Transcriptomic profiles of multiple organ dysfunction syndrome phenotypes in pediatric critical influenza.

Background: Influenza virus is responsible for a large global burden of disease, especially in children. Multiple Organ Dysfunction Syndrome (MODS) is a life-threatening and fatal complication of severe influenza infection. Methods: We measured RNA expression of 469 biologically plausible candidate genes in children admitted to North American pediatric intensive care units with severe influenza virus infection with and without MODS. Whole blood samples from 191 influenza-infected children (median age 6.4 years, IQR: 2.2, 11) were collected a median of 27 hours following admission; for 45 children a second blood sample was collected approximately seven days later. Extracted RNA was hybridized to NanoString mRNA probes, counts normalized, and analyzed using linear models controlling for age and bacterial co-infections (FDR q<0.05). Results: Comparing pediatric samples collected near admission, children with Prolonged MODS for ≥7 days (n=38; 9 deaths) had significant upregulation of nine mRNA transcripts associated with neutrophil degranulation (RETN, TCN1, OLFM4, MMP8, LCN2, BPI, LTF, S100A12, GUSB) compared to those who recovered more rapidly from MODS (n=27). These neutrophil transcripts present in early samples predicted Prolonged MODS or death when compared to patients who recovered, however in paired longitudinal samples, they were not differentially expressed over time. Instead, five genes involved in protein metabolism and/or adaptive immunity signaling pathways (RPL3, MRPL3, HLA-DMB, EEF1G, CD8A) were associated with MODS recovery within a week. Conclusion: Thus, early increased expression of neutrophil degranulation genes indicated worse clinical outcomes in children with influenza infection, consistent with reports in adult cohorts with influenza, sepsis, and acute respiratory distress syndrome.

Multisite validation of a host response signature for predicting likelihood of bacterial and viral infections in patients with suspected influenza.

BACKGROUND: Indiscriminate use of antimicrobials and antimicrobial resistance is a public health threat. IMX-BVN-1, a 29-host mRNA classifier, provides two separate scores that predict likelihoods of bacterial and viral infections in patients with suspected acute infections. We validated the performance of IMX-BVN-1 in adults attending acute health care settings with suspected influenza. METHOD: We amplified 29-host response genes in RNA extracted from blood by NanoString nCounter. IMX-BVN-1 calculated two scores to predict probabilities of bacterial and viral infections. Results were compared against the infection status (no infection; highly probable/possible infection; confirmed infection) determined by clinical adjudication. RESULTS: Amongst 602 adult patients (74.9% ED, 16.9% ICU, 8.1% outpatients), 7.6% showed in-hospital mortality and 15.5% immunosuppression. Median IMX-BVN-1 bacterial and viral scores were higher in patients with confirmed bacterial (0.27) and viral (0.62) infections than in those without bacterial (0.08) or viral (0.21) infection, respectively. The AUROC distinguishing bacterial from nonbacterial illness was 0.81 and 0.87 when distinguishing viral from nonviral illness. The bacterial top quartile's positive likelihood ratio (LR) was 4.38 with a rule-in specificity of 88%; the bacterial bottom quartile's negative LR was 0.13 with a rule-out sensitivity of 96%. Similarly, the viral top quartile showed an infinite LR with rule-in specificity of 100%; the viral bottom quartile had a LR of 0.22 and a rule-out sensitivity of 85%. CONCLUSION: IMX-BVN-1 showed high accuracy for differentiating bacterial and viral infections from noninfectious illness in patients with suspected influenza. Clinical utility of IMX-BVN will be validated following integration into a point of care system.

A robust host-response-based signature distinguishes bacterial and viral infections across diverse global populations.

Limited sensitivity and specificity of current diagnostics lead to the erroneous prescription of antibiotics. Host-response-based diagnostics could address these challenges. However, using 4,200 samples across 69 blood transcriptome datasets from 20 countries from patients with bacterial or viral infections representing a broad spectrum of biological, clinical, and technical heterogeneity, we show current host-response-based gene signatures have lower accuracy to distinguish intracellular bacterial infections from viral infections than extracellular bacterial infections. Using these 69 datasets, we identify an 8-gene signature to distinguish intracellular or extracellular bacterial infections from viral infections with an area under the receiver operating characteristic curve (AUROC) > 0.91 (85.9% specificity and 90.2% sensitivity). In prospective cohorts from Nepal and Laos, the 8-gene classifier distinguished bacterial infections from viral infections with an AUROC of 0.94 (87.9% specificity and 91% sensitivity). The 8-gene signature meets the target product profile proposed by the World Health Organization and others for distinguishing bacterial and viral infections.

