Analysis of Metabolic Changes in Endogenous Metabolites and Diagnostic Biomarkers for Various Diseases Using Liquid Chromatography and Mass Spectrometry.

Analysis of endogenous metabolites in various diseases is useful for searching diagnostic biomarkers and elucidating the molecular mechanisms of pathophysiology. The author and collaborators have developed some LC/tandem mass spectrometry (LC/MS/MS) methods for metabolites and applied them to disease-related samples. First, we identified urinary conjugated cholesterol metabolites and serum N-palmitoyl-O-phosphocholine serine as useful biomarkers for Niemann-Pick disease type C (NPC). For the purpose of intraoperative diagnosis of glioma patients, we developed the LC/MS/MS analysis methods for 2-hydroxyglutaric acid or cystine and found that they could be good differential biomarkers. For renal cell carcinoma, we searched for various biomarkers for early diagnosis, malignancy evaluation and recurrence prediction by global metabolome analysis and targeted LC/MS/MS analysis. In pathological analysis, we developed a simultaneous LC/MS/MS analysis method for 13 steroid hormones and applied it to NPC cells, we found 6 types of reductions in NPC model cells. For non-alcoholic steatohepatitis (NASH), model mice were prepared with special diet and plasma bile acids were measured, and as a result, hydrophilic bile acids were significantly increased. In addition, we developed an LC/MS/MS method for 17 sterols and analyzed liver cholesterol metabolites and found a decrease in phytosterols and cholesterol synthetic markers and an increase in non-enzymatic oxidative sterols in the pre-onset stage of NASH. We will continue to challenge themselves to add value to clinical practice based on cutting-edge analytical chemistry methodology.

A dilute-and-inject liquid-gas chromatography-mass spectrometry method for the analysis of sixteen polycyclic aromatic hydrocarbons in extra-virgin olive oil.

BACKGROUND: Polycyclic aromatic hydrocarbons (PAHs) represent a diverse group of organic compounds characterized by the fusion of two or more benzene rings arranged in various structural forms. Due to their harmful effects on human health, it is essential to implement monitoring systems and preventive measures to regulate human exposure. Given the affinity of PAHs for lipids, extensive research has been focused on their presence in vegetable oils. This study aimed to develop an on-line liquid-gas chromatography (LC-GC) method (using tandem mass spectrometry) with minimized solvent consumption for the determination of 16 PAHs in extra-virgin olive oil (EVOO). RESULTS: A side-by-side comparison of the selected-ion-monitoring and the pseudo multiple-reaction-monitoring (p-MRM) acquisition modes was performed, in terms of specificity and detectability. The results obtained using the p-MRM mode were superior, and for this reason it was selected. The method was linear over the concentration range 1-200 µg kg-1 (except in five cases, over 2-200 and 5-200 µg kg-1 ranges). Accuracy (at the 2 µg kg-1 and 20 µg kg-1 concentration levels) was in the 86.9-109.3 % range, with an RSD <10 %. Intra-day and inter-day precision (at 2 µg kg-1 and 20 µg kg-1 concentration levels) were in the 1.2-9.7 % and 3.2-10.8 % ranges, respectively. For all the PAHs, a negative matrix effect was observed. Three out of sixteen PAHs were detected in three EVOOs (among ten samples), albeit at the low ppb level. Limits of quantification were satisfactory in relation to EU legislation on the presence of PAHs in vegetable oils. SIGNIFICANCE: A dilute-and-inject LC-GC-tandem mass spectrometry method is herein proposed fulfilling EU legislation requirements; sample preparation was very simple, inasmuch that it involved only a dilution step, thus avoiding extraction, clean-up, and thus a high consumption of organic solvents. In fact, considering both oil dilution and the LC mobile phase, less than 8 mL of solvents were used.

Search for new green natural solid phases for sample preparation for PAHs determination in seafood samples followed by LC and GC-MS/MS analysis.

