develop therapies aimed at inhibiting neutrophil recruitment, activation, degranulation, and neutrophil extracellular trap (NET) release. Moreover, we suggest that currently available pharmacologic approaches should be tested as treatments for ARDS in COVID-19. In our view, targeting host-mediated immunopathology holds promise to alleviate progressive pathologic complications of ARDS and reduce morbidities and mortalities in severely ill patients with COVID-19.

Pathway mapping of leukocyte transcriptome in influenza patients reveals distinct pathogenic mechanisms associated with progression to severe infection.

BACKGROUND: Influenza infections produce a spectrum of disease severity, ranging from a mild respiratory illness to respiratory failure and death. The host-response pathways associated with the progression to severe influenza disease are not well understood. METHODS: To gain insight into the disease mechanisms associated with progression to severe infection, we analyzed the leukocyte transcriptome in severe and moderate influenza patients and healthy control subjects. Pathway analysis on differentially expressed genes was performed using a topology-based pathway analysis tool that takes into account the interaction between multiple cellular pathways. The pathway profiles between moderate and severe influenza were then compared to delineate the biological mechanisms underpinning the progression from moderate to severe influenza. RESULTS: 107 patients (44 severe and 63 moderate influenza patients) and 52 healthy control subjects were included in the study. Severe influenza was associated with upregulation in several neutrophil-related pathways, including pathways involved in neutrophil differentiation, migration, degranulation and neutrophil extracellular trap (NET) formation. The degree of upregulation in neutrophil-related pathways were significantly higher in severely infected patients compared to moderately infected patients. Severe influenza was also associated with downregulation in immune response pathways, including pathways involved in antigen presentation such as CD4+ T-cell co-stimulation, CD8+ T cell and Natural Killer (NK) cells effector functions. Apoptosis pathways were also downregulated in severe influenza patients compare to moderate and healthy controls. CONCLUSIONS: These findings showed that there are changes in gene expression profile that may highlight distinct pathogenic mechanisms associated with progression from moderate to severe influenza infection.

Neutrophils-related host factors associated with severe disease and fatality in patients with influenza infection.

Severe influenza infection has no effective treatment available. One of the key barriers to developing host-directed therapy is a lack of reliable prognostic factors needed to guide such therapy. Here, we use a network analysis approach to identify host factors associated with severe influenza and fatal outcome. In influenza patients with moderate-to-severe diseases, we uncover a complex landscape of immunological pathways, with the main changes occurring in pathways related to circulating neutrophils. Patients with severe disease display excessive neutrophil extracellular traps formation, neutrophil-inflammation and delayed apoptosis, all of which have been associated with fatal outcome in animal models. Excessive neutrophil activation correlates with worsening oxygenation impairment and predicted fatal outcome (AUROC 0.817-0.898). These findings provide new evidence that neutrophil-dominated host response is associated with poor outcomes. Measuring neutrophil-related changes may improve risk stratification and patient selection, a critical first step in developing host-directed immune therapy.

A novel immune biomarker IFI27 discriminates between influenza and bacteria in patients with suspected respiratory infection.

Host response biomarkers can accurately distinguish between influenza and bacterial infection. However, published biomarkers require the measurement of many genes, thereby making it difficult to implement them in clinical practice. This study aims to identify a single-gene biomarker with a high diagnostic accuracy equivalent to multi-gene biomarkers.In this study, we combined an integrated genomic analysis of 1071 individuals with in vitro experiments using well-established infection models.We identified a single-gene biomarker, IFI27, which had a high prediction accuracy (91%) equivalent to that obtained by multi-gene biomarkers. In vitro studies showed that IFI27 was upregulated by TLR7 in plasmacytoid dendritic cells, antigen-presenting cells that responded to influenza virus rather than bacteria. In vivo studies confirmed that IFI27 was expressed in influenza patients but not in bacterial infection, as demonstrated in multiple patient cohorts (n=521). In a large prospective study (n=439) of patients presented with undifferentiated respiratory illness (aetiologies included viral, bacterial and non-infectious conditions), IFI27 displayed 88% diagnostic accuracy (AUC) and 90% specificity in discriminating between influenza and bacterial infections.IFI27 represents a significant step forward in overcoming a translational barrier in applying genomic assay in clinical setting; its implementation may improve the diagnosis and management of respiratory infection.

Transcriptional reprogramming of metabolic pathways in critically ill patients.

