Identification of monoamine oxidase and cytochrome P450 isoenzymes involved in the deamination of phenethylamine-derived designer drugs (2C-series)
Introduction
The members of the so-called 2C-series belong to a class of designer drugs that are all phenethylamine derivatives. Their chemical structures comprise a primary amine functionality separated from the phenyl ring by two carbon atoms (“2C”), the presence of methoxy groups in positions 2 and 5 of the aromatic ring, and a lipophilic substituent in position 4 of the aromatic ring (alkyl, halogen, alkylthio, etc.) [1]. Typical 2Cs are 4-bromo-2,5-dimethoxy-β-phenethylamine (2C-B), 4-iodo-2,5-dimethoxy-β-phenethylamine (2C-I), 2,5-dimethoxy-4-methyl-β-phenethylamine (2C-D), 4-ethyl-2,5-dimethoxy-β-phenethylamine (2C-E), 4-ethylthio-2,5-dimethoxy-β-phenethylamine (2C-T-2), and 2,5-dimethoxy-4-propylthio-β-phenethylamine (2C-T-7) [2], [3], [4], [5]. Their chemical structures are depicted in Fig. 1.
Most of known members of the 2C-series were synthesized and described by Shulgin during the 1970s and 1980s [1]. Since the 1990s, they have entered the illicit drug market as recreational drugs [3]. Later the 2Cs were sold in so-called “smart shops” and were mentioned in scene books and on so-called drug information web sites (http://www.erowid.org, http://www.lycaeum.org June 2006) [3]. Furthermore, seizures by the police of tablets containing 2Cs or combinations of them with other drugs were reported in recent years [6], [7], [8], [9], [10], [11]. As a consequence, several 2Cs have been scheduled in many countries [12], [13], [14].
Only little information is available on pharmacological properties of the 2Cs, but it is known, that the compounds of the 2C-series show affinity to 5-HT2 receptors, acting as agonists or antagonists at different receptor subtypes [15], [16], [17], [18], [19], [20], [21], [22], [23]. For 2C-B, partial agonism at the α1-adrenergic receptor was described [24], [25]. Little is known about the toxicology of these compounds, but at least for 2C-T-7 fatal intoxications have been reported during 2000/2001 [4], [12], [26].
In recent studies, the metabolism of several 2Cs was studied mainly in rats [27], [28], [29], [30], [31], [32], [33], but also in humans [34], mice [35], and hepatocytes of different species [36], [37]. One major metabolic step was the deamination of the parent compound to the corresponding aldehyde. These aldehydes could not be detected in urine, most probably because they were rapidly reduced or oxidized to the respective alcohols and carboxylic acids, which were present in urine.
The involvement of particular isoenzymes in the biotransformation of a new therapeutic drug has to be thoroughly investigated before it can be marketed. Such investigations allow to predict possible drug–drug-interactions, inter-individual variations in pharmacokinetic profiles and increased appearance of side effects and serious poisonings [38]. Such risk assessment is typically performed for substances intended for therapeutic use, but not for drugs of the illicit market. In addition, there is good evidence that genetic variations in drug metabolism have important behavioral consequences that can alter the risk of drug abuse and dependence [39].
Regarding the above mentioned deamination reaction, isoenzymes of the monoamine oxidase (MAO) and cytochrome P450 (CYP) type might be able to catalyze this reaction. MAO enzymes A and B are outer mitochondrial membrane-bound flavoenzymes that can be found mainly in neuronal and glia cells, but also in the liver. They catalyze the oxidation of primary, secondary, and some tertiary amines to their corresponding protonated imines with further non-enzymatic hydrolysis of the imine products to the corresponding aldehyde [40]. Their physiological substrates are neurotransmitters such as dopamine or noradrenaline, which show structural similarity to the 2Cs [41]. Consistently, phenethylamine is a specific substrate for MAO-B [41]. CYP enzymes are located in membranes, mainly the endoplasmic reticulum, and can be found mainly in the liver. They are also able to catalyze deamination via oxidation of the α-carbon atom next to the nitrogen [42].
Therefore, isoenzymes of the MAO- and CYP-type were studied concerning their ability to catalyze deamination of the 2Cs. Furthermore, the enzyme kinetics of these reactions was measured and the kinetic data like Michaelis–Menten constants (Km) and the maximal turnover rates (Vmax) were determined.
Section snippets
Materials
For research purposes, hydrochlorides of 2C-D and 2C-E were provided by Dejachem (Schwendi, Germany), 2C-B tartrate by Hessisches Landeskriminalamt (Wiesbaden, Germany), 2C-I hydrochloride by Landeskriminalamt Baden-Württemberg (Stuttgart, Germany), 2C-T-2 hydrochloride by Bundeskriminalamt (Wiesbaden, Germany), and 2C-T-7 hydrochloride by Bayerisches Landeskriminalamt (Munich, Germany).
