An animal model for lung volume reduction therapy of pulmonary emphysema

Experimental animal models for COPD: a methodological review

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a progressive disorder that makes the breathing difficult and is characterized by pathological conditions ranging from chronic inflammation to tissue proteolysis. With regard to ethical issues related to the studies on patients with COPD, the use of animal models of COPD is inevitable. Animal models improve our knowledge about the basic mechanisms underlying COPD physiology, pathophysiology and treatment. Although these models are only able to mimic some of the features of the disease, they are valuable for further investigation of mechanisms involved in human COPD.

METHODS

We searched the literature available in Google Scholar, PubMed and ScienceDirect databases for English articles published until November 2015. For this purpose, we used 5 keywords for COPD, 3 for animal models, 4 for exposure methods, 3 for pathophysiological changes and 3 for biomarkers. One hundred and fifty-one studies were considered eligible for inclusion in this review.

RESULTS

According to the reviewed articles, animal models of COPD are mainly induced in mice, guinea pigs and rats. In most of the studies, this model was induced by exposure to cigarette smoke (CS), intra-tracheal lipopolysaccharide (LPS) and intranasal elastase. There were variations in time course and dose of inducers used in different studies. The main measured parameters were lung pathological data and lung inflammation (both inflammatory cells and inflammatory mediators) in most of the studies and tracheal responsiveness (TR) in only few studies.

CONCLUSION

The present review provides various methods used for induction of animal models of COPD, different animals used (mainly mice, guinea pigs and rats) and measured parameters. The information provided in this review is valuable for choosing appropriate animal, method of induction and selecting parameters to be measured in studies concerning COPD.

Animal models of chronic obstructive pulmonary disease

The mechanisms involved in the genesis of chronic obstructive pulmonary disease (COPD) are poorly defined. This area is complicated and difficult to model because COPD consists of four separate anatomic lesions (emphysema, small airway remodeling, pulmonary hypertension, and chronic bronchitis) and a functional lesion, acute exacerbation; moreover, the disease in humans develops over decades. This review discusses the various animal models that have been used to attempt to recreate human COPD and the advantages and disadvantages of each. None of the models reproduces the exact changes seen in humans, but cigarette smoke-induced disease appears to come the closest, and genetically modified animals also, in some instances, shed light on processes that appear to play a role.

A New, Simple Stapling Technique for Pulmonary Emphysema: Its Effects and Safety for Improving Respiratory Function

PURPOSE

We performed lung volume reduction surgery (LVRS) in an experimental model using a simple stapling technique (SST) for pulmonary emphysema. The technique uses a stapler to isolate the affected lung from the remaining lung instead of removing it. We performed the present experiment using dogs to study the effects and safety of LVRS using the SST.

METHODS

Pulmonary emphysema was induced in 12 dogs with papain. They were divided into three groups: those operated on with SST composed the operation (Op) group; those receiving an experimental thoracotomy composed the sham-operation (Sham-op) group; and those not operated on composed the nonoperation (Non-op) group. Respiratory function was compared among the groups before induction of emphysema (baseline), after induction of emphysema (preoperation), and at 8 weeks after the operation (postoperation Op and Sham-op groups only). The lung was removed and histologically examined 8 weeks after the SST operation.

RESULTS

In the Op group, alteration in forced expiratory volume (FEV) 0.5%, airway resistance (Raw) and specific airway conductance (sGaw) showed significantly favorable results. Histologically, the isolated area was widely replaced by fibrous tissue with numerous blood vessels in the circumference in the Op group; no signs of infection such as polykaryoleukocytes or microabscesses were observed in any of the samples.

CONCLUSION

The LVRS for pulmonary emphysema using a simple stapling technique improved the expiratory flow and alleviated airway resistance. The isolated remaining lung was well organized without any infectious events or secondary adversity, thus demonstrating the safety of this technique. From these results, this technique is therefore suggested to be effective and applicable to clinical use.

