Adoptive transfer of acute lung injury

Differential response of primary alveolar type I and type II cells to LPS stimulation

The alveolar epithelium serves as a barrier between organism and environment and functions as the first line of protection against potential respiratory pathogens. Alveolar type II (TII) cells have traditionally been considered the immune cells of the alveolar epithelium, as they possess immunomodulatory functions; however, the precise role of alveolar type I (TI) cells, which comprise ∼95% of the alveolar epithelial surface area, in lung immunity is not clear. We sought to determine if there was a difference in the response of TI and TII cells to lung injury and if TI cells could actively participate in the alveolar immune response. TI cells isolated via fluorescence activated cell sorting (FACS) from LPS-injured rats demonstrated greater fold-induction of multiple inflammatory mediators than TII cells isolated in the same manner from the same animals. Levels of the cytokines TNF-α, IL-6 and IL-1β from cultured primary rat TI cells after LPS stimulation were significantly increased compared to similarly studied primary rat TII cells. We found that contrary to published reports, cultured TII cells produce relatively small amounts of TNF-α, IL-6 and IL-1β after LPS treatment; the higher levels of cytokine expression from cultured TII cells reported in the literature were likely from macrophage contamination due to traditional non-FACS TII cell isolation methods. Co-culture of TII cells with macrophages prior to LPS stimulation increased TNF-α and IL-6 production to levels reported by other investigators for TII cells, however, co-culture of TI cells and macrophages prior to LPS treatment resulted in marked increases in TNF-α and IL-6 production. Finally, exogenous surfactant blunted the IL-6 response to LPS in cultured TI cells. Taken together, these findings advocate a role for TI cells in the innate immune response and suggest that both TI and TII cells are active players in host defense mechanisms in the lung.

LPS-stimulated cytokine production in type I cells is modulated by the renin-angiotensin system

The alveolar epithelium serves as a barrier to the entry of potential respiratory pathogens. Alveolar Type II (TII) cells have immunomodulatory functions, but whether Type I (TI) cells, which comprise approximately 95% of the alveolar epithelium, also play a role in immunity is unknown. Because the renin-angiotensin system (RAS) is emerging as an important mediator of inflammation, and angiotensin-converting enzyme 2 (ACE2), an element of the RAS, has been implicated in lung injury, we hypothesize that TI cells can produce cytokines in response to LPS stimulation, and that this inflammation can be modulated by the RAS. Alveolar TI cells were isolated from adult Sprague-Dawley rat lungs that had been injured with an intratracheal instillation of LPS. PCR was performed to determine whether TI cells expressed transcripts for TNF-α, IL-6, or IL-1β at baseline and after lung injury. Immunocytochemical and protein analysis detected angiotensin II (Ang II) and ACE2, as well as angiotensin Type 1 receptor (AT1R) and Type 2 receptor (AT2R), in TI cells. To separate cell-specific responses, primary TI cells were isolated, cultured, and exposed to LPS, Ang II, or specific inhibitors of AT1R or AT2R. Cytokine production was assayed by ELISA. LPS stimulated the production of all cytokines, whereas ACE2 and losartan, an AT1R inhibitor, blocked elements of the LPS-induced cytokine response. Primary TI cells produce cytokines when treated with LPS, contain important components of the RAS, and can modulate LPS-induced cytokine production via the RAS, suggesting a role for TI cells in the innate immune response of the lung.

Adenosine deaminase that acts on RNA 1 p150 in alveolar macrophage is involved in LPS-induced lung injury

