A bacterial metabolite, trimethylamine N-oxide, disrupts the hemostasis balance in human primary endothelial cells but no coagulopathy in mice

Hypercoagulability in Sickle Cell Disease: A Thrombo-Inflammatory Mechanism

Sickle cell disease (SCD) is a group of inherited disorders characterized by the presence of abnormal hemoglobin S. Patients with SCD suffer from frequent episodes of anemia, chronic hemolysis, pain crisis, and vaso-occlusion. Additionally, SCD is associated with diverse and serious clinical complications, including thrombosis, which can lead to organ failure, increased morbidity, and eventually, mortality. SCD is known to be a hypercoagulable condition, and the cause of hypercoagulability is multifactorial, with the molecular basis of hemoglobin S being the main driver. The presence of hemoglobin S induces sickling of the RBCs and their subsequent hemolysis, as well as oxidative stress. Both of these processes can alter the hemostatic system, through the activation of platelets, coagulation system, and fibrinolysis, as well as depletion of coagulation inhibitors. These changes can also induce the formation of microvesicles and expression of tissue factor, leading to activation of WBCs, endothelial cell damage, and inflammatory response. Understanding the various factors that drive hypercoagulability as a thrombo-inflammatory mechanism in SCD can help provide explanations for the pathogenesis and other complications of the disease.

Trimethylamine N-Oxide (TMAO) Inducing Endothelial Injury: UPLC-MS/MS-Based Quantification and the Activation of Cathepsin B-Mediated NLRP3 Inflammasome

TMAO is a new risk biomarker for cardiovascular disease. With trimethylammonium as its main chemical skeleton, TMAO is structurally similar to many endogenous metabolites, such as acetylcholine, carnitine, phosphorylcholine, etc. The mechanism of TMAO on the pathological process of CVD is still unclear. In this study, the quantitative analysis of plasma TMAO is conducted, and the contribution of Cathepsin B and NLRP3 inflammasome during the process of TMAO-induced endothelial injury was proposed and investigated at animal and cellular levels. Immunofluorescence assay was applied to represent the protein expression of Cathepsin B and NLRP3 inflammasome located at endothelial cells. The results showed that TMAO could disrupt endothelial cells permeability to induce endothelial injury, meanwhile, TMAO could increase NLRP3 inflammasome activation and promote the activity and expression of Cathepsin B in vitro and in vivo, whereas inhibition of NLRP3 inflammasome activation by MCC950 could protect the endothelial cells from TMAO associated endothelial injury via Cathepsin B. The study reveals that TMAO can cause endothelial injury via Cathepsin B-dependent NLRP3 inflammasome, and inhibition of Cathepsin B and NLRP3 inflammasome can reduce the TMAO-induced damage. The results provide new insight into the role of TMAO in CVD, which can be a potential therapeutic target for disease treatment and drug design.

The Relationship Between Atrial Fibrillation and Intestinal Flora With Its Metabolites

Atrial fibrillation (AF) is characterized by high morbidity and disability rate. The incidence of AF has rapidly increased due to increased aging population, causing a serious burden on society and patients. Therefore, it is necessary to determine the prevention and treatment of AF. Several studies have assessed the occurrence, development mechanism, and intervention measures of AF. The human gut has several non-pathogenic microorganisms forming the gut flora. The human gut microbiota plays a crucial role in the construction and operation of the metabolic system and immune system. Emerging clinical studies and basic experiments have confirmed that intestinal flora and its metabolites have a role in some metabolic disorders and chronic inflammatory diseases. Moreover, the gut microbiota has a role in cardiovascular diseases, such as hypertension and heart failure. However, the relationship between AF and gut microbiota is unclear. This review summarizes the relevant literature on the relationship between AF and intestinal flora with its metabolites, including Trimethylamine N-Oxide, short-chain fatty acids, lipopolysaccharide and bile acids. Therefore, this review may enhance further development of related research.

Vascular endothelial tissue factor contributes to trimethylamine N-oxide-enhanced arterial thrombosis

AIMS

Gut microbiota and their generated metabolites impact the host vascular phenotype. The metaorganismal metabolite trimethylamine N-oxide (TMAO) is both associated with adverse clinical thromboembolic events, and enhances platelet responsiveness in subjects. The impact of TMAO on vascular Tissue Factor (TF) in vivo is unknown. Here, we explore whether TMAO-enhanced thrombosis potential extends beyond TMAO effects on platelets, and is linked to TF. We also further explore the links between gut microbiota and vascular endothelial TF expression in vivo.

