Investigation of cathinone analogs targeting human dopamine transporter using molecular modeling

In a step towards understanding the structure-property relationship among Synthetic Cathinones (SCs), a combined methodology based on Density Functional Theory (DFT), Administration, Distribution, Metabolism, Excretion, and Toxicity (ADMET) predictions, docking and molecular dynamics simulations have been applied to correlate physicochemical descriptors of various SCs to their biological activity. The results from DFT and molecular docking studies correlate well with each other explaining the biological activity trends of the studied SCs. Quantum mechanical descriptors viz. polarizability, electron affinity, ionization potential, chemical hardness, electronegativity, molecular electrostatic potential, and ion interaction studies unravel the distinguishingly reactive nature of Group D (pyrrolidine substituted) and Group E (methylenedioxy and pyrrolidine substituted) compounds. According to ADMET analysis, Group D and Group E molecules have a higher probability of permeating through the blood-brain barrier. Molecular docking results indicate that Phe76, Ala77, Asp79, Val152, Tyr156, Phe320, and Phe326 constitute the binding pocket residues of hDAT in which the most active ligands MDPV, MDPBP, and MDPPP are bound. Finally, to validate the derived quantum chemical descriptors and docking results, Molecular Dynamics (MD) simulations are performed with homology-modelled hDAT (human dopamine transporter). The MD simulation results revealed that the majority of SCs remain stable within the hDAT protein's active sites via non-bonded interactions after 100 ns long simulations. The findings from DFT, ADMET analysis, molecular docking, and molecular dynamics simulation studies complement each other suggesting that pyrrolidine-substituted SCs (Group D and E), specifically, MPBP and PVN are proven potent SCs along with MDPV, validating various experimental observations.Communicated by Ramaswamy H. Sarma.

Metabolic profile of N-ethylhexedrone, N-ethylpentedrone, and 4-chloromethcathinone in urine samples by UHPLC-QTOF-HRMS

Forensic laboratories are constantly required to identify new drugs and their metabolites. N-ethylhexedrone (NEH, HEXEN), N-Ethylpentedrone (NEP), and 4-Chloromethcathinone (4-CMC, clephedrone) are synthetic substances structurally related to natural cathinone, alkaloid present in the leaves of the Catha edulis (Khat) plant. These synthetic cathinones (SC) are members of the heterogenous family of new psychoactive substances (NPS) that raised major concerns in scientific and forensic communities over the past years due to their widespread consumption. In this context, we investigated their metabolic profile using of UHPLC-QTOF-HRMS to elucidate the distribution of the parent drug and its metabolites in urine samples over time. Initially, both male and female volunteers were divided into three groups and eight subjects of each group were administered intranasally or orally with one SC (20-40 mg of NEH or NEP intranasal, 100-150 mg of 4-CMC oral). Urine samples were collected at 0-2 and 2-4 or 2-5 h. Urine (50 μL) was diluted 1:2 with acetonitrile/methanol (95:5) and injected into the UHPLC-QTOF-HRMS. Phase-I and phase-II metabolites were identified on the basis of fragmentation patterns and exact masses. Several phase-I and glucuronide-phase-II metabolites were identified in urine samples. Keto group reduction, hydroxylation and dealkylation were the common metabolic pathways identified for all cathinones and the presence of NEH-glucuronide, NEP-glucuronide and 4-CMC-glucuronide was also relevant. Significant is the slower metabolite formation for 4-CMC, which was detected at high concentrations in its original form even 5 h after administration, due to its long half-life and low intrinsic clearance compared to the other SCs. UHPLC-QTOF-HRMS demonstrated a considerable capability to semi-quantify the three synthetic cathinones and identify the target metabolites with high reliability. The introduction of new target compounds improves the efficiency of toxicological screening analysis on real samples and extends the window of detection of the SCs in biological matrices.

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

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

Clinical manifestations and analytical reports for MDPHP acute intoxication cases

MDPHP is a synthetic cathinone (SC) belonging to α-pyrrolidinophenone derivatives. It is a central nervous system stimulant and may induce hallucinations, paranoia, tachycardia, hypertension, chest pain, and rhabdomyolysis. In literature, a few cases of intoxication have been reported. In the present study, 17 cases of MDPHP intake were described including the analytical findings and clinical manifestations. MDPHP was quantified by liquid chromatography-tandem mass spectrometry in blood (range 1.26-73.30 ng/mL) and urine (range 19.31-8769.64 ng/mL) samples. In three cases the presence of α-PHP was observed. In one case, MDPHP was the only detected substance. Concomitant use of MDPHP with other substances, particularly psychostimulants, was common and it was difficult to describe the peculiar clinical characteristics of this SC. Most of the symptoms overlapped those expected, some of them were unusual and all of them particularly severe thus inducing the research of NPS in laboratory tests. We demonstrated the presence of psychiatric, neurological, and respiratory symptoms, as well as the possible presence of rhabdomyolysis and cardiotoxicity associated with the use of MDPHP. ED admissions were also more frequent in patients with addiction problems. In some cases, MDPHP intake required intensive supportive care. A multidisciplinary approach, including specialist consultation, is recommended for patients showing challenging features. Moreover, we demonstrated that the adoption of advanced analytical techniques, i.e., liquid chromatography-tandem mass spectrometry, is necessary to detect these molecules. Further studies are needed to understand MDPHP intake patterns and associated symptoms. It is essential to raise awareness in addiction treatment centers and among potential users, especially young people, and chemsex addicted.

