Exploring the mechanisms of macrolides in cystic fibrosis

Azithromycin is the answer in paediatric respiratory medicine, but what was the question?

The first clinical indication of non-antibiotic benefits of macrolides was in the Far East, in adults with diffuse panbronchiolitis. This condition is characterised by chronic airway infection, often with Pseudomonas aeruginosa, airway inflammation, bronchiectasis and a high mortality. Low dose erythromycin, and subsequently other macrolides, led in many cases to complete remission of the condition, and abrogated the neutrophilic airway inflammation characteristic of the disease. This dramatic finding sparked a flurry of interest in the many hundreds of macrolides in nature, especially their anti-inflammatory and immunomodulatory effects. The biggest subsequent trials of azithromycin were in cystic fibrosis, which has obvious similarities to diffuse panbronchiolitis. There were unquestionable improvements in lung function and pulmonary exacerbations, but compared to diffuse panbronchiolitis, the results were disappointing. Case reports, case series and some randomised controlled trials followed in other conditions. Three trials of azithromycin in preschool wheeze gave contradictory results; a trial in pauci-inflammatory adult asthma, and a trial in non-cystic fibrosis bronchiectasis both showed a significant reduction in exacerbations, but none matched the dramatic results in diffuse panbronchiolitis. There is clearly a huge risk of antibacterial resistance if macrolides are used widely and uncritically in the community. In summary, Azithromycin is not the answer to anything in paediatric respiratory medicine; the paediatric respiratory community needs to refocus on the dramatic benefits of macrolides in diffuse panbronchiolitis, use modern - omics technologies to determine the endotypes of inflammatory diseases and discover in nature or synthesise designer macrolides to replicate the diffuse panbronchiolitis results. We must now find out how to do better!

Azithromycin add-on therapy in high-risk postendoscopic sinus surgery patients failing corticosteroid irrigations: A clinical practice audit

BACKGROUND

Chronic rhinosinusitis (CRS) has a high potential for recurrence after endoscopic sinus surgery (ESS), despite a postoperative therapy of topical corticosteroid irrigations. Azithromycin (AZI) is a macrolide antibiotic with anti-inflammatory properties that may be of benefit in such steroid-unresponsive patients. Follow-up study was performed to (1) review the effectiveness of the management strategy of adding AZI in high-risk post-ESS patients failing standard management and (2) identify predictive factors for steroid nonresponsiveness.

METHODS

A retrospective audit of the postoperative evolution of all patients undergoing ESS for CRS in 2010 by a single surgeon was undertaken. Patients deemed at high risk of recurrence based on preoperative history and/or perioperative findings received nasal irrigation with 0.5 mg of budesonide (BUD) in 240 mL of saline twice daily after ESS. Patients showing signs of endoscopic recurrence at 4 months, despite BUD, had AZI at 250 mg three times a week added to their treatment regimen.

RESULTS

A total of 57 high-risk patients underwent ESS during this period. At 4 months, 63.2% (36/57) had a favorable outcome solely with BUD. Twelve of the 21 nonresponders received AZI, with an additional 66.7% (8/12) subsequently showing a favorable response. Failure of BUD was associated with female gender (p = 0.048), having elevated alpha-1-antitrypsin levels (p = 0.037) and lower recovery rates of Staphylococcus aureus (p = 0.063). Although the AZI subgroup was too small for statistical analysis, female gender was more frequently associated with failure of both BUD and AZI, while IgE was not useful.

CONCLUSION

A significant subgroup of high-risk patients showing disease recurrence after ESS despite topical corticosteroid therapy may respond to the addition of AZI as part of their therapy. These findings suggest that topical steroid-unresponsive CRS may represent a distinct entity and that alternate anti-inflammatory agents may be required for optimal management.

Macrolides: from in vitro anti-inflammatory and immunomodulatory properties to clinical practice in respiratory diseases

BACKGROUND

Macrolides have long been recognised to exert immunomodulary and anti-inflammatory actions. They are able to suppress the "cytokine storm" of inflammation and to confer an additional clinical benefit through their immunomodulatory properties.

METHODS

A search of electronic journal articles was performed using combinations of the following keywords: macrolides, COPD, asthma, bronchitis, bronchiolitis obliterans, cystic fibrosis, immunomodulation, anti-inflammatory effect, diabetes, side effects and systemic diseases.

