Tryptophan catabolism in Pseudomonas aeruginosa and potential for inter-kingdom relationship.

BACKGROUND: Pseudomonas aeruginosa (Pa) is a Gram-negative bacteria frequently involved in healthcare-associated pneumonia with poor clinical outcome. To face the announced post-antibiotic era due to increasing resistance and lack of new antibiotics, new treatment strategies have to be developed. Immunomodulation of the host response involved in outcome could be an alternative therapeutic target in Pa-induced lung infection. Kynurenines are metabolites resulting from tryptophan catabolism and are known for their immunomodulatory properties. Pa catabolizes tryptophan through the kynurenine pathway. Interestingly, many host cells also possess the kynurenine pathway, whose metabolites are known to control immune system homeostasis. Thus, bacterial metabolites may interfere with the host's immune response. However, the kynurenine pathway in Pa, including functional enzymes, types and amounts of secreted metabolites remains poorly known. Using liquid chromatography coupled to mass spectrometry and different strains of Pa, we determined types and levels of metabolites produced by Pa ex vivo in growth medium, and the relevance of this production in vivo in a murine model of acute lung injury. RESULTS: Ex vivo, Pa secretes clinically relevant kynurenine levels (µM to mM). Pa also secretes kynurenic acid and 3-OH-kynurenine, suggesting that the bacteria possess both a functional kynurenine aminotransferase and kynurenine monooxygenase. The bacterial kynurenine pathway is the major pathway leading to anthranilate production both ex vivo and in vivo. In the absence of the anthranilate pathway, the kynurenine pathway leads to kynurenic acid production. CONCLUSION: Pa produces and secretes several metabolites of the kynurenine pathway. Here, we demonstrate the existence of new metabolic pathways leading to synthesis of bioactive molecules, kynurenic acid and 3-OH-kynurenine in Pa. The kynurenine pathway in Pa is critical to produce anthranilate, a crucial precursor of some Pa virulence factors. Metabolites (anthranilate, kynurenine, kynurenic acid) are produced at sustained levels both ex vivo and in vivo leading to a possible immunomodulatory interplay between bacteria and host. These data may imply that pulmonary infection with bacteria highly expressing the kynurenine pathway enzymes could influence the equilibrium of the host's tryptophan metabolic pathway, known to be involved in the immune response to infection. Further studies are needed to explore the effects of these metabolic changes on the pathophysiology of Pa infection.

Relative contribution of three main virulence factors in Pseudomonas aeruginosa pneumonia.

OBJECTIVE: The pathogenesis and the outcome of Pseudomonas aeruginosa ventilator-acquired pneumonia depend on the virulence factors displayed by the bacteria as well as the host response. Thus, quorum sensing, lipopolysaccharide, and type 3 secretion system have each individually been shown to be important virulence systems in laboratory reference strains. However, the relative contribution of these three factors to the in vivo pathogenicity of clinically relevant strains has never been studied. We analyzed the virulence of 56 nonclonal Pseudomonas aeruginosa strains isolated from critically ill patients with ventilator-acquired pneumonia. To avoid the variation of human immune response, we used a murine model of pneumonia. The aim was to determine which virulence factor was the most important. SETTING: Research laboratory of a university. SUBJECTS: Male adult BALB/c mice. INTERVENTIONS: In vitro, the phenotype of each strain was established as to the expression of quorum sensing-regulated factors (elastase and pyocyanin), type 3 secretion system exotoxin secretion (Exotoxin U, S and/or T, or "nonsecreting"), and lipopolysaccharide O-antigen serotype. Strain pathogenicity was evaluated in vivo in a mouse model of acute pneumonia through lung injury assessment by measuring alveolar-capillary barrier permeability to proteins, lung wet/dry weight ratio, and bacterial dissemination. Associations were then sought between virulence system phenotypes and levels of lung injury. MEASUREMENTS AND MAIN RESULTS: In univariate analysis, elastase production, O11 serotype, and type 3 secretion system exotoxin secretion were associated with increased lung injury and exotoxin U was linked to an increase risk of bacteremia. In multivariate analysis, we observed that type 3 secretion system exotoxin secretion and to a lesser degree elastase production were associated with increased lung injury. CONCLUSION: In a murine model of pneumonia, our data suggest that type 3 secretion system and elastase are the most important virulence factors in clinically relevant P. aeruginosa strains.

