Elsevier

Neuroscience

Volume 146, Issue 4, 8 June 2007, Pages 1743-1757
Neuroscience

Neuropharmacology
Neurotoxicity mechanisms of thioether ecstasy metabolites

https://doi.org/10.1016/j.neuroscience.2007.03.028Get rights and content

Abstract

3,4-Methylenedioxymethamphetamine (MDMA or “ecstasy”), is a widely abused, psychoactive recreational drug that is known to induce neurotoxic effects. Human and rat hepatic metabolism of MDMA involves N-demethylation to 3,4-methylenedioxyamphetamine (MDA), which is also a drug of abuse. MDMA and MDA are O-demethylenated to N-methyl-α-methyldopamine (N-Me-α-MeDA) and α-methyldopamine (α-MeDA), respectively, which are both catechols that can undergo oxidation to the corresponding ortho-quinones. Ortho-quinones may be conjugated with glutathione (GSH) to form glutathionyl adducts, which can be transported into the brain and metabolized to the correspondent N-acetylcysteine (NAC) adducts. In this study we evaluated the neurotoxicity of nine MDMA metabolites, obtained by synthesis: N-Me-α-MeDA, α-MeDA and their correspondent GSH and NAC adducts. The studies were conducted in rat cortical neuronal cultures, for a 6 h of exposure period, under normal (36.5 °C) and hyperthermic (40 °C) conditions. Our findings show that thioether MDMA metabolites are strong neurotoxins, significantly more than their correspondent parent catechols. On the other hand, N-Me-α-MeDA and α-MeDA are more neurotoxic than MDMA. GSH and NAC conjugates of N-Me-α-MeDA and α-MeDA induced a concentration dependent delayed neuronal death, accompanied by activation of caspase 3, which occurred earlier in hyperthermic conditions. Furthermore, thioether MDMA metabolites time-dependently increased the production of reactive species, concentration-dependently depleted intracellular GSH and increased protein bound quinones. Finally, thioether MDMA metabolites induced neuronal death and oxidative stress was prevented by NAC, an antioxidant and GSH precursor. This study provides new insights into the neurotoxicity mechanisms of thioether MDMA metabolites and highlights their importance in “ecstasy” neurotoxicity.

Section snippets

Materials

Materials for cell cultures were obtained from the following sources: Neurobasal medium and supplement B27 from Invitrogen (Paisley, UK); Modified Eagle’s medium, phosphate buffered saline (PBS), Hepes buffer, trypsin/EDTA, penicillin/streptomycin, l-glutamine, collagen-G and poly-l-lysin from Biochrom (Berlin, Germany). 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT), nitro blue tetrazolium (NBT), potassium glycinate, phenylmethylsulfonyl fluoride (PMSF), NAC, reduced (GSH)

Thioether MDMA metabolites induced neurotoxicity in cortical neuronal cultures is concentration-, temperature- and time-dependent. Thioether MDMA metabolites are strong neurotoxins relatively to their parent catechols and MDMA

Neuronal viability assessed by the MTT test at the end of 6 h incubation period revealed toxicity for the GSH and NAC conjugates: 5-(GSH)-N-Me-α-MeDA (Fig. 1C), 5-(NAC)-N-Me-α-MeDA (Fig. 1D), 5-(GSH)-α-MeDA (Fig. 1F) and 5-(NAC)-α-MeDA (Fig. 1G). At this time-point there was a concentration-dependent-induced toxicity at both normothermia and hyperthermia for these compounds. The metabolite 5-(GSH)-N-Me-α-MeDA (Fig. 1D) showed the highest degree of neurotoxicity among the thioether MDMA

Discussion

The key findings of our study were: (1) thioether MDMA metabolites induced neurotoxicity in cortical neuronal cultures is concentration-, temperature- and time-dependent; (2) thioether MDMA metabolites are strong neurotoxins comparatively to their parent catechols and MDMA; (3) thioether MDMA metabolites induced delayed neuronal death, accompanied by activation of caspase 3; (4) thioether MDMA metabolites time-dependently induced the formation of reactive species in neurons; (5) thioether MDMA

Conclusion

In conclusion, MDMA metabolism leading to reactive thioether MDMA metabolites, which produce ROS/RNS and toxic oxidation products, has a key role in the neurotoxic events produced by “ecstasy.”

Acknowledgments

This work was supported by the “Fundação Calouste Gulbenkian” (Ref. FCG 10/04). J.P.C. was the recipient of a PhD grant from “Fundação para a Ciência e Tecnologia” (Ref. SFRD/BD/10908/2002).

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