Dexamethasone impairs pulmonary defence against Pseudomonas aeruginosa through suppressing iNOS gene expression and peroxynitrite production in mice

Ohr - OhrR, a neglected and highly efficient antioxidant system: Structure, catalysis, phylogeny, regulation, and physiological roles

Ohrs (organic hydroperoxide resistance proteins) are antioxidant enzymes that play central roles in the response of microorganisms to organic peroxides. Here, we describe recent advances in the structure, catalysis, phylogeny, regulation, and physiological roles of Ohr proteins and of its transcriptional regulator, OhrR, highlighting their unique features. Ohr is extremely efficient in reducing fatty acid peroxides and peroxynitrite, two oxidants relevant in host-pathogen interactions. The highly reactive Cys residue of Ohr, named peroxidatic Cys (C_p), composes together with an arginine and a glutamate the catalytic triad. The catalytic cycle of Ohrs involves a condensation between a sulfenic acid (C_p-SOH) and the thiol of the second conserved Cys, leading to the formation of an intra-subunit disulfide bond, which is then reduced by dihydrolipoamide or lipoylated proteins. A structural switch takes place during catalysis, with the opening and closure of the active site by the so-called Arg-loop. Ohr is part of the Ohr/OsmC super-family that also comprises OsmC and Ohr-like proteins. Members of the Ohr, OsmC and Ohr-like subgroups present low sequence similarities among themselves, but share a high structural conservation, presenting two Cys residues in their active site. The pattern of gene expression is also distinct among members of the Ohr/OsmC subfamilies. The expression of ohr genes increases upon organic hydroperoxides treatment, whereas the signals for the upregulation of osmC are entry into the stationary phase and/or osmotic stress. For many ohr genes, the upregulation by organic hydroperoxides is mediated by OhrR, a Cys-based transcriptional regulator that only binds to its target DNAs in its reduced state. Since Ohrs and OhrRs are involved in virulence of some microorganisms and are absent in vertebrate and vascular plants, they may represent targets for novel therapeutic approaches based on the disruption of this key bacterial organic peroxide defense system.

Pleiotropic Effects of Glucocorticoids on the Immune System in Circadian Rhythm and Stress

Glucocorticoids (GCs) are a class of steroid hormones secreted from the adrenal cortex. Their production is controlled by circadian rhythm and stress, the latter of which includes physical restraint, hunger, and inflammation. Importantly, GCs have various effects on immunity, metabolism, and cognition, including pleiotropic effects on the immune system. In general, GCs have strong anti-inflammatory and immunosuppressive effects. Indeed, they suppress inflammatory cytokine expression and cell-mediated immunity, leading to increased risks of some infections. However, recent studies have shown that endogenous GCs induced by the diurnal cycle and dietary restriction enhance immune responses against some infections by promoting the survival, redistribution, and response of T and B cells via cytokine and chemokine receptors. Furthermore, although GCs are reported to reduce expression of Th2 cytokines, GCs enhance type 2 immunity and IL-17-associated immunity in some stress conditions. Taken together, GCs have both immunoenhancing and immunosuppressive effects on the immune system.

Impact of dexamethasone on the incidence of ventilator-associated pneumonia and blood stream infections in COVID-19 patients requiring invasive mechanical ventilation: a multicenter retrospective study

Background

Dexamethasone decreases mortality in patients with severe coronavirus disease 2019 (COVID-19) and has become the standard of care during the second wave of pandemic. Dexamethasone is an immunosuppressive treatment potentially increasing the risk of secondary hospital acquired infections in critically ill patients. We conducted an observational retrospective study in three French intensive care units (ICUs) comparing the first and second waves of pandemic to investigate the role of dexamethasone in the occurrence of ventilator-associated pneumonia (VAP) and blood stream infections (BSI). Patients admitted from March to November 2020 with a documented COVID-19 and requiring mechanical ventilation (MV) for ≥ 48 h were included. The main study outcomes were the incidence of VAP and BSI according to the use of dexamethasone. Secondary outcomes were the ventilator-free days (VFD) at day-28 and day-60, ICU and hospital length of stay and mortality.