Short- and long-term stability of synthetic cathinones and dihydro-metabolites in human urine samples

PURPOSE

Synthetic cathinones constitute the second largest group of new psychoactive substances, which are often used for recreational purposes and reported in toxicological analysis. Various factors may influence the stability of synthetic cathinones between sampling and analysis, and therefore, stability studies are required to determine the best storage conditions as well as extend the period of detection.

METHODS

This study involved sixteen synthetic cathinones and ten dihydro-metabolites spiked in human urine to evaluate the stability under common storage conditions to imitate real forensic toxicology samples. The samples were stored at either room temperature (22-23 °C) for up to 3 days, refrigerated (4 °C) for up to 14 days or frozen (-40 °C) for up to 12 months, and analyzed in triplicate using a validated liquid chromatography-tandem mass spectrometry method.

RESULTS

Analytes' concentrations decreased over time, although slower when stored frozen. All analytes remained stable (> 80%) for 1 month when stored frozen before losses in content were more apparent for some compounds, depending on their chemical structure. Under all storage conditions, the highest instability was observed for analytes containing halogens (i.e., chlorine or fluorine). Thus, halogenated analytes were further investigated by using liquid chromatography coupled to quadruple time-of-flight mass spectrometry to attempt identifying degradation products.

CONCLUSIONS

Irrespective of parent analytes, dihydro-metabolites had improved stability at each tested temperature, which highlights their importance as appropriate urine biomarkers when retesting is required after a long period of storage.

Metabolism of dipentylone in zebrafish and human liver microsomes determined by liquid chromatography-high resolution mass spectrometry

The consumption of novel psychoactive substances (NPS) is exceedingly prevalent in society, as these substances are sold and distributed as "legal highs." One novel synthetic cathinone emerging in the market is 1-(1,3-benzodioxol-5-yl)-2-(dimethylamino) pentan-1-one (dipentylone). The goal of this work was to study the in vivo and in vitro metabolism of dipentylone in zebrafish and human liver microsomes (HLMs) by liquid chromatography-high resolution mass spectrometry (LC-HRMS). The zebrafish and HLM samples contained 14 dipentylone metabolites, specifically 12 phase Ⅰ metabolites and 2 phase Ⅱ metabolites. The main metabolic pathways included monohydroxylation (M1 and M2), N-dealkylation (M3), hydroxylation of the aromatic ring and dealkoxylation of M3 (M4), O-dealkylation (M5), N-dealkylation of M5 (M6), reduction of carboxide (M7), monohydroxylation of M5 (M8), dehydrogenation (M9), dealkoxylation (M10), N-dealkylation of M10 (M11), dealkoxylation of M9 (M12), glucuronidation of M5 (M13), and sulfation (M14). The monohydroxylated metabolite (M2) can be recommended as metabolic markers for dipentylone. This study is the first to identify a target compound for monitoring the abuse of dipentylone and to determine the essential chemical structure of the metabolites for further toxicological research.

Relative reinforcing effects of dibutylone, ethylone, and N-ethylpentylone: self-administration and behavioral economics analysis in rats

RATIONALE

Following the emergence of methylone as one of the most popular synthetic cathinones, this group of novel psychoactive substance with names ending in "-lone," such as dibutylone, ethylone, and N-ethylpentylone, appeared on the recreational drug market. The pharmacological mechanisms of dibutylone, ethylone, and N-ethylpentylone are well understood; however, to date, the reinforcing effects of dibutylone, ethylone, and N-ethylpentylone are still unclear.

OBJECTIVES

This study aimed to examine the self-administration of dibutylone, ethylone, and N-ethylpentylone relative to methamphetamine (METH) and to quantify their relative reinforcing effectiveness using behavioral economic analysis.

METHODS

Male Sprague-Dawley rats were trained to self-administer METH (0.05 mg/kg) under a fixed-ratio 1 (FR1) schedule. Following the training, dose substitution was used to generate full dose-response curves for METH and the three synthetic cathinones. According to the first doses on the descending limb of the dose-response curves, rats were trained to self-administer METH (0.05 mg/kg), dibutylone (0.1 mg·kg^-1·infusion^-1), ethylone (0.4 mg·kg^-1·infusion^-1), or N-ethylpentylone (0.1 mg·kg^-1·infusion^-1) under an FR1 schedule, and a behavioral economic evaluation of their reinforcing effectiveness was then performed.

