"Ecstasy" to addiction: Mechanisms and reinforcing effects of three synthetic cathinone analogs of MDMA

Bioisosteric analogs of MDMA: Improving the pharmacological profile?

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is re-emerging in clinical settings as a candidate for the treatment of specific neuropsychiatric disorders (e.g. post-traumatic stress disorder) in combination with psychotherapy. MDMA is a psychoactive drug, typically regarded as an empathogen or entactogen, which leads to transporter-mediated monoamine release. Despite its therapeutic potential, MDMA can induce dose-, individual-, and context-dependent untoward effects outside safe settings. In this study, we investigated whether three new methylenedioxy bioisosteres of MDMA improve its off-target profile. In vitro methods included radiotracer assays, transporter electrophysiology, bioluminescence resonance energy transfer and fluorescence-based assays, pooled human liver microsome/S9 fraction incubations, metabolic stability studies, isozyme mapping, and liquid chromatography coupled to high-resolution mass spectrometry. In silico methods included molecular docking. Compared with MDMA, all three MDMA bioisosteres (ODMA, TDMA, and SeDMA) showed similar pharmacological activity at human serotonin, dopamine, and norepinephrine transporters (hSERT, hDAT, and hNET, respectively) but decreased agonist activity at 5-HT2A/2B/2C receptors. Regarding their hepatic metabolism, they differed from MDMA, with N-demethylation being the only metabolic route shared, and without forming phase II metabolites. In addition, TDMA showed an enhanced intrinsic clearance in comparison to its congeners. Additional screening for their interaction with human organic cation transporters (hOCTs) and plasma membrane monoamine transporter (hPMAT) revealed a weaker interaction of the MDMA analogs with hOCT1, hOCT2, and hPMAT. Our findings suggest that these new MDMA bioisosteres might constitute appealing therapeutic alternatives to MDMA, sparing the primary pharmacological activity at hSERT, hDAT, and hNET, but displaying a reduced activity at 5-HT2A/2B/2C receptors and alternative hepatic metabolism. Whether these MDMA bioisosteres may pose lower risk alternatives to the clinically re-emerging MDMA warrants further studies.

Toxicity of butylone and its enantiomers to Daphnia magna and its degradation/toxicity potential using advanced oxidation technologies

Butylone (BTL) is a chiral synthetic cathinone available as a racemate and reported as contaminant in wastewater effluents. However, there are no studies on its impact on ecosystems and possible enantioselectivity in ecotoxicity. This work aimed to evaluate: (i) the possible ecotoxicity of BTL as racemate or its isolated (R)- and (S)- enantiomers using Daphnia magna; and (ii) the efficiency of advanced oxidation technologies (AOTs) in the removal of BTL and reduction of toxic effects caused by wastewaters. Enantiomers of BTL were obtained by liquid chromatography (LC) using a chiral semi-preparative column. Enantiomeric purity of each enantiomer was > 97 %. For toxicity assessment, a 9-day sub-chronic assay was performed with the racemate (at 0.10, 1.0 or 10 μg L-1) or each enantiomer (at 0.10 or 1.0 μg L-1). Changes in morphophysiological, behavioural, biochemical and reproductive endpoints were observed, which were dependent on the form of the substance and life stage of the organism (juvenile or adult). Removal rates of BTL in spiked wastewater (10 μg L-1) treated with different AOTs (ultraviolet, UV; ozonation, O3; and UV/O3) were similar and lower than 29 %. The 48 h D. magna acute toxicity assays demonstrated a reduction in the toxicity of the treated spiked effluents, but no differences were found amongst AOTs treatments. These results warn for the contamination and negative impact of BTL on ecosystems and highlight the need for efficient removal processes.

Bioisosteric analogs of MDMA with improved pharmacological profile

3,4-Methylenedioxymethamphetamine (MDMA, ' ecstasy' ) is re-emerging in clinical settings as a candidate for the treatment of specific psychiatric disorders (e.g. post-traumatic stress disorder) in combination with psychotherapy. MDMA is a psychoactive drug, typically regarded as an empathogen or entactogen, which leads to transporter-mediated monoamine release. Despite its therapeutic potential, MDMA can induce dose-, individual-, and context-dependent untoward effects outside safe settings. In this study, we investigated whether three new methylenedioxy bioisosteres of MDMA improve its off-target profile. In vitro methods included radiotracer assays, transporter electrophysiology, bioluminescence resonance energy transfer and fluorescence-based assays, pooled human liver microsome/S9 fraction incubation with isozyme mapping, and liquid chromatography coupled to high-resolution mass spectrometry. In silico methods included molecular docking. Compared with MDMA, all three MDMA bioisosteres (ODMA, TDMA, and SeDMA) showed similar pharmacological activity at human serotonin and dopamine transporters (hSERT and hDAT, respectively) but decreased activity at 5-HT 2A/2B/2C receptors. Regarding their hepatic metabolism, they differed from MDMA, with N -demethylation being the only metabolic route shared, and without forming phase II metabolites. Additional screening for their interaction with human organic cation transporters (hOCTs) and plasma membrane transporter (hPMAT) revealed a weaker interaction of the MDMA analogs with hOCT1, hOCT2, and hPMAT. Our findings suggest that these new MDMA analogs might constitute appealing therapeutic alternatives to MDMA, sparing the primary pharmacological activity at hSERT and hDAT, but displaying a reduced activity at 5-HT 2A/2B/2C receptors and reduced hepatic metabolism. Whether these MDMA bioisosteres may pose lower risk alternatives to the clinically re-emerging MDMA warrants further studies.

