Torsten H. Schroeder

CFTR is a pattern recognition molecule that extracts Pseudomonas aeruginosa LPS from the outer membrane into epithelial cells and activates NF-κB translocation

Immune cells are activated during cellular responses to antigen by two described mechanisms: (i) direct uptake of antigen and (ii) extraction and internalization of membrane components from antigen-presenting cells. Although endocytosis of microbial antigens by pattern recognition molecules (PRM) also activates innate immunity, it is not known whether this involves extraction and internalization of microbial surface components. Epithelial cells on mucosal surfaces use a variety of receptors that are distinct from the classical endocytic PRM to bind and internalize intact microorganisms. Nonclassical receptor molecules theoretically could act as a type of endocytic PRM if these molecules could recognize, bind, extract, and internalize a pathogen-associated molecule and initiate cell signaling. We report here that the interaction between the cystic fibrosis transmembrane conductance regulator (CFTR) and the outer core oligosaccharide of the lipopolysaccharide (LPS) in the outer membrane of Pseudomonas aeruginosa satisfies all of these conditions. P. aeruginosa LPS was specifically recognized and bound by CFTR, extracted from the organisms surface, and endocytosed by epithelial cells, leading to a rapid (5- to 15-min) and dynamic translocation of nuclear transcription factor NF-κB. Inhibition of epithelial cell internalization of P. aeruginosa LPS prevented NF-κB activation. Cellular activation depended on expression of wild-type CFTR, because both cultured ΔF508 CFTR human airway epithelial cells and lung epithelial cells of transgenic-CF mice failed to endocytose LPS and translocate NF-κB. CFTR serves as a critical endocytic PRM in the lung epithelium, coordinating the effective innate immune response to P. aeruginosa infection.

Transgenic Cystic Fibrosis Mice Exhibit Reduced Early Clearance of Pseudomonas aeruginosa from the Respiratory Tract

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) has been proposed to be an epithelial cell receptor for Pseudomonas aeruginosa involved in bacterial internalization and clearance from the lung. We evaluated the role of CFTR in clearing P. aeruginosa from the respiratory tract using transgenic CF mice that carried either the ΔF508 Cftr allele or an allele with a Cftr stop codon (S489X). Intranasal application achieved P. aeruginosa lung infection in inbred C57BL/6 ΔF508 Cftr mice, whereas ΔF508 Cftr and S489X Cftr outbred mice required tracheal application of the inoculum to establish lung infection. CF mice showed significantly less ingestion of LPS-smooth P. aeruginosa by lung cells and significantly greater bacterial lung burdens 4.5 h postinfection than C57BL/6 wild-type mice. Microscopy of infected mouse and rhesus monkey tracheas clearly demonstrated ingestion of P. aeruginosa by epithelial cells in wild-type animals, mostly around injured areas of the epithelium. Desquamating cells loaded with P. aeruginosa could also be seen in these tissues. No difference was found between CF and wild-type mice challenged with an LPS-rough mucoid isolate of P. aeruginosa lacking the CFTR ligand. Thus, transgenic CF mice exhibit decreased clearance of P. aeruginosa and increased bacterial burdens in the lung, substantiating a key role for CFTR-mediated bacterial ingestion in lung clearance of P. aeruginosa.

Correlation of meropenem plasma levels with pharmacodynamic requirements in critically ill patients receiving continuous veno-venous hemofiltration.

Background: In patients with acute renal failure, the pharmacokinetics of meropenem depend on the operational characteristics of the renal replacement therapy. Dosage recommendations are based on the correlation of plasma levels with pharmacodynamic requirements. Methods: Eight critically ill patients with acute renal failure were treated by continuous veno-venous hemofiltration with a filtrate flow of 1,600 ml/h and received 500 mg of meropenem every 12 h. Plasma and hemofiltrate concentrations of meropenem at steady state were determined by HPLC. Results: Peak levels in plasma amounted to 39.5 ± 10.5 mg/l (mean ± SD) and trough levels were 2.4 ± 1.5 mg/l. The minimal inhibitory concentration (MIC) for susceptible bacteria (4 mg/l) was covered for 40% of the dosing interval or longer in all patients. The MIC for intermediately susceptible organisms (8 mg/l) was covered for 33% in 6 of the 8 patients. The elimination half-life was prolonged to 3.63 ± 0.77 h. The sieving coefficient of meropenem was 0.91 ± 0.10 and the recovery in hemofiltrate amounted to 30.9 ± 11.5% of the dose. Conclusions: A dosage of 500 mg twice daily provides appropriate serum levels for the treatment of infections caused by susceptible bacteria. A higher dosage is adequate for infections by intermediately susceptible bacteria or for renal replacement therapies with markedly higher filtrate flow rates.

