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2125 In vivo molecular MRI of carotid artery injury in mice using an elastin-binding contrast agent

Introduction

Smooth muscle cell proliferation and extracellular matrix (ECM) synthesis/turnover are thought to play an important role in vessel wall repair after vascular injury. Recently, we identified the cysteine-rich-protein-2 (CRP2) as novel and specific molecular effector of the NO/cGMP/cGMP-dependent-protein-kinase-I (PKG) signaling in vascular smooth muscle. To elucidate whether CRP2 contributes to the postulated pro-proliferative/proatherogenic effect of PKG, we established a CRP2-deficient mouse line by targeted deletion of the exons 2–7 in the CRP2-gene. With the simultaneous development of a novel ECM-specific MR contrast agent (BMS753951) non-invasive assessment of changes in remodeling of the injured mouse carotid wall has become feasible.

Purpose

In this study we investigated whether the use of an elastin-binding contrast agent would allow the detection of vascular remodeling in a mouse model of carotid artery injury and whether it would facilitate the detection of impaired ECM formation in CRP2-/- mice.

Methods

A carotid artery injury model was performed in 8 wild-type and 8 CRP2-deficient (CRP2-/-) mice; the right carotid artery wall was damaged, while the left served as control. Two month after surgical intervention, MRI of the carotid vessel walls was performed in a 1.5 T Philips Achieva clinical MR scanner using a single loop small animal coil, a dedicated cardiac software package (R1.2.2) and a clinical gradient system (30 mT/m, 150 mT/m/ms). Time-of-flight angiography of the carotid arteries was performed for visualization of the injured vessel segment and for subsequent planning of the vessel wall scans. Imaging parameters included TR = 43, TE = 8.1, flip angel = 60°, spatial resolution = 0.2 × 0.2 × 0.5 mm. For assessment of ECM remodeling, an inversion recovery vessel wall sequence was performed approximately 45–60 minutes post injection of 0.1 mmol/kg of BMS753951 (Bristol-Myer-Squibb/Billerica/MA), a novel elastin-binding Gd-based contrast agent. Imaging parameters included TR = 44, TE = 11, flip-angel = 30°, spatial resolution = 0.1 × 0.1 × 0.5 mm, 22 lines per RR-interval, inversion time approx. 250 ms. Signal-to-noise and contrast-to-noise-ratio (SNR, CNR) of the injured vessel wall was determined by manual segmentation of the visually apparent signal of the contrast agent below the carotid bifurcation. Noise was determined within a region of interest drawn outside the animal.

To verify our MR data, we performed histological elastic-staining in a 10 μm-whole-neck paraffin-slice using the common Elastica-Van-Gieson-method.

Results

SNR and CNR of the injured right compared to the non injured left carotid artery was significantly increased (p < 0.001) both in wild-type (SNR: 12.9 ± 2.2 vs. 5.8 ± 1.9; CNR: 10.8 ± 1.8 vs. 4.3 ± 2.3; Figure 1A) and in CRP2-/- mice (SNR: 9.4 ± 1.6 vs. 6.4 ± 2.1; CNR: 7.9 ± 1.8 vs. 4.9 ± 1.7; Figure 1B). More interestingly, SNR (12.9 ± 2.2 vs. 9.4 ± 1.6) and CNR (10.8 ± 1.8 vs. 7.9 ± 1.8) of the injured right carotid artery of CRP2-/- mice was significantly decreased when compared to control animals (p < 0.05) (Figure 2). No significant difference was found between non-injured carotid arteries of both genotypes (SNR: p = 0.35, CNR: p = 0.36).

figure1

Figure 1

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Figure 2

In both genotypes, the carotid injury per se was confirmed in 10 μm-whole-neck paraffin sections stained with Elastica-Van-Gieson (Figure 3). Preliminary evaluation of the carotid wall thickening seem to confirm our MRI findings and suggests that targeted deletion of CRP2 in mice might lead to a reduced vessel wall thickening and thus to a reduced restenosis after vascular injury. However, the semi-quantitative analysis of carotid vessel wall thickening in both genotypes is currently still under investigation.

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Figure 3

Conclusion

In this study, we demonstrate the successful use of molecular MRI for the non-invasive assessment of alterations in the vessel wall after vascular injury in a mouse model of impaired smooth muscle cell proliferation and ECM formation. The use of BMS753951 allows the differentiation of molecular alterations in the injured and non-injured vessel wall, as well as between wild-type and CRP2-/- mice with regard to elastin formation after vascular injury.

Author information

Correspondence to Marcus R Makowski.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Makowski, M.R., Sausbier, U., Liao, Y.L. et al. 2125 In vivo molecular MRI of carotid artery injury in mice using an elastin-binding contrast agent. J Cardiovasc Magn Reson 10, A394 (2008). https://doi.org/10.1186/1532-429X-10-S1-A394

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Keywords

  • Vessel Wall
  • Smooth Muscle Cell Proliferation
  • Injured Vessel
  • Carotid Wall
  • Carotid Artery Wall