Stability of amino acids and related amines in human serum under different preprocessing and pre-storage conditions based on iTRAQ®-LC-MS/MS.

Amino acid analysis or metabonomics requires large-scale sample collection, which makes sample storage a critical consideration. However, functional amino acids are often neglected in metabolite stability studies because of the difficulty in detecting and accurately quantifying them with most analysis methods. Here, we investigated the stability of amino acids and related amines in human serum following different preprocessing and pre-storage procedures. Serum samples were collected and subjected to three storage conditions; cold storage (4°C), room temperature storage (22°C), and freezing (-80°C). The concentration of amino acids and related amines were quantified using iTRAQ®-LC-MS/MS with isobaric tagging reagents. Approximately 54.84%, 58.06%, and 48.39% of detectable and target analytes were altered at the 4°C condition, 22°C condition, and when subjected to freeze-thaw cycles, respectively. Some amino acids which are unstable and relatively stable were found. Our study provides detailed amino acid profiles in human serum and suggests pre-treatment measures that could be taken to improve stability.

Targeted ultra-performance liquid chromatography/tandem mass spectrometric quantification of methylated amines and selected amino acids in biofluids.

RATIONALE: Methylated amino compounds and basic amino acids are important analyte classes with high relevance in nutrition, physical activity and physiology. Reliable and easy quantification methods covering a variety of metabolites in body fluids are a prerequisite for efficient investigations in the field of food and nutrition. METHODS: Targeted ultra-performance liquid chromatography/tandem mass spectrometric (UHPLC/MS) analysis was performed using HILIC separation and timed ESI-MRM detection, combined with a short sample preparation. Calibration in urine and blood plasma was achieved by matrix-matched standards, isotope-labelled internal standards and standard addition. The method was fully validated and the performance was evaluated using a subset from the Karlsruhe Metabolomics and Nutrition (KarMeN) study. RESULTS: Within this method, a total of 30 compounds could be quantified simultaneously in a short run of 9 min in both body fluids. This covers a variety of free amino compounds which are present in very different concentrations. The method is easy, precise and robust, and has a broad working range. As a proof of principle, literature-based associations of certain metabolites with dietary intake of respective foods were clearly confirmed in the KarMeN subset. CONCLUSIONS: Overall, the method turned out to be well suited for application in nutrition studies, as shown for the example of food intake biomarkers in KarMeN. Application to a variety of questions such as food-related effects or physical activity will support future studies in the context of nutrition and health.

Plasma metabolomics in tuberculosis patients with and without concurrent type 2 diabetes at diagnosis and during antibiotic treatment.

Tuberculosis (TB) and type 2 diabetes mellitus (DM), a major TB risk factor, are both accompanied by marked alterations in metabolic processes. Dissecting the specific metabolic changes induced by disease through metabolomics has shown potential to improve our understanding of relevant pathophysiological mechanisms of disease, which could lead to improved treatment. Targeted tandem liquid chromatography-mass spectrometry (LC-MS/MS) was used to compare amine and acylcarnitine levels in plasma samples of patients with TB or TB-DM from Indonesia at time of diagnosis and during antibiotic treatment. Partial least squares discrimination analysis (PLS-DA) showed good separation of patient groups. Amine levels were strongly altered in both disease groups compared to healthy controls, including low concentrations of citrulline and ornithine. Several amino acid ratios discriminated TB from controls (phenylalanine/histidine; citrulline/arginine; kynurenine/tryptophan), possibly reflecting changes in indoleamine-pyrrole 2,3-dioxygenase (IDO) and nitric oxide synthase (NOS) activity. Choline, glycine, serine, threonine and homoserine levels were lower in TB-DM compared to TB, and, in contrast to other analytes, did not normalize to healthy control levels during antibiotic treatment. Our results not only provide important validation of previous studies but also identify novel biomarkers, and significantly enhance our understanding of metabolic changes in human TB and TB-DM.

Electro-Acupuncture Alleviates Cisplatin-Induced Anorexia in Rats by Modulating Ghrelin and Monoamine Neurotransmitters.

