Activated protein C protects against ventilator-induced pulmonary capillary leak

A Razor's Edge: Vascular Responses to Acute Inflammatory Lung Injury/Acute Respiratory Distress Syndrome

Historically considered a metabolically inert cellular layer separating the blood from the underlying tissue, the endothelium is now recognized as a highly dynamic, metabolically active tissue that is critical to organ homeostasis. Under homeostatic conditions, lung endothelial cells (ECs) in healthy subjects are quiescent, promoting vasodilation, platelet disaggregation, and anti-inflammatory mechanisms. In contrast, lung ECs are essential contributors to the pathobiology of acute respiratory distress syndrome (ARDS), as the quiescent endothelium is rapidly and radically altered upon exposure to environmental stressors, infectious pathogens, or endogenous danger signals into an effective and formidable regulator of innate and adaptive immunity. These dramatic perturbations, produced in a tsunami of inflammatory cascade activation, result in paracellular gap formation between lung ECs, sustained lung edema, and multi-organ dysfunction that drives ARDS mortality. The astonishing plasticity of the lung endothelium in negotiating this inflammatory environment and efforts to therapeutically target the aberrant ARDS endothelium are examined in further detail in this review.

Obesity impacts hypoxia adaptation of the lung

Obesity is mostly associated with adverse health consequences, but may also elicit favorable effects under chronic conditions. This "obesity paradox" is under debate for pulmonary diseases. As confounding factors complicate conclusions from human studies, this study used a controlled animal model combining diet-induced obesity and chronic hypoxia as a model for pulmonary hypertension and chronic obstructive pulmonary disease. Male C57BL/6 mice were fed control or high-fat diet for 30 wk, and half of the animals were exposed to chronic hypoxia (13% O2) for 3 wk. Hypoxia induced right ventricular hypertrophy, thickening of pulmonary arterial and capillary walls, higher lung volumes, and increased hemoglobin concentrations irrespective of the body weight. In contrast, lung proteomes differed substantially between lean- and obese-hypoxic mice. Many of the observed changes were linked to vascular and extracellular matrix (ECM) proteins. In lean-hypoxic animals, circulating platelets were reduced and abundances of various clotting-related proteins were altered, indicating a hypercoagulable phenotype. Moreover, the septal ECM composition was changed, and airspaces were significantly distended pointing to lung hyperinflation. These differences were mostly absent in the obese-hypoxic group. However, the obesity-hypoxia combination induced the lowest blood CO2 concentrations, indicating hyperventilation for sufficient oxygen supply. Moreover, endothelial surface areas were increased in obese-hypoxic mice. Thus, obesity exerts differential effects on lung adaptation to hypoxia, which paradoxically include not only adverse but also rather protective changes. These differences have a molecular basis in the lung proteome and may influence the pathogenesis of lung diseases. This should be taken into account for future individualized prevention and therapy.NEW & NOTEWORTHY An "obesity paradox" is discussed for pulmonary diseases. By linking lung proteome analyses to pulmonary structure and function, we demonstrate that diet-induced obesity affects lung adaptation to chronic hypoxia in various ways. The observed changes include not only adverse but also protective effects and are associated with altered abundances of vascular and extracellular matrix proteins. These results highlight the existence of relevant differences in individuals with obesity that may influence the pathogenesis of lung diseases.

Severe Trauma-Induced Coagulopathy: Molecular Mechanisms Underlying Critical Illness

Trauma remains one of the leading causes of death in adults despite the implementation of preventive measures and innovations in trauma systems. The etiology of coagulopathy in trauma patients is multifactorial and related to the kind of injury and nature of resuscitation. Trauma-induced coagulopathy (TIC) is a biochemical response involving dysregulated coagulation, altered fibrinolysis, systemic endothelial dysfunction, platelet dysfunction, and inflammatory responses due to trauma. The aim of this review is to report the pathophysiology, early diagnosis and treatment of TIC. A literature search was performed using different databases to identify relevant studies in indexed scientific journals. We reviewed the main pathophysiological mechanisms involved in the early development of TIC. Diagnostic methods have also been reported which allow early targeted therapy with pharmaceutical hemostatic agents such as TEG-based goal-directed resuscitation and fibrinolysis management. TIC is a result of a complex interaction between different pathophysiological processes. New evidence in the field of trauma immunology can, in part, help explain the intricacy of the processes that occur after trauma. However, although our knowledge of TIC has grown, improving outcomes for trauma patients, many questions still need to be answered by ongoing studies.

Molecular Mechanisms of Vascular Damage During Lung Injury

A variety of pulmonary and systemic insults promote an inflammatory response causing increased vascular permeability, leading to the development of acute lung injury (ALI), a condition necessitating hospitalization and intensive care, or the more severe acute respiratory distress syndrome (ARDS), a disease with a high mortality rate. Further, COVID-19 pandemic-associated ARDS is now a major cause of mortality worldwide. The pathogenesis of ALI is explained by injury to both the vascular endothelium and the alveolar epithelium. The disruption of the lung endothelial and epithelial barriers occurs in response to both systemic and local production of pro-inflammatory cytokines. Studies that evaluate the association of genetic polymorphisms with disease risk did not yield many potential therapeutic targets to treat and revert lung injury. This failure is probably due in part to the phenotypic complexity of ALI/ARDS, and genetic predisposition may be obscured by the multiple environmental and behavioral risk factors. In the last decade, new research has uncovered novel epigenetic mechanisms that control ALI/ARDS pathogenesis, including histone modifications and DNA methylation. Enzyme inhibitors such as DNMTi and HDACi may offer new alternative strategies to prevent or reverse the vascular damage that occurs during lung injury. This review will focus on the latest findings on the molecular mechanisms of vascular damage in ALI/ARDS, the genetic factors that might contribute to the susceptibility for developing this disease, and the epigenetic changes observed in humans, as well as in experimental models of ALI/ADRS.

Pulmonary Effects of Adjusting Tidal Volume to Actual or Ideal Body Weight in Ventilated Obese Mice

Obese patients could be more susceptible to mechanical ventilation (MV)-induced lung injury than non-obese patients due to weight-dependent changes in lung properties. The aim of this study was therefore to evaluate the pulmonary effects of 2 hours low V_T MV in a diet-induced obese mice model, with V_T calculated on either the actual body weight (V_Taw) or the ideal body weight (V_Tiw) . First, we hypothesized that a MV with V_Taw would be associated with altered lung mechanics and an increased lung inflammation. Second, we hypothesised that a MV with a V_Tiw would preserve lung mechanics and limit lung inflammation. We analyzed lung mechanics and inflammation using bronchoalveolar lavage (BAL) cell counts, flow cytometry tissue analysis and histology. Lung mechanics and inflammation were comparable in control and obese mice receiving V_Tiw. By contrast, obese mice receiving V_Taw had significantly more alterations in lung mechanics, BAL cellularity and lung influx of monocytes as compared to control mice. Their monocyte expression of Gr1 and CD62L was also increased. Alveolar neutrophil infiltration was significantly increased in all obese mice as compared to controls. In conclusion, our findings suggest that protective MV with a V_Taw is deleterious, with a marked alteration in lung mechanics and associated lung inflammation as compared to lean mice. With V_Tiw, lung mechanics and inflammation were close to that of control mice, except for an increased alveolar infiltrate of polymorphonuclear neutrophils. This inflammation might be attenuated by a blunted recruitment of inflammatory cells associated with obesity.

