Elevated Circulating Trimethylamine N-Oxide Levels Contribute to Endothelial Dysfunction in Aged Rats through Vascular Inflammation and Oxidative Stress.

Tiejun Li,Chaojun Gua,Xiaodong Li,Yanli Chen

doi:10.3389/fphys.2017.00350

Abstract

Vascular endothelial dysfunction, a characteristic of the aging process, is an important risk factor for cardiovascular disease in aging. Although, vascular inflammation and oxidative stress are major contributors to endothelial dysfunction in aging, the underlying mechanisms during the aging process are not fully understood. Accumulating evidence reveals that gut microbiota-dependent metabolite trimethylamine-N-oxide (TMAO) is implicated in the pathogenesis of many cardiovascular diseases. We tested the hypothesis that aging increases circulating TMAO levels, which induce vascular inflammation and oxidative stress, resulting in age-associated endothelial dysfunction. Old (22-mo-old) and young (4-mo-old) Fischer-344 rats were treated without (control) or with 1.0% 3,3-Dimethyl-1-butanol (DMB, an inhibitor of trimethylamine formation) in drinking water for 8 weeks. Compared with young control group, old control group had markedly higher plasma TMAO levels, which were reduced by DMB treatment. Endothelium-dependent relaxation of aorta in response to acetylcholine was impaired in old control group compared with young control group as indicated by decreased maximal relaxation (Emax) and reduced area under the curve (AUC). Emax and AUC were both normalized in old rats treated with DMB. No difference in endothelial-independent relaxation in response to sodium nitroprusside was observed among groups. Molecular studies revealed that old control group exhibits increased expression of proinflammatory cytokines and superoxide production, and decreased expression of endothelial nitric-oxide synthase (eNOS) in the aorta, all of which were restored by DMB treatment. These results suggest that aging increases circulating TMAO levels, which may impair eNOS-derived NO bioavailability by increasing vascular inflammation and oxidative stress, contributing to aging-associated endothelial dysfunction.

Highlights

Thirty-six young (∼4-mo-old) and 36 old (∼22-mo-old) animals were randomly divided into four experimental groups as follows (n = 18 for each group): (1) young control rats (Y-CON), (2) young rats treated with 3,3-Dimethyl-1-butanol (DMB, an inhibitor of trimethylamine formation) (Y-DMB), (3) old control rats (O-CON), and (4) old rats treated with DMB (O-DMB). 1.0% DMB was given in drinking water for 8 weeks and this dose of DMB has been demonstrated to effectively inhibit trimethylamine formation and reduce circulating TMAO levels in rodent (Wang et al, 2015)
Emax was decreased by 30% in old control group, compared with young control group (O-CON, 62 ± 4 vs. Y-CON, 89 ± 5%; P < 0.05), but was elevated in old DMB group (Figure 2B), resulting in no difference (P > 0.05) between old DMB group (O-DMB: 83 ± 5%) and young control group or young DMB
The novel findings of this study are as follows: (1) compared young rats, old rats have higher plasma TMAO levels, which are prevented by treatment with DMB; (2) endothelium-dependent but not endotheliumindependent relaxation in the aorta is impaired in old rats, and is normalized by treatment with DMB; (4) old rats exhibit increased proinflammatory cytokines and superoxide production, and decreased endothelial nitric-oxide synthase (eNOS) expression in the aorta, all of which are restored by treatment with DMB

Summary

Introduction

Aging is an independent risk factor for cardiovascular disease (Lakatta and Levy, 2003; Herrera et al, 2010; El Assar et al, 2012; Donato et al, 2015), which is the leading cause of death worldwide. Advancing age is accompanied by increased vascular inflammation and oxidative stress, which have been suggested to be the major contributes to aging-associated reduction in NO bioavailability and endothelial dysfunction (Herrera et al, 2010; Donato et al, 2015). We examined whether circulating TMAO levels are elevated with aging and, if so, whether elevated TMAO levels induce vascular inflammation and oxidative stress, resulting in age-associated endothelial dysfunction

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Results

Conclusion