Invasive and non-invasive evaluation of spontaneous arteriogenesis in a novel porcine model for peripheral arterial obstructive disease
Introduction
In the last decades, the treatment of patients with obstructive coronary and/or peripheral artery disease has made significant improvement using novel selective pharmacological and invasive techniques such as angioplasty and stenting as well as bypass surgery. Nevertheless, angioplasty and bypass surgery, the primary interventional invasive therapies for the treatment of atherosclerosis, are itself limited by the development over time of native vessel restenoses and graft occlusions. Moreover, these therapies are not an option for a significant number of patients with diffuse atherosclerotic disease [1], [2].
The human circulation has a pre-existing collateral vascular system, which in case of slowly progressive atherosclerotic narrowing may circumvent the stenosis and ensure blood flow to endangered ischemic territories. The growth of these small arterioles, that are only partially recruited under resting conditions, can be therapeutically enhanced. This process of active proliferation is termed arteriogenesis and results, in contrast to angiogenesis (the sprouting of capillaries) in true functional arteries [3], [4], [5], [6], [7]. Several cytokines such as basic fibroblast-growth-factor, monocyte chemoattractant protein-1, granulocyte and macrophage colony stimulating factor and transforming growth factor beta are known for their stimulatory effect on arteriogenesis [3], [8], [9], [10], [11], [12], [13], [14], [15], [16]. The vast majority of experimental angio- or arteriogenesis data is based on studies in small animal species such as rabbits or mice [13], [17]. These data only partially reflect the situation in humans, since the total amount of new tissue necessary for the morphogenesis of developing collateral arteries is an order of magnitude smaller in mice versus man. This suggests that the time interval needed to transform a recently recruited collateral into a functional artery will take much longer in larger species. Thus, larger animal models are needed to study the time course of arteriogenesis anticipated in humans. Furthermore, animal models for pre-clinical testing of growth factors should provide a similar collateral vascular growth as compared with the human situation. The dog heart for instance, provides a very well developed collateral circulation, whereas the pig and rabbit heart are only poorly equipped with an efficient collateral circulatory system, similar to the human condition [5], [18], [19], [20], [21], [22], [23].
Since current animal models for peripheral atherosclerotic obstructive disease are limited to the mouse, rat or rabbit hind limb, and peripheral vascular data from larger species are not available, we now tested the hypothesis, whether the pig hind limb might provide a model for peripheral collateral artery growth that is more suitable for extrapolation to the human situation with peripheral vascular disease.
Section snippets
Preparation of animals
All animal procedures described in this study were approved by the Bioethical Committee of the District of Baden-Würtemberg, Regierungspräsidium Stuttgart and Freiburg. The animals were handled in accordance with the American Physiological Society guidelines for animal welfare. Animals were housed in standard cages and fed water and chow ad libitum.
Arterial ligation
For this study, 12 farm pigs (Winter, Assmannshardt, Germany) weighing 25–35 kg with a mean age of 3±1 months, and a second group of nine Göttinger
General observation
Overall, no macroscopic necrosis was observed. No signs of clinical infection could be observed (increased body temperature, wound swelling or redness). All animals survived the initial surgery and the follow-up period.
Mean arterial blood pressures
Systemic arterial pressures remained unchanged in both farm pigs and minipigs throughout the study (Table 1). However, mean arterial blood pressure was 10–20 mmHg lower in Göttinger minipigs than in the farm pigs. Blood pressures in the unligated right hindlimb were similar to
Discussion
The present study describes for the first time, a femoral arterial ligation model in the pig, that is suitable for evaluation of arteriogenesis using both non-invasive and invasive evaluation techniques.
Acknowledgements
Jan J. Piek is clinical investigator for the Netherlands Heart Foundation (Grant No. D96.020 and 2000.090). Boehringer Ingelheim is acknowledged for their financial and technical assistance in this project. Especially, T. Dietze, A. Sterner, S. Germeyer, R. Seidler and B. Guth have contributed to this project. Furthermore this work was supported by the German Volkswagenfoundation.
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Both authors contributed equally to this study.