Isotope-coded ESI-enhancing derivatization reagents for differential analysis, quantification and profiling of metabolites in biological samples by LC/MS: A review

Derivatization of carboxylic groups prior to their LC analysis - A review

Carboxylic acids (CAs) represent a large group of important molecules participating in various biologically significant processes. Analytical study of these compounds is typically performed by liquid chromatography (LC) combined with various types of detection. However, their analysis is often accompanied by a wide variety of problems depending on used separation system or detection method. The dominant ones are: i) poor chromatographic behavior of the CAs in reversed-phase LC; ii) absence of a chromophore (or fluorophore); iii) weak ionization in mass spectrometry (MS). To overcome these problems, targeted chemical modification, and derivatization, come into play. Therefore, derivatization still plays an important and, in many cases, irreplaceable role in sample preparation, and new derivatization methods of CAs are constantly being developed. The most commonly used type of reaction for CAs derivatization is amidation. In recent years, an increased interest in the isotopic labeling derivatization method has been observed. In this review, we comprehensively summarize the possibilities and actual trends in the derivatization of CAs that have been published over the past decade.

Highly effective and selective FeBr3-promoted deuterium bromination/cyclization of 1,n-enynes

A highly effective and selective FeBr3-promoted deuterium bromination/cyclization of 1,n-enynes is reported. On the one hand, the Lewis acid FeBr3 as a catalyst promotes cyclization of 1,n-enynes to afford deuterium heterocyclic frameworks with high efficiency. On the other hand, FeBr3 serves as the bromine source (with D2O as the deuterium source) to promote the formation of the desired deuterated pyrrole derivatives containing alkenyl bromide groups. This protocol provides an effective pathway to afford deuterated alkenyl brominative compounds as (Z)-isomers with high yields and selectivity, offering a new method for introducing 2H into organic compounds.

Strategy for characterization and quantification of fatty acids in plasma by parallel d0/d6-dansylhydrazine derivatization combined with UPLC-MS/MS

Fatty acids (FAs) play a vital physiological role in lipid metabolism, which is reported as potential diagnostic biomarker for various diseases. Thus, it is urgent to develop a credible method that can profile FA metabolism with a holistic view. Here, a targeted strategy to screen FAs was developed by parallel labeling with d0/d6-dansylhydrazine (d0/d6-DnsHz) and using ultra-high performance liquid chromatography coupled with high-resolution tandem mass spectrometry (UPLC-MS/MS) in data-dependent MS/MS (ddMS2) mode. The simple and mild derivatization procedure within 3 h allowed for a significant improvement in sensitivity. Additionally, the characteristic product ions introduced by the derivatization reagent assist to identify the unknown FA species. A quantitation method was established by multiple reaction monitoring (MRM) and the d6-DnsHz tagged standards for each analyte were used as internal standards to overcome the matrix effects. By applying the method to determine FA levels in plasma collected from the esophageal squamous cell carcinoma (ESCC) patients and healthy controls, 65 FA metabolites were characterized and six FAs were found to be altered by the invasion of tumors. The parallel derivatization strategy provides insights into the identification of unknown FAs and paves a new way for targeted metabolomics. Also, this novel method is a powerful tool for characterization and quantification of FAs in biological samples, which shows a great potential application in clinical diagnosis and investigation of disease mechanisms.

Development and validation of an LC-MS/MS method for simultaneous determination of EVT201 and its five metabolites in human plasma: Application to a clinical study in Chinese healthy subjects