Effects of positive end-expiratory pressure and recruitment maneuvers in a ventilator-induced injury mouse model

Background

Positive-pressure mechanical ventilation is an essential therapeutic intervention, yet it causes the clinical syndrome known as ventilator-induced lung injury. Various lung protective mechanical ventilation strategies have attempted to reduce or prevent ventilator-induced lung injury but few modalities have proven effective. A model that isolates the contribution of mechanical ventilation on the development of acute lung injury is needed to better understand biologic mechanisms that lead to ventilator-induced lung injury.

Objectives

To evaluate the effects of positive end-expiratory pressure and recruitment maneuvers in reducing lung injury in a ventilator-induced lung injury murine model in short- and longer-term ventilation.

Methods

5–12 week-old female BALB/c mice (n = 85) were anesthetized, placed on mechanical ventilation for either 2 hrs or 4 hrs with either low tidal volume (8 ml/kg) or high tidal volume (15 ml/kg) with or without positive end-expiratory pressure and recruitment maneuvers.

Results

Alteration of the alveolar-capillary barrier was noted at 2 hrs of high tidal volume ventilation. Standardized histology scores, influx of bronchoalveolar lavage albumin, proinflammatory cytokines, and absolute neutrophils were significantly higher in the high-tidal volume ventilation group at 4 hours of ventilation. Application of positive end-expiratory pressure resulted in significantly decreased standardized histology scores and bronchoalveolar absolute neutrophil counts at low- and high-tidal volume ventilation, respectively. Recruitment maneuvers were essential to maintain pulmonary compliance at both 2 and 4 hrs of ventilation.

Conclusions

Signs of ventilator-induced lung injury are evident soon after high tidal volume ventilation (as early as 2 hours) and lung injury worsens with longer-term ventilation (4 hrs). Application of positive end-expiratory pressure and recruitment maneuvers are protective against worsening VILI across all time points. Dynamic compliance can be used guide the frequency of recruitment maneuvers to help ameloriate ventilator-induced lung injury.

Uncoupling of the profibrotic and hemostatic effects of thrombin in lung fibrosis

Fibrotic lung disease, most notably idiopathic pulmonary fibrosis (IPF), is thought to result from aberrant wound-healing responses to repetitive lung injury. Increased vascular permeability is a cardinal response to tissue injury, but whether it is mechanistically linked to lung fibrosis is unknown. We previously described a model in which exaggeration of vascular leak after lung injury shifts the outcome of wound-healing responses from normal repair to pathological fibrosis. Here we report that the fibrosis produced in this model is highly dependent on thrombin activity and its downstream signaling pathways. Direct thrombin inhibition with dabigatran significantly inhibited protease-activated receptor-1 (PAR1) activation, integrin αvβ6 induction, TGF-β activation, and the development of pulmonary fibrosis in this vascular leak-dependent model. We used a potentially novel imaging method - ultashort echo time (UTE) lung magnetic resonance imaging (MRI) with the gadolinium-based, fibrin-specific probe EP-2104R - to directly visualize fibrin accumulation in injured mouse lungs, and to correlate the antifibrotic effects of dabigatran with attenuation of fibrin deposition. We found that inhibition of the profibrotic effects of thrombin can be uncoupled from inhibition of hemostasis, as therapeutic anticoagulation with warfarin failed to downregulate the PAR1/αvβ6/TGF-β axis or significantly protect against fibrosis. These findings have direct and important clinical implications, given recent findings that warfarin treatment is not beneficial in IPF, and the clinical availability of direct thrombin inhibitors that our data suggest could benefit these patients.

Endothelial cell signaling and ventilator-induced lung injury: molecular mechanisms, genomic analyses, and therapeutic targets

Mechanical ventilation is a life-saving intervention in critically ill patients with respiratory failure due to acute respiratory distress syndrome (ARDS). Paradoxically, mechanical ventilation also creates excessive mechanical stress that directly augments lung injury, a syndrome known as ventilator-induced lung injury (VILI). The pathobiology of VILI and ARDS shares many inflammatory features including increases in lung vascular permeability due to loss of endothelial cell barrier integrity resulting in alveolar flooding. While there have been advances in the understanding of certain elements of VILI and ARDS pathobiology, such as defining the importance of lung inflammatory leukocyte infiltration and highly induced cytokine expression, a deep understanding of the initiating and regulatory pathways involved in these inflammatory responses remains poorly understood. Prevailing evidence indicates that loss of endothelial barrier function plays a primary role in the development of VILI and ARDS. Thus this review will focus on the latest knowledge related to 1) the key role of the endothelium in the pathogenesis of VILI; 2) the transcription factors that relay the effects of excessive mechanical stress in the endothelium; 3) the mechanical stress-induced posttranslational modifications that influence key signaling pathways involved in VILI responses in the endothelium; 4) the genetic and epigenetic regulation of key target genes in the endothelium that are involved in VILI responses; and 5) the need for novel therapeutic strategies for VILI that can preserve endothelial barrier function.

Low tidal volume ventilation preconditioning ameliorates lipopolysaccharide-induced acute lung injury in rats

BACKGROUND

Effects of low tidal volume (LTV) ventilation preconditioning in endotoxin-induced acute lung injury (ALI) have not been studied. We investigated the effect of LTV ventilation pre-treatment on ALI induced by lipopolysaccharide (LPS) in rats.

METHODS

Male Sprague-Dawley rats were assigned to four groups (n = 8 each): (1) sham rats injected (i.p.) with 0.9% (physiologic) saline; sham rats pre-treated with tidal volume 6 ml/kg ventilation for 1 h followed by injection (i.p.) of physiologic saline (mechanical ventilation; MV-saline group); (2) LPS group (rats injected with LPS (i.p.); rats pre-treated with tidal volume 6 ml/kg ventilation for 1 h before injection (i.p.) with LPS (MV-LPS group). Animals were observed for 6 h. ALI extent was evaluated by lung wet-to-dry ratio, Evans Blue Dye extravasation, and histologic examination. We measured levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Apoptotic index (AI) and the expression of pulmonary RhoA, ROCK2 mRNA, and ROCK1 protein in lung alveolar cells was determined.

