Effects of Microbiota-Driven Therapy on Circulating Trimethylamine-N-Oxide Metabolism: A Systematic Review and Meta-Analysis

Effects of Dietary Fiber Supplementation on Modulating Uremic Toxins and Inflammation in Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Emerging evidence supports the beneficial effects of dietary fiber supplementation in alleviating gut dysbiosis, which leads to a reduction in uremic toxins and inflammatory markers in chronic kidney disease (CKD) patients. However, current evidence-based renal nutrition guidelines do not provide recommendations regarding dietary fiber intake. We performed a systematic review and meta-analysis to investigate and highlight the effects of dietary fiber supplementation on modulating uremic toxins and inflammatory markers in individuals with CKD, with or without dialysis. The eligible randomized controlled trials (RCTs) were identified from PubMed, Scopus, and Cochrane Central Register of Controlled trials until 27 November 2024. The results were synthesized using a random-effects model and presented as standardized mean differences (SMDs) with a 95% confidence interval (CI). A total of 21 studies with 700 patients were included. When compared with the control group, dietary fiber supplementation ranging from 6 to 50 g/day, for typically more than 4 weeks, could significantly reduce the levels of serum uremic toxins, including p-cresyl sulfate, indoxyl sulfate, and blood urea nitrogen (SMD -0.22, -0.34, -0.25, respectively, with p-values < 0.05), as well as biomarkers of inflammation, including interleukin-6 and tumor necrosis factor alpha (SMD -0.44, -0.34, respectively, with p-values < 0.05). These beneficial effects were consistent across different types of fibers and CKD status (with or without dialysis). However, no significant reduction in serum trimethylamine N-oxide, uric acid, and high-sensitivity C-reactive protein levels was observed with dietary fiber intervention. This study would pave the way for prioritizing dietary quality, particularly a fiber-rich diet, beyond the traditional focus on the quantities of protein, energy, and electrolyte restrictions among individuals with CKD.

Prognostic Value of Serum TMAO Measurement in Patients with STEMI: A Systematic Literature Review

BACKGROUND

Gut microbiota-derived metabolite Trimethylamine-N-oxide (TMAO) is increasingly recognized as a potential novel prognostic biomarker for cardiovascular disease. Our research work aimed to investigate the potential utility of TMAO measurement in patients with STelevation Myocardial Infarction (STEMI).

METHODS

We performed a systematic literature search in PubMed from inception to the 1st of February 2024 to identify all studies examining the association between plasma TMAO levels and disease complexity or clinical outcomes in STEMI patients.

RESULTS

A total of eight prospective cohort studies were included, encompassing a total of 2,378 STEMI patients. Three of the studies provided only in-hospital evidence (i.e., increased odds for more severe coronary artery disease, plaque rupture, and plaque healing in patients with increased TMAO levels). Four studies examined the long-term prognostic value of TMAO after 10-12 months of follow-up post-STEMI (i.e., increased risk of adverse cardiovascular events in patients with increased TMAO levels), while one study provided data for both in-hospital and mid-term prognosis, indicating that 4-months after STEMI patients with greater TMAO elevation had larger infarct size.

CONCLUSION

Higher TMAO levels were associated with a greater prevalence of high-risk coronary plaque characteristics and worse in-hospital and follow-up outcomes in STEMI patients. Further study is needed on whether modulating the diet-dependent TMAO levels could improve clinical outcomes in these patients.

REGISTRATION NUMBER

[(OSF): https://doi.org/10.17605/OSF.IO/WNG8V].

Human Gut Microbiota in Cardiovascular Disease

The gut ecosystem, termed microbiota, is composed of bacteria, archaea, viruses, protozoa, and fungi and is estimated to outnumber human cells. Microbiota can affect the host by multiple mechanisms, including the synthesis of metabolites and toxins, modulating inflammation and interaction with other organisms. Advances in understanding commensal organisms' effect on human conditions have also elucidated the importance of this community for cardiovascular disease (CVD). This effect is driven by both direct CV effects and conditions known to increase CV risk, such as obesity, diabetes mellitus (DM), hypertension, and renal and liver diseases. Cardioactive metabolites, such as trimethylamine N -oxide (TMAO), short-chain fatty acids (SCFA), lipopolysaccharides, bile acids, and uremic toxins, can affect atherosclerosis, platelet activation, and inflammation, resulting in increased CV incidence. Interestingly, this interaction is bidirectional with microbiota affected by multiple host conditions including diet, bile acid secretion, and multiple diseases affecting the gut barrier. This interdependence makes manipulating microbiota an attractive option to reduce CV risk. Indeed, evolving data suggest that the benefits observed from low red meat and Mediterranean diet consumption can be explained, at least partially, by the changes that these diets may have on the gut microbiota. In this article, we depict the current epidemiological and mechanistic understanding of the role of microbiota and CVD. Finally, we discuss the potential therapeutic approaches aimed at manipulating gut microbiota to improve CV outcomes. © 2024 American Physiological Society. Compr Physiol 14:5449-5490, 2024.