EVT201 is a partial GABAA receptor agonist, which inhibits nervous system to treat insomnia. EVT201 can form a variety of metabolites in vivo including Ro46-1927, Ro18-5528, Ro40-9970, Ro66-9196 and Ro66-5448. This study developed a simple method to realize the simultaneous determination of EVT201 and its five metabolites by HPLC-MS/MS with an electrospray ion source (ESI). The deuterium substitute of EVT201 was chosen as the internal standard and the multiple reaction monitoring (MRM) was used for the quantification. The separation of the six compounds was accomplished with an ACE Excel 3 AQ column (50 × 2.1 mm, 3 µm, ACE). The process of protein precipitating-transferring-nitrogen blowing-reconstituting was adopted for the sample pretreatment. This method was successfully validated according to the FDA guidance. Calibration curves were linear over the concentration range of 0.100-100 ng/mL for EVT201, 0.0300-30.0 ng/mL for Ro46-1927, 0.0600-6.00 ng/mL for Ro18-5528, 0.0200-4.00 ng/mL for Ro40-9970, 0.100-20.0 ng/mL for Ro66-9196 and 0.100-20.0 ng/mL for Ro66-5448. The intra-run and inter-run precisions and accuracies were all within 14.5%. This fully validated method was successfully applied to a clinical pharmacokinetic study of EVT201 and its five metabolites in Chinese healthy subjects after the single (2.5 mg and 5 mg, N = 12) and multiple dose (2.5 mg, N = 13) administration of EVT201 capsules. The test results of 2.5 mg dose group showed that for EVT201, Ro46-1927, Ro18-5528, Ro40-9970, Ro66-9196 and Ro66-5448, the Cmax values (ng/mL) were 39.2 ± 9.2, 10.3 ± 1.4, 0.218 ± 0.044, 0.128 ± 0.051, 7.01 ± 1.51, 8.73 ± 3.69, respectively; the AUC0-t values (h·ng/mL) were 231 ± 79, 143 ± 72, 10.9 ± 2.1, 1.84 ± 0.78, 55.9 ± 18.7, 135 ± 40 respectively. For EVT201, Ro46-1927, Ro66-5528, Ro66-9196 and Ro40-5448, the results of Cmax and AUC0-t proved that the five compounds showed linear pharmacokinetic profile over the dose ranges of 2.5 mg to 5 mg. Meanwhile, it is the first report to evaluate the pharmacokinetic characteristics of Ro40-9970, Ro66-9196 and Ro66-5448 in human plasma. It provided meaningful parameters for the safety and tolerability evaluation of EVT201 capsules in human.

Drugs possessing aryloxypropanamine pharmacophore, duloxetine, dapoxetine and propranolol, increase allopregnanolone in rat brain: Possible involvement of allopregnanolone in their central nervous system effects

Allopregnanolone (AP) is a neurosteroid synthesized in the brain and a positive allosteric modulator of γ-aminobutyric acid (GABA) type A receptors. Some drugs possessing the aryloxypropanamine (AOPA) pharmacophore, such as fluoxetine, exert their central nervous system (CNS) effects by increasing the brain AP. Although duloxetine (DLX), dapoxetine (DPX), atomoxetine (ATX) and propranolol (PRL) also possess the AOPA pharmacophore and are used to treat some psychiatric disorders, the capabilities of these drugs to increase the brain AP and the possible involvement of AP in their CNS effects remain to be fully elucidated. To clarify these points, we first developed a method for quantifying AP in the rat brain by liquid chromatography/electrospray ionization-tandem mass spectrometry. Analysis of the changes in the brain AP levels using this method revealed that the intraperitoneal administration of DLX (10 mg/kg), DPX (10 mg/kg) and PRL (20 mg/kg) significantly increased the brain AP (DLX: < 0.40-2.74 ng/g tissue, DPX: 1.48-3.83 ng/g tissue and PRL: < 0.40-2.09 ng/g tissue) compared to the saline administration (<0.40 ng/g tissue). These results suggested the possible involvement of the GABAergic neurosteroid, AP, in the central actions of DLX, DPX and PRL. In contrast, ATX (10 mg/kg) did not affect the AP levels in the brain. In addition, the brain and serum AP levels had a remarkably high positive correlation after the administration of DLX, DPX and PRL. Thus, this study proposed the AP-related novel mechanism of actions of DLX, DPX and PRL in the CNS.

