Forsøksdyr: Intravascular ultrasound imaging of atherosclerotic plaque in aorta in cholesterol-fed rabbit

Godkjenningsdato 02.01.2020

Godkjenningsperiode 02.01.2020-02.01.2023

Atherosclerosis is the leading cause of mortality in developed countries, and further insight into biomarkers and early diagnosis is needed. We will induce atherosclerosis in New Zealand White rabbits and perform ultrasound imaging of microbubbles targeted to identified biomarkers in the aortic plaque lesions with an intravascular ultrasound transducer using novel ultrasound techniques.

The rabbit is a commonly used animal in atherosclerosis research and it is a well-established model for human atherosclerosis. By feeding New Zealand White rabbits a cholesterol-enriched diet they will exhibit hypercholesterolaemia within a few days and develop atherosclerosis in the aortic arch and thoracic and abdominal aorta within a few weeks. The maximum high cholesterol feeding period in these experiments will be 12 weeks and the rabbits will be closely monitored throughout the period. Every four weeks, blood sampling and transcutaneous ultrasound of the aorta will be performed under anesthesia. At the last stage of the experimental period the aortic plaques will be imaged with either minimally invasive intravascular ultrasound or invasive extravascular ultrasound. The plaques will be imaged during injection of both targeted and non-targeted microbubbles and the examination will be done under full surgical anesthesia, and will be a terminal procedure. If blood samples show critical cholesterol values during the diet period, the rabbits will be taken out of the experiment.

The study comprises of three phases, where the first phase includes healthy mice which will be used for optimization of ultrasound imaging parameters. The second phase includes healthy rabbits which will be used for optimization of the ultrasonic imaging of the aorta. Both transcutaneous ultrasound, minimally invasive intravascular and invasive extravascular ultrasound will be tested. Blood sampling will also be done to establish the baseline cholesterol levels of healthy rabbits. The third phase will last for 12 weeks. 16 rabbits will be divided into four treatment groups. Group 1 will be given a standard diet throughout the 12-week period, group 2 will be given a 0.5% cholesterol enriched diet for the whole 12 weeks, and groups 3 and 4 will be given a 0.5% cholesterol enriched diet for 4 weeks and standard diet for the remaining 8 weeks. In addition, group 4 will be given sPCSK9 siRNA and atorvastatin treatment for the last 8 weeks.

Development and optimization of the ultrasound imaging technique will be done by in-vitro lab experiments using tissue mimicking material and microbubbles in flow channels. The first in-vivo experiments with the novel ultrasound equipment will be done in healthy mice, before we move on to testing the imaging schemes on healthy rabbits. Only the last stage of the experiment will include the atherosclerotic rabbits.
The experiment is considered as a mild-to-moderate load experiment. It is a moderate load for the rabbits which will be subject to an unhealthy diet for the full period (12 weeks), but mild for other animals which undergoes a shorter period of high cholesterol diet. The only surgical intervention is terminal.