Time-Dependent Pathological Changes in Hypoperfusion-Induced Abdominal Aortic Aneurysm

Hypoperfusion due to vasa vasorum stenosis can cause wall hypoxia and abdominal aortic aneurysm (AAA) development. Even though hypoperfusion is an important contributor toward pathological changes in AAA, the correlation between hypoperfusion and AAA is not fully understood. In this study, a time-dependent semi-quantitative pathological analysis of hypoperfusion-induced aortic wall changes was performed to understand the mechanisms underlying the gradual degradation of the aortic wall leading to AAA formation. AAA-related factors evaluated in this study were grouped according to the timing of dynamic change, and five groups were formed as follows: first group: angiotensin II type 1 receptor, endothelin-1 (ET-1), and malondialdehyde (MDA); second group: matrix metalloproteinase (MMP)-2, -9, -12, M1 macrophages (Mac387+ cells), and monocyte chemotactic protein-1; third group: synthetic smooth muscle cells (SMCs); fourth group: neutrophil elastase, contractile SMCs, and angiotensinogen; and the fifth group: M2 macrophages (CD163+ cells). Hypoxia-inducible factor-1α, ET-1, MDA, and MMP-9 were colocalized with alpha-smooth muscle actin cells in 3 h, suggesting that hypoperfusion-induced hypoxia directly affects the activities of contractile SMCs in the initial stage of AAA. Time-dependent pathological analysis clarified the cascade of AAA-related factors. These findings provide clues for understanding complicated multistage pathologies in AAA

Data from: Hypoperfusion of the adventitial vasa vasorum develops an abdominal aortic aneurysm

The aortic wall is perfused by the adventitial vasa vasorum (VV). Tissue hypoxia has previously been observed as a manifestation of enlarged abdominal aortic aneurysms (AAAs). We sought to determine whether hypoperfusion of the adventitial VV could develop AAAs. We created a novel animal model of adventitial VV hypoperfusion with a combination of a polyurethane catheter insertion and a suture ligation of the infrarenal abdominal aorta in rats. VV hypoperfusion caused tissue hypoxia and developed infrarenal AAA, which had similar morphological and pathological characteristics to human AAA. In human AAA tissue, the adventitial VV were stenotic in both small AAAs (30–49 mm in diameter) and in large AAAs (> 50 mm in diameter), with the sac tissue in these AAAs being ischemic and hypoxic. These results indicate that hypoperfusion of adventitial VV has critical effects on the development of infrarenal AAA

AAA patient profile

AAA patient profil

Hypoperfusion of the Adventitial Vasa Vasorum Develops an Abdominal Aortic Aneurysm

<div><p>The aortic wall is perfused by the adventitial vasa vasorum (VV). Tissue hypoxia has previously been observed as a manifestation of enlarged abdominal aortic aneurysms (AAAs). We sought to determine whether hypoperfusion of the adventitial VV could develop AAAs. We created a novel animal model of adventitial VV hypoperfusion with a combination of a polyurethane catheter insertion and a suture ligation of the infrarenal abdominal aorta in rats. VV hypoperfusion caused tissue hypoxia and developed infrarenal AAA, which had similar morphological and pathological characteristics to human AAA. In human AAA tissue, the adventitial VV were stenotic in both small AAAs (30–49 mm in diameter) and in large AAAs (> 50 mm in diameter), with the sac tissue in these AAAs being ischemic and hypoxic. These results indicate that hypoperfusion of adventitial VV has critical effects on the development of infrarenal AAA.</p></div

(A) Representative images of aneurysmal tissue with Elastica van Gieson staining in the abdominal aortae of group IV rats immediately after operation (0 days) and 7, 14, and 28 postoperative days (POD). As time passed, the aortic diameter gradually increased and the medial layer became thinner. Scale bar = 500 μm. (B) At POD 28, histological evaluation with Elastica van Gieson staining showed degeneration of the medial elastic lamina, sparse collagen fibers in the aortic adventitia, and marked intimal hyperplasia. Scale bar = 100μm. (C) Measurement of Heme B levels relative to those of phosphatidylcholine(PC16:0/18:1) with matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) in the midpoint of the infra-renal aorta immediately (0h), 6 h, and 24 h after the operation in groups I—IV. MALDI-IMS showed that the ratio of Heme B to PC (16:0/18:1) in group IV had significantly decreased 24h after the operation. Results are the means ± standard deviation of three i

<p>(A) Representative images of aneurysmal tissue with Elastica van Gieson staining in the abdominal aortae of group IV rats immediately after operation (0 days) and 7, 14, and 28 postoperative days (POD). As time passed, the aortic diameter gradually increased and the medial layer became thinner. Scale bar = 500 μm. (B) At POD 28, histological evaluation with Elastica van Gieson staining showed degeneration of the medial elastic lamina, sparse collagen fibers in the aortic adventitia, and marked intimal hyperplasia. Scale bar = 100μm. (C) Measurement of Heme B levels relative to those of phosphatidylcholine(PC16:0/18:1) with matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) in the midpoint of the infra-renal aorta immediately (0h), 6 h, and 24 h after the operation in groups I—IV. MALDI-IMS showed that the ratio of Heme B to PC (16:0/18:1) in group IV had significantly decreased 24h after the operation. Results are the means ± standard deviation of three independent experiments. Statistical analysis was performed using analysis of variance for comparisons among the four groups. Post-hoc comparison was performed using Tukey’s test. **P<0.001 indicates a statistically significant difference. (D) Measurement of adenosine triphosphate (ATP) levels relative to those of PC (16:0/18:1) with MALDI-IMS at the midpoint of the infra-renal aorta immediately (0 h), 6 h, and 24 h after the operation in groups I—IV. MALDI-IMS showed that the ratio of ATP to PC (16:0/18:1) in group IV was significantly decreased at 24 h after the operation. Results are means ± standard deviation of five independent experiments. Statistical analysis was performed using analysis of variance for comparisons among the four groups. Post-hoc comparison was performed using Tukey’s test. **P<0.001 indicates a statistically significant difference.</p

