In vitro toxicokinetics and analytical toxicology of three novel NBOMe derivatives: phase I and II metabolism, plasma protein binding, and detectability in standard urine screening approaches studied by means of hyphenated mass spectrometry

Acute, chronic, and post-mortem toxicity: a review focused on three different classes of new psychoactive substances

PURPOSE

New psychoactive substances (NPS) are not controlled under the Single Convention on Narcotic Drugs of 1961 or the 1971 Convention, but they may pose a public health threat. Knowledge of the main properties and toxicological effects of these substances is lacking. According to the current Drugs Law (Law n. 11.343/2006), the Brazilian Surveillance Agency issues directives for forbidden substances in Brazil, and structural classes of synthetic cannabinoids, cathinones, and phenylethylamines are considered illicit drugs. Considering that data on these controlled substances are scattered, the main objective of this work was to collect and organize data to generate relevant information on the toxicological properties of NPS.

METHODS

We carried out a literature review collecting information on the acute, chronic, and post-mortem toxicity of these classes of NSP. We searched info in five scientific databases considering works from 2017 to 2021 and performed a statistical evaluation of the data.

RESULTS

Results have shown a general lack of studies in this field given that many NPS have not had their toxicity evaluated. We observed a significant difference in the volume of data concerning acute and chronic/post-mortem toxicity. Moreover, studies on the adverse effects of polydrug use are scarce.

CONCLUSIONS

More in-depth information about the main threats involving NPS use are needed.

Acute pharmacological profile of 2C-B-Fly-NBOMe in male Wistar rats—pharmacokinetics, effects on behaviour and thermoregulation

Introduction:N-2-methoxy-benzylated (“NBOMe”) analogues of phenethylamine are a group of new psychoactive substances (NPS) with reported strong psychedelic effects in sub-milligram doses linked to a number of severe intoxications, including fatal ones. In our present work, we provide a detailed investigation of pharmacokinetics and acute behavioural effects of 2C-B-Fly-NBOMe (2-(8-bromo-2,3,6,7-tetrahydrobenzo [1,2-b:4,5-b′]difuran-4-yl)-N-[(2-methoxybenzyl]ethan-1-amine), an analogue of popular psychedelic entactogen 2C-B (4-Bromo-2,5-dimethoxyphenethylamine).

Methods: All experiments were conducted on adult male Wistar rats. Pharmacokinetic parameters of 2C-B-Fly-NBOMe (1 mg/kg subcutaneously; s. c.) in blood serum and brain tissue were analysed over 24 h using liquid chromatography-mass spectrometry (LC/MS). For examination of behavioural parameters in open field test (OFT) and prepulse inhibition (PPI) of acoustic startle reaction (ASR), 2C-B-Fly-NBOMe (0.2, 1 and 5 mg/kg s. c.) was administered in two temporal onsets: 15 and 60 min after administration. Thermoregulatory changes were evaluated in individually and group-housed animals over 8 h following the highest dose used in behavioural experiments (5 mg/kg s. c.).

Results: Peak drug concentrations were detected 30 and 60 min after the drug application in serum (28 ng/ml) and brain tissue (171 ng/g), respectively. The parental compound was still present in the brain 8 h after administration. Locomotor activity was dose-dependently reduced by the drug in both temporal testing onsets. ASR was also strongly disrupted in both temporal onsets, drug’s effect on PPI was weaker. 2C-B-Fly-NBOMe did not cause any significant thermoregulatory changes.

Discussion: Our results suggest that 2C-B-Fly-NBOMe penetrates animal brain tissue in a relatively slow manner, induces significant inhibitory effects on motor performance, and attenuates sensorimotor gating. Its overall profile is similar to closely related analogue 2C-B and other NBOMe substances.

New Psychoactive Substances: Major Groups, Laboratory Testing Challenges, Public Health Concerns, and Community-Based Solutions

Across communities worldwide, various new psychoactive substances (NPSs) continue to emerge, which worsens the challenges to global mental health, drug rules, and public health risks, as well as combats their usage. Specifically, the vast number of NPSs that are currently available, coupled with the rate at which new ones emerge worldwide, increasingly challenges both forensic and clinical testing strategies. The well-established NPS detection techniques include immunoassays, colorimetric tests, mass spectrometric techniques, chromatographic techniques, and hyphenated types. Nonetheless, mitigating drug abuse and NPS usage is achievable through extensive community-based initiatives, with increased focus on harm reduction. Clinically validated and reliable testing of NPS from human samples, along with community-driven solution, such as harm reduction, will be of great importance, especially in combating their prevalence and the use of other illicit synthetic substances. There is a need for continued literature synthesis to reiterate the importance of NPS, given the continuous emergence of illicit substances in the recent years. All these are discussed in this overview, as we performed another look into NPS, from differentiating the major groups and identifying with laboratory testing challenges to community-based initiatives.

