Direct Monitoring of Exogenous γ-Hydroxybutyric Acid in Body Fluids by NMR Spectroscopy

Gamma-hydroxybutyrate (GHB), 1,4-butanediol (1,4BD), and gamma-butyrolactone (GBL) intoxication: A state-of-the-art review

γ-hydroxybutyrate (GHB) is synthesized endogenously from γ-aminobutyric acid (GABA) or exogenously from 1,4-butanediol (butane-1,4-diol; 1,4-BD) or γ-butyrolactone (GBL). GBL, and 1,4-BD are rapidly converted to GHB. The gastric absorption time, volume of distribution, and half-life of GHB are between 5 and 45 min, 0.49 ± 0.9 L/kg, and between 20 and 60 min, respectively. GHB and its analogues have a dose-dependent effect on the activation of GHB receptor, GABA-B, and GABA localized to the central nervous system. After ingestion, most patients present transient neurological disorders (lethal dose: 60 mg/kg). Chronic GHB consumption is associated with disorders of use and a withdrawal syndrome when the consumption is discontinued. GHB, GBL, and 1,4-BD are classified as narcotics but only the use of GHB is controlled internationally. They are used for drug facilitated (sexual) assault, recreational purposes, slamsex, and chemsex. To confirm an exogenous intake or administration of GHB, GBL, or 1-4-BD, the pre-analytical conservation is crucial. The antemortem cutoff doses for detection are 5 and 5-15 mg/L, with detection windows of 6 and 10 h in the blood and urine, respectively Control of GHB is essential to limit the number of users, abuse, associated risks, and death related to their consumption.

Alcohol perturbed locomotor behavior, metabolism, and pharmacokinetics of gamma-hydroxybutyric acid in rats

Gamma-hydroxybutyric acid (GHB), both a metabolic precursor and product of gamma-aminobutyric acid (GABA), is a central nervous system depressant used for the treatment of narcolepsy-associated cataplexy and alcohol withdrawal. However, administration of GHB with alcohol (ethanol) is a major cause of hospitalizations related to GHB intoxication. In this study, we investigated locomotor behavior as well as metabolic and pharmacokinetic interactions following co-administration of GHB and ethanol in rats. The locomotor behavior of rats was evaluated following the intraperitoneal administration of GHB (sodium salt, 500 mg/kg) and/or ethanol (2 g/kg). Further, time-course urinary metabolic profiling of GHB and its biomarker metabolites glutamic acid, GABA, succinic acid, 2,4-dihydroxybutyric acid (OH-BA), 3,4-OH-BA, and glycolic acid as well as pharmacokinetic analysis were performed. GHB/ethanol co-administration significantly reduced locomotor activity, compared to the individual administration of GHB or ethanol. The urinary and plasma concentrations of GHB and other target compounds, except for 2,4-OH-BA, were significantly higher in the GHB/ethanol co-administration group than the group administered only GHB. The pharmacokinetic analysis results showed that the co-administration of GHB and ethanol significantly increased the half-life of GHB while the total clearance decreased. Moreover, a comparison of the metabolite-to-parent drug area under the curve ratios demonstrated that the metabolic pathways of GHB, such α- and β-oxidation, were inhibited by ethanol. Consequently, the co-administration of GHB and ethanol aggravated the metabolism and elimination of GHB and enhanced its sedative effect. These findings will contribute to clinical interpretation of GHB intoxication.

