Identification of in vitro metabolites of ethylphenidate by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry

Comprehensive metabolic investigation of dopamine reuptake inhibitor HDMP-28 in equine liver microsomes and Cunninghamella elegans for doping control

A dopamine reuptake inhibitor is a type of medication or substance that works by blocking the reuptake of dopamine in the brain. Dopamine reuptake inhibitors offer multiple effects, including increased alertness, improved mood, and therapeutic potential for conditions like depression, ADHD, and Parkinson's disease. HDMP-28, or methylnaphthidate, is a potent synthetic stimulant from the phenyltropane class. It surpasses methylphenidate in both dopamine reuptake inhibition and half-life. As a dopamine reuptake inhibitor, it boosts dopamine levels by hindering reuptake into nerve cells, resulting in heightened stimulation and increased energy. In order to comprehensively address both the tangible and potential repercussions of the unauthorized utilization of the aforementioned substance in sports, it is imperative to establish analytical methodologies for the identification of the parent drug and its primary metabolites. Additionally, a comprehensive analysis of the metabolic characteristics of HDMP-28 in both human and animal subjects has yet to be published. This study explores the metabolic conversion of HDMP-28 mediated by equine liver microsomes and Cunninghamella elegans. An extraction and detection method was developed, optimized, and validated for doping assessment in equine urine and plasma. Liquid chromatography-high-resolution mass spectrometry was employed to determine metabolite structures. The study identified 31 (22 phase I and 9 phase II) metabolites of HDMP-28, including hydroxylated, hydrogenated, and hydrolyzed analogs. Glucuronic acid-conjugated metabolites were also detected. This manuscript describes metabolites based on the in vitro studies, which might not be the same in vivo. These findings aid in the detection and understanding of the illicit use of HDMP-28 in equestrian sports.

Transesterification of Indazole-3-carboxamide Synthetic Cannabinoids: Identification of Metabolite Biomarkers for Diagnosing Co-abuse of 5F-MDMB-PINACA and Alcohol

Concurrent use of alcohol with synthetic cannabinoids (SCs) has been widely recorded among drug abusers. The susceptibilities of three indazole-3-carboxamide type SCs with methyl ester moiety, 5F-MDMB-PINACA, 5F-MMB-PINACA, and MMB-FUBINACA, to transesterification in the presence of ethanol warranted further investigation in view of probable augmented toxicity. In vitro metabolite identification experiments were first performed using human liver microsomes (HLMs) to characterize the novel metabolites of the three parent SCs in the presence of ethanol. Formation of transesterified metabolite, hydrolyzed metabolite, and several oxidative metabolites in HLM in the presence of alcohol was further determined for each parent SC and the respective ethyl ester analog, 5F-EDMB-PINACA, 5F-EMB-PINACA, and EMB-FUBINACA, to quantitatively elucidate transesterification and hydrolysis activities. Our results suggested that all three SCs undergo carboxylesterase-mediated transesterification to their respective ethyl ester analog in the presence of ethanol, which was incubation time- and ethanol concentration-dependent. Each ethyl ester metabolite was sequentially and readily metabolized to novel oxidative metabolites with the intact ethyl ester moiety and the same hydrolyzed metabolite as derived from its parent SC. A smaller extent of transesterification was non-enzymatically driven. Notably, we proposed 5F-EDMB-PINACA oxidative defluorination metabolite as the biomarker for diagnosing the potential co-abuse of 5F-MDMB-PINACA and alcohol. Due to the comparable pharmacological activities between each SC and its ethyl ester metabolite, augmented toxicity associated with co-abuse of SCs and alcohol is probable and deserves further investigation.

