In vitro activity of amiloride combined with tobramycin against Pseudomonas isolates from patients with cystic fibrosis

Combination of hypothiocyanite and lactoferrin (ALX-109) enhances the ability of tobramycin and aztreonam to eliminate Pseudomonas aeruginosa biofilms growing on cystic fibrosis airway epithelial cells

OBJECTIVES

Chelating iron may be a promising new therapy to eliminate Pseudomonas aeruginosa biofilms in the lungs of cystic fibrosis (CF) patients. Here, we investigate whether ALX-109 [a defined combination of an investigational drug containing lactoferrin (an iron-binding glycoprotein) and hypothiocyanite (a bactericidal agent)], alone and in combination with tobramycin or aztreonam, reduces P. aeruginosa biofilms grown on human CF airway epithelial cells.

METHODS

P. aeruginosa (PAO1 and six clinical isolates of Pseudomonas) biofilms grown at the apical surface of confluent monolayers of CF airway epithelial cells were treated with ALX-109, either alone or in combination with tobramycin or aztreonam. Bacterial cfu remaining after treatment were determined by plate counting.

RESULTS

ALX-109 alone reduced PAO1 biofilm formation, but had no effect on established biofilms. ALX-109 enhanced the ability of tobramycin and aztreonam to inhibit PAO1 biofilm formation and to reduce established PAO1 biofilms. ALX-109 and tobramycin were additive in disrupting established biofilms formed by six clinical isolates of P. aeruginosa obtained from the sputum of CF patients. Mucoid P. aeruginosa isolates were most susceptible to the combination of ALX-109 and tobramycin. In addition, ALX-109 also enhanced the ability of aztreonam to reduce established PAO1 biofilms.

CONCLUSIONS

Inhalation therapy combining hypothiocyanite and lactoferrin with TOBI(®) (tobramycin) or Cayston(®) (aztreonam) may be beneficial to CF patients by decreasing the airway bacterial burden of P. aeruginosa.

Cystic fibrosis infections: treatment strategies and prospects

Pseudomonas aeruginosa and Burkholderia cepacia are the two major Gram-negative rods that colonize/infect the lungs of patients with cystic fibrosis (CF). These organisms may cause progressive respiratory failure, although occasionally more rapid infections result in the 'Cepacia' syndrome. Many antibiotics have been used against Pseudomonas and Burkholderia, but once chronic colonization has been established, eradication of these organisms is rare. Drug therapy for CF patients is compromised by a number of bacterial factors that render the infectious agents resistant to antibiotics, including efflux pumps that remove antibiotics, lack of penetration of antibiotics into bacterial biofilms, and changes in the cell envelope that reduce the permeability of antibiotics. Any combination of these mechanisms increases the likelihood of bacterial survival. Therefore, combinations of antibiotics or of antibiotic and nonantibiotic compounds are currently being tested against Pseudomonas and Burkholderia. However, progress has been slow, with only occasional combinations showing promise for the eradication of persistent Gram-negative rods in the airways of CF patients. This review will summarize the current knowledge of CF infections and speculate on potential future pathways to treat these chronic infections.

In vitro interactions of tobramycin with various nonantibiotics against Pseudomonas aeruginosa and Burkholderia cenocepacia

Pseudomonas aeruginosa and Burkholderia cepacia are the major pathogens that colonize the airway surface and cause progressive respiratory failure and high mortality, especially in cystic fibrosis (CF) patients. Tobramycin is the treatment of choice, but persistent usage enables the infectious organisms to activate defence mechanisms, making eradication rarely successful. Combinations of antibiotic and nonantibiotic compounds have been tested in vitro against P. aeruginosa and B. cepacia, but with mixed results. Sodium ions interfere with the bacterial tobramycin uptake system, but amiloride partially reverses this antagonism. In this pilot study, we extend previous findings of the effectiveness of tobramycin in combination with amiloride and other nonantibiotics against a P. aeruginosa type strain, and against four P. aeruginosa strains and one Burkholderia cenocepacia strain isolated from CF patients. Significantly, the four clinical P. aeruginosa strains were tobramycin resistant. We also find that Na+ and K+, but not Cl(-), are the chief antagonists of tobramycin efficacy. These results suggest that chemotherapy for CF patients might not only be compromised by antibiotic-resistant pathogens alone, but by a lack of penetration of antibiotics caused either by bacterial biofilms or the high sodium flux in the CF lung, or by antagonistic effects of some drug combinations, any of which could allow the persistence of drug-susceptible bacteria.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Nebulised amiloride in respiratory exacerbations of cystic fibrosis: a randomised controlled trial

OBJECTIVE

To assess the benefit of nebulised amiloride added to the standard inpatient treatment of a respiratory exacerbation in cystic fibrosis.