RESULTS

Dibutylone, ethylone, and N-ethylpentylone functioned as reinforcers, and the inverted U-shaped dose-response curves were obtained. The rank order of reinforcing potency in this procedure was METH > N-ethylpentylone ≈ dibutylone > ethylone. In the economic analysis, the comparisons of the essential value (EV) transformed from demand elasticity (α) indicated that the rank order of efficacy as reinforcers was METH (EV = 7.93) ≈ dibutylone (EV = 7.81) > N-ethylpentylone (EV = 5.21) ≈ ethylone (EV = 4.19).

CONCLUSIONS

These findings demonstrated that dibutylone, ethylone, and N-ethylpentylone function as reinforcers and have addictive potential, suggesting that the modification of α-alkyl and N-alkyl side chains may affect their reinforcing efficacy.

3F-α-pyrrolydinovalerophenone (3F-α-PVP) in vitro human metabolism: Multiple in silico predictions to assist in LC-HRMS/MS analysis and targeted/untargeted data mining

Synthetic cathinones (SCs) constitute a heterogenous class of new psychoactive substances (NPS), structurally related to cathinone. SCs represent the widest NPS class, second to synthetic cannabinoids, accounting for approximately 160 different analogues with substitution at the phenyl group, the amine group, or the alkyl chain. In 2020, α-pyrrolidonophenone analogues were the most trafficked SCs, and were involved in many fatalities and intoxication cases. In particular, 3F-α-pyrrolidinovalerophenone (3F-α-PVP) was the cause of the highest number of SC-related fatal intoxications in Sweden in 2018. Minor structural modifications are used to avoid legal controls and analytical detection, but may also induce different toxicological profile. Therefore, the identification of specific markers of consumption is essential to discriminate SCs in clinical and forensic toxicology. In this study, we assessed 3F-α-PVP metabolic profile. 3F-α-PVP was incubated with 10-donor-pooled human hepatocytes, LC-HRMS/MS analysis, and software-assisted data mining. This well-established workflow was completed by in silico metabolite predictions using three different freeware. Ten metabolites were identified after 3 h incubation, including hydrogenated, hydroxylated, oxidated, and N-dealkylated metabolites. A total of 51 phase I and II metabolites were predicted, among which 7 were detected in the incubations. We suggest 3F-α-PVP N-butanoic acid, 3F-α-PVP pentanol, and 3F-α-PVP 2-ketopyrrolidinyl-pentanol as specific biomarkers of 3F-α-PVP consumption. This is the first time that an N-ethanoic acid is detected in the metabolic pathway of a pyrrolidine SC, demonstrating the importance of a dual targeted/untargeted data mining strategy.

MDPV self-administration in female rats: influence of reinforcement history

RATIONALE

A subset of male rats that self-administer 3,4-methylenedioxypyrovalerone (MDPV) have unusually high levels of drug intake; however, factor(s) that influence this behavior (e.g., reinforcement history and sex) are unknown.

OBJECTIVES

Characterize the reinforcing potency and effectiveness of MDPV in female rats to determine whether (1) a subset of females also develop high levels of MDPV self-administration (i.e., a high-responder phenotype) and (2) the degree to which the high-responder phenotype is influenced by various reinforcement histories (i.e., responding for cocaine or food).

METHODS

Female Sprague Dawley rats initially responded for MDPV (0.032 mg/kg/infusion), cocaine (0.32 mg/kg/infusion), or food (45-mg grain pellet) under fixed ratio (FR) 1 and FR5 schedules of reinforcement. After 20 sessions, the cocaine- and food-history rats responded for MDPV for 20 additional sessions. Dose-response curves for MDPV were generated under FR5 and progressive ratio (PR) schedules of reinforcement.

RESULTS

A subset of rats responding for MDPV developed high levels of MDPV intake. A history of responding for cocaine, but not food, inhibited the development of high levels of MDPV intake. Large individual differences were observed in the level of self-administration when MDPV was available under an FR5, but not PR, schedule of reinforcement.

CONCLUSIONS

MDPV functions as a powerful reinforcer in female rats, as has been previously reported in male rats. The substantial variability in MDPV self-administration between subjects may be related to individual differences in human drug-taking behavior.

Synthetic drugs of abuse

Synthetic drugs of abuse contain various psychoactive substances. These substances have recently emerged as novel drugs of abuse in public; thus, they are known as novel psychoactive substances (NPS). As these compounds are artificially synthesized in a laboratory, they are also called designer drugs. Synthetic cannabinoids and synthetic cathinones are the two primary classes of NPS or designer drugs. Synthetic cannabinoids, also known as "K2" or "Spice," are potent agonists of the cannabinoid receptors. Synthetic cathinones, known as "Bath salts," are beta-keto amphetamine derivatives. These compounds can cause severe intoxication, including overdose deaths. NPS are accessible locally and online. NPS are scheduled in the US and other countries, but the underground chemists keep modifying the chemical structure of these compounds to avoid legal regulation; thus, these compounds have been evolving rapidly. These drugs are not detectable by traditional drug screening, and thus, these substances are mainly abused by young individuals and others who wish to avoid drug detection. These compounds are analyzed primarily by mass spectrometry.

