Abstract
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.
Introduction
During the past decade, there has been a dramatic increase in the number and variety of novel psychoactive substances (NPSs) available on the illicit and gray drug markets (particularly via the Internet and “dark web”). In 2014, the number of NPSs boomed with 101 new compounds detected. In 2016, approximately one new NPS per week was identified, and the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) was monitoring more than 620 NPSs (). One of the first NPSs that became widely used recreationally was the cathinone derivative mephedrone (4-MMC, 4-methylmethcathinone), marketed at the time as a “legal” substitute for ecstasy (MDMA, 3,4-methylenedioxymethamphetamine) and cocaine, sharing effects of both (). Mephedrone and other cathinones such as methylone (βk-MDMA, 3,4-methylenedioxy-N-methcathinone) and butylone (βk-MBDB, β-keto-N-methylbenzodioxolylbutanamine) were initially sold as, e.g., “bath salts” or “plant food,” labeled “not for human consumption.” Mephedrone became very popular due to its low price, high purity, and “legality” and, in the UK, it rapidly became as widespread as cocaine (). In 2009 and 2010, the UK government placed piperazine derivatives, mephedrone, and other related cathinones under legal control (), which resulted in their immediate replacement with new structural analogs and with a new class of NPSs: synthetic aminoindanes. One of the first was 5,6-methylenedioxy-2-aminoindane (MDAI), which claimed to be a “legal,” non-neurotoxic analog of MDMA, with strong empathogenic and weaker stimulatory effects (). Aminoindanes such as MDAI, 5,6-methylenedioxy-N-methyl-2-aminoindane (MDMAI), 5-iodo-2-aminoindane (5-IAI), 2-aminoindane (2-AI), 5-methoxy-6-methyl-2-aminoindane (MMAI), and 5-methoxy-2-aminoindane (MEAI) represent a relatively new generation of NPS. Cases of acute toxicity, including fatal poisoning, have been reported with their use (). Only minimal reliable information on aminoindanes exists at present and, owing to their increasing popularity, the present brief review is timely. The paper summarizes the history of their creation, therapeutic potential in medical research and subsequent discovery by recreational drug users, their pharmacology, behavioral effects, pharmacokinetics, and toxicity.
Method
ISI Web of Knowledge: Web of Science (WoS) was searched during June and July 2017. WoS was selected because it simultaneously searches other databases such as PubMed and ScienceDirect, and includes quality criteria for inclusion (e.g., peer review). Keywords (used separately and in combination) were as follows: aminoindane, MDAI, 5,6-methylenedioxy-2-aminoindane, 5-IAI, 5-Iodo-2-aminoindane, 2-aminoindane, MDMAI, 5,6-Methylenedioxy-N-methyl-2-aminoindane, MMAI, 5-Methoxy-6-methyl-2-aminoindane. Full empirical/review articles containing relevant information about aminoindanes written in the English language were included; no date limits applied (Figure 1). When suitable articles were found, citation searches were also conducted. For subjective effects, typical use and doses, Erowid,1 PsychonautWiki,2 Bluelight,3 and Drugs-Forum4 (Internet discussion fora and wikis) were searched using the same search terms as above. Information about legal status and availability of aminoindanes in the European Union (EU), the EDND was consulted via the senior author, Dr. Palenicek, through the “Working group: Early warning system on new drugs,” National Monitoring Centre for Drugs and Addiction, Czech Republic.
Figure 1
Results
Chemistry
2-aminoindane is an amphetamine (AMPH) analog with a rigid conformation due to a bridge between the α-carbon and the aromatic ring (
Table 1
| Structure | Name | Chemical name | lUPAC name |
|---|---|---|---|
![]() | Amphetamine, AMPH, Speed | Alpha-methylphenethylamine | l-phenylpropan-2-amine |
![]() | MDMA, Ecstasy, Molly, X, XTC | 3,4-methylenedioxymethamphetamine | l-(1,3-benzodioxol-5-yl)-N-methylpropan-2-amine |
![]() | MDA | 3,4-methylenedioxyamphetamine | l-(1,3-benzodioxol-5-yl)propan-2-amine |
![]() | 2-AI | 2-aminoindane | 2,3-dihydro-1H-inden-2-amine |
![]() | 5-IAI | 5-Iodo-2-aminoindane | 5-iodo-2,3-dihydro-1H-inden-2-amine |
![]() | MDAI | 5,6-methylenedioxy-2-aminoindane | 6,7-dihydro-5H-cyclopenta[f][1,3]benzodioxol-6-amine |
![]() | MDMAI | 5,6-methylenedioxy-2-methylaminoindane | N-methyl-6,7-dihydro-5H-cyclopenta[f][1,3]benzodioxol-6-amine |
![]() | MMAI | 5-methoxy-6-methyl-2-aminoindane | 5-methoxy-6-methyl-2,3-dihydro-1H-inden-2-amine |
Chemical structures and names, International Union of Pure and Applied Chemistry (IUPAC) names of amphetamine, MDMA, MDA, 2-aminoindane, and its derivatives with psychoactive effects.
