Summary: 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-κB) 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.

Mechanisms of Action and Clinical Application of Macrolides as Immunomodulatory Medications

Azithromycin: mechanisms of action and their relevance for clinical applications.

During infection, Pseudomonas aeruginosa employs bacterial communication (quorum sensing [QS]) to coordinate the expression of tissue-damaging factors. QS-controlled gene expression plays a pivotal role in the virulence of P. aeruginosa, and QS-deficient mutants cause less severe infections in animal infection models. Treatment of cystic fibrosis (CF) patients chronically infected with P. aeruginosa with the macrolide antibiotic azithromycin (AZM) has been demonstrated to improve the clinical outcome. Several studies indicate that AZM may accomplish its beneficial action in CF patients by impeding QS, thereby reducing the pathogenicity of P. aeruginosa. This led us to investigate whether QS inhibition is a common feature of antibiotics. We present the results of a screening of 12 antibiotics for their QS-inhibitory activities using a previously described QS inhibitor selector 1 strain. Three of the antibiotics tested, AZM, ceftazidime (CFT), and ciprofloxacin (CPR), were very active in the assay and were further examined for their effects on QS-regulated virulence factor production in P. aeruginosa. The effects of the three antibiotics administered at subinhibitory concentrations were investigated by use of DNA microarrays. Consistent results from the virulence factor assays, reverse transcription-PCR, and the DNA microarrays support the finding that AZM, CFT, and CPR decrease the expression of a range of QS-regulated virulence factors. The data suggest that the underlying mechanism may be mediated by changes in membrane permeability, thereby influencing the flux of N-3-oxo-dodecanoyl-L-homoserine lactone.

https://aac.asm.org/content/aac/52/10/3648.full.pdf

Effects of Antibiotics on Quorum Sensing in Pseudomonas aeruginosa

Context Azithromycin is recommended as therapy for cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa infection, but there has not been sufficient evidence to support the benefit of azithromycin in other patients with CF. Objective To determine if azithromycin treatment improves lung function and reduces pulmonary exacerbations in pediatric CF patients uninfected with P aeruginosa. Design, Setting, and Participants A multicenter, randomized, double-blind placebo-controlled trial was conducted from February 2007 to July 2009 at 40 CF care centers in the United States and Canada. Of the 324 participants screened, 260 were randomized and received study drug. Eligibility criteria included age of 6 to 18 years, a forced expiratory volume in the first second of expiration (FEV 1 ) of at least 50% predicted, and negative respiratory tract cultures for P aeruginosa for at least 1 year. Randomization was stratified by age of 6 to 12 years vs 13 to 18 years and by CF center. Intervention The active group (n = 131) received 250 mg (weight 18-35.9 kg) or 500 mg (weight ≥36 kg) of azithromycin 3 days per week (Monday, Wednesday, and Friday) for 168 days. The placebo group (n = 129) received identically packaged placebo tablets on the same schedule. Main Outcome Measures The primary outcome was change in FEV 1 . Exploratory outcomes included additional pulmonary function end points, pulmonary exacerbations, changes in weight and height, new use of antibiotics, and hospitalizations. Changes in microbiology and adverse events were monitored. Results The mean (SD) age of participants was 10.7 (3.17) years. The mean (SD) FEV 1 at baseline and 168 days were 2.13 (0.85) L and 2.22 (0.86) L for the azithromycin group and 2.12 (0.85) L and 2.20 (0.88) L for the placebo group. The difference in the change in FEV 1 between the azithromycin and placebo groups was 0.02 L (95% confidence interval [CI], −0.05 to 0.08; P = .61). None of the exploratory pulmonary function end points were statistically significant. Pulmonary exacerbations occurred in 21% of the azithromycin group and 39% of the placebo group. Participants in the azithromycin group had a 50% reduction in exacerbations (95% CI, 31%-79%) and an increase in body weight of 0.58 kg (95% CI, 0.14-1.02) compared with placebo participants. There were no significant differences between groups in height, use of intravenous or inhaled antibiotics, or hospitalizations. Participants in the azithromycin group had no increased risk of adverse events, but had less cough (−23% treatment difference; 95% CI, −33% to −11%) and less productive cough (−11% treatment difference; 95% CI, −19% to −3%) compared with placebo participants. Conclusion In children and adolescents with CF uninfected with P aeruginosa, treatment with azithromycin for 24 weeks did not result in improved pulmonary function. Trial Registration clinicaltrials.gov Identifier: NCT00431964

https://jamanetwork.com/journals/jama/articlepdf/185799/joc05048_1707_1715.pdf

Effect of azithromycin on pulmonary function in patients with cystic fibrosis uninfected with Pseudomonas aeruginosa: a randomized controlled trial.

