Targeted Profiling of Short-, Medium-, and Long-Chain Fatty Acyl-Coenzyme As in Biological Samples by Phosphate Methylation Coupled to Liquid Chromatography-Tandem Mass Spectrometry

Diazonium-based derivatization for enhanced detection of phosphorylated metabolites by LC-MS in cells

Phosphorylated small molecule metabolites play crucial roles in physiological processes such as glycogen metabolism and inflammation regulation. However, their high polarity, structural similarity, poor chromatographic separation, and weak mass spectrometric signals make their accurate quantification challenging, thereby hindering the study of related metabolic mechanisms and diseases. To address these challenges, we developed a novel derivatization reagent, DMQX (5-diazomethane quinoxaline), and combined it with liquid chromatography-mass spectrometry (LC-MS). This approach achieved baseline separation of five groups of isomers and enabled the quantification of 24 phosphorylated metabolites, providing comprehensive coverage of these metabolites in biological pathways. We applied this method to quantify 21 endogenous phosphorylated metabolites in HepG2 cells with and without vesicular stomatitis virus infection, demonstrating the potential of this analytical approach for advancing the study of metabolic mechanisms through quantitative analysis of phosphorylated metabolites in biological samples.

The association between N-nitrosamines exposure and lipid metabolism in the high incidence area of esophageal cancer: A case-control analysis

Environmental carcinogens such as N-nitrosamines are high-risk factors for the development of esophageal cancer (EC). However, the association between nitrosamines exposure and lipid metabolism disorders in human EC remained largely obscure. Therefore, we conducted a population-based case-control study established with esophageal inflammation (BCH), esophageal heterotrophic hyperplasia (DYS), patients with primary EC and matched controls in high prevalence area of EC in China. Our prospective work investigated the joint and independent effects of N-nitrosamines co-exposure on the risk of EC development. Lipidomics analysis was employed to screen differential lipid biomarkers in serum, and the mediating effects of key lipid metabolites in the association between nitrosamines exposure and EC were evaluated. After adjustment for confounders, N-nitrosodimethylamine (NDMA, 1.79 (95% CI: 1.35, 2.39)), N-nitrosodi-n-propylamine (NDPA, 1.55 (95%CI: 1.15, 2.09)), N-nitrosodiethylamine (NDEA, 1.82 (95%CI: 1.36, 2.45)), N-nitrosodibutylamine (NDBA, 1.60 (95%CI: 1.20, 2.13)), N-nitrosomethylethylamine (NMEA, 1.81 (95%CI: 1.36, 2.41)) and N-nitrosomorpholine (NMOR, 1.84 (95%CI: 1.38, 2.45)) exposure all elevated the risks of EC development. The Bayesian kernel machine regression (BKMR) with hierarchical variable selection showed significant positive joint associations of urinary NDMA, NDPA, NMOR, NDEA and EC development, when all nitrosamines were at the 55th percentiles or above, compared with the median. Lipidomic screening of serum samples from the stages of BCH, DYS and EC suggested the perturbation in the biosynthesis of unsaturated fatty acid metabolism pathway, of which myristic acid (FFA 14:0), palmitoleic acid (FFA 16:1), docosahexaenoic acid (FFA 22:6) exerted remarkable mediation effects in the association between N-nitrosamines exposure and EC development. These findings provided new sights for screening early lipid biomarkers and intervention targets in human EC.

An 8-(Diazomethyl) Quinoline Derivatized Acyl-CoA in Silico Mass Spectral Library Reveals the Landscape of Acyl-CoA in Aging Mouse Organs

