Pediatric septic shock treatment: new clues from genomic profiling

Zinc and Sepsis

Sepsis, defined as a “life-threatening organ dysfunction caused by a dysregulated host-response to infection” is a major health issue worldwide and still lacks a fully elucidated pathobiology and uniform diagnostic tests. The trace element zinc is known to be crucial to ensure an appropriate immune response. During sepsis a redistribution of zinc from serum into the liver has been observed and several studies imply a correlation between zinc and sepsis outcome. Therefore the alterations of zinc concentrations in different tissues might serve as one part of the host’s defense mechanism against pathogens during sepsis by diverse mechanisms. It has been suggested that zinc is involved in nutritional immunity, acts as a hepatoprotective agent, or a differentiation signal for innate immune cells, or supports the synthesis of acute phase proteins. Further knowledge about these events could help in the evaluation of how zinc could be optimally applied to improve treatment of septic patients. Moreover, the changes in zinc homeostasis are substantial and correlate with the severity of the disease, suggesting that zinc might also be useful as a diagnostic marker for evaluating the severity and predicting the outcome of sepsis.

Pediatric sepsis: preparing for the future against a global scourge

Sepsis is a leading cause of morbidity and mortality among children worldwide. As consensus statements emerge regarding early recognition and goal-directed management of sepsis, scrutiny should be given to the unique characteristics of sepsis in children. Pediatric patients are not small adults! Sepsis epidemiology, pathophysiology, and management strategy can vary significantly from those for adults. Herein, we describe the epidemiology of pediatric sepsis, in both resource-rich and resource-poor worlds, and discuss how the pathophysiology of pediatric sepsis differs from that for adults. We discuss the timeline of management of pediatric sepsis, studying how discoveries over the past 50 years have changed the way sepsis is treated. Finally, we discuss the future of pediatric sepsis. We focus on approaches that carry the most substantive impact on the global burden of disease.

Genetics and genomics in pediatric septic shock

OBJECTIVES

Pediatric septic shock continues to be an important public health problem. Several investigative groups have applied genetic and genomic approaches as a means of identifying novel pathways and therapeutic targets, discovery of sepsis-related biomarkers, and identification of septic shock subclasses. This review will highlight studies in pediatric sepsis with a focus on gene association studies and genome-wide expression profiling.

DATA SOURCES

A summary of published literature involving gene association and expression profiling studies specifically involving pediatric sepsis and septic shock.

SUMMARY

Several polymorphisms of genes broadly involved in inflammation, immunity, and coagulation have been linked with susceptibility to sepsis, or outcome of sepsis in children. Many of these studies involve meningococcemia, and the strongest association involves a functional polymorphism of the plasminogen activator inhibitor-1 promoter region and meningococcal sepsis. Expression profiling studies in pediatric septic shock have identified zinc supplementation and inhibition of matrix metalloproteinase-8 activity as potential, novel therapeutic approaches in sepsis. Studies focused on discovery of sepsis-related biomarkers have identified interleukin-8 as a robust outcome biomarker in pediatric septic shock. Additional studies have demonstrated the feasibility and clinical relevance of gene expression-based subclassification of pediatric septic shock.

CONCLUSIONS

Pediatric sepsis and septic shock are increasingly being studied by genetic and genomic approaches and the accumulating data hold the promise of enhancing our future approach to this ongoing clinical problem.

Evaluation of zinc and selenium alterations in children with acute infections: Correlation with markers of inflammation

Objectives: To investigate and assess selenium (Se) and zinc (Zn) serum alterations in children with acute infections. Material and Methods: We determined Se, Zn, C-reactive protein (CRP), serum amyloid A (SAA), and procalcitonin (PCT) in 80 children hospitalized with acute infections. The patients were divided in two groups: Bacterial infections: 40 children (mean age 4.8 years); viral infections: 40 children (mean age 5.7 years). Morning blood samples were collected from each patient in three different periods: (a) in the acute phase (admission), (b) during the inflammatory process (4th day of hospitalization), and (c) after recovery (28–33 days after the first sampling). Results: We found that patients with bacterial infections had significantly lower levels of Se (48.9±16.4 mg/L vs. 58.1±13.7 mg/L, p=0.014) and Zn (69.3±19.4 mg/dL vs. 79.9±13.1 mg/dL, p=0.008) than those with viral infections on admission. Zn and Se levels were significantly increased after remission and the 4th day of hospitalization in patients with bacterial infections. Se and Zn were inversely related with the inflammatory markers CRP (r=−0.480, p=0.002 and r=−0.380, p=0.02, respectively), and PCT (r=−0.670, p < 0.001 and r=−0.510, p<0.01, respectively), in the same patients group on admission. We also found a positive correlation between the two micronutrients (r = 0.400, p<0.01) in children with bacterial infections on admission. Conclusions: Zn and Se behave as negative acute phase reactants and their levels were inversely associated with the progress of infection in patients with bacterial infections. The changes of micronutrients (Se, Zn) during the inflammatory process are transient and resolve without any dietary intervention.

