Lung function and inflammation during murine Pseudomonas aeruginosa airway infection

Change of Serum Inflammatory Cytokines Levels in Patients With Chronic Obstructive Pulmonary Disease, Pneumonia and Lung Cancer

Objective:

This study aimed to investigate the serum inflammatory cytokines levels in patients with COPD, pneumonia and lung cancer, and assess the correlation between the levels of inflammatory cytokines levels and development of these diseases.

Methods:

Two hundred thirty-two patients including 114 patients with pneumonia, 76 patients with chronic obstructive pulmonary disease (COPD) and 42 patients with lung cancer, and 62 age-matched healthy volunteers as controls were enrolled. The pro-inflammatory cytokine IL-6, IL-2, IFN-γ, TNF-α, anti-inflammatory cytokines IL-4 and IL-10 in serum were analyzed by flow cytometry microsphere array (CBA).

Results:

We found that the levels of TNF-α and IL-10 in patients with lung cancer, COPD and pneumonia were significantly higher than control group. The IL-6 in the lung cancer group were significantly increased compared with the controls and COPD group, pneumonia group. IFN-γ and IL-2 levels were lower in lung cancer compared with controls and COPD group, pneumonia group. TNF-α, IL-4 and IL-10 levels were increased in patients with COPD and pneumonia compared with controls. In addition, the concentrations of IFN-γ and IL-6 were increased in acute exacerbation COPD (AECOPD) group compared with stable COPD group.

Conclusion:

In conclusion, elevated TNF-α and IL-10 levels in serum may be related with lung diseases including lung cancer, COPD and pneumonia. Additionally, IFN-γ and IL-6 might be potential biomarkers for the further deterioration of lung disease patients. The increased concentrations of IFN-γ and IL-6 might be used to predict the exacerbation of COPD.

Pulmonary and systemic responses to aerosolized lysate of Staphylococcus aureus and Escherichia coli in calves

Background

Constitutive and inducible defenses protect the respiratory tract from bacterial infection. The objective of this study was to characterize the response to an aerosolized lysate of killed bacteria, as a basis for studying the regulation and in vivo effects of these inducible innate immune responses.

Results

Bacterial lysate consisting of heat-killed and sonicated Staphylococcus aureus and Escherichia coli was aerosolized to 6 calves and systemic and pulmonary innate immune and inflammatory responses were measured in the first 24 h relative to baseline. Evaluated parameters included clinical parameters (body temperature and heart and respiratory rates), blood acute phase proteins and leukocyte counts, and leukocytes and proteins in bronchoalveolar lavage fluid. Mild clinical signs with increased heart rates and rectal temperatures developed following administration of the lysate, with resolution by 24 h. Serum haptoglobin and plasma fibrinogen concentrations were elevated at 24 h relative to baseline. Bronchoalveolar lavage fluid (BALF) had increased cellularity and increased proportion of neutrophils, as well as higher concentrations of interleukin (IL)-8, IL-10 and total protein at 24 h relative to baseline. Mass spectrometry identified 965 unique proteins in BALF: 19 proteins were increased and 26 proteins were decreased relative to baseline. The upregulated proteins included those involved in innate immunity including activation of complement, neutrophils and platelets. At postmortem examination, calves receiving higher doses of lysate had areas of lobular consolidation and interlobular edema. Histologically, neutrophils were present within bronchioles and to a lesser extent within alveoli. Calves receiving highest doses of lysate had patchy areas of neutrophils, hemorrhage and hyaline membranes within alveoli.

Conclusions

Aerosolization of bacterial lysate stimulated an innate immune response in lungs and airways, with alveolar damage observed at higher doses. Such a stimulus could be of value for investigating the effects of inducible innate immune responses on occurrence of disease, or for evaluating how stress, drugs or genetics affect these dynamic responses of the respiratory tract.