RESULTS

Lipopolysaccharide caused severe ALI, as evidenced by increases in ALI extent, impairment of pulmonary functions, and increases in pulmonary levels of TNF-α, IL-1β, IL-6, and AI. LTV ventilation preconditioning mitigated LPS-induced increases in release of pulmonary pro-inflammatory cytokines and AI of alveolar cells. Expression of pulmonary RhoA, ROCK2 mRNA, and ROCK1 protein was upregulated by LPS and reduced by LTV ventilation pre-treatment.

CONCLUSION

Low tidal volume ventilation preconditioning can attenuate release of pulmonary pro-inflammatory cytokines and decrease the AI induced by severe sepsis. Early protection seems to be mediated partly through inhibition of activation of a Rho pathway.

Role of Integrin β4 in Lung Endothelial Cell Inflammatory Responses to Mechanical Stress

Simvastatin, an HMG-CoA reductase inhibitor, has lung vascular-protective effects that are associated with decreased agonist-induced integrin β4 (ITGB4) tyrosine phosphorylation. Accordingly, we hypothesized that endothelial cell (EC) protection by simvastatin is dependent on these effects and sought to further characterize the functional role of ITGB4 as a mediator of EC protection in the setting of excessive mechanical stretch at levels relevant to ventilator-induced lung injury (VILI). Initially, early ITGB4 tyrosine phosphorylation was confirmed in human pulmonary artery EC subjected to excessive cyclic stretch (18% CS). EC overexpression of mutant ITGB4 with specific tyrosines mutated to phenylalanine (Y1440, Y1526 Y1640, or Y1422) resulted in significantly attenuated CS-induced cytokine expression (IL6, IL-8, MCP-1, and RANTES). In addition, EC overexpression of ITGB4 constructs with specific structural deletions also resulted in significantly attenuated CS-induced inflammatory cytokine expression compared to overexpression of wildtype ITGB4. Finally, mice expressing a mutant ITGB4 lacking a cytoplasmic signaling domain were found to have attenuated lung injury after VILI-challenge (V_T = 40 ml/kg, 4 h). Our results provide mechanistic insights into the anti-inflammatory properties of statins and may ultimately lead to novel strategies targeted at ITGB4 signaling to treat VILI.

Novel regulators of endothelial barrier function

Endothelial barrier function is an essential and tightly regulated process that ensures proper compartmentalization of the vascular and interstitial space, while allowing for the diffusive exchange of small molecules and the controlled trafficking of macromolecules and immune cells. Failure to control endothelial barrier integrity results in excessive leakage of fluid and proteins from the vasculature that can rapidly become fatal in scenarios such as sepsis or the acute respiratory distress syndrome. Here, we highlight recent advances in our understanding on the regulation of endothelial permeability, with a specific focus on the endothelial glycocalyx and endothelial scaffolds, regulatory intracellular signaling cascades, as well as triggers and mediators that either disrupt or enhance endothelial barrier integrity, and provide our perspective as to areas of seeming controversy and knowledge gaps, respectively.

Thrombomodulin protects against lung damage created by high level of oxygen with large tidal volume mechanical ventilation in rats

Background

Ventilator-induced lung injury (VILI) is associated with inflammatory responses in the lung. Thrombomodulin (TM), a component of the coagulation system, has anticoagulant and anti-inflammatory effects. We hypothesized that the administration of recombinant human soluble TM (rhsTM) would block the development of lung injury.

Methods

Lung injury was induced by high tidal volume ventilation for 2 h with 100% oxygen in rats. Rats were ventilated with a tidal volume of 35 ml/kg with pretreatment via a subcutaneous injection of 3 mg/kg rhsTM (HV (high tidal volume)/TM) or saline (HV/SAL) 12 h before mechanical ventilation. Rats ventilated with a tidal volume of 6 ml/kg under 100% oxygen with rhsTM (LV (low tidal volume)/TM) or saline (LV/SAL) were used as controls. Lung protein permeability was determined by Evans blue dye (EBD) extravasation.

Results

Lung injury was successfully induced in the HV/SAL group compared with the LV/SAL group, as shown by the significant decrease in arterial oxygen pressure (PaO₂), increased protein permeability, and increase in mean pulmonary artery pressure (mPAP) and ratio of mean pulmonary artery pressure to mean artery pressure (Pp/Ps). Treatment of rats with lung injury with rhsTM (HV/TM) significantly attenuated the decrease in PaO₂ and the increase in both mPAP and Pp/Ps, which was associated with a decrease in the lung protein permeability. Lung tissue mRNA expressions of interleukin (IL)-1α, IL-1β, IL-6, tumor necrosis factor-α, and macrophage inflammatory protein (MIP)-2 were significantly higher in HV than in LV rats. Rats with VILI treated with rhsTM (HV/TM) had significantly lower mRNA expressions of IL-1α, IL-1β, IL-6, and MIP-2 than those expressions in HV/SAL rats.

Conclusions

Administration of rhsTM may prevent the development of lung injury created by high level of oxygen with large tidal volume mechanical ventilation, which has concomitant decrease in proinflammatory cytokine and chemokine expression in the lung.

Ibuprofen protects ventilator-induced lung injury by downregulating Rho-kinase activity in rats

Background. Ventilator-induced lung injury-(VILI-) induced endothelial permeability is regulated through the Rho-dependent signaling pathway. Ibuprofen inhibits Rho activation in animal models of spinal-cord injury and Alzheimer's disease. The study aims to investigate ibuprofen effects on high tidal volume associated VILI. Methods. Twenty-eight adult male Sprague-Dawley rats were randomized to receive a ventilation strategy with three different interventions for 2 h: (1) a high-volume zero-positive end-expiratory pressure (PEEP) (HVZP) group; (2) an HVZP + ibuprofen 15 mg/kg group; and (3) an HVZP + ibuprofen 30 mg/kg group. A fourth group without ventilation served as the control group. Rho-kinase activity was determined by ratio of phosphorylated ezrin, radixin, and moesin (p-ERM), substrates of Rho-kinase, to total ERM. VILI was characterized by increased pulmonary protein leak, wet-to-dry weight ratio, cytokines level, and Rho guanine nucleotide exchange factor (GEF-H1), RhoA activity, p-ERM/total ERM, and p-myosin light chain (MLC) protein expression. Results. Ibuprofen pretreatment significantly reduced the HVZP ventilation-induced increase in pulmonary protein leak, wet-to-dry weight ratio, bronchoalveolar lavage fluid interleukin-6 and RANTES levels, and lung GEF-H1, RhoA activity, p-ERM/total ERM, and p-MLC protein expression. Conclusion. Ibuprofen attenuated high tidal volume induced pulmonary endothelial hyperpermeability. This protective effect was associated with a reduced Rho-kinase activity.

