An endovascular porcine model of abdominal aortic aneurysm for interventional radiology research

Prostanoids are a large family of lipid mediators derived from the arachidonic acid metabolites of the cyclooxygenase (COX) enzymes. Therapeutically, COX is the target of the nonsteroid antiinflammatory drugs (NSAIDs), a chemically diverse group that includes ibuprofen, naproxen, and diclofenac, among dozens of others. Inhibition of prostanoid production by traditional NSAIDs accounts for all their major therapeutic effects, such as the dampening down of inflammation and the reduction of fever, and their potentially severe adverse side effects, most commonly within the gastrointestinal tract.1,2 See page 1137 Since the early 1990’s it has been clear there are two distinct enzymes responsible for the production of prostanoids: a constitutive COX-1 found in all tissues and an inflammation-associated enzyme COX-2.1,2 COX-2 is constitutively expressed in only a few sites, such as parts of the kidney and central nervous system, but is highly upregulated and active at sites of inflammation. These findings led to the hypothesis that selective COX-2 inhibitors could be antiinflammatory without the major side effects associated with traditional NSAIDs. Against this background several COX-2–selective inhibitors have been produced and brought to market, the first two being celecoxib (Celebrex) and rofecoxib (Vioxx). Preclinical studies of these COX-2–selective inhibitors were extremely promising. In animal models, for example, they were demonstrated to be as efficacious as traditional NSAIDs but to be lacking their toxic actions on the gastrointestinal tract. Clinical trials have, however, been marred by controversy. The CLASS trial for celecoxib, a 12-month osteoarthritis study of celecoxib, demonstrated celecoxib to have improved safety relative to ibuprofen but not …

Rationale Abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta that progresses to rupture, which is frequently fatal. The only existing treatments are high risk surgical interventions. These are not offered until the AAA is large (>5.5?cm) so patients remain under surveillance for many years. There is currently no medical therapy to offer. We have previously observed a senescent phenotype in vascular smooth muscle cells (VSMC) isolated from end-stage human AAA. We hypothesise that there is a prior period of pathological VSMC remodelling which may be a promising and novel target for molecular therapies. Methodology Three murine models of early AAA were used – (i) AngII infusion to ApoE-/- mice and (ii) CaCl2 or (iii) porcine pancreatic elastase application to the aortic adventitia of C57BL6/J mice. VSMC remodelling was investigated in fixed and paraffin embedded aortic tissue harvested from the murine models using the histochemical stain Movat’s Pentachrome and immunohistochemistry for the VSMC identification marker, αSMA. Slides were imaged with a digital slide scanner or confocal microscopy as appropriate. Aortic lumen volume was determined by in-vivo ultrasound. Results We observed VSMC remodelling in all three models of AAA. The remodelling was reduced by administration of a novel small-molecule inhibitor of PDGF induced VSMC remodelling. Inhibition of VSMC remodelling also reduced the severity of the aneurysms formed as assessed by 3D in-vivo ultrasound of the aortic lumen. Conclusions There is a major VSMC remodelling response in murine AAA and disrupting this response appears to suppress AAA formation.

A Novel Murine Model of Early Abdominal Aortic Aneurysm Reflects Immunopathology in Human Abdominal Aortic Aneurysms

Intra-aortic infusion of nicotine can induce a novel mouse model of abdominal aortic aneurysm.

A novel rat model of abdominal aortic aneurysm using a combination of intraluminal elastase infusion and extraluminal calcium chloride exposure

Accelerated enlargement of experimental abdominal aortic aneurysms in a mouse model of chronic cigarette smoke exposure

