Imatinib attenuates inflammation and vascular leak in a clinically relevant two-hit model of acute lung injury

Ventilation following established ARDS: a preclinical model framework to improve predictive power

BACKGROUND

Despite advances in understanding the pathophysiology of acute respiratory distress syndrome, effective pharmacological interventions have proven elusive. We believe this is a consequence of existing preclinical models being designed primarily to explore biological pathways, rather than predict treatment effects. Here, we describe a mouse model in which both therapeutic intervention and ventilation were superimposed onto existing injury and explored the impact of β-agonist treatment, which is effective in simple models but not clinically.

METHODS

Mice had lung injury induced by intranasal lipopolysaccharide (LPS), which peaked at 48 hours post-LPS based on clinically relevant parameters including hypoxaemia and impaired mechanics. At this peak of injury, mice were treated intratracheally with either terbutaline or tumour necrosis factor (TNF) receptor 1-targeting domain antibody, and ventilated with moderate tidal volume (20 mL/kg) to induce secondary ventilator-induced lung injury (VILI).

RESULTS

Ventilation of LPS-injured mice at 20 mL/kg exacerbated injury compared with low tidal volume (8 mL/kg). While terbutaline attenuated VILI within non-LPS-treated animals, it was ineffective to reduce VILI in pre-injured mice, mimicking its lack of clinical efficacy. In contrast, anti-TNF receptor 1 antibody attenuated secondary VILI within pre-injured lungs, indicating that the model was treatable.

CONCLUSIONS

We propose adoption of a practical framework like that described here to reduce the number of ultimately ineffective drugs reaching clinical trials. Novel targets should be evaluated alongside interventions which have been previously tested clinically, using models that recapitulate the (lack of) clinical efficacy. Within such a framework, outperforming a failed pharmacologic should be a prerequisite for drugs entering trials.

ABL kinase inhibition promotes lung regeneration through expansion of an SCGB1A1+ SPC+ cell population following bacterial pneumonia

Current therapeutic interventions for the treatment of respiratory infections are hampered by the evolution of multidrug resistance in pathogens as well as the lack of effective cellular targets. Despite the identification of multiple region-specific lung progenitor cells, the identity of molecules that might be therapeutically targeted in response to infections to promote activation of progenitor cell types remains elusive. Here, we report that loss of Abl1 specifically in SCGB1A1-expressing cells leads to a significant increase in the proliferation and differentiation of bronchiolar epithelial cells, resulting in dramatic expansion of an SCGB1A1+ airway cell population that coexpresses SPC, a marker for type II alveolar cells that promotes alveolar regeneration following bacterial pneumonia. Furthermore, treatment with an Abl-specific allosteric inhibitor enhanced regeneration of the alveolar epithelium and promoted accelerated recovery of mice following pneumonia. These data reveal a potential actionable target that may be exploited for efficient recovery after pathogen-induced infections.

Surviving Deadly Lung Infections: Innate Host Tolerance Mechanisms in the Pulmonary System

Much research on infectious diseases focuses on clearing the pathogen through the use of antimicrobial drugs, the immune response, or a combination of both. Rapid clearance of pathogens allows for a quick return to a healthy state and increased survival. Pathogen-targeted approaches to combating infection have inherent limitations, including their pathogen-specific nature, the potential for antimicrobial resistance, and poor vaccine efficacy, among others. Another way to survive an infection is to tolerate the alterations to homeostasis that occur during a disease state through a process called host tolerance or resilience, which is independent from pathogen burden. Alterations in homeostasis during infection are numerous and include tissue damage, increased inflammation, metabolic changes, temperature changes, and changes in respiration. Given its importance and sensitivity, the lung is a good system for understanding host tolerance to infectious disease. Pneumonia is the leading cause of death for children under five worldwide. One reason for this is because when the pulmonary system is altered dramatically it greatly impacts the overall health and survival of a patient. Targeting host pathways involved in maintenance of pulmonary host tolerance during infection could provide an alternative therapeutic avenue that may be broadly applicable across a variety of pathologies. In this review, we will summarize recent findings on tolerance to host lung infection. We will focus on the involvement of innate immune responses in tolerance and how an initial viral lung infection may alter tolerance mechanisms in leukocytic, epithelial, and endothelial compartments to a subsequent bacterial infection. By understanding tolerance mechanisms in the lung we can better address treatment options for deadly pulmonary infections.

