Role of amino terminal substitutions in the pharmacological, rewarding and psychostimulant profiles of novel synthetic cathinones

Unveiling the potential abuse liability of α-D2PV: A novel α-carbon phenyl-substituted synthetic cathinone

Synthetic cathinones are emerging psychoactive substances designed to mimic the effects of classical psychostimulants. Among them, α-D2PV, a novel pyrrolidine-containing cathinone characterized by a phenyl group on the α-carbon atom, has gained significant attention. This study investigates the in vitro and in silico mechanism of action as well as the abuse liability of α-D2PV using rodent models. Dopamine (DA), noradrenaline (NE), and serotonin (5-HT) uptake inhibition assays were conducted in HEK293 cells expressing the corresponding human monoamine transporter, complemented by molecular docking studies at the DA transporter (DAT). Behavioral studies in male Swiss CD-1 mice assessed locomotor activity and conditioned place preference, while microdialysis and self-administration experiments were performed in male Sprague-Dawley rats. The findings reveal that α-D2PV is a potent DA and NE uptake inhibitor, with minimal activity at the 5-HT transporter (SERT). Docking studies showed that the benzene rings of α-PVP and α-D2PV align precisely in their most stable conformations at DAT. In vivo, α-D2PV elicited dose-dependent hyperlocomotion, thigmotaxis, and rewarding effects in mice, alongside increased extracellular DA levels in the nucleus accumbens of awake rats. Self-administration experiments confirmed α-D2PV's high reinforcing efficacy, indicating a significant risk of abuse in humans. Finally, these results underscore the necessity for continued surveillance of α-D2PV within the illicit drug market. Furthermore, novel synthetic cathinones incorporating a phenyl ring at the α-carbon side chain warrant proactive monitoring due to their potential to retain dopaminergic activity and evade initial legal controls.

Acute Pharmacological Effects of Two Synthetic Cathinones in Humans: An Observational Study of N-Ethylhexedrone and N-Ethyl-nor-pentedrone

Background: Synthetic cathinones (SCs) are the second most representative class of New Psychoactive Substances, with more than 100 analogues identified in the illicit drug market up to 2024. According to the United Nations Office on Drugs and Crimes, N-ethylhexedrone (NEH) and N-ethyl-nor-pentedrone (NEP) were identified among the most frequently seized SCs worldwide. However, still, little is known with regard to their pharmacological effects in humans. Methods: For the first time, we conducted a naturalistic, prospective observational study in 16 participants (7 women and 9 men) with a previous history of psychostimulant recreational use. They intranasally self-administered a single dose of NEP (n = 8, 20-40 mg) or NEH (n = 8, 20-40 mg). The physiological effects (systolic and diastolic blood pressure, heart rate, and temperature) and subjective effects (visual analogue scales, Addiction Research Center Inventory questionnaire and Evaluation of Subjective Effects of Substances with Abuse Potential questionnaire) were assessed up to 4 h after the self-administration at different time points (0, 20 and 40 min and 1, 1.5, 2, 3 and 4 h). Results: Despite several differences, both NEP and NEH produced significant effects within 20 min, with a return to baseline 3-4 h after self-administration. In general, NEP showed a faster onset and a more rapid disappearance of subjective effects than NEH. Moreover, intranasal self-administration of NEH and NEP in experienced recreational drug users, within a non-controlled setting, induces a constellation of psychostimulant-like effects. Conclusion: NEH and NEP showed similar pharmacological properties after insufflation, with typical effects of SCs.

Synthesis, Characterization, and Biological Effects of Chloro-Cathinones: Toxicity and Potential Neurological Impact

Cathinones, a class of synthetic new psychoactive substances (NPSs), continue to emerge and pose public threats. Government control efforts often lead to the emergence of new isomers, which have adverse repercussions on NPSs identification and risk prediction. This work reports on the synthesis and structural characterization of twenty chloro-cathinones, including different isomers, to create analytical data to facilitate their identification in forensic and clinical contexts. Additionally, the potential of these cathinones to cause neuronal damage was evaluated. In vitro cytotoxicity was assessed using a differentiated human neuroblastoma cell line (SH-SY5Y) as a dopaminergic neuronal model. The tested cathinones showed LC50 values from 0.6 to 2.5 mM, with 4-CBC being the most cytotoxic. The most toxic cathinones increase reactive oxygen species levels and/or cause mitochondrial membrane potential depolarization. Furthermore, this study explored, for the first time, the effect of cathinones on the cholinergic system through acetylcholinesterase (AChE) inhibition. All tested cathinones inhibited AChE with IC50 values between 0.1 and 2 mM. Molecular docking analysis revealed that the most inhibitory cathinones interacted with the CASs and PASs in AChE's active gorge. These findings provide valuable insights into the effects of cathinones, highlighting potential health risks and structural features that may influence their toxicity towards the cholinergic system and neuronal damage.

