Stereoselective Differences between the Reinforcing and Motivational Effects of Cathinone-Derived 4-Methylmethcathinone (Mephedrone) In Self-Administering Rats

The psychomotor, reinforcing, and discriminative stimulus effects of synthetic cathinone mexedrone in male mice and rats

The chronic use of the novel synthetic cathinone mexedrone, like other psychoactive drugs, can be considered addictive, with a high potential for abuse and the ability to cause psychological dependence in certain users. However, little is known about the neurobehavioral effects of mexedrone in association with its potential for abuse. We investigated the abuse potential for mexedrone abuse through multiple behavioral tests. In addition, serotonin transporter (SERT) levels were measured in the synaptosome of the dorsal striatum, and serotonin (5-HT) levels were measured in the dorsal striatum of acute mexedreone (50 mg/kg)-treated mice. To clarify the neuropharmacological mechanisms underlying the locomotor response of mexedrone, the 5-HT2A receptor antagonist M100907 (0.5 or 1.0 mg/kg) was administered prior to the acute injection of mexedrone in the locomotor activity experiment in mice. Mexedrone (10-50 mg/kg) produced a significant place preference in mice and mexedrone (0.1-0.5 mg/kg/infusion) maintained self-administration behavior in rats in a dose-dependent manner. In the drug discrimination experiment, mexedrone (5.6-32 mg/kg) was fully substituted for the discriminative stimulus effects of cocaine in rats. Mexedrone increased locomotor activity, and these effects were reversed by pretreatment with M100907. Acute mexedrone significantly increased c-Fos expression in the dorsal striatum and decreased SERT levels in the synaptosome of the dorsal striatum of mice, resulting in an elevation of 5-HT levels. Taken together, our results provide the possibility that mexedrone has abuse potential, which might be mediated, at least in part, by the activation of the serotonergic system in the dorsal striatum.

Development of enantioselective high-performance liquid chromatography-tandem mass spectrometry method for quantitative determination of methylone and some of its metabolites in oral fluid

In the present study an enantioselective high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the first time for quantitative determination of the recreational drug of abuse methylone and its major metabolites in oral fluid. The simultaneous chemo- and enantioseparation of methylone and its major metabolites was performed on a polysaccharide-based chiral column based on amylose tris(5-chloro-3-methylphenylcarbamate) as chiral selector (Lux i-Amylose-3) with methanol containing 0.4 % (v/v) aqueous ammonium hydroxide as mobile phase. The time required for enantioselective analysis of methylone and its 2 major metabolites was 15 min. This method was fully validated following the Organization of Scientific Area Committees (OSAC) for Forensic Science guidelines. This method was applied for the enantioselective determination of methylone and its metabolites in oral fluid and enantioselectivity in metabolism and pharmacokinetic of the parent compound and metabolites was observed. While the first enantiomer of methylone was found at higher concentration, both metabolites shown greater concentration for the second enantiomer. The results revealed that MET undergoes an enantioselective biotransformation to its metabolites HMMC and MDC, with S-(-)-MET more rapidly metabolized and eliminated from the body.

Characterization of Three Novel 4-Methylaminorex Derivatives Applied as Designer Drugs

The ongoing development of more and more new psychoactive substances continues to be a huge problem in 2022 affecting the European and international drug market. Through slight alterations in the structure of illicit drugs, a way to circumvent the law is created, as the created derivatives serve as legal alternatives with similar effects. A common way of structure modification is the induction of a halogen residue. Recently, halogenated derivatives of the well-known designer drug 4-methylaminorex appeared on the market and are available in various online shops. In this study, three novel halogenated 4-methylaminorex derivatives, namely 4′-fluoro-4-methylaminorex, 4′-chloro-4-methylaminorex, and 4′-bromo-4-methylaminorex, were purchased online and characterized using nuclear magnetic resonance (NMR) spectroscopy, liquid chromatography-high-resolution mass spectrometry (LC-HRMS), and chiral high-performance liquid chromatography with ultraviolet detection (HPLC-UV). These derivatives possess two stereogenic centers, and analyses revealed that all of them were present as a racemic mixture of the trans diastereomeric form.

