小鼠腹主动脉斑块模型建立的两种方法及超高场强磁共振成像的应用价值

目的 探讨建立腹主动脉粥样硬化斑块模型的方法及超高场强磁共振成像(MRI)在活体监测及量化小鼠腹主动脉粥样硬化斑块中的应用价值.方法 高脂饮食法小鼠腹主动脉粥样硬化斑块模型的建立及磁共振检测(高脂饮食组):选择3批10～12月龄apoE-/-小鼠13只、WT鼠3只高脂饮食喂养,分别于喂养前、喂养3个月、喂养6个月3个时期进行小鼠腹主动脉7.0 T磁共振活体扫描.血管紧张素Ⅱ(AngⅡ)灌注法小鼠腹主动脉粥样硬化斑块模型的建立及磁共振检测(AngⅡ灌注组):选用10只6月龄apoE-/-小鼠,分为AngⅡ1000 ng·kg-1·min-1组3只、AngⅡ500 ng·kg-1·min-1组3只(以上两组均在背部埋置AngⅡ缓释泵14 d)和对照组为4只(埋置生理盐水缓释泵),分别于灌注前后行磁共振扫描,选用FLASH T1WI黑血及MSME-T2WI-PDWI双回波序列.高脂饮食组依次在各时期扫描后分别处死3、5、5只小鼠,AngⅡ灌注组于装泵后14 d行磁共振扫描,然后处死本组小鼠,取处死小鼠的肾动脉段腹主动脉制作病理切片,进行苏木素-伊红(HE)染色、Masson胶原纤维(CME)染色.每只小鼠选5～7层肾动脉段腹主动脉病理图像及多对比MRI图像,分别测量外腔面积(VOA)、内腔面积(LA),计算管肇面积(VWA)并进行MRI与病理测量结果的相关性分析.结果 两种方法建立的小鼠模型,其腹主动脉MRI与病理切片均可见不稳定斑块形成.高脂饮食组随着高脂饮食时间的延长,斑块进展,VWA不断增加,3个时期VWA方差分析F=29.94(P<0.05),斑块信号于PDWI、T2WI逐渐增加,且不均匀.高脂饮食组MRI测量的斑块面积与病理测量的斑块面积有较高的-致性(高脂喂养前、喂养3和6个月3个时期r值分别为0.84、0.95、0.90).病理切片中斑块成分与磁共振显示信号一致,均表现为脂质成分增加,纤维成分减少.AngⅡ1000 ng·kg-1·min-1组AngⅡ灌注后斑块面积与灌注前比较差异有统计学意义(P=0.017),分别为(2.65±0.48)mm2和(1.21±0.21)mm2,部分小鼠可见夹层动脉瘤形成.AngⅡ500 ng·kg-1·min-1组灌注后斑块面积也比灌注前有所进展,面积分别为(1.01±0.17)mm2和(0.85±0.11)mm2,MRI测量的斑块面积与病理测量的斑块面积有较高的一致性(r值为0.93).结论 AngⅡ灌注显著加快动脉粥样硬化进展并促进腹主动脉夹层动脉瘤形成,长期高脂饮食亦可形成晚期斑块.超高场强MRI多种序列黑血技术的综合应用能显示小鼠腹主动脉粥样硬化斑块的进展,其检测分析斑块大小结果与病理表现基本一致,对斑块成分的判定亦有一定价值.

Value of in vivo monitoring of abdominal aortic atherosclerosis by high field magnetic resonance imaging in apoE-/- mice fed a high fat diet or infused with angiotensin II

Objective To explore the value of in vivo dynamic monitoring of abdominal aortic atherosclerosis (AS) by high field magnetic resonance (MR) imaging (MRI) in apoE - / - mice fed a high fat diet or infused with angiotensin. Methods High fat diet or angiotensin Ⅱ infusion was applied to apoE-/- mice for establishment of abdominal aortic atherosclerosis model. Abdominal aorta MRI was performed at 3 time points (baseline, 3 and 6 months) in 13 high fat diet fed apoE -/- mice aged 10 -12months and 3 wild-type control mice; 10 apoE -/- mice aged 6 months were infused with angiotensin Ⅱaortic artery MRI was performed at baseline and 14 d after infusion. Black blood sequences of FLASH T1 weighted images and Proton density weighted -T2 weighted dual echo images were obtained. At each observation time post MRI, mice (n =3, 5 and 5 for high fat diet group and n =5 and 5 for angiotensin Ⅱinfusion group) were sacrificed for pathological examination of the abdominal artery. Results ( 1 ) The abdominal aorta atherosclerosis was identified in both high fat diet and angiotensin Ⅱ treated apoE -/-mice but in WT controls. Lesion progression was documented in high fat diet fed apoE -/- mice characterized by significantly increased vessel wall( a marker of atherosclerotic burden, F = 29. 94, P < 0. 05 )and gradually increased plaque signal in PDW and T2W images. Results derived from MRI corresponded histopathology findings in high fat diet fed apoE -/- mice ( correlative coefficient = 0. 84, 0. 95, 0. 90,P < 0. 05, respectively). Both MRI and histology showed increased lipid composition and decreased fibrotic composition in these mice. (2) The vessel wall area increased significantly [(1.21 ±0.21) mm2 vs.(2. 65 ±0. 48 )mm2 ,P <0. 05] and the abdominal aortic dissection aneurysms was identified in apoE-/-mice infused with high angiotensin Ⅱ. The vessel wall area also increased [(0.85 ±0. 11) mm2 vs. ( 1.01 -0. 17) mm2, P <0. 05] in low angiotensin Ⅱ infused apoE -/- mice and the coefficient between MR and histopathology is 0. 934. Conclusion Abdominal aortic unstable plaque model could be established by both high fat diet and angiotensin Ⅱ infusion in apoE mice, angiotensin Ⅱ infusion can transiently accelerate the progression of AS and can induce abdominal aortic dissection. Serial MR black blood sequences could demonstrate the development and progression of atherosclerosis in mouse abdominal aorta with excellent agreement to histopathology finding in terms of atherosclerotic burden and plaque composition. Thus, MRI appears to be a useful tool for in vivo AS plaque dynamic monitoring in mice.