Abstract 058: Efficacy and Mechanisms of Metformin Therapy in Established Experimental Abdominal Aortic Aneurysms

Objective: Diabetes reduces the risk for abdominal aortic aneurysm (AAA) disease. In prior work in rodent models, pre-treatment with metformin was protective against experimental AAA initiation and progression. This study examined the influence of metformin therapy on progression of existing experimental AAAs. Methods: AAAs were created in 10-12 week old male C57BL/6J mice via transient intra-aortic infusion of porcine pancreatic elastase (PPE). Mice were treated with metformin (250 mg/kg via oral gavage), metformin plus AMPK inhibitor Compound C (the later via 10 mg/kg intraperitoneal injection) or vehicle alone for 10 days starting on day 4 following AAA creation. Outcomes were assessed by serial transabdominal ultrasonographic assessment of aortic diameter during treatment, as well as histological examination at sacrifice. Results: The principal findings are summarized in the Figure. Vehicle-treated mice experienced progressive, time-dependent aortic enlargement from day 3 to 14 following PPE infusion. Metformin treatment substantially attenuated further enlargement of existing AAAs. Treatment with Compound C partially rescued the AAA phenotype in metformin-treated mice. Histologically, characteristic aneurysmal pathologic changes, including medial elastin degradation, smooth muscle cell (SMC) depletion, mural leukocyte accumulation and neoangiogenesis (assessed by CD31 staining), present in PPE-infused, vehicle-treated mice, were substantially attenuated with metformin treatment. Co-treatment with Compound C abrogated the effects of metformin on media elastin degradation, SMC depletion and mural macrophage infiltration, with less influence on mural angiogenesis. Conclusion: Metformin therapy suppresses further expansion of existing experimental AAAs. This effect is abrogated by co-treatment with Compound C. These findings further justify performance of a clinical trial of metformin for medical management of AAA disease.