Synthetic Cathinones: Epidemiology, Toxicity, Potential for Abuse, and Current Public Health Perspective

Synthetic cathinones, derived from cathinone found in the plant Catha edulis, represent the second largest and most frequently seized group of new psychoactive substances. They are considered as β-keto analogs of amphetamine, sharing pharmacological effects with amphetamine and cocaine. This review describes the neurotoxic properties of synthetic cathinones, encompassing their capacity to induce neuroinflammation, dysregulate neurotransmitter systems, and alter monoamine transporters and receptors. Additionally, it discusses the rewarding and abuse potential of synthetic cathinones drawing from findings obtained through various preclinical animal models, contextualized with other classical psychostimulants. The review also offers an overview of current abuse trends of synthetic cathinones on the illicit drug market, specifying the aspects covered, and underscores the risks they pose to public health. Finally, the review discusses public health initiatives and efforts to reduce the hazards of synthetic cathinones, including harm reduction methods, education, and current clinical management strategies.

A narrative review of the neuropharmacology of synthetic cathinones-Popular alternatives to classical drugs of abuse

OBJECTIVE

To review the literature on the neuropharmacology of synthetic cathinones.

METHODS

A comprehensive literature search was carried out across multiple databases (mainly PubMed, World Wide Web, and Google Scholar) using relevant keywords.

RESULTS

Cathinones exhibit a broad toxicological profile, mimicking the effects of a wide variety of 'classic drugs' such as 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine and cocaine. Even small structural changes affect their interactions with key proteins. This article reviews existing knowledge of the mechanisms of action of cathinones at the molecular level, and key findings from research on their structure-activity relationship. The cathinones are also classified according to their chemical structure and neuropharmacological profiles.

CONCLUSIONS

Synthetic cathinones represent one of the most numerous and widespread groups among new psychoactive substances. Initially developed for therapeutic purposes, they quickly started to be used recreationally. With a rapidly increasing number of new agents entering the market, structure-activity relationship studies are valuable for assessing and predicting the addictive potential and toxicity of new and potential future substances. The neuropharmacological properties of synthetic cathinones are still not fully understood. A full elucidation of the role of some key proteins, including organic cation transporters, requires detailed studies.

Structure-Activity Relationship of N-Ethyl-Hexedrone Analogues: Role of the α-Carbon Side-Chain Length in the Mechanism of Action, Cytotoxicity, and Behavioral Effects in Mice

Synthetic cathinones are β-keto amphetamine derivatives whose appearance has increased dramatically in the past decades. N-Ethyl substituted cathinones have been proven to potently inhibit dopamine (DA) uptake and induce psychostimulant and rewarding effects in mice. However, little is known about the influence of the alpha-carbon side-chain length of N-ethyl cathinones on their pharmacological and toxicological effects. Thus, the aim of this study was to synthesize and investigate the in vitro and in vivo effects of five N-ethyl substituted cathinones: N-ethyl-cathinone (NEC), N-ethyl-buphedrone (NEB), N-ethyl-pentedrone, N-ethyl-hexedrone (NEH), and N-ethyl-heptedrone. HEK293 cells expressing the human DA or serotonin transporter (hDAT and hSERT) were used for uptake inhibition and binding assays. PC12 cells were used for the cytotoxicity assays. Swiss CD-1 mice were used to study the in vivo psychostimulant, anxiogenic, and rewarding properties. Our results show that all tested cathinones are able to inhibit DA uptake and are DAT-selective. The potency of DA uptake inhibitors increases with the elongation of the aliphatic side chain from methyl to propyl and decreases when increasing from butyl to pentyl, which correlates with an inverted U-shape psychostimulant response in mice at the medium dose tested. On the other hand, an increase in the α-carbon side-chain length correlates with an increase in the cytotoxic properties in PC12 cells, probably due to better membrane penetration. Moreover, all the cathinones tested have shown higher cytotoxicity than methamphetamine. Finally, our study not only demonstrated the rewarding properties of NEC and NEB but also the anxiety-like behavior induced at high doses by all the cathinones tested.

A proposed mechanism for the MDMA-mediated extinction of traumatic memories in PTSD patients treated with MDMA-assisted therapy

Post-traumatic stress disorder (PTSD) is a devastating psychiatric disorder afflicting millions of people around the world. Characterized by severe anxiety, intrusive thoughts, pervasive nightmares, an assortment of somatic symptoms, associations with severe long-term health problems, and an elevated risk of suicide, as much as 40-70% of patients suffer from refractory disease. 3,4-Methylenedioxy-methamphetamine (MDMA), like classic psychedelics such as psilocybin, have been used to enhance the efficacy of psychotherapy almost since their discovery, but due to their perceived potential for abuse and inclusion on USFDA (United States Food and Drug Administration) schedule 1, research into the mechanism by which they produce improvements in PTSD symptomology has been limited. Nevertheless, several compelling rationales have been explored, with the pro-social effects of MDMA thought to enhance therapeutic alliance and thus facilitate therapist-assisted trauma processing. This may be insufficient to fully explain the efficacy of MDMA in the treatment of psychiatric illness. Molecular mechanisms such as the MDMA mediated increase of brain-derived neurotrophic factor (BDNF) availability in the fear memory learning pathways combined with MDMA's pro-social effects may provide a more nuanced explanation for the therapeutic actions of MDMA.

