Measurement of trimethylamine and trimethylamine N-oxide independently in urine by fast atom bombardment mass spectrometry

Balancing the Equation: A Natural History of Trimethylamine and Trimethylamine-N-oxide

Trimethylamine (TMA) and its N-oxide (TMAO) are ubiquitous in prokaryote and eukaryote organisms as well as in the environment, reflecting their fundamental importance in evolutionary biology, and their diverse biochemical functions. Both metabolites have multiple biological roles including cell-signaling. Much attention has focused on the significance of serum and urinary TMAO in cardiovascular disease risk, yet this is only one of the many facets of a deeper TMA-TMAO partnership that reflects the significance of these metabolites in multiple biological processes spanning animals, plants, bacteria, and fungi. We report on analytical methods for measuring TMA and TMAO and attempt to critically synthesize and map the global functions of TMA and TMAO in a systems biology framework.

Simultaneous Measurement of Urinary Trimethylamine (TMA) and Trimethylamine N-Oxide (TMAO) by Liquid Chromatography-Mass Spectrometry

Trimethylamine (TMA) is a gut microbial metabolite—rendered by the enzymatic cleavage of nutrients containing a TMA moiety in their chemical structure. TMA can be oxidized as trimethylamine N-oxide (TMAO) catalyzed by hepatic flavin monooxygenases. Circulating TMAO has been demonstrated to portend a pro-inflammatory state, contributing to chronic diseases such as cardiovascular disease and chronic kidney disease. Consequently, TMAO serves as an excellent candidate biomarker for a variety of chronic inflammatory disorders. The highly positive correlation between plasma TMAO and urine TMAO suggests that urine TMAO has the potential to serve as a less invasive biomarker for chronic disease compared to plasma TMAO. In this study, we validated a method to simultaneously measure urine TMA and TMAO concentrations by liquid chromatography–mass spectrometry (LC/MS). Urine TMA and TMAO can be extracted by hexane/butanol under alkaline pH and transferred to the aqueous phase following acidification for LC/MS quantitation. Importantly, during sample processing, none of the nutrients with a chemical structure containing a TMA moiety were spontaneously cleaved to yield TMA. Moreover, we demonstrated that the acidification of urine prevents an increase of TMA after prolonged storage as was observed in non-acidified urine. Finally, here we demonstrated that TMAO can spontaneously degrade to TMA at a very slow rate.

Effect of Grape Pomace Polyphenols With or Without Pectin on TMAO Serum Levels Assessed by LC/MS-Based Assay: A Preliminary Clinical Study on Overweight/Obese Subjects

Growing evidence suggests that trimethylamine N-oxide (TMAO) is recognized as a biomarker of increased cardiovascular risk. So far, the evaluation of TMAO serum levels in the clinical practice is limited due to the lack of developing new facile methods with reduced limitations. However, few approaches were achieved to determine TMAO in serum by using mass spectrometry-based technique, some limitations were reported including the use of internal standards. Therefore, in this work, a liquid chromatography-mass spectrometry (LC/MS) based-assay was developed to evaluate the effect of grape pomace extract (Taurisolo^®, group A) or Taurisolo^®+pectin (group B) on TMAO serum levels in a cohort of overweight/obese subjects. The serum levels of TMAO have been assessed before and after treatment, through LC/MS analysis. After 8-week treatment, in both intervention groups TMAO serum levels significantly decreased (-78.58% p = 0.006 and -76.76% p = 0.001, group A and group B, respectively). Moreover, we performed several analyses aimed to validate the LC/MS method we used. The method has high precision (% C.V = from 12.12 to 3.92% and from 8.25 to 1.07% for intraday and interday, respectively) and accuracy (% bias = from -5.52 to 0.5% and from -1.42 to 3.08% for intraday and interday, respectively). TMAO recoveries from serum ranged from 99 to 97%; LOD: 2 ng/ml and LOQ: 6 ng/ml. In conclusion, we demonstrated the efficacy of a novel nutraceutical formulation in reducing TMAO serum levels in high cardiovascular risk-subjects, and proposed a useful, versatile and rapid LC/MS method for identification and quantization of TMAO, without the use of marked/isotopic internal standards. It, thus, may represent a novel and practical method with applications in clinical practice and nutraceutical research. Clinical Trial Registration: This study is listed on the ISRCTN registry with ID ISRCTN10794277 (doi: 10.1186/ISRCTN10794277).