Development of a canine model of pulmonary emphysema and imaging of the emphysematous lung with infrared thoracoscopy

BACKGROUND

The surgeon must use the results of preoperative computed tomography findings and scintigraphic studies to make a subjective decision during lung volume reduction surgery with regard to the best incision line.

OBJECTIVES

Our purpose was to develop an objective and real-time method of detecting areas of pulmonary emphysema by using infrared thoracoscopy.

METHODS

Pulmonary emphysema was developed in various lobes of the lung in the dog by injecting porcine pancreatic elastase through the bronchi. One month after the injection, chest computed tomography and lung biopsy were performed. Infrared thoracoscopic study was then performed to reveal the presence of the emphysematous lung tissue. Simultaneously, indocyanine green was injected intravenously, and the time taken for each type of lung tissue to stain blue was measured.

RESULTS

Chest computed tomography and histologic examinations revealed pulmonary emphysema-like areas in the porcine pancreatic elastase-injected lung. The computed tomography numbers of the porcine pancreatic elastase-injected lung tissue, normal lung tissue, and the tracheal lumen were -868.8 +/- 18.6, -752.2 +/- 32.5, and -1013 +/- 27.1, respectively. There were significant differences between the porcine pancreatic elastase-injected lung and the normal lung (P <.0001). The time for staining to begin was 10.7 +/- 4.8 seconds for normal lung tissue and 25.8 +/- 9.4 seconds for the emphysematous tissue; the onset of staining emphysematous lung tissue was significantly delayed (P =.003).

CONCLUSIONS

We developed a successful canine model of pulmonary emphysema by injecting porcine pancreatic elastase. Infrared thoracoscopic examination revealed that the staining of emphysematous lung using indocyanine green injection was significantly greater than of normal lung.

Effects of a novel implantable elastomer device for lung volume reduction surgery in a rabbit model of elastase-induced emphysema

OBJECTIVES

There is intense interest in lung volume reduction surgery (LVRS) for treatment of severe symptomatic emphysema. LVRS results in objective and subjective improvement in lung function in selected patients. However, LVRS is complicated by substantial morbidity, including prolonged pulmonary air leak associated with resection of emphysematous lung tissue. In this study, we investigated the use of a novel implanted silicone elastomer device that reduces lung volume without surgical resection, in a previously reported emphysematous animal model. The purpose of this investigation was to determine the applicability, physiologic effects, complications, and air-leak results of this lung volume reducer (LVR) approach.

DESIGN

Controlled, randomized, prospective animal study. Emphysema was induced in 20 New Zealand white rabbits with three nebulizations of 10,000 U of porcine elastase. After 6 weeks, the animals were randomized to control sham surgery (n = 10) vs implanted silicone elastomer LVR (n = 10) treatment groups. Lung function, including helium-dilution lung volumes, static respiratory system compliance curves, and diffusion capacity of the lung for carbon monoxide (DLCO), was measured at baseline, following emphysema induction (week 6), and when the animals were killed (1 week after LVR or sham surgery). Histologic evaluation was performed in all lung specimens after fixation.

RESULTS

Moderate emphysema developed after elastase nebulization, assessed by lung function and postmortem histology. Functional residual capacity (FRC) and an upward shift of lung compliance curves was observed with development of emphysema at 6 weeks (p < 0.05). Following LVR, FRC decreased (p = 0.005) and compliance curves shifted back downward (p = 0.002), without reduction in DLCO. There was no change in control sham animals. DLCO did not change in either group.

CONCLUSIONS

In this short-term, randomized, controlled animal model study, the implantable LVR approach produced safe and effective lung volume reduction without tissue resection in the treated animals. The implant procedure produced minimal morbidity, no mortality, and no observed air-leak complications in the treated animals. Limitations include the short-term follow-up and moderate degree of emphysema in this animal model. Further research is required to assess long-term effects and complications of this method for lung volume reduction.