von Willebrand Factor and Prekallikrein in Plasma Are Associated With Thrombus Volume in Abdominal Aortic Aneurysms

Intraluminal thrombus: Innocent bystander or factor in abdominal aortic aneurysm pathogenesis?

BACKGROUND

Abdominal aortic aneurysms (AAAs) represent a complex multifactorial hemodynamic, thrombotic, and inflammatory process that can ultimately result in aortic rupture and death. Despite improved screening and surgical management of AAAs, the mortality rates have remained high after rupture, and little progress has occurred in the development of nonoperative treatments. Intraluminal thrombus (ILT) is present in most AAAs and might be involved in AAA pathogenesis. The present review examined the latest clinical and experimental evidence for possible involvement of the ILT in AAA growth and rupture.

METHODS

A literature review was performed after a search of the PubMed database from 2012 to June 2020 using the terms "abdominal aortic aneurysm" and "intraluminal thrombus."

RESULTS

The structure, composition, and hemodynamics of ILT formation and propagation were reviewed in relation to the hemostatic and proteolytic factors favoring ILT deposition. The potential effects of the ILT on AAA wall degeneration and rupture, including a review of the current controversies regarding the position, thickness, and composition of ILT, are presented. Although initially potentially protective against increased wall stress, increasing evidence has shown that an increased volume and greater age of the ILT have direct detrimental effects on aortic wall integrity, which might predispose to an increased rupture risk.

CONCLUSIONS

ILT does not appear to be an innocent bystander in AAA pathophysiology. However, its exact role remains elusive and controversial. Despite computational evidence of a possible protective role of the ILT in reducing wall stress, increasing evidence has shown that the ILT promotes AAA wall degeneration in humans and in animal models. Further research, with large animal models and with more chronic ILT is crucial for a better understanding of the role of the ILT in AAAs and for the potential development of targeted therapies to slow or halt AAA progression.

von Willebrand factor deficiency does not influence angiotensin II-induced abdominal aortic aneurysm formation in mice

Abdominal aortic aneurysm (AAA) refers to a localized dilation of the abdominal aorta that exceeds the normal diameter by 50%. AAA pathophysiology is characterized by progressive inflammation, vessel wall destabilization and thrombus formation. Our aim was to investigate the potential involvement of von Willebrand factor (VWF), a thrombo-inflammatory plasma protein, in AAA pathophysiology using a dissection-based and angiotensin II infusion-induced AAA mouse model. AAA formation was induced in both wild-type and VWF-deficient mice by subcutaneous implantation of an osmotic pump, continuously releasing 1000 ng/kg/min angiotensin II. Survival was monitored, but no significant difference was observed between both groups. After 28 days, the suprarenal aortic segment of the surviving mice was harvested. Both AAA incidence and severity were similar in wild-type and VWF-deficient mice, indicating that AAA formation was not significantly influenced by the absence of VWF. Although VWF plasma levels increased after the infusion period, these increases were not correlated with AAA progression. Also detailed histological analyses of important AAA hallmarks, including elastic degradation, intramural thrombus formation and leukocyte infiltration, did not reveal differences between both groups. These data suggest that, at least in the angiotensin II infusion-induced AAA mouse model, the role of VWF in AAA pathophysiology is limited.