Experimental Study of Determinants of Aneurysmal Expansion of the Abdominal Aorta

doi:10.1007/BF02018860

Annals of Vascular Surgery

Volume 8, Issue 2, March 1994, Pages 127-136

https://doi.org/10.1007/BF02018860 Get rights and content

The natural history and the factors determining the expansion of aneurysms have not been elucidated. To study the respective roles of elastolysis, collagenolysis, inflammatory cells, and hypertension in the pathogenesis of aneurysms, two previously described in vivo experimental models were used. An isolated segment of the abdominal aorta was infused with 15 units of pancreatic elastase. The maximal diameter of the aorta was measured before and after infusion and the isolated aorta was excised for classic histologic and immunohistologic studies. Twelve hours after the infusion of elastase the mean diameter of the aorta increased by 30%. The aorta had a cylindric form and only collagen fibers remained. Two and a half days after the infusion the aorta was spherical in shape and the diameter increased by 300% (3.09 ± 0.08 mm) (p < 0.05). The entire aortic wall was invested by inflammatory cells. Six days after infusion the diameter increased by 421% (4.38 ± 0.03 mm) (p <0.05), and immunohistochemical staining showed numerous T lymphocytes and macrophages. Between 6 and 12 days, after perfusion inflammation decreased, the final diameter was 4.23 ± 0.14 mm (not significant). Sixteen rats had thioglycollate and plasmin infusion, which are nonspecific activators of inflammation. Nine days after infusion the diameter of the aorta had increased by 288%; the elastic fibers of the media were fragmented and rare and the entire aortic wall was invaded by inflammatory cells, predominantly macrophages. The diameter of the aorta increased progressively. Two groups of 17 hypertensive rats (renovascular and spontaneous hypertension) received an aortic infusion of 15 units of pancreatic elastase. Elastolysis overlapped the limits of the infusion and inflammation persisted after 2 weeks. The mean diameter of the aorta (F = 11, p <0.01) and the mean length of the aneurysms (F = 11.2, p < 0.001) were significantly increased. This study demonstrates that elastolysis and especially collagenolysis are determinants of aneurysmal expansion. Inflammation may be a promoting factor in the degradation of the aortic wall. Hypertension increases the hemodynamic stress to the aorta and activates mural inflammation.

References (28)

JT Powell et al.
Cellular, enzymatic, and genetic factors in the pathogenesis of abdominal aortic aneurysms
J Vasc Surg
(1989)
S Anidjar et al.
Pathogénie des anévrysmes acquis de l'aorte abdominale sous-rénale
Ann Chir Vasc
(1992)
JS Campa et al.
Elastin degradation in abdominal aortic aneurysms
Atherosclerosis
(1987)
RJ Rizzo et al.
Collagen types and matrix protein content in human abdominal aortic aneurysms
J Vasc Surg
(1989)
JL Cronenwett et al.
Variables that affect the expansion rate and outcome of small abdominal aortic aneurysms
J Vasc Surg
(1990)
JF Vollmar et al.
Aortic aneurysms as a late sequelae of above-knee amputation
Lancet
(1989)
PB Dobrin et al.
Elastolytic and collagenolytic studies of arteries: Implications for the mechanical properties of arteries
Arch Surg
(1984)
S Anidjar et al.
Elastase-induced experimental aneruysms in rats
Circulation
(1990)
JG Bieth
Elastase: Catalytic and biological properties
EN Beckman
Plasma cell infiltrates in atherosclerotic abdominal aortic aneurysms
Am J Clin Pathol
(1986)

AG Rose et al.

Inflammatory variants of abdominal aortic aneurysms

Arch Pathol Lab Med

(1981)

AE Koch et al.

Human abdominal aortic aneurysms: Immunophenotypic analysis suggesting an immune-mediated response

Am J Pathol

(1990)

N Rosenberg et al.

The use of arterial implants prepared by enzymatic modification of arterial allografts. II. The physical properties of the elastin and collagen components of the arterial wall

Arch Surg

(1957)

RM Senior et al.