Drinking to death: Hyponatraemia induced by synthetic phenethylamines

Synthetic phenethylamines are widely abused drugs, comprising new psychoactive substances such as synthetic cathinones, but also well-known amphetamines such as methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). Cathinones and amphetamines share many toxicodynamic mechanisms. One of their potentially life-threatening consequences, particularly of MDMA, is serotonin-mediated hyponatraemia. Herein, we review the state of the art on phenethylamine-induced hyponatremia; discuss the mechanisms involved; and present the preventive and therapeutic measures. Hyponatraemia mediated by phenethylamines results from increased secretion of antidiuretic hormone (ADH) and consequent kidney water reabsorption, additionally involving diaphoresis and polydipsia. Data for MDMA suggest that acute hyponatraemia elicited by cathinones may also be a consequence of metabolic activation. The literature often reveals hyponatraemia-associated complications such as cerebral oedema, cerebellar tonsillar herniation and coma that may evolve to a fatal outcome, particularly in women. Ready availability of fluids and the recommendation to drink copiously at the rave scene to counteract hyperthermia, often precipitate water intoxication. Users should be advised about the importance of controlling fluid intake while using phenethylamines. At early signs of adverse effects, medical assistance should be promptly sought. Severe hyponatraemia (<130 mmol sodium/L plasma) may be corrected with hypertonic saline or suppression of fluid intake. Also, clinicians should be made aware of the hyponatraemic potential of these drugs and encouraged to report future cases of toxicity to increase knowledge on this potentially lethal outcome.

Seizures of illicit substances for personal use in two Italian provinces: analysis of trends by type and purity from 2008 to 2017

BACKGROUND

The use of illicit substances represents one of the most difficult problems to confront in the health system. Drug use is a global problem but is not uniform throughout the world, within the same country and changes over time. Therefore, knowing the illicit substances that are used in a territory is essential to better organize health services in that specific geographical area. To this aim, we analysed 4200 samples confiscated from individuals who held them for personal use by police forces in the Italian provinces of Modena and Reggio Emilia from 2008 to 2017.

METHODS

The suspected samples were screened by gas-chromatography-mass spectrometry (GC-MS) and by liquid chromatography-tandem mass spectrometry (LC-MS/MS); all samples were subsequently analysed by gas chromatography-flame ionization detector (GC-FID) for quantitative analyses.

RESULTS

Cannabis was the most seized illicit substance (70.7%). Over the study period, the number of seizures of herb with a high content of Δ⁹-THC increased. The number of cocaine seizures remained stable (total 16.1%), but the median purity of seized cocaine increased to 75% in 2017. Heroin seizures decreased over time, but the median purity of seized heroin reached 16.8% in 2017. In almost all the years, heroin samples with a purity exceeding the 97.5 percentile were found. Especially from 2014, the range of seized substances increased and started to include synthetic cathinones, phenylethylamines, UR-144, LSD, psilocybe, prescription opioid and hypnotics. In two cases, tramadol together with tropicamide was seized. Most of the seizures involved male subjects and 82% of the seizures were from individuals younger than 35 years of age.

CONCLUSIONS

The persistence of old illicit drugs and the rapid emergence of new psychoactive substances represented a serious challenge for public health in the studied Italian area. Some useful interventions might be: informing mainly young people about the possible complications of cannabis use; implementing standardized procedures to diagnose and treat cocaine-related emergencies in hospitals; increasing the distribution of naloxone to antagonize possible heroin overdoses; equipping laboratories to be able to identify the new psychoactive substances.

The new psychoactive substance 3-methylmethcathinone (3-MMC or metaphedrone) induces oxidative stress, apoptosis, and autophagy in primary rat hepatocytes at human-relevant concentrations

