1Department of Cardiothoracic Surgery, Stanford University School of Medicine, 2Stanford University School of Medicine
Deuse, T., Ikeno, F., Robbins, R. C., Schrepfer, S. Imaging In-Stent Restenosis: An Inexpensive, Reliable, and Rapid Preclinical Model. J. Vis. Exp. (31), e1346, doi:10.3791/1346 (2009).
Preclinical models of restenosis are essential to unravel the pathophysiological processes that lead to in-stent restenosis and to optimize existing and future drug-eluting stents.
A variety of antibodies and transgenic and knockout strains are available in rats. Consequently, a model for in-stent restenosis in the rat would be convenient for pathobiological and pathophysiological studies.
In this video, we present the full procedure and pit-falls of a rat stent model suitable for high throughput stent research. We will show the surgical procedure of stent deployment, and the assessment of in-stent restenosis using the most elegant technique of OCT (Optical Coherence Tomography). This technique provides high accuracy in assessing plaque CSAs (cross section areas) and correlates well with histological sections, which require special and time consuming embedding and sectioning techniques. OCT imaging further allows longitudinal monitoring of the development of in-stent restenosis within the same animal compared to one-time snapshots using histology.
Aortic Stent Deployment
Optical Coherence Tomography (OCT) Imaging
OCT images are obtained with the M2 OCT imaging system (LightLab Imaging, Inc., Westford, MA, USA). ImageWire is an imaging probe to deliver the light to the tissue and collect the signals. The ImageWire consists of 0.006"(0.15 mm) fiber-optic core, inside a sheath with a maximum O.D. of 0.019" (0.48 mm).
Analyzing OCT images
OCT measurements are performed using the LightLab OCT imaging proprietary software with a rat-based interface.
Validation of the OCT technique
OCT results correlate well with histopathology (Figure 1). Histologic plaque CSAs are calculated as described above. Histology reveals intimal hyperplasia with high density of spindle-shaped cells and only few mononuclear inflammation cells. After 6 weeks, stents are completely covered with neointimal granulation tissue and the plaque CSA measures 1.3±0.4 mm2 in a 2.5mm stent.
Figure 1: OCT (A) and histological (B; magnification 16x) images of the stent 6 weeks after deployment. Plaque CSA results obtained from OCT images correlate well with histopathology. Please click here to see a larger version of figure 1.
Although the rabbit iliac artery and the pig coronary artery models are the most frequently used for stent placement 1, a combination of radiological and surgical equipment is required, animal housing capacity is limited, and the costs of purchase are high. Limitations of the rat stent model is the necessary use of specifically designed stents for rats, the metal-to-artery ratio resulting in more vascular injury2, and the artificially high incidence of thrombosis3.
The rat stenting model is a simple, inexpensive, rapid, and accurate preclinical model 4. After the initial report of direct stenting of the rat aorta by Lowe et al. 5, feasibility and suitability of this model for the evaluation of the pathophysiology of in-stent restenosis has been thoroughly shown 5,6. The diameter of the rat aorta is adequate to allow expansion of commercially available stents without disruption of the physiologic vessel architecture. It has been shown that pathophysiological mechanisms, such as thrombus formation, inflammation, and SMC proliferation, develop in these rat models as they do in the rabbit and pig. Therefore, these models are good representations of the actual process of restenosis.
The OCT high-resolution imaging technology is useful to evaluate intimal hyperplasia. The penetration depth is only 1.5-2 mm, but its resolution is an order of magnitude greater than that of intravascular ultrasound (IVUS) 7,8. Multiple studies comparing OCT with IVUS conclude that OCT is currently the preferred technique to evaluate neointimal hyperplasia after stent implantation 8-10. Especially in small animals with small vessel diameters, the high resolution of OCT renders it the best imaging modality for the evaluation of restenosis.
In summary, this video shows that (1) rat aortic stenting is easily feasible, (2) rat abdominal aorta stenting is suitable for testing commercially manufactured stents and (3) OCT imaging is an accurate and elegant technique for longitudinal monitoring of in-stent restenosis.
All rats were housed in the animal care facility at Stanford University Medical Center (Stanford, Ca), under standard temperature, humidity, and lighting conditions, and were provided rat chow and water ad libitum. The investigation conformed to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH publication No. 85-23, revised 1996). The study protocol was approved by the Administrative Panel on Laboratory Animal Care, Stanford University.
The present study was supported by the Falk Research Fund for the Department of Cardiothoracic Surgery at Stanford University School of Medicine, Stanford, CA, USA. Tobias Deuse was funded by a research grant of the German Cardiac Society. Sonja Schrepfer has received a research grant from the Deutsche Forschungsgemeinschaft (DFG) (SCHR992/2-1).