Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Sep;173(17):2657-68.
doi: 10.1111/bph.13547. Epub 2016 Jul 31.

Phase I metabolites of mephedrone display biological activity as substrates at monoamine transporters

F P Mayer  1 , L Wimmer  2 , O Dillon-Carter  3 , J S Partilla  3 , N V Burchardt  1 , M D Mihovilovic  2 , M H Baumann  3 , H H Sitte  1   4
Affiliations

Phase I metabolites of mephedrone display biological activity as substrates at monoamine transporters

F P Mayer et al. Br J Pharmacol. 2016 Sep.

Abstract

Background and purpose: 4-Methyl-N-methylcathinone (mephedrone) is a synthetic stimulant that acts as a substrate-type releaser at transporters for dopamine (DAT), noradrenaline (NET) and 5-HT (SERT). Upon systemic administration, mephedrone is metabolized to several phase I compounds: the N-demethylated metabolite, 4-methylcathinone (nor-mephedrone); the ring-hydroxylated metabolite, 4-hydroxytolylmephedrone (4-OH-mephedrone); and the reduced keto-metabolite, dihydromephedrone.

Experimental approach: We used in vitro assays to compare the effects of mephedrone and synthetically prepared metabolites on transporter-mediated uptake and release in HEK293 cells expressing human monoamine transporters and in rat brain synaptosomes. In vivo microdialysis was employed to examine the effects of i.v. metabolite injection (1 and 3 mg·kg(-1) ) on extracellular dopamine and 5-HT levels in rat nucleus accumbens.

Key results: In cells expressing transporters, mephedrone and its metabolites inhibited uptake, although dihydromephedrone was weak overall. In cells and synaptosomes, nor-mephedrone and 4-OH-mephedrone served as transportable substrates, inducing release via monoamine transporters. When administered to rats, mephedrone and nor-mephedrone produced elevations in extracellular dopamine and 5-HT, whereas 4-OH-mephedrone did not. Mephedrone and nor-mephedrone, but not 4-OH-mephedrone, induced locomotor activity.