3-Methylmethcathinone (3-MMC or metaphedrone) has become one of the most popular recreational drugs worldwide after the ban of mephedrone, and was recently deemed responsible for several intoxications and deaths. This study aimed at assessing the hepatotoxicity of 3-MMC. For this purpose, Wistar rat hepatocytes were isolated by collagenase perfusion, cultured and exposed for 24 h at a concentration range varying from 31 nM to 10 mM 3-MMC. The modulatory effects of cytochrome P450 (CYP) inhibitors on 3-MMC hepatotoxicity were evaluated. 3-MMC-induced toxicity was perceived at the lysosome at lower concentrations (NOEC 312.5 µM), compared to mitochondria (NOEC 379.5 µM) and cytoplasmic membrane (NOEC 1.04 mM). Inhibition of CYP2D6 and CYP2E1 diminished 3-MMC cytotoxicity, yet for CYP2E1 inhibition this effect was only observed for concentrations up to 1.3 mM. A significant concentration-dependent increase of intracellular reactive species was observed from 10 μM 3-MMC on; a concentration-dependent decrease in antioxidant glutathione defences was also observed. At 10 μM, caspase-3, caspase-8, and caspase-9 activities were significantly elevated, corroborating the activation of both intrinsic and extrinsic apoptosis pathways. Nuclear morphology and formation of cytoplasmic acidic vacuoles suggest prevalence of necrosis and autophagy at concentrations higher than 10 μM. No significant alterations were observed in the mitochondrial membrane potential, but intracellular ATP significantly decreased at 100 μM. Our data point to a role of metabolism in the hepatotoxicity of 3-MMC, which seems to be triggered both by autophagic and apoptotic/necrotic mechanisms. This work is the first approach to better understand 3-MMC toxicology.

Effects of unconventional recreational drug use in pregnancy

Recreational drug toxicity is a rapidly evolving aspect in clinical practice. The prevalence of recreational drug abuse in the past decade has achieved an epidemic scale due to invention of new agents and ease of accessibility to the abused drugs. "Unconventional recreational drugs" is the term that includes new psychoactive drugs and medications diverted for recreational goals. Misuse of unconventional recreational drugs during pregnancy can affect both the pregnant woman and the fetus. However, the problems are usually unrecognized and overlooked by healthcare professionals. In this articles, obstetric complications, teratogenicity and neonatal abstinence syndrome from exposure during pregnancy to synthetic cannabinoids, synthetic cathinones, tramadol, kratom, olanzapine, quetiapine, ketamine and ketamine are reviewed. The main purpose is to create awareness about maternal, fetal and neonatal effects of these unconventional recreational drugs, so healthcare professionals will have improved vigilance for these under-recognized issues.

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.

Effects of cocaine on the discriminative stimulus and reinforcing effects of mephedrone in male rats

RATIONALE

Abuse of cathinones has been a worldwide health concern for some time. Their chemical structures and wide variation in pharmacodynamic effects have led to clinical and preclinical effects that can be both similar to and different from other psychoactive substances such as methylenedioxymethamphetamine (MDMA), methamphetamine, and cocaine.

OBJECTIVE

The present study examined the discriminative stimulus and reinforcing effects of mephedrone to further characterize the behavioral and pharmacological profile of this first-generation substituted methcathinone.

METHODS

Rats were trained to discriminate mephedrone (3.2 mg/kg) from saline under a fixed-ratio 20 (FR-20) schedule of food presentation. After establishing dose-effect curves for increasing cumulative doses of mephedrone, substitution tests were conducted with bupropion (5.6-32 mg/kg), cocaine (1.8-18 mg/kg), morphine (0.56-10 mg/kg), and amitriptyline (3.2-32 mg/kg). In addition, cocaine (3.2-18 mg/kg) and the serotonin type-2 (5-HT2) receptor antagonist ritanserin (1, 3.2, and 10 mg/kg) were administered prior to the cumulative doses of mephedrone. Lastly, varying infusion doses of cocaine were substituted for mephedrone in subjects trained to self-administer mephedrone, and varying infusion doses of mephedrone were substituted for cocaine in subjects trained to self-administer cocaine to assess the importance of drug history on the reinforcing effects of mephedrone.

RESULTS

Of the drugs tested, cocaine had the highest level of mephedrone-lever responding when administered alone (73.5%). In combination with mephedrone, cocaine shifted the mephedrone dose-effect curve upwards in an infra-additive manner. Ritanserin had a small, but non-significant, effect on mephedrone's discriminative stimulus effects. An extensive history (baseline) of cocaine self-administration increased mephedrone self-administration compared to that obtained in mephedrone-trained subjects, whereas a baseline of mephedrone self-administration decreased cocaine self-administration compared to that obtained in cocaine-trained subjects.

CONCLUSION

The similarity between the discriminative stimulus effects of cocaine and mephedrone in male rats suggests an important overlap and the relative importance of the dopamine (DAT) and serotonin (SERT) transporters. The self-administration data suggest that mephedrone is less reinforcing than cocaine, but that a history of responding for cocaine can increase the reinforcing effects of mephedrone.

Novel complication of Flakka: Stevens-Johnson syndrome/Toxic epidermal necrolysis overlap

Flakka, as the newest member of the synthetic cathinone group, is a substance with serious cardiovascular, neurological, psychiatric, infectious effects and addictive potential. There are only a few case reports and laboratory studies in the literature and there is no dermatological side effects reported yet. We present the first Stevens-Johnson syndrome/Toxic epidermal necrolysis (SJS/TEN) overlap case after Flakka use.