Lung infection caused by Pseudomonas aeruginosa in a CD26/DPP4 deficient F344 rat model

Background

Pseudomonas aeruginosa (PA) is the most important opportunistic pathogen in causing nosocomial infections and, furthermore, poses a permanent threat for severe chronic infections in patients with cystic fibrosis or COPD. The transmembrane protein CD26 with dipeptidyl peptidase-4 (DPP4) activity shows an increased expression in inflamed tissue. We tested whether CD26/DPP4 deficiency leads to reduced inflammation and decreased structural damage when infected with PA.

Methods

CD26/DPP4⁺ and CD26/DPP4⁻ rats were instilled intratracheally with NaCl (controls) or with PA. Six hours later, bacterial distribution was detected with the in vivo imaging system 200 (IVIS). Lungs were then processed for molecular biology, light and electron microscopy and analyzed qualitatively, quantitatively and stereologically. Bacterial numbers were determined in homogenized lungs.

Results

Compared to saline treated controls, in both infected groups (1) the acinar airspace was significantly increased, (2) the volume density of the alveolar epithelium was significantly decreased, (3) the septal thickness was significantly reduced, (4) more than 40% of the alveolar epithelial surface was damaged, and up to 36% of the epithelial surface was covered with edema. In infected CD26⁻ rats, the increase in lung weight was significantly less pronounced, the portion of edematous alveolar airspace was significantly lower and the part of edema interspersed with PA was decreased significantly.

Conclusions

CD26/DPP4 deficiency resulted in reduced pulmonary edema under sublethal PA infection, implicating a role for CD26 in infection progression. The partly pronounced structural damage may mask further possible influences of CD26 on the inflammatory response.

PvdQ Quorum Quenching Acylase Attenuates Pseudomonas aeruginosa Virulence in a Mouse Model of Pulmonary Infection

Pseudomonas aeruginosa is the predominant pathogen in pulmonary infections associated with cystic fibrosis. Quorum sensing (QS) systems regulate the production of virulence factors and play an important role in the establishment of successful P. aeruginosa infections. Inhibition of the QS system (termed quorum quenching) renders the bacteria avirulent thus serving as an alternative approach in the development of novel antibiotics. Quorum quenching in Gram negative bacteria can be achieved by preventing the accumulation of N-acyl homoserine lactone (AHL) signaling molecule via enzymatic degradation. Previous work by us has shown that PvdQ acylase hydrolyzes AHL signaling molecules irreversibly, thereby inhibiting QS in P. aeruginosa in vitro and in a Caenorhabditis elegans model of P. aeruginosa infection. The aim of the present study is to assess the therapeutic efficacy of intranasally instilled PvdQ acylase in a mouse model of pulmonary P. aeruginosa infection. First, we evaluated the deposition pattern of intranasally administered fluorochrome-tagged PvdQ (PvdQ-VT) in mice at different stages of pulmonary infection by in vivo imaging studies. Following intranasal instillation, PvdQ-VT could be traced in all lung lobes with 42 ± 7.5% of the delivered dose being deposited at 0 h post-bacterial-infection, and 34 ± 5.2% at 72 h post bacterial-infection. We then treated mice with PvdQ during lethal P. aeruginosa pulmonary infection and that resulted in a 5-fold reduction of lung bacterial load and a prolonged survival of the infected animals with the median survival time of 57 hin comparison to 42 h for the PBS-treated group. In a sublethal P. aeruginosa pulmonary infection, PvdQ treatment resulted in less lung inflammation as well as decrease of CXCL2 and TNF-α levels at 24 h post-bacterial-infection by 15 and 20%, respectively. In conclusion, our study has shown therapeutic efficacy of PvdQ acylase as a quorum quenching agent during P. aeruginosa infection.

