Utility of Plasma Concentration of Trimethylamine N-Oxide in Predicting Cardiovascular and Renal Complications in Individuals With Type 1 Diabetes

Traditional Chinese medicine improved diabetic kidney disease through targeting gut microbiota

CONTEXT

Diabetic kidney disease (DKD) affects nearly 40% of diabetic patients, often leading to end-stage renal disease that requires renal replacement therapies, such as dialysis and transplantation. The gut microbiota, an integral aspect of human evolution, plays a crucial role in this condition. Traditional Chinese medicine (TCM) has shown promising outcomes in ameliorating DKD by addressing the gut microbiota.

OBJECTIVE

This review elucidates the modifications in gut microbiota observed in DKD and explores the impact of TCM interventions on correcting microbial dysregulation.

METHODS

We searched relevant articles from databases including Web of Science, PubMed, ScienceDirect, Wiley, and Springer Nature. The following keywords were used: diabetic kidney disease, diabetic nephropathy, gut microbiota, natural product, TCM, Chinese herbal medicine, and Chinese medicinal herbs. Rigorous criteria were applied to identify high-quality studies on TCM interventions against DKD.

RESULTS

Dysregulation of the gut microbiota, including Lactobacillus, Streptococcus, and Clostridium, has been observed in individuals with DKD. Key indicators of microbial dysregulation include increased uremic solutes and decreased short-chain fatty acids. Various TCM therapies, such as formulas, tablets, granules, capsules, and decoctions, exhibit unique advantages in regulating the disordered microbiota to treat DKD.

CONCLUSION

This review highlights the importance of targeting the gut-kidney axis to regulate microbial disorders, their metabolites, and associated signaling pathways in DKD. The Qing-Re-Xiao-Zheng formula, the Shenyan Kangfu tablet, the Huangkui capsule, and the Bekhogainsam decoction are potential candidates to address the gut-kidney axis. TCM interventions offer a significant therapeutic approach by targeting microbial dysregulation in patients with DKD.

Molecular mechanisms of gut microbiota in diabetic nephropathy

Diabetic nephropathy is a common complication of diabetes and a considerable contributor to end-stage renal disease. Evidence indicates that glucose dysregulation and lipid metabolism comprise a pivotal pathogenic mechanism in diabetic nephropathy. However, current treatment outcomes are limited, as they only provide symptomatic relief without preventing disease progression. The gut microbiota is a group of microorganisms that inhabit the human intestinal tract and play a crucial role in maintaining host energy balance, metabolism, and immune activity. Patients with diabetic nephropathy exhibit altered gut microbiota, suggesting its potential involvement in the onset and progression of the disease. However, how a perturbed microbiota induces and promotes diabetic nephropathy remains unelucidated. This article summarizes the evidence of the impact of gut microbiota on the progression of diabetic nephropathy, with a particular focus on the molecular mechanisms involved, aiming to provide new insights into the treatment of diabetic nephropathy.

Association of Serum Trimethylamine-N-Oxide Concentration from Childhood to Early Adulthood with Age and Sex

BACKGROUND

Primary prevention is the cornerstone of cardiometabolic health. In the randomized, controlled Special Turku Coronary Risk Factor Intervention Project (STRIP), dietary counseling intervention was given to children from infancy to 20 years of age and a follow-up was completed at age 26 years. We investigated the associations of age, sex, gut microbiome, and dietary intervention with the gut metabolite and the cardiac biomarker trimethylamine-N-oxide (TMAO).

METHODS

Overall, 592 healthy participants (females 46%) from STRIP were investigated. Compared to the control group, the intervention group had received dietary counseling between ages 7 months and 20 years focused on low intakes of saturated fat and cholesterol and the promotion of fruit, vegetable, and whole-grain consumption. TMAO serum concentrations were measured by a liquid chromatography-tandem mass spectrometry method at ages 11, 13, 15, 17, 19, and 26 years. Microbiome composition was assessed using 16S rRNA gene sequencing at 26 years of age.

RESULTS

TMAO concentrations increased from age 11 to 26 years in both sexes. At all measurement time points, males showed significantly higher serum TMAO concentrations compared to females, but concentrations were similar between the intervention and control groups. A direct association between TMAO concentrations and reported fiber intake was found in females. Gut microbiome analysis did not reveal associations with TMAO.

CONCLUSIONS

TMAO concentration increased from childhood to early adulthood but was not affected by the given dietary intervention. In females, TMAO concentrations could be directly associated with higher fiber intake suggesting sex-specific differences in TMAO metabolism.

From Gut to Brain: Unraveling the Intricate Link Between Microbiome and Stroke

Stroke, a neurological disorder, is intricately linked to the gut microbiota, influencing microbial composition and elevating the risk of ischemic stroke. The neuroprotective impact of short-chain fatty acids (SCFAs) derived from dietary fiber fermentation contrasts with the neuroinflammatory effects of lipopolysaccharide (LPS) from gut bacteria. The pivotal role of the gut-brain axis, facilitating bidirectional communication between the gut and the brain, is crucial in maintaining gastrointestinal equilibrium and influencing cognitive functions. An in-depth understanding of the interplay among the gut microbiota, immune system, and neurological outcomes in stroke is imperative for devising innovative preventive and therapeutic approaches. Strategies such as dietary adjustments, probiotics, prebiotics, antibiotics, or fecal transplantation offer promise in modulating stroke outcomes. Nevertheless, comprehensive research is essential to unravel the precise mechanisms governing the gut microbiota's involvement in stroke and to establish effective therapeutic interventions. The initiation of large-scale clinical trials is warranted to assess the safety and efficacy of interventions targeting the gut microbiota in stroke management. Tailored strategies that reinstate eubiosis and foster a healthy gut microbiota hold potential for both stroke prevention and treatment. This review underscores the gut microbiota as a promising therapeutic target in stroke and underscores the need for continued research to delineate its precise role and develop microbiome-based interventions effectively.

Association of serum trimethylamine N-oxide levels and bone mineral density in type 2 diabetes mellitus

PURPOSE

The relationship between trimethylamine N-oxide (TMAO) and bone mineral density (BMD) in type 2 diabetes mellitus (T2DM) is unclear. We explore the relationship between TMAO levels and BMD in T2DM.

METHODS

This is a cross-sectional study. 254 T2DM patients were enrolled and divided into three groups by TMAO tertiles, and the clinical data were collected. BMD was determined by dual-energy X-ray absorptiometry (DXA) and serum TMAO levels was determined by stable isotope dilution high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS).

RESULTS

Patients in the highest tertile of TMAO levels (TMAO > 6.72 μmol/L) showed relatively low BMD and a higher number of fracture history, osteoporosis (OP) than those in the lower tertiles. Spearman correlation analysis showed that serum TMAO was negatively correlated with BMD of whole body (WB), lumbar spine (LS) and femoral neck (FN), while TMAO was positive correlated with osteoporotic fracture (p < 0.05). Logistic regression models showed that TMAO was an independent influencing factor of fracture history after adjusting for confounders in TMAO > 6.72 μmol/L group.

CONCLUSIONS

There is a significant linear correlation between TMAO levels and BMD in T2DM patients. Especially in TMAO > 6.72 μmol/L group, TMAO was negatively correlated with WB, LS, and FN BMD, and was positive correlated with osteoporotic fracture in T2DM patients. The findings suggest that elevated TMAO levels are associated with OP and osteoporotic fracture in T2DM patients.

The Gut Microbial Metabolite Trimethylamine N -oxide, Incident CKD, and Kidney Function Decline

Key Points

In community-based US adults, higher plasma trimethylamine N -oxide levels associated with higher risk of incident CKD and greater rate of kidney function decline. Findings from our study support future clinical trials to examine whether lowering plasma trimethylamine N -oxide levels may prevent CKD development and progression.

Background

Trimethylamine N -oxide (TMAO) is a gut microbiota–derived metabolite of dietary phosphatidylcholine and carnitine. Experimentally, TMAO causes kidney injury and tubulointerstitial fibrosis. Little is known about prospective associations between TMAO and kidney outcomes, especially incident CKD. We hypothesized that higher plasma TMAO levels would be associated with higher risk of incident CKD and greater rate of kidney function decline.

Methods

We included 10,564 participants from two community-based, prospective cohorts with eGFR ≥60 ml/min per 1.73 m2 to assess incident CKD. TMAO was measured using targeted mass spectrometry at baseline and one follow-up visit. Creatinine and cystatin C were measured up to four times during follow-up and used to compute eGFR. Incident CKD was defined as an eGFR decline ≥30% from baseline and a resulting eGFR <60 ml/min per 1.73 m2. Time-varying Cox models assessed the association of serial TMAO measures with incident CKD, adjusting for sociodemographic, lifestyle, diet, and cardiovascular disease risk factors. Linear mixed models assessed the association with annualized eGFR change in 10,009 participants with at least one follow-up eGFR measure without exclusions for baseline eGFR levels.

