5-Iodo-2-aminoindan, a nonneurotoxic analogue of p-iodoamphetamine

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

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

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.

Designer drugs: mechanism of action and adverse effects

Psychoactive substances with chemical structures or pharmacological profiles that are similar to traditional drugs of abuse continue to emerge on the recreational drug market. Internet vendors may at least temporarily sell these so-called designer drugs without adhering to legal statutes or facing legal consequences. Overall, the mechanism of action and adverse effects of designer drugs are similar to traditional drugs of abuse. Stimulants, such as amphetamines and cathinones, primarily interact with monoamine transporters and mostly induce sympathomimetic adverse effects. Agonism at μ-opioid receptors and γ-aminobutyric acid-A (GABAA) or GABAB receptors mediates the pharmacological effects of sedatives, which may induce cardiorespiratory depression. Dissociative designer drugs primarily act as N-methyl-D-aspartate receptor antagonists and pose similar health risks as the medically approved dissociative anesthetic ketamine. The cannabinoid type 1 (CB1) receptor is thought to drive the psychoactive effects of synthetic cannabinoids, which are associated with a less desirable effect profile and more severe adverse effects compared with cannabis. Serotonergic 5-hydroxytryptamine-2A (5-HT2A) receptors mediate alterations of perception and cognition that are induced by serotonergic psychedelics. Because of their novelty, designer drugs may remain undetected by routine drug screening, thus hampering evaluations of adverse effects. Intoxication reports suggest that several designer drugs are used concurrently, posing a high risk for severe adverse effects and even death.

Pharmacology of MDMA- and Amphetamine-Like New Psychoactive Substances

New psychoactive substances (NPS) with amphetamine-, aminoindan-, and benzofuran basic chemical structures have recently emerged for recreational drug use. Detailed information about their psychotropic effects and health risks is often limited. At the same time, it emerged that the pharmacological profiles of these NPS resemble those of amphetamine or 3,4-methylenedioxymethamphetamine (MDMA). Amphetamine-like NPS induce psychostimulation and euphoria mediated predominantly by norepinephrine (NE) and dopamine (DA) transporter (NET and DAT) inhibition and transporter-mediated release of NE and DA, thus showing a more catecholamine-selective profile. MDMA-like NPS frequently induce well-being, empathy, and prosocial effects and have only moderate psychostimulant properties. These MDMA-like substances primarily act by inhibiting the serotonin (5-HT) transporter (SERT) and NET, also inducing 5-HT and NE release. Monoamine receptor interactions vary considerably among amphetamine- and MDMA-like NPS. Clinically, amphetamine- and MDMA-like NPS can induce sympathomimetic toxicity. The aim of this chapter is to review the state of knowledge regarding these substances with a focus on the description of the in vitro pharmacology of selected amphetamine- and MDMA-like NPS. In addition, it is aimed to provide links between pharmacological profiles and in vivo effects and toxicity, which leads to the conclusion that abuse liability for amphetamine-like NPS may be higher than for MDMA-like NPS, but that the risk for developing the life-threatening serotonin syndrome may be increased for MDMA-like NPS.

Synthetic Aminoindanes: A Summary of Existing Knowledge

OBJECTIVES

Aminoindanes ("bath salts," a class of novel psychoactive substances, NPSs) increased rapidly in popularity on the recreational drug market, particularly after mephedrone and other synthetic cathinones were banned in the UK in 2010. Novel aminoindanes continue to emerge, but relatively little is known about their effects and risks. Their history, chemistry, pharmacology, behavioral effects, pharmacokinetics, and toxicity are reviewed in this paper.

METHODS

Scientific literature was searched on ISI Web of Knowledge: Web of Science (WoS) during June and July 2017, using English language terms: aminoindanes such as 5,6-methylenedioxy-2-aminoindane (MDAI), 5-iodo-2-aminoindane (5-IAI), 2-aminoindane (2-AI), 5,6-methylenedioxy-N-methyl-2-aminoindane (MDMAI), and 5-methoxy-6-methyl-2-aminoindane (MMAI). WoS was selected as it searches several databases simultaneously and has quality criteria for inclusion. For typical use and effects, Erowid, PsychonautWiki, Bluelight, and Drugs-Forum were searched; for legal status and epidemiology, the European Information System and Database on New Drugs (EDND) was used.