Cardiovascular and locomotor effects of binary mixtures of common 'bath salts' constituents: Studies with methylone, methylenedioxypyrovalerone and caffeine in rats

BACKGROUND AND PURPOSE

The use of 'bath salts' drug preparations has been associated with high rates of toxicity and death. Preparations often contain mixtures of drugs, including multiple synthetic cathinones or synthetic cathinones and caffeine. Little is known about the interactions of 'bath salts' constituents and adverse effects often reported by users.

EXPERIMENTAL APPROACH

This study used adult male Sprague-Dawley rats to characterise the cardiovascular effects, locomotor effects and pharmacokinetics of methylone, methylenedioxypyrovalerone (MDPV) and caffeine, administered alone and as binary mixtures. Dose-addition analyses were used to determine the effect levels of a strictly additive interaction for dose pairs.

KEY RESULTS

Methylone, MDPV and caffeine increased heart rate (HR) and locomotion, with methylone producing the largest increase in HR, MDPV producing the largest increase in locomotor activity and caffeine being the least effective in stimulating HR and locomotor activity. MDPV and caffeine increased mean arterial pressure (MAP), with caffeine being more effective than MDPV. The nature of the interactions between methylone and MDPV tended towards sub-additivity for all endpoints, whereas interactions between MDPV or methylone and caffeine tended to be additive or sub-additive for cardiovascular endpoints, and additive or supra-additive for increases in locomotion. No pharmacokinetic interactions were observed between individual constituents, but methylone appeared to display nonlinear pharmacokinetics at the largest dose evaluated.

CONCLUSION AND IMPLICATIONS

These findings demonstrate that 'bath salts' preparations can impact both cardiovascular and locomotor effects and suggest that interactions among constituent drugs could contribute to the 'bath salts' toxidrome reported by human users.

Acute Paraoxon-Induced Neurotoxicity in a Mouse Survival Model: Oxidative Stress, Dopaminergic System Alterations and Memory Deficits

The secondary neurotoxicity induced by severe organophosphorus (OP) poisoning, including paraoxon (POX), is associated with cognitive impairments in survivors, who, despite receiving appropriate emergency treatments, may still experience lasting neurological deficits. Thus, the present study provides a survival mouse model of acute and severe POX poisoning to examine secondary neurotoxicity. Swiss CD-1 male mice were injected with POX (4 mg/kg, s.c.) followed by atropine (4 mg/kg, i.p.), pralidoxime (2-PAM; Pyridine-2-aldoxime methochloride) (25 mg/kg, i.p., twice, 1 h apart) and diazepam (5 mg/kg, i.p.), resulting in a survival rate >90% and Racine score of 5-6. Our results demonstrated that the model showed increased lipid peroxidation, downregulation of antioxidant enzymes and astrogliosis in the mouse hippocampus (HP) and prefrontal cortex (PFC), brain areas involved in cognitive functions. Moreover, dopamine (DA) levels were reduced in the hp, but increased in the PFC. Furthermore, the survival mouse model of acute POX intoxication did not exhibit phenotypic manifestations of depression, anxiety or motor incoordination. However, our results demonstrated long-term recognition memory impairments, which are in accordance with the molecular and neurochemical effects observed. In conclusion, this mouse model can aid in researching POX exposure's effects on memory and developing potential countermeasures against the secondary neurotoxicity induced by severe OP poisoning.

Sex differences in the effects of N-ethylpentylone in young CD1 mice: Insights on behaviour, thermoregulation and early gene expression

BACKGROUND AND PURPOSE

New psychoactive substances such as N-ethylpentylone (NEP) are continuously emerging in the illicit drug market, and knowledge of their effects and risks, which may vary between sexes, is scarce. Our present study compares some key effects of NEP in male and female mice.

EXPERIMENTAL APPROACH

Psychostimulant, rewarding and reinforcing effects were investigated by tracking locomotor activity, conditioned place preference (CPP) paradigm and through a self-administration (SA) procedure, respectively, in CD1 mice. Moreover, the expression of early genes (C-fos, Arc, Csnk1e, Pdyn, Pp1r1b and Bdnf in addiction-related brain areas) was assessed by qPCR. Finally, serum and brain levels of NEP were determined by UHPLC-MS/MS.

KEY RESULTS

NEP-treated males experimented locomotor sensitisation and showed higher and longer increases in locomotion as well as higher hyperthermia after repeated administration than females. Moreover, while preference score in the CPP was similar in both sexes, extinction occurred later, and reinstatement was more easily established for males. Female mice self-administered more NEP than males at a higher dose. Differences in early gene expression (Arc, Bdnf, Csnk1e and Ppp1r1b) were found, but the serum and brain NEP levels did not differ between sexes.

