Induction of autoimmune abdominal aortic aneurysm in pigs - A novel large animal model

Abstract

Background: Abdominal aortic aneurysm (AAA) is a common disease with a high mortality. Many animal models have been developed to further understand the pathogenesis of the disease, but no large animal model has been developed to investigate the autoimmune aspect of AAA formation. The aim of this study was to develop a large animal model for abdominal aortic aneurysm induction through autoimmunity by performing sheep-to-pig xenotransplantation.

Methods: Six pigs underwent a xenotransplantation procedure where the infrarenal porcine aorta was replaced by a decellularized sheep aorta. In the following 47 days, the AP-diameter of the xenografts was measured using ultrasound once a week. All xenografts were harvested for histological analyses.

Results: All the xenografts formed aneurysms with a mean increase in AP-diameter of 80.98 ± 30.20% (p < 0.005). The ultrasound measurements demonstrated a progressive aneurysmal expansion with no sign of halting towards the end of the follow-up period. Histology showed destruction of tunica media and the elastic tissue, neointimal hyperplasia, adventitial thickening with neovascularization, infiltration of lymphocytes and granulocytes, and in some cases intramural haemorrhaging.

Conclusion: We developed a novel large animal AAA model by infrarenal aortic sheep-to-pig xenograph transplantation resulting in autoimmune AAA induction with continuously progressive aneurysmal growth. This model can be used to provide a better understand the autoimmune aspect of AAA formation in large animals.

Keywords: Abdominal aortic aneurysm; Autoimmunity; Porcine model; Sheep-to-pig xenotransplantation.

Fig. 1

The transplantation process. (A) The porcine aorta dissected from the renal arteries (right side) to the trifurcation (left side). (B–D) Orthotopic replacement of the infrarenal porcine aorta by the sheep xenograft with end-to-end parachute anastomosis.

Fig. 2

The effect of decellularizing detergents on sheep aortas. No nuclei were detected in SDS decellularized xenografts (B) Non-decellularized controls (A). The specimens are stained with HE.

Fig. 3

Mean increase ± SD in AP-diameter. A progressive aneurysm expansion of the xenografts could be seen from baseline (AP-0) to postoperative day 47.

Fig. 4

Postmortem histological specimens. (A–B) Masson Trichrome staining of control sheep aorta (A) and postmortem aneurysm specimen (B). Collagen and reticular fibres are coloured blue, cytoplasm and SMCs are dark pink and nuclei are purple. Millers Verhoef van Gieson staining of control sheep aorta (C) and postmortem aneurysm specimen (D). Elastic fibres are purple/black, collagen is dark pink and cytoplasm and SMCs are yellow. Postmortem aneurysm specimens (B) and (D) show the xenograft (red arrow) surrounded by intimal and adventitial hyperplasia, and lymphocytes arranged in germinal centers in tunica adventitia (black arrows). Enlargement of D are shown in (E and F) displaying severe destruction of elastic fibers and thinning of tunica media of the decellarized xenograft. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)