Micro-Ultrasonographic Imaging of Atherosclerotic Progression and Correlation with Inflammatory Markers in Apolipoprotein-E Knockout Mice

摘要

We studied prospectively whether atherosclerotic progression in apolipoprotein-E knockout mice could be noninvasively and accurately measured by use of high-resolution ultrasonographic biomicroscopy. We examined the correlation between the ultrasonographic characterization of ascending aortic atherosclerotic plaque and plasma C-reactive protein, interleukin-1, and interleukin-6 levels in these mice. In 4 age groups (8, 16, 24, and 32 wk) of 8 male knockout mice each (atherosclerotic groups) and age-matched male C57BL/6 mice (control groups), we used ultrasonographic biomicroscopy to measure maximal plaque thickness or intima-media thickness in the ascending aorta. We compared the findings with corresponding histologic measurements, and we measured plasma C-reactive protein, interleukin-1, and interleukin-6 levels in each group. Mean atherosclerotic thicknesses and C-reactive protein and interleukin levels were significantly higher in each atherosclerotic group than in the control groups (all P ?/?) mouse model is due to the ready availability of the mice, the relative ease of their breeding and colony maintenance, their spontaneously elevated cholesterol levels on a regular chow diet, and their rapid development of atherosclerotic lesions with histopathologic progression, similar to that in human beings. 1 Noninvasively and accurately measuring the characteristics of vessels in mice has become increasingly important in the field of vascular biology. 2–4 Ultrasonographic biomicroscopy (UBM) with high-resolution scanning enables the noninvasive, real-time evaluation of murine atherosclerotic lesions in vivo. 5 The Vevo? 770 (VisualSonics Inc., a division of SonoSite Inc.; Toronto, Canada), one of the newest UBM imaging systems, enables imaging at a relatively low frequency of 30 MHz and a high resolution of 40 μm. We used this system to study prospectively the progression of atherosclerotic plaque in the ascending aortas of apoE?/? mice. To investigate the feasibility of UBM in evaluating atherosclerotic progression in apoE?/? mice in vivo and without dietary manipulation, we compared UBM and histologic measurements of intima-media thickness (IMT) or maximal plaque thickness. We used C57BL/6 mice as nonatherosclerotic control animals. Proinflammatory cytokines of the interleukin (IL) category are considered to have major roles in the chronic vascular inflammation that is typical of atherosclerosis. 6 The serum levels of several of these cytokines have correlated positively with coronary artery disease and its sequelae. Analysis of local vascular inflammation and the cytokines expressed in atherosclerotic plaques has revealed a balance between proinflammatory and anti-inflammatory cytokines, and this balance is crucial in lesion development. In addition, large studies have shown that C-reactive protein (CRP) is a marker of choice for monitoring cardiovascular risk, because it is an even stronger predictor of atherosclerosis than plasma low-density-lipoprotein concentration. 7,8 Accordingly, we studied how IMT or maximal plaque thickness measured by UBM correlates with plasma levels of the inflammatory markers CRP, IL-1, and IL-6 in apoE?/? mice.