2C-B-Fly-NBOMe Metabolites in Rat Urine, Human Liver Microsomes and C. elegans: Confirmation with Synthesized Analytical Standards

Compounds from the N-benzylphenethylamine (NBPEA) class of novel psychoactive substances are being increasingly utilized in neurobiological and clinical research, as diagnostic tools, or for recreational purposes. To understand the pharmacology, safety, or potential toxicity of these substances, elucidating their metabolic fate is therefore of the utmost interest. Several studies on NBPEA metabolism have emerged, but scarce information about substances with a tetrahydrobenzodifuran ("Fly") moiety is available. Here, we investigated the metabolism of 2-(8-bromo-2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)-N-(2-methoxybenzyl)ethan-1-amine (2C-B-Fly-NBOMe) in three different systems: isolated human liver microsomes, Cunninghamella elegans mycelium, and in rats in vivo. Phase I and II metabolites of 2C-B-Fly-NBOMe were first detected in an untargeted screening and identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Several hypothesized metabolites were then synthesized as reference standards; knowledge of their fragmentation patterns was utilized for confirmation or tentative identification of isomers. Altogether, thirty-five phase I and nine phase II 2C-B-Fly-NBOMe metabolites were detected. Major detected metabolic pathways were mono- and poly-hydroxylation, O-demethylation, oxidative debromination, and to a lesser extent also N-demethoxybenzylation, followed by glucuronidation and/or N-acetylation. Differences were observed for the three used media. The highest number of metabolites and at highest concentration were found in human liver microsomes. In vivo metabolites detected from rat urine included two poly-hydroxylated metabolites found only in this media. Mycelium matrix contained several dehydrogenated, N-oxygenated, and dibrominated metabolites.

Recent trends in drugs of abuse metabolism studies for mass spectrometry-based analytical screening procedures

The still increasing number of drugs of abuse, particularly the so-called new psychoactive substances (NPS), poses an analytical challenge for clinical and forensic toxicologists but also for doping control. NPS usually belong to various classes such as synthetic cannabinoids, phenethylamines, opioids, or benzodiazepines. Like other xenobiotics, NPS undergo absorption, distribution, metabolism, and excretion processes after consumption, but only very limited data concerning their toxicokinetics and safety properties is available once they appear on the market. The inclusion of metabolites in mass spectral libraries is often crucial for the detection of NPS especially in urine screening approaches. Authentic human samples may represent the gold standard for identification of metabolites but are often not available and clinical studies cannot be performed due to ethical concerns. However, numerous alternative in vitro and in vivo models are available. This trends article will give an overview on selected models, discuss current studies, and highlight recent developments.

How to Study the Metabolism of New Psychoactive Substances for the Purpose of Toxicological Screenings-A Follow-Up Study Comparing Pooled Human Liver S9, HepaRG Cells, and Zebrafish Larvae

