The neurotoxicity of psychoactive phenethylamines “2C series” in cultured monoaminergic neuronal cell lines

Purpose: The aim of this study was to evaluate the neurotoxicity of psychoactive abused 2,5-dimethoxy-substituted phenethylamines “2C series” in monoaminergic neurons. Methods: After the exposure to “2C series”, 2,5-dimethoxy-4-propylthiophenethylamine (2C-T-7), 2,5-dimethoxy-4-isopropylthiophenethylamine (2C-T-4), 2,5-dimethoxy-4-ethylthiophenthylamine (2C-T-2), 2,5-dimethoxy-4-iodophenethylamine (2C-I) or 2,5-dimethoxy-4-chlorophenethylamine (2C-C), we examined their neurotoxicity, morphological changes, and effects of concomitant exposure to 3,4-methylenedioxymethamphetamine (MDMA) or methamphetamine (METH), using cultured neuronal dopaminergic CATH.a cells and serotonin-containing B65 cells. Results: Single dose exposure to “2C series” for 24 h showed significant cytotoxicity as increase in lactate dehydrogenase (LDH) release from both monoaminergic neurons: 2C-T-7, 2C-C (EC₅₀; 100 µM) > 2C-T-2 (150 µM), 2C-T-4 (200 µM) > 2C-I (250 µM) in CATH.a cells and 2C-T-7, 2C-I (150 µM) > 2C-T-2 (250 µM) > 2C-C, 2C-T-4 (300 µM) in B65 cells. The “2C series”-induced neurotoxicity in both cells was higher than that of MDMA or METH (EC₅₀: ≥ 1–2 mM). In addition, apoptotic morphological changes were observed at relatively lower concentrations of “2C series”. The concomitant exposure to non-toxic dose of MDMA or METH synergistically enhanced 2C series drugs-induced LDH release and apoptotic changes in B65 cells, but to a lesser extent in CATH.a cells. In addition, the lower dose of 2C-T-7, 2C-T-2 or 2C-I promoted reactive oxygen species production in the mitochondria of B65 cells, even at the early stages (3 h) without apparent morphological changes. Conclusion: The 2,5-dimethoxy-substitution of “2C series” induced severe neurotoxicity in both dopaminergic and serotonin-containing neurons. The non-toxic dose of MDMA or METH synergistically enhanced its neurotoxicity in serotonergic neurons.