Background and objectives Trimethylamine N-oxide (TMAO), a compound derived from byproducts of intestinal bacteria, has been shown to accelerate atherosclerosis in rodents. To date, there are conflicting data regarding the association of serum TMAO with cardiovascular outcomes in patients with ESKD, a population exhibiting both high serum TMAO and excessive atherosclerosis.Design, setting, participants, & measurements We measured baseline serum TMAO concentrations in a subset of participants (n=1243) from the Evaluation of Cinacalcet Hydrochloride Therapy to Lower Cardiovascular Events (EVOLVE) trial and conducted post hoc analyses evaluating the association between baseline serum TMAO and cardiovascular outcomes. ResultsWe observed a wide distribution of serum TMAO in our cohort, with approximately 80% of participants exhibiting TMAO concentrations $56 mM and a maximum TMAO concentration of 1103.1 mM. We found no association between TMAO and our primary outcome, a composite of cardiovascular mortality, myocardial infarction, peripheral vascular event, stroke, and hospitalization for unstable angina. Moreover, in unadjusted and adjusted analyses, we observed no relation between TMAO and all-cause mortality, the independent components of our composite outcome, or the original EVOLVE primary outcome. Although we did observe higher TMAO concentrations in white participants, further subgroup analyses did not confirm the previously identified interaction between TMAO and race observed in a prior study in patients receiving dialysis. ConclusionsWe found no evidence linking TMAO to adverse clinical outcomes in patients receiving maintenance hemodialysis with moderate to severe secondary hyperparathyroidism.All data are shown as n (%) unless otherwise indicated. TMAO, trimethylamine N-oxide; IQR, interquartile range; ECG, electrocardiogram; PTH, parathyroid hormone; spKt/V, single-pool Kt/V; FGF23, fibroblast growth factor 23. a One patient missing dialysis vintage, six patients missing FGF23, 96 patients missing hemoglobin, four patients missing BUN. b 3.6% of patients were missing BMI.

A mechanistic link between trimethylamine N-oxide (TMAO) and atherogenesis has been reported. TMAO is generated enzymatically in the liver by the oxidation of trimethylamine (TMA), which is produced from dietary choline, carnitine and betaine by gut bacteria. It is known that certain members of methanogenic archaea (MA) could use methylated amines such as trimethylamine as growth substrates in culture. Therefore, we investigated the efficacy of gut colonization with MA on lowering plasma TMAO concentrations. Initially, we screened for the colonization potential and TMAO lowering efficacy of five MA species in C57BL/6 mice fed with high choline/TMA supplemented diet, and found out that all five species could colonize and lover plasma TMAO levels, although with different efficacies. The top performing MA, Methanobrevibacter smithii, Methanosarcina mazei, and Methanomicrococcus blatticola, were transplanted into Apoe−/− mice fed with high choline/TMA supplemented diet. Similar to C57BL/6 mice, following initial provision of the MA, there was progressive attrition of MA within fecal microbial communities post-transplantation during the initial 3 weeks of the study. In general, plasma TMAO concentrations decreased significantly in proportion to the level of MA colonization. In a subsequent experiment, use of antibiotics and repeated transplantation of Apoe−/− mice with M. smithii, led to high engraftment levels during the 9 weeks of the study, resulting in a sustained and significantly lower average plasma TMAO concentrations (18.2 ± 19.6 μM) compared to that in mock-transplanted control mice (120.8 ± 13.0 μM, p < 0.001). Compared to control Apoe−/− mice, M. smithii-colonized mice also had a 44% decrease in aortic plaque area (8,570 μm [95% CI 19587–151821] vs. 15,369 μm [95% CI [70058–237321], p = 0.34), and 52% reduction in the fat content in the atherosclerotic plaques (14,283 μm [95% CI 4,957–23,608] vs. 29,870 μm [95% CI 18,074–41,666], p = 0.10), although these differences did not reach significance. Gut colonization with M. smithii leads to a significant reduction in plasma TMAO levels, with a tendency for attenuation of atherosclerosis burden in Apoe−/− mice. The anti-atherogenic potential of MA should be further tested in adequately powered experiments.

A solid-phase extraction (SPE) protocol was developed and combined with HPLC-ESI-MS for the quantification of common cyanobacterial toxins, microcystins (MCs), in water.

Circulating trimethylamine -oxide (TMAO) predicts poor cardiovascular outcomes in patients with chronic kidney disease (CKD). Accumulation of serum TMAO has been observed in CKD patients; however, the mechanisms contributing to this finding have been inadequately explored. The purpose of this study was to investigate the mechanisms responsible for TMAO accumulation in the setting of decreased kidney function using a CKD mouse model. Mice were fed a diet supplemented with 0.2% adenine to induce CKD, which resulted in increased serum TMAO concentrations (females: CKD 29.4 ± 32.1M vs. non-CKD 6.9 ± 6.1 M, < 0.05; males: CKD 18.5 ± 13.1 M vs. non-CKD 1.0 ± 0.5M, < 0.001). As anticipated, accumulation of circulating TMAO was accompanied by a decrease in renal clearance (females: CKD 5.2 ± 3.8 l/min vs. non-CKD 90.4 ± 78.1l/min, < 0.01; males: CKD 10.4 ± 8.1 l/min vs. non-CKD 260.4 ± 134.5l/min; < 0.001) and fractional excretion of TMAO. Additionally, CKD animals exhibited an increase in hepatic flavin monooxygenase (FMO)-mediated formation of TMAO (females: CKD 125920 ± 2181 pmol/mg per 60 minutes vs. non-CKD 110299 ± 4196 pmol/mg per 60 minutes, < 0.001; males: CKD 131286 ± 2776 pmol/mg per 60 minutes vs. non-CKD 74269 ± 1558 pmol/mg per 60 minutes, < 0.001), which likely resulted from increased FMO3 expression in CKD mice. The current study provides evidence that both decreased renal clearance and increased hepatic production of TMAO may contribute to increments in serum TMAO in the setting of CKD. Hepatic FMO activity may represent a novel therapeutic target for lowering circulating TMAO in CKD patients.