High-pressure photon ionization time-of-flight mass spectrometry combined with dynamic purge-injection for rapid analysis of volatile metabolites in urine

Small molecule metabolites are widely used as biomarkers in the research field of metabolomics for disease diagnosis and exposure assessment. As a readily available biofluid containing plenty of volatile organic metabolites (VOMs), urine is ideal for non-invasive metabolomic analysis; however, there is still lack of rapid analysis method for VOMs in urine. Here we report a kind of rapid method for urine analysis by employing high-pressure photon ionization time-of-flight mass spectrometry (HPPI-TOFMS) combined with dynamic purge-injection. Various types of metabolites, such as ketones, alcohols, acids, sulfides, pyrroles and amines were detected directly by simple acidification or alkalization of urines. It is noteworthy that nitrogen-containing compounds, especially polar amines, could be ultrasensitively measured without any derivatization. The analytical capability of the direct HPPI-MS technique was demonstrated by analyzing five valuable metabolites, i.e., toluene, 2,5-dimethylpyrrole, trimethlyamine, styrene, and p-xylene, which exhibited relatively low limits of detection, wide linear range and satisfactory repeatability. Being highly sensitive and humidity-friendly, the whole analytical procedure is easily operated in less than 6 min. Interestingly, a new biomarker 2,5-dimethylpyrrole was exclusively found in the smoker's urine sample besides toluene. The work presents a novel tool for rapid nontarget disease biomarkers screening or target monitoring of specific compounds through the investigation of volatile metabolites in urine.

Simultaneous determination of trimethylamine N-oxide, choline, betaine by UPLC-MS/MS in human plasma: An application in acute stroke patients

Trimethylamine-N-oxide (TMAO) is derived from the gut microbiome and tissues metabolism of dietary choline and betaine. These molecules are closely related to the development of cardiovascular and cerebrovascular diseases. A rapid, sensitive and accurate method has been developed and validated for the simultaneous determination of trimethylamine N-oxide (TMAO), choline and betaine in human plasma using d9-trimethylamine N-oxide (TMAO), d9-choline, d9-betaine as the internal standard (IS). After methanol precipitation with 10 μL plasma samples, the analytes were extracted and then separated on Amide column (2.1 × 100 mm, 1.7 μm, waters) with an isocratic elution program consisting of acetonitrile-water (containing 10 mM ammonium formate pH = 3.0) at a flow of 400 μL/min. The detection was achieved under the selected reaction monitoring (SRM) scan using positive electrospray ionization (ESI+) in 3 min. The mass transitions monitored were as follows: m/z 76.3 → 58.4 for TMAO, m/z 104.2 → 60.3 for choline, m/z 118.1 → 58.3 for betaine, m/z 85.1 → 66.3 for d9-TMAO, m/z 113.2 → 69.3 for d9-choline, and m/z 127.1 → 67.2 for d9-betaine, respectively. The method has been fully validated for specificity, lower limit of quantification, linearity, stability, intra- and inter-day accuracy and precision. This assay combines simple sample processing with a short run time and small plasma volumes, making it well suited for high-throughput routine clinical or research purposes. The newly developed method was successfully applied to the patients (n = 220) suffered from acute stroke, and the concentration of choline was firstly found to be closely related with the prognosis of these patients.

