Macrolide antibiotics and the airway: antibiotic or non-antibiotic effects?

IMPORTANCE OF THE FIELD: The macrolides are a class of antibiotics widely prescribed in infectious disease. More recently, there has been considerable interest in potential indications for these agents, in addition to their simple antibacterial indications, in a number of lung pathophysiologies. AREAS COVERED IN THIS REVIEW: Demonstrated clinical efficacy of macrolides in diseases such as diffuse panbronchiolitis was difficult to ascribe to a direct antimicrobial action. More recently, positive experiences in dealing with post-transplant bronchiolitis obliterans syndrome suggests that other chronic lung diseases may benefit from macrolide therapy. This is important, as the treatment options for such diseases are often very limited. In this review, potential antibiotic and non-antibiotic beneficial actions of macrolide therapy are discussed and conclusions drawn from a limited but growing literature. WHAT THE READER WILL GAIN: The reader will gain an overview of lung diseases that may benefit from macrolides, and a consideration of the possible mechanisms underlying such benefit. TAKE HOME MESSAGE: The key message from our review is that this class of agents may prove to be a useful therapeutic option for a range of respiratory diseases, but that further trials and mechanistic studies are required to clarify their role.

Are clinical parameters and biomarkers predictive of severity of acute pulmonary emboli on CTPA?

BACKGROUND: Previous studies have shown that findings of computed tomography pulmonary angiography (CTPA) relate to outcome in pulmonary embolus (PE). These include clot burden as quantified using an obstruction index and markers of pressure overload such as right ventricle to left ventricle size ratio (RV/LV ratio). Little data exists correlating these findings with clinical presentation and biomarkers. AIM: To explore the link between clinical presentation and biomarkers with CTPA findings. METHODS: Retrospective case note analysis of consecutive cases presenting to a large teaching hospital. An independent radiologist reviewed CTPAs and clot burden quantified using an obstruction index. RESULTS: One hundred and seventy cases were identified and notes retrieved in 137 cases. (i) CLINICAL PRESENTATION: correlation was seen between clot burden and systolic blood pressure (BP) (r = -0.299, P = 0.0006) and heart rate (r = 0.240, P = 0.0056). Median obstruction index was significantly higher in those with a presenting BP <90 mmHg [41.25% (95% CI 30-50) vs. 15% (95% CI 12.5-25), (P = 0.0004)]. Clot burden was significantly higher in patients with temperature of >37.5 degrees C [30% (95% CI 25.0-42.5) vs. 15% (95% CI 12.5-28.3), P = 0.02)] and (ii)Biomarkers: significant correlation between clot burden and D-dimer was seen (r = 0.36, P = 0.0001). Location of thrombus was associated with significant differences in D-dimer level. A subgroup of patients had cardiac biomarkers measured (n = 24). There was a statistically significant correlation between troponin I and clot burden (r = 0.412, P = 0.048) and RV/LV ratio (r = 0.699, P = 0.0013). DISCUSSION: These findings suggest that clinical parameters and biomarkers have a role in predicting the radiological severity of PE. These data support the need for further studies of risk stratification in patients presenting with acute PE.

Targeting allograft injury and inflammation in the management of post-lung transplant bronchiolitis obliterans syndrome.

Chronic allograft dysfunction, manifesting as bronchiolitis obliterans syndrome (BOS), is the major cause of morbidity and mortality in human lung transplant recipients. While alloimmunity has a definite role, there is increasing interest in overall allograft injury and subsequent inflammation and remodeling. This review deals with nonalloimmune factors that may potentiate alloimmune injury. We discuss infection and reflux/aspiration as examples of allograft injury, which may lead to chronic loss of graft function and BOS. Surgical and nonsurgical treatments aimed at preventing these insults and improving survival are considered. The need for further evidence, including randomized-controlled trials, to evaluate the role of medical and surgical therapies is emphasized by the current literature.

Antimicrobial peptides in lung transplant recipients with bronchiolitis obliterans syndrome.