Previous studies showed adenosine deaminase that acts on RNA (ADAR1) up-regulated in alveolar macrophages (AMs) by LPS treatment, whereas its roles in acute lung injury (ALI) are still unclear. Here, we report that up-regulation of inducible ADAR1 p150 isoform in macrophages stimulated with LPS and in AMs harvested from an ALI rat model. Knockdown of ADAR1 p150 by small interfering RNA in AMs suppressed macrophage inflammatory protein 1 (MIP-1) secretion while enhancing that of IL-10 compared with those control cells upon LPS stimulation. To further confirm the role of p150 in AMs, adoptive transfer of LPS-activated NR8383 cells was performed in healthy rats, and severity of inflammatory response was assessed by investigating cellular pattern in bronchoalveolar lavage fluid and calculating alveolar-arterial oxygen difference [D(A-a)O2]. Acute lung injury was induced by LPS-activated NR8383 cells with either normal or lower ADAR1 expression levels, and ALI in rats and the lung inflammation was attenuated significantly by knockdown ADAR1 p150 in transferred cells both in polymorphonuclear leukocyte infiltration and D(A-a)O2. The roles of MIP-1 and IL-10 in the development of ALI were also tested in animals receiving neutralizing antibodies. Administration of anti-MIP-1 inhibited lung polymorphonuclear leukocytes infiltration and lung damage, as well as D(A-a)O2, whereas anti-IL-10 reversed the protection effects. In conclusion, ADAR1 p150 is functionally significant in the development of ALI. It likely exerts its effects in part by mediating the expression of proinflammatory and anti-inflammatory cytokines and influencing tissue neutrophil recruitment and D(A-a)O2. It also implied that ADAR1 inhibitors may help attenuate local inflammatory lung damage.

Mitogen activated protein kinase activated protein kinase 2 regulates actin polymerization and vascular leak in ventilator associated lung injury

Mechanical ventilation, a fundamental therapy for acute lung injury, worsens pulmonary vascular permeability by exacting mechanical stress on various components of the respiratory system causing ventilator associated lung injury. We postulated that MK2 activation via p38 MAP kinase induced HSP25 phosphorylation, in response to mechanical stress, leading to actin stress fiber formation and endothelial barrier dysfunction. We sought to determine the role of p38 MAP kinase and its downstream effector MK2 on HSP25 phosphorylation and actin stress fiber formation in ventilator associated lung injury. Wild type and MK2(-/-) mice received mechanical ventilation with high (20 ml/kg) or low (7 ml/kg) tidal volumes up to 4 hrs, after which lungs were harvested for immunohistochemistry, immunoblotting and lung permeability assays. High tidal volume mechanical ventilation resulted in significant phosphorylation of p38 MAP kinase, MK2, HSP25, actin polymerization, and an increase in pulmonary vascular permeability in wild type mice as compared to spontaneous breathing or low tidal volume mechanical ventilation. However, pretreatment of wild type mice with specific p38 MAP kinase or MK2 inhibitors abrogated HSP25 phosphorylation and actin polymerization, and protected against increased lung permeability. Finally, MK2(-/-) mice were unable to phosphorylate HSP25 or increase actin polymerization from baseline, and were resistant to increases in lung permeability in response to HV(T) MV. Our results suggest that p38 MAP kinase and its downstream effector MK2 mediate lung permeability in ventilator associated lung injury by regulating HSP25 phosphorylation and actin cytoskeletal remodeling.

Mechanical stress activates xanthine oxidoreductase through MAP kinase-dependent pathways

Xanthine oxidoreductase (XOR) plays a prominent role in acute lung injury because of its ability to generate reactive oxygen species. We investigated the role of XOR in ventilator-induced lung injury (VILI). Male C57BL/6J mice were assigned to spontaneous ventilation (sham) or mechanical ventilation (MV) with low (7 ml/kg) and high tidal volume (20 ml/kg) for 2 h after which lung XOR activity and expression were measured and the effect of the specific XOR inhibitor allopurinol on pulmonary vascular leakage was examined. In separate experiments, rat pulmonary microvascular endothelial cells (RPMECs) were exposed to cyclic stretch (5% and 18% elongation, 20 cycles/min) for 2 h before intracellular XOR activity measurement. Lung XOR activity was significantly increased at 2 h of MV without changes in XOR expression. There was evidence of p38 MAP kinase, ERK1/2, and ERK5 phosphorylation, but no change in JNK phosphorylation. Evans blue dye extravasation and bronchoalveolar lavage protein concentration were significantly increased in response to MV, changes that were significantly attenuated by pretreatment with allopurinol. Cyclic stretch of RPMECs also caused MAP kinase phosphorylation and a 1.7-fold increase in XOR activity, which was completely abrogated by pretreatment of the cells with specific MAP kinase inhibitors. We conclude that XOR enzymatic activity is significantly increased by mechanical stress via activation of p38 MAP kinase and ERK and plays a critical role in the pathogenesis of pulmonary edema associated with VILI.

