Modulation of pulmonary clearance of bacteria by antioxidants

A novel in vitro metric predicts in vivo efficacy of inhaled silver-based antimicrobials in a murine Pseudomonas aeruginosa pneumonia model

To address the escalating problem of antimicrobial resistance and the dwindling antimicrobial pipeline, we have developed a library of novel aerosolizable silver-based antimicrobials, particularly for the treatment of pulmonary infections. To rapidly screen this library and identify promising candidates, we have devised a novel in vitro metric, named the “drug efficacy metric” (DEM), which integrates both the antibacterial activity and the on-target, host cell cytotoxicity. DEMs calculated using an on-target human bronchial epithelial cell-line correlates well (R² > 0.99) with in vivo efficacy, as measured by median survival hours in a Pseudomonas aeruginosa pneumonia mouse model following aerosolized antimicrobial treatment. In contrast, DEMs derived using off-target primary human dermal fibroblasts correlate poorly (R² = 0.0595), which confirms our hypothesis. SCC1 and SCC22 have been identified as promising drug candidates through these studies, and SCC22 demonstrates a dose-dependent survival advantage compared to sham treatment. Finally, silver-bearing biodegradable nanoparticles were predicted to exhibit excellent in vivo efficacy based on its in vitro DEM value, which was confirmed in our mouse pneumonia model. Thus, the DEM successfully predicted the efficacy of various silver-based antimicrobials, and may serve as an excellent tool for the rapid screening of potential antimicrobial candidates without the need for extensive animal experimentation.

Induction of type I interferon signaling determines the relative pathogenicity of Staphylococcus aureus strains

The tremendous success of S. aureus as a human pathogen has been explained primarily by its array of virulence factors that enable the organism to evade host immunity. Perhaps equally important, but less well understood, is the importance of the intensity of the host response in determining the extent of pathology induced by S. aureus infection, particularly in the pathogenesis of pneumonia. We compared the pathogenesis of infection caused by two phylogenetically and epidemiologically distinct strains of S. aureus whose behavior in humans has been well characterized. Induction of the type I IFN cascade by strain 502A, due to a NOD2-IRF5 pathway, was the major factor in causing severe pneumonia and death in a murine model of pneumonia and was associated with autolysis and release of peptidogylcan. In contrast to USA300, 502A was readily eliminated from epithelial surfaces in vitro. Nonetheless, 502A caused significantly increased tissue damage due to the organisms that were able to invade systemically and trigger type I IFN responses, and this was ameliorated in Ifnar⁻/⁻ mice. The success of USA300 to cause invasive infection appears to depend upon its resistance to eradication from epithelial surfaces, but not production of specific toxins. Our studies illustrate the important and highly variable role of type I IFN signaling within a species and suggest that targeted immunomodulation of specific innate immune signaling cascades may be useful to prevent the excessive morbidity associated with S. aureus pneumonia.

Fluconazole attenuates lung injury and mortality in a rat peritonitis model

OBJECTIVE

Acute lung injury following peritonitis constitutes an enigmatic clinical problem with no specific therapy. Recently, immunomodulators such as azole compounds have been shown to attenuate shock-related tissue injury. The present investigation was undertaken to study the effect of fluconazole on acute lung injury and survival following faecal peritonitis in rats.

SUBJECTS

Male Wistar rats weighing 225-235 g.

DESIGN AND SETTING

Faecal peritonitis (Fp) was produced in four groups of adult male Wistar rats by intraperitoneal administration of non-sterile faecal suspension (1:1 w/v saline). A fifth group of rats was given sterile faecal material (SFM), which served as control.

INTERVENTIONS

Rats in Fp groups were given fluconazole in doses of 0 mg/kg, 3 mg/kg, 10 mg/kg, and 30 mg/kg by gavage 30 min before induction of peritonitis. The control animals received an equal volume of distilled water.

MEASUREMENTS AND RESULTS

Survival over a period of 72 h, oxidative stress, neutrophil activity, and lung injury were measured. This study showed a 90% survival in the fluconazole-treated group compared to only 20% survival in untreated rats (P<0.008 log-rank test). The lungs of animals with Fp showed massive pathological changes including intraalveolar oedema, fibrosis, and mixed inflammatory cell infiltrate. These changes were dose-dependently attenuated by fluconazole. Enhanced oxidative stress (P<0.001) and neutrophil activity in the peritoneal fluid and lung (P<0.001) in Fp animals was dose-dependently reduced by fluconazole.

CONCLUSION

This study clearly suggests the role of neutrophils in Fp-induced tissue injury/mortality, which may be dose-dependently, attenuated by fluconazole.

