In vivo imaging of the airway wall in asthma: fibered confocal fluorescence microscopy in relation to histology and lung function

Abstract

BackgroundAirway remodelling is a feature of asthma including fragmentation of elastic fibres observed in the superficial elastin network of the airway wall. Fibered confocal fluorescence microscopy (FCFM) is a new and non-invasive imaging technique performed during bronchoscopy that may visualize elastic fibres, as shown by in vitro spectral analysis of elastin powder. We hypothesized that FCFM images capture in vivo elastic fibre patterns within the airway wall and that such patterns correspond with airway histology. We aimed to establish the concordance between the bronchial elastic fibre pattern in histology and FCFM. Second, we examined whether elastic fibre patterns in histology and FCFM were different between asthmatic subjects and healthy controls. Finally, the association between these patterns and lung function parameters was investigated.MethodsIn a cross-sectional study comprising 16 subjects (8 atopic asthmatic patients with controlled disease and 8 healthy controls) spirometry and bronchoscopy were performed, with recording of FCFM images followed by endobronchial biopsy at the airway main carina. Elastic fibre patterns in histological sections and FCFM images were scored semi-quantitatively. Agreement between histology and FCFM was analysed using linearly weighted kappa κw.ResultsThe patterns observed in histological sections and FCFM images could be divided into 3 distinct groups. There was good agreement between elastic fibre patterns in histology and FCFM patterns (κw 0.744). The semi-quantitative pattern scores were not different between asthmatic patients and controls. Notably, there was a significant difference in post-bronchodilator FEV1 %predicted between the different patterns by histology (p = 0.001) and FCFM (p = 0.048), regardless of asthma or atopy.ConclusionFCFM captures the elastic fibre pattern within the airway wall in humans in vivo. The association between post-bronchodilator FEV1 %predicted and both histological and FCFM elastic fibre patterns points towards a structure-function relationship between extracellular matrix in the airway wall and lung function.Trial registrationNetherlands Trial Register NTR1306

Role of Matrix Metalloproteinases-1 and -2 in Interleukin-13–Suppressed Elastin in Airway Fibroblasts in Asthma

“…These data are in agreement with another study that demonstrated significant associations between elastic fiber assembly patterns and postbronchodilator FEV 1 % predicted (31). Our data suggest that increased elastin gene expression is associated with increased post-bronchodilator FEV 1 /FVC, or less airway obstruction, and that elastic fiber staining in airway biopsy tissue is directly correlated with methacholine PC 20 , or inversely correlated with AHR in asthma.…”

Structure–function relationship in COPD revisited: an in vivo microscopy view

“…The distribution of elastic fibres in the bronchial wall was classified as lamellar, loose and mixed pattern according to its orientation, as previously described,11 and it was later confirmed by pathological examination. Fluorescence intensity was quantified using the MedViewer Signal Quantification Toolbox as previously described,6 7 and the ratio between the alveolar/bronchial wall fluorescence intensity (ABI) was calculated 6…”

“…As shown in figure 1, using FCFM we recognised the three previously described11 patterns of bronchial wall fibre distribution (lamellar, loose and mixed patterns). The lamellar pattern was characterised by a linear and parallel bronchial thick fibre orientation (figure 1A), in the loose pattern the fibres were thin and non-specifically orientated (figure 1C) and the mixed pattern showed a combination of the two (figure 1E).…”

“…Using FCFM, Thiberville et al 5 6 described in detail the bronchial wall and acini of both smokers and healthy non-smoker volunteers. More recently, Yick et al 11 used this technique to describe bronchial wall changes in asthma and observed novel relationships between the extracellular matrix of the airway wall and lung function in these patients. Although this technique is not able to explore the upper lobes due to the stiffness of the probe, it allows analysis of the elastic network in the small airways of the lower lobes in regions where the alveolar dimension can also be measured.…”

Optical Coherence Tomography in Respiratory Science and Medicine: From Airways to Alveoli

“…At finer resolutions, optical techniques such as intravital (59) and confocal microscopy (27, 103,118,137) provide cellular-level imaging, aided by the use of intrinsic or exogenous fluorophores (59). However, such optical techniques provide insight only over very superficial surface layers and small fields of view.…”