BCR-ABL Tyrosine Kinase Inhibitors: Which Mechanism(s) May Explain the Risk of Thrombosis?

Imatinib, the first-in-class BCR-ABL tyrosine kinase inhibitor (TKI), had been a revolution for the treatment of chronic myeloid leukemia (CML) and had greatly enhanced patient survival. Second- (dasatinib, nilotinib, and bosutinib) and third-generation (ponatinib) TKIs have been developed to be effective against BCR-ABL mutations making imatinib less effective. However, these treatments have been associated with arterial occlusive events. This review gathers clinical data and experiments about the pathophysiology of these arterial occlusive events with BCR-ABL TKIs. Imatinib is associated with very low rates of thrombosis, suggesting a potentially protecting cardiovascular effect of this treatment in patients with BCR-ABL CML. This protective effect might be mediated by decreased platelet secretion and activation, decreased leukocyte recruitment, and anti-inflammatory or antifibrotic effects. Clinical data have guided mechanistic studies toward alteration of platelet functions and atherosclerosis development, which might be secondary to metabolism impairment. Dasatinib, nilotinib, and ponatinib affect endothelial cells and might induce atherogenesis through increased vascular permeability. Nilotinib also impairs platelet functions and induces hyperglycemia and dyslipidemia that might contribute to atherosclerosis development. Description of the pathophysiology of arterial thrombotic events is necessary to implement risk minimization strategies.

Imatinib Is Protective Against Ischemia-Reperfusion Injury in an Ex Vivo Rabbit Model of Lung Injury

BACKGROUND

Ischemia-reperfusion injury is characterized by an increase in oxidative stress and leads to significant morbidity and death. The tyrosine kinase c-Abl is activated by oxidative stress and mediates processes that affect endothelial barrier function. We hypothesized treatment with the c-Abl inhibitor imatinib would be protective against ischemia-reperfusion injury in our ex vivo rabbit model.

METHODS

Heart-lung blocs were harvested from rabbits and stored in cold in Perfadex (Vitrolife, Englewood, CO) for 18 hours. Blocs were reperfused for 2 hours in an ex vivo circuit with donor rabbit blood alone (untreated group, n = 7) or donor rabbit blood and 4 mg imatinib (treatment group, n = 10). Serial clinical variables measured every 15 minutes (arterial oxygen and carbon dioxide tension and mean pulmonary artery pressures) and biochemistry of tissue samples before and after reperfusion were assessed.

RESULTS

Compared with untreated lungs, imatinib treatment improved physiologic parameters, including oxygen, carbon dioxide, and pulmonary artery pressures. Imatinib-treated lungs had less vascular barrier dysfunction as quantified by wet-to-dry weight ratios and bronchoalveolar lavage protein concentrations. Treated lungs showed less inflammation as measured by bronchoalveolar lavage myeloperoxidase assay, less mitochondrial reactive oxygen species production, and increased antioxidant catalase levels. Finally, imatinib protected lungs from DNA damage and p53 upregulation.

CONCLUSIONS

Imatinib treatment significantly improved the physiologic performance of reperfused lungs and biochemical indicators associated with reperfusion injury in this ex vivo model. Further study is necessary to elucidate the mechanism of tyrosine kinase inhibition in lungs exposed to ischemia and reperfusion.

