Psychostimulant-like effects of p-fluoroamphetamine in the rat

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI): From an Obscure to Pivotal Member of the DOX Family of Serotonergic Psychedelic Agents - A Review

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI, or DOX where X = -I) was first synthesized in 1973 in a structure-activity study to explore the effect of various aryl substituents on the then newly identified, and subsequently controlled, hallucinogenic agent 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM, or DOX where X = -CH3). Over time, DOI was found to be a serotonin (5-HT) receptor agonist using various peripheral 5-HT receptor tissue assays and later, following the identification of multiple families of central 5-HT receptors, an agonist at 5-HT2 serotonin receptors in rat and, then, human brain. Today, classical hallucinogens, currently referred to as serotonergic psychedelic agents, are receiving considerable attention for their potential therapeutic application in various neuropsychiatric disorders including treatment-resistant depression. Here, we review, for the first time, the historical and current developments that led to DOI becoming a unique, perhaps a landmark, agent in 5-HT2 receptor research.

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.

Beyond ecstasy: Alternative entactogens to 3,4-methylenedioxymethamphetamine with potential applications in psychotherapy

The last two decades have seen a revival of interest in the entactogen 3,4-methylenedioxy-N-methylamphetamine (MDMA) as an adjunct to psychotherapy, particularly for the treatment of post-traumatic stress disorder. While clinical results are highly promising, and MDMA is expected to be approved as a treatment in the near future, it is currently the only compound in its class of action that is being actively investigated as a medicine. This lack of alternatives to MDMA may prove detrimental to patients who do not respond well to the particular mechanism of action of MDMA or whose treatment calls for a modification of MDMA's effects. For instance, patients with existing cardiovascular conditions or with a prolonged history of stimulant drug use may not fit into the current model of MDMA-assisted psychotherapy, and could benefit from alternative drugs. This review examines the existing literature on a host of entactogenic drugs, which may prove to be useful alternatives in the future, paying particularly close attention to any neurotoxic risks, neuropharmacological mechanism of action and entactogenic commonalities with MDMA. The substances examined derive from the 1,3-benzodioxole, cathinone, benzofuran, aminoindane, indole and amphetamine classes. Several compounds from these classes are identified as potential alternatives to MDMA.

The potent psychomotor, rewarding and reinforcing properties of 3-fluoromethamphetamine in rodents

3-fluoromethamphetamine (3-FMA), a derivative of methamphetamine (METH), produces behavioral impairment and deficits in dopaminergic transmission in the striatum of mice. The abuse potential of 3-FMA has not been fully characterized. The aim of this study was to evaluate the effects of 3-FMA on locomotor activity as well as its rewarding and reinforcing properties in the conditioned place preference (CPP) and self-administration procedures. Intravenous (i.v.) administration of 3-FMA (0.5 and 1.0 mg/kg) significantly increased locomotor activity in a dose-dependent manner in rats. In the CPP procedure, intraperitoneal administration of 3-FMA (10 and 30 mg/kg) produced a significant alteration in place preference in mice. In the self-administration paradigms, 3-FMA showed drug-taking behavior at the dose of 0.1 mg/kg/infusion (i.v.) during 2 hr sessions under fixed ratio schedules and high breakpoints at the dose of 0.3 and 1.0 mg/kg/infusion (i.v.) during 6 hr sessions under progressive ratio schedule of reinforcement in rats. A priming injection of 3-FMA (0.4 mg/kg, i.v.), METH (0.2 mg/kg, i.v.), or cocaine (2.0 mg/kg, i.v.) reinstated 3-FMA-seeking behavior after an extinction period in 3-FMA-trained rats during 2 hr session. Taken together, these findings demonstrate robust psychomotor, rewarding and reinforcing properties of 3-FMA, which may underlie its potential for compulsive use in humans.

Chiral Serum Pharmacokinetics of 4-Fluoroamphetamine after Controlled Oral Administration: Can (R)/(S) Concentration Ratios Help in Interpreting Forensic Cases?

Over the last two decades, misuse of 4-fluoroamphetamine (4-FA) became an emerging issue in many European countries. Stimulating effects last for 4-6 hours and can impact psychomotor performance. The metabolism of amphetamine-type stimulants is stereoselective and quantification of (R)- and (S)-enantiomers has been suggested for assessing time of use. To date no data on enantioselective pharmacokinetics is available for 4-FA in serum samples. An enantioselective liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed using a chiral Phenomenex® Lux 3 μm AMP column. Validation of the method showed satisfactory selectivity, sensitivity, linearity (0.5-250 ng/mL), precision and accuracy. Recreational stimulant users orally ingested two doses (100 mg, n=12, and 150 mg, n=5) of 4-FA. Blood samples were drawn prior to application and over a period of 12 hours after ingestion and analyzed for 4-FA enantiomers. Peak concentrations and corresponding times did not differ significantly between the enantiomers (mean (R)/(S)-ratio at tmax 1.05, 0.85-1.16). With mean 12.9 (8.3-16.1) hours, apparent elimination half-lives (t1/2) were significantly (p < 0.01) longer for (R)-4-FA than for (S)-4-FA (6.0 hours; range 4.4-10.2 hours) and independent of the dose given. Over time, (R)/(S)-concentration-ratios were linearly increasing in all subjects to maximum ratios of 2.00 (1.08-2.77) in the last samples (after 12 hours). The slopes of the (R)/(S)-ratio exhibited marked inter-individual differences (0.023 to 0.157 h-1, mean 0.095 h-1). Ratios higher than 1.60 only appeared earliest after a minimum of 6 hours and therefore suggest the absence of acute drug effects. Different elimination half-lives of enantiomers lead to constantly increasing (R)/(S)-concentration-ratios. Consequently, ratios of 4-FA enantiomers in serum are a promising indicator for assessment of the time of drug consumption.

