Abstract 5: The Contribution of Microbiome Alterations to Atherosclerotic Plaque Regression in Mice

Abstract

Objective: The human microbiome represents an underexplored driver of atherosclerosis. Alterations to the intestinal microbiome are associated with, systemic inflammation and upregulation of M1 macrophages (Mϕ). Our study aims to determine if alterations to the intestinal microbiome by antibiotic treatment interferes with atherosclerotic plaque regression in mice. Methods: ApoE -/- mice were fed a western diet for 16 weeks to develop complex atherosclerosis in aortic arches. These arches were transplanted into the abdominal aorta of wild-type (WT) mice to model clinical aggressive lipid management and promote plaque regression. To assess the contribution of the microbiome to plaque regression, aortic arches were transplanted in WT mice (n=4), and WT mice pulsed with tylosin (antibiotic, n = 4) 3 days pre-transplant and the duration of the experiment (5 days). Arches were also transplanted into ApoE -/- mice as a plaque progression control (n =4). Results: Antibiotic treatment of WT mice with tylosin compared to control WT mice did not change circulating total cholesterol (TC, 57 ± 21 mg/dl vs. 46 ± 24 mg/dl, p = 0.5), or HDL-C (42 ± 8 mg/dl vs. 34 ± 11 mg/dl, p = 0.32). No statistically significant difference in plaque size (117,801 ± 70,921 μm 2 vs. 133,286 ± 19,871 μm 2 vs. 132,976 ± 40,347 μm 2 , p = 0.88) or the absolute Mϕ content (44,672 ± 27,154 μm 2 vs. 32,546 ± 21,226 μm 2 vs. 54,154 ± 22,418 μm 2 , p = 0.47) was observed in WT mice which received tylosin, compared to control WT and ApoE -/- mice, respectively. The composition of the plaques however did change: When compared to the control ApoE -/- mice, WT recipient mice had a 26% reduction in the percent of the plaques occupied by Mϕ, while WT mice receiving tylosin had only a 4% reduction (p = 0.07). There was a 20% difference between the percent of plaque Mϕ content in the WT receiving tylosin, compared to WT controls (38% ± 4.3 vs. 30% ± 6.2, p = 0.07). Conclusion: Tylosin-treated WT mice undergoing regression had Mϕ enrichment in their plaques compared to WT controls. This study suggests that microbiome alterations can negatively influence plaque regression. Intestinal microbiome analysis and further studies are needed to confirm and extend this finding.