Serotonergic Neurotoxicity of 3,4-(±)-Methylenedioxyamphetamine and 3,4-(±)-Methylendioxymethamphetamine (Ecstasy) Is Potentiated by Inhibition of γ-Glutamyl Transpeptidase

Reactive metabolites, particularly 5-(glutathion-S-yl)-alpha-methyldopamine (5-GSyl-alpha-MeDA), contribute to the serotonergic neurotoxicity caused by the drugs MDA and MDMA (ecstasy). Inhibiting the enzyme gamma-glutamyl transpeptidase (gamma-GT) at the blood-brain barrier with acivicin increased the brain uptake of these thioether metabolites and worsened the depletion of serotonin and its metabolite 5-HIAA in brain regions rich in serotonin nerve terminals. Acivicin pretreatment also increased glial fibrillary acidic protein (GFAP) expression in the striatum when combined with MDA, indicating enhanced neurotoxicity. The findings suggest that thioether metabolites formed from MDA and MDMA are key contributors to the serotonergic damage seen after peripheral drug administration.

Study at a glance

Abstract

Reactive metabolites play an important role in 3,4-(+/-)-methylenedioxyamphetamine (MDA) and 3,4-(+/-)-methylenedioxymethamphetamine (MDMA; ecstasy)-mediated serotonergic neurotoxicity, although the specific identity of such metabolites remains unclear. 5-(Glutathion-S-yl)-alpha-methyldopamine (5-GSyl-alpha-MeDA) is a serotonergic neurotoxicant found in the bile of MDA-treated rats. The brain uptake of 5-GSyl-alpha-MeDA is decreased by glutathione (GSH), but sharply increases in animals pretreated with acivicin, an inhibitor of gamma-glutamyl transpeptidase (gamma-GT) suggesting competition between intact 5-GSyl-alpha-MeDA and GSH for the putative GSH transporter. gamma-GT is enriched in blood-brain barrier endothelial cells and is the only enzyme known to cleave the gamma-glutamyl bond of GSH. We now show that pretreatment of rats with acivicin (18 mg/kg, ip) inhibits brain microvessel endothelial gamma-GT activity by 60%, and potentiates MDA- and MDMA-mediated depletions in serotonin (5-HT) and 5-hydroxylindole acidic acid (5-HIAA) concentrations in brain regions enriched in 5-HT nerve terminal axons (striatum, cortex, hippocampus, and hypothalamus). In addition, glial fibrillary acidic protein (GFAP) expression increases in the striatum of acivicin and MDA (10 mg/kg) treated rats, but remains unchanged in animals treated with just MDA (10 mg/kg). Inhibition of endothelial cell gamma-GT at the blood-brain barrier likely enhances the uptake into brain of thioether metabolites of MDA and MDMA, such as 5-(glutathion-S-yl)-alpha-MeDA and 2,5-bis-(glutathion-S-yl)-alpha-MeDA, by increasing the pool of thioether conjugates available for uptake via the intact GSH transporter. The data indicate that thioether metabolites of MDA and MDMA contribute to the serotonergic neurotoxicity observed following peripheral administration of these drugs.