Targeted metabolomics analysis of aromatic amino acids and their gut microbiota-host cometabolites in rat serum and urine by liquid chromatography coupled with tandem mass spectrometry

Determination of indoxyl sulfate by spectrofluorimetric method in human plasma through extraction with deep eutectic solvent

A rapid and efficient analytical method was established to quantify indoxyl sulfate (IS) in plasma through extraction technique with a deep eutectic solvent (DES) and spectrofluorimetric method. DES (choline chloride: urea) was mixed with plasma samples for the extraction of IS, followed by the addition of dipotassium hydrogen phosphate (K2HPO4) solution to form an aqueous two-phase system. The fluorescence intensity of IS which was first extracted to the DES-rich-phase and then back-extracted into the salt-rich-phase, was measured by spectrofluorimetric method. Some key factors such as pH, centrifugation speed and time, the volume ratio of DES/salt, and salt concentration were optimized. Under the optimized conditions, the suggested method had a dynamic range between 20 and 160 µg/mL with a coefficient of determination (R2) of 0.99. Precision (relative standard deviation) was less than 15% and accuracy (% relative recovery) was ± 15% at the nominal concentration level. In addition, results showed that IS levels in real samples were higher than 40 µg/mL which was compatible with reported IS levels in end-stage renal disease (ESRD) patients. Overall, all the results reflect the fact that the presented analytical method can potentially be used for the determination of IS in real plasma samples.

Mass spectrometry-based analysis of gut microbial metabolites of aromatic amino acids

Small molecules derived from gut microbiota have been increasingly investigated to better understand the functional roles of the human gut microbiome. Microbial metabolites of aromatic amino acids (AAA) have been linked to many diseases, such as metabolic disorders, chronic kidney diseases, inflammatory bowel disease, diabetes, and cancer. Important microbial AAA metabolites are often discovered via global metabolite profiling of biological specimens collected from humans or animal models. Subsequent metabolite identity confirmation and absolute quantification using targeted analysis enable comparisons across different studies, which can lead to the establishment of threshold concentrations of potential metabolite biomarkers. Owing to their excellent selectivity and sensitivity, hyphenated mass spectrometry (MS) techniques are often employed to identify and quantify AAA metabolites in various biological matrices. Here, we summarize the developments over the past five years in MS-based methodology for analyzing gut microbiota-derived AAA. Sample preparation, method validation, analytical performance, and statistical methods for correlation analysis are discussed, along with future perspectives.

Integrative metabolomics science in Alzheimer's disease: Relevance and future perspectives

Alzheimer's disease (AD) is determined by various pathophysiological mechanisms starting 10-25 years before the onset of clinical symptoms. As multiple functionally interconnected molecular/cellular pathways appear disrupted in AD, the exploitation of high-throughput unbiased omics sciences is critical to elucidating the precise pathogenesis of AD. Among different omics, metabolomics is a fast-growing discipline allowing for the simultaneous detection and quantification of hundreds/thousands of perturbed metabolites in tissues or biofluids, reproducing the fluctuations of multiple networks affected by a disease. Here, we seek to critically depict the main metabolomics methodologies with the aim of identifying new potential AD biomarkers and further elucidating AD pathophysiological mechanisms. From a systems biology perspective, as metabolic alterations can occur before the development of clinical signs, metabolomics - coupled with existing accessible biomarkers used for AD screening and diagnosis - can support early disease diagnosis and help develop individualized treatment plans. Presently, the majority of metabolomic analyses emphasized that lipid metabolism is the most consistently altered pathway in AD pathogenesis. The possibility that metabolomics may reveal crucial steps in AD pathogenesis is undermined by the difficulty in discriminating between the causal or epiphenomenal or compensatory nature of metabolic findings.

Dietary fat and low fiber in purified diets differently impact the gut-liver axis to promote obesity-linked metabolic impairments

Selecting the most relevant control diet is of critical importance for metabolic and intestinal studies in animal models. Chow and LF-purified diet differentially impact metabolic and gut microbiome outcomes resulting in major changes in intestinal integrity in LF-fed animals which contributes to altering metabolic homeostasis. Dietary fat and low fiber both contribute to the deleterious metabolic effect of purified HF diets through both selective and overlapping mechanisms.