Autophagy inhibitor 3-methyladenine protects against endothelial cell barrier dysfunction in acute lung injury

Autophagy is an evolutionarily conserved cellular process that facilitates the continuous recycling of intracellular components (organelles and proteins) and provides an alternative source of energy when nutrients are scarce. Recent studies have implicated autophagy in many disorders, including pulmonary diseases. However, the role of autophagy in endothelial cell (EC) barrier dysfunction and its relevance in the context of acute lung injury (ALI) remain uncertain. Here, we provide evidence that autophagy is a critical component of EC barrier disruption in ALI. Using an aerosolized bacterial lipopolysaccharide (LPS) inhalation mouse model of ALI, we found that administration of the autophagy inhibitor 3-methyladenine (3-MA), either prophylactically or therapeutically, markedly reduced lung vascular leakage and tissue edema. 3-MA was also effective in reducing the levels of proinflammatory mediators and lung neutrophil sequestration induced by LPS. To test the possibility that autophagy in EC could contribute to lung vascular injury, we addressed its role in the mechanism of EC barrier disruption. Knockdown of ATG5, an essential regulator of autophagy, attenuated thrombin-induced EC barrier disruption, confirming the involvement of autophagy in the response. Similarly, exposure of cells to 3-MA, either before or after thrombin, protected against EC barrier dysfunction by inhibiting the cleavage and loss of vascular endothelial cadherin at adherens junctions, as well as formation of actin stress fibers. 3-MA also reversed LPS-induced EC barrier disruption. Together, these data imply a role of autophagy in lung vascular injury and reveal the protective and therapeutic utility of 3-MA against ALI.

Transient Receptor Potential Vanilloid 4 and Serum Glucocorticoid-regulated Kinase 1 Are Critical Mediators of Lung Injury in Overventilated Mice In Vivo

BACKGROUND

Mechanical ventilation can cause lung endothelial barrier failure and inflammation cumulating in ventilator-induced lung injury. Yet, underlying mechanotransduction mechanisms remain unclear. Here, the authors tested the hypothesis that activation of the mechanosensitive Ca channel transient receptor potential vanilloid (TRPV4) by serum glucocorticoid-regulated kinase (SGK) 1 may drive the development of ventilator-induced lung injury.

METHODS

Mice (total n = 54) were ventilated for 2 h with low (7 ml/kg) or high (20 ml/kg) tidal volumes and assessed for signs of ventilator-induced lung injury. Isolated-perfused lungs were inflated with continuous positive airway pressures of 5 or 15 cm H2O (n = 7 each), and endothelial calcium concentration was quantified by real-time imaging.

RESULTS

Genetic deficiency or pharmacologic inhibition of TRPV4 or SGK1 protected mice from overventilation-induced vascular leakage (reduction in alveolar protein concentration from 0.84 ± 0.18 [mean ± SD] to 0.46 ± 0.16 mg/ml by TRPV4 antagonization), reduced lung inflammation (macrophage inflammatory protein 2 levels of 193 ± 163 in Trpv4 vs. 544 ± 358 pmol/ml in wild-type mice), and attenuated endothelial calcium responses to lung overdistension. Functional coupling of TRPV4 and SGK1 in lung endothelial mechanotransduction was confirmed by proximity ligation assay demonstrating enhanced TRPV4 phosphorylation at serine 824 at 18% as compared to 5% cyclic stretch, which was prevented by SGK1 inhibition.

CONCLUSIONS

Lung overventilation promotes endothelial calcium influx and barrier failure through a mechanism that involves activation of TRPV4, presumably due to phosphorylation at its serine 824 residue by SGK1. TRPV4 and SGK1 may present promising new targets for prevention or treatment of ventilator-induced lung injury.

Lipopolysaccharide-induced endotoxemia in corn oil-preloaded mice causes an extended course of lung injury and repair and pulmonary fibrosis: A translational mouse model of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia respiratory failure, bilateral pulmonary infiltrates, and pulmonary edema of non-cardiac origin. Effective treatments for ARDS patients may arise from experimental studies with translational mouse models of this disease that aim to delineate the mechanisms underlying the disease pathogenesis. Mouse models of ARDS, however, can be limited by their rapid progression from injured to recovery state, which is in contrast to the course of ARDS in humans. Furthermore, current mouse models of ARDS do not recapitulate certain prominent aspects of the pathogenesis of ARDS in humans. In this study, we developed an improved endotoxemic mouse model of ARDS resembling many features of clinical ARDS including extended courses of injury and recovery as well as development of fibrosis following i.p. injection of lipopolysaccharide (LPS) to corn oil-preloaded mice. Compared with mice receiving LPS alone, those receiving corn oil and LPS exhibited extended course of lung injury and repair that occurred over a period of >2 weeks instead of 3–5days. Importantly, LPS challenge of corn oil-preloaded mice resulted in pulmonary fibrosis during the repair phase as often seen in ARDS patients. In summary, this simple novel mouse model of ARDS could represent a valuable experimental tool to elucidate mechanisms that regulate lung injury and repair in ARDS patients.