Validation of a gene expression-based subclassification strategy for pediatric septic shock

OBJECTIVE

Septic shock heterogeneity has important implications for clinical trial implementation and patient management. We previously addressed this heterogeneity by identifying three putative subclasses of children with septic shock based exclusively on a 100-gene expression signature. Here we attempted to prospectively validate the existence of these gene expression-based subclasses in a validation cohort.

DESIGN

Prospective observational study involving microarray-based bioinformatics.

SETTING

Multiple pediatric intensive care units in the United States.

PATIENTS

Separate derivation (n = 98) and validation (n = 82) cohorts of children with septic shock.

INTERVENTIONS

None other than standard care.

MEASUREMENTS AND MAIN RESULTS

Gene expression mosaics of the 100 class-defining genes were generated for 82 individual patients in the validation cohort. Using computer-based image analysis, patients were classified into one of three subclasses ("A," "B," or "C") based on color and pattern similarity relative to reference mosaics generated from the original derivation cohort. After subclassification, the clinical database was mined for phenotyping. Subclass A patients had higher illness severity relative to subclasses B and C as measured by maximal organ failure, fewer intensive care unit-free days, and a higher Pediatric Risk of Mortality score. Patients in subclass A were characterized by repression of genes corresponding to adaptive immunity and glucocorticoid receptor signaling. Separate subclass assignments were conducted by 21 individual clinicians using visual inspection. The consensus classification of the clinicians had modest agreement with the computer algorithm.

CONCLUSIONS

We have validated the existence of subclasses of children with septic shock based on a biologically relevant, 100-gene expression signature. The subclasses have relevant clinical differences.

Leukocyte subset-derived genomewide expression profiles in pediatric septic shock

OBJECTIVE

To directly assess whether genomewide expression profiles derived from leukocyte subsets are comparable to that of whole blood as measured by enrichment for genes corresponding to metabolic and signaling pathways.

DESIGN

Prospective observational study involving microarray-based bioinformatics based on RNA individually derived from whole blood, neutrophils, monocytes, and lymphocytes, respectively.

SETTING

Three pediatric intensive care units in the United States.

PATIENTS

Children < or =10 yrs of age: five normal control subjects and 13 meeting criteria for septic shock on day 1 of presentation to the pediatric intensive care unit.

INTERVENTIONS

None other than standard care.

MEASUREMENTS AND MAIN RESULTS

Baseline analyses using whole blood-derived RNA demonstrated increased expression of genes corresponding to signaling pathways involving innate immunity, redox balance, and protein ubiquitination and decreased expression of genes corresponding to the adaptive immune system. Subsequent analyses using leukocyte-specific RNA were congruent with the gene expression profiles demonstrated using whole blood-derived RNA as measured by enrichment for genes corresponding to metabolic and signaling pathways. Gene network analysis, derived from a composite gene list involving the individual gene expression profiles of neutrophils, monocytes, and lymphocytes, respectively, revealed a gene network corresponding to antigen presentation, cell-mediated immunity, and humoral-mediated immunity. Finally, a subanalysis focused on network gene nodes localized to the nuclear compartment revealed functional annotations related to transcriptional repression and epigenetic regulation.

CONCLUSIONS

These data demonstrate that genome-level repression of adaptive immunity gene programs early in the course of pediatric septic shock remained evident when analyses were conducted using leukocyte subset-specific RNA.

Admission chemokine (C-C motif) ligand 4 levels predict survival in pediatric septic shock

OBJECTIVE

Stratification with an effective outcome biomarker could improve the design of interventional trials in pediatric septic shock. The objective of this study was to test the usefulness of chemokine (C-C motif) ligand 4 as an outcome biomarker for mortality in pediatric septic shock.

DESIGN

A cross-sectional, observational study.

SETTING

Eighteen pediatric intensive care units in the United States.

PATIENTS

One hundred fifty-six pediatric patients with septic shock.

INTERVENTIONS

Serum samples were obtained within 24 hrs of admission to the pediatric intensive care unit. Serum levels of chemokine (C-C motif) ligand 4 were measured by enzyme-linked immunosorbent assay and compared with mortality in a training set of 34 patients. These data were used to generate a cutoff value whose usefulness was evaluated through prospective application-without post hoc modification-to a larger validation set of 122 patients.

