Kallikrein-1 Blockade Inhibits Aortic Expansion in a Mouse Model and Reduces Prostaglandin E2 Secretion From Human Aortic Aneurysm Explants

Small AAAs: Recommendations for Rodent Model Research for the Identification of Novel Therapeutics

CLINICAL PROBLEM

Most abdominal aortic aneurysms (AAAs) are small with low rupture risk (<1%/y) when diagnosed but slowly expand to ≥55 mm and undergo surgical repair. Patients and clinicians require medications to limit AAA growth and rupture, but drugs effective in animal models have not translated to patients.

RECOMMENDATIONS FOR INCREASING TRANSLATION FROM MOUSE MODELS

Use models that simulate human AAA tissue pathology, growth patterns, and rupture; focus on the clinically relevant outcomes of growth and rupture; design studies with the rigor required of human clinical trials; monitor AAA growth using reproducible ultrasound; and perform studies in both males and females.

SUMMARY OF STRENGTHS AND WEAKNESSES OF MOUSE MODELS

The aortic adventitial elastase oral β-aminopropionitrile model has many strengths including simulating human AAA pathology and modeling prolonged aneurysm growth. The Ang II (angiotensin II) model performed less well as it better simulates acute aortic syndrome than AAA. The elastase plus TGFβ (transforming growth factor-β) blocking antibody model displays a high rupture rate, making prolonged monitoring of AAA growth not feasible. The elastase perfusion and calcium chloride models both display limited AAA growth.

Biomarkers in EndoVascular Aneurysm Repair (EVAR) and Abdominal Aortic Aneurysm: Pathophysiology and Clinical Implications

Circulating biomarkers have been recently investigated among patients undergoing endovascular aortic aneurysm repair (EVAR) for abdominal aortic aneurysm (AAA). Considering the plethora of small descriptive studies reporting potential associations between biomarkers and clinical outcomes, this review aims to summarize the current literature considering both the treated disease (post EVAR) and the untreated disease (AAA before EVAR). All studies describing outcomes of tissue biomarkers in patients undergoing EVAR and in patients with AAA were included, and references were checked for additional sources. In the EVAR scenario, circulating interleukin-6 (IL-6) is a marker of inflammatory reaction which might predict postoperative morbidity; cystatin C is a promising early marker of post-procedural acute kidney injury; plasma matrix metalloproteinase-9 (MMP-9) concentration after 3 months from EVAR might help in detecting post-procedural endoleak. This review also summarizes the current gaps in knowledge and future direction of this field of research. Among markers used in patients with AAA, galectin and granzyme appear to be promising and should be carefully investigated even in the EVAR setting. Larger prospective trials are required to establish and evaluate prognostic models with highest values with these markers.

Kallikrein-1 Blockade Inhibits Aortic Expansion in a Mouse Model and Reduces Prostaglandin E2 Secretion From Human Aortic Aneurysm Explants

Background Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. The kinin B2 receptor agonist, bradykinin, has been implicated in AAA pathogenesis through promoting inflammation. Bradykinin is generated from high- and low-molecular-weight kininogen by the serine protease kallikrein-1. The aims of this study were first to examine the effect of neutralizing kallikrein-1 on AAA development in a mouse model and second to test how blocking kallikrein-1 affected cyclooxygenase-2 and prostaglandin E₂ in human AAA explants. Methods and Results Neutralization of kallikrein-1 in apolipoprotein E-deficient (ApoE^-/-) mice via administration of a blocking antibody inhibited suprarenal aorta expansion in response to angiotensin (Ang) II infusion. Kallikrein-1 neutralization decreased suprarenal aorta concentrations of bradykinin and prostaglandin E₂ and reduced cyclooxygenase-2 activity. Kallikrein-1 neutralization also decreased protein kinase B and extracellular signal-regulated kinase 1/2 phosphorylation and reduced levels of active matrix metalloproteinase 2 and matrix metalloproteinase 9. Kallikrein-1 blocking antibody reduced levels of cyclooxygenase-2 and secretion of prostaglandin E₂ and active matrix metalloproteinase 2 and matrix metalloproteinase 9 from human AAA explants and vascular smooth muscle cells exposed to activated neutrophils. Conclusions These findings suggest that kallikrein-1 neutralization could be a treatment target for AAA.