DESIGN

Prospective, randomised, double blind, placebo controlled trial.

SUBJECTS

27 cystic fibrosis patients (mean age 12.8 years).

SETTING

Two hospitals in Leeds, UK.

RESULTS

Both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) showed improvements over the course of treatment, although there was no difference in respiratory function between the two groups at any of three time periods during the study. The time to reach peak FVC was significantly reduced in the amiloride group (4.2 v 7.6 days; 95% CI 0.4 to 6.4 days), but not in the time to reach peak FEV1 (5.7 v 7.9 days; 95% CI -1.2 to 5.6 days).

CONCLUSIONS

Amiloride did not result in a greater overall improvement in respiratory function. There was a suggestion that it may have an effect on the rate of improvement, and thus may possibly influence the duration of treatment. This hypothesis deserves further evaluation.

In vitro suppression of Pseudomonas cepacia after limited exposure to subinhibitory concentrations of amiloride and 5-(N,N-hexamethylene) amiloride

Amiloride (A) for aerosolized therapy in cystic fibrosis (CF) is under investigation. Antipseudomonal properties of A and A analogs in vitro have recently been described. This study was performed to determine if there was suppression of P. cepacia growth after a limited 2-hour exposure to (subinhibitory) concentrations of A +/- tobramycin (T) or to the analog 5-(N,N-hexamethylene) amiloride (HMA) in vitro. The MIC of each drug against five different P. cepacia strains was determined. Cells were prepared in Mueller Hinton broth to [10(6)] colony forming units (CFU)/mL and incubated at 35 degrees C for 2 hours in the presence and absence of subinhibitory A, HMA, T, or A+T. The CFU were measured before and at 1-hour intervals after dilutional removal of drug. The post-antibiotic effect (PAE) was defined as the time (in minutes) required for the test culture counts to increase 10-fold minus the time required for control counts to increase 10-fold. At 400 micrograms/mL or 200 micrograms/mL, the PAE for A against five different strains was 139 +/- 23 and 83 +/- 24 (mean +/- SD) minutes, respectively. For 100 micrograms/mL and 50 mu cg/mL HMA, the PAE was 122 +/- 38 and 65 +/- 25 minutes. For T and A+T (200 micrograms/mL + 32 micrograms/mL) the PAE ws 168 +/- 30 and 258 +/- 30 minutes. We conclude that A and the analog HMA in (subinhibitory) concentrations have a suppressive effect on P. cepacia after drug removal and potentiate the effect of T in vitro.

Pseudomonas cepacia in lung transplant recipients with cystic fibrosis

Twenty-four isolated double lung transplants (LTXs) have been performed in 22 patients with cystic fibrosis, with a follow-up of 4 to 47 months. Prior to LTX, all patients were colonized with Pseudomonas aeruginosa, and ten patients were also colonized with Pseudomonas cepacia. Both organisms were specifically sought before LTX. All patients who grew P cepacia before LTX did so after LTX. Five additional patients only grew this bacterium after LTX. There was no difference between those who grew P cepacia and those who did not in terms of data before LTX for age, weight, pulmonary function, and 6-min walk. After LTX, 7 of the 15 patients who had ever grown P cepacia died. No patient who grew only P aeruginosa died. The median survival in the subgroup with P cepacia was 28 days. Five of the seven died as a direct result of P cepacia pneumonia and sepsis. One died of cyclosporin A (cyclosporine) neurotoxicity with concurrent P cepacia pneumonia, and one died at the time of a retransplant for graft failure (associated with three bouts of P cepacia pneumonia and cytomegalovirus). Four of seven had not grown this bacterium before LTX. There were no perioperative factors, including antibiotic choices, that distinguished survivors and nonsurvivors. Overall 1-year survival is about 70 percent (15/22). Fourteen bouts of P cepacia pneumonia occurred in 12 patients. Four empyemas, one lung abscess, one suppurative pericarditis, and five cases of sinusitis were also due to this bacterium. In conclusion, P cepacia is responsible for excess morbidity and mortality after LTX. This organism is particularly lethal if isolated for the first time after LTX. Factors predicting its acquisition in this setting are unknown. While it is possible that the facial sinuses may act as an unrecognized reservoir or that patients or equipment provide a source, further study into the epidemiology of this organism is necessary to improve the survival of colonized patients undergoing LTX.