Results

During a median follow-up of 9.4 years (interquartile range, 9.1–11.6 years), 979 incident CKD events occurred. Higher TMAO levels were associated with higher risk of incident CKD (second to fifth versus first quintile hazard ratio [95% confidence interval]=1.65 [1.22 to 2.23], 1.68 [1.26 to 2.25], 2.28 [1.72 to 3.02], and 2.24 [1.68 to 2.98], respectively) and greater annualized eGFR decline (second to fifth versus first quintile annualized eGFR change=−0.21 [−0.32 to −0.09], −0.17 [−0.29 to −0.05], −0.35 [−0.47 to −0.22], and −0.43 [−0.56 to −0.30] ml/min per 1.73 m2, respectively) with monotonic dose–response relationships. These associations were consistent across different racial/ethnic groups examined. The association with eGFR decline was similar to or larger than that seen for established CKD risk factors, including diabetes, per 10 mm Hg of higher systolic BP, per 10 years of older age, and Black race.

Conclusions

In community-based US adults, higher serial measures of plasma TMAO were associated with higher risk of incident CKD and greater annualized kidney function decline.

Multi-trajectories of body mass index, waist circumference, gut microbiota, and incident dyslipidemia: a 27-year prospective study

Background

Evidence is insufficient to establish a longitudinal association between combined trajectories of body mass index (BMI) and waist circumference (WC) and dyslipidemia. Our study aimed to explore the association between multi-trajectories of BMI and WC and incident dyslipidemia and identify microbiota and metabolite signatures of these trajectories.

Methods

Stratified by sex, we used a group-based trajectory modeling approach to identify distinct multi-trajectories of BMI and WC among 10,678 participants from the China Health and Nutrition Survey over a 24-year period. For each sex, we examined the associations between these multi-trajectories (1991-2015) and the onset dyslipidemia (2018) using multivariable logistic regression adjusting for sociodemographic and lifestyles factors. We characterized the gut microbial composition and performed LASSO and logistic regression to identify gut microbial signatures associated with these multi-trajectories in males and females, respectively.

Results

We identified four multi-trajectories of BMI and WC among both males and females: Normal (Group 1), BMI&WC normal increasing (Group 2), BMI&WC overweight increasing (Group 3), and BMI&WC obesity increasing (Group 4). Among males, Group 2 (OR: 2.10, 95% CI: 1.28-3.46), Group 3 (OR: 2.69, 95% CI: 1.56-4.63) and Group 4 (OR: 3.56, 95% CI: 1.85-6.83) had higher odds of developing dyslipidemia. However, among females, only those in Group 2 (OR: 1.54, 95% CI: 1.03-2.30) were more likely to develop dyslipidemia. In males, compared with Group 1, we observed lower alpha-diversity within Groups 2,3, and 4, and significant beta-diversity differences within Groups 3 and 4 (p 0.001). We also identified 3, 8, and 4 characteristic bacterial genera in male Groups 2, 3 and 4, and 2 genera in female Group 2. A total of 23, 25 and 10 differential metabolites were significantly associated with the above genera, except for Group 2 in males.

Conclusions

The ascending combined trajectories of BMI and WC are associated with a higher risk of dyslipidemia, even with normal baseline levels, especially in males. Shared and unique gut microbial and metabolic signatures among these high-risk trajectories could enhance our understanding of the mechanisms connecting obesity to dyslipidemia.

Specific gut microbiome and metabolome changes in patients with continuous ambulatory peritoneal dialysis and comparison between patients with different dialysis vintages

Background

In recent years, the role of gut microbiota and derived metabolites in renal disease has attracted more attention. It has been established that the gut microbiota is a potential target for medical interventions in renal disease including chronic kidney disease (CKD), acute kidney injury (AKI) and renal calculus. Emerging evidence has related dialysis treatment to the microbial composition and function of the intestines, and there are many reports related to HD, but few studies have been related to PD. Previous studies have found that PD patients have intestinal flora disturbances, so we speculate that intestinal flora and its metabolites may be the regulatory factors in long-term therapy of PD. And as far as we know, there have been no studies characterized the gut microbiota in PD patients of different dialysis vintages.

Methods

It is a cross-sectional study based on clinical data and biological samples of 72 patients with CAPD, 13 patients with ESRD and 13 healthy volunteers. The intestinal microecological characteristics of CAPD patients were comprehensively evaluated by combining the intestinal microflora structure, enterotoxin and receptor (serum LPS and LBP), intestinal barrier function index (serum D-Lactate), intestinal uremic toxin (serum IS, PCS, TMAO), fecal SCFAs and other multi-dimensional and multi-omics studies. Furthermore, the changes of intestinal microecology in CAPD patients of different dialysis vintages (≥ 3 and < 12 months, ≥ 12 and < 24 months, ≥ 24 and < 60 months, ≥ 60 months) were further explored, and the correlations between intestinal microecology indicators and some clinical indicators were analyzed. Fecal and serum samples were collected from PD patients (PD group, n = 72), ESRD patients (ESRD group, n = 13) and healthy volunteers (Normal group, n = 13). Fecal samples were subjected to microbiome (16S rDNA) and SCFA (GC-MS) analyses. Serum samples were subjected to LPS, LBP, D-lactate, IS, PCS, and TMAO (ELISA) analyses.

Results

The diversity and richness of intestinal flora in CAPD patients were lower than those in healthy people and ESRD patients, and the microflora structure was different. Anaerobes of Blautia and facultative anaerobes and aerobic bacteria with Bacilli and Lactobacillales those in Firmicutes are the main intestinal flora in CAPD patients. The abundance of Bacteroidaceae, Bacteroides, Faecalibacterium and other dominant bacteria in the intestinal tract of CAPD patients decreased. Proteobacteria, Enterobacteriaceae and Escherichia-Shigella increased their colonization (LDA > 4). In CAPD patients of different dialysis vintages, there was no significant change in the diversity and richness of microflora, and the microflora structure of PDC group was significantly different from that of PDD, which the abnormal expansion of enterobacter group was more prominent in PDC and the abundance of Bacteroides group was relatively higher in PDD. Intestinal barrier damage, intestinal uremic toxin accumulation and short-chain fatty acid reduction were observed in CAPD patients, such as the serum level of D-Lactate, PCS and TMAO were significantly higher than that in the Normal group (P < 0.05),and the fecal levels of BA and CA were significantly lower (P < 0.05). The intestinal microecological disorder of PDC group, while that of PDD group showed a better trend. Such as the PDC group had a significantly higher serum level of LPS, D-Lactate and TMAO (P < 0.01), and significantly lower serum level of LBP (P < 0.01), and lower fecal levels of AA and BA (P > 0.05) than the PDD group.

Conclusion

The intestinal microecology and metabolic system of CAPD patients had changes compared with healthy people and ESRD non-dialysis patients, and there were differences in CAPD patients with different dialysis vintages. PD patients on dialysis for more than 60 months showed a better trend in the intestinal microecology than patients with 24∼36 months, which suggested that the intestinal microecology of PD patients had a certain ability of self-regulation and remodeling under the management of standardized system and it is necessary to strengthen the monitoring of the intestinal status and the occurrence of related complications in PD patients on dialysis of 24∼36 months of dialysis vintage. It is initially considered that the mechanism of intestinal microecology is a potential target for intervention in the diagnosis and treatment of CAPD and incorporating intestinal microecosystem monitoring into the long-term management of CAPD patients is a new strategy.

Trimethylamine-N-oxide (TMAO) and basic fibroblast growth factor (bFGF) are possibly involved in corticosteroid resistance in adult patients with immune thrombocytopenia

PURPOSE

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by accelerated platelet clearance. Gut dysbiosis was associated with its pathogenesis, but the underlying mechanisms have not been fully elucidated. Patients with ITP exhibit varying degrees of responsiveness to corticosteroid treatment. Therefore, prognostic indexes for corticosteroid responsiveness in ITP could offer valuable guidance for clinical practices.

METHODS

The present study examined the signature of six types of gut-microbiota metabolites and forty-eight types of cytokines, chemokines, and growth factors and their clinical significance in patients with ITP.

RESULTS

Both patients with good and poor corticosteroid responsiveness exhibited significantly elevated/suppressed secretion of twenty-two cyto(chemo)kins/growth factors in comparison to healthy controls. Additionally, patients with ITP demonstrated a significant decrease in plasma levels of trimethylamine-N-oxide (TMAO), which was found to be negatively correlated to circulating platelet counts, and positively correlated with Interleukin (IL)-1β and IL-18. Notably, patients who exhibited poor response to corticosteroid treatment displayed elevated levels of TMAO and basic fibroblast growth factor (bFGF) in comparison to responders. Additionally, we found that the amalgamation of TMAO, bFGF and interleukin (IL)-13 could serve as a valuable prognostic tool for predicting CS responsiveness.

CONCLUSION

Patients with ITP were characterized overall by an imbalanced secretion of cyto(cheo)kins/growth factors and inadequate levels of TMAO. The varying degrees of responsiveness to corticosteroid treatment can be attributed to different profiles of basic FGF and TMAO that might be related to overburdened oxidative stress and inflammasome overactivation, and ultimately mediate corticosteroid resistance.

Trimethylamine N-oxide and kidney diseases: what do we know?