Metabolic deuterium oxide (D2O) labeling in quantitative omics studies: A tutorial review

Mass spectrometry (MS) is an invaluable tool for sensitive detection and characterization of individual biomolecules in omics studies. MS combined with stable isotope labeling enables the accurate and precise determination of quantitative changes occurring in biological samples. Metabolic isotope labeling, wherein isotopes are introduced into biomolecules through biosynthetic metabolism, is one of the main labeling strategies. Among the precursors employed in metabolic isotope labeling, deuterium oxide (D₂O) is cost-effective and easy to implement in any biological systems. This tutorial review aims to explain the basic principle of D₂O labeling and its applications in omics research. D₂O labeling incorporates D into stable C-H bonds in various biomolecules, including nucleotides, proteins, lipids, and carbohydrates. Typically, D₂O labeling is performed at low enrichment of 1%-10% D₂O, which causes subtle changes in the isotopic distribution of a biomolecule, instead of the complete separation between labeled and unlabeled samples in a mass spectrum. D₂O labeling has been employed in various omics studies to determine the metabolic flux, turnover rate, and relative quantification. Moreover, the advantages and challenges of D₂O labeling and its future prospects in quantitative omics are discussed. The economy, versatility, and convenience of D₂O labeling will be beneficial for the long-term omics studies for higher organisms.

Deuterated Drugs and Biomarkers in the COVID-19 Pandemic

Coronavirus disease 2019 (COVID-19) is a highly contagious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Initially identified in Wuhan (China) in December 2019, COVID-19 rapidly spread globally, resulting in the COVID-19 pandemic. Carriers of the SARS-CoV-2 can experience symptoms ranging from mild to severe (or no symptoms whatsoever). Although vaccination provides extra immunity toward SARS-CoV-2, there has been an urgent need to develop treatments for COVID-19 to alleviate symptoms for carriers of the disease. In seeking a potential treatment, deuterated compounds have played a critical role either as therapeutic agents or as internal MS standards for studying the pharmacological properties of new drugs by quantifying the parent compounds and metabolites. We have identified >70 examples of deuterium-labeled compounds associated with treatment of COVID-19. Of these, we found 9 repurposed drugs and >20 novel drugs studied for potential therapeutic roles along with a total of 38 compounds (drugs, biomarkers, and lipids) explored as internal mass spectrometry standards. This review details the synthetic pathways and modes of action of these compounds (if known), and a brief analysis of each study.

Analytical derivatizations in environmental analysis

Analytical derivatization is a technique that alters the structure of an analyte and produces a product more suitable for analysis. While this process can be time-consuming and add reagents to the procedure, it can also facilitate the isolation of the analyte(s), enhance analytes' stability, improve separation and sensitivity, and reduce matrix interferences. Since derivatization is a functional group analysis, it improves selectivity by separating reactive from neutral compounds during sample preparation. This technique introduces detector-orientated tags into analytes that lack suitable physicochemical properties for detection at low concentrations. Notably, many regulatory bodies, especially those in the environmental field, require these characteristics in analytical methods. This review focuses on note-worthy analytical derivatization methods employed in environmental analyses with functional groups, phenol, carboxylic acid, aldehyde, ketone, and thiol in aqueous, soil, and atmospheric sample matrices. Both advantages and disadvantages of analytical derivatization techniques are discussed. In addition, we discuss the future directions of analytical derivatization methods in environmental analysis and the potential challenges.

Synthesis and anti-SARS-CoV-2 activity of deuterated GS-441524 analogs

The COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is continuing to spread around the world. GS-441524 is the parent nucleoside of remdesivir which is the first drug approved for the treatment of COVID-19, and demonstrates strong activity against SARS-Cov-2 in vitro and in vivo. Herein, we reported the synthesis of a series of deuterated GS-441524 analogs, which had deuterium atoms up to five at the ribose and the nucleobase moieties. Compared to GS-441524, all the deuterated compounds showed similar inhibitory activities against SARS-CoV-2 in vitro.

