Simultaneous HS-SPME GC-MS determination of short chain fatty acids, trimethylamine and trimethylamine N-oxide for gut microbiota metabolic profile

The Alpine ibex (Capra ibex) gut microbiome, seasonal dynamics, and potential application in lignocellulose bioconversion

Aiming to shed light on the biology of wild ruminants, we investigated the gut microbiome seasonal dynamics of the Alpine ibex (Capra ibex) from the Central Italian Alps. Feces were collected in spring, summer, and autumn during non-invasive sampling campaigns. Samples were analyzed by 16S rRNA amplicon sequencing, shotgun metagenomics, as well as targeted and untargeted metabolomics. Our findings revealed season-specific compositional and functional profiles of the ibex gut microbiome that may allow the host to adapt to seasonal changes in available forage, by fine-tuning the holobiont catabolic layout to fully exploit the available food. Besides confirming the importance of the host-associated microbiome in providing the phenotypic plasticity needed to buffer dietary changes, we obtained species-level genome bins and identified minimal gut microbiome community modules of 11-14 interacting strains as a possible microbiome-based solution for the bioconversion of lignocellulose to high-value compounds, such as volatile fatty acids.

A novel and efficient electrochemiluminescence sensing strategy for the determination of trimethylamine oxide in seafood

A novel and efficient electrochemiluminescence (ECL) sensing strategy and a solid-state ECL sensor was proposed to detect trimethylamine oxide (TMAO), which is widely presented in marine species and has important physiological functions. TMAO was reduced by Fe(II)-EDTA complex to trimethylamine, acting as coreactant, to amplify the ECL response of the Ru (bpy)32+ system. To improve the detection sensitivity and efficiency, a robust solid-state ECL probe was prepared and a flow injection ECL detection system was established with a specially designed flow ECL unit, under the excitation of stepping pulse potentials. Under optimized experimental conditions, the developed ECL sensor worked well for TMAO detection in a wide linear range of 10.00 μM to 1.00 mM with a limit of detection of 3.41 μM. It was successfully applied to determine TMAO in various species of seafood samples. This work provides a promising strategy for TMAO detection.

Quantitative profiling of carboxylic compounds by gas chromatography-mass spectrometry for revealing biomarkers of diabetic kidney disease

Diabetic kidney disease (DKD), a common microvascular complication of diabetes, currently lacks specific diagnostic indicators and therapeutic targets, resulting in miss of early intervention. To profile metabolic conditions in complex and precious biological samples and screen potential biomarkers for DKD diagnosis and prognosis, a rapid, convenient and reliable quantification method for carboxyl compounds by gas chromatography-mass spectrometry (GC-MS) was established with isobutyl chloroformate derivatization. The derivatives were extracted with hexane, injected into GC-MS and quantified with selected ion monitoring mode. This method showed excellent linearity(R2 > 0.99), good recoveries (81.1%-115.5%), good repeatability (RSD < 20%) and sensitivity (LODs: 0.20-499.90 pg, LOQs: 2.00-1007.00 pg). Among the 37 carboxyl compounds analyzed, 12 metabolites in short-chain fatty acids (SCFAs) metabolism pathway and amino acid metabolism pathway were linked with DKD development and among them, 6 metabolites were associated with both development and prognosis of DKD in mice. In conclusion, a reliable, convenient and sensitive method based on isobutyl chloroformate derivatization and GC-MS analysis is established and successfully applied to quantify 37 carboxyl compounds in biological samples of mice and 12 potential biomarkers for DKD development and prognosis are screened.