Novel halogenated synthetic cannabinoids impair sensorimotor functions in mice

JWH-018-Cl, JWH-018-Br and AM-2201 (JWH-018 halogenated-derivatives; JWH-018-R compounds) are synthetic cannabinoid agonists illegally marketed as "Spice", "K2", "herbal blend" and research chemicals for their cannabis-like psychoactive effects. In rodents, JWH-018 and its halogenated derivatives reproduce the typical effects of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), i.e. hypothermia, analgesia, hypolocomotion and akinesia. Yet, the effects of JWH-018-R compounds on sensorimotor functions are still unknown. This study was designed to investigate the effect of an acute intraperitoneal (i.p.) administration of JWH-018-R compounds (0.01-6 mg/kg) on sensorimotor functions in mice and to compare them to those caused by the reference compound JWH-018 and Δ⁹-THC. A well validated battery of behavioral tests was used to investigate the effects of these synthetic cannabinoids on the visual, auditory and tactile responses in mice, while the pre-pulse inhibition (PPI) test was used to investigate their effect on sensorimotor gating. The effect of the synthetic cannabinoids on spontaneous locomotion was also measured by a video tracking analysis to assess potential cannabinoid-induced motor impairment. Results showed that, similarly to JWH-018, systemic administration of JWH-018-R compounds inhibits sensorimotor and PPI responses at lower doses (0.01-0.1 mg/kg) and reduced spontaneous locomotion at intermediate/high doses (1-6 mg/kg). All effects were prevented by the administration of the selective cannabinoid CB₁ receptor antagonist/inverse agonist AM-251 thus confirming a CB₁ receptor-mediated action. Finding that lower doses of JWH-018-R compounds selectively impair sensorimotor and PPI responses without affecting locomotion should be carefully considered to better understand the potential danger that halogenated-derivatives of JWH-018 may pose to public health, with particular reference to decreased performance in driving and hazardous works.

Independent elevation of peripheral oxytocin concentrations and reduction in cognitive empathy during 4-fluoroamphetamine intoxication

OBJECTIVES

4-Fluoroamphetamine (4-FA) is a novel psychoactive substance with a pharmacological profile and reported subjective effects (e.g., empathy) intermediate between 3,4-methylenedioxymethamphetamine (MDMA) and amphetamine. Studies have shown that MDMA and amphetamine increase emotional empathy without affecting cognitive empathy; MDMA simultaneously leads to elevated levels of oxytocin, unrelated to its behavioral effects. The aim of the present study was to assess the reported enhancement of empathy by 4-FA, to assess its effects on oxytocin, and to test potential associations between both.

METHODS

Twelve healthy poly-drug users were included in a double-blind placebo-controlled two-way crossover study. Treatments were 4-FA (100 mg) and placebo; empathy was assessed by means of the multifaceted empathy test, and blood samples were taken before and after treatment administration to determine oxytocin concentrations.

RESULTS

4-FA reduced cognitive empathy, whereas emotional empathy was left unaffected. One hour after treatment, plasma oxytocin levels were significantly increased compared with placebo. Behavioral and hormonal effects were unrelated.

CONCLUSION

Although 4-FA shares its pharmacological mechanism with MDMA and amphetamine, current findings seem to indicate that it affects empathy differently. The 4-FA-induced increase in oxytocin levels was independent of behavioral effects, which confirms previous findings that drug-induced effects on peripheral oxytocin levels are not associated with empathy.

Safety Profile and Neurocognitive Function Following Acute 4-Fluoroamphetamine (4-FA) Administration in Humans

Availability of novel psychoactive substances (NPS) exponentially increased over the last years. Risk evaluations of NPS are hampered by the lack of pharmacological studies in humans on health parameters. The aim of the present study was to evaluate safety and neurocognitive function of healthy volunteers (N = 12) who received single doses of 100 and 150 mg 4-fluoroamphetamine (4-FA), a phenethylamine that has been associated with severe cardiovascular and cerebrovascular complications. The study was set-up as a placebo controlled, within subject, phase 1 trial as it was the first to administer 4-FA to humans under controlled conditions. Overall, 4-FA produced a strong elevation in blood pressure up until 4–5 h after administration that was followed by a sustained increase in heart rate. After an interim review of safety data from five participants, a decision was taken to cancel administration of 150 mg. We subsequently obtained complete datasets for placebo and 100 mg 4-FA treatments only. Effects of 4-FA on mood and neurocognitive function were most distinct at 1 h post drug and included significant elevations of vigor, friendliness, elation, arousal, positive mood, as well as improvements in attention and motor performance. Negative affect was also reported as time progressed in the acute phase and even more so during the subacute phase. Overall, the influence of 4-FA on vital signs, mood, and neurocognition was similar to that observed with other stimulants. Present findings confirm clinical observations of acute toxicity among 4-FA users and warrant warnings about potential health risks associated with 4-FA use.