Urinary concentrations of GHB and its novel amino acid and carnitine conjugates following controlled GHB administration to humans

Gamma-hydroxybutyrate (GHB) remains a challenging clinical/forensic toxicology drug. Its rapid elimination to endogenous levels mainly causes this. Especially in drug-facilitated sexual assaults, sample collection often occurs later than the detection window for GHB. We aimed to investigate new GHB conjugates with amino acids (AA), fatty acids, and its organic acid metabolites for their suitability as ingestion/application markers in urine following controlled GHB administration to humans. We used LC-MS/MS for validated quantification of human urine samples collected within two randomized, double-blinded, placebo-controlled crossover studies (GHB 50 mg/kg, 79 participants) at approximately 4.5, 8, 11, and 28 h after intake. We found significant differences (placebo vs. GHB) for all but two analytes at 4.5 h. Eleven hours post GHB administration, GHB, GHB-AAs, 3,4-dihydroxybutyric acid, and glycolic acid still showed significantly higher concentrations; at 28 h only GHB-glycine. Three different discrimination strategies were evaluated: (a) GHB-glycine cut-off concentration (1 µg/mL), (b) metabolite ratios of GHB-glycine/GHB (2.5), and (c) elevation threshold between two urine samples (> 5). Sensitivities were 0.1, 0.3, or 0.5, respectively. Only GHB-glycine showed prolonged detection over GHB, mainly when compared to a second time- and subject-matched urine sample (strategy c).

Development of Sequence-Controlled, Degradable, and Cytocompatible Oligomers with Explicit Fragmentation Pathways

Sequence-defined and degradable polymers can mimic biopolymers, such as peptides and DNA, to undertake life-supporting functions in a chemical way. The design and development of well-structured oligomers/polymers is the most concern for the public, even to further uncover their degradation process illustrating the degraded products and their properties. However, seldom investigation has been reported on the aforementioned aspects. In this work, the alternating photo-reversible addition-fragmentation chain-transfer (photo-RAFT) single unit monomer insertion (SUMI) of different N-substituted maleimides and thermal radical ring-opening SUMI of a cyclic ketene acetal monomer (i.e., 5,6-benzo-2-methylene-1,3-dioxepane (BMDO)) is adopted, to produce two degradable pentamers owing to the conversion of the exo-methylene group of BMDO into ester bonds along the main chains of the prepared products. Moreover, the possible degraded approach of pentamers is studied by combining high-resolution mass spectrometry (HRMS) and liquid chromatography-mass spectrometry (LC-MS) for the first time. This work also sheds light on the precise structures and cytotoxicity of SUMI products and their degraded compounds, proposing a detailed and credible outlook for biomedical applications.

New gamma-hydroxybutyric acid (GHB) biomarkers: Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of GHB amino acid, carnitine, and fatty acid conjugates in urine

Gamma-hydroxybutyric acid (GHB) represents an important drug in clinical and forensic toxicology, particularly in the context of drug-facilitated crimes. Analytically, GHB remains a major challenge given its endogenous occurrence and short detection window. Previous studies identified a number of potential interesting novel conjugates of GHB with carnitine, amino acids (AA, glutamate, glycine, and taurine), or fatty acids. As a basis for comprehensive studies on the suitability of these novel biomarkers, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in human urine. Additionally, already known markers 2,4-dihydroxy butyric acid (2,4-DHB), 3,4-DHB, glycolic acid, succinic acid, succinylcarnitine, and GHB glucuronide were included. The method was fully validated according to (inter)national guidelines. Synthetic urine proved suitable as a surrogate matrix for calibration. Matrix effects were observed for all analytes with suppression effects of about 50% at QC LOW, and approximately 20% to 40% at QC HIGH, but with consistent standard deviation of <25% at QC LOW and <15% at QC HIGH, respectively. All analytes showed acceptable intra- and inter-day imprecision of below 20%, except for inter-day variation of GHB taurine and FA conjugates at the lowest QC. Preliminary applicability studies proved the usefulness of the method and pointed towards GHB glycine, followed by other AA conjugates as the most promising candidates to improve GHB detection. FA conjugates were not detected in urine samples yet. The method can be used now for comprehensive sample analysis on (controlled) GHB administration to prove the usefulness of the novel GHB biomarkers.

