Early lung disease in cystic fibrosis

Review

Early lung disease in cystic fibrosis Hartmut Grasemann, Felix Ratjen Lancet Respir Med 2013; 1: 148–57 Published Online March 12, 2013 http://dx.doi.org/10.1016/ S2213-2600(13)70026-2 See Review pages 137, 158, and 164 Division of Respiratory Medicine, Department of Paediatrics, and Programme in Physiology and Experimental Medicine, Research Institute, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada (H Grasemann MD, Prof F Ratjen MD) Correspondence to: Prof Felix Ratjen, The Hospital for Sick Children, University of Toronto, Toronto, ON M5G 1X8, Canada [email protected]

Lung disease in patients with cystic fibrosis is characterised by inflammation and recurrent and chronic infections leading to progressive loss in pulmonary function and respiratory failure. Early management of disease results in substantially improved pulmonary function at first testing (at roughly 6 years of age), but the annual decline in pulmonary function tests in older patients has remained unchanged showing how important the early years are in the disease process. Treatment regimens for patients with cystic fibrosis have changed from predominantly symptomatic treatment to preventive or causal (ie, treatments that address the underlying mechanisms of disease) therapeutic interventions. The infant and preschool age (2–5 years) could represent a unique period of opportunity to postpone or even prevent the onset of cystic fibrosis lung disease. We summarise the current knowledge and the methods used to characterise and quantify early lung disease. We discuss treatment strategies including new drugs that are being developed and their potential role in the treatment of early lung disease in patients with cystic fibrosis.

Introduction Improved understanding of disease pathophysiology and enhanced multidisciplinary care in specialised centres has resulted in improved outcomes and life expectancy for patients with cystic fibrosis.1 However, most treatment interventions target secondary consequences of the CFTR defect, and not the underlying mechanisms of the disease. The natural course of cystic fibrosis lung disease, which results in respiratory failure and death, can often be slowed but not prevented. Additionally, treatment is usually delayed until patients become symptomatic, at which point substantial damage to the lung might already exist. Newborn screening for cystic fibrosis has been implemented in many countries and can identify cystic fibrosis in individuals before respiratory symptoms develop. This early identification of disease has opened up new possibilities for studies aiming to improve our understanding of the onset and characteristics of early lung disease in patients with cystic fibrosis, and to start treatment interventions earlier.

Drivers of early changes in the cystic fibrosis lung In 1991, when Anderson and colleagues reported that CFTR acts as a cAMP-activated chloride transporter, it was believed that abnormal chloride transport of

Key messages • Cystic fibrosis lung disease is caused by abnormal epithelial ion transport resulting in diminished airway surface liquid, accumulation of mucus, inflammation, and bacterial infections. • Patients with cystic fibrosis develop substantial lung disease early in life, even before they present with respiratory symptoms. • Because early therapeutic interventions are needed, sensitive and reliable methods are essential to detect and monitor early lung damage and to guide early intervention strategies.

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epithelial cells was thought to explain the pathophysiology recorded in patients with cystic fibrosis.2 Since then, the simple picture of CFTR dysfunction directly causing lung disease has evolved; CFTR has many functions including inhibition of the epithelial sodium channel (ENaC), and the loss of functional CFTR leads to excessive sodium absorption through ENaC.3 This loss of inhibitory control is believed to have a role in the development of airway surface liquid depletion, but whether this is a primary event is unknown.4,5 Animal models were developed to understand early changes associated with disease not easily studied in human beings. Most CFTR-deficient mouse models do not develop cystic fibrosis-like lung disease, which might be partly explained by the activity of alternate chloride channels in airway epithelia of these mice.6 By contrast, in a mouse model with airway-specific overexpression of the β subunit of ENaC, changes in sodium absorption resulted in depleted airway surface liquid, reduced mucus clearance, obstruction of airway mucus, reduced bacterial clearance, and chronic neutrophilic inflammation—typical features of cystic fibrosis lung disease (figure 1).4,7 These findings support the idea that increased sodium absorption is crucial for the development of cystic fibrosis lung disease, and suggest that it is not the direct result of CFTR dysfunction, but the effect this has on other channels that is important in disease development. However, findings from recent studies in transgenic pigs with cystic fibrosis, which developed typical features of cystic fibrosis lung disease and had a normal amount of airway surface liquid and normal sodium transport after birth have challenged this notion.5 These findings could suggest that secondary events such as infection and inflammation are essential for phenotypic changes seen in patients with advanced disease to develop. Findings from studies in pigs also show that deficiency of CFTR-mediated transport of bicarbonate and regulation of the pH of airway surface liquid inhibits antimicrobial function in the cystic fibrosis airways.8 www.thelancet.com/respiratory Vol 1 April 2013

