Rationale: Sepsis syndrome is characterized by inappropriate amplified systemic inflammatory response and bacteremia that promote multiorgan failure and mortality. Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulates a pleiotropic cytoprotective defense program including antioxidants and protects against several inflammatory disorders by inhibiting oxidative tissue injuries. However, the role of enhanced Nrf2 activity in modulating innate immune responses to microbial infection and pathogenesis of sepsis is unclear. Objectives: To determine whether Nrf2 in myeloid leukocytes alters inflammatory response and protects against sepsis. Methods: Mice with deletion of Nrf2 or kelch-like ECH-associated protein (Keap1) in myeloid leukocyte cells and respective floxed controls were subjected to cecal ligation and puncture-induced sepsis and were assessed for survival, organ injury, systemic inflammation, and bacteremia. Using LPS-stimulated peritoneal macrophages, Toll-like receptor (TLR) 4 surface trafficking and downstream signaling events were analyzed. Measurements and Main Results: Mortality, organ injury, circulating levels of inflammatory mediators, and bacteremia were markedly reduced in LysM-Keap1 2/2 compared with respective floxed controls (Keap1 f/f or Nrf2 f/f ) and significantly elevated in LysM-Nrf2 2/2 mice after cecal ligation and puncture. Peritoneal macrophages from septic LysM-Keap1 2/2 mice showed a greater bacterial phagocytic activity compared with LysM-Nrf2 2/2 and floxed controls. LPS stimulation resulted in greater reactive oxygen species-induced cell surface transport of TLR4 from trans-Golgi network and subsequent TLR4 downstream signaling (recruitment of MYD88 and TRIF, phosphorylation of IkB and IRF3, and cytokine expression) in macrophages of LysM-Nrf2 2/2 compared with LysM-Keap1 2/2 mice and floxed controls. Conclusions: Our study shows that Nrf2 acts as a critical immunomodulator in leukocytes, controls host inflammatory response to bacterial infection, and protects against sepsis.

Neutrophils are critical for the rapid eradication of bacterial pathogens, but they also contribute to the development of multiple organ failure in sepsis. We hypothesized that increasing early recruitment of neutrophils to the focus of infection will increase bacterial clearance and improve survival. Sepsis was induced in mice, using cecal ligation and puncture (CLP); blood samples were collected at 6 and 24 h; and survival was followed for 28 d. In separate experiments, peritoneal bacteria and inflammatory cells were measured. Septic mice predicted to die based on IL-6 levels (Die-P) had higher concentrations of CXCL1 and CXCL2 in the peritoneum and plasma compared with those predicted to live (Live-P). At 6 h, Live-P and Die-P had equivalent numbers of peritoneal neutrophils and bacteria. In Die-P mice the number of peritoneal bacteria increased between 6 and 24 h post-CLP, whereas in Live-P it decreased. The i.p. injection of CXCL1 and CXCL2 in naive mice resulted in local neutrophil recruitment. When given immediately after CLP, CXC chemokines increased peritoneal neutrophil recruitment at 6 h after CLP. This early increase in neutrophils induced by exogenous chemokines resulted in significantly fewer peritoneal bacteria by 24 h [CFU (log) = 6.04 versus 4.99 for vehicle versus chemokine treatment; p < 0.05]. Chemokine treatment significantly improved survival at both 5 d (40 versus 72%) and 28 d (27 versus 52%; p < 0.02 vehicle versus chemokines). These data demonstrate that early, local treatment with CXC chemokines enhances neutrophil recruitment and clearance of bacteria as well as improves survival in the CLP model of sepsis.

