Nuala J. Meyer

Inflammasome-regulated Cytokines Are Critical Mediators of Acute Lung Injury

RATIONALE Despite advances in clinical management, there are currently no reliable diagnostic and therapeutic targets for acute respiratory distress syndrome (ARDS). The inflammasome/caspase-1 pathway regulates the maturation and secretion of proinflammatory cytokines (e.g., IL-18). IL-18 is associated with injury in animal models of systemic inflammation. OBJECTIVES We sought to determine the contribution of the inflammasome pathway in experimental acute lung injury and human ARDS. METHODS We performed comprehensive gene expression profiling on peripheral blood from patients with critical illness. Gene expression changes were assessed using real-time polymerase chain reaction, and IL-18 levels were measured in the plasma of the critically ill patients. Wild-type mice or mice genetically deficient in IL-18 or caspase-1 were mechanically ventilated using moderate tidal volume (12 ml/kg). Lung injury parameters were assessed in lung tissue, serum, and bronchoalveolar lavage fluid. MEASUREMENTS AND MAIN RESULTS In mice, mechanical ventilation enhanced IL-18 levels in the lung, serum, and bronchoalveolar lavage fluid. IL-18-neutralizing antibody treatment, or genetic deletion of IL-18 or caspase-1, reduced lung injury in response to mechanical ventilation. In human patients with ARDS, inflammasome-related mRNA transcripts (CASP1, IL1B, and IL18) were increased in peripheral blood. In samples from four clinical centers, IL-18 was elevated in the plasma of patients with ARDS (sepsis or trauma-induced ARDS) and served as a novel biomarker of intensive care unit morbidity and mortality. CONCLUSIONS The inflammasome pathway and its downstream cytokines play critical roles in ARDS development.

Circulating Mitochondrial DNA in Patients in the ICU as a Marker of Mortality: Derivation and Validation

In this paper, Choi and colleagues analyzed levels of mitochondrial DNA in two prospective observational cohort studies and found that increased mtDNA levels are associated with ICU mortality, and improve risk prediction in medical ICU patients. The data suggests that mtDNA could serve as a viable plasma biomarker in MICU patients.

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

Inhibition of PCSK9 function is associated with an increase in pathogen lipid clearance, a decrease in the innate immune inflammatory response, and an improvement in septic shock clinical outcome. An Enemy of Translation Despite nearly 100 clinical trials, potential drugs against murine-derived therapeutic targets for sepsis—a deadly condition caused by overactivation of the innate immune response to microbial infection—have been immune to translation. But humans and microbes have long coexisted fairly symbiotically and have come to share certain biological pathways. Now, Walley et al. show that both host- and pathogen-derived lipids use clearance mechanisms that highlight a well-known protein—proprotein convertase subtilisin/kesin type 9 (PCSK9)—as a possible therapeutic target for selected sepsis patients. The authors show that, compared to wild-type mice, Pcsk9 knockout mice displayed a dampening of various pathophysiological responses to a lipopolysaccharide (LPS) in the cell wall of Gram-negative bacteria. Also, PCSK9 protein inhibited LPS uptake by human liver cells, a crucial step in systemic LPS clearance. Pharmacological inhibition of PCSK9 enhanced survival of mice with polymicrobial peritonitis, a sepsis model. Last, PCSK9 loss-of-function genetic variants were associated with improved survival in septic shock patients. Drugs that reduce serum cholesterol by inhibiting PCSK9 are being studied in clinical trials as treatments for cardiovascular disease. Then, new work suggests that PCSK9-targeted drugs should be tested in clinical trials with sepsis patients who carry the PCSK9 gain-of-function variant. 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.

ANGPT2 Genetic Variant Is Associated with Trauma-associated Acute Lung Injury and Altered Plasma Angiopoietin-2 Isoform Ratio

RATIONALE Acute lung injury (ALI) acts as a complex genetic trait, yet its genetic risk factors remain incompletely understood. Large-scale genotyping has not previously been reported for ALI. OBJECTIVES To identify ALI risk variants after major trauma using a large-scale candidate gene approach. METHODS We performed a two-stage genetic association study. We derived findings in an African American cohort (n = 222) using a cardiopulmonary disease-centric 50K single nucleotide polymorphism (SNP) array. Genotype and haplotype distributions were compared between subjects with ALI and without ALI, with adjustment for clinical factors. Top performing SNPs (P < 10(-4)) were tested in a multicenter European American trauma-associated ALI case-control population (n = 600 ALI; n = 2,266 population-based control subjects) for replication. The ALI-associated genomic region was sequenced, analyzed for in silico prediction of function, and plasma was assayed by ELISA and immunoblot. MEASUREMENTS AND MAIN RESULTS Five SNPs demonstrated a significant association with ALI after adjustment for covariates in Stage I. Two SNPs in ANGPT2 (rs1868554 and rs2442598) replicated their significant association with ALI in Stage II. rs1868554 was robust to multiple comparison correction: odds ratio 1.22 (1.06-1.40), P = 0.0047. Resequencing identified predicted novel splice sites in linkage disequilibrium with rs1868554, and immunoblots showed higher proportion of variant angiopoietin-2 (ANG2) isoform associated with rs1868554T (0.81 vs. 0.48; P = 0.038). CONCLUSIONS An ANGPT2 region is associated with both ALI and variation in plasma angiopoietin-2 isoforms. Characterization of the variant isoform and its genetic regulation may yield important insights about ALI pathogenesis and susceptibility.

