The Gut Axis Involvement in Heart Failure: Focus on Trimethylamine N-oxide.

A novel pathophysiological model of interest is the association between heart failure (HF) and the gastrointestinal system, the 'gut hypothesis'. The choline and carnitine metabolic by-product, Trimethylamine N-oxide (TMAO) is one of the more prominent molecules associated with the link between HF and the gut. Indeed, TMAO levels are increased in HF populations and higher TMAO levels are associated with poor prognosis, whereas low TMAO levels either at baseline/follow up confer better prognosis. Considering that TMAO levels seem not to be affected by guideline-HF treatment, this model could represent a novel and independent therapeutic target for HF.

Evaluation of an 8-Week Vegan Diet on Plasma Trimethylamine-N-Oxide and Postchallenge Glucose in Adults with Dysglycemia or Obesity.

BACKGROUND: Trimethylamine N-oxide (TMAO), a metabolite generated by the gut in response (in part) to meat consumption, is linked to poor cardiometabolic health. OBJECTIVES: We investigate the effect of an 8-week vegan diet, followed by a 4-week period of unrestricted diet, on glucose tolerance and plasma TMAO in human omnivores with obesity or dysglycemia. METHODS: This interventional single-group prospective trial involved 23 regular meat eaters with dysglycemia [glycated hemoglobin ≥ 5.7% and ≤8% (39-64 mmol/mol)], or obesity (ΒΜΙ ≥ 30 kg/m2) aged 57.8 ± 10.0 years. Participants [14 men (60.9%) and 9 women (39.1%)] were supported in following a vegan diet for 8 weeks, followed by 4 weeks of unrestricted diet. The primary outcomes (plasma TMAO and glucose) were assessed at baseline, during the vegan diet (weeks 1 and 8), and after the unrestricted diet period (week 12). TMAO was assessed after fasting and glucose was measured as a time-averaged total AUC using a 180-minute oral-glucose-tolerance test. Generalized estimating equation models with an exchangeable correlation structure were used to assess changes from baseline, adjusting for age, sex, ethnicity, and weight. RESULTS: TMAO levels (marginal mean) were reduced after weeks 1 and 8 of a vegan diet compared to baseline, from 10.7 (97.5% CI, 6.61-17.3) µmol/L to 5.66 (97.5% CI, 4.56-7.02) µmol/L and 6.38 (97.5% CI, 5.25-7.74) µmol/L, respectively; however, levels rebounded at week 12 after resumption of an unrestricted diet (17.5 µmol/L; 97.5% CI, 7.98-38.4). Postprandial glucose levels (marginal means) were reduced after weeks 1 and 8 compared to baseline, from 8.07 (97.5% CI, 7.24-8.90) mmol/L to 7.14 (97.5% CI, 6.30-7.98) mmol/L and 7.34 (97.5% CI, 6.63-8.04) mmol/L, respectively. Results for glucose and TMAO were independent of weight loss. Improvements in the lipid profile and markers of renal function were observed at week 8. CONCLUSIONS: These findings suggest that a vegan diet is an effective strategy for improving glucose tolerance and reducing plasma TMAO in individuals with dysglycemia or obesity. This study was registered at clinicaltrials.gov as NCT03315988.

Association of gut-related metabolites with outcome in acute heart failure.