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic organic pollutants found in various environments, notably aquatic ecosystems and the food chain, posing significant health risks. Traditional methods for detecting PAHs in food involve complex processes and considerable reagent usage, raising environmental concerns. This study explores eco-friendly approaches suing solid phases derived from natural sources in matrix solid phase dispersion. We aimed to develop, optimize, and validate a sample preparation technique for seafood, employing natural materials for PAH analysis. Ten natural phases were compared with a commercial reference phase. The methodology involved matrix solid phase dispersion and pressurized liquid extraction, followed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Three solid phases (perlite, sweet manioc starch, and barley) showed superior performance in LC-MS/MS and were further evaluated with gas chromatography-tandem mass spectrometry (GC-MS/MS), confirming perlite as the most effective phase. Validation followed Brazilian regulatory guidelines and European Community Regulation 2021/808/EC. The resulting method offered advantages in cost-effectiveness, reduced environmental impact, cleaner extracts, and enhanced analytical performance compared to the reference solid phase and LC-MS/MS. Proficiency analysis confirmed method reliability, with over 50% alignment with green analytical chemistry principles. In conclusion, this study developed an environmentally sustainable sample preparation technique for seafood analysis using natural solid phases, particularly perlite, for PAH determination.

Preoperative profiles of plasma amino acids and derivatives distinguish periampullary cancer and benign disease.

Periampullary cancers, including pancreatic ductal adenocarcinoma, ampullary-, cholangio-, and duodenal carcinoma, are frequently diagnosed in an advanced stage and are associated with poor overall survival. They are difficult to differentiate from each other and challenging to distinguish from benign periampullary disease preoperatively. To improve the preoperative diagnostics of periampullary neoplasms, clinical or biological markers are warranted.In this study, 28 blood plasma amino acids and derivatives from preoperative patients with benign (N = 45) and malignant (N = 72) periampullary disease were analyzed by LC-MS/MS.Principal component analysis and consensus clustering both separated the patients with cancer and the patients with benign disease. Glutamic acid had significantly higher plasma expression and 15 other metabolites significantly lower plasma expression in patients with malignant disease compared with patients having benign disease. Phenylalanine was the only metabolite associated with improved overall survival (HR = 0.50, CI 0.30-0.83, P < 0.01).Taken together, plasma metabolite profiles from patients with malignant and benign periampullary disease were significantly different and have the potential to distinguish malignant from benign disease preoperatively.

Clinical value of serum polyunsaturated fatty acids in patients with gastric polyps.

Polyunsaturated fatty acids (PUFAs) are vital nutrients in human physiology and are implicated in various chronic diseases. However, the relationship between PUFAs and gastric polyps remains unclear. This study employed liquid chromatography-tandem mass spectrometry (LC-MS/MS) to assess PUFA levels in the serum of 350 patients, along with analyzing the ω-6 to ω-3 ratio. The results revealed significant differences in the levels of C16:1, C18:1, C18:2, α-C18:3, γ-C18:3, C20:1, C20:4, C20:5, ω-3-C22:5, ω-6-C22:5, and C22:6, as well as ω-6 to ω-3 ratio between the control and gasteic polyp groups. Moreover, setting the threshold for ω-6: ω-3 at 10 revealed a close correlation between polyp occurrence and this ratio. These findings suggest that PUFAs and the ω-6 to ω-3 ratio hold promise as potential early screening markers for gastric polyps. However, further research is imperative to elucidate the underlying mechanisms and therapeutic potential of PUFAs in managing gastric polyps.

The chemical memory of smoking tobacco.

The concentration in urine of N-acetyl-hydroxy-propyl-cisteine (3HPMA), an acrolein metabolite, has been employed as a marker of the risk of illness of smokers and the relative concentration of creatinine has been evaluated to verify the effect of moving from the practice of burning tobacco to nicotine vaping. From the results concerning the urine samples of 38 subjects, collected from 2021 to 2023 and analyzed by LC-MS/MS, corresponding to 5 active smokers, 13 previously heavy smokers who replaced traditional tobacco by vaping, and 20 non-smokers, a dramatic reduction was found in 3HPMA/creatinine in urine. 3HPMA varied from values of 2150-3100 µg gcreatinine-1 to levels of 225-625 µg gcreatinine-1 found for non-smokers, with the time decay described by the equation y = 0.3661x2 - 94.359x + 6246.4 (R2: 0.757), providing a time of approximately 10 years for tobacco memory after the cessation of the consumption of burned tobacco.