In the human gut, there is a metabolically active microbiome whose metabolic products reach various organs and are used in the physiological activities of the body. When dysbiosis of intestinal microbial homeostasis occurs, pathogenic metabolites may increase and one of them is trimethyl amine-N-oxide (TMAO). TMAO is thought to have a role in the pathogenesis of insulin resistance, diabetes, hyperlipidemia, atherosclerotic heart diseases, and cerebrovascular events. TMAO level is also associated with renal inflammation, fibrosis, acute kidney injury, diabetic kidney disease, and chronic kidney disease. In this review, the effect of TMAO on various kidney diseases is discussed.

The potential mechanism of gut microbiota-microbial metabolites-mitochondrial axis in progression of diabetic kidney disease

Diabetic kidney disease (DKD), has become the main cause of end-stage renal disease (ESRD) worldwide. Lately, it has been shown that the onset and advancement of DKD are linked to imbalances of gut microbiota and the abnormal generation of microbial metabolites. Similarly, a body of recent evidence revealed that biological alterations of mitochondria ranging from mitochondrial dysfunction and morphology can also exert significant effects on the occurrence of DKD. Based on the prevailing theory of endosymbiosis, it is believed that human mitochondria originated from microorganisms and share comparable biological characteristics with the microbiota found in the gut. Recent research has shown a strong correlation between the gut microbiome and mitochondrial function in the occurrence and development of metabolic disorders. The gut microbiome's metabolites may play a vital role in this communication. However, the relationship between the gut microbiome and mitochondrial function in the development of DKD is not yet fully understood, and the role of microbial metabolites is still unclear. Recent studies are highlighted in this review to examine the possible mechanism of the gut microbiota-microbial metabolites-mitochondrial axis in the progression of DKD and the new therapeutic approaches for preventing or reducing DKD based on this biological axis in the future.

Depiction of Branched-Chain Amino Acids (BCAAs) in Diabetes with a Focus on Diabetic Microvascular Complications

Type 2 diabetes mellitus (T2DM) still holds the title as one of the most debilitating chronic diseases with rising prevalence and incidence, including its complications such as retinal, renal, and peripheral nerve disease. In order to develop novel molecules for diagnosis and treatment, a deep understanding of the complex molecular pathways is imperative. Currently, the existing agents for T2DM treatment target only blood glucose levels. Over the past decades, specific building blocks of proteins-branched-chain amino acids (BCAAs) including leucine, isoleucine, and valine-have gained attention because they are linked with insulin resistance, pre-diabetes, and diabetes development. In this review, we discuss the hypothetical link between BCAA metabolism, insulin resistance, T2DM, and its microvascular complications including diabetic retinopathy and diabetic nephropathy. Further research on these amino acids and their derivates may eventually pave the way to novel biomarkers or therapeutic concepts for the treatment of diabetes and its accompanied complications.

Precision Medicine and/or Biomarker Based Therapy in T2DM: Ready for Prime Time?

Approximately 30-40% of people with type 2 diabetes mellitus develop chronic kidney disease. This is characterised by elevated blood pressure, declining kidney function and enhanced cardiovascular morbidity and mortality. Increased albuminuria and decreasing estimated glomerular function has to be evaluated regularly to diagsnose kidney disease. New biomarkers may facilitate early diagnosis and provide infomation on undlying pathology thereby supporting early precision intervention for the optimal benefit. A number of biomarkers have been suggested but are not yet implemented in clinical practice. iI the future such bimarkers may pave the way for personalized treatment.

Trimethylamine N-oxide: role in cell senescence and age-related diseases

INTRODUCTION

Hayflick and Moorhead first demonstrated cell senescence as the irreversible growth arrest of cells after prolonged cultivation. Telomere shortening and oxidative stress are the fundamental mechanisms that drive cell senescence. Increasing studies have shown that TMAO is closely associated with cellular aging and age-related diseases. An emerging body of evidence from animal models, especially mice, has identified that TMAO contributes to senescence from multiple pathways and appears to accelerate many neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. However, the specific mechanism of how TMAO speeds aging is still not completely clear.

MATERIAL AND METHODS

In this review, we summarize some key findings in TMAO, cell senescence, and age-related diseases. We focused particular attention on the potential mechanisms for clinical transformation to find ways to interfere with the aging process.

CONCLUSION

TMAO can accelerate cell senescence by causing mitochondrial damage, superoxide formation, and promoting the generation of pro-inflammatory factors.

Phenylacetyl glutamine: a novel biomarker for stroke recurrence warning

BACKGROUND

Stroke is the second leading cause of disease-related death and the third leading cause of disability worldwide. However, how to accurately warn of stroke onset remains extremely challenging. Recently, phenylacetyl glutamine (PAGln) has been implicated in the onset of stroke, but evidences from cohort studies of onset are lacking, especially in patients with first-onset or recurrent. It is necessary to deeply demonstrate the effectiveness of PAGln level on warning stroke onset.

METHODS

One hundred fifteen first onset stroke patients, 33 recurrent stroke patients, and 135 non-stroke controls were included in the analysis. Risk factors associated with stroke attacking were evaluated, and plasma PAGln levels were detected via HPLC-MS based method. LASSO regression, Pearson correlation analysis, and univariate analysis were carried out to demonstrate the associations between PAGln levels and risk factors of stroke. Random forest machine learning algorithm was used to build classification models to achieve the distinction of first-onset stroke patients, recurrent stroke patients, and non-stroke controls, and further demonstrate the contribution of PAGln levels in the distinction of stroke onset.

RESULTS

The median level of PAGln in the first-onset stroke group, recurrent stroke group, and non-stroke group was 933 ng/mL, 1014 ng/mL, and 556 ng/mL, respectively. No statistical correlation was found between PAGln level and subject's living habits, eating preferences, and concomitant diseases (hypertension, hyperlipidemia, and diabetes). Stroke severity indicators, mainly age and NIHSS score, were found associate with the PAGln levels. Machine learning classification models confirmed that PAGln levels, as the main contributing variable, could be used to distinguish recurrent stroke patients (but not first-onset stroke patients) from non-stroke controls.

CONCLUSION

PAGln may be an effective indicator to monitor the recurrence in stroke patients.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Atherosclerotic patients with diabetes mellitus may break through the threshold of healthy TMAO levels formed by long-term statins therapy

Background

Cardiovascular disease (CVD) is the leading course of disease-related death in both developed and developing countries. Atherosclerosis is main pathology of CVD, and its severity is thought to be related to trimethylamine N-oxide (TMAO) level in plasma. Therefore, it is necessary to deeply understand the synergistic patterns between TMAO and other contribution variables to atherosclerosis, allowing for effective and timely monitoring or intervention.

Methods

A total of 359 participants were recruited in our study, including 190 atherosclerosis patients, 82 MI or stroke patients, 68 non-atherosclerosis controls and 19 healthy controls. Information on their risk associated with atherosclerosis and plasma TMAO concentration were collected. LASSO regression, multivariate analysis and univariate analysis were then performed to confirm the correlation between TMAO level and risk factors of atherosclerosis.

Results

Compared to patients and non-atherosclerosis controls, healthy participants had a normal BMI range (lower than 24), lower triglyceride concentration, and healthy lifestyle habits (no smoking and low salt diet). However, under backgrounds of statins treatment and balanced dietary preferences, TMAO levels were not significantly different among patients, non-atherosclerosis controls and healthy controls. Using LASSO regression model, four indicators was identified to have contribution to TMAO levels, including diabetes, atherosclerosis, low-density lipoprotein and total cholesterol. Subsequent univariate analysis further confirmed that the presence or absence of diabetes had a decisive effect on patients' plasma TMAO levels, even though they had been taking statin lipid-lowering drugs for a long time.

Conclusion

Diabetics have abnormally high plasma TMAO levels even under continuous statins treatment, which may contribute to the development and progression of atherosclerosis. Therefore, it is necessary to focus on monitoring TMAO levels in diabetic patients to reduce adverse cardiovascular events in diabetic patients.

Gut microbiota and its metabolites - molecular mechanisms and management strategies in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major microvascular complications of diabetes mellitus and is also one of the serious risk factors in cardiovascular events, end-stage renal disease, and mortality. DKD is associated with the diversified, compositional, and functional alterations of gut microbiota. The interaction between gut microbiota and host is mainly achieved through metabolites, which are small molecules produced by microbial metabolism from exogenous dietary substrates and endogenous host compounds. The gut microbiota plays a critical role in the pathogenesis of DKD by producing multitudinous metabolites. Nevertheless, detailed mechanisms of gut microbiota and its metabolites involved in the occurrence and development of DKD have not been completely elucidated. This review summarizes the specific classes of gut microbiota-derived metabolites, aims to explore the molecular mechanisms of gut microbiota in DKD pathophysiology and progression, recognizes biomarkers for the screening, diagnosis, and prognosis of DKD, as well as provides novel therapeutic strategies for DKD.