Results

Among the 151 patients included, 84 received dexamethasone, all but one during the second wave. VAP occurred in 63% of patients treated with dexamethasone (DEXA+) and 57% in those not receiving dexamethasone (DEXA−) (p = 0.43). The cumulative incidence of VAP, considering death, duration of MV and late immunosuppression as competing factors was not different between groups (p = 0.59). A multivariate analysis did not identify dexamethasone as an independent risk factor for VAP occurrence. The occurrence of BSI was not different between groups (29 vs. 30%; p = 0.86). DEXA+ patients had more VFD at day-28 (9 (0–21) vs. 0 (0–11) days; p = 0.009) and a reduced ICU length of stay (20 (11–44) vs. 32 (17–46) days; p = 0.01). Mortality did not differ between groups.

Conclusions

In this cohort of COVID-19 patients requiring invasive MV, dexamethasone was not associated with an increased incidence of VAP or BSI. Dexamethasone might not explain the high rates of VAP and BSI observed in critically ill COVID-19 patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00876-8.

Dexamethasone along with ciprofloxacin modulates S. aureus induced microglial inflammation via glucocorticoid (GC)-GC receptor-mediated pathway

Microglial inflammation is the hallmark of S. aureus induced brain abscesses. Conventional antibiotic therapy could not regulate inflammation and the use of steroids in CNS infection remained controversial. To address this issue the effect of dexamethasone along with ciprofloxacin on microglial inflammation has been attempted both in glucocorticoid receptor (GR) opened and blocked condition. We have investigated the effects of ciprofloxacin (0.24 μg/ml, pre-treatment) and dexamethasone (150 nM, pre-treatment) in combination with murine microglia infected with S. aureus for 30, 60 and 90 min by either keeping GR opened or blocked with GR antagonist RU486. Alterations in cellular motility, intracellular killing assay, free radical production, antioxidant enzyme activities, corticosterone, and cytokine levels were determined. The expressions of TLR-2, GR, and other inflammatory markers were determined in terms of this combinatorial treatment. Combination treatment significantly (p < 0.05) reduced the bacterial burden of microglia only when GR remained open and effectively suppressed S. aureus induced oxidative stress by augmenting SOD and catalase enzyme activity and suppressing other pro-inflammatory markers at 90 min. Arginase activity, a critical determinant of microglial polarization was found to be higher after treatment at 60 and 90 min. This situation was reversed when this combination treatment was applied by keeping GR blocked using GR antagonist RU486. Therefore, it can be concluded that combination treatment of ciprofloxacin and dexamethasone could regulate S. aureus induced microglial activation, in the presence of functional GR via utilizing glucocorticoid (GC)-GR pathway and ultimately confers protection to the host from brain inflammation.

The nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO), increases survival by attenuating hyperoxia-compromised innate immunity in bacterial clearance in a mouse model of ventilator-associated pneumonia

Mechanical ventilation (MV) with supraphysiological levels of oxygen (hyperoxia) is a life-saving therapy for the management of patients with respiratory distress. However, a significant number of patients on MV develop ventilator-associated pneumonia (VAP). Previously, we have reported that prolonged exposure to hyperoxia impairs the capacity of macrophages to phagocytize Pseudomonas aeruginosa (PA), which can contribute to the compromised innate immunity in VAP. In this study, we show that the high mortality rate in mice subjected to hyperoxia and PA infection was accompanied by a significant decrease in the airway levels of nitric oxide (NO). Decreased NO levels were found to be, in part, due to a significant reduction in NO release by macrophages upon exposure to PA lipopolysaccharide (LPS). Based on these findings, we postulated that NO supplementation should restore hyperoxia-compromised innate immunity and decrease mortality by increasing the clearance of PA under hyperoxic conditions. To test this hypothesis, cultured macrophages were exposed to hyperoxia (95% O₂) in the presence or absence of the NO donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO). Interestingly, D-NO (up to 37.5 µM) significantly attenuated hyperoxia-compromised macrophage migratory, phagocytic, and bactericidal function. To determine whether the administration of exogenous NO enhances the host defense in bacteria clearance, C57BL/6 mice were exposed to hyperoxia (99% O₂) and intranasally inoculated with PA in the presence or absence of D-NO. D-NO (300 µM-800 µM) significantly increased the survival of mice inoculated with PA under hyperoxic conditions, and significantly decreased bacterial loads in the lung and attenuated lung injury. These results suggest the NO donor, D-NO, can improve the clinical outcomes in VAP by augmenting the innate immunity in bacterial clearance. Thus, provided these results can be extrapolated to humans, NO supplementation may represent a potential therapeutic strategy for preventing and treating patients with VAP.

