Reduction of TMAO level enhances the stability of carotid atherosclerotic plaque through promoting macrophage M2 polarization and efferocytosis.

Weihao Shi,Zhou Yang,Yijun Huang,Bo Yu,Liang Zhu

doi:10.1042/bsr20204250

Abstract

It has been demonstrated that trimethylamine N-oxide (TMAO) serves as a driver of atherosclerosis, suggesting that reduction of TMAO level might be a potent method to prevent the progression of atherosclerosis. Herein, we explored the role of TMAO in the stability of carotid atherosclerotic plaques and disclosed the underlying mechanisms. The unstable carotid artery plaque models were established in C57/BL6 mice. L-carnitine (LCA) and methimazole (MMI) administration were applied to increase and reduce TMAO levels. Hematoxylin and eosin (H&E) staining, Sirius red, Perl’s staining, Masson trichrome staining and immunohistochemical staining with CD68 staining were used for histopathology analysis of the carotid artery plaque. M1 and M2 macrophagocyte markers were assessed by RT-PCR to determine the polarization of RAW264.7 cells. MMI administration for 2 weeks significantly decreased the plaque area, increased the thickness of the fibrous cap and reduced the size of the necrotic lipid cores, whereas 5-week of administration of MMI induced intraplate hemorrhage. LCA treatment further deteriorated the carotid atherosclerotic plaque but with no significant difference. In mechanism, we found that TMAO treatment impaired the M2 polarization and efferocytosis of RAW264.7 cells with no obvious effect on the M1 polarization. In conclusion, the present study demonstrated that TMAO reduction enhanced the stability of carotid atherosclerotic plaque through promoting macrophage M2 polarization and efferocytosis.

Highlights

Atherosclerotic diseases, including acute coronary syndromes and stroke, are the leading causes of mortality and disability in developing countries [1,2]
We explored the effects of L-carnitine (LCA), a quaternary ammonium compound which can produce trimethylamine N-oxide (TMAO), and methimazole (MMI), an inhibitor of flavin monooxygenase 3 (FMO3) which triggers TMAO formation on the stability of carotid atherosclerotic plaque in vivo
Neither mice. L-carnitine (LCA) and methimazole (MMI) nor LCA treatment showed any obvious influence in the serum liquids of the unstable carotid artery plaque models, including total cholesterol (T-CHO) (Figure 1B), TG (Figure 1C) and low-density lipoprotein (LDL)-C (Figure 1E)

Summary

Introduction

Atherosclerotic diseases, including acute coronary syndromes and stroke, are the leading causes of mortality and disability in developing countries [1,2]. Atherosclerotic carotid artery stenosis consists of 20% of all the etiological factors of ischemic stroke in the globe [3]. In addition to atherosclerotic plaque size, plaque stability is a major risk factor of stroke, which has been raised as a main concentrated issue in clinic targeting carotid stenosis diseases [4,5]. Atherosclerosis is a complex, multifactorial disease in which multiple cell types are involved, including macrophages [7,8]. During the pathogenesis of atherosclerotic plaques, circulating monocytes move to and reside in the subendothelium of vessel walls and transform into macrophages, which subsequently transform to foam cells after intaking oxidative low-density lipoprotein (LDL). The M1 and M2 phenotypes of macrophages can transform for License 4.0 (CC BY)

Methods

Results

Conclusion