CONCLUSION AND IMPLICATIONS

Our results suggest that male mice are more sensitive to NEP psychostimulant and rewarding effects. These differences may be attributed to different early gene expression but not to pharmacokinetic factors. Moreover, males appear to be more vulnerable to the hyperthermic effects of NEP, while females might be more prone to NEP abuse.

Structure-Activity Relationship of Synthetic Cathinones: An Updated Review

The escalating prevalence of new psychoactive substances (NPSs) poses a significant public health challenge, evidenced by the vast chemical diversity, with over 500 substances reported annually to the United Nations Office on Drugs and Crime-Early Warning Advisory (UNODC-EWA) in the past five years. Among NPSs, synthetic cathinones are gaining a lot of popularity among users. Notably, synthetic cathinones accounted for approximately 50% of the total quantity of NPSs reported as seized by EU Member States in 2021. Preliminary data from UNODC indicates that a total of 209 synthetic cathinones have been reported to date. As their popularity grows, studying the structure-activity relationship (SAR) of synthetic cathinones is essential. SAR studies elucidate how structural features impact biological effects, aiding in toxicity prediction, regulatory compliance, and forensic identification. Additionally, SAR studies play a pivotal role in guiding drug policies, aiding authorities in categorizing and regulating newly emerging synthetic cathinones, mitigate public health risks and offer valuable insights into potential therapeutic applications. Thus, our Review consolidates recent findings on the effects of different substitutions in the chemical scaffold of synthetic cathinones on their mechanism of action as well as pharmacological and toxicological effects of synthetic cathinones, thus enhancing understanding of the SAR of synthetic cathinones' pharmacology and potential implications.

Structure-activity relationships of serotonergic 5-MeO-DMT derivatives: insights into psychoactive and thermoregulatory properties

Recent studies have sparked renewed interest in the therapeutic potential of psychedelics for treating depression and other mental health conditions. Simultaneously, the novel psychoactive substances (NPS) phenomenon, with a huge number of NPS emerging constantly, has changed remarkably the illicit drug market, being their scientific evaluation an urgent need. Thus, this study aims to elucidate the impact of amino-terminal modifications to the 5-MeO-DMT molecule on its interactions with serotonin receptors and transporters, as well as its psychoactive and thermoregulatory properties. Our findings demonstrated, using radioligand binding methodologies, that all examined 5-MeO-tryptamines exhibited selectivity for 5-HT1AR over 5-HT2AR. In fact, computational docking analyses predicted a better interaction in the 5-HT1AR binding pocket compared to 5-HT2AR. Our investigation also proved the interaction of these compounds with SERT, revealing that the molecular size of the amino group significantly influenced their affinity. Subsequent experiments involving serotonin uptake, electrophysiology, and superfusion release assays confirmed 5-MeO-pyr-T as the most potent partial 5-HT releaser tested. All tested tryptamines elicited, to some degree, the head twitch response (HTR) in mice, indicative of a potential hallucinogenic effect and mainly mediated by 5-HT2AR activation. However, 5-HT1AR was also shown to be implicated in the hallucinogenic effect, and its activation attenuated the HTR. In fact, tryptamines that produced a higher hypothermic response, mediated by 5-HT1AR, tended to exhibit a lower hallucinogenic effect, highlighting the opposite role of both 5-HT receptors. Moreover, although some 5-MeO-tryptamines elicited very low HTR, they still act as potent 5-HT2AR agonists. In summary, this research offers a comprehensive understanding of the psychopharmacological profile of various amino-substituted 5-MeO-tryptamines, keeping structural aspects in focus and accumulating valuable data in the frame of NPS. Moreover, the unique characteristics of some 5-MeO-tryptamines render them intriguing molecules as mixed-action drugs and provide insight within the search of non-hallucinogenic but 5-HT2AR ligands as therapeutical agents.

Effects of the Synthetic Cathinone α-Pyrrolidinobutiothiophenone (α-PBT) on Discriminative Stimulus Effects and Intracranial Self-Stimulation Thresholds in Male Rats