The Epidemiology of Acute Respiratory Distress Syndrome in Patients Presenting to the Emergency Department With Severe Sepsis.

ABSTRACT Background: Acute respiratory distress syndrome (ARDS) is a serious complication of sepsis, and sepsis-associated ARDS is associated with significant morbidity and mortality. To date, no study has directly examined the epidemiology of ARDS in severe sepsis from the earliest presentation to the health care system, the emergency department (ED). Methods: This was a single-center retrospective, observational cohort study of 778 adults with severe sepsis presenting to the ED. The primary outcome was the development of ARDS requiring mechanical ventilation during the first 5 hospital days. Acute respiratory distress syndrome was defined using the Berlin definition. We used multivariable logistic regression to identify risk factors associated independently with ARDS development. Results: The incidence of ARDS was 6.2% (48/778 patients) in the entire cohort. Acute respiratory distress syndrome development varied across the continuum of care: 0.9% of patients fulfilled criteria for ARDS in the ED, 1.4% admitted to the ward developed ARDS, and 8.9% admitted to the intensive care unit developed ARDS. Acute respiratory distress syndrome developed a median of 1 day after admission and was associated with a 4-fold higher risk of in-hospital mortality (14% vs. 60%, P < 0.001). Independent risk factors associated with increased risk of ARDS development included intermediate (2–3.9 mmol/L) (P = 0.04) and high (≥4) serum lactate levels (P = 0.008), Lung Injury Prediction score (P < 0.001), and microbiologically proven infection (P = 0.01). Conclusions: In patients presenting to the ED with severe sepsis, the rate of sepsis-associated ARDS development varied across the continuum of care. Acute respiratory distress syndrome developed rapidly and was associated with significant mortality. Elevated serum lactate levels in the ED and a recently validated clinical prediction score were independently associated with the development of ARDS in severe sepsis.

Genome Wide Association Identifies PPFIA1 as a Candidate Gene for Acute Lung Injury Risk Following Major Trauma

Acute Lung Injury (ALI) is a syndrome with high associated mortality characterized by severe hypoxemia and pulmonary infiltrates in patients with critical illness. We conducted the first investigation to use the genome wide association (GWA) approach to identify putative risk variants for ALI. Genome wide genotyping was performed using the Illumina Human Quad 610 BeadChip. We performed a two-stage GWA study followed by a third stage of functional characterization. In the discovery phase (Phase 1), we compared 600 European American trauma-associated ALI cases with 2266 European American population-based controls. We carried forward the top 1% of single nucleotide polymorphisms (SNPs) at p<0.01 to a replication phase (Phase 2) comprised of a nested case-control design sample of 212 trauma-associated ALI cases and 283 at-risk trauma non-ALI controls from ongoing cohort studies. SNPs that replicated at the 0.05 level in Phase 2 were subject to functional validation (Phase 3) using expression quantitative trait loci (eQTL) analyses in stimulated B-lymphoblastoid cell lines (B-LCL) in family trios. 159 SNPs from the discovery phase replicated in Phase 2, including loci with prior evidence for a role in ALI pathogenesis. Functional evaluation of these replicated SNPs revealed rs471931 on 11q13.3 to exert a cis-regulatory effect on mRNA expression in the PPFIA1 gene (p = 0.0021). PPFIA1 encodes liprin alpha, a protein involved in cell adhesion, integrin expression, and cell-matrix interactions. This study supports the feasibility of future multi-center GWA investigations of ALI risk, and identifies PPFIA1 as a potential functional candidate ALI risk gene for future research.

African American race, obesity, and blood product transfusion are risk factors for acute kidney injury in critically ill trauma patients☆

PURPOSE Acute kidney injury (AKI) is a common source of morbidity after trauma. We sought to determine novel risk factors for AKI, by Acute Kidney Injury Network (AKIN) criteria, in critically ill trauma patients. MATERIALS AND METHODS A prospective cohort of 400 patients admitted to the intensive care unit of a level 1 trauma center was followed for the development of AKI over 5 days. RESULTS Acute kidney injury developed in 147 (36.8%) of 400 patients. In multivariable regression analysis, independent risk factors for AKI included African American race (odds ratio [OR], 1.86; 95% confidence interval [CI], 1.08-3.18; P = .024), body mass index of 30 kg/m(2) or greater (OR, 4.72 versus normal body mass index; 95% CI, 2.59-8.61; P < .001), diabetes mellitus (OR, 3.26; 95% CI, 1.30-8.20; P = .012), abdominal Abbreviated Injury Scale score of 4 or more (OR, 3.78; 95% CI, 1.79-7.96; P < .001), and unmatched packed red blood cells administered during resuscitation (OR, 1.13 per unit; 95% CI, 1.04-1.23; P = .004). Acute Kidney Injury Network stages 1, 2, and 3 were associated with hospital mortality rates of 9.8%, 13.7%, and 30.4%, respectively, compared with 3.8% for those without AKI (P < .001). CONCLUSIONS Acute kidney injury in critically ill trauma patients is associated with substantial mortality. The findings of African American race, obesity, and blood product administration as independent risk factors for AKI deserve further study to elucidate underlying mechanisms.