Urinary Profile of Endogenous Gamma-Hydroxybutyric Acid and its Biomarker Metabolites in Healthy Korean Females: Determination of Age-Dependent and Intra-Individual Variability and Identification of Metabolites Correlated With Gamma-Hydroxybutyric Acid

Gamma-hydroxybutyric acid (GHB), used as a therapeutic and an illegal anesthetic, is a human neurotransmitter produced during gamma-aminobutyric acid (GABA) biosynthesis and metabolism. Potential biomarker metabolites of GHB intoxication have been identified previously; however, reference concentrations have not been set due to the lack of clinical study data. Urinary profiling of endogenous GHB and its biomarker metabolites in urine samples (n = 472) of 206 healthy females was performed based on differences in age and time of sample collection using liquid chromatography-tandem mass spectrometry following validation studies. The unadjusted and creatinine-adjusted urinary concentrations ranges were obtained after urinary profiling. The creatinine-adjusted concentrations of glutamic and succinic acids and succinylcarnitine significantly increased, whereas that of glycolic acid significantly decreased with advancing age. Significant inter-day variation of GABA concentration and intra-day variation of 3,4-dihydroxybutyric acid and succinylcarnitine concentrations were observed. The urinary concentrations of 2,4-dihydroxybutyric acid, succinic acid, and 3,4-dihydroxybutyric acid showed the highest correlation with that of GHB. Data from this study suggest population reference limits to facilitate clinical and forensic decisions related to GHB intoxication and could be useful for identification of biomarkers following comparison with urinary profiles of GHB-administered populations.

In situ, real-time, colorimetric detection of γ-hydroxybutyric acid (GHB) using self-protection products coated with chemical receptor-embedded hydrogel

Due to the increase in drug-facilitated sexual assault (DFSA) enabled by the illegal use of drugs, there have been constant demands for simple methods that can be used to protect oneself against crime in real life. γ-Hydroxybutyric acid (GHB), a central nervous system depressant, is one of the most dangerous drugs for use in DFSA because it is colorless and has slow physiological effects, which pose challenges for developing in situ, real-time GHB monitoring techniques. In this study, we developed a method for in situ colorimetric GHB detection using various self-protection products (SPPs) coated with 2-(3-bromo-4-hydroxystyryl)-3-ethylbenzothiazol-3-ium iodide (BHEI) as a chemical receptor embedded in hydrogels. Additionally, smartphone-based detection offers enhanced colorimetric sensitivity compared to that of the naked eye. The developed SPPs will help address drug-facilitated social problems.

A Retrospective Metabolomics Analysis of Gamma-Hydroxybutyrate in Humans: New Potential Markers and Changes in Metabolism Related to GHB Consumption

GHB is an endogenous short-chain organic acid presumably also widely applied as a rape and knock out drug in cases of drug-facilitated crimes or sexual assaults (DFSA). Due to the endogenous nature of GHB and its fast metabolism in vivo, the detection window of exogenous GHB is however narrow, making it challenging to prove use of GHB in DFSA cases. Alternative markers of GHB intake have recently appeared though none has hitherto been validated for forensic use. UHPLC-HRMS based screening of blood samples for drugs of abuse is routinely performed in several forensic laboratories which leaves an enormous amount of unexploited data. Recently we devised a novel metabolomics approach to use archived data from such routine screenings for elucidating both direct metabolites from exogenous compounds, but potentially also regulation of endogenous metabolism and metabolites. In this paper we used UHPLC-HRMS data acquired over a 6-year period from whole blood analysis of 51 drivers driving under the influence of GHB as well as a matched control group. The data were analyzed using a metabolomics approach applying a range of advanced analytical methods such as OPLS-DA, LASSO, random forest, and Pearson correlation to examine the data in depth and demonstrate the feasibility and potential power of the approach. This was done by initially detecting a range of potential biomarkers of GHB consumption, some that previously have been found in controlled GHB studies, as well as several new potential markers not hitherto known. Furthermore, we investigate the impact of GHB intake on human metabolism. In aggregate, we demonstrate the feasibility to extract meaningful information from archived data here exemplified using GHB cases. Hereby we hope to pave the way for more general use of the principle to elucidate human metabolites of e.g. new legal or illegal drugs as well as for applications in more global and large scale metabolomics studies in the future.