Metabolic Alteration Analysis of Steroid Hormones in Niemann-Pick Disease Type C Model Cell Using Liquid Chromatography/Tandem Mass Spectrometry

Niemann–Pick disease type C (NPC) is an autosomal recessive disease caused by a functional deficiency of cholesterol-transporting proteins in lysosomes, and exhibits various clinical symptoms. Since mitochondrial dysfunction in NPC has recently been reported, cholesterol catabolism to steroid hormones may consequently be impaired. In this study, we developed a comprehensive steroid hormone analysis method using liquid chromatography/tandem mass spectrometry (LC–MS/MS) and applied it to analyze changes in steroid hormone concentrations in NPC model cells. We investigated the analytical conditions for simultaneous LC–MS/MS analysis, which could be readily separated from each other and showed good reproducibility. The NPC phenotype was verified as an NPC model with mitochondrial abnormalities using filipin staining and organelle morphology observations. Steroid hormones in the cell suspension and cell culture medium were also analyzed. Steroid hormone analysis indicated that the levels of six steroid hormones were significantly decreased in the NPC model cell and culture medium compared to those in the wild-type cell and culture medium. These results indicate that some steroid hormones change during NPC pathophysiology and this change is accompanied by mitochondrial abnormalities.

Multiplatform Metabolomics Studies of Human Cancers With NMR and Mass Spectrometry Imaging

The status of metabolomics as a scientific branch has evolved from proof-of-concept to applications in science, particularly in medical research. To comprehensively evaluate disease metabolomics, multiplatform approaches of NMR combining with mass spectrometry (MS) have been investigated and reported. This mixed-methods approach allows for the exploitation of each individual technique's unique advantages to maximize results. In this article, we present our findings from combined NMR and MS imaging (MSI) analysis of human lung and prostate cancers. We further provide critical discussions of the current status of NMR and MS combined human prostate and lung cancer metabolomics studies to emphasize the enhanced metabolomics ability of the multiplatform approach.

Progress and Challenges in Quantifying Carbonyl-Metabolomic Phenomes with LC-MS/MS

Carbonyl-containing metabolites widely exist in biological samples and have important physiological functions. Thus, accurate and sensitive quantitative analysis of carbonyl-containing metabolites is crucial to provide insight into metabolic pathways as well as disease mechanisms. Although reversed phase liquid chromatography electrospray ionization mass spectrometry (RPLC-ESI-MS) is widely used due to the powerful separation capability of RPLC and high specificity and sensitivity of MS, but it is often challenging to directly analyze carbonyl-containing metabolites using RPLC-ESI-MS due to the poor ionization efficiency of neutral carbonyl groups in ESI. Modification of carbonyl-containing metabolites by a chemical derivatization strategy can overcome the obstacle of sensitivity; however, it is insufficient to achieve accurate quantification due to instrument drift and matrix effects. The emergence of stable isotope-coded derivatization (ICD) provides a good solution to the problems encountered above. Thus, LC-MS methods that utilize ICD have been applied in metabolomics including quantitative targeted analysis and untargeted profiling analysis. In addition, ICD makes multiplex or multichannel submetabolome analysis possible, which not only reduces instrument running time but also avoids the variation of MS response. In this review, representative derivatization reagents and typical applications in absolute quantification and submetabolome profiling are discussed to highlight the superiority of the ICD strategy for detection of carbonyl-containing metabolites.

Development of an LC-MS/MS method for quantification of 3-chloro-L-tyrosine as a candidate marker of chlorine poisoning