Anorexia is common in patients with cancer, mostly as a side effect of chemotherapy. The effect of electro-acupuncture (EA) on ameliorating cancer-related symptoms have been studied in animal models and in clinical trials. The aim of this study was to determine optimal conditions for the application of EA to alleviate anorexia, followed by the study of molecular mechanisms affecting its therapeutics. Anorexia was induced in male Wistar rats by injecting cisplatin, which was then followed by EA treatment at CV12, the acupuncture point located in the center of the abdominal midline. Body weight and food intake were measured daily throughout the duration of the study. The levels of monoamine neurotransmitters in the plasma were quantitatively analyzed by HPLC-ECD. Gastrointestinal hormone concentrations were elucidated with ELISA kits. RT-qPCR was performed to evaluate the mRNA expression of ghrelin (GHRL), neuropeptide Y (NPY), and pro-opiomelanocortin. The expression of c-Fos in the nucleus tractus solitarii was detected using western blotting analysis. The optimal conditions of EA to alleviate anorexia in rats was determined to be 1 unit for intensity and 10 Hz for frequency. EA treatment at CV12 reduced the levels of plasma monoamine neurotransmitters 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, dopamine, and norepinephrine; as well as stimulated the expression of GHRL and NPY to alleviate cisplatin-induced anorexia in rats. EA stimulation at CV12 could be used to treat cisplatin-induced anorexia in rats.

Chiral Metabolomics Using Triazine-Based Chiral Labeling Reagents by UPLC-ESI-MS/MS.

The determination of enantiomers of biological molecules is an important issue because a significant difference in the activity of the enantiomers is generally observed in biological systems. Chiral separations can be carried out by direct resolution using a chiral stationary column or by indirect resolution based on the derivatization with a chiral reagent. Many chiral-labeling reagents for ultraviolet-visible and fluorescence detections have been developed for various functional groups, such as amine and carboxylic acid. However, there are hardly any labeling reagents for LC-MS-specific detection. Based on this observation, we have developed several chiral-labeling reagents for LC-MS/MS analysis.This chapter describes methodologies and applications for the indirect LC-MS/MS determination of biological chiral molecules using triazine-based chiral-labeling reagents, i.e., (S and R)-1-(4,6-dimethoxy-1,3,5-triazin-2-yl)pyrrolidin-3-amine (DMT-3(S and R)-Apy) for carboxylic acids and (S and R)-2,5-dioxopyrrolidin-1-yl-1-(4,6-dimethoxy-1,3,5-triazin-2-yl)pyrrolidine-2-carboxylate (DMT-(S and R)-Pro-OSu) for amines and amino acids. A reliable method for the non-targeted chiral metabolomics is also described in this chapter.

Isotope Corrected Chiral and Achiral Nontargeted Metabolomics: An Approach for High Accuracy and Precision Metabolomics Based on Derivatization and Its Application to Cerebrospinal Fluid of Patients with Alzheimer's Disease.

We propose a chiral metabolomics approach based on a data-dependent MS/MS analysis (DDA) using high-resolution quadrupole-time-of-flight mass spectrometry (Q-TOFMS) and 13C-isotope coded derivatization (ICD) reagents, i.e., iDMT-( S)-A and iDMT-( S)-PO. The advantage of the method is the correction of all detected derivatives by parallel derivatization of the isotope-coded and noncoded reagents. The automatic data analysis platform using an MSDIAL and ICD discrimination program, called DINA, was also developed and used for the data analysis process. As a result, a 0.5-2.0% (d-/l-isomer) variation of the isomers was correctly recognized in the automatic data analysis step. Both the semiquantitative comparison and identification efficiency were improved as a result of the high resolution/accuracy of the MS and MS/MS spectra derived from the DDA analysis. This method was used for biomarker discovery in the cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD). Twenty-four biomarker candidates were successfully determined, including 8 chiral ones.

Highly Sensitive Quantification Method for Amine Submetabolome Based on AQC-Labeled-LC-Tandem-MS and Multiple Statistical Data Mining: A Potential Cancer Screening Approach.