Conclusions and implications: Our results demonstrate that phase I metabolites of mephedrone are transporter substrates (i.e. releasers) at DAT, NET and SERT, but dihydromephedrone is weak in this regard. When administered in vivo, nor-mephedrone increases extracellular dopamine and 5-HT in the brain whereas 4-OH-mephedrone does not, suggesting the latter metabolite does not penetrate the blood-brain barrier. Future studies should examine the pharmacokinetics of nor-mephedrone to determine its possible contribution to the in vivo effects produced by mephedrone.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Proposed pathways for the metabolism of mephedrone to its phase I metabolites. (i) demethylation forms 4‐methylcathinone (NOR‐MEPH); (ii) benzylic oxidation forms 4‐hydroxytolylmephedrone (4‐OH‐MEPH); (iii) carbonyl reduction forms dihydromephedrone (DIHYDRO‐MEPH). Chemical synthesis started from non‐chiral precursors for the generation of racemic NOR‐MEPH and 4‐OH‐MEPH and from chiral precursors for DIHYDRO‐MEPH (racemic diastereomers obtained by mixing of enantiomers).
Figure 2
Figure 2
Effects of mephedrone (MEPH), nor‐mephedrone (NOR‐MEPH), 4‐OH‐mephedrone (4‐OH‐MEPH) and dihydromephedrone (DIHYDRO) on transporter‐mediated uptake in HEK293 cells expressing hDAT, hNET and hSERT. Uptake of [3H]‐MPP+ via hDAT and hNET, and uptake of [3H]‐5‐HT by hSERT, was performed as described in Methods; all symbols represent mean values ± SEM, and the numbers in parentheses indicate the number of individual experiments performed in triplicate: hDAT: MEPH (3), NOR‐MEPH (4), 4‐OH‐MEPH (4), DIHYDRO‐MEPH (3); hNET: MEPH (4), NOR‐MEPH (4), 4‐OH‐MEPH (3), DIHYDRO‐MEPH (4); hSERT: MEPH (3), NOR‐MEPH (3), 4‐OH‐MEPH (3), DIHYDRO‐MEPH (3).
Figure 3
Figure 3
Effects of mephedrone (MEPH), nor‐mephedrone (NOR‐MEPH), 4‐OH‐mephedrone (4‐OH‐MEPH) and dihydromephedrone (DIHYDRO‐MEPH) on transporter‐mediated release of preloaded radiolabelled substrate in HEK293 cells expressing hNET, hDAT and hSERT. [3H]‐MPP+ was used as the radiolabelled substrate for hDAT and hNET while release by hSERT‐expressing cells was performed using [3H]‐5‐HT as the radiolabelled substrate. (A) Representative experiment showing the effect of nor‐mephedrone (10 μM) in the presence or absence of monensin (10 μM) on DAT‐mediated efflux of pre‐loaded [3H]‐MPP+ (presence of substances indicated by black bar; n = 5 independent experiments performed in triplicate). (B–D) For each transporter, AUC was calculated from nine fractions collected after drug treatment (10 μM) in the absence or presence of monensin (MON, 10 μM). Solid bars indicate vehicle + drug, whereas hatched bars indicate MON + drug. Bars represent mean values ± SEM, and the numbers in parentheses indicate the number of individual experiments performed in triplicate: hDAT: MEPH (6), NOR‐MEPH (5), 4‐OH‐MEPH (5), DIHYDRO‐MEPH (5); hNET: MEPH (5), NOR‐MEPH (5), 4‐OH‐MEPH (6), DIHYDRO‐MEPH (5); hSERT: MEPH (5), NOR‐MEPH (5), 4‐OH‐MEPH (5), DIHYDRO‐MEPH (5). *P < 0.05 (Bonferroni's) compared with corresponding vehicle + drug group.
Figure 4
Figure 4
Effects of mephedrone (MEPH), nor‐mephedrone (NOR‐MEPH) and 4‐OH‐mephedrone (4‐OH‐MEPH) on transporter‐mediated release of preloaded radiolabelled substrate in rat brain synaptosomes. [3H]‐MPP+ was the radiolabelled substrate for DAT and NET assays while [3H]‐5‐HT was the radiolabelled substrate for SERT assays. Symbols represent mean values ± SEM obtained from three individual experiments performed in triplicate.
Figure 5
Figure 5
Effects of i.v. administration of mephedrone (MEPH), nor‐mephedrone (NOR‐MEPH) and 4‐OH‐mephedrone (4‐OH‐MEPH) or saline (SAL) on neurochemistry and behaviour in rats undergoing microdialysis in the nucleus accumbens. Drugs were administered i.v. at 1 mg·kg−1 at time zero, followed by 3 mg·kg−1 60 min later. Dopamine and 5‐HT were detected by HPLC‐EC as described in Methods. Forward locomotion (activity) was determined by photo‐beam breaks. Data are presented as mean ± SEM, n = 6 rats in the control group (SAL) and n = 7 rats for all other groups (MEPH, NOR‐MEPH and 4‐OH‐MEPH), arrows indicate time of drug administration. Individual symbols represent significant differences from saline‐treated control at corresponding time points (P < 0.05; Bonferroni's): * denotes significance of MEPH compared to saline, and # denotes significance of NOR‐MEPH compared to saline.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Alexander SP, Fabbro D, Kelly E, Marrion N, Peters JA, Benson HE et al. (2015b). The Concise Guide to PHARMACOLOGY 2015/16: enzymes. Br J Pharmacol 172: 6024–6109. - PMC - PubMed
    1. Alexander SP, Kelly E, Marrion N, Peters JA, Benson HE, Faccenda E et al. (2015a). The Concise Guide to PHARMACOLOGY 2015/16: transporters. Br J Pharmacol 172: 6110–6202. - PMC - PubMed
    1. Archer JR, Dargan PI, Lee HM, Hudson S, Wood DM (2014). Trend analysis of anonymised pooled urine from portable street urinals in central London identifies variation in the use of novel psychoactive substances. Clin Toxicol (Phila) 52: 160–165. - PubMed
    1. Baumann MH, Ayestas MA Jr, Partilla JS, Sink JR, Shulgin AT, Daley PF et al. (2012). The designer methcathinone analogs, mephedrone and methylone, are substrates for monoamine transporters in brain tissue. Neuropsychopharmacology 37: 1192–1203. - PMC - PubMed
    1. Baumann MH, Clark RD, Woolverton WL, Wee S, Blough BE, Rothman RB (2011). In vivo effects of amphetamine analogs reveal evidence for serotonergic inhibition of mesolimbic dopamine transmission in the rat. J Pharmacol Exp Ther 337: 218–225. - PMC - PubMed

Publication types

Substances

-