RESULTS

Macrolide effects are time- and dose-dependent, and the mechanisms underlying these effects remain incompletely understood. Both in vitro and in vivo studies have provided ample evidence of their immunomodulary and anti-inflammatory actions. Importantly, this class of antibiotics is efficacious with respect to controlling exacerbations of underlying respiratory problems, such as cystic fibrosis, asthma, bronchiectasis, panbrochiolitis and cryptogenic organising pneumonia. Macrolides have also been reported to reduce airway hyper-responsiveness and improve pulmonary function.

CONCLUSION

This review provides an overview on the properties of macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin), their efficacy in various respiratory diseases and their adverse effects.

Mechanisms of action and clinical application of macrolides as immunomodulatory medications

Macrolides have diverse biological activities and an ability to modulate inflammation and immunity in eukaryotes without affecting homeostatic immunity. These properties have led to their long-term use in treating neutrophil-dominated inflammation in diffuse panbronchiolitis, bronchiectasis, rhinosinusitis, and cystic fibrosis. These immunomodulatory activities appear to be polymodal, but evidence suggests that many of these effects are due to inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and nuclear factor kappa B (NF-kappaB) activation. Macrolides accumulate within cells, suggesting that they may associate with receptors or carriers responsible for the regulation of cell cycle and immunity. A concern is that long-term use of macrolides increases the emergence of antimicrobial resistance. Nonantimicrobial macrolides are now in development as potential immunomodulatory therapies.

Azithromycin paradox in the treatment of cystic fibrosis airway disease

Evaluation of: Saiman L, Anstead M, Mayer-Hamblett N et al.: Effect of azithromycin on pulmonary function in patients with cystic fibrosis uninfected with Pseudomonas aeruginosa: a randomized controlled trial. JAMA 303(17), 1707–1715 (2010). Chronic airway infection and inflammation are hallmarks of cystic fibrosis (CF). Disease progression can be described as chronic inflammation punctuated by acute exacerbations with overt immunological responses. Macrolide antibiotics, which have both immunomodulatory and antibacterial activities, have been shown to be beneficial in the management of CF airway disease, although the mechanism of action is unknown. It is also unclear whether all patients, particularly those not colonized with Pseudomonas aeruginosa, benefit from this treatment. In this article, Saiman et al. examine the effects of azithromycin on lung function in pediatric and adolescent CF patients who are not colonized with P. aeruginosa. The data indicate beneficial effects of azithromycin treatment and suggest the mechanisms of action of azithromycin is at least partially independent of P. aeruginosa.

Azithromycin increases chloride efflux from cystic fibrosis airway epithelial cells

It was investigated whether azithromycin (AZM) stimulates chloride (Cl-) efflux from cystic fibrosis (CF) and non-CF airway epithelial cells, possibly secondary to up-regulation of the multidrug resistance protein (MDR). CF and non-CF human airway epithelial cell lines (CFBE and 16HBE) were treated with 0.4, 4, and 40 microg/mL AZM for 4 days. Cl- efflux was explored in the presence or absence of specific inhibitors of CFTR and alternative Cl- channels. Six CF patients received AZM (500 mg daily) for 6 months. The percentage of predicted forced vital capacity (FVC%), forced expiratory volume (FEV1%), and the number of acute exacerbations were compared before and after treatment. Nasal biopsies were taken before and after treatment, and mRNA expression of MDR and CFTR was determined by in situ hybridization. A significant dose-dependent increase of Cl- efflux from CFBE cells (but not from 16HBE cells) was observed after AZM treatment. A CFTR inhibitor significantly reduced AZM-stimulated Cl- efflux from CFBE cells. A significant improvement in FEV1%, and fewer exacerbations were observed. AZM treatment did not affect mRNA expression of MDR and CFTR. The stimulation of Cl- efflux could be part of the explanation for the clinical improvement seen among the patients.

Chronic inflammation in the cystic fibrosis lung: alterations in inter- and intracellular signaling

A vicious cycle of airway obstruction, infection, and inflammation continues to cause most of the morbidity and mortality in cystic fibrosis (CF). Mutations that result in decreased expression or function of the membrane Cl(-) channel, cystic fibrosis transmembrane regulator (CFTR), result in a decrease in the volume (and hence the depth) of liquid on the airway surface, impaired ciliary function, and dehydrated glandular secretions. In turn, these abnormalities contribute to a milieu, which promotes chronic infection with a limited but unique spectrum of microorganisms. Defects in CFTR also perturb regulation of several intracellular signaling pathways including signal transducers and activator of transcription, I-kappaB and nuclear factor-kappa B, and low molecular weight GTPases. Together, these abnormalities result in excessive production of NF-kappaB dependent cytokines such as interleukin (IL)-1, tumor necrosis factor (TNF), IL-6, and IL-8. There are decreased responses to interferon gamma and transforming growth factor beta leading to decreased production of iNOS and NO. Abnormalities of lipid mediators and decreased secretion of counter/regulatory cytokines have also been reported. Together, these effects combine to create a chronic inflammatory process, which damages and obstructs the airways, and eventually claims the life of the patient.

