Analysis of biologically-active, endogenous carboxylic acids based on chromatography-mass spectrometry

Validation of a LC-MS/MS assay for citric acid, cysteine and oxalic acid determination and its application to explore pre-analytical sample storage

Objectives

Citrate, oxalate and cystine in 24-h urine are considered to be associated with the incidence and recurrence risk of urinary stone disease (USD). An evaluation of the LC-MS/MS kit for simultaneous quantification of the three analytes was undertaken.

Design

& Methods: The analytical performance of the kit was investigated based on FDA, EMA and CLSI guidelines. To promote the standardization of sample storage, this kit has been applied to perform systematic pre-analytical stability study of these analytes in urine.

Results

This method was validated with good linearity with accuracy of 93.1%-104 %. Intra-day and inter-day imprecision were ≤5.55 % and 5.34 %, respectively. Recoveries of citrate, oxalate and cystine added to clinical samples were in the range of 92.0-103 %, 94.8-100 % and 99.0-107 % with CV ≤ 5.52 %. It was recommended that urine preserved with hydrochloric acid could be preferable in consideration of both reliable test results and neglected sample heterogeneity.

Conclusions

This kit is suitable for measurement of citrate, oxalate and cystine for understanding the etiology of urinary stones, and the proper storage of urine samples is crucial for the correctness of the test results.

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.

High-resolution ion mobility spectrometry-mass spectrometry for isomeric separation of prostanoids after Girard's reagent T derivatization

RATIONALE

Isomeric separation of prostanoids is often a challenge and requires chromatography and time-consuming sample preparation. Multiple prostanoid isomers have distinct in vivo functions crucial for understanding the inflammation process, including prostaglandins E₂ (PGE₂ ) and D₂ (PGD₂ ). High-resolution ion mobility spectrometry (IMS) based on linear ion transport in low-to-moderate electric fields and nonlinear ion transport in strong electric fields emerges as a broad approach for rapid separations prior to mass spectrometry.

METHODS

Derivatization with Girard's reagent T (GT) was used to overcome inefficient ionization of prostanoids in negative ionization mode due to poor deprotonation of the carboxylic acid group. Three high-resolution IMS techniques, namely linear cyclic IMS, linear trapped IMS, and nonlinear high-field asymmetric waveform IMS, were compared for the isomeric separation and endogenous detection of prostanoids present in intestinal tissue.

RESULTS

Direct infusion of GT-derivatized prostanoids proved to increase the ionization efficiency in positive ionization mode by a factor of >10, which enabled detection of these molecules in endogenous concentration levels. The high-resolution IMS comparison revealed its potential for rapid isomeric analysis of biologically relevant prostanoids. Strengths and weaknesses of both linear and nonlinear IMS are discussed. Endogenous prostanoid detection in intestinal tissue extracts demonstrated the applicability of our approach in biomedical research.

CONCLUSIONS

The applied derivatization strategy offers high sensitivity and improved stereoisomeric separation for screening of complex biological systems. The high-resolution IMS comparison indicated that the best sensitivity and resolution are achieved by linear and nonlinear IMS, respectively.

Recent advances in metabolomics analysis for early drug development

The pharmaceutical industry adapted proteomics and other 'omics technologies for drug research early following their initial introduction. Although metabolomics lacked behind in this development, it has now become an accepted and widely applied approach in early drug development. Over the past few decades, metabolomics has evolved from a pure exploratory tool to a more mature and quantitative biochemical technology. Several metabolomics-based platforms are now applied during the early phases of drug discovery. Metabolomics analysis assists in the definition of the physiological response and target engagement (TE) markers as well as elucidation of the mode of action (MoA) of drug candidates under investigation. In this review, we highlight recent examples and novel developments of metabolomics analyses applied during early drug development.