Bacterial Nucleotidyl Cyclase Inhibits the Host Innate Immune Response by Suppressing TAK1 Activation

Exoenzyme Y (ExoY) is a type III secretion system effector found in 90% of the Pseudomonas aeruginosa isolates. Although it is known that ExoY is a soluble nucleotidyl cyclase that increases the cytoplasmic levels of nucleoside 3',5'-cyclic monophosphates (cNMPs) to mediate endothelial Tau phosphorylation and permeability, its functional role in the innate immune response is still poorly understood. Transforming growth factor β-activated kinase 1 (TAK1) is critical for mediating Toll-like receptor (TLR) signaling and subsequent activation of NF-κB and AP-1, which are transcriptional activators of innate immunity. Here, we report that ExoY inhibits proinflammatory cytokine production through suppressing the activation of TAK1 as well as downstream NF-κB and mitogen-activated protein (MAP) kinases. Mice infected with ExoY-deficient P. aeruginosa had higher levels of tumor necrosis factor (TNF) and interleukin-6 (IL-6), more neutrophil recruitment, and a lower bacterial load in lung tissue than mice infected with wild-type P. aeruginosa Taken together, our findings identify a previously unknown mechanism by which P. aeruginosa ExoY inhibits the host innate immune response.

Inflammation: A Double-Edged Sword in the Response to Pseudomonas aeruginosa Infection

The Gram-negative opportunistic pathogen Pseudomonas aeruginosa exploits failures of barrier defense and innate immunity to cause acute infections at a range of anatomic sites. We review the defense mechanisms that normally protect against P. aeruginosa pulmonary infection, as well as the bacterial products and activities that trigger their activation. Innate immune recognition of P. aeruginosa is critical for pathogen clearance; nonetheless, inflammation is also associated with pathogen persistence and poor host outcomes. We describe P. aeruginosa adaptations that improve this pathogen's fitness in the inflamed airway, and briefly discuss strategies to manipulate inflammation to benefit the host. Such adjunct therapies may become increasingly important in the treatment of acute and chronic infections caused by this multi-drug-resistant pathogen.

Understanding the acute inflammatory response to Pseudomonas aeruginosa infection: differences between susceptible and multidrug-resistant strains in a mouse peritonitis model

The increasing emergence of multidrug-resistant (MDR) Pseudomonas aeruginosa strains is associated with the spread of a few international epidemic clones called high-risk clones. The existence of a fitness cost associated with multidrug resistance remains unclear, and little is known about the host inflammatory response in acute P. aeruginosa infections. This study aimed to investigate how the inflammatory response occurs in the most relevant high-risk clones and to compare the process with that recorded in clinical susceptible isolates. Nine P. aeruginosa strains were studied, including the most relevant MDR high-risk clones (ST111, ST175 and ST235) circulating worldwide. The inflammatory response in terms of the release of interleukins in serum was investigated in a mouse peritonitis-sepsis model at three time points (4, 8 and 12 h). TNFα and interleukin-10 (IL-10) levels were significantly higher at all time points in mice inoculated with clinical susceptible strains compared with those inoculated with MDR strains. IL-6 levels were significantly higher in the clinical susceptible strain group at 8 h and 12 h (P = 0.036 and P = 0.007, respectively). Bacterial counts (log CFU/mL) in peritoneal fluid were higher in the clinical susceptible strain group compared with the MDR strain group at 8 h [6.00 (4.30-6.90) vs. 4.46 (3.30-5.34); P = 0.005] and 12 h [7.75 (4.00-7.97) vs. 4.04 (2.58-4.94); P = 0.003]. MDR P. aeruginosa strains elicited a weaker inflammatory response than susceptible strains in an experimental mouse model, suggesting the existence of a fitness cost associated with multidrug resistance.

IL-17A-mediated expression of epithelial IL-17C promotes inflammation during acute Pseudomonas aeruginosa pneumonia