Plasma-based lipidomics reveals potential diagnostic biomarkers for esophageal squamous cell carcinoma: a retrospective study.

Background: Esophageal squamous cell carcinoma (ESCC) is highly prevalent and has a high mortality rate. Traditional diagnostic methods, such as imaging examinations and blood tumor marker tests, are not effective in accurately diagnosing ESCC due to their low sensitivity and specificity. Esophageal endoscopic biopsy, which is considered as the gold standard, is not suitable for screening due to its invasiveness and high cost. Therefore, this study aimed to develop a convenient and low-cost diagnostic method for ESCC using plasma-based lipidomics analysis combined with machine learning (ML) algorithms. Methods: Plasma samples from a total of 40 ESCC patients and 31 healthy controls were used for lipidomics study. Untargeted lipidomics analysis was conducted through liquid chromatography-mass spectrometry (LC-MS) analysis. Differentially expressed lipid features were filtered based on multivariate and univariate analysis, and lipid annotation was performed using MS-DIAL software. Results: A total of 99 differential lipids were identified, with 15 up-regulated lipids and 84 down-regulated lipids, suggesting their potential as diagnostic targets for ESCC. In the single-lipid plasma-based diagnostic model, nine specific lipids (FA 15:4, FA 27:1, FA 28:7, FA 28:0, FA 36:0, FA 39:0, FA 42:0, FA 44:0, and DG 37:7) exhibited excellent diagnostic performance, with an area under the curve (AUC) exceeding 0.99. Furthermore, multiple lipid-based ML models also demonstrated comparable diagnostic ability for ESCC. These findings indicate plasma lipids as a promising diagnostic approach for ESCC.

Identification of urine biomarkers of endometriosis-Protein mass spectrometry.

INTRODUCTION: Endometriosis is a chronic inflammatory disease that leads to a series of pathological reactions. The basis is a changed proinflammatory activated immune system, which results in more pronounced oxidative stress, disturbed function of proteolysis and cell apoptosis. These processes are crucial in the development of the disease because their dysfunctional activities cause the progression of the disease. It is believed that the proteins excreted in the urine interact with each other and promote pathological processes in endometriosis. METHODS: We analyzed the urine proteome of patients and aimed to detect a potential protein biomarker for endometriosis in the urine proteome. We collected urine samples from 16 patients with endometriosis and 16 patients in the control group with functional ovarian cysts. The diagnosis for all patients was confirmed through pathohistological analysis. After the preanalytical preparation of the urine, chromatography and mass spectrometry (LC-MS/MS) used the technology of urine proteome analysis. RESULTS: The main finding was a significantly different concentration of 14 proteins in the urine samples. We recorded a considerably higher concentration of proteins that have a significant role in activating the immune system (SELL), iron metabolism (HAMP) and cell apoptosis (CHGA) in endometriosis compared to controls. Proteins having an antioxidant function (SOD1) and a role in proteolysis of the extracellular matrix (MMP-9) were significantly reduced in endometriosis compared to controls. CONCLUSION: Consistent with the known pathogenesis of endometriosis, the study results complement the pathological responses that occur with disease progression.

A simple and highly sensitive LC-MS workflow for characterization and quantification of ADC cleavable payloads.

Antibody-drug conjugates (ADC) payloads are cleavable drugs that act as the warhead to exert an ADC's cytotoxic effects on cancer cells intracellularly. A simple and highly sensitive workflow is developed and validated for the simultaneous quantification of six ADC payloads, namely SN-38, MTX, DXd, MMAE, MMAF and Calicheamicin (CM). The workflow consists of a short and simple sample extraction using a methanol-ethanol mixture, followed by a fast liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The results showed that well-validated linear response ranges of 0.4-100 nM for SN38, MTX and DXd, 0.04-100 nM for MMAE and MMAF, 0.4-1000 nM for CM were achieved in mouse serum. Recoveries for all six payloads at three different concentrations (low, medium and high) were more than 85%. An ultra-low sample volume of only 5 µL of serum is required due to the high sensitivity of the method. This validated method was successfully applied to a pharmacokinetic study to quantify MMAE in mouse serum samples.