Discriminative stimulus and locomotor effects of para-substituted and benzofuran analogs of amphetamine

Novel psychoactive substances have maintained a prominent role in the global drug culture, despite increased regulation by governing bodies. Novel compounds continue to become available on the market, often in "Ecstasy" or "Molly" formulations in lieu of MDMA, at a much faster rate than they can be properly characterized. The current study aimed to investigate the discriminative stimulus and locomotor effects of three putatively entactogenic compounds that have become increasingly prevalent on the drug market: 5-(2-aminopropyl)-benzofuran (5-APB), 6-(2-aminopropryl)-2,3-dihydrobenzofuran (6-APDB), and 4-fluoroamphetamine (4-FA). Locomotor stimulant effects were assessed in an open-field assay for locomotor activity using Swiss-Webster mice. Discriminative stimulus effects were assessed in Sprague-Dawley rats trained to discriminate either cocaine, methamphetamine, DOM, or MDMA from vehicle. The benzofuran compounds produced locomotor stimulation whereas 4-FA depressed locomotor activity. The benzofurans substituted for the discriminative stimulus effects of MDMA, but only partially or not at all for methamphetamine, cocaine, and DOM, whereas 4-FA fully substituted for MDMA, methamphetamine and cocaine, but not DOM. These results indicate an MDMA-like pattern of abuse might be expected for the benzofurans, whereas 4-FA may be substituted for psychostimulants and MDMA.

Effect fingerprinting of new psychoactive substances (NPS): What can we learn from in vitro data?

The use of new psychoactive substances (NPS) is increasing and currently >600 NPS have been reported. However, limited information on neuropharmacological and toxicological effects of NPS is available, hampering risk characterization. We reviewed the literature on the in vitro neuronal modes of action to obtain effect fingerprints of different classes of illicit drugs and NPS. The most frequently reported NPS were selected for review: cathinones (MDPV, α-PVP, mephedrone, 4-MEC, pentedrone, methylone), cannabinoids (JWH-018), (hallucinogenic) phenethylamines (4-fluoroamphetamine, benzofurans (5-APB, 6-APB), 2C-B, NBOMes (25B-NBOMe, 25C-NBOMe, 25I-NBOMe)), arylcyclohexylamines (methoxetamine) and piperazine derivatives (mCPP, TFMPP, BZP). Our effect fingerprints highlight the main modes of action for the different NPS studied, including inhibition and/or reversal of monoamine reuptake transporters (cathinones and non-hallucinogenic phenethylamines), activation of 5-HT₂receptors (hallucinogenic phenethylamines and piperazines), activation of cannabinoid receptors (cannabinoids) and inhibition of NDMA receptors (arylcyclohexylamines). Importantly, we identified additional targets by relating reported effect concentrations to the estimated human brain concentrations during recreational use. These additional targets include dopamine receptors, α- and β-adrenergic receptors, GABA_Areceptors and acetylcholine receptors, which may all contribute to the observed clinical symptoms following exposure. Additional data is needed as the number of NPS continues to increase. Also, the effect fingerprints we have obtained are still incomplete and suffer from a large variation in the reported effects and effect sizes. Dedicated in vitro screening batteries will aid in complementing specific effect fingerprints of NPS. These fingerprints can be implemented in the risk assessments of NPS that are necessary for eventual control measures to reduce Public Health risks.

Fluorinated phenmetrazine "legal highs" act as substrates for high-affinity monoamine transporters of the SLC6 family

A variety of new psychoactive substances (NPS) are appearing in recreational drug markets worldwide. NPS are compounds that target various receptors and transporters in the central nervous system to achieve their psychoactive effects. Chemical modifications of existing drugs can generate NPS that are not controlled by current legislation, thereby providing legal alternatives to controlled substances such as cocaine or amphetamine. Recently, 3-fluorophenmetrazine (3-FPM), a derivative of the anorectic compound phenmetrazine, appeared on the recreational drug market and adverse clinical effects have been reported. Phenmetrazine is known to elevate extracellular monoamine concentrations by an amphetamine-like mechanism. Here we tested 3-FPM and its positional isomers, 2-FPM and 4-FPM, for their abilities to interact with plasma membrane monoamine transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). We found that 2-, 3- and 4-FPM inhibit uptake mediated by DAT and NET in HEK293 cells with potencies comparable to cocaine (IC₅₀ values < 2.5 μM), but display less potent effects at SERT (IC₅₀ values >80 μM). Experiments directed at identifying transporter-mediated reverse transport revealed that FPM isomers induce efflux via DAT, NET and SERT in HEK293 cells, and this effect is augmented by the Na⁺/H⁺ ionophore monensin. Each FPM evoked concentration-dependent release of monoamines from rat brain synaptosomes. Hence, this study reports for the first time the mode of action for 2-, 3- and 4-FPM and identifies these NPS as monoamine releasers with marked potency at catecholamine transporters implicated in abuse and addiction. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Measuring inhibition of monoamine reuptake transporters by new psychoactive substances (NPS) in real-time using a high-throughput, fluorescence-based assay

The prevalence and use of new psychoactive substances (NPS) is increasing and currently over 600 NPS exist. Many illicit drugs and NPS increase brain monoamine levels by inhibition and/or reversal of monoamine reuptake transporters (DAT, NET and SERT). This is often investigated using labor-intensive, radiometric endpoint measurements. We investigated the applicability of a novel and innovative assay that is based on a fluorescent monoamine mimicking substrate. DAT, NET or SERT-expressing human embryonic kidney (HEK293) cells were exposed to common drugs (cocaine, dl-amphetamine or MDMA), NPS (4-fluoroamphetamine, PMMA, α-PVP, 5-APB, 2C-B, 25B-NBOMe, 25I-NBOMe or methoxetamine) or the antidepressant fluoxetine. We demonstrate that this fluorescent microplate reader-based assay detects inhibition of different transporters by various drugs and discriminates between drugs. Most IC₅₀ values were in line with previous results from radiometric assays and within estimated human brain concentrations. However, phenethylamines showed higher IC₅₀ values on hSERT, possibly due to experimental differences. Compared to radiometric assays, this high-throughput fluorescent assay is uncomplicated, can measure at physiological conditions, requires no specific facilities and allows for kinetic measurements, enabling detection of transient effects. This assay is therefore a good alternative for radiometric assays to investigate effects of illicit drugs and NPS on monoamine reuptake transporters.