Disruption of the microbiota-gut-brain axis is a defining characteristic of the α-Gal A (-/0) mouse model of Fabry disease

Fabry disease (FD) is an X-linked metabolic disease caused by a deficiency in α-galactosidase A (α-Gal A) activity. This causes accumulation of glycosphingolipids, especially globotriaosylceramide (Gb3), in different cells and organs. Neuropathic pain and gastrointestinal (GI) symptoms, such as abdominal pain, nausea, diarrhea, constipation, and early satiety, are the most frequent symptoms reported by FD patients and severely affect their quality of life. It is generally accepted that Gb3 and lyso-Gb3 are involved in the symptoms; nevertheless, the origin of these symptoms is complex and multifactorial, and the exact mechanisms of pathogenesis are still poorly understood. Here, we used a murine model of FD, the male α-Gal A (-/0) mouse, to characterize functionality, behavior, and microbiota in an attempt to elucidate the microbiota-gut-brain axis at three different ages. We provided evidence of a diarrhea-like phenotype and visceral hypersensitivity in our FD model together with reduced locomotor activity and anxiety-like behavior. We also showed for the first time that symptomology was associated with early compositional and functional dysbiosis of the gut microbiota, paralleled by alterations in fecal short-chain fatty acid levels, which partly persisted with advancing age. Interestingly, most of the dysbiotic features suggested a disruption of gut homeostasis, possibly contributing to accelerated intestinal transit, visceral hypersensitivity, and impaired communication along the gut-brain axis.

Determination of short-chain fatty acids as putative biomarkers of cancer diseases by modern analytical strategies and tools: a review

Short-chain fatty acids (SCFAs) are the main metabolites produced by bacterial fermentation of non-digestible carbohydrates in the gastrointestinal tract. They can be seen as the major flow of carbon from the diet, through the microbiome to the host. SCFAs have been reported as important molecules responsible for the regulation of intestinal homeostasis. Moreover, these molecules have a significant impact on the immune system and are able to affect inflammation, cardiovascular diseases, diabetes type II, or oncological diseases. For this purpose, SCFAs could be used as putative biomarkers of various diseases, including cancer. A potential diagnostic value may be offered by analyzing SCFAs with the use of advanced analytical approaches such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) coupled with mass spectrometry (MS). The presented review summarizes the importance of analyzing SCFAs from clinical and analytical perspective. Current advances in the analysis of SCFAs focused on sample pretreatment, separation strategy, and detection methods are highlighted. Additionally, it also shows potential areas for the development of future diagnostic tools in oncology and other varieties of diseases based on targeted metabolite profiling.

Non-targeted screening and trimethylamine determination in Tilletia foetida-infected wheat using HS-SPME-GC-MS

Common bunt disease of wheat in China is caused mainly by Tilletia foetida. However, reliable approaches for determining disease-associated biochemical markers are rarely reported. Here, a headspace-solid-phase microextraction coupled with headspace GC-tandem mass spectrometry (HS-SPME-GC-MS) was used to screen volatile substances in infected wheat, and an optimal chemical marker was selected to establish analytical methods for disease determination. Non-targeted screening of 13 volatile compounds unique to diseased wheat allowed a metabolite with rotten fish-like smell, trimethylamine (TMA), to be selected as the inspection marker. Subsequently, two analytical methodologies, HS-SPME-GC-MS and headspace gas chromatography with flame ionization detection (HS-GC-FID), were established to determinate the TMA content in wheat. The linear relationship, recovery and reproducibility of the methods were validated. The limit of detection (LOD) was 0.02 µg/kg for the former method, 5000-fold lower than that for the latter. When analysing samples, HS-SPME-GC-MS showed excellent sensitivity and allowed for the determination of 0.05% infected kernels among whole wheat grains. Therefore, TMA determination using HS-SPME-GC-MS is an effective alternative method to detect wheat common bunt disease occurring at extremely low infection rate.