S1P3 receptor-induced reorganization of epithelial tight junctions compromises lung barrier integrity and is potentiated by TNF

Pulmonary pathologies including adult respiratory distress syndrome are characterized by disruption of pulmonary integrity and edema compromising respiratory function. Sphingosine 1-phosphate (S1P) is a lipid mediator synthesized and/or stored in mast cells, platelets, and epithelial cells, with production up-regulated by the proinflammatory cytokines IL-1 and TNF. S1P administration via the airways but not via the vasculature induces lung leakage. Using receptor-null mice, we show that S1P, acting on S1P3 receptor expressed on both type I and type II alveolar epithelial cells but not vascular endothelium, induces pulmonary edema by acute tight junction opening. WT but not S1P3-null mice showed disruption of pulmonary epithelial tight junctions and the appearance of paracellular gaps between epithelial cells by electron microscopy within 1 h of airways exposure to S1P. We further show by fluorescence microscopy that S1P induced rapid loss of ZO-1 reactivity, an essential component of the cytoplasmic plaque associated with tight junctions, as well as of the tetraspannin Claudin-18, an integral membrane organizer of tight junctions. S1P shows synergistic activity with the proinflammatory cytokine TNF, showing both pulmonary edema and mortality at subthreshold S1P doses. Specifically, preexposure of mice to subthreshold doses of TNF, which alone induced no lung edema, exacerbated S1P-induced edema and impaired survival. S1P, acting through S1P3, regulates epithelial integrity and acts additively with TNF in compromising respiratory barrier function. Because S1P3-null mice are resistant to S1P-induced pulmonary leakage, either alone or in the presence of TNF, S1P3 antagonism may be useful in protecting epithelial integrity in pulmonary disease.

Effect of Ulinastatin, a human urinary trypsin inhibitor, on the oleic acid-induced acute lung injury in rats via the inhibition of activated leukocytes

BACKGROUND

The acute respiratory distress syndrome (ARDS) is often caused by fat tissue embolism. One of the most common animal models of ARDS is produced by direct administration of oleic acid (OA). Activated leukocytes are critically involved in the pathological mechanism in this model. Human urinary trypsin inhibitor (UTI) is known to inhibit production of tumor necrosis factor (TNF)-alpha, which potently stimulates leukocyte activation. The purpose of this study was to clarify whether UTI improves OA-induced lung injury in rats by inhibiting activated leukocytes via TNF-alpha production.

MATERIALS AND METHODS

Rats were subjected to a single intravenous administration of OA into the pedicle vein. Acute lung injury was evaluated by arterial blood gases and histological changes in lungs. Pulmonary vascular permeability, accumulation of neutrophils, and the levels of TNF-alpha in lung tissues were also examined. Rats were divided into four experimental groups: a sham operated, OA, OA + UTI, and OA + nitrogen mustard (NM)-induced leukocytopenia group. UTI was intravenously administered 30 min before OA administration. Leukocytopenia was induced by the administration of NM.

RESULTS

UTI significantly improved the OA-induced histological changes for 4 h after OA administration. The OA-induced reduction of PaO2, the increase of pulmonary vascular permeability, and the levels of MPO activity and TNF-alpha in lung tissues were significantly improved in rats administrated UTI. The effects in the leukocytopenia group were similar to those in the UTI-administered group.

CONCLUSION

Leukocytes play a critical role in the development of OA-induced lung injury. It was suggested that UTI contributed to the reduction in the OA-induced lung injury by inhibiting TNF-alpha and thereby suppressing leukocyte.