METHODS AND RESULTS

In initial exploratory clinical studies, we observed that among sequential stable subjects (n = 2989) on anti-platelet therapy undergoing elective diagnostic cardiovascular evaluation at a single-site referral centre, TMAO levels were associated with an increased incident (3 years) risk for major adverse cardiovascular events (MACE) (myocardial infarction, stroke, or death) [4th quartile (Q4) vs. Q1 adjusted hazard ratio (HR) 95% confidence interval (95% CI), 1.73 (1.25-2.38)]. Similar results were observed within subjects on aspirin mono-therapy during follow-up [adjusted HR (95% CI) 1.75 (1.25-2.44), n = 2793]. Leveraging access to a second higher risk cohort with previously reported TMAO data and monitoring of anti-platelet medication use, we also observed a strong association between TMAO and incident (1 year) MACE risk in the multi-site Swiss Acute Coronary Syndromes Cohort, focusing on the subset (n = 1469) on chronic dual anti-platelet therapy during follow-up [adjusted HR (95% CI) 1.70 (1.08-2.69)]. These collective clinical data suggest that the thrombosis-associated effects of TMAO may be mediated by cells/factors that are not inhibited by anti-platelet therapy. To test this, we first observed in human microvascular endothelial cells that TMAO dose-dependently induced expression of TF and vascular cell adhesion molecule (VCAM)1. In mouse studies, we observed that TMAO-enhanced aortic TF and VCAM1 mRNA and protein expression, which upon immunolocalization studies, was shown to co-localize with vascular endothelial cells. Finally, in arterial injury mouse models, TMAO-dependent enhancement of in vivo TF expression and thrombogenicity were abrogated by either a TF-inhibitory antibody or a mechanism-based microbial choline TMA-lyase inhibitor (fluoromethylcholine).

CONCLUSION

Endothelial TF contributes to TMAO-related arterial thrombosis potential, and can be specifically blocked by targeted non-lethal inhibition of gut microbial choline TMA-lyase.

Platelet Function in CKD: A Systematic Review and Meta-Analysis

BACKGROUND

Patients with CKD are at high risk for thrombotic and hemorrhagic complications. Abnormalities in platelet function are central to these complications, but reports on platelet function in relation to CKD are conflicting, and vary from decreased platelet reactivity to normal or increased platelet responsiveness. The direct effects of uremic toxins on platelet function have been described, with variable findings.

METHODS

To help clarify how CKD affects platelet function, we conducted a systematic review and meta-analysis of platelet activity in CKD, with a focus on nondialysis-induced effects. We also performed an extensive literature search for the effects of individual uremic toxins on platelet function.

RESULTS

We included 73 studies in the systematic review to assess CKD's overall effect on platelet function in patients; 11 of them described CKD's effect on ex vivo platelet aggregation and were included in the meta-analysis. Although findings on platelet abnormalities in CKD are inconsistent, bleeding time was mostly prolonged and platelet adhesion mainly reduced. Also, the meta-analysis revealed maximal platelet aggregation was significantly reduced in patients with CKD upon collagen stimulation. We also found that relatively few uremic toxins have been examined for direct effects on platelets ex vivo; ex vivo analyses had varying methods and results, revealing both platelet-stimulatory and inhibitory effects. However, eight of the 12 uremic toxins tested in animal models mostly induced prothrombotic effects.

CONCLUSIONS

Overall, most studies report impaired function of platelets from patients with CKD. Still, a substantial number of studies find platelet function to be unchanged or even enhanced. Further investigation of platelet reactivity in CKD, especially during different CKD stages, is warranted.

Gut microbiota and their metabolites in cardiovascular disease

The gut microbiome affects the development and progress of various types of disease such as obesity, diabetes, atherosclerosis and arterial thrombosis. Gut microbiome derived metabolites have been established to be predictive of arterial thrombosis in epidemiological studies. In these studies atherosclerosis and prothrombotic effect cannot be distinguished but preclinical studies show gut derived metabolites can induce platelet hyperreactivity and increase thrombotic potential. Gut commensals can also influence platelets through serotonin synthesis and may enhance Von Willebrand factor production. The effects on secondary haemostasis are less studied. In antiphospholipid syndrome, a thrombotic auto-immune disorder, autoreactive T cells and antibodies cross-react with auto-antigen mimicking peptides from gut commensals which appears to contribute to the pathophysiology. This review focusses on the prothrombotic effect of the gut microbiome and aims to provide insight into its influence on thromboembolic disease and the haemostatic system.