Recently, the abuse of synthetic cathinones is increasing among young people. α-Pyrrolidinobutiothiophenone (α-PBT), a synthetic cathinone, is a designer drug that is freely traded online with no legal restrictions. Moreover, there is currently no scientific basis for legal regulation. Here, we examined the addictive properties of α-PBT using a drug discrimination (DD) task. We also investigated the role of α-PBT in brain stimulation reward (BSR) using an intracranial self-stimulation (ICSS) paradigm in rats. Initially, the rats were trained to discriminate between cocaine and saline. After the discrimination training criteria were met, we determined the dose-effect curves of cocaine and conducted generalization tests with α-PBT and α-pyrrolidinopentiothiophenone (α-PVT) using a cumulative dosing protocol. In a separate set of studies, we examined the dopaminergic mechanisms underlying the function of α-PBT as an interoceptive stimulus (17.8 mg/kg) by intraperitoneally injecting either the dopamine (DA) D1 antagonist SCH23390 (0.06 and 0.12 mg/kg) or the D2 antagonist eticlopride (0.05 and 0.1 mg/kg) 15 min before DD testing. Brain reward function was measured using an ICSS procedure to examine the effects of α-PBT on ICSS threshold under the frequency-rate procedure. Our results showed that α-PBT functioned as a discriminative cue similar to cocaine in rats. More importantly, SCH23390 abolished the effects of α-PBT as an interoceptive stimulus in a dose-dependent manner in rats trained to press a lever to receive cocaine. Similarly, eticlopride dose-dependently attenuated the effect of α-PBT used as a discriminative cue. Additionally, cumulative α-PBT administration dose-dependently lowered ICSS thresholds compared with those in saline-treated rats. Furthermore, α-PBT-induced potentiation of BSR was abolished by pretreatment with both SCH23390 and eticlopride. Taken together, our results suggest that α-PBT can function as a cocaine-like discriminative cue via the activation of D1 and D2 receptors. α-PBT also appears to influence BSR by reducing the brain reward threshold via changes in D1 and D2 receptors. The present study suggests that α-PBT could have addictive properties through DA D1 and D2 receptors and thus poses a threat to humans.

Synthetic cathinones in drug-facilitated sexual assault: A case report involving the novel generation substituted cathinone N-ethylpentedrone and a review of the literature

The use of 3,4-methylenedioxymethamphetamine (MDMA) in drug-facilitated sexual assault (DFSA) is not uncommon. Indeed, the effects associated with the use of this substance may lead to disinhibition. Several synthetic cathinones, such as mephedrone or methylone, also possess marked entactogenic properties. This manuscript aims to (i) report a DFSA case involving a novel cathinone derivative, namely N-ethyl-pentedrone (NEPD) and (ii) review previously reported DFSA cases involving synthetic cathinones. Using liquid chromatography-high-resolution mass spectrometry (LC-HRMS), NEPD was detected in both plasma and urine collected from a 36-year-old male who had been victim of DFSA. Furthermore, an exhaustive, non-period-specific English-language literature search was performed using several different electronic databases to identify DFSA cases involving synthetic cathinones. Overall, five synthetic cathinones have been associated with DFSA:methylenedioxypyrovalerone, 4-methylethcathinone, α -pyrrolidinopentiophenone, mephedrone, α -pyrrolidinohexiophenone, and methylone, which appears to be the most frequently reported. Methylone is the β-keto analog of MDMA, with which it shares substantial pharmacological similarities. Indeed, the pharmacological effects of methylone are similar to those associated with MDMA. By contrast, little is known regarding NEPD's pharmacological effects in humans. Based on subjective reports, NEPD can produce both positive and negative effects in human. Unlike what is reported in the case of methylone or mephedrone, only a small minority of NEPD users report slightly entactogenics effects. Such properties theoretically make NEPD more suitable for use in a chemsex context than in DFSA context; even though, the boundary between these two specific forms of sexualized drug use can sometimes appear tenuous.

α-Pyrrolidinohexanophenone (α-PHP) and α-Pyrrolidinoisohexanophenone (α-PiHP): A Review

New Psychoactive Substances are currently a serious and growing problem affecting public health worldwide. By 2022, 1184 of these substances had been identified over a period of 16 years. Within these, α-pyrrolidinohexanophenone (α-PHP) and α-pyrrolidinoisohexanophenone (α-PiHP) have emerged, two synthetic cathinones from the pyrovalerone derivates subgroup that are positional isomers of each other. Alpha-PHP appeared on the Japanese illicit drug market in 2014 and, two years later, α-PiHP was identified for the first time in China. They were placed in schedule II on the list of Psychotropic Substances under International Control in 2020 and in March 2023, respectively. Both cathinones have no therapeutic potential for medical use and therefore are abused for recreational habits, which can lead to fatalities. The most frequent adverse effects reported are cardiac, psychiatric, and neurologic, and fatal intoxications have already been described. In Portugal, their consumption and consequent seizures are more prevalent on the archipelagos, which has been aggravating the health situation. In conclusion, these types of substances are a challenge for forensic toxicology since they are easily synthesized, modified, and placed on the market. Therefore, more studies to develop analytical methods to detect them and more comprehensive legislation should be applied. Thus, this review aimed to address the legislative, physicochemical, toxicological, and analytical aspects of both substances.