A highly sensitive liquid chromatography electrospray ionization mass spectrometry method for quantification of TMA, TMAO and creatinine in mouse urine

Our method describes the quantification in mouse urine of trimethylamine (TMA), trimethylamine N-oxide (TMAO) and creatinine. The method combines derivatization of TMA, with ethyl bromoacetate, and LC chromatographic separation on an ACE C₁₈ column. The effluent was continuously electrosprayed into the linear ion trap mass spectrometer (LTQ), which operated in selective ion monitoring (SIM) modes set for targeted analytes and their internal standards (IS). All validation parameters were within acceptable ranges of analytical method validation guidelines. Intra- and inter-day assay precision and accuracy coefficients of variation were <3.1%, and recoveries for TMA and TMAO were 97–104%. The method developed uses a two-step procedure. Firstly, TMA and TMAO are analyzed without a purification step using a 5-min gradient cap-LC- SIMs analysis, then creatinine is analyzed using the same experimental conditions. The method is robust, highly sensitive, reproducible and has the high-throughput capability of detecting TMA, TMAO and creatinine at on-column concentrations as low as 28 pg/mL, 115 pg/mL and 1 ng/mL, respectively. The method is suitable for analysis of TMA, TMAO and creatinine in both male and female mouse urine.

The key benefits of the method are:

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The small sample volume of urine required, which overcomes the difficulties of collecting sufficient volumes of urine at defined times.

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No sample pre-treatment is necessary.

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The quantification of TMA, TMAO and creatinine using the same cap-LC-MS method.

A multiplexed targeted assay for high-throughput quantitative analysis of serum methylamines by ultra performance liquid chromatography coupled to high resolution mass spectrometry

Methylamines are biologically-active metabolites present in serum and urine samples, which play complex roles in metabolic diseases. Methylamines can be detected by proton nuclear magnetic resonance (NMR), but specific methods remain to be developed for their routine assay in human serum in clinical settings. Here we developed and validated a novel reliable "methylamine panel" method for simultaneous quantitative analysis of trimethylamine (TMA), its major detoxification metabolite trimethylamine-N-oxide (TMAO), and precursors choline, betaine and l-carnitine in human serum using Ultra Performance Liquid Chromatography (UPLC) coupled to High Resolution Mass Spectrometry (HRMS). Metabolite separation was carried out on a HILIC stationary phase. For all metabolites, the assay was linear in the range of 0.25-12.5 μmol/L and enabled to reach limit of detection of about 0.10 μmol/L. Relative standard deviations were below 16% for the three levels of concentrations. We demonstrated the strong reliability and robustness of the method, which was applied to serum samples from healthy individuals to establish the range of concentrations of the metabolites and their correlation relationships and detect gender differences. Our data provide original information for implementing in a clinical environment a MS-based diagnostic method with potential for targeted metabolic screening of patients at risk of cardiometabolic diseases.

Measurement of trimethylamine-N-oxide by stable isotope dilution liquid chromatography tandem mass spectrometry

Trimethylamine-N-oxide (TMAO) levels in blood predict future risk for major adverse cardiac events including myocardial infarction, stroke, and death. Thus, the rapid determination of circulating TMAO concentration is of clinical interest. Here we report a method to measure TMAO in biological matrices by stable isotope dilution liquid chromatography tandem mass spectrometry (LC/MS/MS) with lower and upper limits of quantification of 0.05 and >200μM, respectively. Spike and recovery studies demonstrate an accuracy at low (0.5μM), mid (5μM), and high (100μM) levels of 98.2, 97.3, and 101.6%, respectively. Additional assay performance metrics include intraday and interday coefficients of variance of <6.4 and <9.9%, respectively, across the range of TMAO levels. Stability studies reveal that TMAO in plasma is stable both during storage at -80°C for 5years and to multiple freeze thaw cycles. Fasting plasma normal range studies among apparently healthy subjects (n=349) show a range of 0.73-126μM, median (interquartile range) levels of 3.45 (2.25-5.79)μM, and increasing values with age. The LC/MS/MS-based assay reported should be of value for further studies evaluating TMAO as a risk marker and for examining the effect of dietary, pharmacologic, and environmental factors on TMAO levels.