Neurocognitive dysfunction following repeated binge-like self-administration of the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV)

Synthetic cathinones, frequently referred to as "bath salts", have significant abuse potential, and recent evidence suggests that these novel psychoactive substances can also produce cognitive deficits as well as cytotoxic effects. However, most of these latter findings have been obtained either using high concentrations in vitro or following non-contingent high dose administration in vivo. The present study utilized a model of long-term voluntary binge-like self-administration to determine potential detrimental effects of synthetic cathinones on cognitive function and their known underlying neural circuits, collectively referred to as neurocognitive dysfunction. Male Sprague-Dawley rats were allowed to self-administer the cocaine-like synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV, 0.03 mg/kg/infusion i.v.) in 96-hr sessions, or saline as a control. A total of five 96-hr sessions were conducted, each separated by 3 days of abstinence in the home cage. Three weeks following the last 96-hr session, animals underwent assessment of cognitive function using spatial object recognition (SOR) and novel object recognition (NOR) tasks, after which brains were harvested and assessed for neurodegeneration using FluoroJade C (FJC). Compared to animals self-administering saline, animals self-administering MDPV demonstrated (1) robust drug intake that escalated over time, (2) deficits in NOR but not SOR, and (3) neurodegeneration in the perirhinal and entorhinal cortices. These results indicate that repeated binge-like intake of MDPV can induce neurocognitive dysfunction. In addition, utilization of rodent models of extended binge-like intake may provide insight into potential mechanisms and/or approaches to prevent or reverse the detrimental effects of abused substances on cognitive and neurobiological functioning. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Evaluation of training dose in male Sprague-Dawley rats trained to discriminate 4-methylmethcathinone

RATIONALE

Although the synthetic cathinone 4-methylmethcathinone (4-MMC, mephedrone) has been a subject of intensive research investigation, the pharmacological mechanisms involved in its interoceptive stimulus effects have yet to be fully characterized.

OBJECTIVE

The present study employed drug discrimination methods in rats to compare the interoceptive stimulus properties of two different training doses of 4-MMC to other substances with similar pharmacological actions.

METHODS

Sixteen male Sprague-Dawley rats were trained to discriminate either 1.0 mg/kg (N = 8) or 3.0 mg/kg (N = 8) 4-MMC from saline. Substitution tests were conducted with drugs that increase extracellular monoamine levels (d-amphetamine, (+)-methamphetamine, 4-MMC, MDMA, MDPV, and (-)-cocaine), a serotonin releaser (+)-fenfluramine, and a serotonergic (5-HT_2A) hallucinogen (+)-LSD.

RESULTS

Stimulus control was established in fewer sessions in the subjects trained with 3.0 mg/kg compared to those trained with 1.0 mg/kg 4-MMC. Cocaine, MDMA, and d-amphetamine produced full substitution in the 1.0 mg/kg 4-MMC-trained rats at doses that did not decrease response rate. However, doses of test drugs that engendered > 80% 4-MMC-lever selection concurrently produced rate-decreasing effects in rats trained to discriminate 3.0 mg/kg 4-MMC.

CONCLUSIONS

These findings further characterize the interoceptive stimulus effects of 4-MMC and indicate that these effects vary little with training dose; however, qualitative differences in substitutability of test drugs were observed between training groups. This study expands existing knowledge regarding the psychopharmacology of 4-MMC and the potential neurochemical substrates contributing to its subjective effects.

Role of hypocretin/orexin receptor blockade on drug-taking and ultrasonic vocalizations (USVs) associated with low-effort self-administration of cathinone-derived 3,4-methylenedioxypyrovalerone (MDPV) in rats

RATIONALE

Synthetic psychostimulant abuse, including cathinone-derived 3,4-methylenedioxypyrovalerone (MDPV), continues to increase in many countries. Similar to cocaine but with greater potency, MDPV elicits a transient sympathomimetic response by blocking cellular uptake of dopamine (DA) and norepinephrine (NE)-administration in some users is reported as euphoria-inducing much like cocaine and amphetamine. Pharmacological agents that disrupt excitatory transmission onto midbrain DA-producing neurons, including hypothalamic hypocretin/orexin (hcrt/ox) receptor antagonists, present attractive targets to aide abstinence maintenance by reducing psychostimulant-associated reward and reinforcement.

OBJECTIVE

The present study sought to assess the degree to which suvorexant, a dual hcrt/ox receptor antagonist, influences drug-taking as well as ultrasonic vocalizations (USVs) associated with MDPV self-administration.

METHODS

Rats were trained to self-administer MDPV (~0.03 mg/kg/inf, 3-s) for 14 days under a fixed-ratio 1 schedule of reinforcement, and effects of suvorexant (0, 3, 10, 30 mg/kg, i.p.) on drug-taking was assessed. USVs were recorded during a 30-min pre-lever period as well as during 2-h of MDPV self-administration.

RESULTS

We observed that suvorexant modestly suppressed the number of MDPV infusions earned. Notably, we observed that suvorexant reduced 50-kHz USVs associated with pre- and post-lever time-points but did not noticeably alter call type profiles. Upon comparison of the two measures, we observed trending positive associations between suvorexant-induced changes in drug-taking and 50-kHz USVs.