Inflammatory and deleterious role of gut microbiota-derived trimethylamine on colon cells

Trimethylamine (TMA) is produced by the intestinal microbiota as a by-product of metabolism of dietary precursors. TMA has been implicated in various chronic health conditions. However, the effect of TMA in the colon and the underlying mechanism was not clear. In this study, TMA exhibited toxic effects in vitro as well as in vivo. TMA-induced oxidative stress causes DNA damage, and compromised cell membrane integrity leading to the release of LDH outside the cells which ultimately leads to cell death. Besides, TMA also exhibited pronounced increase in cell cycle arrest at G2/M phase in both HCT116 and HT29 cell lines. TMA was found to be genotoxic and cytotoxic as the TMA concentration increased from 0.15 mM. A decreased ATP intracellular content was observed after 24 h, 48 h, and 72 h treatment in a time and dose-dependent manner. For in vivo research, TMA (100 mM, i.p. and intra-rectal) once a week for 12 weeks caused significant changes in cellular morphology of colon and rectum epithelium as assessed by H & E staining. TMA also significantly increased the infiltration of inflammatory cells in the colon and rectal epithelium indicating the severity of inflammation. In addition, TMA caused extensive mucosal damage and distortion in the epithelium, decrease in length of small intestine compared to control mice. In conclusion, these results highlight the detrimental effects of TMA in the colon and rectal epithelium.

Metabolic alterations of short-chain fatty acids and TCA cycle intermediates in human plasma from patients with gastric cancer

AIMS

Short-chain fatty acids (SCFAs) are produced by gut microbiota from dietary fiber. Since absorbed SCFAs could be introduced into the tricarboxylic acid (TCA) cycle in host cells, the relationships between SCFAs and TCA cycle intermediates might influence to energy metabolism in the human body. For this reason, information on profile changes between SCFAs and TCA cycle intermediates could help unveil pathological mechanisms of gastric cancer.

MAIN METHODS

A gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed to simultaneously determine SCFAs and TCA cycle intermediates in human plasma from patients with chronic superficial gastritis (CSG), intestinal metaplasia (IM), and gastric cancer. We applied a tetra-alkyl ammonium pairing method to prevent loss of volatile SCFAs and base decarboxylation of TCA cycle intermediates during sample preparation. To assess gastric diseases, metabolic alterations of SCFAs and TCA cycle intermediates in human plasma with gastric disorders were analyzed by their plasma levels.

KEY FINDINGS

Significantly different metabolic alterations based on the plasma levels of SCFAs and TCA cycle intermediates were investigated in cancer metabolic pathways. Not only propionate and butyrate, mainly produced by gut microbiota, were significantly decreased, but also cis-aconitate, α-ketoglutarate, and fumarate were significantly increased in plasma with IM or gastric cancer, compared to CSG. Further, based on ratios of product to precursor, three metabolic pathways (succinate/propionate, succinate/α-ketoglutarate, and cis-aconitate/citrate) were supposed to be distorted between gastric diseases.

SIGNIFICANCE

In conclusion, propionate, cis-aconitate, α-ketoglutarate, and fumarate could be used to assess the progression of gastric cancer.

A Novel Gas Sensor for Detecting Pork Freshness Based on PANI/AgNWs/Silk

A novel, operational, reliable, flexible gas sensor based on silk fibroin fibers (SFFs) as a substrate was proposed for detecting the freshness of pork. Silk is one of the earliest animal fibers utilized by humans, and SFFs exposed many biological micromolecules on the surface. Thus, the gas sensor was fabricated through polyaniline (PANI) and silver nanowires (AgNWs) and deposited on SFFs by in-suit polymerization. With trimethylamine (TMA) as a model gas, the sensing properties of the PANI/AgNWs/silk composites were examined at room temperature, and the linear correlativity was very prominent between these sensing measures and the TMA measures in the range of 3.33 μg/L-1200 μg/L. When the pork sample is detected by the sensor, it can be classified into fresh or stale pork with the total volatile basic nitrogen (TVB-N) as an index. The result indicated that the gas sensor was effective and showed great potential for applications to detect the freshness of pork.

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.