The paradigm of SIRS-to-CARS transition implies that hyperinflammation triggers acute sepsis mortality, while hypoinflammation (release of anti-inflammatory cytokines) in late sepsis induces chronic deaths. However, the exact humoral inflammatory mechanisms attributable to sepsis outcomes remain elusive. In part I of the study, we characterized the systemic dynamics of the chronic inflammation in dying (DIE) and surviving (SUR) mice suffering from CLP sepsis (days 6-28). In part II, we combined the current chronic and previous acute/chronic sepsis data to compare the outcome-dependent inflammatory signatures between these two phases. To compare global inflammatory responses, a composite cytokine score (CCS) was calculated. Mice were never sacrificed but sampled daily (20μl) for blood. Part I: parameters from chronic DIE mice were clustered into the 72h, 48h and 24h prior-to-death time-points and compared to SUR of the same post-CLP day. Cytokine increases were mixed and never preceded chronic deaths earlier than 48h (3 to 180-fold increase). CCS demonstrated simultaneous and similar upregulation of pro-and anti-inflammatory compartments at 24h prior to chronic death (DIE 80 and 50-fold higher vs. SUR). Part II: cytokine ratios across sepsis phases/outcomes indicated steady pro-vs. anti-inflammatory balance. CCS showed the inflammatory response in chronic DIE was 5-fold lower versus acute DIE mice, yet identical to acute SUR. Concluding, the systemic MARS-like pattern (concurrent release of pro-and anti-inflammatory cytokines) occurs irrespectively of the sepsis phase, response magnitude and/or outcome. Although different in magnitude, neither acute nor chronic septic mortality is associated with a predominating pro-and/or anti-inflammatory signature in the blood.

Objective The cause of death in murine models of sepsis remains unclear. The primary purpose of this study was to determine if significant lung injury develops in mice predicted to die following cecal ligation and puncture induced sepsis compared to those predicted to live. Design Prospective, laboratory controlled experiments. Setting University research laboratory. Subjects Adult, female, outbred ICR mice. Interventions Mice underwent cecal ligation and puncture (CLP) to induce sepsis. Two groups of mice were sacrificed at 24 and 48 hours post-CLP and samples were collected. These mice were further stratified into groups predicted to die (Die-P) and predicted to live (Live-P) based on plasma interleukin 6 (IL-6) levels obtained 24 hours post-CLP. Multiple measures of lung inflammation and lung injury were quantified in these two groups. Results from a group of mice receiving intratracheal normal saline without surgical intervention were also included as a negative control. As a positive control, bacterial pneumonia was induced with Pseudomonas aeruginosa to cause definitive lung injury. Separate mice were followed for survival until day 28 post-CLP. These mice were used to verify the IL-6 cut-offs for survival prediction. Measurements and Main Results Following sepsis, both the Die-P and Live-P mice had significantly suppressed measures of respiratory physiology but maintained normal levels of arterial oxygen saturation. Bronchoalveolar lavage (BAL) levels of pro and anti-inflammatory cytokines were not elevated in the Die-P mice compared to the Live-P. Additionally, there was no increase in the recruitment of neutrophils to the lung, pulmonary vascular permeability, or histological evidence of damage. In contrast, all of these pulmonary injury and inflammatory parameters were increased in mice with Pseudomonas pneumonia. Conclusions These data demonstrate that mice predicted to die during sepsis have no significant lung injury. In murine intra-abdominal sepsis, pulmonary injury cannot be considered the etiology of death in the acute phase.

Fibrinogen (Fg) has been implicated in the pathogenesis of several fibrotic disorders by acting as a profibrotic ligand for a variety of cellular surface receptors and by modulating the provisional fibrin matrix formed after injury. We demonstrated increased renal Fg expression after unilateral ureteral obstruction and folic acid (FA) nephropathy in mice, respectively. Urinary Fg excretion was also increased in FA nephropathy. Using in vitro and in vivo approaches, our results suggested that IL-6 mediates STAT3 activation in kidney fibrosis and that phosphorylated (p)STAT3 binds to Fgα, Fgβ, and Fgγ promoters in the kidney to regulate their transcription. Genetically modified Fg heterozygous mice (∼75% of normal plasma Fg levels) exhibited only 3% kidney interstitial fibrosis and tubular atrophy after FA nephropathy compared with 24% for wild-type mice. Fibrinogenolysis through Ancrod administration after FA reduced interstitial fibrosis more than threefold compared with vehicle-treated control mice. Mechanistically, we show that Fg acts synergistically with transforming growth factor (TGF)-β1 to induce fibroblast proliferation and activates TGF-β1/pSMAD2 signaling. This study offers increased understanding of Fg expression and molecular interactions with TGF-β1 in the progression to kidney fibrosis and, importantly, indicates that fibrinogenolytics like Ancrod present a treatment opportunity for a yet intractable disease.