Rattus Model Utilizing Selective Pulmonary Ischemia Induces Bronchiolitis Obliterans Organizing Pneumonia

Abstract

Background Bronchiolitis obliterans organizing pneumonia (BOOP), a morbid condition when associated with lung transplant and chronic lung disease, is believed to be a complication of ischemia. Our goal was to develop a simple and reliable model of lung ischemia in the Sprague-Dawley rat that would produce BOOP. Methods Unilateral ischemia without airway occlusion was produced by an occlusive slipknot placed around the left main pulmonary artery. Studies were performed 7 days later. Relative pulmonary and systemic flow to each lung was measured by injection of 99mTc-macroaggregated albumin. Histological sections were examined for structure and necrosis and scored for BOOP. Apoptosis was detected by immunohistochemistry with an antibody against cleaved caspase-3. Results Pulmonary artery blood flow to left lungs was <0.1% of the cardiac output, and bronchial artery circulation was ~2% of aortic artery flow. Histological sections from ischemic left lungs consistently showed Masson bodies, inflammation and young fibroblasts filling the distal airways and alveoli, consistent with BOOP. Quantitative evaluation of BOOP using epithelial changes, inflammation and fibrosis were higher in ischemic left lungs than right or sham-operated left lungs. Apoptosis was increased in areas exhibiting histological BOOP, but there was no histological evidence of necrosis. TLR4 expression was increased in ischemic left lungs over right. Conclusions An occlusive slipknot around the main left PA in rats produces BOOP, providing direct evidence that ischemia without immunomodulation or coinfection is sufficient to initiate this injury. It also affords an excellent model to study signaling and genetic mechanisms underlying BOOP.

Lung injury pathways: Adenosine receptor 2B signaling limits development of ischemic bronchiolitis obliterans organizing pneumonia

“…We have reported that unilateral ischemia of the lung induced by pulmonary artery tie results in bronchiolitis obliterans organizing pneumonia (BOOP) and inflammatory changes seven days after surgery in SD rats (6). To begin to test the contribution of A 2B AR expression to the development of BOOP, we quantified percent BOOP in ischemic lungs of a genetically modified rat strain with deletions of A 2B AR relative to the background strain (Dahl SS)(22).…”

“…Four-micron thick slices of paraffin-embedded, fixed whole-mount coronal sections of left and right lung were stained for hematoxylin and eosin. Extent of bronchiolitis obliterans organizing pneumonia (BOOP) was quantified by assessing percentage of the cross sectional area of the lung involved at low power, morphology confirmed with high resolution JPEG images, as we previously reported (6). Histology consistent with BOOP (Masson bodies, inflammation, and young fibroblasts filling the distal airways and alveoli) was assessed with high power images.…”

“…To create unilateral ischemia without compromise of airflow or reperfusion, we used a left anterior thoracotomy to complete an occlusive slip knot tie over the left main pulmonary artery under general anesthesia using isoflurane (2%), as we previously reported (6). In brief, the left main pulmonary artery was identified on the superior aspect of the left mainstem bronchus and then dissected free from the bronchus.…”

“…Histology consistent with BOOP (Masson bodies, inflammation, and young fibroblasts filling the distal airways and alveoli) was assessed with high power images. Using a scale developed for quantification of BOOP (6, 21), we also performed grading of epithelial injury, fibrosis, and inflammatory changes (EFI) in the most severely affected areas of cross sectional lung images, each on a zero to three scale. The presence or absence of pulmonary vascular changes (thickening of intima or media or vascular drop out) and necrosis were noted in each image (Table 1).…”

“…This provides a contralateral control lung for comparison. This model completely avoids immunomodulation and maintains ventilation to both lungs (6). In the present work, we explore the role of adenosine signaling in this injury response.…”