The gut microbiota - a modulator of endothelial cell function and a contributing environmental factor to arterial thrombosis

Trimethylamine-N-Oxide Promotes High-Glucose-Induced Dysfunction and NLRP3 Inflammasome Activation in Retinal Microvascular Endothelial Cells

Introduction

Along with blood glucose levels, diabetic retinopathy (DR) development also involves endogenous risk factors, such as trimethylamine-N-oxide (TMAO), a product of intestinal flora metabolic disorder, which exacerbates diabetic microvascular complications. However, the effect of TMAO on retinal cells under high-glucose conditions remains unclear. Therefore, this study examined the effects of TMAO on high-glucose-induced retinal dysfunction in the context of NLRP3 inflammasome activation, which is involved in DR.

Materials and Methods

TMAO was assessed in the serum and aqueous humor of patients using ELISA. Human retinal microvascular endothelial cells (HRMECs) were treated for 72 h as follows: NG (normal glucose, D-glucose 5.5 mM), NG + TMAO (5 μM), HG (high glucose, D-glucose 30 mM), and HG + TMAO (5 μM). The CCK8 assay was then used to assess cell proliferation; wound healing, cell migration, and tube formation assays were used to verify changes in cell phenotype. ZO-1 expression was determined using immunofluorescence and western blotting. Reactive oxygen species (ROS) formation was assessed using DCFH-DA. NLRP3 inflammasome complex activation was determined using a western blot.

Results

The serum and aqueous humor from patients with PDR contained higher levels of TMAO compared to patients with nontype 2 diabetes (Control), non-DR (NDR), and non-PDR (NPDR). TMAO showed significant acceleration of high-glucose-induced cell proliferation, wound healing, cell migration, and tube formation. ZO-1 expression decreased remarkably with the combined action of TMAO and a high glucose compared to either treatment alone. TMAO also promoted high-glucose-activated NLRP3 inflammasome complex.

Conclusion

The combination of TMAO and high-glucose results in increased levels of ROS and NLRP3 inflammasome complex activation in HRMECs, leading to exacerbated retinal dysfunction and barrier failure. Thus, TMAO can accelerate PDR occurrence and development, thus indicating the need for early fundus monitoring in diabetic patients with intestinal flora disorders.

Bidirectional effects of oral anticoagulants on gut microbiota in patients with atrial fibrillation

Background

The imbalance of gut microbiota (GM) is associated with a higher risk of thrombosis in patients with atrial fibrillation (AF). Oral anticoagulants (OACs) have been found to significantly reduce the risk of thromboembolism and increase the risk of bleeding. However, the OAC-induced alterations in gut microbiota in patients with AF remain elusive.

Methods

In this study, the microbial composition in 42 AF patients who received long-term OAC treatment (AF-OAC group), 47 AF patients who did not (AF group), and 40 volunteers with the risk of AF (control group) were analyzed by 16S rRNA gene sequencing of fecal bacterial DNA. The metagenomic functional prediction of major bacterial taxa was performed using the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) software package.

Results

The gut microbiota differed between the AF-OAC and AF groups. The abundance of Bifidobacterium and Lactobacillus decreased in the two disease groups at the genus level, but OACs treatment mitigated the decreasing tendency and increased beneficial bacterial genera, such as Megamonas. In addition, OACs reduced the abundance of pro-inflammatory taxa on the genus Ruminococcus but increased certain potential pathogenic taxa, such as genera Streptococcus, Escherichia-Shigella, and Klebsiella. The Subgroup Linear discriminant analysis effect size (LEfSe) analyses revealed that Bacteroidetes, Brucella, and Ochrobactrum were more abundant in the anticoagulated bleeding AF patients, Akkermansia and Faecalibacterium were more abundant in the non-anticoagulated-bleeding-AF patients. The neutrophil-to-lymphocyte ratio (NLR) was lower in the AF-OAC group compared with the AF group (P < 0.05). Ruminococcus was positively correlated with the NLR and negatively correlated with the CHA2DS2-VASc score (P < 0.05), and the OACs-enriched species (Megamonas and Actinobacteria) was positively correlated with the prothrombin time (PT) (P < 0.05). Ruminococcus and Roseburia were negatively associated with bleeding events (P < 0.05).

Conclusions

Our study suggested that OACs might benefit AF patients by reducing the inflammatory response and modulating the composition and abundance of gut microbiota. In particular, OACs increased the abundance of some gut microbiota involved in bleeding and gastrointestinal dysfunction indicating that the exogenous supplementation with Faecalibacterium and Akkermansia might be a prophylactic strategy for AF-OAC patients to lower the risk of bleeding after anticoagulation.