Gut Microbiota and the Quality of Oral Anticoagulation in Vitamin K Antagonists Users: A Review of Potential Implications

The efficacy and safety of vitamin K antagonists (VKAs) as oral anticoagulants (OACs) depend on the quality of anticoagulation control, as reflected by the mean time in therapeutic range (TTR). Several factors may be involved in poor TTR such as comorbidities, high inter-individual variability, interacting drugs, and non-adherence. Recent studies suggest that gut microbiota (GM) plays an important role in the pathogenesis of cardiovascular diseases, but the effect of the GM on anticoagulation control with VKAs is unknown. In the present review article, we propose different mechanisms by which the GM could have an impact on the quality of anticoagulation control in patients taking VKA therapy. We suggest that the potential effects of GM may be mediated first, by an indirect effect of metabolites produced by GM in the availability of VKAs drugs; second, by an effect of vitamin K-producing bacteria; and finally, by the structural modification of the molecules of VKAs. Future research will help confirm these hypotheses and may suggest profiles of bacterial signatures or microbial metabolites, to be used as biomarkers to predict the quality of anticoagulation. This could lead to the design of intervention strategies modulating gut microbiota, for example, by using probiotics.

Dietary bioactive ingredients to modulate the gut microbiota-derived metabolite TMAO. New opportunities for functional food development

There is a growing body of clinical evidence that supports a strong association between elevated circulating trimethylamine N-oxide (TMAO) levels with increased risk of developing adverse cardiovascular outcomes such as atherosclerosis and thrombosis. TMAO is synthesized through a meta-organismal stepwise process that involves (i) the microbial production of TMA in the gut from dietary precursors and (ii) its subsequent oxidation to TMAO by flavin-containing monooxygenases in the liver. Choline, l-carnitine, betaine, and other TMA-containing compounds are the major dietary precursors of TMA. TMAO can also be absorbed directly from the gastrointestinal tract after the intake of TMAO-rich foods such as fish and shellfish. Thus, diet is an important factor as it provides the nutritional precursors to eventually produce TMAO. A number of studies have attempted to associate circulating TMAO levels with the consumption of diets rich in these foods. On the other hand, there is growing interest for the development of novel food ingredients that reduce either the TMAO-induced damage or the endogenous TMAO levels through the interference with microbiota and host metabolic processes involved in TMAO pathway. Such novel functional food ingredients would offer great opportunities to control circulating TMAO levels or its effects, and potentially contribute to decrease cardiovascular risk. In this review we summarize and discuss current data regarding the effects of TMA precursors-enriched foods or diets on circulating TMAO levels, and recent findings regarding the circulating TMAO-lowering effects of specific foods, food constituents and phytochemicals found in herbs, individually or in extracts, and their potential beneficial effect for cardiovascular health.

Trimethylamine N-oxide promotes apoE-/- mice atherosclerosis by inducing vascular endothelial cell pyroptosis via the SDHB/ROS pathway

Trimethylamine N-oxide (TMAO) is produced from the phosphatidylcholine metabolism of gut flora and acts as a risk factor of cardiovascular disease. However, the underlying mechanisms for its proatherogenic action remain unclear. This study aimed to observe the effect of TMAO on endothelial cell pyroptosis and explore the underlying mechanisms. Our results showed that TMAO promoted the progression of atherosclerotic lesions in apolipoprotein E-deficient (apoE^-/- ) mice fed a high-fat diet. Pyroptosis and succinate dehydrogenase complex subunit B (SDHB) upregulation were detected in the vascular endothelial cells of apoE^-/- mice and in cultured human umbilical vein endothelial cells (HUVECs) treated with TMAO. Overexpression of SDHB in HUVECs enhanced pyroptosis and impaired mitochondria and high reactive oxygen species (ROS) level. Pyroptosis in the SDHB overexpression of endothelial cells was inhibited by the ROS scavenger NAC. In summary, TMAO promotes vascular endothelial cell pyroptosis via ROS induced through SDHB upregulation, thereby contributing to the progression of atherosclerotic lesions.

The Gut Microbiota in Cardiovascular Disease and Arterial Thrombosis

The gut microbiota has emerged as a contributing factor in the development of atherosclerosis and arterial thrombosis. Metabolites from the gut microbiota, such as trimethylamine N-oxide and short chain fatty acids, were identified as messengers that induce cell type-specific signaling mechanisms and immune reactions in the host vasculature, impacting the development of cardiovascular diseases. In addition, microbial-associated molecular patterns drive atherogenesis and the microbiota was recently demonstrated to promote arterial thrombosis through Toll-like receptor signaling. Furthermore, by the use of germ-free mouse models, the presence of a gut microbiota was shown to influence the synthesis of endothelial adhesion molecules. Hence, the gut microbiota is increasingly being recognized as an influencing factor of arterial thrombosis and attempts of dietary pre- or probiotic modulation of the commensal microbiota, to reduce cardiovascular risk, are becoming increasingly significant.