Self-Administration of Entactogen Psychostimulants Dysregulates Gamma-Aminobutyric Acid (GABA) and Kappa Opioid Receptor Signaling in the Central Nucleus of the Amygdala of Female Wistar Rats

Male rats escalate intravenous self-administration of entactogen psychostimulants, 3,4-methylenedioxymethcathinone (methylone) and 3,4-methylenedioxymethamphetamine (MDMA) under extended access conditions, as with typical psychostimulants. Here, we investigated whether female rats escalate self-administration of methylone, 3,4-methylenedioxypentedrone (pentylone), and MDMA and then studied consequences of MDMA and pentylone self-administration on GABAA receptor and kappa opioid receptor (KOR) signaling in the central nucleus of the amygdala (CeA), a brain area critically dysregulated by extended access self-administration of alcohol or cocaine. Adult female Wistar rats were trained to self-administer methylone, pentylone, MDMA (0.5 mg/kg/infusion), or saline-vehicle using a fixed-ratio 1 response contingency in 6-h sessions (long-access: LgA) followed by progressive ratio (PR) dose-response testing. The effects of pentylone-LgA, MDMA-LgA and saline on basal GABAergic transmission (miniature post-synaptic inhibitory currents, mIPSCs) and the modulatory role of KOR at CeA GABAergic synapses were determined in acute brain slices using whole-cell patch-clamp. Methylone-LgA and pentylone-LgA rats similarly escalated their drug intake (both obtained more infusions compared to MDMA-LgA rats), however, pentylone-LgA rats reached higher breakpoints in PR tests. At the cellular level, baseline CeA GABA transmission was markedly elevated in pentylone-LgA and MDMA-LgA rats compared to saline-vehicle. Specifically, pentylone-LgA was associated with increased CeA mIPSC frequency (GABA release) and amplitude (post-synaptic GABAA receptor function), while mIPSC amplitudes (but not frequency) was larger in MDMA-LgA rats compared to saline rats. In addition, pentylone-LgA and MDMA-LgA profoundly disrupted CeA KOR signaling such as both KOR agonism (1 mM U50488) and KOR antagonism (200 nM nor-binaltorphimine) decreased mIPSC frequency suggesting recruitment of non-canonical KOR signaling pathways. This study confirms escalated self-administration of entactogen psychostimulants under LgA conditions in female rats which is accompanied by increased CeA GABAergic inhibition and altered KOR signaling. Collectively, our study suggests that CeA GABA and KOR mechanisms play a critical role in entactogen self-administration like those observed with escalation of alcohol or cocaine self-administration.

Structure-Activity Relationship of Novel Second-Generation Synthetic Cathinones: Mechanism of Action, Locomotion, Reward, and Immediate-Early Genes

Several new synthetic cathinones, which mimic the effect of classical psychostimulants such as cocaine or MDMA, have appeared in the global illicit drug market in the last decades. In fact, the illicit drug market is continually evolving by constantly adding small modifications to the common chemical structure of synthetic cathinones. Thus, the aim of this study was to investigate the in vitro and in vivo structure–activity relationship (SAR) of six novel synthetic cathinones currently popular as recreational drugs, pentedrone, pentylone, N-ethyl-pentedrone (NEPD), N-ethyl-pentylone (NEP), 4-methyl-pentedrone (4-MPD), and 4-methyl-ethylaminopentedrone (4-MeAP), which structurally differ in the absence or presence of different aromatic substituents and in their amino terminal group. Human embryonic kidney (HEK293) cells expressing the human isoforms of SERT and DAT were used for the uptake inhibition and release assays. Moreover, Swiss CD-1 mice were used to investigate the psychostimulant effect, rewarding properties (3, 10, and 30 mg/kg, i.p.), and the induction of immediate-early genes (IEGs), such as Arc and c-fos in the dorsal striatum (DS) and ventral striatum (VS) as well as bdnf in the medial prefrontal cortex (mPFC), of the test compounds. Our results demonstrated that all tested synthetic cathinones are potent dopamine (DA) uptake inhibitors, especially the N-ethyl analogs, while the ring-substituted cathinones tested showed higher potency as SERT inhibitors than their no ring-substituted analogs. Moreover, unlike NEP, the remaining test compounds showed clear “hybrid” properties, acting as DAT blockers but SERT substrates. Regarding the locomotion, NEP and NEPD were more efficacious (10 mg/kg) than their N-methyl analogs, which correlates with their higher potency inhibiting the DAT and an overexpression of Arc levels in the DS and VS. Furthermore, all compounds tested induced an increase in c-fos expression in the DS, except for 4-MPD, the least effective compound in inducing hyperlocomotion. Moreover, NEP induced an up-regulation of bdnf in the mPFC that correlates with its 5-HTergic properties. Finally, the present study demonstrated for the first time that NEP, 4-MPD, and 4-MeAP induce reward in mice. Altogether, this study provides valuable information about the mechanism of action and psychostimulant and rewarding properties as well as changes in the expression of IEGs related to addiction induced by novel second-generation synthetic cathinones.