A simple and sensitive liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method for the determination of 3-chloro-L-tyrosine (Cl-Tyr) was developed and validated. For sample preparation, 50 μL of the body fluids or tissue extracts were processed by protein precipitation followed by the derivatization with dansyl chloride. The calibration curve was linear over the concentration range of 2.0-200 ng/mL blood or 4.0-400 ng/g tissue. Our method allowed the reproducible and accurate quantification. That is, the intra- and inter-assay coefficients of variation were below 7.73 and 6.94%, respectively in both the blood and lung. We applied the developed method to the analysis of Cl-Tyr in the human autopsy samples, which were suspected of chlorine poisoning, and detected 55.2 ng/mL and 206.6 ng/g Cl-Tyr in left heart blood and lung, respectively. Furthermore, in more than 20 autopsy samples, which were obtained from other causes of death including burn, drowning, hanging, internal disease, trauma and drug poisoning, Cl-Tyr was almost not detected in their both body fluids and organ tissues. In conclusion, the data here reported demonstrate that the LC/ESI-MS/MS method allows the Cl-Tyr in the autopsy samples and that chlorine exposure strongly affects its level, providing a basis for novel identification tool of chlorine poisoning.

Quantitative analysis of the relationship of derivatization reagents and detection sensitivity of electrospray ionization-triple quadrupole tandem mass spectrometry: Hydrazines as prototypes

Chemical derivatization-assisted electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQ-MS) has become an efficient tool for the quantification of low-molecular-weight molecules. Many studies found that the derivatives of the same analytes derivatized by different derivatization reagents with the same reaction group had different detection sensitivity, even under the same conditions of electrospray ionization-mass spectrometry (ESI-MS). This phenomenon was suggested to be caused by the different modifying groups in the derivatization reagents. However, there is still a lack of systematic study on how modifying groups in the derivatization reagents affect the detection sensitivity of their corresponding derivatives of analytes, especially theoretical investigations. In this study, we employed a quantitative structure-activity relationship (QSAR) modeling approach to explore the relationship between modifying group structures and the detection sensitivity of derivatization reagents and their derivatives during ESI-MS detection. A total of 110 derivatization reagents of the hydrazine family and their hexanal derivatives (substituted hydrazones) were selected as the prototypes to construct QSAR models. The established models suggested that several molecular descriptors, related to hydrophobicity, electronegativity, and molecular shape, were related to the detection sensitivity of hexanal derivatives induced by different modifying groups in the derivatization reagents. Besides, we found that the detection sensitivity of compounds detected in selected ion mode (SIM) showed a positive correlation with that obtained in multiple reaction monitoring mode (MRM), and the ionization efficiency was the key factor on the detection sensitivity in both modes.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Reliable and generic liquid chromatography/mass spectrometry quantification of short peptides using a stable-isotope-labeled labeling agent

RATIONALE

It is important to investigate the behavior of protein hydrolysate components in both in vitro and in vivo studies, to support the elucidation of their biological functions. As protein hydrolysates and biological matrices are highly complex mixtures, it is essential to apply fully reliable and flexible analytical approaches.

METHODS

A novel and generic Liquid Chromatography/Mass Spectrometry methodology was developed to analyze short peptides. A stable-isotope-labeled labeling agent 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (¹³ C₃ ) was synthesized and used to prepare internal standards from non-labeled analyte peptides. The amino acid and peptides p, pG, Pp, GPp and PpG (where p stands for hydroxyproline) were used for proof of principle.

RESULTS

The method showed acceptable performance in solvent, in simulated gastrointestinal fluid and in serum. The (linear) dynamic range expanded to over four orders of magnitude, which is very useful when multiple analytes are analyzed in a biological matrix, due to the large differences in concentrations observed for endogenous and protein hydrolysate components. The method provides absolute-quantitative results and is fully accountable on the single-sample and single-component level.

CONCLUSIONS

The methodology can be applied to reliably quantify protein hydrolysate nutraceutical components at various stages during their in vivo processing. Internal standards can also be synthesized for other short peptides whenever they are expected to have biological relevance and require quantification. Overall this provides an excellent analytical tool to support the elucidation of the biological functions of protein hydrolysate components.