Photoredox-Catalyzed Tandem Cyclization of Enaminones with N-Sulfonylaminopyridinium Salts toward the Synthesis of 3-Sulfonaminated Chromones

A photoredox-catalyzed intermolecular tandem sulfonamination/cyclization of enaminones was realized by using N-aminopyridinium salts as the sulfonaminated reagents without transition-metal catalysts or bases. The reaction exhibits a broad scope and good functional group tolerance, good yields, and regioselectivity. Preliminary mechanistic studies support the radical property of the reaction and the involvement of N-centered radical intermediates.

Organic cation transporters in psychiatric and substance use disorders

Psychiatric and substance use disorders inflict major public health burdens worldwide. Their widespread burden is compounded by a dearth of effective treatments, underscoring a dire need to uncover novel therapeutic targets. In this review, we summarize the literature implicating organic cation transporters (OCTs), including three subtypes of OCTs (OCT1, OCT2, and OCT3) and the plasma membrane monoamine transporter (PMAT), in the neurobiology of psychiatric and substance use disorders with an emphasis on mood and anxiety disorders, alcohol use disorder, and psychostimulant use disorder. OCTs transport monoamines with a low affinity but high capacity, situating them to play a central role in regulating monoamine homeostasis. Preclinical evidence discussed here suggests that OCTs may serve as promising targets for treatment of psychiatric and substance use disorders and encourage future research into their therapeutic potential.

The differentiation of N-butyl pentylone isomers using GC-EI-MS and NMR

Forensic laboratories are faced with an ever-expanding seized drug landscape including the increasing prevalence of novel psychoactive substances (NPS), such as synthetic cathinones, that have varying potencies and scheduling. This study demonstrates a combined gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and nuclear magnetic resonance (NMR) spectroscopy approach for the differentiation of N-butyl pentylone isomers based on distinct retention times, characteristic EI mass spectra, and NMR characterization. Retention time reproducibility was assessed from 60 replicate measurements for each isomer over the course of a month. In addition, the effect of the mass spectrometer tune and the stability of an identified characteristic ion ratio using spectral data from ± 1 scan on either side of the peak apex were also statistically assessed using Welch's ANOVA testing. The presence of diastereomers for N-sec-butyl pentylone was identified using the developed GC-EI-MS method, which was confirmed using one-dimensional and two-dimensional NMR spectroscopy. The retention time reproducibility of the chromatographic method was ± 0.076% or less over the course of a month. An identified characteristic ion ratio between the abundance of the fragment ion at m/z 128 and the fragment ion at m/z 72 enabled the differentiation of the four N-butyl pentylone isomers, even when accounting for the effect of the mass spectrometer tune and mass spectral scans used to calculate the characteristic ion ratio. The 95% confidence interval mean abundance ratio of the fragment ions at m/z 128 and m/z 72 was 17.14 ± 0.14 for N-butyl pentylone, 6.44 ± 0.05 for N-isobutyl pentylone, 3.38 ± 0.02 for N-sec-butyl pentylone, and 0.75 ± 0.01 for N-tert-butyl pentylone. These results highlight the capabilities of a combined GC-EI-MS and NMR approach for the differentiation and characterization of synthetic cathinone isomers.

Synthetic Cathinones and Neurotoxicity Risks: A Systematic Review

According to the EU Early Warning System (EWS), synthetic cathinones (SCs) are the second largest new psychoactive substances (NPS) class, with 162 synthetic cathinones monitored by the EU EWS. They have a similar structure to cathinone, principally found in Catha Edulis; they have a phenethylamine related structure but also exhibit amphetamine-like stimulant effects. Illegal laboratories regularly develop new substances and place them on the market. For this reason, during the last decade this class of substances has presented a great challenge for public health and forensic toxicologists. Acting on different systems and with various mechanisms of action, the spectrum of side effects caused by the intake of these drugs of abuse is very broad. To date, most studies have focused on the substances’ cardiac effects, and very few on their associated neurotoxicity. Specifically, synthetic cathinones appear to be involved in different neurological events, including increased alertness, mild agitation, severe psychosis, hyperthermia and death. A systematic literature search in PubMed and Scopus databases according to PRISMA guidelines was performed. A total of 515 studies published from 2005 to 2022 (350 articles from PubMed and 165 from Scopus) were initially screened for eligibility. The papers excluded, according to the criteria described in the Method Section (n = 401) and after full text analyses (n = 82), were 483 in total. The remaining 76 were included in the present review, as they met fully the inclusion criteria. The present work provides a comprehensive review on neurotoxic mechanisms of synthetic cathinones highlighting intoxication cases and fatalities in humans, as well as the toxic effects on animals (in particular rats, mice and zebrafish larvae). The reviewed studies showed brain-related adverse effects, including encephalopathy, coma and convulsions, and sympathomimetic and hallucinogenic toxidromes, together with the risk of developing excited/agitated delirium syndrome and serotonin syndrome.