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CFTR has an important role in the maintenance of glutathione and thiocyanate concentrations in the fluid of the epithelial lining. Glutathione deficiency in the airways of patients with cystic fibrosis might contribute to lung inflammation and oxidative stress.9 An understanding of the underlying mechanisms of cystic fibrosis lung disease development could be important to decide how to initiate strategies for early personalised treatment. Further important questions that need to be addressed include the potential role of socioeconomic status and environmental factors in the heterogeneity of early cystic fibrosis lung disease. Environmental factors including access to care, variation in practice between centres, adherence to treatment, and exposures to inhaled toxins (eg, ozone and cigarette smoke) could contribute to the heterogeneity of early cystic fibrosis lung disease. Other risk factors are age of infection with specific pathogens and initiation of, and response to, specific antibiotic treatments. Genetic factors other than CFTR mutations can act as modifiers of cystic fibrosis lung disease, and might contribute to the establishment and timing of infections with Pseudomonas aeruginosa.10,11 Genes involved in innate immune response such as mannose-binding lectin 2 (MBL2), and regulatory genes such as transforming growth factor beta 1 (TGFβ1), play a part in the progression of cystic fibrosis lung disease by affecting infectioninduced inflammatory responses in the lungs.12,13 Genetic modifiers have also been identified in other organ manifestations of cystic fibrosis including liver disease and meconeum ileus.14–16 Constituents of the apical plasma membrane including the transporter proteins SLC9A3 and SLC6A14 (that have been found to be associated with meconeum ileus14) show evidence of pleiotropic effects— ie, an increased risk of meconeum ileus and early manifestation of cystic fibrosis lung disease in children.15 These genetic studies might identify molecules or pathways that are important in the pathogenesis of cystic fibrosis lung disease, and could help to identify at-risk patients who could benefit from specific treatments targeting these disease-modifying pathways. Studies addressing the early histopathological abnormalities in children with cystic fibrosis are scarce because they need invasive sampling. Additionally, little information is available from old autopsy studies in babies with meconium ileus. Although sophisticated techniques to visualise the airway surface liquid layer were not available at the time of these autopsies, the epithelium seemed largely normal, and the earliest airway abnormalities were mucous-gland plugging leading to peripheral airway dilatation.17 Abnormalities were subtle, and these observations, and function measurements done in the first months of life, suggest that the lungs are largely normal at birth. Therefore, early intervention might not only postpone deterioration of existing lung disease, but if initiated soon after birth, keep cystic fibrosis lungs healthy. www.thelancet.com/respiratory Vol 1 April 2013

Normal

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Figure 1: Depleted airway surface liquid in cystic fibrosis airways results in reduced mucus clearance, neutrophilic inflammation, and bacterial infection

Early cystic fibrosis lung disease The best evidence of how early lung disease manifests itself comes from a series of studies in infants enrolled in the Australian Respiratory Early Surveillance Team for Cystic Fibrosis (AREST CF).18–20 In a longitudinal assessment of young children (aged 1·0–3·2 years) with cystic fibrosis diagnosed by newborn screening, CT evidence for bronchiectasis (figure 2) was reported in 44% of patients at initial assessment. Although 26% of the scans showed apparent resolution on follow-up scans after 1 year, bronchiectasis seen at the initial scan persisted in 74% and showed progression in 63%. Air trapping was the most common finding (reported in 88% of the scans) and persisted in 81% of subsequent scans. Most patients with structural abnormalities shown by CT had no clinically apparent lung disease. The progression of structural changes was associated with neutrophilic inflammation and pulmonary infection.18 Findings from a prospective multicentre observational study in England also showed high rates of abnormalities in newborn-screened infants (aged 1 year) with cystic fibrosis.21 In this study, highresolution CTs were done under general anaesthesia in infants across three tertiary respiratory centres with identical protocols. Volumetric inspiratory scans at 25 cm water and expiratory images were taken. The frequency of bronchiectasis in this cohort was similar to that in the Australian AREST CF study,19,20 although air trapping was less common.20 Poor interobserver agreement was evident, particularly in scans showing mild changes.21 Could differences in the patient populations, early treatment strategies, or technical aspects of CT acquisition or interpretation protocols 149