BACKGROUND: Trimethylamine N-oxide (TMAO), a gut-related metabolite, is associated with heart failure (HF) outcomes. However, TMAO is the final product of a complex metabolic pathway (ie, choline/carnitine) that has never been entirely investigated in HF. The present study investigates a panel of metabolites involved in the TMAO-choline/carnitine metabolic pathway for their associations with outcome in acute HF patients. METHODS: In total, 806 plasma samples from acute HF patients were analyzed for TMAO, trimethyllysine, L-carnitine, acetyl-L-carnitine, γ-butyrobetaine, crotonobetaine, trimethylamine, betaine aldehyde, choline, and betaine using a developed liquid chromatography-tandem mass spectrometry method. Associations with outcome of all-cause mortality (death) and a composite of all-cause mortality and/or rehospitalization caused by HF (death/HF) at 30 days and 1 year were investigated. RESULTS: TMAO, trimethyllysine, L-carnitine, acetyl-L-carnitine, and γ-butyrobetaine were associated with death and death/HF at 30 days (short term; hazard ratio 1.30-1.49, P≤ .021) and at 1 year (long term; hazard ratio 1.15-1.25, P≤ .026) when adjusted for cardiac risk factors. L-carnitine and acetyl-L-carnitine were superior for short-term outcomes whereas TMAO was the superior metabolite for association with long-term outcomes. Furthermore, acetyl-L-carnitine and L-carnitine were superior for in-hospital mortality and improved risk stratification when combined with current clinical risk scores (ie, Acute Decompensated HEart Failure National REgistry, Organized Program To Initiate Lifesaving Treatment In Hospitalized Patients With Heart Failure, and Get With The Guidelines-Heart Failure; odds ratio (OR) ≥ 1.52, P≤ .020). CONCLUSIONS: Carnitine-related metabolites show associations with adverse outcomes in acute HF, in particular L-carnitine and acetyl-L-carnitine for short-term outcomes, and TMAO for long-term outcomes. Further studies are warranted to investigate the role and implications of carnitine metabolites including intervention in the pathogenesis of HF.

Associations between physical activity and trimethylamine N-oxide in those at risk of type 2 diabetes.

INTRODUCTION: Trimethylamine N-oxide (TMAO) has been identified as a novel gut-derived molecule that is associated with the risk of cardiometabolic diseases. However, the relationship between TMAO and physical activity is not well understood. This study prospectively investigates the association between TMAO and objectively assessed physical activity in a population at high risk of type 2 diabetes mellitus. RESEARCH DESIGN AND METHODS: Baseline and 12-month follow-up data were used from the Walking Away from Type 2 Diabetes trial, which recruited adults at high risk of type 2 diabetes from primary care in 2009-2010. TMAO was analyzed using targeted mass spectrometry. Generalized estimating equation models with an exchangeable correlation structure were used to investigate the associations between accelerometer-assessed exposures (sedentary time, light physical activity, moderate to vigorous physical activity (MVPA)) and TMAO, adjusting for demographic, clinical and lifestyle factors in varying degrees. RESULTS: Overall, 483 individuals had plasma samples available for the analysis of TMAO (316 (65.4%) men, 167 (34.6%) women), contributing 886 observations to the analysis. MVPA (min/day) was associated with TMAO in all models. In the fully adjusted model, each 30 min or SD difference in MVPA was associated with 0.584 µmol/L (0.070, 1.098) and 0.456 µmol/L (0.054, 0.858) lower TMAO, respectively. Sedentary time and light physical activity were not associated with TMAO in any model. CONCLUSIONS: Engagement with MVPA was associated with lower TMAO levels, suggesting a possible new mechanism underlining the inverse relationship between physical activity and cardiometabolic health.

Ethnic differences in association of outcomes with trimethylamine N-oxide in acute heart failure patients.

AIMS: The aim of this study was to investigate whether ethnicity influences the associations between trimethylamine N-oxide (TMAO) levels and heart failure (HF) outcomes. METHODS AND RESULTS: Trimethylamine N-oxide levels were measured in two cohorts with acute HF at two sites. The UK Leicester cohort consisted mainly of Caucasian (n = 842, 77%) and South Asian (n = 129, 12%) patients, whereas patients in the Japanese cohort (n = 116, 11%) were all Japanese. The primary endpoint was the measurement of all-cause mortality and/or HF rehospitalization within 1 year post-admission. Association of TMAO levels with outcome was compared in the entire population and between ethnic groups after adjustment for clinical parameters. TMAO levels were significantly higher in Japanese patients [median (interquartile range): 9.9 µM (5.2-22.8)] than in Caucasian [5.9 µM (3.6-10.8)] and South Asian [4.5 µM (3.1-8.4)] (P < 0.001) patients. There were no differences in the rate of mortality and/or HF rehospitalization between the ethnic groups (P = 0.096). Overall, higher TMAO levels showed associations with mortality and/or rehospitalization after adjustment for confounders ( P = 0.002). Despite no differences between ethnicity and association with mortality/HF after adjustment (P = 0.311), only in Caucasian patients were TMAO levels able to stratify for a mortality/HF event (P < 0.001). CONCLUSIONS: Differences were observed in the association of mortality and/or rehospitalization based on circulating TMAO levels. Elevated TMAO levels in Caucasian patients showed increased association with adverse outcomes, but not in non-Caucasian patients.