The new psychoactive substances (NPS) market continues to be very dynamic. A large number of compounds belonging to diverse chemical groups continue to emerge. This makes their detection in biological samples challenging for clinical and forensic toxicologists. Knowledge of the metabolic fate of NPS is crucial for developing comprehensive screening procedures. As human studies are not feasible due to ethical concerns, the current study aimed to compare the NPS' metabolic pattern in incubations with pooled human liver S9 fraction (pHLS9), human liver HepaRG cells, and zebrafish larvae. The latter model was recently shown to be a promising preclinical surrogate for human hepatic metabolism of a synthetic cannabinoid. However, studies concerning other NPS classes are still missing and therefore an amphetamine-based N-methoxybenzyl (NBOMe) compound, a synthetic cathinone, a pyrrolidinophenone analog, a lysergamide, as well as another synthetic cannabinoid were included in the current study. Liquid chromatography coupled to Orbitrap-based high-resolution tandem mass spectrometry was used to analyze metabolic data. Zebrafish larvae were found to produce the highest number of phase I but also phase II metabolites (79 metabolites in total), followed by HepaRG cells (66 metabolites). Incubations with pHLS9 produced the least metabolites (57 metabolites). Furthermore, the involvement of monooxygenases and esterases in the metabolic phase I transformations of 4F-MDMB-BINACA was elucidated using single-enzyme incubations. Several cytochrome P450 (CYP) isozymes were shown to contribute, and CYP3A5 was involved in all CYP-catalyzed reactions, while amide and ester hydrolysis were catalyzed by the human carboxylesterase (hCES) isoforms hCES1b and/or hCES1c. Finally, metabolites were compared to those present in human biosamples if data were available. Overall, the metabolic patterns in HepaRG cells provided the worst overlap with that in human biosamples. Zebrafish larvae experiments agreed best with data found in human plasma and urine analysis. The current study underlines the potential of zebrafish larvae as a tool for elucidating the toxicokinetics of NPS in the future.

Toxicokinetics and toxicodynamics of the fentanyl homologs cyclopropanoyl-1-benzyl-4´-fluoro-4-anilinopiperidine and furanoyl-1-benzyl-4-anilinopiperidine

The two fentanyl homologs cyclopropanoyl-1-benzyl-4´-fluoro-4-anilinopiperidine (4F-Cy-BAP) and furanoyl-1-benzyl-4-anilinopiperidine (Fu-BAP) have recently been seized as new psychoactive substances (NPS) on the drugs of abuse market. As their toxicokinetic and toxicodynamic characteristics are completely unknown, this study focused on elucidating their in vitro metabolic stability in pooled human liver S9 fraction (pHLS9), their qualitative in vitro (pHLS9), and in vivo (zebrafish larvae) metabolism, and their in vitro isozyme mapping using recombinant expressed isoenzymes. Their maximum-tolerated concentration (MTC) in zebrafish larvae was studied from 0.01 to 100 µM. Their µ-opioid receptor (MOR) activity was analyzed in engineered human embryonic kidney (HEK) 293 T cells. In total, seven phase I and one phase II metabolites of 4F-Cy-BAP and 15 phase I and four phase II metabolites of Fu-BAP were tentatively identified by means of liquid chromatography high-resolution tandem mass spectrometry, with the majority detected in zebrafish larvae. N-Dealkylation, N-deacylation, hydroxylation, and N-oxidation were the most abundant metabolic reactions and the corresponding metabolites are expected to be promising analytical targets for toxicological analysis. Isozyme mapping revealed the main involvement of CYP3A4 in the phase I metabolism of 4F-Cy-BAP and in terms of Fu-BAP additionally CYP2D6. Therefore, drug-drug interactions by CYP3A4 inhibition may cause elevated drug levels and unwanted adverse effects. MTC experiments revealed malformations and changes in the behavior of larvae after exposure to 100 µM Fu-BAP. Both substances were only able to produce a weak activation of MOR and although toxic effects based on MOR activation seem unlikely, activity at other receptors cannot be excluded.

Toxicokinetics and Analytical Toxicology of Flualprazolam: Metabolic Fate, Isozyme Mapping, Human Plasma Concentration and Main Urinary Excretion Products

An increasing number of benzodiazepine-type compounds are appearing on the new psychoactive substances market. 8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine (well known as flualprazolam) represents a potent ‘designer benzodiazepine’ that has been associated with sedation, loss of consciousness, memory loss and disinhibition. The aims of the present study were to tentatively identify flualprazolam metabolites using in vitro incubations with pooled human liver S9 fraction or HepaRG cells by means of liquid-chromatography-high resolution tandem mass spectrometry. Isozymes involved in phase I and II biotransformation were identified in vitro. Results were then confirmed using human biosamples of an 18-year old male who was admitted to the emergency department after suspected flualprazolam ingestion. Furthermore, the plasma concentration was determined using the standard addition method. Seven flualprazolam metabolites were tentatively identified. Several cytochrome P450 and UDP-glucuronosyltransferase isozymes, amongst them CYP3A4 and UGT1A4, were shown to be involved in flualprazolam biotransformation reactions, and an influence of polymorphisms as well as drug–drug or drug–food interactions cannot be excluded. Alpha-hydroxy flualprazolam glucuronide, 4-hydroxy flualprazolam glucuronide and the parent glucuronide were identified as most abundant signals in urine, far more abundant than the parent compound flualprazolam. These metabolites are thus recommended as urine-screening targets. If conjugate cleavage was performed during sample preparation, the corresponding phase I metabolites should be added as targets. Both hydroxy metabolites can also be recommended for blood screening. The flualprazolam plasma concentration determined in the intoxication case was as low as 8 μg/L underlining the need of analytical methods with sufficient sensitivity for blood-screening purposes.