Qualitative and quantitative analysis of the major constituents in Spatholobi Caulis by UFLC-Triple TOF-MS/MS and UFLC-QTRAP-MS/MS

There have been few comprehensive studies on the holistic chemical composition of Spatholobi Caulis (SC) and consequently, the information is lacking for the in-depth study of the major constituents. SC is a kind of widely used traditional Chinese medicine with its xylem and phloem alternately arranged in 3-10 rings, but the relationship of phloem ring number and the quality remains unclear. In this study, the characterization of the major constituents in SC was analyzed by ultra-fast liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (UFLC-Triple TOF-MS/MS), and the content of 19 flavonoids in SC with different phloem ring numbers was simultaneously determined by ultra-fast liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (UFLC-QTRAP-MS/MS). Correlation analysis was performed to evaluate the quality of SC with different phloem ring numbers according to the content of 19 flavonoids. Results showed that 50 constituents in SC were identified and the fragmentation pathways of different types of compounds were preliminarily deduced by the fragmentation behavior of the 50 constituents. In addition, the content of flavonoids increased with phloem ring number, which demonstrated that the content of flavonoids in SC was positively correlated with the number of phloem rings. Our research will contribute to the variety identification and quality evaluation of SC, and provide a scientific basis for evaluating the quality of medicinal materials based on its appearance and characteristics.

Derivatization procedures and their analytical performances for HPLC determination in bioanalysis

Derivatization, or chemical structure modification, is often used in bioanalysis performed by liquid chromatography technique in order to enhance detectability or to improve the chromatographic performance for the target analytes. The derivatization process is discussed according to the analytical procedure used to achieve the reaction between the reagent and the target compounds (containing hydroxyl, thiol, amino, carbonyl and carboxyl as the main functional groups involved in derivatization). Important procedures for derivatization used in bioanalysis are in situ or based on extraction processes (liquid-liquid, solid-phase and related techniques) applied to the biomatrix. In the review, chiral, isotope-labeling, hydrophobicity-tailored and post-column derivatizations are also included, based on representative publications in the literature during the last two decades. Examples of derivatization reagents and brief reaction conditions are included, together with some bioanalytical applications and performances (chromatographic conditions, detection limit, stability and sample biomatrix).

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.

Chemical Toolbox to Decode the Microbiota Lexicon

The human microbiota deploys a diverse range of molecules and metabolites to engage in chemical communications with the host, mediating fundamental aspects of host health. Studies of the structures and activities of bioactive molecules produced by the microbiota are imperative to address their implications in microbiota associated diseases in human. By drawing experiences from different research fields, chemists and chemical biologists, who are experts in dealing with chemical molecules, are uniquely positioned to contribute to the emerging knowledge of human microbiota. In this minireview, we discuss the current chemical tools and methods that are pertinent to the discovery of microbiota molecules and metabolites, characterizations of their protein targets, as well as evaluations of their biodistributions in hosts. These are key aspects in understanding the chemical underpinnings of the microbiota-host interactions that would enable future development of diagnostics and therapeutics targeting the human microbiota.

Development of analytical method of melamine in placenta from pregnant women by isotope-dilution liquid chromatography/tandem mass spectrometry

RATIONALE

Melamine is ubiquitously present in our daily life. It has a known effect on the kidneys, but it may also adversely affect the reproduction system. We have developed an analytical method for measuring melamine levels in maternal placenta and correlated these levels with melamine concentrations in urine, a necessary step in finding out if melamine might cross the placenta and enter the circulation of the fetus.

METHODS

We used liquid-liquid extraction, clean up by solid-phase extraction (SPE), and isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) to measure melamine in placenta specimens. The results of this method were assessed for linearity, limits of quantitation (LOQs), and intra- and inter-assay precision as well as accuracy, matrix effect, and recovery rate.

RESULTS

Calibration curves indicated good linearity (r >0.995) over concentrations ranging from 5 to 500 ng/mL in placenta specimens, intra- and inter-assay precision from 0.89% to 27.07%, and accuracy from 92.4% to123.5%. Recovery ranged from 63.9 to 83.9%, and the LOQ was 5 ng/mL in placenta (0.2 g). Placental melamine levels ranged from 7.87 to19.64 ng/mL, all detectable (n = 8). Pregnant women with higher levels of urinary melamine had higher placenta melamine levels than those with non-detectable urinary melamine, though the results were not significantly different (p = 0.149, n = 4 in each group).