GHB related acids are useful in routine casework of suspected GHB intoxication cases

GHB related acids (3,4-dihydroxy butyric acid, 2,4-dihydroxy butyric acid and glycolic acid) are produced through oxidative GHB metabolism. These analytes could be potential biomarkers to ensure the diagnosis of a GHB intoxication and even prolong the detection window. Within this study, forensic routine cases were measured to consider the potential of additional gas chromatographic mass spectrometric analysis on these acids. 17 GHB positive real cases (10 serum samples and 7 urine samples) and 40 cases with suspicion of drugging in DFC cases and negative GHB results (21 serum samples and 19 urine samples) were evaluated. Increased GHB related acid concentrations were detected in all serum and most urine samples positive on GHB. In some GHB negative cases, especially in serum samples, concentrations of GHB related acids gave hints that GHB actually was taken. We recommend to use the following cut-offs for a more reliable interpretation of potential GHB intoxication cases: 3,4-OH-BA:>3 mg/L in serum and>50 mg/L in urine; 2,4-OH-BA:>2 mg/L in serum and>25 mg/L in urine; GA:>5 mg/L in serum and>400 mg/L in urine.

Detection of γ-hydroxybutyric acid-related acids in blood plasma and urine: Extending the detection window of an exogenous γ-hydroxybutyric acid intake?

In crimes facilitated by γ-hydroxybutyric acid (GHB) administration, the frequent occurrence of anterograde amnesia of the victims as well as the short detection window and variations of endogenous GHB concentrations complicate obtaining analytical proof of GHB administration. Because elevated endogenous organic acid concentrations have been found in the urine of patients with succinic semialdehyde deficiency (leading to accumulation of GHB in human specimens) and after GHB ingestion, we searched for an alternative way to prove GHB administration via detection of elevated organic acid concentrations in blood plasma and urine. We collected blood and urine samples from narcolepsy patients (n = 5) treated with pharmaceuticals containing GHB sodium salt (1.86-3.72 g GHB as free acid per dose). Although GHB was detectable only up to 4 h in concentrations greater than the commonly used cutoff levels in blood plasma, 3,4-dihydroxybutyric acid (3,4-DHB) could be detected up to 12 h in blood plasma in concentrations exceeding initial concentrations of the same patient before GHB ingestion. Furthermore, four of the five patients showed an increase above endogenous levels described in the scientific literature. In urine, GHB concentrations above commonly used cutoff levels could be observed 4.5-9.5 h after GHB intake. Creatinine standardized initial concentrations were reached again for glycolic acid (GA), 3,4-DHB, and 2,4-dihydroxybutyric (2,4-DHB) acid at 6.5-22, 11.5-22, and 8.5-70 h after GHB intake, respectively. Therefore, 2,4-DHB, 3,4-DHB, and GA are promising and should be further investigated as potential biomarkers to prolong the detection window of GHB intake.

Applications of Metabolomics in Forensic Toxicology and Forensic Medicine

Forensic toxicology and forensic medicine are unique among all other medical fields because of their essential legal impact, especially in civil and criminal cases. New high-throughput technologies, borrowed from chemistry and physics, have proven that metabolomics, the youngest of the “omics sciences”, could be one of the most powerful tools for monitoring changes in forensic disciplines. Metabolomics is a particular method that allows for the measurement of metabolic changes in a multicellular system using two different approaches: targeted and untargeted. Targeted studies are focused on a known number of defined metabolites. Untargeted metabolomics aims to capture all metabolites present in a sample. Different statistical approaches (e.g., uni- or multivariate statistics, machine learning) can be applied to extract useful and important information in both cases. This review aims to describe the role of metabolomics in forensic toxicology and in forensic medicine.