Effect of Cordyceps militaris on formation of short-chain fatty acids as postbiotic metabolites

The aim of the current study was to determine the growth-promoting-effect of Cordyceps militaris, known as a medicinal mushroom, on Lactobacillus casei and Lactobacillus acidophilus. To evaluate the best growth-promoting activity of the test substrates including glucose, inulin, and at different concentrations of C. militaris (0.5%, 1%, and 2%), the cell counts, optical density (OD), prebiotic activity scores, and postbiotics (lactic, acetic, butyric, and propionic acids) were determined. The highest cell count was found for L. casei in media containing 0.5% C. militaris and for L. acidophilus in media containing 1% C. militaris. In the case of both strains, the OD values of the medium with C. militaris (1%) and (2%) increased similar to those of glucose. The prebiotic activity scores for both strains were positive. The concentration of lactic acid ranged from 0.56 to 8.07 g L^-1 for L. casei and 0.82 to 5.38 g L^-1 for L. acidophilus. Moreover, propionic acid was the highest among short-chain fatty acids (SCFAs) produced by both strains. According to the results of the present study, the tested Lactobacillus species can utilize C. militaris as carbon source and is able to form postbiotics in the media.

A validated simple LC-MS/MS method for quantifying trimethylamine N-oxide (TMAO) using a surrogate matrix and its clinical application

Trimethylamine N-oxide (TMAO) is a small molecular amine oxide generated from dietary choline and carnitine through intestinal microbial metabolism. Recently, TMAO has attracted much public attention as its role in disease progression has been proven in many clinical studies. The plasma concentration of TMAO in humans was found to be positively associated with the increased risk of many diseases including cardiovascular diseases and chronic kidney diseases. To achieve accurate and sensitive quantitation of TMAO for clinical applications, we established and validated a simple quantitative method using a liquid chromatography tandem mass spectrometry (LC-MS/MS) system. We constructed an eight-point calibration curve in an artificial surrogate matrix instead of the commonly used biological matrices to avoid interference from the endogenous TMAO. The calibration curve showed excellent linearity in the range of 1 to 5,000 ng/mL, with a correlation coefficient (R²) higher than 0.996 in each validation batch. Moreover, both the intra-day and inter-day assays achieved satisfactory precision and accuracy results ranging from 1.65–7.15% and 96.36–111.43%, respectively. Further, this method was cross-validated using a human plasma matrix and applied to a clinical pharmacology study. Overall, these results demonstrate that the developed quantitation method is applicable in clinical research for monitoring disease progression and evaluating drug effects.

Simultaneous quantification of eleven short-chain fatty acids by derivatization and solid phase microextraction - Gas chromatography tandem mass spectrometry

As metabolites of the gut microbiome, short-chain fatty acids (SCFAs) played an important role in the diagnosis of the metabolic diseases. Because of the high polarity, high volatility and complex matrix of biological samples, the highly sensitive, selective and accurate method to determine SCFAs remains a major challenge. Herein, a new method for simultaneous quantification of eleven SCFAs by derivatization combined with solid phase microextraction (SPME) and gas chromatography tandem mass spectrometry (GC-MS/MS) was developed. Isobutyl chloroformate coupled with isobutanol was used as the reaction reagent to derivatize SCFAs. The method validation data showed a satisfactory linearity with the linear regression coefficients (R) ranging from 0.9964 to 0.9996. The limit of detection (LOD) of all SCFAs ranges from 0.01 ng·mL^-1 to 0.72 ng·mL^-1 and the limit of quantification (LOQ) ranges from 0.04 ng·mL^-1 to 2.41 ng·mL^-1. The intra-day and inter-day precision (RSDs) ranged from 0.65% to 8.92% and 1.62% to 15.61%, respectively. The recovery ranged from 88.10% to 108.71%. Finally, the developed method was successfully used to determine SCFAs in mice fecal sample, and ten of the SCFAs were found in feces of mice, including formic acid.