Recombinant human activated protein C in the treatment of acute respiratory distress syndrome: a randomized clinical trial

RATIONALE

Pulmonary coagulopathy may play a pathogenetic role in acute respiratory distress syndrome (ARDS), by contributing to alveolocapillary inflammation and increased permeability. Recombinant human activated protein C (rh-APC) may inhibit this process and thereby improve patient outcome.

METHODS

A prospective randomized, saline-controlled, single-blinded clinical trial was performed in the intensive care units of two university hospitals, and patients with ARDS were included within 24 h after meeting inclusion criteria.

INTERVENTION

A 4-day course of intravenous rh-APC (24 mcg/kg/h) (n = 33) versus saline (n = 38).

OUTCOMES

The primary outcome parameter was the pulmonary leak index (PLI) of 67Gallium-transferrin as a measure of alveolocapillary permeability and secondary outcomes were disease severity scores and ventilator-free days, among others.

RESULTS

Baseline characteristics were similar; in 87% of patients the PLI was above normal and in 90% mechanical or non-invasive ventilation was instituted at a median lung injury score of 2.5. There was no evidence that Rh-APC treatment affected the PLI or attenuated lung injury and sequential organ failure assessment scores. Mean ventilator-free days amounted to 14 (rh-APC) and 12 days (saline, P = 0.35). 28-day mortality was 6% in rh-APC- and 18% in saline-treated patients (P = 0.12). There was no difference in bleeding events. The study was prematurely discontinued because rh-APC was withdrawn from the market.

CONCLUSION

There is no evidence that treatment with intravenous rh-APC during 4 days for infectious or inflammatory ARDS ameliorates increased alveolocapillary permeability or the clinical course of ARDS patients. We cannot exclude underpowering.

TRIAL REGISTRATION

Nederlands Trial Register ISRCTN 52566874.

The endothelial protein C receptor impairs the antibacterial response in murine pneumococcal pneumonia and sepsis

Pneumococcal pneumonia is a frequent cause of gram-positive sepsis and has a high mortality. The endothelial protein C receptor (EPCR) has been implicated in both the activation of protein C (PC) and the anti-inflammatory actions of activated (A)PC. The aim of this study was to determine the role of the EPCR in murine pneumococcal pneumonia and sepsis. Wild-type (WT), EPCR knockout (KO) and Tie2-EPCR mice, which overexpress EPCR on the endothelium, were infected intranasally (pneumonia) or intravenously (sepsis) with viable Streptococcus pneumoniae and euthanised at 24 or 48 hours after initiation of the infection for analyses. Pneumonia did not alter constitutive EPCR expression on pulmonary endothelium but was associated with an influx of EPCR positive neutrophils into lung tissue. In pneumococcal pneumonia EPCR KO mice demonstrated diminished bacterial growth in the lungs and dissemination to spleen and liver, reduced neutrophil recruitment to the lungs and a mitigated inflammatory response. Moreover, EPCR KO mice displayed enhanced activation of coagulation in the early phase of disease. Correspondingly, in pneumococcal sepsis EPCR KO mice showed reduced bacterial growth in lung and liver and attenuated cytokine release. Conversely, EPCR-overexpressing mice displayed higher bacterial outgrowth in lung, blood, spleen and liver in pneumococcal sepsis. In conclusion, EPCR impairs antibacterial defense in both pneumococcal pneumonia and sepsis, which is associated with an enhanced pro-inflammatory response.

Barrier enhancing signals in pulmonary edema

Increased endothelial permeability and reduction of alveolar liquid clearance capacity are two leading pathogenic mechanisms of pulmonary edema, which is a major complication of acute lung injury, severe pneumonia, and acute respiratory distress syndrome, the pathologies characterized by unacceptably high rates of morbidity and mortality. Besides the success in protective ventilation strategies, no efficient pharmacological approaches exist to treat this devastating condition. Understanding of fundamental mechanisms involved in regulation of endothelial permeability is essential for development of barrier protective therapeutic strategies. Ongoing studies characterized specific barrier protective mechanisms and identified intracellular targets directly involved in regulation of endothelial permeability. Growing evidence suggests that, although each protective agonist triggers a unique pattern of signaling pathways, selected common mechanisms contributing to endothelial barrier protection may be shared by different barrier protective agents. Therefore, understanding of basic barrier protective mechanisms in pulmonary endothelium is essential for selection of optimal treatment of pulmonary edema of different etiology. This article focuses on mechanisms of lung vascular permeability, reviews major intracellular signaling cascades involved in endothelial monolayer barrier preservation and summarizes a current knowledge regarding recently identified compounds which either reduce pulmonary endothelial barrier disruption and hyperpermeability, or reverse preexisting lung vascular barrier compromise induced by pathologic insults.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Overexpression of the endothelial protein C receptor is detrimental during pneumonia-derived gram-negative sepsis (Melioidosis)

BACKGROUND

The endothelial protein C receptor (EPCR) enhances anticoagulation by accelerating activation of protein C to activated protein C (APC) and mediates anti-inflammatory effects by facilitating APC-mediated signaling via protease activated receptor-1. We studied the role of EPCR in the host response during pneumonia-derived sepsis instigated by Burkholderia (B.) pseudomallei, the causative agent of melioidosis, a common form of community-acquired Gram-negative (pneumo)sepsis in South-East Asia.

METHODOLOGY/PRINCIPAL FINDINGS

Soluble EPCR was measured in plasma of patients with septic culture-proven melioidosis and healthy controls. Experimental melioidosis was induced by intranasal inoculation of B. pseudomallei in wild-type (WT) mice and mice with either EPCR-overexpression (Tie2-EPCR) or EPCR-deficiency (EPCR(-/-)). Mice were sacrificed after 24, 48 or 72 hours. Organs and plasma were harvested to measure colony forming units, cellular influxes, cytokine levels and coagulation parameters. Plasma EPCR-levels were higher in melioidosis patients than in healthy controls and associated with an increased mortality. Tie2-EPCR mice demonstrated enhanced bacterial growth and dissemination to distant organs during experimental melioidosis, accompanied by increased lung damage, neutrophil influx and cytokine production, and attenuated coagulation activation. EPCR(-/-) mice had an unremarkable response to B. pseudomallei infection as compared to WT mice, except for a difference in coagulation activation in plasma.