Antithrombotic Activity of Heparinoid G2 and Its Derivatives from the Clam Coelomactra antiquata

Clam heparinoid G2 (60.25 kDa) and its depolymerized derivatives DG1 (24.48 kDa) and DG2 (6.75 kDa) prepared from Coelomactra antiquata have been documented to have excellent fibrinolytic and anticoagulant activity. In this study, to further explore the antithrombotic activity of G2, DG1 and DG2, azure A, sheep plasma, and clot lytic rate assays were used to determine their anticoagulant and thrombolytic activity in vitro. The results indicated that the anticoagulant titer of G2 was approximately 70% that of heparin and the thrombolytic activity of DG2 was greater than G2, DG1, and heparin activities. Moreover, in a carrageenan-induced venous thrombosis model, oral administration of G2 and DG1 each at 20 mg/kg and 40 mg/kg for 7 days significantly reduced blacktail thrombus formation, increased tissue-type plasminogen activator, fibrin degradation products, and D-dimer levels, decreased von Willebrand factor and thromboxane B2 levels, and restored phylum and genus abundance changes of intestinal bacteria. DG2 had no antithrombotic effect. At 20 mg/kg, G2, DG1, and heparin had comparable antithrombotic activities, and DG1 at 40 mg/kg had more muscular antithrombotic activity than G2. Thus, DG1 could be an antithrombotic oral agent owing to its more robust antithrombotic activity and lower molecular weight.

Role of Gut Microbiota, Probiotics and Prebiotics in the Cardiovascular Diseases

In recent years, there has been a growing interest in identifying and applying new, naturally occurring molecules that promote health. Probiotics are defined as “live microorganisms which, when administered in adequate amounts, confer health benefits on the host”. Quite a few fermented products serve as the source of probiotic strains, with many factors influencing the effectiveness of probiotics, including interactions of probiotic bacteria with the host’s microbiome. Prebiotics contain no microorganisms, only substances which stimulate their growth. Prebiotics can be obtained from various sources, including breast milk, soybeans, and raw oats, however, the most popular prebiotics are the oligosaccharides contained in plants. Recent research increasingly claims that probiotics and prebiotics alleviate many disorders related to the immune system, cancer metastasis, type 2 diabetes, and obesity. However, little is known about the role of these supplements as important dietary components in preventing or treating cardiovascular disease. Still, some reports and clinical studies were conducted, offering new ways of treatment. Therefore, the aim of this review is to discuss the roles of gut microbiota, probiotics, and prebiotics interventions in the prevention and treatment of cardiovascular disease.

How strong is the evidence that gut microbiota composition can be influenced by lifestyle interventions in a cardio-protective way?

Alterations in composition and function of the gut microbiota have been demonstrated in diseases involving the cardiovascular system, particularly coronary heart disease and atherosclerosis. The data are still limited but the typical altered genera include Roseburia and Faecalibacterium. Plausible mechanisms by which microbiota may mediate cardio-protective effects have been postulated, including the production of metabolites like trimethylamine (TMA), as well as immunomodulatory functions. This raises the question of whether it is possible to modify the gut microbiota by lifestyle interventions and thereby improve cardiovascular health. Nevertheless, lifestyle intervention studies that have involved modifications of dietary intake and/or physical activity, as well as investigating changes in the gut microbiota and subsequent modifications of the cardioprotective markers, are still scarce, and the results have been inconclusive. Current evidence points to benefits of consuming high-fibre foods, nuts and an overall healthy dietary pattern to achieve beneficial effects on both gut microbiota and serum cardiovascular markers, primarily lipids. The relationship between physical exercise and gut microbiota is probably complex and may be dependent on the intensity of exercise. In this article, we review the available evidence on lifestyle, specifically diet, physical activity and smoking as modifiers of the gut microbiota, and subsequently as modifiers of serum cardiovascular health markers. We have attempted to elucidate the plausible mechanisms and further critically appraise the caveats and gaps in the research.

Is the gut microbiota dysbiotic in patients with classical homocystinuria?

Classical homocystinuria (HCU) is characterized by increased plasma levels of total homocysteine (tHcy) and methionine (Met). Treatment may involve supplementation of B vitamins and essential amino acids, as well as restricted Met intake. Dysbiosis has been described in some inborn errors of metabolism, but has not been investigated in HCU. The aim of this study was to investigate the gut microbiota of HCU patients on treatment. Six unrelated HCU patients (males = 5, median age = 25.5 years) and six age-and-sex-matched healthy controls (males = 5, median age = 24.5 years) had their fecal microbiota characterized through partial 16S rRNA gene sequencing. Fecal pH, a 3-day dietary record, medical history, and current medications were recorded for both groups. All patients were nonresponsive to pyridoxine and were on a Met-restricted diet and presented with high tHcy. Oral supplementation of folate (n = 6) and pyridoxine (n = 5), oral intake of betaine (n = 4), and IM vitamin B12 supplementation (n = 4), were reported only in the HCU group. Patients had decreased daily intake of fat, cholesterol, vitamin D, and selenium compared to controls (p < 0.05). There was no difference in alpha and beta diversity between the groups. HCU patients had overrepresentation of the Eubacterium coprostanoligenes group and underrepresentation of the Alistipes, Family XIII UCG-001, and Parabacteroidetes genera. HCU patients and controls had similar gut microbiota diversity, despite differential abundance of some bacterial genera. Diet, betaine, vitamin B supplementation, and host genetics may contribute to these differences in microbial ecology.

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.