Effects of Antirejection Drugs on Innate Immune Cells After Kidney Transplantation

Over the last decades, our understanding of adaptive immune responses to solid organ transplantation increased considerably and allowed development of immunosuppressive drugs targeting key alloreactive T cells mechanism. As a result, rates of acute rejection dropped and short-term graft survival improved significantly. However, long-term outcomes are still disappointing. Recently, increasing evidence supports that innate immune responses plays roles in allograft rejection and represents a valuable target to further improve long-term allograft survival. Innate immune cells are activated by molecules with stereotypical motifs produced during injury (i.e., damage-associated molecular patterns, DAMPS) or infection (i.e., pathogen-associated molecular patterns, PAMPs). Activated innate immune cells can exert direct pro- and anti-inflammatory effects, while also priming adaptive immune responses. These cells are activated after transplantation by multiple stimuli, including ischemia-reperfusion injury, rejection, and infections. Data from animal models of graft rejection, show that inhibition of innate immunity promotes development of tolerance. Therefore, understanding mechanisms of innate immunity is important to improve graft outcomes. This review discusses effects of currently used immunosuppressive agents on innate immune responses in kidney transplantation.

How Glucocorticoids Affect the Neutrophil Life

Glucocorticoids are hormones that regulate several functions in living organisms and synthetic glucocorticoids are the most powerful anti-inflammatory pharmacological tool that is currently available. Although glucocorticoids have an immunosuppressive effect on immune cells, they exert multiple and sometimes contradictory effects on neutrophils. From being extremely sensitive to the anti-inflammatory effects of glucocorticoids to resisting glucocorticoid-induced apoptosis, neutrophils are proving to be more complex than they were earlier thought to be. The aim of this review is to explain these complex pathways by which neutrophils respond to endogenous or to exogenous glucocorticoids, both under physiological and pathological conditions.

Treatment of infected lungs by ex vivo perfusion with high dose antibiotics and autotransplantation: A pilot study in pigs

The emergence of multi-drug resistant bacteria threatens to end the era of antibiotics. Drug resistant bacteria have evolved mechanisms to overcome antibiotics at therapeutic doses and further dose increases are not possible due to systemic toxicity. Here we present a pilot study of ex vivo lung perfusion (EVLP) with high dose antibiotic therapy followed by autotransplantation as a new therapy of last resort for otherwise incurable multidrug resistant lung infections. Severe Pseudomonas aeruginosa pneumonia was induced in the lower left lungs (LLL) of 18 Mini-Lewe pigs. Animals in the control group (n = 6) did not receive colistin. Animals in the conventional treatment group (n = 6) received intravenous application of 2 mg/kg body weight colistin daily. Animals in the EVLP group (n = 6) had their LLL explanted and perfused ex vivo with a perfusion solution containing 200 μg/ml colistin. After two hours of ex vivo treatment, autotransplantation of the LLL was performed. All animals were followed for 4 days following the initiation of treatment. In the control and conventional treatment groups, the infection-related mortality rate after five days was 66.7%. In the EVLP group, there was one infection-related mortality and one procedure-related mortality, for an overall mortality rate of 33.3%. Moreover, the clinical symptoms of infection were less severe in the EVLP group than the other groups. Ex vivo lung perfusion with very high dose antibiotics presents a new therapeutic option of last resort for otherwise incurable multidrug resistant pneumonia without toxic side effects on other organs.

Ohr plays a central role in bacterial responses against fatty acid hydroperoxides and peroxynitrite

Organic hydroperoxide resistance (Ohr) enzymes are unique Cys-based, lipoyl-dependent peroxidases. Here, we investigated the involvement of Ohr in bacterial responses toward distinct hydroperoxides. In silico results indicated that fatty acid (but not cholesterol) hydroperoxides docked well into the active site of Ohr from Xylella fastidiosa and were efficiently reduced by the recombinant enzyme as assessed by a lipoamide-lipoamide dehydrogenase-coupled assay. Indeed, the rate constants between Ohr and several fatty acid hydroperoxides were in the 10⁷-10⁸ M^-1⋅s^-1 range as determined by a competition assay developed here. Reduction of peroxynitrite by Ohr was also determined to be in the order of 10⁷ M^-1⋅s^-1 at pH 7.4 through two independent competition assays. A similar trend was observed when studying the sensitivities of a ∆ohr mutant of Pseudomonas aeruginosa toward different hydroperoxides. Fatty acid hydroperoxides, which are readily solubilized by bacterial surfactants, killed the ∆ohr strain most efficiently. In contrast, both wild-type and mutant strains deficient for peroxiredoxins and glutathione peroxidases were equally sensitive to fatty acid hydroperoxides. Ohr also appeared to play a central role in the peroxynitrite response, because the ∆ohr mutant was more sensitive than wild type to 3-morpholinosydnonimine hydrochloride (SIN-1 , a peroxynitrite generator). In the case of H₂O₂ insult, cells treated with 3-amino-1,2,4-triazole (a catalase inhibitor) were the most sensitive. Furthermore, fatty acid hydroperoxide and SIN-1 both induced Ohr expression in the wild-type strain. In conclusion, Ohr plays a central role in modulating the levels of fatty acid hydroperoxides and peroxynitrite, both of which are involved in host-pathogen interactions.