CONCLUSION/SIGNIFICANCE

Increased EPCR-levels correlate with accelerated mortality in patients with melioidosis. In mice, transgenic overexpression of EPCR aggravates outcome during Gram-negative pneumonia-derived sepsis caused by B. pseudomallei, while endogenous EPCR does not impact on the host response. These results add to a better understanding of the regulation of coagulation during severe (pneumo)sepsis.

The endothelial protein C receptor and activated protein C play a limited role in host defense during experimental tuberculosis

The protein C (PC) system is an important regulator of both coagulation and inflammation. Activated PC (APC), together with its receptor the endothelial protein C receptor (EPCR), has anticoagulant and anti-inflammatory properties. During tuberculosis (TB), a devastating chronic pulmonary disease caused by Mycobacterium (M.) tuberculosis, both a local inflammatory reaction characterised by the recruitment of mainly mononuclear cells and the formation of pulmonary granulomas as well as activation of coagulation occurs as part of the host immune response. We investigated the role of EPCR and APC in a mouse model of TBusing mice overexpressing EPCR (Tie2-EPCR), mice deficient for EPCR (EPCR-/-), mice treated with APC-inhibiting antibodies and mice overexpressing APC (APChigh) and compared them with wild-type (WT) mice. Blood and organs were harvested to quantify bacterial loads, cellular influxes, cytokines, histopathology and coagulation parameters. Additionally observation studies were performed. Lung EPCR expression was upregulated during experimental TB. No significant differences in bacterial growth were seen between WT and Tie2-EPCR mice. However, Tie2-EPCR mice had decreased pulmonary coagulation activation, displayed an increased influx of macrophages 2 and 6 weeks after infection, but no increase in other proinflammatory markers. On the other hand, in EPCR-/--mice coagulation activation was decreased 6 weeks post-infection, with little impact on other inflammation markers. APC-overexpression or treatment with anti-(A)PC antibodies displayed minimal effects during experimental TB. In conclusion, EPCR and APC play a limited role in the host response during experimental pulmonary TB.

Critical role of S1PR1 and integrin β4 in HGF/c-Met-mediated increases in vascular integrity

Vascular endothelial cell (EC) barrier integrity is critical to vessel homeostasis whereas barrier dysfunction is a key feature of inflammatory disorders and tumor angiogenesis. We previously reported that hepatocyte growth factor (HGF)-mediated increases in EC barrier integrity are signaled through a dynamic complex present in lipid rafts involving its receptor, c-Met. We extended these observations to confirm that S1PR1 (sphingosine 1-phosphate receptor 1) and integrin β4 (ITGB4) are essential participants in HGF-induced EC barrier enhancement. Immunoprecipitation experiments demonstrated HGF-mediated recruitment of c-Met, ITGB4 and S1PR1 to caveolin-enriched lipid rafts in human lung EC with direct interactions of c-Met with both S1PR1 and ITGB4 accompanied by c-Met-dependent S1PR1 and ITGB4 transactivation. Reduced S1PR1 expression (siRNA) attenuated both ITGB4 and Rac1 activation as well as c-Met/ITGB4 interaction and resulted in decreased transendothelial electrical resistance. Furthermore, reduced ITGB4 expression attenuated HGF-induced c-Met activation, c-Met/S1PR1 interaction, and effected decreases in S1P- and HGF-induced EC barrier enhancement. Finally, the c-Met inhibitor, XL880, suppressed HGF-induced c-Met activation as well as S1PR1 and ITGB4 transactivation. These results support a critical role for S1PR1 and ITGB4 transactivation as rate-limiting events in the transduction of HGF signals via a dynamic c-Met complex resulting in enhanced EC barrier integrity.

Infrared fluorescence for vascular barrier breach in vivo--a novel method for quantitation of albumin efflux

Vascular hyperpermeability contributes to morbidity in inflammation. Current methodologies for in vivo assessment of permeability based on extravasation of Evans Blue (EB)-bound albumin are cumbersome and often lack sensitivity. We developed a novel infrared fluorescence (IRF) methodology for measurement of EB-albumin extravasation to quantify vascular permeability in murine models. Vascular permeability induced by endotoxaemia was examined for all solid organs, brain, skin and peritoneum by IRF and the traditional absorbance-based measurement of EB in tissue extracts. Organ IRF increased linearly with increasing concentrations of intravenous EB (2.5-25 mg/kg). Tissue IRF was more sensitive for EB accumulation compared to the absorbance-based method. Accordingly, differences in vascular permeability and organ EB accumulation between lipopolysaccharide-treated and saline-treated mice were often significant when analysed by IRF-based detection but not by absorbance-based detection. EB was detected in all 353 organs analysed with IRF but only in 67% (239/353) of organs analysed by absorbance-based methodology, demonstrating improved sensitivity of EB detection in organs with IRF. In contrast, EB in plasma after EB administration was readily measured by both methods with high correlation between the two methods (n=116, r2=0.86). Quantitation of organ-specific EB-IRF differences due to endotoxin was optimal when IRF was compared between mice matched for weight, gender, and age, and with appropriate corrections for organ weight and EB plasma concentrations. Notably, EB-IRF methodology leaves organs intact for subsequent histopathology. In summary, EB-IRF is a novel, highly sensitive, rapid, and convenient method for the relative quantification of EB in intact organs of treatment versus control mice.

Ventilation with "clinically relevant" high tidal volumes does not promote stretch-induced injury in the lungs of healthy mice

OBJECTIVE

Ventilator-induced lung injury is a crucial determinant of the outcome of mechanically ventilated patients. Increasing numbers of mouse studies have identified numerous pathways and mediators that are modulated by ventilation, but it is conceptually difficult to reconcile these into a single paradigm. There is substantial variability in tidal volumes used in these studies and no certainty about the pathophysiology that such varied models actually represent. This study was designed to investigate whether ventilation strategies ranging from "very high" to more "clinically relevant" tidal volumes induce similar pathophysiologies in healthy mice or represent distinct entities.

DESIGN

In vivo study.

SETTING

University research laboratory.

SUBJECTS

C57/Bl6 mice.

INTERVENTIONS

Anesthetized mice were ventilated with various tidal volumes up to 40 mL/kg.

MEASUREMENTS AND MAIN RESULTS

Respiratory system compliance and arterial blood gases were used to evaluate physiological variables of injury. Lung wet:dry weight ratio, lavage fluid protein, and cytokines were used to assess pulmonary edema and inflammation. All ventilation strategies induced changes in respiratory system compliance, although the pattern of change was unique for each strategy. Ventilation with 10 mL/kg and 40 mL/kg also induced decreases in arterial PO2 and blood pressure. Any physiological changes induced during the 10, 20, and 30 mL/kg strategies were largely reversed by recruitment maneuvers at the end of the protocol. Markers of pulmonary edema and inflammation indicated that only 40 mL/kg induced substantial increases in both, consistent with development of lung injury.