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 review of synthetic cathinones emerging in recent years (2019-2022)

Purpose

The emergence of novel psychoactive substances (NPS) has been being a continuous and evolving problem for more than a decade. Every year, dozens of new, previously unknown drugs appear on the illegal market, posing a significant threat to the health and lives of their users. Synthetic cathinones are one of the most numerous and widespread groups among NPS. The purpose of this work was to identify and summarize available data on newly emerging cathinones in very recent years.

Methods

Various online databases such as PubMed, Google Scholar, but also databases of government agencies including those involved in early warning systems, were used in search of reports on the identification of newly emerging synthetic cathinones. In addition, threads on various forums created by users of these drugs were searched for reports on the effects of these new substances.

Results

We have identified 29 synthetic cathinones that have been detected for the first time from early 2019 to mid-2022. We described their structures, known intoxication symptoms, detected concentrations in biological material in poisoning cases, as well as the countries and dates of their first appearance. Due to the lack of studies on the properties of the novel compounds, we compared data on the pharmacological profiles of the better-known synthetic cathinones with available information on the newly emerged ones. Some of these new agents already posed a threat, as the first cases of poisonings, including fatal ones, have been reported.

Conclusions

Most of the newly developed synthetic cathinones can be seen as analogs and replacements for once-popular compounds that have been declining in popularity as a result of legislative efforts. Although it appears that some of the newly emerging cathinones are not widely used, they may become more popular in the future and could become a significant threat to health and life. Therefore, it is important to continue developing early warning systems and identifying new compounds so that their widespread can be prevented.

Repeated administration of N-ethyl-pentedrone induces increased aggression and impairs social exploration after withdrawal in mice

N-ethyl-pentedrone (NEPD, 2-(ethylamino)-1-phenyl-1-pentanone) is one of the latest synthetic cathinone derivatives that emerged into the illicit drug market. This drug has psychostimulant properties and has been related with several intoxications and even fatalities. However, information about the consequences of its acute and repeated consumption is lacking. Thus, the aim of our study was to investigate the behavioral effects after both acute and repeated NEPD exposure as well as the neurochemical changes. Male OF1 mice were treated with an acute dose (1, 3 or 10 mg/kg, i.p.) or received repeated injections of these doses (twice/day, 5 days) of NEPD. Shortly after drug-exposure or during drug-withdrawal, anxiety-like behavior, aggressiveness, social interaction, depressive-like symptoms, body weight and temperature were assessed. Also, monoamine synthesis enzymes, levels of neurotransmitters and their precursors and main metabolites, as well as ΔFosB, were determined in striatum and prefrontal cortex from post-mortem tissue. Acute administration of NEPD induced anxiolytic effects and reduced social exploration whereas during withdrawal after repeated administration the anxiolytic effect had vanished, and the reduced social exploration was still present and accompanied with increased aggressive behavior. Moreover, NEPD (10 mg/kg) induced slight hyperthermia and reduced weight gain during the repeated administration, whereas increased locomotor activity and lack of depressive symptoms were found during withdrawal. This was accompanied by increased plasma corticosterone and decrease in striatal dopamine. Finally, the long-lasting and robust increase in ΔFosB levels found in striatum after NEPD chronic exposure suggests a high risk of dependence. The increased aggressivity and locomotor activity, together with this potential of inducing dependence justify a warning about the risks of consumption of NEPD if translated to humans.

Occlusion of the human serotonin transporter is mediated by serotonin-induced conformational changes in the bundle domain

The human serotonin transporter (hSERT) terminates neurotransmission by removing serotonin (5HT) from the synaptic cleft, an essential process for proper functioning of serotonergic neurons. Structures of the hSERT have revealed its molecular architecture in four conformations, including the outward-open and occluded states, and show the transporter's engagement with co-transported ions and the binding mode of inhibitors. In this study, we investigated the molecular mechanism by which the hSERT occludes and sequesters the substrate 5HT. This first step of substrate uptake into cells is a structural change consisting of the transition from the outward-open to the occluded state. Inhibitors such as the antidepressants citalopram, fluoxetine, and sertraline inhibit this step of the transport cycle. Using molecular dynamics simulations, we reached a fully occluded state, in which the transporter-bound 5HT becomes fully shielded from both sides of the membrane by two closed hydrophobic gates. Analysis of 5HT-triggered occlusion showed that bound 5HT serves as an essential trigger for transporter occlusion. Moreover, simulations revealed a complex sequence of steps and showed that movements of bundle domain helices are only partially correlated. 5HT-triggered occlusion is initially dominated by movements of transmembrane helix 1b, while in the final step, only transmembrane helix 6a moves and relaxes an intermediate change in its secondary structure.