Role of LecA and LecB lectins in Pseudomonas aeruginosa-induced lung injury and effect of carbohydrate ligands.

Pseudomonas aeruginosa is a frequently encountered pathogen that is involved in acute and chronic lung infections. Lectin-mediated bacterium-cell recognition and adhesion are critical steps in initiating P. aeruginosa pathogenesis. This study was designed to evaluate the contributions of LecA and LecB to the pathogenesis of P. aeruginosa-mediated acute lung injury. Using an in vitro model with A549 cells and an experimental in vivo murine model of acute lung injury, we compared the parental strain to lecA and lecB mutants. The effects of both LecA- and Lec B-specific lectin-inhibiting carbohydrates (alpha-methyl-galactoside and alpha-methyl-fucoside, respectively) were evaluated. In vitro, the parental strain was associated with increased cytotoxicity and adhesion on A549 cells compared to the lecA and lecB mutants. In vivo, the P. aeruginosa-induced increase in alveolar barrier permeability was reduced with both mutants. The bacterial burden and dissemination were decreased for both mutants compared with the parental strain. Coadministration of specific lectin inhibitors markedly reduced lung injury and mortality. Our results demonstrate that there is a relationship between lectins and the pathogenicity of P. aeruginosa. Inhibition of the lectins by specific carbohydrates may provide new therapeutic perspectives.

Monocyte deactivation in neutropenic acute respiratory distress syndrome patients treated with granulocyte colony-stimulating factor.

INTRODUCTION: In severely neutropenic septic acute respiratory distress syndrome (ARDS) patients, macrophages and monocytes are the last potentially remaining innate immune cells. We have previously shown, however, a deactivation of the alveolar macrophage in neutropenic septic ARDS patients. In the present study, we tried to characterize in vitro monocyte baseline cytokine production and responsiveness to lipopolysaccharide exposure. METHODS: Twenty-two consecutive patients with cancer were prospectively enrolled into a prospective observational study in an intensive care unit. All patients developed septic ARDS and were divided into two groups: neutropenic patients (n = 12) and non-neutropenic patients (n = 10). All of the neutropenic patients received granulocyte colony-stimulating factor whereas no patient in the non-neutropenic group received granulocyte colony-stimulating factor. We compared monocytes from neutropenic patients with septic ARDS with monocytes from non-neutropenic patients and healthy control individuals (n = 10). Peripheral blood monocytes were cultured, and cytokine levels (TNFalpha, IL-1beta, IL-6, IL-10, and IL-1 receptor antagonist) were assayed with and without lipopolysaccharide stimulation. RESULTS: TNFalpha, IL-6, IL-10 and IL-1 receptor antagonist levels in unstimulated monocytes were lower in neutropenic patients compared with non-neutropenic patients. Values obtained in the healthy individuals were low as expected, comparable with neutropenic patients. In lipopolysaccharide-stimulated monocytes, both inflammatory and anti-inflammatory cytokine production were significantly lower in neutropenic patients compared with non-neutropenic patients and control individuals. CONCLUSION: Consistent with previous results concerning alveolar macrophage deactivation, we observed a systemic deactivation of monocytes in septic neutropenic ARDS. This deactivation participates in the overall immunodeficiency and could be linked to sepsis, chemotherapy and/or the use of granulocyte colony-stimulating factor.

Inhaled nitric oxide increases endothelial permeability in Pseudomonas aeruginosa pneumonia.