Chemotactic activity of elastin-derived peptides

J Clin Invest

(1980)

Cited by (42)

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2018, Blood
Citation Excerpt :
Recent addition of BAPN (inhibitor of lysly oxidase) to the drinking water of the elastase aneurysm model does result in spontaneous ILT formation, similar to humans.45 Furthermore, although human aneurysms have an abundance of neutrophil infiltration (∼70% neutrophil contribution), most animal models are characterized by high monocyte/macrophage and lymphocyte infiltration (∼10% neutrophil contribution).46,47 However, although it is difficult to model a complex and heterogenous pathophysiology in animal models, these models are still useful to define mechanisms and pathways that may affect the human condition and provide complementary studies to test targeted therapeutics.
Abdominal aortic aneurysm (AAA) is a degenerative vascular pathology resulting in significant morbidity and mortality in older adults due to rupture and sudden death. Despite 150 000 new cases and nearly 15 000 deaths annually, the only approved treatment of AAA is surgical or endovascular intervention when the risk for aortic rupture is increased. The goal of the scientific community is to develop novel pharmaceutical treatment strategies to reduce the need for surgical intervention. Because most clinically relevant AAAs contain a complex structure of fibrin, inflammatory cells, platelets, and red blood cells in the aneurysmal sac known as an intraluminal thrombus (ILT), antithrombotic therapies have emerged as potential pharmaceutical agents for the treatment of AAA progression. However, the efficacy of these treatments has not been shown, and the effects of shrinking the ILT may be as detrimental as they are beneficial. This review discusses the prospect of anticoagulant and antiplatelet (termed collectively as antithrombotic) therapies in AAA. Herein, we discuss the role of the coagulation cascade and platelet activation in human and animal models of AAA, the composition of ILT in AAA, a possible role of the ILT in aneurysm stabilization, and the implications of antithrombotic drugs in AAA treatment.
Resveratrol counteracts systemic and local inflammation involved in early abdominal aortic aneurysm development
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AAA induction in rat by in situ elastase infusion raises an inflammatory process where RAS, proteases activity and leucocytes contribute to the aortic tissue damage outlining the aneurysm progression [31, 40, 41]. Previous studies have defined the time course of AAA development, indicating that the main burst of inflammation occurs within 2 wk from the elastase infusion [42, 43]. Hence, we chose an experimental time-window of 14 d, considered suitable to evaluate, at circulating level, the pattern of monocytes associated mainly to the AAA progression, rather than the acute initial inflammatory response triggered also by the surgical procedure of AAA induction, and, at tissue level, the possible modulatory effects of Resveratrol administration on the vessel wall remodeling induced by elastase.
Monocyte activation, macrophage infiltration, vascular oxidative stress and matrix proteolysis are inflammatory key steps contributing to abdominal aortic aneurysm (AAA) development. A phenotypical and functional heterogeneity is recognizable in monocytes by the differential expression of surface molecules: CD62L− subset corresponds to activated monocytes, while CD143/ACE surface expression increases during their differentiation into macrophages. In this work, Resveratrol, which is an antioxidant polyphenol with vasoprotective properties, has been evaluated for its potential to limit aneurysm development and monocyte-dependent inflammatory response in a model of elastase-induced AAA.
Male Sprague-Dawley rats received Resveratrol (10 mg/kg/die) (Rsv group, n = 15) or vehicle (ethanol) alone (Et-OH group, n = 15) continuously from 7 d before until 14 d after the AAA induction with elastase; five littermates were used as untreated control group (Ctr group, n = 5). At the end of treatment, CD143 and CD62L monocyte expression was analyzed by flow cytometry, serum antioxidant capacity was evaluated using the TRAP method and circulating TNFα, and MMP-9 were measured with ELISA and gel zymography, respectively. Aortas were subjected to histology and immunohistochemistry for morphological analysis, macrophage infiltration, and MMP-9, TNFα, and VEGF expression.
Resveratrol counteracted the CD62L-monocyte subset expansion, CD143 monocyte expression, and circulating levels of MMP-9 activity and TNFα associated to AAA induction. Similarly, treatment with Resveratrol significantly attenuated AAA expansion, vessel wall macrophage infiltration and MMP-9, VEGF, and TNFα expression, compared with AAA from Et-OH group.