Measurement of urinary trimethylamine and trimethylamime oxide by direct infusion electrospray quadrupole time-of-flight mass spectrometry

Urinary trimethylamine (TMA) and its oxide (TMAOx) are measured separately and as a mixture using (15)N-labeled internal standards and direct infusion electrospray with a quadrupole time-of-flight (Q-ToF) instrument. TMA is quaternized with trideuteromethyl iodide to avoid inclusion of endogenous tetramethylammonium ion in the TMA measurement, whereas TMAOx is measured as the protonated molecule. Measurements reported as percentage TMA made with separate and combined samples agree within 6% of the measured values and demonstrate that both TMA and TMAOx can be measured simultaneously in a single analysis. Moreover, the analysis is simpler and less tedious and time-consuming than some earlier methods.

A flow injection electrospray ionization tandem mass spectrometric method for the simultaneous measurement of trimethylamine and trimethylamine N-oxide in urine

Key metabolites for the diagnosis of the genetic disorder trimethylaminuria are trimethylamine (TMA) and trimethylamine N-oxide (TMAO). A rapid, automatable flow injection ESI-MS/MS method for their measurement in urine has been developed. The TMA was derivatized with ethyl bromoacetate to form ethyl betaine bromide. The 2 min ESI-MS/MS analysis employed four multiple reaction monitoring (MRM) ion pairs for derivatized TMA (146.1, 118.1), derivatized (2)H(9)-TMA (155.1, 127.1), TMAO (76.1, 58.1) and (2)H(9)-TMAO (85.1, 66.1). In control urine samples (n = 27) referred for suspected metabolic problems TMA was 0.11-1.19 mmol/mol creatinine, TMAO was 13.5-181 mmol/mol creatinine and the TMA/TMAO ratio was 0.0025-0.055. In five patients with diagnosed trimethylaminuria, TMA was 5.3-230 mmol/mol creatinine, TMAO was 0.36-607 mmol/mol creatinine and the TMA/TMAO ratio was 0.20-134.

Rapid screening assay of trimethylaminuria in urine with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Trimethyamine (TMA) and trimethylamine N-oxide (TMAO) are the most important urine parameters for diagnosing and monitoring trimethylaminuria. A rapid, simple, and specific method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was developed to determine the presence of TMA and TMAO in urine samples from patients with trimethylaminuria. Formation of the quaternary tetramethylamino iodide by derivatization of TMA with methyl iodide allows measurement of TMA by MALDI-TOFMS. The method is repeatable and reproducible, with coefficients of variance (CVs)<3%. This new method was used for direct determination of TMA and TMAO in urine specimens obtained from normal children and patients. The proposed method allows for rapid and reliable measurements of TMA and TMAO in urine specimens from patients affected by trimethylaminuria.