Molecular Mechanisms of Action of Novel Psychoactive Substances (NPS). A New Threat for Young Drug Users with Forensic-Toxicological Implications

Novel psychoactive substances (NPS) represent a severe health risk for drug users. Even though the phenomenon has been growing since the early 2000s, the mechanisms of action of NPS at the receptors and beyond them are still scarcely understood. The aim of the present study was to provide a systematic review of the updated knowledge regarding the molecular mechanisms underlying the toxicity of synthetic opioids, cannabinoids, cathinones, and stimulants. The study was conducted on the PubMed database. Study eligibility criteria included relevance to the topic, English language, and time of publication (2010–2020). A combined Mesh and free-text protocols search was performed. Study selection was performed on the title/abstract and, in doubtful cases, on the full texts of papers. Of the 580 records identified through PubMed searching and reference checking, 307 were excluded by title/abstract and 78 additional papers were excluded after full-text reading, leaving a total of 155 included papers. Molecular mechanisms of synthetic opioids, synthetic cannabinoids, stimulants, psychedelics, and hallucinogens were reviewed and mostly involved both a receptor-mediated and non-receptor mediated cellular modulation with multiple neurotransmitters interactions. The molecular mechanisms underlying the action of NPS are more complex than expected, with a wide range of overlap among activated receptors and neurotransmitter systems. The peculiar action profile of single compounds does not necessarily reflect that of the structural class to which they belong, accounting for possible unexpected toxic reactions.

Discriminative-Stimulus Effects of Synthetic Cathinones in Squirrel Monkeys

BACKGROUND

Synthetic cathinones display overlapping behavioral effects with psychostimulants (e.g., methamphetamine [MA]) and/or entactogens (e.g., 3,4-methylenedioxymethaphetamine [MDMA])-presumably reflecting their dopaminergic and/or serotonergic activity. The discriminative stimulus effects of MDMA thought to be mediated by such activity have been well characterized in rodents but have not been fully examined in nonhuman primates.

METHODS

The present studies were conducted to systematically evaluate the discriminative stimulus effects of 5 abused synthetic cathinones (methylenedioxypyrovalerone [MDPV], α-pyrrolidinovalerophenone [α-PVP], methcathinone [MCAT], mephedrone, and methylone) in adult male squirrel monkeys trained to distinguish intramuscular injections of MA (0.1 mg/kg; n = 4) or MDMA (0.6 mg/kg; n = 4) from vehicle.

RESULTS

Each training drug produced dose-dependent effects and, at the highest dose, full substitution. MDMA produced predominantly vehicle-like responding in the MA-trained group, whereas the highest dose of MA (0.56 mg/kg) produced partial substitution (approximately 90% appropriate lever responding in one-half of the subjects) in the MDMA-trained group. MDPV, α-PVP, and MCAT produced full substitution in MA-trained subjects, but, at the same or higher doses, only substituted for MDMA in one-half of the subjects, consistent with primarily dopaminergically mediated interoceptive effects. In contrast, mephedrone and methylone fully substituted in MDMA-trained subjects but failed to fully substitute for the training drug in MA-trained subjects, suggesting a primary role for serotonergic actions in their interoceptive effects.

CONCLUSIONS

These findings suggest that differences in the interoceptive effects of synthetic cathinones in nonhuman primates reflect differing compositions of monoaminergic actions that also may mediate their subjective effects in humans.

Eutylone and Its Structural Isomers Interact with Monoamine Transporters and Induce Locomotor Stimulation

Synthetic cathinones are a class of new psychoactive substances that induce psychostimulant effects and pose risk for hospitalizations, overdose, and death. At the present time, derivatives of the synthetic cathinone, methylone, are being confiscated in nonmedical (i.e., recreational) drug markets worldwide. In particular, eutylone is a newly emerging methylone analog that possesses ethyl groups at the α-carbon and amine positions. Little information is available about the pharmacological effects of eutylone, but based on its structure, we surmised that the compound interacts with monoamine transporters in the brain. To test this hypothesis, we compared the effects of eutylone and its structural isomers, dibutylone and pentylone, using in vitro transporter assays in rat brain synaptosomes and in vivo locomotor activity assessments in mice. All drugs displayed dose-related inhibition of [³H]neurotransmitter uptake at dopamine transporters (DAT) and norepinephrine transporters (NET), but effects at DAT were 10-fold more potent (IC₅₀ = 120 nM). Eutylone and pentylone inhibited uptake at serotonin transporters (SERT), while dibutylone did not. Additionally, eutylone and pentylone displayed weak partial releasing actions at SERT which achieved 50% of maximal response. All drugs stimulated dose-related locomotion in mice, and eutylone was most potent and efficacious in this regard (ED₅₀ = 2 mg/kg, sc). Our results demonstrate that eutylone is a hybrid transporter compound with uptake inhibition properties at DAT and NET but substrate activity at SERT. The effects of eutylone are similar to those produced by pentylone, which suggests that eutylone will exhibit abuse liability and pose risks for psychostimulant side-effects in human users.

Methylenedioxymethamphetamine-like discriminative stimulus effects of seven cathinones in rats

Synthetic cathinone derivatives are commonly considered quasi-legal alternatives for stimulant drugs, such as cocaine and methamphetamine, but some derivatives are increasingly being detected in club drug formulations of Ecstasy or 'Molly' as substitutes for methylenedioxymethamphetamine (±-MDMA). Although several studies have evaluated the psychostimulant-like effects of synthetic cathinones, few cathinone compounds have been assessed for MDMA-like activity. In order to determine their likelihood of interchangeability with entactogenic club drugs, the discriminative stimulus effects of methcathinone, 4-fluoromethcathinone, 4-methylmethcathinone, 4-methylethcathinone, 3-fluoromethcathinone, pentedrone, and ethylone were assessed in Sprague-Dawley rats trained to discriminate 1.5 mg/kg racemic methylenedioxymethamphetamine (±-MDMA) from vehicle. Methamphetamine and the cathinones 4-fluoromethcathinone, 4-methylmethcathinone, 4-methylethcathinone, 3-fluoromethcathinone, pentedrone, and ethylone fully substituted for the discriminative stimulus effects of ±-MDMA. In contrast, methcathinone produced a maximum of only 43% ±-MDMA-appropriate responding and higher doses suppressed responding. Most, but not all of the cathinone compounds tested have discriminative stimulus effects similar to those of MDMA as well as psychostimulant-like effects; however, the potency of MDMA versus psychostimulant substitution varies substantially among the compounds, suggesting that a subset of synthetic cathinones are more MDMA-like than psychostimulant-like. These findings further highlight the highly-variable pharmacology of this class of compounds and suggest that those cathinones with MDMA-like effects may also have increased use as club drugs.

