DARK Classics in Chemical Neuroscience: Bucinnazine

Study of metabolism and potential toxicity of nine synthetic opioid analogs using the zebrafish larvae model

The use of novel psychoactive substances (NPSs) has dramatically increased worldwide, and among them, synthetic opioids are one of the fastest growing groups, where cinnamylpiperazines and 2-benzylbenzimidazoles represent two of the most relevant subclasses. However, the data on their toxicity and metabolism are still limited. The aim of the present study was to evaluate the toxicity and metabolic pathways of some compounds belonging to these families, namely, AP-237, 2-methyl AP-237, isotonitazene, flunitazene, etodesnitazene, metonitazene, metodesnitazene, N-pyrrolidino etonitazene, and butonitazene. The study was performed using a zebrafish early life stages model. In fact, zebrafish (Danio rerio) embryos and larvae have recently been recognized as a suitable animal model in alternative to mammals, because they require less time and resources and do not need complex procedures for ethics approval. The cellular toxicity after a single administration was assessed at the fourth day post-fertilization with acridine orange staining. Possible morphological defects were evaluated with a light microscope after 24 h of exposure to 1 μmol/L concentration of each drug. Subsequently, the larvae were euthanized and underwent analysis of drug metabolites using UPLC coupled to an Orbitrap high-resolution mass spectrometer. High rates of morphological defects, as well as of cellular death, were detected, but no significant difference in mortality between treatment and control groups was observed. In addition, several metabolites, mainly produced through monohydroxylation, N-dealkylation, and O-dealkylation, were identified in the larvae extracts.

Human metabolism and basic pharmacokinetic evaluation of AP-238: A recently emerged acylpiperazine opioid

As a consequence of recently implemented legal restrictions on fentanyl analogs, a new generation of acylpiperazine opioids appeared on the illicit drug market. AP-238 was the latest opioid in this series to be notified by the European Early Warning System in 2020 and was involved in an increasing number of acute intoxications. AP-238 metabolism was investigated to provide useful markers of consumption. For the tentative identification of the main phase I metabolites, a pooled human liver microsome assay was performed. Further, four whole blood and two urine samples collected during post-mortem examinations and samples from a controlled oral self-administration study were screened for anticipated metabolites. In total, 12 AP-238 phase I metabolites were identified through liquid chromatography-quadrupole time-of-flight mass spectrometry in the in vitro assay. All of these were confirmed in vivo, and additionally, 15 phase I and five phase II metabolites were detected in the human urine samples, adding up to a total of 32 metabolites. Most of these metabolites were also detected in the blood samples, although mostly with lower abundances. The main in vivo metabolites were built by hydroxylation combined with further metabolic reactions such as O-methylation or N-deacylation. The controlled oral self-administration allowed us to confirm the usefulness of these metabolites as proof of intake in abstinence control. The detection of metabolites is often crucial to documenting consumption, especially when small traces of the parent drug can be found in real samples. The in vitro assay proved to be suitable for the prediction of valid biomarkers of novel synthetic opioid intake.

In silico and in vitro metabolism studies of the new synthetic opiate AP-237 (bucinnazine) using bioinformatics tools

The recent emergence of new synthetic opioids (NSOs) compounds in the illicit market is increasingly related to fatal cases. Identification and medical care of NSO intoxication cases are challenging, particularly due to high frequency of new products and extensive metabolism. As the study of NSO metabolism is crucial for the identification of these drugs in cases of intoxication, we aimed to investigate the metabolism of the piperazine NSO AP-237 (= bucinnazine). Two complementary approaches (in silico and in vitro) were used to identify putative AP-237 metabolites which could be used as consumption markers. In silico metabolism studies were realized by combining four open access softwares (MetaTrans, SyGMa, Glory X, Biotransformer 3.0). In vitro experiments were performed by incubating AP-237 (20 µM) in differentiated HepaRG cells during 0 h, 8 h, 24 h or 48 h. Cell supernatant were extracted and analyzed by liquid chromatography coupled to high-resolution mass spectrometry and data were reprocessed using three strategies (MetGem, GNPS or Compound Discoverer®). A total of 28 phase I and six phase II metabolites was predicted in silico. Molecular networking identified seven putative phase I metabolites (m/z 203.154, m/z 247.180, m/z 271.180, two m/z 289.191 isomers, m/z 305.186, m/z 329.222), including four previously unknown metabolites. Overall, this cross-disciplinary approach with molecular networking on data acquired in vitro and in silico prediction enabled to propose relevant candidate as AP-237 consumption markers that could be added to mass spectrometry libraries to help diagnose intoxication.