The ARP 2/3 complex mediates endothelial barrier function and recovery

Pulmonary endothelial cell (EC) barrier dysfunction and recovery is critical to the pathophysiology of acute respiratory distress syndrome. Cytoskeletal and subsequent cell membrane dynamics play a key mechanistic role in determination of EC barrier integrity. Here, we characterizAQe the actin related protein 2/3 (Arp 2/3) complex, a regulator of peripheral branched actin polymerization, in human pulmonary EC barrier function through studies of transendothelial electrical resistance (TER), intercellular gap formation, peripheral cytoskeletal structures and lamellipodia. Compared to control, Arp 2/3 inhibition with the small molecule inhibitor CK-666 results in a reduction of baseline barrier function (1,241 ± 53 vs 988 ± 64 ohm; p < 0.01), S1P-induced barrier enhancement and delayed recovery of barrier function after thrombin (143 ± 14 vs 93 ± 6 min; p < 0.01). Functional changes of Arp 2/3 inhibition on barrier integrity are associated temporally with increased intercellular gap area at baseline (0.456 ± 0.02 vs 0.299 ± 0.02; p < 0.05) and thirty minutes after thrombin (0.885 ± 0.03 vs 0.754 ± 0.03; p < 0.05). Immunofluorescent microscopy reveals reduced lamellipodia formation after S1P and during thrombin recovery in Arp 2/3 inhibited cells. Individual lamellipodia demonstrate reduced depth following Arp 2/3 inhibition vs vehicle at baseline (1.83 ± 0.41 vs 2.55 ± 0.46 µm; p < 0.05) and thirty minutes after S1P treatment (1.53 ± 0.37 vs 2.09 ± 0.36 µm; p < 0.05). These results establish a critical role for Arp 2/3 activity in determination of pulmonary endothelial barrier function and recovery through formation of EC lamellipodia and closure of intercellular gaps.

Dysregulated Nox4 ubiquitination contributes to redox imbalance and age-related severity of acute lung injury

Acute respiratory distress syndrome (ARDS) is a devastating critical illness disproportionately affecting the elderly population, with both higher incidence and mortality. The integrity of the lung endothelial cell (EC) monolayer is critical for preservation of lung function. However, mechanisms mediating EC barrier regulation in the context of aging remain unclear. We assessed the severity of acute lung injury (ALI) in young (2 mo) and aged (18 mo) mice using a two-hit preclinical model. Compared with young cohorts, aged mice exhibited increased ALI severity, with greater vascular permeability characterized by elevated albumin influx and levels of bronchoalveolar lavage (BAL) cells (neutrophils) and protein. Aged/injured mice also demonstrated elevated levels of reactive oxygen species (ROS) in the BAL, which was associated with upregulation of the ROS-generating enzyme, Nox4. We evaluated the role of aging in human lung EC barrier regulation utilizing a cellular model of replicative senescence. Senescent EC populations were defined by increases in β-galactosidase activity and p16 levels. In response to lipopolysaccharide (LPS) challenge, senescent ECs demonstrate exacerbated permeability responses compared with control "young" ECs. LPS challenge led to a rapid induction of Nox4 expression in both control and senescent ECs, which was posttranslationally mediated via the proteasome/ubiquitin system. However, senescent ECs demonstrated deficient Nox4 ubiquitination, resulting in sustained expression of Nox4 and alterations in cellular redox homeostasis. Pharmacological inhibition of Nox4 in senescent ECs reduced LPS-induced alterations in permeability. These studies provide insight into the roles of Nox4/senescence in EC barrier responses and offer a mechanistic link to the increased incidence and mortality of ARDS associated with aging.