Pharmacokinetics, pharmacodynamics and toxicology of new psychoactive substances (NPS): 2C-B, 4-fluoroamphetamine and benzofurans

BACKGROUND

Recently, the number of new psychoactive substances (NPS) appearing on the illicit drug market has shown a marked increase. Although many users perceive the risk of using NPS as medium or low, these substances can pose a serious health risk and several NPS have been implicated in drug-related deaths. In Europe, frequently detected NPS are 4-bromo-2,5-dimethoxyphenethylamine (2C-B), 4-fluoroamphetamine (4-FA) and benzofurans (5-(2-aminopropyl)benzofuran (5-APB) or 6-(2-aminopropyl)benzofuran (6-APB)). However, little is known about the health risks of these specific NPS.

METHODS

In this paper, existing literature on the pharmacokinetics and pharmacodynamics of 2C-B, 4-FA and benzofurans (5-APB/6-APB) was reviewed.

RESULTS

Our review showed that the clinical effects of 2C-B, 4-FA and benzofurans (5-APB/6-APB) are comparable with common illicit drugs like amphetamine and 3,4-methylenedioxymethamphetamine (MDMA). Therefore, NPS toxicity can be handled by existing treatment guidelines that are based on clinical effects instead of the specific drug involved. Even so, information on the health risks of these substances is limited to a number of case reports that are complicated by confounders such as analytical difficulties, mislabelling of drugs, concomitant exposures and interindividual differences.

CONCLUSION

To aid in early legislation, data on clinical effects from poisons centres and user fora should be combined with (in vitro) screening methods and collaboration on an (inter)national level is essential. As a result, potentially hazardous NPS could be detected more quickly, thereby protecting public health.

Abuse-Related Neurochemical Effects of Para-Substituted Methcathinone Analogs in Rats: Microdialysis Studies of Nucleus Accumbens Dopamine and Serotonin

Methcathinone (MCAT) is a monoamine releaser and parent compound to a new class of designer drugs that includes the synthetic cathinones mephedrone and flephedrone. Using MCAT and a series of para-substituted (or 4-substituted) MCAT analogs, it has been previously shown that expression of abuse-related behavioral effects in rats correlates both with the volume of the para substituent and in vitro neurochemical selectivity to promote monoamine release via the dopamine (DA) versus serotonin (5-HT) transporters in rat brain synaptosomes. The present study used in vivo microdialysis to determine the relationship between these previous measures and the in vivo neurochemical selectivity of these compounds to alter nucleus accumbens (NAc) DA and 5-HT levels. Male Sprague-Dawley rats were implanted with bilateral guide cannulae targeting the NAc. MCAT and five para-substituted analogs (4-F, 4-Cl, 4-Br, 4-CH3, and 4-OCH3) produced dose- and time-dependent increases in NAc DA and/or 5-HT levels. Selectivity was determined as the dose required to increase peak 5-HT levels by 250% divided by the dose required to increase peak DA levels by 250%. This measure of in vivo neurochemical selectivity varied across compounds and correlated with 1) in vivo expression of abuse-related behavioral effects (r = 0.89, P = 0.02); 2) in vitro selectivity to promote monoamine release via DA and 5-HT transporters (r = 0.95, P < 0.01); and 3) molecular volume of the para substituent (r = -0.85, P = 0.03). These results support a relationship between these molecular, neurochemical, and behavioral measures and support a role for molecular structure as a determinant of abuse-related neurochemical and behavioral effects of MCAT analogs.

4-Fluoroamphetamine in the Netherlands: more than a one-night stand

AIMS

To investigate the temporal pattern of appearance of a new psychoactive substance (4-fluoroamphetamine) on the Dutch drug market, as well as its patterns of use and effects.

DESIGN

Data from the Drug Information and Monitoring System (DIMS) was used to investigate the emergence of 4-fluoroamphetamine on the Dutch drug market. An on-line questionnaire was used to study its patterns of use and effects.

SETTING

Dutch drug-related websites and social media.

PARTICIPANTS

A convenience sample of 249 life-time 4-fluoroamphetamine users was recruited through the internet.

MEASUREMENTS

Samples containing 4-fluoroamphetamine were extracted from the DIMS database for further investigation. Patterns of use, settings of use and the subjective effects of 4-fluoroamphetamine, amphetamine and 3,4-methylenedioxymethamphetamine (MDMA) were investigated with the on-line questionnaire.

FINDINGS

4-Fluoroamphetamine was first encountered on the Dutch drug market, sold mainly as amphetamine or ecstasy (MDMA), between 2007 and 2009. These misrepresented drug samples declined when the MDMA and amphetamine markets recovered after a period of shortage, whereas purposefully bought 4-fluoroamphetamine samples showed an increase. Survey results showed that 4-fluoroamphetamine is used predominantly [77.1%, 95% confidence interval (CI) = 72.0-82.3] for its specific effects, rather than its legal status (17.7%, 95% CI = 10.7-22.1). The subjective effects of 4-fluoroamphetamine were compared with those of amphetamine and MDMA. Subjective effect scores of 4-fluoroamphetamine ranged between those of amphetamine and MDMA.

CONCLUSIONS

The stimulant 4-fluoroamphetamine is increasingly popular in the Netherlands, which might be due to its subjective effects profile, which lies intermediate between amphetamine and MDMA.