Progress towards next-generation therapeutics for cystic fibrosis

Cystic fibrosis (CF) is the most common inherited genetic condition amongst Caucasian ethnicities, affecting 1 in 2500 live births. There remains a significant unmet medical need for more and better therapies for this chronic, degenerative condition, in particular those that address the respiratory dysfunction and respiratory infections that characterise CF. CF is caused by mutations in the cystic transmembrane conductance regulator gene (CFTR). The key pathology driver of CF is dysregulated ion transport across the epithelial cell barriers that line the respiratory tract, gastrointestinal tract and other organ systems. This review focuses on the state-of-the-art advances and future directions in therapeutic strategies to combat and manage the symptoms of CF and/or restore functionality of the defective CFTR.

Inhaled fluticasone propionate impairs pulmonary clearance of Klebsiella pneumoniae in mice

Background

Recent trials demonstrate increased pneumonia risk in chronic obstructive pulmonary disease patients treated with the inhaled corticosteroid (ICS) fluticasone propionate (FP). There is limited work describing FP effects on host defenses against bacterial pneumonia.

Methods

C57BL/6 mice received daily, nose-only exposure to nebulized FP or vehicle for 8 days, followed by pulmonary challenge with Klebsiella pneumoniae. Bacterial burden, phagocytosis, leukocyte recruitment, cytokine expression, nitric oxide release, and survival were measured.

Results

Inhaled FP increased bacterial burden in lungs and blood 48 h after infection but affected neither in vivo phagocytosis of bacteria by alveolar macrophages (AM) nor alveolar neutrophil recruitment. AM from FP-treated mice showed impaired expression of infection induced TNF-alpha, IP-10 (CXCL-10), and interleukin 6 (IL-6), and AM also showed a trend towards impaired intracellular pathogen control following in vivo infection. In vitro FP treatment resulted in a dose-dependent impairment of cytokine expression by AM. Furthermore, infection-induced nitric oxide (but not hydrogen peroxide) production was impaired by FP in vivo and in vitro. FP decreased survival in this model.

Conclusions

Exposure to inhaled FP impairs pulmonary clearance of K. pneumoniae in mice, an effect associated with greater systemic bacteremia and death. Decreased AM cytokine and nitric oxide expression parallel the failure to control infection. These results support the study of ICS effects on human pulmonary host defenses.

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.

Functional genomics to identify therapeutic prophylactic targets

Infectious diseases are a leading cause of global human mortality. The use of antimicrobials remains the most common strategy for treatment. However, the isolation of pathogens resistant to virtually all antimicrobials makes it urgent to develop effective therapeutics based on new targets. Here we review a new drug discovery paradigm focusing on identifying and targeting host factors important for infection as well as pathogen determinants involved in disease progression. We summarize innovative strategies which by combining bioinformatics with transcriptomics and chemical genetics have already identified host factors essential for pathogen entry, survival and replication. We describe how the discovery of RNA interference which allows loss-of-function studies has facilitated functional genomic studies in human cells. It is expected that these studies will identify targets to be used as host-directed drug therapy which, together with antimicrobials targeting microbial virulence factors, will efficiently eliminate the invading pathogen.