Assessment of two brands of fentanyl test strips with 251 synthetic opioids reveals "blind spots" in detection capabilities

BACKGROUND

Fentanyl test strips (FTS) are a commonly deployed tool in drug checking, used to test for the presence of fentanyl in street drug samples prior to consumption. Previous reports indicate that in addition to fentanyl, FTS can also detect fentanyl analogs like acetyl fentanyl and butyryl fentanyl, with conflicting reports on their ability to detect fentanyl analogs like Carfentanil and furanyl fentanyl. Yet with hundreds of known fentanyl analogs, there has been no large-scale study rationalizing FTS reactivity to different fentanyl analogs.

METHODS

In this study, 251 synthetic opioids-including 214 fentanyl analogs-were screened on two brands of fentanyl test strips to (1) assess the differences in the ability of two brands of fentanyl test strips to detect fentanyl-related compounds and (2) determine which moieties in fentanyl analog chemical structures are most crucial for FTS detection. Two FTS brands were assessed in this study: BTNX Rapid Response and WHPM DanceSafe.

RESULTS

Of 251 screened compounds assessed, 121 compounds were detectable at or below 20,000 ng/mL by both BTNX and DanceSafe FTS, 50 were not detectable by either brand, and 80 were detectable by one brand but not the other (n = 52 BTNX, n = 28 DanceSafe). A structural analysis of fentanyl analogs screened revealed that in general, bulky modifications to the phenethyl moiety inhibit detection by BTNX FTS while bulky modifications to the carbonyl moiety inhibit detection by DanceSafe FTS.

CONCLUSIONS

The different "blind spots" are caused by different haptens used to elicit the antibodies for these different strips. By utilizing both brands of FTS in routine drug checking, users could increase the chances of detecting fentanyl analogs in the "blind spot" of one brand.

Non-fentanyl new synthetic opioids - An update

BACKGROUND

New synthetic opioids (NSO) constitute one of the fastest-growing group of New Psychoactive Substances, which emerged on the illicit drug marker in the second half of 2000's. The most popular and the largest NSO subgroup are high potency fentanyl and its analogs. Subsequent to core-structure scheduling of fentanyl-related substances many opioids with different chemical structures are now emerging on the illicit drug market, rendering the landscape highly complex and dynamic.

METHODS

PubMed, Scopus and Google Scholar were searched for appropriate articles up to December 2022. Moreover, a search for reports was conducted on Institutional websites to identify documentation published by World Health Organization, United Nations Office on Drugs and Crime, United States Drug Enforcement Administration, and European Monitoring Centre for Drugs and Drug Addiction. Only articles or reports written in English were selected.

RESULTS

Non-fentanyl derived synthetic opioids, i.e., 2-benzylbenzimidazoles (nitazenes), brorphine, U-compounds, AH-7921, MT-45 and related compounds are characterized, describing them in terms of available forms, pharmacology, metabolism as well as their toxic effects. Sample procedures and analytical techniques available for detection and quantification of these compounds in biological matrices are also presented. Finally, as overdoses involving highly potent NSO may be difficult to reverse, the effectiveness of naloxone as a rescue agent in NSO overdose is discussed.

CONCLUSIONS

Current review presents key information on non-fentanyl derived NSO. Access to upto-date data on substances of abuse is of great importance for clinicians, public health authorities and professionals performing analyses of biological samples.