Lung epithelial cells are suggested to promote pathogen-induced pulmonary inflammation by the release of chemokines, resulting in enhanced recruitment of circulating leukocytes. Recent studies have shown that the interleukin-17C (IL-17C) regulates innate immune functions of epithelial cells in an autocrine manner. The aim of this study was to investigate the contribution of IL-17C to pulmonary inflammation in a mouse model of acute Pseudomonas aeruginosa pneumonia. Infection with P. aeruginosa resulted in an increased expression of IL-17C in lung tissue of wild-type mice. Numbers of neutrophils and the expression of the neutrophil-recruiting chemokines keratinocyte-derived chemokine and macrophage inflammatory protein 2 were significantly decreased in lungs of IL-17C-deficient (IL-17C^-/-) mice infected with P. aeruginosa at 24 h. Systemic concentrations of interleukin-6 (IL-6) were significantly decreased in infected IL-17C^-/- mice at 24 h and the survival of IL-17C^-/- mice was significantly increased at 48 h. The expression of IL-17C was reduced in infected mice deficient for interleukin-17A (IL-17A), whereas pulmonary concentrations of IL-17A were not affected by the deficiency for IL-17C. Stimulation of primary alveolar epithelial cells with IL-17A resulted in a significantly increased expression of IL-17C in vitro. Our data suggest that IL-17A-mediated expression of epithelial IL-17C amplifies the release of chemokines by epithelial cells and thereby contributes to the recruitment of neutrophils and systemic inflammation during acute P. aeruginosa pneumonia.

IL-17A attracts inflammatory cells in murine lung infection with P. aeruginosa

IL-17A-dependent immunity is of importance in the protection against extracellular bacterial pathogens. However, IL-17A is also suggested to mediate the pathogenesis of lung diseases, such as acute respiratory distress syndrome. Here, we studied the role of IL-17A in a mouse model of acute pneumonia. IL-17A mediated the expression of keratinocyte-derived chemokine (KC) and the recruitment of inflammatory cells in mice infected with a sub-lethal dose of Pseudomonas aeruginosa. IL-17A deficiency protected mice from lethal P. aeruginosa lung infection. A sub-lethal infection with Streptococcus pneumoniae resulted in increased bacterial burden associated with increased pulmonary inflammation. Thus, the type of infectious bacteria seemed to influence the way in which IL-17A functions during pulmonary infection. Reducing pulmonary inflammation by targeting IL-17A may be a therapeutic option in acute P. aeruginosa pneumonia.

Possible mechanisms of Pseudomonas aeruginosa-associated lung disease

Pseudomonas aeruginosa is an opportunistic bacterium causing lung injury in immunocompromised patients correlated with high morbidity and mortality. Many bacteria, including P. aeruginosa, use extracellular signals to synchronize group behaviors, a process known as quorum sensing (QS). In the P. aeruginosa complex QS system controls expression of over 300 genes, including many involved in host colonization and disease. P. aeruginosa infection elicits a complex immune response due to a large number of immunogenic factors present in the bacteria or released during infection. Here, we focused on the mechanisms by which P. aeruginosa triggers lung injury and inflammation, debating the possible ways that P. aeruginosa evades the host immune system, which leads to immune suppression and resistance.

Imaging regional lung function: a critical tool for developing inhaled antimicrobial therapies

Alterations in regional lung function due to respiratory infection have a significant effect on the deposition of inhaled treatments. This has consequences for treatment effectiveness and hence recovery of lung function. In order to advance our understanding of respiratory infection and inhaled treatment delivery, we must develop imaging techniques that can provide regional functional measurements of the lung. In this review, we explore the role of functional imaging for the assessment of respiratory infection and development of inhaled treatments. We describe established and emerging functional lung imaging methods. The effect of infection on lung function is described, and the link between regional disease, function, and inhaled treatments is discussed. The potential for lung function imaging to provide unique insights into the functional consequences of infection, and its treatment, is also discussed.

Probenecid reduces infection and inflammation in acute Pseudomonas aeruginosa pneumonia

The activation of inflammasome signaling mediates pathology of acute Pseudomonas aeruginosa pneumonia. This suggests that the inflammasome might represent a target to limit the pathological consequences of acute P. aeruginosa lung infection. Pannexin-1 (Px1) channels mediate the activation of caspase-1 and release of IL-1β induced by P2X7 receptor activation. The approved drug probenecid is an inhibitor of Px1 and ATP release. In this study, we demonstrate that probenecid reduces infection and inflammation in acute P. aeruginosa pneumonia. Treatment of mice prior to infection with P. aeruginosa resulted in an enhanced clearance of P. aeruginosa and reduced levels of inflammatory mediators, such as IL-1β. In addition, probenecid inhibited the release of inflammatory mediators in murine alveolar macrophages and human U937 cell-derived macrophages upon bacterial infection but not in human bronchial epithelial cells. Thus, Px1 blockade via probenecid treatment may be a therapeutic option in P. aeruginosa pneumonia by improving bacterial clearance and reducing negative consequences of inflammation.

