Animal models for the study of lower extremity chronic venous disease: lessons learned and future needs

In vivo veritas: Thrombosis mechanisms in animal models

Experimental models have enhanced our understanding of atherothrombosis pathophysiology and have played a major role in the search for adequate therapeutic interventions. Various animal models have been developed to simulate thrombosis and to study in vivo parameters related to hemodynamics and rheology that lead to thrombogenesis. Although no model completely mimics the human condition, much can be learned from existing models about specific biologic processes in disease causation and therapeutic intervention. In general, large animals such as pigs and monkeys have been better suited to study atherosclerosis and arterial and venous thrombosis than smaller species such as rats, rabbits, and dogs. On the other hand, mouse models of arterial and venous thrombosis have attracted increasing interest over the past two decades, owing to direct availability of a growing number of genetically modified mice, improved technical feasibility, standardization of new models of local thrombosis, and low maintenance costs. To simulate rupture of an atherosclerotic plaque, models of arterial thrombosis often involve vascular injury, which can be achieved by several means. There is no animal model that is sufficiently tall, that can mimic the ability of humans to walk upright, and that possesses the calf muscle pump that plays an important role in human venous hemodynamics. A number of spontaneous or genetically engineered animals with overexpression or deletion of various elements in the coagulation, platelet, and fibrinolysis pathways are now available. These animal models can replicate important aspects of thrombosis in humans, and provide a valuable resource in the development of novel concepts of disease mechanisms in human patients.

A study of seven different types of grafts for jugular vein transplantation in the horse

The aim of this study was to investigate the biological behaviour of vascular grafts replacing a section of the jugular vein in order to improve the results of the surgical treatment of complete thrombosis of the jugular vein in the horse. Seven graft types: fresh allograft, home frozen allograft, glutaraldehyde-fixed allograft, cryo-preserved allograft, PTFE-graft (Gore), small intestinal submucosa preparation (Cook) and fresh autograft, were randomly implanted in ponies. The grafts were removed after one month and examined histologically for: preservation of the graft structures, acceptance by the host, intima proliferation, presence of endothelium and patency. The glutaraldehyde- and cryopreserved grafts show reasonable results and the PTFE and autograft had the best results especially with respect to host acceptance, endothelium presence and patency. Further research is necessary to improve graft behaviour, especially to the aspect of endothelisation. Obstruction of the jugular vein in horses can be treated surgically.

Tissue-engineered bioprosthetic venous valve: a long-term study in sheep

OBJECTIVE

to develop a graft bearing an immunologically tolerated tissue-engineered venous valve (TE graft) that will be incorporated into a native vessel, and restore normal valve function for the treatment of chronic venous insufficiency.

METHODS

twenty-four TE grafts were grown using decellularised allogeneic ovine veins as donor matrix, which was subsequently repopulated with the future recipient's myofibroblasts (MFB) and endothelial cells (EC). TE grafts were implanted into the external jugular vein. Animals were sacrificed at 1, 6, and 12 weeks (n=4, each). Autografts served as controls (1 week, n=4; 6 weeks, n=4). Specimen for histology and immunohistochemistry were taken.

RESULTS

the matrix was successfully repopulated with MFB and EC (n=8). Patency on venography in the TE graft-group was44,44, and 34 at 1, 6, and 12 weeks, and44 (44) in autografts at 1 (6) weeks, respectively. Except for 2 TE grafts after 12 weeks, valves were competent (duplex ultrasound). Patent TE grafts were merely distinguishable from autografts with minor inflammatory reactions. Reflux was caused by neo-intima formation related to the basis of the TE graft.

CONCLUSION

acellularisation and consecutive in vitro autogeneic re-seeding of valved venous conduits can lead to immunologically acceptable, patent, and competent implants in sheep.