Assessment of Untargeted Metabolomics by Hydrophilic Interaction Liquid Chromatography-Mass Spectrometry to Define Breast Cancer Liquid Biopsy-Based Biomarkers in Plasma Samples.

An early diagnosis of cancer is fundamental not only in regard to reducing its mortality rate but also in terms of counteracting the progression of the tumor in the initial stages. Breast cancer (BC) is the most common tumor pathology in women and the second deathliest cancer worldwide, although its survival rate is increasing thanks to improvements in screening programs. However, the most common techniques to detect a breast tumor tend to be time-consuming, unspecific or invasive. Herein, the use of untargeted hydrophilic interaction liquid chromatography-mass spectrometry analysis appears as an analytical technique with potential use for the early detection of biomarkers in liquid biopsies from BC patients. In this research, plasma samples from 134 BC patients were compared with 136 from healthy controls (HC), and multivariate statistical analyses showed a clear separation between four BC phenotypes (LA, LB, HER2, and TN) and the HC group. As a result, we identified two candidate biomarkers that discriminated between the groups under study with a VIP > 1 and an AUC of 0.958. Thus, targeting the specific aberrant metabolic pathways in future studies may allow for better molecular stratification or early detection of the disease.

Advancements in metabolomics research in benign gallbladder diseases: A review.

The burgeoning field of metabolomics has piqued the interest of researchers in the context of benign gallbladder diseases, which include conditions such as gallbladder polyps, gallstones, and cholecystitis, which are common digestive system disorders. As metabolomics continues to advance, researchers have increasingly focused their attention on its applicability in the study of benign gallbladder diseases to provide new perspectives for diagnostic, therapeutic, and prognostic evaluation. This comprehensive review primarily describes the techniques of liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, and nuclear magnetic resonance and their respective applications in the study of benign gallbladder disease. Metabolomics has made remarkable progress in various aspects of these diseases, ranging from early diagnosis, etiological research, assessment of disease progression and prognosis, and optimization of therapeutic strategies. However, challenges remain in the field of metabolomics in the study of benign gallbladder diseases. These include issues related to data processing and analysis, biomarker discovery and validation, interdisciplinary research integration, and the advancement of personalized medicine. This article attempts to summarize research findings to date, highlight future research directions, and provide a reference point for metabolomics research in benign gallbladder disease.

LC-qTOF-MS/MS phytochemical profiling of Tabebuia impetiginosa (Mart. Ex DC.) Standl. leaf and assessment of its neuroprotective potential in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Tabebuia impetiginosa (Bignoniaceae) was traditionally used for memory enhancement and central nervous system (CNS) stimulation. AIM OF THE STUDY: This study aims to create a metabolic profile of the ethyl acetate fraction of T. impetiginosa (TEF) and investigate for the first time its neuroprotective potential on cyclophosphamide (CP)-induced chemobrain, validating its traditional use. MATERIALS AND METHODS: Metabolite profiling of TEF was performed using Liquid Chromatography coupled with Quadrupole Time of Flight-Mass/Mass Spectrometry (LC-qTOF-MS/MS). For the in vivo study, CP (200 mg/kg, i.p.) was administered to induce cognitive impairment in rats; TEF (30 mg/kg, p.o.) was administered throughout the 14 days of the experiment to assess its role in mitigating CP-induced neuronal deficits. Behavioral tests including locomotor, Y-maze, and passive avoidance tests were conducted. Additionally, biochemical markers such as reduced glutathione (GSH), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), and caspase-3 immunoexpression were assessed in the hippocampus area. RESULTS: Forty-four phytoconstituents were tentatively identified in TEF, mainly iridoids and organic acids. TEF showed significant memory enhancement as evidenced by the increase in step-through latency in the passive avoidance test by 1.5 folds and the increase in sequence alternation percentage (SAP) in the Y-maze test by 67.3%, as compared to CP-group. Moreover, it showed pronounced antioxidant and anti-inflammatory potentials evidenced by the significant elevation in reduced glutathione (GSH) levels by 80% and a pronounced decline in MDA and TNF-α levels by 24% and 45%, respectively relative to the CP group. TEF treatment restored normal hippocampal histological features and attenuated apoptotic caspase-3 expression by 70% compared to the CP group. CONCLUSIONS: TEF can act as a promising natural scaffold in managing the chemobrain induced by CP in cancer patients.