Synthetic Cathinones: Recent Developments, Enantioselectivity Studies and Enantioseparation Methods

New psychoactive substances represent a public health threat since they are not controlled by international conventions, are easily accessible online and are sold as a legal alternative to illicit drugs. Among them, synthetic cathinones are widely abused due to their stimulant and hallucinogenic effects. To circumvent the law, new derivatives are clandestinely synthesized and, therefore, synthetic cathinones keep emerging on the drug market, with their chemical and toxicological properties still unknown. In this review, a literature assessment about synthetic cathinones is presented focusing on the recent developments, which include more than 50 derivatives since 2014. A summary of their toxicokinetic and toxicodynamic properties are also presented. Furthermore, synthetic cathinones are chiral compounds, meaning that they can exist as two enantiomeric forms which may present different biological and toxicological activities. To analyze the enantiomers, the development of enantiomeric resolution methods for synthetic cathinones is crucial. Many methods have been reported over the years that include mostly chromatographic and electromigration techniques, with liquid chromatography using chiral stationary phases being the technique of choice. This review intended to present an overview of enantioselectivity studies and enantioseparation analysis regarding synthetic cathinones, highlighting the relevance of chirality and current trends.

Effects of Hydroxylated Mephedrone Metabolites on Monoamine Transporter Activity in vitro

Mephedrone is a largely abused psychostimulant. It elicits the release of monoamines via the high affinity transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). Stereoselective metabolic reactions are involved in the inactivation and the elimination of its chemical structure. However, during these processes, several structures are generated and some of them have been reported to be still pharmacologically active. In this study 1) we have newly synthetized several putative mephedrone metabolites, 2) compared their activity at monoamine transporters, 3) generated quantitative structure activity relationships, and 4) exploited the chemical structure of the putative metabolites to screen a urine sample from a drug user and dissect mephedrone metabolism. We have found that most of the tested metabolites are weak inhibitors of monoamine transporters and that all of them are more potent at DAT and NET in comparison to SERT. The only exception is represented by the COOH-metabolite which shows no pharmacological activity at all three monoamine transporters. The enantioselectivity of mephedrone and its metabolites is present mainly at SERT, with only minor effects at DAT and NET being introduced when the β-keto group is reduced to an OH-group. Importantly, while at DAT the putative metabolites did not show changes in inhibitory potencies, but rather changes in their substrate/blocker profile, at SERT they showed mainly changes in inhibitory potencies. Molecular modeling suggests that the hydrophobic nature of a specific SERT subpocket may be involved in such loss of affinity. Finally, the assessment of the putative metabolites in one urine sample of mephedrone user displayed two previously uncharacterized metabolites, 4-COOH-nor-mephedrone (4-COOH-MC) and dihydro-4- nor-mephedrone (dihydro-4-MC). These results confirm and expand previous studies highlighting the importance of the stereochemistry in the pharmacodynamics of phase-1 metabolites of mephedrone, established their structure-activity relationships at DAT, NET and SERT and pave the way for a systematic dissection of mephedrone metabolic routes. Given the number of structures found having residual and modified pharmacological profiles, these findings may help in understanding the complex subjective effects of administered mephedrone. Moreover, the dissection of mephedrone metabolic routes may help in developing new therapies for treating psychostimulants acute intoxications.

Measuring mania-like elevated mood through amphetamine-induced 50-kHz ultrasonic vocalizations in rats

Rats emit 50-kHz ultrasonic vocalizations (USV) in appetitive situations, reflecting a positive affective state. Particularly high rates of 50-kHz USV are elicited by the psychostimulant d-amphetamine. Exaggerated 50-kHz USV emission evoked by d-amphetamine is modulated by dopamine, noradrenaline and 5-hydroxytyrptamine receptor ligands and inhibited by the mood stabilizer lithium, the gold standard anti-manic drug for treating bipolar disorder. This indicates that exaggerated 50-kHz USV emission can serve as a reliable and valid measure for assessing mania-like elevated mood in rats with sufficient translational power for gaining a better understanding of relevant pathophysiological mechanisms and the identification of new therapeutic targets. The improved capacity to study the effects of anti-manic pharmacological interventions on a broader range of behaviours by including exaggerated 50-kHz USV emission as preclinical outcome measure complementary to locomotor hyperactivity will refine rodent models for mania.

