Metformin does not reduce inflammation in diabetics with abdominal aortic aneurysm or at high risk of abdominal aortic aneurysm formation

Introduction: The protective effect of diabetes mellitus on abdominal aortic aneurysm formation and growth has been repeatedly observed in population studies but continues to be poorly understood. However, recent investigations have suggested that metformin, a staple antihyperglycemic medication, may be independently protective against abdominal aortic aneurysm formation and growth. Therefore, we describe the effect of metformin in abdominal aortic aneurysm and at-risk patients on markers of inflammation, the driver of early abdominal aortic aneurysm formation and growth.

Methods: Peripheral blood was collected from patients previously diagnosed with abdominal aortic aneurysm or presenting for their U.S. Preventive Task Force-recommended abdominal aortic aneurysm screening. Plasma and circulating peripheral blood mononuclear cells were isolated using Ficoll density centrifugation. Circulating plasma inflammatory and regulatory cytokines were assessed with enzyme-linked immunosorbent assays. CD4⁺ cell phenotyping was performed using flow cytometric analysis and expressed as a proportion of total CD4⁺ cells. To determine the circulating antibody to self-antigen response, a modified enzyme-linked immunosorbent assay was performed against antibodies to collagen type V and elastin fragments.

Results: Peripheral blood was isolated from 266 patients without diabetes mellitus ( n=182), with diabetes mellitus not treated with metformin ( n=34), and with diabetes mellitus actively taking metformin ( n=50) from 2015 to 2017. We found no differences in the expression of Tr1, Th17, and Treg CD4⁺ fractions within diabetics ± metformin. When comparing inflammatory cytokines, we detected no differences in IL-1β, IL-6, IL-17, IL-23, IFN-γ, and TNF-α. Conversely, no differences were observed pertaining to the expression to regulatory cytokines IL-4, IL-10, IL-13, TSG-6, or TGF-β. Lastly, no differences in expression of collagen type V and elastin fragment antigen and/or antibodies were detected with metformin use in diabetics.

Conclusion: Metformin in diabetics at-risk for abdominal aortic aneurysm or diagnosed with abdominal aortic aneurysm does not seem to alter the peripheral inflammatory environment.