Introduction: AAA rupture occurs as a consequence of the imbalance between aortic wall's strength and the loading stress. FEM provides information on the regional distribution of stresses in the wall of AAA and proved to be a more accurate predictor of aneurysm rupture. The risk of rupture is expressed through peak wall stress (PWS) and rupture risk equivalent diameter (RRED) that includes wall strength in calculation. Aim: To determine the influence of FEM and subsequent biomechanical analysis of AAA on treatment decisions in common clinical practice. Material and methods: This prospective study included 48 patients with asymptomatic AAA. The specific anatomical and biomechanical parameters were determined by a FEM analysis: location of the PWS and diameter of the aorta, parietal thrombus in the level of PWS and the maximum value of the measured diameter (MD) as well as rupture risk equivalent diameter (RRED). Decision of treatment would change if maximal aneurysm diameter and RRED are on different sides of the 55 mm that is contemporary treatment threshold for AAA. Results: In 20 patients (41.67%) values of RRED could change treatment decisions. Four patients (20%) with aneurysm diameter (MD) less than 55 mm would be transferred to the group of patients with indications for surgical treatment because their RRED was higher than the limit of 55 mm. Sixteen patients (80%) would be transferred to the group of patients for further follow up without surgical treatment, because their RRED was less than the limit of 55 mm although their MD was higher than 55mm. Conclusion: Finite element model (FEM) of abdominal aortic aneurysm (AAA) and subsequent biomechanical analysis would lead to change of surgical indications for treatment of AAA in almost half of included patients.

The self-healing phenomenon can be found in the elastase-induced abdominal aortic aneurysm (AAA) model, and an enlarging AAA model was successfully induced by coarctation. Unfortunately, aortic coarctation in these enlarging models is generally not found in human AAA disease. This study aimed to create an experiment model of enlarging AAA in rabbits to better mimic human aortic aneurysm disease. Eighty-four male New Zealand white rabbits were randomly divided into three equal groups: two aneurysm groups (A and B) and a SHAM group. Aneurysm group rabbits underwent extrinsic aortic stenosis below the right renal artery and received a 10-minute incubation of 60 μl elastase (1 unit/μl). Absorbable suture was used in Group A and nonabsorbable cotton thread was used in Group B. A sham operation was performed in the SHAM group. Aortic diameter was measured after 1, 3, 7, and 15 weeks; thereafter animals were sacrificed for histopathological, immunohistochemical and quantitative studies. Two rabbits died at 29 and 48 days, respectively, after operation in Group B. All aneurysms formed and enlarged progressively by 3 weeks in the Aneurysm groups. However, diameter enlargement in Group A was significantly lower than that in Group B at 7 weeks. Aneurysm groups developed intimal hyperplasia; intima-media thickness (IMT) increased significantly by week 7, and aortic media thickness and intima-media ratio (IMR) increased significantly by week 15. Marked destruction of elastin fibers and smooth muscle cells (SMCs) occurred 1 week later and increased progressively thereafter. Intimal hyperplasia and SMCs content in Group A increased significantly by week 15 compared with Group B. Aneurysm groups exhibited strong expression of matrix metalloproteinases 2 and 9 and RAM11 by week 1, and decreased progressively thereafter. In conclusion, this novel rabbit AAA model enlarges progressively without coarctation and is capable of better mimicking human aortic aneurysm disease.

Background: In our previous canine model of abdominal aortic aneurysm, although aneurysm growth was observed, the aneurysms did not rupture. This prompted us to develop a swine model, which has the advantage of fibrinolytic and coagulation systems similar to those found in humans. Methods: We simulated aneurysms by connecting fascia pouches to the aorta. In nine pigs, two pieces of fascia (5 x 8 cm each) were sutured to the posterior surface of the aorta. After the lateral edges of the aorta were sutured together, the aorta was clamped below the renal arteries and at the aortic bifurcation. We then resected a piece of aorta within the pouch, clamped the pouch below the open roof, and unclamped the aorta. When the entire pouch had been sutured, the last clamp was removed and blood flowed into the "aneurysm." The total aortic cross clamp time was between 4 and 25 minutes. Results: "Aneurysm" size ranged from 3.0 x 2.5 cm to 7.5 x 4.0 cm (length x width). Aneury sm rupture occurred in seven pigs between 4 and 43 days after initial surgery; however, rupture never occurred at a suture site. Aneurysm size at rupture was two to four times greater than that of the original pouch. We found thrombus in all of the aneurysms examined more than 2 days after surgery. Histology revealed aneurysm walls that were thicker than the fascia. Although fascia segments could be identified because of their characteristic trilayer of thick collagen fibers, most of the aneurysm wall contained thin collagen fibers. These observations are consistent with new collagen production. Conclusion: We constructed a swine model of abdominal aortic aneurysm that possessed the features of growth and rupture necessary to simulate human aneurysms. Our method will allow techniques designed to isolate aneurysms from the circulation to be tested in a model with a fibrinolytic system similar to that of humans.