Profiling chromatin accessibility responses in human neutrophils with sensitive pathogen detection.

Sepsis, sequela of bloodstream infections and dysregulated host responses, is a leading cause of death globally. Neutrophils tightly regulate responses to pathogens to prevent organ damage. Profiling early host epigenetic responses in neutrophils may aid in disease recognition. We performed assay for transposase-accessible chromatin (ATAC)-seq of human neutrophils challenged with six toll-like receptor ligands and two organisms; and RNA-seq after Escherichia coli exposure for 1 and 4 h along with ATAC-seq. ATAC-seq of neutrophils facilitates detection of pathogen DNA. In addition, despite similarities in genomic distribution of differential chromatin changes across challenges, only a fraction overlaps between the challenges. Ligands depict shared signatures, but majority are unique in position, function, and challenge. Epigenomic changes are plastic, only ∼120 are shared by E coli challenges over time, resulting in varied differential genes and associated processes. We identify three classes of gene regulation, chromatin access changes in the promoter; changes in the promoter and distal enhancers; and controlling expression through changes solely in distal enhancers. These and transcription factor footprinting reveal timely and challenge specific mechanisms of transcriptional regulation in neutrophils.

Gene Expression-Based Diagnosis of Infections in Critically Ill Patients-Prospective Validation of the SepsisMetaScore in a Longitudinal Severe Trauma Cohort.

OBJECTIVES: Early diagnosis of infections is pivotal in critically ill patients. Innovative gene expression-based approaches promise to deliver precise, fast, and clinically practicable diagnostic tools to bedside. This study aimed to validate the SepsisMetaScore, an 11-gene signature previously reported by our study group, in a representative longitudinal cohort of trauma patients. DESIGN: Prospective observational cohort study. SETTING: Surgical ICUs of the University Medical Center Goettingen, Germany. PATIENTS: Critically ill patients with severe traumatic injuries. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Paired box gene (PAXgene) RNA blood tubes were drawn at predefined time points over the course of disease. The performance of the SepsisMetaScore was tested using targeted polymerase chain reaction and compared with Procalcitonin using area under the receiver operating characteristics analyses. The SepsisMetaScore showed significant differences between infected and noninfected patients (n = 52). It was able to accurately discriminate infectious from noninfectious acute inflammation with an area under the receiver operating characteristics of 0.92 (95% CI, 0.85-0.99) and significantly outperformed Procalcitonin (area under the receiver operating characteristics curve = 0.53; 95% CI, 0.42-0.64) early in the course of infection (p = 0.014). CONCLUSIONS: We demonstrated the clinical utility for diagnosis of infections with higher accuracy using the SepsisMetaScore compared with Procalcitonin in a prospective cohort of severe trauma patients. Future studies should assess whether the SepsisMetaScore may substantially improve clinical practice by accurate differentiation of infections from sterile inflammation and identification of patients at risk for sepsis. Our results support further investigation of the SepsisMetaScore for the development of tailored precision treatment of critically ill patients.

Transcriptomic similarities and differences in host response between SARS-CoV-2 and other viral infections.

The pandemic 2019 novel coronavirus disease (COVID-19) shares certain clinical characteristics with other acute viral infections. We studied the whole-blood transcriptomic host response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using RNAseq from 24 healthy controls and 62 prospectively enrolled patients with COVID-19. We then compared these data to non-COVID-19 viral infections, curated from 23 independent studies profiling 1,855 blood samples covering six viruses (influenza, respiratory syncytial virus (RSV), human rhinovirus (HRV), severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), Ebola, dengue). We show gene expression changes in COVID-19 versus non-COVID-19 viral infections are highly correlated (r = 0.74, p < 0.001). However, we also found 416 genes specific to COVID-19. Inspection of top genes revealed dynamic immune evasion and counter host responses specific to COVID-19. Statistical deconvolution of cell proportions maps many cell type proportions concordantly shifting. Discordantly increased in COVID-19 were CD56bright natural killer cells and M2 macrophages. The concordant and discordant responses mapped out here provide a window to explore the pathophysiology of the host response to SARS-CoV-2.