Reinforcing effects of synthetic cathinones in rhesus monkeys: Dose-response and behavioral economic analyses

The abuse of synthetic cathinones ("bath salts") with psychomotor stimulant and/or entactogenic properties emerged as a public health concern when they were introduced as "legal" alternatives to drugs of abuse such as cocaine or MDMA. In this study, experiments were conducted in nonhuman primates to examine how differences in transporter selectivity might impact the reinforcing effects of synthetic cathinones. Rhesus monkeys (N = 5) were trained to respond for intravenous injections under a fixed-ratio (FR) 30, timeout 60-s schedule of reinforcement. The reinforcing effects of selected cathinones (e.g., MDPV, αPVP, MCAT, and methylone) with a range of pharmacological effects at dopamine and serotonin transporters were compared to cocaine and MDMA using dose-response analysis under a simple FR schedule and behavioral economic procedures that generated demand curves for two doses of each drug. Results show that one or more doses of all drugs were readily self-administered in each subject and, excepting MDMA (21 injections/session), peak levels of self-administration were similar across drugs (between 30 and 40 injections/session). Demand elasticity for the peak and the peak + 1/2-log dose of each drug did not significantly differ, and when data for the two doses were averaged for each drug, the following rank-order of reinforcing strength emerged: cocaine > MCAT = MDPV = methylone > αPVP = MDMA. These results indicate that the reinforcing strength of synthetic cathinones are not related to their selectivity in binding dopamine or serotonin transporter sites.

Assessment of aversive effects of methylone in male and female Sprague-Dawley rats: Conditioned taste avoidance, body temperature and activity/stereotypies

Methylone's rewarding effects have been well characterized; however, little is known about its aversive effects and how such effects may be impacted by sex. In this context, the present study investigated the aversive effects of methylone (vehicle, 5.6, 10 or 18 mg/kg, IP) in 35 male and 31 female Sprague-Dawley rats assessed by conditioned taste avoidance and changes in body temperature and activity/stereotypies. Methylone induced significant taste avoidance, changes in temperature and increased activity and stereotypies in both males and females. Similar to work with other synthetic cathinones, methylone has aversive effects as indexed by significant taste avoidance and changes in temperature and activity (two characteristics of methylone overdose in humans). The only endpoint for which there were significant sex differences was in general activity with males displaying a faster onset and females displaying a longer duration. Although sex was not a factor with taste avoidance and temperature, separate analyses for males and females revealed different patterns, e.g., males displayed a more rapid acquisition of taste avoidance and females displayed changes in temperature at lower doses. Males displayed a faster onset and females displayed a longer duration of activity (consistent with the analyses considering sex as a factor), while time- and dose-dependent stereotypies did not show consistent pattern differences. Although sex differences were relatively limited when sex was specifically assessed as a factor (or only evident when sex comparisons were made in the patterns of effects), sex as a biological variable in the study of drugs should be made to determine if differences exist and, if evident, the basis for these differences.

Methylenedioxymethamphetamine-like discriminative stimulus effects of pyrrolidinyl cathinones in rats

BACKGROUND

Synthetic cathinone derivatives are used as alternatives both for stimulant drugs such as cocaine and methamphetamine and for club drugs such as 3,4-methylenedioxymethamphetamine (MDMA), but little is known about their MDMA-like subjective effects.

METHODS

In order to determine their similarity to MDMA, the discriminative stimulus effects of 10 pyrrolidinyl cathinones (α-pyrrolidinopropiophenone, 4'-methyl-α-pyrrolidinopropiophenone (4'-MePPP), α-pyrrolidinobutiophenone, 3',4'-methylenedioxy-α-pyrrolidinobutyrophenone (MD-PBP), α-pyrrolidinovalerophenone, 3,4-methylenedioxy-pyrovalerone (MDPV), α-pyrrolidinopentiothiophenone, napthylpyrovalerone (naphyrone), α-pyrrolidinohexiophenone, and 4'-methyl-α-pyrrolidinohexiophenone (4'-MePHP)) were assessed in Sprague-Dawley rats trained to discriminate 1.5 mg/kg racemic ±-MDMA from vehicle.

RESULTS

Compounds with no substitutions on the phenyl ring and the thiophene produced 44-67% MDMA-appropriate responding. In contrast, the substituted pyrrolidinyl cathinones produced a range of MDMA-appropriate responding dependent upon the length of the alpha side chain. 4'-MePPP, with a single carbon on the alpha position, produced 99.8% MDMA-appropriate responding, MD-PBP (two carbons) produced 83%, naphyrone (three carbons) produced 71%, MDPV (three carbons) produced, 66%, and 4'-MePHP (four carbons) produced 47%.

CONCLUSIONS

Many cathinone compounds have discriminative stimulus effects similar to those of MDMA. However, the pyrrolidine substitution appears to reduce serotonergic effects, with a commensurate decrease in MDMA-like effects. Substitutions on the phenyl ring appear to be able to restore MDMA-like responding, but only in compounds with short alpha side chains. These findings agree with earlier findings of increasing dopaminergic effects and stronger reinforcing effects with increasing side chain. Assessment of more compounds is necessary to establish the replicability/robustness of this phenomenon. These findings may be of use in predicting which compounds will have MDMA/club drug-like effects versus psychostimulant-like effects.