CONCLUSIONS

Tidal volumes up to 20 mL/kg are unlikely to induce substantial lung overstretch in models using healthy, young mice. Signs of injury/inflammation using such models are likely to result from other factors, particularly alveolar derecruitment and atelectasis. The results of such studies may need to be reevaluated before clinical relevance can be accurately determined.

Rapid vascular responses to anthrax lethal toxin in mice containing a segment of chromosome 11 from the CAST/Ei strain on a C57BL/6 genetic background

Host allelic variation controls the response to B. anthracis and the disease course of anthrax. Mouse strains with macrophages that are responsive to anthrax lethal toxin (LT) show resistance to infection while mouse strains with LT non-responsive macrophages succumb more readily. B6.CAST.11M mice have a region of chromosome 11 from the CAST/Ei strain (a LT responsive strain) introgressed onto a LT non-responsive C57BL/6J genetic background. Previously, B6.CAST.11M mice were found to exhibit a rapid inflammatory reaction to LT termed the early response phenotype (ERP), and displayed greater resistance to B. anthracis infection compared to C57BL/6J mice. Several ERP features (e.g., bloat, hypothermia, labored breathing, dilated pinnae vessels) suggested vascular involvement. To test this, Evan’s blue was used to assess vessel leakage and intravital microscopy was used to monitor microvascular blood flow. Increased vascular leakage was observed in lungs of B6.CAST.11M mice compared to C57BL/6J mice 1 hour after systemic administration of LT. Capillary blood flow was reduced in the small intestine mesentery without concomitant leukocyte emigration following systemic or topical application of LT, the latter suggesting a localized tissue mechanism in this response. Since LT activates the Nlrp1b inflammasome in B6.CAST.11M mice, the roles of inflammasome products, IL-1β and IL-18, were examined. Topical application to the mesentery of IL-1β but not IL-18 revealed pronounced slowing of blood flow in B6.CAST.11M mice that was not present in C57BL/6J mice. A neutralizing anti-IL-1β antibody suppressed the slowing of blood flow induced by LT, indicating a role for IL-1β in the response. Besides allelic differences controlling Nlrp1b inflammasome activation by LT observed previously, evidence presented here suggests that an additional genetic determinant(s) could regulate the vascular response to IL-1β. These results demonstrate that vessel leakage and alterations to blood flow are part of the rapid response in mice resistant to B. anthracis infection.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Stimulation of Rho signaling by pathologic mechanical stretch is a "second hit" to Rho-independent lung injury induced by IL-6

Most patients with acute lung injury (ALI) and acute respiratory distress syndrome of septic and nonseptic nature require assisted ventilation with positive pressure, which at suboptimal range may further exacerbate lung dysfunction. Previous studies described enhancement of agonist-induced Rho GTPase signaling and endothelial cell (EC) permeability in EC cultures exposed to pathologically relevant cyclic stretch (CS) magnitudes. This study examined a role of pathologic CS in modulation of pulmonary EC permeability caused by IL-6, a cytokine increased in sepsis and acting in a Rho-independent manner. IL-6 increased EC permeability, which was associated with activation of Jak/signal transducers and activators of transcription, p38 MAP kinase, and NF-κB signaling and was augmented by EC exposure to 18% CS. Rho kinase inhibitor Y-27632 suppressed the synergistic effect of 18% CS on IL-6-induced EC monolayer disruption but did not alter the IL-6 effects on static EC culture. 18% CS also increased IL-6-induced ICAM-1 expression by pulmonary EC and neutrophil adhesion, which was attenuated by Y-27632. Intratracheal IL-6 administration in C57BL/6J mice increased protein content and cell count in bronchoalveolar lavage fluid. These changes were augmented by high tidal volume mechanical ventilation (HTV; 30 ml/kg, 4 h). Intravenous injection of Y-27632 suppressed IL6/HTV-induced lung injury. In conclusion, this study proposes a novel mechanism contributing to two-hit model of ALI: in addition to synergistic effects on Rho-dependent endothelial hyper-permeability triggered by thrombin, TNFα, LPS, or other agonists, ventilator-induced lung injury-relevant CS may also exacerbate Rho-independent mechanisms of EC permeability induced by other inflammatory mediators such as IL-6 via mechanisms involving Rho activity.

Induction of cellular antioxidant defense by amifostine improves ventilator-induced lung injury

OBJECTIVES

To test the hypothesis that preconditioning animals with amifostine improves ventilator-induced lung injury via induction of antioxidant defense enzymes. Mechanical ventilation at high tidal volume induces reactive oxygen species production and oxidative stress in the lung, which plays a major role in the pathogenesis of ventilator-induced lung injury. Amifostine attenuates oxidative stress and improves lipopolysaccharide-induced lung injury by acting as a direct scavenger of reactive oxygen and nitrogen species. This study tested effects of chronic amifostine administration on parameters of oxidative stress, lung barrier function, and inflammation associated with ventilator-induced lung injury.

DESIGN

Randomized and controlled laboratory investigation in mice and cell culture.

SETTING

University laboratory.

SUBJECTS

C57BL/6J mice.

INTERVENTIONS

Mice received once-daily dosing with amifostine (10-100 mg/kg, intraperitoneal injection) 3 days consecutively before high tidal volume ventilation (30 mL/kg, 4 hrs) at day 4. Pulmonary endothelial cell cultures were exposed to pathologic cyclic stretching (18% equibiaxial stretch) and thrombin in a previously verified two-hit model of in vitro ventilator-induced lung injury.

MEASUREMENTS AND MAIN RESULTS

Three-day amifostine preconditioning before high tidal volume attenuated high tidal volume-induced protein and cell accumulation in the alveolar space judged by bronchoalveolar lavage fluid analysis, decreased Evans Blue dye extravasation into the lung parenchyma, decreased biochemical parameters of high tidal volume-induced tissue oxidative stress, and inhibited high tidal volume-induced activation of redox-sensitive stress kinases and nuclear factor-kappa B inflammatory cascade. These protective effects of amifostine were associated with increased superoxide dismutase 2 expression and increased superoxide dismutase and catalase enzymatic activities in the animal and endothelial cell culture models of ventilator-induced lung injury.

CONCLUSIONS

Amifostine preconditioning activates lung tissue antioxidant cell defense mechanisms and may be a promising strategy for alleviation of ventilator-induced lung injury in critically ill patients subjected to extended mechanical ventilation.

The suppression of myosin light chain (MLC) phosphorylation during the response to lipopolysaccharide (LPS): beneficial or detrimental to endothelial barrier?