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Figure 2: Cystic fibrosis bronchiectasis

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Figure 3: Factors contributing to lung disease in cystic fibrosis

explain these differences? Although the time course of early structural changes needs further study, by school age (5 years of age), bronchiectasis is found in most patients despite spirometric lung function within the normal range.22 Many studies have assessed airway inflammation and infection in infants with cystic fibrosis, and findings have shown increased inflammation in the presence of infection.19,23,24 However, whether inflammation arises without previous or present infection is unknown. Flexible bronchoscopy and bronchoalveolar lavage (BAL) are used to obtain biomaterial from the lower airways and can be used to define and study the effects of treatment on the progression of airway inflammation and airway infection. BAL done in infants (<6 months) after diagnosis by newborn screening showed that most patients had neutrophilic inflammation.19,23,24 Whereas initial data suggested the presence of lower-airway inflammation in the absence of infection,23 findings from an Australian study24 showed that asymptomatic patients without pathogens in their BAL fluid had inflammation profiles similar to patients with pathogens in BAL. However, these results have been questioned because the control group included patients undergoing bronchoscopy for clinical indications.24 Data from a study in newborn-screened infants from England suggest that compared with healthy controls, absolute 150

BAL fluid cell count and neutrophil differential count in asymptomatic infants with cystic fibrosis were already increased by 4 months of age, even in those who were culture negative.25 These data suggest that inflammation in early cystic fibrosis lung disease is not always secondary to infection. While the debate regarding the onset of inflammation continues, there is consensus that infection is the main driver of airway inflammation in early cystic fibrosis lung disease (figure 3). Despite the absence of respiratory symptoms in most infants in AREST CF, increased numbers of inflammatory markers and culture positivity for bacteria were found in a marked proportion of BAL samples.19 Inflammation was further increased in patients with clinical signs of infection and respiratory symptoms. Structural lung disease shown by CT images was associated with increased free-neutrophil elastase activity, suggesting an important role of neutrophils in early lung damage.19 Present treatment fails to control this clinically silent disease progression; therefore, more effective treatment interventions targeting early inflammation and infection could be important. CT imaging and findings from BAL studies have suggested that pulmonary function testing alone is not sensitive enough to detect early manifestations of lung disease in young children with cystic fibrosis.22 However, abnormal pulmonary function in cystic fibrosis is evident in preschool children (2–5 years of age), toddlers (younger than 2 years), and infants, even as early as 3 months of age.26–28 Airway inflammation in BAL was associated with decreased results from infant pulmonary function testing, and infection of the lower airways with Staphylococcus aureus or Pseudomonas aeruginosa was associated with an increased rate of lung-function decline.29 In addition to spirometric measures of lung function, multiple breath washout methods showed changes in the lung clearance index (LCI; a measure of ventilation inhomogeneity) in young children with cystic fibrosis. Multiple breath inert gas washout tests describe the rate of clearance of an inert gas from the lungs or the uniformity of gas mixing. Because LCI is abnormal (increased) in patients with cystic fibrosis who have normal spirometry values, the index can be used to detect changes early in the course of cystic fibrosis lung disease. Increased (worse) LCI was associated with infection and inflammation. LCI was higher in patients with cystic fibrosis positive for P aeruginosa, and correlated positively with BAL inflammatory markers.30 In newborn-screened infants with cystic fibrosis (aged 3 months) studied in the London Cystic Fibrosis Collaboration, LCI, forced expiratory volume in 0·5 s (FEV0·5), and forced expiratory flow between 25% and 75% of vital capacity (FEF25–75) were significantly reduced. The use of LCI and plethysmographic functional residual capacity seemed to be complimentary, and together identified abnormalities in 35% of infants.26 www.thelancet.com/respiratory Vol 1 April 2013