Microbial Dimethylsulfoxide and Trimethylamine-N-Oxide Respiration

Over the last two decades, the biochemistry and genetics of dimethylsulfoxide (DMSO) and trimethylamine-N-oxide (TMAO) respiration has been characterised, particularly in Escherichia coli marine bacteria of the genus Shewanella and the purple phototrophic bacteria, Rhodobacter sphaeroides and R. capsulatus. All of the enzymes (or catalytic subunits) involved the final step in DMSO and TMAO respiration contain a pterin molybdenum cofactor and are members of the DMSO reductase family of molybdoenzymes. In E. coli, the dimethylsulfoxide reductase (DmsABC) can be purified from membranes as a complex, which exhibits quinol-DMSO oxidoreductase activity. The enzyme is anchored to the membrane via the DmsC subunit and its catalytic subunit DmsA is now considered to face the periplasm. Electron transfer to DmsA involves the DmsB subunit, which is a polyferredoxin related to subunits found in other molybdoenzymes such as nitrate reductase and formate dehydrogenase. A characteristic of the DmsAB-type DMSO reductase is its ability to reduce a variety of S- and N-oxides. E. coli contains a trimethylamine-N-oxide reductase (TorA) that is highly specific for N-oxides. This enzyme is located in the periplasm and is connected to the quinone pool via a membrane-bound penta-haem cytochrome (TorC). DorCA in purple phototrophic bacteria of the genus Rhodobacter is very similar to TorCA with the critical difference that DorA catalyses reduction of both DMSO and TMAO. It is known as a DMSO reductase because the S-oxide is the best substrate. Crystal structures of DorA and TorA have revealed critical differences at the Mo active site that may explain the differences between substrate specificity between the two enzymes. DmsA, TorA and DorA possess a "twin arginine" N-terminal signal sequence consistent with their secretion via the TAT secretory system and not the Sec system. The enzymes are secreted with their bound prosthetic groups: this take place in the cytoplasm and the biogenesis involves a chaperone protein, which is cognate for each enzyme. Expression of the DMSO and TMAO respiratory operons is induced in response to a fall in oxygen tension. dmsABC expression is positively controlled by the oxygen-responsive transcription factor, Fnr and ModE, a transcription factor that binds molybdate. In contrast, torCAD expression is not under Fnr- or ModE-control but is dependent upon a sensor histidine kinase-response regulator pair, TorSR, which activate gene expression under conditions of low oxygen tension in the presence of N- or S-oxide. Regulation of dorCDA expression is similar to that seen for torCAD but it appears that the expression of the sensor histidine kinase-response regulator pair, DorSR is regulated by Fnr and there is an additional tier of regulation involving the ModE-homologue MopB, molybdate and the transcription factor DorX. Analysis of microbial genomes has revealed the presence of dms and tor operons in a wide variety of bacteria and in some archaea and duplicate dms and tor operons have been identified in E. coli. Challenges ahead will include the determination of the significance of the presence of the dms operon in bacterial pathogens and the determination of the significance of DMSO respiration in the global turnover of marine organo-sulfur compounds.

In vivo variability of TMA oxidation is partially mediated by polymorphisms of the FMO3 gene

Trimethylaminuria (TMAU) results from an accumulation of an excessive amount of unoxidized trimethylamine that is excreted in urine and body secretions. Mutations of the flavin-containing monooxygenase 3 (FMO3) gene (a hepatic phase I drug-metabolizing enzyme) account for the severe recessively encoded form of this condition. We have previously described a number of FMO3 polymorphisms which in vitro exhibit reduced substrate affinity for several FMO substrates. Here we show that three prevalent polymorphisms (E158K, V257M, and E308G) inherited in particular combinations confer a slight decrease in TMA oxidation under normal physiological conditions, which may be clinically "silent." With the use of substrate loading or with the interaction of other known modulators of FMO3 activity such as hormonal influences, these genotypes may predispose to mild TMAU.

A novel deletion in the flavin-containing monooxygenase gene (FMO3) in a Greek patient with trimethylaminuria

Mutations of the flavin-containing monooxygenase type 3 gene (FMO3) that encode the major functional form present in adult human liver, have been shown to cause trimethylaminuria. We now report a novel homozygous deletion of exons 1 and 2 in an Australian of Greek ancestry with TMAuria, the first report of a deletion causative of trimethylaminuria. The deletion occurs 328 bp upstream from exon 1. The 3'-end of the deletion occurs in intron 2, 10013 base pairs downstream from the end of exon 2. The deletion is 12226 bp long. For the proband homozygous for the human FMO3 gene deletion, it is predicted that in addition to loss of monooxygenase function for human FMO3 substrates, such as TMA and other amines, the proband will exhibit decreased tolerance of biogenic amines, both medicinal and those found in foods.