Rationale: Bronchiolitis obliterans syndrome (BOS) remains the leading cause of death after lung transplantation. Treatment is difficult, although azithromycin has recently been shown to improve FEV1. The exact mechanism of action is unclear.Hypotheses: (1) Azithromycin reduces airway neutrophilia and interleukin (IL)-8 and (2) airway neutrophilia predicts the improvement in FEV1.Methods: Fourteen lung transplant patients with BOS (between BOS 0-p and BOS 3) were treated with azithromycin, in addition to their current immunosuppressive treatment. Before and 3 mo after azithromycin was introduced, bronchoscopy with bronchoalveolar lavage (BAL) was performed for cell differentiation and to measure IL-8 and IL-17 mRNA ratios.Results: The FEV1 increased from 2.36 (± 0.82 L) to 2.67 L (± 0.85 L; p = 0.007), whereas the percentage of BAL neutrophilia decreased from 35.1 (± 35.7%) to 5.7% (± 6.5%; p = 0.0024). There were six responders to azithromycin (with an FEV1 increase of > 10%) and eight nonresponders. Usi...

https://www.atsjournals.org/doi/pdf/10.1164/rccm.200601-071OC

Azithromycin reduces airway neutrophilia and interleukin-8 in patients with bronchiolitis obliterans syndrome

Macrolides exert their effects on the host by modulation of immune responses. In this study, we assessed the therapeutic efficacy of azithromycin in a murine model of mucoid Pseudomonas aeruginosa endobronchial infection. The clearance of Pseudomonas from the airway of mice treated with the macrolide azithromycin was not different than untreated mice challenged with Pseudomonas beads. However, the azithromycin-treated mice showed a remarkable reduction in lung cellular infiltrate in response to Pseudomonas beads, as compared with untreated mice. This effect was associated with significant decreases in lung levels of tumor necrosis factor-alpha and keratinocyte-derived chemokine in azithromycin-treated mice compared with untreated mice. Furthermore, there was a significant reduction in the response of both mouse and human neutrophils to chemokine-dependent and -independent chemoattractants when studied in vitro. Inhibition of chemotaxis correlated with azithromycin-mediated inhibition of extracellular signal-regulated kinase-1 and -2 activation. This study indicates that the azithromycin treatment in vivo results in significant reduction in airway-specific inflammation, which occurs in part by inhibition of neutrophil recruitment to the lung through reduction in proinflammatory cytokine expression and inhibition of neutrophil migration via the extracellular signal-regulated kinase-1 and -2 signal transduction pathway.

https://www.atsjournals.org/doi/pdf/10.1164/rccm.200402-200OC

Azithromycin blocks neutrophil recruitment in Pseudomonas endobronchial infection

Myelofibrosis is a rare progressive cancer of the bone marrow that disrupts the normal production of healthy blood cells, leading to bone marrow failure. Patients with myelofibrosis and severe thrombocytopenia (platelet count below 50 × 109/L) have a wide range of unmet medical needs compared with those without thrombocytopenia. Usually, these patients have an increased disease burden, increased transfusion dependence, shorter overall survival, and limited treatment options. Pacritinib is a new oral kinase inhibitor specifically targeting Janus kinase 2 (JAK2), interleukin-1 receptor-associated kinase 1 (IRAK-1) and colony-stimulating factor 1 receptor (CSF-1R), and is indicated for the treatment of adults with moderate or high risk of primary or secondary myelofibrosis (post-polycythemia or post-primary thrombocytopenia) whose platelet count is less than 50 × 109/L. In this review, we introduce pacritinib and make a brief comparison of different JAK inhibitors in clinical application.

Katherine S. Young

Papers

Azithromycin blocks neutrophil recruitment in Pseudomonas endobronchial infection

Pacritinib for myelofibrosis in adults with thrombocytopenia.