Simultaneous quantification of trimethylamine N-oxide, trimethylamine, choline, betaine, creatinine, and propionyl-, acetyl-, and L-carnitine in clinical and food samples using HILIC-LC-MS

Quantification of trimethylamine-N-oxide (TMAO) and its main related trimethylammonium-containing compounds in human plasma by LC-MS/MS

BACKGROUND

Trimethylammonium-containing compounds, including choline (CHOL), carnitine (CAR), trimethylglycine (TMG), ergothioneine (ERT), Nε,Nε,Nε-trimethyllysine (TML), γ-butyrobetaine (gBB), and dimethylglycine (DMG) contribute to trimethylamine N-oxide (TMAO) production, a metabolite linked to cardiovascular, renal, and metabolic diseases. An LC-MS/MS method has been established for their simultaneous measurement in human plasma, as an accurate quantification of TMAO and its precursors is crucial for understanding its clinical relevance.

METHODS

Blood samples from ten healthy male volunteers were processed using acetonitrile protein precipitation. Analysis was performed using a HILIC column and an isocratic methanol-formic acid mobile phase, achieving a total run time of less than 6 min. Linearity was adequate for all analytes (R2 > 0.995), with mean intra- and inter-assay variation coefficients of 2.88 % and 4.23 %, respectively. Recoveries ranged from 95 % to 101 %, limits of detection from 0.009 to 0.068 µmol/L, and limits of quantification from 0.031 to 0.187 µmol/L. Plasma mean concentrations were 3.18 ± 0.73 µmol/L for TMAO, 3.99 ± 0.65 µmol/L for DMG, 9.84 ± 2.08 µmol/L for CHOL, 24.22 ± 6.19 µmol/L for TMG, 0.54 ± 0.22 µmol/L for gBB, 57.29 ± 8.89 µmol/L for CAR, 1.10 ± 0.42 µmol/L for ERT, and 0.40 ± 0.11 µmol/L for TML. Significant inter-individual variability (mean RSD% of 26 %) was observed.

CONCLUSION

The developed LC-MS/MS method enables rapid, sensitive, and selective quantification of TMAO and its precursors in human plasma. The analytical performance supports its application in clinical and metabolomic studies, contributing to a better understanding the role of TMAO in disease states.

PALM-T2: A colorimetric paper sensor for detecting heterocyclic amine/carbonyl, lactate, moisture, trimethylamine and tryptophan derivatives in wound infections

Conventional bacteria detection from wound infections requires costly or time-consuming methods that require either trained personnel, tedious sample preparation, or complex instrumentation. Hence, it is crucial to develop simple and inexpensive methods that enable accurate, point-of-care assessment of wound infections. Herein, we developed a Paper sensor to detect metabolites, i.e. heterocyclic Amine/Carbonyl, Lactate, Moisture, Trimethylamine and Tryptophan derivatives (termed PALM-T2), released from prevalent wound bacterial species. PALM-T2 consists of five sensing zones that are connected via a sampling arm. Each sensing zone contains a colorimetric sensor that generates unique colour response to certain bacteria metabolites. Images of PALM-T2 were captured using a smartphone and ImageJ was used to analyze colour changes in each sensing zones, eventually revealing the type and concentration of prevalent wound bacterial species. Simulated wound fluid and ex-vivo pig skin 'wound' models were used to demonstrate PALM-T2's performance in simultaneous detection of multiple bacteria metabolites within 30 min. The PALM-T2 sensor displays a great potential for point-of-care detection of bacteria at 105 CFU/mL, the lowest concentration observed from an infected wound.

Derivatization to reduce background interferences for simultaneous quantitation of trimethylamine (TMA) and trimethylamine-N-oxide (TMAO) using liquid chromatography with tandem mass spectrometry

Trimethylamine (TMA) and trimethylamine-N-oxide (TMAO) play a crucial role in many biochemical processes within diverse organisms including animals, plants, fungi and bacteria. Studies have linked these metabolites with cardiovascular and kidney diseases; however, emerging evidence demonstrates their protective properties. Owing to these controversies and co-existence of these metabolites in biological samples, it is crucial to accurately quantify these metabolites to associate their concentrations with various physiological and pathophysiological conditions to elucidate their potential roles. We reported interferences on TMA quantification without derivatizing the analyte. A combined sample preparation method, including sample derivatization with ethyl bromoacetate and use of ion pairing reagent (sodium heptanesulfonate), minimized these interferences and provided improved accuracy and precision for simultaneous quantification of TMA and TMAO. The linearity for TMAO ranged from 0.01 µM to 300 µM and 0.1 µM - 300 µM for TMA. With the application of this method, we reported that the circulating concentrations of TMA was 4 times higher in male mice (33.1 ± 5.9 µmol/L) compared to females (8.3 ± 1.39 µmol/L), whereas TMAO levels were 6 times lower in male (7.2 ± 0.4 µmol/L) than female mice (42.1 ± 4.5 µmol/L). In contrast, concentrations of TMA and TMAO in the colonic tissue did not differ significantly between males and females. The robust analytical method for simultaneously quantifying TMA and TMAO presents a significant value in facilitating investigations on TMA and TMAO biology.