TMAO enhances TNF-α mediated fibrosis and release of inflammatory mediators from renal fibroblasts

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite and TNF-α is proinflammatory cytokine, both known to be associated with renal inflammation, fibrosis and chronic kidney disease. However, today there are no data showing the combined effect of TMAO and TNF-α on renal fibrosis-and inflammation. The aim of this study was to investigate whether TMAO can enhance the inflammatory and fibrotic effects of TNF-α on renal fibroblasts. We found that the combination of TNF-α and TMAO synergistically increased fibronectin release and total collagen production from renal fibroblasts. The combination of TMAO and TNF-α also promoted increased cell proliferation. Both renal proliferation and collagen production were mediated through Akt/mTOR/ERK signaling. We also found that TMAO enhanced TNF-α mediated renal inflammation by inducing the release of several cytokines (IL-6, LAP TGF-beta-1), chemokines (CXCL-6, MCP-3), inflammatory-and growth mediators (VEGFA, CD40, HGF) from renal fibroblasts. In conclusion, we showed that TMAO can enhance TNF-α mediated renal fibrosis and release of inflammatory mediators from renal fibroblasts in vitro. Our results can promote further research evaluating the combined effect of TMAO and inflammatory mediators on the development of kidney disease.

Berberine Decreases Thrombosis Potential Induced by a High-choline Diet by Inhibiting CutC Enzyme

INTRODUCTION

Gut microbes influence thrombosis potential by generating trimethylamine N-oxide (TMAO). However, whether the antithrombotic effect of berberine is associated with TMAO generation remains unclear.

OBJECTIVE

The present study was designed to explore whether berberine decreases the TMAO-induced thrombosis potential and the possible mechanism underneath it.

METHODS

C57BL/6J female mice under a high-choline diet or standard diet were treated with/without berberine for 6 weeks. The TMAO level, carotid artery occlusion time following FeCl3 injury and platelet responsiveness were measured. The binding of berberine to the CutC enzyme was analysed with molecular docking, and molecular dynamics simulations were verified with enzyme activity assays.

RESULTS

The results showed that berberine increased the carotid artery occlusion time following FeCl3 injury and decreased the platelet hyperresponsiveness induced by a high-- choline diet, both offset by intraperitoneal injection of TMAO. The effect of berberine on thrombosis potential was associated with decreasing the generation of TMAO by inhibiting the CutC enzyme.

CONCLUSION

Targeting TMAO generation with berberine might be a promising therapy for ischaemic cardiac-cerebral vascular diseases.

Probiotics as potential treatments to reduce myocardial remodelling and heart failure via the gut-heart axis: State-of-the-art review

Probiotics are considered to represent important modulators of gastrointestinal health through increased colonization of beneficial bacteria thus altering the gut microflora. Although these beneficial effects of probiotics are now widely recognized, emerging evidence suggests that alterations in the gut microflora also affect numerous other organ systems including the heart through a process generally referred to as the gut-heart axis. Moreover, cardiac dysfunction such as that seen in heart failure can produce an imbalance in the gut flora, known as dysbiosis, thereby further contributing to cardiac remodelling and dysfunction. The latter occurs by the production of gut-derived pro-inflammatory and pro-remodelling factors which exacerbate cardiac pathology. One of the key contributors to gut-dependent cardiac pathology is trimethylamine N-oxide (TMAO), a choline and carnitine metabolic by-product first synthesized as trimethylamine which is then converted into TMAO by a hepatic flavin-containing monooxygenase. The production of TMAO is particularly evident with regular western diets containing high amounts of both choline and carnitine. Dietary probiotics have been shown to reduce myocardial remodelling and heart failure in animal models although the precise mechanisms for these effects are not completely understood. A large number of probiotics have been shown to possess a reduced capacity to synthesize gut-derived trimethylamine and therefore TMAO thereby suggesting that inhibition of TMAO is a factor mediating the beneficial cardiac effects of probiotics. However, other potential mechanisms may also be important contributing factors. Here, we discuss the potential benefit of probiotics as effective therapeutic tools for attenuating myocardial remodelling and heart failure.