Resveratrol limited the monocyte-dependent inflammatory response, macrophage differentiation and aortic lumen enlargement in elastase-induced AAA. These data suggest that Resveratrol might be tested in selected patients with small AAA to modulate the early systemic and local inflammatory response associated to AAA progression.
Downregulation of remodelling enzymatic activity induced by an angiotensin-converting enzyme inhibitor (perindopril) reduces the degeneration of experimental abdominal aortic aneurysms in a rat model
2011, European Journal of Vascular and Endovascular Surgery
Angiotensin-converting enzyme (ACE) inhibitors have proven their ability to affect vascular wall remodelling, in addition to their anti-hypertensive effects. The aim of this study was to assess the impact of perindopril on the development of abdominal aortic aneurysm (AAA) in a rat model, and its correlation to enzyme activities involved in vascular wall remodelling.
The model of the decellularised aortic xenograft in Lewis rat was chosen. Rats were randomised to two groups: group P fed with 3 mg kg⁻¹ of perindopril daily during 30 days, or control group C (n = 15 per group)). Rats were euthanised at 30 days for analysis. AAA growth and histological changes in the aortic wall were measured by histomorphometry. Proteolytic activities were measured by gelatin zymography of conditioned medium for activematrix metalloproteinase 9/pro-matrix metalloproteinase 9 (MMP9/pro-MMP9) and activeMMP2/pro-MMP2, and by quantitative immunofluorescence tissue for elastase and plasmin.
The mean maximal diameter of AAAs at 30 days was significantly lower in the treated group P compared with the control group C (2.5 ± 1.0 vs. 4.9 ± 2.1 mm; P < 0.01). The expansion rate of AAAs after 30 days was significantly reduced in group P compared with group C (36 ± 14% vs. 67 ± 23%; P < 0.01). Pro-MMP9 and MMP9 activities were significantly decreased in relative intensity (RI) in group P compared with group C (0.43 ± 0.64 RI vs. 1.02 ± 0.61 RI, P = 0.01; 0.18 ± 0.57 RI vs. 0.66 ± 1.19 RI, P = 0.004). The activation rate of MMP2 was also significantly lower in group P compared with group C (1.27 ± 0.42 vs. 1.67 ± 0.44; P = 0.002). Elastase and plasmin tissue activities were significantly lower in group P compared with group C, respectively (3.9 ± 3.3 vs. 5.8 ± 3.7 IF min⁻¹ g⁻¹,and 25.9 ± 23.9 vs. 49.1 ± 38.7 IF min⁻¹ g⁻¹; P < 0.05).
After 30 days of treatment by perindopril, a significant decrease in aneurysmal degeneration of the decellularised aortic xenograft AAA model was observed. This phenomenon appears to be induced by a downregulation of enzymes involved in the aortic wall remodelling during aneurysmal degeneration.
Effect of blocking platelet activation with AZD6140 on development of abdominal aortic aneurysm in a rat aneurysmal model
2009, Journal of Vascular Surgery
Citation Excerpt :
Within the wall, MMP-9 is produced locally by macrophages but may also originate from thrombus-stored MMP-9 by flow-mediated conveyance from ILT to the wall.35 The experimental model used in the present study, as other murine models of AAA (elastase perfusion and angiotensin-II infusion in APOE–/– mice), displays several limitations, including the inversion of the leukocyte count (80% lymphocytes and 10% PMN leukocytes) compared with humans (20% lymphocytes and 70% PMN leukocytes) and the predominant immune-dependency of arterial wall injury.36 Nevertheless, these models are all characterized by the development of a thrombus and, as shown in the present study, by a spontaneous colonization of mesenchymal cells that limits the progression of the dilatation and is probably linked to a lesser involvement of PMN leukocytes in rats compared with humans.
Platelet activation and thrombus renewal are keys to intraluminal thrombus formation and progression of abdominal aortic aneurysms (AAA). This study explored the ability of AZD6140, a P2Y₁₂ receptor antagonist, to inhibit platelet activation and prevent aneurysm development in a rat experimental model of AAA.
Aortic aneurysms were induced by implanting a segment of sodium dodecyl sulfate-decellularized guinea pig aorta in rat aortas. One day later, rats were randomized to AZD6140 (10 mg/kg twice daily by mouth) or diluent (n = 23 per group) for either 10 (n = 18) or 42 days (n = 28). Adenosine diphosphate (ADP)–mediated platelet aggregation, aneurysm expansion, intraluminal thrombus formation, inflammatory infiltration, matrix metalloproteinase-9 (MMP-9) expression, and smooth muscle cell colonization were measured.