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Diagnostic methods in early cystic fibrosis lung disease Although sensitivity to detect early changes is important for research studies assessing the natural history of the disease, diagnostic methods that can be easily applied in young and non-compliant patients and used in routine clinical practice to assess response to interventions are needed (figure 4). The accuracy of BAL in definition of early infection is better than other techniques in infants and young children unable to produce sputum although a negative upper-airway culture for P aeruginosa is highly predictive of a negative BAL culture.31 However, routine BAL has not been shown to improve clinical outcome when targeted at detection, treatment, and eradication of P aeruginosa infections in children with cystic fibrosis younger than 6 years.32 Although the procedural risk of BAL is low in patients with cystic fibrosis, because of the relative invasiveness,33 general anaesthesia is usually needed, at least in younger children. Although most centres do not routinely use BAL in this age group, the threshold to do BAL should be low in symptomatic children not responding to treatment with empirical antibiotics. CT imaging of the chest is a sensitive method to visualise structural changes in the lung, and quantification with validated scoring systems allows for longitudinal monitoring of observed changes. Chest CT scores improve in children with cystic fibrosis given antibiotic treatment for a pulmonary exacerbation,34,35 and in small pilot studies, after treatment with dornase alfa36 and tobramycin solution for inhalation.37,38 A disadvantage of CT scans is exposure of the patient to ionising radiation. Because routine monitoring has not been shown to affect clinical outcome, routine annual or biannual scans are not done worldwide. However, new scanners and improved analysis algorithms will result in decreased radiation-dose exposures and related risks. Imaging methods that do not use ionising radiation such as MRI, either alone or in combination with polarised gas ventilation, are not sensitive enough to detect subtle changes to lung structure, but might be suitable alternatives in the future.39,40 The ability of lung-function testing to detect early abnormalities in infants with cystic fibrosis has been reviewed.41 The raised volume rapid thoraco-abdominal compression technique can detect abnormalities in forced expiratory flows in a large proportion of infants with cystic fibrosis diagnosed clinically or by newborn screening.27,42,43 Although infant pulmonary-function testing is safe and is undertaken by an increasing number of institutions worldwide, adequate sedation is essential because tests are usually done when the infant is asleep. Pulmonary-function tests seem to be less sensitive than CT imaging for the detection of early cystic fibrosis lung disease and for monitoring of progression in both infants and children,18,20,22,44 but infant lungwww.thelancet.com/respiratory Vol 1 April 2013

Imaging (CT, MRI) Structure

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Figure 4: Diagnostic methods to detect early cystic fibrosis lung disease

function testing did show a treatment effect in a 2012 interventional trial.45 Generally, forced expiratory volume in 1 s (FEV1) is the main measure of lung disease in older patients (6 years and older) with cystic fibrosis. Age-appropriate changes of the spirometry testing environment and of quality-control criteria46 have made forced expiratory manoeuvres suitable for children in the preschool age group. Data for spirometry values in preschool children with cystic fibrosis compared with those with normal values, and for the sensitivity of preschool spirometry to detect early pulmonary abnormalities are scarce.47,48 However, data from a 2012 multicentre trial suggested that spirometry outcomes in preschool patients with cystic fibrosis are more discriminative than are those from forced oscillation or inductance plethysmography.49 Multiple breath inert gas washout tests are done during tidal breathing and are therefore feasible in infants and preschool children. In infants, sedation might be needed because tests are usually done when the infant is asleep. In preschool children, tests are done while the child is awake and sitting in an upright position. Findings from studies done in the past 3 years show that LCI can improve substantially in paediatric patients with cystic fibrosis with otherwise normal pulmonary function after treatment interventions with inhaled hypertonic saline,50 dornase alfa,51 or the CFTR potentiator ivacaftor.52 A pilot study of the use of inhaled hypertonic saline in infants and preschool children supports these findings.53 Therefore, multiple breath inert gas washout is a promising method to assess and follow up early cystic fibrosis lung disease (figure 5).