Dexamethasone suppresses interleukin-22 associated with bacterial infection in vitro and in vivo

Interleukin (IL)-22 production triggered by innate immune mechanisms has been identified as key to efficient intestinal anti-bacterial host defence and preservation of homeostasis. We hypothesized that glucocorticoid therapy may impair IL-22 expression, which should promote intestinal epithelial damage with the potential of subsequent bacterial translocation. High-dose corticosteroid therapy in Crohn's disease has been associated with an increased rate of abscess formation and ultimately with a higher risk of developing postoperative infectious complications, including abdominal sepsis. Thus, we sought to investigate effects of the prototypic glucocorticoid dexamethasone on IL-22 production in the context of bacterial infection. Enhanced IL-22 plasma levels were detectable in rat sepsis. Moreover, heat-inactivated Staphylococcus epidermidis, used as a prototypic activator of innate immunity, induced robust production of IL-22 by human peripheral blood mononuclear cells (PBMC). Here, we report for the first time that dexamethasone mediates remarkable suppression of IL-22 as detected in S. epidermidis-activated PBMC and rat sepsis, respectively. The data presented herein suggest that insufficient IL-22 function may contribute to impaired intestinal host defence in the context of corticosteroid therapy.

Bacteria challenge in smoke-exposed mice exacerbates inflammation and skews the inflammatory profile

RATIONALE

The pathogenesis of chronic obstructive pulmonary disease is associated with acute episodes of bacterial exacerbations. The most commonly isolated bacteria during episodes of exacerbation is nontypeable Haemophilus influenzae (NTHI).

OBJECTIVES

In this study, we investigated the in vivo consequences of cigarette smoke exposure on the inflammatory response to an NTHI challenge.

METHODS

C57BL/6 and BALB/c mice were exposed to cigarette smoke for 8 weeks and subsequently challenged intranasally with NTHI.

MEASUREMENTS AND MAIN RESULTS

We observed increased pulmonary inflammation and lung damage in cigarette smoke-exposed NTHI-challenged mice as compared with control NTHI-challenged mice. Furthermore, although NTHI challenge in control mice was marked by increases in tumor necrosis factor-alpha, IL-6, MIP-2, and KC/GROalpha, NTHI challenge in cigarette smoke-exposed mice led to a prominent up-regulation of a different subset of inflammatory mediators, most notably MCP-1, -3, and -5, IP-10, and MIP-1gamma. This skewed inflammatory mediator expression was also observed after ex vivo NTHI stimulation of alveolar macrophages, signifying their importance to this altered response. Importantly, corticosteroids attenuated inflammation after NTHI challenge in both cigarette smoke-exposed and control mice; however, this was associated with significantly increased bacterial burden.

CONCLUSIONS

Collectively, these data suggest that cigarette smoke exacerbates the inflammatory response to a bacterial challenge via skewed inflammatory mediator expression.

Critical Illness Stress-induced Immune Suppression

Despite the use of Centers for Disease Control and Prevention (CDC) recommended practices to minimize infection risk, nosocomial sepsis and multiple organ failure (MOF) remain a leading cause of morbidity and mortality in critically ill patients. It is well documented that the use of immunosuppressant therapies dramatically increases this risk in patients with cancer, transplantation, and immunologic disease. Although immune monitoring has yet to be universally embraced, withdrawal of immunosuppressant therapies and use of immune restoration therapies is the standard of care when these patients develop sepsis. Critical illness stress can also induce a level of immunosuppression which is as life-threatening as is seen in the purposefully immunosuppressed patient. This chapter reviews the role of critical illness stress-induced immunosuppression in the development of nosocomial sepsis and MOF, and outlines clinical strategies which can be employed to maintain and restore immune function, and reduce morbidity and mortality in critically ill patients.

Dynamics of dendritic cell migration and the subsequent induction of protective immunity in the lung after repeated airway challenges by nontypeable Haemophilus influenzae outer membrane protein

To determine the dynamics of dendritic cell (DCs) migration and their role in recurrent infections by nontypeable Haemophilus influenzae (NTHi), the migration of mature DC into pulmonary lymph nodes (LN) and the development of a P6-specific immune response and bacterial clearance in the lung were examined after repeated airway challenges with outer membrane protein (OMP) at 1-week intervals in mice. Although the migration of mature DC into the pulmonary LN is attenuated after repeated airway challenge with OMP, the in vitro P6-specific T cell proliferation in the cultured pulmonary LN cells was enhanced and was subsequently linked to the development of P6-specific IgA production and the development of protective immunity in the airway of mice.