Acyl-Coenzyme As (acyl-CoAs) are essential intermediates to incorporate carboxylic acids into the bioactive metabolic network across all species, which play important roles in lipid remodeling, fatty acids, and xenobiotic carboxylic metabolism. However, due to the poor liquid chromatographic behavior, the relatively low mass spectrometry (MS) sensitivity, and lack of authentic standards for annotation, the in-depth untargeted profiling of acyl-CoAs is challenging. We developed a chemical derivatization strategy of acyl-CoAs by employing 8-(diazomethyl) quinoline (8-DMQ) as the labeling reagent, which increased the detection sensitivity by 625-fold with good peak shapes. By applying the MS/MS fragmentation rules learned from the MS/MS spectra of 8-DMQ-acyl-CoA authentic standards, an 8-DMQ-acyl-CoA in silico mass spectral library containing 33,344 high-resolution tandem mass spectra of 8,336 acyl-CoA species was created. The in silico library facilitated the high-throughput and automatic annotation of acyl-CoA using multiple metabolomic data processing tools, such as NIST MS Search and MSDIAL. The feasibility of the in silico library in a complex sample was demonstrated by profiling endogenous acyl-CoAs in multiple organs of an aging mouse. 53 acyl-CoA species were annotated, including 12 oxidized fatty acyl-CoAs and 3 novel nonfatty acyl-CoAs. False positive annotations were further screened by developing an eXtreme Gradient Boosting (XGBoost) based retention time prediction model. The organ distribution and the aging dynamics of acyl-CoAs in a mouse model were discussed for the first time, which helped to elucidate the organ-specific function of acyl-CoAs and the role of different acyl-CoA species during aging.

A global LC-MS2 -based methodology to identify and quantify anionic phospholipids in plant samples

Anionic phospholipids (PS, PA, PI, PIPs) are low-abundant phospholipids with impactful functions in cell signaling, membrane trafficking and cell differentiation processes. They can be quickly metabolized and can transiently accumulate at defined spots within the cell or an organ to respond to physiological or environmental stimuli. As even a small change in their composition profile will produce a significant effect on biological processes, it is crucial to develop a sensitive and optimized analytical method to accurately detect and quantify them. While thin-layer chromatography (TLC) separation coupled with gas chromatography (GC) detection methods already exist, they do not allow for precise, sensitive, and accurate quantification of all anionic phospholipid species. Here we developed a method based on high-performance liquid chromatography (HPLC) combined with two-dimensional mass spectrometry (MS2 ) by MRM mode to detect and quantify all molecular species and classes of anionic phospholipids in one shot. This method is based on a derivatization step by methylation that greatly enhances the ionization, the separation of each peak, the peak resolution as well as the limit of detection and quantification for each individual molecular species, and more particularly for PA and PS. Our method universally works in various plant samples. Remarkably, we identified that PS is enriched with very long chain fatty acids in the roots but not in aerial organs of Arabidopsis thaliana. Our work thus paves the way for new studies on how the composition of anionic lipids is finely tuned during plant development and environmental responses.

Development of targeted hydrophilic interaction liquid chromatography-tandem mass spectrometry method for acyl-Coenzyme A covering short- to long-chain species in a single analytical run

Acyl-CoAs play a significant role in numerous physiological and metabolic processes making it important to assess their concentration levels for evaluating metabolic health. Considering the important role of acyl-CoAs, it is crucial to develop an analytical method that can analyze these compounds. Due to the structural variations of acyl-CoAs, multiple analytical methods are often required for comprehensive analysis of these compounds, which increases complexity and the analysis time. In this study, we have developed a method using a zwitterionic HILIC column that enables the coverage of free CoA and short- to long-chain acyl-CoA species in one analytical run. Initially, we developed the method using an LC-QTOF instrument for the identification of acyl-CoA species and optimizing their chromatography. Later, a targeted HILIC-MS/MS method was created in scheduled multiple reaction monitoring mode using a QTRAP MS detector. The performance of the method was evaluated based on various parameters such as linearity, precision, recovery and matrix effect. This method was applied to identify the difference in acyl-CoA profiles in HepG2 cells cultured in different conditions. Our findings revealed an increase in levels of acetyl-CoA, medium- and long-chain acyl-CoA while a decrease in the profiles of free CoA in the starved state, indicating a clear alteration in the fatty acid oxidation process.