RESULTS

Aminoindanes were first synthesized for medical use, e.g., as anti-Parkinsonian drugs and later as a potential compound facilitating psychotherapy; however, they are now widely substituted for ecstasy. Their mechanisms of action (primarily via serotonin) mean that they may pose a significant risk of serotonin syndrome at high doses or when combined with other drugs. Fatally toxic effects have been observed both in the laboratory in animal studies and in clinic, where deaths related with aminoindanes have been reported.

CONCLUSION

Greater knowledge about aminoindanes is urgently required to decrease risks of fatal intoxication, and appropriate legislation is needed to protect public health without impeding research.

Pharmacological profiles of aminoindanes, piperazines, and pipradrol derivatives

Aminoindanes, piperazines, and pipradrol derivatives are novel psychoactive substances found in "Ecstasy" tablets as replacements for 3,4-methylenedioxymethamphetamine (MDMA) or substances sold as "ivory wave." The pharmacology of these MDMA- and methylphenidate-like substances is poorly known. We characterized the pharmacology of the aminoindanes 5,6-methylenedioxy-2-aminoindane (MDAI), 5-iodoaminoindane (5-IAI), and 2-aminoindane (2-AI), the piperazines meta-chlorophenylpiperazine (m-CPP), trifluoromethylphenylpiperazine (TFMPP), and 1-benzylpiperazine (BZP), and the pipradrol derivatives desoxypipradrol (2-diphenylmethylpiperidine [2-DPMP]), diphenylprolinol (diphenyl-2-pyrrolidinemethanol [D2PM]), and methylphenidate. We investigated norepinephrine (NE), dopamine (DA), and serotonin (5-hydroxytryptamine [5-HT]) uptake inhibition using human embryonic kidney 293 (HEK 293) cells that express the respective human monoamine transporters (NET, DAT, and SERT). We also evaluated the drug-induced efflux of NE, DA, and 5-HT from monoamine-preloaded cells and the binding affinity to monoamine transporters and receptors, including trace amine-associated receptor 1 (TAAR1). 5-IAI and MDAI preferentially inhibited the SERT and NET and released 5-HT. 2-AI interacted with the NET. BZP blocked the NET and released DA. m-CPP and TFMPP interacted with the SERT and serotonergic receptors. The pipradrol derivatives were potent and selective catecholamine transporter blockers without substrate releasing properties. BZP, D2PM, and 2-DPMP lacked serotonergic activity and TAAR1 binding, in contrast to the aminoindanes and phenylpiperazines. In summary, all of the substances were monoamine transporter inhibitors, but marked differences were found in their DAT vs. SERT inhibition profiles, release properties, and receptor interactions. The pharmacological profiles of D2PM and 2-DPMP likely predict a high abuse liability.

Designer psychostimulants: pharmacology and differences

More than 200 novel psychoactive drugs have been reported in Europe, with 73 added in 2012 and additional compounds encountered every week in 2013. Many of these are "designer psychostimulants" which aim to mimic the subjective effects of amphetamines, cocaine or 3,4-methylenedioxymethylamphetamine (MDMA; "Ecstasy"). Several drugs are based on the beta-ketoamphetamine cathinone chemical structure, others include aminoindanes, aminotetralins, piperazines, amphetamine analogues and pipradrol derivatives. Although a detailed analysis of the pharmacology of these novel drugs is largely lacking, a number of scientific studies have been reported in 2011-2013 and these are reviewed. All of the novel psychostimulants activate monoamine systems in the brain - with differing dopamine (DA) v serotonin (5-HT) preferences. Those activating principally DA systems are amphetamine-like stimulants, such as naphyrone, desoxypipradrol, 3,4-methylenedioxypyrovalerone (MDPV), and benzylpiperazine while those preferentially activating 5-HT mechanisms are MDMA-like or cocaine-like stimulants, such as mephedrone, methylone and other substituted cathinones, aminoindanes, aminotetralins and piperazines. The ability of mephedrone and other novel psychostimulants to substitute for methylamphetamine or cocaine in drug discrimination tests in rats, and the ability of mephedrone to induce conditioned place preference and to sustain self-administration behaviour suggests that this and other cocaine/methylamphetamine-like drugs have dependence liability. This article is part of the Special Issue entitled 'CNS Stimulants'.