Amiloride antagonizes beta-adrenergic stimulation of cAMP synthesis and Cl- secretion in human tracheal epithelial cells

Amiloride, a potent blocker of the sodium channel in airway epithelium, has been administered by aerosol as a therapeutic agent for cystic fibrosis. Because amiloride in high concentration has been reported to interfere with cell functions, including adrenergic responses, we tested the ability of amiloride to inhibit beta-adrenergic responses in human tracheal epithelial cells. Amiloride (10(-4) M), applied from the basolateral surface of a cell monolayer, inhibited the changes in transepithelial potential and short circuit current to isoproterenol (10(-6) M). The stimulation of cyclic adenosine monophosphate (cAMP) synthesis by isoproterenol was inhibited in dose-dependent fashion by amiloride (P = 0.007 by multivariate ANOVA with multiple samples correction). Amiloride did not affect baseline transepithelial potential, short circuit current, basal cAMP levels, cAMP response to prostaglandin E2, or basal adenylate cyclase activity measured directly in membrane preparations. Therefore, it is unlikely that amiloride exerts a nonspecific toxic effect on adenylate cyclase, receptor-cyclase coupling, or substrate or cofactor supply. The binding of [125I]iodocyanopindolol (ICYP), a beta-adrenergic receptor antagonist, to membranes from human tracheal epithelial cells could be displaced by amiloride with IC50 = 410 microM; displacement was 70% at 10(-3) M amiloride. These data are most consistent with the hypothesis that amiloride inhibits beta-adrenergic responses in airway epithelial cells by occupying beta-adrenergic receptor sites. Therapeutic administration of amiloride should take into account its affinity for adrenergic receptors.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

Cystic fibrosis, pathophysiological and clinical aspects

Cystic fibrosis is a lethal, hereditary, until recently little understood disease, which leads to progressive functional disturbances in various organs, including the lungs, liver and pancreas. Knowledge of the genetic and cellular abnormalities is rapidly progressing, but therapy is still symptomatic and based on insufficiently controlled and short-term studies. At present the therapeutic approach aims to combat respiratory infections by optimal antibiotic therapy, combined with techniques to promote sputum evacuation. Additional measures attempt to optimise both nutritional state and physical condition. Median survival has improved from approximately 1 year to about 25 years during the past 3 decades. This article summarises present information on disease mechanisms and treatment.

A pilot study of aerosolized amiloride for the treatment of lung disease in cystic fibrosis

Excessive active absorption of sodium is a unique abnormality of the airway epithelium in patients with cystic fibrosis. This defect is associated with thickened mucus and poor clearance of airway secretions and may contribute to the pulmonary disease in these patients. To study whether the inhibition of excessive absorption of sodium might affect the course of lung disease in cystic fibrosis, we performed a double-blind, crossover trial comparing aerosolized amiloride (5 mmol per liter; 3.5 ml four times daily), a sodium-channel blocker, with vehicle alone. Fourteen of the 18 adult patients initially enrolled in the study completed the one-year trial (25 weeks for each treatment). The mean (+/- SEM) loss of forced vital capacity (FVC) was reduced from 3.39 +/- 1.13 ml per day during treatment with vehicle alone to 1.44 +/- 0.67 ml per day during treatment with amiloride (P less than 0.04). A measured index of sputum viscosity and elasticity was abnormal during treatment with vehicle alone and improved during treatment with amiloride. Calculated indexes of mucociliary and cough clearance also improved during amiloride treatment. No systemic, respiratory, or subjective toxic effects of amiloride were noted. We conclude from this preliminary study that aerosolized amiloride can be safely administered to adults with cystic fibrosis. The slowing of the loss of FVC and the improvement in sputum viscosity and elasticity suggest a beneficial clinical effect. Aerosolized amiloride deserves further evaluation in the treatment of lung disease in patients with cystic fibrosis.