OBJECTIVE: Pneumonia is a frequent cause of acute respiratory distress syndrome (ARDS), and Pseudomonas aeruginosa is a leading pathogen in nosocomial pneumonia. The management of ARDS remains a major problem, and only a limited number of options can improve the oxygenation. Inhaled nitric oxide (iNO) has been widely used, although this molecule is a free radical potentially harmful through the generation of toxic radical derivatives. The goal of our study was to assess the consequences of iNO (10 ppm) in a rat model of P. aeruginosa-induced lung injury. DESIGN: The animals were exposed for 24 h to iNO after instillation of the pathogen. Distal alveolar fluid clearance (DAFC) and epithelial and endothelial permeability were measured with a double flux of radio-labeled albumin. RESULTS: DAFC and epithelial permeability were increased in pneumonia but not influenced by iNO. In contrast, endothelial permeability was statistically significantly higher in the pneumonic animals exposed to iNO than in the pneumonic group without iNO (0.24+/-0.03 vs 0.47+/-0.1, p<0.05). This increase was not related to the production of nitrate/nitrite, nor to the increase of the inflammatory response evaluated by cytokine levels in the bronchoalveolar lavage fluid (TNF-alpha, IL-6, IL-10). The alveolar recruitment of polymorphonuclear neutrophils was comparable in the pneumonic group exposed to iNO and the pneumonic group without iNO. CONCLUSION: iNO increases the endothelial permeability in P. aeruginosa pneumonia. The mechanism is not related to the production of nitrate/nitrite or to a greater inflammatory response.

Intravenous administration of activated protein C in Pseudomonas-induced lung injury: impact on lung fluid balance and the inflammatory response.

BACKGROUND: Acute lung injury (ALI) induces a coagulation/fibrinolysis imbalance and leads to fibrin deposition. The protein C pathway is an important regulator of the coagulation system and reduces the inflammatory response. The aim of the study was to examine the effects of recombinant human activated protein C (rhAPC) in the early phase of Pseudomonas aeruginosa (Pa)-induced lung injury. METHODS: The study was conducted in vivo on a rat model of Pa-induced ALI. Continuous intravenous (IV) rhAPC was administrated simultaneously with intratracheal (IT) Pa. We instilled into the airspaces a 5% bovine albumin solution with 1 mu(Ci of (125)I-albumin and injected IV 1 mu(Ci of (111)In-albumin to measure lung liquid clearance (LLC) and endothelial injury. Cytokines levels (TNFalpha and IL-6) and thrombin-antithrombin (TAT) complexes were measured in blood and bronchoalveolar lavage fluid (BALF) at 4 hours. Four groups were compared: control (CTR), pneumonia (PNP) receiving IT Pa (0.5 ml/kg of 1 x 10(9) cfu), APC: IV rhAPC (300 microg/kg/h), A-PNP: IT Pa /IV rhAPC. RESULTS: Alveolar-capillary permeability was increased in the PNP versus the CTR group (0.28 +/- 0.08 vs. 0.03 +/- 0.01, p < 0.05). IV rhAPC in Pa-induced ALI led to further injury (0.47 +/- 0.17 vs. 0.28 +/- 0.08, p = 0.2). The LLC was significantly decreased in the A-PNP group compared to PNP group (9.1 +/- (4.3% vs. 33.4 +/- 2.6%, p < 0.05). The lung wet to dry weight ratio was significantly increased in the PNP group (4.62 +/- 0.31) compared to the CTR group (3.87 +/- 0.22, p < 0.05). IV rhAPC administration tends to increase this parameter in Pa-induced ALI (5.80 +/- 0.66, p = 0.07). These findings were associated with a loss of inflammatory response compartmentalization measured by TNFalpha and IL-6 systemic levels. TAT complexes in BALF were increased in the A-PNP group (23.17 +/- 2.89 ng/ml) compared to the CTR group (0.92 +/- 0.17 ng/ml, p < 0.05) and the PNP group (11.06 +/- 2.76 ng/ml, p < 0.05). CONCLUSION: rhAPC reduces LLC following Pa-induced ALI and may influence pulmonary edema formation. The early massive fibrin formation is probably beneficial in ALI limiting both the extent of injury and permeability disorders.