Quantitative structure-activity relationship analysis of the pharmacology of para-substituted methcathinone analogues

BACKGROUND AND PURPOSE

Methcathinone (MCAT) is a potent monoamine releaser and parent compound to emerging drugs of abuse including mephedrone (4-CH3 MCAT), the para-methyl analogue of MCAT. This study examined quantitative structure-activity relationships (QSAR) for MCAT and six para-substituted MCAT analogues on (a) in vitro potency to promote monoamine release via dopamine and serotonin transporters (DAT and SERT, respectively), and (b) in vivo modulation of intracranial self-stimulation (ICSS), a behavioural procedure used to evaluate abuse potential. Neurochemical and behavioural effects were correlated with steric (Es ), electronic (σp ) and lipophilic (πp ) parameters of the para substituents.

EXPERIMENTAL APPROACH

For neurochemical studies, drug effects on monoamine release through DAT and SERT were evaluated in rat brain synaptosomes. For behavioural studies, drug effects were tested in male Sprague-Dawley rats implanted with electrodes targeting the medial forebrain bundle and trained to lever-press for electrical brain stimulation.

KEY RESULTS

MCAT and all six para-substituted analogues increased monoamine release via DAT and SERT and dose- and time-dependently modulated ICSS. In vitro selectivity for DAT versus SERT correlated with in vivo efficacy to produce abuse-related ICSS facilitation. In addition, the Es values of the para substituents correlated with both selectivity for DAT versus SERT and magnitude of ICSS facilitation.

CONCLUSIONS AND IMPLICATIONS

Selectivity for DAT versus SERT in vitro is a key determinant of abuse-related ICSS facilitation by these MCAT analogues, and steric aspects of the para substituent of the MCAT scaffold (indicated by Es ) are key determinants of this selectivity.

New synthetic drugs in addictovigilance

New substances, also known as "designer drugs" or "legal highs" are increasingly available to drug users. Two hundred and fifteen hitherto unlisted substances have been notified by European Union member states since 2005. These synthetic drugs, which have been developed to side-step the legislation on drugs, are analogues or derivatives of existing drugs and medications. The availability of these "legal highs", sold on Internet under various denominations such as bath salt, plant fertilizer, chemical not intended for human use, or spice, is unlimited. The effects felt by users vary, and the substances may be stimulant, entactogenic, hallucinogenic, psychedelic or dissociative. The pharmacological targets also vary, and may be either the increase of extracellular levels of neurotransmitters via different mechanisms (reuptake inhibition, stimulation of intracellular release) or else fixation on specific receptors. Several chemical classes, themselves divided into sub-classes, are involved: phenethylamines, tryptamines, piperazines, cathinones, cannabinoids etc. The toxicity of the main members of these categories is increasingly well known, the most deleterious being behavioural effects, physical manifestations, and cardiovascular consequences. However, small variations in their chemical structure can generate effects that are quantitatively different, thus enhancing their toxicity or addictive potential, and much remains to be achieved in terms of knowledge about these new drugs. These substances are indeed present on the French territory, as shown by data provided by the Observatoire Français des Drogues et Toxicomanies, and notifications by the French Addictovigilance network. Screening in clinical toxicology laboratories is not widespread, since these molecules are not detected by the standard screening tests, so that there is probably an under-estimation of the use of these new drugs. The legislation on these substances changes regularly, with more and more countries classifying them as "narcotics" or illegal psychotropic drugs so as to restrict their use, applying a generic classification when possible.

Monoamine transporter and receptor interaction profiles of novel psychoactive substances: para-halogenated amphetamines and pyrovalerone cathinones

The pharmacology of novel psychoactive substances is mostly unknown. We evaluated the transporter and receptor interaction profiles of a series of para-(4)-substituted amphetamines and pyrovalerone cathinones. We tested the potency of these compounds to inhibit the norepinephrine (NE), dopamine (DA), and serotonin (5-HT) transporters (NET, DAT, and SERT, respectively) using human embryonic kidney 293 cells that express the respective human transporters. We also tested the substance-induced efflux of NE, DA, and 5-HT from monoamine-loaded cells, binding affinities to monoamine receptors, and 5-HT2B receptor activation. Para-(4)-substituted amphetamines, including 4-methylmethcathinone (mephedrone), 4-ethylmethcathinone, 4-fluoroamphetamine, 4-fluoromethamphetamine, 4-fluoromethcatinone (flephedrone), and 4-bromomethcathinone, were relatively more serotonergic (lower DAT:SERT ratio) compared with their analogs amphetamine, methamphetamine, and methcathinone. The 4-methyl, 4-ethyl, and 4-bromo groups resulted in enhanced serotonergic properties compared with the 4-fluoro group. The para-substituted amphetamines released NE and DA. 4-Fluoramphetamine, 4-flouromethamphetamine, 4-methylmethcathinone, and 4-ethylmethcathinone also released 5-HT similarly to 3,4-methylenedioxymethamphetamine. The pyrovalerone cathinones 3,4-methylenedioxypyrovalerone, pyrovalerone, α-pyrrolidinovalerophenone, 3,4-methylenedioxy-α-pyrrolidinopropiophenone, and 3,4-methylenedioxy-α-pyrrolidinobutiophenone potently inhibited the NET and DAT but not the SERT. Naphyrone was the only pyrovalerone that also inhibited the SERT. The pyrovalerone cathinones did not release monoamines. Most of the para-substituted amphetamines exhibited affinity for the 5-HT2A receptor but no relevant activation of the 5-HT2B receptor. All the cathinones exhibited reduced trace amine-associated receptor 1 binding compared with the non-β-keto-amphetamines. In conclusion, para-substituted amphetamines exhibited enhanced direct and indirect serotonergic agonist properties and are likely associated with more MDMA-like effects. The pharmacological profile of the pyrovalerone cathinones predicts pronounced stimulant effects and high abuse liability.

