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* These authors contributed equally
This novel model creates robust infrarenal abdominal aortic aneurysms in swine using a combination of balloon angioplasty, elastase/collagenase perfusion, topical elastase application, and oral compound β-aminopropionitrile administration, which interferes with collagen cross-linking.
Large animal models to study abdominal aortic aneurysms are sparse. The purpose of this model is to create reproducible, clinically significant infrarenal abdominal aortic aneurysms (AAA) in swine. To achieve this, we use a combination of balloon angioplasty, elastase and collagenase, and a lysyl oxidase inhibitor, called β-aminopropionitrile (BAPN), to create clinically significant infrarenal aortic aneurysms, analogous to human disease.
Noncastrated male swine are fed BAPN for 7 days prior to surgery to achieve a steady state in the blood. A midline laparotomy is performed and the infrarenal aorta is circumferentially dissected. An initial measurement is recorded prior to aneurysm induction with a combination of balloon angioplasty, elastase (500 units)/collagenase (8000 units) perfusion, and topical elastase application. Swine are fed BAPN daily until terminal procedure on either postoperative day 7, 14, or 28, at which time the aneurysm is measured, and tissue procured. BAPN + surgery pigs are compared to pigs that underwent surgery alone.
Swine treated with BAPN and surgery had a mean aortic dilation of 89.9% ± 47.4% at day 7, 105.4% ± 58.1% at day 14, and 113.5% ± 30.2% at day 28. Pigs treated with surgery alone had significantly smaller aneurysms compared to BAPN + surgery animals at day 28 (p < 0.0003). The BAPN + surgery group had macroscopic and immunohistochemical evidence of end stage aneurysmal disease.
Clinically significant infrarenal AAA can be induced using balloon angioplasty, elastase/collagenase perfusion and topical application, supplemented with oral BAPN. This model creates large, clinically significant AAA with hallmarks of human disease. This has important implications for the elucidation of AAA pathogenesis and testing of novel therapies and devices for the treatment of AAA. Limitations of the model include variation in BAPN ingested by swine, quality of elastase perfusion, and cost of BAPN.
According to the Center for Disease Control (CDC), aortic aneurysms (AA) are a leading cause of death in the United States and represent a significant disease burden1. An aortic aneurysm is defined as a dilation of a discrete portion of the vessel lumen by over 50%2. A subset of AA in the abdomen, referred to as abdominal aortic aneurysms (AAA) are a growing concern. AAA remain clinically silent until impending rupture or dissection, with acute onset, severe abdominal pain generally being the only presenting symptom3,4. Rupture of AAA is almost always fatal with a mortality rate of 90%5. Open or endovascular surgery is the only therapeutic option for patients, and can be a highly morbid procedure. Importantly, AAA are one of the few cardiovascular diseases with no medical therapy for cure.
To date, much of the research on AAA pathogenesis has focused on rodent models, using elastase, which is an enzyme that degrades elastin found within the aortic media, to induce aneurysms.6,7 However, the clinical translatability of small animal models to human aneurysmal disease is restricted, as evaluation of structural changes in the aorta, and altered hemodynamics are limited due to size. Because of anatomical and size similarity, the porcine circulatory system correlates better with human biology than rodents8. Large animal models allow further understanding of cellular mechanisms of the disease process, can be used develop novel treatments at therapeutic doses for large mammals, and test mechanical repair devices, which would not be feasible in small animal models. Additionally, the acute nature of rodent models does not replicate the chronicity and pathologic characteristics of human aneurysmal disease.
The combination of elastase and a compound called β-aminopropionitrile (BAPN) has revolutionized murine AAA models, by creating aneurysms that are larger and contain sequela of chronic aneurysmal disease, including mural thrombus, dissection, and rupture9. BAPN is an inhibitor of lysyl oxidase, which is essential for collagen crosslinking, a crucial component of the aortic wall10,11,12. Lysyl oxidase activity decreases with aging and given the association of age and the chronic nature of complicated AA, BAPN has great potential to experimentally mimic the effects of aging9,13,14. The use of BAPN and its ability to replicate chronic disease in a subacute setting offers a novel advantage over alternative large animal models of AAA. Compared to other established porcine AAA models, this model creates the largest aneurysms with hallmarks of end-stage disease, and the results have been previously published8,11,15.