New treatments for cystic fibrosis Optimised growth and nutrition are essential for lung health in young patients with cystic fibrosis. New developments in treatments for cystic fibrosis have been reviewed elsewhere.4,54 Observations of early structural and functional abnormalities suggest that treatment should be initiated early, before the infant becomes symptomatic. However, evidence of starting treatment early is scarce because most data for treatment of young children with cystic fibrosis are 151

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Figure 5: Multiple breath washout test in a child with cystic fibrosis (A) and a healthy preschool child (B) The black line represents flow and the green line the tracer gas sulphur hexafluoride during the washout. The red and blue lines define the section of the last breath of the washout used to calculate lung clearance index. The dashed red line is the time point used to determine lung clearance index. These are less crucial for the reader to know. The duration of the washout is longer in the child with cystic fibrosis versus the control child (49 vs 22 breaths), showing a longer washout in the diseased lung.

from clinical trials in children older than 6 years or adults. One reason why clinical studies of treatment interventions in young children with cystic fibrosis are scarce is that clinically meaningful pulmonary endpoints in this age group have not been defined. However, the development of sensitive new clinical methods should bridge this gap in the near future. In 2012, a multicentre study assessing the efficacy of hypertonic saline in infants and young children with cystic fibrosis was the first large interventional trial assessing non-microbiological endpoints in young children.45 This trial helped to increase our understanding of suitable clinical endpoints for future interventional trials.45 Furthermore, a 2012 workshop supported by the European Respiratory Society summarised the benefits and disadvantages of the use of the different clinical trial endpoints in children younger than 6 years, and prioritised methods that are already sufficiently developed.55 Although multiple breath washout and CT scans evolved as the two most advanced technologies in the validation process, a one152

size-fits-all approach is unlikely to be the best strategy, and study endpoints will need to be tailored on the basis of individual trials. Most centres introduce physiotherapy to improve airway clearance shortly after diagnosis. However, little convincing evidence for the efficacy of physiotherapy in infants and young children is available. Postural drainage combined with percussion is commonly used in this age group, but should avoid positions where the head is tilted downwards because this position induces gastro-oesophageal reflux and has been linked to decreased lung function in later life.56 Mucolytic agents that decrease elasticity and viscosity of mucus are used in older patients to improve clearance by optimisation of the viscoelasticity of mucus.57 The best studied compound is inhaled recombinant human DNase (dornase alfa)—a drug that reduces sputum viscosity, improves pulmonary function, and reduces the number of pulmonary exacerbations in patients with cystic fibrosis.51,58–65 Evidence in older children (older than 5 years) with www.thelancet.com/respiratory Vol 1 April 2013

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early lung disease also suggests that dornase alfa has a positive effect on airway inflammation.66 Additionally, findings from a retrospective database analysis show that long-term treatment reduces lung function decline.67 The mechanism of action is digestion of extracellular neutrophil-derived DNA that accumulates in the airways of patients with cystic fibrosis and contributes to the increased viscosity of airway secretions. The beneficial effects of dornase alfa are well established in adult patients and older children with cystic fibrosis. In a preliminary study of children (<5 years of age) with cystic fibrosis, the administration of dornase alfa was associated with improvement in the high-resolution CT scan.68 Use of dornase alfa in children is fairly common (about 30% of patients treated with the drug are younger than 6 years8), and evidence for its safety exists.69 Inhaled nebulised hypertonic saline improves mucociliary clearance in a dose-dependent way in patients with cystic fibrosis.70 The use of hypertonic saline has also shown promising results in infants with respiratory syncytial virus-induced bronchiolitis.71 Whereas in bronchiolitis, the beneficial effect can be partly explained by hypertonic saline’s beneficial effect on airway mucosal oedema, the proposed mechanism in cystic fibrosis is the reversal of airway dehydration.72 In a multicentre trial, Elkins and colleagues concluded that pulmonary exacerbations were lower in older individuals (aged 18±9 years) with cystic fibrosis given hypertonic saline treatment for 1 year than in individuals given placebo.73 Use of hypertonic saline treatment was also associated with improvements in lung function. Patients in the placebo group who received isotonic saline also did not have reduced lung function during the observation period, raising the question of whether isotonic saline might also be effective as a hydrator in patients with cystic fibrosis.73 The findings of another study showed beneficial effects in patients with mild cystic fibrosis lung disease given hypertonic saline.50 Areas with adequate ventilation are likely to have improved deposition of inhaled agents; therefore, treatment with hypertonic saline might be most efficacious when initiated before substantial mucus accumulation in the airways has occurred. Because nebulised 7% saline solution does not have acute effects on lung function in most patients, it can be used safely in infants with cystic fibrosis.74,75 Furthermore, data from a 2-week open-label study suggested that repeated administration of the solution in infants with cystic fibrosis is safe.76 However, a recently published large multicentre trial in infants and children younger than 6 years did not show an effect of 48-week treatment with inhaled hypertonic saline on the rate of pulmonary exacerbation compared with normal saline inhalation.45 Additionally, secondary endpoints did not differ significantly between the two groups. Infant pulmonaryfunction testing was done as an exploratory outcome in www.thelancet.com/respiratory Vol 1 April 2013