The drug purity discounting task: Ecstasy use likelihood is reduced by probabilistic impurity according to harmfulness of adulterants

BACKGROUND

Ecstasy typically contains adulterants in addition to, or in lieu of, MDMA which may pose a greater risk to users than MDMA itself. The current study aimed to evaluate the effectiveness of adulterant-related informational prompts in reducing Ecstasy use using a novel probability discounting task.

METHODS

An online sample of past-month Ecstasy users (N = 278) were randomized to one of four different framing prompt conditions: no prompt; a prompt describing MDMA's effects; a prompt describing adulterants as inert "filler"; or a prompt describing adulterants as pharmacologically-active, potentially-harmful compounds. Each prompt contained general, potential public-health information that was not specifically related to subsequent behavioral tasks. All participants then completed an identical Drug Purity Discounting Task, in which they indicated the likelihood of using a sample of Ecstasy across different probabilities of the sample being impure, and then completed a hypothetical Ecstasy purchasing task.

RESULTS

Likelihood of Ecstasy use decreased as impurity probability increased across conditions. Ecstasy use likelihood was highest in the "inert" prompt condition, whereas pharmacologically-active adulterant or adulterant-nonspecific prompts resulted in comparably low likelihood of use. Ecstasy-use likelihood did not differ among conditions when the likelihood of sample impurity was 0. Ecstasy purchasing did not differ among groups. Inelastic purchasing was associated with greater likelihood of using potentially-impure Ecstasy.

CONCLUSIONS

Altogether, these data highlight the necessity of education regarding pharmacologically-active, rather than inert, adulterants in Ecstasy, and suggest that increased access to drug checking kits and services may mitigate some of the harms associated with Ecstasy use.

Synthetic Cathinones Induce Cell Death in Dopaminergic SH-SY5Y Cells via Stimulating Mitochondrial Dysfunction

Increasing reports of neurological and psychiatric complications due to psychostimulant synthetic cathinones (SCs) have recently raised public concern. However, the precise mechanism of SC toxicity is unclear. This paucity of understanding highlights the need to investigate the in-vitro toxicity and mechanistic pathways of three SCs: butylone, pentylone, and 3,4-Methylenedioxypyrovalerone (MDPV). Human neuronal cells of SH-SY5Y were cultured in supplemented DMEM/F12 media and differentiated to a neuronal phenotype using retinoic acid (10 μM) and 12-O-tetradecanoylphorbol-13-acetate (81 nM). Trypan blue and lactate dehydrogenase assays were utilized to assess the neurotoxicity potential and potency of these three SCs. To investigate the underlying neurotoxicity mechanisms, measurements included markers of oxidative stress, mitochondrial bioenergetics, and intracellular calcium (Ca²⁺), and cell death pathways were evaluated at two doses (EC₁₅ and EC₄₀), for each drug tested. Following 24 h of treatment, all three SCs exhibited a dose-dependent neurotoxicity, characterized by a significant (p < 0.0001 vs. control) production of reactive oxygen species, decreased mitochondrial bioenergetics, and increased intracellular Ca²⁺ concentrations. The activation of caspases 3 and 7 implicated the orchestration of mitochondrial-mediated neurotoxicity mechanisms for these SCs. Identifying novel therapeutic agents to enhance an altered mitochondrial function may help in the treatment of acute-neurological complications arising from the illicit use of these SCs.

The clinical challenges of synthetic cathinones

AIMS

Within the new psychoactive substances (NPS) scenario, several hundred different molecules, mostly including synthetic cannabinoids and cathinones, have been identified so far. The aims of the paper were to: (i) identify the number of synthetic cathinones mentioned in a range of psychonaut, NPS-related, online sources; and (ii) describe the associated acute/long term clinical scenario and the related treatment/management plan.

METHODS

After about 18 months of operation and exclusion of false positives/duplicates, some 4204 unique NPS molecules were included in the NPSfinder® crawling/navigating software database. Most popular NPS included: 1265 psychedelic phenethylamines (30.1%; confidence interval [CI] 95%: 28.7-31.5%); 1253 synthetic cannabinoids (29.8%; CI 95%: 28.4-31.2%); 429 synthetic opioids (10.2%; CI 95%: 9.3-10.2%); and 171 synthetic cathinones (4.1%; CI 95% 3.5-4.7%). Conversely, the United Nations Office on Drugs and Crime and the European Monitoring Centre for Drugs and Drug Addiction databases respectively included 169 and 140 cathinones. Overall, the 3 databases reported some 222 synthetic cathinones, and 41 were uniquely identified by the NPSfinder®.

RESULTS

In terms of clinical scenarios, synthetic cathinone ingestion is initially associated with stimulant effects; however, psychopathological disturbances, violence, suicidal behaviour, hyperthermia, coma and death have also been described.

CONCLUSION

The proportion of cathinones commented on by psychonaut fora appeared to be relatively small, and similar to those reported by both the United Nations Office on Drugs and Crime and European Monitoring Centre for Drugs and Drug Addiction. This may be associated with a recent significant decline in both cathinone-related consumption and acute medical presentation. Due to their complex behavioural and medical toxicity issues, healthcare professionals should be, however, be educated to recognise the signs and symptoms of NPS, including synthetic cathinone, ingestion.