Origins of Aminoindanes in Pharmacological Research
Owing to an amino group, aminoindanes are potentially vasoactive and bronchodilatory, which was the main focus for their initial development (
Based on Kier’s receptor mapping technique (
Kalir et al. (
Aminoindanes–A Unique Drug Class with Entactogenic Properties
Contemporary research has focused on the psychoactive effects of substituted 2-AIs (
Nichols et al. (
A study on in vitro monoamine reuptake inhibition (using rats’ synaptosomes) identified MDAI as a highly potent inhibitor of 5-HT and dopamine (DA) reuptake rather than causing non-vesicular DA release. 5-IAI and MMAI were subsequently evaluated, both of them increased non-vesicular release of 5-HT, DA, and norepinephrine (NE), but MMAI had 100- and 50-fold selectivity for 5-HT over DA and NE uptake inhibition, indicating that it is a very selective serotonergic releaser (
The pharmacokinetics of MDAI in Wistar rats have been described in our recently published paper (
Subjective Effects and Acute Behavioral Studies
Very little is known about acute behavioral effects of aminoindanes in animal studies. We described acute behavior in Wistar rats after MDAI administration. Three different s.c. doses of MDAI (5, 10, 20, and 40 mg/kg) administered (at two testing onsets 15 respectively 60 min) prior to open field test (OFT) and prepulse inhibition test (PPI) were examined to evaluate effects on locomotor activity and sensorimotor gating. At all doses used, MDAI showed a disruptive effect on sensorimotor gating and, most evidently, at testing onset 15 min. The same disruptive effect on PPI can be seen after MDMA, AMPH or other psychoactive drugs (
Since no clinical trial has yet been performed in humans with recreational aminoindanes, information about subjective effects and health risks comes from subjective personal experiences shared on drug website platforms, wikis, and discussion fora. Based on users’ reports on PsychonautWiki, Erowid, Drugs-Forum, and Bluelight, MDAI and 5-IAI effects are mainly euphoria, empathy, stimulation (not the case with MDAI), and cognitive enhancement. The adverse effects described by users include dehydration, increased perspiration, anxiety, depression, panic attacks, and tachycardia. Several routes of administration have been reported from insufflation, oral ingestion to rectal application. The latter has the fastest onset of effects. Smoking and injecting have not been described (
Toxicity and Health Risks
Palenicek et al. (
Since recreational users take these ecstasy-like drugs frequently in the environment of rave/dance parties for euphoric and entactogenic effects but also to enhance their abilities to dance for long periods, many users desire stimulatory effects. However, in the case of aminoindanes, where primary activity is on the 5-HT system, stimulation is limited. This often leads users to consume aminoindanes in larger doses (to increase the DA release) or in drug cocktails with stimulants such as AMPH, cocaine, or MDMA to potentiate the stimulatory properties of the drug. In these combinations, when 5-HT-ergic substances potentiate DA-ergic substances, an unexpected neurotoxicity and cardiotoxicity may occur (
Legal Status
At the time of writing, only a few aminoindanes are controlled in some parts of the EU. 2-AI is controlled in Croatia, Denmark, Estonia, Finland, Hungary, Lithuania, Poland, and Portugal. MDAI is controlled in Cyprus, Czech Republic, Denmark, Estonia, Finland, Hungary, Italy, Lithuania, Portugal, and Sweden. 5-IAI is controlled in Finland, Hungary, Lithuania, and Portugal. For instance, the UK has not specifically restricted aminoindanes yet (
Conclusion
Although there are some existing studies focusing on MDAI, more research should be performed on the behavioral effects and toxicity of this substance. As we have shown in this review, fatal intoxications connected with MDAI have been reported and animal studies provided evidence of its potentially deadly toxicity due to serotonin syndrome. Furthermore, there is lack of information about toxicity, pharmacokinetics, and behavioral effects of the other aminoindanes. An important issue is also the legal status of these substances, since just a few EU countries control aminoindanes. This may increase the probability of their recreational use and, in turn, the incidence of acute toxicity.
Statements
Author contributions
NP contributed to the writing of the paper, searched for relevant literature, and composed the main idea for the study. RH and TP discussed the content of manuscript, added comments and critical feedback, and contributed to the final version of the paper.
Funding
This work was supported by the MEYS CR under the NPU I program (grant number LO1611) and 260388/SVV/2017.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Footnotes
2.^https://psychonautwiki.org/.
5.^http://www.emcdda.europa.eu/themes/new-drugs/early-warning.
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Summary
Keywords
aminoindanes, 5,6-methylenedioxy-2-aminoindane, 5-iodo-2-aminoindane, 2-aminoindane, 5,6-methylenedioxy-N-methyl-2-aminoindane, 5-methoxy-6-methyl-2-aminoindane
Citation
Pinterova N, Horsley RR and Palenicek T (2017) Synthetic Aminoindanes: A Summary of Existing Knowledge. Front. Psychiatry 8:236. doi: 10.3389/fpsyt.2017.00236
Received
14 September 2017
Accepted
31 October 2017
Published
17 November 2017
Volume
8 - 2017
Edited by
Liana Fattore, Consiglio Nazionale Delle Ricerche (CNR), Italy
Reviewed by
Oussama Kebir, Institut national de la santé et de la recherche médicale, France; John Martin Corkery, University of Hertfordshire, United Kingdom
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Copyright
© 2017 Pinterova, Horsley and Palenicek.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Tomas Palenicek, tomas.palenicek@nudz.cz
Specialty section: This article was submitted to Addictive Disorders, a section of the journal Frontiers in Psychiatry
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