Lack of Adherence of Clinical Isolates of Pseudomonas aeruginosa to Asialo-GM1 on Epithelial Cells

ABSTRACT Numerous studies have reported that asialo-GM1, gangliotetraosylceramide, or moieties serve as epithelial cell receptors for Pseudomonas aeruginosa. Usually this interaction is confirmed with antibodies to asialo-GM1. However, few, if any, of these reports have evaluated the binding of fresh clinical isolates of P. aeruginosa to asialo-GM1 or the specificity of the antibodies for the asialo-GM1 antigen. We confirmed that asialo-GM1 dissolved in dimethyl sulfoxide could be added to the apical membrane of Madin-Darby canine kidney cells growing as a polarized epithelium on Transwell membranes (J. C. Comolli, L. L. Waite, K. E. Mostov, and J. N. Engel, Infect. Immun. 67:3207–3214, 1999) and that such treatment enhanced the binding of P. aeruginosa strain PA103. However, no otherP. aeruginosa strain, including eight different clinical isolates, exhibited enhanced binding to asialo-GM1-treated cells. Studies with commercially available antibodies to asialo-GM1 showed that these preparations had high titers of antibody to P. aeruginosa antigens, including whole cells, purified lipopolysaccharide (LPS), and pili. Inhibition studies showed that adsorption of an antiserum to asialo-GM1 withP. aeruginosa cells could remove the reactivity of antibodies to asialo-GM1, and adsorption of this serum with asialo-GM1 removed antibody binding to P. aeruginosa LPS. Antibodies in sera raised to asialo-GM1 were observed to bind to P. aeruginosa cells by immunoelectron microscopy. Antibodies to asialo-GM1 inhibited formation of a biofilm by P. aeruginosa in the absence of mammalian cells, indicating a direct inhibition of bacterial cell-cell interactions. These findings demonstrate that asialo-GM1 is not a major cellular receptor for clinical isolates of P. aeruginosa and that commercially available antibodies raised to this antigen contain high titers of antibody to multiple P. aeruginosa antigens, which do not interfere with the binding of P. aeruginosa to mammalian cells but possibly interfere with the binding of P. aeruginosa cells to each other.

Synthetic colloids attenuate leukocyte-endothelial interactions by inhibition of integrin function

Background: It has been suspected that synthetic colloids may interfere with leukocyte adhesion by down-regulation of endothelial cell adhesion molecules. Although inhibition of endothelial inflammation might reduce leukocyte-related tissue injury, the same mechanism may be detrimental for host defense during severe infection. Regarding the widespread use of colloids, the authors performed a laboratory investigation to determine the mechanisms by which synthetic colloids interfere with leukocyte-endothelial interactions. Methods: Adhesion molecule expression on native and cytokine-activated endothelium from umbilical veins was measured after pretreatment with gelatin and various preparations of dextran or hydroxyethyl starch. Inhibition of neutrophil adhesion to activated endothelium was examined in a flow chamber by perfusion of untreated and colloid-treated neutrophils over colloid-pretreated endothelium at 2 dyn/cm2. Comparisons were made between untreated controls, colloid-pretreated endothelium, and colloid-cotreated neutrophils. Results: Intercellular adhesion molecule 1, vascular cell adhesion molecule 1, E-selectin, and P-selectin were not attenuated by any colloid. Accordingly, colloid pretreatment of endothelium alone did not reduce neutrophil adhesion. In contrast, when neutrophils were cotreated by addition of colloids to the perfusate immediately before perfusion, adhesion decreased by 31–51% (P < 0.05) regardless of the colloid type. As indicated by the twofold increased rolling fractions, this reduction was due to an inhibition of neutrophil integrins. Conclusions: This study shows that synthetic colloids inhibit neutrophil adhesion by a neutrophil-dependent mechanism rather than interfering with endothelial cell activation. This suggests that inhibition of leukocyte sequestration by volume support is a common and transient phenomenon depending on the colloid concentration in plasma.

Treatment with Tigecycline of Recurrent Urosepsis Caused by Extended-Spectrum-β-Lactamase-Producing Escherichia coli

ABSTRACT A 25-year-old female was admitted to our intensive care unit with septic shock and multiorgan failure caused by extended-spectrum β-lactamase-producing Escherichia coli originating from the right renal pelvis. A 16-day course of treatment with meropenem reversed the septic condition, but the infection recurred thereafter. The patient recovered fully after therapy was changed to tigecycline.

The Effect of Remifentanil or Fentanyl on Postoperative Vomiting and Pain in Children Undergoing Strabismus Surgery

Postoperative vomiting (POV) after strabismus surgery in children results in discomfort and prolonged hospital stays. Opioids increase the incidence of POV. Remifentanil has a context-sensitive half-life of 3 to 4 min, and how this short half-life influences POV in those patients is unknown. We conducted a prospective, double-blinded study in 81 ASA status I or II children from 2 to 12 yr of age undergoing elective strabismus surgery under general anesthesia. Patients were randomized to receive either remifentanil (bolus 1 &mgr;g/kg; infusion 0.1–0.2 &mgr;g · kg−1 · min−1) or fentanyl (2 &mgr;g/kg, and 1 &mgr;g/kg every 45 min). POV episodes were recorded for 25 h. Pain scores were obtained by using an objective pain scale for 60 min during recovery. The number of patients who experienced POV did not differ significantly between groups (49% vs 48%). However, in the Remifentanil group, POV episodes were significantly less frequent (0.95 vs 2.2 episodes). In contrast, fentanyl was associated with lower pain scores during the first 30 min of recovery. We conclude that children undergoing strabismus surgery under balanced anesthesia with remifentanil, compared with fentanyl, showed less frequent POV. However, early postoperative analgesia was better with fentanyl.

