Neuropharmacological characterization of the new psychoactive substance methoxetamine

Methoxetamine (MXE), a ketamine analogue used as a new psychoactive substance, has multiple neuropharmacological effects. In rat primary cortical cells, 10 µM MXE increased glutamate-evoked calcium influx, while ketamine did not. Both MXE and ketamine inhibited spontaneous neuronal activity, with IC50 values of 0.5 µM and 1.2 µM respectively. In human SH-SY5Y cells, MXE slightly reduced calcium increases triggered by potassium and acetylcholine. In human stem cell-derived neurons, MXE only slightly reduced ATP-evoked calcium increases and inhibited spontaneous activity at higher concentrations. MXE also potently blocked human monoamine transporters, especially the serotonin transporter (SERT, IC50 2 µM), followed by norepinephrine (NET, 20 µM) and dopamine (DAT, 33 µM). These in vitro findings provide initial insight into MXE's mechanisms of action.

Study at a glance

Abstract

&NA; The use of new psychoactive substances (NPS) is steadily increasing. One commonly used NPS is methoxetamine (MXE), a ketamine analogue. Several adverse effects have been reported following MXE exposure, while only limited data are available on its neuropharmacological modes of action. We investigated the effects of MXE and ketamine on several endpoints using multiple in vitro models. These included rat primary cortical cells, human SH‐SY5Y cells, human induced pluripotent stem cell (hiPSC)‐derived iCell® Neurons, DopaNeurons and astrocyte co‐cultures, and human embryonic kidney (HEK293) cells. We investigated effects on several neurotransmitter receptors using single cell intracellular calcium [Ca2+]i imaging, effects on neuronal activity using micro‐electrode array (MEA) recordings and effects on human monoamine transporters using a fluorescence‐based plate reader assay. In rat primary cortical cells, 10 &mgr;M MXE increased the glutamate‐evoked increase in [Ca2+]i, whereas 10 &mgr;M ketamine was without effect. MXE and ketamine did not affect voltage‐gated calcium channels (VGCCs), but inhibited spontaneous neuronal activity (IC50 0.5 &mgr;M and 1.2 &mgr;M respectively). In human SH‐SY5Y cells, 10 &mgr;M MXE slightly inhibited the K+‐ and acetylcholine‐evoked increase in [Ca2+]i. In hiPSC‐derived iCell®(Dopa)Neurons, only the ATP‐evoked increase in [Ca2+]i was slightly reduced. Additionally, MXE inhibited spontaneous neuronal activity (IC50 between 10 and 100 &mgr;M). Finally, MXE potently inhibits uptake via monoamine transporters (DAT, NET and SERT), with IC50 values in the low micromolar range (33, 20, 2 &mgr;M respectively). Our combined in vitro data provide an urgently needed first insight into the multiple modes of action of MXE. The use of different models and different (neuronal) endpoints can be complementary in pharmacological profiling. Rapid in vitro screening methods as those presented here, could be of utmost importance for gaining a first mechanistic insight to aid the risk assessment of emerging NPS. HighlightsMXE increases the glutamate‐evoked increase in [Ca2+]i in rat cortical cultures.MXE and ketamine potently inhibit neuronal activity in rat cortical cultures.MXE inhibits voltage‐gated calcium channels in human SH‐SY5Y cells.MXE inhibits neuronal activity in human iPSC‐derived neurons.MXE inhibits human monoamine uptake transporters, particularly SERT.