5-Iodo-2-aminoindan (5-IAI): chemistry, pharmacology, and toxicology of a research chemical producing MDMA-like effects

In 2010, an internet snapshot of EMCDDA anticipated the presence of 5-iodo-2-aminoindan (5-IAI) within the recreational drug market. In 2011, this compound, a psychoactive derivative of 2-aminoindane, was identified in recreational products sold in the United Kingdom. 5-IAI is a rigid analogue of p-iodoamphetamine producing MDMA-like effects. The aim of this paper is to summarize the clinical, pharmacological, and toxicological information about this new potential drug of abuse.

Synthesis and pharmacological evaluation of ring-methylated derivatives of 3,4-(methylenedioxy)amphetamine (MDA)

The three isomeric ring-methylated derivatives of the well-known hallucinogen and entactogen MDA (1a) were synthesized and evaluated for pharmacological activity as monoamine-releasing agents and as serotonin agonists. The 2-methyl derivative 2a and the 5-methyl derivative 2b were found to be more potent and more selective than the parent compound in inhibiting [3H]-serotonin accumulation in rat brain synaptosomal preparations. Their activity in vivo was confirmed in rats trained to discriminate serotonin-releasing agents and hallucinogens from saline. The results indicate that compounds 2a,b are among the most potent 5-HT-releasing compounds known and show promise as lead compounds in the search for antidepressant drugs that release serotonin rather than inhibit its uptake.

Indan analogs of fenfluramine and norfenfluramine have reduced neurotoxic potential

N-Ethyl-5-trifluoromethyl-2-aminoindan (ETAI) and 5-trifluoromethyl-2-aminoindan (TAI) were synthesized to examine the effects of side-chain cyclization on the pharmacology of the anorectic drugs fenfluramine (FEN) and norfenfluramine (norFEN), respectively. ETAI and TAI inhibited synaptosomal accumulation of 5-HT but were less effective at inhibiting catecholamine uptake than FEN or norFEN, respectively. In vivo, ETAI and TAI were less neurotoxic than FEN or norFEN; decreases in the number of [3H]paroxetine-labeled 5-HT uptake sites were 50% less than the decreases produced by FEN or norFEN. Rats treated with ETAI. TAI, FEN, and norFEN lost 10-15% of their pretreatment body weight over a 4-day period, while saline-treated control animals gained 8%. In two-lever drug discrimination (DD) assays in rats, TAI fully substituted for the 5-HT releaser/uptake inhibitor, (+)-MBDB [(+)-N-methyl-1-(1,3-benzodioxol-5-yl)-2-aminobutane]. ETAI produced only partial substitution in this test. Neither TAI nor ETAI mimicked (+)-amphetamine in the DD assay. These studies demonstrate that incorporation of the side-chain of phenylisopropylamines into the five-membered ring of a 2-aminoindan changes both the molecular pharmacology and the neurotoxic profile of FEN and norFEN, but does not diminish the drugs' ability to reduce body weight.

The effect of N-methylation on fenfluramine's neurotoxic and pharmacologic actions

N-Methylation separates methamphetamine's neurotoxic and pharmacologic effects. In particular, N-methylation eliminates methamphetamine's neurotoxic activity while preserving its behavioral pharmacologic activity. The purpose of the present studies was to determine whether N-methylation could also be used to separate fenfluramine's neurotoxic and pharmacologic effects. Fenfluramine-induced serotonin neurotoxicity was assessed by measuring serotonin axonal markers 2 weeks after fenfluramine administration. Pharmacologic effects of fenfluramine were assessed by measuring fenfluramine-induced anorexia and fenfluramine discrimination. Both fenfluramine and its N-methylated analog, N-methylfenfluramine, produced dose-related effects in food intake, drug-discrimination and neurotoxicity studies. Although N-methylation reduced the neurotoxic potency of fenfluramine, it also reduced its pharmacologic activity. Neurotoxic potency was reduced 4- to 8-fold (depending on brain region), while pharmacologic potency was reduced 4- to 10-fold (depending on paradigm). Notably, N-methylation did not change the efficacy of fenfluramine as a serotonin neurotoxin, anorectic agent or discrimination stimulus. These results indicate that fenfluramine's behavioral and neurotoxic effects, unlike those of methamphetamine, are not dissociated by N-methylation. Further, the present results suggest that the effectiveness of side-chain nitrogen substitution in separating the behavioral and neurotoxic effects of amphetamine derivatives is strongly influenced by ring substitutions.