CONCLUSIONS

Results from this exploratory study provide support for the following: (1) studying how suvorexant may provide benefit to humans with stimulant use disorders, (2) identifying a potential role for orexin transmission in cathinone abuse, and (3) further interrogating the potential utility of rat USVs to predict drug consumption in preclinical models of substance use disorders.

Glutamate carboxypeptidase II (GCPII) inhibitor 2-PMPA reduces rewarding effects of the synthetic cathinone MDPV in rats: a role for N-acetylaspartylglutamate (NAAG)

RATIONALE

Metabotropic glutamate 2 and 3 (mGluR2/3) receptors are implicated in drug addiction as they limit excessive glutamate release during relapse. N-acetylaspartylglutamate (NAAG) is an endogenous mGluR2/3 agonist that is inactivated by the glutamate carboxypeptidase II (GCPII) enzyme. GCPII inhibitors, and NAAG itself, attenuate cocaine-seeking behaviors. However, their effects on the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) have not been examined.

OBJECTIVES

We determined whether withdrawal following repeated MDPV administration alters GCPII expression in corticolimbic regions. We also examined whether a GCPII inhibitor (2-(phosphonomethyl)-pentanedioic acid (2-PMPA)), and NAAG, reduce the rewarding and locomotor-stimulant effects of MDPV in rats.

METHODS

GCPII was assessed following repeated MDPV exposure (7 days). The effects of 2-PMPA and NAAG on acute MDPV-induced hyperactivity were determined using a locomotor test. We also examined the inhibitory effects of 2-PMPA and NAAG on MDPV-induced place preference, and whether the mGluR2/3 antagonist LY341495 could prevent these effects.

RESULTS

MDPV withdrawal reduced GCPII expression in the prefrontal cortex. Systemic injection of 2-PMPA (100 mg/kg) did not affect the hyperactivity produced by MDPV (0.5-3 mg/kg). However, nasal administration of NAAG did reduce MDPV-induced ambulation, but only at the highest dose (500 μg/10 μl). We also showed that 2-PMPA (10-30 mg/kg) and NAAG (10-500 μg/10 μl) dose-dependently attenuated MDPV place preference, and that the effect of NAAG was blocked by LY341495 (3 mg/kg).

CONCLUSIONS

These findings demonstrate that MDPV withdrawal produces dysregulation in the endogenous NAAG-GCPII signaling pathway in corticolimbic circuitry. Systemic administration of the GCPII inhibitor 2-PMPA, or NAAG, attenuates MDPV reward.

α-Pyrrolidinononanophenone provokes apoptosis of neuronal cells through alterations in antioxidant properties

In this study, we found that exposure to α-pyrrolidinononanophenone (α-PNP), a highly lipophilic synthetic cathinone, provokes apoptosis of human neuronal SK-N-SH cells. The drug sensitivity of the cells (50% lethal concentration of 12μM) was similar to those of aortic endothelial and smooth muscle cells, and was higher than those of cells derived from colon, liver, lung and kidney, suggesting that α-PNP overdose and abuse cause serious damage in central nervous and vascular systems. SK-N-SH cell treatment with lethal concentrations (20 and 50μM) of α-PNP facilitated the reactive oxygen species (ROS) production. The treatment also prompted elevation of Bax/Bcl-2 ratio, lowering of mitochondrial membrane potential, release of cytochrome-c into cytosol, and resultant activation of caspase-9 and caspase-3. The apoptotic events (caspase-3 activation and DNA fragmentation) were abolished by pretreatment with antioxidants, N-acetyl-l-cysteine and polyethyleneglycol-conjugated catalase. These results suggest that ROS production, mitochondrial dysfunction and caspase activation are potential events in the mechanism underlying the α-PNP-triggered neuronal cell apoptosis. Intriguingly, the α-PNP treatment of SK-N-SH cells was found to promote formation of 4-hydroxynonenal, a reactive aldehyde generated from lipid peroxidation. The α-PNP treatment also decreased cellular levels of total and reduced glutathiones, expression of γ-glutamylcysteine synthetase mRNA and glutathione reductase activity. Furthermore, the α-PNP treatment resulted in both decrease in proteasomal activities and increase in expression of autophagy-related factors, which were significantly prevented by pretreating with N-acetyl-l-cysteine. Therefore, the ROS formation by α-PNP treatment may be ascribable to the decrease in glutathione level through its consumption during 4-hydroxynonenal detoxification and dysfunction of both de novo synthesis and regeneration of glutathione, in addition to impairments in proteasomal and autophagic systems that degrade cellular oxidized components.