Towards Extending the Detection Window of Gamma-Hydroxybutyric Acid-An Untargeted Metabolomics Study in Serum and Urine Following Controlled Administration in Healthy Men

In forensic toxicology, gamma-hydroxybutyrate (GHB) still represents one of the most challenging drugs of abuse in terms of analytical detection and interpretation. Given its rapid elimination, the detection window of GHB in common matrices is short (maximum 12 h in urine). Additionally, the differentiation from naturally occurring endogenous GHB, is challenging. Thus, novel biomarkers to extend the detection window of GHB are urgently needed. The present study aimed at searching new potential biomarkers of GHB use by means of mass spectrometry (MS) metabolomic profiling in serum (up to 16.5 h) and urine samples (up to 8 h after intake) collected during a placebo-controlled crossover study in healthy men. MS data acquired by different analytical methods (reversed phase and hydrophilic interaction liquid chromatography; positive and negative electrospray ionization each) were filtered for significantly changed features applying univariate and mixed-effect model statistics. Complementary to a former study, conjugates of GHB with glycine, glutamate, taurine, carnitine and pentose (ribose) were identified in urine, with particularly GHB-pentose being promising for longer detection. None of the conjugates were detectable in serum. Therein, mainly energy metabolic substrates were identified, which may be useful for more detailed interpretation of underlying pathways but are too unspecific as biomarkers.

Metabolic Alterations Associated with γ-Hydroxybutyric Acid and the Potential of Metabolites as Biomarkers of Its Exposure

γ-Hydroxybutyric acid (GHB) is an endogenous short chain fatty acid that acts as a neurotransmitter and neuromodulator in the mammalian brain. It has often been illegally abused or misused due to its strong anesthetic effect, particularly in drug-facilitated crimes worldwide. However, proving its ingestion is not straightforward because of the difficulty in distinguishing between endogenous and exogenous GHB, as well as its rapid metabolism. Metabolomics and metabolism studies have recently been used to identify potential biomarkers of GHB exposure. This mini-review provides an overview of GHB-associated metabolic alterations and explores the potential of metabolites for application as biomarkers of GHB exposure. For this, we discuss the biosynthesis and metabolism of GHB, analytical issues of GHB in biological samples, alterations in metabolic pathways, and changes in the levels of GHB conjugates in biological samples from animal and human studies. Metabolic alterations in organic acids, amino acids, and polyamines in urine enable discrimination between GHB-ingested animals or humans and controls. The potential of GHB conjugates has been investigated in a variety of clinical settings. Despite the recent growth in the application of metabolomics and metabolism studies associated with GHB exposure, it remains challenging to distinguish between endogenous and exogenous GHB. This review highlights the significance of further metabolomics and metabolism studies for the discovery of practical peripheral biomarkers of GHB exposure.

Detection of ɣ-hydroxybutyric acid (GHB) and ɣ-butyrolactone (GBL) in alcoholic beverages via total vaporization solid-phase microextraction (TV-SPME) and gas chromatography-mass spectrometry

Total Vaporization Solid-Phase Microextraction (TV-SPME) relies on the same technique as standard SPME but completely vaporizes a sample extract, and analytes are sorbed directly from the vapor phase. On-fiber derivatization may also be performed using TV-SPME, where the fiber is first exposed to the headspace of a vial containing the derivatization agent, then exposed to a new vial containing the sample. ɣ-Hydroxybutyric acid (GHB) and ɣ-butyrolactone (GBL) are drugs of concern in that they may be used in drug facilitated sexual assault by surreptitiously spiking them into a victim's beverage. These drugs cause sedation, memory loss, and are difficult to detect in biological samples. One challenge in their analysis is that they can interconvert in aqueous samples, which was demonstrated in samples allowed to stand at room temperature for long periods. A volume study of GBL in water was performed with volumes ranging from 1 to 10,000 µl to compare the efficacy of TV-SPME, headspace SPME, and immersion SPME. Lastly, water, beer, wine, liquor, and mixed drinks were spiked with either GHB or GBL with realistic concentrations (mg/ml) and microliter quantities were analyzed using a TV-SPME Gas Chromatography-Mass Spectrometry method. The GBL volume study demonstrated an increased sensitivity in GBL detection when TV-SPME was utilized. Additionally, GHB and GBL were identified in various beverages at realistic concentrations. Overall, TV-SPME is beneficial because it requires no sample preparation and uses smaller sample volumes than immersion and headspace SPME.