BACKGROUND: Critical illness causes a shift away from mitochondrial metabolism towards a greater dependence on glycolysis. This metabolic shift is thought to be associated with lactic acidosis, organ dysfunction and poor clinical outcomes. The current paradigm is that low oxygen supply causes regional hypoxia, which in turn drives such a metabolic shift. In this study, we evaluated whether the shift towards glycolysis can also occur in cells where oxygen supply is plentiful. METHODS: We used circulating blood cells from non-hypoxic critically ill patients (n = 47) as a model to study cellular metabolism in a normal oxygen milieu. We measured the transcriptomic profiles of canonical metabolic pathways in these cells and compared them to cells obtained from healthy controls (n = 18). RESULTS: Transcriptomic profiling revealed a significant reprogramming of metabolic pathways during critical illness. In well-oxygenated cells, there was a reduced expression of tricarboxylic acid cycle genes and genes associated with pyruvate entry into the mitochondria suggesting decreased mitochondrial oxidation. In contrast, glycolysis was accelerated, as reflected by an up-regulation of genes coding for enzymes of early and late glycolytic pathway that were associated with increased lactate production. The pentose phosphate pathway genes for NADPH production were also up-regulated suggesting enhanced antioxidant production during increased oxidative stress. CONCLUSIONS: Contrary to the established paradigm, aerobic glycolysis does occur in non-hypoxic cells during critical illness and its occurrence may represent an adaptive strategy common to cells under increased oxidative stress. Further study of this previously under-recognized metabolic phenomenon might identify novel drug target for antioxidant therapy.

Is lactate the new panacea for endothelial dysfunction?

Fluid resuscitation in the critically ill is a hot topic. The current strategy of rapid and adequate resuscitation in shock followed by conservative fluid administration is often difficult to achieve with standard crystalloid solutions. Research into alternative intravenous fluids tailored to individual patient needs is required. In the previous issue of Critical Care, Somasetia and colleagues compare the effects of hypertonic sodium lactate with the World Health Organization-recommended strategy of Ringer's lactate resuscitation in children with severe Dengue, a viral infection for which causal treatment and vaccination are not available. The results not only suggest unimpaired lactate metabolism during shock in children but document improvement in endothelial barrier function, limited coagulopathy, and avoidance of fluid overload with hypertonic sodium lactate. Their study invites several important questions to be answered. Is hypertonicity or lactate per se important for the beneficial effects? Are the metabolic or anti-inflammatory effects responsible? Is the raised lactate in shock an adaptive response? Should reduction in lactate levels be the goal of resuscitation? These questions may trigger further research into the role of lactate and lactate-based intravenous fluids in resuscitation of the critically ill.

Identifying key regulatory genes in the whole blood of septic patients to monitor underlying immune dysfunctions.

There is currently no reliable tool available to measure immune dysfunction in septic patients in the clinical setting. This proof-of-concept study assesses the potential of gene expression profiling of whole blood as a tool to monitor immune dysfunction in critically ill septic patients. Whole-blood samples were collected daily for up to 5 days from patients admitted to the intensive care unit with sepsis. RNA isolated from whole-blood samples was assayed on Illumina HT-12 gene expression microarrays consisting of 48,804 probes. Microarray analysis identified 3,677 genes as differentially expressed across 5 days between septic patients and healthy controls. Of the 3,677 genes, biological pathway analysis identified 86 genes significantly downregulated in the sepsis patients were present in pathways relating to immune response. These 86 genes correspond to known immune pathways implicated in sepsis, including lymphocyte depletion, reduced T-lymphocyte activation, and deficient antigen presentation. Furthermore, expression levels of these genes correlated with clinical severity, with a significantly greater degree of downregulation found in nonsurvivors compared with survivors. The results show that whole-blood gene expression analysis can capture systemic immune dysfunctions in septic patients. Our study provides an experimental basis to support further study on the use of a gene expression-based assay, to assess immunosuppression, and to guide immunotherapy in future clinical trials.

Identification of sepsis subtypes in critically ill adults using gene expression profiling.

INTRODUCTION: Sepsis is a syndromic illness that has traditionally been defined by a set of broad, highly sensitive clinical parameters. As a result, numerous distinct pathophysiologic states may meet diagnostic criteria for sepsis, leading to syndrome heterogeneity. The existence of biologically distinct sepsis subtypes may in part explain the lack of actionable evidence from clinical trials of sepsis therapies. We used microarray-based gene expression data from adult patients with sepsis in order to identify molecularly distinct sepsis subtypes. METHODS: We used partitioning around medoids (PAM) and hierarchical clustering of gene expression profiles from neutrophils taken from a cohort of septic patients in order to identify distinct subtypes. Using the medoids learned from this cohort, we then clustered a second independent cohort of septic patients, and used the resulting class labels to evaluate differences in clinical parameters, as well as the expression of relevant pharmacogenes. RESULTS: We identified two sepsis subtypes based on gene expression patterns. Subtype 1 was characterized by increased expression of genes involved in inflammatory and Toll receptor mediated signaling pathways, as well as a higher prevalence of severe sepsis. There were differences between subtypes in the expression of pharmacogenes related to hydrocortisone, vasopressin, norepinephrine, and drotrecogin alpha. CONCLUSIONS: Sepsis subtypes can be identified based on different gene expression patterns. These patterns may generate hypotheses about the underlying pathophysiology of sepsis and suggest new ways of classifying septic patients both in clinical practice, and in the design of clinical trials.

