Popliteal artery aneurysms differ from abdominal aortic aneurysms in cellular topography and inflammatory markers

Apolipoprotein E (ApoE) Rescues the Contractile Smooth Muscle Cell Phenotype in Popliteal Artery Aneurysm Disease

Popliteal artery aneurysm (PAA) is the most frequent peripheral aneurysm, primarily seen in male smokers with a prevalence below 1%. This exploratory study aims to shed light on cellular mechanisms involved in PAA progression. Sixteen human PAA and eight non-aneurysmatic popliteal artery samples, partially from the same patients, were analyzed by immunohistochemistry, fluorescence imaging, Affymetrix mRNA expression profiling, qPCR and OLink proteomics, and compared to atherosclerotic (n = 6) and abdominal aortic aneurysm (AAA) tissue (n = 19). Additionally, primary cell culture of PAA-derived vascular smooth muscle cells (VSMC) was established for modulation and growth analysis. Compared to non-aneurysmatic popliteal arteries, VSMCs lose the contractile phenotype and the cell proliferation rate increases significantly in PAA. Array analysis identified APOE higher expressed in PAA samples, co-localizing with VSMCs. APOE stimulation of primary human PAA VSMCs significantly reduced cell proliferation. Accordingly, contractile VSMC markers were significantly upregulated. A single case of osseous mechanically induced PAA with a non-diseased VSMC profile emphasizes these findings. Carefully concluded, PAA pathogenesis shows similar features to AAA, yet the mechanisms involved might differ. APOE is specifically higher expressed in PAA tissue and could be involved in VSMC phenotype rescue.

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.

X-ray scanning microscopies of microcalcifications in abdominal aortic and popliteal artery aneurysms

Abdominal aortic and popliteal artery aneurysms are vascular diseases which show massive degeneration, weakening of the vascular wall and loss of the vascular tissue functionality. They are driven by inflammatory, hemodynamical factors and biological alterations that may lead, in the case of an abdominal aortic aneurysm, to sudden and dangerous ruptures of the arteries. Here, human aortic and popliteal aneurysm tissues were obtained during surgical repair, and studied by synchrotron radiation X-ray scanning microdiffraction and small-angle scattering, to investigate the microcalcifications present in the tissues. Data collected during the experiments were transformed into quantitative microscopy images through the combination of statistical approaches and crystallographic methods. As a result of this multi-step analysis, microcalcifications, which are markers of the pathology, were classified in terms of chemical and structural content. This analysis helped to identify the presence of nanocrystalline hy-droxy-apatite and microcrystalline cholesterol, embedded in myofilament, and elastin-containing tissue with low collagen content in predominantly nanocrystalline areas. The generality of the approach allows it to be transferred to other types of tissue and other pathologies affected by microcalcifications, such as thyroid carcinoma, breast cancer, testicular microli-thia-sis or glioblastoma.

Multiple sites of vascular dilation or aneurysmal disease and matrix metalloproteinase genetic variants in patients with abdominal aortic aneurysm

OBJECTIVE

The objective of this study was to assess whether functional genetic polymorphisms of matrix metalloproteinases (MMPs) 1, 3, 9, and 12 are associated with arterial enlargements or aneurysms of the thoracic aorta or popliteal arteries in patients with abdominal aortic aneurysm (AAA).

METHODS

The associations between MMP1 (-1607 G in/del, rs1799750), MMP3 (-1171 A in/del rs35068180), MMP9 (13-26 CA repeats around -90, rs2234681, rs917576, rs917577), and MMP12 (G/T missense variation, rs652438) polymorphisms and enlargements or aneurysms of the thoracic aorta and popliteal arteries were tested in 169 consecutive AAA patients.

RESULTS

Thoracic aorta enlargement or aneurysm (TE/A; maximum diameter, >35 mm) was detected in 34 patients (20.1% prevalence). MMP9 rs2234681 microsatellite was the only genetic determinant of TE/A in AAA patients (P = .003), followed by hypercholesterolemia and antiplatelet use. Carriers of both alleles with ≥22 CA repeats had a 5.9 (95% confidence interval, 1.9-18.6; P < .0001) increased odds of TE/A, and a score considering all three variables showed 98% negative predictive value and 30% positive predictive value for thoracic aortic aneurysm detection. Eighty-two popliteal artery enlargements or aneurysms (diameter >10 mm) occurred in 55 patients (33.1% prevalence). Carriers of MMP12 rs652438 C allele showed an 18% (P = .006) increased diameter in popliteal arteries and a 2.8 (95% confidence interval, 1.3-6; P = .008) increased odds of popliteal artery enlargement or aneurysm compared with TT genotype.

CONCLUSIONS

Among patients with AAA, carriers of homozygous ≥22 CA repeats in MMP9 rs12234681 and of C allele in MMP12 rs652438 have a substantial risk of carrying thoracic and popliteal enlargements, respectively.