Analytical and clinical validation of a microbial cell-free DNA sequencing test for infectious disease.

Thousands of pathogens are known to infect humans, but only a fraction are readily identifiable using current diagnostic methods. Microbial cell-free DNA sequencing offers the potential to non-invasively identify a wide range of infections throughout the body, but the challenges of clinical-grade metagenomic testing must be addressed. Here we describe the analytical and clinical validation of a next-generation sequencing test that identifies and quantifies microbial cell-free DNA in plasma from 1,250 clinically relevant bacteria, DNA viruses, fungi and eukaryotic parasites. Test accuracy, precision, bias and robustness to a number of metagenomics-specific challenges were determined using a panel of 13 microorganisms that model key determinants of performance in 358 contrived plasma samples, as well as 2,625 infections simulated in silico and 580 clinical study samples. The test showed 93.7% agreement with blood culture in a cohort of 350 patients with a sepsis alert and identified an independently adjudicated cause of the sepsis alert more often than all of the microbiological testing combined (169 aetiological determinations versus 132). Among the 166 samples adjudicated to have no sepsis aetiology identified by any of the tested methods, sequencing identified microbial cell-free DNA in 62, likely derived from commensal organisms and incidental findings unrelated to the sepsis alert. Analysis of the first 2,000 patient samples tested in the CLIA laboratory showed that more than 85% of results were delivered the day after sample receipt, with 53.7% of reports identifying one or more microorganisms.

The IL20 Genetic Polymorphism Is Associated with Altered Clinical Outcome in Septic Shock.

BACKGROUND: The IL10 family of genes includes crucial immune regulators. We tested the hypothesis that single nucleotide polymorphisms (SNPs) in IL10, IL19, IL20, and IL24 of the IL10 family gene cluster alter the clinical outcome of septic shock. METHODS: Patients with septic shock (n = 1,193) were genotyped for 13 tag SNPs of IL10, IL19, IL20, and IL24. IL20 gene expression was measured in genotyped lymphoblastoid cells in vitro. Cardiac surgical ICU patients (n = 981) were genotyped for IL20 rs2981573 A/G. The primary outcome variable was 28-day mortality. RESULTS: Patients with the G allele of IL20 rs2981573 had a significantly increased hazard of death over the 28-day period compared to patients with the A allele in the septic shock cohort (adjusted hazard ratio 1.27; 95% confidence interval 1.10-1.47; p = 8.0 × 10-4). Patients with the GG genotype had more organ dysfunction (p < 0.05). The GG genotype was associated with increased IL20 gene expression in stimulated lymphoblastoid cells in vitro (p < 0.05). The cardiac surgical ICU patients with the GG genotype had an increased length of ICU stay (p = 0.032). CONCLUSIONS: The GG genotype of IL20 rs2981573 SNP was associated with increased IL20 gene expression and increased adverse outcomes in patients with septic shock and following cardiac surgery.

Microbial Typing by Machine Learned DNA Melt Signatures.

There is still an ongoing demand for a simple broad-spectrum molecular diagnostic assay for pathogenic bacteria. For this purpose, we developed a single-plex High Resolution Melt (HRM) assay that generates complex melt curves for bacterial identification. Using internal transcribed spacer (ITS) region as the phylogenetic marker for HRM, we observed complex melt curve signatures as compared to 16S rDNA amplicons with enhanced interspecies discrimination. We also developed a novel Naïve Bayes curve classification algorithm with statistical interpretation and achieved 95% accuracy in differentiating 89 bacterial species in our library using leave-one-out cross-validation. Pilot clinical validation of our method correctly identified the etiologic organisms at the species-level in 59 culture-positive mono-bacterial blood culture samples with 90% accuracy. Our findings suggest that broad bacterial sequences may be simply, reliably and automatically profiled by ITS HRM assay for clinical adoption.

TNFAIP2 Inhibits Early TNFα-Induced NF-x03BA;B Signaling and Decreases Survival in Septic Shock Patients.

