The synthetic cathinones, butylone and pentylone, are stimulants that act as dopamine transporter blockers but 5-HT transporter substrates

Abstract

Rationale: Synthetic cathinones continue to emerge in recreational drug markets worldwide. 1-(1,3-Benzodioxol-5-yl)-2-(methylamino)butan-1-one (butylone) and 1-(1,3-benzodioxol-5-yl)-2-(methylamino)pentan-1-one (pentylone) are derivatives of the cathinone compound, 1-(1,3-benzodioxol-5-yl)-2-(methylamino)propan-1-one (methylone), that are being detected in drug products and human casework.

Objectives: The purpose of the present study was to examine the neuropharmacology of butylone and pentylone using in vitro and in vivo methods.

Methods: In vitro uptake and release assays were carried out in rat brain synaptosomes and in cells expressing human dopamine transporters (DAT) and 5-HT transporters (SERT). In vivo microdialysis was performed in the nucleus accumbens of conscious rats to assess drug-induced changes in neurochemistry.

Results: Butylone and pentylone were efficacious uptake blockers at DAT and SERT, though pentylone was more DAT-selective. Both drugs acted as transporter substrates that evoked release of [³H]5-HT at SERT, while neither evoked release at DAT. Consistent with the release data, butylone and pentylone induced substrate-associated inward currents at SERT but not DAT. Administration of butylone or pentylone to rats (1 and 3 mg/kg, i.v.) increased extracellular monoamines and motor activity, but pentylone had weaker effects on 5-HT and stronger effects on motor stimulation.

Conclusions: Our data demonstrate that increasing the α-carbon chain length of methylone creates "hybrid" transporter compounds which act as DAT blockers but SERT substrates. Nevertheless, butylone and pentylone elevate extracellular dopamine and stimulate motor activity, suggesting both drugs possess significant risk for abuse.

Keywords: 5-HT; Cathinone; Dopamine; Microdialysis; Neurochemistry; Transporter.

Figure 1.

Chemical structures of MDMA, methylone, butylone and pentylone.

Figure 2.

Dose-response effects of butylone and pentylone on [³H]neurotransmitter uptake in rat brain synaptosomes and cells transfected with human transporters. Data from rat brain synaptosomes are depicted in Panel A for [³H]DA uptake by DAT and Panel B for [³H]5-HT uptake by SERT. Data from HEK-293 cells are depicted in Panel C for [³H]DA uptake by human DAT and Panel D for [³H]5-HT uptake by human SERT. Effects of butylone and pentylone are shown as closed circles and open squares, respectively. Data are mean ± SD expressed as percent of control uptake, for n=3 experiments performed in triplicate.

Figure 3.

Effects of butylone and pentylone on transporter-mediated release in rat brain synaptosomes and cells transfected with human transporters. Data from rat brain synaptosomes are depicted in Panel A for [³H]MPP⁺ efflux via DAT and Panel B for [³H]5-HT efflux via SERT; effects of butylone and pentylone are shown as closed circles and open squares, respectively. Data from HEK-293 cells are depicted in Panel C for [³H]MPP⁺ efflux via human DAT and Panel D for [³H]5-HT efflux via human SERT; effects of 10 μM butylone in the presence of Krebs-Henseleit-Phosphate buffer (KHP) or 10 μM monensin are shown as open or closed circles, whereas effects of 10 μM pentylone in the presence of KHP or 10 μM monensin are shown as open or closed squares. Arrows indicate beginning of butylone or pentylone perfusion. Data are mean ± SD for n=3 experiments performed in triplicate.

Figure 4.

Effects of butylone and pentylone on transporter-mediated currents measured in HEK-293 cells stably transfected with human transporters. Representative traces of currents produced by butylone at DAT and SERT are depicted in Panels A and B, respectively. Representative traces of currents produced by pentylone at DAT and SERT are depicted in Panels C and D, respectively.

Figure 5.

Dose-response effects of butylone and pentylone to produce transporter-mediated currents at human DAT and SERT. The Y-axis represents normalized current obtained by dividing current obtained with drug treatment by the current obtained with a 10 μM concentration of the endogenous substrate. The X-axis represents drug concentration in log scale. Effects of butylone on DAT and SERT are represented by open and closed circles, whereas effects of pentylone on DAT and SERT are represented as open and closed squares. Data are mean ± SD for n=3 experiments.

Figure 6.

Neurochemical and behavioral effects produced by butylone and pentylone in conscious rats undergoing microdialysis in the nucleus accumbens. Effects of drugs on extracellular dopamine (DA) are shown in Panel A while effects on extracellular 5-HT are shown in Panel B. Effects of drugs on forward locomotion (Motor) and repetitive movements (Stereotypy) are shown in Panels C and D. Arrows indicate time of intravenous injection: 1 mg/kg of butylone or pentylone was given at time zero followed by 3 mg/kg given 60 min later. Saline was injected at 1 mL/kg at the same time points. Data are mean ± SEM expressed a percent of basal preinjection values for N=6-7 rats/group. Filled symbols represent significant effects of drugs compared to saline treatment at specific time points, whereas asterisks represent significant differences compared to butylone at specific time points (p<0.05, Bonferroni’s test).