While conferring certain advantages, significant resources and investment are required to successfully complete this model that may deter some investigators. Among these resources include access to operating rooms, qualified surgeons and anesthesia providers, animal housing, and veterinary staff to assist with post-operative care. Additionally, the cost of BAPN may be prohibitively expensive for some labs.
Few large animal models exist to study the complex pathophysiology of AAA formation and translate to human disease. Large animal models of AAA are critical to help assess the viability of novel technologies and treatments for human disease. Therefore, the purpose of this study was to create a reproducible model of advanced stage infrarenal AAA in swine. The rationale for the use of BAPN and elastase swine model is to better understand the pathophysiology of AAA by mimicking the chronic nature and sequela of human aneurysmal disease in an acute or subacute setting, as well as to test novel therapies and devices for AAA treatment.
Animal protocols were approved by the University of Virginia Institutional Animal Care and Use Committee (No. 3848).
NOTE: This model has been previously published by Cullen et al. and is a modified protocol described by Hynecek et al.8,15.
1. Animals
2. Anesthesia
3. Surgical technique
4. Postoperative care
5. Aortic tissue procurement
All statistical analyses were performed using Fisher exact test or chi squared test as appropriate. Data values are reported as mean aortic dilation (%) ± standard deviation (%). Statistical significance was set P < 0.05. The combination of BAPN and surgery providing elastase treatment (surgery/elastase) creates more robust and reproducible AAA in swine at day 28 compared to those treated with surgery and elastase alone (mean aortic dilation (%) ± standard deviation (%): 113.5% ± 30.2% (n = 8) versus 5...
A novel model of infrarenal AAA in swine was created using a combination of balloon angioplasty, perfusion and topical elastase, and dietary as BAPN. Using this model, aortic dilation of >100% was achieved with gross and histologic characteristics of chronic human aneurysmal disease. This model provides a gateway to further understand the complex pathophysiology of AAA and translate potential therapies to human disease.
Prior models of AAA in swine have been achieved with modest success. M...
None
We thank Anthony Herring and Cindy Dodson for their knowledge and technical expertise.
Sources of Funding:
Funding for this study was provided by the National Heart, Lung, and Blood Institute of the National Institute of Health under Award No. T32HL007849 and Grant Nos. R01HL081629-07 (G.R.U.) and R01HL124131-01 (G.R.U.).
Name | Company | Catalog Number | Comments |
Arrow Ergo Pack System | Arrow | CDC-21242-X1A | Just need 7 Fr dilator |
Atlas PTA Balloon dilation catheter | Bard | AT-120184 | 16 mm x 4 cm x 120 cm |
Bovie electrocautery | Bovie Medical | A2350 | |
Collagenase Type 1 (5 gm) | Worthington | LS004196 | |
Crile Needle drviers | MFI medical | 61-2201 | |
DeBakey Atraumatic Forceps | MFI medical | 52-4977 | |
DeBakey Peripheral Vascular Clamp | Medline | MDS1318119 | |
Glidewire | Terumo Interventional Systems | GS3506 | outer Wire diameter 0.035 mm, Length 150 cm |
GraphPad Prism 6 | GraphPad Software Inc. La Jolla, Calif) | statistical software | |
Metzenbaum Scissors | MFI medical | 61-0004 | |
Mayo-Hegar Needle Holder | tiger medical | N407322 | |
Micropuncture Introducer Set | Cook | G47946 | |
Mixter Forceps, Standard Grade, Right angle | Cole-Parmer | UX-10818-16 | |
Monocryl suture | Ethicon | Y496G-BX | 4-0 monocryl |
PDS II suture | Ethicon | D8926 | Number 1 looped |
Porcine Pancreatic Elastase | Sigma-Aldrich | E1250 | |
Satinsky Vascular Clamps | Medline | MDs5632515 | |
Suction canister | Cardinal Health | 65651212 | |
Schuco Aspirator | MFI medical | S430A | |
Vicryl suture | Ethicon | J789D-SD | 2-0 vicryl |
Yankauer Suction tube | Sklarcorp | 07-1801 |
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