Development of analytical method for the determination of methylphenidate, the analog ethylphenidate and their metabolite ritalinic acid in oral fluid samples by micro-QuEChERS and liquid chromatography-tandem mass spectrometry

The aim of this study was to develop a quantitative method for the analysis of methylphenidate, the analog ethylphenidate and their metabolite ritalinic acid in oral fluid, using micro-QuEChERS extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Oral fluid samples were collected with Quantisal™ device, extracted by micro-QuEChERS technique and analyzed by LC-MS/MS. The developed method met the validation criteria of Academy Standards Board (ASB) Standard Practices for Method Validation in Forensic Toxicology (Standard 036, 2019) with limits of detection and quantification of 0.5 ng/mL and calibration curve from 0.5 to 50 ng/mL. Within-run imprecision was greater than 18.7% while between-run imprecision was greater than 17.0 % for all analytes. Bias did not vary more than 7.7 %. No evidence of carryover was found. Stability studies presented satisfactory results for 24 h on autosampler (10 °C), after 3 cycles of freeze/thaw, 7 days on freezer (-20 °C) and until 7 days on refrigerator (4 °C) for methylphenidate. The validated method was further successfully applied to the analysis of 5 authentic oral fluid samples collected from volunteers at parties and music festivals from different cities in Brazil. Four samples had positive results for methylphenidate and ritalinic acid, and only one sample was positive for methylphenidate. Ethylphenidate was not detected in the samples. The method showed acceptable analytical performance and is environmentally friendly, requiring reduced use of solvents and reagents, with potential to be applied to clinical and forensic analyses.

Analytical Detection of Novel Stimulants by Immunoassay and Liquid Chromatography-High Resolution Mass Spectrometry: Case Studies on Ethylphenidate and Mephedrone

The advent of hundreds of new compounds aimed at the substance misuse market has posed new analytical challenges. A semi-quantitative liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method has been developed to detect exposure to two novel stimulants, mephedrone and ethylphenidate, and selected metabolites. Centrifuged urine (50 µL) was diluted with LC eluent containing internal standards (mephedrone-d3, methylphenidate-d9 and ritalinic acid-d10; all 0.02 mg/L) (450 µL). Intra- and inter-assay accuracy and precision were within ±15% and <6%, respectively, for all analytes. The limit of detection was 0.01 mg/L for all analytes. Urine samples from mephedrone and ethylphenidate users were analyzed using immunoassay (amphetamine-group cloned enzyme donor immunoassay [CEDIA]) and LC-HRMS. Ethylphenidate, mephedrone and selected metabolites all had low cross-reactivity (<1%) with the immunoassay. The median (range) amphetamine-group CEDIA concentration in urine samples from mephedrone users (n = 11) was 0.30 (<0.041-3.04) mg/L, with only 1 sample giving a positive CEDIA result. The amphetamine-group CEDIA concentration in the urine sample from an ethylphenidate user was <0.041 mg/L. Improving the detection of novel compounds is of increasing importance to enable accurate diagnosis and treatment. Immunoassay methods used for drug screening may be inappropriate and lead to false-negative results. Conversely, detection of these compounds is possible through use of LC-HRMS and can provide information on the metabolites present after exposure to these drugs.

Use of UPLC-HRMS/MS for In Vitro and In Vivo Metabolite Identification of Three Methylphenidate-derived New Psychoactive Substances