Inflammatory mechanisms underlying the rat pulmonary neutrophil influx induced by airway exposure to staphylococcal enterotoxin type A

Association between staphylococcal infection and pathogenesis of upper airways disease has been reported. This study aimed to investigate the mechanisms underlying the rat pulmonary inflammation induced by airway exposure to staphylococcal enterotoxin A (SEA). SEA (0.3-10 ng trachea(-1)) caused dose-dependent neutrophil accumulation in BAL fluid, reaching maximal responses at 4 h (25-fold increase for 3 ng trachea(-1)). Significant accumulation of both lymphocytes and macrophages in BAL fluid was also observed at 4 h (2.1- and 1.9-fold increase, respectively, for 3 ng trachea(-1)). At later times (16 h), neutrophil counts in bone marrow (immature forms) and peripheral blood increased by 63 and 81%, respectively. SEA failed to directly induce chemotaxis and adhesion of isolated neutrophils. Analysis of mRNA expression for iNOS, COX-2 and CINC-2 in lung tissue showed an upregulation of these enzymes, which paralleled elevated levels of LTB4, PGE2, TNF-alpha, IL-6 and NO2- in BAL fluid. Expression of CINC-1 was unchanged, whereas CINC-3 was reduced in SEA-treated rats. Incubation of isolated alveolar macrophages with SEA (3 microg ml(-1)) resulted in significant elevations of TNF-alpha and NO2- levels in the cell supernatants. Dexamethasone (0.5 mg kg(-1)), celecoxib (3 mg kg(-1)) and compound 1400 W (5 mg kg(-1)) markedly reduced SEA-induced lung neutrophil influx and NO2- levels in BAL fluid. The lipoxygenase inhibitor AA-861 (100 microg kg(-1)) partly inhibited the neutrophil influx in SEA-treated rats without modifying the NO2- levels. None of these treatments reduced the number of mononuclear cells in BAL fluid (except of dexamethasone, which abolished the increased lymphocyte counts). Our study shows that airways exposure to SEA results in marked neutrophil influx through mechanisms involving increased expressions of CINC-2, iNOS and COX-2, as well as enhanced production of NO, PGE2, LTB4, TNF-alpha and IL-6.

The role of nitric oxide in resistance to P. aeruginosa ocular infection

PURPOSE

This study determined the role of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) in the resistance response of BALB/c mice to P. aeruginosa-induced keratitis.

METHODS

RT-PCR, nitrite detection, iNOS inhibition, ELISA, and immunohistochemistry were used.

RESULTS

Early after infection, iNOS mRNA expression and nitrite levels in cornea were elevated compared to levels in the uninfected cornea. Treatment with aminoguanidine sulfate (AG), an inhibitor of iNOS, resulted in extensive corneal destruction, reduced nitrite levels, and reduced nitrotyrosine staining. Infected mice also had increased bacterial burden and elevated levels of MIP-1alpha, IL-1beta, and MIP-2 in the cornea. Dual-labeling immunohistochemistry established the macrophage as the major source of iNOS in the infected cornea.

CONCLUSIONS

These data provide evidence that iNOS is constitutively expressed in the BALB/c cornea; that iNOS-derived NO is required for bacterial killing/stasis; and that the macrophage is the major cell source of NO.

Preoperative glucocorticoids decrease pulmonary hypertension in piglets after cardiopulmonary bypass and circulatory arrest

BACKGROUND

Glucocorticoids during cardiopulmonary bypass benefit pediatric patients undergoing repair of congenital heart defects and are routine therapy, but underlying mechanisms have not been fully examined. The hypothesis was that glucocorticoids could improve cardiopulmonary recovery after cardiopulmonary bypass and deep hypothermic circulatory arrest.

METHODS

Crossbred piglets (5 to 7 kg) were cooled with cardiopulmonary bypass, followed by 120-min deep hypothermic circulatory arrest. Animals were then warmed to 38 degrees C, removed from bypass, and maintained for 120 min. Methylprednisolone (60 mg/kg) was administered in the cardiopulmonary bypass pump prime (intraoperative glucocorticoids) or 6 hours before bypass (30 mg/kg) in addition to the intraoperative dose (30 mg/kg; preoperative and intraoperative glucocorticoids). Controls (no glucocorticoids) received saline.

