Investigating the nature of small airways disease in mild/moderate COPD: micro-CT analysis of paraffin embedded lung tissue

Koo, H. -K., Vasilescu, D. M., Booth, S., Scott, A. E., Katsamenis, O., Warner, J., Sinclair, I., Hogg, J. C. and Hackett, T. -L. (2016) Investigating the nature of small airways disease in mild/moderate COPD: micro-CT analysis of paraffin embedded lung tissue. American Journal of Respiratory and Critical Care Medicine, 193.

Abstract

Rationale: Airflow obstruction, the hallmark characteristic of Chronic Obstructive Pulmonary Disease (COPD) has long been attributed to a combination of small airways disease and emphysematous destruction, however, the relative role of each pathological feature is not well understood. McDonough et al. (NEJM, 2011), reported a significant reduction in terminal bronchiolar number in end-stage COPD compared to controls with normal lung function. Further, the study reported that the loss of terminal bronchioles occurred in regions of lung with and without emphysema, leading to our hypothesis that ‘The obstruction and obliteration of small airways occurs early in mild/moderate COPD and precedes the emphysematous destruction’. Methods: Lung samples were obtained from patients with known pulmonary function undergoing surgical resection for lung cancer or transplant. Lungs were inflated, sliced and sampled prior to formalin fixation and paraffin embedding (FFPE). Eight FFPE cores per patient were randomly sampled throughout the lung and scanned using a Nikon Metrology micro-CT scanner. Volumetric data sets were examined to determine mean linear intercept (Lm), number of terminal (TB) and transitional (TrB) bronchioles per ml of tissue. Image registration was used to precisely locate regions of interest, enabling efficient sectioning and staining with Movat’s Pentachrome for a more comprehensive analysis of airway morphology. Results: Our study demonstrates that micro-CT scans of FFPE cores provide adequate resolution of fine lung architecture when compared to mean linear intercept measurements obtained from matched histological sections (Bland-Altman). We report that the total number of terminal bronchioles is significantly decreased from 6.2±1.1 TB/ml in smokers with normal lung function, to 4.6±1.0 TB/ml in mild/moderate COPD patients and 2.8±1.8 TB/ml in severe COPD. Further, we demonstrate a significant decrease in transitional bronchiolar number from 16.7 ± 7.2 TrB/ml in the control group to 10.0 ± 6.0 TrB/ml in mild/moderate COPD, and 2.1±2.7 TrB/ml in severe COPD. When correlating the number of terminal and transitional bronchioles to Lm, we find that bronchioles are destroyed in tissues where no emphysema is present. Lesions of interest are characterized by histology to further understand the pathological process. Conclusions: Clinical trials and the treatment of COPD have traditionally focused on patients with severe disease and no current pharmacological therapies have been shown to affect long term, lung function decline. Our findings suggest that irreversible pathological events occur in the early stages of disease, emphasizing the importance of early diagnosis and intervention to modify the progression of this debilitating respiratory disorder.

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Contributors

Author: O. Katsamenis

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