Mechanistic Insights into Alzheimer's Disease Unveiled through the Investigation of Disturbances in Central Metabolites and Metabolic Pathways

Hydrophilic metabolites are closely involved in multiple primary metabolic pathways and, consequently, play an essential role in the onset and progression of multifactorial human disorders, such as Alzheimer’s disease. This review article provides a comprehensive revision of the literature published on the use of mass spectrometry-based metabolomics platforms for approaching the central metabolome in Alzheimer’s disease research, including direct mass spectrometry, gas chromatography-mass spectrometry, hydrophilic interaction liquid chromatography-mass spectrometry, and capillary electrophoresis-mass spectrometry. Overall, mounting evidence points to profound disturbances that affect a multitude of central metabolic pathways, such as the energy-related metabolism, the urea cycle, the homeostasis of amino acids, fatty acids and nucleotides, neurotransmission, and others.

Black Phosphorus Nanosheets Induced Oxidative Stress In Vitro and Targeted Photo-thermal Antitumor Therapy

Black phosphorus (BP) nanosheets with excellent features have been broadly employed for cancer therapy. BPs in blood were known to form BP nanomaterial-corona complexes, yet not explored their biological effects. In this study, BPs as delivery vehicles loaded with doxorubicin (DOX) (BP-DOX) by electrostatic interaction had been successfully prepared for photo-thermal/chemotherapy with a tumor inhibition rate of 81.47% more than the rates of BPs (69.50%) and free DOX (51.91%) in the Hela-bearing mice model by a pH/photo-responsive controlled drug release property. Then, in vivo experiments demonstrated that the treatment of healthy mice with BPs led to mild inflammation in the body and oxidative stress in the liver and lung which caused cell apoptosis. In vitro studies further showed that oxidative stress and metabolic disorders could be induced by BPs in A549, HepG2, Beas-2B, and LO2 cells. Lastly, the RGD peptide-conjugated red blood cell (RBC) membrane-coated BPs (RGD-RBC@BP) was prepared by lipid insertion and co-ultrasound methods for efficient photo-thermal therapy (PTT) cancer via a tumor-targeted strategy. RGD-RBC@BP showed positive biocompatibility, photo-thermal properties, and increased cellular uptake by Hela cells benefited by the long circulation property of RBC and RGD peptides. Pharmacokinetics and bio-distribution study of RGD-RBC@BP were found to prolong circulation time and tended to accumulate in the tumors, which overexpression of ανβ3 integrin rather than livers after intravenous injection 24 h in vivo. After 808 nm laser irradiation, RGD-RBC@BP nanoparticles exhibited a better PTT than PEGylated BPs (BP-PEG). The active-targeting strategy of biomimetic nanomaterials based on the tumor microenvironment have been proved to have favorable biological prospects in cancer PTT.

High-throughput metabolomics method based on liquid chromatography-mass spectrometry: Insights into the underlying mechanisms of salinity-alkalinity exposure-induced metabolites changes in Barbus capito

It is critical to investigate the adaptive development and the physiological mechanism of fish in external stimulation. In this study, the response of Barbus capito to salinity-alkalinity exposure was explored by high-throughput nontargeted and liquid chromatography-mass spectrometry-based metabolomics to investigate metabolic biomarker and pathway changes. Meanwhile, the biochemical indexes of Barbus capito were measured to discover the chronic impairment response to salinity-alkalinity exposures. A total of 29 tissue metabolites were determined to deciphering the endogenous metabolic changes of fishes during the different concentration salinity-alkalinity exposures environment, which were mainly involved in the key metabolism including the phenylalanine, tyrosine, and tryptophan biosynthesis, arachidonic acid metabolism, pyruvate metabolism, citrate cycle, and glycerophospholipid metabolism. Finally, we found the amino acid metabolism as key target was associated with the endogenous metabolites and metabolic pathways of Barbus capito to salinity-alkalinity exposures. In conclusion, metabolomics is a potentially powerful tool to reveal the mechanism information of fish in various exposure environments.