Chronic pneumonia with Pseudomonas aeruginosa and impaired alveolar fluid clearance.

BACKGROUND: While the functional consequences of acute pulmonary infections are widely documented, few studies focused on chronic pneumonia. We evaluated the consequences of chronic Pseudomonas lung infection on alveolar function. METHODS: P. aeruginosa, included in agar beads, was instilled intratracheally in Sprague Dawley rats. Analysis was performed from day 2 to 21, a control group received only sterile agar beads. Alveolar-capillary barrier permeability, lung liquid clearance (LLC) and distal alveolar fluid clearance (DAFC) were measured using a vascular (131I-Albumin) and an alveolar tracer (125I-Albumin). RESULTS: The increase in permeability and LLC peaked on the second day, to return to baseline on the fifth. DAFC increased independently of TNF-alpha or endogenous catecholamine production. Despite the persistence of the pathogen within the alveoli, DAFC returned to baseline on the 5th day. Stimulation with terbutaline failed to increase DAFC. Eradication of the pathogen with ceftazidime did not restore DAFC response. CONCLUSIONS: From these results, we observe an adequate initial alveolar response to increased permeability with an increase of DAFC. However, DAFC increase does not persist after the 5th day and remains unresponsive to stimulation. This impairment of DAFC may partly explain the higher susceptibility of chronically infected patients to subsequent lung injury.

Massive alveolar thrombin activation in Pseudomonas aeruginosa-induced acute lung injury.

In acute lung injury (ALI), a coagulation/fibrinolysis imbalance leads to fibrin deposition, persistence of which contributes to fibrotic evolution. Our study evaluated the effects of early inhibition of coagulation in Pseudomonas aeruginosa (Pa)-induced ALI through the use of recombinant human antithrombin (rhAT). The study was conducted in vivo on a murine model of Pa-induced ALI. Intravenous rhAT was administered simultaneously with intratracheal Pa. Four experimental groups were compared: CTR, intratracheal saline (0.5 mL/kg)/intravenous saline (1 mL); PNP, intratracheal Pa (0.5 mL/kg of 2 x 10(9) cfu)/intravenous saline; AT, intratracheal saline/intravenous rhAT (500 IU/kg); ATPNP, intratracheal Pa/intravenous rhAT. Epithelial and endothelial permeabilities were evaluated with radiolabeled albumin flux across the alveolar barrier (125I- and 131I-labeled albumin). Thrombin-antithrombin (TAT) complexes levels were used as markers of coagulation activation in blood samples and in BAL fluid. Epithelial and endothelial protein permeability were increased in Pa-induced ALI versus control. Intravenous rhAT administration led to further permeability disorders. Administration of rhAT in Pa ALI led to a rise in TAT complexes in ATPNP blood serum and BAL fluids compared with the other groups. In Pa-induced ALI the administration intravenous rhAT leads to major histologic damage, alveolar capillary barrier injury, and permeability increase. Such effects of the inhibition of thrombin activation by rhAT lead to the hypothesis of a probable beneficial role of early coagulation activation in ALI as a factor limiting both the extent of injury and permeability disorders. Our study suggests that inhibition of this initial procoagulative imbalance is potentially dangerous.

Ventilation-induced lung injury is associated with an increase in gut permeability.