a subgroup of participants and differed significantly between treatment groups; the mean change in FEV0·5 was 38 mL greater in the hypertonic group than in the normal saline group.45 25 patients enrolled at the Toronto site had paired baseline and follow-up multiple breath inert gas washout measurements taken after 1 year. Infants given hypertonic-saline had significantly reduced LCI from baseline to follow-up, whereas LCI remained stable in infants in the isotonic saline group.53 Although these data are promising, because they were obtained in a subgroup of the overall study population they are not conclusive evidence that hypertonic saline has beneficial effects in infants and young children with cystic fibrosis. Antibiotic treatment has a major role in the treatment and prevention of infection-related damage of the cystic fibrosis lung. A broad range of bacteria can be found in routine microbiology testing of lower-airway secretions or throat swabs in patients with cystic fibrosis who are unable to produce sputum, including organisms that colonise the airways of healthy children.77 Therefore, the detection of an organism might not prompt initiation of antibiotic treatment in the absence of any symptoms. However, this is different for organisms such as Pseudomonas aeruginosa and early eradication of newly acquired P aeruginosa has become a successful strategy. Initial colonisation might be transient, and even in patients with persistent infection with non-mucoid strains, the initial phase might not be associated with a change in clinical status.78–80 However, if untreated, most patients will eventually develop chronic infection that can no longer be eradicated even with intensive antibiotic treatment.81 Therefore, antibiotic treatment should be initiated in response to a new detection of P aeruginosa to prevent or delay the onset of chronic infection.82–88 If early infection is cleared, decline in lung function can be avoided.89 Eradication of P aeruginosa from the airways with inhaled tobramycin can be as effective in infants and small children as it is in adults.90 Decisions about treatment strategies are generally made on the basis of oropharyngeal cultures (despite their lack of specificity) because BAL-directed treatment during the first 5 years of life does not decrease the prevalence of infections with P aeruginosa or improve outcome with CT scores.32 Macrolide antibiotics have mucolytic properties and attenuate the production of pro-inflammatory cytokines by neutrophils, monocytes, and bronchial epithelial cells in vitro.91,92 Macrolides reduce the accumulation of neutrophils by inhibition of ICAM-1 on epithelial cell surfaces.93 In-vitro evidence suggests that the macrolide azithromycin has antimicrobial efficacy against P aeruginosa growing in biofilms.94 The clinical benefit of azithromycin treatment is well established for patients with cystic fibrosis who are chronically infected with P aeruginosa.95–97 Patients with cystic fibrosis not infected with P aeruginosa can also benefit from azithromycin 153

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Search strategy and selection criteria We searched PubMed from Jan 1, 2007, to Jan 31, 2013, for publications in English with the terms “cystic fibrosis and early lung disease”, “cystic fibrosis and children”, and “cystic fibrosis and infants”. We also searched the reference lists of the identified articles for further relevant papers, and included selected abstracts presented on the topic from the 2012 North American Cystic Fibrosis Conference.

treatment because the drug has been shown to reduce the rate of pulmonary exacerbations.98,99 However, azithromycin can have negative effects–eg, the development of resistance of common organisms such as S aureus and Haemophilus influenzae. Additionally, treatment could predispose to lung infection by nontuberculous mycobacteria.100 An interventional trial (NCT01270074) is planned to investigate whether early azithromycin treatment can postpone structural lung damage in infants with cystic fibrosis diagnosed by newborn screening. This is likely to be the first of several early-intervention studies in the next decade that have the potential to change the trajectory of infants with cystic fibrosis diagnosed by newborn screening. Excessive neutrophilic inflammation in individuals with cystic fibrosis is thought to promote lung damage, making inflammation a promising target for therapeutic interventions. However, because infection coexists with inflammation in most patients, a challenge is to find the ideal balance between specific treatments that target just inflammation and do not have negative effects on defence against infections. Nevertheless, treatment with non-specific antiinflammatory drugs such as high-dose ibuprofen has beneficial effects on pulmonary function in older children with cystic fibrosis.101,102 Since neutrophil elastase in BAL predicts subsequent bronchiectasis,23 treatment with antiproteases could be effective in the prevention of lung damage. Treatment with inhaled α1antitrypsin has resulted in moderate reduction in activity of neutrophil elastase and decreased Pseudomonas load in older patients.103 An explanation for this effect is that reduced neutrophil elastase activity after inhalation of α1-antitrypsin leads to increased expression of CXCR1, a chemokine receptor that mediates neutrophil activation by interleukin 8.104 Therefore, although data from clinical studies in this age group are scarce, antiprotease could be a potential early intervention strategy. To minimise the development and progression of lung disease, clinically effective treatments targeting the underlying defect in CFTR function should be introduced immediately after diagnosis by newborn screening. Up to now, little evidence for this strategy from studies in human beings exists. In animal studies, treatment with the ENaC inhibitor amiloride in mice 154