Neuropsychopharmacology of Emerging Drugs of Abuse: meta- and para-Halogen-Ring-Substituted α-PVP (“flakka”) Derivatives

Changes in the molecular structure of synthetic cathinones has led to an increase in the number of novel emerging drugs in the illicit drug market at an unprecedented rate. Unfortunately, little is known about the neuropsychopharmacology of recently emerged halogen-substituted α-PVP derivatives. Thus, the aim of this study was to investigate the role of para- and meta-halogen (F-, Cl-, and Br-) substitutions on the in vitro, in silico, and in vivo effects of α-pyrrolidinopentiophenone (α-PVP) derivatives. HEK293 cells expressing the human dopamine or serotonin transporter (hDAT and hSERT) were used for the uptake inhibition and transporter affinity assays. Molecular docking was used to model the interaction mechanism against DAT. Swiss CD-1 mice were used for the horizontal locomotor activity, open field test, and conditioned place preference paradigm. All compounds demonstrated potent DA uptake inhibition and higher DAT selectivity than cocaine. Meta-substituted cathinones showed higher DAT/SERT ratios than their para- analogs, which correlates with an increased psychostimulant effect in vivo and with different meta- and para-in silico interactions at DAT. Moreover, all compounds induced rewarding and acute anxiogenic effects in mice. In conclusion, the present study demonstrates the role of meta- and para-halogen substitutions in the mechanism of action and provides the first evidence of the rewarding and anxiety-like properties of halogenated α-PVP derivatives.

Photoredox-Catalyzed Cascade of o-Hydroxyarylenaminones to Access 3-Aminated Chromones

Reported herein is a photoredox-catalyzed amination of o-hydroxyarylenaminones with tert-butyl ((perfluoropyridin-4-yl)oxy)carbamate, a versatile amidyl-radical precursor developed in our laboratory. This work establishes a new cascade pathway for the assembly of a range of 3-aminochromones under mild conditions. Downstream transformations of the obtained 3-aminochromones to construct diverse amino pyrimidines greatly broaden the applications of this photocatalyzed protocol.

3,4-Methylenedioxy methamphetamine, synthetic cathinones and psychedelics: From recreational to novel psychotherapeutic drugs

The utility of classical drugs used to treat psychiatric disorders (e.g., antidepressants, anxiolytics) is often limited by issues of lack of efficacy, delayed onset of action or side effects. Psychoactive substances have a long history of being used as tools to alter consciousness and as a gateway to approach the unknown and the divinities. These substances were initially obtained from plants and animals and more recently by chemical synthesis, and its consumption evolved toward a more recreational use, leading to drug abuse-related disorders, trafficking, and subsequent banning by the authorities. However, these substances, by modulation of certain neurochemical pathways, have been proven to have a beneficial effect on some psychiatric disorders. This evidence obtained under medically controlled conditions and often associated with psychotherapy, makes these substances an alternative to conventional medicines, to which in many cases the patient does not respond properly. Such disorders include post-traumatic stress disease and treatment-resistant depression, for which classical drugs such as MDMA, ketamine, psilocybin and LSD, among others, have already been clinically tested, reporting successful outcomes. The irruption of new psychoactive substances (NPS), especially during the last decade and despite their recreational and illicit uses, has enlarged the library of substances with potential utility on these disorders. In fact, many of them were synthetized with therapeutic purposes and were withdrawn for concrete reasons (e.g., adverse effects, improper pharmacological profile). In this review we focus on the basis, existing evidence and possible use of synthetic cathinones and psychedelics (specially tryptamines) for the treatment of mental illnesses and the properties that should be found in NPS to obtain new therapeutic compounds.

Interaction Profiles of Central Nervous System Active Drugs at Human Organic Cation Transporters 1-3 and Human Plasma Membrane Monoamine Transporter

Many psychoactive compounds have been shown to primarily interact with high-affinity and low-capacity solute carrier 6 (SLC6) monoamine transporters for norepinephrine (NET; norepinephrine transporter), dopamine (DAT; dopamine transporter) and serotonin (SERT; serotonin transporter). Previous studies indicate an overlap between the inhibitory capacities of substances at SLC6 and SLC22 human organic cation transporters (SLC22A1-3; hOCT1-3) and the human plasma membrane monoamine transporter (SLC29A4; hPMAT), which can be classified as high-capacity, low-affinity monoamine transporters. However, interactions between central nervous system active substances, the OCTs, and the functionally-related PMAT have largely been understudied. Herein, we report data from 17 psychoactive substances interacting with the SLC6 monoamine transporters, concerning their potential to interact with the human OCT isoforms and hPMAT by utilizing radiotracer-based in vitro uptake inhibition assays at stably expressing human embryonic kidney 293 cells (HEK293) cells. Many compounds inhibit substrate uptake by hOCT1 and hOCT2 in the low micromolar range, whereas only a few substances interact with hOCT3 and hPMAT. Interestingly, methylphenidate and ketamine selectively interact with hOCT1 or hOCT2, respectively. Additionally, 3,4-methylenedioxymethamphetamine (MDMA) is a potent inhibitor of hOCT1 and 2 and hPMAT. Enantiospecific differences of R- and S-α-pyrrolidinovalerophenone (R- and S-α-PVP) and R- and S-citalopram and the effects of aromatic substituents are explored. Our results highlight the significance of investigating drug interactions with hOCTs and hPMAT, due to their role in regulating monoamine concentrations and xenobiotic clearance.