Mechanical ventilation is associated with several harmful effects mainly related to high tidal volumes (Vt). Ventilator-induced lung injury can be responsible for an increased production of inflammatory mediators. We evaluated remote consequences on the gut of lung triggered inflammatory response, neutralizing anti-tumor necrosis factor (TNF) antibody was administered to assess the role of TNF in lung and gut permeability changes. Rats were anesthetized and ventilated for 2 h. A control group (Con: Vt = 10 mL/kg) was compared with a high Vt group (HV: Vt = 30 ml/kg). One microCi of I125-labeled human serum albumin was injected to measure extravascular albumin space. Gut permeability was evaluated by plasma-to-lumen ratio leakage of I125 human serum albumin. Extravascular albumin space increased in the HV group from 446 +/- 50 microL to 2783 +/- 887 microL. Gut index of permeability increased from 5.1 +/- 1.2 to 14.2 +/- 4.9. Anti-TNF antibody prevented both lung and gut increase in permeability. High tidal volume ventilation resulted in an increase in lung edema and gut permeability, antagonism of TNF with neutralizing antibodies abrogated the increase in gut permeability as well as lung edema.

Deactivation of alveolar macrophages in septic neutropenic ARDS.

STUDY OBJECTIVES: Neutrophils often have been involved in the pathophysiology of ARDS. However, authentic ARDS has been described in patients with severe neutropenia, suggesting the presence of other potential mechanisms that are responsible of this syndrome. Alveolar macrophages (AMs) could be involved in the development of ARDS, and so we decided to study AM activation in neutropenic patients. PATIENTS: We designed a prospective study and enrolled two subgroups of consecutive patients (group A, 18 patients; group B, 22 patients) with septic ARDS. In the first period, 7 of 18 patients were neutropenic, and in the second period 10 of 22 patients were neutropenic. All neutropenic patients were treated with granulocyte colony-stimulating factor (G-CSF). MEASUREMENTS AND RESULTS: In group A, BAL fluid samples were analyzed for differential and total cell counts, and alveolar activation marker expression (ie, human leukocyte antigen [HLA]-DR locus) was determined. Basal and lipopolysaccharide (LPS)-stimulated production of tumor necrosis factor, interleukin (IL)-1 beta, IL-6, and IL-10 was evaluated in group B. In neutropenic patients, the BAL fluid total cell count and the neutrophil absolute count was significantly lower compared to those in nonneutropenic patients (p = 0.029 and p = 0.046, respectively). HLA-DR expression on AMs was significantly decreased (p = 0.016), and the percentage of AMs expressing HLA-DR was also significantly lower (p = 0.041). In neutropenic patients, the mean percentage of AMs expressing HLA-DR was significantly lower in deceased patients compared to survivors (30 +/- 7 vs 43 +/- 1, respectively; p = 0.047). Basal AMs released cytokines was comparable between the two groups; however, LPS stimulation yielded a deactivation of AMs in neutropenic patients. CONCLUSION: These results suggest a deactivation and/or hypoactivation of AMs in septic ARDS patients. This deactivation/hypoactivation could be linked to the use of G-CSF as this molecule has been shown to generate a down-regulation of HLA-DR expression.

Apoptosis inhibition in P. aeruginosa-induced lung injury influences lung fluid balance.

OBJECTIVE: Pseudomonas aeruginosa-induced lung injury is characterized not only by the alteration in lung fluid movement but also by apoptosis of lung epithelial and endothelial cells. We studied whether inhibition of apoptosis using a broad spectrum caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone (Z-VAD.fmk), would affect lung fluid balance in rat P. aeruginosa pneumonia. METHODS: Z-VAD.fmk (3 mg/kg) was administered intravenously simultaneously with P. aeruginosa intratracheal instillation (0.5 ml/kg, 2 x 10(9) CFU/ml). Apoptosis was evaluated with the TUNEL technique, cytoplasmic oligonucleosome assay, and caspase 3 activation. To evaluate lung permeability, extravascular plasma equivalent (EPE) and lung wet to dry weight ratio (W/D) were measured 4 h after intratracheal instillation of P. aeruginosa. RESULTS: We found an increase of lung apoptosis 4 h after P. aeruginosa instillation: cytoplasmic oligonucleosome assay increased from 3.17+/-0.78 to 26.82+/-4.67 ODx1000/mg of proteins/ml, Z-VAD.fmk administration decreased this parameter to 10.3+/-2.98 ODx1000/mg of proteins/ml. Caspase 3 levels followed the same pattern. Apoptosis involved both epithelial cells and endothelial cells. Endothelial permeability was increased after Pseudomonas instillation: W/D increased from 3.75+/-0.28 in the Co group to 4.42+/-0.23 in the Pn group; EPE was also higher in the Pn group compared with the Co group (0.125+/-0.04 and 0.002+/-0.01 ml, respectively). Both of these parameters were improved after Z-VAD.fmk administration; W/D decreased to 3.36+/-0.25 and EPE to 0.02+/-0.02 ml. CONCLUSION: Apoptosis occurs in the early phase of P. aeruginosa pneumonia. Administration of Z-VAD.fmk significantly decreases DNA fragmentation and caspase 3 levels. This is associated with an improvement of endothelial permeability and lung fluid balance.