Popliteal Artery Aneurysm in Women

OBJECTIVES

Ninety-five per cent of those operated on for popliteal artery aneurysm (PA) are men. Thus, PAs in women are difficult to investigate. The aim was to study the disease in women.

METHODS

Women treated for PA in 1987-2012, prospectively registered in the Swedish vascular registry, Swedvasc, supplemented by case records, were compared with the larger male cohort. Survival was determined through cross linkage with the National Population Registry.

RESULTS

1509 patients (men and women), 1872 legs, were identified; of these 74 patients (4.9%) were women, 81 legs (4.3%). The median age was 70 years in women versus 69 in men. Twenty-nine centres operated on women (range 1-7 women/centre). There were no time trends in the proportion of women operated on (p=.5). Bilateral PA occurred in 9.5% of women and 27.0% of men (p=.002). For symptomatic aneurysms, there was a larger proportion of small aneurysms (<2 cm) among women than men (24% vs. 8%, p=.005), there was no such difference in asymptomatic aneurysms. Distribution between asymptomatic and symptomatic PA was 31% versus 69%, similar to men. The prevalence of concomitant aneurysms in the aorto-iliac and femoral arteries, and the frequency of presenting symptoms were similar compared with men. Three PA were ruptured (3.7%). Thrombolysis was used in 23 of 45 legs treated for acute ischaemia (51%). Eight legs were treated with endovascular stent grafts (9.8%), compared with 7.9% in men (p=.5). Seven legs were amputated (8.6%). Crude survival was similar to men.

CONCLUSIONS

PA is similar in women and men, but bilateral disease was less common in women and symptomatic PA were more often <2 cm in diameter. Women had the same survival as men, despite women generally having better life expectancy. Although the largest series ever published on women with PA, the sample size is small, making it prone to type II statistical error.

Adventitial adipogenic degeneration is an unidentified contributor to aortic wall weakening in the abdominal aortic aneurysm

OBJECTIVE

The processes driving human abdominal aortic aneurysm (AAA) progression are not fully understood. Although antiinflammatory and proteolytic strategies effectively quench aneurysm progression in preclinical models, so far all clinical interventions failed. These observations hint at an incomplete understanding of the processes involved in AAA progression and rupture. Interestingly, strong clinical and molecular associations exist between popliteal artery aneurysms (PAAs) and AAAs; however, PAAs have an extremely low propensity to rupture. We thus reasoned that differences between these aneurysms may provide clues toward (auxiliary) processes involved in AAA-related wall debilitation. A better understanding of the pathophysiologic processes driving AAA growth can contribute to pharmaceutical treatments in the future.

METHODS

Aneurysmal wall samples were collected during open elective and emergency repair. Control perirenal aorta was obtained during kidney transplantation, and reference popliteal tissue obtained from the anatomy department. This study incorporates various techniques including (immuno)histochemistry, Western Blot, quantitative polymerase chain reaction, microarray, and cell culture.

RESULTS

Histologic evaluation of AAAs, PAAs, and control aorta shows extensive medial (PAA) and transmural fibrosis (AAA), and reveals abundant adventitial adipocytes aggregates as an exclusive phenomenon of AAAs (P < .001). Quantitative polymerase chain reaction, immunohistochemistry, Western blotting, and microarray analysis showed enrichment of adipogenic mediators (C/EBP family P = .027; KLF5 P < .000; and peroxisome proliferator activated receptor-γ, P = .032) in AAA tissue. In vitro differentiation tests indicated a sharply increased adipogenic potential of AAA adventitial mesenchymal cells (P < .0001). Observed enrichment of adipocyte-related genes and pathways in ruptured AAA (P < .0003) supports an association between the extent of fatty degeneration and rupture.

CONCLUSIONS

This translational study identifies extensive adventitial fatty degeneration as an ignored and distinctive feature of AAA disease. Enrichment of adipocyte genesis and adipocyte-related genes in ruptured AAA point to an association between the extent of fatty degeneration and rupture. This observation may (partly) explain the failure of medical therapy and could provide a lead for pharmaceutical alleviation of AAA progression.

The pathophysiologic basis of abdominal aortic aneurysm progression: a critical appraisal

An aneurysm of the abdominal aorta is a common pathology and a major cause of sudden death in the elderly. Currently, abdominal aortic aneurysms (AAAs) can only be treated by surgery and an effective medical therapy is urgently missing. The pathophysiology of AAAs is complex and is believed to be best described as a comprehensive inflammatory response with an accompanying proteolytic imbalance; the latter being held responsible for the progressive weakening of the aortic wall. Remarkably, while interference in inflammatory and/or proteolytic cascades proves highly effective in preclinical studies, emerging clinical studies consistently fail to show a benefit. In fact, some anti-inflammatory interventions appear to adversely influence the disease process. Altogether, recent clinical observations not only challenge the prevailing concepts of AAA progression, but also raise doubt on the translatability of findings from rodent models for growing AAA.