Forensic NMR metabolomics: one more arrow in the quiver

INTRODUCTION

NMR metabolomics is increasingly used in forensics, due to the possibility of investigating both endogenous metabolic profiles and exogenous molecules that may help to describe metabolic patterns and their modifications associated to specific conditions of forensic interest.

OBJECTIVES

The aim of this work was to review the recent literature and depict the information provided by NMR metabolomics. Attention has been devoted to the identification of peculiar metabolic signatures and specific ante-mortem and post-mortem profiles or biomarkers related to different conditions of forensic concern, such as the identification of biological traces, the estimation of the time since death, and the exposure to drugs of abuse.

RESULTS AND CONCLUSION

The results of the described studies highlight how forensics can benefit from NMR metabolomics by gaining additional information that may help to shed light in several forensic issues that still deserve to be further elucidated.

Comparative Untargeted Metabolomics Analysis of the Psychostimulants 3,4-Methylenedioxy-Methamphetamine (MDMA), Amphetamine, and the Novel Psychoactive Substance Mephedrone after Controlled Drug Administration to Humans

Psychoactive stimulants are a popular drug class which are used recreationally. Over the last decade, large numbers of new psychoactive substances (NPS) have entered the drug market and these pose a worldwide problem to human health. Metabolomics approaches are useful tools for simultaneous detection of endogenous metabolites affected by drug use. They allow identification of pathways or characteristic metabolites, which might support the understanding of pharmacological actions or act as indirect biomarkers of consumption behavior or analytical detectability. Herein, we performed a comparative metabolic profiling of three psychoactive stimulant drugs 3,4-methylenedioxymethamphetamine (MDMA), amphetamine and the NPS mephedrone by liquid chromatography-high resolution mass spectrometry (LC-HRMS) in order to identify common pathways or compounds. Plasma samples were obtained from controlled administration studies to humans. Various metabolites were identified as increased or decreased based on drug intake, mainly belonging to energy metabolism, steroid biosynthesis and amino acids. Linoleic acid and pregnenolone-sulfate changed similarly in response to intake of all drugs. Overall, mephedrone produced a profile more similar to that of amphetamine than MDMA in terms of affected energy metabolism. These data can provide the basis for further in-depth targeted metabolome studies on pharmacological actions and search for biomarkers of drug use.

Metabolomic Strategies in Biomarker Research-New Approach for Indirect Identification of Drug Consumption and Sample Manipulation in Clinical and Forensic Toxicology?

Drug of abuse (DOA) consumption is a growing problem worldwide, particularly with increasing numbers of new psychoactive substances (NPS) entering the drug market. Generally, little information on their adverse effects and toxicity are available. The direct detection and identification of NPS is an analytical challenge due to their ephemerality on the drug scene. An approach that does not directly focus on the structural detection of an analyte or its metabolites, would be beneficial for this complex analytical scenario and the development of alternative screening methods could help to provide fast response on suspected NPS consumption. A metabolomics approach might represent such an alternative strategy for the identification of biomarkers for different questions in DOA testing. Metabolomics is the monitoring of changes in small (endogenous) molecules (<1,000 Da) in response to a certain stimulus, e.g., DOA consumption. For this review, a literature search targeting "metabolomics" and different DOAs or NPS was conducted. Thereby, different applications of metabolomic strategies in biomarker research for DOA identification were identified: (a) as an additional tool for metabolism studies bearing the major advantage that particularly a priori unknown or unexpected metabolites can be identified; and (b) for identification of endogenous biomarker or metabolite patterns, e.g., for synthetic cannabinoids or also to indirectly detect urine manipulation attempts by chemical adulteration or replacement with artificial urine samples. The majority of the currently available literature in that field, however, deals with metabolomic studies for DOAs to better assess their acute or chronic effects or to find biomarkers for drug addiction and tolerance. Certain changes in endogenous compounds are detected for all studied DOAs, but often similar compounds/pathways are influenced. When evaluating these studies with regard to possible biomarkers for drug consumption, the observed changes appear, albeit statistically significant, too small to reliably work as biomarker for drug consumption. Further, different drugs were shown to affect the same pathways. In conclusion, metabolomic approaches possess potential for detection of biomarkers indicating drug consumption. More studies, including more sensitive targeted analyses, multi-variant statistical models or deep-learning approaches are needed to fully explore the potential of omics science in DOA testing.