The neurobehavioral effects of the designer drug naphyrone - an experimental investigation with pharmacokinetics and concentration/effect relationship in mice

RATIONALE

The recreational use of naphyrone, a potent synthetic cathinone with a pyrovalerone structure, has raised questions about possible deleterious neurobehavioral consequences.

OBJECTIVE

To investigate naphyrone-induced neurobehavioral effects and alterations in brain monoamines using two patterns of abuse, i.e., single and repeated (binge) use.

METHODS

We studied naphyrone dose/induced locomotor activity relationship at 3, 10, 30, and 100 mg/kg in mice. We investigated the effects of single (30 mg/kg; acute injection) versus repeated (30 mg/kg ×3/day for 3 days; binge injection) intraperitoneal naphyrone administration on locomotor activity, anxiety-like behavior, spatial recognition memory, anhedonia, behavioral despair, and social interaction. We measured post-mortem prefrontal cortex levels of monoamines and modeled naphyrone pharmacokinetics and concentration/locomotor effect relationship.

RESULTS

Both naphyrone administration patterns induced time-dependent increases in locomotor activity (p < 0.001 and p < 0.0001, respectively) and social interaction (p < 0.05 and p < 0.001, respectively) but did not alter spatial recognition memory or anhedonia. Acute naphyrone injection induced anxiety-like behavior (p < 0.01) and reduced resignation (p < 0.01) whereas binge administration induced non-anxiety-like behavior (p < 0.05) and did not alter behavioral despair. Both patterns increased the prefrontal cortex dopamine (p < 0.0001) and norepinephrine (p < 0.05 and p < 0.01, respectively) but not serotonin content. Naphyrone pharmacokinetics followed a two-compartment model with an overall elimination half-life of 0.3 h. The naphyrone concentration/locomotor effect relationship was described by an additive E_max model with an EC₅₀ of 672 μg/L.

CONCLUSIONS

Single naphyrone administration increases locomotor activity according to a direct concentration/effect relationship. The neurobehavioral effects after binge differs from those after single administration and are not explained by drug accumulation given the relatively fast elimination.

Successful use of a novel lux® i-Amylose-1 chiral column for enantioseparation of "legal highs" by HPLC

Bath salts, fumigations, cleaners and air fresheners, behind these terms substances are hidden, which count as "Legal Highs". These fancy names are used to pretend Legal Highs as harmless compounds, to circumvent legal regulations for marketing as well as to increase the sales. Besides classic illicit drugs of synthetic origin such as amphetamines, cocaine and MDMA, the trade of these compounds, also known as new psychoactive substances (NPS), is not uncommon today. In many countries, NPS are still not subject to drug control. Among them, there are stimulants such as new amphetamine derivatives or cathinones, which possess a chiral centre. Little is known about the fact that the two possible enantiomers may differ in their pharmacological effect. The aim of this study was to test a novel HPLC column for the enantioseparation of a set of 112 NPS coming from different chemical groups and collected by internet purchases during the years 2010-2018. The CSP, namely Lux® 5 μm i-Amylose-1, LC Column 250 x 4.6 mm, was run in normal phase mode under isocratic conditions, UV detection was performed at 245 nm and 230 nm, injection volume was 10 μl and flow rate was 1 ml/min. With a mobile phase consisting of n-hexane/isopropanol/diethylamine (90:10:0.1), herein, 79 NPS were resolved into their enantiomers successfully, for 37 of them baseline resolution was achieved. After increase of lipophily of the mobile phase to 99:1:0.1, another 27 compounds were baseline separated. It was found that all separated NPS are traded as racemic compounds.

Effects of dopaminergic and serotonergic compounds in rats trained to discriminate a high and a low training dose of the synthetic cathinone mephedrone

RATIONALE

The underlying pharmacological mechanisms of mephedrone, especially as related to interactions with different neurotransmitter systems, are a critical area of study as mephedrone continues to be abused.

