Novel experimental model of enlarging abdominal aortic aneurysm in rabbits Yonghua Bi, MD, PhD,a,b,c Hongshan Zhong, MD, PhD,b,c Ke Xu, MD, PhD,b,c Xun Qi, MD, PhD,b,c Zhen Zhang, MD, PhD,c,d Gang Wu, MD, PhD,a and Xinwei Han, MD, PhD,a Zhengzhou and Shenyang, China Objective: This study tested the hypothesis that an experimental model of abdominal aortic aneurysm in rabbits results in progressive enlargement when induced by a combination of periaortic elastase administration and aortic coarctation. Methods: Male New Zealand white rabbits were randomly divided into four groups: (A) stenosis (n [ 12), (B) elastase (n [ 12), (C) aneurysm (n [ 15), and (D) control (n [ 12). The stenosis group received an extrinsic coarctation below the right renal artery, the elastase group received a 10-minute administration of 60 mL elastase (1 U/mL) in a 1.5-cm aortic segment, the aneurysm group received stenosis and elastase, and a sham operation was performed in the control group. The aortic diameter was measured after 1, 2, 4, 8, and 16 weeks, and animals were subsequently euthanized for histopathologic and immunohistochemical studies. Results: All animals in the aneurysm group developed aneurysm by 2 weeks after treatment, with average diameters of 5.21 6 0.74 mm by 2 weeks, 6.23 6 1.10 mm by 4 weeks, 7.87 6 0.50 mm by 8 weeks, and 9.40 6 0.36 mm by 16 weeks. Aortic diameter dilated progressively, and all aneurysms developed by 4 weeks in the stenosis group (4.17 6 0.22 mm). Only one aneurysm was seen in the elastase group by week 1 (3.60 6 0.64 mm), and no aneurysm formed in the control group by week 8 (2.47 6 0.38 mm). The aneurysm group exhibited less media thickness, elastin content, and endothelial recovery, but stronger expression of matrix metalloproteinase 2 and 9 and rabbit macrophage compared with the control group. Conclusions: This novel rabbit abdominal aortic aneurysm model with a gradually enlarging diameter is simply and reliably induced, appropriately mimicking human aortic aneurysm disease. (J Vasc Surg 2014;-:1-10.) Clinical Relevance: Experimental abdominal aortic aneurysm (AAA) models can be useful to investigate its pathogenesis and to mimic human AAA disease. Medial injury aneurysms induced by elastase or calcium chloride are popular models. Unfortunately, the elastase-induced aneurysm dilates 50%) were scored as 3, moderate positive expression (10%-50%) was scored as 2, and weak expression ( .05). No aneurysm was seen in the sham group (Fig 1). Hemodynamic changes. Stenosis was seen in group SE and in group S, with a diameter of 1.35 6 0.38 and a stenosis rate of 42.93% 6 9.31%. Peak systolic velocity was higher in group SE (n ¼ 12) than in the sham group (n ¼ 9; P < .05) and group E (n ¼ 9; P < .05) by 2 weeks. In group S, peak systolic velocity was highest at 1 week and decreased after 2 weeks, although it remained higher than in the sham group (n ¼ 9; P < .05). WSS in group SE was higher than that in the sham group, although the difference was not significant. WSS was lower than group S by week 1 in group SE (P < .0001), which increased and remained stable after 2 weeks. The difference in WSS between group E and the sham group was not significant, and WSS in group E was significantly lower than that in group SE and group S by 4 weeks. The bidirectional spectrum distribution of blood flow and jet-like flow were seen in group SE and group S. However, there was no jet-like flow or turbulence blood flow in group E or the sham group (Fig 2). Aortic wall thickness changes. Media thickness increased significantly in group S at 4 and 8 weeks (P < .01 vs sham group), whereas media thickness in group E decreased significantly by 1 week (P < .05 vs sham

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Fig 2. The changes of hemodynamic condition, peak systolic velocity (PSV) and wall shear stress (WSS) in the elastase (Group E), stenosis (Group S), stenosis and elastase (Group SE ), and the control (SHAM) groups. *P < .05, **P < .01, and ***P < .0001. The error bars indicate the standard deviation.

Fig 3. Profiles of (A) intima-media ratio (IMR), (B) media thickness, (C) intima thickness, and (D) intima-media thickness (IMT ) in histopathologic findings are shown in the elastase (Group E), stenosis (Group S), stenosis and elastase (Group SE ), and the control (SHAM ) groups. The error bars indicate the standard deviation.*P < .05, **P < .01, and ***P < .0001.

group), but increased gradually thereafter. Media thickness in group E thinned by 1 week (P < .05 vs sham group), but showed gradual thickness after 2 weeks, and both thicknesses by weeks 4 and 8 were higher than those by

week 1. Media thickness decreased gradually in group SE, although the decrease was not significant. Intimal hyperplasia was seen in group E, which increased significantly by weeks 4 and 8 (P < .05 vs week 1). Intimal

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Fig 4. Changes in elastin fibers are shown (A) in the elastase (Group E), stenosis (Group S), stenosis and elastase (Group SE), and the control (SHAM) groups #8 weeks and (B) in group SE by week 16 (bar ¼ 20 mm, original magnification 200). C, Profiles of elastin content change are shown. The error bars indicate the standard deviation. **P < .01 and ***P < .0001.

hyperplasia was also obvious in group SE; however, the degrees of hyperplasia by weeks 4 and 8 were lower than those in group E (P < .0001). There was almost no intimal hyperplasia in group S #2 weeks. The sham group showed no intimal hyperplasia. Intimal hyperplasia was calculated by the intima-media ratio, revealing results that were similar to intima thickness described above. The overall thickness of the aortic wall in group S and group E,

calculated by IMT, also increased gradually after operation, although group SE and the SHAM group showed stable IMT (Fig 3). Changes in elastic lamellae. Elastic van Gieson staining for elastic fibers showed that elastin content in group S decreased gradually and significantly by week 8 (P < .01 vs week 1). Elastic fibers were dramatically destroyed in group E, with the elastin contents being lower than the

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Fig 5. Changes in collagen fibers are shown (A) in the elastase (Group E), stenosis (Group S), stenosis and elastase (Group SE), and the control (SHAM) groups #8 weeks and (B) in group SE by week 16 (original magnification 200, except for entire aorta ring 20). C, Profiles of content change are shown. The error bars indicate the standard deviation.*P < .05, **P < .01, and ***P < .0001.

sham group by weeks 1 and 2 (P < .0001). However, elastin content showed a tendency to increase in group E when compared with week 1. Elastic fibers were significantly destroyed in group SE, and the elastin content remained stable during follow-up, although lower than the sham group (Fig 4). Changes in type I and III collagen fibers. Type I collagen decreased significantly in group S and group E by week 2 (P < .01); however, group E showed a significant increase by week 4 (P < .05 vs sham group). In group SE, type I collagen content decreased significantly by 1 week (P < .01 vs sham group) and thereafter showed a gradual increase, returning to normal levels by week 8 and increasing further by week 16 (P < .0001 vs week 1). Compared with the sham group, type III collagen content in group S decreased dramatically by weeks 4 (P < .01) and 8 (P < .0001), whereas type III collagen fibers in group E were destroyed after the surgical operation and increased gradually during follow-up. Type III collagen content in group SE was decreased by 1 week (P < .01 vs sham group), increased significantly by week 4 (P < .0001), but

decreased gradually thereafter. Type III collagen content accounted for

Novel experimental model of enlarging abdominal aortic aneurysm in rabbits.

This study tested the hypothesis that an experimental model of abdominal aortic aneurysm in rabbits results in progressive enlargement when induced by...
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