NBOMes-Highly Potent and Toxic Alternatives of LSD

Recently, a new class of psychedelic compounds named NBOMe (or 25X-NBOMe) has appeared on the illegal drug market. NBOMes are analogs of the 2C family of phenethylamine drugs, originally synthesized by Alexander Shulgin, that contain a N-(2-methoxy)benzyl substituent. The most frequently reported drugs from this group are 25I-NBOMe, 25B-NBOMe, and 25C-NBOMe. NBOMe compounds are ultrapotent and highly efficacious agonists of serotonin 5-HT_2A and 5-HT_2C receptors (Ki values in low nanomolar range) with more than 1000-fold selectivity for 5-HT_2A compared with 5-HT_1A. They display higher affinity for 5-HT_2A receptors than their 2C counterparts and have markedly lower affinity, potency, and efficacy at the 5-HT_2B receptor compared to 5-HT_2A or 5-HT_2C. The drugs are sold as blotter papers, or in powder, liquid, or tablet form, and they are administered sublingually/buccally, intravenously, via nasal insufflations, or by smoking. Since their introduction in the early 2010s, numerous reports have been published on clinical intoxications and fatalities resulting from the consumption of NBOMe compounds. Commonly observed adverse effects include visual and auditory hallucinations, confusion, anxiety, panic and fear, agitation, uncontrollable violent behavior, seizures, excited delirium, and sympathomimetic signs such mydriasis, tachycardia, hypertension, hyperthermia, and diaphoresis. Rhabdomyolysis, disseminated intravascular coagulation, hypoglycemia, metabolic acidosis, and multiorgan failure were also reported. This survey provides an updated overview of the pharmacological properties, pattern of use, metabolism, and desired effects associated with NBOMe use. Special emphasis is given to cases of non-fatal and lethal intoxication involving these compounds. As the analysis of NBOMes in biological materials can be challenging even for laboratories applying modern sensitive techniques, this paper also presents the analytical methods most commonly used for detection and identification of NBOMes and their metabolites.

Toxicokinetic Studies and Analytical Toxicology of the New Synthetic Opioids Cyclopentanoyl-Fentanyl and Tetrahydrofuranoyl-Fentanyl

The growing number of new synthetic opioids (NSO) on the new psychoactive substances (NPS) market bears new challenges in toxicology. As their toxicodynamics and particularly their toxicokinetics are usually unknown, impact on human health is not yet fully understood. Detection of the 2 NSO cyclopentanoyl-fentanyl (CP-F) and tetrahydrofuranoyl-fentanyl (THF-F) was first reported in 2016. Both were involved in several fatal intoxication cases, but no detailed information about their toxicological characteristics is available so far. The main purpose of this study was therefore to investigate the in vitro toxicokinetics and in vivo analytical toxicology of CP-F and THF-F by means of liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). These studies included metabolic stability, phase I and II metabolism, isozyme mapping, plasma protein binding and detectability in LC-HRMS/MS standard urine screening approaches (SUSA) using rat urine samples. In total, 12 phase I metabolites of CP-F and 13 of THF-F were identified, among them 9 metabolites described for the first time. Overall, N-dealkylations, hydroxylations and dihydroxylations were the main metabolic reactions. The cytochrome P450 (CYP) isozymes mainly involved were CYP2D6 and CYP3A4, leading to elevated drug levels and intoxications in CYP2D6 poor metabolizers. CP-F showed a high plasma protein binding of 99%, which may increase the risk of toxicity by simultaneous intake of other highly bound drugs. Detectability studies showed that neither the parent compounds nor their metabolites were detectable in rat urine using LC-HRMS/MS SUSA. However, a more sophisticated analytical strategy was successfully applied and should be used for analytical confirmation of an intake of CP-F and/or THF-F.