The gut microbial metabolite trimethylamine N-oxide and cardiovascular diseases

Morbidity and mortality of cardiovascular diseases (CVDs) are exceedingly high worldwide. Researchers have found that the occurrence and development of CVDs are closely related to intestinal microecology. Imbalances in intestinal microecology caused by changes in the composition of the intestinal microbiota will eventually alter intestinal metabolites, thus transforming the host physiological state from healthy mode to pathological mode. Trimethylamine N-oxide (TMAO) is produced from the metabolism of dietary choline and L-carnitine by intestinal microbiota, and many studies have shown that this important product inhibits cholesterol metabolism, induces platelet aggregation and thrombosis, and promotes atherosclerosis. TMAO is directly or indirectly involved in the pathogenesis of CVDs and is an important risk factor affecting the occurrence and even prognosis of CVDs. This review presents the biological and chemical characteristics of TMAO, and the process of TMAO produced by gut microbiota. In particular, the review focuses on summarizing how the increase of gut microbial metabolite TMAO affects CVDs including atherosclerosis, heart failure, hypertension, arrhythmia, coronary artery disease, and other CVD-related diseases. Understanding the mechanism of how increases in TMAO promotes CVDs will potentially facilitate the identification and development of targeted therapy for CVDs.

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.

Four missense genetic variants in CUBN are associated with higher levels of eGFR in non-diabetes but not in diabetes mellitus or its subtypes: A genetic association study in Europeans

AIM

Rare genetic variants in the CUBN gene encoding the main albumin-transporter in the proximal tubule of the kidneys have previously been associated with microalbuminuria and higher urine albumin levels, also in diabetes. Sequencing studies in isolated proteinuria suggest that these variants might not affect kidney function, despite proteinuria. However, the relation of these CUBN missense variants to the estimated glomerular filtration rate (eGFR) is largely unexplored. We hereby broadly examine the associations between four CUBN missense variants and eGFR_creatinine in Europeans with Type 1 (T1D) and Type 2 Diabetes (T2D). Furthermore, we sought to deepen our understanding of these variants in a range of single- and aggregate- variant analyses of other kidney-related traits in individuals with and without diabetes mellitus.

METHODS

We carried out a genetic association-based linear regression analysis between four CUBN missense variants (rs141640975, rs144360241, rs45551835, rs1801239) and eGFR_creatinine (ml/min/1.73 m², CKD-EPI_{creatinine(2012)}, natural log-transformed) in populations with T1D (n ~ 3,588) or T2D (n ~ 31,155) from multiple European studies and in individuals without diabetes from UK Biobank (UKBB, n ~ 370,061) with replication in deCODE (n = 127,090). Summary results of the diabetes-group were meta-analyzed using the fixed-effect inverse-variance method.

RESULTS

Albeit we did not observe associations between eGFR_creatinine and CUBN in the diabetes-group, we found significant positive associations between the minor alleles of all four variants and eGFR_creatinine in the UKBB individuals without diabetes with rs141640975 being the strongest (Effect=0.02, P_{eGFR_creatinine}=2.2 × 10^-9). We replicated the findings for rs141640975 in the Icelandic non-diabetes population (Effect=0.026, P_{eGFR_creatinine}=7.7 × 10^-4). For rs141640975, the eGFR_creatinine-association showed significant interaction with albuminuria levels (normo-, micro-, and macroalbuminuria; p = 0.03). An aggregated genetic risk score (GRS) was associated with higher urine albumin levels and eGFR_creatinine. The rs141640975 variant was also associated with higher levels of eGFR_{creatinine-cystatin C} (ml/min/1.73 m², CKD-EPI₂₀₂₁, natural log-transformed) and lower circulating cystatin C levels.

CONCLUSIONS

The positive associations between the four CUBN missense variants and eGFR in a large population without diabetes suggests a pleiotropic role of CUBN as a novel eGFR-locus in addition to it being a known albuminuria-locus. Additional associations with diverse renal function measures (lower cystatin C and higher eGFR_{creatinine-cystatin C} levels) and a CUBN-focused GRS further suggests an important role of CUBN in the future personalization of chronic kidney disease management in people without diabetes.

High-risk genotypes for type 1 diabetes are associated with the imbalance of gut microbiome and serum metabolites

Background

The profile of gut microbiota, serum metabolites, and lipids of type 1 diabetes (T1D) patients with different human leukocyte antigen (HLA) genotypes remains unknown. We aimed to explore gut microbiota, serum metabolites, and lipids signatures in individuals with T1D typed by HLA genotypes.

Methods

We did a cross-sectional study that included 73 T1D adult patients. Patients were categorized into two groups according to the HLA haplotypes they carried: those with any two of three susceptibility haplotypes (DR3, DR4, DR9) and without any of the protective haplotypes (DR8, DR11, DR12, DR15, DR16) were defined as high-risk HLA genotypes group (HR, n=30); those with just one or without susceptibility haplotypes as the non-high-risk HLA genotypes group (NHR, n=43). We characterized the gut microbiome profile with 16S rRNA gene amplicon sequencing and analyzed serum metabolites with liquid chromatography-mass spectrometry.

Results

Study individuals were 32.5 (8.18) years old, and 60.3% were female. Compared to NHR, the gut microbiota of HR patients were characterized by elevated abundances of Prevotella copri and lowered abundances of Parabacteroides distasonis. Differential serum metabolites (hypoxanthine, inosine, and guanine) which increased in HR were involved in purine metabolism. Different lipids, phosphatidylcholines and phosphatidylethanolamines, decreased in HR group. Notably, Parabacteroides distasonis was negatively associated (p ≤ 0.01) with hypoxanthine involved in purine metabolic pathways.

Conclusions

The present findings enabled a better understanding of the changes in gut microbiome and serum metabolome in T1D patients with HLA risk genotypes. Alterations of the gut microbiota and serum metabolites may provide some information for distinguishing T1D patients with different HLA risk genotypes.

The modulation of gut microbiota by herbal medicine to alleviate diabetic kidney disease - A review

The treatment of diabetic kidney disease (DKD) has been the key concern of the medical community. Herbal medicine has been reported to alleviate intestinal dysbiosis, promote the excretion of toxic metabolites, and reduce the secretion of uremic toxins. However, the current understanding of the modulation of the gut microbiota by herbal medicine to delay the progression of DKD is still insufficient. Consequently, we reviewed the knowledge based on peer-reviewed English-language journals regarding regulating gut microbiota by herbal medicines in DKD. It was found that herbal medicine or their natural extracts may have the following effects: modulating the composition of intestinal flora, particularly Akkermansia, Lactobacillus, and Bacteroidetes, as well as adjusting the F/B ratio; increasing the production of SCFAs and restoring the intestinal barrier; reducing the concentration of uremic toxins (p-cresol sulfate, indole sulfate, TMAO); inhibiting inflammation and oxidative stress.

Therapeutic mechanism and clinical application of Chinese herbal medicine against diabetic kidney disease

Diabetic kidney disease (DKD) is the major complications of type 1 and 2 diabetes, and is the predominant cause of chronic kidney disease and end-stage renal disease. The treatment of DKD normally consists of controlling blood glucose and improving kidney function. The blockade of renin-angiotensin-aldosterone system and the inhibition of sodium glucose cotransporter 2 (SGLT2) have become the first-line therapy of DKD, but such treatments have been difficult to effectively block continuous kidney function decline, eventually resulting in kidney failure and cardiovascular comorbidities. The complex mechanism of DKD highlights the importance of multiple therapeutic targets in treatment. Chinese herbal medicine (active compound, extract and formula) synergistically improves metabolism regulation, suppresses oxidative stress and inflammation, inhibits mitochondrial dysfunction, and regulates gut microbiota and related metabolism via modulating GLP-receptor, SGLT2, Sirt1/AMPK, AGE/RAGE, NF-κB, Nrf2, NLRP3, PGC-1α, and PINK1/Parkin pathways. Clinical trials prove the reliable evidences for Chinese herbal medicine against DKD, but more efforts are still needed to ensure the efficacy and safety of Chinese herbal medicine. Additionally, the ideal combined therapy of Chinese herbal medicine and conventional medicine normally yields more favorable benefits on DKD treatment, laying the foundation for novel strategies to treat DKD.

Role of the Gut Microbiome in Diabetes and Cardiovascular Diseases Including Restoration and Targeting Approaches- A Review

Metabolic diseases, including cardiovascular diseases (CVD) and diabetes, have become the leading cause of morbidity and mortality worldwide. Gut microbiota appears to play a vital role in human disease and health, according to recent scientific reports. The gut microbiota plays an important role in sustaining host physiology and homeostasis by creating a cross-talk between the host and microbiome via metabolites obtained from the host's diet. Drug developers and clinicians rely heavily on therapies that target the microbiota in the management of metabolic diseases, and the gut microbiota is considered the biggest immune organ in the human body. They are highly associated with intestinal immunity and systemic metabolic disorders like CVD and diabetes and are reflected as potential therapeutic targets for the management of metabolic diseases. This review discusses the mechanism and interrelation between the gut microbiome and metabolic disorders. It also highlights the role of the gut microbiome and microbially derived metabolites in the pathophysiological effects related to CVD and diabetes. It also spotlights the reasons that lead to alterations of microbiota composition and the prominence of gut microbiota restoration and targeting approaches as effective treatment strategies in diabetes and CVD. Future research should focus onunderstanding the functional level of some specific microbial pathways that help maintain physiological homeostasis, multi-omics, and develop novel therapeutic strategies that intervene with the gut microbiome for the prevention of CVD and diabetes that contribute to a patient's well-being.