Improvised method for urinary p-cresol detection and measurement using high performance liquid chromatography/mass spectrometry

Gut microbiota has been implicated in many disorders including Autism Spectrum Disorder (ASD). ASD is a neurodevelopmental brain disorder affecting individuals leading to restricted and repetitive pattern of behaviour and disruption of communication and social interactions. Altered microbiome and the presence or absence of key species capable of affecting specific responses in levels of their fermentation products are reflected in the urinary metabolite profile of patients. The aim of our study is to develop an improvised method for the detection and quantification of urinary p-cresol levels which could serve as an indicator for GI microbial dysbiosis. The p-cresol analysis was achieved using HPLC by a reverse phase C18 column with mobile phase composition of Acetonitrile/water/formic acid (10:90:0.05, v/v/v) in an isocratic mode of elution with a flow rate of 1.0 mL/min. The mass analysis of p-cresol was performed using LC-MS [Triple Quadrupole Liquid Chromatography Mass Spectrometer] in negative ESI mode with electron multiplier detector. p-cresol was eluted at a retention time of approximately 3.4 min. The standard calibration curves had a superior regression coefficient of greater than 0.99 (R² > 0.99) and were linear over a range from 0.0005 mg/mL to 0.015 mg/mL. The method was validated by analysis of six replicates with 0.08% relative standard deviation and method detection and quantification limits were 20 ng/mL and 50 ng/mL respectively. Further validation of method on real urine samples from two groups of children (Control population:< 10 years of age; 5M: 3F and ASD individuals: <10 years of age; All males) showed that detection was effective over a wide range of metabolite at levels as high as 149.73 μg/mL to as low as 0.897 μg/mL. This study reports a rapid, validated and sensitive method for the detection of p-cresol in urine samples.

Metabolomics technology and bioinformatics for precision medicine

Precision medicine is rapidly emerging as a strategy to tailor medical treatment to a small group or even individual patients based on their genetics, environment and lifestyle. Precision medicine relies heavily on developments in systems biology and omics disciplines, including metabolomics. Combination of metabolomics with sophisticated bioinformatics analysis and mathematical modeling has an extreme power to provide a metabolic snapshot of the patient over the course of disease and treatment or classifying patients into subpopulations and subgroups requiring individual medical treatment. Although a powerful approach, metabolomics have certain limitations in technology and bioinformatics. We will review various aspects of metabolomics technology and bioinformatics, from data generation, bioinformatics analysis, data fusion and mathematical modeling to data management, in the context of precision medicine.

Targeted metabolomics for the quantitative measurement of 9 gut microbiota-host co-metabolites in rat serum, urine and feces by liquid chromatography-tandem mass spectrometry

Gut microbiota-host co-metabolites play an essential role in maintaining homeostasis, and their concentration changes are closely related to a variety of diseases. Developing a targeted metabolomics analytical platform for these co-metabolites will help to elucidate the relationship between intestinal flora and host. Here we present a simple and sensitive liquid chromatography-tandem mass spectrometry method for the analysis of nine gut microbiota-host co-metabolites in rat serum, urine and feces. The compounds were separated on a reversed-phase C₁₈ column using gradient elution with a solvent system consisting of methanol and water (containing 0.05% formic acid) and a 7-min run time. All of the calibration curves exhibited good linear relationships (R² ≥ 0.9984, Percent Residual Accuracy ≥93.27%). The intra- and interday precision, expressed as relative standard deviation (RSD), was ≤ 14.84%. The accuracy was within 100 ± 13.16% for all analytes. The recovery of the nine compounds in biological samples was ≥ 85.80% with an appropriate RSD (≤12.04%). The validated method was successfully applied to monitor the global changes of these metabolites in obesity. Taken together, these results demonstrate that the method can simultaneously determine the nine co-metabolites in multiple biological matrices and is an essential part of the targeted metabolomics analytical platform, which may become an approach to evaluate the occurrence, development and therapeutic effects of metabolic diseases.

Sample preparation for polar metabolites in bioanalysis

Sample preparation is a primary step of any bioanalytical workflow, especially in metabolomics where maximum information has to be obtained without spoiling the analytical instrument. The sample extraction of polar metabolites is still challenging but strategies exist to enable the phase transfer of hydrophilic metabolites from the biological phase to a clean interference-free phase.