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.

Blockade of CXC chemokine receptor 3 on endothelial cells protects against sepsis-induced acute lung injury

BACKGROUND

CXCR3, a G-protein coupled chemokine receptor, has been shown to play a critical role in recruiting inflammatory cells into lungs in several studies. However, its roles in polymicrobial septic acute lung injury (ALI) is yet unknown. Therefore, the purpose of this study was to elucidate the protective effects of CXCR3 blockade on pulmonary microvascular endothelial cells (PMVECs) in septic ALI and explore potential mechanisms.

MATERIALS AND METHODS

ALI was induced by polymicrobial sepsis through cecal ligation and puncture surgery. The expression of CXCR3 on pulmonary microvascular endothelial cells was measured 24 h after cecal ligation and puncture surgery. In addition, the protective effects of neutralizing antibody were detected, including protein concentration, inflammation cell counts, lung ​wet-to-dry ratio, and lung damages. In human umbilical vein endothelial cells (HUVECs) culture condition, CXCR3 expression was measured after exposure to tumor necrosis factor-α. The permeability and apoptosis ratio were detected through CXCR3 gene silencing on HUVECs. The p38 mitogen-activated protein kinase (MAPK) was analyzed with Western blot.

RESULTS

CXCR3 expression was upregulated both in vivo and in vitro. After CXCR3 neutralizing antibody administrated intraperitoneally, the protein concentration, inflammatory cell counts in BALF and lung ​wet-to-dry ratio were decreased significantly, as well as the lung tissue damages. In vitro, CXCR3 gene silencing inhibited tumor necrosis factor-α and CXCL10-induced hyperpermeability and apoptosis in HUVECs. In addition, p38 mitogen-activated protein kinase activation was essential for CXCR3-mediated apoptosis.

CONCLUSIONS

CXCR3 blockade exerts protective effects on ALI at least partly by inhibiting endothelial cells apoptosis and decreasing the leakage of protein-rich fluid and inflammatory cells. Blockade of CXCR3 may be a promising therapeutic strategy for severe sepsis-induced ALI.

Absence of TNF-α enhances inflammatory response in the newborn lung undergoing mechanical ventilation

Bronchopulmonary dysplasia (BPD), characterized by impaired alveolarization and vascularization in association with lung inflammation and apoptosis, often occurs after mechanical ventilation with oxygen-rich gas (MV-O2). As heightened expression of the proinflammatory cytokine TNF-α has been described in infants with BPD, we hypothesized that absence of TNF-α would reduce pulmonary inflammation, and attenuate structural changes in newborn mice undergoing MV-O2 Neonatal TNF-α null (TNF-α(-/-)) and wild type (TNF-α(+/+)) mice received MV-O2 for 8 h; controls spontaneously breathed 40% O2 Histologic, mRNA, and protein analysis in vivo were complemented by in vitro studies subjecting primary pulmonary myofibroblasts to mechanical stretch. Finally, TNF-α level in tracheal aspirates from preterm infants were determined by ELISA. Although MV-O2 induced larger and fewer alveoli in both, TNF-α(-/-) and TNF-α(+/+) mice, it caused enhanced lung apoptosis (TUNEL, caspase-3/-6/-8), infiltration of macrophages and neutrophils, and proinflammatory mediator expression (IL-1β, CXCL-1, MCP-1) in TNF-α(-/-) mice. These differences were associated with increased pulmonary transforming growth factor-β (TGF-β) signaling, decreased TGF-β inhibitor SMAD-7 expression, and reduced pulmonary NF-κB activity in ventilated TNF-α(-/-) mice. Preterm infants who went on to develop BPD showed significantly lower TNF-α levels at birth. Our results suggest a critical balance between TNF-α and TGF-β signaling in the developing lung, and underscore the critical importance of these key pathways in the pathogenesis of BPD. Future treatment strategies need to weigh the potential benefits of inhibiting pathologic cytokine expression against the potential of altering key developmental pathways.