Differential effects of heating modes on the immunogenic potential of soy-derived peptides released after in vitro infant digestion.

During production of soy-based infant formula, soy protein undergoes heating processes. This study investigated the differential impact of heating modes on the immunogenic potential of peptides in soy protein digests. Wet or dry heating was applied, followed by in vitro gastrointestinal infant digestion. The released peptides were analyzed by LC-MS/MS. Bioinformatics tools were utilized to predict and identify potential linear B-cell and T-cell epitopes, as well as to explore cross-reactivity with other legumes. Subsequently, the peptide intensities of the same potential epitope across different experimental conditions were compared. As a result, we confirmed the previously observed enhancing effect of wet heating on infant digestion and inhibitory effect of dry heating. A total of 8,546 peptides were detected in the digests, and 6,684 peptides were with a score over 80. Among them, 29 potential T-cell epitopes and 27 potential B-cell epitopes were predicted. Cross-reactivity between soy and other legumes, including peanut, pea, chickpea, lentil, kidney bean, and lupine, was also detected. Overall, heating and digestion time could modulate the potential to trigger peptide-induced immune responses.

Exploration of circulating metabolic signature of erythrodermic psoriasis based on LC-MS metabolomics.

Erythrodermic psoriasis (EP) is a rare and life-threatening disease, the pathogenesis of which remains to be largely unknown. Metabolomics analysis can provide global information on disease pathophysiology, candidate biomarkers, and potential intervention strategies. To gain a better understanding of the mechanisms of EP and explore the serum metabolic signature of EP, we conducted an untargeted metabolomics analysis from 20 EP patients and 20 healthy controls. Furthermore, targeted metabolomics for focused metabolites were identified in the serum samples of 30 EP patients and 30 psoriasis vulgaris (PsV) patients. In the untargeted analysis, a total of 2992 molecular features were extracted from each sample, and the peak intensity of each feature was obtained. Principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed significant difference between groups. After screening, 98 metabolites were found to be significantly dysregulated in EP, including 67 down-regulated and 31 up-regulated. EP patients had lower levels of L-tryptophan, L-isoleucine, retinol, lysophosphatidylcholine (LPC), and higher levels of betaine and uric acid. KEGG analysis showed differential metabolites were enriched in amino acid metabolism and glycerophospholipid metabolism. The targeted metabolomics showed lower L-tryptophan in EP than PsV with significant difference and L-tryptophan levels were negatively correlated with the PASI scores. The serum metabolic signature of EP was discovered. Amino acid and glycerophospholipid metabolism were dysregulated in EP. The metabolite differences provide clues for pathogenesis of EP and they may provide insights for therapeutic interventions.

The profile of steroid hormones in human fetal and adult ovaries.

BACKGROUND: Reproduction in women is at risk due to exposure to chemicals that can disrupt the endocrine system during different windows of sensitivity throughout life. Steroid hormone levels are fundamental for the normal development and function of the human reproductive system, including the ovary. This study aims to elucidate steroidogenesis at different life-stages in human ovaries. METHODS: We have developed a sensitive and specific LC-MS/MS method for 21 important steroid hormones and measured them at different life stages: in media from cultures of human fetal ovaries collected from elective terminations of normally progressing pregnancy and in media from adult ovaries from Caesarean section patients, and follicular fluid from women undergoing infertility treatment. Statistically significant differences in steroid hormone levels and their ratios were calculated with parametric tests. Principal component analysis (PCA) was applied to explore clustering of the ovarian-derived steroidogenic profiles. RESULTS: Comparison of the 21 steroid hormones revealed clear differences between the various ovarian-derived steroid profiles. Interestingly, we found biosynthesis of both canonical and "backdoor" pathway steroid hormones and corticosteroids in first and second trimester fetal and adult ovarian tissue cultures. 17α-estradiol, a less potent naturally occurring isomer of 17ß-estradiol, was detected only in follicular fluid. PCA of the ovarian-derived profiles revealed clusters from: adult ovarian tissue cultures with relatively high levels of androgens; first trimester and second trimester fetal ovarian tissue cultures with relatively low estrogen levels; follicular fluid with the lowest androgens, but highest corticosteroid, progestogen and estradiol levels. Furthermore, ratios of specific steroid hormones showed higher estradiol/ testosterone and estrone/androstenedione (indicating higher CYP19A1 activity, p < 0.01) and higher 17-hydroxyprogesterone/progesterone and dehydroepiandrosterone /androstenedione (indicating higher CYP17A1 activity, p < 0.01) in fetal compared to adult ovarian tissue cultures. CONCLUSIONS: Human ovaries demonstrate de novo synthesis of non-canonical and "backdoor" pathway steroid hormones and corticosteroids. Elucidating the steroid profiles in human ovaries improves our understanding of physiological, life-stage dependent, steroidogenic capacity of ovaries and will inform mechanistic studies to identify endocrine disrupting chemicals that affect female reproduction.

