Sequential and Quantitative Analysis of a Murine Model of Elastase-Induced Emphysema

Abstract

Chronic obstructive pulmonary disease (COPD) is one of the serious causative diseases in death of aging people.1) Emphysema, one of COPD, is characterized as destruction of airway wall and small airway inflammation.1) An imbalance between elastinolytic proteases and their natural inhibitors is thought to play a role in the pathogenesis of emphysema. One animal model of emphysema is made by administrating of elastase into the lungs.2-4) Cigarette smoke-induced emphysema is another common model of emphysema. A study of elastase-deficient mice has revealed that elastase is also critical in smoke-induced emphysema.5) As several months are required to establish cigarette smoke-induced emphysema, the elastase-induced model is more convenient for assessing drug effects.To quantitatively assess the murine model of emphysema, historical assessment using mean linear intercept (Lm) has been used. 6) Because the elastase-induced destruction of airway wall is not homogenous, random several views are taken to estimate the destruction.The non-homogenous region of the disease is also applicable for human. In human, noninvasive computed tomography (CT) is commonly used for diagnosis and disease staging by assessing areas of low attenuation.1,7) The primary benefits of CT monitoring are the ability to assess the lungs in their entirety and the ability to follow the same mice over time.Micro-computed tomography has been developed, resulting in low-noise CT images in a small animal. CT images are used to follow-up tumor growth in the lung.8) High respiration rates of mice cause difficulty for high quality of images of the lung. Although invasive methods using tracheostomy enable high quality images, 9,10) we employed free-breathing method to take the images serially in a deeply-anesthetized condition, in which respiration rates were reduced. The purpose of present study is to clarify whether the kinetics of a murine elastase-induced emphysema model can be assessed using CT and to compare the results with morphological analysis. MATERIALS AND METHODSAdministration of Elastase C57BL/6N mice were obtained from Charles River Japan (Kanagawa, Japan) and bred in the animal facilities of Musashino University School of Medicine under specific pathogen-free (SPF) conditions. Care and use of animals followed the guidelines of the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research.Four cycles of sequential CT analysis were performed using 26 mice, six of which were also under histological examination at the end points. For histological analysis only, 12 mice were used for each time points, and in 8 different time points were examined. Another six mice were employed under CT and histological analysis once at the same day.Mice were anesthetized with ether or intraperitoneal injection of ketamine (90 mg/kg) and xylazine (1 mg/kg) and given intranasal administration of 0.3 or 1.2 units of porcine pancreatic elastase (Sigma-Aldrich, St. Louis, MO, U.S.A.) in 30 ml saline solution. Control mice were intra...

Longitudinal and noninvasive assessment of emphysema evolution in a murine model using proton MRI

“…From this equation, it appears that the alveolar surface area per unit lung volume is proportional to 1/L m . Notably, the changes in alveolar surface area are closely related to the extent of tissue destruction and thus to the tissue density, as demonstrated from reported correlations between L m and lung mean density assessed with micro-CT in elastase murine model of emphysema (20). In MRI, information about tissue density can be obtained from the MR signal intensity variations induced by changes in proton spin density.…”

“…For each radial view, the k-space origin was acquired with a repetition time of 80 ms. The flip angle was set to 20 according to the Ernst angle condition, with an estimated lung T 1 value of 1600 ms (measurements not published). The minimum effective echo time was equal to 550 ms (the effective echo time is defined as the interval between the center of the radiofrequency pulse and the first data point of the acquisition) and was achieved with a gaussian-shape pulse excitation of duration of 0.4 ms and slice thickness of 1.7 mm.…”

Elastase-induced pulmonary emphysema: insights from experimental models

“…A single dose of elastase leads to airspace enlargement inducing emphysema-like lesions (Lucey et al 1998, Kononov et al 2001, Inoue et al 2003, Ishizawa et al 2004, Ito et al 2005, Kawakami et al 2008. In gen- Fig.…”

“…Kawakami and colleagues (2008) held a sequential and quantitative analysis using micro-computed tomography in a murine model of elastase emphysema, demonstrating the persistence of morphological changes up to four weeks after elastase instillation (Kawakami et al 2008). Other investigators have observed persistent elastase emphysema up to eight weeks and more after elastase instillation (Otto-Verbene et al 1992).…”

“…Lesion severity is modulated by enzyme dose, and the induced morphological and functional changes are detectable in the long term. Therefore, elastase emphysema has become a useful tool to validate a variety of new drugs and interventions, such as simvastatin (Takahashi et al 2008) and bone marrow-derived cell therapy (Ishizawa et al 2004), or to develop mechanistic investigations of severe pulmonary tissue abnormalities (Sawada et al 2007, Kawakami et al 2008. Additionally, several features of human emphysema (genetic or cigarette smoke-induced) have been reproduced by elastase emphysema, including systemic inflammation and chronic adaptations (Table II).…”