Mouse Abdominal Aortic Aneurysm Model Induced by Perivascular Application of Elastase

Summary

The present protocol describes a standardized surgical method for the elastase-induced AAA model through the direct application of elastase to the adventitia of infrarenal abdominal aorta in mice.

Abstract

Abdominal aortic aneurysm (AAA), although primarily asymptomatic, is potentially life-threatening as the rupture of AAA usually has a devastating outcome. Currently, there are several distinct experimental models of AAA, each emphasizing a different aspect in the pathogenesis of AAA. The elastase-induced AAA model is the second most used rodent AAA model. This model involves direct infusion or application of porcine pancreatic elastase (PPE) to the infrarenal segment of the aorta. Due to technical challenges, most elastase-induced AAA model nowadays is performed with the external application rather than an intraluminal infusion of PPE. The infiltration of elastase will cause degradation of elastic lamellae in the medial layers, resulting in the loss of aortic wall integrity and subsequent dilation of the abdominal aorta. However, one disadvantage of the elastase-induced AAA model is the inevitable variation of how the surgery is performed. Specifically, the surgical technique of isolating the infrarenal segment of the aorta, the material used for aorta wrapping and PPE incubation, the enzymatic activity of PPE, and the time duration of PPE application can all be important determinants that affect the eventual AAA formation rate and aneurysm diameter. Notably, the difference in these factors from different studies on AAA can lead to reproducibility issues. This article describes a detailed surgical process of the elastase-induced AAA model through direct application of PPE to the adventitia of the infrarenal abdominal aorta in the mouse. Following this procedure, a stable AAA formation rate of around 80% in male and female mice is achievable. The consistency and reproducibility of AAA studies using an elastase-induced AAA model can be significantly enhanced by establishing a standard surgical procedure.

Introduction

Abdominal aortic aneurysm (AAA) is defined as a segmental dilatation of the abdominal aorta with at least a 50% increase of vessel diameter¹. AAA is potentially fatal, as the rupture can result in an extremely high mortality rate, even with intervention^2,3,4. It has been reported that AAA is responsible for approximately 13,000 deaths annually in the USA, which makes it the 10^th leading cause of death^1,5.

The pathogenesis of AAA is not yet wholly understoo....

Protocol

The animal protocols were approved by the University of Michigan Institutional Animal Care and Use Committee (PRO00010092). Male and female C57BL/6J wild-type (WT) mice, ~7 weeks of age, were used for the experiments.

1. Animal preparation

1. Feed the mice with the standard chow diet (see Table of Materials) before and after the surgery.
   ​NOTE: Different strains and ages of mice can be used. However, age ranging from 5.5-12 week-old is recommended to achieve maximal incidence rate.
2. For each mouse, administer 5 mg/kg of Carprofen subcutaneously 30 min before the induction of a....

Results

A total of twenty-three 7-week-old wild-type (WT) mice, including 12 females and 11 males, were operated following the presented protocol. The survival rate was 100% (surgical mortality excluded). Maximal abdominal aorta diameter was measured by a caliper.

AAA was defined as dilating the abdominal aorta with a 50% vessel diameter increase. Therefore, a 50% increase in the maximal abdominal aorta diameter was selected as the cut-off point for successful AAA induction. Based upon this criterion,.......

Discussion

The elastase-induced AAA model was first reported by Anidjar et al. using rats in 1990¹⁷. A variety of modified versions have been introduced in the past thirty years, along with significant improvement in the surgical techniques^19,20,21,22. Hundreds of institutes use elastase-induced AAA models as the second most used rodent experimental model for AAA studies

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
6-0 non-absorbable monofilament suture	Pro Advantage	P420697
Carprofen	Zoetis Inc.	NDC: 54771-8507
Chow Diet	LabDiet	3005659-220	PicoLab 5L0D
Cotton Applicator	Dynarex	4303
Cotton Pad	Rael	UPC: 810027130969
GraphPad Prism 8	GraphPad Software Inc.		Version 8.4.3
Grarfe Forceps	Fine Science Tools	11051-10
Halsted Mosquito Hemostats	Fine Science Tools	13009-12
Ketamine	Par Pharmaceutical	NDC: 42023-0115-10
Nitrile gloves	Fisherbrand	19-130-1597
Penicillin-Streptomycin	Thermo Fisher	15140122
Porcine pancreatic elastase	Sigma-Aldrich	E1250-100MG
Scissors	Fine Science Tools	14068-12
Sterile 0.9% saline solution	Baxter	2B1324X
Xylazine	Akorn	NDC: 59399-110-20