The distribution of so-called new psychoactive substances (NPS) as substitute for common drug of abuse was steadily increasing in the last years, but knowledge about their toxicodynamic and toxicokinetic properties is lacking. However, a comprehensive knowledge of their toxicokinetics, particularly their metabolism, is crucial for developing reliable screening procedures and to verify their intake, e.g., in case of intoxications. The aim of this study was therefore to tentatively identify the metabolites of the methylphenidate-derived NPS isopropylphenidate (isopropyl 2-phenyl-2-(2-piperidyl) acetate, IPH), 4-fluoromethylphenidate (methyl 2-(4-fluorophenyl)-2-(piperidin-2-yl) acetate, 4-FMPH) and 3,4-dichloromethylphenidate (methyl 2-(3,4-dichlorophenyl)-2-(piperidin-2-yl) acetate, 3,4-CTMP) using different in vivo and in vitro techniques and ultra-high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS/MS). Urine samples of male rats were analyzed, and the transfer to human metabolism was done by using pooled human S9 fraction (pS9), which contains the microsomal fraction of liver homogenisate as well as its cytosol. UHPLC-HRMS/MS analysis of rat urine revealed 17 metabolites for IPH (14 phase I and 3 phase II metabolites), 13 metabolites were found for 4-FMPH (12 phase I metabolites and 1 phase II metabolite) and 7 phase I metabolites and no phase II metabolites were found for 3,4-CTMP. pS9 incubations additionally indicated that all investigated substances were primarily hydrolyzed, resulting in the corresponding carboxy metabolites. Finally, these carboxy metabolites should be used as additional analytical targets besides the parent compounds for comprehensive mass spectrometry-based screening procedures.

In vitro investigations of the metabolism of Victoria pure blue BO dye to identify main metabolites for food control in fish

Although banned, dyes, such as Victoria pure blue BO (VPBO), are illicitly used in aquaculture to treat or prevent infections due to their therapeutic activities. The present study examined the formation of phase I and phase II metabolites derived from VPBO using trout liver microsomes and S9 proteins. The well-known malachite green (MG) dye was also studied as a positive control and to compare its metabolism with that of VPBO. First, we optimised the incubation conditions for the detection of VPBO and MG metabolites by studying the formation of cytochrome P450 (CYP) substrates. Using the determined conditions (2 h at 20 °C), we incubated VPBO with trout microsomal and S9 fractions induced with β-naphtoflavone, and analysed the supernatant in a LC-LTQ-Orbitrap-HRMS system. The in vitro assays led to the detection of 16 VPBO metabolites from Phase I reactions, arising in particular from reactions with CYP1A. No metabolites were detected from Phase II reactions. The main metabolite detected, deethyl-VPBO, was CID-fragmented to determine its chemical structure, and thus recommend a potential biomarker for the control of VPBO in farmed fish foodstuffs.

Wide-scope target and suspect screening methodologies to investigate the occurrence of new psychoactive substances in influent wastewater from Athens

Almost all licit and illicit drugs consumed by the society end up either unchanged or as a mixture of metabolites in the sewage systems. The analysis of influent wastewater samples and the estimation of drug consumption is the field of wastewater-based epidemiology (WBE). A new trend of WBE is the estimation of the consumption of New Psychoactive Substances (NPS), which are legal replacements of established narcotic and psychotropic drugs with slightly modified chemical structures and similar or new effects. To investigate the occurrence of NPS, 30 composite daily influent wastewater samples from the wastewater treatment plant (WWTP) of Athens (Greece) were collected in a four-year sampling campaign (2015-2018). A generic four-sorbent solid-phase extraction (SPE) sample preparation protocol able to retain compounds with wide physicochemical properties was used. Extracts were analyzed by liquid-chromatography coupled to quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS) using target screening for 278 NPS and suspect screening for 451 NPS. Target screening method was validated for a subset of 49 representative NPS and illicit drugs with similar structures with the NPS. 24 NPS and related compounds were detected by target screening and two compounds were tentatively identified based on mass accuracy, prediction of retention time using in-house QSRR prediction models, isotopic pattern and HRMS/MS fragmentation, whereas the excreted mass loads were also calculated. The results indicated an occasional and low occurrence of NPS in wastewater during the week and over the years, whereas the estimation of the exact sources and the evaluation of the patterns in wastewater were critically discussed.