Matrix-assisted laser desorption ionisation (MALDI) mass spectrometry (MS): basics and clinical applications.

Background Matrix-assisted laser desorption ionisation (MALDI) mass spectrometry (MS) has been used for more than 30 years. Compared with other analytical techniques, it offers ease of use, high throughput, robustness, cost-effectiveness, rapid analysis and sensitivity. As advantages, current clinical techniques (e.g. immunoassays) are unable to directly measure the biomarker; rather, they measure secondary signals. MALDI-MS has been extensively researched for clinical applications, and it is set for a breakthrough as a routine tool for clinical diagnostics. Content This review reports on the principles of MALDI-MS and discusses current clinical applications and the future clinical prospects for MALDI-MS. Furthermore, the review assesses the limitations currently experienced in clinical assays, the advantages and the impact of MALDI-MS to transform clinical laboratories. Summary MALDI-MS is widely used in clinical microbiology for the screening of microbial isolates; however, there is scope to apply MALDI-MS in the diagnosis, prognosis, therapeutic drug monitoring and biopsy imaging in many diseases. Outlook There is considerable potential for MALDI-MS in clinic as a tool for screening, profiling and imaging because of its high sensitivity and specificity over alternative techniques.

The Gut Axis Involvement in Heart Failure: Focus on Trimethylamine N-oxide.

A novel pathophysiological model of interest is the association between heart failure (HF) and the gastrointestinal system, the 'gut hypothesis'. The choline and carnitine metabolic by-product, Trimethylamine N-oxide (TMAO) is one of the more prominent molecules associated with the link between HF and the gut. Indeed, TMAO levels are increased in HF populations and higher TMAO levels are associated with poor prognosis, whereas low TMAO levels either at baseline/follow up confer better prognosis. Considering that TMAO levels seem not to be affected by guideline-HF treatment, this model could represent a novel and independent therapeutic target for HF.

Quantitative LC-HRMS determination of selected cardiovascular drugs, in dried blood spots, as an indicator of adherence to medication.

Dried blood spot (DBS) sampling was investigated as a means of obtaining micro-volume blood samples for the quantitative analyses of ten commonly UK prescribed cardiovascular drugs as an indicator of medication adherence. An 8mm disc was punched out from each DBS from calibration, quality control and volunteer samples and extracted using methanol containing the internal standard. Each extract was evaporated to dryness, the residue reconstituted in methanol:water (40:60v/v) containing 0.1% formic acid and analysed by LC-HRMS. Chromatography was performed using gradient elution on a Zorbax Eclipse C18 HD 100mm×2.1mm, 1.8µm pore size column with the column oven temperature at 40°C. Flow rate of the mobile phase was 0.6ml/min with a run time of 2.5min. Electrospray positive ionization was used for MS detection. Drug recoveries from spiked blood spots were 68% for simvastatin and ≥87% for all other target drugs. Compound specificity was obtained operating the MS with a 5ppm mass window. The LC-HRMS method was validated, with results for accuracy and precision within acceptable limits; analytes were stable at room temperature for at least 10 weeks and different blood spot volumes and haematocrit values had no significant effect. The LC-HRMS assay was used to analyse DBS samples from volunteers, some of whom were prescribed one or more of the target drugs. In results from 37 volunteers the assay successfully identified volunteers who were known to be either adherent or nonadherent; confirmed the correct drug/drugs for multiple prescriptions; demonstrated no false positives from other cardiovascular drugs; revealed several examples of unsuspected non-adherence. These results indicated that the developed assay was suitable for trials with patients.