Low-dose recombinant properdin provides substantial protection against Streptococcus pneumoniae and Neisseria meningitidis infection

Modern medicine has established three central antimicrobial therapeutic concepts: vaccination, antibiotics, and, recently, the use of active immunotherapy to enhance the immune response toward specific pathogens. The efficacy of vaccination and antibiotics is limited by the emergence of new pathogen strains and the increased incidence of antibiotic resistance. To date, immunotherapy development has focused mainly on cytokines. Here we report the successful therapeutic application of a complement component, a recombinant form of properdin (Pn), with significantly higher activity than native properdin, which promotes complement activation via the alternative pathway, affording protection against N. menigitidis and S. pneumoniae. In a mouse model of infection, we challenged C57BL/6 WT mice with N. menigitidis B-MC58 6 h after i.p. administration of Pn (100 µg/mouse) or buffer alone. Twelve hours later, all control mice showed clear symptoms of infectious disease while the Pn treated group looked healthy. After 16 hours, all control mice developed sepsis and had to be culled, while only 10% of Pn treated mice presented with sepsis and recoverable levels of live Meningococci. In a parallel experiment, mice were challenged intranasally with a lethal dose of S. pneumoniae D39. Mice that received a single i.p. dose of Pn at the time of infection showed no signs of bacteremia at 12 h postinfection and had prolonged survival times compared with the saline-treated control group (P < 0.0001). Our findings show a significant therapeutic benefit of Pn administration and suggest that its antimicrobial activity could open new avenues for fighting infections caused by multidrug-resistant neisserial or streptococcal strains.

Assessing Pseudomonas virulence using mammalian models: acute infection model

The acute murine lung infection model monitors Pseudomonas aeruginosa airway infections by multiple continuous and endpoint parameters. After intratracheal or intranasal infection it characterizes the course of infection via head-out spirometry, rectal temperature, weight loss, a body condition score based on nine physiological parameters, lung bacterial numbers, organ dissemination of bacteria, and a semiquantitative assessment of lung inflammation and further analysis. The generated data allows a robust classification of virulence of mutant or wild-type P. aeruginosa strains and/or of the susceptibility of wild-type or engineered mouse strains to infection. If standardized, the model is applicable to the preclinical assessment of antipseudomonal prevention and intervention strategies.

Modular strategies for structure and function employed by marine cyanobacteria: characterization and synthesis of pitinoic acids

Novel bioactive lipids were identified from a Guamanian cyanobacterium, the Pseudomonas aeruginosa quorum sensing inhibitor pitinoic acid A (1) and the anti-inflammatory pitinoic acids B (2) and C. The structure of 2 was confirmed by synthesis, which also allowed for biological evaluation. Since 2 is an ester of pitinoic acids A and C, it represents a prodrug strategy to liberate dual biological activity for the management of P. aeruginosa infections and their associated inflammation.

In vivo efficacy of biapenem with ME1071, a novel metallo-β-lactamase (MBL) inhibitor, in a murine model mimicking ventilator-associated pneumonia caused by MBL-producing Pseudomonas aeruginosa