The relationship between amine submetabolome and cancer has been increasingly investigated. However, no study was performed to evaluate the current methods of amine submetabolomics comprehensively, or to use such quantification results to provide an applicable approach for cancer screening. In this study, a highly sensitive and practical workflow for quantifying amine submetabolome, which was based on 6-aminoquinolyl- N-hydroxysuccinimidyl carbamate (AQC)-labeled-HPLC-MS/MS analysis combined with multiple statistical data processing approach, was established and optimized. Comparison and optimization of two analytical approaches, HILIC separation and precolumn derivatization, and three types of surrogate matrices of plasma were performed systematically. The detection sensitivities of AQC-labeled amines were increased by 50-1000-fold compared with the underivatization-HILIC method. Surrogate matrix was also used to verify the method after a large dilution factor was employed. In data analysis, the specific amino-index for each cancer sample was identified and validated by univariate receiver operating characteristic (ROC) curve analysis, partial least-squares discrimination analysis (PLS-DA), and multivariate ROC curve analysis. These amino indexes were innovatively quantified by multiplying the raised markers and dividing the reduced markers. As a result, the numerical intervals of amino indexes for healthy volunteers and cancer patients were provided, and their clinical value was also improved. Finally, the integrated workflow successfully differentiated the value of the amino index for plasma of lung, breast, colorectal, and gastric cancer samples from controls and among different types of cancer. Furthermore, it was also used to evaluate therapeutic effects. Taken together, the developed methodology, which was characterized by high sensitivity, high throughput, and high practicality, is suitable for amine submetabolomics in studying cancer biomarkers and could also be applied in many other clinical and epidemiological research.

Development of a novel UHPLC-MS/MS-based platform to quantify amines, amino acids and methylarginines for applications in human disease phenotyping.

Amine quantification is an important strategy in patient stratification and personalised medicine. This is because amines, including amino acids and methylarginines impact on many homeostatic processes. One important pathway regulated by amine levels is nitric oxide synthase (NOS). NOS is regulated by levels of (i) the substrate, arginine, (ii) amino acids which cycle with arginine and (iii) methylarginine inhibitors of NOS. However, biomarker research in this area is hindered by the lack of a unified analytical platform. Thus, the development of a common metabolomics platform, where a wide range of amino acids and methylarginines can be measured constitutes an important unmet need. Here we report a novel high-throughput ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) platform where ≈40 amine analytes, including arginine and methylarginines can be detected and quantified on a molar basis, in a single sample of human plasma. To validate the platform and to generate biomarkers, human plasma from a well-defined cohort of patients before and after coronary artery bypass surgery, who developed systemic inflammatory response syndrome (SIRS), were analysed. Bypass surgery with SIRS significantly altered 26 amine analytes, including arginine and ADMA. Consequently, pathway analysis revealed significant changes in a range of pathways including those associated with NOS.

Pharmacokinetics of immediate release, extended release, and gastric retentive gabapentin formulations in healthy adults
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OBJECTIVE: Gabapentin immediate release (GBP-IR), gabapentin gastric retentive (GBP-GR), and the prodrug gabapentin enacarbil extended release formulation (GEn) have been approved for management of postherpetic neuralgia (PHN) in adults. This is the first pharmacokinetic (PK) comparison of all three formulations using FDA-recommended doses for PHN. MATERIALS: This study compared the steady-state PK of GBP-IR 600 mg t.i.d., GBP-GR 1,800 mg q.d., and GEn 600 mg b.i.d. in healthy adults. METHODS: The open-label study consisted of a 3-day lead-in of escalating doses of GBP-IR, 5 days of treatment with each formulation (GPB-IR, GPB-GR, and GEn), and a 7-day taper period on 600 mg GEn q.d.. Plasma concentrations were collected on day 5 for each formulation. PK parameters were estimated from plasma concentration data. RESULTS: 14 healthy subjects (7 men, 7 women; mean (SD) age, 46.8 (7.60) years; mean (SD) body mass index, 26.7 (1.7) kg/m2) received all doses and completed the study. GBP-GR resulted in substantially (~ 4-fold) higher peak-to-trough ratio and percent fluctuation compared to GEn. GEn resulted in more sustained and less fluctuating daily exposure relative to GBP-IR, particularly at the end of 24 hours of dosing. In contrast, gabapentin fluctuation from GBP-IR consisted of 3 distinct peaks. After dose normalization, gabapentin exposure with GEn was ~ 2.2-fold and ~ 1.4-fold higher compared to GBP-GR and GBP-IR, respectively. All treatments were well tolerated. CONCLUSION: GEn requires less frequent dosing compared with GBP-IR and fluctuates less with sustained gabapentin exposure throughout the day. These PK differences may have clinically relevant implications.
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Prevalence of gabapentin in drug overdose postmortem toxicology testing results.