Mechanisms other than classical alloimmunity are implicated in the pathogenesis of bronchiolitis obliterans syndrome (BOS). It was hypothesised that antimicrobial peptides (AMPs), elements of the innate immune response, have a role in BOS pathogenesis. Pulmonary expression of the neutrophil-derived AMPs human cathelicidin (hCAP)-18/LL-37 and alpha-defensins (human neutrophil peptides (HNP) 1-3), and the epithelial cell-derived AMPs human beta-defensin (hBD)-2, elafin and secretory leukoprotease inhibitor (SLPI) were measured in stable lung transplant recipients and those with BOS. The relationship between airway pathogens and AMP levels was examined. Bronchoalveolar lavage (BAL) was performed on 44 lung transplant recipients (30 stable, 14 with BOS). BAL was cultured for pathogens and ELISA for AMPs was performed. The presence of airway pathogens was associated with significantly increased levels of neutrophil-derived and epithelial-derived AMPs. When patients without pathogens in BAL fluid were analysed, eight recipients with BOS had elevated hCAP-18/LL-37 and HNP 1-3 compared with 25 stable recipients. hBD-2 and elafin levels were comparable in BOS and stable recipients, but SLPI levels were reduced in BOS. Bronchiolitis obliterans syndrome is associated with elevated airway human cathelicidin 18/LL-37 and human neutrophil peptides 1-3 from activated neutrophils, even in the absence of pathogens. Together with reduced airway secretory leukoprotease inhibitor this may favour nonalloimmune airway injury with reduced antiprotease defence and increased neutrophil degranulation.

Primary airway epithelial cell culture from lung transplant recipients.

Long-term survival in lung transplantation is limited by the development of obliterative bronchiolitis, a condition characterised by inflammation, epithelial injury, fibroproliferation and obliteration of bronchioles leading to airflow obstruction. To investigate the role of the bronchial epithelium in the pathogenesis of obliterative bronchiolitis the current study aimed to establish primary bronchial epithelial cell cultures (PBEC) from lung allografts. Four to six bronchial brushings were obtained from sub-segmental bronchi of lung allografts. Cells were seeded onto collagen-coated plates and grown to confluence in bronchial epithelial growth medium. Bronchial brushings (n=33) were obtained from 27 patients. PBECs were grown to confluence from 12 out of 33 (39%) brushings. Failure to reach confluence was due to early innate infection. Bacteria were usually isolated from both bronchoalveolar lavage and culture media, but a separate population was identified in culture media only. Primary culture of bronchial epithelial cells from lung transplant recipients is feasible, despite a high rate of early, patient-derived infection. Latent infection of the allograft, identified only by bronchial brushings, may itself be a persistent stimulus for epithelial injury. This technique facilitates future mechanistic studies of airway epithelial responses in the pathogenesis of obliterative bronchiolitis.

Pepsin like activity in bronchoalveolar lavage fluid is suggestive of gastric aspiration in lung allografts.

BACKGROUND: A biologically plausible link between gastro-oesophageal reflux (GOR), aspiration, and lung allograft dysfunction has been suggested, but there is no systematic evidence indicating the presence of gastric contents in the lung. We have tested the hypothesis that pepsin, as a marker of aspiration, is detectable in bronchoalveolar lavage (BAL) fluid of allograft recipients who had not reported symptoms of GOR. METHODS: Standardised 3 x 60 ml surveillance BAL fluid samples from 13 chronologically sequential stable lung allograft recipients without chronic rejection (10 patients treated with a prophylactic proton pump inhibitor) were studied. Lavage supernatants were assayed by an ELISA based on a monospecific goat antibody for pepsin/pepsinogen. Pepsin levels were compared with those from four normal volunteer controls. RESULTS: Pepsin levels were measurable in all allograft recipients, in keeping with gastric aspiration (median 109 ng/ml (range 35-1375)). In the control group the pepsin levels were below the limit of detection. Treatment with a proton pump inhibitor was not correlated with pepsin levels. There was no correlation between BAL fluid neutrophils and pepsin levels. CONCLUSION: These data demonstrate lung epithelial lining fluid concentrations of pepsin in lung allograft recipients which are much higher than blood reference levels, with no detectable pepsin in controls. This provides direct evidence of gastric aspiration, which is potentially injurious to the allograft.

Phenotype of airway epithelial cells suggests epithelial to mesenchymal cell transition in clinically stable lung transplant recipients.