5-hydroxytryptamine- and dopamine-releasing effects of ring-substituted amphetamines on rat brain: a comparative study using in vivo microdialysis

Using in vivo microdialysis, a comparative study was conducted to examine the effects of amphetamine-related compounds (methamphetamine, MAP; 3,4-methylenedioxymethamphetamine, MDMA; p-methoxyamphetamine, PMA; p-methoxymethamphetamine, PMMA; 4-methylthioamphetamine, 4-MTA; 3,4,5-trimethoxyamphetamine, TMA; 2,5-dimethoxy-4-iodoamphetamine, DOI) on extracellular levels of serotonin (5-HT) and dopamine (DA). Dialysates were assayed using HPLC equipped with electrochemical detector following i.p. administration with each drug at a dose of 5 mg/kg. MAP was found to drastically and rapidly increase 5-HT and DA levels (870% and 1460%, respectively). PMA, PMMA, and 4-MTA slightly increased DA levels (150-290%) but remarkably increased 5-HT levels (540-900%). In contrast, TMA and DOI caused no detectable changes in levels of both monoamines. We observed that the potent DA-releasing action of MAP was remarkably decreased by introduction of methoxy or methylthio group at the para position (MAP vs. PMMA or 4-MTA), but introduction of two additional adjacent methoxy groups into PMA totally abolished its 5-HT-/DA-releasing action (PMA vs. TMA). In addition, para-mono-substituted compounds inhibited both monoamine oxidase (MAO) enzymes more strongly than other compounds; PMA and 4-MTA exhibited submicromolar IC50 values for MAO-A. On the other hand, TMA scarcely affected the activity of both MAO enzymes as well as extracellular levels of 5-HT and DA. In this comparative study, MDMA, PMA, and 4-MTA functioned similar to PMMA, a typical empathogen; these findings therefore could be helpful in clarifying the psychopharmacological properties of amphetamine-related, empathogenic designer drugs.

Understanding the risks associated with the use of new psychoactive substances (NPS): high variability of active ingredients concentration, mislabelled preparations, multiple psychoactive substances in single products

New psychoactive substances (NPS), are now a large group of substances of abuse not yet completely controlled by international drug conventions, which may pose a public health threat. Anxiety, paranoia, hallucinations, seizures, hyperthermia and cardiotoxicity are some of the common adverse effects associated with these compounds. In this paper, three case reports taken from the archive of processed cases of the authors' laboratory are presented and discussed to stress the risks of possible adverse consequences for NPS users: in particular, (i) the risk deriving from the difficulty of predicting the actual consumed dose, due to variability of active ingredients concentration in consumed products, (ii) the risk deriving from the difficulty of predicting the actual active ingredients present in consumed products, as opposed to those claimed by the manufacturer, and (iii) the risk deriving from the difficulty of predicting the actual pharmacological and toxicological effects related to the simultaneous consumption of different psychoactive ingredients contained in single products, whose interactions are mostly unknown. Each of them individually provide a source of concern for possible serious health related consequences. However, they should be considered in conjunction with each others, with the worldwide availability of NPS through the web and also with the incessantly growing business derived from the manipulation and synthesis of new substances. The resulting scenario is that of a cultural challenge which demands a global approach from different fields of knowledge.

Rapid screening and determination of designer drugs in saliva by a nib-assisted paper spray-mass spectrometry and separation technique

A method for the rapid screening and determination of amphetamine-type designer drugs in saliva by a novel nib-assisted paper spray-mass spectrometry procedure is described. Under optimized conditions, the limit of detections for amphetamine derivatives (model samples: o-, m-, p-chloroamphetamine and o-, m-, p-fluoroamphetamine, respectively) were determined to 0.1 μg/mL by the nib-assisted paper spray-mass spectrometry method. This method is easier and has a higher sensitivity than similar methodologies, including atmospheric pressure/matrix-assisted laser desorption ionization mass spectrometry and electrospray-assisted laser desorption ionization/mass spectrometry. Data obtained using more classical separation methods, including liquid chromatography and capillary electrophoresis, are also reported.

Ring positional differentiation of isomeric N-alkylated fluorocathinones by gas chromatography/tandem mass spectrometry

In analogy to our previously published procedure for the differentiation of regioisomeric fluoroamphetamines a method was developed, to differentiate ring positional isomeric fluorocathinones by product ion spectrometry of ions generated by chemical ionization (CI) under GC-MS conditions using methane as reagent gas. N-alkylated ortho-, meta- and para-fluorocathinones could be unequivocally differentiated by product ion spectrometry of the hydrogen fluoride loss ions [M+H-HF](+) using a triple quadrupole mass spectrometer with argon as collision gas under normalized collision conditions. This method enables the differentiation of ring positional isomers of fluorocathinones even in complex mixtures and low concentrations. The applicability of the method was shown by the analysis of synthesized N-alkylated ortho-, meta- and para-fluorocathinones and seized designer drug mixtures.

Linking the pharmacological content of ecstasy tablets to the subjective experiences of drug users

RATIONALE

Most studies on the subjective effects of ecstasy are based on the assumption that the substance that was taken is 3,4-methylenedioxymethamphetamine (MDMA). However, many tablets sold as ecstasy contain other substances and MDMA in varying doses. So far, few attempts have been made to take this into account while assessing subjective effects.

OBJECTIVES

This study aims to link the pharmacological content of tablets sold as ecstasy to the subjective experiences reported by ecstasy users.

METHODS

Self-reported effects on ecstasy tablets were available from 5,786 drug users who handed in their tablets for chemical analysis at the Drug Information and Monitoring System (DIMS) in the Netherlands. Logistic regression was employed to link the pharmacological content of ecstasy tablets to the self-reported subjective effects and compare effects with MDMA to other substances present.