Detection and development of a quantitation method for undeclared compounds in antidiabetic biologically active additives and its validation by high performance liquid chromatography

An isocratic, high-performance liquid chromatography (HPLC) quantitation method was developed for the quantitative determination of metformin, glibenclamide, gliclazide, glimepiride in some antidiabetic biologically active additives. A Nucleosil C18, 5 μm, 4.6 mm × 150 mm, column with mobile phase containing buffer (10 mm Na2HPO4, 10 mm sodium dodecyl sulfate): acetonitrile = 68 : 32 (V/V), pH = 7.5 was used. The flow rate was 1.0 mL/min, and effluents were monitored at 226 nm. The retention times of gliclazide glibenclamide, glimepiride and metformin, were 2.203, 4.587, 5.667 and 10.182 min, respectively. Linearity was studied by preparing standard solutions of gliclazide, glibenclamide, glimepiride and metformin at the concentration range of 50% to 150% of working concentration from a stock solution. The method was successfully applied to the estimation of gliclazide, glibenclamide, glimepiride and metformin in some antidiabetic biologically active additives. This method was validated to confirm its system suitability, selectivity, linearity, precision and accuracy according to international conference on harmonization (ICH) guidelines.

Metabolite discovery: Biochemistry's scientific driver

Metabolite identification represents a major challenge, and opportunity, for biochemistry. The collective characterization and quantification of metabolites in living organisms, with its many successes, represents a major biochemical knowledgebase and the foundation of metabolism's rebirth in the 21^st century; yet, characterizing newly observed metabolites has been an enduring obstacle. Crystallography and NMR spectroscopy have been of extraordinary importance, although their applicability in resolving metabolism's fine structure has been restricted by their intrinsic requirement of sufficient and sufficiently pure materials. Mass spectrometry has been a key technology, especially when coupled with high-performance separation technologies and emerging informatic and database solutions. Even more so, the collective of artificial intelligence technologies are rapidly evolving to help solve the metabolite characterization conundrum. This perspective describes this challenge, how it was historically addressed, and how metabolomics is evolving to address it today and in the future.

Analytical methods in fatty acid analysis for microbial applications: the recent trends

Fatty acids are among the most important components of many biological systems and have been highlighted in many research fields in recent decades. In the food industry, it is important to check the amount and types of fatty acids in edible oils, beverages and other foods products, and checking the fatty acids parameters are among the quality control parameters for those products. In medical applications, investigation of fatty acids in biological samples and comparing imbalances in them can help to diagnose some diseases. On the other hand, the development of cell factories for the production of biofuels and other valuable chemicals requires the accurate analysis of fatty acids, which serve as precursors in development of those products. As a result, given all these different applications of fatty acids, rapid and accurate methods for characterization and quantification of fatty acids are essential. In recent years, various methods for the analysis of fatty acids have been proposed, which according to the specific purpose of the analysis, some of them can be used with consideration of speed, accuracy and cost. In this article, the available methods for the analysis of fatty acids are reviewed with a special emphasis on the analysis of microbial samples to pave the way for more widespread metabolic engineering research.

Quantification and Bitter Taste Contribution of Lipids and Their Oxidation Products in Pea-Protein Isolates (Pisum sativum L.)

An ultra-high-performance liquid chromatography-differential ion mobility (DMS)-tandem mass spectrometry method was developed to quantify 14 bitter-tasting lipids in 17 commercial pea-protein isolates (Pisum sativum L.). The DMS technology enabled the simultaneous quantification of four hydroxyoctadecadienoic acid isomers, namely, (10E,12Z)-9-hydroxyoctadeca-10,12-dienoic acid (5), (10E,12E)-9-hydroxyoctadeca-10,12-dienoic acid (6), (9Z,11E)-13-hydroxyoctadeca-9,11-dienoic acid (7), and (9E,11E)-13-hydroxyoctadeca-9,11-dienoic acid (8). Based on quantitative data and human bitter taste recognition thresholds, dose-over-threshold factors were determined to evaluate the individual lipids' bitter impact and compound classes. The free fatty acids α-linolenic acid (10) and linoleic acid (13), as well as the trihydroxyoctadecenoic acids, especially 9,10,11-trihydroxyoctadec-12-enoic (3), and 11,12,13-trihydroxyoctadec-9-enoic acids (4), were shown to be key inducers to bitterness in the isolates. Additionally, the impact of 1-linoleoyl glycerol (9) on the bitter taste could be shown for 14 of the 17 tested pea-protein isolates.