Suspect and non-target screening workflows to investigate the in vitro and in vivo metabolism of the synthetic cannabinoid 5Cl-THJ-018

The use of synthetic cannabinoids causes similar effects as Δ⁹ -tetrahydrocannabinol and long-term (ab)use can lead to health hazards and fatal intoxications. As most investigated synthetic cannabinoids undergo extensive biotransformation, almost no parent compound can be detected in urine, which hampers forensic investigations. Limited information about the biotransformation products of new synthetic cannabinoids makes the detection of these drugs in various biological matrices challenging. This study aimed to identify the main in vitro biotransformation pathways of 5Cl-THJ-018 and to compare these findings with an authentic urine sample of a 5Cl-THJ-018 user. The synthetic cannabinoid was incubated with pooled human liver microsomes and cytosol to simulate phase I and phase II biotransformations. Resulting extracts were analyzed with liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Three different data analysis workflows were applied to identify biotransformation products. A suspect screening workflow used an in-house database built from literature data and in silico biotransformation predictions. Two non-target screening workflows used a commercially available software and an open-source software for mass spectrometry data processing. A total of 23 in vitro biotransformation products were identified, with hydroxylation, oxidative dechlorination, and dihydrodiol formation pathways as the main phase I reactions. Additionally, five glucuronidated and three sulfated phase II conjugates were identified. The predominant in vivo pathway was through oxidative dechlorination and in total six metabolites of 5Cl-THJ-018 were identified. Biotransformation products both in vitro and in vivo were successfully identified using complementary suspect and non-target screening workflows.

L- and D-threo ethylphenidate concentrations, pharmacokinetics, and pharmacodynamics in horses

Ethylphenidate is a psychostimulant and analog of the commonly prescribed compound, methylphenidate (Ritalin®). There are a limited number of studies describing the disposition and pharmacologic/toxicological effects of ethylphenidate in any species. The abuse potential in equine athletes along with the limited data available regarding administration in horses necessitates further study. The objectives of the current study were to describe drug concentrations, develop an analytical method that could be used to regulate its use, and describe the pharmacodynamic effects of ethylphenidate in horses. To that end, 12 horses were randomized into 3 dose groups (intravenous: 10 mg or 40 mg, oral: 40 mg). Ethylphenidate was administered and blood and urine samples were collected prior to and for up to 72 hours post drug administration. Concentrations of D-threo ethylphenidate and the metabolite ritalinic acid were measured using Liquid Chromatography-tandem Mass Spectrometry. L-threo ethylphenidate concentrations were estimated from D-threo ethylphenidate concentrations. Serum concentrations of ethylphenidate were below detectable levels by 8, 18, and 12 hours following intravenous administration of 10 mg and 40 mg and oral administration of 40 mg, respectively. Ritalinic acid was non-detectable at 72 hours in the group that received a 10-mg intravenous and 40-mg oral dose of ethylphenidate. Ritalinic acid concentrations were below the LOQ at 72 hours following intravenous administration of 40 mg of ethylphenidate. While the number of animals per dose group were small, no stimulatory behavior or significant changes in heart rate were noted. Untoward effects including gastrointestinal adverse effects were noted in all dose groups.

Qualitative screening for new psychoactive substances in wastewater collected during a city festival using liquid chromatography coupled to high-resolution mass spectrometry

The inclusion of new psychoactive substances (NPS) in the wastewater-based epidemiology approach presents challenges, such as the reduced number of users that translates into low concentrations of residues and the limited pharmacokinetics information available, which renders the choice of target biomarker difficult. The sampling during special social settings, the analysis with improved analytical techniques, and data processing with specific workflow to narrow the search, are required approaches for a successful monitoring. This work presents the application of a qualitative screening technique to wastewater samples collected during a city festival, where likely users of recreational substances gather and consequently higher residual concentrations of used NPS are expected. The analysis was performed using liquid chromatography coupled to high-resolution mass spectrometry. Data were processed using an algorithm that involves the extraction of accurate masses (calculated based on molecular formula) of expected m/z from an in-house database containing about 2,000 entries, including NPS and transformation products. We positively identified eight NPS belonging to the classes of synthetic cathinones, phenethylamines and opioids. In addition, the presence of benzodiazepine analogues, classical drugs and other licit substances with potential for abuse was confirmed. The screening workflow based on a database search was useful in the identification of NPS biomarkers in wastewater. The findings highlight the specific classical drugs and low NPS use in the Netherlands. Additionally, meta-chlorophenylpiperazine (mCPP), 2,5-dimethoxy-4-bromophenethylamine (2C-B), and 4-fluoroamphetamine (FA) were identified in wastewater for the first time.