During septic shock, tumor necrosis factor alpha (TNFα) is an early response gene and induces a plethora of genes and signaling pathways. To identify robust signals in genes reliably upregulated by TNFα, we first measured microarray gene expression in vitro and searched methodologically comparable, publicly available data sets to identify concordant signals. Using tag single-nucleotide polymorphisms in the genes common to all data sets, we identified a genetic variant of the TNFAIP2 gene, rs8126, associated with decreased 28-day survival and increased organ dysfunction in an adult cohort in the Vasopressin and Septic Shock Trial. Similar to this cohort, we found that an association with rs8126 and increased organ dysfunction is replicated in a second cohort of septic shock patients in the St. Paul's Hospital Intensive Care Unit. We found that TNFAIP2 inhibits NF-x03BA;B activity, impacting the downstream cytokine interleukin (IL)-8. The minor G allele of TNFAIP2 rs8126 resulted in greater TNFAIP2 expression, decreased IL-8 production and was associated with decreased survival in patients experiencing septic shock. These data suggest that TNFAIP2 is a novel inhibitor of NF-x03BA;B that acts as an autoinhibitor of the TNFα response during septic shock.

VPS13D Gene Variant Is Associated with Altered IL-6 Production and Mortality in Septic Shock.

BACKGROUND: Genetic variations contribute to septic shock mortality. To discover a novel locus, we performed in vitro genome-wide association studies (GWAS) and further tested the result in a cohort of septic shock patients. METHODS: Two in vitro GWAS using a quantitative trait locus analysis of stimulated IL-6 production in lymphoblastoid cells from 60 individuals of European ancestry were performed. VPS13D rs6685273 was genotyped in European ancestry patients (n = 498). The VPS13D gene was silenced in vitro. RESULTS: Two GWAS using lymphoblastoid cells identified the locus of VPS13D rs6685273 that was significant in the same direction in both GWAS. The VPS13D rs6685273 C allele was associated with increased IL-6 production. Patients with septic shock who had the VPS13D rs6685273 CC genotype had an increased 28-day mortality (p = 0.023) and more organ failure (p < 0.05) compared to the CT/TT genotypes. VPS13D in vitro gene silencing in the HeLa cell line increased IL-6 production. Furthermore, the rs6685273 genotype was associated with differential VPS13D splice variant expression. CONCLUSIONS: The VPS13D rs6685273 C allele was associated with increased IL-6 production in vitro. The patients with the VPS13D rs6685273 CC genotype had increased 28-day mortality and increased organ failure. VPS13D appears to regulate IL-6 production.

Identification of a nonsynonymous polymorphism in the SVEP1 gene associated with altered clinical outcomes in septic shock.

OBJECTIVES: Mortality from septic shock is highly heritable. The identification of causal genetic factors is insufficient. To discover key contributors, we first identified nonsynonymous single-nucleotide polymorphisms in conserved genomic regions that are predicted to have significant effects on protein function. We then test the hypothesis that these nonsynonymous single-nucleotide polymorphisms across the genome alter clinical outcome of septic shock. DESIGN: Genetic-association study plus in vitro experiment using primary cells plus in silico analysis using genomic DNA and protein database. SETTING: Twenty-seven ICUs at academic teaching centers in Canada, Australia, and the United States. PATIENTS: Patients with septic shock of European ancestry (n = 520). INTERVENTIONS: Patients with septic shock were genotyped for 843 nonsynonymous single-nucleotide polymorphisms in conserved regions of the genome and are predicted to have damaging effects from the protein sequence. MEASUREMENTS AND MAIN RESULTS: The primary outcome variable was 28-day mortality. Secondary outcome variables were organ dysfunction. Productions of adhesion molecules including interleukin-8, growth-regulated oncogene-α, monocyte chemoattractant protein-1, and monocyte chemoattractant protein-3 were measured in human umbilical vein endothelial cells after SVEP1 gene silencing by RNA interference. Patients with septic shock having the SVEP1 C allele of nonsynonymous single-nucleotide polymorphism, SVEP1 c.2080A>C (p. Gln581His, rs10817033), had a significant increase in the hazard of death over the 28 days (hazard ratio, 1.72; 95% CI, 1.31-2.26; p = 9.7 × 10-5) and increased organ dysfunction and needed more organ support (p < 0.05). Silencing SVEP1 significantly increased interleukin-8, growth-regulated oncogene-α, monocyte chemoattractant protein-1, monocyte chemoattractant protein-3 production in human umbilical vein endothelial cells under lipopolysaccharide stimulation (p < 0.01). CONCLUSIONS: C allele of SVEP1 c.2080A>C (p. Gln581His) single-nucleotide polymorphism, a non-synonymous single-nucleotide polymorphism in conserved regions and predicted to have damaging effects on protein structure, was associated with increased 28-day mortality and organ dysfunction of septic shock. SVEP1 appears to regulate molecules of the leukocyte adhesion pathway.