Remifentanil or sufentanil for coronary surgery: comparison of postoperative respiratory impairment.

Background and objective: High‐dose opioid anaesthesia contributes to decreasing metabolic and hormonal stress responses in patients undergoing cardiac surgery. However, the increase in context‐sensitive half‐life of opioids given as a high‐dose regimen can affect postoperative respiratory recovery. In contrast, remifentanil can be given in high doses without prolonging context‐sensitive half‐life due to its rapid metabolism. Therefore, we performed a prospective, randomized trial to compare anaesthesia consisting of propofol/remifentanil or propofol/sufentanil with regard to postoperative respiratory function and outcome. Methods: Patients undergoing coronary artery bypass grafting were randomized to a propofol/remifentanil (0.5–1.0 μg kg−1 min−1) or propofol/sufentanil (30–40 ng kg−1 min−1) based anaesthetic. Carbon dioxide response, forced expiratory volume in one second, vital capacity, and functional residual capacity were measured 1 day prior to the operation, 1 h before extubation, 1, 24 and 72 h after extubation. In addition, the incidence of atelectasis, pulmonary infiltrates, intensive care unit and postoperative length of stay were compared. Patients and physicians were blinded to the treatment group. Results: Twenty‐five patients in each treatment group completed the study. There was no difference between patients of the treatment groups regarding demographics, risk‐ or pain scores. In all patients, carbon dioxide response, forced expiratory volume in one second, vital capacity and functional residual capacity were decreased postoperatively compared to baseline. Patients randomized to remifentanil had less depression of carbon dioxide response, less atelectasis and shorter postoperative length of stay (12 d vs. 10 d) than after sufentanil (P < 0.05). Conclusions: Intraoperative use of high‐dose remifentanil for coronary artery bypass grafting may be associated with improved recovery of pulmonary function and shorter postoperative hospital length of stay than sufentanil.

Effect of tracheal intubation or laryngeal mask airway™ insertion on intraocular pressure using balanced anesthesia with sevoflurane and remifentanil

STUDY OBJECTIVES To study the effect of tracheal intubation or laryngeal mask airway (LMA) insertion on intraocular pressure (IOP) in strabismus patients undergoing balanced anesthesia with sevoflurane and remifentanil. DESIGN Open, prospective, randomized study. SETTING Tertiary care academic medical institution. PATIENTS 40 adult ASA physical status I and II patients scheduled for elective strabismus surgery. INTERVENTION Patients were randomized to receive either tracheal intubation or LMA insertion following mask induction with sevoflurane in combination with IV remifentanil. MEASUREMENTS Intraocular pressure, mean arterial pressure (MAP), and heart rate (HR) were measured before induction, immediately following induction, and after airway insertion. MAIN RESULTS Intraocular pressure after tracheal intubation or LMA insertion did not differ significantly from preoperative baseline values. Mean arterial pressure and HR did not significantly differ between groups at any time point. CONCLUSIONS Remifentanil and sevoflurane are not associated with an increase in IOP response during tracheal intubation or LMA insertion above baseline in healthy patients undergoing ophthalmic surgery.

Audit of motor weakness and premature catheter dislodgement after epidural analgesia in major abdominal surgery.

In a quality improvement audit on epidural analgesia in 300 patients after major abdominal surgery, we identified postoperative lower leg weakness and premature catheter dislodgement as the most frequent causes of premature discontinuation of postoperative epidural infusion. Lower limb motor weakness occurred in more than half of the patients with lumbar epidural analgesia. In a second period monitoring 177 patients, lumbar catheter insertion was abandoned in favour of exclusive thoracic placement for epidural catheters. Additionally, to prevent outward movement, the catheters were inserted deeper into the epidural space (mean (SD) 5.2 (1.5) cm in Period Two vs 4.6 (1.3) cm in Period One ). Lower leg motor weakness declined from 14.7% to 5.1% (odds ratio 0.35; 95% confidence interval 0.16–0.74) between the two periods. Similarly, the frequency of premature catheter dislodgement was reduced from 14.5% to 5.7% (odds ratio 0.35; 95% confidence interval 0.17–0.72). With a stepwise logistic regression model we demonstrated that the odds of premature catheter dislodgement was reduced by 43% for each centimetre of additional catheter advancement in Period Two . We conclude that careful audit of specific complications can usefully guide changes in practice that improve success of epidural analgesia regimens.