Management of invasive candidiasis and candidemia in adult non-neutropenic intensive care unit patients: Part II. Treatment.

BACKGROUND: Invasive candidiasis and candidemia are frequently encountered in the nosocomial setting particularly in the intensive care unit (ICU). OBJECTIVE AND METHODS: To review the current management of invasive candidiasis and candidemia in non-neutropenic adult ICU patients based on a review of the literature and an European expert panel discussion. RESULTS AND CONCLUSIONS: Empiric and directed treatment for invasive candidiasis are predicated on the hemodynamic status of the patient. Unstable patients may benefit from broad-spectrum antifungal agents, which can be narrowed once the patient has stabilized and the identity of the infecting species is established. In stable patients, a more classical approach using fluconazole may be satisfactory provided that the patient is not colonized with fluconazole resistant strains or there has been recent past exposure to an azole (<30 days). In contrast, pre-emptive therapy is based on the presence of surrogate markers.

Management of invasive candidiasis and candidemia in adult non-neutropenic intensive care unit patients: Part I. Epidemiology and diagnosis.

BACKGROUND: Invasive candidiasis and candidemia are frequently encountered in the nosocomial setting, particularly in the intensive care unit (ICU). OBJECTIVES AND METHODS: To review the current management of invasive candidiasis and candidemia in non-neutropenic adult ICU patients based on a review of the literature and a European expert panel discussion. RESULTS AND CONCLUSIONS: Candida albicans remains the most frequently isolated fungal species followed by C. glabrata. The diagnosis of invasive candidiasis involves both clinical and laboratory parameters, but neither of these are specific. One of the main features in diagnosis is the evaluation of risk factor for infection which will identify patients in need of pre-emptive or empiric treatment. Clinical scores were built from those risk factors. Among laboratory diagnosis, a positive blood culture from a normally sterile site provides positive evidence. Surrogate markers have also been proposed like 1,3 beta-D: glucan level, mannans, or PCR testing. Invasive candidiasis and candidemia is a growing concern in the ICU, apart from cases with positive blood cultures or fluid/tissue biopsy, diagnosis is neither sensitive nor specific. The diagnosis remains difficult and is usually based on the evaluation of risk factors.

Omega-3 polyunsaturated fatty acids improve host response in chronic Pseudomonas aeruginosa lung infection in mice.