Development of a liquid chromatography-electrospray ionization tandem mass spectrometric method for the simultaneous analysis of free fatty acids

Fatty acids (FAs) play important roles in several physiological and pathophysiological processes, functioning as both non-esterified free FAs (FFAs) and components of other lipid classes. Although many lipid classes are readily measured using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS), the measurement of FFAs by this method is not straightforward because of inconsistent fragmentation behaviors. In this study, we describe a strategy to measure FFAs using conventional reverse-phase LC-ESI-MS/MS, without derivatization. The strategy combines three key methods: 1) an isocratic LC separation with a high organic solvent ratio, 2) post-column base addition, and 3) pseudo-multiple reaction monitoring. The method facilitates the measurement of ultra-long-chain FAs, the accumulation of which is a common biochemical abnormality in peroxisomal disorders. This study delivers a broad strategy that measures a wide spectrum of FFA species in complex biological samples.

Methods of Lipidomic Analysis: Extraction, Derivatization, Separation, and Identification of Lipids

Lipidomics refers to the large-scale study of pathways and networks of cellular lipids in biological systems. A lipidomic analysis often involves the identification and quantification of the thousands of cellular lipid molecular species within a complex biological sample and therefore requires a well optimized method for lipid profiling. In this chapter, the methods for lipidomic analysis, including sample collection and preparation, lipid derivatization and separation, mass spectrometric identification of lipids, data processing and interpretation, and quality control, are overviewed.

Moving forward with isoprostanes, neuroprostanes and phytoprostanes: where are we now?

Polyunsaturated fatty acids (PUFAs) are essential components in eukaryotic cell membrane. They take part in the regulation of cell signalling pathways and act as precursors in inflammatory metabolism. Beside these, PUFAs auto-oxidize through free radical initiated mechanism and release key products that have various physiological functions. These products surfaced in the early nineties and were classified as prostaglandin isomers or isoprostanes, neuroprostanes and phytoprostanes. Although these molecules are considered robust biomarkers of oxidative damage in diseases, they also contain biological activities in humans. Conceptual progress in the last 3 years has added more understanding about the importance of these molecules in different fields. In this chapter, a brief overview of the past 30 years and the recent scope of these molecules, including their biological activities, biosynthetic pathways and analytical approaches are discussed.

Ion-Mobility-Based Liquid Chromatography-Mass Spectrometry Quantitation of Taste-Enhancing Octadecadien-12-ynoic Acids in Mushrooms

For the accurate quantitation of kokumi-enhancing and bitter-tasting octadecadien-12-ynoic and octadecadienoic acids in chanterelles (Cantharellus cibarius Fr.), a sensitive ultra-high-performance liquid chromatography-differential ion mobility spectrometry-tandem mass spectrometry method was developed. On the basis of these quantitative data and the taste thresholds, dose-over-threshold factors were calculated to determine the contribution of these sensometabolites to the kokumi and bitter taste of chanterelles; e.g., 14,15-dehydrocrepenynic acid (3) and (9Z,15E)-14-oxooctadeca-9,15-dien-12-ynoic acid (7) were identified as key kokumi substances in raw chanterelles. Quantitative profiling of these compounds in various mushroom species demonstrated a unique accumulation of octadecadien-12-ynoic acids in Cantharellus. Furthermore, storage experiments highlighted dynamic processes, including the biosynthesis of these substances as a result of lipid peroxidation mechanisms.

Anti-Melanogenic Effect of Ethanolic Extract of Sorghum bicolor on IBMX-Induced Melanogenesis in B16/F10 Melanoma Cells