(A) Preoperative contrast-enhanced 3D-multiple-detector computed tomographic images of a patient with an abdominal aortic aneurysm (AAA). Scale bar = 20 mm. AAAs 30–49 mm in diameter were classified as small, and those more than 50 mm in diameter were classified as large. (B) Upper: representative images of cross-sections of small and large AAAs, (Elastica van Gieson staining). In the small AAAs, medial elastic fibers are relatively well preserved in comparison with the large AAAs. In these large AAAs, the medial elastic lamina is extensively disrupted, with a thick intraluminal thrombus. Ad;,adventitia; Me, media; In, intima. Scale bar = 500 μm. Lower part: representative images from the immunohistochemical assay for hypoxia-inducible factor-1α (HIF-1α) in a small and a large AAA. Nuclear and cytoplasmic expression of HIF-1α was observed in the media/adventitia in both AAAs. Scale bar = 500 μm. (C) Representative images of immunofluorescence staining for smooth muscle cells (SMCs; alp

<p>(A) Preoperative contrast-enhanced 3D-multiple-detector computed tomographic images of a patient with an abdominal aortic aneurysm (AAA). Scale bar = 20 mm. AAAs 30–49 mm in diameter were classified as small, and those more than 50 mm in diameter were classified as large. (B) Upper: representative images of cross-sections of small and large AAAs, (Elastica van Gieson staining). In the small AAAs, medial elastic fibers are relatively well preserved in comparison with the large AAAs. In these large AAAs, the medial elastic lamina is extensively disrupted, with a thick intraluminal thrombus. Ad;,adventitia; Me, media; In, intima. Scale bar = 500 μm. Lower part: representative images from the immunohistochemical assay for hypoxia-inducible factor-1α (HIF-1α) in a small and a large AAA. Nuclear and cytoplasmic expression of HIF-1α was observed in the media/adventitia in both AAAs. Scale bar = 500 μm. (C) Representative images of immunofluorescence staining for smooth muscle cells (SMCs; alpha-smooth muscle cell actin, ASMA) (green) and HIF-1α (red). Merged images showed that HIF-1α was positive in SMCs. Scale bar = 20 μm. (D) Representative images of immunofluorescence staining for fibroblasts (S-100; green) and HIF-1α (red). Merged images showed that HIF-1α was positive in fibroblasts. Scale bar = 20 μm. (E) Patency of the adventitial vasa vasorum (VV) in human tissues (Elastica van Gieson staining). The VVs are patent in the normal aorta but stenotic in the small and larger AAA sacs. Scale bar = 50μm. (F) Lumen patency of the VV was measured as the ratio of the lumen area to the total area, which was bounded by the external elastic lamina (EEL) in each VV. The figure compares lumen patency of adventitial VV among a normal aorta, a small AAA sac, and a large AAA sac adventitial VV. Data were obtained from six cadavers with normal aortae, seven patients with small AAAs, and 30 patients with large AAAs). **P < 0.01.</p

Characterization of rats that underwent polyurethane catheter insertion and aortic ligation resulting in aortic aneurysms (group IV).

<p>Data were collected using aortic specimens harvested on postoperative day 28 (n = 10). Group I was used as a control group. The specimens included infra-renal proximal aorta (Prox.A) and aneurysmal sac (Sac). All data are expressed as means ± standard deviation. (<b>A</b>) Representative photomicrographs of smooth muscle cells (SMCs; alpha-smooth muscle cell actin, ASMA), elastin (Elastica van Gieson staining, EVG), and collagen fibers (picrosirius red; PSR). Scale bar in upper panels = 500 μm, in lower panels = 100 μm. (<b>B</b>) Quantitative analysis of SMC, elastin fragmentation and collagen distribution. SMC depletion was scored as mild (1) to severe (5) using a histological grading system. Areas positive for collagen fibers were quantitated per aortic section. Results are means ± standard deviation of three independent experiments. Statistical analysis was performed using analysis of variance for comparisons among the three groups. Post-hoc comparison was performed using Tukey’s test. **P<0.01 indicates a statistically significant difference.</p

(A) Representative images of serial ultrasonographic studies (longitudinal and transverse views) of the abdominal aorta in group IV rats immediately after operation (0), and on postoperative days (POD) 7, 14, and 28. The aortic diameter gradually increased. An intraluminal thrombus was first seen at POD 14 and extended to the entire circumference at POD 28. Scale bar = 1mm. (B) Representative images of an aortic wall under high-power magnification with Elastica van Gieson staining in the abdominal aorta of group IV rats immediately after operation (0) and on postoperative days (POD) 7, 14, and 28. The medial elastic lamina became thinner over time. An intraluminal thrombus was first seen at POD 14 and had become thicker by POD 28. Scale bar = 100 μm.

<p>(A) Representative images of serial ultrasonographic studies (longitudinal and transverse views) of the abdominal aorta in group IV rats immediately after operation (0), and on postoperative days (POD) 7, 14, and 28. The aortic diameter gradually increased. An intraluminal thrombus was first seen at POD 14 and extended to the entire circumference at POD 28. Scale bar = 1mm. (B) Representative images of an aortic wall under high-power magnification with Elastica van Gieson staining in the abdominal aorta of group IV rats immediately after operation (0) and on postoperative days (POD) 7, 14, and 28. The medial elastic lamina became thinner over time. An intraluminal thrombus was first seen at POD 14 and had become thicker by POD 28. Scale bar = 100 μm.</p