Increased plasma trimethylamine-N-oxide levels are associated with mild cognitive impairment in high cardiovascular risk elderly population

Trimethylamine-N-oxide (TMAO) has been shown to be associated with cardiovascular (CV) disease and cognitive impairment. The association between early stages of cognitive impairment and TMAO in a high CV risk population has not been previously investigated. This study aimed to investigate the association between the plasma TMAO level and cognitive function in a population with a high risk of CV disease. Participants at a high risk of CV were included. The cognition was evaluated using the Montreal Cognitive Assessment. A score lower than 25 out of 30 was used to indicate mild cognitive impairment (MCI). Blood samples of all participants (n = 233) were collected to measure the plasma levels of TMAO and other metabolic parameters, including fasting blood sugar and lipid profiles. Logistic regression was used to evaluate the association between MCI and high plasma TMAO levels, adjusted for confounding factors. Of 233 patients, the mean age of patients in this study was 64 years old (SD 8.4). The median TMAO level was 4.31 μM (IQR 3.95). The high TMAO level was an independent risk factor of MCI (aOR 2.36, 95% CI 1.02 to 5.47; p 0.046), when adjusted for age, gender, health care service scheme, smoking history, metabolic syndrome, and history of established CV events. The high TMAO level was associated with MCI, after adjustment for potential confounding factors. These findings demonstrate that plasma TMAO levels can serve for target prediction as an independent risk factor for MCI in this population.

The role and mechanisms of gut microbiota in diabetic nephropathy, diabetic retinopathy and cardiovascular diseases

Type 2 diabetes mellitus (T2DM) and T2DM-related complications [such as retinopathy, nephropathy, and cardiovascular diseases (CVDs)] are the most prevalent metabolic diseases. Intriguingly, overwhelming findings have shown a strong association of the gut microbiome with the etiology of these diseases, including the role of aberrant gut bacterial metabolites, increased intestinal permeability, and pathogenic immune function affecting host metabolism. Thus, deciphering the specific microbiota, metabolites, and the related mechanisms to T2DM-related complications by combined analyses of metagenomics and metabolomics data can lead to an innovative strategy for the treatment of these diseases. Accordingly, this review highlights the advanced knowledge about the characteristics of the gut microbiota in T2DM-related complications and how it can be associated with the pathogenesis of these diseases. Also, recent studies providing a new perspective on microbiota-targeted therapies are included.

Plasmatic trimethylamine N-oxide and its relation to stroke: A systematic review and dose-response meta-analysis

BACKGROUND

Elevated circulating concentrations of the gut metabolite, trimethylamine N-oxide (TMAO), were found in patients who experienced stroke. However, it has not been reported whether a high level of TMAO is associated with a significantly increased risk of stroke. This study aimed to review the available scientific evidence about the relationship between TMAO levels and the risk of stroke in a dose-response meta-analysis.

METHODS

The PubMed, Embase, Cochrane library, and China National Knowledge Infrastructure databases were searched for studies starting from September 1996 to December 2020. Nine studies including 4402 subjects were reviewed in this study.

RESULTS

The results of meta-analysis showed that high levels of circulating TMAO were associated with an increased risk of stroke in patients in the random-effects model (odds ratio [OR], 1.64; 95% confidence interval [CI], 1.12-2.41; P = 0.047). The OR for the prevalence of stroke increased by 48% per 5-μmol/L increment (OR, 1.05; 95% CI, 1.16-1.78; P < 0.001) and by 132% per 10-μmol/L increment (OR, 2.32; 95% CI, 1.38-3.86; P < 0.001) in circulating TMAO concentration according to the dose-response meta-analysis.

CONCLUSION

There was a significant association between higher plasma TMAO concentrations and the risk of stroke. Further in-depth studies are warranted to validate this interaction and explore potential mechanisms.

THE INCREASED PLASMA LEVELS OF INTERMEDIN IN PATIENTS WITH TYPE 2 DIABETES MELLITUS

Context

Intermedin (IMD) is the member of calcitonin gene-related peptide family, and tightly associated with type 2 diabetes mellitus (T2DM). The change of plasma IMD levels in T2DM is still unknown.

Objective

We aimed to investigate the plasma levels of IMD in patients with T2DM.

Design

Fortyone patients with T2DM who were hospitalized in the endocrinology department of Civil Aviation General Hospital from January 2012 to June 2015 were enrolled, and 44 volunteers were selected as the control group.

Subjects and Methods

Plasma level of IMD was detected by ELISA. Diagnostic value of IMD was analyzed by area under the receiver operating characteristic (ROC) curve (AUC).

Results

The plasma level of IMD in T2DM group was higher than that in the healthy control group, whereas smoking or cardiovascular complications did no influence the IMD levels. IMD levels were correlated with BMI, DBP, triglyceride, uric acid, urea nitrogen, fasting and 2 hours postprandial blood glucose, and HbA1C. The greatest value of AUC for IMD was only 58.73%.

Conclusions

Although plasma levels of IMD were increased in patients with T2DM, the very low diagnostic value of IMD for T2DM might not be used for the disease diagnosis.

The heart and gut relationship: a systematic review of the evaluation of the microbiome and trimethylamine-N-oxide (TMAO) in heart failure

There is an expanding body of research on the bidirectional relationship of the human gut microbiome and cardiovascular disease, including heart failure (HF). Researchers are examining the microbiome and gut metabolites, primarily trimethylamine-N-oxide (TMAO), to understand clinically observed outcomes. This systematic review explored the current state of the science on the evaluation and testing of the gut biome in persons with HF. Using electronic search methods of Medline, Embase, CINAHL, and Web of Science, until December 2021, we identified 511 HF biome investigations between 2014 and 2021. Of the 30 studies included in the review, six were 16S rRNA and nineteen TMAO, and three both TMAO and 16S rRNA, and two bacterial cultures. A limited range of study designs were represented, the majority involving single cohorts (n = 10) and comparing individuals with HF to controls (n = 15). Patients with HF had less biodiversity in fecal samples compared to controls. TMAO is associated with age, BNP, eGFR, HF severity, and poor outcomes including hospitalizations and mortality. Inconsistent across studies was the ability of TMAO to predict HF development, the independent prognostic value of TMAO when controlling for renal indices, and the relationship of TMAO to LVEF and CRP. Gut microbiome dysbiosis is associated with HF diagnosis, disease severity, and prognostication related to hospitalizations and mortality. Gut microbiome research in patients with HF is developing. Further longitudinal and multi-centered studies are required to inform interventions to promote clinical decision-making and improved patient outcomes.

The Specific Alteration of Gut Microbiota in Diabetic Kidney Diseases—A Systematic Review and Meta-Analysis

Background

Emerging evidence indicates that gut dysbiosis is involved in the occurrence and development of diabetic kidney diseases (DKD). However, the key microbial taxa closely related to DKD have not been determined.

Methods

PubMed, Web of Science, Cochrane, Chinese Biomedical Databases, China National Knowledge Internet, and Embase were searched for case-control or cross-sectional studies comparing the gut microbiota of patients with DKD and healthy controls (HC) from inception to February 8, 2022, and random/fixed-effects meta-analysis on the standardized mean difference (SMD) were performed for alpha diversity indexes between DKD and HC, and beta diversity indexes and the relative abundance of gut microbiota were extracted and summarized qualitatively.

Results

A total of 16 studies (578 patients with DKD and 444 HC) were included. Compared to HC, the bacterial richness of patients with DKD was significantly decreased, and the diversity indexes were decreased but not statistically, companying with a distinct beta diversity. The relative abundance of phylum Proteobacteria, Actinobacteria, and Bacteroidetes, family Coriobacteriaceae, Enterobacteriaceae, and Veillonellaceae, genus Enterococcus, Citrobacter, Escherichia, Klebsiella, Akkermansia, Sutterella, and Acinetobacter, and species E. coli were enriched while that of phylum Firmicutes, family Lachnospiraceae, genus Roseburia, Prevotella, and Bifidobacterium were depleted in patients with DKD.

Conclusions

The gut microbiota of patients with DKD may possess specific features characterized by expansion of genus Escherichia, Citrobacter, and Klebsiella, and depletion of Roseburia, which may contribute most to the alterations of their corresponding family and phylum taxa, as well as the bacterial diversity and composition. These microbial taxa may be closely related to DKD and serve as promising targets for the management of DKD.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42021289863.

Characteristics of Serum Metabolites and Gut Microbiota in Diabetic Kidney Disease

Disturbance of circulating metabolites and disorders of the gut microbiota are involved in the progression of diabetic kidney disease (DKD). However, there is limited research on the relationship between serum metabolites and gut microbiota, and their involvement in DKD. In this study, using an experimental DKD rat model induced by combining streptozotocin injection and unilateral nephrectomy, we employed untargeted metabolomics and 16S rRNA gene sequencing to explore the relationship between the metabolic profile and the structure and function of gut microbiota. Striking alterations took place in 140 serum metabolites, as well as in the composition and function of rat gut microbiota. These changes were mainly associated with carbohydrate, lipid, and amino acid metabolism. In these pathways, isomaltose, D-mannose, galactonic acid, citramalic acid, and prostaglandin B2 were significantly upregulated. 3-(2-Hydroxyethyl)indole, 3-methylindole, and indoleacrylic acid were downregulated and were the critical metabolites in the DKD model. Furthermore, the levels of these three indoles were restored after treatment with the traditional Chinese herbal medicine Tangshen Formula. At the genera level, g_Eubacterium_nodatum_group, g_Lactobacillus, and g_Faecalibaculum were most involved in metabolic disorders in the progression of DKD. Notably, the circulating lipid metabolites had a strong relationship with DKD-related parameters and were especially negatively related to the mesangial matrix area. Serum lipid indices (TG and TC) and UACR were directly associated with certain microbial genera. In conclusion, the present research verified the anomalous circulating metabolites and gut microbiota in DKD progression. We also identified the potential metabolic and microbial targets for the treatment of DKD.