AZD6140 inhibited ADP-induced platelet aggregation in vivo for 12 hours, justifying twice-daily administration in rats. The spontaneous increase in aortic diameter shown in the aneurysmal model (2.22 ± 0.56 mm at day 10 vs 5.21 ± 1.22 mm at day 42) was reduced with AZD6140 (3.61 ± 1.46 mm at day 42, P < .01). This beneficial effect was associated with a significant reduction of thrombus development, platelet CD41 expression (P < .05), and leukocyte infiltration of the mural thrombus at days 10 and 42 (P < .01). MMP-9 expression correlated with mural thrombus area and was significantly reduced by AZD6140 (P < .05). AZD6140 limited elastic fiber degradation (P < .05) and enhanced progressive colonization of the thrombus by smooth muscle cells at day 42 (P < .01).
These data suggest that inhibition of platelet activation limits intraluminal thrombus biologic activities, thereby impairing aneurysm development.
Abdominal aortic aneurysms: Basic mechanisms and clinical implications
2002, Current Problems in Surgery
Citation Excerpt :
Consistent with the notion that elastase-induced AAAs are dependent on chronic inflammation, several studies have demonstrated a reduction in aneurysmal degeneration using anti-inflammatory strategies. It has been shown that elastase-induced aneurysms can be prevented effectively by treatment with corticosteroids or cyclosporin A,280-282 panleukocyte-depleting (anti-CD18) antibodies,283 and non-steroidal anti-inflammatory agents.284,285 Other studies have shown that elastase-induced aortic dilatation is accelerated in hypertensive rats286 and that this deleterious hemodynamic effect is associated with increased infiltration of mononuclear phagocytes into the aortic wall; although these adverse effects of hypertension were normalized by treatment with propranolol, propranolol was not effective in reducing elastase-induced AAAs in normotensive animals.287
Elastase is not sufficient to induce experimental abdominal aortic aneurysms
2001, Journal of Vascular Surgery
Purpose: Research investigating abdominal aortic aneurysms (AAAs) commonly uses a rat model dependent on aortic infusion of porcine pancreatic elastase to initiate AAA formation. Unfortunately, the sizes of AAAs generated by this model have varied widely among published studies. This may reflect lot-to-lot variations in commercial elastase preparations. This study was undertaken to investigate the ability of different lots of elastase to induce AAAs and explain the variability identified. Methods: Four lots of elastase were evaluated in the standard rat AAA model. Saline solution was used as a control. Additional groups of rats were treated with higher concentrations of elastase with or without the macrophage activator thioglycollate medium. Aortic diameters were measured in all rats. Inflammation and elastin degradation was examined histologically. Elastase activity and purity were evaluated for all lots. Results: Of the four lots tested, only one was able to consistently generate AAAs at the standard dose (P < .05). Increasing the amount of elastase infused produced AAAs in some ineffective lots. Infusion of thioglycollate medium in combination with otherwise ineffective elastase produced AAAs (P = .02). However, the elastase with the highest purity failed to generate AAAs, even at the highest dose tested or in combination with thyioglycollate medium. Thioglycollate medium alone failed to result in AAA formation. All elastase lots displayed elastolytic activity in vitro and produced elastin degradation in vivo. Elastin degradation did not correlate with AAA size in elastase-treated rats (P = NS). Aneurysm size correlated with extent of inflammation (P = .005). Conclusion: Induction of AAAs does not correlate with elastolytic activity. Infusion of pure elastase alone is not sufficient to induce AAA formation in spite of evidence of elastin degradation. Presumed inflammatory modifiers, which contaminate some elastase preparations, enhance AAA formation. Future use of this rat model will need to take the variability of elastase preparations into account with controls for each new elastase lot. (J Vasc Surg 2001;33:1255-62.)

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Experimental Study of Determinants of Aneurysmal Expansion of the Abdominal Aorta

J Vasc Surg

Ann Chir Vasc

Atherosclerosis

J Vasc Surg

J Vasc Surg

Lancet

Elastolytic and collagenolytic studies of arteries: Implications for the mechanical properties of arteries

Arch Surg

Elastase-induced experimental aneruysms in rats

Circulation

Elastase: Catalytic and biological properties

Plasma cell infiltrates in atherosclerotic abdominal aortic aneurysms

Am J Clin Pathol

Inflammatory variants of abdominal aortic aneurysms

Arch Pathol Lab Med

Human abdominal aortic aneurysms: Immunophenotypic analysis suggesting an immune-mediated response

Am J Pathol

The use of arterial implants prepared by enzymatic modification of arterial allografts. II. The physical properties of the elastin and collagen components of the arterial wall

Arch Surg

Chemotactic activity of elastin-derived peptides

J Clin Invest