NADP+ was obtained from Biomol, isocitrate and isocitrate dehydrogenase from Sigma, all other chemicals and
GC–MS procedures
The aldehyde metabolites were identified by their MS fragmentation pattern in the full-scan mode. The EI mass spectra, the structures and predominant fragmentation patterns of them are shown in Fig. 2. As observed for many other metabolites of the 2Cs [27], [28], [29], [30], [31], the benzyl cleavage was the major fragmentation step, and the resulting m/z value was chosen as target ion in the SIM procedure. Since the extraction was done at acidic pH, the parent compounds were not extracted and
Discussion
In the current study, the isoenzyme dependency of one of the major metabolic steps in the metabolism of six compounds of the 2C-series was studied. The deamination reaction might principally be catalyzed by MAO or CYP isoenzymes. Therefore, MAO-A and MAO-B, as well as the most important CYPs involved in drug metabolism were tested for their capability to catalyze this reaction. The incubation procedure for the CYPs was a well established and published method, which was already used to study
Acknowledgements
The authors would like to thank Peter Roesner, Liane D. Paul and Roland F. Staack, Frank T. Peters, Andreas H. Ewald, Markus R. Meyer, and Armin A. Weber for their assistance and helpful discussions.
References (60)
- et al.
[125I]-2-(2,5-dimethoxy-4-iodophenyl)aminoethane ([125I]-2C-I) as a label for the 5-HT2 receptor in rat frontal cortex
Pharmacol Biochem Behav
(1990) - et al.
A preliminary investigation of the psychoactive agent 4-bromo-2,5-dimethoxyphenethylamine: a potential drug of abuse
Pharmacol Biochem Behav
(1988) - et al.
5-HT2A receptor antagonists inhibit potassium-stimulated gamma-aminobutyric acid release in rat frontal cortex
Eur J Pharmacol
(1996) - et al.
Stimulus effects of three sulfur-containing psychoactive agents
Pharmacol Biochem Behav
(2004) - et al.
The action of the psychoactive drug 2C-B on isolated rat thoracic aorta
Gen Pharmacol
(1992) - et al.
Alpha-adrenergic and 5-HT2-serotonergic effects of some beta-phenylethylamines on isolated rat thoracic aorta
Gen Pharmacol
(1994) - et al.
Metabolism of the designer drug 4-bromo-2,5-dimethoxyphenethylamine (2C-B) in mice, after acute administration
J Chromatogr B: Anal Technol Biomed Life Sci
(2004) - et al.
Metabolic pathways of 4-bromo-2,5-dimethoxyphenethylamine (2C-B): analysis of phase I metabolism with hepatocytes of six species including human
Toxicology
(2005) - et al.
A study of the metabolism of methamphetamine and 4-bromo-2,5-dimethoxyphenethylamine (2C-B) in isolated rat hepatocytes
Forensic Sci Int
(2005) - et al.
Fenproporex N-dealkylation to amphetamine-enantioselective in vitro studies in human liver microsomes as well as enantioselective in vivo studies in Wistar and Dark Agouti rats
Biochem Pharmacol
(2004)
Cytochrome P450 dependent metabolism of the new designer drug 1-(3-trifluoromethylphenyl)piperazine (TFMPP). In vivo studies in Wistar and Dark Agouti rats as well as in vitro studies in human liver microsomes
Biochem Pharmacol
Monoamine oxidase inhibitory properties of some methoxylated and alkylthio amphetamine derivatives: structure-activity relationships
Biochem Pharmacol
Chemical love story
#142 PEA; phenethylamine
A new trend in drugs-of-abuse; the 2C-series of phenethylamine designer drugs
Pharm World Sci
New trends in the cyber and street market of recreational drugs? The case of 2C-T-7 (‘Blue Mystic’)
J Psychopharmacol
BZP and Nexus tablets
Microgram
2,5-Dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7)
Microgram
Dipropyltryptamine and 2C-I in portland, oregon
Microgram
2C-I tablets in the Balearic Islands (spain)
Microgram
2,5-Dimethoxy-4-ethylphenethylamine (2C-E) encountered in FT. Pierce, Florida and Royal Oak, Michigan
Microgram
2,5-Dimethoxy-4-ethylphenethylamine (2C-E) capsules in Bettendorf, Iowa
Microgram
Schedules of controlled substances; placement of 2,5-dimethoxy-4-(n)-propylthiophenethylamine and N-benzylpiperazine into schedule i of the controlled substances act
Fed Register
Binding of phenylalkylamine derivatives at 5-HT1C and 5-HT2 serotonin receptors: evidence for a lack of selectivity
J Med Chem
1-(2,5-Dimethoxy-4-(trifluoromethyl)phenyl)-2-aminopropane: a potent serotonin 5-HT2A/2C agonist
J Med Chem
Differences in potency and efficacy of a series of phenylisopropylamine/phenylethylamine pairs at 5-HT(2A) and 5-HT(2C) receptors
Br J Pharmacol
4-Bromo-2,5-dimethoxyphenethylamine (2C-B) and structurally related phenylethylamines are potent 5-HT2A receptor antagonists in Xenopus laevis oocytes
Br J Pharmacol
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