Paper-based electrochemiluminescence device for the rapid estimation of trimethylamine in fish via the quenching effect of thioglycolic acid-capped cadmium selenide quantum dots

A paper-based electrochemiluminescence device (µPAD-ECL) for the estimation of trimethylamine (TMA) concentration in fish was developed using tris(2,2'-bipyridyl)ruthenium(II) complex coupled with water soluble thioglycolic acid-capped CdSe quantum dots on the inkjet-printed paper-based device. The quenching effect of tertiary amines on the ECL intensity was found to be sensitive and concentration dependent. This effect allows the measurement of TMA at low concentrations. Under the optimal conditions, the linear concentration range was exhibited from 1 × 10^-12 to 1 × 10^-7 M and a detection limit of 2.09 × 10^-13 M, with relative standard deviation of 1.97 %. The applicability of µPAD-ECL is demonstrated by the rapid estimation of trimethylamine concentration in fish tissue, and could be used as a method for screening the total amount of tertiary amines in fishery products in remote communities. The results obtained using the paper-based devices agreed well with those obtained applying high performance liquid chromatography with benzoyl derivatization, at a confidence level of 95%.

Fluorescent assay for quantitative analysis of trimethylamine N-oxide

Trimethylamine N-oxide (TMAO), a gut microbial metabolite involved in cardiovascular and kidney diseases, has great potential as a biomarker, thus making TMAO quantification of great significance. The current assay methods are mainly established on mass spectrometry. However, the classic enzymatic approach is absent, which may be because there is no appropriate single-enzyme reaction. Here, we prepared TMAO demethylase and formaldehyde dehydrogenase and found that these two bacterial enzymes catalyze an efficient coupled reaction that produces NADH from TMAO conversion. With the participation of another enzyme, diaphorase, the multienzymatic coupling system was constructed, which realizes the output of fluorescence signals from TMAO input using resazurin as a probe, thus laying the foundation for fluorescent assay. Through optimization, the sensitivity and specificity were improved. A pretreatment procedure was developed to eliminate formaldehyde that pre-exists with TMAO to avoid an interference effect. Our assay is suitable for quantifying serum TMAO in the range of 2.05-50 μM, covering actual levels in clinical samples, and exhibits a high degree of accordance with mass spectrometry. Therefore, the established fluorometric microplate assay is facile, sensitive and accurate and may enable low-cost and high-throughput analysis of TMAO in clinical laboratory diagnosis.

Trimethylamine N-oxide (TMAO) in human health

Due to numerous links between trimethylamine-N-oxide (TMAO) and various disorders and diseases, this topic is very popular and is often taken up by researchers. TMAO is a low molecular weight compound that belongs to the class of amine oxides. It is formed by the process of oxidation of trimethylamine (TMA) by the hepatic flavin monooxygenases (FMO1 and FMO3). TMAO is mainly formed from nutritional substrates from the metabolism of phosphatidylcholine/choline, carnitine, betaine, dimethylglycine, and ergothioneine by intestinal microflora in the colon. Its level is determined by many factors, such as age, gender, diet, intestinal microflora composition, kidney function, and also liver flavin monooxygenase activity. Many studies report a positive relationship between the level of TMAO concentration and the development of various diseases, such as cardiovascular diseases and cardiorenal disorders, including atherosclerosis, hypertension, ischemic stroke, atrial fibrillation, heart failure, acute myocardial infarction, and chronic kidney disease, and also diabetes mellitus, metabolic syndrome, cancers (stomach, colon), as well as neurological disorders. In this review, we have summarized the current knowledge on the effects of TMAO on human health, the relationship between TMAO and intestinal microbiota, the role of TMAO in different diseases, and current analytical techniques used in TMAO determination in body fluids.

A simple liquid chromatography/differential ion mobility spectrometry tandem mass spectrometry method for the determination of trimethylamine-N-oxide in human serum: An application in dialysis patients

RATIONALE

Trimethylamine-N-oxide (TMAO) is a potential indicator of cardiovascular disease and chronic kidney disorders. It is important to monitor the TMAO level in plasma or serum of hemodialysis patients. A simple liquid chromatography/differential ion mobility spectrometry tandem mass spectrometry (HPLC/DMS-MS/MS) method was established and validated for the determination of TMAO in the serum of hemodialysis patients.