PCSK9 is a critical regulator of the innate immune response and septic shock outcome.

A decrease in the activity of proprotein convertase subtilisin/kexin type 9 (PCSK9) increases the amount of low-density lipoprotein (LDL) receptors on liver cells and, therefore, LDL clearance. The clearance of lipids from pathogens is related to endogenous lipid clearance; thus, PCSK9 may also regulate removal of pathogen lipids such as lipopolysaccharide (LPS). Compared to controls, Pcsk9 knockout mice displayed decreases in inflammatory cytokine production and in other physiological responses to LPS. In human liver cells, PCSK9 inhibited LPS uptake, a necessary step in systemic clearance and detoxification. Pharmacological inhibition of PCSK9 improved survival and inflammation in murine polymicrobial peritonitis. Human PCSK9 loss-of-function genetic variants were associated with improved survival in septic shock patients and a decrease in inflammatory cytokine response both in septic shock patients and in healthy volunteers after LPS administration. The PCSK9 effect was abrogated in LDL receptor (LDLR) knockout mice and in humans who are homozygous for an LDLR variant that is resistant to PCSK9. Together, our results show that reduced PCSK9 function is associated with increased pathogen lipid clearance via the LDLR, a decreased inflammatory response, and improved septic shock outcome.

A multibiomarker-based outcome risk stratification model for adult septic shock*.

OBJECTIVES: Clinical trials in septic shock continue to fail due, in part, to inequitable and sometimes unknown distribution of baseline mortality risk between study arms. Investigators advocate that interventional trials in septic shock require effective outcome risk stratification. We derived and tested a multibiomarker-based approach to estimate mortality risk in adults with septic shock. DESIGN: Previous genome-wide expression studies identified 12 plasma proteins as candidates for biomarker-based risk stratification. The current analysis used banked plasma samples and clinical data from existing studies. Biomarkers were assayed in plasma samples obtained from 341 subjects with septic shock within 24 hours of admission to the ICU. Classification and regression tree analysis was used to generate a decision tree predicting 28-day mortality based on a combination of both biomarkers and clinical variables. The derived tree was first tested in an independent cohort of 331 subjects, then calibrated using all subjects (n = 672), and subsequently validated in another independent cohort (n = 209). SETTING: Multiple ICUs in Canada, Finland, and the United States. SUBJECTS: Eight hundred eighty-one adults with septic shock or severe sepsis. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: The derived decision tree included five candidate biomarkers, admission lactate concentration, age, and chronic disease burden. In the derivation cohort, sensitivity for mortality was 94% (95% CI, 87-97), specificity was 56% (50-63), positive predictive value was 50% (43-57), and negative predictive value was 95% (89-98). Performance was comparable in the test cohort. The calibrated decision tree had the following test characteristics in the validation cohort: sensitivity 85% (76-92), specificity 60% (51-69), positive predictive value 61% (52-70), and negative predictive value 85% (75-91). CONCLUSIONS: We have derived, tested, calibrated, and validated a risk stratification tool and found that it reliably estimates the probability of mortality in adults with septic shock.

Cytokines and signaling molecules predict clinical outcomes in sepsis.