Red Blood Cells Induce Necroptosis of Lung Endothelial Cells and Increase Susceptibility to Lung Inflammation

RATIONALE Red blood cell (RBC) transfusions are associated with increased risk of acute respiratory distress syndrome (ARDS) in the critically ill, yet the mechanisms for enhanced susceptibility to ARDS conferred by RBC transfusions remain unknown. OBJECTIVES To determine the mechanisms of lung endothelial cell (EC) High Mobility Group Box 1 (HMGB1) release following exposure to RBCs and to determine whether RBC transfusion increases susceptibility to lung inflammation in vivo through release of the danger signal HMGB1. METHODS In vitro studies examining human lung EC viability and HMGB1 release following exposure to allogenic RBCs were conducted under static conditions and using a microengineered model of RBC perfusion. The plasma from transfused and nontransfused patients with severe sepsis was examined for markers of cellular injury. A murine model of RBC transfusion followed by LPS administration was used to determine the effects of RBC transfusion and HMGB1 release on LPS-induced lung inflammation. MEASUREMENTS AND MAIN RESULTS After incubation with RBCs, lung ECs underwent regulated necrotic cell death (necroptosis) and released the essential mediator of necroptosis, receptor-interacting serine/threonine-protein kinase 3 (RIP3), and HMGB1. RIP3 was detectable in the plasma of patients with severe sepsis, and was increased with blood transfusion and among nonsurvivors of sepsis. RBC transfusion sensitized mice to LPS-induced lung inflammation through release of the danger signal HMGB1. CONCLUSIONS RBC transfusion enhances susceptibility to lung inflammation through release of HMGB1 and induces necroptosis of lung EC. Necroptosis and subsequent danger signal release is a novel mechanism of injury following transfusion that may account for the increased risk of ARDS in critically ill transfused patients.

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

RATIONALE Acute respiratory distress syndrome (ARDS) behaves as a complex genetic trait, yet knowledge of genetic susceptibility factors remains incomplete. OBJECTIVES To identify genetic risk variants for ARDS using large scale genotyping. METHODS A multistage genetic association study was conducted of three critically ill populations phenotyped for ARDS. Stage I, a trauma cohort study (n = 224), was genotyped with a 50K gene-centric single-nucleotide polymorphism (SNP) array. We tested SNPs associated with ARDS at P < 5 × 10(-4) for replication in stage II, a trauma case-control population (n = 778). SNPs replicating their association in stage II (P < 0.005) were tested in a stage III nested case-control population of mixed subjects in the intensive care unit (n = 2,063). Logistic regression was used to adjust for potential clinical confounders. We performed ELISA to test for an association between ARDS-associated genotype and plasma protein levels. MEASUREMENTS AND MAIN RESULTS A total of 12 SNPs met the stage I threshold for an association with ARDS. rs315952 in the IL1RN gene encoding IL-1 receptor antagonist (IL1RA) replicated its association with reduced ARDS risk in stages II (P < 0.004) and III (P < 0.02), and was robust to clinical adjustment (combined odds ratio = 0.81; P = 4.2 × 10(-5)). Plasma IL1RA level was associated with rs315952C in a subset of critically ill subjects. The effect of rs315952 was independent from the tandem repeat variant in IL1RN. CONCLUSIONS The IL1RN SNP rs315952C is associated with decreased risk of ARDS in three populations with heterogeneous ARDS risk factors, and with increased plasma IL1RA response. IL1RA may attenuate ARDS risk.

Lower serum endocan levels are associated with the development of acute lung injury after major trauma

PURPOSE Endocan is a proteoglycan expressed by endothelial cells in the lung that may inhibit leukocyte recruitment and thus prevent the development of acute lung injury (ALI). We tested the association of serum endocan levels with subsequent development of ALI after major trauma. MATERIALS AND METHODS This was a single-center nested case-control study within a prospective cohort study of major trauma patients. Using an enzyme-linked immunosorbent assay test, we measured endocan levels from admission serum in 24 controls (no ALI) and 24 cases (ALI within 5 days of trauma). Multivariable logistic regression was used to test the association of admission serum endocan levels with subsequent ALI. RESULTS Patients who developed ALI had lower levels of endocan on admission (mean, 3.5 ± 1.4 ng/mL vs 4.9 ± 2.6 ng/mL in controls; P = .02). For each 1-unit increase in serum endocan level, the odds ratio for ALI development decreased (0.69; 95% confidence interval, 0.49-0.97; P = .03). Lower endocan levels remained associated with a higher incidence of ALI after adjustment for age and illness severity. CONCLUSIONS Lower levels of serum endocan on admission are associated with subsequent development of ALI in trauma patients. These observations may be explained by endocan-mediated blockade of leukocyte recruitment in the lung.