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.

Human Neuronal Cell Lines as An In Vitro Toxicological Tool for the Evaluation of Novel Psychoactive Substances

Novel psychoactive substances (NPS) are synthetic substances belonging to diverse groups, designed to mimic the effects of scheduled drugs, resulting in altered toxicity and potency. Up to now, information available on the pharmacology and toxicology of these new substances is very limited, posing a considerable challenge for prevention and treatment. The present in vitro study investigated the possible mechanisms of toxicity of two emerging NPS (i) 4′-methyl-alpha-pyrrolidinoexanophenone (3,4-MDPHP), a synthetic cathinone, and (ii) 2-chloro-4,5-methylenedioxymethamphetamine (2-Cl-4,5-MDMA), a phenethylamine. In addition, to apply our model to the class of synthetic opioids, we evaluated the toxicity of fentanyl, as a reference compound for this group of frequently abused substances. To this aim, the in vitro toxic effects of these three compounds were evaluated in dopaminergic-differentiated SH-SY5Y cells. Following 24 h of exposure, all compounds induced a loss of viability, and oxidative stress in a concentration-dependent manner. 2-Cl-4,5-MDMA activates apoptotic processes, while 3,4-MDPHP elicits cell death by necrosis. Fentanyl triggers cell death through both mechanisms. Increased expression levels of pro-apoptotic Bax and caspase 3 activity were observed following 2-Cl-4,5-MDMA and fentanyl, but not 3,4-MDPHP exposure, confirming the different modes of cell death.

Molecular and clinical aspects of potential neurotoxicity induced by new psychoactive stimulants and psychedelics

New psychoactive stimulants and psychedelics continue to play an important role on the illicit new psychoactive substance (NPS) market. Designer stimulants and psychedelics both affect monoaminergic systems, although by different mechanisms. Stimulant NPS primarily interact with monoamine transporters, either as inhibitors or as substrates. Psychedelic NPS most potently interact with serotonergic receptors and mediate their mind-altering effects mainly through agonism at serotonin 5-hydroxytryptamine-2A (5-HT_2A) receptors. Rarely, designer stimulants and psychedelics are associated with potentially severe adverse effects. However, due to the high number of emerging NPS, it is not possible to investigate the toxicity of each individual substance in detail. The brain is an organ particularly sensitive to substance-induced toxicity due to its high metabolic activity. In fact, stimulant and psychedelic NPS have been linked to neurological and cognitive impairments. Furthermore, studies using in vitro cell models or rodents indicate a variety of mechanisms that could potentially lead to neurotoxic damage in NPS users. Cytotoxicity, mitochondrial dysfunction, and oxidative stress may potentially contribute to neurotoxicity of stimulant NPS in addition to altered neurochemistry. Serotonin 5-HT_2A receptor-mediated toxicity, oxidative stress, and activation of mitochondrial apoptosis pathways could contribute to neurotoxicity of some psychedelic NPS. However, it remains unclear how well the current preclinical data of NPS-induced neurotoxicity translate to humans.

Psychoactive Drugs-From Chemical Structure to Oxidative Stress Related to Dopaminergic Neurotransmission. A Review

Nowadays, more and more young people want to experience illegal, psychoactive substances, without knowing the risks of exposure. Besides affecting social life, psychoactive substances also have an important effect on consumer health. We summarized and analyzed the published literature data with reference to the mechanism of free radical generation and the link between chemical structure and oxidative stress related to dopaminergic neurotransmission. This review presents data on the physicochemical properties, on the ability to cross the blood brain barrier, the chemical structure activity relationship (SAR), and possible mechanisms by which neuronal injuries occur due to oxidative stress as a result of drug abuse such as "bath salts", amphetamines, or cocaine. The mechanisms of action of ingested compounds or their metabolites involve intermediate steps in which free radicals are generated. The brain is strongly affected by the consumption of such substances, facilitating the induction of neurodegenerative diseases. It can be concluded that neurotoxicity is associated with drug abuse. Dependence and oxidative stress are linked to inhibition of neurogenesis and the onset of neuronal death. Understanding the pathological mechanisms following oxidative attack can be a starting point in the development of new therapeutic targets.