BACKGROUND: Obliterative bronchiolitis in chronic rejection of lung allografts is characterised by airway epithelial damage and fibrosis. The process whereby normal epithelium is lost and replaced by fibroblastic scar tissue is poorly understood, but recent findings suggest that epithelial cells can become fibroblasts through epithelial-mesenchymal transition (EMT). It is hypothesised that EMT occurs in lung allografts and plays a potential role in airway remodelling. METHODS: Sixteen stable lung transplant recipients underwent bronchoscopy with bronchoalveolar lavage (BAL), endobronchial biopsies, and bronchial brushings. Biopsy sections were stained for the fibroblast marker S100A4. Brushings were cultured on collagen, stained with anti-S100A4, and examined for further EMT markers including matrix metalloproteinase (MMP) zymographic activity and epithelial invasion through collagen coated filters. RESULTS: A median 15% (0-48%) of the biopsy epithelium stained for S100A4 in stable lung transplant recipients and MMP-7 co-localisation was observed. In non-stimulated epithelial cultures from lung allografts, S100A4 staining was identified with MMP-2 and MMP-9 production and zymographic activity. MMP total protein and activity was increased following stimulation with transforming growth factor (TGF)-beta1. Non-stimulated transplant epithelial cells were invasive and penetration of collagen coated filters increased following TGF-beta1 stimulation. CONCLUSIONS: This study provides evidence of EMT markers in lung allografts of patients without loss of lung function. The EMT process may represent a final common pathway following injury in more common diseases characterised by airway remodelling.

Hypothesis: epithelial-to-mesenchymal transition is a common cause of chronic allograft failure.

Renal, hepatic, and lung allografts are compromised by aggressively deteriorating function. This chronic process is produced by an overall burden of organ damage, but the pathophysiology remains poorly understood. Rates of chronic rejection in the lung, for example, have not substantially improved over the last decade, despite new immunosuppressive drugs and improvements in surgical procedure. We present a hypothesis that epithelial-to-mesenchymal transition is a common cause of chronic allograft failure. Research in this area may provide insights into chronic rejection of kidney, liver, and lung allografts that impact on future therapeutic strategies.

Reticular basement membrane thickening in airways of lung transplant recipients is not affected by inhaled corticosteroids.

INTRODUCTION: Chronic rejection is a major problem for all lung transplant programmes, which is functionally manifested by fixed airflow limitation, Bronchiolitis Obliterans Syndrome (BOS). The inclusion of a Pre-BOS category, BOS(0 approximately p), in newly revised guidelines, recognizes the potential importance of early changes. We have previously demonstrated reticular basement membrane (Rbm) thickening in clinically stable lung transplant recipients free from BOS. The present study extends this, testing the hypothesis that inhaled corticosteroid (ICS) therapy will lead to a decrease in Rbm thickness in lung transplant recipients. METHODS: A parallel group, bronchoscopic intervention study of clinically stable lung allograft recipients, free from BOS, but with evidence of airway inflammation. Following baseline assessment of Rbm thickening, subjects were randomized to 3 months of either chlorofluorocarbon-driven beclomethasone diproprionate (BDP) 400 microg b.i.d., or a formulation designed to yield at least an equivalent dose, hydrofluoroalkane-driven BDP, 200 microg b.i.d. RESULTS: Three months treatment with a moderate dose of ICS, including a formulation designed for preferential small airway deposition, had no effect on Rbm thickening (13+/-3 vs. 14+/-5 microm post-ICS). CONCLUSION: Our data would suggest that airway remodelling can occur early in lung allografts and is not affected by moderate dose ICS therapy. Longitudinal studies are required to describe the pathophysiological processes involved in BOS, and specifically to elucidate potential relationships between airway remodelling, airflow obstruction and allograft failure.

Effect of nebulized epoprostenol (prostacyclin) on exhaled nitric oxide in patients with pulmonary hypertension due to congenital heart disease and in normal controls.

Inhaled epoprostenol (prostacyclin) may be used in the treatment of severe pulmonary hypertension, improving oxygenation and reducing pulmonary artery pressures. We have observed symptomatic benefits of epoprostenol in patients with congenital heart disease that extend beyond acute haemodynamic effects of the drug, which has a short biological half-life. The aim of this study was to examine the effects of epoprostenol in patients and normal subjects on exhaled nitric oxide (eNO), based on the hypothesis that the drug may alter the resting vasoconstrictor/vasodilator balance. Nine patients with pulmonary hypertension complicating left-to-right cardiac shunts and nine healthy controls received 100 microgram of nebulized epoprostenol. Exhaled eNO was measured, using a chemiluminescence method, before, immediately after and 18 h after nebulization. There was no significant difference between the two groups in baseline eNO or eNO immediately following nebulized epoprostenol. Epoprostenol produced a delayed elevation in eNO 18 h after nebulization in patients, but not in normal controls. This study supports the concept that epoprostenol, while having no effect on the normal pulmonary circulation, acts on the hypertensive circulation via a mechanism that may result in a delayed alteration of vasoconstrictor/vasodilator balance.