overexpressing ENaC was very efficacious when initiated after birth, whereas rescue treatment in older animals had minimum efficacy.105 The CFTR potentiator ivacaftor (kalydeco), which has been shown to substantially improve lung function in adults and children with the Gly551Asp mutation,106 is being studied in 2–5 year old children with cystic fibrosis (NCT017051450).

Conclusions Lung disease in patients with cystic fibrosis starts early in childhood and progresses even in the absence of clinical signs and symptoms. Methods sensitive enough to detect these early abnormalities in infants and young children have become available and are being used in early-intervention trials. These new methods will help address the important question of whether early intervention can not only delay, but ultimately halt lung disease development in patients with cystic fibrosis. Contributors Both authors contributed equally to the literature search, data interpretation, writing of the Review, and the design of the figures. Both authors edited and approved the submitted version of the Review. Conflicts of interest FR acts as a consultant for Bayer, Genentech, Novartis, Talecris, and Vertex. None of these conflicts are directly related to the preparation of the Review. HG declares that he has no conflicts of interest. Acknowledgments FR has received funding from the Canadian Institutes of Health Research, US National Institutes of Health, Cystic Fibrosis Foundation, and Cystic Fibrosis Canada for previous and continuing research projects. HG has received research funding from the Canadian Institutes of Health Research, Cystic Fibrosis Canada and The Irwin Family Foundation. No honorarium, grant, or other form of payment was related to this Review. References 1 Cystic Fibrosis Foundation. Cystic Fibrosis Foundation patient registry: 2011 annual data report. http://www.cff.org/UploadedFiles/ research/ClinicalResearch/2011-Patient-Registry.pdf (accessed March 4, 2013). 2 Anderson MP, Gregory RJ, Thompson S, et al. Demonstration that CFTR is a chloride channel by alteration of its anion selectivity. Science 1991; 253: 202–05. 3 Knowles MR, Olivier K, Noone P, Boucher RC. Pharmacologic modulation of salt and water in the airway epithelium in cystic fibrosis. Am J Respir Crit Care Med 1995; 151: 65–69. 4 Mall M, Grubb BR, Harkema JR, O’Neal WK, Boucher RC. Increased airway epithelial Na+ absorption produces cystic fibrosis-like lung disease in mice. Nat Med 2004; 10: 487–93. 5 Chen JH, Stoltz DA, Karp PH, et al. Loss of anion transport without increased sodium absorption characterizes newborn porcine cystic fibrosis airway epithelia. Cell 2010; 143: 911–23. 6 Guilbault C, Saeed Z, Downey GP, Radzioch D. Cystic fibrosis mouse models. Am J Respir Cell Mol Biol 2007; 36: 1–7. 7 Mall MA, Harkema JR, Trojanek JB, et al. Development of chronic bronchitis and emphysema in beta-epithelial Na+ channel-overexpressing mice. Am J Respir Crit Care Med 2008; 177: 730–42. 8 Pezzulo AA, Tang XX, Hoegger MJ, et al. Reduced airway surface pH impairs bacterial killing in the porcine cystic fibrosis lung. Nature 2012; 487: 109–13. 9 Day BJ, van Heeckeren AM, Min E, Velsor LW. Role for cystic fibrosis transmembrane conductance regulator protein in a glutathione response to bronchopulmonary pseudomonas infection. Infect Immun 2004; 72: 2045–51.

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