Case report: Identification of AP-238 and 2-fluorodeschloroketamine in internet available powder samples sold as bucinnazine

Novel synthetic opioids (NSOs) are a class of opioid agonists that include analogs of fentanyl and structurally distinct non-fentanyl compounds normally used as standalone products, heroin adulterants, or constituents of counterfeit pain pills. Most NSOs are not currently scheduled in the U.S., are predominantly illegally synthesized, and sold on the Darknet. Among them, the cinnamylpiperazine derivatives such as bucinnazine (AP-237), AP-238, and 2-methyl-AP-237 and the arylcyclohexylamine derivatives, analogs of ketamine, such as 2-fluoro-deschloroketamine (2 F-DCK) have appeared in several monitoring systems. Two white powders purchased on the internet as bucinnazine were first analyzed with polarized light microscopy followed by direct analysis in real time-mass spectrometry (DART-MS) and gas chromatography-mass spectrometry (GC-MS). Both powders were white crystals with no other significant microscopic properties. The DART-MS analysis showed the presence of 2-fluorodeschloroketamine in powder #1, and AP-238 in powder #2. Identification was confirmed by GC-MS. The purity of each substance was 78.0% for powder #1, and 88.9% for powder #2, respectively. The toxicological risk associated with the misuse of NSOs still needs further study. The absence of bucinnazine and the presence of different active compounds in internet purchased samples raises public health and safety concerns.

Detection of AP-237 and synthetic cannabinoids on an infused letter sent to a German prisoner

In the past years, new psychoactive substances (NPS) started circulating in prisons, leading to health risks and challenges for the criminal justice system. Seizures of papers and cards impregnated with synthetic cannabinoid (SCs) have been reported. In November 2021, a letter suspected to be drug-infused was sent from a German prison to this laboratory. Toxicological analyses were performed by means of gas chromatography-mass spectrometry (GC-MS) for drug screening and liquid chromatography-tandem mass spectrometry (LC-MS/MS) as well as high-performance (HP) LC with diode-array detection (DAD) for semi-quantification of the compounds. The novel synthetic opioid (NSO) AP-237 was detected on the letter, with an estimated concentration of 1.2 μg/cm² , together with the SCs MDMB-4en-PINACA (77 μg/cm² ) and 5F-ADB (6.5 μg/cm² ). To the best of the authors' knowledge, this is the first time an NSO was detected on a drug-infused paper seized in a prison. Highly potent NSOs could easily be dissolved in organic solvents to produce impregnated papers and textiles, and this might represent a serious threat to the health of people in prison. Given the inhomogeneity in drug concentrations, health risks might in particular arise from the consumption of highly concentrated areas of the paper-so-called "hot spots"-especially when highly potent NSOs are used for infusion. Laboratories engaged in analyzing such impregnated papers should be aware of the potential presence of NSOs and adapt the respective methods accordingly.

Toxicological and pharmacological characterization of novel cinnamylpiperazine synthetic opioids in humans and in vitro including 2-methyl AP-237 and AP-238

The recent scheduling actions of fentanyl-related substances in both the United States and China have sparked the emergence and proliferation of other generations of "legal" opioids that are structurally distinct from fentanyl, including the recently emerged class of cinnamylpiperazines. In contrast to fentanyl, which contains a piperidine core and a phenethyl moiety, the primary structural components of cinnamylpiperazines are the piperazine core and a cinnamyl moiety. This manuscript reports on the toxicological profile for antemortem and postmortem cases where a cinnamylpiperazine was detected. Samples were quantitatively confirmed using liquid chromatography tandem mass spectrometry. The cases were received between February 2020 and April 2021. Concentrations of 2-methyl AP-237 from four postmortem cases ranged from 820 to 5800 ng/mL, and concentrations of AP-238 from two postmortem cases were 87 and 120 ng/mL. µ-Opioid receptor (MOR) activation potential for 2-methyl AP-237, AP-237, para-methyl AP-237, and AP-238 were studied using a βarr2 recruitment assay. Efficacies (E_max, relative to hydromorphone) and potencies (EC₅₀) were derived and of the compounds tested AP-238 was the most potent compound in the panel with an EC₅₀ of 248 nM. 2-Methyl AP-237 was found to be the most efficacious drug (E_max = 125%) of the tested cinnamylpiperazines; however, it had substantially less efficacy than fentanyl. The in vitro MOR activation potential of the studied cinnamylpiperazines was lower than that of fentanyl and other novel synthetic opioids (NSOs), in line with the relatively higher concentrations observed in postmortem toxicology samples-an important observational link between in vitro pharmacology and in vivo toxicology.