Preparation and characterization of stationary phase gradients on C8 liquid chromatography columns.

Continuous C8 stationary phase gradients are created on commercial Waters Symmetry Shield RP8 columns by strategically cleaving the C8 moieties in a time-dependent fashion. The method relies on the controlled infusion of a trifluoroacetic acid/water/acetonitrile solution through the column to cleave the organic functionality (e.g., C8) from the siloxane framework. The bond cleavage solution is reactive enough to cleave the functional groups, even with polar groups embedded within the stationary phase to protect the silica. Both the longitudinal and radial heterogeneity were evaluated by extruding the silica powder into polyethylene tubing and evaluating the percent carbon content in the different sections using thermogravimetric analysis (TGA). TGA analysis shows the presence of a stationary phase gradient in the longitudinal direction but not in the radial direction. Two different gradient profiles were formed with good reproducibility by modifying the infusion method: one exhibited an 'S'-shaped gradient while the other exhibited a steep exponential-like gradient. The gradients were characterized chromatographically using test mixtures, and the results showed varied retention characteristics and an enhanced ability to resolve nicotine analytes.

Metabolism and cytotoxicity studies of the two hallucinogens 1cP-LSD and 4-AcO-DET in human liver and zebrafish larvae models using LC-HRMS/MS and a high-content screening assay.

The continuous emergence of new psychoactive substances (NPS) attracted a great deal of attention within recent years. Lately, the two hallucinogenic NPS 1cP-LSD and 4-AcO-DET have appeared on the global market. Knowledge about their metabolism to identify potential metabolic targets for analysis and their cytotoxic properties is lacking. The aim of this work was thus to study their in vitro and in vivo metabolism in pooled human liver S9 fraction (pHLS9) and in zebrafish larvae (ZL) by means of liquid chromatography-high-resolution tandem mass spectrometry. Monooxygenases involved in the initial metabolic steps were elucidated using recombinant human isozymes. Investigations on their cytotoxicity were performed on the human hepatoma cell line HepG2 using a multiparametric, fluorescence-based high-content screening assay. This included measurement of CYP-enzyme mediated effects by means of the unspecific CYP inhibitor 1-aminbenzotriazole (ABT). Several phase I metabolites of both compounds and two phase II metabolites of 4-AcO-DET were produced in vitro and in vivo. After microinjection of 1cP-LSD into the caudal vein of ZL, three out of seven metabolites formed in pHLS9 were also detected in ZL. Twelve 4-AcO-DET metabolites were identified in ZL after exposure via immersion bath and five of them were found in pHLS9 incubations. Notably, unique metabolites of 4-AcO-DET were only produced by ZL, whereas 1cP-LSD specific metabolites were found both in ZL and in pHLS9. No toxic effects were observed for 1cP-LSD and 4-AcO-DET in HepG2 cells, however, two parameters were altered in incubations containing 4-AcO-DET together with ABT compared with incubations without ABT but in concentrations far above expected in vivo concentration. Further investigations should be done with other hepatic cell lines expressing higher levels of CYP enzymes.

Insights into the selectivity of polar stationary phases based on quantitative retention mechanism assessment in hydrophilic interaction chromatography.