Trimethylamine N-Oxide (TMAO) Mediates Increased Inflammation and Colonization of Bladder Epithelial Cells during a Uropathogenic E. coli Infection In Vitro

Urinary tract infections (UTIs) are among the most common infections in humans and are often caused by uropathogenic E. coli (UPEC). Trimethylamine N-oxide (TMAO) is a proinflammatory metabolite that has been linked to vascular inflammation, atherosclerosis, and chronic kidney disease. As of today, no studies have investigated the effects of TMAO on infectious diseases like UTIs. The aim of this study was to investigate whether TMAO can aggravate bacterial colonization and the release of inflammatory mediators from bladder epithelial cells during a UPEC infection. We found that TMAO aggravated the release of several key cytokines (IL-1β and IL-6) and chemokines (IL-8, CXCL1 and CXCL6) from bladder epithelial cells during a CFT073 infection. We also found that CFT073 and TMAO mediate increased release of IL-8 from bladder epithelial cells via ERK 1/2 signaling and not bacterial growth. Furthermore, we showed that TMAO enhances UPEC colonization of bladder epithelial cells. The data suggest that TMAO may also play a role in infectious diseases. Our results can be the basis of further research to investigate the link between diet, gut microbiota, and urinary tract infection.

TMAO Suppresses Megalin Expression and Albumin Uptake in Human Proximal Tubular Cells Via PI3K and ERK Signaling

Trimethylamine-N-oxide (TMAO) is a uremic toxin, which has been associated with chronic kidney disease (CKD). Renal tubular epithelial cells play a central role in the pathophysiology of CKD. Megalin is an albumin-binding surface receptor on tubular epithelial cells, which is indispensable for urine protein reabsorption. To date, no studies have investigated the effect of TMAO on megalin expression and the functional properties of human tubular epithelial cells. The aim of this study was first to identify the functional effect of TMAO on human renal proximal tubular cells and second, to unravel the effects of TMAO on megalin-cubilin receptor expression. We found through global gene expression analysis that TMAO was associated with kidney disease. The microarray analysis also showed that megalin expression was suppressed by TMAO, which was also validated at the gene and protein level. High glucose and TMAO was shown to downregulate megalin expression and albumin uptake similarly. We also found that TMAO suppressed megalin expression via PI3K and ERK signaling. Furthermore, we showed that candesartan, dapagliflozin and enalaprilat counteracted the suppressive effect of TMAO on megalin expression. Our results may further help us unravel the role of TMAO in CKD development and to identify new therapeutic targets to counteract TMAOs effects.

Serum Trimethylamine N-Oxide Level Is Associated with Peripheral Arterial Stiffness in Advanced Non-Dialysis Chronic Kidney Disease Patients

Trimethylamine N-oxide (TMAO) is a gut-derived uremic toxin involved in cardiovascular diseases (CVD). Peripheral arterial stiffness (PAS), measured by the brachial-ankle pulse wave velocity (baPWV) is a valuable indicator of the existence of CVD alongside other diseases. The study recruited 157 patients with chronic kidney disease (CKD) stages 3 to 5, and aimed to determine the correlation between serum TMAO and PAS, defined as a baPWV of >18.0 m/s. Patients with CKD who were diagnosed with PAS (68 patients, 43.3%) were older, had a higher percentage of hypertension or diabetes mellitus, higher systolic blood pressure, and higher fasting glucose, C-reactive protein, and TMAO levels. Furthermore, besides old age and SBP, patients with CKD who had higher serum TMAO were more likely to have PAS, with an odds ratio of 1.016 (95% confidence interval = 1.002−1.029, p = 0.021) by multivariate logistic regression analysis. Correlation analysis demonstrated that serum TMAO was positively correlated with C-reactive protein level and either left or right baPWV. Thus, we supposed that serum TMAO levels were associated with PAS in patients with advanced non-dialysis CKD.

Trimethylamine N-Oxide in Heart Failure: A Meta-Analysis of Prognostic Value

Objective

The present study aimed to explore the prognostic value of trimethylamine N-oxide (TMAO) in heart failure (HF).

Methods

PubMed, Excerpta Medica Database (EMBASE), Cochrane Library, Web of Science, Wanfang Database, SINOMED, China Science and Technology Journal Database (VIP), and China National Knowledge Infrastructure (CNKI) were searched up to June 1, 2021. Studies recording the major adverse cardiovascular events (MACEs) or all-cause mortality in HF patients and their circulating TMAO concentrations were included. Meta-analysis was performed using Stata 13.0.

Results

Ten articles (12 studies) involving 13,425 participants from 2014 to 2021 were considered. Compared to low-level TMAO, elevated TMAO was correlated with MACEs and all-cause mortality in HF (RR: 1.28, 95% CI: 1.17, 1.39, P < 0.0001, random-effects model and RR: 1.35, 95% CI: 1.28, 1.42, P < 0.0001, random-effects model, respectively). Consistent results were obtained in all examined subgroups as well as in the sensitivity analysis.

Conclusion

Elevated TMAO may be an adverse prognostic indicator in patients with HF.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=267208