Self-administration of the synthetic cathinones 3,4-methylenedioxypyrovalerone (MDPV) and α-pyrrolidinopentiophenone (α-PVP) in rhesus monkeys

RATIONALE

The availability and abuse of synthetic analogues of cathinone have increased dramatically around the world. Synthetic cathinones, such as 3,4-methylenedioxypyrovalerone [MDPV] and α-pyrrolidinopentiophenone [α-PVP], are cocaine-like inhibitors of monoamine transporters and common constituents of "bath salts" or "flakka" preparations. Studies in rats suggest that MDPV and α-PVP are 3 to 4-fold more effective reinforcers than cocaine; however, comparisons of the relative reinforcing effectiveness of MDPV and α-PVP have not been reported in other species.

OBJECTIVES

Accordingly, in the present study, 4 adult male rhesus monkeys responding under a progressive ratio schedule of reinforcement were used to characterize the reinforcing effects of MDPV and α-PVP and to compare directly these effects with those of cocaine and methamphetamine.

RESULTS

MDPV was the most potent reinforcer, followed by α-PVP, methamphetamine, and cocaine. α-PVP was the most effective reinforcer, followed by MDPV, cocaine, and methamphetamine. In addition to making more responses to obtain MDPV and α-PVP, monkeys also responded for longer periods of time when MDPV or α-PVP was available compared with when either cocaine or methamphetamine was available for infusion.

CONCLUSIONS

These studies confirm recent reports from rodents and provide strong evidence that the synthetic cathinones MDPV and α-PVP are capable of maintaining high levels of responding for prolonged periods of time, and that they function as more effective reinforcers than either cocaine or methamphetamine. The relative strength of these reinforcing effects may account for the high rates of "bath salts" use reported in humans.

Locomotor activity and discriminative stimulus effects of five novel synthetic cathinone analogs in mice and rats

BACKGROUND

The development of novel synthetic psychoactive substances continues to accelerate. There are little or no data on the pharmacological mechanisms, behavioral effects, or abuse liability of many of the newer compounds, despite increasing reports of severe adverse effects in recreational users.

METHODS

The current study investigated the discriminative stimulus and locomotor stimulant effects of a group of synthetic cathinone analogs: N-ethylpentylone, dimethylone, dibutylone, clephedrone, 3',4'-tetramethylene-α-pyrrolidinovalerophenone (TH-PVP). Locomotor activity was assessed in an open-field assay using Swiss-Webster mice. Discriminative stimulus effects were assessed in Sprague-Dawley rats trained to discriminate either cocaine, methamphetamine or MDMA from vehicle.

RESULTS

N-Ethylpentylone, dimethylone, dibutylone and clephedrone increased locomotor activity. Maximal effects were similar among the test compounds. Relative potencies were: methamphetamine > N-ethylpentylone > clephedrone > dimethylone > MDMA > cocaine > dibutylone. TH-PVP dose-dependently depressed locomotor activity. N-Ethylpentylone, dimethylone, dibutylone and clephedrone substituted fully for the discriminative stimulus effects of methamphetamine. N-Ethylpentylone, dibutylone and clephedrone fully substituted for cocaine, whereas dimethylone produced a maximum of 67% drug-appropriate responding. Dimethylone, dibutylone and clephedrone fully substituted for MDMA, whereas N-ethylpentylone produced only 50% drug-appropriate responding. TH-PVP produced a maximum of 38% methamphetamine-appropriate responding, 50% cocaine-appropriate responding, and less than 1% MDMA-appropriate responding.

CONCLUSIONS

These data provide initial evidence that the novel psychoactive substances N-ethylpentylone, dimethylone, dibutylone, and clephedrone demonstrate potential for abuse as psychostimulants and/or club drugs, given their ability to stimulate locomotor activity and their substitution for the discriminative stimulus effects of methamphetamine, cocaine and/or MDMA. TH-PVP has minimal activity in the assays tested and may have little or no abuse liability.

Cognitive deficits and neurotoxicity induced by synthetic cathinones: is there a role for neuroinflammation?

RATIONALE

The number of synthetic derivatives of cathinone, the primary psychoactive alkaloid found in Catha edulis (khat), has risen exponentially in the past decade. Synthetic cathinones (frequently referred to as "bath salts") produce adverse cognitive and behavioral sequelae, share similar pharmacological mechanisms of action with traditional psychostimulants, and may therefore trigger similar cellular events that give rise to neuroinflammation and neurotoxicity.

OBJECTIVES

In this review, we provide a brief overview of synthetic cathinones, followed by a summary of cognitive deficits in animals and humans that have been documented following acute or repeated exposure. We also summarize growing evidence from in vitro and in vivo studies for synthetic cathinone-induced neurotoxicity, and provide a working hypothetic model of potential cellular mechanisms.

RESULTS

Synthetic cathinones produce varying effects on markers of monoaminergic terminal function and can increase the formation of reactive oxygen and nitrogen species, induce apoptotic signaling, and cause neurodegeneration and cytotoxicity. We hypothesize that these effects result from biochemical events similar to those induced by traditional psychostimulants. However, empirical evidence for the ability of synthetic cathinones to induce neuroinflammatory processes is currently lacking.

CONCLUSIONS

Like their traditional psychostimulant counterparts, synthetic cathinones appear to induce neurocognitive dysfunction and cytotoxicity, which are dependent on drug type, dose, frequency, and time following exposure. However, additional studies on synthetic cathinone-induced neuroinflammation are clearly needed, as are investigations into the neurochemical and neuroimmune mechanisms underlying their neurotoxic effects. Such endeavors may lead to novel therapeutic avenues to promote recovery in habitual synthetic cathinone users.