Recent developments in the analytical approaches of acyl-CoAs to assess their role in mitochondrial fatty acid oxidation disorders

Fatty acid oxidation disorders (FAOD) are inborn errors of metabolism that occur due to deficiency of specific enzyme activities and transporter proteins involved in the mitochondrial metabolism of fatty acids, causing a deficiency in ATP production. The identification of suitable biomarkers plays a crucial role in predicting the future risk of disease and monitoring responses to therapies. Acyl-CoAs are directly involved in the steps of fatty acid oxidation and are the primary biomarkers associated with FAOD. However, acyl-CoAs are not used as diagnostic biomarkers in hospitals and clinics as they are present intracellularly with low endogenous levels. Additionally, the analytical method development of acyl-CoAs is quite challenging due to diverse physicochemical properties and instability. Hence, secondary biomarkers such as acylcarnitines are used for the identification of FAOD. In this review, the focus is on the analytical techniques that have evolved over the years for the identification and quantitation of acyl-CoAs. Among these techniques, liquid chromatography-mass spectrometry clearly has an advantage in terms of sensitivity and selectivity. Stable isotope labeling by essential nutrients in cell culture (SILEC) enables the generation of labeled internal standards. Each acyl-CoA species has a distinct pattern of instability and degradation, and the use of appropriately matched internal standards can compensate for such issues. Although significant progress has been made in measuring acyl-CoAs, more efforts are needed for bringing these technical advancements to hospitals and clinics. This review also highlights the difficulties involved in the routine use of acyl-CoAs as a diagnostic biomarker and some of the measures that can be adopted by clinics and hospitals for overcoming these limitations.

Development of Pseudo-targeted Profiling of Isotopic Metabolomics using Combined Platform of High Resolution Mass Spectrometry and Triple Quadrupole Mass Spectrometry with Application of 13C6-Glucose Tracing in HepG2 Cells

Isotope tracing assisted metabolic analysis is becoming a unique tool to understand metabolic regulation in cell biology and biomedical research. Targeted mass spectrometry analysis based on selected reaction monitoring (SRM) has been widely applied in isotope tracing experiment with the advantages of high sensitivity and broad linearity. However, its application for new pathway discovery is largely restrained by molecular coverage. To overcome this limitation, we describe a strategy called pseudo-targeted profiling of isotopic metabolomics (PtPIM) to expand the analysis of isotope labeled metabolites beyond the limit of known pathways and chemical standards. Pseudo-targeted metabolomics was first established with ion transitions and retention times transformed from high resolution (orbitrap) mass spectrometry. Isotope labeled MRM transitions were then generated according to chemical formulas of fragments, which were derived from accurate ion masses acquired by HRMS. An in-house software "PseudoIsoMRM" was developed to simulate isotope labeled ion transitions in batch mode and correct the interference of natural isotopologues. This PtPIM strategy was successfully applied to study ¹³C₆-glucose traced HepG2 cells. As 313 molecules determined as analysis targets, a total of 4104 ion transitions were simulated to monitor ¹³C labeled metabolites in positive-negative switching mode of QQQ mass spectrometer with minimum dwell time of 0.3 ms achieved. A total of 68 metabolites covering glycolysis, TCA cycle, nucleotide biosynthesis, one-carbon metabolism and related derivatives were found to be labeled (> 2%) in HepG2 cells. Active pentose phosphate pathway was observed with diverse labeling status of glycolysis intermediates. Meanwhile, our PtPIM strategy revealed that rotenone severely suppressed mitochondrial function e.g. oxidative phosphorylation and fatty acid beta-oxidation. In this case, anaerobic respiration became the major source of energy metabolism by producing abundant lactate. Conclusively, the simulation based PtPIM method demonstrates a strategy to broaden metabolite coverage in isotope tracing analysis independent of standard chemicals.