RESULTS

Pulmonary vascular resistance in controls increased from a baseline of 152 +/- 40 to 364 +/- 29 dynes. s/cm(5) at 2 hours of recovery (p < 0.001). Intraoperative glucocorticoids did not alleviate the increase in pulmonary vascular resistance (301 +/- 55 dynes. s/cm(5) at 2 hours of recovery, p < 0.001). However, animals receiving pre and intraoperative glucocorticoids had no increase in pulmonary vascular resistance (155 +/- 54 dynes. s/cm(5)). Plasma endothelin-1 in controls increased from 1.3 +/- 0.2 at baseline to 9.9 +/- 2.0 pg/mL at 2 hours recovery (p < 0.01), whereas glucocorticoid-treated animals had lower endothelin-1 levels (4.5 +/- 2.1 pg/ml, preoperative and intraoperative glucocorticoids; 4.9 +/- 1.7 pg/mL, intraoperative glucocorticoids) at the end of recovery (p < 0.05). Intracellular adhesion molecule-1 in lung tissue was lower in animals receiving pre and intraoperative glucocorticoids (p < 0.05). Myeloperoxidase activity was elevated in control lungs at 2 hours of recovery compared with glucocorticoid-treated groups (p < 0.05). Inhibitor kappaBalpha, the inhibitor of nuclear factor-kappaB, was higher in lungs of animals receiving glucocorticoids compared with controls (p < 0.05).

CONCLUSIONS

Glucocorticoids prevented pulmonary hypertension after cardiopulmonary bypass and deep hypothermic circulatory arrest, which was associated with reduced plasma endothelin-1. Glucocorticoids also reduced pulmonary intercellular adhesion molecule-1 and myeloperoxidase activity. Inhibition of nuclear factor-kappaB, along with reduced neutrophil activation, contributed to glucocorticoid alleviation of pulmonary hypertension after cardiopulmonary bypass and deep hypothermic circulatory arrest.

Effects of nitric oxide on Pseudomonas aeruginosa infection of epithelial cells from a human respiratory cell line derived from a patient with cystic fibrosis

Cystic fibrosis (CF) is characterized by airway inflammation and chronic bacterial lung infection, most commonly with Pseudomonas aeruginosa, an opportunistic human pathogen. Despite the persistent airway inflammation observed in patients with CF, although phagocyte inducible nitric oxide synthase (iNOS) production is upregulated, expression of iNOS in the respiratory epithelium is markedly reduced. Given the antimicrobial action of NO, this may contribute to the chronic airway infection of this disease. To define the role of epithelium-derived NO in airway defense against P. aeruginosa, we infected differentiated human bronchial epithelial cells derived from a patient with CF (CFBE41o- cells) with different strains of this pathogen at low multiplicities of infection. Using cells transfected with human iNOS cDNA, we studied the effect of NO on P. aeruginosa replication, adherence, and internalization. P. aeruginosa adherence to iNOS-expressing cells was reduced by 44 to 72% (P = 0.02) compared with control values. Absolute P. aeruginosa uptake into these cells was reduced by 44%, but uptake expressed as a percentage of adherent bacteria did not differ from the control uptake. Survival of P. aeruginosa within iNOS-expressing cells was reduced at late times postinfection (P = 0.034). NO production did not alter host cell viability. NO production reduced P. aeruginosa adherence to human bronchial epithelial cells and enhanced killing of internalized bacteria, suggesting that a lack of epithelial iNOS in patients with CF may contribute to P. aeruginosa infection and colonization.

Pseudomonas aeruginosa pneumonia

PURPOSE OF REVIEW

Recent articles of clinical interest on Pseudomonas aeruginosa respiratory tract infections including CAP, nosocomially-acquired pneumonia, particularly in the ventilated patient, and chronic infections in cystic fibrosis patients are reviewed.

RECENT FINDINGS

The growing importance of P. aeruginosa as an etiologic agent of CAP, the occurrence of CAP in previously healthy adults and its high prevalence as an etiologic agent of late VAP are stressed in recent studies. The effect of antibiotics on the recovery of bacteria in respiratory samples of patients with VAP can be marked and as early as 12 h after administration of antimicrobials certain organisms are no longer cultivable; in contrast, P. aeruginosa can still be recovered even after 48 h of adequate therapy. Type III secretory proteins are recognized as important virulent factors in P. aeruginosa. This phenotype predicts a worse outcome in patients with VAP. Fluoroquinolones have a major role in the emergence of multiply resistant P. aeruginosa in patients with VAP. Pharmacokinetic/pharmacodynamic parameters of antimicrobials with antipseudomonal activity are gaining importance as a means of optimization of antibiotic therapy. In CF, the knowledge of the pharmacokinetics and bioavailability of inhaled tobramycin and its long term beneficial effect in lung function are important developments in this area.