Gut microbiota-derived metabolite trimethylamine-N-oxide and multiple health outcomes: an umbrella review and updated meta-analysis

BACKGROUND

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite produced from dietary nutrients. Many studies have discovered that circulating TMAO concentrations are linked to a wide range of health outcomes.

OBJECTIVES

This study aimed to summarize health outcomes related to circulating TMAO concentrations.

METHODS

We searched the Embase, Medline, Web of Science, and Scopus databases from inception to 15 February, 2022 to identify and update meta-analyses examining the associations between TMAO and multiple health outcomes. For each health outcome, we estimated the summary effect size, 95% prediction CI, between-study heterogeneity, evidence of small-study effects, and evidence of excess-significance bias. These metrics were used to evaluate the evidence credibility of the identified associations.

RESULTS

This umbrella review identified 24 meta-analyses that investigated the association between circulating TMAO concentrations and health outcomes including all-cause mortality, cardiovascular diseases (CVDs), diabetes mellitus (DM), cancer, and renal function. We updated these meta-analyses by including a total of 82 individual studies on 18 unique health outcomes. Among them, 14 associations were nominally significant. After evidence credibility assessment, we found 6 (33%) associations (i.e., all-cause mortality, CVD mortality, major adverse cardiovascular events, hypertension, DM, and glomerular filtration rate) to present highly suggestive evidence.

CONCLUSIONS

TMAO might be a novel biomarker related to human health conditions including all-cause mortality, hypertension, CVD, DM, cancer, and kidney function. Further studies are needed to investigate whether circulating TMAO concentrations could be an intervention target for chronic disease.This review was registered at www.crd.york.ac.uk/prospero/ as CRD42021284730.

Increased Serum Trimethylamine N-Oxide Level in Type 2 Diabetic Patients with Mild Cognitive Impairment

PURPOSE

Trimethylamine N-oxide (TMAO) is a metabolite of phosphatidylcholine in red meat and other diets, which is associated with cardiovascular and other diseases. The aim of this study is to evaluate the associations of serum TMAO with mild cognitive impairment (MCI) in the Chinese type 2 diabetes mellitus (T2DM) population.

MATERIALS AND METHODS

A total of 253 hospitalized T2DM patients and 150 healthy controls were included in this cross-sectional study. Montreal Cognitive Assessment (MoCA) assessed the cognition function, and the 253 T2DM patients were divided into 74 subjects with MCI and 179 with non-MCI. Demographic data and biochemical test results were evaluated. Serum TMAO level was measured by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).

RESULTS

A higher serum TMAO level was observed in T2DM patients compared with the healthy controls (P < 0.001). Among all T2DM patients, the MCI group (n = 74) showed higher serum TMAO levels than the non-MCI group. Spearman correlation test showed that TMAO levels were significantly positively correlated with age (r = 0.147, P = 0.019), body mass index (BMI) (r = 0.153, P = 0.015), diabetes duration (r = 0.160, P = 0.011), HbA1c (r = 0.138, P = 0.029), triglyceride (TG) (r = 0.138, P = 0.029), creatinine (r = 0.184, p = 0.003), hs-CRP (r = 0.243, P < 0.001), and were negatively correlated with HDL-C (r = -0.144, P = 0.022), BDNF (r = -0.165, p = 0.009), and MoCA (r = -0.386, P < 0.001) score (all P < 0.05). Multivariable Logistic regression identified high serum TMAO level as a significant independent factor of MCI in the T2DM patients (OR = 1.404, 95% CI = 1.255-1.571; P < 0.001).

CONCLUSION

Our study showed that T2DM patients with MCI have elevated serum TMAO levels.

The Association of Plasma Trimethylamine N-Oxide with Coronary Atherosclerotic Burden in Patients with Type 2 Diabetes Among a Chinese North Population

PURPOSE

We aimed to examine the association between plasma trimethylamine N-oxide (TMAO), a gut microbial metabolite from dietary phosphatidylcholine, and coronary atherosclerotic burden in patients with type 2 diabetes (T2D).

METHODS

In total, 349 patients with T2D were studied, including 70 controls and 279 patients with coronary artery disease (CAD) by coronary angiography. Coronary atherosclerotic burden is quantified by the number of diseased coronary branches and SYNTAX (Synergy between PCI with Taxus and Cardiac Surgery) score. Plasma TMAO levels were determined by UHPLC-MS/MS technique.

RESULTS

The TMAO concentration was significantly higher in the patients with triple vessel disease (TVD) (3.33 [IQR: 1.81-6.65] μM) than those without TVD (2.62 [IQR: 1.50-4.73] μM) (P = 0.015). A similar difference was found between patients with SYNTAX score >22 (3.93 [IQR: 1.81-6.82] μM) and those with SYNTAX score ≤22 (2.54 [IQR: 1.44-4.54] μM) (P = 0.014). TMAO was not significantly correlated with the presence of CAD. Among patients with eGFR <60 mL/min/1.73 m², the highest tertile of TMAO was significantly associated with TVD (OR = 25.28, 95% CI [2.55-250.33], P = 0.006) and SYNTAX score >22 (OR = 7.23, 95% CI [1.51-34.64], P = 0.013) independent of known risk factors of CAD, compared with lower TMAO tertiles.

CONCLUSION

TMAO was not independently correlated with the presence of CAD and severity of coronary atherosclerosis in the included population. Nevertheless, the significant association between circulating TMAO and higher coronary atherosclerotic burden was observed in patients with eGFR of lower than 60 mL/min/1.73 m².

Sex-dependent effects on the gut microbiota and host metabolome in type 1 diabetic mice

Sexual dimorphism exists in the onset and development of type 1 diabetes (T1D), but its potential pathological mechanism is poorly understood. In the present study, we examined sex-specific changes in the gut microbiome and host metabolome of T1D mice via 16S rRNA gene sequencing and nuclear magnetic resonance (NMR)-based metabolomics approach, and aimed to investigate potential mechanism of the gut microbiota-host metabolic interaction in the sexual dimorphism of T1D. Our results demonstrate that female mice had a greater shift in the gut microbiota than male mice during the development of T1D; however, host metabolome was more susceptible to T1D in male mice. The correlation network analysis indicates that T1D-induced host metabolic changes may be regulated by the gut microbiota in a sex-specific manner, mainly involving short-chain fatty acids (SCFAs) metabolism, energy metabolism, amino acid metabolism, and choline metabolism. Therefore, our study suggests that sex-dependent "gut microbiota-host metabolism axis" may be implicated in the sexual dimorphism of T1D, and the link between microbes and metabolites might contribute to the prevention and treatment of T1D.

Gut microbiota: A potential therapeutic target for management of diabetic retinopathy?

Diabetic Retinopathy (DR) is one of the main complications of Diabetes Mellitus (DM), drastically impacting individuals of working age over the years, being one of the main causes of blindness in the world. The existing therapies for its treatment consist of measures that aim only to alleviate the existing clinical signs, associated with the microvasculature. These treatments are limited only to the advanced stages and not to the preclinical ones. In response to a treatment with little resolution and limited for many patients with DM, investigations of alternative therapies that make possible the improvement of the glycemic parameters and the quality of life of subjects with DR, become extremely necessary. Recent evidence has shown that deregulation of the microbiota (dysbiosis) can lead to low-grade, local and systemic inflammation, directly impacting the development of DM and its microvascular complications, including DR, in an axis called the intestine-retina. In this regard, the present review seeks to comprehensively describe the biochemical pathways involved in DR as well as the association of the modulation of these mechanisms by the intestinal microbiota, since direct changes in the microbiota can have a drastic impact on various physiological processes. Finally, emphasize the strong potential for modulation of the gut-retina axis, as therapeutic and prophylactic target for the treatment of DR.

Regulation of blood-brain barrier integrity by microbiome-associated methylamines and cognition by trimethylamine N-oxide

BACKGROUND

Communication between the gut microbiota and the brain is primarily mediated via soluble microbe-derived metabolites, but the details of this pathway remain poorly defined. Methylamines produced by microbial metabolism of dietary choline and L-carnitine have received attention due to their proposed association with vascular disease, but their effects upon the cerebrovascular circulation have hitherto not been studied.

RESULTS

Here, we use an integrated in vitro/in vivo approach to show that physiologically relevant concentrations of the dietary methylamine trimethylamine N-oxide (TMAO) enhanced blood-brain barrier (BBB) integrity and protected it from inflammatory insult, acting through the tight junction regulator annexin A1. In contrast, the TMAO precursor trimethylamine (TMA) impaired BBB function and disrupted tight junction integrity. Moreover, we show that long-term exposure to TMAO protects murine cognitive function from inflammatory challenge, acting to limit astrocyte and microglial reactivity in a brain region-specific manner.