Behavioral economic analysis of the reinforcing effects of "bath salts" mixtures: studies with MDPV, methylone, and caffeine in male Sprague-Dawley rats

RATIONALE

"Bath salts" preparations often contain combinations of synthetic cathinones (e.g., 3,4-methylenedioxymethcathinone [methylone], 3,4-methylenedioxypyrovalerone [MDPV]), and caffeine, and evidence suggests that mixtures of synthetic cathinones and caffeine (e.g., MDPV + caffeine or methylone + caffeine) can be more potent and/or effective reinforcers than predicted for an additive interaction.

OBJECTIVE

To use demand curve analyses to compare the reinforcing effectiveness of MDPV and methylone to mixtures of MDPV + caffeine and methylone + caffeine.

METHODS

Male Sprague-Dawley rats acquired methylone self-administration (0.32 mg/kg/inf) under a fixed ratio (FR) 1 schedule of reinforcement and generated full dose-response curves for methylone (0.01-1 mg/kg/inf) under an FR5 schedule of reinforcement. Demand curves were then obtained for methylone, MDPV, caffeine, and methylone + caffeine and MDPV + caffeine mixtures by increasing the FR across sessions according to the following series: 3, 10, 18, 32, 56, 100, 178, etc. RESULTS: Self-administration of methylone was rapidly acquired by 87.5% of rats and was maintained across a range of doses, producing an inverted U-shaped dose-response curve. Rank order demand for the individual constituents was MDPV > methylone > caffeine. Demand for the 3:1 (but not 10:1) methylone + caffeine mixture was greater than that for methylone alone, and demand for MDPV alone was similar to both MDPV + caffeine mixtures evaluated.

CONCLUSIONS

These studies provide additional evidence that although methylone is an effective reinforcer, combining methylone with caffeine results in an enhanced reinforcing effectiveness compared to methylone alone. Thus, abused "bath salts" preparations containing synthetic cathinones and caffeine may have higher abuse liability than preparations containing only synthetic cathinones.

The synthetic cathinones, butylone and pentylone, are stimulants that act as dopamine transporter blockers but 5-HT transporter substrates

RATIONALE

Synthetic cathinones continue to emerge in recreational drug markets worldwide. 1-(1,3-Benzodioxol-5-yl)-2-(methylamino)butan-1-one (butylone) and 1-(1,3-benzodioxol-5-yl)-2-(methylamino)pentan-1-one (pentylone) are derivatives of the cathinone compound, 1-(1,3-benzodioxol-5-yl)-2-(methylamino)propan-1-one (methylone), that are being detected in drug products and human casework.

OBJECTIVES

The purpose of the present study was to examine the neuropharmacology of butylone and pentylone using in vitro and in vivo methods.

METHODS

In vitro uptake and release assays were carried out in rat brain synaptosomes and in cells expressing human dopamine transporters (DAT) and 5-HT transporters (SERT). In vivo microdialysis was performed in the nucleus accumbens of conscious rats to assess drug-induced changes in neurochemistry.

RESULTS

Butylone and pentylone were efficacious uptake blockers at DAT and SERT, though pentylone was more DAT-selective. Both drugs acted as transporter substrates that evoked release of [³H]5-HT at SERT, while neither evoked release at DAT. Consistent with the release data, butylone and pentylone induced substrate-associated inward currents at SERT but not DAT. Administration of butylone or pentylone to rats (1 and 3 mg/kg, i.v.) increased extracellular monoamines and motor activity, but pentylone had weaker effects on 5-HT and stronger effects on motor stimulation.

CONCLUSIONS

Our data demonstrate that increasing the α-carbon chain length of methylone creates "hybrid" transporter compounds which act as DAT blockers but SERT substrates. Nevertheless, butylone and pentylone elevate extracellular dopamine and stimulate motor activity, suggesting both drugs possess significant risk for abuse.

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.

Dopamine and serotonin antagonists fail to alter the discriminative stimulus properties of ±methylenedioxymethamphetamine

Most studies on discriminative stimulus effects of 3,4-methylenedioxymethamphetamine (MDMA) have been conducted using a relatively low dose (1.5 mg/kg), and those studies have invariably implicated serotonergic mechanisms. In contrast, dopaminergic mechanisms mediate the discriminative stimulus effects of amphetamine (AMPH). Some studies have suggested that the discriminative stimulus effects of a higher (3.0 mg/kg) dose of MDMA might rely on both serotonergic and dopaminergic mechanisms. This study aimed to determine effects of selective dopamine (DA) and serotonin (5HT) antagonists on the discriminative stimulus properties of AMPH (0.5 mg/kg) and MDMA (3.0 mg/kg). Separate groups of rats were trained to discriminate AMPH (0.5 mg/kg) or MDMA (3.0 mg/kg) from saline using a food-reinforced drug-discrimination procedure. Effects of DA (SCH 23390: 0.003-0.03 mg/kg and eticlopride: 0.03-0.3 mg/kg) or 5HT (ritanserin: 1.0-10.0 mg/kg, WAY-100635: 0.3-1.0 mg/kg and GR129375: 1.0-3.0 mg/kg) antagonists on the discriminative stimulus effects of both drugs were determined. Both DA antagonists dose-dependently decreased the AMPH but not the MDMA discrimination. None of the 5HT antagonists altered the discriminative stimulus effects of either drug. The MDMA (3.0 mg/kg) stimulus comprises both a DAergic and 5HTergic response, and the results suggest that either one is sufficient, but not required, to maintain the stimulus effects.