Longitudinal in vivo µCT for characterization of acute exacerbations in a pulmonary fibrosis mouse model

Abstract

Pulmonary fibrosis is a life-threatening condition for which effective treatment is still lacking. To improve preclinical research, we introduced an in vivo µCT protocol to repeatedly assess lung fibrosis progression in a silica-induced mouse model. µCT-derived biomarkers allow longitudinal assessment of a lung fibrosis model in free-breathing animals and are therefore highly relevant to evaluate early and acute exacerbations.

Mice were endotracheally instilled with crystalline silica or saline and scanned bi-weekly for 15 weeks with respiratory gated high-resolution low-dose µCT. To evaluate the inflammatory and fibrotic phases of disease onset and progress, we used three lung biomarkers derived from the scans. At four different time points after instillation (day 7, 35, 63 and 105) lung function measurements, cellular, biochemical and histological analysis were obtained and cross-validated with the imaging data.

Silica instillation resulted in a significant increase of non-aerated lung volume (corresponding with inflammatory and fibrotic processes) and total lung volume (corresponding to compensatory host response). The aerated lung volume decreased to gradually increase again, indicating an acute inflammatory response. Imaging results were confirmed by a significantly decreased tiffeneau index (d35 and d63), increased neutrophilic inflammation (d7 - d105), increased collagen content (d35 - d105) and increased granuloma formation (d35 - 105).

Our findings indicate that µCT is an excellent technique to longitudinally evaluate pulmonary fibrosis in mice, a novel approach that allows evaluation of acute exacerbations, disease progression and stabilization over several weeks.