Elastic fibers reconstructed using adenovirus-mediated expression of tropoelastin and tested in the elastase model of abdominal aortic aneurysm in rats

BackgroundConstructing an ideal model of abdominal aortic aneurysm (AAA) is of great significance to elucidate its complex pathogenesis. Therefore, we introduce a new and simple method to simulate human AAA and construct a rat AAA model through a retroperitoneal approach.MethodsForty healthy adult Sprague Dawley (SD) rats were randomly divided into a control group, elastase + calcium chloride group (PPE+CaCl2), elastase group (PPE), and elastase + beta aminopropionitrile group (PPE+BAPN) according to a male-female ratio of 1:1, with 10 rats in each group. A retroperitoneal approach was used to free the infrarenal abdominal aorta in all four groups. In the PPE + CaCl2 group, 0.1 ml of elastase (approximately 5 U) was perfused into the arterial cavity for 20 min, and 1.0 mol/L calcium chloride was infiltrated out of the arterial cavity for 10 min. In the PPE group, 0.1 mL of elastase (approximately 5U) was perfused into the arterial cavity for 20 min, and normal saline was infiltrated out of arterial cavity for 10 min; the PPE + BAPN group combined with 0.3% BAPN drinking water/day on the basis of PPE group; the control group was treated with saline instead of elastase and calcium chloride. Abdominal aortic specimens were collected after 4 weeks of feeding. The diagnostic criteria of AAA were 50% dilation of the abdominal aorta or rupture of the aneurysm at 4 weeks after the operation. Histopathology, immunohistochemistry, quantitative PCR (qPCR), western blotting assay, gelatine zymogram, and other methods were used.ResultsThe operation time of the four groups was controlled at approximately 40 min, and the success rate of the operation was 100%. Survival rate: Control Group (100%) = PPE Group (100%) > PPE + CaCl2 Group (90%) > PPE + BAPN Group (40%); Aneurysm formation rate: PPE + BAPN Group (100%) > PPE + CaCl2 Group (80%) > PPE Group (60%) > Control Group (0%); Aneurysm rupture rate: PPE + BAPN group (60%) > PPE + CaCl2 group (12.5%) > PPE group (0%);Inflammatory cells (macrophages, T cells, B cells, dendritic cells) infiltrated in different degrees in the PPE + CaCl2, PPE and PPE + BAPN groups. Vascular thickness, elastic fiber content, collagen fiber content, and vascular smooth muscle cell content in the PPE + CaCl2 group and PPE + BNPA group were significantly lower than those in Control group (P < 0.05). The content of elastic fibers and vascular smooth muscle cells in the PPE group were significantly lower than that in Control group (P < 0.05). The expression and activity of matrix metalloproteinase 2 (MMP2) and MMP9 in the PPE + CaCl2 group, PPE group, and PPE + BNPA group were significantly higher than those in the control group (P < 0.05).ConclusionsA new, simple, and reproducible rat AAA model can be constructed by a retroperitoneal approach. The pathological features of the three models are effective simulation of human AAA inflammatory cell infiltration, protease activity enhancement, and extracellular matrix destruction. The PPE+ CaCl2 model has the advantages of a high survival rate, high aneurysm formation rate, good stability, and reproducibility. It is an ideal animal model for studying the pathogenesis of AAA. The PPE + BAPN model can simulate the characteristics of spontaneous rupture of aneurysms. It is an ideal animal model to study the mechanism of AAA rupture.