ME1071, a maleic acid derivative, is a novel, specific inhibitor of metallo-β-lactamases (MBLs). In vitro, ME1071 can potentiate the activity of carbapenems against MBL-producing Pseudomonas aeruginosa. To confirm the clinical efficacy of ME1071 in ventilator-associated pneumonia (VAP) caused by MBL-producing P. aeruginosa, a mouse model that mimics VAP by placement of a plastic tube in the bronchus was used. Biapenem (100 mg/kg) or ME1071 plus biapenem (each 100 mg/kg) was administered intraperitoneally every 12 h beginning at 12 h after inoculation. Survival was evaluated over 7 days. At 30 h post infection, mice were sacrificed and the numbers of viable bacteria in the lungs and bronchoalveolar lavage fluid (BALF) were compared. Histopathological analysis of lung specimens was also performed. The pharmacokinetics of ME1071 was analysed after initial treatment. The ME1071 plus biapenem combination group displayed significantly longer survival compared with the control and biapenem monotherapy groups (P<0.05). Furthermore, the number of viable bacteria in the lungs was significantly lower in the combination group (P<0.05). Histopathological examination of lung specimens indicated that progression of lung inflammation was prevented in the combination group. Furthermore, total cell and neutrophil counts, as well as cytokine levels, in BALF were significantly decreased (P<0.05) in the combination group. The percentage time above the MIC (%T>MIC) for biapenem without ME1071 was 0% in plasma; however, this value was elevated to 10.8% with ME1071. These results suggest that ME1071 is potent and effective for treatment of VAP caused by MBL-producing P. aeruginosa.

Manuka honey: an emerging natural food with medicinal use

The health value of honey is universally acknowledged from time immemorial. Manuka (Leptospermum scoparium) is a tree, indigenous to New Zealand and South East Australia, and from the myrtle family, Myrtaceae. The honey produced from its flowers is a uni-floral honey largely produced in New Zealand. It is becoming increasingly popular as a functional food, seen in the aisles of health stores as its displays superior nutritional and phytochemistry profile over other varieties of honey. Examining existing research databases revealed its biological properties ranging from anti-oxidant, anti-inflammatory, anti-bacterial, anti-viral, anti-biotic and wound healing to immune-stimulatory properties. Methylglyoxal is the unique compound in the honey responsible for some of its potent anti-microbial properties. Further, propolis another component of honey contains chiefly flavonoids (i.e. galangin, pinocembrin), phenolic acids and their esters that may also contribute to its immuno-stimulant properties. Recent findings of the biological roles have been discussed with emphasis on the underlying mechanisms. The hurdles associated in its development as a functional food and also nutraceutical with future scopes have also been mentioned. Relevant data published in MEDLINE, Cochrane library, and EMBASE in the past decade have been gathered to formulate this review.

MudPIT analysis of released proteins in Pseudomonas aeruginosa laboratory and clinical strains in relation to pro-inflammatory effects

Pseudomonas aeruginosa (Pa) is the most common virulent pathogen contributing to the pathogenesis of cystic fibrosis (CF). During bacterial lung colonization, the products of its metabolism are released in the extracellular space contributing to the pathogenic events associated with its presence. To gain insights on the mechanisms involved in the Pa pathogenesis we focused our attention on proteins released by Pa using a MudPIT approach combined with cell biology assays. Conditioned medium (CM) collected under aerobic and microaerobic conditions from Pa clinical strains (in early and late colonization), unlike the laboratory strain, induced expression of IL-8 mRNA in CF airway epithelial cells. We have identified proteins released by clinically relevant Pa strains, focusing on the pro-inflammatory effects as metalloproteases (MMPs). In fact, their expression pattern was associated with the highest pro-inflammatory activity measured in the early clinically isolated strain. The relation was further supported by the result of the analysis of a larger and independent set of Pa isolates derived from sporadically and chronically infected CF patients: 76% of sporadic samples expressed protease activity (n = 44), while only 27% scored positive in the chronically infected individuals (n = 38, p < 0.0001, Fisher's exact test). Finally, looking for a possible mechanism of action of bacterial MMPs, we found that CM from early clinical isolates can cleave CXCR1 on the surface of human neutrophils, suggesting a potential role for the bacterially released MMPs in the protection of the pathogen from the host's response.

Innate immune responses to Pseudomonas aeruginosa infection

Innate immune responses play a critical role in controlling acute infections due to Pseudomonas aeruginosa in both mice and in humans. In this review we focus on innate immune recognition and clearance mechanisms that are important for controlling P. aeruginosa in the mammalian lung, with particular attention to those that influence the outcome of in vivo infection in murine models.