Persistent transgene expression following intravenous administration of a liposomal complex: role of interleukin-10-mediated immune suppression

Studies conducted in non-tumor-bearing, immunocompetent mice have shown that intravenous administration of liposome-DNA complex elicits an inflammatory response that results in a failure to sustain adequate transgene expression. In the present study, however, we investigated the effects of a cationic liposomal DOTAP:cholesterol (DOTAP:Chol)-DNA complex on cytokine production and transgene expression in both experimental lung tumor-bearing (TB) mice and non-tumor-bearing (NTB) syngeneic mice and nude mice. Intravenous injection of DOTAP:Chol-luciferase (luc) DNA complex resulted in tumor necrosis factor-alpha levels that were 50% lower and interleukin-10 levels that were 50-60% higher in TB mice than in NTB mice. Furthermore, a significant increase in luc expression (P = 0.001) that persisted for 7 days was observed in TB mice. In contrast, luc expression decreased significantly from day 1 to day 2 in NTB mice. Also, luc expression was two- to threefold higher in TB mice that were given multiple injections of DOTAP:Chol-luc complex than in mice who received a single injection. In contrast, luc expression was significantly suppressed following multiple injections in NTB mice (P = 0.01). Further analysis revealed IL-10 protein expression by the tumor cells in TB mice. Injection of anti-IL-10 antibody in TB mice resulted in a significant decrease in luc expression (P = 0.01) compared with that in mice injected with a control antibody. Based on these findings, we conclude that transgene expression persists in TB mice and is partly mediated by IL-10. Additionally, multiple injections of liposome-DNA complex can increase transgene expression in TB mice. These findings have clinical applications in the treatment of cancer.

Protective effects of sphingosine 1-phosphate in murine endotoxin-induced inflammatory lung injury

Our prior in vitro studies indicate that sphingosine 1-phosphate (S1P), a phospholipid angiogenic factor, produces endothelial cell barrier enhancement through ligation of endothelial differentiation gene family receptors. We hypothesized that S1P may reduce the vascular leak associated with acute lung injury and found that S1P infusion produced a rapid and significant reduction in lung weight gain (more than 50%) in the isolated perfused murine lung. The effect of S1P was next assessed in a murine model of LPS-mediated microvascular permeability and inflammation with marked increases in parameters of lung injury at both 6 and 24 hours after intratracheal LPS. Each parameter assessed was significantly reduced by intravenous S1P (1 microM final) and in selected experiments by the S1P analogue FTY720 (0.1 mg/kg, intraperitoneally) delivered 1 hour after LPS. S1P produced an approximately 40-50% reduction in LPS-mediated extravasation of Evans blue dye albumin, bronchoalveolar lavage protein content, and lung tissue myeloperoxidase activity (reflecting phagocyte infiltration). Consistent with systemic barrier enhancement, S1P significantly decreased Evans blue dye albumin extravasation and myeloperoxidase content in renal tissues of LPS-treated mice. These studies indicate that S1P significantly decreases pulmonary/renal vascular leakage and inflammation in a murine model of LPS-mediated acute lung injury and may represent a novel therapeutic strategy for vascular barrier dysfunction.

Therapeutic hypercapnia is not protective in the in vivo surfactant-depleted rabbit lung