The calcium chloride-induced rodent model of abdominal aortic aneurysm

Current experimental models of abdominal aortic aneurysm (AAA) do not accurately reproduce the major features of human AAA. We hypothesized that blockade of TGFβ (transforming growth factor-β) activity-a guardian of vascular integrity and immune homeostasis-would impair vascular healing in models of nondissecting AAA and would lead to sustained aneurysmal growth until rupture. Here, we test this hypothesis in the elastase-induced AAA model in mice. We analyze AAA development and progression using ultrasound in vivo, synchrotron-based ultrahigh resolution imaging ex vivo, and a combination of biological, histological, and flow cytometry-based cellular and molecular approaches in vitro. Systemic blockade of TGFβ using a monoclonal antibody induces a transition from a self-contained aortic dilatation to a model of sustained aneurysmal growth, associated with the formation of an intraluminal thrombus. AAA growth is associated with wall disruption but no medial dissection and culminates in fatal transmural aortic wall rupture. TGFβ blockade enhances leukocyte infiltration both in the aortic wall and the intraluminal thrombus and aggravates extracellular matrix degradation. Early blockade of IL-1β or monocyte-dependent responses substantially limits AAA severity. However, blockade of IL-1β after disease initiation has no effect on AAA progression to rupture. Endogenous TGFβ activity is required for the healing of AAA. TGFβ blockade may be harnessed to generate new models of AAA with better relevance to the human disease. We expect that the new models will improve our understanding of the pathophysiology of AAA and will be useful in the identification of new therapeutic targets.

Introduction: Abdominal aortic aneurysms (AAA) are responsible for over 150,000 deaths worldwide annually. Attempts at producing a reliable large-animal model of AAA have proven challenging. We sought to create a reproducible swine model of AAA using enzymatic degradation of the aortic wall. Methods: A total of 9 male Yorkshire swine received periadventitial injections of type 1 collagenase (23.5 mg) and porcine pancreatic elastase (500 mg) into a 4 cm segment of infrarenal aorta. Aortic diameter growth was monitored at POD 7 and 14 using ultrasound. The animals were euthanized on POD 21, and the suprarenal (control) and infrarenal (treated) aorta was harvested for analysis, after gross measurement of aortic diameter under physiologic blood pressure. Sections of control and treated aorta were used to obtain tensile strength using a tensiometer. Additional segments of the aorta were collected for histopathological analysis (H&amp;E, elastin, alpha smooth muscle actin). PCR of matrix metalloproteinases (MMP9) was conducted. Groups were compared with paired t-tests, or ANOVA for repeated measures, where appropriate. Results: Average percent growth of aortic diameter at POD 21 for treated segments was 27% +/- 16.5% versus 4.5% +/- 4% for control tissue. The average difference in aortic growth by subject, was 26.7% [14.6%-38.8%]; (p&lt;0.001). Aortic medial thickness was decreased in treated tissue; 235 um +/- 208 um versus 645 um +/- 191 um (p&lt;0.0001). Quantity of both medial elastin fibers, and vascular smooth muscles cells was decreased in treated tissue; 1.8% +/- 3.16%, compared to 9.9% +/- 6.85% (p&lt;0.0001), and 24% +/- 6.8% versus 37.4% +/- 6.9%, respectively. Tensile strength was also decreased in treated tissue; 16.7 MPa +/- 7 MPa versus 29.5 MPa +/- 10.7 MPa (p=0.0002). A 12-fold increase in expression of MMP9 mRNA was also demonstrated in aneurysmal tissue (p=0.002) Conclusion: A reproducible, large-animal model of AAA, with anatomical, histopathological, and biomechanical properties that are clinically translatable, can be achieved with extraluminal enzymatic degradation.

Development of a novel murine model of aortic aneurysms using peri-adventitial elastase