Sepsis-induced vascular leakage is a major underlying cause of the respiratory dysfunction seen in severe sepsis. Here, we studied the role of MLC phosphorylation in LPS-induced endothelial hyperpermeability and assessed how the changes in phospho-MLC distribution affect LPS-induced barrier dysfunction. We demonstrated that the changes in human lung microvascular endothelial permeability are preceded by the increase in intracellular calcium level, and increase in MYPT and MLC phosphorylation. Using the siRNA approach, we showed that both LPS-induced barrier dysfunction and MLC phosphorylation are attenuated by the depletion of the smooth muscle isoform of MLC kinase (MLCK) and Rho kinase 2 (ROCK2). Surprisingly, pharmacological inhibition of both ROCK1 and 2 with Y-27632 exacerbated LPS-induced drop in transendothelial resistance, although significantly decreasing MLC phosphorylation level. We next studied the involvement of protein kinase A (PKA)-dependent pathways in LPS-induced barrier dysfunction. We showed that LPS decreased the level of PKA-dependent phosphorylation in endothelial cells; and the pretreatment with forskolin or PKA activator bnz-cAMP counteracted this effect. Forskolin and bnz-cAMP also attenuated LPS-induced increase in MLC phosphorylation level. As we have shown earlier (Bogatcheva et al., 2009), forskolin and bnz-cAMP provide protection from LPS-induced barrier dysfunction. We compared the effects of bnz-cAMP and Y-27632 on phospho-MLC distribution and observed that while bnz-cAMP increased the association of the phospho-MLC signal with the cortical structures, Y-27632 decreased this association. These data indicate that an overall decrease in MLC phosphorylation could be either beneficial or detrimental to endothelial barrier, depending on the intracellular locale of major phospho-MLC changes.

Activated protein C inhalation: a novel therapeutic strategy for acute lung injury

Acute lung injury (ALI) is a critical illness syndrome with a mortality rate of 25–40%. Despite recent advances of our understanding of the pathophysiology of ALI, no pharmacologic therapies have been proven effective. The key pathogenesis of ALI is the activation of the coagulation cascade and impaired fibrinolysis, resulting in extensive fibrin and hyaline membrane deposition. Activated protein C (APC), an endogenous protein that promotes fibrinolysis and inhibits thrombosis, can modulate the coagulation and inflammation associated with ALI. It is therefore reasonable to suggest that preventing the progression of pulmonary coagulopathy, by restoring normal intraalveolar levels of protein C, will be of therapeutic benefit to patients with ALI. However, a recent clinical trial demonstrated that APC did not improve outcomes from ALI, raising the possibility that the method of APC administration, intravenous infusion or inhalation, may influence the outcomes. In this article we propose the hypothesis that APC inhalation might be a promising and novel choice in the treatment of ALI.

Recurrent recruitment manoeuvres improve lung mechanics and minimize lung injury during mechanical ventilation of healthy mice

INTRODUCTION

Mechanical ventilation (MV) of mice is increasingly required in experimental studies, but the conditions that allow stable ventilation of mice over several hours have not yet been fully defined. In addition, most previous studies documented vital parameters and lung mechanics only incompletely. The aim of the present study was to establish experimental conditions that keep these parameters within their physiological range over a period of 6 h. For this purpose, we also examined the effects of frequent short recruitment manoeuvres (RM) in healthy mice.

METHODS

Mice were ventilated at low tidal volume V(T) = 8 mL/kg or high tidal volume V(T) = 16 mL/kg and a positive end-expiratory pressure (PEEP) of 2 or 6 cm H(2)O. RM were performed every 5 min, 60 min or not at all. Lung mechanics were followed by the forced oscillation technique. Blood pressure (BP), electrocardiogram (ECG), heart frequency (HF), oxygen saturation and body temperature were monitored. Blood gases, neutrophil-recruitment, microvascular permeability and pro-inflammatory cytokines in bronchoalveolar lavage (BAL) and blood serum as well as histopathology of the lung were examined.

RESULTS

MV with repetitive RM every 5 min resulted in stable respiratory mechanics. Ventilation without RM worsened lung mechanics due to alveolar collapse, leading to impaired gas exchange. HF and BP were affected by anaesthesia, but not by ventilation. Microvascular permeability was highest in atelectatic lungs, whereas neutrophil-recruitment and structural changes were strongest in lungs ventilated with high tidal volume. The cytokines IL-6 and KC, but neither TNF nor IP-10, were elevated in the BAL and serum of all ventilated mice and were reduced by recurrent RM. Lung mechanics, oxygenation and pulmonary inflammation were improved by increased PEEP.

CONCLUSIONS

Recurrent RM maintain lung mechanics in their physiological range during low tidal volume ventilation of healthy mice by preventing atelectasis and reduce the development of pulmonary inflammation.

Cytoprotective-selective activated protein C attenuates Pseudomonas aeruginosa-induced lung injury in mice

Inhibition of the small GTPase RhoA attenuates the development of pulmonary edema and restores positive alveolar fluid clearance in a murine model of Pseudomonas aeruginosa pneumonia. Activated protein C (aPC) blocks the development of an unfavorably low ratio of small GTPase Rac1/RhoA activity in lung endothelium through endothelial protein C receptor (EPCR)/protease-activated receptor-1 (PAR-1)-dependent signaling mechanisms that include transactivating the sphingosine-1-phosphate (S1P) pathway. However, whether aPC's cytoprotective effects can attenuate the development of pulmonary edema and death associated with P. aeruginosa pneumonia in mice remains unknown. Thus, we determined whether the normalization of a depressed ratio of activated Rac1/RhoA by aPC would attenuate the P. aeruginosa-mediated increase in protein permeability across lung endothelial and alveolar epithelial barriers. Pretreatment with aPC significantly reduced P. aeruginosa-induced increases in paracellular permeability across pulmonary endothelial cell and alveolar epithelial monolayers via an inhibition of RhoA activation and a promotion of Rac1 activation that required the EPCR-PAR-1 and S1P pathways. Furthermore, pretreatment with aPC attenuated the development of pulmonary edema in a murine model of P. aeruginosa pneumonia. Finally, a cytoprotective-selective aPC mutant, aPC-5A, which lacks most of aPC's anticoagulant activity, reproduced the protective effect of wild-type aPC by attenuating the development of pulmonary edema and decreasing mortality in a murine model of P. aeruginosa pneumonia. Taken together, these results demonstrate a critical role for the cytoprotective activities of aPC in attenuating P. aeruginosa-induced lung vascular permeability and mortality, suggesting that cytoprotective-selective aPC-5A with diminished bleeding risks could attenuate the lung damage caused by P. aeruginosa in critically ill patients.