Permissive hypercapnia because of reduced tidal volume is associated with improved survival in lung injury, whereas therapeutic hypercapnia-deliberate elevation of arterial Pco2-protects against in vivo reperfusion injury and injury produced by severe lung stretch. No published studies to date have examined the effects of CO2 on in vivo models of neonatal lung injury. We used an established in vivo rabbit model of surfactant depletion to investigate whether therapeutic hypercapnia would improve oxygenation and protect against ventilator-induced lung injury. Animals were randomized to injurious (tidal volume, 12 mL/kg; positive end-expiratory pressure, 0 cm H2O) or protective ventilatory strategy (tidal volume, 5 mL/kg; positive end-expiratory pressure, 12.5 cm H2O), and to receive either control conditions or therapeutic hypercapnia (fraction of inspired CO2, 0.12). Oxygenation (alveolar-arterial O2 difference, arterial Po2), lung injury (alveolar-capillary protein leak, impairment of static compliance), and selected bronchoalveolar lavage and plasma cytokines (IL-8, growth-related oncogene, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha) were measured. Injurious ventilation resulted in a large alveolar-arterial O2 gradient, elevated peak airway pressure, increased protein leak, and impaired lung compliance. Therapeutic hypercapnia did not affect any of these outcomes. Tumor necrosis factor-alpha was not increased by mechanical stretch in any of the groups. Therapeutic hypercapnia abolished the stretch-induced increase in bronchoalveolar lavage monocyte chemoattractant protein-1, but did not affect any of the other mediators studied. Therapeutic hypercapnia may attenuate the impairment in oxygenation and inhibit certain cytokines. Because hypercapnia inhibits certain cytokines but does not alter lung injury, the pathogenic role of these cytokines in lung injury is questionable.

Increased uptake of liposomal-DNA complexes by lung metastases following intravenous administration

We have investigated the effects of an improved liposomal formulation (extruded DOTAP:cholesterol (DOTAP:Chol)-DNA complex) on transgene expression in tumor cells and normal cells of murine and human origin both in vitro and in vivo. In vitro, transgene expression was significantly increased (P = 0.01) in human tumor cells compared to normal human cells. The increased transgene expression was due to increased uptake of the liposome-DNA complex by tumor cell phagocytosis. Furthermore, immunohistochemical analysis demonstrated a greater transgene expression in lung tumors than in surrounding normal tissues. Increased transgene expression due to enhanced uptake of the liposome-DNA complexes by tumor cells in vivo was also demonstrated using fluorescently labeled DOTAP:Chol liposomes. Finally, evaluation of lung tissue explants obtained from patients undergoing pulmonary resection demonstrated significantly higher (P = 0.001) transgene expression in tumor cells than in normal cells. Thus, we demonstrated that intravenous injection of DOTAP:Chol-DNA complex results in increased transgene expression in tumor and is due to increased phagocytosis of the complexes by tumor cells.

Shock-induced neutrophil mediated priming for acute lung injury in mice: divergent effects of TLR-4 and TLR-4/FasL deficiency

Acute lung injury (ALI) leading to respiratory distress is a common sequela of shock/trauma, however, modeling this process in mice with a single shock or septic event is inconsistent. One explanation is that hemorrhage is often just a "priming insult," thus, secondary stimuli may be required to "trigger" ALI. To test this we carried out studies in which we assessed the capacity of hemorrhage alone or hemorrhage followed by septic challenge (CLP) to induce ALI. Lung edema, bronchoalveolar lavage interleukin (IL)-6, alveolar congestion, as well as lung IL-6, macrophage inflammatory protein (MIP)-2, and myeloperoxidase (MPO) activity were all increased in mice subjected to CLP at 24 but not 72 hours following hemorrhage. This was associated with a marked increase in the susceptibility of these mice to septic mortality. Peripheral blood neutrophils derived from 24 hours post-hemorrhage, but not Sham animals, exhibited an ex vivo decrease in apoptotic frequency and an increase in respiratory burst capacity, consistent with in vivo "priming." Subsequently, we observed that adoptive transfer of neutrophils from hemorrhaged but not sham-hemorrhage animals to neutropenic recipients reproduce ALI when subsequently septically challenged, implying that this priming was mediated by neutrophils. We also found marked general increases in lung IL-6, MIP-2, and MPO in mice deficient for toll-like receptor (TLR-4) or the combined lack of TLR-4/FasL. However, the TLR-4 defect markedly attenuated neutrophil influx into the lung while not altering the change in local cytokine/chemokine expression. Alternatively, the combined loss of FasL and TLR-4 did not inhibit the increase in MPO and exacerbated lung IL-6/MIP-2 levels even further.