CONCLUSIONS

The results of this study suggest that pregnant women were exposed to low doses of melamine in their daily lives as measured in urine samples and placenta specimens. It is unclear whether placenta melamine concentrations can better represent long-term exposure than urine or whether melamine in the uterus can enter the fetus via this route.

Comprehensive and semi-quantitative analysis of carboxyl-containing metabolites related to gut microbiota on chronic kidney disease using 2-picolylamine isotopic labeling LC-MS/MS

Carboxyl-containing metabolites, such as bile acids and fatty acids, have many important functions and microbiota is involved in the production of them. In the previous study, we found that the chronic kidney disease (CKD) model mice raised under germ-free conditions provided more severe renal damage than the mice with commensal microbiota. However, the precise influence by the microbiome and carboxyl-containing metabolites to the renal functions is unknown. In this study, we aimed to develop a novel chemical isotope labeling-LC-MS/MS method using the 2-picolylamine and its isotopologue and applied the analysis of effects of microbiome and CKD pathophysiology. The developed semi-quantitative method provided the high accuracy not inferior to the absolute quantification. By comparing of four groups of mice, we found that both microbiota and renal function can alter the composition and level of these metabolites in both plasma and intestine. In particular, the intestinal level of indole-3-acetic acid, short-chain fatty acids and n-3 type of polyunsaturated fatty acid, which play important roles in the endothelial barrier function, were significantly lower in germ-free conditions mice with renal failure. Accordingly, it is suggested these metabolites might have a renoprotective effect on CKD by suppressing epithelial barrier disruption.

Quantitative mapping of specific proteins in biological tissues by laser ablation-ICP-MS using exogenous labels: aspects to be considered

Laser ablation (LA) coupled with inductively coupled plasma mass spectrometry (ICP-MS) is a versatile tool for direct trace elemental and isotopic analysis of solids. The development of new strategies for quantitative elemental mapping of biological tissues is one of the growing research areas in LA-ICP-MS. On the other hand, the latest advances are related to obtaining not only the elemental distribution of heteroatoms but also molecular information. In this vein, mapping of specific proteins in biological tissues can be done with LA-ICP-MS by use of metal-labelled immunoprobes. However, although LA-ICP-MS is, in principle, a quantitative technique, critical requirements should be met for absolute quantification of protein distribution. In this review, progress based on the use of metal-labelled antibodies for LA-ICP-MS mapping of specific proteins is reported. Critical requirements to obtain absolute quantitative mapping of specific proteins by LA-ICP-MS are highlighted. Additionally, illustrative examples of the advances made so far with LA-ICP-MS are provided. Graphical abstract In the proposed critical review, last advances based on the use of metal-labelled antibodies and critical requirements for LA-ICP-MS quantitative mapping of specific proteins are tackled.

A chemical derivatization based UHPLC-LTQ-Orbitrap mass spectrometry method for accurate quantification of short-chain fatty acids in bronchoalveolar lavage fluid of asthma mice

Recent studies have demonstrated the important role of short-chain fatty acids (SCFAs) in the maintenance of homeostasis of respiratory immunity. However, there is still no report focus on the determination of SCFAs level in bronchoalveolar lavage fluid (BALF), the most common sample used for screening biomarkers of the pulmonary diseases. Herein, an ultra-high-performance liquid chromatography with LTQ-Orbitrap mass spectrometer (UHPLC-LTQ-Orbitrap) oriented 3-nitrophenylhydrazine (3-NPH)-based derivatization method was developed for the quantification of SCFAs in BALF. To achieve accurate quantitation, d4-acetate was used as internal standard to compensate for the matrix effects. Method validation showed a good linearity (R² > 0.9992) with wide concentration range, and the intra-day and inter-day precision for determination of eight SCFAs in BALF samples was ≤ 14.79%. The quantitation accuracy, assessed by relative recoveries, ranged from 90% to 110% for target SCFAs at three concentration levels. Matrix effects ranged from 85% to 115%, and the lower limits of quantification of these targeted SCFAs were varied from 3 to 24 nmol/L. The SCFAs-targeted method was then applied to determine the changed levels in BALF samples from OVA-induced asthma mice and normal mice. In addition, the universality of our developed method was also demonstrated by determining the SCFAs concentrations in feces, serum and lung tissue samples from asthma and normal mice. These results indicate that 3-NPH derivatization based UHPLC-LTQ-Orbitrap provides accurate view of global SCFAs alternation in different samples, giving a support to deduce the origin of SCFAs in lung. The present study is of great importance for understanding the role of SCFAs in modulation of host metabolism and immunity.

