Trimethylamine‐N‐Oxide Induces Vascular Inflammation by Activating the NLRP3 Inflammasome Through the SIRT3‐SOD2‐mtROS Signaling Pathway

Abstract

BackgroundTrimethylamine‐N‐oxide (TMAO) has recently been identified as a novel and independent risk factor for promoting atherosclerosis through inducing vascular inflammation. However, the exact mechanism is currently unclear. Studies have established a central role of nucleotide‐binding oligomerization domain–like receptor family pyrin domain–containing 3 (NLRP3) inflammasome in the pathogenesis of vascular inflammation. Here, we examined the potential role of the NLRP3 inflammasome in TMAO‐induced vascular inflammation in vitro and in vivo and the underlying mechanisms.Methods and ResultsExperiments using liquid chromatography‐tandem mass spectrometry, Western blot, and fluorescent probes showed that TMAO‐induced inflammation in human umbilical vein endothelial cells (HUVECs) and aortas from ApoE−/− mice. Moreover, TMAO promoted NLRP3 and activated caspase‐1 p20 expression and caspase‐1 activity in vitro and in vivo. Notably, a caspase‐1 inhibitor (YVAD), an NLRP3 inhibitor (MCC950), as well as NLRP3 short interfering RNA attenuated TMAO‐induced activation of the NLRP3 inflammasome, subsequently leading to suppression of inflammation in HUVECs. TMAO additionally stimulated reactive oxygen species (ROS) generation, in particular, mitochondrial ROS, while inhibiting manganese superoxide dismutase 2 (SOD2) activation and sirtuin 3 (SIRT3) expression in HUVECs and aortas from ApoE−/− mice. TMAO‐induced endothelial NLRP3 inflammasome activation was ameliorated by the mitochondrial ROS scavenger Mito‐TEMPO, or SIRT3 overexpression in HUVECs. Conversely, TMAO failed to further inhibit magnesium SOD2 and activate the NLRP3 inflammasome or induce inflammation in SIRT3 short interfering RNA–treated HUVECs and aortas from SIRT3−/− mice.Conclusions TMAO promoted vascular inflammation by activating the NLRP3 inflammasome, and the NLRP3 inflammasome activation in part was mediated through inhibition of the SIRT3‐SOD2–mitochondrial ROS signaling pathway.

L-Carnitine Supplementation Increases Trimethylamine-N-Oxide but not Markers of Atherosclerosis in Healthy Aged Women

“…While the studies show the ability of TMAO to promote atherosclerosis [10,11,17,18,30,31], there are numerous contrasting results [19,[32][33][34][35][36]. Treatment of male Fischer 344 rats by L-carnitine in drinking water for 1 year induced tenfold higher TMAO plasma concentration when compared to the control (2.5 vs. 25.0 μM) [36].…”

“…Ma et al [18], using human umbilical vein endothelial cells, demonstrated that TMAO up-regulates VCAM-1 expression and promotes monocyte adhesion. In the same human umbilical vein endothelial cells model, TMAO promotes early pathological process of atherosclerosis by accelerating inflammation and triggering oxidative stress [17,30,31].…”

“…Clinical studies show a positive correlation between elevated plasma TMAO and an increased risk for major adverse cardiovascular events defined as death, myocardial infarction or stroke [12,[14][15][16]. Several experimental studies suggest a possible contribution of TMAO to the ethology of cardiovascular diseases by affecting cholesterol homeostasis [10,11] or promoting vascular inflammation [17,18].…”

Endocrine organs of cardiovascular diseases: Gut microbiota

“…TMAO can affect lipid metabolism causing accumulation of cholesterol in cells and it can also have a direct impact on platelet function, promote an inflammatory response and so on. The effect of the TMAO will accelerate the development of atherosclerosis and the level of plasma TMAO and its associated metabolites are directly proportional to the risk of cardiovascular disease (CVD), which will be pointed out in the following sections …”

“…15 There are also studies showing that TMAO enhanced the platelet reactivity and thrombosis risk and promoted vascular inflammation by activating the NLRP3 inflammasome. 16 Using pyrosequencing to analyse the microbial species of atherosclerotic plaques and intestinal microflora in the same atherosclerotic patients, the results show that several bacteria exist simultaneously, suggesting that bacteria found in the plaque may be derived from intestinal flora. 64 In another study using shotgun sequencing method it was found that atherosclerosis patients were rich in Collinsell, and healthy people were rich in Roseburia and Eubacterium.…”