Reaction-Based Fluorescence Assays for the Determination of Food Trimethylamine Oxide

Trimethylamine oxide (TMAO), a microbial metabolite commonly found in foods, has been attracting increasing attention as it is associated with the risk of several diseases. Simple and accurate analytical methods are crucial for TMAO study. In the present study, we proposed a chemical reaction-based fluorescence assay for TMAO detection using synthetic small molecular probes. After systematic screening and optimization, the sensitive and selective quantification of TMAO has been achieved based on a fluorescence probe P6 (3-iodopropanyl group modified resorufin). Excellent linearity (R2 = 0.997) was found between 6.25 and 50 μM, and the limit of detection (LOD) was 0.20 μM. Using this method, TMAO levels in several marine fishes and shellfishes have been successfully analyzed. The probe-based assay offers a simple and useful way for TMAO determination. The design is inspired by the unique oxidation reaction between TMAO and halogen, which opens a new perspective in the development of more advanced analytical assays for TMAO in the future.

L-carnitine: food sources, adequate and clinically effective doses

L-carnitine plays a key role in cell bioenergetics, it belongs to vitamin-like substances, but unlike vitamins, it not only comes from food, but is also synthesized in the body. Endogenous synthesis decreases with age, under certain physiological conditions, taking medications. In this regard, specialized food products (SFP) and food supplements are being developed, containing L-carnitine as one of the functional ingredients. Comparison of doses of L-carnitine approved for use in biologically active food supplements and specialized food products with doses that provide a clinical effect.A review of existing literature on this issue in recent years was carried out using the RSCI, Pubmed databases and in the Google Scholar, ResearchGate systems. The amount of L-carnitine contained in a daily portion of SPP is established by domestic regulatory documents based on an adequate level of daily intake for adults, which is 300 mg and the upper permissible level of daily intake in the composition of SFP and food supplements is 900 mg/day. Reception of L-carnitine 1–2 g per day. within 5–12 weeks led to an increase in its concentration in the blood plasma, and also improved the indicators of the antioxidant status. Long-term intake of L-carnitine in doses of 2–3 g in patients with dyslipidemia, type 2 diabetes (DM2) and cardiovascular diseased (CVD) led to an improvement in the lipid profile of blood plasma, glycemic control, and had an anti-inflammatory effect. The condition for achieving a clinical effect in patients is long-term use and high doses. The intake of physiological doses of L-carnitine is appropriate for individuals from risk groups. Clinically effective doses of L-carnitine, when used for at least 12 weeks, correspond to or are 2 times higher than the upper permissible intake level in the composition of SPP and dietary supplements.

Microbiome metabolite quantification methods enabling insights into human health and disease

Many of the health-associated impacts of the microbiome are mediated by its chemical activity, producing and modifying small molecules (metabolites). Thus, microbiome metabolite quantification has a central role in efforts to elucidate and measure microbiome function. In this review, we cover general considerations when designing experiments to quantify microbiome metabolites, including sample preparation, data acquisition and data processing, since these are critical to downstream data quality. We then discuss data analysis and experimental steps to demonstrate that a given metabolite feature is of microbial origin. We further discuss techniques used to quantify common microbial metabolites, including short-chain fatty acids (SCFA), secondary bile acids (BAs), tryptophan derivatives, N-acyl amides and trimethylamine N-oxide (TMAO). Lastly, we conclude with challenges and future directions for the field.

Liquid chromatography-tandem mass spectrometry for therapeutic drug monitoring of immunosuppressants and creatinine from a single dried blood spot using the Capitainer® qDBS device

In recent years, a lot of attention has been given to a more patient-centric therapeutic drug monitoring (TDM) of immunosuppressant drugs (tacrolimus, sirolimus, everolimus and cyclosporin A) by the use of microsampling techniques. By adopting Dried Blood Spots (DBS) after a finger prick, instead of conventional venous blood draws, follow-up can (partially) be established from patients' homes. Despite the many advantages of DBS, one of the major disadvantages associated with this technique is the well described hematocrit (hct) effect. In order to overcome the hct area bias, different strategies have been proposed, amongst which the use of dried blood sampling techniques based on the volumetric collection of blood. The aim of this study was to evaluate the use of the Capitainer® qDBS (quantitative Dried Blood Spot) device for the combined TDM of four immunosuppressants and creatinine from a single qDBS. The set-up of an adequate sample preparation allowing both immunosuppressants and creatinine quantification was one of the key challenges in the method development due to device-specific interferences. Liquid chromatography tandem-mass spectrometry methods for the quantification of tacrolimus, sirolimus, everolimus, cyclosporin A and creatinine from qDBS (10 μL) were developed and validated based on international guidelines, also taking into account DBS-specific parameters. The methods proved to be accurate and reproducible, with absolute biases below 10% and within-run CVs (%) below 8% over a calibration range from 1 to 50 ng/mL for tacrolimus, sirolimus and everolimus, 20-1500 ng/mL for cyclosporin A, and 15-700 μmol/L for creatinine. Reproducible (CV < 15%) IS-compensated relative recovery values were obtained, showing no hematocrit-dependence (compared to a hct of 0.37), except for cyclosporin A at higher hct values. Application on venous blood left-over patient samples showed good agreement between the results of Capitainer® qDBS and whole blood with 98% (47/48), 93% (41/44), 89% (41/46), 88% (38/43) and 89% (116/131) of the samples lying within 20% of the whole blood result for tacrolimus, sirolimus, everolimus, cyclosporin A and plasma/serum for creatinine, respectively. For creatinine a blood/plasma ratio of 0.85 was found and used to convert qDBS results to plasma/serum results. As a next step, capillary finger prick samples will need to demonstrate the clinical applicability of the method in a real life setting.