The effect of N-acetylcysteine on total serum anti-oxidant potential and urinary albumin excretion in critically ill patients

OBJECTIVE

To investigate the effects of N-acetylcysteine (NAC) when given as an early treatment to critically ill patients on the serum total anti-oxidant potential (TAP) and urine micro-albumin:creatinine (M:Cr) ratio.

DESIGN

Prospective, placebo controlled double blinded clinical trial.

SETTING

General intensive care unit in a teaching hospital.

PATIENTS

Sixty critically ill patients were recruited but ten were withdrawn due to less than 48 h of ICU stay.

INTERVENTIONS

After envelope randomisation, patients received either NAC (n = 23): a bolus of 150 mg/kg in 250 ml of 5% dextrose followed by a continuous infusion of 12 mg/kg per h in 500 ml of 5% dextrose over 24 h or, as controls (n = 27), the equal volume of placebo. Treatment lasted for a minimum of 3, up to a maximum of 5, days. Blood and urine samples were collected on admission (0 h) and then 6 hourly up 18 h.

MEASUREMENTS AND RESULTS

There was no significant difference between NAC and placebo groups regarding the required length of inotropic support, mechanical ventilation and ICU stay. There was no significant difference in TAP or M:Cr ratio over 18 h or between the groups.

CONCLUSIONS

Our results suggest that NAC had no significant effects on the progress of the TAP and the urinary albumin excretion in our patients, which may suggest that NAC at the given dose has no clinical relevance as an early treatment in the critically ill.

Anti-interleukin-8 monoclonal antibody reduces free radical production and improves hemodynamics and survival rate in endotoxic shock in rabbits

BACKGROUND

Although high levels of interleukin-8 (IL-8) have been found in patients with sepsis and a monoclonal antibody (MoAb) against IL-8 has been successfully used in some animal models of inflammation, no specific therapeutic agent against IL-8 has been tested for the treatment of sepsis. We studied the effects of a MoAb against IL-8 in the treatment of endotoxic shock with a prospective randomized rabbit endotoxic shock model.

METHODS

Twenty New Zealand white rabbits were anesthetized and divided into four groups: normal, anti-IL-8, control-Ab, and lipopolysaccharide (LPS). Anti-IL-8 and control-Ab groups received a MoAb (immunoglobulin G, 3 mg/kg) 5 minutes before the LPS injection. All groups, except the normal group, received a continuous 20-minute infusion of LPS (500 micrograms/kg). The normal group received NaCl (0.9%) rather than LPS.

RESULTS

The 7-day survival rates were 100% for normal group, 80% for anti-IL-8 group, 40% for control-Ab group, and 0% for LPS group. Compared with the LPS group, anti-IL-8 rabbits had a smaller decrease in mean arterial blood pressure (p < 0.05) and increased urinary volume (p < 0.05). Anti-IL-8 rabbits had lower plasmatic levels of IL-1 beta, less free radical production (p < 0.05), and a higher survival rate (p < 0.01).

CONCLUSIONS

IL-8 plays a significant role in endotoxic shock, and IL-8 blockage results in attenuation of the hypotensive and tachypneic effects of LPS, reduced free radical production, and an increased survival rate after lethal endotoxic shock.

Analysis of the effects of immune cell motility and chemotaxis on target elimination dynamics

White blood cells of the immune system must encounter specific targets such as bacteria, malignant cells, virus-infected cells or other cells of the immune response in order to carry out their function of protecting the host from infectious and malignant disease. To analyze the dynamics of this process, a mathematical model has been developed for elimination of proliferating targets by a constant population of motile immune system cells in two dimensions. Encounter is assumed to be the rate-limiting step for elimination. This model makes use of a previously derived analysis of single cell-target encounter times, which yields an encounter rate constant that is incorporated into a kinetic conservation equation for target number density. This paper focuses on the influence of directed cell movement, or chemotaxis, as well as other cell motility properties, such as cell speed and persistence, on target elimination dynamics. A particularly significant result is that a given relative decrease in chemotactic responsiveness leads to much more severe deficiencies in target clearance rates for low levels of baseline chemotactic responsiveness than for high levels of baseline responsiveness. The general model results are then applied to the particular example of bacterial clearance from the lung surface by alveolar macrophages. It is shown that moderate levels of macrophage chemotactic responsiveness, similar to those measured in vitro, can account for the experimentally observed rates of bacterial elimination from the lung for typical values of bacterial specific growth rate and alveolar macrophage number density.