Pseudomonas aeruginosa is a gram-negative bacilli frequently encountered in human pathology. This pathogen is involved in a large number of nosocomial infections and chronic diseases. Herein we investigated the effects of polyunsaturated fatty acids (PUFA) in chronic Pseudomonas aeruginosa lung infection. C57BL/6 mice were fed for 5 wk with specifically designed diets with high contents in either omega-3 (omega-3) or omega-6 PUFA and compared to a control diet. P. aeruginosa included in agarose beads was then instilled intratracheally, and the animals were studied for 7 days. On the 4th day, the mice fed with the omega-3 diet had a higher lean body mass gain and a lower omega-6:omega-3 ratio of fatty acids extracted from the lung tissue compared with the other groups (P < 0.05). The omega-3 group had the lowest mortality. Distal alveolar fluid clearance (DAFC) as well as the inflammatory response and the cellular recruitment were higher in the omega-3 group on the 4th day. The effect on DAFC was independent of alpha-epithelial Na(+) channels (alpha-ENaC), beta-ENaC, and alpha(1)-Na-K-ATPase mRNA expressions, which were not altered by the different diets. In conclusion, a diet enriched in omega-3 PUFA can change lung membrane composition and improve survival in chronic pneumonia. This effect on survival is probably multifactorial involving the increased DAFC capacity as well as the optimization of the initial inflammatory response. This work suggests that a better control of the omega-6/omega-3 PUFA balance may represent an interesting target in the prevention and/or control of P. aeruginosa infection in patients.

Long-chain polyunsaturated fatty acids modulate lung inflammatory response induced by Pseudomonas aeruginosa in mice.

Polyunsaturated fatty acid (PUFA) immunomodulatory properties have been studied extensively in chronic infections. Few studies have focused on acute infection; thus, PUFA effects in a mouse model of Pseudomonas aeruginosa (PA)-induced lung injury were evaluated. C57BL/6 mice were randomized to be fed for 3 wk with an eicosapentaenoic acid (EPA) diet, an arachidonic acid (AA) diet, or a control diet [saturated fatty acids]. Lung injury was induced by intratracheal instillation of 10(7) CFU of PA per mouse. In each diet group, animals were studied either without or after PA-inducing lung injury. Evaluation criteria were early mortality; inflammatory response assessed with tumor necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6 and IL-10 levels in bronchoalveolar lavage; lung injury evaluation; and extravascular lung water, assessed 24 h after the injury. After PA-induced lung injury, no difference in early mortality was observed; TNF-alpha level was significantly higher in the EPA diet than in the other two diet groups. No difference for the other cytokines was found among the groups. Lung edema was also more important in the EPA group, consistent with the variations of TNF-alpha levels. Our study clearly shows that in PA-induced acute lung injury, n-3 PUFA induces differences in the inflammatory response with a higher level of lung edema. Modulation of the inflammatory response with n-3 PUFA can influence the response to a bacterial challenge.

Chronic bronchial allergic inflammation increases alveolar liquid clearance by TNF-alpha -dependent mechanism.

Bronchial inflammation in allergic asthma is associated with active exudation from the bronchial tree into the interstitial space of both mucosa and submucosa. The aim of this study was to evaluate epithelial and endothelial permeability as well as alveolar fluid movement in a model of chronic allergic inflammation in Brown-Norway rats sensitized and challenged with ovalbumin (OA). Control groups were challenged with saline solution (C), and rats were immunized by OA but not challenged (Se). Lung sections showed a marked inflammatory infiltrate associated with perivascular and peribronchiolar edema in OA. To measure alveolar liquid clearance, a 5% bovine albumin solution with 1 microCi of (125)I-labeled human albumin was instilled into the air spaces. Alveolar-capillary barrier permeability was evaluated by intravascular injection of 1 microCi of (131)I-labeled albumin. Endothelial permeability was significantly increased in OA, from 0.08 +/- 0.01 in the C group to 0.19 +/- 0.03 in OA group (P < 0.05). Final-to-initial protein ratio was also statistically higher in OA (1.6 +/- 0.05) compared with C (1.38 +/- 0.03, P = 0.01) and Se groups (1.42 +/- 0.03, P = 0.04). Administration of anti-tumor necrosis factor-alpha antibodies within the instillate significantly decreased this ratio (1.32 +/- 0.08, P = 0.003 vs. OA). To conclude, we demonstrated a tumor necrosis factor-alpha-dependent increase in alveolar fluid movement in a model of severe bronchial allergic inflammation associated with endothelial and epithelial leakage.