INTRODUCTION: Inflammatory response during sepsis is incompletely understood due to small sample sizes and variable timing of measurements following the onset of symptoms. The vasopressin in septic shock trial (VASST) compared the addition of vasopressin to norepinephrine alone in patients with septic shock. During this study plasma was collected and 39 cytokines measured in a 363 patients at both baseline (before treatment) and 24 hours. Clinical features relating to both underlying health and the acute organ dysfunction induced by the severe infection were collected during the first 28 days of admission. HYPOTHESIS: Cluster analysis of cytokines identifies subgroups of patients at differing risk of death and organ failure. METHODS: Circulating cytokines and other signaling molecules were measured using a Luminex multi-bead analyte detection system. Hierarchical clustering was performed on plasma values to create patient subgroups. Enrichment analysis identified clinical outcomes significantly different according to these chemically defined patient subgroups. Logistic regression was performed to assess the importance of cytokines for predicting patient subgroups. RESULTS: Plasma levels at baseline produced three subgroups of patients, while 24 hour levels produced two subgroups. Using baseline cytokine data, one subgroup of 47 patients showed a high level of enrichment for severe septic shock, coagulopathy, renal failure, and risk of death. Using data at 24 hours, a larger subgroup of 81 patients that largely encompassed the 47 baseline subgroup patients had a similar enrichment profile. Measurement of two cytokines, IL2 and CSF2 and their product were sufficient to classify patients into these subgroups that defined clinical risks. CONCLUSIONS: A distinct pattern of cytokine levels measured early in the course of sepsis predicts disease outcome. Subpopulations of patients have differing clinical outcomes that can be predicted accurately from small numbers of cytokines. Design of clinical trials and interventions may benefit from consideration of cytokine levels.

Noncanonical Nuclear Factor Kappa B (NF-κB) Signaling and Potential for Therapeutics in Sepsis.

NF-κB signaling plays a central role in the pathophysiology of severe sepsis and septic shock. Despite tremendous and missed efforts, novel therapeutics for severe sepsis and septic shock are still needed. Many drugs have been designed to target the canonical NF-κB signaling pathway with limited success, potentially due to the nonspecificity of the drugs for other kinases and the interaction of canonical signaling with other pathways. Here, we review the canonical and noncanonical signaling pathways of NF-κB, the cross talk and negative regulation of the two pathways, and the potential for therapeutics arising from the noncanonical NF-κB pathway in relation to the pathophysiology of septic shock.

Vasopressin compared with norepinephrine augments the decline of plasma cytokine levels in septic shock.

RATIONALE: Changes in plasma cytokine levels may predict mortality, and therapies (vasopressin versus norepinephrine) could change plasma cytokine levels in early septic shock. OBJECTIVES: Our hypotheses were that changes in plasma cytokine levels over 24 hours differ between survivors and nonsurvivors, and that there are different effects of vasopressin and norepinephrine on plasma cytokine levels in septic shock. METHODS: We studied 394 patients in a randomized, controlled trial of vasopressin versus norepinephrine in septic shock. We used hierarchical clustering and principal components analysis of the baseline cytokine concentrations to subgroup cytokines; we then compared survivors to nonsurvivors (28 d) and compared vasopressin- versus norepinephrine-induced changes in cytokine levels over 24 hours. MEASUREMENTS AND MAIN RESULTS: A total of 39 plasma cytokines were measured at baseline and at 24 hours. Hierarchical clustering and principal components analysis grouped cytokines similarly. Survivors (versus nonsurvivors) had greater decreases of overall cytokine levels (P < 0.001). Vasopressin decreased overall 24-hour cytokine concentration compared with norepinephrine (P = 0.037). In less severe septic shock, the difference in plasma cytokine reduction over 24 hours between survivors and nonsurvivors was less pronounced than that seen in more severe septic shock. Furthermore, vasopressin decreased interferon-inducible protein 10 and granulocyte colony-stimulating factor more than did norepinephrine in less severe septic shock, whereas vasopressin decreased granulocyte-macrophage colony-stimulating factor in patients who had more severe shock. CONCLUSIONS: Survivors of septic shock had greater decreases of cytokines, chemokines and growth factors in early septic shock. Vasopressin decreased 24-hour plasma cytokine levels more than did norepinephrine. The vasopressin-associated decrease of cytokines differed according to severity of shock. Clinical trial registered with www.controlled-trials.com (ISRCTN94845869).

Sepsis in transit: from clinical to molecular classification.

In the previous issue of Critical Care, Maslove and colleagues studied circulating neutrophil transcriptional expression to discover and validate a molecular subclassification of adult patients with sepsis. The authors divided patients into small derivation (n = 55) and validation (n = 71) cohorts. Their complex methodology included partitioning around medoid and hierarchical clustering methods to define two transcriptionally distinct subtypes of sepsis. Pathway analysis found that chemokine and cytokine pathways as well as Toll-like receptor signaling were enhanced. Investigation of specific drug target genes relevant to sepsis found significantly different expression levels between the two molecular subtypes. Interestingly, most patient characteristics did not differ between groups, except for an increase in the proportion of severe sepsis in molecular subtype 1. Possible confounders of this study were the small sample size, population stratification, and lack of information regarding drug interventions, all of which support the need for more studies with larger cohorts that include transcriptional profiles. This thought-provoking hypothesis-generating study could lead to a new neutrophil expression-based molecular classification of adult sepsis.