Progress and prediction of multicomponent quantification in complex systems with practical LC-UV methods

Complex systems exist widely, including medicines from natural products, functional foods, and biological samples. The biological activity of complex systems is often the result of the synergistic effect of multiple components. In the quality evaluation of complex samples, multicomponent quantitative analysis (MCQA) is usually needed. To overcome the difficulty in obtaining standard products, scholars have proposed achieving MCQA through the "single standard to determine multiple components (SSDMC)" approach. This method has been used in the determination of multicomponent content in natural source drugs and the analysis of impurities in chemical drugs and has been included in the Chinese Pharmacopoeia. Depending on a convenient (ultra) high-performance liquid chromatography method, how can the repeatability and robustness of the MCQA method be improved? How can the chromatography conditions be optimized to improve the number of quantitative components? How can computer software technology be introduced to improve the efficiency of multicomponent analysis (MCA)? These are the key problems that remain to be solved in practical MCQA. First, this review article summarizes the calculation methods of relative correction factors in the SSDMC approach in the past five years, as well as the method robustness and accuracy evaluation. Second, it also summarizes methods to improve peak capacity and quantitative accuracy in MCA, including column selection and two-dimensional chromatographic analysis technology. Finally, computer software technologies for predicting chromatographic conditions and analytical parameters are introduced, which provides an idea for intelligent method development in MCA. This paper aims to provide methodological ideas for the improvement of complex system analysis, especially MCQA.

On the effect of flavonoids and dietary fibre in lingonberries on atherosclerotic plaques, lipid profiles and gut microbiota composition in Apoe-/- mice

It has not been clarified whether the anti-atherosclerotic effect of lingonberry can be ascribed to its content of flavonoids or dietary fibre or both. The aim of this study was to evaluate the metabolic effects of whole lingonberries compared with isolated flavonoid and fibre fractions on atherosclerotic plaques, plasma lipid profiles, gut microbiota and microbiota-dependent metabolites in an Apoe^-/- mouse model. Mice fed whole lingonberries showed the lowest amount of atherosclerotic plaques, while mice fed the fibre fraction had the highest formation of caecal butyric acid. Flavonoids, rather than dietary fibre, were suggested to be the components that favour proliferation of Akkermansia, as judged by the lowest abundance of this bacterium in mice fed the fibre fraction. All groups fed lingonberry diets had both, lower Firmicutes/Bacteroidetes ratios and creatinine concentrations, compared with the control. To conclude, different components in lingonberries are associated with different physiological effects in Apoe^-/- mice.

Effects of Whole Brown Bean and Its Isolated Fiber Fraction on Plasma Lipid Profile, Atherosclerosis, Gut Microbiota, and Microbiota-Dependent Metabolites in Apoe-/- Mice

The health benefits of bean consumption are widely recognized and are largely attributed to the dietary fiber content. This study investigated and compared the effects of whole brown beans and an isolated bean dietary fiber fraction on the plasma lipid profile, atherosclerotic plaque amount, gut microbiota, and microbiota-dependent metabolites (cecal short-chain fatty acids (SCFAs) and plasma methylamines) in Apoe^−/− mice fed high fat diets for 10.5 weeks. The results showed that both whole bean and the isolated fiber fraction had a tendency to lower atherosclerotic plaque amount, but not plasma lipid concentration. The whole bean diet led to a significantly higher diversity of gut microbiota compared with the high fat diet. Both bean diets resulted in a lower Firmicutes/Bacteroidetes ratio, higher relative abundance of unclassified S24-7, Prevotella, Bifidobacterium, and unclassified Clostridiales, and lower abundance of Lactobacillus. Both bean diets resulted in higher formation of all cecal SCFAs (higher proportion of propionic acid and lower proportion of acetic acid) and higher plasma trimethylamine N-oxide concentrations compared with the high fat diet. Whole beans and the isolated fiber fraction exerted similar positive effects on atherosclerotic plaque amount, gut microbiota, and cecal SCFAs in Apoe^−/− mice compared with the control diets.