Psychostimulant-like effects of p-fluoroamphetamine in the rat

The present study was undertaken to compare the pharmacological properties of p-fluoroamphetamine with those of amphetamine and of other halogenated amphetamines, using several in vivo and in vitro tests. These included substitution testing in (+)-amphetamine (1 mg/kg, 5.4 mu mol/kg, i.p.)-, (+)-N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine [(+)-MBDB] (1.75 mg/kg, 7.8 mu mol/kg, i.p.)-, and 5-methoxy-6-methyl-2-aminoindan (MMAI) (1.71 mg/kg, 8 mu mol/kg, i.p.)-trained rats, [3H]5-HT and [3H]dopamine uptake inhibition in whole brain synaptosomes, and changes in striatal extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) as measured by in vivo microdialysis in freely moving rats. In drug discrimination substitution tests, p-fluoroamphetamine fully mimicked (+)-amphetamine (ED50 0.43 mg/kg, 2.11 mu mol/kg), whereas 'no substitution' was observed in rats trained to discriminate the serotonin (5-hydroxytryptamine, 5-HT)-releasing agents (+)-MBDB or MMAI from saline. p-Chloroamphetamine did not substitute for amphetamine but fully substituted for the (+)-MBDB and MMAI cues (ED50 0.17 mg/kg, 0.82 mu mol/kg, and 0.14 mg/kg, 0.69 mu mol/kg, respectively). p-Fluoroamphetamine, in comparison with p-chloroamphetamine and p-iodoamphetamine, showed much stronger inhibition of [3H]dopamine than [3H]5-HT uptake into rat brain synaptosomes but was less selective than amphetamine. p-Fluoroamphetamine (7.0 mg/kg, i.p.), 1 h after administration, strongly elevated (849% of baseline) extracellular dopamine in rat striatum measured using in vivo microdialysis. Amphetamine (2 mg/kg, i.p.) increased extracellular dopamine in rat striatum with a maximum at the same time as did p-fluoroamphetamine, but the latter gave a smaller increase. The data presented suggest that p-fluoroamphetamine resembles amphetamie more than it does the 5-HT-releasing type amphetamines.

[3H]monoamine releasing and uptake inhibition properties of 3,4-methylenedioxymethamphetamine and p-chloroamphetamine analogues

The ability of several 3,4-methylenedioxymethamphetamine (MDMA) analogues to inhibit the uptake of [3H]serotonin (5-HT), dopamine (DA) and norepinephrine (NE) into synaptosomes was examined. In addition, the ability of the compounds to inhibit the uptake of [3H]5-HT and DA into synaptosomes from rats pretreated with reserpine (5 mg/kg i.p., 16 h pretreatment) was compared to control experiments. All of the test compounds were found to be potent releasers of non-vesicular 5-HT (the reserpine IC50 was significantly smaller than the control IC50). The range of 5-HT inhibitory activity corresponds well to the small range of ED50 values of the test compounds to substitute in drug discrimination experiments with animals trained to discriminate MDMA or S-(+)-N-methyl-1-(1,3-benzodioxol-5-yl)-2-aminobutane (S-MBDB) from saline. In contrast, there was a wide range of potency for the inhibition of NE and DA uptake. In addition, several of the analogues appeared to be pure uptake inhibitors of DA while others were found to be releasers of non-vesicular DA. Several of the compounds were very selective for 5-HT over DA or NE uptake inhibition, including 3-methoxy-4-methylamphetamine (MMA) and 5-methoxy-6-methyl-2-aminoindan (MMAI). A correlation was noted between the 5-HT neurotoxic potential of some of the test compounds and their relative ability to induce a release of non-vesicular DA. The potential catechol metabolites of the methylenedioxy-substituted compounds also showed potent monoamine releasing properties, suggesting that metabolism may play a role in the neurotoxic actions of some of these drugs. The present data support the hypothesis that drug-stimulated non-vesicular 5-HT release is primarily responsible for the discriminative cue of MDMA.