RESULTS

MDMA showed a strong association with desirable subjective effects, unparalleled by any other psychoactive substance. However, the association of MDMA was dose-dependent, with higher doses (>120 mg/tablet) likely to evoke more adverse effects. The novel psychostimulants mephedrone and p-fluoroamphetamine were considered relatively desirable, whereas meta-chlorophenylpiperazine (mCPP) and p-methoxymethamphetamine (PMMA) were strongly associated with adverse subjective effects. Also, 3,4-methylene-dioxyamphetamine (MDA) and benzylpiperazine (BZP) were not appreciated as replacement for MDMA.

CONCLUSION

Linking the pharmacological content of ecstasy sold on the street to subjective experiences contributes to a better understanding of the wide range of subjective effects ascribed to ecstasy and provides a strong rationale for the prolonged endurance of MDMA as the key ingredient of the ecstasy market.

In vivo effects of amphetamine analogs reveal evidence for serotonergic inhibition of mesolimbic dopamine transmission in the rat

Evidence suggests that elevations in extracellular serotonin (5-HT) in the brain can diminish stimulant effects of dopamine (DA). To assess this proposal, we evaluated the pharmacology of amphetamine analogs (m-fluoroamphetamine, p-fluoroamphetamine, m-methylamphetamine, p-methylamphetamine), which display similar in vitro potency as DA releasers (EC(50) = 24-52 nM) but differ in potency as 5-HT releasers (EC(50) = 53-1937 nM). In vivo microdialysis was used to assess the effects of drugs on extracellular DA and 5-HT in rat nucleus accumbens, while simultaneously measuring ambulation (i.e., forward locomotion) and stereotypy (i.e., repetitive movements). Rats received two intravenous injections of drug, 1 mg/kg at time 0 followed by 3 mg/kg 60 min later. All analogs produced dose-related increases in dialysate DA and 5-HT, but the effects on DA did not agree with in vitro predictions. Maximal elevation of dialysate DA ranged from 5- to 14-fold above baseline and varied inversely with 5-HT response, which ranged from 6- to 24-fold above baseline. All analogs increased ambulation and stereotypy, but drugs causing greater 5-HT release (e.g., p-methylamphetamine) were associated with significantly less forward locomotion. The magnitude of ambulation was positively correlated with extracellular DA (p < 0.001) and less so with the ratio of DA release to 5-HT release (i.e., percentage DA increase divided by percentage 5-HT increase) (p < 0.029). Collectively, our findings are consistent with the hypothesis that 5-HT release dampens stimulant effects of amphetamine-type drugs, but further studies are required to address the precise mechanisms underlying this phenomenon.

Discriminative stimulus and reinforcing effects of p-fluoro-L-deprenyl in monkeys

RATIONALE

para-Fluoro-L-deprenyl (Fludepryl), a halogenated derivative of L-deprenyl, shares structural similarities with amphetamine and may have potential as a medication for psychostimulant abuse.

OBJECTIVES

p-Fluoro-L-deprenyl was evaluated for psychomotor stimulant, discriminative stimulus, and reinforcing effects in squirrel monkeys.

METHODS

One group of monkeys was trained under a ten-response fixed-ratio (FR10) schedule of stimulus termination to discriminate between methamphetamine (0.32 mg/kg, i.m.) and saline. Other monkeys were trained to self-administer i.v. cocaine under either a simple FR10 schedule or a second-order fixed-interval 5-min schedule with FR10 components.

RESULTS

Full generalization to the methamphetamine-training stimulus was produced by an i.m. dose of 10.0 mg/kg p-fluoro-L-deprenyl. L-Deprenyl and the metabolites of p-fluoro-L-deprenyl, p-fluoro-L-amphetamine, and p-fluoro-L-methylamphetamine were more potent, producing full generalization at doses of 1.0-3.2 mg/kg. Under the FR10 schedule of drug injection, persistent self-administration behavior was maintained by i.v. cocaine injections but not by injections of vehicle or injection doses of p-fluoro-L-deprenyl up to 1.0 mg/kg. However, p-fluoro-L-deprenyl did maintain moderate levels of i.v. self-administration responding under the second-order schedule of drug injection. Peak response rates maintained by 0.1-mg/kg injections of p-fluoro-L-deprenyl were significantly greater than those associated with saline substitution, yet significantly lower than those maintained by cocaine or D-amphetamine.

CONCLUSIONS

p-Fluoro-L-deprenyl has methamphetamine-like discriminative-stimulus properties in squirrel monkeys that appear at higher doses than for its parent compound, L-deprenyl. It also appears to function as a relatively limited reinforcer of intravenous self-administration behavior in monkeys trained to self-administer i.v. cocaine.