A distinct influenza infection signature in the blood transcriptome of patients with severe community-acquired pneumonia.

INTRODUCTION: Diagnosis of severe influenza pneumonia remains challenging because of a lack of correlation between the presence of influenza virus and clinical status. We conducted gene-expression profiling in the whole blood of critically ill patients to identify a gene signature that would allow clinicians to distinguish influenza infection from other causes of severe respiratory failure, such as bacterial pneumonia, and noninfective systemic inflammatory response syndrome. METHODS: Whole-blood samples were collected from critically ill individuals and assayed on Illumina HT-12 gene-expression beadarrays. Differentially expressed genes were determined by linear mixed-model analysis and overrepresented biological pathways determined by using GeneGo MetaCore. RESULTS: The gene-expression profile of H1N1 influenza A pneumonia was distinctly different from those of bacterial pneumonia and systemic inflammatory response syndrome. The influenza gene-expression profile is characterized by upregulation of genes from cell-cycle regulation, apoptosis, and DNA-damage-response pathways. In contrast, no distinctive gene-expression signature was found in patients with bacterial pneumonia or systemic inflammatory response syndrome. The gene-expression profile of influenza infection persisted through 5 days of follow-up. Furthermore, in patients with primary H1N1 influenza A infection in whom bacterial co-infection subsequently developed, the influenza gene-expression signature remained unaltered, despite the presence of a superimposed bacterial infection. CONCLUSIONS: The whole-blood expression-profiling data indicate that the host response to influenza pneumonia is distinctly different from that caused by bacterial pathogens. This information may speed the identification of the cause of infection in patients presenting with severe respiratory failure, allowing appropriate patient care to be undertaken more rapidly.

Genome-wide transcription profiling of human sepsis: a systematic review.

INTRODUCTION: Sepsis is thought to be an abnormal inflammatory response to infection. However, most clinical trials of drugs that modulate the inflammatory response of sepsis have been unsuccessful. Emerging genomic evidence shows that the host response in sepsis does not conform to a simple hyper-inflammatory/hypo-inflammatory model. We, therefore, synthesized current genomic studies that examined the host response of circulating leukocytes to human sepsis. METHODS: Electronic searches were performed in Medline and Embase (1987 to October 2010), supplemented by additional searches in multiple microarray data repositories. We included studies that (1) used microarray, (2) were performed in humans and (3) investigated the host response mediated by circulating leukocytes. RESULTS: We identified 12 cohorts consisting of 784 individuals providing genome-wide expression data in early and late sepsis. Sepsis elicited an immediate activation of pathogen recognition receptors, accompanied by an increase in the activities of signal transduction cascades. These changes were consistent across most cohorts. However, changes in inflammation related genes were highly variable. Established inflammatory markers, such as tumour necrosis factor-α (TNF-α), interleukin (IL)-1 or interleukin-10, did not show any consistent pattern in their gene-expression across cohorts. The finding remains the same even after the cohorts were stratified by timing (early vs. late sepsis), patient groups (paediatric vs. adult patients) or settings (clinical sepsis vs. endotoxemia model). Neither a distinctive pro/anti-inflammatory phase nor a clear transition from a pro-inflammatory to anti-inflammatory phase could be observed during sepsis. CONCLUSIONS: Sepsis related inflammatory changes are highly variable on a transcriptional level. We did not find strong genomic evidence that supports the classic two phase model of sepsis.

Use of corticosteroids in acute lung injury and acute respiratory distress syndrome: a systematic review and meta-analysis.