OBJECTIVE

Direct-acting 5-HT_2A/2C receptor agonists and antagonists and D_1-3 receptor antagonists were examined in two groups of rats trained to discriminate mephedrone. A high dose of mephedrone was trained to extend previous results with traditional monoamine transporter inhibitors and substrate releasers. A very low dose of mephedrone was trained to preferentially capture serotonergic activity and to minimize the influence of rate-decreasing effects on substitution patterns. Selective 5-HT_2A/2C and D_1-3 receptor antagonists were examined in both groups.

METHODS

Male Sprague-Dawley rats were trained to discriminate either a low dose of 0.5 mg/kg mephedrone (N = 24) or a high dose of 3.2 mg/kg mephedrone (N = 11) from saline.

RESULTS

In the low training-dose group, mephedrone, MDMA, methamphetamine, d-amphetamine, cocaine, and enantiomers of mephedrone substituted for mephedrone; mCPP partially substituted overall for mephedrone; and DOI, WAY163909, and morphine failed to substitute for mephedrone. In the high training-dose group, only mephedrone and MDMA substituted for mephedrone. Sulpiride produced a small antagonism of the low training dose of mephedrone while SCH23390, SB242084, and ketanserin altered response rates.

CONCLUSIONS

A lower training dose of mephedrone produces a discriminative stimulus fully mimicked by MDMA, methamphetamine, cocaine, and d-amphetamine, whereas a higher training dose of mephedrone requires a discriminative stimulus that was only mimicked by MDMA. Dopaminergic or serotoninergic antagonists failed to produce significant blockade of mephedrone at either training dose.

DARK Classics in Chemical Neuroscience: Cathinone-Derived Psychostimulants

Cathinone is a plant alkaloid found in khat leaves of perennial shrubs grown in East Africa. Similar to cocaine, cathinone elicits psychostimulant effects which are in part attributed to its amphetamine-like structure. Around 2010, home laboratories began altering the parent structure of cathinone to synthesize derivatives with mechanisms of action, potencies, and pharmacokinetics permitting high abuse potential and toxicity. These "synthetic cathinones" include 4-methylmethcathinone (mephedrone), 3,4-methylenedioxypyrovalerone (MDPV), and the empathogenic agent 3,4-methylenedioxymethcathinone (methylone) which collectively gained international popularity following aggressive online marketing as well as availability in various retail outlets. Case reports made clear the health risks associated with these agents and, in 2012, the Drug Enforcement Agency of the United States placed a series of synthetic cathinones on Schedule I under emergency order. Mechanistically, cathinone and synthetic derivatives work by augmenting monoamine transmission through release facilitation and/or presynaptic transport inhibition. Animal studies confirm the rewarding and reinforcing properties of synthetic cathinones by utilizing self-administration, place conditioning, and intracranial self-stimulation assays and additionally show persistent neuropathological features which demonstrate a clear need to better understand this class of drugs. This Review will thus detail (i) historical context of cathinone use and the rise of "dark" synthetic derivatives, (ii) structural features and mechanisms of synthetic cathinones, (iii) behavioral effects observed clinically and in animals under controlled laboratory conditions, and (iv) neurotransmitters and circuits that may be targeted to manage synthetic cathinone abuse in humans.

Multi-milligram resolution and determination of absolute configuration of pentedrone and methylone enantiomers

The enantioresolution of pentedrone and methylone was carried out at a multi-milligram scale by liquid chromatography on a Chiralpak AS® stationary phase. The excellent enantioresolution using this column allowed to collect highly pure enantiomeric fractions, achieving enantiomeric ratios higher than 98%. An overall recovery of 72% was achieved for pentedrone enantiomers and 80% for methylone. Furthermore, the absolute configuration of the enantiomers of both cathinones was determined for the first time by electronic circular dichroism (ECD) spectroscopy, with the aid of theoretical calculations, as (+)‑(S) and (-)‑(R)-pentedrone, and (-)‑(S) and (+)‑(R)‑methylone.