Longitudinal micro-CT-derived biomarkers: the new standard readouts for preclinical evaluation of pulmonary fibrosis and therapy

Pulmonary fibrosis is life-threatening and effective treatment is still lacking. To improve translation of mouse models to man, we introduced an in vivo µCT protocol to repeatedly assess lung fibrosis progression in a silica-induced mouse model. Mice were endotracheally instilled with crystalline silica or saline and scanned weekly for 15 weeks with respiratory gated high-resolution low radiation-dose µCT. We evaluated the disease onset and progress, using biomarkers derived from the scans. At day 7, 35, 63 and 105 after instillation, imaging data were cross-validated with lung function, cellular, histochemical, molecular and histological readouts. Silica instillation resulted in a significant and progressive 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 transiently decreased to 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 IL-13, MCP-1, MIP-2 and TNF-α concentration in BAL fluid (d7 - d105), increased collagen content (d35 - d105) and granuloma formation (d35 - 105). Our findings indicate that µCT is an excellent technique to longitudinally evaluate pulmonary fibrosis, a novel approach that allows assessment of disease progression and stabilization over several weeks. This will facilitate the evaluation of therapeutic interventions at the level of the individual animal.