METHODS

Chromatographic separation was performed on a Waters Atlantis HILIC silica column (2.1 × 50 mm, 3 μm). The gradient mobile phase consisted of 10 mM ammonium formate buffer and acetonitrile with 0.1% formic acid in both solvents. The serum sample was precipitated with acidic acetonitrile prior to HPLC/DMS-MS/MS analysis and TMAO-d₉ was used as the internal standard. Data acquisition was performed in positive ion mode with a DMS system before the electrospray ionization source. The selected reaction monitoring transitions were m/z 76.0 → 58.0 and m/z 85.2 → 66.1 for TMAO and the internal standard, respectively.

RESULTS

Excellent linearity was observed over the calibration range 0.05-20 μg/mL (r²  > 0.995). The method was validated for good specificity and sensitivity. The inter-run and intra-run precision and accuracy were less than 13.6% and 10.7%, respectively.

CONCLUSIONS

We established a novel and robust HPLC/DMS-MS/MS method for the quantification of TMAO in human serum samples. The validated assay was simple, rapid, sensitive and reliable. The developed method could be applied to the assay of serum samples from patients with kidney disease who are undergoing hemodialysis.

The role of gut microbiota (GM) and GM-related metabolites in diabetes and obesity. A review of analytical methods used to measure GM-related metabolites in fecal samples with a focus on metabolites' derivatization step

Disruption of gut microbiota (GM) composition is increasingly related to the pathogenesis of various metabolic diseases. Additionally, GM is responsible for the production and transformation of metabolites involved in the development of metabolic disorders, such as obesity and type 2 diabetes mellitus (T2DM). The current state of knowledge regarding the composition of GM and GM-related metabolites in relation to the progress and development of obesity and T2DM is presented in this review. To understand the relationships between GM-related metabolites and the development of metabolic disorders, their accurate qualitative and quantitative measurement in biological samples is needed. Feces represent a valuable biological matrix which composition may reflect the health status of the lower gastrointestinal tract and the whole organism. Mass spectrometry (MS), mainly in combination with gas chromatography (GC) or liquid chromatography (LC), is commonly used to measure fecal metabolites. However, profiling metabolites in such a complex matrix as feces is challenging from both analytical chemistry and biochemistry standpoints. Chemical derivatization is one of the most effective methods used to overcome these problems. In this review, we provide a comprehensive summary of the derivatization methods of GM-related metabolites prior to GC-MS or LC-MS analysis, which have been published in the last five years (2015-2020). Additionally, analytical methods used for the analysis of GM-related metabolites without the derivatization step are also presented.

Applying mass spectrometry-based assays to explore gut microbial metabolism and associations with disease

The workings of the gut microbiome have gained increasing interest in recent years through the mounting evidence that the microbiota plays an influential role in human health and disease. A principal focus of this research seeks to further understand the production of metabolic by-products produced by bacteria resident in the gut, and the subsequent interaction of these metabolites on host physiology and pathophysiology of disease. Gut bacterial metabolites of interest are predominately formed via metabolic breakdown of dietary compounds including choline and ʟ-carnitine (trimethylamine N-oxide), amino acids (phenol- and indole-containing uremic toxins) and non-digestible dietary fibers (short-chain fatty acids). Investigations have been accelerated through the application of mass spectrometry (MS)-based assays to quantitatively assess the concentration of these metabolites in laboratory- and animal-based experiments, as well as for direct circulating measurements in clinical research populations. This review seeks to explore the impact of these metabolites on disease, as well as to introduce the application of MS for those less accustomed to its use as a clinical tool, highlighting pertinent research related to its use for measurements of gut bacteria-mediated metabolites to further understand their associations with disease.