Cystic fibrosis: a review of pulmonary and nutritional therapies

In summary, there is a significant interplay between the pulmonary manifestations and nutritional status of CF patients. The advances in CF clinical care in the past 2 decades are mainly attributed to anti-infective therapy as well as aggressive nutritional management. Currently, there are multiple therapeutic agents that are in clinical trial that target either the underlying CFTR defect or the downstream effects of CFTR. The broad spectrum of therapeutic agents being studied as well as the advances in therapies that target the underlying CFTR defect are exciting, making it likely that at least one of the treatments will make a major difference in how we will treat CF in the future.

Anti-inflammatory approaches to cystic fibrosis airways disease

PURPOSE OF REVIEW

Therapy aimed at combating excessive lung inflammation should benefit patients with cystic fibrosis. This article reviews anti-inflammatory strategies, focusing on new evidence published since 2006.

RECENT FINDINGS

Use of oral corticosteroids was associated with benefit in an epidemiological study but they are still not recommended; high dose inhaled corticosteroids may cause harm (effect on growth), but they can safely be withdrawn in many patients. Some small beneficial effect of ibuprofen was seen in a multicentre study, but it is unlikely that this will change practice. Altering the imbalance seen in fatty acid metabolism with omega3 polyunsaturated fatty acid supplementation may be helpful but therapeutic benefit is not yet proven. Combating cysteinyl leukotrienes has potential but benefit remains to be proved. The beneficial effect of macrolides has been confirmed in patients with milder disease, but caution is needed because of emerging resistance patterns. Renewed research interest in antiproteases has not demonstrated any significant benefit.

SUMMARY

The ideal therapeutic drug, with the optimal balance of benefit and harm, is not yet available.

Macrolides beyond the conventional antimicrobials: a class of potent immunomodulators

The historical change in the natural course of diffuse panbronchiolitis (DPB), a fatal disorder of the airways, following the introduction of erythromycin in its treatment has focused attention of researchers on the anti-inflammatory properties of macrolides. Chronic inflammation of the airways accompanied by infiltration by neutrophils and overproduction of mucus and pro-inflammatory cytokines is observed in bronchial asthma, cystic fibrosis (CF), DPB, chronic obstructive pulmonary disease (COPD) and bronchiectasis. The airways of these patients are often colonised by mucoid Pseudomonas aeruginosa attached to epithelium by a biofilm. Bacteria intercommunicate for biofilm formation by a system of lactones known as quorum sensing. Macrolides inhibit mobility and quorum sensing of P. aeruginosa; they also decrease production of mucus by epithelial cells and biosynthesis of pro-inflammatory cytokines from monocytes and epithelial cells by inhibiting nuclear factor-kappaB. Large, randomised clinical trials for the management of these disorders with macrolides are not available, with the sole exception of four trials denoting benefit following long-term administration of azithromycin in patients with CF. That benefit is consistent with an increase in forced expiratory volume in 1s (FEV(1)) and a decrease in the rate of bacterial exacerbations. Studies with small numbers of patients with COPD revealed attenuation of the inflammatory reaction by macrolides. Experimental studies of Gram-negative sepsis have shown considerable attenuation of the systemic inflammatory response following intravenous administration of clarithromycin. Results of the effects of clarithromycin in patients with ventilator-associated pneumonia and sepsis in a large, randomised study of 200 patients are awaited.

[Will we still have antibiotics tomorrow?]

Since the discovery of antibiotics, it has been generally believed that these antimicrobials are capable of curing almost all bacterial infections. More recently, the appearance of increasing resistance to antibiotics and the emergence of multiresistant microorganisms have given rise to growing concern among physicians, and that concern has now started to filter through to society in general. The problem is further aggravated by a situation that not many people are currently aware of, that is, the limited prospects for future development of new antibiotics in the short to medium term. Appropriate use of available antibiotics based on a thorough understanding of their in vivo activity and the emergence of new forms of administration, such as inhalers, may help to alleviate the problem.