Hydrophilic interaction chromatography (HILIC) offers different selectivity than reversed-phase liquid chromatography (RPLC). However, our knowledge of the driving force for selectivity is limited and there is a need for a better understanding of the selectivity in HILIC. Quantitative assessment of retention mechanisms makes it possible to investigate selectivity based on understanding the underlying retention mechanisms. In this study, selected model compounds from the Ikegami selectivity tests were evaluated on different polar stationary phases. The study results revealed significant insights into the selectivity in HILIC. First, hydroxy and methylene selectivity is driven by hydrophilic partitioning; but surface adsorption for 2-deoxyuridine or 5-methyluridine reduces the selectivity factor. Furthermore, the retention of 2-deoxyuridine or 5-methyluridine by surface adsorption in combination with the phase ratio explain the difference in hydroxy or methylene selectivity observed among different stationary phases. Investigations on xanthine positional isomers (1-methylxanthine/3-methylxanthine, theophylline/theobromine) indicate that isomeric selectivity is controlled by surface adsorption; however, hydrophilic partitioning may contribute to resolution by enhancing overall retention. In addition, two pairs of nucleoside isomers (adenosine/vidarabine, 2'-deoxy and 3'-deoxyguanosine) provide an example that isomeric selectivity can also be controlled by hydrophilic partitioning if their partitioning coefficients are significantly different in HILIC. Although more data is needed, the current study provides a mechanistic based understanding of the selectivity in HILIC and potentially a new way to design selectivity tests.

Sensitive and effective method with 96-well plate for determination of levamlodipine in human plasma using LC-MS/MS.

we developed an effective protein precipitation method for determination of levamlodipine in human plasma using LC-MS/MS. Sample extraction was carried out by using liquid-liquid extraction in 96-well plate format. (S)-Amlodipine-d4 was used as internal standard (IS). The chromatographic separation was achieved using Philomen Chiral MX (2) column (3 µm, 2.1 × 100 mm). Mobile phase A was comprised of Acetonitrile (ACN), Mono ethanol amine (MEA) and Iso-Propyl alcohol (IPA) (1000:1:10, v/v/v), Mobile phase B was IPA-ACN (2:1, v/v). The flow rate was 0.4 mL/min. The total run time of each sample was 4.0 min with gradient elution. LC-MS/MS spectra were generated in positive ion mode, and multiple reaction monitoring (MRM) was used to detect the following transitions: m/z 409.20 â†’ 238.15 for levamlodipine and 415.25 â†’ 240.20 for (S)-Amlodipine-d4 (the IS). The method was linear from 50 to 10000 pg/mL（R2＝0.9988489）,and the lower limit of quantification (LLOQ) was 50 pg/mL. This method was applied to a bioequivalence study of levamlodipine.

Highly sensitive and accurate measurement of underivatized phosphoenolpyruvate in plasma and serum via EDTA-facilitated hydrophilic interaction liquid chromatography-tandem mass spectrometry.

Phosphoenolpyruvate (PEP) is an essential intermediate metabolite that is involved in various vital biochemical reactions. However, achieving the direct and accurate quantification of PEP in plasma or serum poses a significant challenge owing to its strong polarity and metal affinity. In this study, a sensitive method for the direct determination of PEP in plasma and serum based on ethylenediaminetetraacetic acid (EDTA)-facilitated hydrophilic interaction liquid chromatography-tandem mass spectrometry was developed. Superior chromatographic retention and peak shapes were achieved using a zwitterionic stationary-phase HILIC column with a metal-inert inner surface. Efficient dechelation of PEP-metal complexes in serum/plasma samples was achieved through the introduction of EDTA, resulting in a significant enhancement of the PEP signal. A PEP isotopically labelled standard was employed as a surrogate analyte for the determination of endogenous PEP, and validation assessments proved the sensitivity, selectivity, and reproducibility of this method. The method was applied to the comparative quantification of PEP in plasma and serum samples from mice and rats, as well as in HepG2 cells, HEK293T cells, and erythrocytes; the results confirmed its applicability in PEP-related biomedical research. The developed method can quantify PEP in diverse biological matrices, providing a feasible opportunity to investigate the role of PEP in relevant biomedical research.