To evaluate possibility as a skin whitening agent of Sorghum bicolor (S. bicolor), its antioxidant activity and anti-melanogenic effect on 3-isobutyl-1-methylxanthine (IBMX)-induced melanogenesis in B16/F10 melanoma cells were investigated. The result of total phenolic contents (TPC) indicated that 60% ethanol extract of S. bicolor (ESB) has the highest contents than other ethanol extracts. Antioxidant activity was evaluated using the 2,2'-azino-bis-(3-ethylbenzothiazolin-6-sulfonic acid) diammonium salt (ABTS)/1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activities and malondialdehyde (MDA) inhibitory effect. These results showed ESB has significant antioxidant activities. Inhibitory effect against tyrosinase was also assessed using L-tyrosine (IC₅₀ value = 89.25 μg/mL) and 3,4-dihydroxy-L-phenylalanine (L-DOPA) as substrates. In addition, ESB treatment effectively inhibited melanin production in IBMX-induced B16/F10 melanoma cells. To confirm the mechanism on anti-melanogenic effect of ESB, we examined melanogenesis-related proteins. ESB downregulated melanogenesis by decreasing expression of microphthalmia-associated transcription factor (MITF), tyrosinase and tyrosinase-related protein (TRP)-1. Finally, 9-hydroxyoctadecadienoic acid (9-HODE), 1,3-O-dicaffeoylglycerol and tricin as the main compounds of ESB were analyzed using the ultra-performance liquid chromatography-ion mobility separation-quadrupole time of flight/tandem mass spectrometry (UPLC-IMS-QTOF/MS²). These findings suggest that ESB may have physiological potential to be used skin whitening material.

Polarity-Tuning Derivatization-LC-MS Approach for Probing Global Carboxyl-Containing Metabolites in Colorectal Cancer

Carboxyl-containing metabolites (CCMs) widely exist in living systems and are the essential components for life. Global characteristics of CCMs in biological samples are critical for the understanding of physiological processes and the discovery for the onset of relevant diseases. However, their determination represents a challenge due to enormous polarity differences, structural diversity, high structural similarity, and poor ionization efficiency in mass spectrometry. Herein, 5-(diisopropylamino)amylamine (DIAAA) derivatization coupled with liquid chromatography-mass spectrometry (LC-MS) was developed for mapping the CCMs. With this methodology, the sensitivity was significantly enhanced. More importantly, the hydrophobicity of polar CCMs, amino acids, TCA cycle intermediates, and short-chain fatty acids and the hydrophilicity of low-polar CCMs, long-chain fatty acids, and bile acids were significantly increased, resulting in a remarkable separation efficiency for which 68 CCMs can be simultaneously determined. Furthermore, the polarity-tuning effect was confirmed to be induced by the different impacts of aliphatic chains and nitrogen atom in DIAAA, the latter existing as a cation in the acidic mobile phase, using different derivatization reagents. Finally, this derivatization method was utilized to hunt for the potential biomarkers in colorectal cancer (CRC) patients and 52 CCMs, related with several key metabolic pathways, including amino acids metabolism, TCA cycle, fatty acid metabolism, pyruvate metabolism, and gut flora metabolism were identified. This innovative polarity-tuning derivatization-LC-MS approach was proved to be a valuable tool for probing global metabolome with high separation efficiency and sensitivity in various biological samples.

Tributyl phosphate assisted hollow-fiber liquid-phase microextraction of short-chain fatty acids in microbial degradation fluid using capillary electrophoresis-contactless coupled conductivity detection

A tributyl phosphate assisted hollow-fiber liquid-phase microextraction coupled with capillary electrophoresis-contactless coupled conductivity detection (HF-LPME/CE-C⁴D) method has been developed for trace analysis of common short-chain fatty acids (SCFAs) without derivatization. Under the optimum conditions, ten SCFAs including a pair of isomers were well separated from their homologous FAs and the main coexisting inorganic anions within 40 min. Tributyl phosphate assisted HF-LPME produced excellent purification and enrichment for the model sample with high-salt matrix, microbial degradation fluid, and the limits of detection could reach 0.072-0.67 ng/mL (S/N = 3). Owing to its high sensitivity, good linearity, and acceptable recovery, this proposed method provided a sensitive and environment-friendly alternative for trace analysis of SCFAs in complicated samples.

GC-MS Analysis of Medium- and Long-Chain Fatty Acids in Blood Samples

Our body contains a wide variety of fatty acids that differ in chain length, the degree of unsaturation, and location of the double bonds. As the various fatty acids play distinct roles in health and disease, methods that can specifically determine the fatty acid profile are needed for fundamental and clinical studies. Here we describe a method for the separation and quantification of fatty acids ranging from 8 to 24 carbon chain lengths in blood samples using gas chromatography-mass spectrometry following derivatization using pentafluorobenzyl bromide. This method quantitatively monitors fatty acid composition in a manner that satisfies the requirements for comprehensiveness, sensitivity, and accuracy.

