A rapid dynamic in vivo near-infrared fluorescence imaging assay to track lung vascular permeability after acute radiation injury
Purpose: Develop an in vivo near-infrared (NIR) fluorescence imaging assay to quantify sequential changes in lung vascular permeability-surface area product (PS) in rodents. Methods: Dynamic NIR imaging methods for determining lung vascular permeability-surface area product were developed and tested on non-irradiated and 13 Gy irradiated rats with/without treatment with lisinopril. A physiologically-based pharmacokinetic (PBPK) model of Indocyanine Green (ICG) pulmonary disposition was applied to in vivo imaging data and PS was estimated. In vivo results were validated by five accepted assays: ex vivo perfused lung imaging, endothelial filtration coefficient (Kf) measurement, pulmonary vascular resistance measurement, Evan's blue dye uptake and histopathology. Results: PBPK modeled lung PS increased from 2.60±0.40 [CL: 2.42-2.78] mL/min in the non-irradiated group to 6.94±8.25 [CL: 3.56-10.31] mL/min in 13 Gy group after 42 days. Lisinopril treatment lowered PS in the 13Gy group to 4.76±6.17 [CL: 2.12-7.40] mL/min. A higher 5X change in PS was observed in rats exhibiting severe radiation injury. Ex vivo Kf (mL/min/cm H2O/g dry lung weight), a measure of pulmonary vascular permeability, showed similar trends in lungs of irradiated rats (0.164±0.081 [CL: 0.11-0.22]) compared to non-irradiated controls (0.022±0.003 [CL: 0.019-0.025]), with reduction to 0.070±0.035 [CL: 0.045-0.096] for irradiated rats treated with lisinopril. Similar trends were observed for ex vivo pulmonary vascular resistance, Evan's blue uptake, and histopathology. Conclusion: Our results suggest that dynamic in vivo NIR fluorescence imaging can replace current terminal assays. In vivo imaging accurately tracks changes in PS and lung interstitial transport in response to radiation injury.