BACKGROUND: The goal of this study was to establish and compare baseline data on the prevalence of gabapentin identified through postmortem toxicology testing among drug overdose decedents in several geographically diverse states/jurisdictions with differing levels of drug overdose fatality burdens in 2015. METHODS: Death certificates and postmortem toxicology result reports from five U.S. jurisdictions were used to identify residents who died from drug overdoses in year 2015 and to calculate prevalence rates of gabapentin in postmortem toxicology by jurisdiction. RESULTS: On average, 22% of all drug overdose decedents in our study tested positive for gabapentin. The percentage of gabapentin-positive overdose deaths varied significantly among jurisdictions: 4% in Northeast Tennessee, 7% in Maricopa County, 15% in West Virginia, 20% in North Carolina, and 41% in Kentucky (p < 0.0001). Among the drug overdose decedents who tested positive for opioids (including heroin), 26% also tested positive for gabapentin, with significant variation among states/jurisdictions (p < 0.0001). There was a significant difference in the gender distribution among drug overdose decedents who tested positive for gabapentin (46% male) vs. those who tested negative for gabapentin (65% male) (p < 0.0001). In Kentucky, gabapentin was listed as a contributing drug on the death certificate in 40% of the overdose deaths with gabapentin-positive toxicology; in North Carolina this percentage was 57%. CONCLUSIONS: Routine gabapentin postmortem testing and linking of death certificate, medical examiner, coroner, toxicology, and prescription history data will provide more reliable information on the extent of gabapentin misuse, diversion, and implications for clinical care.

Bifunctional Fluorescent Probe for Sequential Sensing of Thiols and Primary Aliphatic Amines in Distinct Fluorescence Channels.

Thiols and primary aliphatic amines (PAA) are ubiquitous and extremely important species in biological systems. They perform significant interplaying roles in complex biological events. A single fluorescent probe differentiating both thiols and PAA can contribute to understanding the intrinsic inter-relationship of thiols and PAA in biological processes. Herein, we rationally constructed the first fluorescent probe that can respond to thiols and PAA in different fluorescence channels. The probe exhibited a high selectivity and sensitivity to thiols and PAA. In addition, it displayed sequential sensing ability when the thiols and PAA coexisted. The application experiments indicated that the probe can be used for sensing thiols and PAA in human blood serum. Moreover, the fluorescence imaging of endogenous thiols and PAA as well as antihypertensive drugs captopril and amlodipine in living cells were successfully conducted.

Vitamin D prenatal programming of childhood metabolomics profiles at age 3 y.