Immunomodulatory effects of macrolide antibiotics in respiratory disease: therapeutic implications for asthma and cystic fibrosis

The macrolide antibiotics are a family of related 14- or 15-membered lactone ring antibiotics. There has been recent interest in the beneficial effects of these drugs as immune modulators in respiratory conditions in children. Cystic fibrosis (CF) and asthma, both of which occur in childhood, have an underlying inflammatory component and are associated with significant morbidity. The pathogenesis of both conditions is poorly understood but several molecular mechanisms have been suggested. In CF, these mechanisms broadly involve altered chloride transport and alteration of the airway surface liquid with disordered neutrophilic inflammation. There is much evidence for a proinflammatory propensity in CF immune effector and epithelial cells and many studies indicate that macrolides modulate these inflammatory processes. Recent studies have confirmed a clinical improvement in CF following treatment with macrolides, but the exact mechanisms by which they work are unknown. Asthma is likely to represent several different phenotypes but in all of these, airway obstruction, bronchial hyperresponsiveness, and inflammation are central processes. Results from trials using macrolides have suggested an improvement in clinical outcome. The putative mechanisms of macrolide immunomodulatory action include improvement of the primary defense mechanisms, inhibition of the bacteria-epithelial cell interaction, modulation of the signaling pathway and chemokine release, and direct neutrophil effects. Putative mechanisms of phenotypic modulation have also been proposed involving interactions with nitric oxide, endothelin-1, and bronchoconstriction, endothelial growth factors and airway remodeling, and bioactive phospholipids in both CF and asthma. Further characterization of these effects and development of targeted designer drugs will further expand our therapeutic repertoire and lead to improved quality and quantity of life for patients with CF and asthma.

Pseudomonas aeruginosa chronic colonization in cystic fibrosis patients

PURPOSE OF REVIEW

Chronic infection with Pseudomonas aeruginosa is a leading cause of morbidity and mortality in individuals with cystic fibrosis despite the aggressive use of antibiotics. P. aeruginosa employs a number of strategies that promote chronic pulmonary colonization instead of acute infection. These include biofilm formation, evasion of the host immune system, and conversion to a mucoid phenotype. This review discusses recent advances regarding P. aeruginosa pathogenesis and biofilm behavior in the setting of chronic pulmonary disease.

RECENT FINDINGS

Biofilm formation in the cystic fibrosis lung likely occurs under anaerobic conditions, is controlled by bacterial quorum-sensing mechanisms, and is enhanced by environmental components in the cystic fibrosis airway. P. aeruginosa possesses regulatory pathways that recognize environmental cues to favor either acute infection or chronic colonization. P. aeruginosa that inhabit the respiratory tract accumulate mutations favoring chronic colonization. Azithromycin, a macrolide with clinical benefit in cystic fibrosis, alters P. aeruginosa biofilm formation. Promising new therapies that target biofilm formation include molecules that disrupt quorum sensing.

SUMMARY

Eradication of P. aeruginosa in cystic fibrosis patients remains problematic. As more information emerges about P. aeruginosa behavior in vivo, potential therapeutics directed against biofilms and mucoid P. aeruginosa are being developed.

Azithromycin reduces spontaneous and induced inflammation in DeltaF508 cystic fibrosis mice

Background

Inflammation plays a critical role in lung disease development and progression in cystic fibrosis. Azithromycin is used for the treatment of cystic fibrosis lung disease, although its mechanisms of action are poorly understood. We tested the hypothesis that azithromycin modulates lung inflammation in cystic fibrosis mice.

Methods

We monitored cellular and molecular inflammatory markers in lungs of cystic fibrosis mutant mice homozygous for the ΔF508 mutation and their littermate controls, either in baseline conditions or after induction of acute inflammation by intratracheal instillation of lipopolysaccharide from Pseudomonas aeruginosa, which would be independent of interactions of bacteria with epithelial cells. The effect of azithromycin pretreatment (10 mg/kg/day) given by oral administration for 4 weeks was evaluated.

Results

In naive cystic fibrosis mice, a spontaneous lung inflammation was observed, characterized by macrophage and neutrophil infiltration, and increased intra-luminal content of the pro-inflammatory cytokine macrophage inflammatory protein-2. After induced inflammation, cystic fibrosis mice combined exaggerated cellular infiltration and lower anti-inflammatory interleukin-10 production. In cystic fibrosis mice, azithromycin attenuated cellular infiltration in both baseline and induced inflammatory condition, and inhibited cytokine (tumor necrosis factor-α and macrophage inflammatory protein-2) release in lipopolysaccharide-induced inflammation.

Conclusion

Our findings further support the concept that inflammatory responses are upregulated in cystic fibrosis. Azithromycin reduces some lung inflammation outcome measures in cystic fibrosis mice. We postulate that some of the benefits of azithromycin treatment in cystic fibrosis patients are due to modulation of lung inflammation.