MEASUREMENTS AND MAIN RESULTS

On inspection of the training set data, a cutoff value of 140 pg/mL was chosen. When applied to the validation set, serum chemokine (C-C motif) ligand 4 levels >140 pg/mL yielded a sensitivity of 92% and a specificity of 40% for mortality. A serum level of < or =140 pg/mL had a negative predictive value for mortality of 98%.

CONCLUSIONS

A serum level of chemokine (C-C motif) ligand 4 of < or =140 pg/mL, when obtained within 24 hrs of admission, predicts a very high likelihood of survival in pediatric septic shock. Exclusion of patients with a chemokine (C-C motif) ligand 4 level of < or =140 pg/mL from interventional clinical trials in pediatric septic shock could create a study population in which survival benefit from the study agent could be more readily demonstrated.

Identification of pediatric septic shock subclasses based on genome-wide expression profiling

BACKGROUND

Septic shock is a heterogeneous syndrome within which probably exist several biological subclasses. Discovery and identification of septic shock subclasses could provide the foundation for the design of more specifically targeted therapies. Herein we tested the hypothesis that pediatric septic shock subclasses can be discovered through genome-wide expression profiling.

METHODS

Genome-wide expression profiling was conducted using whole blood-derived RNA from 98 children with septic shock, followed by a series of bioinformatic approaches targeted at subclass discovery and characterization.

RESULTS

Three putative subclasses (subclasses A, B, and C) were initially identified based on an empiric, discovery-oriented expression filter and unsupervised hierarchical clustering. Statistical comparison of the three putative subclasses (analysis of variance, Bonferonni correction, P < 0.05) identified 6,934 differentially regulated genes. K-means clustering of these 6,934 genes generated 10 coordinately regulated gene clusters corresponding to multiple signaling and metabolic pathways, all of which were differentially regulated across the three subclasses. Leave one out cross-validation procedures indentified 100 genes having the strongest predictive values for subclass identification. Forty-four of these 100 genes corresponded to signaling pathways relevant to the adaptive immune system and glucocorticoid receptor signaling, the majority of which were repressed in subclass A patients. Subclass A patients were also characterized by repression of genes corresponding to zinc-related biology. Phenotypic analyses revealed that subclass A patients were younger, had a higher illness severity, and a higher mortality rate than patients in subclasses B and C.

CONCLUSION

Genome-wide expression profiling can identify pediatric septic shock subclasses having clinically relevant phenotypes.

Genomic expression profiling across the pediatric systemic inflammatory response syndrome, sepsis, and septic shock spectrum

OBJECTIVES

To advance our biological understanding of pediatric septic shock, we measured the genome-level expression profiles of critically ill children representing the systemic inflammatory response syndrome (SIRS), sepsis, and septic shock spectrum.

DESIGN

Prospective observational study involving microarray-based bioinformatics.

SETTING

Multiple pediatric intensive care units in the United States.

PATIENTS

Children <or=10 years of age: 18 normal controls, 22 meeting criteria for SIRS, 32 meeting criteria for sepsis, and 67 meeting criteria for septic shock on day 1. The available day 3 samples included 20 patients still meeting sepsis criteria, 39 patients still meeting septic shock criteria, and 24 patients meeting the exclusive day 3 category, SIRS resolved.

INTERVENTIONS

None other than standard care.

MEASUREMENTS AND MAIN RESULTS

Longitudinal analyses were focused on gene expression relative to control samples and patients having paired day 1 and day 3 samples. The longitudinal analysis focused on up-regulated genes revealed common patterns of up-regulated gene expression, primarily corresponding to inflammation and innate immunity, across all patient groups on day 1. These patterns of up-regulated gene expression persisted on day 3 in patients with septic shock, but not to the same degree in the other patient classes. The longitudinal analysis focused on down-regulated genes demonstrated gene repression corresponding to adaptive immunity-specific signaling pathways and was most prominent in patients with septic shock on days 1 and 3. Gene network analyses based on direct comparisons across the SIRS, sepsis, and septic shock spectrum, and all available patients in the database, demonstrated unique repression of gene networks in patients with septic shock corresponding to major histocompatibility complex antigen presentation. Finally, analyses focused on repression of genes corresponding to zinc-related biology demonstrated that this pattern of gene repression is unique to patients with septic shock.

CONCLUSIONS

Although some common patterns of gene expression exist across the pediatric SIRS, sepsis, and septic shock spectrum, septic shock is particularly characterized by repression of genes corresponding to adaptive immunity and zinc-related biology.