Background: Vitamin D deficiency is implicated in a range of common complex diseases that may be prevented by gestational vitamin D repletion. Understanding the metabolic mechanisms related to in utero vitamin D exposure may therefore shed light on complex disease susceptibility.Objective: The goal was to analyze the programming role of in utero vitamin D exposure on children's metabolomics profiles.Design: First, unsupervised clustering was done with plasma metabolomics profiles from a case-control subset of 245 children aged 3 y with and without asthma from the Vitamin D Antenatal Asthma Reduction Trial (VDAART), in which pregnant women were randomly assigned to vitamin D supplementation or placebo. Thereafter, we analyzed the influence of maternal pre- and postsupplement vitamin D concentrations on cluster membership. Finally, we used the metabolites driving the clustering of children to identify the dominant metabolic pathways that were influential in each cluster.Results: We identified 3 clusters of children characterized by 1) high concentrations of fatty acids and amines and low maternal postsupplement vitamin D (mean ± SD; 27.5 ± 11.0 ng/mL), 2) high concentrations of amines, moderate concentrations of fatty acids, and normal maternal postsupplement vitamin D (34.0 ± 14.1 ng/mL), and 3) low concentrations of fatty acids, amines, and normal maternal postsupplement vitamin D (35.2 ± 15.9 ng/mL). Adjusting for sample storage time, maternal age and education, and both child asthma and vitamin D concentration at age 3 y did not modify the association between maternal postsupplement vitamin D and cluster membership (P = 0.0014). Maternal presupplement vitamin D did not influence cluster membership, whereas the combination of pre- and postsupplement concentrations did (P = 0.03).Conclusions: Young children can be clustered into distinct biologically meaningful groups by their metabolomics profiles. The clusters differed in concentrations of inflammatory mediators, and cluster membership was influenced by in utero vitamin D exposure, suggesting a prenatal programming role of vitamin D on the child's metabolome. This trial was registered at clinicaltrials.gov as NCT00920621.

Factors in Variability of Serial Gabapentin Concentrations in Elderly Patients with Epilepsy.

OBJECTIVES: To characterize and quantify the variability of serial gabapentin concentrations in elderly patients with epilepsy. METHODS: This study included 83 patients (age ≥ 60 yrs) from an 18-center randomized double-blind double-dummy parallel study from the Veterans Affairs Cooperative 428 Study. All patients were taking 1500 mg/day gabapentin. Within-person coefficient of variation (CV) in gabapentin concentrations, measured weekly to bimonthly for up to 52 weeks, then quarterly, was computed. Impact of patient characteristics on gabapentin concentrations (linear mixed model) and CV (linear regression) were estimated. RESULTS: A total of 482 gabapentin concentration measurements were available for analysis. Gabapentin concentrations and intrapatient CVs ranged from 0.5 to 22.6 µg/ml (mean 7.9 µg/ml, standard deviation [SD] 4.1 µg/ml) and 2% to 79% (mean 27.9%, SD 15.3%), respectively, across all visits. Intrapatient CV was higher by 7.3% for those with a body mass index of ≥ 30 kg/m2 (coefficient = 7.3, p=0.04). CVs were on average 0.5% higher for each 1-unit higher CV in creatinine clearance (coefficient = 0.5, p=0.03) and 1.2% higher for each 1-hour longer mean time after dose (coefficient = 1.2, p=0.04). CONCLUSIONS: Substantial intrapatient variability in serial gabapentin concentration was noted in elderly patients with epilepsy. Creatinine clearance, time of sampling relative to dose, and obesity were found to be positively associated with variability.

Association of amine biomarkers with incident dementia and Alzheimer's disease in the Framingham Study.

INTRODUCTION: The identification of novel biomarkers associated with Alzheimer's disease (AD) could provide key biological insights and permit targeted preclinical prevention. We investigated circulating metabolites associated with incident dementia and AD using metabolomics. METHODS: Plasma levels of 217 metabolites were assessed in 2067 dementia-free Framingham Offspring Cohort participants (mean age = 55.9 ± 9.7 years; 52.4% women). We studied their associations with future dementia and AD risk in multivariate Cox models. RESULTS: Ninety-three participants developed incident dementia (mean follow-up = 15.6 ± 5.2 years). Higher plasma anthranilic acid levels were associated with greater risk of dementia (hazard ratio [HR] = 1.40; 95% confidence interval [CI] = [1.15-1.70]; P = 8.08 × 10-4). Glutamic acid (HR = 1.38; 95% CI = [1.11-1.72]), taurine (HR = 0.74; 95% CI = [0.60-0.92]), and hypoxanthine (HR = 0.74; 95% CI = [0.60-0.92]) levels also showed suggestive associations with dementia risk. DISCUSSION: We identified four biologically plausible, candidate plasma biomarkers for dementia. Association of anthranilic acid implicates the kynurenine pathway, which modulates glutamate excitotoxicity. The associations with hypoxanthine and taurine strengthen evidence that uric acid and taurine may be neuroprotective.