CONCLUSION

Our findings demonstrate the mechanisms through which microbiome-associated methylamines directly interact with the mammalian BBB, with consequences for cerebrovascular and cognitive function. Video abstract.

Trimethylamine N-Oxide and Stroke Recurrence Depends on Ischemic Stroke Subtypes

BACKGROUND AND PURPOSE

Trimethylamine N-oxide (TMAO) has been recognized as a risk factor for cardiovascular disease. However, the role of TMAO in ischemic stroke remains unclear. As we know, ischemic stroke is a heterogeneous disease with variable pathogenesis. Hence, we aimed to investigate the association between TMAO and stroke recurrence according to etiology subtypes.

METHODS

A total of 10 756 ischemic stroke/transient ischemic attack patients from the Third China National Stroke Registry were enrolled, and 1-year follow-up data for stroke recurrence were analyzed. TOAST (Trial of ORG 10172 in Acute Stroke Treatment) criteria was used to classify the etiology subtypes. Plasma TMAO levels were quantified by liquid chromatography-mass spectrometry. The association between TMAO and stroke outcomes was analyzed using Cox regression models. We also conducted a meta-analysis on the association of TMAO levels and stroke risk.

RESULTS

Elevated TMAO level was independently associated with the risk of stroke recurrence (Q4 versus Q1: adjusted hazard ratio, 1.37 [95% CI, 1.15-1.64]) in multivariate Cox regression model. After stratification by TOAST subtypes, there was a significant association between TMAO and stroke recurrence in small artery occlusion subtype (adjusted hazard ratio, 1.43 [95% CI, 1.03-2.00]) but not in the others subtype (large-artery atherosclerosis, 1.19 [0.95-1.48]; cardioembolism, 1.54 [0.95-2.48]; others, 1.19 [0.98-1.44]). The meta-analysis reported on stroke recurrence for the highest versus lowest TMAO levels with a pooled hazard ratio of 1.66 (95% CI, 0.91-3.01) and similarly found an increased risk of stroke recurrence.

CONCLUSIONS

Elevated TMAO level is associated with increased risk of stroke recurrence in patients with small artery occlusion subtype, but this association seems to be attenuated in large-artery atherosclerosis, cardioembolism, and others subtypes.

At the Intersection of Gut Microbiome and Stroke: A Systematic Review of the Literature

Background: Ischemic and hemorrhagic stroke are associated with a high rate of long-term disability and death. Recent investigations focus efforts to better understand how alterations in gut microbiota composition influence clinical outcomes. A key metabolite, trimethylamine N-oxide (TMAO), is linked to multiple inflammatory, vascular, and oxidative pathways. The current biochemical underpinnings of microbial effects on stroke remain largely understudied. The goal of our study is to explore the current literature to explain the interactions between the human gut microbiome and stroke progression, recovery, and outcome. We also provide a descriptive review of TMAO.

Methods: A systematic literature search of published articles between January 1, 1990, and March 22, 2020, was performed on the PubMed database to identify studies addressing the role of the microbiome and TMAO in the pathogenesis and recovery of acute stroke. Our initial investigation focused on human subject studies and was further expanded to include animal studies. Relevant articles were included, regardless of study design. The analysis included reviewers classifying and presenting selected articles by study design and sample size in a chart format.

Results: A total of 222 titles and abstracts were screened. A review of the 68 original human subject articles resulted in the inclusion of 24 studies in this review. To provide further insight into TMAO as a key player, an additional 40 articles were also reviewed and included. Our findings highlighted that alterations in richness and abundance of gut microbes and increased plasma TMAO play an important role in vascular events and outcomes. Our analysis revealed that restoration of a healthy gut, through targeted TMAO-reducing therapies, could provide alternative secondary prevention for at-risk patients.

Discussion: Biochemical interactions between the gut microbiome and inflammation, resulting in metabolic derangements, can affect stroke progression and outcomes. Clinical evidence supports the importance of TMAO in modulating underlying stroke risk factors. Lack of standardization and distinct differences in sample sizes among studies are major limitations.

Diabetes, Vascular Aging and Stroke: Old Dogs, New Tricks?

BACKGROUND

Stroke remains a leading cause of death and disability throughout the world. It is well established that Diabetes Mellitus (DM) is a risk factor for stroke, while other risk factors include dyslipidaemia and hypertension. Given that the global prevalence of diabetes steadily increases, the need for adequate glycaemic control and prevention of DM-related cardiovascular events remains a challenge for the medical community. Therefore, a re-examination of the latest data related to this issue is of particular importance.

OBJECTIVE

This review aims to summarise the latest data on the relationship between DM and stroke, including epidemiology, risk factors, pathogenesis, prevention and biomarkers.

METHODS

For this purpose, comprehensive research was performed on the platforms PubMed, Google Scholar and EMBASE with a combination of the following keywords: diabetes mellitus, stroke, macrovascular complications, diabetic stroke, cardiovascular disease.

CONCLUSIONS

Much progress has been made in stroke in people with DM in terms of prevention and early diagnosis. In the field of prevention, the adaptation of the daily habits and the regulation of co-morbidity of individuals play a particularly important role. Simultaneously, the most significant revolution has been brought by the relatively new treatment options that offer protection to the cardiovascular system. Moreover, many prognostic and diagnostic biomarkers have been identified, paving the way for early and accurate diagnoses. However, to date, there are crucial points that remain controversial and need further clarification.

The Low-Expression Variant of FABP4 Is Associated With Cardiovascular Disease in Type 1 Diabetes

Fatty acid binding protein 4 (FABP4) is implicated in the pathogenesis of cardiometabolic disorders. Pharmacological inhibition or genetic deletion of FABP4 improves cardiometabolic health and protects against atherosclerosis in preclinical models. As cardiovascular disease (CVD) is common in type 1 diabetes, we examined the role of FABP4 in the development of complications in type 1 diabetes, focusing on a functional, low-expression variant (rs77878271) in the promoter of the FABP4 gene. For this, we assessed the risk of CVD, stroke, coronary artery disease (CAD), end-stage kidney disease, and mortality using Cox proportional hazards models for the FABP4 rs77878271 in 5,077 Finnish individuals with type 1 diabetes. The low-expression G allele of rs77878271 increased the risk of CVD, independent of confounders. Findings were tested for replication in 852 Danish and 3,678 Finnish individuals with type 1 diabetes. In the meta-analysis, each G allele increased the risk of stroke by 26% (P = 0.04), CAD by 26% (P = 0.006), and CVD by 17% (P = 0.003). In Mendelian randomization, a 1-SD unit decrease in FABP4 increased risk of CAD 2.4-fold. Hence, in contrast with the general population, among patients with type 1 diabetes the low-expression G allele of rs77878271 increased CVD risk, suggesting that genetically low FABP4 levels may be detrimental in the context of type 1 diabetes.

Gut microbiota dependent trimethylamine N-oxide aggravates angiotensin II-induced hypertension

Gut microbiota produce Trimethylamine N-oxide (TMAO) by metabolizing dietary phosphatidylcholine, choline, l-carnitine and betaine. TMAO is implicated in the pathogenesis of chronic kidney disease (CKD), diabetes, obesity and atherosclerosis. We test, whether TMAO augments angiotensin II (Ang II)-induced vasoconstriction and hence promotes Ang II-induced hypertension. Plasma TMAO levels were indeed elevated in hypertensive patients, thus the potential pathways by which TMAO mediates these effects were explored. Ang II (400 ng/kg⁻¹min⁻¹) was chronically infused for 14 days via osmotic minipumps in C57Bl/6 mice. TMAO (1%) or antibiotics were given via drinking water. Vasoconstriction of renal afferent arterioles and mesenteric arteries were assessed by microperfusion and wire myograph, respectively. In Ang II-induced hypertensive mice, TMAO elevated systolic blood pressure and caused vasoconstriction, which was alleviated by antibiotics. TMAO enhanced the Ang II-induced acute pressor responses (12.2 ± 1.9 versus 20.6 ± 1.4 mmHg; P < 0.05) and vasoconstriction (32.3 ± 2.6 versus 55.9 ± 7.0%, P < 0.001). Ang II-induced intracellular Ca²⁺ release in afferent arterioles (147 ± 7 versus 234 ± 26%; P < 0.001) and mouse vascular smooth muscle cells (VSMC, 123 ± 3 versus 157 ± 9%; P < 0.001) increased by TMAO treatment. Preincubation of VSMC with TMAO activated the PERK/ROS/CaMKII/PLCβ3 pathway. Pharmacological inhibition of PERK, ROS, CaMKII and PLCβ3 impaired the effect of TMAO on Ca²⁺ release. Thus, TMAO facilitates Ang II-induced vasoconstriction, thereby promoting Ang II-induced hypertension, which involves the PERK/ROS/CaMKII/PLCβ3 axis.

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Orally administered TMAO aggravates Ang II-induced hypertension. Antibiotics alleviate Ang II-induced hypertension by reducing TMAO generation.

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High concentrations of TMAO constrict afferent arterioles and mesenteric arteries and increase blood pressure.

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Low concentrations of TMAO enhance Ang II-induced vasoconstriction and acute pressor response via activating PERK/ROS/CaMKII/PLCβ3/Ca²⁺ pathway.