Improving metabolome coverage and data quality: advancing metabolomics and lipidomics for biomarker discovery

This Feature Article highlights some of the key challenges within the field of metabolomics and examines what role separation and analytical sciences can play to improve the use of metabolomics in biomarker discovery and personalized medicine. Recent progress in four key areas is highlighted: (i) improving metabolite coverage, (ii) developing accurate methods for unstable metabolites including in vivo global metabolomics methods, (iii) advancing inter-laboratory studies and reference materials and (iv) improving data quality, standardization and quality control of metabolomics studies.

The evolution of methods for urinary steroid metabolomics in clinical investigations particularly in childhood

The metabolites of cortisol, and the intermediates in the pathways from cholesterol to cortisol and the adrenal sex steroids can be analysed in a single separation of steroids by gas chromatography (GC) coupled to MS to give a urinary steroid profile (USP). Steroids individually and in profile are now commonly measured in plasma by liquid chromatography (LC) coupled with MS/MS. The steroid conjugates in urine can be determined after hydrolysis and derivative formation and for the first time without hydrolysis using GC-MS, GC-MS/MS and liquid chromatography with mass spectrometry (LC-MS/MS). The evolution of the technology, practicalities and clinical applications are examined in this review. The patterns and quantities of steroids changes through childhood. Information can be obtained on production rates, from which children with steroid excess and deficiency states can be recognised when presenting with obesity, adrenarche, adrenal suppression, hypertension, adrenal tumours, intersex condition and early puberty, as examples. Genetic defects in steroid production and action can be detected by abnormalities from the GC-MS of steroids in urine. New mechanisms of steroid synthesis and metabolism have been recognised through steroid profiling. GC with tandem mass spectrometry (GC-MS/MS) has been used for the tentative identification of unknown steroids in urine from newborn infants with congenital adrenal hyperplasia. Suggestions are made as to areas for future research and for future applications of steroid profiling. As routine hospital laboratories become more familiar with the problems of chromatographic and MS analysis they can consider steroid profiling in their test repertoire although with LC-MS/MS of urinary steroids this is unlikely to become a routine test because of the availability, cost and purity of the internal standards and the complexity of data interpretation. Steroid profiling with quantitative analysis by mass spectrometry (MS) after chromatography now provides the most versatile of tests of adrenal function in childhood.

Current and future perspectives of functional metabolomics in disease studies-A review

Functional metabolomics is a new concept, which studies the functions of metabolites and related enzymes focused on metabolomics. It overcomes the shortcomings of traditional discovery metabolomics of mainly relying on literatures for biological interpretation. Functional metabolomics has many advantages. Firstly, the functional roles of metabolites and related metabolic enzymes are focused. Secondly, the in vivo and in vitro experiments are conducted to validate the metabolomics findings, therefore, increasing the reliability of metabolomics study and producing the new knowledge. Thirdly, functional metabolomics can be used by biologists to investigate functions of metabolites, and related genes and proteins. In this review, we summarize the analytical, biological and clinical platforms used in functional metabolomics studies. Recent progresses of functional metabolomics in cancer, metabolic diseases and biological phenotyping are reviewed, and future development is also predicted. Because of the tremendous advantages of functional metabolomics, it will have a bright future.