Enteral Nutrition in Pediatric Patients Undergoing Hematopoietic SCT Promotes the Recovery of Gut Microbiome Homeostasis

Hematopoietic stem cell transplantation (HSCT) is the first-line immunotherapy to treat several hematologic disorders, although it can be associated with many complications reducing the survival rate, such as acute graft-versus-host disease (aGvHD) and infections. Given the fundamental role of the gut microbiome (GM) for host health, it is not surprising that a suboptimal path of GM recovery following HSCT may compromise immune homeostasis and/or increase the risk of opportunistic infections, with an ultimate impact in terms of aGvHD onset. Traditionally, the first nutritional approach in post-HSCT patients is parenteral nutrition (PN), which is associated with several clinical adverse effects, supporting enteral nutrition (EN) as a preferential alternative. The aim of the study was to evaluate the impact of EN vs. PN on the trajectory of compositional and functional GM recovery in pediatric patients undergoing HSCT. The GM structure and short-chain fatty acid (SCFA) production profiles were analyzed longitudinally in twenty pediatric patients receiving HSCT—of which, ten were fed post-transplant with EN and ten with total PN. According to our findings, we observed the prompt recovery of a structural and functional eubiotic GM layout post-HSCT only in EN subjects, thus possibly reducing the risk of systemic infections and GvHD onset.

Derivatization-free determination of short-chain volatile amines in human plasma and urine by headspace gas chromatography-mass spectrometry

BACKGROUND

Short-chain volatile amines (SCVA) are an interesting compound class playing crucial roles in physiological and toxicological human settings. Dimethylamine (DMA), trimethylamine (TMA), diethylamine (DEA), and triethylamine (TEA) were investigated in detail.

METHODS

Headspace gas chromatography coupled to mass spectrometry (HS-GC-MS) was used for the simultaneous qualitative and quantitative determination of four SCVA in different human body fluids. Four hundred microliters of Li-heparin plasma and urine were analyzed after liberation of volatile amines under heated conditions in an aqueous alkaline and saline environment. Target analytes were separated on a volatile amine column and detected on a Thermo DSQ II mass spectrometer scheduled in single ion monitoring mode.

RESULTS

Chromatographic separation of selected SCVA was done within 7.5 minutes. The method was developed and validated with respect to accuracy, precision, recovery and stability. Accuracy and precision criteria were below 12% for all target analytes at low and high levels. The selected extraction procedure provided recoveries of more than 92% from both matrices for TMA, DEA and TEA. The recovery of DMA from Li-heparin plasma was lower but still in the acceptable range (>75%). The newly validated method was successfully applied to plasma and urine samples from healthy volunteers. Detected concentrations of endogenous metabolites DMA and TMA are comparable to already known reference ranges.

CONCLUSION

Herein, we describe the successful development and validation of a reliable and broadly applicable HS-GC-MS procedure for the simultaneous and quantitative determination of SCVA in human plasma and urine without relying on derivatization chemistry.

Assessment of gut microbiota fecal metabolites by chromatographic targeted approaches

Gut microbiota, the specific microbial community of the gastrointestinal tract, by means of the production of microbial metabolites provides the host with several functions affecting metabolic and immunological homeostasis. Insights into the intricate relationships between gut microbiota and the host require not only the understanding of its structure and function but also the measurement of effector molecules acting along the gut microbiota axis. This article reviews the literature on targeted chromatographic approaches in analysis of gut microbiota specific metabolites in feces as the most accessible biological matrix which can directly probe the connection between intestinal bacteria and the (patho)physiology of the holobiont. Together with a discussion on sample collection and preparation, the chromatographic methods targeted to determination of some classes of microbiota-derived metabolites (e.g., short-chain fatty acids, bile acids, low molecular masses amines and polyamines, vitamins, neurotransmitters and related compounds) are discussed and their main characteristics, summarized in Tables.