Qualitative screening of new psychoactive substances in pooled urine samples from Belgium and United Kingdom

Concerns about new psychoactive substances (NPS) are increasing due to the rising frequency of serious intoxications. Analysis of biological fluids (urine) is necessary to get reliable information about the use of these substances. However, it is a challenging task due to the lack of analytical standards and the dynamic character of the NPS market. In the present work, a qualitative screening of NPS was carried out in 23 pooled urine samples collected from a city center in the UK and festivals in the UK and Belgium. The analytical method was based on data-independent acquisition mode using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. An in-house library was used with >1500 entries corresponding to NPS, classical drugs and metabolites. All samples contained 53 and 28 compounds of interest from the UK and Belgium respectively. Of the different compounds detected, about 70% were confirmed using retention time and product ions while the remaining compounds were identified using elucidated fragmentation pathways. The highest numbers of NPS identified in both countries were from the cathinone and phenylethylamine families, with a higher number being detected in samples from the festival in the UK. Moreover, several cathinone metabolites in human urine were detected and identified. The screening method proved useful to detect a large number of compounds and determine the use of NPS.

New psychoactive substances: an overview on recent publications on their toxicodynamics and toxicokinetics

This review article covers English-written and PubMed-listed review articles and original studies published between January 2015 and April 2016 dealing with the toxicodynamics and toxicokinetics of new psychoactive substances. Compounds covered include stimulants and entactogens, synthetic cannabinoids, tryptamines, NBOMes, phencyclidine-like drugs, benzodiazepines, and opioids. First, an overview and discussion is provided on timely review articles followed by an overview and discussion on recent original studies. Both sections are then concluded by an opinion on these latest developments. This review shows that the NPS market is still highly dynamic and that the data published on their toxicodynamics and toxicokinetics can hardly keep pace with the appearance of new entities. However, data available are very helpful to understand and predict how NPS may behave in severe intoxication. The currently best-documented parameter is the in vitro metabolism of NPS, a prerequisite to allow detection of NPS in biological matrices in cases of acute intoxications or chronic consumption. However, additional data such as their chronic toxicity are still lacking.

Identification of in vitro and in vivo human metabolites of the new psychoactive substance nitracaine by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry

The purpose of this work was to investigate the in vitro metabolism of nitracaine, a new psychoactive substance, using human liver microsome incubations, to evaluate the cytochrome P450 (CYP) enzyme isoforms responsible for the phase-I metabolism and to compare the information from the in vitro experiments with data resulting from an authentic user's urine sample. Accurate mass spectra of metabolites were obtained using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) and were used in the structural identification of metabolites. Two major and three minor phase-I metabolites were identified from the in vitro experiments. The observed phase-I metabolites were formed through N-deethylation, N,N-deethylation, N-hydroxylation, and de-esterification, with CYP2B6 and CYP2C19 being the main enzymes catalyzing their formation. One glucuronidated product was identified in the phase-II metabolism experiments. All of these metabolites are reported for the first time in this study except the N-deethylation product. All the in vitro metabolites except the minor N,N-deethylation product were also present in the human urine sample, thus demonstrating the reliability of the in vitro experiments in the prediction of the in vivo metabolism of nitracaine. In addition to the metabolites, three transformation products (p-nitrobenzoic acid, p-aminobenzoic acid, and 3-(diethylamino)-2,2-dimethylpropan-1-ol) were identified, as well as several glucuronides and glutamine derived of them.