Molecular mechanisms of sepsis.

In cancer, therapies are targeted at 6 important pathways. In sepsis, there is ongoing controversy regarding the number and relative roles of pathways that are activated or repressed and which are important in the progression from health to death. Adding to complexity, there is interaction of pathways, there are differences in temporal pattern of up and down-regulation of pathways and there are different responses of pathways to therapies of sepsis. In this review, we define four key pathways of sepsis: (1) inflammation and immunity, (2) coagulation and fibrinolysis, (3) apoptosis, and (4) endocrine. Each of these pathways can impair endothelial function, a unifying aspect of the pathophysiology of sepsis. There are few studies of interactions of pathways except for the interacttion of inflammation/immunity with coagulation/fibrinolysis. Successful treatment of cancer requires that cancer therapies interrupt several key pathways of cancer. Accordingly, we suggest that successful treatment of sepsis will require therapies that interrupt several key pathways of sepsis. Perhaps the paucity of approved therapies for sepsis is related in part to the underevaluation of novel pathways, to lack of understanding of interactions of pathways and to lack of interruption of key pathways of sepsis.

Association of angiotensin II type 1 receptor-associated protein gene polymorphism with increased mortality in septic shock.

OBJECTIVE: Angiotensin II and its postreceptor signaling are crucial in regulating vasomotor tone. The objective of this study was to test the hypothesis that single nucleotide polymorphisms in angiotensin II pathway genes alter outcome of septic shock. DESIGN: Genetic association study and in vitro experiment. SETTING: Intensive care units at academic teaching centers. PATIENTS: Derivation and validation septic shock cohorts (n = 589 and n = 616, respectively) and a coronary artery bypass surgery cohort (n = 551). INTERVENTIONS: Patients with septic shock in the derivation cohort were genotyped for tag single nucleotide polymorphisms: angiotensin-converting enzyme (six single nucleotide polymorphisms), angiotensin II receptor type 1 (five single nucleotide polymorphisms), and angiotensin II type 1 receptor-associated protein (three single nucleotide polymorphisms), which is a negative regulator of angiotensin II receptor type 1. Patients in the septic shock replication cohort and the coronary artery bypass graft cohort were genotyped for the angiotensin II type 1 receptor-associated protein rs11121816. MEASUREMENTS AND MAIN RESULTS: The primary outcome variable was 28-day mortality. Secondary outcome variables were blood pressure and heart rate. Angiotensin II type 1 receptor-associated protein messenger RNA expression was measured in genotyped lymphoblastoid cells in vitro. Patients with septic shock patients the GG genotype of angiotensin II type 1 receptor-associated protein rs11121816 had increased 28-day mortality in the derivation cohort (54.8% vs. 41.4%; adjusted hazard ratio, 1.46; 95% confidence interval, 1.09-1.93; p = .010 [all ethnicities]; p = .050 [white]) and in the replication cohort (43.8% vs. 32.3%; hazard ratio, 1.42; 95% confidence interval, 1.03-1.98; p = .035 [all ethnicities]; p = .037 [white]). Patients having the GG genotype had decreased mean arterial pressure (98.3% of other genotype, p = .058 [derivation cohort]; 97.7%, p = .00060 [replication cohort]) and increased heart rate (104.1%, p = .023 [derivation cohort], 102.9%, p = nonsignificant [replication cohort]). GG genotype patients undergoing coronary artery bypass grafting had decreased postoperative mean arterial pressure and increased postoperative heart rate (p < .05). GG genotype lymphoblastoid cells had 2.0-fold higher angiotensin II type 1 receptor-associated protein messenger RNA expression (p < .05). CONCLUSIONS: For angiotensin II type 1 receptor-associated protein, the negative regulator of angiotensin II receptor type 1, the GG genotype of rs11121816 was associated with increased angiotensin II type 1 receptor-associated protein expression, decreased blood pressure, and increased heart rate as well as increased 28-day mortality in septic shock.