Quantification of Dolichyl Phosphates Using Phosphate Methylation and Reverse-Phase Liquid Chromatography-High Resolution Mass Spectrometry

Dolichyl monophosphates (DolPs) are essential lipids in glycosylation pathways that are highly conserved across almost all domains of life. The availability of DolP is critical for all glycosylation processes, as these lipids serve as membrane-anchored building blocks used by various types of glycosyltransferases to generate complex post-translational modifications of proteins and lipids. The analysis of DolP species by reverse-phase liquid chromatography-mass spectrometry (RPLC-MS) remains a challenge due to their very low abundance and wide range of lipophilicities. Until now, a method for the simultaneous qualitative and quantitative assessment of DolP species from biological membranes has been lacking. Here, we describe a novel approach based on simple sample preparation, rapid and efficient trimethylsilyl diazomethane-dependent phosphate methylation, and RPLC-MS analysis for quantification of DolP species with different isoprene chain lengths. We used this workflow to selectively quantify DolP species from lipid extracts derived of Saccharomyces cerevisiae, HeLa, and human skin fibroblasts from steroid 5-α-reductase 3- congenital disorders of glycosylation (SRD5A3-CDG) patients and healthy controls. Integration of this workflow with global lipidomics analyses will be a powerful tool to expand our understanding of the role of DolPs in pathophysiological alterations of metabolic pathways downstream of HMG-CoA reductase, associated with CDGs, hypercholesterolemia, neurodegeneration, and cancer.

Optimization of metabolomic data processing using NOREVA

A typical output of a metabolomic experiment is a peak table corresponding to the intensity of measured signals. Peak table processing, an essential procedure in metabolomics, is characterized by its study dependency and combinatorial diversity. While various methods and tools have been developed to facilitate metabolomic data processing, it is challenging to determine which processing workflow will give good performance for a specific metabolomic study. NOREVA, an out-of-the-box protocol, was therefore developed to meet this challenge. First, the peak table is subjected to many processing workflows that consist of three to five defined calculations in combinatorially determined sequences. Second, the results of each workflow are judged against objective performance criteria. Third, various benchmarks are analyzed to highlight the uniqueness of this newly developed protocol in (1) evaluating the processing performance based on multiple criteria, (2) optimizing data processing by scanning thousands of workflows, and (3) allowing data processing for time-course and multiclass metabolomics. This protocol is implemented in an R package for convenient accessibility and to protect users' data privacy. Preliminary experience in R language would facilitate the usage of this protocol, and the execution time may vary from several minutes to a couple of hours depending on the size of the analyzed data.

Isomer Selective Comprehensive Lipidomics Analysis of Phosphoinositides in Biological Samples by Liquid Chromatography with Data Independent Acquisition Tandem Mass Spectrometry

Phosphoinositides (PIPx) play central roles in membrane dynamics and signal transduction of key functions like cellular growth, proliferation, differentiation, migration, and adhesion. They are highly regulated through a network of distinct phosphatidylinositol phosphates consisting of seven groups and three regioisomers in two groups (PIP and PIP2), which arise from phosphorylation at 3', 4', and 5' positions of the inositol ring. Numerous studies have revealed the importance of both fatty acyl chains, degree of phosphorylation, and phosphorylation positions under physiological and pathological states. However, a comprehensive analytical method that allows differentiation of all regioisomeric forms with different acyl side chains and degrees of phosphorylation is still lacking. Here, we present an integrated comprehensive workflow of PIPx analysis utilizing a chiral polysaccharide stationary phase coupled with electrospray ionization high-resolution mass spectrometry with a data independent acquisition technique using the SWATH technology. Correspondingly, a targeted data mining strategy in the untargeted comprehensively acquired MS and MS/MS data was developed. This powerful highly selective method gives a full picture of PIPx profiles in biological samples. Herein, we present for the first time the full PIPx profiles of NIST SRM1950 plasma, Pichia pastoris lipid extract, and HeLa cell extract, including profile changes upon treatment with potential PI3K inhibitor wortmannin. We also illustrate using this inhibitor that measurements of the PIPx profile averaged over the distinct regioisomers by analytical procedures, which cannot differentiate between the individual PIPx isomers, can easily lead to biased conclusions.