Divergence of canonical danger signals: the genome-level expression patterns of human mononuclear cells subjected to heat shock or lipopolysaccharide

BACKGROUND

Peripheral blood mononuclear cells (PBMC) serve a sentinel role allowing the host to efficiently sense and adapt to the presence of danger signals. Herein we have directly compared the genome-level expression patterns (microarray) of a human PBMC model (THP-1 cells) subjected to one of two canonical danger signals, heat shock or lipopolysaccharide (LPS).

RESULTS AND DISCUSSION

Based on sequential expression and statistical filters, and in comparison to control cells, we found that 3,988 genes were differentially regulated in THP-1 cells subjected to LPS stress, and 2,921 genes were differentially regulated in THP-1 cells subjected to heat shock stress. Venn analyses demonstrated that the majority of differentially regulated genes (> or = 70%) were uniquely expressed in response to one of the two danger signals. Functional analyses demonstrated that the two danger signals induced expression or repression of genes corresponding to unique pathways, molecular functions, biological processes, and gene networks. In contrast, there were 184 genes that were commonly upregulated by both stress signals, and 430 genes that were commonly downregulated by both stress signals. Interestingly, the 184 commonly upregulated genes corresponded to a gene network broadly related to inflammation, and more specifically to chemokine signaling.

CONCLUSION

These data demonstrate that the mononuclear cell responses to the canonical stress signals, heat shock and LPS, are highly divergent. However, there is a heretofore unrecognized common pattern of gene network expression corresponding to chemokine-related biology. The data also serve as a reference database for investigators in the field of stress signaling.

Interleukin-8 as a stratification tool for interventional trials involving pediatric septic shock

RATIONALE

Interventional clinical trials involving children with septic shock would benefit from an efficient preenrollment stratification strategy.

OBJECTIVES

To test the predictive value of interleukin (IL)-8 for 28-day mortality in pediatric septic shock.

METHODS

A training data set (n = 40) identified a serum IL-8 of greater than 220 pg/ml as having a 75% sensitivity and specificity for predicting 28-day mortality. This cutoff was then subjected to a series of validation steps.

MEASUREMENTS AND MAIN RESULTS

Subjects were drawn from two large, independent pediatric septic shock databases. Prospective application of the IL-8 cutoff to validation data set 1 (n = 139) demonstrated 78% sensitivity and 64% specificity for 28-day mortality. A serum IL-8 level of 220 pg/ml or less, however, had a negative predictive value for 28-day mortality of 95% in validation data set 1, which was subsequently applied to an independently generated data set of children with septic shock (validation set 2, n = 193). A serum IL-8 level of 220 pg/ml or less had a negative predictive value for 28-day mortality of 94% when applied to validation set 2.

CONCLUSIONS

A serum IL-8 level of 220 pg/ml or less, obtained within 24 hours of admission, predicts a high likelihood of survival in children with septic shock. We propose that IL-8 can be used to exclude such patients from interventional clinical trials and ultimately derive a study population with a more favorable risk to benefit ratio when subjected to a study agent.

Validating the genomic signature of pediatric septic shock

We previously generated genome-wide expression data (microarray) from children with septic shock having the potential to lead the field into novel areas of investigation. Herein we seek to validate our data through a bioinformatic approach centered on a validation patient cohort. Forty-two children with a clinical diagnosis of septic shock and 15 normal controls served as the training data set, while 30 separate children with septic shock and 14 separate normal controls served as the test data set. Class prediction modeling using the training data set and the previously reported genome-wide expression signature of pediatric septic shock correctly identified 95-100% of controls and septic shock patients in the test data set, depending on the class prediction algorithm and the gene selection method. Subjecting the test data set to an identical filtering strategy as that used for the training data set, demonstrated 75% concordance between the two gene lists. Subjecting the test data set to a purely statistical filtering strategy, with highly stringent correction for multiple comparisons, demonstrated <50% concordance with the previous gene filtering strategy. However, functional analysis of this statistics-based gene list demonstrated similar functional annotations and signaling pathways as that seen in the training data set. In particular, we validated that pediatric septic shock is characterized by large-scale repression of genes related to zinc homeostasis and lymphocyte function. These data demonstrate that the previously reported genome-wide expression signature of pediatric septic shock is applicable to a validation cohort of patients.

Genetic approach to pediatric septic shock

Septic shock is a complex and heterogeneous clinical syndrome, triggered by infection, and having significant morbidity and mortality in children. Emerging data indicate that the genetic make-up of the pediatric host may have a strong influence on the development and outcome of septic shock in children. Herein, we review this broad topic by focusing on pediatric-specific data (both recent and historical), as well as the broad topics of SNPs, genome-wide association studies and epigenetics. The historical and emerging data strongly suggest that a genetics-based perspective will need to be considered in future investigations and strategies aimed at improving the outcome of children with septic shock.