SUMMARY

P. aeruginosa continues to be a serious problem worldwide as a cause of respiratory tract infections in selected populations. Microbiologic diagnosis remains difficult and plagued with pitfalls. The application of modern PK/PD concepts should help to optimize antibiotic therapy of this increasingly difficult to treat infection, particularly at the respiratory tract level and with an increasing prevalence of resistance to all antipseudomonal agents. Inhaled antibiotics, particularly tobramycin, are increasingly used for the prevention and treatment of P. aeruginosa infection in CF patients.

Fourteen-member macrolides promote the phosphatidylserine receptor-dependent phagocytosis of apoptotic neutrophils by alveolar macrophages

An inflammation of the airway of patients with diffuse panbronchiolitis (DPB), is characterized by dense neutrophil infiltration. Resolution of the inflammation can be achieved by the removal of apoptotic neutrophils by human alveolar macrophages (AM) without liberating neutrophil proteases in the airway. To understand clinical efficacy for the treatment of DPB by 14- or 15-member macrolides, their effects on the phagocytosis of apoptotic neutrophils by AM were examined. Treatment of AM with erythromycin (ERY) or clarithromycin at clinically achievable levels significantly increased the levels of phagocytosis of apoptotic neutrophils. A serum factor was not essential for the enhancement by these 14-member macrolides. Of the antibiotics tested, these effects were specific for the 14-member macrolides and a 15-member macrolide, azithromycin, but not for the 16-member macrolides, clindamycin or beta-lactam antibiotics. The enhanced phagocytosis of apoptotic neutrophils by ERY had no effect on the levels of interleukin-8 or tumor necrosis factor alpha production by lipopolysaccharide-stimulated AM after phagocytosis of the apoptotic neutrophils. The increased phagocytosis of apoptotic neutrophils by ERY was also found to be phosphatidylserine receptor-dependent for AM. These data indicate a novel anti-inflammatory action of 14-member and 15-member macrolides, and suggest that such antibiotics achieve clinical efficacy for patients with DPB, in part, through enhancing the nonphlogistic phagocytosis of apoptotic neutrophils by AM.

Adrenal insufficiency in the critically ill: a new look at an old problem

Stress from many sources, including pain, fever, and hypotension, activates the hypothalamic-pituitary-adrenal (HPA) axis with the sustained secretion of corticotropin and cortisol. Increased glucocorticoid action is an essential component of the stress response, and even minor degrees of adrenal insufficiency can be fatal in the stressed host. HPA dysfunction is a common and underdiagnosed disorder in the critically ill. We review the risk factors, pathophysiology, diagnostic approach, and management of HPA dysfunction in the critically ill.

Pseudomonas aeruginosa activates human mast cells to induce neutrophil transendothelial migration via mast cell-derived IL-1 alpha and beta

The mechanisms of neutrophil (PMN) recruitment to Pseudomonas aeruginosa infection remain incompletely defined. Mast cells (MC) involvement in this process has not been studied previously. In this study, we demonstrate that human cord blood-derived MC phagocytose P. aeruginosa and release mediators that activate HUVEC monolayers for supporting PMN transmigration. Pretreatment of supernatants from P. aeruginosa-MC cocultures with neutralizing anti-IL-1alpha plus anti-IL-1beta Abs, or IL-1R antagonist before addition to HUVEC for stimulation completely abrogated MC-induced PMN transmigration, while anti-TNF-alpha treatment had no effect. The expression of E-selectin and ICAM-1 on HUVEC, the latter a ligand for PMN CD11/CD18, was significantly up-regulated by P. aeruginosa-induced MC mediators. Pretreatment of human PMN with anti-CD18 mAb or pretreatment of HUVEC with a combination of three mAbs (against ICAM-1, ICAM-2, and E-selectin) inhibited by 85% the MC-dependent PMN transmigration. Moreover, P. aeruginosa-induced production of IL-1alpha and IL-1beta was down-regulated by IL-10 and dexamethasone. This study demonstrates for the first time that MC may mediate P. aeruginosa-induced PMN recruitment via production of IL-1alpha and beta. These findings have important implications for diseases involving P. aeruginosa infection and suggest novel targets for modulating P. aeruginosa-induced inflammation.

Fourteen-member macrolides suppress interleukin-8 production but do not promote apoptosis of activated neutrophils

A 14-member macrolide was found to inhibit interleukin-8 (IL-8) synthesis in lipopolysaccharide-stimulated neutrophils but did not accelerate apoptosis in activated neutrophils. These data suggest that 14-member macrolides achieve clinical efficacy for chronic airway diseases partly by suppressing IL-8 production by activated neutrophils, but not by enhancing apoptosis in these cells.