3,4(+)-methylenedioxyamphetamine (MDA) and 3,4-(+)-methylenedioxy-methamphetamine (MDMA) are serotonergic neurotoxicants. Both drugs are ring-substituted amphetamine derivatives structurally related to psychomotor stimulant amphetamines and the hallucinogen mescaline. Their clandestine manufacture and appearance on the street have made them popular drugs of abuse. The actions of MDA and MDMA are biphasic, initially causing an acute release of 5-hydroxytryptamine (5-HT) followed by prolonged depletion of 5-HT and 5-hydroxyindoleacetic acid and structural damage to 5-HT terminal and preterminal axons in various regions of the CNS. These neurotoxic effects are dependent on the route and frequency of drug administration. Direct injection of either MDMA or MDA into the brain fails to reproduce the neurotoxicity following peripheral administration, indicating that the parent drugs are unlikely to be responsible for the neurotoxic effects. Therefore, it has been proposed that metabolites of MDMA and MDA mediate their neurotoxic effects. However, to date, none of the known major metabolites of these drugs are capable of producing the neurobehavioral or neurotoxicological effects. It is the applicants' hypothesis that quantitatively minor metabolites of MDA and MDMA contribute to the neurotoxicity. The investigator specifically hypothesizes that one such class of metabolites arises from the oxidation of (alpha-MeDA) followed by scavenging of the o-quinone with glutathione (GSH). The resulting quinone-thioethers are potent neurotoxicants. The investigator's hypothesis is based upon: (a) the inherent reactivity of o-quinones; (b) the presence of GSH in peripheral tissues and in the CNS; (c) the diverse toxicology of quinone-thioethers, in particular their potent effects on cells and tissues expressing gamma-glutamyl transpeptidase, such as renal proximal tubules; and (d) the biochemical and physiological similarities between the blood-brain and blood-CSF barriers, and renal proximal tubular epithelia. Preliminary data support this hypothesis and the specific aims are designed to extend our understanding of these novel neurotoxic metabolites in MDA/MDMA neurotoxicity, and to provide initial insights into their cellular and molecular mechanism of action. The investigator proposes to: (i) quantitate quinone-thioether formation from MDA and MDMA in vivo, and the brain uptake index for peripherally administered 5-(GSyl)-alpha-MeDA and 2,5-bis-(GSyl)-alpha-MeDA; (ii) optimize the neurotoxic effects of 2,5-bis-(GSyl)-alpha-MeDA, and determine the toxicity of 5-(GSyl)-alpha-MeDA following multiple dose regimens; (iii) determine the effects of 2,5-bis-(GSyl)-alpha-MeDA on intracellular thiol and energy homeostasis and on central iron homeostasis; (iv) immunohistologically characterize 2,5-bis-(GSyl)-alpha-MeDA lesions; and (v) determine the effects of MDA and 2,5-bis-(GSyl)-alpha-MeDA on extracellular neurotransmitter concentrations.