Analytical considerations for (un)-targeted metabolomic studies with special focus on forensic applications

Over the past few years, the interest in metabolomics has increased in various fields including forensic toxicology. Forensic analysis typically requires a high degree of accuracy, which is often a problem in metabolomics applications. We aimed for a systematic evaluation of different analytical considerations of a metabolomics workflow allowing a targeted approach within an untargeted setup. Samples with 69 metabolites from different chemical classes were qualitatively and quantitatively analyzed on a high resolution quadrupole time of flight mass spectrometer coupled to liquid chromatography (UHPLC-QTOF). Three issues were addressed: (a) Two different approaches on "blind matrix" a simulated body fluid (SBF) and plasma-filtrate, were tested for calibration samples; (b) comparison of two different HPLC columns, reverse-phase (RP) and hydrophilic interaction chromatography (HILIC); and (c) comparison of three different acquisition modes (TOF-MS, information dependent data acquisition (IDA), and sequential window acquisition of all theoretical fragment-ion spectra (SWATH). Samples were measured repeatedly for method comparison based on sensitivity, accuracy, precision, and detection robustness. The blind matrices showed similar accuracy for most analytes, while SBF provided an easier preparation with satisfying results. To cover a wide part of the human metabolome, a combination of RP and HILIC showed the best results. The different scan modes performed equally regarding metabolite quantification while TOF-MS was more sensitive but lacked MS/MS spectra generation. IDA and SWATH files were aligned to various databases where IDA showed good MS/MS spectra matches. SWATH seemed to be beneficial in detection rate but was incompatible with many important software tools in metabolomics.

Urinary Metabolomics Study of Patients with Gout Using Gas Chromatography-Mass Spectrometry

Objectives

Gout is a common type of inflammatory arthritis. The aim of this study was to detect urinary metabolic changes in gout patients which may contribute to understanding the pathological mechanism of gout and discovering potential metabolite markers.

Methods

Urine samples from 35 gout patients and 29 healthy volunteers were analyzed by gas chromatography-mass spectrometry (GC-MS). Orthogonal partial least-squares discriminant analysis (OPLS-DA) was performed to screen differential metabolites between two groups, and the variable importance for projection (VIP) values and Student's t-test results were combined to define the significant metabolic changes caused by gout. Further, binary logistic regression analysis was performed to establish a model to distinguish gout patients from healthy people, and receiver operating characteristic (ROC) curve was made to evaluate the potential for diagnosis of gout.

Result

A total of 30 characteristic metabolites were significantly different between gout patients and controls, mainly including amino acids, carbohydrates, organic acids, and their derivatives, associated with perturbations in purine nucleotide synthesis, amino acid metabolism, purine metabolism, lipid metabolism, carbohydrate metabolism, and tricarboxylic acid cycle. Binary logistic regression and ROC curve analysis showed the combination of urate and isoxanthopterin can effectively discriminate the gout patients from controls with the area under the curve (AUC) of 0.879.

Conclusion

Thus, the urinary metabolomics study is an efficient tool for a better understanding of the metabolic changes of gout, which may support the clinical diagnosis and pathological mechanism study of gout.