Isomeric Fluoro-methoxy-phenylalkylamines: a new series of controlled-substance analogues (designer drugs)

An impressively large number of clandestinely produced controlled-substance analogues (designer drugs) of amphetamine with high structural variety have been encountered in forensic samples in recent years. The continuous designer drug exploration and their widespread consumption results in an increasing number of reports regarding abuse and intoxication. This study presents the analytical properties of a series of new fluoro-methoxy-substituted controlled-substance analogues of amphetamine. Three ring positional isomeric fluoroamphetamines, two isomeric fluoromethoxyamphetamines, two N-alkyl 4-fluoroamphetamines, and one 4-fluorophenylbutan-2-amine were identified and differentiated by gas chromatography-mass spectrometry (GC-MS), 1H- and 13C-nuclear magnetic resonance (NMR), and gas chromatography-infrared spectroscopy (GC-IR). The regioisomeric 2-, 3-, and 4-fluoroamphetamines and the regioisomeric fluoro-methoxyamphetamines show virtually identical mass spectra so that this method is insufficient to discriminate between these closely related compounds. The mass spectra of the acetylated compounds allowed a differentiation of the 4-fluoroamphetamine from its regioisomeric 2- and 3-fluoroamphetamines. The gas chromatographic properties of the three regioisomeric fluoroamphetamines and their acetylated and trifluoroacetylated derivatives are also so similar that a complete separation of these compounds could not be achieved under GC-MS conditions. The two isomeric compounds 5-fluoro-2-methoxyamphetamine and 3-fluoro-4-methoxyamphetamine on the other hand showed significant different gas chromatographic retention times so that a separation was uncomplicated. The trifluoroacetylation of these compounds proved to be an effective method for their mass spectral differentiation. Gas chromatography-infrared spectroscopy and 1H- and 13C-nuclear magnetic resonance allowed an unequivocal differentiation of all studied regioisomeric fluoroamphetamines and fluoro-methoxyamphetamines.

Relationship between the serotonergic activity and reinforcing effects of a series of amphetamine analogs

It has been reported that among drugs with mixed actions on central nervous system monoamine systems, increased serotonergic activity is associated with decreased potency as a reinforcer. The present experiment was designed to examine this relationship for amphetamine analogs that varied in serotonin releasing potency and to evaluate whether serotonergic actions can affect reinforcing efficacy. Compounds PAL 313 and 314 are para- and meta-methylamphetamine, respectively. PAL 303 and 353 are para- and meta-fluoroamphetamine, respectively. All compounds had similar potencies as in vitro releasers of dopamine (DA) and norepinephrine (NE) but differed in potency for 5-hydroxytryptamine (serotonin) (5-HT) release [EC(50) (nanomolar) PAL 313 = 53.4; PAL 314 = 218; PAL 303 = 939; PAL 353 = 1937]. When made available to rhesus monkeys (Macaca mulatta)(n = 4) for self-administration under a fixed-ratio 25 schedule, all were positive reinforcers with biphasic dose-response functions (0.003-1.0 mg/kg) and were equipotent. PAL 313 was self-administered at a lower rate than the other compounds, which were indistinguishable. Under a progressive-ratio schedule (n = 5), all drugs were positive reinforcers. Dose-response functions increased to a maximum or were biphasic (0.01-1.0 mg/kg), and drugs were equipotent. At maximum, PAL 313 maintained less responding than other PAL drugs, which maintained similar maxima. Thus, all compounds were positive reinforcers under both schedules, consistent with their potent DA actions. Responding was lower when 5-HT potency was higher and comparable with DA and NE potency. The results suggest that the mechanism for this effect involves a decrease in reinforcing potency and efficacy among monoamine releasing agents when 5-HT releasing potency is increased relative to DA.

Distinct molecular recognition of psychostimulants by human and Drosophila serotonin transporters

In this study, human embryonic kidney (HEK)-293 cells stably expressing human, Drosophila, or a chimeric serotonin (5-hydroxytryptamine, 5-HT) transporter (hSERT, dSERT, and H(1-281)D(282-476)H(477-638), respectively) were used to explore the ability of two libraries of structurally distinct psychostimulants to inhibit 5-HT uptake. One library consisted of 3-phenyltropane analogs, whereas the second library consisted of several substituted amphetamines. hSERT exhibited a lower K(i) value for all the compounds in both libraries compared with dSERT, whereas the chimeric SERT exhibited properties more closely resembling those of dSERT. This species selectivity was explored using computer-generated comparative molecular field analysis to model the interactions of the cocaine analogs and substituted amphetamines at hSERT, dSERT, and the cross-species chimera. Models for the 3-phenyltropane analogs indicate that a region exists around the aromatic ring where decreased electron density is favored, particularly for hSERT. This finding may indicate pi-pi stacking with an aromatic amino acid residue in SERT. Also, electronegative substituents in the 4'-position provide favorable interactions. This structural feature was demonstrated by increased potency of analogs with electronegative substituents on the aromatic ring that withdraw electron density. For the substituted amphetamines, key areas for interaction exist around the amine, an electrostatic component surrounding the 3-position on the aromatic ring, and a steric component surrounding the 4-position.

Differential sensitivities to the lethal, but not the neurotoxic, effects of p-chloroamphetamine in inbred rat strains

The Lewis, Fischer 344, Brown Norway, Spontaneously Hypertensive, and Wistar-Kyoto inbred rat strains were, respectively, compared for the lethal and neurotoxic effects of acute p-chloroamphetamine (PCA, 2.5-10 mg/kg i.p.). The lethal properties of the amphetamine were recorded within 24 h after its administration whereas neurotoxicity (as assessed by frontocortical 5-hydroxytryptamine (5-HT) reuptake and 5-HT transporter binding assays) was analyzed 1 week after PCA administration. Preliminary experiments indicated that neither the rapid hyperlocomotor and/or the hypoexploratory effect of PCA nor the in vitro potency of PCA to inhibit frontocortical [(3)H]5-HT reuptake varied between strains. On the other hand, strain differences were observed with respect to the rapid fatal effects of the 5 and 10 mg/kg doses of PCA administration. Lastly, frontocortical [(3)H]5-HT reuptake and [(3)H]citalopram binding at 5-HT transporters diminished in a dose-dependent, but strain-independent, manner 1 week after the acute injection of PCA. This study reveals an independency between the mechanisms underlying the fatal effects of PCA on the one hand, and the long-term damaging effects of PCA on serotonergic neurons on the other hand.