Ion Pair Chromatography for Endogenous Metabolites LC-MS Analysis in Tissue Samples Following Targeted Acquisition

A protocol for the preparation of tissue extracts for the targeted analysis of ca. 150 polar metabolites, including those involved in central carbon metabolism is described, using a reversed-phase ion pair U(H)PLC-MS method. Data collection enabled by multiple-reaction monitoring provides highly specific, sensitive acquisition of metabolic intermediates with a wide range of physicochemical properties and pathway coverage. Technical aspects are discussed for method transfer along with the basic principles of sample sequence setup, data analysis, and validation. General comments are given to help the assessment of data quality and system performance.

Isoprostanes, neuroprostanes and phytoprostanes: An overview of 25years of research in chemistry and biology

Since the beginning of the 1990's diverse types of metabolites originating from polyunsaturated fatty acids, formed under autooxidative conditions were discovered. Known as prostaglandin isomers (or isoprostanoids) originating from arachidonic acid, neuroprostanes from docosahexaenoic acid, and phytoprostanes from α-linolenic acid proved to be prevalent in biology. The syntheses of these compounds by organic chemists and the development of sophisticated mass spectrometry methods has boosted our understanding of the isoprostanoid biology. In recent years, it has become accepted that these molecules not only serve as markers of oxidative damage but also exhibit a wide range of bioactivities. In addition, isoprostanoids have emerged as indicators of oxidative stress in humans and their environment. This review explores in detail the isoprostanoid chemistry and biology that has been achieved in the past three decades.

Quantitative NMR analysis of intra- and extracellular metabolism of mammalian cells: A tutorial

Metabolomics analysis of body fluids as well as cells is depended on many factors. While several well-accepted standard operating procedures for the analysis of body fluids are available, the NMR based quantitative analysis of cellular metabolites is less well standardized. Experimental designs depend on the cell type, the quenching protocol and the applied post-acquisition workflow. Here, we provide a tutorial for the quantitative description of the metabolic phenotype of mammalian cells using NMR spectroscopy. We discuss all key steps of the process, starting from the selection of the appropriate culture medium, quenching techniques to arrest metabolism in a reproducible manner, the extraction of the intracellular components and the profiling of the culture medium. NMR data acquisition and methods for both qualitative and quantitative analysis are also provided. The suggested methods cover experiments for adherent cells and cells in suspension. We ultimately describe the application of the discussed workflow to a thyroid cancer cell line. Although this tutorial focuses on mammalian cells, the given guidelines and procedures may be adjusted for the analysis of other cell types.

Fatty acid profiling of blood cell membranes by gas chromatography with mass spectrometry

Fatty acids, which are well-known for their influence on human metabolism and signal transduction, are also a substantial component of cellular membranes and regulate the basic properties and functions of membranes. Owing to their multiple functions, fatty acid profiles of cell membranes are of great interest to those who are studying the relationship between membrane biochemical compositions and functions. A HCl-catalyzed derivation method and a gas chromatography with mass spectrometry analysis method were developed to accurately profile the fatty acids in cell membranes of erythrocytes, leukocytes, and platelets. The detection limits of all 35 fatty acids ranged from 0.58 to 22 ng/mL and the limits of quantitation were between 2.1 and 72 ng/mL. Finally, the established method was used to profile the membrane fatty acids of 44 healthy volunteers from the north and south of China. Results revealed significant differences in the fatty acid profiles from the two regions, particularly those of the erythrocytes. This technique may be applied to cell membrane studies to generate new biological hypotheses concerning fatty acid composition and membrane functions as well as to construct related disease profiles.

Derivatization methods for LC–MS analysis of endogenous compounds

Sensitive and reliable analysis of endogenous compounds is critically important for many physiological and pathological studies. Methods based on LC–MS have progressed to become the method of choice for analyzing endogenous compounds. However, the analysis can be challenging due to various factors, including inherent low concentrations in biological samples, low ionization efficiency, undesirable chromatographic behavior and interferences of complex biological. The integration of chemical derivatization with LC–MS could enhance its capabilities in sensitivity and selectivity, and extend its application to a wider range of analytes. In this article, we will review the derivatization strategies in the LC–MS analysis of various endogenous compounds, and provide applications highlighting the impact of these important techniques in the evaluation of pathological events.