The Accumulation and Molecular Effects of Trimethylamine N-Oxide on Metabolic Tissues: It's Not All Bad

Since elevated serum levels of trimethylamine N-oxide (TMAO) were first associated with increased risk of cardiovascular disease (CVD), TMAO research among chronic diseases has grown exponentially. We now know that serum TMAO accumulation begins with dietary choline metabolism across the microbiome-liver-kidney axis, which is typically dysregulated during pathogenesis. While CVD research links TMAO to atherosclerotic mechanisms in vascular tissue, its molecular effects on metabolic tissues are unclear. Here we report the current standing of TMAO research in metabolic disease contexts across relevant tissues including the liver, kidney, brain, adipose, and muscle. Since poor blood glucose management is a hallmark of metabolic diseases, we also explore the variable TMAO effects on insulin resistance and insulin production. Among metabolic tissues, hepatic TMAO research is the most common, whereas its effects on other tissues including the insulin producing pancreatic β-cells are largely unexplored. Studies on diseases including obesity, diabetes, liver diseases, chronic kidney disease, and cognitive diseases reveal that TMAO effects are unique under pathologic conditions compared to healthy controls. We conclude that molecular TMAO effects are highly context-dependent and call for further research to clarify the deleterious and beneficial molecular effects observed in metabolic disease research.

Gut Microbiota-Derived Trimethylamine N-Oxide and Kidney Function: A Systematic Review and Meta-Analysis

Elevated circulating trimethylamine N-oxide (TMAO) concentrations have been observed in patients with chronic kidney disease (CKD). We aimed to systematically estimate and quantify the association between TMAO concentrations and kidney function. The PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science databases were systematically searched from 1995 to 1 June, 2020, for clinical studies on circulating TMAO concentrations and kidney function indicators. We used R software to conduct meta-analyses of the extracted data. A cumulative meta-analysis was applied to test whether health status affected the pooled effect value. Meta-regression and subgroup analyses were performed to identify possible sources of heterogeneity. Ultimately, we included a total of 32 eligible clinical studies involving 42,062 participants. In meta-analyses of continuous-outcome variables, advanced CKD was associated with a 67.9 μmol/L (95% CI: 52.7, 83.2; P < 0.01) increase in TMAO concentration, and subjects with high concentrations of TMAO had a 12.9 mL/(min·1.73 m2) (95% CI: -16.6, -9.14; P < 0.01) decrease in glomerular filtration rate (GFR). In meta-analyses of the correlations, TMAO was strongly inversely correlated with GFR [Fisher's z-transformed correlation coefficient (ZCOR): -0.45; 95% CI: -0.58, -0.32; P < 0.01] and positively associated with the urine albumin-to-creatinine ratio (UACR; ZCOR: 0.26; 95% CI: 0.08, 0.43; P < 0.01), serum creatinine (sCr; ZCOR: 0.43; 95% CI: 0.28, 0.58; P < 0.01), urine albumin excretion rate (UAER; ZCOR: 0.06; 95% CI: 0.04, 0.09; P < 0.01), blood urea (ZCOR: 0.50; 95% CI: 0.29, 0.72; P < 0.01), blood uric acid (ZCOR: 0.32; 95% CI: 0.25, 0.38; P < 0.01), and serum cystatin C (CysC; ZCOR: 0.47, 95% CI: 0.44, 0.51; P < 0.01). This is the first systematic review and meta-analysis to reveal a negative association between circulating TMAO concentrations and kidney function.

Gut Microbial Metabolites and Blood Pressure Regulation: Focus on SCFAs and TMAO

Shifts in the gut microbiome play a key role in blood pressure regulation, and changes in the production of gut microbial metabolites are likely to be a key mechanism. Known gut microbial metabolites include short-chain fatty acids, which can signal via G-protein-coupled receptors, and trimethylamine-N oxide. In this review, we provide an overview of gut microbial metabolites documented thus far to play a role in blood pressure regulation.

Trimethylamine N-Oxide Exacerbates Renal Inflammation and Fibrosis in Rats With Diabetic Kidney Disease

The gut microbiota plays a pivotal role in the onset and development of diabetes and its complications. Trimethylamine N-oxide (TMAO), a gut microbiota-dependent metabolite of certain nutrients, is associated with type 2 diabetes and its complications. Diabetic kidney disease (DKD) is one of the most serious microvascular complications. However, whether TMAO accelerates the development of DKD remains unclear. We tested the hypothesis that TMAO accelerates the development of DKD. A high-fat diet/low-dose streptozotocin-induced diabetes rat model was established, with or without TMAO in the rats’ drinking water. Compared to the normal rats, the DKD rats showed significantly higher plasma TMAO levels at the end of the study. TMAO treatment not only exacerbated the kidney dysfunction of the DKD rats, but also renal fibrosis. Furthermore, TMAO treatment activated the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome and resulted in the release of interleukin (IL)-1β and IL-18 to accelerate renal inflammation. These results suggested that TMAO aggravated renal inflammation and fibrosis in the DKD rats, which provides a new perspective to understand the pathogenesis of DKD and a potential novel target for preventing the progression of DKD.

Total volatile basic nitrogen and trimethylamine in muscle foods: Potential formation pathways and effects on human health

The use of total volatile basic nitrogen (TVB-N) as a quality parameter for fish is rapidly growing to include other types of meat. Investigations of meat quality have recently focused on TVB-N as an index of freshness, but little is known on the biochemical pathways involved in its generation. Furthermore, TVB-N and methylated amines have been reported to exert deterimental health effects, but the relationship between these compounds and human health has not been critically reviewed. Here, literature on the formative pathways of TVB-N has been reviewed in depth. The association of methylated amines and human health has been critically evaluated. Interventions to mitigate the effects of TVB-N on human health are discussed. TVB-N levels in meat can be influenced by the diet of an animal, which calls for careful consideration when using TVB-N thresholds for regulatory purposes. Bacterial contamination and temperature abuse contribute to significant levels of post-mortem TVB-N increases. Therefore, controlling spoilage factors through a good level of hygiene during processing and preservation techniques may contribute to a substantial reduction of TVB-N. Trimethylamine (TMA) constitutes a significant part of TVB-N. TMA and trimethylamine oxide (TMA-N-O) have been related to the pathogenesis of noncommunicable diseases, including atherosclerosis, cancers, and diabetes. Proposed methods for mitigation of TMA and TMA-N-O accumulation are discussed, which include a reduction in their daily dietary intake, control of internal production pathways by targeting gut microbiota, and inhibition of flavin monooxygenase 3 enzymes. The levels of TMA and TMA-N-O have significant health effects, and this should, therefore, be considered when evaluating meat quality and acceptability. Agreed international values for TVB-N and TMA in meat products are required. The role of feed, gut microbiota, and translocation of methylated amines to muscles in farmed animals requires further investigation.

Circulating trimethylamine N-oxide in association with diet and cardiometabolic biomarkers: an international pooled analysis

BACKGROUND

Trimethylamine N-oxide (TMAO), a diet-derived, gut microbial-host cometabolite, has been linked to cardiometabolic diseases. However, the relations remain unclear between diet, TMAO, and cardiometabolic health in general populations from different regions and ethnicities.

OBJECTIVES

To examine associations of circulating TMAO with dietary and cardiometabolic factors in a pooled analysis of 16 population-based studies from the United States, Europe, and Asia.

METHODS

Included were 32,166 adults (16,269 white, 13,293 Asian, 1247 Hispanic/Latino, 1236 black, and 121 others) without cardiovascular disease, cancer, chronic kidney disease, or inflammatory bowel disease. Linear regression coefficients (β) were computed for standardized TMAO with harmonized variables. Study-specific results were combined by random-effects meta-analysis. A false discovery rate <0.10 was considered significant.

RESULTS

After adjustment for potential confounders, circulating TMAO was associated with intakes of animal protein and saturated fat (β = 0.124 and 0.058, respectively, for a 5% energy increase) and with shellfish, total fish, eggs, and red meat (β = 0.370, 0.151, 0.081, and 0.056, respectively, for a 1 serving/d increase). Plant protein and nuts showed inverse associations (β = -0.126 for a 5% energy increase from plant protein and -0.123 for a 1 serving/d increase of nuts). Although the animal protein-TMAO association was consistent across populations, fish and shellfish associations were stronger in Asians (β = 0.285 and 0.578), and egg and red meat associations were more prominent in Americans (β = 0.153 and 0.093). Besides, circulating TMAO was positively associated with creatinine (β = 0.131 SD increase in log-TMAO), homocysteine (β = 0.065), insulin (β = 0.048), glycated hemoglobin (β = 0.048), and glucose (β = 0.023), whereas it was inversely associated with HDL cholesterol (β = -0.047) and blood pressure (β = -0.030). Each TMAO-biomarker association remained significant after further adjusting for creatinine and was robust in subgroup/sensitivity analyses.

CONCLUSIONS

In an international, consortium-based study, animal protein was consistently associated with increased circulating TMAO, whereas TMAO associations with fish, shellfish, eggs, and red meat varied among populations. The adverse associations of TMAO with certain cardiometabolic biomarkers, independent of renal function, warrant further investigation.