Stacking-cyclodextrin-microchip electrokinetic chromatographic determination of gabapentinoid drugs in pharmaceutical and biological matrices.

A facile, rapid, and highly sensitive microchip-based electrokinetic chromatographic method was developed for the simultaneous analysis of two gabapentinoid drugs, gabapentin (GPN) and pregabalin (PGN). Both drugs were first reacted with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) via nucleophilic substitution reactions to yield highly fluorescent products with λex/em 470/540nm. Analyses of both fluorescently labeled compounds were achieved within 200s in a poly(methyl methacrylate) (PMMA) microchip with a 30mm separation channel. Optimum separation was achieved using a borate buffer (pH 9.0) solution containing methylcellulose and ß-cyclodextrin (ß-CD) as buffer additives. Methylcellulose acted as a dynamic coating to prevent adsorption of the studied compounds on the inner surfaces of the microchannels, while ß-CD acted as a pseudo-stationary phase to improve the separation efficiency between the labeled drugs with high resolution (Rs>7). The fluorescence intensities of the labeled drugs were measured using a light emitting diode-induced fluorescence detector at 540nm after excitation at 470nm. The sensitivity of the method was enhanced 14- and 17-fold for PGN and GPN, respectively by field-amplified stacking relative to traditional pinched injection so that it could quantify 10ngmL-1 for both analytes, with a detection limit lower than 3ngmL-1. The developed method was efficiently applied to analyze PGN and GPN in their pharmaceutical dosage forms and in biological fluids. The extraction recoveries of the studied drugs from plasma and urine samples were more than 89% with%RSD values lower than 6.2.

A literature review of blood concentrations of new psychoactive substances classified as phenethylamines, aminoindanes, arylalkylamines, arylcyclohexylamines, and indolalkylamines.

Interpretation of blood concentrations of new psychoactive substances (NPS) requires comparison of the results to previously published case reports; as only a few experimental studies for these substances exist. A large number of articles representing single or multiple cases have been published for a great number of substances, making a unified overview difficult. In this review we have collected all published blood concentrations from the NPS groups classified as phenethylamines, aminoindanes, arylalkylamines, arylcyclohexylamines, and indolalkylamines, and also included unpublished results for MPA, MXE, 4-FMA, 4-FA and 4-MA analyzed in our laboratory. In total, 71 publications on 35 different drugs were summarized. For most of the drugs, the total number of reported cases was very low (≤5). For some of the synthetic drugs, however, a higher number of blood concentrations are now available; especially for 5-IT (32 reported cases in total), MPA (31 reported cases in total) and MXE (36 reported cases in total), thus the published results are more substantial. The present compilation could be a helpful tool for forensic toxicologists when blood concentrations of NPS are assessed.

Validated Method for the Screening and Quantification of Baclofen, Gabapentin and Pregabalin in Human Post-Mortem Whole Blood Using Protein Precipitation and Liquid Chromatography-Tandem Mass Spectrometry.

There has been a rapid increase in the number of prescriptions for baclofen (BLF), gabapentin (GBP) and pregabalin (PGL) in the UK since their introduction to therapy. Recent studies across the European Union and USA have shown the illicit abuse potential of these drugs and deaths have been observed. A simple, reliable and fully validated method was developed for the screening and quantification of BLF, GBP and PGL in human post-mortem (PM) blood. The analytes and their deuterated analogs as internal standard were extracted from blood using a single addition acetonitrile protein precipitation reaction followed by analysis using liquid chromatography-tandem mass spectrometry (LC-MS-MS) with triggered dynamic multiple reaction monitoring mode for simultaneous confirmation and quantification. The assay was linear from 0.05 to 1.00 µg/mL for BLF and 0.5 to 50.0 µg/mL for GBP and PGL, respectively with r2 > 0.999 (n = 9) for all analytes. Intra-day and inter-day imprecisions (n = 80) were calculated using one-way ANOVA; no significant difference (P > 0.99) was observed for all analytes over 8 non-consecutive days. The average recovery for all analytes was >98.9%. The limits of detection and quantification were both 0.05 µg/mL for BLF, and 0.5 µg/mL for GBP and PGL. The method was highly selective with no interference from endogenous compounds or from 54 drugs commonly encountered in PM toxicology. To prove method applicability, 17 PM blood samples submitted for analysis were successfully analyzed. The concentration range observed in PM blood for BLF was 0.08-102.00 µg/mL (median = 0.25 µg/mL), for GBP 1.0-134.0 µg/mL (median = 49.0 µg/mL) and 2.0-540.0 µg/mL (median = 42.0 µg/mL) for PGL.