Substance Use, Intoxication, and Withdrawal in the Critical Care Setting

Substance use is common among individuals admitted to the critical care setting and may complicate treatment of underlying disorders. Management issues include the effects of intoxication as well as the risk posed by substance-withdrawal syndromes in patients being treated for critical illness. This article reviews the epidemiology of substance use in this population and the identification and treatment of common intoxication and withdrawal syndromes. The authors stress the importance of long-term planning as part of the overall treatment protocol beyond the acute presentation.

Self-administration and behavioral economics of second-generation synthetic cathinones in male rats

RATIONALE

Synthetic cathinones have become increasingly available as drugs of abuse. Distribution of these drugs is made possible by altering the chemical structures of prohibited cathinones and marketing them under misleading labels. Very little is known about the relative reinforcing effectiveness of new synthetic cathinones relative to known drugs of abuse.

OBJECTIVE

We examined self-administration of three second-generation synthetic cathinones: alpha-pyrrolidinopentiophenone (alpha-PVP), 4-methyl-N-ethylcathinone (4-MEC), and 4-methyl-alpha-pyrrolidinopropiophenone (4-MePPP) relative to methamphetamine.

METHOD

Male, Sprague-Dawley rats, implanted with intravenous catheters, were trained to self-administer methamphetamine (0.05 mg/kg/injection) under a fixed-ratio schedule. Following training, various doses of methamphetamine (0.006-0.1 mg/kg/injection), alpha-PVP (0.0015-0.1 mg/kg/injection), 4-MEC (0.1-3.2 mg/kg/injection), or 4-MePPP (0.1-0.8 mg/kg/injection) were available for self-administration in separate groups, followed by a behavioral-economics evaluation of the reinforcing effectiveness of each drug.

RESULTS

For all drugs, at least one dose functioned as a reinforcer. Alpha-PVP and 4-MePPP maintained the highest numbers of infusions per session and both were more effective reinforcers relative to methamphetamine. 4-MEC and methamphetamine were not significantly different in terms of infusions per session or reinforcing effectiveness.

CONCLUSION

Emerging synthetic cathinones whose primary pharmacological mechanism is to block dopamine uptake but with little effects on monoamine release or serotonin uptake may have a greater degree of abuse potential compared with known abused stimulants.

Successful quantification of 4'-methyl-α-pyrrolidinohexanophenone (MPHP) in human urine using LC-TOF-MS in an autopsy case

The toxicological detection of the new synthetic cathinone 4′-methyl-α-pyrrolidinohexanophenone (MPHP) in urine samples has been impossible, because much of MPHP is metabolized before its excretion into urine. In this study, we successfully quantified unmetabolized MPHP in urine of an autopsy case using a sensitive method by liquid chromatography–time-of-flight-mass spectrometry. The quantification method showed good linearity in the range of 1.00–100 ng/mL, and the limit of detection was 0.5 ng/mL in human urine. In the autopsy case, the concentrations of MPHP in urine, plasma, and liver tissue samples were determined to be 60.1, 32.9 ng/mL, and 63.1 ng/g, respectively.

Bath salts and synthetic cathinones: an emerging designer drug phenomenon

Synthetic cathinones are an emerging class of designer drugs abused for psychostimulant and hallucinogenic effects similar to cocaine, methylenedioxymethamphetamine (MDMA), or other amphetamines. Abuse of synthetic cathinones, frequently included in products sold as 'bath salts', became prevalent in early 2009, leading to legislative classification throughout Europe in 2010 and schedule I classification within the United States in 2011. Recent pre-clinical and clinical studies indicate that dysregulation of central monoamine systems is a principal mechanism of synthetic cathinone action and presumably underlie the behavioral effects and abuse liability associated with these drugs. This review provides insight into the development of synthetic cathinones as substances of abuse, current patterns of their abuse, known mechanisms of their action and toxicology, and the benefits and drawbacks of their classification.

Mephedrone: Public health risk, mechanisms of action, and behavioral effects

The recent shortage of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) has led to an increased demand for alternative amphetamine-like drugs such as the synthetic cathinone, 4-methylmethcathinone (mephedrone). Despite the re-classification of mephedrone as a Class B restricted substance by the United Kingdom and restrictive legislation by the United States, international policy regarding mephedrone control is still developing and interest in synthetic amphetamine-like drugs could drive the development of future mephedrone analogues. Currently, there is little literature investigating the mechanism of action and long-term effects of mephedrone. As such, we reviewed the current understanding of amphetamines, cathinones, and cocaine emphasizing the potentially translational aspects to mephedrone, as well as contrasting with the work that has been done specifically on mephedrone in order to present the current state of understanding of mephedrone in terms of its risks, mechanisms, and behavioral effects. Emerging research suggests that while there are structural and behavioral similarities of mephedrone with amphetamine-like compounds, it appears that serotonergic signaling may mediate more of mephedrone's effects unlike the more dopaminergic dependent effects observed in traditional amphetamine-like compounds. As new designer drugs are produced, current and continuing research on mephedrone and other synthetic cathinones should help inform policymakers' decisions regarding the regulation of novel 'legal highs.'