Year in review 2009: Critical Care--shock

The research papers on shock that have been published in Critical Care throughout 2009 are related to four major subjects: first, alterations of heart function and, second, the role of the sympathetic central nervous system during sepsis; third, the impact of hemodynamic support using vasopressin or its synthetic analog terlipressin, and different types of fluid resuscitation; as well as, fourth, experimental studies on the treatment of acute respiratory distress syndrome. The present review summarizes the key results of these studies together with a brief discussion in the context of the relevant scientific and clinical background published both in this and other journals.

Inhaled activated protein C protects mice from ventilator-induced lung injury

INTRODUCTION

Activated Protein C (APC), an endogenous anticoagulant, improves tissue microperfusion and endothelial cell survival in systemic inflammatory states such as sepsis, but intravenous administration may cause severe bleeding. We have thus addressed the role of APC delivered locally by inhalation in preventing acute lung injury from alveolar overdistention and the subsequent ventilator-induced lung injury (VILI). We also assessed the effects of APC on the activation status of Extracellular- Regulated Kinase 1/2 (ERK) pathway, which has been shown to be involved in regulating pulmonary responses to mechanical stretch.

METHODS

Inhaled APC (12.5 microg drotrecogin-alpha x 4 doses) or saline was given to tracheotomized C57/Bl6 mice starting 20 min prior to initiation of injurious mechanical ventilation with tidal volume 25 mL/Kg for 4 hours and then hourly thereafter; control groups receiving inhaled saline were ventilated with 8 mL/Kg for 30 min or 4 hr. We measured lung function (respiratory system elastance H), arterial blood gases, surrogates of vascular leak (broncho-alveolar lavage (BAL) total protein and angiotensin-converting enzyme (ACE)-activity), and parameters of inflammation (BAL neutrophils and lung tissue myeloperoxidase (MPO) activity). Morphological alterations induced by mechanical ventilation were examined in hematoxylin-eosin lung tissue sections. The activation status of ERK was probed in lung tissue homogenates by immunoblotting and in paraffin sections by immunohistochemistry. The effect of APC on ERK signaling downstream of the thrombin receptor was tested on A549 human lung epithelial cells by immunoblotting. Statistical analyses were performed using ANOVA with appropriate post-hoc testing.

RESULTS

In mice subjected to VILI without APC, we observed hypoxemia, increased respiratory system elastance and inflammation, assessed by BAL neutrophil counts and tissue MPO activity. BAL total protein levels and ACE activity were also elevated by VILI, indicating compromise of the alveolo-capillary barrier. In addition to preserving lung function, inhaled APC prevented endothelial barrier disruption and attenuated hypoxemia and the inflammatory response. Mechanistically, we found a strong activation of ERK in lung tissues by VILI, which was prevented by APC, suggestive of pathogenetic involvement of the Mitogen-Activated Kinase pathway. In cultured human lung epithelial cells challenged by thrombin, APC abrogated the activation of ERK and its downstream effector, cytosolic Phospholipase A2.

CONCLUSIONS

Topical application of APC by inhalation may effectively reduce lung injury induced by mechanical ventilation in mice.

Transcriptional analysis of kidneys during repair from AKI reveals possible roles for NGAL and KIM-1 as biomarkers of AKI-to-CKD transition

Acute kidney injury (AKI) is being increasingly shown to be a risk factor for chronic kidney disease (CKD), but little is known about the possible mechanistic links. We hypothesized that analysis of the genomic signature in the repair stage after AKI would reveal pathways that could link AKI and CKD. Unilateral renal pedicle clamping for 45 min was performed in male C57BL/6J mice. Mice were euthanized at 3, 10, and 28 days after ischemia-reperfusion injury (IRI). Total RNA was isolated from kidney and analyzed using an Illumina mouse array. Among 24,600 tested genes, 242, 146, and 46 genes were upregulated at days 3, 10, and 28 after IRI, and 85, 35, and 0 genes were downregulated, respectively. Gene ontology analysis showed that gene expression changes were primarily related to immune and inflammatory pathways both early and late after AKI. The most highly upregulated genes late after AKI were hepatitis A virus cellular receptor 1 (Havcr1) and lipocalin 2 (Lcn2), which code for kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL), respectively. This was unexpected since they are both primarily potential biomarkers of the early stage of AKI. Furthermore, increases observed in gene expression in amiloride binding protein 1, vascular cell adhesion molecule-1, and endothelin 1 could explain the salt-sensitive hypertension that can follow AKI. These data suggested that 1) persistent inflammation and immune responses late after AKI could contribute to the pathogenesis of CKD, 2) late upregulation of KIM-1 and NGAL could be a useful marker for sustained renal injury after AKI, and 3) hypertension-related gene changes could underlie mechanisms for persistent renal and vascular injury after AKI.

Lung endothelial barrier protection by iloprost in the 2-hit models of ventilator-induced lung injury (VILI) involves inhibition of Rho signaling

Mechanical ventilation at high tidal volume (HTV) may cause pulmonary capillary leakage and acute lung inflammation culminating in ventilator-induced lung injury. Iloprost is a stable, synthetic analog of prostaglandin I(2) used to treat pulmonary hypertension, which also showed endothelium-dependent antiedemagenic effects in the models of lung injury. To test the hypothesis that iloprost may attenuate lung inflammation and lung endothelial barrier disruption caused by pathologic lung distension and coagulation system component thrombin, we used cell and animal 2-hit models of ventilator-induced lung injury. Mice received a triple injection of iloprost (2 microg/kg, intravenous instillation) at 0, 40, and 80 min after the onset of HTV mechanical ventilation (30 mL/kg, 4h), combined with the administration of a thrombin receptor-activating peptide 6 (TRAP6, 3 x 10(-7)mol/mouse, intratracheal instillation). After 4h of ventilation, bronchoalveolar lavage (BAL), histologic analysis, and measurements of Evans blue accumulation in the lung tissue were performed. The effects of iloprost on endothelial barrier dysfunction were subsequently assessed in pulmonary endothelial cells (ECs) exposed to thrombin and pathologic (18%) cyclic stretch. The combination of HTV and TRAP6 enhanced the accumulation of neutrophils in BAL fluid and lung parenchyma, as well as increased the BAL protein content and endothelial permeability judged by Evans blue extravasation in the lung tissue. These effects were markedly attenuated by iloprost. The application of 18% cyclic stretch to pulmonary ECs enhanced the thrombin-induced EC paracellular gap formation and Rho-GTPase-mediated phosphorylation of regulatory myosin light chains and myosin phosphatase. Iloprost markedly inhibited the Rho-kinase-mediated site-specific phosphorylation of myosin phosphatase, and it prevented cyclic stretch- and thrombin-induced endothelial monolayer disruption. This study characterizes for the first time the protective effects of iloprost in the in vitro and in vivo 2-hit models of VILI and supports consideration of iloprost as a new therapeutic treatment of VILI.