High-Speed Quantitative UPLC-MS Analysis of Multiple Amines in Human Plasma and Serum via Precolumn Derivatization with 6-Aminoquinolyl-N-hydroxysuccinimidyl Carbamate: Application to Acetaminophen-Induced Liver Failure.

A targeted reversed-phase gradient UPLC-MS/MS assay has been developed for the quantification /monitoring of 66 amino acids and amino-containing compounds in human plasma and serum using precolumn derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQTag Ultra). Derivatization of the target amines required minimal sample preparation and resulted in analytes with excellent chromatographic and mass spectrometric detection properties. The resulting method, which requires only 10 µL of sample, provides the reproducible and robust separation of 66 analytes in 7.5 min, including baseline resolution of isomers such as leucine and isoleucine. The assay has been validated for the quantification of 33 amino compounds (predominantly amino acids) over a concentration range from 2 to 20 and 800 µM. Intra- and interday accuracy of between 0.05 and 15.6 and 0.78-13.7% and precision between 0.91 and 16.9% and 2.12-15.9% were obtained. A further 33 biogenic amines can be monitored in samples for relative changes in concentration rather than quantification. Application of the assay to samples derived from healthy controls and patients suffering from acetaminophen (APAP, paracetamol)-induced acute liver failure (ALF) showed significant differences in the amounts of aromatic and branched chain amino acids between the groups as well as a number of other analytes, including the novel observation of increased concentrations of sarcosine in ALF patients. The properties of the developed assay, including short analysis time, make it suitable for high-throughput targeted UPLC-ESI-MS/MS metabonomic analysis in clinical and epidemiological environments.

Hydralazine is involved in tele-methylhistamine metabolism by inhibiting monoamine oxidase B in pregnancy-associated hypertensive mice.

Hypertensive disorders of pregnancy globally affect 6-8% of gestation and remain a major cause of both foetal and maternal morbidity and mortality. However, the antihypertensive medications for the patients of this disease are strictly limited due to the teratogenic potentials. Here, we found that tele-methylhistamine (tMH) increased in response to the administration of hydralazine (Hdz), a vasodilative agent, in the pregnancy-associated hypertensive (PAH) mice. Hdz abrogated the degradation of tMH catalyzed by monoamine oxidase B (MAO-B) in vitro. These results suggested that Hdz inhibited the MAO-B activity and consequently tMH increased in the maternal circulation of PAH mice.

Dried blood spot analysis of gabapentin as a valid alternative for serum: a bridging study.

We evaluated the applicability of a validated GC-MS method for the determination of gabapentin in dried blood spots (DBS). Important for the acceptance of DBS sampling as an alternative sampling strategy is the possibility to base solid conclusions on the quantification. Therefore, bridging studies -studies in which the correlation between both DBS and a reference matrix (e.g. serum) is evaluated statistically- need to be conducted. To this end, a comparative study was set up to quantify gabapentin in both blood (DBS) and serum samples. Statistically significant differences between DBS and serum concentrations were found (p<0.001). A mean blood-to-serum ratio of 0.85 was observed, which is in line with expectations. Calculated serum concentrations (obtained by dividing the DBS concentrations by 0.85) demonstrated a good correlation with measured serum concentrations, with 87% of samples fulfilling the criterion for incurred sample reanalysis. Furthermore, our data indicate a good correlation between capillary and venous concentrations. Conclusively, this study demonstrated that DBS are a valid alternative to serum for the determination of gabapentin.