OBJECTIVE: Controversy remains as to whether low-dose corticosteroids can reduce the mortality and morbidity of acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS) without increasing the risk of adverse reactions. We aimed to evaluate all studies investigating prolonged corticosteroids in low-to-moderate dose in ALI or ARDS. DATA SOURCES: MEDLINE, EMBASE, Current Content, and Cochrane Central Register of Controlled Trials, and bibliographies of retrieved articles. STUDY SELECTION: Randomized controlled trials (RCTs) and observational studies reported in any language that used 0.5-2.5 mg.kg.d of methylprednisolone or equivalent to treat ALI/ARDS. DATA EXTRACTION: Data were extracted independently by two reviewers and included study design, patient characteristics, interventions, and mortality and morbidity outcomes. DATA SYNTHESIS: Both cohort studies (five studies, n = 307) and RCTs (four trials, n = 341) showed a similar trend toward mortality reduction (RCTs relative risk 0.51, 95% CI 0.24-1.09; p = 0.08; cohort studies relative risk 0.66, 95% CI 0.43-1.02; p = 0.06). The overall relative risk was 0.62 (95% CI 0.43-0.91; p = 0.01). There was also improvement in length of ventilation-free days, length of intensive care unit stay, Multiple Organ Dysfunction Syndrome Score, Lung Injury Scores, and improvement in Pao2/Fio2. There was no increase in infection, neuromyopathy, or any major complications. There was significant heterogeneity in the pooled studies. Subgroup and meta-regression analyses showed that heterogeneity had minimal effect on treatment efficacy; however, these findings were limited by the small number of studies used in the analyses. CONCLUSION: The use of low-dose corticosteroids was associated with improved mortality and morbidity outcomes without increased adverse reactions. The consistency of results in both study designs and all outcomes suggests that they are an effective treatment for ALI or ARDS. The mortality benefits in early ARDS should be confirmed by an adequately powered randomized trial.

Gene-expression profiling of peripheral blood mononuclear cells in sepsis.

OBJECTIVES: It has been shown that gene-expression profiling of circulating neutrophils could identify signature genes of sepsis. However, whether similar transcriptional changes occurred in peripheral blood mononuclear cells (PBMC) was not known. Using microarray technology, we performed gene-expression profiling of PBMC to identify signature genes that distinguish sepsis from noninfectious causes of systemic inflammatory response syndrome (SIRS), between Gram-positive and Gram-negative sepsis. DESIGN: A cross-sectional, observational study. SETTING: A 20-bed general intensive care unit of a tertiary referral hospital. PATIENTS: Seventy critically ill patients (46 sepsis and 24 SIRS). INTERVENTIONS: Intravenous blood was collected for leukocyte separation and RNA extraction. Gene-expression profiling was performed on PBMC using Affymetrix GeneChip microarrays with 54,675 transcripts. Data were divided into a training set (n = 35) and a validation set (n = 35). A molecular signature was developed in the training set using support vector machine and was then validated in the validation set. MEASUREMENTS AND MAIN RESULTS: We identified a molecular signature of 138 genes that could differentiate between sepsis and SIRS patients with 91% and 80% accuracy in the training and validation sets, respectively. There were no signature genes that could differentiate between Gram-positive and Gram-negative sepsis. The expression of genes involved in inflammatory response and immune function was significantly reduced in septic patients when compared with those with SIRS. Genes involved in apoptosis, on the other hand, were more highly expressed in septic patients. CONCLUSION: There was evidence of sepsis-related immunosuppression and reduced inflammatory response in mononuclear cells on a transcriptome level. These characteristic transcriptional changes can be used to aid the diagnosis of sepsis.

Gene-expression profiling of gram-positive and gram-negative sepsis in critically ill patients.

OBJECTIVE: It is unclear whether the host response of gram-positive sepsis differs from gram-negative sepsis at a transcriptome level. Using microarray technology, we compared the gene-expression profiles of gram-positive sepsis and gram-negative sepsis in critically ill patients. DESIGN: A prospective cross-sectional study. SETTING: A 20-bed general intensive care unit of a tertiary referral hospital. PATIENTS: Seventy-two patients admitted to the intensive care unit. INTERVENTIONS: Intravenous blood was collected for leukocyte separation and RNA extraction. Microarray experiments were then performed examining the expression level of 18,664 genes in each sample. MEASUREMENTS AND MAIN RESULTS: There was no difference in the expression profile between gram-positive and gram-negative sepsis. The finding remained unchanged even when genes with lower expression level were included or after statistical stringency was lowered. There were, however, 94 genes differentially expressed between sepsis and control patients. These genes included those involved in immune regulation, inflammation, and mitochondrial function. Hierarchical cluster analysis confirmed that the difference in gene expression profile existed between sepsis and control patients but not between gram-positive and gram-negative patients. CONCLUSIONS: Gram-positive sepsis and gram-negative sepsis share a common host response at a transcriptome level. These findings support the hypothesis that the septic response is nonspecific and is designed to provide a more general response that can be elicited by a wide range of different microorganisms.

Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis.

BACKGROUND: Whether calcium supplementation can reduce osteoporotic fractures is uncertain. We did a meta-analysis to include all the randomised trials in which calcium, or calcium in combination with vitamin D, was used to prevent fracture and osteoporotic bone loss. METHODS: We identified 29 randomised trials (n=63 897) using electronic databases, supplemented by a hand-search of reference lists, review articles, and conference abstracts. All randomised trials that recruited people aged 50 years or older were eligible. The main outcomes were fractures of all types and percentage change of bone-mineral density from baseline. Data were pooled by use of a random-effect model. FINDINGS: In trials that reported fracture as an outcome (17 trials, n=52 625), treatment was associated with a 12% risk reduction in fractures of all types (risk ratio 0.88, 95% CI 0.83-0.95; p=0.0004). In trials that reported bone-mineral density as an outcome (23 trials, n=41 419), the treatment was associated with a reduced rate of bone loss of 0.54% (0.35-0.73; p<0.0001) at the hip and 1.19% (0.76-1.61%; p<0.0001) in the spine. The fracture risk reduction was significantly greater (24%) in trials in which the compliance rate was high (p<0.0001). The treatment effect was better with calcium doses of 1200 mg or more than with doses less than 1200 mg (0.80 vs 0.94; p=0.006), and with vitamin D doses of 800 IU or more than with doses less than 800 IU (0.84 vs 0.87; p=0.03). INTERPRETATION: Evidence supports the use of calcium, or calcium in combination with vitamin D supplementation, in the preventive treatment of osteoporosis in people aged 50 years or older. For best therapeutic effect, we recommend minimum doses of 1200 mg of calcium, and 800 IU of vitamin D (for combined calcium plus vitamin D supplementation).

The use of gene-expression profiling to identify candidate genes in human sepsis.

RATIONALE: Our understanding of the pathophysiology of sepsis remains incomplete. Genomewide study offers an unbiased, system biology approach to examine the expression patterns of circulating leukocytes and may reveal novel insights into the host response to sepsis. OBJECTIVES: We examined whether gene-expression profiling of neutrophils could identify signature genes and important pathways in the clinical syndrome of sepsis. METHODS: Gene-expression profiling was performed using oligonucleotide microarrays on peripheral blood samples of 94 critically ill patients (71 septic and 23 nonseptic). Using a supervised learning algorithm based on support vector machine, a molecular signature of sepsis was generated from a training set of 44 samples and validated in an independent set of 50 samples. The diagnostic performance of the signature genes was assessed against a reference standard based on the International Sepsis Forum Consensus Conference definition of infection. MEASUREMENTS AND MAIN RESULTS: A set of 50 signature genes correctly identified sepsis with a prediction accuracy of 91 and 88% in the training and validation sets, respectively. The diagnostic performance remained high regardless of patient's age, comorbidities, or prior antibiotic treatment. Compared with controls, genes involved in immune modulation and inflammatory response had reduced expression in patients with sepsis. In particular, the activation of nuclear factor-kappaB pathway was reduced, whereas its inhibitor gene, NFKBIA, was significantly up-regulated. CONCLUSIONS: The signature genes reflect suppression of neutrophils' immune and inflammatory function by sepsis. Gene-expression profiling therefore provides a novel approach to advance our understanding of the host response in sepsis.

Accuracy of procalcitonin for sepsis diagnosis in critically ill patients: systematic review and meta-analysis.

Procalcitonin is widely reported as a useful biochemical marker to differentiate sepsis from other non-infectious causes of systemic inflammatory response syndrome. In this systematic review, we estimated the diagnostic accuracy of procalcitonin in sepsis diagnosis in critically ill patients. 18 studies were included in the review. Overall, the diagnostic performance of procalcitonin was low, with mean values of both sensitivity and specificity being 71% (95% CI 67-76) and an area under the summary receiver operator characteristic curve of 0.78 (95% CI 0.73-0.83). Studies were grouped into phase 2 studies (n=14) and phase 3 studies (n=4) by use of Sackett and Haynes' classification. Phase 2 studies had a low pooled diagnostic odds ratio of 7.79 (95% CI 5.86-10.35). Phase 3 studies showed significant heterogeneity because of variability in sample size (meta-regression coefficient -0.592, p=0.017), with diagnostic performance upwardly biased in smaller studies, but moving towards a null effect in larger studies. Procalcitonin cannot reliably differentiate sepsis from other non-infectious causes of systemic inflammatory response syndrome in critically ill adult patients. The findings from this study do not lend support to the widespread use of the procalcitonin test in critical care settings.